8
Immunomodulators
HESHAM EL ENSHASY1,2
CONTENTS
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II. Immunosuppressants . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Cyclosporins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Biosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. New Generations . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Mycophenolic Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Biosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Mizoribine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Other Immunosuppressants. . . . . . . . . . . . . . . . . . .
1. Ovalicins and Fumagillins . . . . . . . . . . . . . . . . .
2. Gliotoxin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3. Trichopolyns. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Myriocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5. Flavidulols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6. Kobiins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7. Mycestericins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8. Terprenins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9. FR901483. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10. Colutellin A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
III. Mushroom Immunomodulators . . . . . . . . . . . . . . . . . .
A. Lectins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Terpenoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Polysaccharides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Fungal Immunomodulator Proteins . . . . . . . . . .
E. Industrial Production of Mushroom
Immunomodulators. . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. Introduction
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1
Chemical Engineering Pilot Plant (CEPP), Faculty of Chemical
and Natural Resources Engineering, Universiti Teknologi
Malaysia (UTM), 81310 Skudai, Johor, Malaysia; e-mail: hesham@
utm.my
2
Bioprocess Development Department, Mubarak City for Scientific Research and Technology Applications (MuCSAT), New Burg
Al Arab, Alexandria, Egypt
Immunomodulators are actually natural products
of the immune system (Pirofski and Casadevall
2006). The immune system of healthy organism
produces a diverse range of metabolites to keep
the body in homeostasis condition. An immunomodulator may be defined as a substance, of
biological or synthetic origin, which can stimulate, suppress or modulate any of the components
of the immune system including both innate and
adaptive arms of the immune response (Agawal
and Singh 1999). In clinical practice, immunomodulators are classified into three main categories:
1. Immunosuppressants are agents that somehow inhibit the immune system. They can be
used for the control of pathological immune
response after organ transplantation and for
the treatment of autoimmune diseases, hypersensitivity immune reactions as well as
immune pathology associated with infections.
2. Immunostimulators are agents that stimulate
the immune system by inducing the activation
or increasing activity of any of its components. They enhance the body’s resistance
against allergy, infection, cancer and autoimmunity.
3. Immunoadjuvants are agents used to enhance
the vaccine efficacy. This can be also considered as a specific immune stimulator effect.
The industrial importance of immunomodulators
is based on their large market value. The market
size of immunomodulators was evaluated at US
$43 billion in 2006, and is expected to grow at a
compound annual growth rate (CAGR) of 13% to
reach US $80 billion by 2011 (Research and Market
2007). Although some potential immunomodulating substances can be chemically synthesized
and have been successfully tested for modulation
of the immune system [e.g. synthetic muramyl
dipeptide (MDP) analogues], research activities
Industrial Applications, 2nd Edition
The Mycota X
M. Hofrichter (Ed.)
© Springer-Verlag Berlin Heidelberg 2010
166
Hesham El Enshasy
in this field have been focused on immunomodulatory active compounds from natural resources.
Among them, fungal immunomodulators represent the most interesting group of metabolites.
This review outlines the current state of knowledge on fungal immunomodulators used already
for different medical applications and discusses
the future potential of new compounds of fungal
origin.
II. Immunosuppressants
The importance of immunosuppressants arose in
the mid of the twentieth century in the context
of new developments in organ transplantation.
The principal goal of immunosuppressant application in organ transplantation is to minimize the
risk of allo-graft rejection or graft-dysfunction by
achieving adequate immunosuppression, yet also
to ensure that the level of immunosuppression
does not contribute to long term morbidity (Patel
and Kobashigawa 2008). The first organ transplantation was performed in 1933 when a kidney was
transplanted from a cadaver. Total lymphoid irradiation was used for the immune suppression but
the tissue was rejected and the patient eventually
died. This was followed by the use of corticosteroids as immunosuppressive agents, but unfortunately, these steroids as such did also not give the
positive results expected. In the early 1960s, cytotoxic agents such as modified corticosteroids were
introduced to suppress the immune system after
organ transplantation (Khan 2008). The first clinically used fungal immunosuppressive agent was
introduced into the market in the mid of 1980s
when cyclosporine became available for clinical
applications after getting its approval from the
United States Food and Drug Administration (US
FDA). This was one of the most important milestones in the history of organ transplantation.
Beside their important roles in organ transplantation, immunosuppressive agents are used for other
applications, for example, in the prevention of the
newborn Rh hemolytic disease (Contreas and
DeSilva 1994) or for the treatment of some autoimmune diseases. The chemical structures of the three
main fungal immunosuppressive agents (cyclosporine, mycophenolic acid, mizoribine), which
all are used in organ transplantation and for other
medical applications, are shown in Fig. 8.1.
A. Cyclosporins
Cyclosporins (Cys) are a family of neutral, high
lipophilic, cyclic undecapeptides containing some
unusual amino acids and having a remarkable
spectrum of biological activities. The first member
of this class of compounds was named cyclosporine A. To date, more than 30 members of this
family of compounds have been isolated from
natural resources and were classified as cyclosporins A to Z (CyA–Z; Traber et al. 1982, 1987). CyA
was originally described as an antifungal peptide
with a narrow spectrum of efficacy. However, the
interest in this compound only increased significantly after the demonstration of its specific
immunosuppressive activity. In 1983, Sandoz
first introduced a cyclosporine-A-based drug,
Sandimmun, into the market. The modified form
of this drug with increased bioavailability, Neoral,
became available on the market in 1994 in form of
soft gelatins and oral applicable solutions. Since
then, Sandimmun and Neoral have been Novartis’
leading pharmaceutical products and these drugs
generated a revenue of US $1.216 billion in 1997
(Svarstad et al. 2000). Nowadays, based on market
research data, only five members of the cyclosporin family, namely CyA (CAS 59865-13-3),
CyB (CAS 63775-95-1), CyC (CAS 59787-61-0),
CyD (CAS 63775-96-2) and CyH (CAS 83602-39-5)
are commercially available for pharmaceutical
applications as immunosuppressive agents.
According to their immunosuppressive mode
of action, cyclosporins belong to the specific calcineurin inhibitors. Immunosuppressant activity
is mediated through blocking the activation and
proliferation of CD4þ- and CD8þ-T lymphocytes
by inhibiting IL-2 production (Siekierka et al.
1989; Shibasaki et al. 2002). Under normal conditions, the binding of major histo-compatibility
peptides to the T-cell receptors results in the formation of an activated form of calcium/calmodulin-dependent serine/threonine phosphatase
calcineurin. This leads to dephosphorylation and
nuclear translocation of the nuclear factor of activated T-cells (NF-AT), Subsequently, NF-AT
binds genes encoding pro-inflamatory cytokine
IL-2, resulting in an up-regulated gene transcription (Schreiber and Crabtree 1992; Butch 2008).
CyA freely crosses lymphocyte membranes and
forms complexes with the specific cytoplasmatic
binding protein immunophilin cyclophilin A. The
CyA-cyclophilin A complex inhibits calcineurin
CH3
H3C
CH3
CH3
CH3
O
N
O
CH3
CH3
H3C
N
O
CH3
NH2
OH
N
2-Mycophenolic acid (MPA)
C
H3
CH3
H3CO
O
CH
CH3
O
O
N
O
CH3
CH3
C O
H3
H
N
N
H
C
H3 N
N
O
HO
CH3
H
N
H3C
O
HO
CH3
CH3
CH3
OH
N
O
O
N
CH3
O
OH
OH
O
Immunomodulators
H3C
CH3
H3C
N
H
O
O
O
N
N
H3C
CH3
O
OH
HO
O
O
O
H3CO
CH3
1- cyclosporins
3- Mycophenolic acid
4- Mirozoribine
Fig. 8.1. Chemical structure of the main clinically important fungal immunosuppressives compounds
167
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Hesham El Enshasy
activity and the nuclear translocation of NF-AT.
This leads to the down-regulation of the proinflammatory molecules gene transcription and
subsequently halts the production of IL-2 and
TNF-a (Jorgensen et al. 2003).
Currently, CyA is approved and used worldwide as an immunosuppressive drug to prolong
organ and patient survival after kidney, liver,
heart and bone-marrow transplants. CyA is available on the market under the trade name Sadimmune for both oral and intravenous applications.
A nano-sized pre-concentrate formulation of
CyA (CyA-MEPC or Neoral) exhibiting a better
absorption characteristic is used orally in form
of solutions or soft-gelatin capsules (Vonderscher
and Meinzer 1994; Uchida et al. 2004). Besides
the products of the market leader Novartis, several generic formulations are nowadays available
and are often referred to as modified CyAs
(Alloway 1999).
1. Chemistry
CyA, the most important member of the cyclosporin family, is a cyclic undecapeptide with a 33membered ring composed of 11 lipophilic aliphatic
amino acids, of which four are leucine and three
are the non-proteogenic amino acids D-alanine,
(4R)-4-[(E)-2-butenul]-4-methyl-L-threonine (Bmt)
and L-a-aminobutyric acid. The full chemical
name of CyA is 32-ethyl-2-[(E,1R,2R)-1-hydroxy2-methylhex-4-enyl]-3,6,9,12,14,17,21,27,30-nonamethyl-8,11,20,26-tetrakis-(2-methylpropyl)-5,
23-di-(propan-2-yl)-3,6,9,12,15,18,21,24,27,30,33undecaza-cyclotritriacontane-1,4,7,10,13,16,19,22,
25,28,31-undecone. The molecular formula and
molecular weight of CyA are C62H111N11O12 and
1202.61 g mol–1, respectively. The non-proteogenic
amino acids are found at the positions 1 (Bmt),
2 (L-a-amino butyric acid) and 8 (D-alanine).
Remarkably, seven of the 11 peptide bonds are
N-methylated, which has several important implications. First, the N-methylated peptide bonds
and the cyclic structure of the molecule renders
cyclosprins stable toward mammalian digestive
and systemic proteases. Cyclosporin metabolism
in animals and humans is exclusively carried
out by cytochrome P450 enzymes catalyzing its
oxidative transformation. Therefore, cyclosporins
are not only well absorbed when given orally
but also characterized by high and long-lasting
plasma levels. A second consequence of the
N-methylation pattern is rigid conformation in
the non-polar environment characterized by
intramolecular hydrogen bonds being oriented
towards the hydrophobic environment (Kallen
et al. 1997).
Plain cyclosporin is difficult to crystallize on
its own and therefore, was initially analyzed as
crystalline iodo-cyclosporin. The structural analysis of such CyA crystals by X-ray diffraction
revealed a rigid conformation (Loosli et al.
1985). The rigidity can be attributed to a number
of unique structural properties. Predominantly,
the four intra-molecular hydrogen bonds maintain it by stabilizing the backbone structure. Not
least, this is evident from the increase in the number of backbone conformations observed in polar
solvents due to the formation of inter-molecular
hydrogen bonds with the solvent molecules
(Kratochvil et al. 1999). In addition to the four
intra-molecular hydrogen bonds, CyA exhibits a
cis-amide bond between the N-methylleucine residues at positions 9 and 10. Moreover, the N-methyl
moiety of MeVal in the loop makes backbone contacts, which further contribute to the rigidity of the
structure (Velkov and Lawen 2003).
2. Biosynthesis
The biosynthesis of bioactive peptides like
cyclosporins proceeds non-ribosomally and is
catalyzed by complex multi-functional enzymes
termed non-ribosomal peptide synthetases
(NRPS). Cyclosporin synthetase (CySyn) is one
of the best studied enzyme complexes of this type
and capable of catalyzing a total of at least 39
different reaction steps in the synthesis of cycloundecapaptides via an assembly belt-like mechanism: 11 amino acyladenylation reactions, ten
transpeptidations, seven N-methylations, ten
chain elongation reactions and a final cyclization
reaction (Dittmann et al. 1994; Velkov and
Lawen 2003).
The enzyme consists of 11 protein modules, each being
responsible for the recognition, activation and modification of one substrate (Lawen and Zocher 1990; Weber
et al. 1994) and a small 12th module putatively responsible for cyclization. Based on the gene sequence and the
established models for non-ribosomal peptide synthetases
(Marahiel et al. 1997), each module of CySyn essentially
consists of a central adenylation domain (A-domain;
Immunomodulators
169
well. The biosynthesis of Bmt is catalyzed by a polyketide
synthase (PKS) that forms the polyketide backbone by the
head-to-tail condensation of four acetate units, resulting in
a 3(R)-hydroxy-4-(R)-methyl-6-(E)-octenoic acid thioester;
the C-methyl in the carbon chain is derived from AdoMet
(Offenzeller et al. 1993). The polyketide 3(R)-hydroxy-4(R)-methyl-6-(E)-octenoyl-CoA is then transformed into
the b-amino acid form which is utilized by CySyn as a
substrate for cyclosporine biosynthesis. D-Alanine is
provided by a distinct pyridoxal phosphate dependent alanine racemase (Hoffmann et al. 1994). The remaining
amino acid constituents of the CyA molecule are synthesized by classic biosynthetic pathways, as confirmed by
Senn et al. (1991) using 13C-labeling experiments.
recognition, activation), a thiolation domain (T-domain,
covalent binding of adenylated amino acid on phosphopantethein) and a condensation domain (C-domain; elongation step). During elongation, the activated amino acids
are linked by peptide bonds leading to enzyme-bound
nascent peptide chains.
CySyn substrates include L-valine, L-leucine,
a-amino butyric acid (Abu),
4-methylthreonine, and D-alanine. With the adenulation domain, cyclosporine synthetase generates the acyl-adenylated amino acids and then
covalently binds the amino acid to phosphopantetheine through a thioester linkage. Seven of the
substrate amino acids become N-methylated by
S-adenosylmethionine via respective methyltransferase activites of CySyn. The final cyclization step
releases CyA from the enzyme complex (Hoppert
et al. 2001).
L-alanine, L-glycine,
The massive CySyn polypeptide represents the
upper limit of molecular size of the NRPS
enzymes. A molecular mass of 1.69 MDa (15 281
amino acids), was delineated from the sequence of
the CySyn gene, simA, which constitutes an intronless genomic open-reading frame (ORF) of 45.8 kb
(Weber et al. 1994; Velkov and Lawen 2003). The
role of this gene in CyA biosynthesis was proved
by Weber and Leitner (1994). They demonstrated
that the knock-out of the simA gene in Tolypocladium inflatum resulted in its inability to produce
cyclosporins.
Several members of Cy family (like CyA) contain nonproteinogenic amino acids (D-alanine, Abu and unusual
Bmt or a similar C9-amino acid; Fig. 8.2), which have to
be synthesized by a pathway independent of the primary
metabolism. Therefore, besides CySyn, the presence of
some other enzymes is crucial for CyA biosynthesis as
MeBmt
L1
MeVal
L11
MeLeu
L10
CH3
Abu
L2
CH3
CH3
H3C
H3C
H3C
CH3
O
CH3
HO
N
CH3
N
O
H3C
CH3
N
CH3
O
MeLeu
L9
O
H
N
H
N
CH3
O
OH C
3
H3 C
CH3
O
O
D-Ala
L8
CH3
H
N
H
N
H3C
N
O
N
Sar
L3
N
H
N
CH3
L-Ala
L7
O
O
CH3
H3C
MeLeu
L6
H3C
CH3
CH3
Val
L5
MeLeu
L4
Fig. 8.2. The chemical structure of cyclosporin A including the numbering system. It is composed of 11 amino acid unit,
with seven of the amide nitrogen methylated. The three non-proteogenic amino acids are: D-alanine, Abu (L-2 aminobutyric acid) and Bmt (4R)-4-[(E)-2-butyl]-4-methyl-L-threonine (modified from Velkov et al. 2006)
170
Hesham El Enshasy
Transmission electron micrographs of negatively stained
CySyn macromolecules showed large globular complexes
of 25-30 nm in diameter, built up by smaller interconnected units associated with smaller particles of 7 nm
length. Complexes of CySyn and D-alanine racemase are
linked and localized at the fungal vacular membrane,
where Cy synthesis is carried out (Hoppert et al. 2001).
CySyn and D-alanine racemase seem to be located in close
vicinity to each other, since D-alanine is the leading
amino acid of the polypeptide chain synthesized by
CySyn. Cyclosporin is subsequently accumulated inside
the vacuoles and released slowly through vacuolar and
cytoplasmatic membranes or rapidly upon cell lysis.
CySyn was prepared in purified form at pilot scale and
used as a model to produce large amounts of CyA in vitro.
The process included ammonium sulfate precipitation, gel
filtration, hydrophobic interaction chromatography and
anion exchange chromatography, and it yielded an electrophoretically homogenous cyclosprin synthetase preparation (Velkov et al. 2006). The obtained enzyme exhibited
an optimal temperature range between 24 and 29 ºC and a
pH optimum around 7.6.
3. Production
The production of cyclosporins at the laboratory
scale can be carried out using different aerobic
filamentous fungi such as Tolypocladium inflatum,
Fusarium solani (Sawai et al. 1981), Neocosmospora
vasinfecta (Nakajima et al. 1989), Acremonium
luzulae (Moussaı̈f et al. 1997) and T. cylindrosporum (Sekar et al. 1997). The industrial production of cyclosporins is mainly performed using
highly productive strains of T. inflatum.
This organism was originally mis-classified as Trichoderma polysporum Gams, however, later it turned out
that it belonged to a new genus of ascomycetous molds,
Tolypocladium and coined the name T. inflatum (Gams
1971). In 1983, another research group found that T. inflatum was identical to Pachybasium niveum, and since the
latter older name has priority under the rules of the International Code of Botanical Nomenclature, the strain was
renamed as T. niveum (Bissett 1983). This fungus was
again re-classified as Beauveria nivea (Von Arx 1986).
Based on the research of Kathie Hodge, this strain was
found to be the asexual state of Cordyceps subsessilis
(Hodge et al. 1996). Due to the economic importance of
this fungus, the classification as T. inflatum was neverteless conserved for cyclosporin producers to avoid any
confusion with other strains (Dreyfuss and Gams 1994).
In spite of some efforts to produce CyA with
immobilized cells or by solid-state fermentation
(SSF), the industrial production of this immunosuppressive agent is mostly carried out using
free cells in submerged cultures in stirred-tank
bioreactors. The particular role of the type of
strain on the production of CyA along with
some characteristic morphological features was
reported by several authors.
In case of T. inflaturm, large intra-population variations in
colony color and shape were observed on solid media.
Thus, colony color can range from white to brownish
(including yellow, orange and red colonies) (Aarnio and
Agathos 1990). The production of a pink pigment was
found to be associated with cyclosporin production in
certain T. inflatum strains (Chun and Agathos 1989).
Besides the selection of highly productive colonies of
wild-type strains, attempts were undertaken to increase
the strain productivity by mutation using chemical mutagens such as methyl sulphate, epichlorohydrin or nitrosoguanidine (Agathos et al. 1986). A recent study of Mi-Jin
and coworkers (2009) has demonstrated the possibility of
the improvement of T. niveum productivity by using random mutagenesis combined with protoplast transformation. The mutant strain, generated using a random UV
method, produced more than ninefold higher amounts of
CyA than the wild-type strain. Additionally, a bacterial
gene of a Vitreoscilla spp. (hemoglobin gene, VHb) was
transferred to the UV-irradiated mutant to increase oxygen uptake in liquid culture and led to an additional
increase in CyA production of more than 30%. Besides
the type-strain used, the production levels of CyA are
dependent on several regulating factors such as inoculum
type and size, medium composition and additives as
well as process parameters such as temperature, pH and
partial oxygen pressure. A high density of the sporeinoculum was found to be necessary for the development
of small pellets, which is the preferred morphology for
cyclosporin production (Dayfuss et al. 1976; Isaac et al.
1990). However, inoculum size is only one of more than
20 other factors controlling the fungal pellet formation
(El Enshasy 2007).
The influence of the type and concentration of
carbon and nitrogen sources on CyA production
has been examined in wild-type and mutant
strains of T. inflatum. Among different carbon
sources tested, 3% sorbose gave the highest CyA
titre (Agathos et al. 1986). A feeding strategy using
the sequential addition of two carbon sources
(sorbose and maltose) was also reported to be
successful in attaining a higher volumetric production (Agathos et al. 1986). Another study
showed that an optimal medium for CyA production can be developed by factorial experimental
design and consisted of the three carbon sources
glucose, sucrose and starch in different ratios
(Abdel Fattah et al. 2007).
Biosynthesis of CyA was found to be heavily
influenced by the external addition of amino acid
Immunomodulators
constituents of the molecule. Addition of L-valine
increased the specific production of CyA by 60%
in semi-synthetic media and even by 400% in
synthetic media. Experiments using repeated
addition of L-valine indicated that the amino acid
has to be present in the exponential growth phase
of the fungus for optimal CyA production (Lee
and Agathos 1989). Based on this finding, a mathematical model for the production of CyA in the
presence of supplemented L-valine was developed,
which also considered kinetic information and
mechanistic data on CyA biosynthesis (Agathos
and Lee 1993). Concomitant addition of L-leucine
and L-valine to a synthetic medium was found
to stimulate CyA production as well (Balakrishnan
and Pandey 1996). When fungal cells enter the
stationary phase and CyA accumulates in the
medium, they partially undergo lysis and CyA degradation sets in, especially under carbon source
limitation. The intensity of cell lysis and CyA degradation in the bioreactor was higher than in
agitated flasks, especially under an uncontrolled
pH regime (El Enshasy et al. 2008).
Several attempts have been made to use immobilized cells
for CyA production. On example is the successful production of CyA in high amounts using carrageenan-entrapped
cells of T. inflatum in an airlift bioreactor (Foster et al.
1983). CyA was also produced in relevant amounts by a
Tolypocladium sp. immobilized in calcium alginate beads
in a packed-bed reactor (Sekar and Balaraman 1998a).
Continuous production of CyA was realized using immobilized spores of T. inflatum on celite beads (Chun and
Agathos 1989). The CyA productivity by cells immobilized on celite beads (100–500 mm) was reported to be
4–6 mg l–1 h–1. This value is about six- to tenfold higher
than those of batch fermentations in suspension cultures
(Lee et al. 1997). Furthermore, attempts were made to
produce CyA by solid-state fermentation (SSF) to reduce
the production costs. So in a study, wheat-bran was used
as a solid support and yielded up to 1400 mg CyA kg–1
substrate (Sekar et al. 1997). After optimizing different
cultivation parameters, such as the type and design of
tray, thickness of the solid substrate bed, type and size of
inoculum as well as relative humidity, the CyA production
increased to a value of 1920 mg kg–1 (Sekar and Balaraman
1998b). However, SSF up-scaling raises severe engineering
problems due to difficulties of adjusting temperature, pH,
oxygen and moisture content as well as of managing gradient formation inside the cultivation system. Recently, a
novel process for CyA production by F. solani using a
large-scale SSF bioreactor of an area of 226 m2 has been
developed (Khedkar et al. 2007). Besides the continuous
optimization of the up-stream part of the production process, improvement of CyA extraction methods has also
contributed to increase the overall yield of the process.
CyA is a hydrophobic molecule with high solubility in
171
low-molecular-weight alcohols, and extraction could be
optimized using different alcohols as solvent system and
varying temperatures during the extraction process (Ly
and Margaritis 2007; Ly et al. 2007).
4. New Generations
A recent study has demonstrated that CyA has a
number of side-effects causing among others
hypertension, dyslipidemia, hirsuitism and
chronic renal insufficiency that leads in 10% of
cardiac transplant recipients to an end-stage renal
disease (Patel and Kobashigawa 2008). Numerous
analogues and derivatives of CyA have been tested
in order to improve the drug’s therapeutic properties. For example, CyG, a cyclosprin A analogue
with a L-novaline substituent at position 2, displays equal immunosuppressive effects as CyA
but with less nephrotoxicity (Hiestand et al.
1985). Another derivative SZZ IMM-125, which
is a hydroxyethyl derivative of D-serine-8-cyclosporine, was found to be slightly more potent but
far less nephrotoxic than CyA in both in vitro and
in vivo models (Hiestand et al. 1992; Ferraresso
and Kahan 1993). ISATX247 is a potent derivative
with higher activity and lower nephrotoxicity
compared to CyA (Gregory et al. 2004). Several
other cyclosprin analogues with high immunosuppressive activity were obtained through the
chemical modification of the side chains at the
first amino acid and optionally at third amino
acid (Molino and Yang 2006).
B. Mycophenolic Acid
Mycophenolic acid (MPA), [6-(4-hydroxy-6methoxy-7-methyl-3-oxophthalanyl)-4-methyl-4hexenic acid; CAS 24280-93-1; Figs. 8.1–8.2], is
one of the oldest known secondary metabolites.
The compound was first detected in 1896 by Gozio
in the fermentation broth of Penicillium glaucum
and recognized as a lipid-soluble weak organic
acid. This compound was also isolated from the
culture filtrate of Penicillium stoloniferum Thom
by Alsberg and Black (1913), who named it MPA
(Alsberg and Black 1913; Jekkel et al. 2001). Since
then, numerous reports have been published dealing with the production of MPA by different
microorganisms. The complete chemical structure
of MPA was first reported by Birkinshaw et al
(1952).
OH
CH3
OH
CH3
HO
HO2C
O
O
methylphthalide
+
3 CH2COSCoA
CH3COSCoA
HO2C
O
Fig. 8.3. Different steps of MPA biosynthesis
O
CH3
O
HO
2
OH
CH3
OH
5-methyl-orsellinic acid
SCOA
HO
CH2
Demythylmycophenolic acid (DMPA)
O
O
CH3
OH
CH3
CO2H
HO
5,7-dihydroxy-4-methylphthalide
O
O
HO2C
Mycophenolic acid
O
O
CH3
H3CO
6-farnesyl- 5,7-dihydroxy-4-
O
CH3
HO
3
OH
CH3
CH3
The MPA 2-morpholinoethyl ester (also named mycophenolate
mofetil, MMF) of the chemical structure 2-morpholinoethyl-(E)-6-(1,3-dihydro-4-hydroxy-6-methoxy-7-methyl3-oxo-5-isobenzofuranyl)-4-methyl-4-hexeneoate (CAS
128794-94-5; Figs. 8.1–8.3), is one of the most important
MFA derivatives and approved by the FDA in 1995 as
immunosuppressive agent for the prevention of acute
renal allo-graft rejection and in 1998 for heart transplantation. A further improved generation of MPA drugs,
based on sodium mycophenolate in controlled release
formulations with good gastrointestinal absorption and
bioavailability, was approved in 2005 (Xy and Yang
2007). In addition to the well established market for organs
transplantations, MPA and its derivatives have been recognized by many physicians as an effective option for the
treatment of immune-mediated diseases (Bentley 2000;
Mydlarski 2005). Another pro-drug of MPA was developed
in Japan during the early 1980s, initially as antitumor
agent against various experimental cancers (Mitsui et al.
1981; Matsuzawa and Nakase 1984). In this derivative, the
hydroxyl group of MPA was derivatized and the carboxylic
functionality was replaced by an ethyl ester to produce
ethyl-[N-(p-carboxyphenyl)-carbamoyl]-mycophenolate,
abbreviated as CAM. The chemical structure of CAM was
fully characterized and its crystal structure solved by
Nawata and coworkers (Nawata et al. 1988; 1989). An
early study using CAM as immunosuppressive drug
demonstrated that it can suppress acute allergic cephalomelitis in Lewis rats (Mizobuchi et al. 1997). Based on this
study, it was suggested that CAM might be also a useful
adjunct for the long-term immunosuppressive therapy
of inflammatory diseases of the central nervous system.
At the same time, a study of Sawada and his group
demonstrated the usefulness of CAM in bowel transplantation (Sawada et al. 1996). Using a rat model, the
immunosuppressive activity of CAM was explained
through the inhibition of the interphotoreceptor retinoid-binding protein (IRBP) mediated autoimmune
CH3
At the early stage of its biomedical applications, MPA was used as a broad-spectrum antibiotic due to its antibacterial, antifungal, antiviral
and antiprotozoal activities (Abraham 1945; Ando
et al. 1968; Cline et al. 1969; Noto et al. 1969).
Moreover, it was found to exhibit also some antitumor and antipsoriasis as well as anti-inflammatory activities (Carter et al. 1969; Spatz et al. 1978;
Epinette et al. 1987). MPA was produced during
that time under the trademark Bialin (Vinkurova
et al. 2005). However, it has not widely used in
practice as antibiotic because most microbes were
found to readily become resistant to this compound. In spite of its low acute toxicity to mammals, MPA was also described as a mycotoxin by
some authors (Sanchis et al. 1988; Puel et al. 2005).
New interest in MPA and its derivatives has
remarkably grown after the discovery of their
immunosuppressive properties.
O
Hesham El Enshasy
C
172
Immunomodulators
uveoretinitis by a decrease in cytokine production (Sakai
et al. 1999). Compared to other immunosuppressive
drugs, CAM has only minor adverse side-effects due to
its relatively specific action on lymphocytes. Furthermore, this new derivative was more effective than MMF
in prolongation of heart-graft survival in rats at each dose
applied (Takazawa et al. 1995).
Nowadays, MPA derivatives used as immunosuppressant drug in organ tansplantation are
marketed under different trade names, such as
CellCept (mycophenolate mofetil, Roche) and
Myfortic (mycophenolate sodium; Novartis). In
case of oral applications of MMF, the pro-drug
mycophenolate mofetil is rapidly hydrolyzed to
MPA after administration and suppresses the
immune system via a non-competitive reversible
inhibition of inosine-5’-monophosphate dehydrogenase (IMPDH; EC 1.1.1.205). This enzyme
catalyzes the NAD-dependent oxidation of inosine-5’-monophsphate (IMP) to xanthosine-5’monophosphate (XMP), which is the committed
step in the de novo biosynthesis of guanosine
monophosphate (GMP). This reaction is particularly important to generate the guanosine nucleotide levels needed to initiate a proliferation
response of B- and T-lymphocytes to mitogens
and antigens (Sintchak et al. 1996). Thus, MPA
acts as a potent anti-proliferative agent (Hood and
Zarembski 1997) affecting cytokine-dependent
signals and causing in vivo the inhibition of lymphocyte reactions (Allison and Eugui 2000). In
consequence, MPA and its derivatives are being
widely used in the transplantation of different
organs in humans at different ages (Budde et al.
2006; Tönshoff 2006; Aw et al. 2008).
Besides the wide application of MPA in organ transplantation, it is also used in the treatment of immune
related diseases such as rheumatoid arthritis, lupus
inflammatory bowel disease and other kidney or skin
disorders (Liu and Mackool 2003; Appel et al. 2005;
Hartmann and Enk 2005; Iaccarino et al. 2007). Moreover, MPA has recently been used in the treatment of
rare diseases like interstitial nephritis (Preddie et al.
2006) and focal segmental glomerulosclerosis (Cattran
et al. 2004).
In general, MMF has several advantages over
cyclosporins as maintenance therapy of organgraft recipients (Eugui and Allison 1993). Above
all, MMF is well tolerated by the human body and
has a lower toxicity and hence fewer side-effects
than CyA.
173
1. Chemistry
Already before the discovery of its immunosuppressive activity, MPA was used as drug due to its
wide biological activity against bacteria, parasites
and viruses. Thus for many years modifications of
the MPA structure were the subject of intensive
research in order to increase its biological activity, bioavailability and the range of applications
(Lee et al. 1990; Nelson et al. 1990; Rohloff et al.
1995).
Most studies focused on increasing the antitumor activity of MPA through the production of
monocyclic analogues and carboxamide derivatives without any change in the aromatic ring
and the surrounding side chains, since the free
phenolic structure is an absolute prerequisite for
MPA activity (McCorkindale and Baxter 1981;
Anderson et al. 1996; Menza-Aviñ et al. 2005).
The methoxy and methyl groups of the aromatic
ring represent two other key structural elements
influencing the activity of MPA (El-Araby et al.
2004). The study of Nelson et al. (1996) demonstrated that the aromatic methyl group of MPA
is essential for its biological activity and the
replacement of the methoxyl group by other
ethers resulted in compounds with two- to fourfold higher potency in vitro and in vivo.
Further improvement of MPA activity was
achieved by the development of new MPA analogues, which have overcome the drawback of
glucuronidation of the phenolic hydroxyl group
at C7 (Chen et al. (2007). In these derivatives, a
truncated MPA is connected to an adenosine moiety via a linker (e.g. methylene bis-phosphonate)
leading to mycophenolic adenine dinucleotide
derivatives. The new molecules show a better
biological activity and chemical stability. Moreover, a new series of IMPDH inhibitors based on
the replacement of the benzofuranone moiety in
MPA by a methoxy-(5-oxazolyl)-phenyl (MOP)
moiety has recently been developed (Chen et al.
2008). Besides the different methods of chemical
modification, several attempts were made to
transform MPA using different microorganisms
(Jekkel et al. 2001). In the course of these bioconversions, mycophenolic acid was found to undergo
one or more of the following transformations:
hydroxylation at the side chain or the lactone
ring, amide or alcohol formation at the carboxylic
acid group, oxidative cyclizations of the side chain
or glycosylation (Jekkel et al. 2002).
174
Hesham El Enshasy
2. Biosynthesis
The molecule of MPA consists of an acetatederived aromatic nucleus, a terpenoid side chain,
and two methyl groups (the 5-methoxyl and the 4methyl group). Different schemes of MPA biosynthesis have been proposed by different authors
(Bedford et al. 1973; Muth and Nash III 1975,
Nulton and Campbell 1978). In 2000, Bentley summarized and updated the synthesis pathway in his
excellent review (Fig. 8.3). Accordingly, MPA biosynthesis involves two major pathways of secondary metabolite formation: the polyketide and the
isoprenoid pathway as well as methylation reactions on oxygen and carbon atoms.
In this process, a typical acetate-polymalonate condensation with a methylation prior to condensation leads to the
aromatic structure, 5-methyl-orsellinic acid. It proceeds
thereafter through lactone formation followed by addition
of the C15-farnesyl diphosphate unit and formation of the
intermediate 6-farnesyl-5,7-dihydroxy-4-methylphthalide
(Fig. 8.3). This compound undergoes several oxidative degradation steps to remove eight carbon atoms from the side
chain by two possible mechanisms: one involves two oxidative cleavages at the two side chain double bonds removing
levulinic acid and acetone from the aromatic ring.
The other possible mechanism is a direct oxidation at the
central double bond of the farnesyl side chain. The two
pathways are regarded as being of equal importance
(Bentley 2000). Early studies had already shown that the
basic carbocyclic skeleton of the molecule was acetatederived and that methionine provided the O- and C-linked
methyl groups attached to the aromatic ring (Birch et al.
1958; Jaureguiberry et al. 1964). The last step of MPA
biosynthesis was found to be the transfer of a methyl
group from S-adenosyl-L-methionine (SAM) to demethylmycophenolic acid (DMPA). This step is catalyzed by a
specific SAM:DMP O-methyltransferase (Muth and Nash
1975).
3. Production
MPA was originally isolated from culture filtrates
of Penicillium glaucum and P. stoloniferum as a
weak acid with antifungal activity (Alsberg and
Black 1913); later MPA production was reported
for 12 strains of the species P. brevicompactum
(Clutterbuck et al. 1932).
Since that time, many reports have been published dealing with the production of MPA
using different species of the genus Penicillium
(Vinokurova et al. 2005), such as P. brevicompactum (Doerfler et al. 1979; Ozaki et al. 1987a; Alani
et al. 2009), P. brunneostoloniferum (Nakajima
et al. 1979); P. roqueforti (Lafont et al. 1979,
Engel et al. 1982; Schneweis et al. 2000) and other
molds like Neocosmospora spp. and Byssochlamys
nivea (Puel et al. 2005). Unfortunately, most of the
studies on MFA production were carried out on a
small scale and data on the detailed effects of
media components and cultivation conditions are
scarely found in the literature.
Among different MPA producers, the highest productivity was obtained for strains of P. brevicompactum and P.
stoloniferum which both are suitable for industrial fermentation (Queener and Nash 1978; Kida et al. 1984;
Sircar et al. 2005). Several attempts have been made to
improve MPA production by using antibiotic-resistant
mutants with a high internal ergosterol level (Queener
et al. 1982). Also, rational breeding procedures based on
the biosynthetic pathway were used to select strains with
improved MPA productivity. Among the different antibiotic-resistant mutants developed, a clofibrate and
dodecyltrimehylammonium chloride double resistant
mutant produced about 4.7 g l–1 MPA (about three
times more than the parent strain, P. brevicompactum
ATCC 16024). A glutamate auxotroph of this antibioticresistant mutant was even able to produce up to 5.8 g l–1
MPA. This strain was found to grow on L-aspartate
instead of L-glutamate and exhibited only one-third of
the pyruvate carboxylase activity of the parent strain
(Ozaki et al. 1987a).
Cultivation in submerged culture showed
that the production of MPA starts concomitantly
with the hyphal aggregation phase just before
pellet formation (Doerfler et al. 1978). Unlike
most secondary metabolites, MPA is produced
growth-associated in the exponential phase (in
both batch and continuous cultures) and independent of the medium composition (Nulton
and Campbell 1977; Doerfler et al. 1979). The
production process is carried out either in submerged cultures or by solid-state fermentation
(SSF).
For many years, the optimal medium for MPA production
has been a semi-synthetic mixture composed of glucose
(C-source), ammonium salts or casein (N-source), potassium dihydrogen phosphate (P-source), magnesium sulphate and trace elements. Some authors supplement other
components like the amino acid glycine (Xu and Yang
2007) to further increase MPA production. More recently,
it has been reported that, among different nitrogen
sources, urea in concentrations up to 5 g l–1 was the Nsource of choice to support MPA production (Roh 2008).
However all in all, only little efforts haven been done to
optimize media composition and cultivation conditions
compared to the production of other important fungal
metabolites.
Immunomodulators
Like other production processes involving
fungal cells, growth morphology is a critical factor
determining the growth rate and production yield.
Fungi can grow either in form of pellets or mycelia
and thus, controlling the growth morphology to a
desired shape is important to improve the cell
productivity. Altogether, more than 30 factors
have been reported in the literature to influence
the growth morphology; these include straindependent factors (type of strain, inoculums size,
physiology, etc.), cultivation conditions (pH,
temperature, osmotic stress, etc.) and medium
composition (C-source, N-source, C/N ratio, surfactants, presence of insoluble particles) and
many other factors (El Enshasy 2007).
Using spores as inoculum for MPA production in
submerged culture, it was shown that the increase of
spore density from 104 to 107 spores ml–1 resulted in
significant reduction in pellet size with a concomitant
increase in MPA production from 0.2 up to 4.8 g l–1.
Further, it was found that MPA can be continously produced, independent of spore concentration, in the presence of 1% celite in the culture medium. In the case of
celite addition, growth occurred in form of pellets (500 mm
in diameter) regardless of the inoculated spore concentration (Ozaki et al. 1987b). New cultivation approaches try to
overcome the problem of changed cell morphology by
applying rotating fibrous-bed bioreactors (RFB). Accordingly immobilized cells in RFBs produced MPA up to a
concentration of 5.7 g l–1 within 14 days using the standard
wild-type strain P. brevicompactum ATCC 16024. Other
advantages of RFB fermentation include the ease of product separation and purification from the fermentation
broth as well as the possible repeated use of cells for
long-term operation (Xu and Yang 2007).
Several attempts were made to use solid-state
fermentation (SSF) as an alternative cultivation
method. In general, filamentous fungi are well
suited for SSF and a number of valuable metabolites can be produced under these conditions,
since they perfectly reflect the natural habitats of
the fungi (Krishna 2005).
175
(2009) has demonstrated that MPA production by SSF in a
packed-bed bioreactor can lead to yields up to 6900 mg
MPA kg–1 pearl barley within just 168 h.
Due to its low molecular weight and the relatively simple chemical structure, MPA and its derivatives can nowadays also prepared chemically.
Different procedures for MPA total synthesis have
been published using different starting materials.
Patterson (1993) synthesized MPA using silyloxy-1,3cyclohexadiene and allylic alcohol via an ortho-ester
Claisen rearrangement. Another interesting method for a
convergent synthesis of MPA via a palladium-tin coupling
reaction between the alkyl side chain and the phthalide
ring was described by Plé et al. (1997). A further method
involves 2-geranyl-1,3-acetonedicarboxylate and 4-pivaloyoxy-2-butynal and a specific cyclization as key step
(Covarrubias-Zúñiga and Gonzlez-Lucas 1998). The production of MPA using this new synthetic strategy is based
on a ring annulation sequence involving a Michael addition reaction and an intra-molecular Dieckmann condensation in situ (Covarrubias-Zúñiga et al. 2003).
C. Mizoribine
The immunosuppressive antibiotic mizoribine
or bredinin (5-hydroxy-1-b-D-ribofuranosyl1H-imidazole-4-carboxamide; CAS 50924-49-7;
Fig. 8.4) was first isolated from the culture
medium of Eupenicillium brefeldianum isolated
from soil samples on Hachijo island (Japan;
Mizuno et al. 1974). Mizoribine (MZA) is an imidazole nucleoside and the metabolite MZ-5-P exerts
its activity through selective inhibition of inosine
monophosphate synthetase and guanosine monophosphate synthetase, resulting in the complete
inhibition of guanine nucleotide biosynthesis
(Shumpei 2002). Based on this immunosuppressive mechanism, mizoribine is superior to many
O
An early study by Bartman et al. (1981) demonstrated that,
when cells grew as surface culture, MPA production was
associated with the aerial mycelium and its production
ceased completely when the formation of aerial hyphae
was blocked. However, the yield of MPA in this study
was relatively low (only 0.3 mg g–1 wet weight). SSF production of MPA was optimized using a response surface
methodology and the maximal yield achieved was 3300 mg
kg–1 wheat bran (Sadhukhan et al. 1999). Further improvement was achieved by using a fed-batch strategy (Tiwari
et al. 2003). Furthermore, a recent study of Alani et al.
NH2
N
OH
N
OH
O
OH
Fig. 8.4. Mizoribine
OH
176
Hesham El Enshasy
other clinically used drugs, since it may not cause
damage to normal cells and nucleic acids.
In contrast to other immunosuppressive
agents widely used at the time of its discovery
(e.g. azathioprine), mizoribine was shown in animal experiments to lack oncogenicity and exhibited a clinically low incidence of side-effects such
as hepatotoxicity and myelosuppression. These
facts together supported its use in clinical application in long-term immunosuppression therapies.
In 1984, MZR was first approved for the treatment
of graft rejection after kidney transplantation
(Takei 2002). Later, it was also approved for the
treatment of other diseases including lupus
nephritis, rheumatoid arthritis and primary nephritic syndrome. It is currently marketed in China,
Korea and Japan under the trade name Bredinin
(Tanaka et al. 2006). The drug is mainly produced
by the fungi E. brefeldianum and E. javanicum in
submerged culture under aerobic conditions, however, little information is available on the biosynthesis pathway and the production process
(Mizuno et al. 1975; Benedetti et al. 2002).
D. Other Immunosuppressants
In addition to the three clinically approved fungal
immunosuppressants, Cyclosporins, MPA and mizoribine, many other fungal metabolites possess also
potent immunosuppressive activities (Fig. 8.5). Some
of them were found to be not suitable for clinical
applications due to their side-effects, whereas others
are still subject of intensive studies and currently
undergoing different levels of clinical trials till final
approval by FDA.
1. Ovalicins and Fumagillins
The fungal metabolites ovalicin, fumagillin and
their related derivatives belong to the most potent
anti-angiogenic compounds. They bind convalently to the active site of the enzyme methionineaminopeptidase type 2 (MetAP2) and irreversibly
block its proteolytic activity (Liu et al. 1998; Turk
et al. 1998).
Ovalicin or Graphinone (CAS 19683-98-8) is a sesquiterpene that was first isolated from culture filtrates of Pseudeurotium ovalis in 1962 and found to have antimicrobial
and cytotoxic activities. It was chemically characterized by
Sigg and Weber (1968). The chemical structure of this
compound is related to the antibiotic fumagillin. The
immunosuppressive properties of ovalicin were evaluated
using the mouse hemagglutinin test, which reflects the
degree of antibody production. It was found be not toxic
to the cells of bone marrow, which distinguished it from
existing immunosuppressants at that time. Unfortunately,
when tested in humans it later turned out to have other
toxic side-effects.
A Metarhizium sp. isolated from soil in Japan was
found to produce a 12-hydroxyovalicin (Kuboki et al.
1999), which was named Mer-f3. This compound was
examined for its influence on mixed lymphocyte cultures,
and showed a similar inhibitory activity as ovalicin. Mer-f3
had an immunosuppressant activity in the murine mixed
lymphocyte test with IC50 ¼ 1 nM which is even better than
that of CyA (110 nM). Moreover, Mer-f3 had no inhibitory
activity on leukemia L-1210 which indicates a low mammalian toxicity. Another Metarhizium sp. isolated from
soil was reported to produce a novel immunosuppressive
substance, which was named metacytofilin (Iijima et al.
1992); this compound had not any antimicrobial activity,
while showing strong immunosuppressive effects.
Chlovalicin, a chlorinated compound derived from
the epoxide ring attached to ovalicin, was discovered in
the fermentation broth of the soil fungus Sporothrix sp.
It inhibited the IL-6 dependent growth of MH60 cells and
appeared to be a new IL-6 inhibitor (Hayashi et al. 1996).
Two ovalicin related compounds, FR 65814 (CAS 10347060-6) and Fumagillol (CAS 108102-51-8), were isolated
from culture filtrates of the soil fungus Penicillium jensenii. They both showed significant immunosuppressive
activity at low concentrations (Hatanaka et al. 1988).
A chiral and stereoselective total synthesis of FR 65814
using glucose as starting material was described by Amano
et al. (1998, 1999), and fumagillol can be also synthesized
using other starting materials (Kim et al. 1997, 2005a;
Boiteau et al. 2001). TNP-470, a semisynthetic derivative
of fumagillin, reduced the proliferation of endothelial cells
with an IC50 value of 2.510–11 M. Therefore, it entered
clinical trials as immunosuppressive and anti-tumor
agent. The main drawbacks of its therapeutic properties
were the short physiological half-life span and the severe
side-effects such as ataxia, vertigo and agitation (Figg et al.
1997). The relation between the chemical structure and
bioactivity of fumagillin and its derivatives was studied
by several authors. It was shown that the spiro-epoxide is
essential for the activity of fumagillin and its conversion
into a methylene group results in a considerable reduction
of eficacy (Logothetis et al. 2001). On the other hand, the
epoxide of the side chain has no major effect on the
biological activity. New synthetic analogues of ovalicin
and fumagillin lacking reactive epoxy functionalities,
which are thought to be responsible for the severe toxic
side-effects, were synthesized by Mazitschek et al. (2005).
2. Gliotoxin
Gliotoxin (CAS 67-99-2) is a sulfur-containing
antibiotic that belongs to the epipolythiodioxopiperazine group of secondary metabolites and
Immunomodulators
R
CH3
O
CH3
O
CH3
CH3
O
CH3
Ovalicin
Ovalicin
:R=H
: R = OH
CH3
OH
Fumagillin
CH3
CH3
O
N
OCH3 O
S
S
CH3
N
OH
OH
OH
Cl
O
O
4
Fumagillin
TNP470
CH3
CH3
O
NH
O
CH3
HO
OCH3 O
O
Fumagillin
CH3
O
O
H
OCH3
OH
O
CH3
O
OH
OCH3
CH3
CH3
O
OH
O
177
Gliotoxin
CH3
OH
OH
OH
OH
CH3
CH3
CH3
H3C
H3C
H3C
H
OCH3
OCH3
OCH3
Flavidulols
Flavidulols
Flavidulos
OCH3
OH
OH
HO
CH3
NH2
O
OH
O
Myriocin
CH3
OH
NH2
OH
Myriocin
Fig. 8.5. Molecular structure of different types of fungal immunosuppressive agents
exhibits antifungal, antiviral as well as strong
immunosuppressive activities. Gliotoxin was originally isolated from Gliocladium fimbriatum and
named accordingly. It was reported thereafter that
this compound is commonly produced by several
genera of molds such as Aspergillus, Trichoderma
and Penicillium. Gliotoxin was also claimed to be
produced in yeasts of the genus Candida, however, a recent study being based on a screening of
100 clinical isolates of Candida doubted the
occurrence of this compound in yeasts (Kupfahl
et al. 2007).
The immunosuppressive effects of gliotoxin have been
explained by different mechanisms. It suppresses cell
activity and induces apoptosis in a variety of cell types
including neutrophils, esosinophils and granulocytes
(Ward et al. 1999). It inhibits the chymotrypsin-like activity of the 20S proteasome in a non-competitive manner
(Kroll et al. 1999) and likewise the activation of NF-kB in
T- and B-cells when applied at nanomolar concentrations
(Pahl et al. 1996). The immunosuppressive activity of
gliotoxin was also attributed to the inhibition of perforin-dependent and Fas-ligand-dependent cytotoxic
T-lymphocyte-(CTL)-mediated cytotoxicity (Yamada
et al. 2000). Another study has furthermore demonstrated
that gliotoxin suppresses the mast cells, which play a key
178
Hesham El Enshasy
O
O
H
N
Pro
H3C
CH3
H
Ala-Alb-Alb-X-Ala-Alb-Y
NH
H
MDA
H
CH3 H OH
H
O
H3C
N
CH3
O
H
H3C
OH
HO
H
H3C
HMDA
Trichopolyn
Acyl group
I
II
III
IV
V
X group
MDA
MDA
MDA
MDA
HMDA
Ileu
Val
Ileu
Val
leu
OH
OH
CH3
H
H3C
H
H3C
O
OCH3
Kobifuranone A
H3C
Kobiin
OH
R
1
OH
CH3
O
O
Kobifuranone B
Kobifuranone C
H2N
R=H
R=OH
Terprenin
3-Methoxyterprenin
4'-Deoxyterprenin
1
2
: R = OH , R = OH
1
2
: R = OCH3 , R = OH
1
2
: R = OH , R = H
OH
HO
CH3O
HO
Mycestericin A
O
H3CO
R
CH3
R2
O
CH2
CH3
OH
CH3
CH3
HO
Y group
α-aminoisobutyric acid
α-aminoisobutyric acid
Ala
Ala
α-aminoisobutyric acid
O
R
HO
O
P
OH
OH
R=
A
CH3
HO H
B
N
C
Mycestericin B
R=
CH3
NHCH3
HO H
Mycestericin C
R=
CH3
FR901483
O
Fig. 8.5. (continued)
role in host defense and are important in both innate
and adaptive immunity (Niido et al. 2006). As this compound is produced by many potential human pathogens
in vivo during the course of infection, gliotoxin may also
contribute to the etiology of fungal diseases (Waring and
Beaver 1996).
3. Trichopolyns
Trichopolyns (TPs) are peptabiotic compounds
produced by Trichoderma polysporum. TPs I
and II were first isolated as new antifungal and
antibacterial antibiotics in 1978 by Fuji and
coworkers. The chemical structures of TP I (CAS
66554-87-8) and TP II (CAS 6655-88-9) were identified as peptide antibiotics three years after their
discovery (Fujita et al. 1981). Nowadays, the structures of five different trichopolyns (I–V) are
known. Trychopolyns I and II are ten-residue
peptides characterized by the presence of a 2methyldecanoyl group at the N-terminus, and
the C-terminal residue is protected by trichodiaminol. The other three analogues, TPs III-V differ
from TPs I and II in that way that Aib (a-aminoisobutyric acid) is replaced by L-alanine. In contrast, TP V has the same amino acid sequence as
Immunomodulators
TP I, but the N-terminal acyl group is substituted
by 3-hydroxy-2-methyldecanoic acid (instead of
2-methyldecanoic acid). These peptabiotics have
been shown to suppress the proliferation of lymphocytes in mouse allogeneic mixed lymphocyte
reactions (Lida et al. 1999). The TP I activity was
even stronger than that of CyA.
4. Myriocin
Myriocin (antibiotic ISP-1 or thermozymocidin;
CAS 35891-70-4) was first isolated from the thermopholic fungus Myriococcum albomyces by
Kluepfel and his group in 1972 and patented in
the United States in 1975 (Kluepfel et al. 1975). The
compound was recognized as an active antibiotic
against yeasts and dermatophytes when applied
in vitro. However, the compound appeared to be
too toxic for therapeutic purposes in humans.
More than 20 years later, the same compound and its
derivatives (mycestericins) were isolated from Isaria sinclairii, which is the imperfect stage of Cordyceps sinclairii,
and showed strong immunosuppressive activities. Myriocin
was 10- to 100-fold more effective than cyclosporin A both
in in vivo and in vitro tests (Fujita et al. 1994; Sasaki et al.
1994). Isaria sp. belong to the entomopathogenic fungi
colloquially called “vegetable wasps and plant worms”,
which have been used in oriental medicine for more than
1000 years (Im 2003). Myriocin was found to suppress both
the production of antibodies against red blood cells of
sheep and the induction of cytotoxic T-lymphocytes more
strongly than cyclosporine A. It is also a potent inhibitor of
serine palmitoyltransferase (SPT), the enzyme that catalyzes the first step in sphingosine biosynthesis (Miyake
et al. 1995). Thus, it is used in biochemical research as a
tool for depleting cells of sphingolipids. Myriocin can also
be produced by chemical methods (Banfi et al. 1982; Oishi
et al. 2002; Jones and Marsden 2008).
Fingolimod or FTY720 (CAS 162359-55-9) is a
novel immunosuppressant obtained by chemical
modification of myriocin (Adachi et al. 1995). A
number of alternative ways for its preparation
using shorter pathways for synthesis with higher
overall yields have been published over recent
years (Seidel et al. 2004; Adachi and Chiba 2007).
Fingolimod was actually designed to eliminate the
GI toxicity of the original compound myriocin. The
exact mechanism of its immunosuppressive activity, however, remains still unclear. Some researchers have hypothesized that FTY720 may induce the
apoptosis of lymphocytes (Suzuki 1996; Fujino
et al. 2002). Others have proposed that the number
179
of lymphocytes decreases as a result of their movement towards secondary lymphoid organs such as
lymph nodes and peyer’s patches (Sugito et al.
2005). It is certain that this novel immunosuppressant prolongs the survival of allo-graft transplants
and is effective in the treatment of some immunological diseases. At the moment, FTY720 is being
further developed by Novartis in phase II clinical
trials. Not least, this compound may have a great
clinical potential because of eficacy as oral drug for
the treatment of multiple sclerosis (Gullo et al.
2006; Klatt et al. 2007).
5. Flavidulols
The immunosuppressive geranylphenols, flavidulols A (CAS 117568-32-8), B (CAS 117568-33-9)
and C (CAS 117568-34-0), were originally isolated
from fruiting body extracts of the mushroom Lactarius flavidulus in the course of a screening for
new inhibitors of the proliferation of mouse lymphocytes (Takahashi et al. 1988). The chemical
structure of these compounds was determined by
NMR analysis (Takahashi et al. 1993); this paper
also reported on the isolation of a new flavidulol D
(CAS 156980-40-4). The suppressive effects of flavidulols A, B and C on the proliferartion of mouse
lymphocytes were stimulated in the presence of
mitogens such as concavalin A (CoA) and lipopolysaccharides (LPS). Their IC50 values for the
inhibition of mitogen-induced concavalin A proliferation of mouse lymphocytes were between 9
and 36 mg ml–1 and against lipopolysaccharideinduced proliferation between 7 and 28 mg ml–1
(Fujimoto et al. 1993).
6. Kobiins
The sesterterpenetriol immunosuppressant kobiin
and another three related 2-furanones named
kobifuranones A, B and C were first isolated
from the ascomycetes Gelasinospora kobi by
Fujimoto et al. (1998). Kobiin posses a bicyclic
skeleton of five- and fifteen-membered rings.
Kobifuranones A, B and C were supposed to be
metabolites formed from a common intermediate
biosynthesized through the acetate-malonate
pathway. AcOEt extracts of fungal mycelia containing kobiin and the three kobifuranones were
found to suppress proliferation of mouse spleen
lymphocytes stimulated with the mitogens CoA
180
Hesham El Enshasy
and LPS. After solvent fractionation followed by
repeated chromatography, the purified kobiin prepartion obtained showed the highest immunosuppressive activity.
7. Mycestericins
Mycestericins are a group of unique immunosuppressive compounds and chemically, hydroxylated a-hydroxymethyl a-aminoalkanoic acids.
All known types of mycestericins were isolated
from the cultures of mycelia sterila (i.e. filamentous fungi without any morphological structures,
neither sexual organs and spores nor conidia
and other asexual spores). The chemical structures of mycestericin A (CAS 128440-98-2),
B (CAS 128341-87-7), C (CAS 37817-99-5), D
(CAS 157183-67-0) and E were determined on
the basis of comprehensive spectroscopic studies
and chemical tests (Sasaki et al. 1994). Mycestericins suppress the proliferation of lymphocytes in
the mouse allogeneic mixed lymphocyte reaction
with a potency similar to that of myriocin. Further
studies led to the isolation of two more active
compounds, mycestericins F and G, from the
same fungus (Fujita et al. 1996). The chemical
structures of mycestericins F and G were identical
to the respective dihydromycestericins D and E.
Mycestericin A has also been chemically synthesized using simple tartrate as starting compound
(Sato et al. 2008); total chemical synthesis of
mycestericins E was accomplished by a cinchona
alkaloid-catalyzed asymmetric Baylis-Hillman
reaction (Iwabuchi et al. 2001). Mycestericins D–G
can enzymatically be prepared using L-threonine
aldolase from Candida humicola in the key step
reaction (Nishide et al. 2000).
8. Terprenins
Terprenin (CAS 197899-11-9) was discovered by
Kamigauchi et al. (1998) in the fermentation broth
of Aspergillus candidus during a screening for natural immunosuppressants (Kamigauchi et al.
1998). It has a novel highly oxygenated p-terphenul structure with a prenyloxy side chain. Two
terprenin derivatives, 3-methoxy-terprenin and
40 -deoxyterprenin, were also isolated from the fermentation liquid and showed significant immunosuppressive effects when tested with respect to
the proliferation of mouse spleen lymphocytes.
The most relevant activity of terprenin is its suppressive effect on the production of immunoglobulin E (IgE), which is a factor of 104 stronger than
that of FK506, and interestingly, without any toxicological side-effect (Kawada et al. 1998). In mice
experiments, terprenin suppressed IgE production
in a typical dose dependent manner. Even after
immunization with ovalbumin, when the IgE
value had reached a high level, terprenin still
exhibited a significant suppressive effect at 20–40
mg kg–1 (Liu 2006). The total synthesis of terprenin is possible and was reported by different
authors (Kawada et al. 1998; Yonezawa et al. 1998).
9. FR901483
A potent immunosuppressant, FR901483, was
isolated in 1996 from the fermentation broth of
Cladobotryum sp. by Fujisawa Pharmaceutical Co.
in Japan (Sakamoto et al. 1996). It was found
to exert a potent immunosuppressive activity
in vitro and significantly prolonged graft survival
in the rat-skin allograft model, apparently by the
inhibition of purine nucleotide biosynthesis. This
compound has an intriguing tricyclic structure
possessing a phosphate ester in its molecule.
Since its discovery, FR901483 has garnered significant attention from the organic chemists due to
its biological activity and unique aza-tricyclic
nature. Thus, different synthesis schemes were
published for the total synthesis of this important
immunosuppressant (Maeng and Funk 2001;
Kropf et al. 2006; Carson and Kerr 2009).
10. Colutellin A
Colutellin A is a new immunosuppressive peptide
recently isolated from Colletrichum dematium. It
showed CDþ T-cell activation of interleukin
2 (IL-2) production with an IC50 of 167 nM. Moreover, it exhibited no cytotoxicity to human
peripheral blood mononuclear cells in respective
in vitro tests. Thus, it could be medicinally used
as a novel immunosuppressive compound in the
near future (Ren et al. 2008).
III. Mushroom Immunomodulators
Nowadays, immunostimulators (biological response modifiers) are becoming increasingly
more popular in the health and wellness industries
Immunomodulators
as people have started to realize the importance of
a healthy immune system as a first barrier for the
prevention of diseases. These pro-drugs or prophylactic medicines have a long history in traditional medicine, in particular in Asian and
Mediterranean countries. Thus the medical use
of mushrooms has a long tradition in Japan,
China, Korea and Southeast Asia, whereas, in
Europe and the United States, this field has just
been developing since the early 1980s. The positive medicinal properties of mushrooms are based
on various cellular compounds and secondary
metabolites, which can be isolated from different
parts of the fruiting body or from the mycelium
during growth in solid-state or liquid cultures
(Tang et al. 2007). The immunomodulating effects
of mushroom metabolites are especially valuable
in the prophylaxis as a mild and non-invasive
form of a treatment, which can even prevent the
proliferation of metastatic tumors, and is used as
a co-treatment in combination with classic
chemo- and radiotherapies (Wasser 2002). The
most potent immunomodulators produced by
mushrooms belong to the lectins, terpenoids and
polysaccharides.
A. Lectins
The immunomodulatory activities of lectins
(highly glycolylated proteins with specific binding
capacities) from different organisms have been
known for decades. Mushroom lectins are characterized by their particular antiproliferative and
antitumor activities.
Boletus satanas lectin, bolesatine, was shown to have a
potent mitogenic activity on human peripheral blood
lymphocytes, and also to stimulate the release of IL-1a,
IL2 and TNF-a from mononuclear cell cultures (Licastro
et al. 1993). A fruiting- body lectin of Grifola frondosa
showed cytotoxic activity against HeLa cells, when
applied at low concentration (Kawagishi et al. 1990). A
heterodimeric melibiose-binding lectin from fruiting
bodies of the oyster mushroom Pleurotus ostreatus was
reported to be an in vivo inhibitor of sarcoma S-180 and
hepatoma H-22 tumor cells (Wang et al. 2000). A specific
lectin was identified in fruiting bodies and mycelia of the
straw mushroom (Volvariella volvacea) and had a stronger immunomodulatory effect than concanavalin A (She
et al. 1998). Two lectins, TML-1 and TML-2, with immunomodulatory and antitumor activities were isolated
from Tricholoma mongolicum; however, when these
181
lectins were directly tested in vitro, no antitumor activity
was observed. This suggests that the lectins are rather
immunomodulatory substances than substances exerting
acute cytotoxicity. Peritoneal macrophages in mice treated with TML-1 or TML-2 revealed – after LPS stimulation – an enhanced production of nitrite and TNF-a. Both
compounds inhibited also the growth of P815 mastocytoma cells by stimulating peritoneal macrophages to produce more macrophage-activating factors including
interferon-g and some other cytokines (Wang et al.
1996, 1997).
B. Terpenoids
Terpenes are built up of isoprene sub-units consisting of five carbon atoms. Among the huge
number of terpenes, are special triterpenoids
which are exclusively found in certain macrofungi
(mostly basidiomycetes) and are famous for their
biological activities and medicinal properties.
One example of such a triterpenoid compound is
the highly oxidized lanostane which can be
isolated from wood-decay fungi of the families
Polyporaceae and Ganodermaceae (e.g. Ganoderma
lucidum). This and related compounds show different biological activities including anti-infective,
cytotoxic and immunomodulating efficacy
(Moradali et al. 2007). Ganoderic, ganoderenic,
ganodermic and applanoxidic acids, ganoderals,
ganoderols, lucidone, ganodermanontriol as well
as ganodermanondiol are the most common triterpenoids found in these mushrooms. Mixtures of
these compounds can be prepared by the extraction
of respective fruiting bodies with organic solvents.
They were shown to have an antitumor activity that
is comparable to that of certain b-D-glucans (see
below). Fungal terpenoids can stimulate the NF-kB
pathway and modulate Ras/Erk, c-myc and CREB
proteins as well as mitogen-activated protein
kinases (Gao et al. 2003). In consequence, these
activation mechanisms can lead to other immune
stimulations which are finally effective against
tumor cells.
C. Polysaccharides
Various polysaccharides of microbial and nonmicrobial origin have been widely used as potential biological response modifiers (BRMs) as
reviewed by Leung et al. (2006). Mushroom
derived polysaccharides are regarded as excellent
182
Hesham El Enshasy
immunostimulators due to their suitable therapeutic properties, i.e. they are barely toxic and
have just negligible side-effects compared to
other immunostimulants. Respective polysaccharides occur in relevant amounts in the macroscopic
fruiting bodies and cultured mycelia but also to
some extent in the culture filtrates of fungi. Most
macrofungal polysaccharides belong either to the
homoglycans or heteroglycans, and can bind to
structure proteins to form polysaccharide-protein
complexes. In general, immunomodulator polysaccharides appear to be related to the fungal cell
wall and comprise (1!3)- and (1!6)-b-glucans
as well as (1!3)-a-glucans or polysaccharide
complexes of the galactomannan- and glucuromannan-protein type.
Research on mushroom polysaccharides can
be traced back to the 1960s when Ikegawa’s group
in Japan first investigated the host-mediated antitumor activity of hot-water extracts of several
edible mushrooms against sarcoma 180 cells of
mice (Ikekawa et al. 1969). Until the late 1980s,
three antitumor-immunomodulators of the b-glucan type were isolated and characterized, namely
lentinan, schizophyllan and a protein-bound bglucan (PSK Kresin). They originate from the
white-rot fungi Lentinus edodes, Schizophyllum
commune and Coriolus versicolor, respectively,
and have successfully been introduced into the
probiotic and pharmaceutical market in Japan. A
similar polysaccharopeptide as PSK, abbreviated
as PSP is produced in China and widely used in
the clinical treatment of tumors and in anticancer
therapy (Ooi and Liu 2000). Although their mode
of action against tumore cells is not yet fully
understood, they have been demonstrated to act
as biological response modifiers (BRMs), which
are able to restore or enhance various immune
responses in vitro and in vivo.
The mushroom polysaccharides or polysaccharide-protein
complexes stimulate the non-specific immune system and
thereby exert antitumor activities through the stimulation
of the body’s own defence mechanisms (Wasser and Weis
1999; Reshetnikov et al. 2001). They can activate effector
cells like macrophages and T-lymphocytes or prompt NK
cells to secrete cytokines like TNF-a, IFN-g and IL-1b. In
turn, some of these cytokines are able to directly promote
the cytotoxicity of macrophages. The production of cytokines by immune cells can be considered as a key event in
the initiation and regulation of the body’s immune
response (Lull et al. 2005). In this context, mushroom
polysaccharides can act as antiproliferative effectors and
induce apoptosis in tumor cells.
Certain mushroom polysaccharides (e.g. BRMs) were
shown to reduce the tumor size by more than 50% and
considerably prolonged the survival of tumor-bearing
mice (Wasser 2002). Though the exact mechanism of
BRM action is not known, it has been proposed that they
initiate a cascade of singal transduction that is responsible
for the immune response. Since polysaccharides are not
able to penetrate cells (due to their high molecular mass),
the first step of the cascade may be the recognition of BRM
and its specific binding to immunocell receptors. Some
evidence exists that there are pattern recognition receptors
(PRRs) for the molecular reception of the polysaccharide
BRM (Lowe et al. 2001). The binding of the BRM-ligand to
PRRs may initiate Rel/NF-kB-mediated signaling events,
which leads to the induction of gene expression and the
stimulation of specific cellular functions of the innate
immunity system (Leung et al. 2006). Whilst it is known
that mushroom extracts have immunomodulatory activity,
the standard approach has always been to isolate, characterize and administer pure active compounds. However,
different types of polysaccharides in a mushroom extract
may have synergistic acitivities (Borchers et al. 2004; Lull
et al. 2005). The responses to different polysaccharides are
mediated by different PRRs on the cell surface. An appropriate combination of strong responses involving different
parts of the cell may provide greater therapeutic effects
than a single polysaccharide. A brief list of immunomodulator polysaccharides and polysaccharide–protein complexes from mushroom is given in Table 8.1.
Mushroom polysaccharides greatly differ in their
sugar composition, branching configuration, helical conformation and other physical properties. The structure
relationship between immunomodulator and the anticancer activities of polysaccharides have been reviewed by
several authors (Ooi and Liu 2000; Lull et al. 2005; Zhang
et al. 2007; Ooi 2008). It has been stated that structural
features such as (1!3)-b-linkages in the main chain of the
glucan and additional (1!6)-b-branching points, represent important factors influencing their biological effectiveness. b-Glucans containing mainly (1!6)-linkages are
less effective, maybe due to their inherent flexibility and
the large number of possible conformations (Zhang et al.
2007). In general, b-glucans exhibit immunomodulatory
and/or antitumor activities when their main chain (“backbone”) forms a linear structure and do not have long
branches. For example, pachyman, a branched (1!3)b-D-glucan obtained from the brown-rot fungus Poria
cocos is inactive, whereas pachymaran obtained by the
debranching of pachyman using selective periodate oxidation and mild hydrolysis, shows a pronounced activity
(Chihara et al. 1970a).
Lentinan (2/5) and schizophyllan (1/3) are (1!3)-b-D
glucans with two or one branches for every 5-D-glucopyranosyl and 3-D-glucopyranosyl residue, respectively
(Tabata et al. 1981; Chihara 1992). The polysaccharide
moiety in PSK (1/5) is a (1!3)-b-/(1!4)-b-D-glucan
with one branch for every 5-D-glucopyranosyl residue
(Tsukagoshi et al. 1984). Although the degree of their
branches is different, their bioactivities are similar (Ooi
and Liu 2000). Interstingly, debranched lentinan preparations were found to be more effective against cancer cells
than the native lentinan when applied during in vivo studies
Immunomodulators
183
Table 8.1. Immunomodulator polysaccharides from mushrooms
Mushroom species
Polysaccharide source
Active component
References
Coriolus versicolor
Mycelium,
Culture broth
Fruiting body,
Mycelium,
Culture broth
Fruiting body,
Mycelium
Fruit body,
Culture broth
Polysaccharopeptide
Cui and Chisti 2003
Glucan, heteroglycan,
Cordyglucan
Yalin et al. 2005 Russell
and Paterson 2008
Glucan-protein complex,
glycoprotein
Heteroglycan, mannoglucan,
glycopeptide
Leung et al. 1997
Cordyceps sinensis.
Flammulina velutipes
Ganoderma lucidum
Grifola frondosa
Fruiting body,
Culture broth
Hericum erinaceus
Fruiting body,
Mycelium
Fruiting body,
Mycelium
Fruiting body,
Culture broth
Inonotus obliquus
Lentinus edodes
Peziza verculosa
Pleurotus ostreatus
Sclerotinia sclerotiorum
Fruiting body
Fruit body,
Mycelium,
Culture broth
Mycelium
Fruiting body,
Mycelium,
Culture broth
Sclerotium
Tremella aurantialba
Tricholoma lobayense
Fruiting body
Culture broth
Polyporus umbellatus
Polystrictus versicolar
(Sasaki et al. 1976). Overall, the relationship between the
molecule’s biological activity and the branching pattern/
ratio of b-glucans seems to be rather complicate. The available data indicate that the (1!3)-b-D-glucan backbone is
essential and that the most active polymers have degrees of
branching between 0.2 and 0.33 (Ooi 2008). The molecular
weight of the polysaccharide plays also an important
role for the bioactivity. For a (1!3)-b-glucan extract of
G. frondosa consisting of fractions of different size,
the highest immunomodulatory activity was detected for
molecular masses around 800 kDa (Adachi et al. 1990).
When PSK was separated into four fractions (F1, <50
kDa; F2, 50–100 kDa; F3, 100–200 kDa, F4, >200 kDa) by
successive ultrafiltration, the highest immunomodulatory
activity was obtained with the high-molecular mass fraction
F4 (Kim et al. 1990). Chemically modified (1!3)-b-D-glucans, such as schizophyllan and lentinan having a linear
“worm-like”, triple-helical structure and average molecular
masses of <50 000 g mol–1 or >110 000 g mol–1 efficiently
stimulated monocytes in vivo and caused the secretion of
more TNF-a than the samples with molecular masses
between 67 000 and 110 000 g mol–1 did Therefore, the actual
Proteoglycan, glucan,
heteroglycan,
galactomannan, grifolan
Heteroglycan,
Heteroglycan-peptide
Glucan
Mannoglucan, glucan,
Lentinan, polysaccharide
protein complex
Glucan, Proteoglycan
Heteroglactan,
Proteoglycan
Glucan
Heteroglycan,
glycopeptides,
krestin (PSK)
Glucan, scleroglucan
(SSG)
Heteroglycan
Polysaccharideprotein complex
Miyazaki and
Nishijima 1981
Gao and Zhou 2003
Cun et al. 1994
Yang et al. 2007
Mizuno 1992
Kim et al. 2005b
Chihara et al. 1970b
Hobbs 2000
Mimura et al. 1985
Sarangi et al. 2006
Yang et al. 2004
Cui and Chisti 2003
Palleschi et al. 2005
Survase et al. 2007
Liu et al. 2003
Liu et al. 1996
relation between the polysaccharide molecular mass and its
immunomodulation activity remains to be clarified. Conformations of polysaccharides include single helices and triplehelices as well as random-coiled structures. A triple-helix
conformation is usually more stable than a single-helix.
Lentinan, schizophyllan and the glucan moiety of PSK
have all triple helix structures. Also the cytokine-stimulating
activity of (1!3)-b-D-glucans was found to be associated
with the triple-helix conformation (Falch et al. 2000). Therefore, the immunological activities of polysaccharides must
be dependent on appropriate helical conformation.
To improve the biological activity of polysaccharides by chemical modification, carboxymethylated, hydroxylated, formylmethylated,
aminethylated and sulfated products have been
designed. For example, a hydroxylated schizophyllan was found to induce in vivo the production of higher concentrations of nitric oxide
(NO) and TNF-a in macrophages than native
184
Hesham El Enshasy
schizophyllan (Ohno et al. 1995). A sulfated
(1!3)-a-D-glucan prepared by respective modification of native cell-wall glucan from L. edodes
exhibited a strong antiproliferation activity
against breast carcinoma cells, whereas its native
water-insoluble precursor glucan had only moderate antitumor activity (Zhang and Cheung,
2002). Another study conducted by Zhang et al.
(2004) showed that the high bioactivity of carboxymethylated b-glucan was mainly attributed to the
increase of water-solubility and the latter was also
the main factor that enhanced the efficacy of the
hyperbranched b-glucan TM3b after sulfatation
(Tao et al. 2006).
D. Fungal Immunomodulator Proteins
Recently, different mushrooms have been reported
to produce a new family of fungal immunomodulatory proteins (FIPs) with possible applications in
therapy (Chen and Wang 2007). These include Ling
Zhi-8 (LZ-8) from Ganoderma lucidum (Kino et al.
1989), FIP-fve from Flammulina velutipes (Gr.)
Sing (Ko et al. 1995), FIP-vvo and FIP-vvl from
Volvariella volvacea (Bull.; Fr.) sing (Hsu et al.
1997), FIP-gts from Ganoderma tsugae Murr (Lin
et al. 1997) and PCP from Poria cocos (Schw.) Wolf
(Chang and Sheu 2007). All these compounds were
grouped together in a distinct protein family based
on similarities in their amino acids sequence and
their effects on compounds of the immunological
response system (Ko et al. 1995).
FIPs were found to be mitogenic in vitro for human
peripheral blood lymphocytes (hPBLs) and mouse splenocytes. They induce a bell-shaped dose–response curve
similar to that of lectin mitogens. In the course of in vivo
studies, the FIP-like substance LZ-8 could act as an
immunosuppressive agent through the prevention of systemic anaphylactic reactions and significantly decreased
footpad edema during the Arthus reaction (Tanaka et al.
1989). Moreover, it suppressed autoimmune diabetic reactions in diabetic mice and increased graft survival in
transplanted allogenic mouse skin and pancreatic rats
without producing the severe toxic effects known for
CyA (Van der Hem et al. 1994; 1996). FIP-fve isolated
from fruiting bodies of F. velutipes stimulated mitogenesis
of human peripheral lymphocytes, suppressed systemic
anaphylaxis reactions and enhanced the transcription of
interleukin-2 (IL-2) and interferon-g (Ko et al. 1995). The
induction mechanism of interferon-g production was proposed to be mediated by a signaling pathway involving the
p38 mitogen-activated protein kinase (Wang et al. 2004).
FIP-gts was reported to significantly induce cytokine
secretion, cellular proliferation in human peripheral
mononuclear cells (HPBMCs) and interferon-g expression. The effect of FIP-gts may be caused by the activation
of phosphatidylinositol 3-kinase (Hsiao et al. 2008).
Finally, the immunostimulus initiated by the recently
isolated FIP-PCP is mediated via an enhanced production
of NO, IL-1b, IL-6, IL-18 and TNF-a (Chang and Sheu
2007).
E. Industrial Production of Mushroom
Immunomodulators
Immunomdulator metabolites can be isolated from
fruiting bodies, cultured mycelia or culture filtrates. All medicinal mushrooms are lignocellulose
degraders (white-rots, brown-rots, litter decomposers) and can utilize woody materials as growth
substrates and for fruiting body production. One
historical method of cultivation, that is still
practiced mainly in Asia, is fungal cultivation on
hardwood tree-logs. This process occurs over several years and yields two crops of mushrooms each
year. It continues until the log physically “disappears” due to wood decay and lignocellulose
decomposition. The use of polypropylene bags
containing crushed lignocellulosics (including
waste materials) and selected nutrients can be
regarded as a modified version of the log method
and actually represents a kind of solid-state fermentation (SSF). After autoclaving, the bags are
inocultated with the mushroom mycelium of
choice and can be incubated in the greenhouse
under controlled conditions. This way, the production cycle for fruiting bodies can be shortened
to 1–3 months (Smith et al. 2002). Mushroom production using SSF techniques was recently
reviewed by Fan et al. (2008; see also Chapter 4 of
this book). However, for the production of biomolecules, the production process should be carried
out under more defined and controlled conditions
to fulfil the strict requirements of the current good
manufacturing practice (cGMP) for the production
of active pharmaceutical ingredients (API). Quality
control of mushroom cultivation poses several
challenges, such as maintaining a constant substrate quality, temperature, moisture, a stable
yield of the desired compounds and sterility.
To overcome these problems, more specific research was
carried to cultivate mushrooms under submerged conditions. This method of cultivation has some advantages over
SSF, for example, high yields in fungal mycelium under
more defined conditions in a closed and well controlled
Immunomodulators
volume (higher space–time yields). Furthermore, sterility
is easier to guarantee in a stirred-tank bioreactor than in
logs or plastic bags (Lull et al. 2005). Nowadays, different
bioactive metabolites from mushrooms can successfully be
produced in submerged culture both in form of intracellular and extracellular products. However, in order to scaleup these methods to an industrial scale, various technical
problems will have to be solved (Tang et al. 2007). Like in
case of other fungal metabolites, medium composition
governs the bioactive agents’ production; for example,
the production of mushroom polysaccharides was found
to be regulated by the type and concentration of carbon
and nitrogen souces (Wasser et al. 2003; Cui et al. 2006), the
C/N ratio (Wang et al. 2005), by the ammonium ion concentration (Mao and Zhong 2006) and by different other
components supplemented to the medium (Lim and Yun
2006). Other main key parameters influencing product
yield are shear stress (Gong and Zhong 2005) and the
mode of oxygen sypply to the culture (Tang and Zhong
2003). The steady-state concentration of the latter in the
culture medium was found to be very important for the
over-production of mushroom metabolites in bioreactors
(Mao and Zhong 2004). Among different cultivation strategies applied, fed-batch cultivation was proved to be the
method of choice for most mushrooms tested so far (Kim
et al. 2006; Zou 2006). The recent reviews of Zhong and
Tang (2004) and Tang et al. (2007) summarize and discuss
the latest developments in this field.
185
are known so far. Assuming that the proportion
of “useful” mushrooms among the undiscovered
and unexamined species will be only 5%, this
implies a number of 7000 promising species as a
future source of immunomodulators (Lindequist
et al. 2005). Moreover, it has to been taken into
consideration that different strains of one species
can produce different bioactive compounds. For
example, strains of G. lucidum can produce more
than 120 different triterpenes and in addition also
bioactive polysaccharides and proteins.
Based on the increased knowledge of the
biochemistry and molecular biology of bioactive
metabolites as well as the advanced technology of
high-throughput screenings using omic approaches
(genomics, proteomics, metabolomics), a rapid
development of this research field is expected and
will lead to the discovery of many novel immunomodulators in the near future. Not least, the investigation of novel immunomodulators and their
effects will widen our knowledge of the complex
mechanisms regulating the immune system and
body defense.
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molecules for many medical applications. The
number of known fungal immunomodulators is
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