80
D.C. Hill et al.
Myriocin had no effect on the growth of human leukaemia cell lines demonstrating that, like CsA, its anti-proliferative activity was not due to non-specific
growth-inhibitory activity. Myriocin was ten times more potent than CsA in
inhibiting T cell dependent antibody production in an in vivo delayed type
hypersensitivity (DTH) response to SRBC antigen. The compound was also 100
times more potent than CsA in suppression of allograft rejection. As a result of
this promising activity, 14 myriocin derivatives were synthesised and evaluated
[17]. Of these, 14-deoxomyriocin was found to have the most potent immunosuppressive activity on the mouse allogenic MLR and was ten times more potent
in allograft rejection in vivo. Mycestericins A, B, D and E had similar potency to
myriocin in the mouse allogenic MLR [18].
Other programmes using MLR assays for microbial product discovery have
identified FR901459 (Fig. 1), a novel cyclosporin analogue from Stachybotrys
chartarum [19] and MLR-52, a novel staurosporine analogue from a Streptomyces sp. [20], which was found to inhibit protein kinase C (PKC). FR901459
inhibited lymphocyte proliferation in a dose-dependent fashion with approximately one third of the potency of CsA. As CsA effects are primarily mediated by
inhibition of lymphokine mRNA transcription, the effect of FR901459 on IL-2
production was examined. FR901459 was found to suppress IL-2 mRNA
transcription, and cell proliferation. In addition, FR901459 inhibited a
DTH reaction to the T cell dependent antigen on SRBC in Balb/c mice, and
increased graft survival time in orally treated mice. MLR-52 had similar
potency to staurosporine in inhibition of the MLR, and was demonstrated
to inhibit PKC-catalysed phosphorylation of a small tyrosine-containing
peptide.
2.1.3 Inhibition of Cell Adhesion
Recent studies have shown that cell adhesion plays an important role in
inflammatory responses and tumour metastasis. IC101, a novel, cyclic depsipeptide, was isolated from Streptomyces albulus and characterised as an
inhibitor of cell adhesion using concanavalin A (con-A) activated EL4 cells and
B16 cells [21]. Cells were added to microtitre plates coated with the extracellular matrix (ECM) proteins fibronectin, laminin and type IV collagen. The assays
were performed in the presence of cycloheximide to minimise the production of
endogenous adhesion proteins.
IC101 strongly inhibited binding of EL4 and B16 cells to each ECM
component. IC101 also inhibited the MLR as determined by [3H]-thymidine
incorporation into rat spleen cells, did not suppress antibody formation on
inoculation of mice with SRBC, and strongly suppressed the DTH response in
vivo. ICI01 showed some toxicity in vitro and in vivo.
Further extracellular matrix receptor antagonists, the delaminomycins, were
also isolated from spent media of the IC101-producing organism [22]. The
delaminomycins have complex, non-peptidic structures based on substituted
D.C. Hill et al.
Myriocin had no effect on the growth of human leukaemia cell lines demonstrating that, like CsA, its anti-proliferative activity was not due to non-specific
growth-inhibitory activity. Myriocin was ten times more potent than CsA in
inhibiting T cell dependent antibody production in an in vivo delayed type
hypersensitivity (DTH) response to SRBC antigen. The compound was also 100
times more potent than CsA in suppression of allograft rejection. As a result of
this promising activity, 14 myriocin derivatives were synthesised and evaluated
[17]. Of these, 14-deoxomyriocin was found to have the most potent immunosuppressive activity on the mouse allogenic MLR and was ten times more potent
in allograft rejection in vivo. Mycestericins A, B, D and E had similar potency to
myriocin in the mouse allogenic MLR [18].
Other programmes using MLR assays for microbial product discovery have
identified FR901459 (Fig. 1), a novel cyclosporin analogue from Stachybotrys
chartarum [19] and MLR-52, a novel staurosporine analogue from a Streptomyces sp. [20], which was found to inhibit protein kinase C (PKC). FR901459
inhibited lymphocyte proliferation in a dose-dependent fashion with approximately one third of the potency of CsA. As CsA effects are primarily mediated by
inhibition of lymphokine mRNA transcription, the effect of FR901459 on IL-2
production was examined. FR901459 was found to suppress IL-2 mRNA
transcription, and cell proliferation. In addition, FR901459 inhibited a
DTH reaction to the T cell dependent antigen on SRBC in Balb/c mice, and
increased graft survival time in orally treated mice. MLR-52 had similar
potency to staurosporine in inhibition of the MLR, and was demonstrated
to inhibit PKC-catalysed phosphorylation of a small tyrosine-containing
peptide.
2.1.3 Inhibition of Cell Adhesion
Recent studies have shown that cell adhesion plays an important role in
inflammatory responses and tumour metastasis. IC101, a novel, cyclic depsipeptide, was isolated from Streptomyces albulus and characterised as an
inhibitor of cell adhesion using concanavalin A (con-A) activated EL4 cells and
B16 cells [21]. Cells were added to microtitre plates coated with the extracellular matrix (ECM) proteins fibronectin, laminin and type IV collagen. The assays
were performed in the presence of cycloheximide to minimise the production of
endogenous adhesion proteins.
IC101 strongly inhibited binding of EL4 and B16 cells to each ECM
component. IC101 also inhibited the MLR as determined by [3H]-thymidine
incorporation into rat spleen cells, did not suppress antibody formation on
inoculation of mice with SRBC, and strongly suppressed the DTH response in
vivo. ICI01 showed some toxicity in vitro and in vivo.
Further extracellular matrix receptor antagonists, the delaminomycins, were
also isolated from spent media of the IC101-producing organism [22]. The
delaminomycins have complex, non-peptidic structures based on substituted