Novel Screen Methodologies for Identification of New Microbial Metabolites
89
is a critical domain for CD4 function and also overlaps the HIV - gpl20 binding
site.
This assay was used to screen microbial samples for CD4-binding activity,
resulting in the discovery of a family of novel fungal metabolites produced by
Penicillium glabrum (Wehmer) Westling [60]. The most potent member of this
family, 411F (Fig. 3), inhibited anti-Leu 3a binding to srCD4 with an IC5o of
2 pmol 1-1. It only weakly inhibited the binding of HIV-gpl20. 41IF inhibited
the binding of a representative MHC class II molecule, HLA-DRB*0401, with
an IC5o of 1 ~tmol 1-1. In functional assays, 41IF inhibited the antigen-induced,
CD4-dependent, T cell proliferative responses of peripheral blood mononuclear
cells. The compound also exhibited selectivity at the clonal level by inhibiting
peptide-induced CD4 § T cell proliferative responses, but not alloantigen-induced CD8 § T cell proliferation.
411F is an acidic chromone-substituted xanthone which carries negative
charge in aqueous solution at neutral pH. The compound was hypothesised to
be acting by binding over a broad area of the positively charged amino terminal
domains of CD4 which are implicated in the interaction with MHC Class II
molecules. It has also been reported as a phospholipase C inhibitor (Sect. 4.2.1).
3.2 Cancer
Receptor binding assays have also been used to search for compounds active
against targets for cancer therapy.
3.2.1 Hormone Binding Inhibitors
Assays based on hormone-receptor interactions have been used to search for
new compounds which may be used for treatment of hormone responsive cancer
and other diseases.
An assay for binding of [125I]-1713-estradiol to estrogen receptors in the hog
uterus cell cytosol was used to discover the BE-14348 family of substituted
flavanones from Streptomyces 9raminofaciens, four of which were novel 1-61]. In
this case the bound ligand was separated from free by addition of dextrancoated charcoal followed by centrifugation, and measurement of radioactivity in
the supernatant.
As BE-14348B was the most active estrogen binding inhibitor from this
series, its effects were compared with tamoxifen, an estrogen antagonist which
has been used for breast cancer hormone therapy, and diethylstilbestrol, an
estrogen agonist used in the treatment of prostate cancer. BE-14348B inhibited
receptor binding with much more potency than tamoxifen, and a little more
strongly than diethylstilbesterol. Measurement of the effect of the BE-14348
family on proliferation of estrogen-responsive human breast carcinoma MCF-7
cells showed that, like estrogen, compounds stimulated proliferation in a
89
is a critical domain for CD4 function and also overlaps the HIV - gpl20 binding
site.
This assay was used to screen microbial samples for CD4-binding activity,
resulting in the discovery of a family of novel fungal metabolites produced by
Penicillium glabrum (Wehmer) Westling [60]. The most potent member of this
family, 411F (Fig. 3), inhibited anti-Leu 3a binding to srCD4 with an IC5o of
2 pmol 1-1. It only weakly inhibited the binding of HIV-gpl20. 41IF inhibited
the binding of a representative MHC class II molecule, HLA-DRB*0401, with
an IC5o of 1 ~tmol 1-1. In functional assays, 41IF inhibited the antigen-induced,
CD4-dependent, T cell proliferative responses of peripheral blood mononuclear
cells. The compound also exhibited selectivity at the clonal level by inhibiting
peptide-induced CD4 § T cell proliferative responses, but not alloantigen-induced CD8 § T cell proliferation.
411F is an acidic chromone-substituted xanthone which carries negative
charge in aqueous solution at neutral pH. The compound was hypothesised to
be acting by binding over a broad area of the positively charged amino terminal
domains of CD4 which are implicated in the interaction with MHC Class II
molecules. It has also been reported as a phospholipase C inhibitor (Sect. 4.2.1).
3.2 Cancer
Receptor binding assays have also been used to search for compounds active
against targets for cancer therapy.
3.2.1 Hormone Binding Inhibitors
Assays based on hormone-receptor interactions have been used to search for
new compounds which may be used for treatment of hormone responsive cancer
and other diseases.
An assay for binding of [125I]-1713-estradiol to estrogen receptors in the hog
uterus cell cytosol was used to discover the BE-14348 family of substituted
flavanones from Streptomyces 9raminofaciens, four of which were novel 1-61]. In
this case the bound ligand was separated from free by addition of dextrancoated charcoal followed by centrifugation, and measurement of radioactivity in
the supernatant.
As BE-14348B was the most active estrogen binding inhibitor from this
series, its effects were compared with tamoxifen, an estrogen antagonist which
has been used for breast cancer hormone therapy, and diethylstilbestrol, an
estrogen agonist used in the treatment of prostate cancer. BE-14348B inhibited
receptor binding with much more potency than tamoxifen, and a little more
strongly than diethylstilbesterol. Measurement of the effect of the BE-14348
family on proliferation of estrogen-responsive human breast carcinoma MCF-7
cells showed that, like estrogen, compounds stimulated proliferation in a