ASSAYS TO DETECT AND CHARACTERIZE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1(HIV-1) RECEPTOR ANTAGONISTS, COMPOUNDS THAT INHIBIT BINDING OF THE HIV-1 SURFACE GLYCOPROTEIN, GP120, TO THE CD4 RECEPTOR ON HUMAN T-LYMPHOCYTES

Human immunodeficiency virus type 1 infects human helper T lymphocytes by an interaction between gp120, the viral coat protein, and the T-ce ll receptor CD4. Two microtiter-based immunoassays, an enzyme-linked i mmunosorbent assay (ELISA) and a particle concentration fluorescence a ssay, were developed to measure gp120-CD4 binding and were then used t o screen a variety of compounds for the inhibition of this interaction . Additional protocols, called ''consumption assays,'' were defined to distinguish inhibitors which functioned by sequestering either gp120 or CD4 to prevent the final effective bimolecular interaction. Monoclo nal antibodies of defined specificity and compounds known from other p ublished studies to inhibit gp120-CD4 binding were tested in an attemp t to validate the assays used in the study. Once the capacity of these assays to detect known gp120-CD4 inhibitors was confirmed, they were used to screen synthetic agents and fermentation broths for novel comp ounds that might be used as human immunodeficiency virus receptor anta gonists. A 2,4-diaminoquinazoline, CP-101,816-1, was found to inhibit this interaction (50% inhibitory concentration in ELISA, 32.5 mu g/ml) and to interact more strongly with CD4 than with gp120 in the consump tion assays. The identification of a novel inhibitor, a 2,4-diaminoqui nazoline, confirmed that such assays are useful for the detection of h uman immunodeficiency virus type 1 receptor antagonists.