MODE OF ACTION OF SDZ NIM-811, A NONIMMUNOSUPPRESSIVE CYCLOSPORINE-A ANALOG WITH ACTIVITY AGAINST HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 (HIV-1) - INTERFERENCE WITH EARLY AND LATE EVENTS IN HIV-1 REPLICATION

SDZ NIM 811 is a cyclosporin A analog that is completely devoid of imm unosuppressive capacity but exhibits potent and selective anti-human i mmunodeficiency virus type 1 (HIV-1) activity. The mechanism of action of SDZ NIM 811 is clearly different from those of all other anti-HIV agents described so far. In cell-free assays, it is not an inhibitor o f reverse transcriptase, protease, integrase, and it does not interfer e with Rev or Tat function, SDZ NIM 811 does not down-regulate CD4 or inhibit fusion between infected and uninfected, CD4-expressing cells, p24 production from chronically HIV-infected cells is not impaired eit her. To elucidate the mode of action of SDZ NIM 811, we performed DNA PCR analysis in HIV-1 IIIB-infected MT4 cells in one cycle of virus re plication. The effects of SDZ NLM 811 on the kinetics of viral DNA syn thesis, appearance of two-long terminal repeat circles (2-LTR circles) , and integration of DNA were studied. SDZ NIM 811 inhibited 2-LTR cir cle formation in a concentration dependent manner, which is indicative of nuclear localization of preintegration complexes. Half-maximal inh ibition was achieved at 0.17 mu g/ml; this concentration is close to t he 50% inhibitory concentrations (0.01 to 0.2 mu g/ml) for viral growt h inhibition. As expected, integration of proviral DNA into cellular D NA was also inhibited by SDZ NIM 811. Analysis of the viral particles produced by SDZ NIM 811-treated, chronically infected cells revealed a mounts of capsid proteins, reverse transcriptase activity, and viral R NA comparable to those of the untreated control. However, these partic les showed a dose-dependent reduction in infectivity (50% inhibitory c oncentration of 0.028 mu g/ml) which indicates that the assembly proce ss is also impaired by SDZ NIM 811. Gag proteins are postulated to pla y a role not only in assembly but also in early steps of viral replica tion, e.g., nuclear localization of the preintegration complex. Recent ly, it was reported that HIV-1 Gag protein binds to cyclophilin A, the intracellular receptor for cyclosporin A. Interference with Gag-cyclo philin interaction may be the molecular basis for the antiviral activi ty of cyclosporin A and its analogs.