Background:  All drugs currently approved to treat HIV-1 infection target 1 of 3 steps in the HIV-1 replication cycle. Given that viruses resistant to one drug of a particular class often exhibit cross-resistance to other drugs in the same class, therapeutic options for treatment-experienced patients are often limited. One way to address this problem is to identify HIV-1 inhibitors directed against new targets in the HIV-1 replication cycle. As part of an effort to search for inhibitors targeting new mechanisms, a high throughput HIV-1 full-replication screen (HIV Rep) was executed resulting in the identification of a novel HIV-1 envelope (Env) maturation inhibitor.

Methods:  An antiviral screen was conducted using the HIV-1 NL4-3 strain, MT-2 T-cells, and HeLa CD4 LTR/beta-Gal indicator cells. The antiviral activity of UK-201844 was determined after infection of MT-2 cells or HeLa CD4 LTR/beta-Gal indicator cells with HIV-1 NL4-3 or NL4-3 derivatives. The effect of UK-201844 on infectious virus production was analyzed after transfection of HEK293 cells with HIV-1 NL4-3 infectious cDNAs. 

Results:  More than 10⁶ compounds were evaluated in the HIV Rep screen resulting in the identification of a novel small molecule inhibitor (UK-201844) that targets HIV-1 Env maturation. UK-201844 exhibited antiviral activity against HIV-1 NL4-3 in full replication assays but was not active in single-cycle infection assays using HIV-1 NL4-3 derived reporter viruses, suggesting that the compound targets a late event in the HIV-1 replication cycle. Consistent with these observations, UK-201844 specifically inhibited the production of infectious virions in an HIV-1 Env dependent manner. These results confirm that UK201844 acts during the late stages of HIV replication and suggest that HIV-1 Env is the target of the compound. In vitro resistant virus studies showed that HIV-1 Env sequences are critical determinants of compound susceptibility, thus confirming that UK-201844 targets HIV-1 Env function. Additional mechanism-of-action studies demonstrated that UK-201844 interferes with HIV-1 gp160 processing in infected cells, resulting in the production of non-infectious virions.

Conclusions:  UK-201844 represents the prototype for a unique HIV-1 inhibitor class that directly or indirectly inhibits HIV-1 gp160 processing, resulting in the production of virions with non-functional Env proteins.