Inhibition of human endogenous retrovirus-K10 protease in cell-free and cell-based assays

A full-length and C-terminally truncated version of human endogenous retrov irus (HERV)-K10 protease were expressed in Escherichia coil and purified to homogeneity. Both versions of the protease efficiently processed HERV-K10 Gag polyprotein substrate. HERV-K10 Gag was also cleaved by human immunodef iciency virus, type 1 (HIV-1) protease, although at different sites. To ide ntify compounds that could inhibit protein processing dependent on the HERV -K10 protease, a series of cyclic ureas that had previously been shown to i nhibit HIV-1 protease was tested. Several symmetric bisamides acted as very potent inhibitors of both the truncated and full-length form of HERV-K10 p rotease, in subnanomolar or nanomolar range, respectively. One. of the cycl ic ureas, SD146, can inhibit the processing of in vitro translated HERV-K10 Gag polyprotein substrate by HERV-K10 protease. In addition, in virus-like particles isolated from the teratocarcinoma cell line NCCIT, there is sign ificant accumulation of Gag and Gag-Pol precursors upon treatment with SD14 6, suggesting the compound efficiently blocks HERV-K Gag processing in cell s. This is the first report of an inhibitor able to block cell-associated p rocessing of Gag polypeptides of an endogenous retrovirus.