Background:  NNRTI constitute an important class of drugs used in HIV-1 therapy. Mutant viruses resistant to the most widely used NNRTI, efavirenz (EFV) and nevirapine, lead to treatment failure. The characterization of activities against a panel of NNRTI-resistant HIV-1 and in vitro toxicological studies suggest the novel NNRTI RDEA427 and RDEA640 have the potential to overcome the most prevalent of these resistant strains.

Methods:  Antiviral activities of the NNRTI were determined using VSV-g pseudotyped HIV-1-containing wild type and NNRTI-resistant sequences. These assays were also performed with human serum and human serum albumin to assess the effect of protein binding on antiviral activity. Cytotoxicity was evaluated in primary human cells and cell lines. Non-linear regression analysis was used to calculate IC₅₀ values. CYP3A4 induction was determined in vitro using a CYP3A4 promoter-driven luciferase reporter cell line carrying the pregnane X receptor.

Results:  RDEA427 and RDEA640 are potent inhibitors of wild type HIV-1 with EC₅₀ values of 0.9 nM and 0.8 nM, respectively, and CC₅₀ values of  >50 µM. The fold-changes in EC₅₀ against the major NNRTI-resistant viruses found in patients failing EFV therapy are significantly lower than those of EFV. Fold-changes for both RDEA427 and RDEA640 against the K103N and G190S mutants are 0.9 and 0.3, respectively, vs 16 and 63 for EFV. While the K103N/L100I mutant caused a fold-change of 1700 for EFV, and 2.4 and 5.4 for TMC125 and TMC278, respectively, the fold-change of RDEA640 was 0.4 against this mutant. RDEA640 had a 6-fold EC₅₀ shift in the presence of 40% human serum and RDEA427 and RDEA640 had 9-fold shifts in the presence of 45 mg/mL human serum albumin, values similar to the fold-changes for TMC125 and better than those for EFV and TMC278. At 6 µM, RDEA427 and RDEA640 caused 2.6-fold increases in CYP3A4 promoter-driven luciferase activity compared with 8.7-fold and 7.5-fold increases for TMC125 and TMC278, respectively.

Conclusions:  RDEA427 and RDEA640 are superior to EFV against a panel of NNRTI-resistant viruses and are less affected by binding to serum proteins than EFV and TMC278. RDEA427 and RDEA640 also show a low potential for CYP induction and a large selectivity index. The in vitro characterization of these novel NNRTI shows strong potential for improved performance over current NNRTI and warrants evaluation in humans.