Preclinical and Clinical Profile of HIV-1 Integrase Strand-transfer InhibitorGS-9224 Compared to its Parent Compound GS-9160

In an effort to optimize the pharmacokinetic profile of GS-9160, a potent (EC50=1.2 – 4 nM) antiviral tri-cyclic HIV-1 integrase (IN) strand transfer inhibitor (INSTI), various substitutions on the p-fluorobenzyl moiety of GS-9160 were explored. This effort led to the discovery of GS-9224, an analog containing a 5-chloro-2,4-di-fluorobenzyl moiety. GS-9224, like its predecessor GS-9160, has potent (EC50=1.3 – 9 nM) and selective antiviral activity against HIV-1 and acts as a bona fide integration inhibitor through elevation of 2-long terminal repeat (2-LTR) circles and decrease of integration junctions in HIV-1 infected cells, markers of failed viral integration. Viral resistance selections with GS-9224 yielded three mutations within the catalytic core domain of HIV-1 IN: G140S, L74M and Q148K. When tested against a panel of HIV-1 clones engineered to express INSTI resistance mutations, the profile of GS-9224 was comparable to GS-9160. GS-9224 exhibits improved hepatic microsome stability, better absorption potential and a lower in vitro intestinal efflux ratio compared to GS-9160. In addition, GS-9224 displayed higher dog plasma protein binding (~99%) than GS-9160 (~93%) suggesting a potential for protein restricted clearance. However, the improved metabolic stability, absorption potential and serum protein binding of GS-9224 compared to GS-9160 did not translate into an improved clinical pharmacokinetic profile. Results from a single-dose study in human healthy subjects revealed a fast systemic clearance of GS-9224 with a terminal half-life of ~ 1 h, resulting in a pharmacokinetic profile that would not support once-daily dosing in HIV-infected patients.