No abstract

S/GSK1349572 is a next-generation HIV integrase (IN) inhibitor designed to deliver potent antiviral activity with a low-milligram once-daily dose requiring no pharmacokinetic (PK) booster. In addition, S/GSK1349572 demonstrates activity against clinically relevant IN mutant viruses and has potential for a high genetic barrier to resistance. S/GSK1349572 is a two-metal-binding HIV integrase strand transfer inhibitor whose mechanism of action was established through in vitro integrase enzyme assays, resistance passage experiments, activity against viral strains resistant to other classes of anti-HIV agents, and mechanistic cellular assays. In a variety of cellular antiviral assays, S/GSK1349572 inhibited HIV replication with low-nanomolar or subnanomolar potency and with a selectivity index of 9,400. The protein-adjusted half-maximal effective concentration (PA-EC 50 ) extrapolated to 100% human serum was 38 nM. When virus was passaged in the presence of S/GSK1349572, highly resistant mutants were not selected, but mutations that effected a low fold change (FC) in the EC 50 (up to 4.1 fold) were identified in the vicinity of the integrase active site. S/GSK1349572 demonstrated activity against site-directed molecular clones containing the raltegravir-resistant signature mutations Y143R, Q148K, N155H, and G140S/Q148H (FCs, 1.4, 1.1, 1.2, and 2.6, respectively), while these mutants led to a high FC in the EC 50 of raltegravir (11-to >130-fold). Either additive or synergistic effects were observed when S/GSK1349572 was tested in combination with representative approved antiretroviral agents; no antagonistic effects were seen. These findings demonstrate that S/GSK1349572 would be classified as a nextgeneration drug in the integrase inhibitor class, with a resistance profile markedly different from that of first-generation integrase inhibitors.Twenty-three compounds are currently approved for the treatment of HIV infection. These drugs can be assigned to six classes: nucleoside (nucleotide) reverse transcriptase inhibitors [N(t)RTIs], nonnucleoside reverse transcriptase inhibitors [NNRTIs], protease inhibitors [PIs], integrase inhibitors [INIs], CCR5 antagonists, and fusion inhibitors. The development of resistance to all currently marketed drugs has been observed and is a major reason for failure of therapy. Thus, the development of new, potent antiretroviral compounds with different resistance profiles and mechanisms of action is urgently needed for patients who have multidrugresistant HIV. In addition to these characteristics, an improved side effect profile and improved dosing convenience (oncedaily dosing, fixed-dose combination pills) are desirable, because they would promote high compliance, decrease the emergence of drug-resistant variants, and thus enhance the length and quality of life.After an initial period of false starts, advances in the field of HIV integrase drug discovery since the late 1990s have been outstanding. Beginning with the discovery that molecules capable of binding two metals within the int...

Integrase (IN) strand transfer inhibitors (INSTIs) have been developed to inhibit the ability of HIV-1 integrase to irreversibly link the reverse-transcribed viral DNA to the host genome. INSTIs have proven their high efficiency in inhibiting viral replication in vitro and in patients. However, first-generation INSTIs have only a modest genetic barrier to resistance, allowing the virus to escape these powerful drugs through several resistance pathways. Second-generation INSTIs, such as dolutegravir (DTG, S/GSK1349572), have been reported to have a higher resistance barrier, and no novel drug resistance mutation has yet been described for this drug. Therefore, we performed in vitro selection experiments with DTG using viruses of subtypes B, C, and A/G and showed that the most common mutation to emerge was R263K. Further analysis by site-directed mutagenesis showed that R263K does confer low-level resistance to DTG and decreased integration in cell culture without altering reverse transcription. Biochemical cell-free assays performed with purified IN enzyme containing R263K confirmed the absence of major resistance against DTG and showed a slight decrease in 3= processing and strand transfer activities compared to the wild type. Structural modeling suggested and in vitro IN-DNA binding assays show that the R263K mutation affects IN-DNA interactions.T he high mutation rate of HIV-1 reverse transcriptase (RT) allows the virus to escape pressure through adaptive mutations that include drug resistance mutations that limit the effectiveness of antiretroviral drugs (5,31,66,69,70). The use of multiple drugs in combination can hamper this process by restraining viral replication, limiting the emergence of resistant strains. The addition of integrase inhibitors to the arsenal of drugs against HIV-1 is important since these inhibitors are active against viruses resistant to other drug classes (16,49,63).The HIV-1 integrase enzyme catalyzes two reactions. The first is 3= processing, which consists of cleavage of a dinucleotide at both 3= ends of the reverse-transcribed linear viral DNA and results in the exposure of reactive hydroxyl groups. The second step termed "strand transfer" is carried out through a nucleophilic attack by exposed 3= hydroxyl groups on host genomic DNA (26, 47). Even though 3= processing may be a suitable therapeutic target, the integrase inhibitors developed so far are integrase strand transfer inhibitors (INSTIs) that preferentially inhibit strand transfer while only modestly affecting 3= processing (18,24,26). Raltegravir (RAL) was the first INSTI to be approved for therapy in 2007 (64) and is safe and efficient in both treatment-naïve and treatment-experienced subjects (11,17,23,35,49,62,63). Elvitegravir (EVG) is another INSTI currently in advanced clinical trials (10,12,77).Although first-generation INSTIs strongly inhibit HIV-1 replication, they possess only a modest genetic barrier to resistance. Three main resistance pathways have been identified for RAL, involving initial mutations of the N1...