Inhibition of human immunodeficiency virus type 1 isolates by the integrase inhibitor L-731,988, a diketo Acid

Dolutegravir: clinical efficacy and role in HIV therapy

The human immunodeficiency virus type-1 (HIV-1) integrase enzyme has recently emerged as a primary alternative target to block viral replication, and integrase strand transfer inhibitors (INSTIs) are now considered an alternative 'third agent' class of antiretroviral (ARV) drugs. Dolutegravir is the first next-generation INSTI showing some novel and intriguing characteristics: it has a favorable pharmacokinetic profile with a prolonged intracellular halflife, rendering feasible a once daily dosing without the need for pharmacokinetic boosting. Secondly, it is largely metabolized via uridine diphosphate glucuronosyltransferase-1A1 with a minor component of cytochrome P450 isoforms, thus allowing a low grade of drug-drug interactions, so that its metabolic profile consents co-administration with the majority of the other ARV drugs without dose adjustments. Lastly, but no less important, virological studies have clearly demonstrated that dolutegravir has a significant activity against HIV-1 isolates showing raltegravir and/or elvitegravir associated resistance mutations. The attributes of once daily administration and the potential to treat INSTI-resistant viruses make dolutegravir an interesting and promising new agent in the treatment of both naïve and experienced HIV-1 subjects. In this review, the main concerns on dolutegravir efficacy are focused through the analysis of the currently available data from clinical studies in naïve and experienced patients, evaluating its possible place within the anti-HIV-1 drug armamentarium. The development of newer once daily, single tablet coformulations improved drug adherence and maximized the success of ARV therapy. Pharmacokinetic studies and dose-ranging trials suggested that dolutegravir is a good candidate for a single tablet regimen in one or more new coformulated pills that will be available in the near future.

Past and future. Current drugs targeting HIV-1 integrase and reverse transcriptase-associated ribonuclease H activity: single and dual active site inhibitors

Catalytic HIV type-1 (HIV-1) integrase (IN) and ribonuclease H (RNase H) domains belong to the polynucleotidyl transferase superfamily and are characterized by highly conserved motifs that coordinate two divalent Mg(2+) cations and are attractive targets for new antiviral agents. Several structural features of both domains are now available. Drugs targeting the HIV-1 IN are currently approved for anti-HIV therapy, while no drug targeting the HIV-1 RNase H function is yet available. This review describes HIV-1 IN and the RNase H function and structures, compounds targeting their active sites and dual inhibition as a new approach for drug development.

Potential benefit of dolutegravir once daily: efficacy and safety

The viral integrase enzyme has recently emerged as a primary alternative target to block HIV-1 replication, and integrase inhibitors are considered a pivotal new class of antiretroviral drugs. Dolutegravir is an investigational next-generation integrase inhibitor showing some novel and intriguing characteristics, ie, it has a favorable pharmacokinetic profile with a prolonged intracellular half-life, rendering feasible once-daily dosing without the need for ritonavir boosting and without regard to meals. Moreover, dolutegravir is primarily metabolized via uridine diphosphate glucuronosyltranferase 1A1, with a minor component of the cytochrome P450 3A4 isoform, thereby limiting drug–drug interactions. Furthermore, its metabolic profile enables coadministration with most of the other available antiretroviral agents without dose adjustment. Recent findings also demonstrate that dolutegravir has significant activity against HIV-1 isolates with resistance mutations associated with raltegravir and/or elvitegravir. The attributes of once-daily administration and the potential to treat integrase inhibitor-resistant viruses make dolutegravir an interesting and promising investigational drug. In this review, the main concerns about the efficacy and safety of dolutegravir as well as its resistance profile are explored by analysis of currently available data from preclinical and clinical studies.

HIV Drug Resistance and the Advent of Integrase Inhibitors

This review focuses on the topic of HIV integrase inhibitors that are potent antiretroviral drugs that efficiently decrease viral load in patients. However, emergence of resistance mutations against this new class of drugs represents a threat to their long-term efficacy. Here, we provide new information about the most recent mutations identified and other mutations that confer resistance to several integrase inhibitors, such as new resistance mutations-for example, G118R, R263K, and S153Y-that have been identified through in vitro selection studies with second-generation integrase strand transfer inhibitors (INSTIs). These add to the three main resistance pathways involving mutations at positions Y143, N155, and Q148. Deep sequencing, structural modeling, and biochemical analyses are methods that currently help in the understanding of the mechanisms of resistance conferred by these mutations. Although the new resistance mutations appear to confer only low levels of cross-resistance to second-generation drugs, the Q148 pathway with numerous secondary mutations has the potential to significantly decrease susceptibility to all drugs of the INSTI family of compounds.

The Need for Development of New HIV-1 Reverse Transcriptase and Integrase Inhibitors in the Aftermath of Antiviral Drug Resistance

The use of highly active antiretroviral therapy (HAART) involves combinations of drugs to achieve maximal virological response and reduce the potential for the emergence of antiviral resistance. There are two broad classes of reverse transcriptase inhibitors, the nucleoside reverse transcriptase inhibitors (NRTIs) and nonnucleoside reverse transcriptase inhibitors (NNRTIs). Since the first classes of such compounds were developed, viral resistance against them has necessitated the continuous development of novel compounds within each class. This paper considers the NRTIs and NNRTIs currently in both preclinical and clinical development or approved for second line therapy and describes the patterns of resistance associated with their use, as well as the underlying mechanisms that have been described. Due to reasons of both affordability and availability, some reverse transcriptase inhibitors with low genetic barrier are more commonly used in resource-limited settings. Their use results to the emergence of specific patterns of antiviral resistance and so may require specific actions to preserve therapeutic options for patients in such settings. More recently, the advent of integrase strand transfer inhibitors represents another major step forward toward control of HIV infection, but these compounds are also susceptible to problems of HIV drug resistance.

Novel therapeutic strategies targeting HIV integrase

Integration of the viral genome into host cell chromatin is a pivotal and unique step in the replication cycle of retroviruses, including HIV. Inhibiting HIV replication by specifically blocking the viral integrase enzyme that mediates this step is an obvious and attractive therapeutic strategy. After concerted efforts, the first viable integrase inhibitors were developed in the early 2000s, ultimately leading to the clinical licensure of the first integrase strand transfer inhibitor, raltegravir. Similarly structured compounds and derivative second generation integrase strand transfer inhibitors, such as elvitegravir and dolutegravir, are now in various stages of clinical development. Furthermore, other mechanisms aimed at the inhibition of viral integration are being explored in numerous preclinical studies, which include inhibition of 3' processing and chromatin targeting. The development of new clinically useful compounds will be aided by the characterization of the retroviral intasome crystal structure. This review considers the history of the clinical development of HIV integrase inhibitors, the development of antiviral drug resistance and the need for new antiviral compounds.

Resistance mutations in human immunodeficiency virus type 1 integrase selected with elvitegravir confer reduced susceptibility to a wide range of integrase inhibitors

Integration of viral DNA into the host chromosome is an essential step in the life cycle of retroviruses and is facilitated by the viral integrase enzyme. The first generation of integrase inhibitors recently approved or currently in late-stage clinical trials shows great promise for the treatment of human immunodeficiency virus (HIV) infection, but virus is expected to develop resistance to these drugs. Therefore, we used a novel resistance selection protocol to follow the emergence of resistant HIV in the presence of the integrase inhibitor elvitegravir (GS-9137). We find the primary resistance-conferring mutations to be Q148R, E92Q, and T66I and demonstrate that they confer a reduction in susceptibility not only to elvitegravir but also to raltegravir (MK-0518) and other integrase inhibitors. The locations of the mutations are highlighted in the catalytic sites of integrase, and we correlate the mutations with expected drug-protein contacts. In addition, mutations that do not confer reduced susceptibility when present alone (H114Y, L74M, R20K, A128T, E138K, and S230R) are also discussed in relation to their position in the catalytic core domain and their proximity to known structural features of integrase. These data broaden the understanding of antiviral resistance against integrase inhibitors and may give insight facilitating the discovery of second-generation compounds.

Broad antiretroviral activity and resistance profile of the novel human immunodeficiency virus integrase inhibitor elvitegravir (JTK-303/GS-9137)

Integrase (IN), an essential enzyme of human immunodeficiency virus (HIV), is an attractive antiretroviral drug target. The antiviral activity and resistance profile in vitro of a novel IN inhibitor, elvitegravir (EVG) (also known as JTK-303/GS-9137), currently being developed for the treatment of HIV-1 infection are described. EVG blocked the integration of HIV-1 cDNA through the inhibition of DNA strand transfer. EVG inhibited the replication of HIV-1, including various subtypes and multiple-drug-resistant clinical isolates, and HIV-2 strains with a 50% effective concentration in the subnanomolar to nanomolar range. EVG-resistant variants were selected in two independent inductions, and a total of 8 amino acid substitutions in the catalytic core domain of IN were observed. Among the observed IN mutations, T66I and E92Q substitutions mainly contributed to EVG resistance. These two primary resistance mutations are located in the active site, and other secondary mutations identified are proximal to these primary mutations. The EVG-selected IN mutations, some of which represent novel IN inhibitor resistance mutations, conferred reduced susceptibility to other IN inhibitors, suggesting that a common mechanism is involved in resistance and potential cross-resistance. The replication capacity of EVG-resistant variants was significantly reduced relative to both wild-type virus and other IN inhibitor-resistant variants selected by L-870,810. EVG and L-870,810 both inhibited the replication of murine leukemia virus and simian immunodeficiency virus, suggesting that IN inhibitors bind to a conformationally conserved region of various retroviral IN enzymes and are an ideal drug for a range of retroviral infections.

Nef expressed from human immunodeficiency virus type 1 extrachromosomal DNA downregulates CD4 on primary CD4+ T lymphocytes: implications for integrase inhibitors

Recently developed integrase inhibitors targeting the HIV-1 integrase (IN) protein block integration of HIV DNA in the target cell, preventing subsequent virus replication. In the absence of integration, viral DNA is shunted towards the formation of extrachromosomal DNA (E-DNA). Although HIV-1 E-DNA does not support productive replication, it is transcriptionally active and produces viral proteins. However, the significance of E-DNA in virus replication and pathogenesis is poorly understood. In this study, the functional activity of the HIV-1 Nef protein expressed in the absence of viral integration was analysed. Using both a recombinant HIV-1 IN defective virus and a diketo acid IN inhibitor, evidence was provided showing that Nef expressed from E-DNA downregulates CD4 surface expression on primary CD4(+) T lymphocytes. These results suggest that proteins expressed in the absence of integration may have potential clinical consequences, an issue that should be further explored with the introduction of IN inhibitors.

Potential drug resistance polymorphisms in the integrase gene of HIV type 1 subtype A

Variation in HIV-1 genes within and between subtypes has been best defined in the env gene, however, other more conserved genes vary between subtypes. Integrase (IN) and other regions of the pol gene are highly conserved due to their integral role in HIV replication and therefore are targets for antiviral drugs. In this study 3 individuals, infected heterosexually with HIV-1 subtype A, were examined for IN polymorphisms. Two patients' sequences clustered phylogenetically with other subtype A sequences and one patient's sequence was most similar to the circulating recombinant form CRF_02. No polymorphisms were observed in either of the motifs containing residues critical residues for IN activity. Polymorphisms were observed in a residue associated with resistance to anti-integrase drugs. In addition, a number of unique polymorphisms were observed in one individual (WM1666). IN can vary significantly within a subtype as well as between subtypes, and mutations associated with resistance to anti-integrase compounds can be present in drug naive individuals.

Human immunodeficiency virus type 1 (HIV-1) integrase: resistance to diketo acid integrase inhibitors impairs HIV-1 replication and integration and confers cross-resistance to L-chicoric acid

The diketo acids are potent inhibitors of human immunodeficiency virus (HIV) integrase (IN). Mutations in IN, T66I, S153Y, and M154I, as well as T66I-S153Y and T66I-M154I double mutations, confer resistance to diketo acids (D. J. Hazuda et al., Science 287:646-650, 2000). The effects of these IN mutations on viral replication, enzymatic activity, and susceptibility to other HIV inhibitors are reported herein. By immunofluorescence assay and real-time PCR, all mutant viruses demonstrated a modest delay in viral spread compared to that of reference HIV. These viruses also showed a statistically significant defect in integration without defects in reverse transcription. Recombinant IN containing S153Y, T66I, and M154I-T66I mutations had an approximately twofold decrease in both disintegration and 3'-end-processing-strand transfer activities in vitro. In contrast, IN containing M154I demonstrated a greater than twofold increase in specific activity in both reactions. All mutant HIVs were resistant to l-chicoric acid, a dicaffeoyltartaric acid IN inhibitor, both in tissue culture and in biochemical assays, yet remained susceptible to the reverse transcriptase inhibitors zidovudine and nevirapine. Thus, IN mutations conferring resistance to the diketo acids can yield integration defects, attenuated catalysis in vitro, and cross-resistance to l-chicoric acid.