A Single Polymorphism in HIV-1 Subtype C SP1 Is Sufficient To Confer Natural Resistance to the Maturation Inhibitor Bevirimat

Abstract

3-O-(3,3-Dimethylsuccinyl) betulinic acid (DSB), also known as PA-457, bevirimat (BVM), or MPC-4326, is a novel HIV-1 maturation inhibitor. Unlike protease inhibitors, BVM blocks the cleavage of the Gag capsid precursor (CA-SP1) to mature capsid (CA) protein, resulting in the release of immature, noninfectious viral particles. Despite the novel mechanism of action and initial progress made in small-scale clinical trials, further development of bevirimat has encountered unexpected challenges, because patients whose viruses contain genetic polymorphisms in the Gag SP1 (positions 6 to 8) protein do not generally respond well to BVM treatment. To better define the role of amino acid residues in the HIV-1 Gag SP1 protein that are involved in natural polymorphisms to confer resistance to the HIV-1 maturation inhibitor BVM, a series of Gag SP1 chimeras involving BVM-sensitive (subtype B) and BVM-resistant (subtype C) viruses was generated and characterized for sensitivity to BVM. We show that SP1 residue 7 of the Gag protein is a primary determinant of SP1 polymorphism-associated drug resistance to BVM.3-O-(3Ј,3Ј-Dimethylsuccinyl) betulinic acid (DSB), also known as bevirimat (BVM), is a potent inhibitor of HIV-1 maturation (7,8,20,21). BVM targets the HIV-1 Gag CA-SP1 boundary region by blocking viral protease cleavage of SP1 from the CA-SP1 precursor and inhibiting release of the mature CA protein, which is the final step required for virion maturation. Despite the novel mechanism of action and initial progress made in small-scale clinical trials (11-13, 17), further development of BVM has encountered unexpected challenges in the clinical setting, because patients whose viruses contain genetic polymorphisms in the Gag SP1 (positions 6 to 8) protein do not respond well to BVM treatment (3,10,14,16). These three residues (glutamine-valine-threonine [QVT]) are referred to as the SP1 polymorphism motif. Interestingly, these naturally occurring mutations that confer intrinsic resistance to BVM were not identified by in vitro drug resistance selection experiments and are not located in the region immediately flanking the CA-SP1 cleavage site (2,7,8). Extensive in vitro drug selection experiments identified six amino acid changes (proximal to the CA-SP1 cleavage site) that independently confer BVM resistance (2). Three substitutions were located at the 1st and 3rd residues of SP1 (A1V, A3V, and A3T), and three substitutions were identified at the extreme C terminus of CA (H226Y, L231M, and L231F).There are extensive data on HIV-1 subtype B viruses and their representative molecular clone pNL4-3 concerning BVM's mechanism of action and antiviral activity (2,4,7,8,20,21). In contrast, HIV-1 non-B subtypes and derived molecular clones have received less attention, despite knowledge that these non-B subtypes are responsible for nearly 90% of the current worldwide HIV-1 pandemic (6,19). Additionally, we noted that non-B subtypes exhibit more frequent changes in the identified SP1 polymorphism motif than B subtype viruses do. The...

Mechanistic Studies and Modeling Reveal the Origin of Differential Inhibition of Gag Polymorphic Viruses by HIV-1 Maturation Inhibitors

“…For example, BMS-955176 retains activity toward variants with substitutions at Gag V370 by alanine or methionine (1.4- and 1.5-fold, respectively), and V362I (2.4-fold), as compared to 54-, 177- and 7.2-fold losses of sensitivity by BVM, respectively. In addition, BMS-955176 retains activity toward virus with V370A/ΔT371 and ΔV370 substitutions, both minor polymorphs in subtype B, but characteristic of subtype C isolates[24] (FCs of 3.5 and 6.8-fold, respectively). By comparison, BVM is >100-fold less active toward both V370A/ΔT371 and ΔV370-containing viruses.…”

Prevalent Polymorphisms in Wild-Type HIV-1 Integrase Are Unlikely To Engender Drug Resistance to Dolutegravir (S/GSK1349572)

“…Marcelin et al (9) concluded that "HIV-1 subtype and baseline integrase polymorphisms do not influence the virologic response to RAL," whereas Armenia et al (8) concluded that "among all integrase polymorphisms, only T122I and S119P were associated with poorer virologic response to raltegravir either at 24 or 48 weeks during treatment." Overall, these studies indicate that the effect of polymorphisms on response and resistance in the INI class is not as clear as has been observed for bevirimat (2) and suggest that additional investigation may be needed. Dolutegravir (DTG; S/GSK1349572) is being developed for INI-naive patients as a once-daily, unboosted, HIV INI.…”

“…Prevalent polymorphisms can affect the antiviral activity of some HIV antiretrovirals, as has been shown recently for the maturation inhibitor bevirimat (2) and historically for nonnucleoside reverse transcriptase inhibitors in HIV-2 infection. Thus, an examination of the effects of polymorphic sites of the IN gene on susceptibility to integrase inhibitors (INIs) is important.…”

HIV-1 Capsid Inhibitors as Antiretroviral Agents

“…The examination of patient-derived virus revealed that BMV resistance was linked to naturally occurring polymorphisms within SP1 downstream of CA-SP1 cleavage site, in the “QVT motif” comprising SP1 residues 6, 7 and 8 [91, 92]. In vitro assays confirmed that SP1 polymorphisms, particularly SP1 V7A, reduced sensitivity of HIV-1 to BMV [88, 93]. This lack of response in a significant percentage of treated patients promoted the development of BMV analogs.…”