Effects of an HIV-1 maturation inhibitor on the structure and dynamics of CA-SP1 junction helices in virus-like particles.

HIV-1 maturation involves conversion of the immature Gag polyprotein lattice, which lines the inner surface of the viral membrane, to the mature capsid protein (CA) lattice, which encloses the viral RNA. Maturation inhibitors such as bevirimat (BVM) bind within six-helix bundles, formed by a segment that spans the junction between the CA and spacer peptide 1 (SP1) subunits of Gag, and interfere with cleavage between CA and SP1 catalyzed by the HIV-1 protease (PR). We report solid-state NMR (ssNMR) measurements on spherical virus-like particles (VLPs), facilitated by segmental isotopic labeling, that provide information about effects of BVM on the structure and dynamics of CA-SP1 junction helices in the immature lattice. Although BVM strongly blocks PR-catalyzed CA-SP1 cleavage in VLPs and blocks conversion of VLPs to tubular CA assemblies, 15N and 13C ssNMR chemical shifts of segmentally labeled VLPs with and without BVM are very similar, indicating that interaction with BVM does not alter the six-helix bundle structure appreciably. Only the 15N chemical shift of A280 (the first residue of SP1) changes significantly, consistent with BVM binding to an internal ring of hydrophobic side chains of L279 residues. Measurements of transverse 15N spin relaxation rates reveal a reduction in the amplitudes and/or timescales of backbone N-H bond motions, corresponding to a rigidification of the six-helix bundles. Overall, our data show that inhibition of HIV-1 maturation by BVM involves changes in structure and dynamics that are surprisingly subtle, but still sufficient to produce a large effect on CA-SP1 cleavage.

New Phosphorus Analogs of Bevirimat: Synthesis, Evaluation of Anti-HIV-1 Activity and Molecular Docking Study.

Since the beginning of the human immunodeficiency virus (HIV) epidemic, many groups of drugs characterized by diverse mechanisms of action have been developed, which can suppress HIV viremia. 3-O-(3',3'-Dimethylsuccinyl) betulinic acid, known as bevirimat (BVM), was the first compound in the class of HIV maturation inhibitors. In the present work, phosphate and phosphonate derivatives of 3-carboxyacylbetulinic acid were synthesized and evaluated for anti-HIV-1 activity. In vitro studies showed that 30-diethylphosphonate analog of BVM (compound 14a) has comparable effects to BVM (half maximal inhibitory concentrations (IC50) equal to 0.02 µM and 0.03 µM, respectively) and is also more selective (selectivity indices: 3450 and 967, respectively). To investigate the possible mechanism of antiviral effect of 14a, molecular docking was carried out on the C-terminal domain (CTD) of HIV-1 capsid (CA)-spacer peptide 1 (SP1) fragment of Gag protein, designated as CTD-SP1, which was described as a molecular target for maturation inhibitors. Compared with interactions between BVM and the protein, an increased number of strong interactions between ligand 14a and protein, generated by the phosphonate group, was observed.

Discovery of a novel and potent class of anti-HIV-1 maturation inhibitors with improved virology profile against gag polymorphisms.

A new class of betulin-derived α-keto amides was identified as HIV-1 maturation inhibitors. Through lead optimization, GSK8999 was identified with IC50 values of 17nM, 23nM, 25nM, and 8nM for wild type, Q369H, V370A, and T371A respectively. When tested in a panel of 62 HIV-1 isolates covering a diversity of CA-SP1 genotypes including A, AE, B, C, and G using a PBMC based assay, GSK8999 was potent against 57 of 62 isolates demonstrating an improvement over the first generation maturation inhibitor BVM. The data disclosed here also demonstrated that the new α-keto amide GSK8999 has a mechanism of action consistent with inhibition of the proteolytic cleavage of CA-SP1.

Fluorinated betulinic acid derivatives and evaluation of their anti-HIV activity.

Several fluorinated derivatives of the anti-HIV maturation agent bevirimat (1) were synthesized and evaluated for anti-HIV replication activity. The modified positions were the C-2, C-3, C-28, and C-30 positions, either directly on the betulinic acid (2) skeleton or in the attached side chains. Compound 18, which has a trifluoromethyl group added to C-30 of its isopropenyl group, exhibited similar potency to 1 against HIV-1NL4-3. In total, our current studies support our prior conclusion that C-30 allylic modification is unlikely to be a pharmacophore for anti-HIV activity, but could be a meaningful route to manipulate other properties of 2-related compounds.

Betulinic Acid Decorated with Polar Groups and Blue Emitting BODIPY Dye: Synthesis, Cytotoxicity, Cell-Cycle Analysis and Anti-HIV Profiling.

Betulinic acid (BA) is a potent triterpene, which has shown promising potential in cancer and HIV-1 treatment. Here, we report a synthesis and biological evaluation of 17 new compounds, including BODIPY labelled analogues derived from BA. The analogues terminated by amino moiety showed increased cytotoxicity (e.g., BA had on CCRF-CEM IC50 > 50 µM, amine 3 IC50 0.21 and amine 14 IC50 0.29). The cell-cycle arrest was evaluated and did not show general features for all the tested compounds. A fluorescence microscopy study of six derivatives revealed that only 4 and 6 were detected in living cells. These compounds were colocalized with the endoplasmic reticulum and mitochondria, indicating possible targets in these organelles. The study of anti-HIV-1 activity showed that 8, 10, 16, 17 and 18 have had IC50i > 10 µM. Only completely processed p24 CA was identified in the viruses formed in the presence of compounds 4 and 12. In the cases of 2, 8, 9, 10, 16, 17 and 18, we identified not fully processed p24 CA and p25 CA-SP1 protein. This observation suggests a similar mechanism of inhibition as described for bevirimat.

Phosphate Derivatives of 3-Carboxyacylbetulin: SynThesis, In Vitro Anti-HIV and Molecular Docking Study.

Lupane-type pentacyclic triterpenes such as betulin and betulinic acid play an important role in the search for new therapies that would be effective in controlling viral infections. The aim of this study was the synthesis and evaluation of in vitro anti-HIV-1 activity for phosphate derivatives of 3-carboxyacylbetulin 3-5 as well as an in silico study of new compounds as potential ligands of the C-terminal domain of the HIV-1 capsid-spacer peptide 1 (CA-CTD-SP1) as a molecular target of HIV-1 maturation inhibitors. In vitro studies showed that 28-diethoxyphosphoryl-3-O-(3',3'-dimethylsuccinyl)betulin (compound 3), the phosphate analog of bevirimat (betulinic acid derivative, HIV-1 maturation inhibitor), has IC50 (half maximal inhibitory concentration) equal to 0.02 µM. Compound 3 inhibits viral replication at a level comparable to bevirimat and is also more selective (selectivity indices = 1250 and 967, respectively). Molecular docking was used to examine the probable interaction between the phosphate derivatives of 3-carboxyacylbetulin and C-terminal domain (CTD) of the HIV-1 capsid (CA)-spacer peptide 1 (SP1) fragment of Gag protein, designated as CTD-SP1. Compared with interactions between bevirimat (BVM) and the protein, an increased number of strong interactions between ligand 3 and the protein, generated by the phosphate group, were observed. These compounds might have the potential to also inhibit SARS-CoV2 proteins, in as far as the intrinsically imprecise docking scores suggest.

Pharmacological intervention of HIV-1 maturation.

Despite significant advances in antiretroviral therapy, increasing drug resistance and toxicities observed among many of the current approved human immunodeficiency virus (HIV) drugs indicate a need for discovery and development of potent and safe antivirals with a novel mechanism of action. Maturation inhibitors (MIs) represent one such new class of HIV therapies. MIs inhibit a late step in the HIV-1 Gag processing cascade, causing defective core condensation and the release of non-infectious virus particles from infected cells, thus blocking the spread of the infection to new cells. Clinical proof-of-concept for the MIs was established with betulinic acid derived bevirimat, the prototype HIV-1 MI. Despite the discontinuation of its further clinical development in 2010 due to a lack of uniform patient response caused by naturally occurring drug resistance Gag polymorphisms, several second-generation MIs with improved activity against viruses exhibiting Gag polymorphism mediated resistance have been recently discovered and are under clinical evaluation in HIV/AID patients. In this review, current understanding of HIV-1 MIs is described and recent progress made toward elucidating the mechanism of action, target identification and development of second-generation MIs is reviewed.

Pharmacological intervention of HIV-1 maturation

Despite significant advances in antiretroviral therapy, increasing drug resistance and toxicities observed among many of the current approved human immunodeficiency virus (HIV) drugs indicate a need for discovery and development of potent and safe antivirals with a novel mechanism of action. Maturation inhibitors (MIs) represent one such new class of HIV therapies. MIs inhibit a late step in the HIV-1 Gag processing cascade, causing defective core condensation and the release of non-infectious virus particles from infected cells, thus blocking the spread of the infection to new cells. Clinical proof-of-concept for the MIs was established with betulinic acid derived bevirimat, the prototype HIV-1 MI. Despite the discontinuation of its further clinical development in 2010 due to a lack of uniform patient response caused by naturally occurring drug resistance Gag polymorphisms, several second-generation MIs with improved activity against viruses exhibiting Gag polymorphism mediated resistance have been recently discovered and are under clinical evaluation in HIV/AID patients. In this review, current understanding of HIV-1 MIs is described and recent progress made toward elucidating the mechanism of action, target identification and development of second-generation MIs is reviewed.