A single G10T polymorphism in HIV-1 subtype C Gag-SP1 regulates sensitivity to maturation inhibitors.

BACKGROUND: Maturation inhibitors (MIs) potently block HIV-1 maturation by inhibiting the cleavage of the capsid protein and spacer peptide 1 (CA-SP1). Bevirimat (BVM), a highly efficacious first-in-class MI against HIV-1 subtype B isolates, elicited sub-optimal efficacy in clinical trials due to polymorphisms in the CA-SP1 region of the Gag protein (SP1:V7A). HIV-1 subtype C inherently contains this polymorphism thus conferring BVM resistance, however it displayed sensitivity to second generation BVM analogs. RESULTS: In this study, we have assessed the efficacy of three novel second-generation MIs (BVM analogs: CV-8611, CV-8612, CV-8613) against HIV-1 subtype B and C isolates. The BVM analogs were potent inhibitors of both HIV-1 subtype B (NL4-3) and subtype C (K3016) viruses. Serial passaging of the subtype C, K3016 virus strain in the presence of BVM analogs led to identification of two mutant viruses-Gag SP1:A1V and CA:I201V. While the SP1:A1V mutant was resistant to the MIs, the CA:I120V mutant displayed partial resistance and a MI-dependent phenotype. Further analysis of the activity of the BVM analogs against two additional HIV-1 subtype C strains, IndieC1 and ZM247 revealed that they had reduced sensitivity as compared to K3016. Sequence analysis of the three viruses identified two polymorphisms at SP1 residues 9 and 10 (K3016: N9, G10; IndieC1/ZM247: S9, T10). The N9S and S9N mutants had no change in MI-sensitivity. On the other hand, replacing glycine at residue 10 with threonine in K3016 reduced its MI sensitivity whereas introducing glycine at SP1 10 in place of threonine in IndieC1 and ZM247 significantly enhanced their MI sensitivity. Thus, the specific glycine residue 10 of SP1 in the HIV-1 subtype C viruses determined sensitivity towards BVM analogs. CONCLUSIONS: We have identified an association of a specific glycine at position 10 of Gag-SP1 with an MI susceptible phenotype of HIV-1 subtype C viruses. Our findings have highlighted that HIV-1 subtype C viruses, which were inherently resistant to BVM, may also be similarly predisposed to exhibit a significant degree of resistance to second-generation BVM analogs. Our work has strongly suggested that genetic differences between HIV-1 subtypes may produce variable MI sensitivity that needs to be considered in the development of novel, potent, broadly-active MIs.

Construction of a HIV-1 subtype C 3D model using homology modeling and in-silico docking, molecular dynamics simulation, and MM-GBSA calculation of second-generation HIV-1 maturation inhibitor(s).

Maturation inhibitors (MIs) efficiently block HIV-1 maturation by inhibiting the cleavage of the capsid protein and spacer peptide 1 (CA-SP1) leading to the production of immature and non-infectious virus particles. We have previously reported that second-generation MIs were more potent than bevirimat (BVM) against HIV-1 subtype C. In-silico studies on interaction of with BVM and their analogs have been limited to HIV-1 subtype B(5I4T) due to lack of an available 3D structure for HIV-1 subtype C virus. In our current study, we have developed a 3D model of HIV-1C Gag CA-SP1 region using protein homology modeling with HIV-1 subtype B(514T) as a template. The HIV-1 C homology model generated was extensively validated using several online tools and served as a template to perform molecular docking studies with eight well-characterized MIs. The docked complex of HIV-1C and all nine MIs was subjected to molecular dynamics simulation for 100 ns using AMBER and binding free energy calculations were done using MM-GBSA. Based on our data, CV8611 exhibited highest binding energy of -6.5 Kcal/mol among all BVM analogs. CV8611 formed strong interactions with Gly222 and Met235 of HIV-1C Gag CA-SP1 during MD simulation and remained intact. The root mean square deviation and root mean square fluctuation values of the complex were stable during the simulations. Our study is the first to report construction and validation of 3D model for the HIV-1C Gag CA-SP1, which could serve as a crucial tool in the structure-aided design of novel and broadly acting maturation inhibitors.Communicated by Ramaswamy H. Sarma.

Oxadiazoles as ester bioisosteric replacements in compounds related to disoxaril. Antirhinovirus activity.

A series of 1,2,4-oxadiazoles has been prepared as ester bioisosteres and tested against 15 human rhinovirus serotypes, and the MIC80, the concentration which inhibits 80% or 12 of the serotypes tested, was determined. Homologation of the alkyl group attached to the oxadiazole ring resulted in a reduction in activity with increased chain length. Introduction of hydrophilic groups in this position rendered the compounds inactive. Increasing the length of the side chain attached to the isoxazole ring resulted in an increase in activity. Replacement of the methyl with alkoxyalkyl substituents retained activity; however, introduction of a hydroxyl group on to the side chain reduced activity. Compound 8a, where both the isoxazole and oxadiazole rings were substituted with methyl groups, was one of the most active compounds in the series. A comparison was made between 8a and the two isomeric oxadiazoles 41 and 46, and an attempt was made to explain the difference in activity by examining electrostatic potential maps and by an energy profiling study. No conclusive results were obtained from these studies.

Antipicornavirus activity of tetrazole analogues related to disoxaril.

A series of tetrazole analogues of Win 54954, a broad-spectrum antipicornavirus compound, has been synthesized to address the acid lability of the oxazoline ring of this series of compounds. The results of X-ray crystallography studies of several members of the oxazoline series bound to human rhinovirus type 1A and 14 have been used to design compounds in the tetrazole series with a broad spectrum of activity. Compound 16b, which has a three-carbon linkage between the isoxazole and phenyl rings and a propyl chain extending from the isoxazole ring, exhibiting an MIC80 for 15 rhinovirus serotypes of 0.20 microM as compared to 0.40 microM for Win 54954. X-ray studies of 16b bound to human rhinovirus-14 show that the propyl side chain extends into a pore in the binding site with the possibility of hydrophobic interactions with a pocket formed by Leu106 and a portion of Ser107.

Picornavirus inhibitors: trifluoromethyl substitution provides a global protective effect against hepatic metabolism.

Several modifications of the oxazoline ring of WIN 54954, a broad spectrum antipicornavirus compound, have been prepared in order to address the acid lability and metabolic instability of this compound. We have previously shown that the oxadiazole analogue 3 displayed comparable activity against a variety of rhinoviruses and appeared to be stable to acid. A monkey liver microsomal assay was developed to examine the metabolic stability in vitro of both compounds, and it was determined that WIN 54954 displayed 18 metabolic products while 3 was converted to 8 products. Two major products of 3 were determined by LC-MS/MS to be monohydroxylated at each of the terminal methyl groups. Replacement of the methyl on the isoxazole ring with a trifluoromethyl group, while preventing hydroxylation at this position, did not reduce the sensitivity of the molecule to microsomal metabolism at other sites. However, the (trifluoromethyl)oxadiazole 9 not only prevented hydroxylation at this position but also provided protection at the isoxazole end of the molecule, resulting in only two minor products to the extent of 4%. The major product was identified as the monohydroxylated compound 23. The global metabolic protective effect of trifluoromethyl group on the oxadiazole ring was further demonstrated by examining a variety of analogues including heterocyclic replacements of the isoxazole ring. In each case, the trifluoromethyl analogue displayed a protective effect when compared to the corresponding methyl analogue.

Tetrahydrobenzothiophene inhibitors of hepatitis C virus NS5B polymerase.

A novel series of selective HCV NS5B RNA dependent RNA polymerase inhibitors has been disclosed. These compounds contain an appropriately substituted tetrahydrobenzothiophene scaffold. This communication will detail the SAR and activities of this series.

Synthesis and receptor binding affinity of both E- and Z-dehydrophenylalanine4 enkephalins.

The dehydrophenylalanine4-enkephalin having the E-configuration (delta EPhe; phenyl and C = 0, cis) was prepared by photoisomerization of the Z-isomer with 3100 A light, followed by reversed-phase HPLC separation of the resulting mixture of the Z- and E-isomers. In the radioligand receptor binding assays, the E-isomer of [D-Ala2, delta Phe4, Leu5]enkephalin exhibited an extremely diminished affinity as compared with the Z-isomer, namely 150-260-fold loss of affinity for the delta and mu opiate receptors. The results indicate that the interrelationship of the Tyr1 and Phe4 residues in the enkephalin molecule seems to be of great importance in receptor recognition.

Importance of the stereo-orientation of aromatic groups in enkephalins to opiate receptor recognition.

PO +Dehydrophenylalanine (delta Phe) having the E-configuration (delta EPhe ; phenyl and C = O cis) was incorporated into [Leu5]-enkephalin in order to restrict its conformation. Compared with the Z-isomer, in the radio-ligand receptor binding assays, [D-Ala2, delta EPhe4 , Leu5] enkephalin showed drastically decreased potency for the delta and mu opiate receptors, i.e., 260- and 150-fold loss of affinity, respectively. The results strongly indicate that the opiate receptors require the Z-configuration (phenyl and C = O, trans) of the delta Phe4 residue and may require a specific interrelationship between the aromatic rings of the Tyr1 and Phe4 residues in the molecule for binding. The conformation of [Leu5]-enkephalin specific for the delta receptors was analyzed and a comparison made with its crystal structure recently elucidated.

Parallel synthesis of 1,2,4-oxadiazoles using CDI activation.

1,2,4-Oxadiazoles have been prepared in parallel using 1,1'-carbonyldiimidazole (CDI) as a reagent for both formation and cyclodehydration of O-acyl benzamidoximes. The use of CDI facilitates parallel purification of the oxadiazole products by simple liquid-liquid extraction and filtration.