Identification of a Potential Inhibitor of the FIV p24 Capsid Protein and Characterization of Its Binding Site.

Feline immunodeficiency virus (FIV) is a veterinary infective agent for which there is currently no efficient drug available. Drugs targeting the lentivirus capsid are currently under development for the treatment of human immunodeficiency virus 1 (HIV-1). Here we describe a lead compound that interacts with the FIV capsid. This compound, 696, modulates the in vitro assembly of and stabilizes the assembled capsid protein. To decipher the mechanism of binding of this compound to the protein, we performed the first nuclear magnetic resonance (NMR) assignment of the FIV p24 capsid protein. Experimental NMR chemical shift perturbations (CSPs) observed after the addition of 696 enabled the characterization of a specific binding site for 696 on p24. This site was further analyzed by molecular modeling of the protein:compound interaction, demonstrating a strong similarity with the binding sites of existing drugs targeting the HIV-1 capsid protein. Taken together, we characterized a promising capsid-interacting compound with a low cost of synthesis, for which derivatives could lead to the development of efficient treatments for FIV infection. More generally, our strategy combining the NMR assignment of FIV p24 with NMR CSPs and molecular modeling will be useful for the analysis of future compounds targeting p24 in the quest to identify an efficient treatment for FIV.

Identification of 2-(4-N,N-Dimethylaminophenyl)-5-methyl-1-phenethyl-1H-benzimidazole targeting HIV-1 CA capsid protein and inhibiting HIV-1 replication in cellulo.

The capsid (CA) subunit of the HIV-1 Gag polyprotein is involved in several steps of the viral cycle, from the assembly of new viral particles to the protection of the viral genome until it enters into the nucleus of newly infected cells. As such, it represents an interesting therapeutic target to tackle HIV infection. In this study, we screened hundreds of compounds with a low cost of synthesis for their ability to interfere with Gag assembly in vitro. Representatives of the most promising families of compounds were then tested for their ability to inhibit HIV-1 replication in cellulo. From these molecules, a hit compound from the benzimidazole family with high metabolic stability and low toxicity, 2-(4-N,N-dimethylaminophenyl)-5-methyl-1-phenethyl-1H-benzimidazole (696), appeared to block HIV-1 replication with an IC50 of 3 µM. Quantitative PCR experiments demonstrated that 696 does not block HIV-1 infection before the end of reverse transcription, and molecular docking confirmed that 696 is likely to bind at the interface between two monomers of CA and interfere with capsid oligomerization. Altogether, 696 represents a promising lead molecule for the development of a new series of HIV-1 inhibitors.

Review and Perspectives on the Structure-Function Relationships of the Gag Subunits of Feline Immunodeficiency Virus.

The Gag polyprotein is implied in the budding as well as the establishment of the supramolecular architecture of infectious retroviral particles. It is also involved in the early phases of the replication of retroviruses by protecting and transporting the viral genome towards the nucleus of the infected cell until its integration in the host genome. Therefore, understanding the structure-function relationships of the Gag subunits is crucial as each of them can represent a therapeutic target. Though the field has been explored for some time in the area of Human Immunodeficiency Virus (HIV), it is only in the last decade that structural data on Feline Immunodeficiency Virus (FIV) Gag subunits have emerged. As FIV is an important veterinary issue, both in domestic cats and endangered feline species, such data are of prime importance for the development of anti-FIV molecules targeting Gag. This review will focus on the recent advances and perspectives on the structure-function relationships of each subunit of the FIV Gag polyprotein.

Looking for Novel Capsid Protein Multimerization Inhibitors of Feline Immunodeficiency Virus.

Feline immunodeficiency virus (FIV) is a member of the retroviridae family of viruses. It causes acquired immunodeficiency syndrome (AIDS) in worldwide domestic and non-domestic cats and is a cause of an important veterinary issue. The genome organization of FIV and the clinical characteristics of the disease caused by FIV are similar to human immunodeficiency virus (HIV). Both viruses infect T lymphocytes, monocytes, and macrophages, with a similar replication cycle in infected cells. Thus, the infection of cats with FIV is also a useful tool for the study and development of novel drugs and vaccines against HIV. Anti-retroviral drugs studied extensively with regards to HIV infection have targeted different steps of the virus replication cycle: (1) disruption of the interaction with host cell surface receptors and co-receptors; (2) inhibition of fusion of the virus and cell membranes; (3) blocking of the reverse transcription of viral genomic RNA; (4) interruption of nuclear translocation and integration of viral DNA into host genomes; (5) prevention of viral transcript processing and nuclear export; and (6) inhibition of virion assembly and maturation. Despite the great success of anti-retroviral therapy in slowing HIV progression in humans, a similar therapy has not been thoroughly investigated for FIV infection in cats, mostly because of the little structural information available for FIV proteins. The FIV capsid protein (CA) drives the assembly of the viral particle, which is a critical step in the viral replication cycle. During this step, the CA protein oligomerizes to form a protective coat that surrounds the viral genome. In this work, we perform a large-scale screening of four hundred molecules from our in-house library using an in vitro assembly assay of p24, combined with microscale thermophoresis, to estimate binding affinity. This screening led to the discovery of around four novel hits that inhibited capsid assembly in vitro. These may provide new antiviral drugs against FIV.