Fullerene Derivatives Prevent Packaging of Viral Genomic RNA into HIV-1 Particles by Binding Nucleocapsid Protein.

Fullerene derivatives with hydrophilic substituents have been shown to exhibit a range of biological activities, including antiviral ones. For a long time, the anti-HIV activity of fullerene derivatives was believed to be due to their binding into the hydrophobic pocket of HIV-1 protease, thereby blocking its activity. Recent work, however, brought new evidence of a novel, protease-independent mechanism of fullerene derivatives' action. We studied in more detail the mechanism of the anti-HIV-1 activity of N,N-dimethyl[70]fulleropyrrolidinium iodide fullerene derivatives. By using a combination of in vitro and cell-based approaches, we showed that these C70 derivatives inhibited neither HIV-1 protease nor HIV-1 maturation. Instead, our data indicate effects of fullerene C70 derivatives on viral genomic RNA packaging and HIV-1 cDNA synthesis during reverse transcription-without impairing reverse transcriptase activity though. Molecularly, this could be explained by a strong binding affinity of these fullerene derivatives to HIV-1 nucleocapsid domain, preventing its proper interaction with viral genomic RNA, thereby blocking reverse transcription and HIV-1 infectivity. Moreover, the fullerene derivatives' oxidative activity and fluorescence quenching, which could be one of the reasons for the inconsistency among reported anti-HIV-1 mechanisms, are discussed herein.

Glucose-dependent aerobic glycolysis contributes to recruiting viral components into HIV-1 particles to maintain infectivity.

The cellular environment affects optimal viral replication because viruses cannot replicate without their host cells. In particular, metabolic resources such as carbohydrates, lipids, and ATP are crucial for viral replication, which is sensitive to cellular metabolism. Intriguingly, recent studies have demonstrated that human immunodeficiency virus type 1 (HIV-1) infection induces a metabolic shift from oxidative phosphorylation to aerobic glycolysis in CD4+ T cells to produce the virus efficiently. However, the importance of aerobic glycolysis in maintaining the quality of viral components and viral infectivity has not yet been fully investigated. Here, we show that aerobic glycolysis is necessary not only to override the inhibitory effect of virion-incorporated glycolytic enzymes, but also to maintain the enzymatic activity of reverse transcriptase and the adequate packaging of envelope proteins into HIV-1 particles. To investigate the effect of metabolic remodeling on the phenotypic properties of HIV-1 produced by infected cells, we replaced glucose with galactose in the culture medium because the cells grown in galactose-containing medium are forced to carry out oxidative metabolism instead of aerobic glycolysis. We found that the packaging levels of glyceraldehyde 3-phosphate dehydrogenase, alpha-enolase and pyruvate kinase muscle type 2, which decrease HIV-1 infectivity by packaging into viral particles, are increased in progeny viruses produced by the cells grown in galactose-containing medium. Furthermore, we found that the entry and reverse transcription efficiency of the progeny viruses were reduced, which was caused by a decrease in the enzymatic activity of reverse transcriptase in the viral particles and a decrease in the packaging levels of envelope proteins and reverse transcriptase. These results indicate that the aerobic glycolysis environment in HIV-1-infected cells may contribute to the quality control of viruses.

HIV-1 Maturation: Lessons Learned from Inhibitors.

Since the emergence of HIV and AIDS in the early 1980s, the development of safe and effective therapies has accompanied a massive increase in our understanding of the fundamental processes that drive HIV biology. As basic HIV research has informed the development of novel therapies, HIV inhibitors have been used as probes for investigating basic mechanisms of HIV-1 replication, transmission, and pathogenesis. This positive feedback cycle has led to the development of highly effective combination antiretroviral therapy (cART), which has helped stall the progression to AIDS, prolong lives, and reduce transmission of the virus. However, to combat the growing rates of virologic failure and toxicity associated with long-term therapy, it is important to diversify our repertoire of HIV-1 treatments by identifying compounds that block additional steps not targeted by current drugs. Most of the available therapeutics disrupt early events in the replication cycle, with the exception of the protease (PR) inhibitors, which act at the virus maturation step. HIV-1 maturation consists of a series of biochemical changes that facilitate the conversion of an immature, noninfectious particle to a mature infectious virion. These changes include proteolytic processing of the Gag polyprotein by the viral protease (PR), structural rearrangement of the capsid (CA) protein, and assembly of individual CA monomers into hexamers and pentamers that ultimately form the capsid. Here, we review the development and therapeutic potential of maturation inhibitors (MIs), an experimental class of anti-HIV-1 compounds with mechanisms of action distinct from those of the PR inhibitors. We emphasize the key insights into HIV-1 biology and structure that the study of MIs has provided. We will focus on three distinct groups of inhibitors that block HIV-1 maturation: (1) compounds that block the processing of the CA-spacer peptide 1 (SP1) cleavage intermediate, the original class of compounds to which the term MI was applied; (2) CA-binding inhibitors that disrupt capsid condensation; and (3) allosteric integrase inhibitors (ALLINIs) that block the packaging of the viral RNA genome into the condensing capsid during maturation. Although these three classes of compounds have distinct structures and mechanisms of action, they share the ability to block the formation of the condensed conical capsid, thereby blocking particle infectivity.