Attacking HIV by stabilizing its capsid: Current HIV treatments require drugs that must be taken daily, and care would be improved with an effective drug that is long-acting. GS-6207 (Lenacapavir) is a drug developed by Gilead Sciences that shows potential for a 6-month dosing interval and is in phase 2/3 clinical trials. Bester et al. describe structural and biophysical studies that provide a basis for the potent antiviral activity of GS-6207. The HIV capsid is cone shaped, and GS-6207 binds two neighboring capsid subunits and stabilizes the curved capsid. GS-6207 also interferes with capsid binding of cofactors that play a role in viral infection. This insight into GS-6207 activity provides a platform for the rational development of improved long-acting therapies. Science , this issue p. 360

Cellular proteins CPSF6, NUP153 and SEC24C play crucial roles in HIV-1 infection. While weak interactions of short phenylalanine-glycine (FG) containing peptides with isolated capsid hexamers have been characterized, how these cellular factors functionally engage with biologically relevant mature HIV-1 capsid lattices is unknown. Here we show that prion-like low complexity regions (LCRs) enable avid CPSF6, NUP153 and SEC24C binding to capsid lattices. Structural studies revealed that multivalent CPSF6 assembly is mediated by LCR-LCR interactions, which are templated by binding of CPSF6 FG peptides to a subset of hydrophobic capsid pockets positioned along adjoining hexamers. In infected cells, avid CPSF6 LCR-mediated binding to HIV-1 cores is essential for functional virus-host interactions. The investigational drug lenacapavir accesses unoccupied hydrophobic pockets in the complex to potently impair HIV-1 inside the nucleus without displacing the tightly bound cellular cofactor from virus cores. These results establish previously undescribed mechanisms of virus-host interactions and antiviral action.

LEN is an investigational long-acting agent for future HIV-1 treatment regimens. While ongoing clinical trials have highlighted a largely beneficial profile of LEN for the treatment of HIV-1 infected people with limited therapy options, one notable shortcoming is a relatively low barrier of viral resistance to the inhibitor.

A large number of human immunodeficiency virus 1 (HIV-1) integrase (IN) alterations, referred to as class II substitutions, exhibit pleiotropic effects during virus replication. However, the underlying mechanism for the class II phenotype is not known. Here we demonstrate that all tested class II IN substitutions compromised IN-RNA binding in virions by one of the three distinct mechanisms: (i) markedly reducing IN levels thus precluding the formation of IN complexes with viral RNA; (ii) adversely affecting functional IN multimerization and consequently impairing IN binding to viral RNA; and (iii) directly compromising IN-RNA interactions without substantially affecting IN levels or functional IN multimerization. Inhibition of IN-RNA interactions resulted in the mislocalization of viral ribonucleoprotein complexes outside the capsid lattice, which led to premature degradation of the viral genome and IN in target cells. Collectively, our studies uncover causal mechanisms for the class II phenotype and highlight an essential role of IN-RNA interactions for accurate virion maturation.

Allosteric HIV-1 integrase (IN) inhibitors (ALLINIs) are a promising new class of antiretroviral agents that disrupt proper viral maturation by inducing hyper-multimerization of IN. Here we show that lead pyridine-based ALLINI KF116 exhibits striking selectivity for IN tetramers versus lower order protein oligomers. IN structural features that are essential for its functional tetramerization and HIV-1 replication are also critically important for KF116 mediated higher-order IN multimerization. Live cell imaging of single viral particles revealed that KF116 treatment during virion production compromises the tight association of IN with capsid cores during subsequent infection of target cells. We have synthesized the highly active (-)-KF116 enantiomer, which displayed EC₅₀ of ~7 nM against wild type HIV-1 and ~10 fold higher, sub-nM activity against a clinically relevant dolutegravir resistant mutant virus suggesting potential clinical benefits for complementing dolutegravir therapy with pyridine-based ALLINIs.