Molecule of the Month: Lenacapavir

The AIDS epidemic, which started in the early 1980s, is caused by human immunodeficiency virus (HIV), a retrovirus that attacks the immune system. Although there is currently no cure for HIV, antiretroviral therapy can suppress viral replication when taken consistently, preventing disease progression and transmission and allowing HIV-positive individuals to live long and healthy lives. Maintaining a strict and life-long daily medication regimen, however, can pose a challenge for many people living with HIV, and lapses in adherence can lead to viral proliferation and allow the virus to be transmitted. While the number of new HIV infections has dropped significantly since its peak in the 1990s, the AIDS epidemic persists globally, with an estimated 1.3 million people newly infected with HIV in 2024.

For decades, HIV drug development focused on targeting viral enzymes such as reverse transcriptase, protease, and integrase, or on structural proteins on the viral surface, such as envelope protein. CA protein, which self-assembles to form a conical capsid protein shell around the viral genome, was not widely considered a "druggable" target. Starting in the late 1990s, however, a growing body of scientific studies from HIV researchers described the structure of CA and the capsid shell and showed that viral replication was dependent on the integrity of the capsid. These findings convinced a team at Gilead Sciences to initiate a program to discover and develop a capsid-targeting drug that could complement existing antiretroviral therapies.

Over the next ten years, Gilead scientists iteratively designed, modified, and tested thousands of capsid-binding compounds to optimize drug potency, stability, and bioavailability (some of these compounds are shown in the "Exploring the Structure" section below). The final result was a drug called lenacapavir, a first-in-class capsid inhibitor that was approved for treatment of multidrug-resistant HIV in 2022, and for pre-exposure prophylaxis (PrEP) in 2025. Lenacapavir's remarkably high potency and long half-life in the body allows for twice-yearly injectable dosing that dramatically improves adherence compared with daily oral antiretroviral regimens.

As shown in the illustration on the right, lenacapavir binds to the interface between two adjacent CA subunits (pdb_00006v2f). Studies have shown that lenacapavir is able to disrupt different stages of the HIV life cycle, most notably impacting viral import into the nucleus and subsequent integration of viral DNA into the host genome, as well as the assembly and maturation of newly formed viruses.