Lopinavir

The HIV lifecycle is comprised of 3 distinct stages: assembly, involving creation and packaging of essential viral components; budding, wherein the viral particle crosses the host cell plasma membrane and forms a lipid envelope; and maturation, wherein the viral particle alters its structure and becomes infectious. At the center of this lifecycle is the Gag polyprotein which, along with the products of its proteolysis, coordinate these stages and function as the major structural proteins of the virus. The HIV-1 protease enzyme, a dimeric aspartic protease, is the enzyme responsible for cleaving the Gag polyprotein and thus plays a critical role in many aspects of the HIV viral lifecycle.

Lopinavir is an inhibitor of the HIV-1 protease enzyme. Its design is based on the "peptidomimetic" principle, wherein the molecule contains a hydroxyethylene scaffold which mimics the normal peptide linkage (cleaved by HIV protease) but which itself cannot be cleaved. By preventing HIV-1 protease activity, and thus the proteolysis of the Gag polyprotein, lopinavir results in the production of immature, non-infectious viral particles.