Sildenafil blocks PDE5a, an enzyme that breaks down cGMP. Up to this point, the action is identical to erectile dysfunction treatment.

Undecomposed cGMP accumulates inside the cell. While it acts as a relaxation signal in blood vessels, it encounters a different target inside cancer cells.

cGMP binds to the lysosomal cholesterol transporter NPC1. Cholesterol is trapped and cannot exit the lysosome. This is a state similar to Niemann-Pick type C disease.

Lipid raft structures are disrupted and mitochondrial energy production decreases. The cancer cell's ability to migrate, invade, and form metastatic colonies decreases accordingly.