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 different targets within cancer cells.

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

The lipid raft structure is disrupted and mitochondrial energy production decreases. The cancer cell's ability to migrate, invade, and form metastatic colonies decreases accordingly.