I feel a little awkward talking about Viagra, but that’s what those blue pills are. So what does erectile dysfunction (ED) have to do with cancer immunology? Nothing. But right now there are several clinical trials evaluating this well known pill as a potential cancer drug.
Viagra is just the brand name. The drug’s actual name is sildenafil. Almost all medications have a generic name and a brand name. If you’re a little confused still, read on. Arco, Exxon, Chevron are brand names. Gasoline is the generic name. Breyers, Haagen-Dazs, Ben & Jerry’s are brand names. Ice cream is the generic name.
So how does Viagra fight cancer? Sildenafil reverses one of the mechanisms that cancer cells use to fight off the immune system’s attack. Many cancers are known to contain myeloid-derived suprressor cells (MDSC). These are our own immune cells and have the job of being one of the “brakes” of our immune system. Many cancers have too many of these cells, partly explaining the cancer’s seeming ability to keep growing without interference from our immune system. Well sildenafil somehow chases these immune suppressor cells away and makes the cancer more vulnerable to attack by the “accelerator” part of our immune system. (If you’re wondering why it sounds like I’m talking about how to drive a car, read the post “Accelerator & Brakes“).
There has been a movement of drug repurposing (or drug repositioning). For example, minoxodil was an old drug for treating high blood pressure. It worked but had an unintended side effect of excessive hair growth (hypertrichosis). Unfortunately, many of the affected patients were not bald AND were not Chewbaca wannabes. Well, there were many other drugs to treat hypertension, but no drug to treat baldness. So minoxidil got repurposed (and given the brand name, Rogaine).
If the clinical trials turn out promising, sildanefil will be getting its second repurposing. It originally was developed as a medication for ischemic heart disease. But some interesting side effects were noticed in the patients taking it for their hearts (particularly men), and Viagra was born. Who said you can’t teach an old dog new tricks?