What do Post-It notes and Viagra have in common? They both had strange beginnings, and what was initially considered a failing feature, turned out to be the very feature that made them so successful. When a scientist with 3M set out to make a super-strong adhesive, he failed miserably—the adhesive barely stuck. The story of what happened next varies fromsecretaries using the adhesive-backed strips of paper to affix easily removable notes to their bosses on documents they typed, to someone using them to mark pages in a book. But whatever the story, the qualities that made the adhesive such a failure were the very qualities that made it such a success—it was an adhesive that didn’t stick, at least not for very long. That might not have made it useful for the original intended use, but it made it spectacularly useful for an unintended use.

As for Viagra, the brand name of Sildenfil, it was a drug that was intended to treat hypertension (high blood pressure) and angina (chest pains). It did work for that, but it had a curious side effect—men taking it reported prolonged erections. But what is one man’s side effect, is another man’s happy evening. Patented in 1996 for treatment of hypertension, by 1998 the FDA approved Sildenfil for erectile dysfunction and soon after two other similar drugs for treating erectile dysfunction came along—Cialis and Levitra.
How can they help treat cancer, you ask, and are they safe for women? Yes, they are safe for women and I’ll get to that in a moment, but here’s how they work on your immune system and give you a boost in fighting cancer.
Viagra, Cialis and Levitra are all members of a class of PDE-5 drugs. That means that one of their own “side effects” is that they reduce MDSCs (myeloid-derived suppressor cells), which is exactly what you want if you want your immune system to take on those tumors.
MDSCs are similar to the T regulatory cells we discussed in Chapter 2. Remember how they work as screening agents, determining if something was a friend or foe, and were easily tricked by the clever cancer that pretended to be a friend and belonged in the body? Well, like T regulatory cells, MDSCs also interfere with anti-tumor immunity, and they do so by using L-Arginine metabolism to suppress immunity.17