Higher purpose
A boon in the bedroom, Viagra has also been repurposed to treat hypertension. It’s just one example of medicines that can target ailments they weren’t initially intended for.
The little blue pill millions of men take for erectile dysfunction is perhaps the world’s most famous example of successful drug repurposing. In the late 1990s, drug company Pfizer ran clinical trials to test Sildenafil, the active ingredient in what would become Viagra.
They hoped it could be used to treat cardiovascular problems such as hypertension and angina. But the scientists found that patients on the trials developed an erection after receiving the drug. Viagra hit the market in 1998 and became a massive seller for Pfizer and the saviour of many a man’s sex life. But nearly a decade later, it was also approved for treating pulmonary arterial hypertension and sold under the brand name Revatio.
Such stories aren’t uncommon in the area of drug discovery. As Nobel prizewinning Scottish physician Sir James Black once said, “The most fruitful basis for the discovery of a new drug is to start with an old drug.”
But when it comes to treating cancer, repurposing drugs has had very limited success. Many trials have failed to produce compelling results. Cancer is complex and our understanding of cancer biology is patchy, limiting our ability to pick which drugs in our existing pharmacopoeia hold the most promise.
But there are also commercial issues standing in the way. Pharmaceutical companies tend to pursue novel therapies that they can patent and sell exclusively for a 20-year period. Repurposing generic drugs to target an ailment they weren’t initially intended to treat can be difficult to secure a patent for. As such, repurposing efforts receive scant funding from the industry, despite their attractiveness from a cost point of view.
A repurposed drug costs about US$300 million to take to market, compared with US$2-3 billion for an entirely new one. New partnerships between drug companies, universities and not-for-profits have emerged to give repurposing efforts more critical mass. Boston-based charity Reboot Rx is one that’s on the Gillies McIndoe team’s radar.
It is seeking to speed up the drugdevelopment process and raise money to address the “market failure” facing drug repurposing for targeting cancer.
Swee Tan’s work is one tiny part of this growing drug-repurposing effort. “We have to think out of the box,” he says. “We need low-cost treatments that can be available to the people of New Zealand and others around the world.”