April 13 (UPI) -- Drugs that are prescribed to treat erectile dysfuction, including Viagra, Cialis and Levitra, may be tested to treat rare forms of cancer, according to a new study.
Researchers have identified selective phosphodiesterase 5, or PDE5, inhibitors that have the potential to be used in new cancer drug trials. The Repurposing Drugs in Oncology project, an international collaboration between the Anticancer Fund, Belgium and USA-based GlobalCures, published the study Wednesday in the journal Ecancermedicalscience.
The Anticancer Fund has said its mission is to identify cheap and widely available drugs with untapped life-saving potential.
"These low-cost, low-toxicity drugs show potential to be included with current and emerging standard of care treatments in oncology," the researchers wrote. "The combination with immune checkpoint inhibitors or possible use as perioperative therapies are particularly compelling strategies with the potential to positively improve survival outcomes in a relatively short time frame."
The PDE5 inhibitors are a class of drugs that include sildenafil, tadalafil and vardenafil, which have shown a wide range of effectiveness in different cancer types, such as glioblastoma multiforme, a rare disease without much drug help.
"In many respects, sildenafil is the ultimate repurposing success story," Dr. Pan Pantziarka of the Anticancer Fund said in a press release. "It was originally developed for angina, repurposed for erectile dysfunction and then again for pulmonary arterial hypertension, and now it has the potential to be repurposed again as an anti-cancer drug."
These drugs now have generic versions.
"It would be ironic if the key to improving outcomes from some of the most expensive drugs in oncology comes from repurposing some of the cheapest non-oncology drugs," Pantziarka said.
The researchers wrote there is some evidence that drugs not currently licensed for cancer treatment, like including PDE5 inhibitors, can help other drugs improve delivery to brain tumors.
The ReDO recommended larger clinical trials to begin.
Other ReDO project research has shown that other inexpensive, common drugs such as beta-blockers and anti-fungal remedies can be "repurposed" in cancer treatments.
And last month, researchers at the Medical College of Georgia at Augusta University have found that a small, daily dose of Viagra greatly lowered colorectal cancer risk in a test with mice.
Because Viagra relaxes the smooth muscle cells around blood vessels, they more easily fill with blood -- which is how it helps men with erectile dysfunction
It has also be used in premature infants with pulmonary hypertension.