Giving Mice Viagra Has Some Unexpected Benefits

Bone marrow is essential for our survival, but for transplants the stem cells that form new blood cells need to be persuaded to leave the bone. Viagra can help the process, mice studies suggest. Sciencepics/Shutterstock

A combination of drugs could improve the prospects for bone marrow transplants if mice trials are replicated in humans. That’s great news for cancer patients and sufferers of lesser-known diseases, but we’ll admit we’re only reporting it because one of the drugs is much more famous for other sorts of boners.

Our blood cells are made in our bone marrow, without which we can’t survive. Certain cancers are treated by destroying the bone marrow with chemotherapy and replacing it, either with stem cells harvested from the patient’s own marrow prior to treatment, or with cells from a matched donor.

Once, to access these stem cells it was necessary to drill into the bones and scoop some out – deterring all but the most dedicated donors. Today drugs are used that induce some bone marrow stem cells to leave their safe hidey-holes and enter the bloodstream, where they can be collected for storage and transplantation.

Nevertheless, existing drug regimes are themselves painful, have side effects, and sometimes fail altogether, so the search is on for better ones. After noting vascular permeability enhances stem cell migration Professor Camilla Forsberg of the University of California, Santa Cruz proposed combining Plerixafor, already used as a stem cell mobilizer, with the well-known vascular dilator Viagra.

In Stem Cell Reports Forsberg describes giving mice oral Viagra, followed two hours later with a Plerixafor injection. Marrow stem cell availability increased 7.5 times, more than double what Plerixafor alone achieved and nearly matching the best existing treatments. Extending the Viagra dosage improved stem cell availability still further. On transplantation into recipient mice, the cells formed functional and self-sustaining blood cell factories.

The existing most common method for mobilizing bone marrow stem cells (left) compared to the quicker, cheaper, and less painful Viagra/Plerixafor alternative. Smith-Berdan et al./ Stem Cell Reports, 2019

Clinical trials on humans are of course essential, but given that both drugs are already approved and considered safe, this should be a much shorter process than for something completely new. The treatment program would be cheaper and probably much less painful than existing options. Instead of being hard to find, the bone marrow donors may be found to be hard.

Even if Viagra/Plerixafor doesn’t completely replace GCSF, the most widely used stem cell mobilizer, it could be a life-saver for some patients. Gene therapies have been used to treat sickle-cell disease, but GCSF exacerbates the symptoms of this condition which affects the blood cells of millions of people, preventing access to the stem cells to correct their mutations.

"If we can make bone marrow transplants a super safe procedure, there are a lot of other disorders for which it could be life-changing, especially for children. Doctors could provide a one-time treatment for conditions that currently have to be managed over a patient's lifetime," Forsberg said in a statement

It is not recorded whether the study also assisted the lab mice breeding program.

Viagra’s unexpected uses include extending the life of cut flowers and having potential for fighting malaria.

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