A combination of Viagra and Plerixafor, both clinically approved drugs, could improve the efficacy of bone marrow stem cell transplants.

Haemopoietic Stem cell transplants are life-saving treatments for a range of blood cancers, including lymphoma and leukaemia. The cells can differentiate into all types of blood cells to replace the abnormal cancer cells and restore blood and immune function.

The bone marrow stem cells are extracted using a long needle drilled into the hip of the donor. However, newly developed drugs can instead stimulate the bone marrow cells to leave the bone marrow and enter the bloodstream, where they can be extracted much less invasively. As these drugs come with significant side-effects for the donor, new efforts to develop alternative therapies are ongoing.

Although now approved as an erectile dysfunction drug, Viagra was originally intended as a therapy for the heart disease angina because it causes vasodilation, the widening of the blood vessels. As previous experiments indicated that increased vascular permeability could encourage the movement of stem cells from the bone marrow into the blood, Viagra was considered as a promising drug candidate to initiate stem cell migration.

However, when Viagra was dosed to mice it failed to induce substantial migration of marrow cells into the blood. When it was combined with Plerixafor there was a 7.5 fold increase in migration, with the blood stem cell levels returning to baseline 4 hours after treatment. Three days of oral Viagra and a single injection of Plerixafor was found to induce the best results; with an 8.4 fold increase in stem cell migration.

The stem cells harvested from the mice blood after they were treated with Viagra and Plerixafor were implanted into recipient mice. The stem cells were able to differentiate and restore blood function and maintained significant longevity. The additional advantage of using Viagra and Plerixafor is that they are already both clinically approved; their safety and side-effects are well understood and it easier to get regulatory approval for new treatments using existing drugs. Known as drug repurposing, this phenomenon enables existing drugs to be applied to new functions, avoiding the lengthy and costly drug discovery process.

Making bone marrow donation a less invasive and safer process will likely encourage more people to donate.

To find out more about becoming a stem cell donor, visit the Anthony Nolan website here