Selinexor for Treatment of Multiple Myeloma

“Looking at next-generation proteasome inhibitors, and next-generation targeted therapies, one that’s of particular interest is called selinexor,” says Dr. Paul Richardson, Director of Clinical Research at Dana-Farber Cancer Institute’s Multiple Myeloma Center. “It’s a completely new class of drugs which stops the ability of a cancer cell to move out tumor suppressor proteins.”

Dr. Richardson explained that the mechanism by which selinexor functions is a bit like parents putting an end to a party that’s growing out of control. “It’s almost as if you’re having a wild and crazy party at home, and you want your parents to leave so you can go even wilder and more crazy,” he said. “Well, this drug stops that, and your parents stay at home. And as a result of that, the party settles down.”

As of July 2019, selinexor, which is also known by its brand name, Xpovio, had been granted accelerated approval (also known as “fast track” approval) by the U.S. Food and Drug Administration (FDA). This means that it has shown enough promise in early-phase clinical trials to convince the FDA to allow it to enter the market for widespread use before the completion of its phase 3 clinical trial–which will test the drug for efficacy on a larger scale for a longer period of time.

The pharmaceutical company sponsoring the drug, Karyopharm, will still need to complete this additional clinical trial phase, but the difference is that patients who could potentially benefit from the drug will be able to access it in the meantime. The drug’s final approval, the FDA has announced, will be contingent on the results of that forthcoming phase 3 clinical trial.

The accelerated FDA approval was granted specifically for patients who have received at least four prior therapies and have demonstrated resistance to multiple drug classes. The FDA also stipulated that selinexor would be given in combination with dexamethasone, which is a type of prescription anti-inflammatory drug.

According to the FDA, the trial that led to the drug’s fast track approval evaluated selinexor in 84 patients with relapsed refractory multiple myeloma. Ultimately, 25.3 percent of the participants responded to the drug, which took four weeks, on average. That response lasted a median of 3.8 months. “The efficacy evaluation was supported by additional information from an ongoing, randomized trial in patients with multiple myeloma,” the FDA wrote in a statement on the drug’s accelerated approval.

Though the early-phase clinical trials have established that selinexor is safe for widespread use, that does not mean that the drug is not free of side effects. Through clinical trials, selinexor has been linked to several side effects, including:

• Less severe:  nausea, vomiting, anorexia, diarrhea, and decreased appetite
• Severe: low white blood cell count and anemia (low red blood cell count)

Despite these side effects, selinexor has the potential to offer an innovate new therapy to treat patients with one of the most stubborn forms of their disease, relapsed refractory multiple myeloma.

Importantly, it is worth noting that the FDA’s accelerated approval comes in the wake of the FDA Oncologic Drugs Advisory Committee’s previous decision to hold off on approval until more information was available about how well it worked relative to its side effects. The decision to grant accelerated approval reverses this, but because the phase 3 trial is not yet complete, it remains to be seen whether the FDA will uphold its approval in the wake of the final results.

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