Karyopharm Therapeutics must finish a randomized phase 3 trial of selinexor plus dexamethasone before the Food and Drug Administration will proceed with a safety and tolerability assessment for the first-in-class multiple myeloma drug.
By an 8-5 vote, the FDA Oncologic Drugs Advisory Committee said that data from STORM 2, Karyopharm’s single-arm phase 2b trial, didn’t sufficiently show that selinexor exerted any significant benefit over dexamethasone alone, used because the company claims it potentiates selinexor’s action.
Committee members also expressed concerns about the drug’s challenging adverse event profile. In STORM Part 2, 60% of patients experienced serious treatment-emergent adverse events and 10 died from them.
“This trial design is not adequate to assess tolerability and efficacy,” and move the drug along, said Christian S. Hinrichs, MD, of the National Cancer Institute. For that to happen, “we’d be looking for several things. We’d be looking for a subset of patients who benefited profoundly, which could be somewhat compelling despite a lower overall response rate. Next we might be looking for durable response, and here we see 4-month responses. And finally, what we look for in a single-arm trial is a really favorable side effect profile, like we see in checkpoint inhibitors. That is clearly not the case with this drug. So, on the basis of both the trial design and the results, I find it hard to conclude that these data allow for an adequate assessment that safety and efficacy are proven.”
The decision came despite the pleas of 15 patients and one patient advocate who said the drug improved clinical status and quality of life, and even extended life beyond what anyone expected. However, several committee members noted that Karyopharm paid for speakers’ travel and that patients who had negative experiences would probably be too sick to attend.
Selinexor is a completely new therapeutic option for relapsed multiple myeloma patients. It is a twice-weekly, oral tablet that inhibits nuclear export protein Exportin 1 (XPO1), which regulates the localization of tumor suppressor proteins and is associated with poor prognosis. Aberrant XPO1 expression causes tumor suppressors to locate away from their targets, allowing tumors to grow. Inhibiting it with selinexor blocks signal transduction pathways, interrupting tumor cell proliferation and inducing apoptosis while sparing normal cells.
