Karyopharm Shares Nosedive On Tough FDA Briefing For Multiple Myeloma Drug

Karyopharm Therapeutics Inc KPTI shares were nosediving on roughly 11 times their average volume Friday following the release of the FDA briefing document prepared for review by the adcom panel that is evaluating the company's new drug application for selinexor.

What Happened

Karyopharm submitted a NDA for a combination of selinexor and dexamethasone that is being evaluated for penta-refractory multiple myeloma.

Selinexor functions by binding with and inhibiting the nuclear export protein XPO1, resulting in the accumulation of tumor suppressor proteins in the cell nucleus.

The NDA was submitted based on Part 2 of the Phase 2b trial dubbed STORM — a multicenter, open-label, single-arm trial.

The FDA accepted the application Oct. 5, according it Priority Review status, which reduces the review period to six months.

Why It's Important

The FDA briefing document released Friday shows that the agency is skeptical about both efficacy and safety.

"Given the limited efficacy and significant toxicity demonstrated in this population, it is unclear whether treatment with selinexor-dexamethasone provides a clinically meaningful benefit that outweighs the risks of treatment," FDA staffers said in the document.

The review document also said it is difficult to isolate the treatment effect of selinexor, as historically high-dose dexamethasone has shown a 10-27-percent response rate to relapsed/refractory multiple myeloma — and selinexor did not show single-agent activity in a Phase 1 trial.

Top-line results released from the STORM study in May showed that Selinexor combo achieved a 25.4-percent overall response rate and a median duration of response of 4.4 months.

The staffers also expressed worries about toxicity, and the overall survival was worse in the selinexor arm in a study conducted in patients with acute myeloid leukemia, which evaluated selinexor versus physician's choice.