FDA Extends Review of Selinexor Application for Myeloma

Sharon Shacham, PhD, MBA

Sharon Shacham, PhD, MBA

Following a recommendation from the Oncologic Drugs Advisory Committee (ODAC) against the accelerated approval of selinexor for the treatment of patients with penta-refractory multiple myeloma, the FDA has added 3 months to the review period for the new drug application (NDA), making the new action date July 6, 2019.

The NDA was submitted by Karyopharm Therapeutics, Inc, the manufacturer of the XPO1 (CRM1) inhibitor, seeking an accelerated approval of selinexor for patients with myeloma who have received ≥3 prior lines of therapy and whose disease is refractory to at least 1 proteasome inhibitor, 1 immunomodulatory agent, and 1 CD38-targeted antibody, and to their most recent treatment. Under the FDA’s priority review program, the original action date for the NDA had been set for April 6, 2019.

Following the ODAC meeting, the FDA, which is not required to follow the ODAC recommendation, requested further information form Karyopharm as an amendment to the NDA.

"We look forward to the continued collaboration with FDA in trying to meet the needs of patients with relapsed refractory multiple myeloma," Sharon Shacham, PhD, MBA, founder, president and chief scientific officer of Karyopharm, said in a statement.

The NDA is based on Part 2 of the phase IIb STORM study. Findings from the trial presented at the 2018 ASH annual meeting showed that the combination of selinexor and dexamethasone elicited a 26.2% overall response rate (ORR) and an 8.6-month median overall survival (OS).¹

However, ODAC panel members expressed several concerns about the NDA during the February meeting. First, STORM was a single-arm combination trial and a previous phase I study had not demonstrated strong single-agent activity with selinexor. Thus, isolating the specific impact of selinexor is difficult. Additionally, there was significant toxicity with selinexor in the STORM trial, including treatment-emergent adverse events (TEAEs), serious adverse events (SAEs), and TEAEs that resulted in patient deaths.

The panel members expressed their hope that the phase III BOSTON trial (NCT03110562) will allow the FDA to make a more informed decision on selinexor. The open-label trial is evaluating the addition of selinexor to bortezomib (Velcade) and low-dose dexamethasone versus bortezomib and low-dose dexamethasone alone in patients with relapsed/refractory multiple myeloma who have received 1 to 3 prior anti—multiple myeloma regimens.

In the multicenter STORM trial, 122 patients with penta-refractory multiple myeloma were enrolled, 85 of whom were treated per-protocol. The median patient age was 65 years (range, 40-85). Patients were treated with 80 mg of oral selinexor plus 20 mg of oral dexamethasone twice weekly until disease progression. The primary endpoint was ORR; secondary endpoints included duration of response and clinical benefit rate.

To be eligible for enrollment, patients had to have received prior treatment with bortezomib (Velcade), carfilzomib (Kyprolis), lenalidomide (Revlimid), pomalidomide (Pomalyst), daratumumab (Darzalex), an alkylator, and glucocorticoids. Those with smoldering multiple myeloma, plasma cell leukemia, systemic amyloid light chain amyloidosis, and central nervous system myeloma were excluded.

In the study, patients had undergone a median of 7 prior treatments (range, 3-18), and all were refractory to proteasome inhibitor/immunomodulatory drugs/daratumumab/glucocorticoid. Additionally, 96% of patients were refractory to carfilzomib/pomalidomide/daratumumab, 84% had undergone stem cell transplant, and 28% had undergone ≥2 transplants.

Additional updated results of part 2 of the trial, which were presented during the 2018 ASH Annual Meeting, showed that the 26.2% ORR included a 19.7% very good partial response rate (VGPR) and a 6.5% ≥VGPR. This included 2 patients with stringent complete responses, with minimum residual disease (MRD) negativity at a level of 10-6 in 1 patient and 10-4 in the second patient. Additionally, 2 patients who progressed on chimeric antigen receptor T-cell therapy achieved a partial response.

The median time to response was 1 month (range, 1-14 weeks) and the median duration of response was 4.4 months. Of the evaluable patients, 71% experienced a reduction in the M-protein. Response rates were similar, regardless of the patient’s last prior therapy.

The safety population included 123 patients from Part 2 of the STORM trial.²TEAEs occurring in ≥20% of patients included anemia (65.9%), leukopenia (30.9%), neutropenia (38.2%), thrombocytopenia (71.5%), constipation (22%), diarrhea (42.3%), nausea (69.9%), vomiting (37.4%), fatigue (72.4%), weight decreased (48.8%), decreased appetite (53.7%), hyponatremia (35%), and dyspnea (21.1%).

Almost a third (28.5%) of patients discontinued study treatment due to a TEAE and 88.6% of patients needed ≥1 dose modification due to a TEAE. There were 23 patient deaths that occurred within 30 days of study treatment. Of these deaths, 10 were due to a fatal TEAE and 13 were due to disease progression.

Of the 23 deaths that occurred on or within 30 days of study treatment in Part 2 of STORM, 13 (10.6%) were due to disease progression, and 10 (8.1%) were due to a fatal TEAE.

References:

1. Chari A, Vogl DT, Dimopoulos MA, et al. Results of the pivotal STORM study (Part 2) in penta-refractory multiple myeloma (MM): deep and durable responses with oral selinexor plus low dose dexamethasone in patients with penta-refractory MM. In: Proceedings from the 2018 ASH Annual Meeting; Dec. 1-4, 2018; San Diego, CA. Abstract 598.
2. FDA. Draft Questions for the February 26, 2019 Meeting of the Oncologic Drugs Advisory Committee (ODAC). Accessed February 26, 2019. https://bit.ly/2XnqwpW.

In February, however, the FDA’s ODAC voted 8 to 5 against accelerated approval of the NDA, recommending delaying a decision on the drug until results are available from the pivotal phase III BOSTON trial.