FDA Approves Xpovio (selinexor) for the Treatment of Patients with Relapsed or Refractory Multiple Myeloma

Karyopharm Therapeutics Inc. an oncology-focused pharmaceutical company, today announced that the U.S. Food and Drug Administration (FDA) has approved oral Xpovio (selinexor), a nuclear export inhibitor, in combination with dexamethasone for the treatment of adult patients with relapsed or refractory multiple myeloma (RRMM) who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody. This indication is approved under accelerated approval based on response rate. Continued approval for this indication may be contingent upon verification and description of clinical benefit in a confirmatory trial. The ongoing, randomized Phase 3 BOSTON study evaluating selinexor in combination with Velcade® (bortezomib) and low-dose dexamethasone will serve as the confirmatory trial. The FDA’s Accelerated Approval Program was developed to allow for expedited approval of drugs that treat serious conditions and that fill an unmet medical need.  

Karyopharm expects Xpovio to become commercially available in the U.S. on or before July 10, 2019.  A Marketing Authorization Application for selinexor is also currently under review by the European Medicines Agency.

"With today’s accelerated approval of Xpovio by the FDA, patients with heavily pretreated multiple myeloma will now have a new therapeutic option to treat their disease," said Sharon Shacham, PhD, MBA, Founder, President and Chief Scientific Officer of Karyopharm. "Discovering, developing and securing FDA approval for XPOVIO with its novel mechanism of action over the past decade required the dedication of many people, including the patients, caregivers and physicians involved in our clinical trials, along with the many employees at Karyopharm.  We are tremendously grateful for everyone’s contributions to this important milestone, and we look forward to the next stage in our pursuit of improving the lives of patients with cancer."

"The 25.3% response rate seen in the subgroup of 83 patients in the pivotal Phase 2b STORM study that served as the basis for Xpovio's accelerated approval is clinically meaningful and a validated surrogate marker for clinical benefit in our patients with advanced refractory disease," said Sundar Jagannath, MD, Director of the Multiple Myeloma Program, Professor of Medicine (Hematology and Medical Oncology) at Tisch Cancer Institute at Mount Sinai School of Medicine, and principal investigator of the STORM study.

"Despite recent advances in the treatment of multiple myeloma, almost all our patients will develop disease that is resistant to the five most commonly used anti-myeloma drugs we currently have available, and the prognosis for this patient population is particularly poor.  The accelerated approval of oral Xpovio marks an important advance in the treatment paradigm for patients with relapsed refractory multiple myeloma, and in my view, is an important addition to our therapeutic armamentarium," said Dr. Paul Richardson, MD, Clinical Program Leader and Director of Clinical Research, Jerome Lipper Multiple Myeloma Center at the Dana-Farber Cancer Institute.

Michael G. Kauffman, MD, PhD, Chief Executive Officer of Karyopharm, commented, "Having worked on novel drugs in myeloma beginning with Velcade in the year 2000, I have been thrilled to see such exciting progress overall in the field where there are substantial increases in patients’ duration and quality of life.  The accelerated approval of oral Xpovio targeting XPO1 represents the first approval against a new target in myeloma since 2015, and we look forward to advancing the further clinical development of Xpovio."

About the Phase 2b STORM Pivotal Trial

The accelerated FDA approval of Xpovio is based on results from the Phase 2b STORM (Selinexor Treatment of Refractory Myeloma) trial, which was a multicenter, single-arm, open-label study of patients with RRMM. STORM Part 2 included 122 patients with RRMM who had previously received three or more anti-myeloma treatment regimens including an alkylating agent, glucocorticoids, bortezomib, carfilzomib, lenalidomide, pomalidomide, and an anti-CD38 monoclonal antibody; and whose myeloma was documented to be refractory to glucocorticoids, a proteasome inhibitor, an immunomodulatory agent, an anti-CD38 monoclonal antibody, and to the last line of therapy. 

In STORM Part 2, a total of 122 patients were treated with Xpovio (80 mg) in combination with dexamethasone (20 mg) on Days 1 and 3 of every week. Eighty-three patients had RRMM that was documented to be refractory to bortezomib, carfilzomib, lenalidomide, pomalidomide, and daratumumab. Treatment continued until disease progression, death, or unacceptable toxicity.

The major efficacy outcome measure was overall response rate (ORR), as assessed by an Independent Review Committee based on the International Myeloma Working Group (IMWG) Uniform Response Criteria for Multiple Myeloma. The approval of Xpovio was based upon the efficacy and safety in a prespecified subgroup analysis of the 83 patients whose disease was refractory to bortezomib, carfilzomib, lenalidomide, pomalidomide, and daratumumab, as the benefit-risk ratio appeared to be greater in this more heavily pretreated population than in the overall trial population.

For the STORM Part 2 study’s major efficacy outcome measure, the ORR was 25.3% in the subgroup of 83 patients, which included one stringent complete response, no complete responses, four very good partial responses and 16 partial responses.  The median time to first response for these patients was 4 weeks and the median duration of response was 3.8 months. 

Amongst the 202 patients enrolled in STORM Parts 1 and 2 who were treated with Xpovio (80 mg) in combination with dexamethasone (20 mg) on days 1 and 3 weekly, the most common adverse reactions (incidence ≥20%) were thrombocytopenia, fatigue, nausea, anemia, decreased appetite, decreased weight, diarrhea, vomiting, hyponatremia, neutropenia, leukopenia, constipation, dyspnea, and upper respiratory tract infections.  The treatment discontinuation rate due to adverse reactions was 27%; 53% of patients had a reduction in the Xpovio dose, and 65.3% had the dose of Xpovio interrupted. The most frequent adverse reactions requiring permanent discontinuation in 4% or greater of patients who received Xpovio included fatigue, nausea, and thrombocytopenia. The rate of fatal adverse reactions was 8.9%.

About Multiple Myeloma

According to the National Cancer Institute (NCI), multiple myeloma is the second most common cancer of the blood in the U.S. with more than 32,000 new cases each year and over 130,000 patients living with the disease. Despite recent therapeutic advances, there is currently no cure and most patients’ disease will typically progress following treatment with currently available therapies. According to the NCI, nearly 13,000 deaths due to multiple myeloma are expected in the U.S. in 2019.

About Xpovio (selinexor)

Xpovio is a first-in-class, oral Selective Inhibitor of Nuclear Export (SINE) compound. Xpovio functions by selectively binding to and inhibiting the nuclear export protein exportin 1 (XPO1, also called CRM1). XPOVIO blocks the nuclear export of tumor suppressor, growth regulatory and anti-inflammatory proteins, leading to accumulation of these proteins in the nucleus and enhancing their anti-cancer activity in the cell. The forced nuclear retention of these proteins can counteract a multitude of the oncogenic pathways that, unchecked, allow cancer cells with severe DNA damage to continue to grow and divide in an unrestrained fashion. In addition to receiving accelerated FDA approval of Xpovio in July 2019 in combination with dexamethasone for the treatment of adult patients with relapsed refractory multiple myeloma (RRMM) who have received at least four prior therapies and whose disease is refractory to at least two proteasome inhibitors, at least two immunomodulatory agents, and an anti-CD38 monoclonal antibody, Karyopharm has also submitted a Marketing Authorization Application (MAA) to the European Medicines Agency (EMA) with a request for conditional approval of selinexor.  Selinexor is also being studied in patients with relapsed or refractory diffuse large B-cell lymphoma (DLBCL). In 2018, Karyopharm reported positive top-line results from the Phase 2b SADAL study evaluating selinexor in patients with relapsed or refractory DLBCL after at least two prior multi-agent therapies and who are ineligible for transplantation, including high dose chemotherapy with stem cell rescue. Selinexor has received Fast Track designation from the FDA for the patient population evaluated in the SADAL study. Selinexor is also being evaluated in several other mid-and later-phase clinical trials across multiple cancer indications, including in multiple myeloma in a pivotal, randomized Phase 3 study in combination with Velcade® (bortezomib) and low-dose dexamethasone (BOSTON), as a potential backbone therapy in combination with approved therapies (STOMP), in liposarcoma (SEAL), in recurrent gliomas (KING) and in endometrial cancer (SIENDO), among others. Additional Phase 1, Phase 2 and Phase 3 studies are ongoing or currently planned, including multiple studies in combination with approved therapies in a variety of tumor types to further inform Karyopharm's clinical development priorities for selinexor. Additional clinical trial information for selinexor is available at www.clinicaltrials.gov.

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