Salarius blood cancer study partially halted after serious adverse event

Shares of Salarius Pharmaceuticals dropped significantly by up to 26% on Thursday after the company announced that the FDA had placed a partial clinical hold on its primary drug candidate, seclidemstat (SP-2577). Seclidemstat, an oral LSD1 inhibitor, is currently undergoing early-stage trials for both haematological and solid tumors.

In a regulatory filing in the United States on Thursday, Salarius disclosed that researchers at MD Anderson Cancer Center (MDACC) had informed them about a "serious and unexpected Grade 4 adverse event" in a patient participating in an MDACC-sponsored trial. The trial is assessing the combination of seclidemstat and azacitidine for adult patients suffering from myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML). Due to the partial hold, no new patients can be enrolled in the study, although those already enrolled and benefiting from the treatment may continue with the study procedures.

Salarius stated that it will assist MDACC researchers in evaluating the available data and responding to FDA inquiries. However, the company did not provide specific details regarding the nature of the Grade 4 adverse event. According to the National Cancer Institute's classification, a Grade 4 adverse event typically refers to life-threatening or severely disabling side effects.

This issue arose just weeks after Salarius presented data on seclidemstat at the European Hematology Association (EHA) annual meeting. During the EHA meeting, the Phase I/II dose-escalation study of seclidemstat reported an overall response rate of 43% among 14 patients, primarily those with higher-risk MDS and CMML who had previously failed or relapsed after undergoing hypomethylating agent therapy. The study indicated a median overall survival of 18.5 months and a median event-free survival of 7.2 months.

At the time of the data presentation, the chair of the board, William McVicar, expressed optimism about the preliminary results. He stated, "We are encouraged by these promising results at this early stage of the study when seclidemstat is combined with azacitidine at doses below what we believe will be the recommended Phase II dose."

In addition to the trials for MDS and CMML, seclidemstat is also being tested in a Phase I/II company-sponsored study focused on Ewing sarcoma.