FDA Awards Orphan Drug Designation to SLS009 in AML


The FDA has granted an orphan drug designation to SLS009 for the treatment of patients with acute myeloid leukemia.



The FDA has granted an orphan drug designation to SLS009 (formerly GFH009) for the treatment of patients with acute myeloid leukemia (AML), according to an announcement from SELLAS Life Sciences Group.1

SLS009 is a novel, small-molecule, highly selective CDK9 inhibitor that is currently being evaluated in an open-label, single-arm, multicenter phase 1/2a trial (NCT04588922) in patients with relapsed/refractory AML and other hematologic malignancies.

“We are honored to receive the orphan drug designation from the FDA,” Angelos Stergiou, MD, ScD hc, president and chief executive officer of SELLAS, stated in a press release. “This designation underscores the potential of SLS009 to address a significant unmet medical need for patients with AML. SLS009 is a novel and highly selective CDK9 inhibitor that has already shown a favorable safety profile, strong initial efficacy signals, and evidence of antitumor activity.”

SELLAS previously reported positive data from the phase 1 portion of the trial, which showed that treatment with SLS009 generated clinical activity and demonstrated safety in patients with relapsed/refractory lymphomas.2 Evaluable patients (n = 34) experienced an overall response rate (ORR) of 14.7% with a reduction in tumor burden of up to 62%. Furthermore, 20.6% of patients achieved stable disease, and the disease control rate was 35.3%.

In the ongoing trial, investigators are evaluating SLS009 in patients at least 18 years of age with cytologically or histologically confirmed relapsed/refractory hematologic malignancies, including AML, chronic lymphocytic leukemia/small lymphocytic lymphoma, and lymphoma. Patients with lymphoma must have at least 1 measurable or evaluable lesion per 2014 Lugano response criteria, and at least 2 prior lines of systemic therapy are required. Patients with relapsed/refractory AML being enrolled to group 3 must have relapsed on or been refractory to venetoclax (Venclexta)-based regimens.3

Key exclusion criteria for all patients include bulky disease of at least 10 cm requiring cytoreductive chemotherapy, and the presence of symptomatic central nervous system (CNS) metastases or primary lymphoma, including primary CNS lymphoma, leptomeningeal disease, or spinal cord compression. Additionally, patients with severe cardiovascular disease within 6 months of enrollment are not eligible for the trial.

In the phase 2a portion of the study, patients with relapsed/refractory AML are being treated with SLS009 once per week—at 45 mg or at the recommended phase 2 dose of 60 mg—in combination with azacitidine (Vidaza) and venetoclax.1

The primary end points of the study are safety, tolerability, and efficacy at both the 45-mg and 60-mg dose levels.

“With the support of this orphan drug designation, we look forward to accelerating SLS009 clinical development and bringing new hope to those suffering from this devastating disease,” Stergiou added.

Topline data from the phase 2a study are expected to read out by the end of 2023.


  1. SELLAS receives FDA orphan drug designation for SLS009 for treatment of acute myeloid leukemia. News release. SELLAS. October 11, 2023. Accessed October 11, 2023. https://www.sellaslifesciences.com/investors/news/News-Details/2023/SELLAS-Receives-FDA-Orphan-Drug-Designation-for-SLS009-for-Treatment-of-Acute-Myeloid-Leukemia/default.aspx
  2. SELLAS announces positive topline data in lymphoma cohort from SLS009 phase 1 dose-escalation trial, supporting advancement to phase 2 clinical study; primary and secondary endpoints met. News release. SELLAS Life Sciences Group. September 21, 2023. Accessed October 11, 2023. https://www.sellaslifesciences.com/investors/news/News-Details/2023/SELLAS-Announces-Positive-Topline-Data-in-Lymphoma-Cohort-from-SLS009-Phase-1-Dose-Escalation-Trial
  3. A study of GFH009 in patients with hematologic malignancies. ClinicalTrials.gov. Updated September 1, 2023. Accessed October 11, 2023. https://classic.clinicaltrials.gov/ct2/show/NCT04588922
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