Oncternal Therapeutics Announces Opening of Phase 1b Expansion Cohort of Clinical Trial of TK216, Targeted ETS Inhibitor, in Patients with Ewing Sarcoma

Oncternal Therapeutics, Inc. (Nasdaq: ONCT), a clinical-stage biopharmaceutical company focused on the development of novel oncology therapies, today announced that it has opened for enrollment a Phase 1b expansion cohort of its ongoing clinical trial evaluating TK216, a first-in-class, targeted, investigational small-molecule inhibitor of the E26 transformation-specific (ETS) family of oncoproteins, in patients with relapsed or refractory Ewing sarcoma.

The decision to open an expansion cohort was based on favorable interim results from the dose-finding cohort of the trial, including a deep and sustained clinical response reported for one of the patients treated at the current, highest exposure dose regimen, who is without evidence of Ewing sarcoma after more than eight months on study and has tolerated treatments with TK216, alone and in combination with vincristine, well. TK216 has been generally well tolerated in this trial. Dose limiting toxicities consisted of transient and manageable myelosuppression, primarily neutropenia.

The expansion cohort will further evaluate the recommended Phase 2 dose regimen of TK216 (200 mg/m²/day for 14 days) in combination with vincristine and is anticipated to enroll approximately 18 patients with relapsed or refractory Ewing sarcoma.

“We are encouraged by the initial clinical activity demonstrated by TK216 in the dose-finding portion of this clinical trial in patients with relapsed/refractory Ewing sarcoma and look forward to further evaluating the recommended Phase 2 dose regimen of TK216 in a larger number of patients with this devastating disease,” said James Breitmeyer, M.D., Ph.D., Oncternal’s President and CEO. “This first-in-class targeted investigational agent may also be applicable in other malignancies driven by ETS alterations including acute myeloid leukemia (AML) and prostate cancer, which we continue to explore in preclinical studies.”

About TK216

TK216 is an investigational, potentially first-in-class, targeted small-molecule inhibitor of the E26 transformation-specific (ETS) family of oncoproteins including fusion proteins. Tumorigenic fusion proteins involving the EWS protein and an ETS protein can be found in most cases of Ewing sarcoma. ETS-related translocations or overexpression are also found in many other tumors such as prostate cancer and acute myeloid leukemia (AML). TK216 was developed based on discoveries in the laboratory of Jeffrey Toretsky, M.D., at Georgetown Lombardi Comprehensive Cancer Center, who discovered inhibitors of EWS-FLI1 using a novel chemical screening assay. In preclinical models, TK216 was observed to bind to EWS-FLI1, blocking the interaction between this fusion protein and other transcriptome proteins such as RNA helicase A, leading to tumor cell apoptosis and inhibiting tumor growth in animal models. The U.S. Food and Drug Administration (FDA) has granted Orphan Designation and Fast Track designation to TK216 for the treatment of Ewing sarcoma. TK216 is an investigational medication that has not been approved by the FDA for any indication.