First-in-class ETS inhibitor TK216: Translational Biology and Oral Dosage Form Development

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TK216 is an investigational, potentially first-in-class, targeted small molecule that is designed to specifically inhibit the biological activity of the ETS family of oncoproteins. Tumorigenic gene fusions involving ETS factors are frequently found in tumors, such as Ewing sarcoma (ES) as well as childhood leukemias and prostate cancer. ETS factors are also often overexpressed in other tumors, such as neuroblastoma, lymphomas, acute myeloid leukemia and high-grade glioma brain tumors. Based on work in the laboratory of our collaborator Jeffrey Toretsky (Georgetown University), Oncternal Therapeutics, Inc. created the novel ETS family inhibitor TK216. In preclinical models, TK216 inhibits the interaction between ETS family members and RNA helicase A (RHA) leading to transcriptional changes and apoptosis. Oncternal is currently enrolling patients with relapsed or refractory ES, a rare pediatric cancer that has historically been very challenging to treat effectively, in a Phase 1 clinical trial. Interim analysis has shown TK216 to be generally well-tolerated, with dose limiting toxicity of manageable myelosuppression and no obvious off-target toxicity. Notably, the current dosing regimen demonstrated early exciting evidence of activity in seven evaluable patients with 1 surgical complete response (CR) and 1 very good partial response (PR; 90% tumor shrinkage). TK216 has received Orphan Drug and Fast Track Designations from the U.S. Food and Drug Administration (FDA) for treatment of relapsed/refractory ES. ES is driven by an EWS-ETS fusion protein, which occurs through a reciprocal chromosomal translocation. The EWS-ETS fusion protein was considered ‘undruggable’. However, the mechanism of EWS-FLI1 is driven by its partnering with other proteins, thus TK216, similar to YK-4-279, targets the EWS-ETS by disrupting or preventing protein-protein interactions (PPI). Given the significant need for an EWS-ETS targeted therapy, the clinical development is being accelerated by administering TK216 as a continuous infusion via ambulatory pump over 14 days. This allowed relapsed ES patients to gain access and provide proof of efficacy. While this current form of administration is acceptable to patients suffering from cancers with few or no other treatment options available, it poses a significant inconvenience hurdle for ES patients as well as effectively prevents its clinical application in other unmet medical needs driven by ETS- dysregulation. Therefore, we propose 2 main objectives for our proposal to support the TK216-based therapies: a) delineation of the activity spectrum of TK216 against members of the ETS transcription factor family and b) development an oral dosing form of TK216, including GLP pharmacology/toxicology studies and GMP manufacturing. Our intent regarding ES is to offer a more convenient dosing form for ES patients and to allow for expansion of TK216 studies into other oncology indications. The overarching goal of this project is to complete the development of an oral formulation and obtain preclinical data supportive of Investigational New-Drug (IND) applications for indication expansion.