TK216, a Novel, Small Molecule Inhibitor of the ETS-Family of Transcription Factors, Displays Anti-Tumor Activity in AML and DLBCL
Authors: Jessen Katayoun , Moseley Eric , Chung Elaine Yee Lin , Otuski Lauren , Tarantelli Chiara , Gaudio Eugenio , Breitmeyer James , Freddo James , Toretsky Jeffrey , Bertoni Francesco , Lannutti Brian J 
Published: October 2019

Abstract
The ETS family of transcription factors is critical for development, differentiation, proliferation, and plays an important role in apoptosis and tissue remodeling. Transcriptional consequences of ETS protein deregulation by overexpression, gene fusion, and modulation by RAS/MAPK and PI3K signaling are linked to alterations in normal cell functions, and lead to increased proliferation, sustained angiogenesis, invasion, and metastasis. Overexpressed ETS proteins and ETS family fusion proteins have been reported in acute myeloid leukemia (AML) and diffuse large B cell lymphoma (DLBCL). In DLBCL, the 11q24.3 region has been identified as a recurrent lesion and a contributor to the pathogenesis of disease, leading to the deregulation of ETS family members, ETS1 and FLI1. Additionally, in AML, the overexpression and translocations of ERG, an ETS family member, has been shown to be associated with poor prognosis in complex or normal karyotypes.
TK216 is a first in class, small molecule that directly binds EWS-FLI1 inhibiting the biological activity of ETS-family transcription factor oncoproteins and is currently under clinical investigation in patients with Ewing sarcoma (NCT02657005). The EWS1-FLI1 is a fusion protein that has been shown to be the driver of Ewing Sarcoma (ES). In preclinical potency models, TK216 blocked the binding between EWS-FLI1 and RNA helicase A, showed a significant transcriptional decrease in COS7 cells transfected with a EWS-FLI1 responsive promoter (EC50 < 100 nM), and inhibited the proliferation of A4573 cells (EWS-FLI1 expressing Ewing sarcoma cell line) at nanomolar concentrations (EC50 < 200 nM). Here we show that TK216 has anti-proliferative effects, causes cell cycle arrest, and induces apoptosis in a panel of AML and DLBCL cell lines with deregulated ETS family members. We report an upregulation of FLI1 and/or ERG ETS family members in 5 of 5 myeloid cell lines evaluated (HL60, Kasumi-1, ML-2, MOLM-13, and MOLM-16). Treatment with TK216 showed a decrease in cellular viability and induced dose-dependentapoptosis of cells at 48 hours. Similarly, in a panel of DLBLC cell lines (TMD8, HBL1, U2932, DOHH2, WSUDLCL2 and OCI-Ly18), TK216 treatment resulted in a decrease in cellular proliferation and an increase in apoptosis. In vivo efficacy studies in xenograft models of DLBCL are underway; the preliminary anti-tumor activity that is being seen is encouraging and consistent with our in vitro findings.
We believe that our findings provide compelling evidence of the utility and potential efficacy of TK216 in the treatment of AML and DLBCL by targeting the aberrant expression and translocations in the ETS-family of transcription factors, which contribute to the pathogenesis of the disease.

Disclosures
Jessen: Oncternal: Employment. Otuski:Oncternal: Employment, Equity Ownership. Breitmeyer:Oncternal: Employment, Equity Ownership. Freddo:Oncternal: Employment, Equity Ownership. Toretsky:Oncternal: Research Funding. Lannutti:Oncternal: Employment, Equity Ownership.