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Abstract 5639: NT219, a novel dual inhibitor of STAT3 and IRS1/2, demonstrates anti-tumor activity with and without cetuximab in pembrolizumab-resistant head and neck cancer PDX models

Background: Pembrolizumab with chemotherapy is approved as first line therapy for recurrent and metastatic (R/M) head and neck squamous cell carcinoma (HNSCC). Patients refractory to this regimen are often treated with cetuximab. Historically, cetuximab monotherapy resulted in a median response rate of ~13% and an overall survival of ~6 months in patients with platinum-resistant R/M HNSCC. Better therapies for this population are therefore highly warranted. Insulin Receptor Substrate 1 and 2 (IRS1/2) and STAT3 are major signaling junctions regulated by various oncogenes and altered during epithelial-to-mesenchymal transition and drug resistance. Feedback activation of STAT3 and IGF1R/IRS plays a prominent role in mediating drug resistance to EGFR blockers. STAT3 has also been demonstrated to play an active role in tumor9s immune evasion. NT219 is a novel small molecule dual inhibitor of IRS1/2 and STAT3. The purpose of this study was to evaluate NT219 anti-tumor activity with and without cetuximab in pembrolizumab-resistant head and neck cancer PDX models. Methods: Mice were inoculated with biopsies from naive or platinum and anti-PD1 treated head and neck cancer patients. PBMCs or CD34+ cells from the same patient from whom the biopsy was obtained, were injected to allow immune system involvement in the anti-tumoral effect. Immunoblotting, immunohistochemistry and FACS analyses were used to assess the pharmacodynamic effect of NT219 and to explore mechanism of action. Results: HNSCC cells treated with NT219 demonstrated elimination of IRS1/2 and dephosphorylation of STAT3. A short exposure to NT219 induced prolonged inhibition of both IRS and STAT3 and resulted in cancer cell apoptosis. In PDX models of the head and neck cancer, NT219 induced tumor growth inhibition and regression as a monotherapy (3/6), and in combination with cetuximab or pembrolizumab (5/6), respectively. Of particular interest was a model, which originated from a biopsy of R/M HNSCC patient previously treated and progressed on radiation, various chemotherapies, and pembrolizumab, where autologous PBMC9s were injected. Administration of NT219 as a monotherapy resulted in tumor growth inhibition (TGI) of 69% (p-value=0.017). In combination with cetuximab, NT219 induced regression of all tumors. While cetuximab alone demonstrated modest TGI (17%), the addition of NT219 showed synergistic effect and complete TGI (p-value=0.001). Similar results were obtained in a repeated experiment where CD34+ cells were used. Conclusion: NT219 induced tumor regression of R/M HNSCC and sensitized resistant tumors to cetuximab and pembrolizumab. The unique mechanism of NT219, targeting two central mechanisms involved in cancer drug resistance, supports further clinical development of NT219 which may present an attractive 2nd and 3rd line therapy. Citation Format: Hadas Reuveni, Lana Kupershmidt, Emmanuelle Merquiol, Galia Blum, Ohad Ronen, Izhak Haviv. NT219, a novel dual inhibitor of STAT3 and IRS1/2, demonstrates anti-tumor activity with and without cetuximab in pembrolizumab-resistant head and neck cancer PDX models [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5639.