Abstract 5830: Senolytic drug ABT-263 enhances cisplatin- and TIL-induced cell death in vitro but has limited in vivo activity in preclinical models of head and neck cancer
Authors: Hong Youji , Gunti Sreenivasulu , Robbins Yvette , Schmitt Nicole C. 
Published: September 2020

Abstract
Background/Objectives: Cisplatin and other cytotoxic chemotherapy drugs may induce senescence, rather than cell death, at sublethal doses. We hypothesized that the senolytic drug ABT-263 (navitoclax) might enhance cisplatin cytotoxicity and anti-tumor immunity in preclinical models of head and neck squamous cell carcinoma (HNSCC).
Methods/Results: When human HNSCC cell lines were treated with sublethal doses of cisplatin for 72 hours, they expressed increased levels of senescence markers p16 and beta-galactosidase. In additional experiments, cells were rendered senescent with cisplatin and then treated for another 72 hours with navitoclax, which enhanced cisplatin-induced cell death. Three different cisplatin-sensitive syngeneic mouse models were then used to investigate whether the addition of navitoclax can enhance cisplatin-induced tumor cell death in vivo. Mice were treated with weekly cycles consisting of cisplatin on day 1 (5-6 mg/kg IP) followed by navitoclax on days 3, 4, and 5 (100 mg/kg, OG). The addition of navitoclax caused an early, very slight improvement in tumor growth delay in the TC-1 model, but not in the MEER or MOC1 models.
We next investigated whether navitoclax might enhance the anti-tumor immune effects of cisplatin and/or tumor infiltrating leukocytes (TIL) ex vivo. Naive tumors were harvested and TIL were cultured with IL-2 for 10-14 days, then sorted. Murine tumor cells were then cultured with cisplatin, navitoclax, and/or TIL. In the TC-1 and MOC1 models, but not in the MEER model, navitoclax modestly enhanced tumor-cell killing by TIL. Tumor cell killing was greatest with cisplatin, navitoclax, and TIL in combination. We then investigated whether navitoclax might enhance the anti-tumor activity of cisplatin and anti-PD-1 in vivo. With twice-weekly anti-PD-1 antibody alone or added to the cisplatin and/or navitoclax in the TC-1 model, no additional anti-tumor activity was noted; flow cytometry of naïve TC-1 tumors showed extremely low numbers of CD8+ T cells as a possible explanation. Similar experiments in the MOC1 model, along with mechanistic experiments to investigate resistance to navitoclax in vivo, are in progress.
Conclusions: Navitoclax enhances cisplatin-induced death of human HNSCC cells in vitro and enhances the killing of murine tumor cells when cultured with TIL ex vivo. However, in multiple syngeneic mouse models, navitoclax failed to enhance anti-tumor activity of cisplatin or anti-PD-1 checkpoint blockade. Possible mechanisms of navitoclax resistance in vivo may include enhanced trafficking of immunosuppressive cells to the tumor microenvironment following secretion of senescence-associated cytokines by cisplatin-treated tumor cells.
Supported by NIDCD intramural project number ZIA-DC000090.
Citation Format: Youji Hong, Sreenivasulu Gunti, Yvette Robbins, Nicole C. Schmitt. Senolytic drug ABT-263 enhances cisplatin- and TIL-induced cell death in vitro but has limited in vivo activity in preclinical models of head and neck cancer [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 5830.