Abstract 4011: Preferential cytotoxicity of ESK981 in neuroendocrine prostate cancer
Authors: Zheng Yang , Garcia-Rogers Kyle J. , Bao Yi , Mannan Rahul , He Tongchen , Yee Sarah N. , Cheng Caleb , Jiang Xia , Taylor Isabella E. , Cao Xuhong , Wang Yuzhuo , Qiao Yuanyuan , Chinnaiyan Arul M. 
Published: April 2023

Abstract
Introduction: Despite advances in the understanding of neuroendocrine prostate cancer (NEPC) development, effective therapeutic options remain limited. We previously reported that ESK981, a phase I-cleared multi-tyrosine kinase inhibitor (MTKI), exhibited tumor growth inhibitory abilities in multiple preclinical castration resistant prostate cancer (CRPC) and androgen-negative models by blocking the PIKfyve activity and disrupting autophagy. The results suggested that AR-negative prostate cancer have better response to ESK981 induced tumor inhibition than AR+ prostate cancer (Qiao et al, Nature Cancer 2022).
Methods: In order to examine the tumor growth efficacy of ESK981 in NEPC, we assessed the efficacy of ESK981 monotherapy in six NEPC (LTL-352, LTL-331R, LTL-545, and LTL-610 patient-derived xenografts (PDXs); and NCI-H660 cell line-derived xenograft) in vivo models. PDXs were maintained in CB17 SCID male mice and passaged by subcutaneous implantation. When the tumors reached ~100mm3, mice were randomized and treated with either vehicle (Ora-plus) or 30mg/kg ESK981 administered by oral gavage once a day in a five-day per week schedule. Mouse body weight and tumor volume was monitored throughout the treatment schedule. Subcutaneous tumors were collected post five days of treatment for early assessment and long-term treatment for efficacy evaluation, respectively. H&E staining, TUNEL in situ cell death assay, and western blotting were performed to determine the morphology changes and apoptosis after ESK981 treatment. Single cells were isolated from tumors and stained with Zombie live/dead dye, CD45, CD11b and Ly6G fluorescently conjugated antibodies to assess neutrophil population by flow cytometry.
Conclusions: We demonstrated that ESK981 monotherapy is well tolerated in all in vivo models and ESK981 exerted greater cytotoxicity in NEPC than previous evaluated prostate adenocarcinoma by percent tumor growth inhibition. ESK981 also induced dramatic cell deaths in NEPC preclinical models, determined by H&E staining, TUNEL-positive apoptotic tumor cells, and increased protein level of PARP cleavage via western blotting. Moreover, flow cytometry analysis revealed a dramatic increase in the intratumoral neutrophil infiltration after ESK981 treatment in the NEPC preclinical models in a time-dependent manner. NEPC tumors are sensitive to ESK981 monotherapy in vivo, suggesting NEPC patients may be the right population to target with ESK981. Together, ESK981 monotherapy is safe and effective therapy in NEPC preclinical models, and these results will warrant the clinical trial of ESK981 on NEPC patients.
Citation Format: Yang Zheng, Kyle J. Garcia-Rogers, Yi Bao, Rahul Mannan, Tongchen He, Sarah N. Yee, Caleb Cheng, Xia Jiang, Isabella E. Taylor, Xuhong Cao, Yuzhuo Wang, Yuanyuan Qiao, Arul M. Chinnaiyan. Preferential cytotoxicity of ESK981 in neuroendocrine prostate cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4011.