Abstract 2297: Profound anti-tumor efficacy of dual CDK7 and PD1 blockade in novel syngeneic prostate cancer models
Authors: Wise David , Pereira Luiza Doro , Wu Jiansheng , Febles Victor R. Adorno , Melamed Jonathan , Deng Fang-Ming , Zhang Hua , Wong Kwok-Kin 
Published: June 2022

Abstract
Background: Anti-PD1 immune checkpoint blockade (ICB) has largely failed as a monotherapy for metastatic prostate cancer likely due to inadequate tumor neoantigen load and inadequate T cell filtration (TILs). Strategies to increase TILs that can be tested in novel syngeneic mouse models are needed in order to fulfill this critical medical need. CDK7 is a major regulator of the cell cycle that is under investigation as a novel therapeutic target. CDK7 inhibition can trigger robust anti-tumor immunity by causing genomic instability and DNA damage in lung cancer mouse models. Herein, we characterize our novel syngeneic mouse models and report on the anti-tumor activity of CDK7 alone and in combination with anti-PD1 ICB as an immunotherapeutic strategy.
Methods: We generated two models of prostate cancer organoids and syngeneic mouse models. APC and PTEN are tumor suppressor genes commonly lost in metastatic prostate cancer and are emerging as a putative mechanism of resistance to immunotherapy. The MPA and MPP models were established by ex-vivo Lenti-Cas9-sgRNA knock-out of APC or PTEN from the prostate organoids grown in 3D cultures established from the prostate of a MYCT/TP53-/- GEMM.
Results: Organoids from the MPA and MPP models form orthotopic high grade prostate adenocarcinoma from 2 to 3 weeks post-implantation and spontaneously develop lung metastases 10-12 weeks after orthotopic implantation. In addition, the MPA model developed immediate castration resistance and neuroendocrine transformation following hormone deprivation in vivo. By contrast, the MPP tumors significantly regressed after in vivo androgen deprivation. Baseline immunoprofiling of the MPA and MPP orthotopic tumors showed increased infiltration from monocytic MDSCs and expression of T cell exhaustion markers. Treatment of the MPA and MPP orthotopic models with YKL-5-124, a CDK7 inhibitor, led to substantial in vivo tumor growth inhibition, which was further augmented by the addition of anti-PD-1 ICB. Immunoprofiling of tumors treated with combined YKL-5-124 and PD-1 blockade showed activation of CD4+ and CD8+ T cells, and a decrease in the Treg, B cell and NK cell population.
Conclusions: The MPA and MPP orthotopic models recapitulate the biology and immune suppressive microenvironment of advanced prostate cancer and provide useful tools for immunotherapy drug development. Combination of CDK7 inhibition with anti-PD-1 blockade profoundly inhibited in vivo orthotopic tumor growth in both MPA and MPP model, providing a rationale for exploring CDK7 in combination with PD-1 checkpoint immunotherapy as a novel therapeutical strategy for advanced prostate cancer.
Funding Acknowledgements: DRW is funded through 2018YI2295 Prostate Cancer Foundation Young Investigator Award and PC160944 Department of Defense Physician Research Career Development Award.
Citation Format: David Wise, Luiza Doro Pereira, Jiansheng Wu, Victor R. Adorno Febles, Jonathan Melamed, Fang-Ming Deng, Hua Zhang, Kwok-Kin Wong. Profound anti-tumor efficacy of dual CDK7 and PD1 blockade in novel syngeneic prostate cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2297.