Abstract 2877: Profiling of myeloid-derived suppressor cells in Pten-deficient in prostate cancer progression

Myeloid-derived suppressor cells (MDSCs) are a heterogenous population of immature immune cells that expand during cancer and can induce potent immune suppression. These cells play critical roles in supporting tumor growth and progression and their induction has been associated with the inactivation of PTEN. To date, few therapies targeting these cells are available which is partly due to their increasingly complex nature and context-dependent functions. Moreover, there is no clear definition to identify these cells. Enhancing our understanding of this cell population will aid in developing more effective cancer therapies. Here, we used gene expression profiling, flow cytometry, and quantitative immunohistochemistry to characterize tumor-infiltrating and circulating MDSCs in prostate carcinogenesis and progression in transgenic mouse models of prostate cancer driven by the conditional inactivation of Pten and Trp53. Transcriptomic profiling revealed enrichment of various myeloid-derived cell signatures in the early stages of prostate cancer including MDSCs, macrophages, and neutrophils. Flow cytometric analysis confirmed the increased infiltration of CD11b+/Ly6G+ (polymorphonuclear MDSCs (pMDSCs)) and CD11b+/Ly6C+ (monocytic MDSCs (mMDSCs)) cells in prostate tumors. The temporal dynamics of tumor-infiltrating myeloid cells were further profiled and showed that pMDSC and mMDSC abundances were 1.6 and 5.7-fold higher, respectively, in older mice with late-stage locally invasive adenocarcinomas (AdCa) compared to younger mice with early-stage prostatic intraepithelial neoplasia (PIN). In both instances, pMDSCs comprised most of the leukocyte infiltrate, however, mMDSCs tended to be positively correlated with tumor burden in AdCa but not PIN. In peripheral blood, CD44+/CD62L+ immature neutrophils were associated with high tumor burden in aged mice. Treatments targeting the androgen receptor (AR) signaling further exacerbated pMDSC infiltration in tumors and was associated with resistance to second androgen receptor-targeted agent (ARTA) therapy in a model of castration resistant prostate cancer. Our findings indicate that MDSCs are a prominent population in Pten-null prostate cancer and are implicated with resistance to prostate cancer treatment. MDSCs constitute a potentially targetable population and these models serve as viable platforms to further investigate their biological activity and further evaluate novel MDSC-directed therapies. Citation Format: Marco A. De Velasco, Yurie Kura, Noriko Sako, Naomi Ando, Kazuko Sakai, Eri Banno, Shogo Adomi, Mitsuhisa Nishimoto, Takafumi Minami, Yasunori Mori, Kazutoshi Fujita, Masahiro Nozawa Nozawa, Kazuhiro Yoshimura, Kazuto Nishio, Hirotsugu Uemura. Profiling of myeloid-derived suppressor cells in Pten-deficient in prostate cancer progression [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 2877.