BACKGROUND: The interaction between prostate cancer cells and osteoblast is essential for the development of bone metastasis. Recently, novel androgen receptor signal inhibitors (ARSi) have been approved for metastatic castration naïve (mCNPC), or non-metastatic castration resistant prostate cancer (nmCRPC), both of which should be pivotal to investigate the association between bone microenvironment and tumor. We established a novel 3D in vitro culture method reflecting bone microenvironment and evaluated the drug susceptibility of ARSi including enzalutamide, apalutamide, darolutamide, and abiraterone (Abi) with/without dutasteride (Duta).

METHODS: GFP-transferred C4-2 (CRPC cell line) and RFP-transferred human osteoblast differentiated from human-mesenchymal stem cell was co-cultured in chitosan nanofiber, a mimicry of 3D scaffold of bone microenvironment, coated culture plate (Cosmo bio Co., LTD). The growth of C4-2 cell was quantified using live-cell imaging and analysis system, Cell3 iMager duos (SCREEN). Abi metabolites including delta-4 abiraterone (D4A) and 3-keto-5-alfa abiraterone in C4-2 cells were measured by ESI-TOF-MS method.

RESULTS: We could non-invasively quantify the sustained growth of C4-2 cells at maximum of 30 days. IC50 of each drugs and combination effect of Abi and Duta was evaluated using this model. Combination treatment synergistically inhibited the growth of C2-4 cells compared with each drug alone. D4A, the strongest anti-proliferative metabolite of Abi under the CRPC-specific backdoor pathway, was detected from the treated C4-2 cell. These results were coincided with the effective cases of pharmacokinetics of Abi metabolites in our ongoing phase II clinical trial of combination therapy of Abi with Duta for CRPC (UMIN000027795). Furthermore, combination of abiraterone and dutasteride was most potent cell growth inhibitor than other ARis tested in this model. This model is applying for international patent (C12N 5/09).

CONCLUSIONS: Our bone microenvironment model is unique and useful to evaluate the new drug susceptibility testing in prostate cancer cells. This model may help in disclose unknown mechanisms from micro- to clinical bone metastasis in prostate cancer.

Citation Format: Masahiro Samoto, Hiroaki Matsumoto, Hiroshi Hirata, Sho Ozawa, Junichi Mori, Ryo Inoue, Seiji Yano, Yoshiaki Yamamoto, Hideyasu Matsuyama. Novel bone microenvironment model of prostate cancer with chitosan fiber matrix and osteoblast in 3D culture [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 321.