Abstract 1634: Orthotopic and bone metastasis prostate cancer models using the 22Rv1 cell line

Prostate cancer is the most common cancer in men. Upon diagnosed malignancy the growth of the tumors is androgen driven in a majority of the cases. For that reason, the tumors are treated with androgen deprivation therapy (ADT) to stop or reduce tumor growth. Later, the tumors often become resistant to ADT and at this stage the disease is described as castration-resistant prostate cancer (CRPC). Bone metastasis is one of the hallmark of disease progression. Metastatic disease can be either androgen sensitive or castration resistant (mCRPC) in which the mortality rate is over 50%. Prostate cancer metastases are commonly formed in bones. The 22Rv1 human prostate carcinoma cell line is androgen sensitive and shown to express androgen receptor (AR). The 22Rv1 cells are an invaluable model system to study AR function, the efficacy of existing drugs and to design novel anti-AR therapies that also target non-truncated regions of AR. The aim of this study was to establish predictive orthotopic and intratibial preclinical in vivo prostate cancer models that can be used in drug development when targeting cancer cells and their local environment. Male athymic nude mice (5-6 weeks old) and NOG mice (over 20 weeks old) were used in the study. 2.5 × 105 22Rv1 cells were inoculated orthotopically into the prostate of NOG mice, and 0.5 × 106 cells were inoculated intratibially into the bone marrow cavity of athymic nude mice. 22Rv1 human prostate cancer cells (ATCC) were cultured in RPMI 1640 medium supplemented with 10% iFBS, 2 mM L-Glutamine, 10 mM HEPES, 1 mM sodium pyruvate, 4500 mg/l D-Glucose and P/S. Tumor growth was followed by PSA measurements using Human PSA ELISA assay. In addition, in the intratibial model, tumor-induced bone changes were monitored by X-ray imaging of the hind limbs. Prostates and hind limbs were collected at sacrifice, fixed in 10% NBF, and processed to paraffin blocks for further histological analysis. Sections of prostate were stained with hematoxylin-eosin (HE) and AR. Tumor-bearing and contralateral (healthy) tibias were stained with HE - OrangeG, MGT, TRAP, and AR. For enhanced visualization of tumor models in 3D, we reconstructed the tissue from serial sections using a tailored computational pipeline based on applying a deformable model for corresponding points from adjacent sections. The observed tumor take rate was 100% in both models. Confirmed by IHC, tumors formed in both the orthotopic and intratibial models expressed AR. 22Rv1 cells formed osteoblastic - lytic mixed bone lesions in the intratibial model. Based on lesion areas, randomization of the tumor bearing mice in the intratibial model can be done after 2 weeks from cancer cell inoculation. In conclusion, both presented models are suited to test the anticancer efficacy of new drug candidates. In addition, the intratibial model can be used to test the efficacy of novel drug candidates on prostate cancer cells in bone metastatic microenvironment. Citation Format: Justyna Zdrojewska, Tiina E. Kahkonen, Jenni H. Maki-Jouppila, Masi Valkonen, Pekka Ruusuvuori, Jussi M. Halleen, Jenni Bernoulli. Orthotopic and bone metastasis prostate cancer models using the 22Rv1 cell line [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 1634.