Abstract 4850: The relevance of using proper preclinical models when developing therapeutics for localized or bone metastatic prostate cancer

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Abstract Early stages of prostate cancer are sensitive to androgen deprivation therapy, but upon progression the disease develops to metastatic castration-resistant prostate cancer, where bone is the dominant metastatic site. Despite of recent advances in drug development, the advanced stage is still incurable. Tumor microenvironment in metastatic locations differs from the primary site and may cause resistance to used therapy and modulate tumor properties. Therefore, it is crucial to use proper models in preclinical drug development. Aim of this study was to establish predictive preclinical in vitro and in vivo prostate cancer models that can be used in drug development when targeting cancer cells or tumor microenvironment at different stages. Androgen receptor (AR) positive human prostate cancer cell line LNCaP was used in all studies. In the in vitro assay, the effects of the antiandrogen enzalutamide on viability of LNCaP cells was determined using CellTiter Glo assay in the presence and absence of a synthetic androgen R1881. In two in vivo studies, male NMRI nude mice were used. In a subcutaneous model, part of the mice received dihydrotestosterone (DHT) supplement prior to cancer cell inoculation. In a bone metastasis model, LNCaP cells were inoculated into tibia bone marrow. The mice were randomized to treatment groups based on similar serum PSA levels and cancer-induced changes in bone determined by X-ray imaging at 6 weeks after inoculation of the cancer cells. The mice were treated with 300 kBq/kg of Radium-223 dichloride or vehicle at 6 and 10 weeks. Bone lesions were followed by X-ray imaging during the study. The study was terminated at 12 weeks after inoculation of the cancer cells and the tibias were removed for histological analysis and AR staining. In the in vitro assay, 0.1 and 0.01 nM R1881 increased LNCaP cell viability, and enzalutamide reduced cell viability in the presence of R1881 compared to the group with only R1881. In the subcutaneous model, tumors formed within 2-3 weeks after inoculation and the maximum tumor volume was reached within 10-12 weeks. LNCaP tumors grew in NMRI nude mice without DHT supplement, but DHT supplement supported tumor growth. In the bone metastasis model, LNCaP tumors induced osteoblastic-mixed bone lesions without additional androgen supplement, and immunohistochemical staining demonstrated strong AR expression. Radium-223 dichloride reduced the progression of tumor-induced bone lesions, decreased serum PSA levels, and decreased tumor area analyzed by histology. This study showcases relevant models that can be used at different phases of preclinical drug development when evaluating efficacy or safety of new therapeutics as mono- or combination therapies. The choice of a preclinical model and key readouts should be carefully selected based on whether developing therapeutics for localized or metastatic prostate cancer. Citation Format: Tiina E. Kähkönen, Jenni H.E. Mäki-Jouppila, Mari I. Suominen, Jussi M. Halleen, Jenni Bernoulli. The relevance of using proper preclinical models when developing therapeutics for localized or bone metastatic prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4850.