MP46-20 CARMUSTINE AND SELENITE COMBINATION THERAPY EFFECTIVELY INHIBITS CASTRATION RESISTANT PROSTATE CANCER IN PRECLINICAL MODELS

THE JOURNAL OF UROLOGYâ

Vol. 193, No. 4S, Supplement, Sunday, May 17, 2015

e551

MP46-19

MP46-20

MICRODISTRIBUTION OF ALPHA PARTICLE EMITTING RADIUM223 DICHLORIDE IN MODELS OF PROSTATE CANCER BONE METASTASIS

CARMUSTINE AND SELENITE COMBINATION THERAPY EFFECTIVELY INHIBITS CASTRATION RESISTANT PROSTATE CANCER IN PRECLINICAL MODELS

Diane Abou, Baltimore, MD; David Ulmert, New York, NY; Robert Hobbs, Ryan Riddle, Daniel Thorek*, Baltimore, MD

Vijayalakshmi Thamilselvan*, Mani Menon, Sivagnanam Thamilselvan, Detroit, MI

INTRODUCTION AND OBJECTIVES: Radium-223 dichloride (Xofigo, Bayer HealthCare Pharmaceuticals) is a first in class alpha particle emitter producing a survival benefit for patients with late stage bone metastatic castrate resistant prostate cancer (bmCRPC). Dosed at 45 kBq per kg every 4 weeks for 6 total injections, the bone seeking radionuclide delivers 4 high-energy alpha particles across a path length of only several cell diameters. Mechanism of action for the survival benefit is not fully understood, hampering our ability to best utilize this novel therapy. We tested 223Ra in naïve and bone metastatic models of disease, to define the whole body and sub-organ distribution of the radionuclide. Our results shed light on important considerations for pre- and clinical evaluation of 223Ra for personalized radiotherapy. METHODS: Animals were dosed with 45 kBq per kg of clinical grade 223Ra. Whole body distribution was monitored by gamma counting in multiple skeletally-mature murine models. Organ and whole body retention were assessed at 1, 4 and 24 h. Detailed 223Ra microdistribution was assessed by cross-modality imaging of whole body and long bone autoradiography, histochemistry and alpha-camera imaging of whole-mount, undecalcified tissues. Uptake dependence and radiobiological effect of 223Ra on bone morphology were evaluated by 10 mm isotropic resolution mCT (SkyScan). RESULTS: In contrast to previous preclinical work, our distribution studies recapitulate the planar scintigraphy results in man (Carrasquillo et al., EJNMMI, 2013), with 223Ra accumulation observed in bowel, stomach, and spleen. In particular, whole-body autoradiography demonstrated the radioisotope bound to the contents of the digestive organs. Kinetic analysis revealed rapid clearance from the blood, and delayed clearance from kidney and intestine. In the bone, 223 Ra predominantly localized to the growth plates; largely sparing the marrow cavity. In bone metastatic models, including the osteoblastic LNCaP, 223Ra uptake was significantly lower than that in the epiphyseal plate (Figure). CONCLUSIONS: Here we provide greater understanding of the in vivo biological fate of this radiopharmaceutical, with significant implications for enhanced dosing strategies in bmCRPC.

INTRODUCTION AND OBJECTIVES: As of today, docetaxel chemotherapy remains the standard of care for metastatic castration-resistant prostate cancer(CRPC) but it only gives a modest survival advantage. In addition, evidence strongly suggests that the nuclear androgen receptor (AR) and AR variants in CRPC builds resistance to anti-cancer drugs including next-generation therapies such as abiraterone and MDV3100. Therefore, there is an urgent need to develop novel therapies for CRPC. We have previously demonstrated that treatment of carmustine in combination with selenite effectively induced apoptosis in prostate cancer cells (Cancer Manag Res. 2012; 4: 383-95) without causing DNA damage to normal prostate epithelial cells. In this study, we tested whether carmustine and selenite in combination inhibits growth and survival of CRPC in cell culture and xenograft model and whether this response is mediated by down regulating AR full length and AR variants. METHODS: CRPC (22Rv1 and PC-3) and normal prostate epithelial cell lines were used to study the efficacy of carmustine and selenite in combination. Cell viability and cell death were measured by MTT assay and ELISA respectively. Protein expression levels of prostate specific antigen (PSA), PARP, Phospho-H2A.X, Akt, and AR (full length and variants) in total and subcellular fractions were analyzed by Western blot. An anchorageeindependent growth of tumor cells is estimated by a softeagar colony formation assay. In vivo antitumor efficacy of combination treatment was determined in xenograft models using male athymic nu/nu mice. Drug toxicity was determined as body weight loss. RESULTS: Carmustine and selenite in combination treatment markedly suppressed cell viability and substantially induce cell death, phospho-H2A.X, PARP cleavage in 22Rv1 cells without causing damage to normal prostate epithelial cells. Carmustine and selenite treatment significantly decreased protein expression levels of AR full length, AR variants, PSA, and Akt in 22Rv1 cells. Combination treatment exhibited a strong inhibitory effect on the anchorage-independent growth of both 22Rv1 and PC-3 cells. Combined treatment exhibited a dramatic inhibition of tumor growth in 22Rv1 xenografts without causing toxicity as evidenced by decreased body weight loss. CONCLUSIONS: Carmustine in combination with selenite dramatically inhibited growth and survival of CRPC in cell culture and xenografts. The results of our preclinical studies will likely lead to human clinical trials in the near future and improve quality of life in prostate cancer patients. Source of Funding: Henry Ford Health System-H10062

Source of Funding: This work was supported by the Prostate Cancer Foundation David Koch (DU) and Steve Wynn Young Investigator Awards (DLJT).