Abstract LB-105: Radium-223 dichloride monotherapy and combination therapy with zoledronic acid or doxorubicin improve survival in a mouse model of breast cancer bone metastasis.

Abstract

Abstract Breast cancer metastasis to bone results in significant morbidity and poor prognosis. Radium-223 dichloride is an alpha-emitting calcium mimetic that localizes to bone and provides targeted radiation therapy. A phase III clinical study on prostate cancer patients with bone metastases showed that radium-223 dichloride improved overall survival (ALSYMPCA, Parker et al. ECCO/ESMO 2011). We have previously reported that radium-223 decreases osteolysis and tumor burden in bone in a mouse model of breast cancer bone metastasis in preventive and micro-metastatic settings (Suominen et al. AACR Annual Meeting 2012), as well as, in mice with established bone metastases (Suominen et al. AACR Annual Meeting 2011). Here, we investigated the effects of radium-223 dichloride monotherapy compared to and in combination with either doxorubicin or zoledronic acid on survival in a mouse model of established breast cancer bone metastasis. Human MDA-MB-231(SA)/GFP cells were inoculated intracardially into nude mice, and 15 days later, a single dose of vehicle, radium-223 dichloride (300 kBq/kg, iv injection) and/or zoledronic acid (0.1 mg/kg, sc injection) was administered. Doxorubicin (5 mg/kg, ip injection) was administered once weekly. Radium-223 dichloride monotherapy extended time to sacrifice (P = 0.039), unlike doxorubicin or zoledronic acid monotherapy which did not improve survival as compared to the vehicle group. Radium-223 dichloride in combination with zoledronic acid (P = 0.004) or doxorubicin (P < 0.001) also extended time to sacrifice as compared to the vehicle but did not provide additional survival benefit as compared to the radium-223 dichloride monotherapy. Histological examination revealed that radium-223 dichloride treatment induced tumor cell necrosis in bone metastases. Therefore, the effect of radium-223 dichloride in inducing double-strand breaks in cancer cells was evaluated by immunohistochemical staining of γ-H2AX molecules. A 3-fold increase in the number of tumor cells with double-strand breaks in the radium-223 dichloride-treated as compared to the vehicle control mice was observed (P < 0.001). This finding supports our previous observations that radium-223 dichloride has an effect on both tumor cells and osteoclasts. In conclusion, radium-223 dichloride therapy alone or in combination with doxorubicin or zoledronic acid increases survival in breast cancer bone metastasis mouse model via dual action by targeting tumor growth and osteolysis, both important players in the destructive vicious cycle of bone metastasis. Our findings strongly support the development of radium-223 dichloride for the treatment of patients with bone metastatic breast cancer. Citation Format: Mari I. Suominen, Jukka P. Rissanen, Rami Kakonen, Katja M. Fagerlund, Esa Alhoniemi, Dominik Mumberg, Karl Ziegelbauer, Jussi M. Halleen, Sanna-Maria Kakonen, Arne Scholz. Radium-223 dichloride monotherapy and combination therapy with zoledronic acid or doxorubicin improve survival in a mouse model of breast cancer bone metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-105. doi:10.1158/1538-7445.AM2013-LB-105