The bisphosphonate olpadronate inhibits skeletal prostate cancer progression in a green fluorescent protein nude mouse model

Purpose: Metastatic bone disease is one of the major causes of morbidity and mortality in prostate cancer patients. Bisphosphonates are currently used to inhibit bone resorption and reduce tumor-induced skeletal complications. More effective bisphosphonates would enhance their clinical value. Experimental Design: We tested several bisphosphonates in a green fluorescent protein (GFP) - expressing human prostate cancer nude mouse model. The in vivo effects of four bisphosphonates, including pamidronate, etidronic acid, and olpadronate, on bone tumor burden in mice intratibially inoculated with PC-3-GFP human prostate cancer cells were visualized by whole-body fluorescence imaging and X-ray. Results: The PC-3-GFP cells produced extensive bone lesions when injected into the tibia of immunocompromised mice. The skeletal progression of the PC-3-GFP cell growth was monitored by GFP fluorescence and the bone destruction was evaluated by X-ray. We showed that 3,3-dimethylaminopropane-1-hydroxy-1,1- diphosphonic acid (olpadronate) was the most effective bisphosphonate treatment in reducing tumor burden as assessed by GFP imaging and radiography. The GFP tumor area and X-ray score significantly correlated. Reduced tumor growth in the bone was accompanied by reduced serum calcium, parathyroid hormone - related protein, and osteoprotegerin. Conclusions: The serum calcium, parathyroid hormone - related protein, and osteoprotegerin levels were significantly correlated with GFP area and X-ray scores. Treatment with olpadronate reduced tumor growth in the bone measured by GFP and X-ray imaging procedures. Imaging of GFP expression enables monitoring of tumor growth in the bone and the GFP results complement the X-ray assessment of bone disease. The data in this report suggest that olpadronate has potential as an effective inhibitor of the skeletal progression of clinical prostate cancer.