Early detection of bone metastases in a murine model using fluorescent human breast cancer cells: Application to the use of the bisphosphonate zoledronic acid in the treatment of osteolytic lesions

A very common metastatic site for human breast cancer is bone. The traditio nal bone metastasis model requires human MDA-MB-231 breast carcinoma cell i noculation into the left heart ventricle of nude mice. MDA-MB-231 cells usu ally develop osteolytic lesions 3-4 weeks after intracardiac inoculation in these animals. Here, we report a new approach to study the formation of bo ne metastasis in animals using breast carcinoma cells expressing the biolum inescent jellyfish protein (green fluorescent protein [GFP]). We first esta blished a subclone of MDA-MB-231 cells by repeated in vivo passages in bone using the heart injection model. On stable transfection of this subclone w ith an expression vector for GFP and subsequent inoculation of GFP-expressi ng tumor cells (B02/GFP.2) in the mouse tail vein, B02/GFP.2 cells displaye d a unique predilection for dissemination to bone. Externally, fluorescence imaging of live animals allowed the detection of fluorescent bone metastas es approximately 1 week before the occurrence of radiologically distinctive osteolytic lesions. The number, size, and intensity of fluorescent bone me tastases increased progressively with time and was indicative of breast can cer cell progression within bone. Histological examination of fluorescent l ong bones from B02/GFP.2. bearing mice revealed the occurrence of profound bone destruction. Treatment of B02/GFP.2-bearing mice with the bisphosphona te zoledronic acid markedly inhibited the progression of established osteol ytic lesions and the expansion of breast cancer cells within bone. Overall, this new bone metastasis model of breast cancer combining both fluorescenc e imaging and radiography should provide an invaluable tool to study the ef fectiveness of pharmaceutical agents that could suppress cancer colonizatio n in bone.