The purpose of this study was to evaluate the role of BMPs on the formation of metastatic prostate cancer lesions to bone. Our results show that BMPs influence the development and progression of osteoblastic lesions and suggest that therapies that inhibit BMP activity may reduce the formation and progression of osteoblastic lesions.
Introduction: Prostate adenocarcinoma is the leading cause of cancer in North American men. The formation of skeletal metastases affects approximately 70% of patients with advanced disease, and a majority of these patients have osteoblastic lesions. Although BMPs have been found to be expressed in multiple oncogenic cell lines, their role in the formation of metastatic osteoblastic lesions remains uncharacterized. We hypothesized that BMPs influence the development of metastatic osteoblastic lesions associated with prostate cancer.
Materials and methods: Western blot analysis and RT-PCR was used to determine BMP receptor expression on osteoblastic prostate cancer cell lines LAPC-4 and LAPC-9. Migration, invasion, and cellular proliferation assays were used to quantify the effects of BMP-2, -4, and -7 on LAPC-4 cells in vitro. LAPC-9 cells alone or transfected with a retrovirus overexpressing noggin were injected into the tibias of SCID mice, and the animals were followed for 8 weeks. Tumor size was determined by radiographs and direct measurement. Histology was performed at the time of death.
Results: We determined that BMP receptor mRNA and protein was expressed on osteoblastic prostate cancer cell lines LAPC-4 and LAPC-9. In vitro studies showed that BMP-2 and -7 stimulated cellular migration and invasion of prostate cancer cells in a dose-dependent fashion, although BMP-4 had no effect. Noggin inhibited cellular migration and invasion of BMP-2- and -7-stimulated LAPC-4 cells. LAPC-9 cells implanted into immunodeficient mouse tibias formed an osteoblastic lesion with sclerotic bone at 8 weeks. Formation of osteoblastic lesions was inhibited by overexpression of noggin by prostate cancer cells transduced with a retrovirus containing the cDNA for noggin.
Conclusions: BMPs are critical in the formation of the osteoblastic lesions associated with prostate cancer metastases, and future treatment strategies that inhibit local BMP activity may reduce the formation and progression of osteoblastic lesions.