Introduction: Although a majority of metastatic prostate cancer lesions are osteoblastic in nature, some are mixed or lytic; and, osteoblastic lesions require osteolytic activity in order to progress. The role of BMPs in the formation of prostate cancer metastases to bone remains unknown. We hypothesized that BMPs influence the development and progression of osteolytic prostate cancer lesions.
Methods: RT-PCR and Western blot analysis were used to determine BMP receptor expression on the osteolytic prostate cancer cell line PC-3. Migration, invasion, and cellular proliferation assays were performed on PC-3 cells to quantify the effects of BMP-2, -4, and -7. In vivo, PC-3 cells were injected alone, with an empty retroviral vector, or with a retroviral vector overexpressing noggin, into the tibias of SCID mice. The animals were followed for 8 weeks, and histologic and radiographic analysis were performed at 2, 4, 6, and 8 weeks.
Results: BMP receptors are expressed on PC-3 cells, suggesting that they would be responsive to host BMP secretion. BMP-2, and to a lesser extent, BMP-4, stimulated PC-3 cell migration and invasion in a dose-dependent fashion. Noggin inhibited cellular migration and invasion of BMP-2 and -4 stimulated PC-3 cells. BMP-2 alone stimulated PC-3 cell proliferation, but BMP-4 had no effect. BMP-7 had no effect on proliferation, migration, or invasion. PC-3 cells implanted into SCID mouse tibias formed osteolytic lesions as early as 2 weeks and completely destroyed the proximal tibia by 8 weeks. Overexpression of noggin in PC-3 cells inhibited the expansion of the lesion in vivo.
Conclusions: BMPs influence the formation of the osteolytic prostate cancer metastases, and treatment modalities that inhibit BMP activity may limit the progression of the lytic component of prostate cancer metastases.