Effects of platelet-derived growth factor, vitamin D and parathyroid hormone on osteoblasts derived from cancer patients on chronic bisphosphonate therapy

Bisphosphonates consist of a family of pyrophosphate analogues that are currently being used to treat metastatic bone diseases as well as systemic bone diseases such as osteoporosis. There is accumulating evidence suggesting that patients treated with these bisphosphonates can develop, particularly with invasive dental procedures, osteonecrosis of the jaw. This present study investigated the ability of osteoblastic cells obtained from the alveolar bone of patients on long term intravenous bisphosphonate therapy to respond to agents normally involved in bone regulation and repair. The effects of platelet-derived growth factor-BB (PDGF-BB), 1,25-dihydroxycholecalciferol [1,25(OH)2VitaminD3] and parathyroid hormone (PTH) on basic parameters of cell viability, proliferation, and differentiation were studied. Osteoblastic cells from a diagnosed necrotic alveolar bone specimen obtained with consent from a multiple myeloma female patient, and a non-necrotic sample from a breast cancer female patient both on chronic bisphosphonate therapy (zolendronic acid) were successfully cultured. Cells from an alveolar bone specimen obtained from a female donor with no known medical conditions were also studied for comparative responses. The cells were exposed to 1,25(OH)2D3, PDGF, or PTH under various incubation conditions. The osteoblastic cell differentiation marker, alkaline phosphatase activity, was assayed using a biochemical analysis. Cell viability was assessed with an MTT assay which measures mitochondrial activity and cell proliferation with a tritiated thymidine assay. This study on osteoblastic cells grown from a necrotic alveolar bone from a multiple myeloma patient and a non-necrotic sample from a breast cancer patient, both on long term bisphosphonate treatment, suggests that viable cells from the bone are responsive to agents such as PTH, PDGF and 1,25(OH)2D3 with changes in alkaline phosphatase activity, proliferation and viability suggestive of normal osteoblastic cell responses observed in cultures from a donor of the same gender and age, but not on bisphosphonate treatment. This work provides a rationale for clinical studies to further assess whether the osteonecrosis that sometimes develops in patients treated with bisphosphonates, can be controlled or prevented by close attention to the levels of bone/calcium regulatory agents and/or, in some cases, therapeutic intervention with PDGF to restore regenerative processes that may be compromised at the necrotic site.