Enhancement of osteogenesis in vitro and in vivo by a novel osteoblast differentiation promoting compound, TAK-778

TAK-778 [(2R,4S)-(-)-N-(4-diethoxyphosphorylmethylphenyl)-1,2,4, 5-tetrahydro-4-methyl-7, 8-methylenedioxy-5-oxo-3-benzothiepin-2-carboxyamide; mw 505.53], a novel osteoblast differentiation promoting compound, was characterized in vitro and in vivo models. TAK-778 at doses of 10(-6) M and higher promoted potently bone-like nodule formation in the presence of dexamethasone in rat bone marrow stromal cell culture. This was accompanied by increases in cellular alkaline phosphatase activity, soluble collagen release, and osteocalcin secretion. Under the culture conditions, TAK-778 also stimulated the secretion of transforming growth factor-beta and insulin-like growth factor-I, indicating that TAK-778 may exert regulatory effects on osteoblast differentiation via autocrine/paracrine mechanisms. Furthermore, the in vivo osteogenic potential of TAK-778 was studied in bony defect and osteotomy animal models, using sustained release microcapsules consisted of a biodegradable polymer, poly (dl-lactic/glycolic) acid (PLGA). Single local injection of TAK-778/PLGA-microcapsules (PLGA-MC) (0.2-5 mg/site) to rat skull defects resulted in a dose-dependent increase in new bone area within the defects after 4 weeks. When the pellet containing TAK-778/PLGA-MC (4 mg/pellet) was packed into place to fill the tibial segmental defect in rabbit, this pellet induced osseous union within 2 months, whereas the placebo pellet did not. In addition, single local application of TAK-778/PLGA-MC (10 mg/site) to rabbit tibial osteotomy site enhanced callus formation accompanied by an increase in breaking force after 30 days. These results reveal for the first time that a nonendogenous chemical compound promotes potently osteogenesis in vitro and enhances new bone formation during skeletal regeneration and bone repair in vivo and should be useful for the stimulation of fracture healing.