Dibotermin alfa

In the same pathway shared by endogenous BMPs, recombinant human BMP-2 (rhBMP-2) binds and initiates intracellular signal cascade through an oligomeric transmembrane receptor complex formed by type I and II serine/threonine kinase receptor proteins. These BMP receptors are expressed on the surface of mesenchymal cells and upon binding of BMP-2 to the BMP receptor type II, type II receptor phosphorylates and activates type I receptor. Type I receptor may also undergo autophosphorylation. Activated BMP type I receptor then phosphorylates intracellular effector proteins, the receptor-regulated Smads (R-Smads). Smad1, Smad 5 and Smad 8 associate with the Co-Smad, Smad4 and once activated via complex formation, they translocate to the nucleus where they associate with other transcription factors and bind promoters of target genes to control their expression. This ultimately results in bone formation at the site of implantation. Dibotermin alfa causes mesenchymal cells to differentiate into cartilage- and bone-forming cells. Implantation of dibotermin alfa in trabecular bone results in transient resorption of the bone surrounding the implant, followed by replacement of degraded matrix by newly differentiated cells.

In human bone cells isolated from adult mandibulae, recombinant human BMP-2 (rhBMP-2) was shown to stimulate the activity of early biomarkers of osteoblast differentiation, including alkaline phosphatase and parathyroid hormone (PTH)-dependent 3', 5'-cyclic adenosine monophosphate accumulation. At concentrations of 500 ng/mL, rhBMP-2 also enhanced the mRNA expression level of PTH/PTH related-peptide receptor in human bone cells. There was evidence that rhBMP-2 inhibits 1,25-dihydroxyvitamin D3-induced osteocalcin synthesis at both the mRNA and protein level. rhBMP-2 also significantly suppressed MMP-1 production and MMP-1 mRNA expression at concentrations exceeding 500 ng/mL.