title: Effects of Vitaxin, a novel therapeutic in trial for metastatic bone tumors, on osteoclast functions in vitro.
abstract: The integrin alphavbeta3 mediates cell-matrix interactions. Vitaxin(R), a humanized monoclonal antibody that blocks human and rabbit alphavbeta3 integrins, is in clinical trials for metastatic melanoma and prostate cancer. alphavbeta3 is the predominant integrin on osteoclasts, the cells responsible for bone resorption in health and disease. Here, we report the first investigation of Vitaxin's effects on osteoclast activity. Vitaxin (100-300 ng/ml) decreased total resorption by 50%, but did not alter resorptive activity per osteoclast. Vitaxin (300 ng/ml) decreased osteoclast numbers on plastic by 35% after 48 h. Similarly, attachment after 2 h was reduced by 30% when osteoclasts were incubated with Vitaxin (300 ng/ml) for 25 min prior to plating; however, the rate of fusion of osteoclast precursors in Vitaxin-treated and control groups was equal. Using time-lapse microscopy, we evaluated the effect of Vitaxin on osteoclast morphology and found a significant reduction in osteoclast planar area only when cells were pretreated with macrophage colony stimulating factor (M-CSF). Extracellular Ca(2+) and M-CSF have opposite effects on alphavbeta3 conformation. Elevation of extracellular Ca(2+) eliminated the inhibitory effect of Vitaxin on osteoclast attachment. In contrast, the effect of Vitaxin was enhanced in cells pretreated with M-CSF. This action of M-CSF was suppressed by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor wortmannin, suggesting that M-CSF increases Vitaxin's inhibitory effect by inside-out activation of alphavbeta3. In conclusion, Vitaxin decreases resorption by impairing osteoclast attachment, without affecting osteoclast formation and multinucleation. Our data also show that Vitaxin's inhibitory effects on osteoclasts can be modulated by factors known to alter the conformation of alphavbeta3.
authors: Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada.
authors: Azza
authors: A
authors: Gramoun
authors: Seema
authors: S
authors: Shorey
authors: Jill D
authors: JD
authors: Bashutski
authors: S Jeffrey
authors: SJ
authors: Dixon
authors: Stephen M
authors: SM
authors: Sims
authors: Johan N M
authors: JN
authors: Heersche
authors: Morris F
authors: MF
authors: Manolson
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001859:Bone Neoplasms / Q000188:drug therapy / Q000556:secondary; D001862:Bone Resorption / Q000188:drug therapy / Q000473:pathology; D002118:Calcium / Q000502:physiology; D002448:Cell Adhesion / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D045604:Extracellular Fluid / Q000378:metabolism; D066298:In Vitro Techniques; D039302:Integrin alphaVbeta3 / Q000037:antagonists & inhibitors / Q000737:chemistry; D016173:Macrophage Colony-Stimulating Factor / Q000494:pharmacology; D010010:Osteoclasts / Q000187:drug effects* / Q000502:physiology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011487:Protein Conformation; D011817:Rabbits; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; D002118:Calcium; D039302:Integrin alphaVbeta3; D016173:Macrophage Colony-Stimulating Factor; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D000077191:Wortmannin; C112567:etaracizumab