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Effects of Vitaxin®, a novel therapeutic in trial for metastatic bone tumors, on osteoclast functions in vitro
Author(s) -
Gramoun Azza,
Shorey Seema,
Bashutski Jill D.,
Dixon S. Jeffrey,
Sims Stephen M.,
Heersche Johan N. M.,
Manolson Morris F.
Publication year - 2007
Publication title -
journal of cellular biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.028
H-Index - 165
eISSN - 1097-4644
pISSN - 0730-2312
DOI - 10.1002/jcb.21296
Subject(s) - osteoclast , bone resorption , wortmannin , resorption , chemistry , extracellular , multinucleate , integrin , kinase , medicine , endocrinology , in vitro , cancer research , microbiology and biotechnology , cell , biology , biochemistry , phosphatidylinositol
The integrin αvβ3 mediates cell–matrix interactions. Vitaxin®, a humanized monoclonal antibody that blocks human and rabbit αvβ3 integrins, is in clinical trials for metastatic melanoma and prostate cancer. αvβ3 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 αvβ3 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 αvβ3. 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 αvβ3. J. Cell. Biochem. 102: 341–352, 2007. © 2007 Wiley‐Liss, Inc.