LB-267

Objective:Bone metastasis is a common complication of breast Ca and one for which only palliative treatment is available.We aim to inhibit the vicous cycle between tumor cells and the bone microenvironment ,which results in increased tumor burden and bone destruction.

Methodology:Breast Ca cells (ER-) obtained from a metastatic patient were inoculated into the left cardia ventricle of nude mice.After osteoclastic and osteoblastic metastases were observed radiographicaly,the mice were treated with pegylated trispecific disulfide linked Fv(sdFv) targeting epitopes of PTHrP,RANKL and EGFR conjugated covalently with SATA to vinorelbine tartrate.

Results:Post-treatment,we observed autocrine inhibition of breast cancer cells and paracrine inhibition of tumor associated endothelial cells and bone microvascular endothelial cells.Downregulation of EGFR led to inhibition of expression of AP1 blocking transcription of VEGF and its receptors KDR and Flt-1 exerting an angiocidal effect.EGFR downregulation led to reduced activity of osteoclasts and inhibition of PI3K,MAPK and MMP-9. Down-regulation of PTHrP and RANKL inhibited osteoclastogenesis and proliferation of stromal/osteoblastic cells.Subsequently,release of growth factors TGF-a and IGF from the bone matrix was blocked.Vinorelbine destabilised MT dynamics of tumor and endothelial cells blocking cell cycle at G2/M.It also phosphorylated bcl-2 blocking uPAR and SP1 DNA binding activity through ERK signaling pathway.This led to inhibition of osteoblast proliferation by inhibiting hydrolysis of IGF-binding proteins and down-regulation of MMP-1,3,9.We observed antibody dept cellular toxicity and antibody mediated phagocytosis.In breast cancer cells,tumor associated and bone derived endothelial cells,we observed inhibition of DNA synthesis and metabolic activity by BrdU and MTT analysis.TEM exhibited nuclear PCD type III with pyknosis and zeiosis leading to secondary necrosis. Type I PCD which is caspase-3 dependent and autophagic type II PCD led to a bystander killing effect of tumor and endothelial cells.There was not radiographic evidence of osteolytic and sclerotic bone metastases of breast Ca cells.

Conclusion:These findings suggest that this strategy may provide a new therapeutic approach to inhibiting the processes involved in bone metastases.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA