O092 SRC intervention for treating breast cancer

Abstract

Abstract Introduction The non-receptor tyrosine kinase SRC interacts with multiple signalling pathways and has important roles in tumourigenesis. Thus far, SRC intervention for treating breast cancer remains inconclusive. To investigate the underlying molecular mechanisms affecting responses we generated breast cancer cells resistant to the SRC-inhibitor, Bosutinib (BOS). Methods BOS-Resistant (BOS-R) cell lines: ER+ (MCF-7, ZR-75-30) and ER- (Hs578T, MDA-MB-231) were developed by cultivation in increasing concentrations of BOS (0.1-10uM); protein expression changes were determined by Western Blot and densitometry. Dose-responses to [BOS] were assessed by IC50, mitochondrial and LDH assays. Results BOS sensitivity did not correlate with sub-type: MCF-7, ZR-75-30, Hs578T were inhibited significantly (p<0.05) by 5uM BOS and above (IC50=6uM, 6.4uM, 5.5uM respectively) while MDA-MB-231 tolerated >8.5uM BOS (IC50 7.6uM). Sustained growth of ZR-75-30BOS-R and Hs578TBOS-R was achieved in 5uM, MCF-7BOS-R in 7.5uM and MDA-MB-231BOS-R in 10uM BOS (proliferation rates similar to MDA-MB-231). Densitometry comparisons showed increased levels of SRC/SFK (SRC Family Kinases) in all BOS-R cells (range: 12%-57%). In contrast, expression of CSK (C-terminal SRC Kinase) was reduced by >34% (MCF-7BOS-R, MDA-MB-231BOS-R) or lost (ZR-75-30BOS-R, Hs578TBOS-R). Expression of FAK (Focal Adhesion Kinase) increased in all BOS-R cells (range 25%-50%). Furthermore, differential expression of SRC/SFK and alternative SRC-transcripts distinguished five ER+ from four ER- cell lines. Conclusion Regulation of SRC/SFK and their interactions are highly complex. We show resistance to BOS is, in part, associated with increased expressions of SRC/SFK and FAK.