Branched chain amino acids regulate the sensitivity of breast and ovarian cancer cells to paclitaxel


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Alan Richardson1,Mohammed Abed1,Suad Ibrahim2
1Keele University,2keele university

Abstract

Background

Paclitaxel is a chemotherapeutic agent used in the treatment of several cancers including breast and ovarian cancer. However, resistance to paclitaxel can limit its clinical effectiveness, making it desirable to identify drugs which increase the sensitivity of resistant cell to paclitaxel. We have previously conducted an siRNA screen to identify genes which regulate the sensitivity of ovarian cancer cells to paclitaxel. One of the genes identified by this screen encodes Branched-chain amino acid dehydrogenase kinase (BCKDK) which inhibits the catabolism of branched chain amino acids (BCAA).

Method

The expression of BCKDK was repressed in ovarian and breast cancer cells in culture using siRNA. Alternatively, BCKDK was inhibited with either (S)-2-Chloro-4-methylvaleric acid (CMVA)  or 3,6-Dichloro-1-Benzothiophene-2-Carboxylic acid (DBCA). Hap1 cells gene-edited to lack BCKDK were also assessed. The effect of inhibition of BCKDK on sensitivity to paclitaxel was assessed using a suite of cell growth, survival and apoptosis assays.

Results

3 different BCKDK siRNA increased the sensitivity of Ovcar-4 and COV318 ovarian and MCF-7 breast cancer cells to paclitaxel in cell growth assays, trypan blue exclusion, caspase-3/7 activation and PARP cleavage assays. CMVA and DCBA inhibited phosphorylation of branched chain amino acid dehydrogenase (BCKDH) and were synergistic (CI= 0.5-0.8) with paclitaxel in the same cells in drug combination experiments. Importantly, addition of exogenous BCAA blocked the synergy between paclitaxel and the BCKDK inhibitors. COV362 cells expressed low levels of branched chain amino acid dehydrogenase (BCKDH) and synergy was not observed in these cells. Cells engineered to lack BCKDK showed an apparent compensatory down-regulation of BCKDH and the sensitivity to paclitaxel was not altered substantially. BCKDK inhibitors reduced mTORC1 phosphorylation, suggesting a potential mechanism underlying the synergy.

Conclusion

These results identify BCKDK as a potential target to develop drugs to increase the effectiveness of paclitaxel.