Background STAT3 is activated by Janus kinases (JAKs), which are recruited and activated by numerous cytokine receptors, receptor tyrosine kinases (including EGFR) and non-receptor tyrosine kinases (such as Src). A recent study has shown that high STAT3 activation is positively associated with adverse outcome in colorectal cancer, supporting its potential role as a therapeutic target. Kras mutations occur in 40%-45% of colorectal cancer (CRC) patients and confer resistance to EGFR targeted therapies. The aim of this study was to evaluate JAK2/STAT3 signalling as novel Kras synthetic lethal interactions in CRC. Method STAT3 and JAK2 inhibition was obtained using siRNA and small molecule approaches. Analysis of cell viability was carried out using MTT assay, apoptosis was measured using Western blotting and Flow cytometry and migration using xCELLigence system. The isogenic KrasMT/WT HCT116 cell line model and a panel of KrasWT&MT CRC cells were used. Results Using different siRNA sequences, we found that silencing of STAT3 and JAK2 was lethal in KrasMT HCT116 cell line compared to its KrasWT clone, and these results were confirmed using the small molecule JAK2/STAT3 inhibitor ‘cucurbitacin’. Similar data were obtained in our panel of KrasMT CRC cells. Interestingly, significant higher constitutive levels of pSTAT3 were observed in KrasMT HCT116 cells compared to its WT clone. Combination of STAT3 or JAK2 silencing with MEK1/2 inhibition or chemotherapy (5-FU, oxaliplatin) resulted in synergistic decreases in cell viability and increase in apoptosis in KrasMT HCT116 cell line and this was associated with potent increase in STAT3 activity following MEK1/2i or chemotherapy. Furthermore, STAT3 silencing resulted in strong decreases in cell migration in KrasMT HCT116 cell line. Conclusion These results indicate that KrasMT CRC models are dependent on JAK2/STAT3 pathway for survival. We are now further evaluating the effect of JAK2/STAT3 inhibition in combination with MEKi/chemotherapy in in vivo models.
|Title of host publication
|Identification of JAK2/STAT3 as a novel therapeutic target in Kras mutant colorectal cancer
|Place of Publication
|Proffered paper sessions
|National Cancer Research Institute
|Published - Nov 2011