Poster Presentation 25th Lorne Cancer Conference 2013

Identifying predictors of sensitivity to PF-00477736 in melanoma (#397)

Britanto Wicaksono 1 , Grant McArthur 1 2 3 4 , Petranel Ferrao 1 3 4
  1. Cancer Research, Peter MacCallum Cancer Centre, East Melbourne, Australia
  2. Medicine, St. Vincent's Hospital, Melbourne, Australia
  3. Pathology, University of Melbourne, Parkville, Australia
  4. Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Australia

Inhibition of CHK1 and CHK2 is a potential approach to sensitise p53 mutant cancers with a defective G1 checkpoint, to DNA damaging chemotherapy. However, a recent study reported that p53 mutation alone did not predict for sensitivity to CHK1 inhibitors. Furthermore, we have previously shown that inhibition of CHK1 by PF-00477736 (PF-736) as a single agent can induce p53-mediated apoptosis in Myc-driven mouse lymphoma cells, suggesting that DNA damage induced by oncogenes such as Myc may be important for CHK1 inhibitor-induced cell death in cancers with functional p53. This led us to the hypothesis that melanomas which are predominantly p53 wild-type and BRAF or NRAS mutant would be responsive to CHK1 inhibition. Screening for drug responses across a panel of 30 melanoma cell lines showed a range of sensitivities (measured by IC50) following 3 days treatment with PF-736, with few undergoing cell death. We predicted that p53-mediated apoptosis could be defective in melanomas due to the anti-apoptotic protein MCL1 or the p53 negative regulator MDMX, which are frequently overexpressed in melanomas. Overexpression of BCL2 or BCLxl was able to prevent apoptosis in C002-M1, a cell line that undergoes apoptosis following PF-736 treatment. However, MCL1 overexpression did not have the same effect. Our data showed that MDMX knockdown by shRNA in cell lines with high MDMX protein expression did not result in sensitisation to PF-736. In an attempt to identify γ-H2AX as a biomarker of response, we have shown that the average fold increase in levels after treatment across the entire cell line panel did not significantly correlate with PF-736 IC50. We are currently assessing combination treatment with other targeted therapeutics in cell lines that are sensitive to PF-736 as a potential treatment strategy particularly in BRAF wild-type melanomas.

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