Abstract C218: Relevance of p53 status for the response of tumor cells to MET inhibitors combined with irradiation.
Authors: Mikami Kei , Medová Michaela , Streit Bruno , Tschan Mario P. , Blaukat Andree , Bladt Friedhelm , Aebersold Daniel M. , Zimmer Yitzhak 
Published: August 2014

Abstract
The MET receptor tyrosine kinase is an established molecular target for cancer treatment due to the receptor driven uncontrolled cell proliferation, angiogenesis, local invasion and metastasis. Several studies reported that MET signaling may crosstalk with cellular responses to DNA damage and protect tumor cells from cancer treatment with DNA damaging agents including ionizing radiation (IR).
In this respect, our group previously demonstrated that MET inhibition in tumor cells with deregulated MET activity results in their sensitization to IR. Recent finding suggests that this radiosensitization is accompanied by the MET inhibition associated downregulation of ATR-Chk1-CDC25 pathway, a major signaling cascade responsible for the intra-S and G2/M cell cycle arrests following DNA damage. Here we hypothesized that further improvement of the efficacy of IR in combination with MET inhibition in p53-proficient cancer cells could be achieved by a p53 knock-down that would disrupt the remaining G1/S checkpoint arrest. Consequently, tumor cells revealing abrogated both G2/M and G1/S checkpoints would enter mitosis carrying substantial DNA lesions and undergo cell death in a greater extent than p53-proficient cells with functional G1/S checkpoint.
In order to validate our working hypothesis, GTL-16, a human gastric carcinoma line that reveals MET-dependence and expresses wildtype p53, was used to generate p53-proficient and p53-deficient isogenic cell lines. Following combined treatment of novel selective MET small molecule inhibitor EMD-1214063 and IR, various biological endpoints, such as viability, cytotoxicity, apoptosis, and cell cycle distribution were evaluated in p53 knock-down cells along with their corresponding parental variants.
The data suggests that p53-deficient cells are more susceptible to EMD-1214063 and combination treatment than the wildtype-p53 lines as inferred from elevated γH2AX expression and increased cell death. Furthermore, cell cycle distribution profile indicates constantly lower G1 and higher G2/M population as well as up to 3-fold higher expression of a mitotic marker p-Histone H3 Ser10 following MET inhibition combined with IR in p53 knock-down variant as compared to p53 wildtype cells. Interestingly, p53-deficient cells treated by EMD-1214063/IR tend to be rather resistant to apoptosis, suggesting cell death through an alternative mechanism (i.e. mitotic catastrophe). This assumption is supported by imaging analysis that indicates formation of micronuclei in these cells.
The concept of MET inhibition-mediated radiosensitization enhanced by p53 deficiency reported in our current work is of high clinical relevance, since p53 is frequently inactivated as a consequence of mutations in numerous types of human cancer and has the potential to overcome the major challenge in cancer treatment due to tumor resistance to conventional chemo- and radiation therapy.
Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C218.
Citation Format: Kei Mikami, Michaela Medová, Bruno Streit, Mario P. Tschan, Andree Blaukat, Friedhelm Bladt, Daniel M. Aebersold, Yitzhak Zimmer. Relevance of p53 status for the response of tumor cells to MET inhibitors combined with irradiation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C218.