MET Inhibition Results in DNA Breaks and Synergistically Sensitizes Tumor Cells to DNA-Damaging Agents Potentially by Breaching a Damage-Induced Checkpoint Arrest.

While recent studies implicate that signaling through the receptor tyrosine kinase MET protects cancer cells from DNA damage, molecular events linking MET to the DNA damage response machinery are largely unknown. Here, we studied the impact of MET inhibition by the small molecule PHA665752 on cytotoxicity induced by DNA-damaging agents. We demonstrate that PHA665752 reduces clonogenic survival of tumor cells with MET overexpression when combined with ionizing radiation and synergistically cooperates with ionizing radiation or adriamycin to induce apoptosis. In search of mechanisms underlying the observed synergism, we show that PHA665752 alone considerably increases γH2AX levels, indicating the accumulation of double-strand DNA breaks. In addition, PHA665752 treatment results in sustained high levels of γH2AX and phosphorylated ATM postirradiation, strengthening the assumption that MET inhibition attenuates postdamage DNA repair. PHA665752, alone or in combination with irradiation, leads also to a massive increase of γH2AX tyrosine phosphorylation and its subsequent interaction with the proapoptotic kinase JNK1. Finally, MET inhibition reduces activation of ATR, CHK1, and CDC25B and abrogates an associated DNA damage-induced S phase arrest. This indicates that MET inhibition compromises a critical damage-dependent checkpoint that may enable DNA-damaged cells to exit cell cycle arrest before repair is completed.