Investigation of the DNA damage response to SFOM-0046, a new small-molecule drug inducing DNA double-strand breaks.

2-Ethylphenyl 4-(3-ethylureido)benzenesulfonate (SFOM-0046) is a novel anticancer agent that arrests cell cycle in S-phase and causes DNA replication stress leading to the phosphorylation of H2AX into γ-H2AX. First, using the M21, HT29, HT-1080 and HeLa cell lines, we confirmed that S-phase cell cycle arrest and γ-H2AX foci induction by SFOM-0046 is a general mechanism occurring in diverse cancer cell lines. In addition to γ-H2AX, SFOM-0046 activates preferentially ATR-Chk1 in M21 and HT29 cells while both ATR-Chk1 and ATM-Chk2 pathways are activated in HCT116 cells. Co-localization of SFOM-0046-induced 53BP1 foci with γ-H2AX foci validates that the DNA damage generated corresponds to double-strand-breaks (DSBs). Consistent with an S-phase arrest, SFOM-0046 treatment induces RAD51 foci formation but not DNA-PKcs foci, confirming that homologous recombination is the major DSB repair pathway targeted by the drug. Furthermore, using isogenic HCT116 p53+/+ and HCT116 p53-/- cells, we showed that p53 plays a key role in the survival mechanism to SFOM-0046. Finally, SFOM-0046 exhibits a dose-dependent antitumor activity on human fibrosarcoma HT-1080 tumours grafted onto chick chorioallantoic membranes without showing embryo toxicity even at high doses. Altogether, our results highlight SFOM-0046 as a very promising drug that induces a replication stress response.