Malignant melanoma is one of the most increasing forms of cancer worldwide, in addition to being notoriously resistant to therapy. Despite recent advances, there are no curative treatments once the cancer has spread (stage IV); there is thus a precarious need to find new and better treatment alternatives. Unlike normal cells, the majority of cancer cells have a defective G1/S DNA-damage checkpoint and are therefore more dependent on the G2/M checkpoint when DNA damages arise. Central in regulating the latter checkpoint is Wee1, a kinase which may stop the cell cycle by adding a negative phosphorylation on CDK1. Wee1 is regulated by Chk1 which upon DNA damage can also inhibit the complimentary counterpart of Wee1; CDC25. In recent studies, Wee1 and Chk1 have additionally been indicated as key players in regulating DNA replication in S-phase. We have previously reported that increased Wee1 protein expression was associated with malignancy in melanoma tumour samples, and that siWee1 transfection led to reduced viability in melanoma cell lines. In the present study we have combined inhibitors of Wee1 (MK1775) and Chk1 (AZD7762) in a panel consisting of both metastatic melanoma- and normal cells, including a Plexxikon resistant melanoma cell line (MelJR post3.3). We found that the combination synergistically reduced the amount of viable cells in the melanoma cell lines (∼50-80% reduction), whilst only having very moderate effect (∼10% reduction) in the normal cells. Interestingly, the reduction in number of viable cells was found in both p53WT and p53Mut cell lines, indicating that the p53 status do not predict the response to such treatment. Furthermore, combinational treatment with the inhibitors caused increased cleavage of PARP and caspases, indicative of apoptosis, as compared to MK1775 or AZD7762 treatment alone. The combination also caused a marked increase in DNA double-strand breaks, as demonstrated by augmented levels of γ-H2AX (predominantly found in S-phase cells). In line with this, preliminary results from melanoma cells grown as spheroids, revealed the same tendency, with approximately 50% reduction in spheroid volume when combining the inhibitors. In vivo experiments using melanoma cells grown in SCID mice are currently ongoing. In conclusion, our results indicate a potential new role for inhibitors of Wee1 and Chk1 in treatment of malignant melanoma.

Citation Format: Gry I. Magnussen, Vivi A. Florenes, Birgit Engesæter, Elisabeth Emilsen. Increased anticancer effect of combining Wee1 (MK1775) and Chk1 (AZD7762) inhibitors in malignant melanoma cell lines. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3417. doi:10.1158/1538-7445.AM2013-3417