MSH6 and neoplasm: MMR-deficient tumor cell lines and mouse embryonic fibroblasts (MEFs) from Msh2, Mlh1 and Msh6 knockout mice are less sensitive to treatment with the DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) [10], [21], [22], [23], [24], [25].