Stereoisomeric mitomycins interstrand crosslinks differently impact gene expression in MCF-7 and K562 cancer cells.

Mitomycin C (MC) is an anticancer drug used to treat stomach, anal and lung cancers. The main cytotoxicity of MC is due to its ability to form interstrand crosslinks with DNA (ICLs). The stereochemical configuration at C1″ of MC major ICL is R (α-ICL). In contrast, decarbamoylmitomycin C, a synthetic derivative of MC, generates the major S stereoisomeric ICL (β-ICL). Here, we investigated the effect of the stereochemical configuration of the α/β-ICL on the cellular response by focusing on gene expression changes in MCF-7 and K562 cell lines, one with wild type and the other with mutated TP53, upon treatment with both ICLs. We transfected both cell lines with duplex oligonucleotides containing either the α- or β-ICL at a single site and extracted RNA for transcriptome analysis. Results show that the stereochemical configuration of the α/β-ICL is responsible for distinct gene expression changes in MCF-7 and K562 cells. Our data also show that, in MCF-7 cells, α-ICL treatment triggers a strong increase in CDKN1A expression which is also observed at the protein level, contrary to what happens upon β-ICL treatment. In addition, β-ICL treatment led to a strong downregulation of a greater number of genes than the α-ICL in both cell lines, in particular in K562 cells, which harbor a TP53 mutation. This suggests that the β-ICL toxicity relies on a mechanism which leads to an overall downregulation of gene expression and may explain the greater toxicity of DMC toward TP53 mutant cells.