Abstract The overarching goal of this proposal is to investigate the relationship between the structure of stereoisomeric DNA Interstrand Crosslinks (ICLs) formed by Mitomycin C and Decarbamoylmitomycin C and the molecular mechanisms of these drugs. Mitomycin C (MC) is an anticancer drug currently used to treat stomach, anal and lung cancers. The stereochemical configuration at C1’’ of MC major ICL is R (α ICL). In contrast, Decarbamoylmitomycin C (DMC), a derivative of MC lacking the O10 carbamoyl group, generates the S stereoisomeric ICL (β ICL). The scientific premise of the proposed research is that ICLs constitute the molecular basis for the cytotoxic effects of mitomycins. The central hypothesis is that differences in the local DNA structures of the α and β-ICLs are responsible for the distinct biochemical responses triggered by MC and DMC. In particular, contrary to MC, the DNA-adducts generated by DMC treatment (-ICL) rapidly activate a p53-independent cell death pathway. Thus, the study MC- DMC provides an ideal model for identifying structural features determining the cell signaling outcome in the presence or the absence of a functioning p53 pathway. The significance of this project lies in determining the structure-activity relationship for stereoisomeric DNA crosslink adducts. In addition, the proposed research will establish how the α and β-ICLs behave as biological signals to different cell death pathways. The key innovation of this project is to generate stereoisomeric ICLs on a scale which will allow the study of biochemical responses using our newly developed biomimetic method. Finally, since p53 tumor suppressor is frequently mutated in human cancers, the need to identify drugs and pathways that induce cell death or cell cycle arrest independently of p53 deserves substantial attention. In order to correlate MC and DMC-adducts structures with the toxicity of the α-ICL and β-ICL, the following three aims will be pursued: 1) Synthesis of MC and DMC DNA adducts. 2) Determination of p53-dependent and independent MC/DMC DNA adducts response mechanisms using proteomics. 3) Determination of the molecular signaling pathway involved the in G2/M cell cycle arrest triggered by MC/DMC DNA-adducts. Our study will reveal molecular and cellular networks up or downregulated by MC/DMC and the α/β-ICLs in p53-dependent and p53-independent cell lines. The proposed work will therefore identify novel critical molecular therapeutic targets of MC and DMC.