Alkyne modification of DNA cross-linking antitumor agent SJG-136 to monitor induced lesions in cells by click chemistry

The Pyrrolo[2,1-c][1,4]benzodiazepine dimer, SJG-136, selectively induces DNA interstrand crosslinks (ICL) between guanine residues and exhibits potent in vitro cytotoxicity. SJG-136 demonstrated significant in vivo anti-tumor activity in rodents. Clinical trials showed interesting but incomplete responses. Pharmacokinetic and pharmacodynamic profiles of the molecule displayed high interpatient variability highlighting the need for biomarker-driven patient selection. Accurate detection and assessment of ICL in patients' samples is one such approach. Here we report a modified SJG-136 harboring an alkyne handle suitable for click chemistry, designated as Click-SJG-136. We compared cellular toxicity of the clickable version to the native molecule and ICL-generating activity in vitro and in vivo. Click-SJG-136-induced DNA lesions were revealed via ligation to fluorescent reporters using in situ click chemistry in cells and mouse bone marrow, permitting their detection and quantitation by fluorescence microscopy and flow cytometry. The strategy applied in this study is rapid and could be used for direct pharmacodynamic studies of SJG-136.