Emissive Alkylated Guanine Analogs as Probes for Monitoring O ⁶-Alkylguanine-DNA-transferase Activity

Human O ⁶-alkylguanine-DNA-transferase (hAGT) is a repair protein that provides protection from mutagenic events caused by O ⁶-alkylguanine lesions. As this stoichiometric activity is tissue-specific, indicative of tumor status, and correlated to chemotherapeutic success, tracking the activity of hAGT could prove to be informative for disease diagnosis and therapy. Herein, we explore two families of emissive O ⁶-methyl- and O ⁶-benzylguanine analogs based on our previously described ^th G _N and ^tz G _N , thieno- and isothiazolo-guanine surrogates, respectively, as potential reporters. We establish that O ⁶ -Bn ^th G _N and O ⁶ -Bn ^tz G _N provide a spectral window to optically monitor hAGT activity, can be used as substrates for the widely used SNAP-Tag delivery system, and are sufficiently bright to be visualized in mammalian cells using fluorescence microscopy.