Endogenous H₂S-Assisted Cancer-Cell-Specific Activation of Theranostics with Emission Readout

Abstract

Realizing the importance of activation of the anticancer drug, its distribution, and for cancer management, a new theranostic probe has been developed. Endogenous H₂S stimulated the theranostic molecular prodrug (<b>TP-HS</b>) which is activated in cancer cells; it monitors the actual time of formation of therapeutic agent SN-38 in cellular milieu through fluorescence imaging. Upon exposure to H₂S in a similar physiological condition, the azide functionality converted to amine (-NH₂) in <b>TP-HS</b> which allows self-immolative scission of the labile benzyl-carbonate moiety for release of rhodol and SN-38 in a concerted manner. Thus, an intense emission band centered at 548 nm has appeared for quantifying the active therapeutic component. The fluorescence image revealed that the <b>TP-HS</b> preferentially releases rhodol and SN-38 in colon cancer (HCT116 cells) and lung cancer cells (A549 cells) compared to normal human fibroblast cells (WI-38). Further, the dose-dependent antiproliferative activity of <b>TP-HS</b> against various cells supports that <b>TP-HS</b> releases SN-38 based on endogenous H₂S in cancer cells followed by its apoptotic progression monitored by (a) live-dead, i.e., acridine orange-ethidium bromide double staining assay, (b) APOPercentage apoptotic assay, and (c) Annexin V-FITC staining by flow cytometry. The theranostic prodrug <b>TP-HS</b> showed anticancer efficacy via the desirable apoptotic pathway. It is the first demonstration of a strategic theranostic molecular prodrug system that could be delivered chemotherapeutically with validating the real-time activation of chemotherapy in the cancer cells without the support of a cancer-directing ligand.