Esterase-Responsive\nFluorogenic Prodrugs of Aldose\nReductase Inhibitor Epalrestat: An Innovative Strategy toward Enhanced\nAnticancer Activity

In addition to the conventional chemotherapeutic\ndrugs,\npotent\ninhibitors of key enzymes that are differentially overexpressed in\ncancer cells and associated with its progression are often considered\nas the drugs of choice for treating cancer. Aldose reductase (AR),\nwhich is primarily associated with complications of diabetes, is\nknown to be closely related to the development of cancer and drug\nresistance. Epalrestat (EPA), an FDA-approved drug, is a potent inhibitor\nof AR and exhibits anticancer activity. However, its poor pharmacokinetic\nproperties limit its bioavailability and therapeutic benefits. We\nreport herein the first examples of esterase-responsive turn-on fluorogenic\nprodrugs for the sustained release of EPA to cancer cells with a turn-on\nfluorescence readout. Carboxylesterases are known to be overexpressed\nin several organ-specific cancer cells and help in selective uncaging\nof drug from the prodrugs. The prodrugs were synthesized using a multistep\norganic synthesis and successfully characterized. Absorption and emission\nspectroscopic studies indicated successful activation of the prodrugs\nin the presence of porcine liver esterase (PLE) under physiological\ncondition. HPLC studies revealed a simultaneous release of both the\ndrug and the fluorophore from the prodrugs over time with mechanistic\ninsights. While the inhibitory potential of EPA released from the\nprodrugs toward the enzyme AR was validated in the aqueous medium,\nthe anticancer activity of the prodrugs was studied in a representative\ncervical cancer cell line. Interestingly, our results revealed that\nthe development of the prodrugs can significantly enhance the anticancer\npotential of EPA. Finally, the drug uncaging process from the prodrugs\nby the intracellular esterases was studied in the cellular medium\nby measuring the turn-on fluorescence using fluorescence microscopy.\nTherefore, the present study highlights the rational development of\nthe fluorogenic prodrugs of EPA, which will help enhance its anticancer\npotential with better therapeutic potential.