Cancer Cell-Directed Drug Delivery and Chemopotentiating Effects by GSTP1-Activated Nitric Oxide (NO)-Releasing Prodrug

Abstract

Overexpressed glutathione S-transferase P1 (GSTP1) has been associated with chemotherapy resistance. GSTP1 activated arylated diazeniumdiolates causes significant DNA damage by nitric oxide (NO) release. Poly(ADP-ribose) polymerases (PARP) inhibitors induces DNA damage. A hybrid prodrug was designed by combining the structural features of established PARP-1 inhibitors and arylated diazeniumdiolates to exacerbate DNA damage. The prodrug is activated by GSTP1 catalyzed reaction with glutathione and releases NO and a moiety that inhibits PARP-1. It has also proven to be effective as anticancer agent in both in vitro and in vivo models. The chemopotentiating effects of the prodrug were also observed in combination with microtubule targeting agents or proteasome inhibitors, accompanied by increase in DNA damage, and induction of apoptosis. Interestingly, S-nitrosation of Cys101 of GSTP1 by the prodrug upon activation by GSTP1 was observed. This modification significantly decreased the catalytic activity of GSTP1, suggesting that the prodrug executes synergistic effects through multiple cellular effects, including direct inhibitory effect on GSTP1. These findings demonstrate that S-nitrosation of GSTP1 may affect proper protein folding and induce unfolded protein and endoplasmic reticulum stress. Our strategy not only activates prodrug by GSTP1 catalytic activity but also inhibits GSTP1 upon activation and delivers the compound at the cancer site. Thus, a three-pronged attack on cancer cells may be afforded by such a novel strategy. Additionally, GSTP1 inhibition by designed prodrug may provide a translational opportunity to target GSTP1 for its role in MAP kinase cascades, which participates in cellular survival and death signaling. As future studies are warranted to confirm our hypothesis, we plan to continue our structure based design to improve the hybrid prodrug for higher GSTP1 selectivity and higher bioavailability.