Abstract 3334: GSTP1-activated nitric oxide-releasing/PARP inhibitor hybrid prodrugs induce cancer cell death through ROS/RNS, DNA damage, ER stress, and apoptosis.
Authors: Maciag Anna E. , Saavedra Joseph E. , Holland Ryan J. , Kim Youseung , Kumari Vandana , Luthers Christina E. , Sehareen Waheed S. , Ji Xinhua , Anderson Lucy M. , Keefer Larry K. 
Published: August 2014

Abstract
Poly [ADP-ribose] polymerase (PARP) has been recognized as a potential molecular target in cancer therapy. PARP inhibitors have been evaluated in clinical trials, both in combination with DNA damaging chemotherapy, and also as single agents in patients with BRCA deficiencies. However, there are problems associated with the clinical applicability of PARP inhibitors that include theoretical genotoxicity of these DNA damage repair inhibitors, and increased toxicity in combination with chemotherapy. Therefore targeted delivery of PARP inhibitors selectively to cancer cells would be clinically beneficial.
Diazeniumdiolate-based nitric oxide (NO)-releasing prodrugs developed in our laboratory have proven effective as anticancer agents in a number of in vitro and in vivo models. The lead prodrug JS-K exhibits a multifaceted mechanism of action that includes generation of oxidative/nitrosative stress and DNA damage. We hypothesized that inhibiting PARP may increase effectiveness of JS-K. More importantly, creating a PARP inhibitor prodrug that is activated specifically in the cancer cell could diminish dose-limiting adverse events observed in clinical trials.
Using structure-based molecular modeling approaches we have designed and synthesized novel diazeniumdiolate/PARP inhibitor hybrid prodrugs that are activated by glutathione S-transferase P1 (GSTP1), an enzyme frequently overexpressed by cancer cells. This GSTP1-catalyzed activation allows for the selective delivery of nitric oxide and PARP inhibitor simultaneously to the cancer cell. Biological evaluation of the prodrugs in vitro in lung adenocarcinoma and leukemia cells reveals that their mechanism of action involves oxidative/nitrosative stress associated with NO release and depletion of cellular GSH, leading to DNA strand break damage. The compounds induce aryl-mediated crosslinking glutathionylation of cellular thiols that is irreversible, and may lead to observed endoplasmic reticulum (ER) stress. The tumor suppressor p53 pathway is involved in cells bearing wildtype p53. We have also observed the activation of stress kinases p38 and SAPK/JNK. All of the above events led to initiation of apoptosis through both intrinsic and extrinsic pathways.
Cancer cells often exhibit specific stress-related phenotypes, caused by insults such as reactive oxygen species, DNA damage, metabolic stress, or ER stress, and agents that further enhance these stresses could be developed as potential therapies. GSTP1-activated diazeniumdiolate/PARP inhibitor hybrid prodrugs selectively induce cancer cell death through ROS/DNA damage and ER stress overload, leading to apoptosis.
Citation Format: Anna E. Maciag, Joseph E. Saavedra, Ryan J. Holland, Youseung Kim, Vandana Kumari, Christina E. Luthers, Waheed S. Sehareen, Xinhua Ji, Lucy M. Anderson, Larry K. Keefer. GSTP1-activated nitric oxide-releasing/PARP inhibitor hybrid prodrugs induce cancer cell death through ROS/RNS, DNA damage, ER stress, and apoptosis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3334. doi:10.1158/1538-7445.AM2013-3334