Abstract 5918: A novel glutathione S-transferase P (GSTP) siRNA (NDT-05-1040) for the treatment of KRAS-driven non-small cell lung cancer

Lung cancer is the most common form of cancer worldwide and the leading cause of cancer-related deaths. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancers, and KRAS mutation occurs in 25-30% of NSCLC. However, to date, direct therapeutic targeting of KRAS has not been achieved. Our approach to developing a KRAS mutant NSCLC therapeutic agent was to identify a selective novel target involved in modulating signaling proteins in the RAS pathway without impacting healthy cells. Numerous studies have shown that glutathione S-transferase P (GSTP) is strongly upregulated in many cancer types, specifically lung, colon, and pancreas. Besides being a well-known Phase II detoxification enzyme, GSTP is also known to influence cell signaling through interaction with MAP kinases such as JNK and c-jun. We therefore hypothesized that GSTP knockdown (KD) could be an effective therapeutic approach to treat KRAS mutant tumors. To test this hypothesis, we designed a series of novel GSTP siRNAs and identified our lead candidate, a highly potent and selective GSTP siRNA (NDT-05-1040) to specifically target and downregulate GSTP protein. A panel of KRAS mutant NSCLC cell lines was utilized to determine the GSTP KD potency and antiproliferative activity of NDT-05-1040. Western blot analysis and co-immunoprecipitation (co-IP) were conducted to identify the proteins that were regulated by GSTP in the proliferation and apoptosis pathways. These studies demonstrated that NDT-05-1040 is a very potent and selective GSTP siRNA. Furthermore, transfection of NDT-05-1040 led to significant growth inhibition and induced apoptosis in NSCLC cells without affecting normal cell viability. Western blot analysis showed that NDT-05-1040 effectively decreased the phosphorylation of CRAF, ERK, MEK, in the MAP kinase pathway. Interestingly, with NDT-05-1040 treatment, the phosphorylation of Akt and mTOR in the PI3K pathway was also decreased. Moreover, the activity of p-JNK, PUMA, caspase-3/7, and p53 in the KRAS mutant cells was upregulated by NDT-05-1040. Co-IP experiments demonstrated that GSTP formed a complex with both p-CRAF and JNK. In summary, GSTP KD by NDT-05-1040 targeted the RAS/MEK/ERK, Akt, mTOR and apoptosis pathways. This selective multipronged attack on the growth and survival pathways of cancer cells makes it a compelling target and could potentially serve as a novel therapeutic agent for KRAS mutant NSCLC. Citation Format: Cima Cina, Jens Harborth, Zhihong O9Brien, Nish Beltran-Raygoza, Jung-kang Jin, Jessica Xu, Sang Jun Lee, Kwok Tsang, Jiping Yao, Roger Adami, Sonya Zabludoff, Wenbin Ying. A novel glutathione S-transferase P (GSTP) siRNA (NDT-05-1040) for the treatment of KRAS-driven non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5918.