Abstract 1963: Novel small molecule inhibitor of the endonuclease function of the APE1 DNA repair and redox signaling enzyme blocks proliferation and reduces viability of glioblastoma cells

Abstract

Abstract The DNA Base Excision Repair (BER) pathway repairs DNA damaged by endogenous and exogenous agents including chemotherapeutic agents. Removal of the damaged base by a DNA glycosylase creates an apurinic / apyrimidinic (AP) site. AP Endonuclease1 (APE1), a critical component in this pathway that hydrolyzes the phosphodiester backbone 5’ to the AP site. Failure to repair AP sites leads to DNA strand breaks, enhanced cytotoxicity, cell cycle arrest and increased apoptosis. In addition to APE1's role in repair, it also functions as a redox signaling factor to activate key transcription factors such as AP1 (Fos/Jun), p53, NFkB, HIF-1α, and others controlling the expression of genes important for cell survival and cancer promotion and progression. APE1 has been shown to have an altered level of expression in a variety of cancers including pancreatic, breast, prostate, gliomas, sarcomas and others. High APE1 expression has also been associated with chemoradiotherapy poor outcome, poor complete response rate, shorter local relapse-free interval, poorer survival and high angiogenesis. Due to APE1's critical role in repairing chemotherapy- and IR-induced DNA damage, we hypothesize that inhibiting APE1's DNA repair activity would not only allow us to further elucidate the role of DNA repair that elevated levels of APE1 play in tumors, but would also allow us to delineate the importance of its DNA repair and redox functions in normal cellular processes. While reducing the amount of APE1 in cancer cells using anti-sense oligonucleotide technology and RNA interference sensitizes tumor cells to chemotherapeutic agents, it may not be the most efficacious route of treatment. We have concluded a screen of small molecule compounds for their ability to inhibit APE1 AP endonuclease activity. Four families of compounds with IC50 values less than 10 μM were identified, validated and characterized. One of the most promising compounds, designated AR03 inhibited cleavage of AP sites in vivo in SF767 glioblastoma cells, in vitro in whole cell extracts and inhibits purified human APE1 in vitro. AR03 has low affinity for dsDNA and it does not affect the redox function of APE1. AR03 also potentiates the cytotoxicity of methyl methane sulfonate (MMS) and temozolomide (TMZ) in SF767 cells. AR03 is chemically distinct from all the previously reported small molecule inhibitors of APE1 which are either ineffective in vivo due to poor cellular uptake, not tested in cellular based scenarios, or lacking in specificity. Thus, AR03 is a novel small molecule inhibitor of APE1, which may have potential as an oncotherapeutic drug for treating glioblastoma and other cancers. Additional studies are needed to determine the effect of AR03 in combination with other cancer chemotherapeutic agents, in combination with other APE1 inhibitors or other emerging BER targets such as PARP. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1963.