The DNA base excision repair (BER) pathway utilizes DNA glycosylases to initiate repair of specific DNA lesions, including base damage caused by reactive oxygen species. Human clinical trials suggest that inhibition of enzymes in the BER pathway (such as PARP1) can be useful in anti-cancer strategies, particularly when combined with certain DNA-damaging agents or tumor-specific genetic deficiencies. In this regard, there is a growing body of evidence that suggests inhibition of another BER enzyme, 8-oxoguanine DNA glycosylase-1 (OGG1) which initiates repair of the most abundant oxidatively-produced DNA base damage, 8-oxo-dG could be useful to treat certain types of cancer. Specifically, in acute myeloid leukemia (AML), both the RUNX1-ETO fusion subtype and the CBFB-MYH11 subtype share the common characteristic of having significant decreases in the expression of OGG1. Additionally, these two subtypes consistently correlate with the best prognosis for improved relapse-free and overall survival. Conversely, the 75-80% of AML patients with subtypes characterized by normal OGG1 message are strongly correlated with adverse cytogenetics, worse relapse-free and overall survival. Thus, decreased levels of OGG1 may contribute to increased therapeutic-induced cytotoxicities and improved patient responsiveness. Based on these human AML clinical outcomes data and transcriptomic analyses, it is postulated that in the majority of AML patients with normal levels of OGG1 message, OGG1 could be a novel target for therapeutic intervention to improve the long-term prognosis. Accordingly, we hypothesize that small molecule OGG1 inhibitors could be efficacious as an addition to current standard of care treatment for these patients. Consistent with this hypothesis, our preliminary data demonstrate that both immortalized human leukemia cells from the RUNX1-ETO fusion subtype, and Ogg1-/- mouse embryo fibroblasts are more sensitive to ROS-inducing conditions relative to cells expressing normal levels of OGG1 message. The goal of Aim 1, validation of OGG1 as a novel enzyme for therapeutic targeting, will be achieved as follows: 1) using human AML cells expressing normal levels of OGG1, determine if reduction in OGG1-initiated repair through either genetic manipulations or treatment with small molecule inhibitors will enhance cytotoxicity from standard chemotherapeutic treatments; and 2) test whether the sensitivity of cells from OGG1-deficient subtypes can be reversed by correcting this deficiency. These data will test the hypothesis that expression levels of OGG1 predict the relative cytotoxic responsiveness of various AML subtypes. Since our preliminary studies have identified two highly specific OGG1 inhibitor chemotypes, the goal of Aim 2 is to establish structure- activity relationships for these core structures and to validate their efficacy in high throughput cell biology assays. Collectively, these objectives will provide sufficient data to evaluate the potential of OGG1 as a novel therapeutic target and identify OGG1-specific drug-like precursor molecules.
Generally, patients diagnosed with acute myeloid leukemia (AML) have a poor 5-year survival prognosis. However, some AML patients have a better 5-year prognosis and many of these patients share a common feature of being deficient in a DNA repair pathway that when functioning normally, allows the leukemia cells to survive chemotherapy. This research will validate a DNA repair enzyme from this pathway as a novel target for AML therapeutics and develop drug molecules that will inhibit its activity to augment current chemotherapeutic treatments.
