Abstract 1875: Enhanced lung cancer treatment using AOH1996, a potent PCNA inhibitor

Abstract AOH1996 targets a cancer-associated form of PCNA (caPCNA) by altering the protein-protein interface between caPCNA and its many binding partners. AOH1996 does this by inserting into the PCNA-interacting protein-box (PIP-box) pocket that is, in part, defined by the interdomain connecting loop (IDCL), the site of interaction between PCNA and most of its many binding partners. As a result, AOH1996 inhibits PCNA functions such as DNA replication, DNA repair, and transcription-replication conflict (TRC) resolution leading to cell cycle arrest and apoptosis. These effects are cancer specific and AOH1996 has little effect on non-cancerous cells even at 6-fold the effective dose in cancer cells. AOH1996 was developed in our lab and is currently in Phase I human clinical trials. Six patients have been enrolled in the trial and have not experienced AOH1996-related toxicities as the doses have been escalated to levels found to be efficacious in preclinical animal studies. Resistance to EGFR tyrosine kinase inhibitors (TKIs) poses a significant challenge in the treatment of non-small cell lung cancer (NSCLC) patients harboring EGFR activating mutations. Initially, EGFR TKIs like gefitinib, erlotinib, afatinib and osimertinib deliver remarkable responses, inducing tumor regression and improving overall survival. However, the emergence of resistance mechanisms, such as secondary EGFR mutations and bypass signaling pathway activation, hampers the efficacy of these drugs over time. The functional relationship between PCNA and EGFR has implications for the treatment of lung cancer patients with activating EGFR mutations. Membrane-localized EGFR modulates the PCNA-centric process of DNA replication through signaling pathways such as the Ras-Raf-Mek-Erk, PI3K/AKT, and PLCγ1/PKC signaling pathways. Nucleus-localized EGFR enhances PCNA stability by phosphorylating PCNA on tyrosine 211 (Y211), which prevents its degradation. In addition, phosphorylation at Y211 by EGFR results in decreased association of PCNA with MutS, which results in reduced mismatch repair (MMR). In this study, we combine AOH1996 and osimertinib as an innovative approach to treating NSCLC cancers with activating EGFR mutations and find that the drug combination: 1.) enhances the killing of NSCLC cell lines with activating EGFR mutations and acquired resistance to TKIs; 2.) enhances the destabilization of PCNA on chromatin; and 3.) causes changes in the localization and colocalization of PCNA and EGFR. We conclude that the combination of AOH1996 and osimertinib holds much potential as an improved treatment regimen for lung cancer patients with activating EGFR mutations. Citation Format: Robert G. Lingeman, Robert J. Hickey, Linda H. Malkas. Enhanced lung cancer treatment using AOH1996, a potent PCNA inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1875.