Abstract 1221: Selective translational activation of PBK (PDZ- binding kinase) reveals a molecular vulnerability of drug-tolerant persister cells to targeted therapies in EGFR-mutant lung adenocarcinoma

Abstract In lung adenocarcinoma (LUAD), EGFR-targeted therapies often result in incomplete tumor responses followed by disease progression caused by acquired resistance. As EGFR mutations are truncal (i. e. , present in every cell of a tumor), it remains unclear why a fraction of tumor cells can survive in the presence of drug treatment. It is increasingly recognized that drug-tolerant persister cells (DTPCs) can escape selective drug pressure and are important drivers of therapy failure and tumor relapse. The mechanisms underlying tumor cell adaptation and survival of DTPCs during therapy are not fully understood. Using EGFR-mutant LUAD cell lines treated with osimertinib, we unexpectedly observed that DTPCs display uncoupled mRNA and protein variations of PBK (PDZ Binding Kinase), a spindle assembly serine/threonine protein kinase. Mechanistically we discovered that although global protein synthesis is decreased upon osimertinib treatment, PBK translation is selectively maintained in DTPCs. The establishment and survival of DTPCs following EGFR inhibition is critically dependent on PBK, as genetic depletion of PBK reduces persistence to osimertinib treatment in vitro. PBK knockout leads to suppression of ERK1/2 reactivation following EGFR inhibition, and results in decreased expression of ZEB1 and Vimentin, key effectors of epithelial-to-mesenchymal transition (EMT), a hallmark of the DTPC phenotype. Consistently, combined treatment with osimertinib and OTS514 (PBK inhibitor) in vitro, reduces the DTPC fraction and decreases the enrichment of EMT-related transcriptional signatures. Similar results were obtained in LUAD patient-derived organoids, used to recapitulate the phenotype of residual disease in patients. In PDX treated with osimertinib, PBK is activated at both residual disease and acquired resistance. Concordantly, combined EGFR/PBK pharmacological inhibition was also effective in reverting osimertinib acquired resistance in vitro. Finally, in matched diagnosis and relapse samples from 7 EGFR-mutant LUAD patients treated with EGFR inhibitors, we observed increased PBK activation at the time of acquired resistance in 5 cases, including 3 EGFRT790M-positive cases, suggesting that PBK activation may co-occur with genetic resistant alterations. Our findings unveil a novel mechanism by which EGFR-mutant lung cancer DTPCs selectively translate PBK mRNA as an adaptive survival mechanism to persist during osimertinib treatment; and provide a therapeutic target of non-genetic drug resistance otherwise unlooked-for in routine transcriptomic analyses. A deeper understanding on the mRNA translational reprogramming in DTPCs is currently performed to uncover therapeutic vulnerabilities to reduce residual disease and delay or revert the emergence of acquired resistance. Citation Format: Camille Leonce, Anne-Laure Désage, Nour El-Houda Mourksi, Geneviève De Souza, Béatrice Vanbervliet, Camille Charrondière, Constance Nicq, Jérémy Néri, Aurélie Swalduz, Laurie Tonon, Eric Cumunel, Nicolas Gadot, Gabriel Ichim, Jean-Jacques Diaz, Christine Lovly, Julien Mazières, Mayeul Tabutin, Maurice Pérol, Sylvie Lantuejoul, Olivier Calvayrac, Fabien Forest, Virginie Marcel, Pierre Saintigny, Sandra Ortiz-Cuaran. Selective translational activation of PBK (PDZ- binding kinase) reveals a molecular vulnerability of drug-tolerant persister cells to targeted therapies in EGFR-mutant lung adenocarcinoma 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 (6Suppl): Abstract nr 1221.