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Drug-tolerant “dormant” cells (DTC) have emerged as one of the major non-genetic mechanisms driving resistance to targeted therapy in lung cancer, although the sequence of events leading to entry and exit from dormancy remain poorly described. Here, we performed real-time monitoring of the cell cycle dynamics during the adaptive response to Epidermal Growth Factor Receptor tyrosine kinase inhibitors (EGFR-TKi) in a panel of EGFR-mutated lung cancer cell lines. We identified a rare population of S/G2 cycling cells (referred to as early escapers) that emerged in the first hours of treatment amongst stably arrested and progressively dying G1 cells. We determined that early escapers evolved from a non-proliferative differentiated alveolar type 1 (AT1) phenotype which was invariably associated with cytoskeletal remodeling through Rho/ROCK pathway activation. Using a panel of Rho-pathway inhibitors, we found that the farnesyltransferase inhibitor tipifarnib induced a complete clearance of EGFR-TKi-induced DTC thus fully preventing relapse in vitro. Using a xenograft model and a PDX model of EGFRL858R/T790M lung cancer, co-treatment with tipifarnib prevented relapse to osimertinib for up to 6 months with no evidence of toxicity. Among the farnesylated proteins regulated during osimertinib treatment, concomitant inhibition of RHOE and LaminB1 was sufficient to recapitulated FTIs’ effect. Osimertinib and tipifarnib co-treatment completely suppressed the emergence of AT1 phenotype, prevented mitosis of S/G2-treated cells and increased the apoptotic response through activation of ATF4-CHOP-dependent Integrated Stress Response (ISR) pathway. Our data strongly support the use of tipifarnib in combination with osimertinib in patients to effectively and durably prevent relapse.

Purpose: Drug-tolerance has emerged as one of the major non-genetic mechanism that drives resistance to targeted therapies in lung cancers. Identification of drug-tolerant cells (DTC) vulnerabilities thus represents an attractive strategy to prevent relapse in patients. We observed that EGFR-TKI-derived DTC displayed an increased level of DNA Double Strand Breaks (DSB), raising the hypothesis that genomic instability in these cells could favor the onset of resistance mechanisms. We tested AsiDNA, a small molecule that interferes with the DNA repair machinery, to prevent the emergence of resistances Experimental design: AsiDNA is a double stranded DNA molecule (decoy oligonucleotide) that mimics DNA DSB to interfere with DNA repair, by over-activating a false signaling of DNA damage through DNA-PK and PARP enzymes. We used EGFR-mutated (PC9 and HCC827) or ALK-translocated (H3122) lung tumor cells as well as a PC9 xenograft model, to assess whether a long-term combination of AsiDNA and TKI (erlotinib or osimertinib for EGFR-mutated and alectinib for ALK-translocated cells) could prevent the emergence of resistances arising from DTC. We also performed RNAseq to identify molecular mechanisms underlying AsiDNA effect on TKI-derived DTC. Results:Concomitant treatment of TKI with AsiDNA strongly prevented the emergence of TKI-resistant clones in the three cell lines tested, whereas AsiDNA alone did not display cytotoxic activity. Interestingly, AsiDNA didn’t increase the apoptotic activity of TKI but rather prevented the re-entry of drug-tolerant “dormant” cells into a proliferative state, ultimately resulting in DTC death. RNAseq data revealed a strong downregulation of gene signatures associated with cell cycle, DNA repair but also several pathways known to promote DTC survival such as Epithelial-to-Mesenchymal Transition (EMT) or Interferon pathway in AsiDNA+osimertinib vs osimertinib alone. In vivo, AsiDNA strongly interfered with the emergence of resistances in a PC9 xenograft model treated with erlotinib, resulting in a delayed relapse for the majority of tumors and a complete tumor regression for 20% of them, with no evidence of toxicity for mice. Conclusion: Inhibition of the DNA repair machinery using AsiDNA efficiently prevented the emergence of resistances to tyrosine kinase inhibitors and point to the therapeutic opportunity of combining AsiDNA and TKI to overcome resistance in clinical situation. These findings should have immediate implications to design drug combination strategies to prevent TKI-induced resistance in lung cancers. Citation Format: Sarah Figarol, Sandra Pagano, Wael Jdey, Hugo Guillaume, Gilles Favre, Olivier Calvayrac. DNA repair-interfering molecule AsiDNA® overcomes resistance to tyrosine kinase inhibitors in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 656.

International audience; Lung cancer is the leading cause of cancer-related deaths among men and women worldwide. Epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) are effective therapies for advanced non-small-cell lung cancer (NSCLC) patients harbouring EGFR-activating mutations, but are not curative due to the inevitable emergence of resistances. Recent in vitro studies suggest that resistance to EGFR-TKI may arise from a small population of drug-tolerant persister cells (DTP) through non-genetic reprogramming, by entering a reversible slow-to-non-proliferative state, before developing genetically derived resistances. Deciphering the molecular mechanisms governing the dynamics of the drug-tolerant state is therefore a priority to provide sustainable therapeutic solutions for patients. An increasing number of molecular mechanisms underlying DTP survival are being described, such as chromatin and epigenetic remodelling, the reactivation of anti-apoptotic/survival pathways, metabolic reprogramming, and interactions with their micro-environment. Here, we review and discuss the existing proposed mechanisms involved in the DTP state. We describe their biological features, molecular mechanisms of tolerance, and the therapeutic strategies that are tested to target the DTP.

Although lung cancer patients harboring EGFR mutations benefit from treatment with EGFR-tyrosine kinase inhibitors (EGFR-TKI), most of them rapidly relapse. RHOB GTPase is a critical player in both lung carcinogenesis and the EGFR signaling pathway; therefore, we hypothesized that it could play a role in the response to EGFR-TKI. In a series of samples from EGFR-mutated patients, we found that low RHOB expression correlated with a good response to EGFR-TKI treatment while a poor response correlated with high RHOB expression (15.3 versus 5.6 months of progression-free survival). Moreover, a better response to EGFR-TKI was associated with low RHOB levels in a panel of lung tumor cell lines and in a lung-specific tetracycline-inducible EGFR L858R transgenic mouse model. High RHOB expression was also found to prevent erlotinib-induced AKT inhibition in vitro and in vivo. Furthermore, a combination of the new-generation AKT inhibitor G594 with erlotinib induced tumor cell death in vitro and tumor regression in vivo in RHOB-positive cells. Our results support a role for RHOB/ AKT signaling in the resistance to EGFR-TKI and propose RHOB as a potential predictor of patient response to EGFR-TKI treatment.

Lung cancer is the leading cause of cancer mortality worldwide, with adenocarcinomas of the non‐small cell lung carcinoma (NSCLC) subtype accounting for the majority of cases. Therefore, an urgent need exists for a more detailed dissection of the molecular events driving NSCLC development and the identification of clinically relevant biomarkers. Even though originally identified as a tumour suppressor, recent studies associate the cytoplasmically (mis)localised CDK inhibitor p27Kip1 (p27) with unfavourable responses to chemotherapy and poor outcomes in NSCLC, supporting the hypothesis that the protein can execute oncogenic activities. In a recent issue of The Journal of Pathology, Calvayrac and coworkers uncover a novel molecular mechanism that can explain this oncogenic role of p27. They demonstrate that cytoplasmic p27 binds and inhibits the small GTPase RhoB and thereby relieves a selection pressure for RhoB loss that is frequently observed in NSCLC. This is supported not only by studies with genetically modified mice, but also through identification of a cohort of human lung cancer patients with cytoplasmic p27 and continued RhoB expression, where this signature correlates with decreased survival. This not only establishes a potentially useful biomarker, but also provides yet another facet of the complex roles p27 undertakes in tumourigenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.