Evaluating activation of MAPK signaling as a potential mechanism of acquired resistance to lorlatinib in ALK-rearranged lung cancer.

e20000 Background: The third-generation ALK tyrosine kinase inhibitor (TKI) lorlatinib has significantly advanced the clinical management of advanced ALK-rearranged non-small cell lung cancer (NSCLC). However, most patients develop acquired resistance within one to two years of treatment, and the molecular mechanisms underlying this resistance remain poorly understood. Methods: We conducted an integrated analysis of whole-exome sequencing (WES), RNA sequencing (RNAseq), and reverse phase protein array (RPPA) data to investigate the mechanisms of resistance to lorlatinib. Additionally, lorlatinib-resistant cell lines and cell line-derived xenograft (CDX) models were used to evaluate the efficacy of potential combination therapies. Results: WES analysis from an ALK-rearranged NSCLC patient who sequentially received crizotinib, ceritinib, and lorlatinib, but eventually developed resistance, identified a MAP2K2P298L mutation associated with lorlatinib resistance. This mutation led to the activation of ERK1/2. Integrated RNAseq and RPPA data analyses confirmed MAPK signaling pathway activation in lorlatinib-resistant H3122-LR cells. Immunohistochemical staining of pre- and post-lorlatinib tumor specimens revealed significantly elevated pERK1/2 levels following the emergence of resistance. Combination therapy using lorlatinib and the MEK inhibitor trametinib demonstrated synergistic effects, significantly inhibiting tumor proliferation and reversing resistance in both H3122-LR cells and CDX models. Conclusions: Activation of the MAPK signaling pathway contributes to acquired resistance to lorlatinib in ALK-rearranged NSCLC. Combining lorlatinib with trametinib represents a promising therapeutic strategy to overcome this resistance and improve clinical outcomes for patients who no longer respond to lorlatinib.