PO-035 Lkb1 deficiency renders non-small-cell lung cancer cells sensitive to erk inhibitor

Introduction Lung Cancer is the first cause of cancer-related death in the world. The alterations in KRAS oncogene are very frequent (25%), but, unfortunately, this protein is at present undruggable. KRAS mutations determine over-activation of important pathways of growth and proliferation (PI3K-AKT-mTOR and MAPK). KRAS-mutated tumours are also frequently co-mutated in LKB1 (50%), an important regulator of metabolic homeostasis and oxidative stress in the cells. LKB1 modulates catabolic processes through AMPK-mediated mTOR inhibition. Thereafter, the inactivation of LKB1 causes in KRAS mutated-tumours further activation of PI3K-AKT-mTOR and MAPK pathways, making them particularly aggressive. The possibility to specifically target tumours with both KRAS and LKB1 alterations represent an important medical need. Material and methods We generated from the NSCLC cell line NCI-H1299 clones over-expressing KRAS WT or KRAS G12C forms. These clones have been subsequently modified through CRISPR-CAS9 system to obtain deletions in LKB1 gene. We successfully generated isogenic cells differing only for the status of KRAS and LKB1 (KRAS wt /LKB1 wt , KRAS mut /LKB1 wt , KRAS wt /LKB1 mut , KRAS mut /LKB1 mut ). These clones were treated with a panel of inhibitors of MAPK and PI3K pathways. Viability was evaluated with MTS assay. Molecular characterizations were performed by western blot analysis. In vivo antitumor activity was determined after subcutaneous injection of NSCLC cells in immunodeficient mice. Results and discussions Using the isogenic system generated we tested the activity of several inhibitors of MAPK and PI3K pathways. The results highlighted a strong response of the clones with deletion in LKB1 to ERK inhibitor, independently from the KRAS status. These results were confirmed ‘ in vivo ’, where tumours with LKB1 deletion showed a significant sensitivity to ERK inhibitor, compared to LKB1 WT tumours. At molecular level we tested the activation of proteins related to MAPK and PI3K pathway such as p70, S6, 4-EBP1, ERK. The results showed that the response to ERK inhibitor was mainly due to mTOR signalling inhibition. Conclusion The results obtained highlight a possible strategy to target NSCLC with KRAS-LKB1 co-mutations, that, at moment are those with a worse prognosis. The sensitivity to ERK inhibitor is remarkable, also in presence of KRAS WT, therefore this strategy could be applied to all LKB1-mutated lung tumours, that represent 30% of all NSCLC. These studies are being confirmed in other NSCLC backgrounds and mouse models.