2324P - Trametinib and PD-1 combined blockade impairs tumor growth and improves survival of KRAS-mutant lung cancer through Id1 downregulation

Background

Although anti-PD-1/PD-L1 antibodies represent a major breakthrough in NSCLC therapy, this treatment’s efficacy is highly dependent on tumor PD-L1 expression. We previously reported the role of Id1 in lung adenocarcinoma and the efficacy of a combined blockade of PD-1 and Id1, through RNA silencing, in KRAS-mutant LUAD murine models. Trametinib, an oral MEK1/2 inhibitor, acts downstream of KRAS. Here we evaluate trametinib as a pharmacological Id1 inhibitor able to enhance immunotherapy efficacy through PD-L1 overexpression.

Methods

To explore whether MEK1/2 inhibition reduces Id1 expression, in vitro and in vivo experiments were conducted in NSCLC cells and in murine models. RNAseq analysis was performed to elucidate the pathways involved in Id1 inhibition. Apoptosis and PD-L1 expression was measured by flow cytometry. Synergy of trametinib anti-PD1 combo was investigated in KRAS-mutant LUAD models.

Results

Experiments in KRAS-mutant NSCLC cells and mice models showed Id1 inhibition after MEK1/2 blockade. Blockade of proteasome activity with MG-132, restored Id1 levels. Trametinib-resistant (TR) cells did not show Id1 inhibition, moreover, Id1 silencing rescued the sensitivity to trametinib in human and murine NSCLC TR cells (p<0.001). Flow cytometry analysis showed increased PD-L1 expression (p<0.001) in NSCLC cell lines after trametinib administration. In contrast, Id1-overexpressing cells did not show PD-L1 upregulation after trametinib. In vivo experiments confirmed a synergistic therapeutic efficacy of the trametinib and anti-PD-1 combo, reducing tumor growth (p<0.05) and increasing mice survival (p<0.05), compared with either trametinib or immunotherapy alone. Moreover, the immune population’s analysis showed a significant increase in CD8⁺ T and a reduction in Treg cells in tumors of mice receiving combination treatment.

Conclusions

Pharmacological inhibition of MEK1/2 decreased Id1 expression in vitro and in vivo, replicating the effect of a shRNA against Id1, through proteasome activation. PD-L1 upregulation induced by Id1 blockade after trametinib treatment sensitized NSCLC cells to anti-PD-1 immunotherapy, blocking tumor growth and improving overall survival.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

The authors.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.