Abstract 200P
Background
Non-small cell lung cancer (NSCLC), the most common cause of cancer-related deaths, harbors RET rearrangements in up to 2% of cases. Novel selective RET inhibitors, BLU-667 and LOXO-292, showed promising anti-tumor activity. Despite the positive clinical outcomes, not all patients benefit from RET inhibitors and a significant fraction eventually progress, underscoring the need to discover novel therapeutic approaches.
Methods
We chronically exposed CCDC6/RET Lc-2/AD NSCLC cells to increasing doses of BLU-667 and LOXO-292 to generate cells resistant to the drugs (BluR and LoxoR, respectively). RNA-Seq analysis was used to define transcriptional profiles sustaining resistance. SiRNA-mediated knock-down and pharmacological treatment were used to re-sensitize resistant cells, while stable over-expression of candidate gene to induce resistant phenotype in sensitive cells. We further tested combination therapies in vivo.
Results
RNA-Seq studies revealed (i) a significant enrichment of Epidermal Growth Factor Receptor (EGFR) signaling pathway in BluR and LoxoR cells compared to sensitive parental cells, and (ii) AP1 complex members hyper-activation in resistant models. We hypothesized that, under AP1 regulation, EGFR could prompt compensatory mechanisms to RET inhibition, in turn pushing signalling pathways (MAPK) responsible for cell proliferation. siEGFR, as well as AP1 complex members siRNAs, led to a drastic reduction of cell viability and a significant decrease of MAPK activation in BluR/LoxoR cells, overcoming the resistant phenotype. On the other hand, we verified that EGFR over-expression reduced sensitivity of NSCLC cells to RET inhibitors. Since combination study revealed a synergistic effect of BLU-667 and anti-EGFR (afatinib) in vitro, we injected Lc-2/AD-BluR xenografts in Balb/c mice and we verified that tumor growth resulted impaired by combination of afatinib and BLU-667. These data strongly support our hypothesis of a pivotal role for EGFR in anti-RET resistance.
Conclusions
Our findings suggested that targeting EGFR signaling pathway in combination with RET inhibitors therapy may provide a novel treatment strategy for patients unresponsive to RET inhibitors in NSCLC.
Legal entity responsible for the study
The authors.
Funding
Italian Association for Cancer Research (AIRC).
Disclosure
D. Esposito: Financial Interests, Institutional, Funding: AIRC. A. Servetto: Financial Interests, Institutional, Funding: AIRC. L. Formisano: Financial Interests, Institutional, Funding: AIRC. R. Bianco: Financial Interests, Institutional, Funding: AIRC. All other authors have declared no conflicts of interest.