Early radiotherapy delays acquired gefitinib resistance in EGFR-mutant NSCLC by suppressing c-FOS-associated survival signaling.

BACKGROUND

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have been widely used in the treatment of non-small cell lung cancer (NSCLC) harboring EGFR-sensitive mutations. However, acquired resistance remains a major clinical challenge. In a previous phase II clinical trial conducted by our group, early radiotherapy significantly delayed acquired resistance to EGFR-TKIs. Nevertheless, the optimal timing of radiotherapy and the underlying molecular mechanisms remain unclear.

METHODS

We compared gefitinib alone with gefitinib plus radiotherapy in EGFR-mutant NSCLC xenograft models and evaluated early versus late radiotherapy intervention. RNA sequencing of xenograft tumors was performed to identify timing-associated mediators of radiotherapy-delayed gefitinib resistance. Based on these findings, we used gefitinib-resistant NSCLC cell lines, radiotherapy, c-FOS perturbation, and pathway inhibition assays to validate the underlying mechanisms and assess treatment efficacy in vitro.

RESULTS

Gefitinib combined with radiotherapy showed enhanced antitumor activity in the xenograft model. Compared with gefitinib alone, early radiotherapy reduced tumor volume by approximately 70%-75% at the experimental endpoint, whereas late radiotherapy reduced tumor volume by approximately 50%. Early radiotherapy was associated with improved survival during the observation period compared with late radiotherapy; notably, median survival was not reached in the early radiotherapy group during follow-up. RNA-seq identified c-FOS as a timing-associated differentially expressed gene in xenograft tumors. In vitro, radiotherapy enhanced the sensitivity of gefitinib-resistant cells and reduced c-FOS expression. Mechanistically, c-FOS promoted survival and proliferation while inhibiting apoptosis in resistant cells, in association with increased PI3K/AKT and JNK/p38 signaling activity, thereby contributing to gefitinib resistance.

CONCLUSIONS

This study indicates that early radiotherapy delays acquired gefitinib resistance, at least in part, by suppressing c-FOS in the tested model system. c-FOS may serve as a candidate biomarker for radiotherapy timing and as a hypothesis-generating therapeutic target for combination strategies, although further validation in other EGFR-mutant subtypes and with later-generation EGFR-TKIs is required.