Caspase-8 as a candidate mediator associated with everolimus resistance in neuroendocrine tumors

Everolimus, an mTORC1 inhibitor, is approved for treating pancreatic and lung neuroendocrine tumors (NETs), yet acquired resistance limits its long-term efficacy. The molecular mechanisms underlying resistance and potential strategies to overcome it remain poorly defined. RNA sequencing was performed in everolimus-sensitive and everolimus-resistant QGP-1 pancreatic NET cells (QS and QR, respectively) to identify transcriptional changes associated with everolimus resistance. Key differentially expressed genes were validated in QGP-1, H727 lung NET cells, and patient-derived Pa-NET cells using RT-qPCR. The potential functional involvement of caspase-8 (CASP8) was investigated pharmacologically using the preferential CASP8 inhibitor Z-IETD-FMK, alone or in combination with everolimus, by evaluating effects on cell viability and CASP activity. Differential expression analysis identified 292 genes significantly dysregulated in QR versus QS cells, including CASP8, A2M, MGP, PTGS1, and IGFBP5. Enrichment analysis highlighted pathways related to ECM remodeling, neuroactive ligand-receptor interactions, and GPCR signaling. Validation in H727 cells and primary Pa-NET samples showed some conserved transcriptional changes, with CASP8 upregulation emerging as a particularly consistent alteration. CASP8 inhibition reduced viability in both QS and QR cells, while combined Z-IETD-FMK and everolimus treatment produced the greatest decrease in QS viability and was associated with reduced CASP3/7 activity. Our study identifies CASP8 as a candidate mediator associated with everolimus resistance in NETs, together with alterations in ECM remodeling and receptor signaling. These findings support further investigation of CASP8-targeting strategies, particularly in combination with mTOR inhibition, as a potential approach to enhance therapeutic efficacy.