Dual CHK1 and WNT Inhibition as a Synergistic Therapy for Gastrointestinal Neuroendocrine Carcinoma.

UNLABELLED: Gastrointestinal neuroendocrine carcinoma (GIS-NEC) is a highly aggressive malignancy with limited therapeutic options. To identify a therapeutic target, we performed transcriptomic profiling of 34 GIS-NEC and 30 well-differentiated gastrointestinal neuroendocrine tumors (GIS-NET) and found that checkpoint kinase 1 (CHEK1) is significantly overexpressed in GIS-NEC. Although CHEK1 expression was not prognostic across overall GIS-NEC, it was associated with poor outcome specifically in pancreatic NEC, in which it correlated with replication stress-associated genes, including cell division cycle 6 (CDC6) and claspin (CLSPN), both at the intercase level and across spatially distinct regions within individual tumors. Pharmacologic inhibition of checkpoint kinase 1 (CHK1) using prexasertib (LY2606368) suppressed cell proliferation, induced cell-cycle arrest, and increased DNA damage in most GIS-NEC cell lines, recapitulating the effects of CHEK1 knockdown. Antitumor efficacy was further confirmed in vivo. However, pancreatic NEC cell lines exhibited relative resistance to CHK1 inhibition, and transcriptomic analysis revealed enrichment of WNT signaling-related genes in these cells. Low-density lipoprotein receptor-related protein 8 (LRP8) was highly expressed in pancreatic NEC cases with high CHEK1 expression. WNT inhibition suppressed MYC-dependent transcriptional programs and downregulated replication-associated genes, including CDC6, thereby impairing replication capacity. Combined WNT and CHK1 inhibition further exacerbated replication stress and DNA damage, even at low CHK1 inhibitor doses. Collectively, these findings identify CHK1 as a therapeutic vulnerability in GIS-NEC and indicate that WNT-MYC signaling contributes to resistance by sustaining replication programs. Dual targeting of CHK1 and WNT-MYC pathways may therefore represent a promising therapeutic strategy, particularly in pancreatic NEC.

SIGNIFICANCE: CHEK1 is overexpressed in GIS-NEC and represents a therapeutic vulnerability. In tumors in which CHK1 inhibition alone is ineffective, combined CHK1 and WNT inhibition exerts synergistic effects, enhancing replication stress and DNA damage.