Telotristat ethyl affects tumour-fibroblast crosstalk in small intestinal neuroendocrine tumours.

Small intestinal neuroendocrine tumours (SI-NETs) are associated with mesenteric fibrosis, which causes significant morbidity and mortality. Telotristat ethyl was developed to treat carcinoid syndrome in SI-NET patients. Recent studies indicated telotristat ethyl could have anti-tumour activity; however, the mechanism remains unclear. This study aimed to investigate the effects of telotristat ethyl on SI-NET-fibroblast crosstalk in tumour progression and mesenteric fibrosis. A co-culture paracrine model with GOT1 (tumour) cells and LX2 (stromal) cells was optimized. Cells were treated with conditioned medium with/without telotristat ethyl followed by RNA sequencing and Gene Set Enrichment Analysis. Quantitative RT-PCR, immunohistochemistry, and Western blot were performed on first and second tier targets in tissue from 34 SI-NET patients grouped into categories of mesenteric fibrosis severity. Telotristat ethyl significantly decreased proliferation and serotonin secretion in a dose-dependent manner in GOT1 cells. GSEA data indicated ECM-related reactomes were downregulated in GOT1 cells grown in conditioned medium of LX2 cells with telotristat ethyl. LAMA5, COL6A2, and COL12A1 expression was significantly increased in mild and severely fibrotic patients. Immunohistochemistry determined the localization of proteins such as COL4A2 in the stroma and ADAM12 in tumour cells. Protein analysis of second tier targets showed differences in expression, including β-catenin, which was significantly upregulated, and pAKT/AKT, which tended to increase in primary tumour compared to normal SI. Telotristat ethyl affects the expression of genes associated with the ECM and interferes with SI-NET-fibroblast crosstalk. Further analysis is required; however, this study represents an important step in understanding the mechanisms of telotristat ethyl when treating SI-NET patients.