Thiocoraline alters neuroendocrine phenotype and activates the N otch pathway in MTC ‐ TT cell line

Medullary thyroid cancer ( MTC ) is an aggressive neuroendocrine tumor ( NET ). Previous research has shown that activation of N otch signaling has a tumor suppressor role in NET s. The potential therapeutic effect of thiocoraline on the activation of the N otch pathway in an MTC cell line ( TT ) was investigated. Thiocoraline was isolated from a marine bacterium V errucosispora sp. MTT assay (3‐[4, 5‐dimethylthiazole‐2‐yl]‐2, 5‐diphenyltetrazolium bromide) was used to determine the IC 50 value and to measure cell proliferation. W estern blot revealed the expression of N otch isoforms, NET , and cell cycle markers. Cell cycle progression was validated by flow cytometry. The mRNA expression of N otch isoforms and downstream targets were measured using real‐time PCR. The IC 50 value for thiocoraline treatment in TT cells was determined to be 7.6 nmol/L. Thiocoraline treatment decreased cell proliferation in a dose‐ and time‐dependent manner. The mechanism of growth inhibition was found to be cell cycle arrest in G1 phase. Thiocoraline activated the N otch pathway as demonstrated by the dose‐dependent increase in mRNA and protein expression of N otch isoforms. Furthermore, treatment with thiocoraline resulted in changes in the expression of downstream targets of the N otch pathway ( HES 1, HES 2, HES 6, HEY 1, and HEY 2) and reduced expression of NET markers, CgA, and ASCL 1. Thiocoraline is a potent N otch pathway activator and an inhibitor of MTC ‐ TT cell proliferation at low nanomolar concentrations. These results provide exciting evidence for the use of thiocoraline as a potential treatment for intractable MTC .