The study aimed at evaluating the effects of calcitriol and of its analogues on the
proliferation of TT and rMTC cells (human and rat line tumour cells originating
from thyroid medullary carcinoma) and at examining the effects of the substances
on the secretion of the principal hormones of the cells, calcitonin (CT)
and calcitonin gene-related peptide (CGRP). Cells of thyroid medullary carcinoma
(human TT cells and rat rMTC cells) were cultured for 5 days in the absence
or in the presence of calcitriol and of its two analogues (PRI-1906 and PRI-2191)
in concentrations of 10-9 to 10-6 M. Calcitriol and the applied analogues weakly
inhibited proliferation of thyroid medullary carcinoma in in vitro conditions. The
evident effect of analogues on hormone secretion points to their effect on the
process of CT gene expression