Endocrine Abstracts

Vitamin D receptor (VDR) and its ligand 1,25-Dihydroxyvitamin D3 (1,25OHD3) play, in general, an inhibitory role on the growth of normal and malignant cells. However, the mechanisms for this anti-proliferative action remain not completely understood. Recently, a 1,25OHD3-mediated effect on hormone production and steroidogenic genes has been reported in the human steroid-secreting adrenocortical cancer cell line NCI-H295R (Lundqvist J et al. 2010). The aim of this study was twofold: i) to test expression of vitamin D metabolism genes in normal adrenals and in a series of adrenal tumors as well as in the NCI-H295R cells; ii) to investigate the potential anti-proliferative action of 1,25OHD3 on NCI-H295R cells underlying the molecular mechanisms behind this effect. mRNA levels for CYP2R1 (i.e. the enzyme converting vitamin D3 to 25OHD3), CYP27B1 (i.e. the enzyme converting 25OHD3 to 1,25OHD3) and VDR were measured by RT-PCR and/or western blotting in both NCI-H29R cells and adrenal tissues. DNA synthesis was evaluated according to (3H)TdR cell incorporation after 96 h treatment of NCI-H295R cells with 1,25OHD3 at increasing doses, in comparison to untreated control cells. The effect of 1,25OHD3 on cell apoptosis and cell cycle was analyzed with a flow cytometer. CYP2R1, CYP27B1 and VDR were expressed in NCI-H295R cells and in all adrenal tissues analyzed (non-functioning adenomas, n=5; cortisol/aldosterone-secreting adenomas, n=9; cortisol-producing carcinoma, n=1). 1,25OHD3 inhibited cell proliferation by 20% at a dose of 10⁻⁸ M and induced a concomitant decrease in aldosterone and DHEA-S production. 1,25OHD3 induced cell cycle arrest, promoting accumulation of cells in G0/G1 phase without inducing apoptosis.

Conclusions: 1,25OHD3 has cytotoxic effects on the NCI-H295R cells by promoting cell cycle arrest. Expression of vitamin D metabolism genes in NCI-H295R cells as well as in normal and tumor adrenals suggests a potential paracrine role of vitamin D in adrenal growth and function. Because of its anti-proliferative action 1,25OHD3 could be considered for the treatment of patients with adrenocortical cancer.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This research did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.