Human breast tumor slices: a model for identification of vitamin D regulated genes in the tumor microenvironment.

While many studies have addressed the direct effects of 1α,25(OH)2D3 on breast cancer (BC) cells, stromal–epithelial interactions, which are important for the tumor development, have been largely ignored. In addition, high concentrations of the hormone, which cannot be attained in vivo, have been used. Our aim was to establish a more physiological breast cancer model, represented by BC tissue slices, which maintain epithelial–mesenchymal interactions, cultured with a relatively low 1α,25(OH)2D3 concentration, in order to evaluate the vitamin D pathway. Freshly excised human BC samples were sliced and cultured in complete culture media containing vehicle, 0.5nM or 100nM 1α,25(OH)2D3 for 24h. BC slices remained viable for at least 24h, as evaluated by preserved tissue morphology in hematoxylin and eosin (HE) stained sections and bromodeoxyuridine (BrdU) incorporation by 10% of tumor cells. VDR mRNA expression was detected in all samples and CYP24A1 mRNA expression was induced by 1α,25(OH)2D3 in both concentrations (but mainly with 100nM). Our results indicate that the vitamin D signaling pathway is functional in BC slices, a model which preserves stromal–epithelial interactions and mimics in vivo conditions.