Effects of vitamin D and retinoic acid on human glioblastoma cell lines

The biological significance of vitamin D receptors expressed by glioblastoma and other glial tumours is still unclear. In an effort to clarify this issue we studied the effects of increasing concentrations of 25-dihydroxyvitamin D₃ and its metabolite 1 α, 25-dihydroxyvitamin D₃ on two human glioblastoma cell lines. Both substances were capable of inducing a significant (> 50%) reduction in growth of the two glioblastoma cell lines at dosages over 5 μM. When the HU 70 cell line was treated by increasing dilutions of 25-dihydroxyvitamin D₃ combined with 1 μM all trans-retinoic acid, significant inhibition was apparent even after addition of 25-dihydroxyvitamin D³ in the nanomolar range. Reduction of growth index was mainly due to induced cell death. Our results provide in vitro evidence that vitamin D metabolites alone or in combination with retinoids may be potentially useful agents in the differentiation therapy of human malignant gliomas.