We determined the in vitro
biological activities of 1 alpha, 25-dihdroxyvitamin D(3) (1,25-D(3)) and its analogue, 20-epi-22-oxa-24a, 26a, 27a-trihomo-1 alpha, 25 (
OH)(2)
vitamin D(3) (
KH1060) in six human
neuroblastoma (NB) cell lines (SH-SY5Y, NB69, SK-N-AS, IMR5, CHP-134, NGP). The ability of these compounds to inhibit cell growth and
DNA synthesis was evaluated by
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and
BrdU incorporation, respectively. The induction of cell death was monitored by
caspase-3 activity. Their
antineoplastic effect was assessed by clonal proliferation in soft
agar.
KH1060 was more effective than 1,25 D(3) in inhibiting cell growth and
DNA synthesis. The IC-(50) (inhibition of 50% cell viability) indicated that
KH1060 was about 10-20-fold more potent than 1,25 D(3). This growth inhibition was also accompanied by induction of
caspase-3 activity, indicating that these compounds induce cell death in a
caspase-dependent fashion. Moreover,
KH1060 exerted potent
antineoplastic activity by suppressing the clonal proliferation of the six NB cells. For the first time we demonstrate that
KH1060 induces the expression of
retinoic acid receptor-beta and p21(Cip1) suggesting that these
proteins in part mediate the growth inhibitory effects. Taken together, all the six NB cells were more susceptible to growth inhibition by
KH1060 than 1,25-D(3), suggesting its possible use in NB to potentiate the action of
retinoids, which are in clinical use for this disease.