VDR and melanoma: The effect exerted on cell proliferation by our novel analogs was observed to be dependent on the presence of VDR in cells, as the SK-MEL 188b cells which lack VDR expression were largely unresponsive to the analogs Indeed, a lack of VDR has been reported to be a mechanism that underlies unresponsiveness of melanoma cells to the antiproliferative effects of vitamin D analogs, as reported by Seifert et al. in the case of the SK-MEL 5 cell line [61] (see also Szyszka et al. [40] for recent review).