Humoral hypercalcemia of malignancy, a frequent complication of squamous cell 
carcinomas of the lung, is mediated by the parathyroid hormone-related peptide 
(PTHrP). This study was undertaken to determine whether 1,25-dihydroxyvitamin 
D(3) [1,25(OH)(2)D(3)] and two nonhypercalcemic analogues. EB1089 and 
22-oxa-1,25(OH)(2)D(3) (OCT), suppress PTHrP gene expression in a human lung 
squamous cancer cell line, NCI H520. All three compounds (1) decreased 
steady-state PTHrP mRNA and secreted peptide levels via a transcriptional 
mechanism; (2) modulated promoter activity of 1,25(OH)(2)D(3)-responsive DNA 
sequences; and (3) activated the vitamin D receptor (VDR) both in vitro and in 
vivo. Thus, EB1089 and OCT inhibit PTHrP gene expression in NCI H520 cells and 
modulate gene expression through the same mechanism as 1,25(OH)(2)D(3), namely, 
activation of the VDR. 1,25(OH)(2)D(3) is hypercalcemic in vivo. However, the 
noncalcemic analogues EB1089 and OCT have a therapeutic potential through 
suppression of PTHrP gene transcription.