Growth inhibition and differentiation in human prostate carcinoma cells induced by the vitamin D analog 1α,24‐dihydroxyvitamin D2

Background Vitamin D has been suggested as a chemopreventive and therapeutic modality for prostate cancer. However, hypercalcemic toxicity has limited the use of 1α,25-dihydroxyvitamin D3 (1,25-(OH)2D3) in clinical trials, prompting the search for analogs of vitamin D with less toxicity while retaining efficacy as a modality for cancer intervention. In this study, the less hypercalcemic vitamin D analog 1α,24-dihydroxyvitamin D2 (1,24-(OH)2D2) was examined for its effects on cellular growth inhibition and differentiation induction in the LNCaP human prostate carcinoma cell line. Methods LNCaP cell growth was determined by quantifying DNA levels. Protein levels were determined using the ELISA method and immunoblotting. Levels of mRNA were determined using real-time quantitative reverse transcriptase PCR. Results LNCaP growth was decreased 50% by exposure to 0.01 nM 1,24-(OH)2D2 after 96 hr in the presence of a growth stimulatory 0.1 nM dose of the androgen R1881. Prostate specific antigen (PSA) levels were increased 3.5-fold with 10 nM 1,24-(OH)2D2 treatment compared to a 1.9-fold increase in PSA levels found with 10 nM 1,25-(OH)2D3 under low androgen conditions. Neither 1,24-(OH)2D2 nor 1,25-(OH)2D3 affected the expression of cytokeratin 18 protein levels. Treatment with 10 nM 1,24-(OH)2D2 alone produced a 1.3-fold increase in AR mRNA and a 2.2-fold increase in AR protein levels after 96 hr. Surprisingly, the addition of 1.0 nM R1881 alone or in combination with 10 nM 1,24-(OH)2D2 produced an approximately 60% decrease in AR mRNA, whereas AR protein levels were increased 1.6-fold. Conclusions Overall, 1,24-(OH)2D2 was found to be at least as effective as 1,25-(OH)2D3 at inhibiting growth and inducing differentiation markers in LNCaP prostate carcinoma cells and may thus prove useful in prostate cancer treatment. Prostate 55: 159–167, 2003. © 2003 Wiley-Liss, Inc.