ELSEVIER BASIC SCIENCE CME ARTICLE VITAMIN D INHIBITION OF PROSTATE ADENOCARCINOMA GROWTH AND METASTASIS IN THE DUNNING RAT PROSTATE MODEL SYSTEM ROBERT H. GETZENBERG, BENJAMIN W. LIGHT, PAUL E. LAPCO, BADRINATH R. KONETY, AJAY K. NANGIA, JAMES S. ACIERNO, RAJIV DHIR, ZOYA SHURIN, ROGER S. DAY, DONALD L. TRUMP, AND CANDACE S. JOHNSON ABSTRACT Objectives. Risk factors for prostate cancer (PCs)-related mortality include old age, black race, and residence in northern latitudes. The objectives of this study are to examine the in vitro and in vivo effects of 1,25-dihydroxycholecalciferol [ 1 ,25-D3) and less-hypercalcemic analogues on the Dunning rat prostate adenocarcinoma model. Methods. To evaluate the effect of 1,25-D, on PCs in vitro, we used the highly metastatic Mat-lylu (MLL) and moderately metastatic R3327-AT-2 (AT-2) Dunning prostate cell lines, and examined effects on growth, clonogenicity, differentiation, and cell cycle. In vivo analysis included examination of the effects of these compounds on tumor growth and metastasis. Results. Using both the 3-day MTT and 7-day clonogenic assay, 1,25-D, demonstrated a growth inhibitory effect with a concentration for 50% inhibition (I&,) of approximately 20 FM for both MLL and AT-2. Cell cycle analysis of treated MLL cells (10 PM 1,25-D, for 48 hours) had 25% more cells in the Go/G, phase than did control cells. To examine the in vivo effect of 1,25-D, and the less hypercalcemic vitamin D analogue, Ro25-6760 (or 6760), on MLL PCs growth and metastasis, tumors (5 x lo5 cells) were implanted subcu- taneously into the flank of Copenhagen rats on the same day that treatment was initiated with 1,25-D, (1 pg) or 6760 (1 or 5 pg); rats received treatment three times a week. After 3 weeks, 1 ,25-D3 and 6760 (5 pg dosing) resulted in an inhibition of tumor volume and a reduction in the number and size of lung metastases. Conclusions. These preclinical studies demonstrate the profound in vitro, or in vivo, or both antiproliferative and differentiating effects of 1,25-D, and 6760 on PCs and suggest that these drugs may have potential beneficial effects in the treatment of advanced PCs. UROLOGY 50: 999-l 006, 1997. 0 1997, Elsevier Science Inc. All rights reserved. P rostate cancer (PCs) is currently the most often diagnosed cancer in the United States. Given the large number of men diagnosed each year with PCs, adequate therapy, if not prevention, of this disease will be necessary to reduce its huge clinical impact. Epidemiologic data demonstrate that many of the major risk factors for clinically signif- This work was supported by USPHS grants CA 67267, CA 60397, and P30 CA47904from the National Cancer Institute, NH. From the Departments of Pathology, Medicine, Otolaryngol- ogy, Surgery, Biostatistics, and Pharmacology, University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania Reprint requests: Robert H. Getzenberg, Ph.D., University of Pittsburgh Cancer Institute, 200 Lothrop Street, BST E-1056, Pittsburgh, PA 15213-2582 Submitted: April 24, 1997, accepted (with revisions):June 19, 1997 0 1997, ELSEVIER SCIENCE INC. ALL RIGHTS RESERVED icant PCs can be correlated with low serum levels of 1,25dihydroxycholecalciferol (1,25-D,) (vita- min D,),l the form of 1,25-D, that is known to be active in various mammalian tissues, including the prostate. Schwartz and Hulkal found mortality rates from PCs to be higher in northern latitudes and that PCs mortality rates by county within the United States were inversely correlated with the availability of ultraviolet radiation.2 The major source of 1,25-D, for most Americans is endoge- nous synthesis dependent on and, in some, limited by casual integument exposure to sunlight. These authors, proposing that 1,25-D, may serve to maintain the differentiated phenotype of prostatic cells, postulate that inadequate levels of 1,25-D, could permit neoplastic growth. Older age and black race are also associated with lower serum 0090-4295/97/$17.00 PII SOO90-4295(97)00408-l 9%