[CANCER RESEARCH 64, 1252–1254, February 15, 2004] Advances in Brief Effect of Isocaloric Low-Fat Diet on Prostate Cancer Xenograft Progression to Androgen Independence Tung H. Ngo, 1 R. James Barnard, 1 Todd Anton, 1 Chris Tran, 2 David Elashoff, 3 David Heber, 2 Stephen J. Freedland, 4 and William J. Aronson 4 1 Departments of Physiological Science, 2 Medicine, 3 Biostatistics, and 4 Urology, University of California, Los Angeles, Los Angeles, California Abstract An isocaloric low-fat diet has been shown to slow androgen-sensitive Los Angeles Prostate Cancer-4 (LAPC-4) tumor growth in a mouse xe- nograft model. LAPC-4 cells were injected into male severe combined immunodeficient mice. After palpable tumors developed, the mice were divided into three groups, high-fat intact, high-fat castration, and low-fat castration. Tumor latency (18 versus 9 weeks; P < 0.001) and mouse survival (20.8  1.3 versus 13  0.7 weeks; P < 0.01) were significantly longer in the low-fat castration versus high-fat castration group. Reduced dietary fat intake delayed conversion from androgen-sensitive to -insen- sitive prostate cancer and significantly prolonged survival of severe com- bined immunodeficient mice bearing LAPC-4 xenografts. Introduction Prostate cancer growth is initially highly dependent on androgens, and androgen suppression leads to significant reduction in tumor burden in most patients. However, androgen insensitive (AI) disease inevitably develops resulting in tumor regrowth, metastasis, and even- tual mortality. Presently, the biological mechanisms involved in the conversion from androgen sensitive (AS) to AI disease remain unde- termined, and no effective treatments exist to prolong survival in men with AI prostate cancer. Dietary fat intake may play a role in AI prostate cancer growth. Linoleic acid (-6 polyunsaturated fatty acid) from corn oil is the predominant fatty acid in the American diet (largely in baked and fried goods). Linoleic acid has been found to exert a stimulatory effect on the growth of AS (LNCaP) and AI (PC-3) human prostate cancer cell lines (1). Moreover, animal feeding studies found increased -6 dietary fat intake increased the growth of AS prostate cancer xe- nografts (2, 3). Membrane arachidonic acid (-6) derived from lino- leic acid is converted by cyclooxygenase-2 to prostaglandin E 2 , which has been shown to promote prostate cancer cells growth in vitro (4, 5). Arachidonic acid is also metabolized by the lipoxygenase pathway to eicosanoids (leukotrienes and hydroxy derivatives of fatty acids) that play an important role in tumor progression and metastasis (6). Materials and Methods Animal Husbandry, Feeding Protocol, and Los Angeles Prostate Cancer-4 (LAPC-4) Injection. Twenty-four male CB17 beige severe com- bined immunodeficiency mice (8 weeks old) were obtained from the Univer- sity of California Los Angeles Department of Laboratory Animal Medicine facility, which is accredited by the American Association for Accreditation of Laboratory Animal Care. The mice were housed 1 per cage to allow for the maintenance of isocaloric intake between the groups. The experiments were approved by the University of California Los Angeles Chancellor’s Animal Research Committee, and animals were cared for in accordance with institu- tional guidelines. The diets were prepared and sterilized (irradiated) by DYETS, Inc. (Beth- lehem, PA). The high-fat diet contained 42% calories from corn oil, and the low-fat diet contained 12% calories from corn oil (Table 1). Equal caloric intake between the groups was maintained throughout the experiment by using a modified paired-feeding technique as described previously (2, 7). After 2 weeks of the high-fat diet, 10 5 LAPC-4 tumor cells in 0.1 ml of Matrigel (Collaborative Biomedical Products, Bedford, MA) were injected s.c. in the flank of all of the mice. Tumor cells were obtained from separately caged severe combined immunodeficient mice used for tumor propagation. All of the animals were maintained on a high-fat diet until they developed palpable tumors, at which time they were divided into three groups; group 1 (n = 4) continued to receive the high-fat diet (HF) and did not undergo castration; group 2 (n = 10) underwent castration and continued to receive the high-fat diet (HFC); and group 3 (n = 10) underwent castration and was placed on the low-fat diet (LFC). LAPC-4 Xenografts. The LAPC-4 cell line was a generous gift from Drs. Robert Reiter and Charles Sawyers (UCLA Departments of Urology and Medicine, Los Angeles, CA). Throughout the experiment, mice were weighed and tumors examined weekly. Tumor volumes, measured by calipers, were calculated using the formula length  width  height  0.5236. Serum Studies and Tumor Studies. The animals were euthanized when they met institutional guidelines (ruffled fur, hunched posture, impaired am- bulation, lethargy, decreased feeding, weight loss, and so forth). Serum from the brachial artery was collected at the time of sacrifice and stored at -80°C. Serum was also obtained from the LFC mice via the tail vein at the time the HFC mice were euthanized. Human serum prostate-specific antigen (PSA) was measured by ELISA (Diagnostic Systems Laboratories, Inc., Webster, TX). At the time of sacrifice, the tumors were removed, weighed, and tumor dimen- sions measured. Statistical Analysis. Statistical analyses (InStat Statistical Software; Graphpad, San Diego, CA) were performed by Student’s t test, Wilcoxon rank-sum, and ANOVA followed by Newman-Keuls post hoc analyses. Cor- relations between outcome variables were computed as the Pearson correlation coefficient. Survival curves between the different groups were compared using a log-rank survivorship analysis. Tumor latency times were calculated by modeling tumor growth as a linear latent phase followed by a linear growth phase. The latency time was determined by finding the optimal transition point between the two phases for each tumor. P  0.05 was considered significant. Data are expressed as means  SE. Results The mice in the HF, HFC, and LFC groups maintained equal caloric intake with each mouse consuming an average of 11.0 kcal/mouse/day Received 12/8/03; accepted 12/16/03. Grant support: NIH Specialized Programs of Research Excellence Grant P50 CA92131-01A1, CA42710, CAT00151, CA100938, and P50 AT00151-01 T. H. Ngo is currently a medical student at Western University, College of Osteopathic Medicine of the Pacific, Pomona, CA, and is supported by the American Federation for Aging Research (AFAR). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: S. J. Freedland is currently at Brady Urological Institute, Johns Hopkins Uni- versity School of Medicine, Baltimore, MD 21287. Requests for reprints: William J. Aronson, University of California Los Angeles, Department of Urology, 66-124 Center for the Health Sciences, Los Angeles, CA 90095-1738. Phone: (310) 268-3446; Fax: (310) 268-4858; E-mail: waronson@ucla.edu. 1252 Research. on January 30, 2016. © 2004 American Association for Cancer cancerres.aacrjournals.org Downloaded from