Evidence for Feedback Regulation Following Cholesterol Lowering Therapy in a Prostate Cancer Xenograft Model.

BACKGROUND: Epidemiologic data suggest cholesterol-lowering drugs may prevent the progression of prostate cancer, but not the incidence of the disease. However, the association of combination therapy in cholesterol reduction on prostate or any cancer is unclear. In this study, we compared the effects of the cholesterol lowering drugs simvastatin and ezetimibe alone or in combination on the growth of LAPC-4 prostate cancer in vivo xenografts. METHODS: Proliferation assays were conducted by MTS solution and assessed by Student's t-test. 90 male nude mice were placed on a high-cholesterol Western-diet for 7 days then injected subcutaneously with 1 × 105 LAPC-4 cells. Two weeks post-injection, mice were randomized to control, 11 mg/kg/day simvastatin, 30 mg/kg ezetimibe, or the combination and sacrificed 42 days post-randomization. We used a generalized linear model with the predictor variables of treatment, time, and treatment by time (i.e., interaction term) with tumor volume as the outcome variable. Total serum and tumor cholesterol were measured. Tumoral RNA was extracted and cDNA synthesized from 1 ug of total RNA for quantitative real-time PCR. RESULTS: Simvastatin directly reduced in vitro prostate cell proliferation in a dose-dependent, cell line-specific manner, but ezetimibe had no effect. In vivo, low continuous dosing of ezetimibe, delivered by food, or simvastatin, delivered via an osmotic pump had no effect on tumor growth compared to control mice. In contrast, dual treatment of simvastatin and ezetimibe accelerated tumor growth. Ezetimibe significantly lowered serum cholesterol by 15%, while simvastatin had no effect. Ezetimibe treatment resulted in higher tumor cholesterol. A sixfold induction of low density lipoprotein receptor mRNA was observed in ezetimibe and the combination with simvastatin versus control tumors. CONCLUSIONS: Systemic cholesterol lowering by ezetimibe did not slow tumor growth, nor did the cholesterol independent effects of simvastatin and the combined treatment increased tumor growth. Despite lower serum cholesterol, tumors from ezetimibe treated mice had higher levels of cholesterol. This study suggests that induction of low density lipoprotein receptor is a possible mechanism of resistance that prostate tumors use to counteract the therapeutic effects of lowering serum cholesterol. Prostate 77:446-457, 2017. © 2016 Wiley Periodicals, Inc.

Low-carbohydrate diets and prostate cancer: how low is "low enough"?

Previous studies indicate that carbohydrate intake influences prostate cancer biology, as mice fed a no-carbohydrate ketogenic diet (NCKD) had significantly smaller xenograft tumors and longer survival than mice fed a Western diet. As it is nearly impossible for humans to consume and maintain NCKD, we determined whether diets containing 10% or 20% carbohydrate kcal showed similar tumor growth as NCKD. A total of 150 male severe combined immunodeficient mice were fed a Western diet ad libitum, injected with the human prostate cancer cell line LAPC-4, and then randomized 2 weeks later to one of three arms: NCKD, 10% carbohydrate, or 20% carbohydrate diets. Ten mice not injected were fed an ad libitum low-fat diet (12% fat kcal) serving as the reference in a modified-paired feeding protocol. Mice were sacrificed when tumors reached 1,000 mm(3). Despite consuming extra calories, all mice receiving low-carbohydrate diets were significantly lighter than those receiving a low-fat diet (P < 0.04). Among the low-carbohydrate arms, NCKD-fed mice were significantly lighter than the 10% or 20% carbohydrate groups (P < 0.05). Tumors were significantly larger in the 10% carbohydrate group on days 52 and 59 (P < 0.05), but at no other point during the study. Diet did not affect survival (P = 0.34). There were no differences in serum insulin-like growth factor-I or insulin-like growth factor binding protein-3 at sacrifice among the low-carbohydrate arms (P = 0.07 and P = 0.55, respectively). Insulin was significantly lower in the 20% carbohydrate arm (P = 0.03). LAPC-4 xenograft mice fed a low-carbohydrate diet (10-20% carbohydrate kcal) had similar survival as mice consuming NCKD (0% carbohydrate kcal).

Effect of isocaloric low fat diet on prostate cancer xenograft progression in a hormone deprivation model.

PURPOSE: Previous mouse studies suggesting that low fat diets slow prostate cancer growth often used corn oil (omega-6), which enhances prostate cancer growth, as the primary fat. Using a saturated fat based diet we previously found no significant difference in tumor growth between low and high fat fed SCID mice (Taconic Farms, Hudson, New York) xenografted with LAPC-4 cells. Whether similar results would hold in a castration model is unclear. MATERIALS AND METHODS: A total of 80 male SCID mice were fed a Western diet (40% fat and 44% carbohydrate) and injected with LAPC-4 human prostate cancer cells. When tumors were 200 mm(3), the mice were castrated and randomized to an isocaloric Western or a low fat diet (12% fat and 72% carbohydrate). Animals were sacrificed when tumors were 1,000 mm(3). Serum was collected and assayed for prostate specific antigen, insulin, insulin-like growth factor 1 and insulin-like growth factor binding protein 3. Tumors were assayed for total and phosphorylated Akt. RESULTS: Mouse weight was equivalent in the 2 groups. Overall dietary group was not significantly associated with survival (log rank p = 0.32). There were no statistically significant differences in prostate specific antigen (p = 0.53), insulin-like growth factor axis parameters (each p >0.05) or p-Akt-to-t-Akt ratios (p = 0.22) between the groups at sacrifice. CONCLUSIONS: In this xenograft model we found no difference in tumor growth or survival between low fat vs Western fed mice when the fat source was saturated fat. These results conflict with those of other studies in which corn oil was used to show that low fat diets delay prostate cancer growth, suggesting that fat type may be as important as fat amount in the prostate cancer setting.