BackgroundThe risk of pancreatic cancer, the 4th deadliest cancer for both men and women in the United States, is increased by obesity. Calorie restriction (CR) is a well-known dietary regimen that prevents or reverses obesity and suppresses tumorigenesis in a variety of animal models, at least in part via inhibition of mammalian target of rapamycin (mTOR) signaling. Branched-chain amino acids (BCAA), especially leucine, activate mTOR and enhance growth and proliferation of myocytes and epithelial cells, which is why leucine is a popular supplement among athletes. Leucine is also increasingly being used as a treatment for pancreatic cancer cachexia, but the effects of leucine supplementation on pancreatic tumor growth have not been elucidated.ResultsSupplementation with leucine increased pancreatic tumor growth in both lean (104 ± 17 mm3 versus 46 ± 13 mm3; P <0.05) and overweight (367 ± 45 mm3 versus 230 ± 39 mm3; P <0.01) mice, but tumor enhancement was associated with different biological outcomes depending on the diet. In the lean mice, leucine increased phosphorylation of mTOR and downstream effector S6 ribosomal protein, but in the overweight mice, leucine reduced glucose clearance and thus increased the amount of circulating glucose available to the tumor.ConclusionsThese findings show that leucine supplementation enhances tumor growth in both lean and overweight mice through diet-dependent effects in a murine model of pancreatic cancer, suggesting caution against the clinical use of leucine supplementation for the purposes of skeletal muscle enhancement in cachectic patients.

New molecular targets and intervention strategies for breaking the obesity-pancreatic cancer link are urgently needed. Using relevant spontaneous and orthotopically transplanted murine models of pancreatic cancer, we tested the hypothesis that dietary energy balance modulation impacts pancreatic cancer development and progression through an insulin-like growth factor (IGF)-1–dependent mechanism. In LSL-KrasG12D/Pdx-1-Cre/Ink4a/Arflox/+ mice, calorie restriction, versus overweight- or obesity-inducing diet regimens, decreased serum IGF-1, tumoral Akt/mammalian target of rapamycin (mTOR) signaling, pancreatic desmoplasia, and progression to pancreatic ductal adenocarcinoma (PDAC); and increased pancreatic tumor-free survival. Serum IGF-1, Akt/mTOR signaling, and orthotopically transplanted PDAC growth were decreased in liver-specific IGF-1–deficient mice (versus wild-type mice), and rescued with IGF-1 infusion. Thus, dietary energy balance modulation impacts spontaneous pancreatic tumorigenesis induced by mutant Kras and Ink4a deficiency, the most common genetic alterations in human pancreatic cancer. Furthermore, IGF‐1 and components of its downstream signaling pathway are promising mechanistic targets for breaking the obesity-pancreatic cancer link.

BackgroundCalorie restriction (CR) prevents obesity and exerts anticancer effects in many preclinical models. CR is also increasingly being used in cancer patients as a sensitizing strategy prior to chemotherapy regimens. While the beneficial effects of CR are widely accepted, the mechanisms through which CR affects tumor growth are incompletely understood. In many cell types, CR and other nutrient stressors can induce autophagy, which provides energy and metabolic substrates critical for cancer cell survival. We hypothesized that limiting extracellular and intracellular substrate availability by combining CR with autophagy inhibition would reduce tumor growth more effectively than either treatment alone.ResultsA 30 % CR diet, relative to control diet, in nude mice resulted in significant decreases in body fat, blood glucose, and serum insulin, insulin-like growth factor-1, and leptin levels concurrent with increased adiponectin levels. In a xenograft model in nude mice involving H-RasG12V-transformed immortal baby mouse kidney epithelial cells with (Atg5+/+) and without (Atg5−/−) autophagic capacity, the CR diet (relative to control diet) genetically induced autophagy inhibition and their combination, each reduced tumor development and growth. Final tumor volume was greatest for Atg5+/+ tumors in control-fed mice, intermediate for Atg5+/+ tumors in CR-fed mice and Atg5−/− tumors in control-fed mice, and lowest for Atg5−/− tumors in CR mice. In Atg5+/+ tumors, autophagic flux was increased in CR-fed relative to control-fed mice, suggesting that the prosurvival effects of autophagy induction may mitigate the tumor suppressive effects of CR. Metabolomic analyses of CR-fed, relative to control-fed, nude mice showed significant decreases in circulating glucose and amino acids and significant increases in ketones, indicating CR induced negative energy balance. Combining glucose deprivation with autophagy deficiency in Atg5−/− cells resulted in significantly reduced in vitro colony formation relative to glucose deprivation or autophagy deficiency alone.ConclusionsCombined restriction of extracellular (via CR in vivo or glucose deprivation in vitro) and intracellular (via autophagy inhibition) sources of energy and nutrients suppresses Ras-driven tumor growth more effectively than either CR or autophagy deficiency alone. Interventions targeting both systemic energy balance and tumor-cell intrinsic autophagy may represent a novel and effective anticancer strategy.

New molecular targets and intervention strategies for breaking the obesity-pancreatic cancer link are urgently needed. Using relevant murine spontaneous and orthotopically transplanted models of pancreatic cancer, we tested the hypothesis that dietary energy balance modulation impacts pancreatic cancer development and progression through an insulin-like growth factor (IGF) 1—dependent mechanism. In LSL-KrasG12D/Pdx-1-Cre/Ink4a/Arflox/+ mice, calorie restriction, versus overweight- or obesity-inducing diet regimens, decreased serum IGF-1, tumoral Akt/mammalian target of rapamycin (mTOR) signaling, pancreatic desmoplasia, and progression to pancreatic ductal adenocarcinoma (PDAC); and increased pancreatic tumor-free survival by 50%. Serum IGF-1, Akt/mTOR signaling, and orthotopically transplanted PDAC growth were decreased in liver-specific IGF-1—deficient mice (versus wild-type mice), and rescued with IGF-1 infusion. Thus, dietary energy balance modulation impacts spontaneous pancreatic tumorigenesis induced by mutant Kras and Ink4a/Arf deficiency, the most common genetic alterations in human pancreatic cancer. Furthermore, IGF-1 and components of its downstream signaling pathway are promising mechanistic targets for breaking the obesity-pancreatic cancer link. Citation Format: Laura M. Lashinger, Lauren M. Harrison, Audrey J. Rasmussen, Craig D. Logsdon, Susan M. Fischer, Mark J. McArthur, Stephen D. Hursting. Dietary energy balance modulation of Kras- and Ink4a/Arf+/-driven pancreatic cancer: the role of insulin-like growth factor-1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-187. doi:10.1158/1538-7445.AM2013-LB-187

Branched chain amino acids (BCAA), prevalent in soy proteins, are commonly consumed at high levels in the form of food supplements. Of the BCAAs, leucine is the most potent activator of mTOR, a kinase at the crux of energy and growth factor signaling. mTOR is also frequently involved in dysregulated proliferation and survival signals in various cancers. We have previously shown that calorie restriction (CR) exerts potent anti-pancreatic cancer effects through reduced activation of the IGF-1/mTOR pathway. Thus we hypothesized that leucine supplementation would offset the anticancer effects of CR through restoration of mTOR signaling. To test this, 5×105 Panc02 mouse pancreatic cancer cells were subcutaneously injected into C57BL/6 male mice (n=15/group) that were fed one of three diets for 23 weeks beginning 4-6 weeks of age: AIN-76A control fed ad libitum (CON, 12 kcal%fat diet); CR (70% of weekly CON intake); and CR supplemented with L-Leucine (CR+Leu, 91-120 mg/day/mouse). Assigned diets were continued and tumors were palpated weekly for four more weeks (when 50% of CON tumors reached 1 cm in diameter) then tumors were measured ex vivo with calipers. Prior to tumor injection, body composition and insulin sensitivity were assessed by magnetic resonance imaging and a glucose tolerance test, respectively, at week 21 (n=11/group). Levels of energy balance-responsive hormones were assayed using serum collected at week 22 (CR groups, n=10; CON group, n=9). At week 21, the CR and CR+Leu groups had significantly reduced body weight (19.7 ± 0.3g and 21.3 ± 0.3g), lean mass (14.8 ± 0.4g and 15.6 ± 0.3g) and percent body fat (14.1 ± 1.1% and 16.3 ± 0.7%) relative to the CON group (36.0 ± 0.5g, 21.3 ± 0.6g and 35.0 ± 1.0%, p&lt;0.01), respectively. CR and CR+Leu displayed an enhanced rate of glucose clearance relative to the CON diet (p&lt;0.05). CR reduced circulating levels of IGF-1 (22.5 ± 1.2ng/mL), insulin (0.19 ± 0.08ng/mL) and leptin (0.69 ± 0.17ng/mL) relative to CON (61.3 ± 3.3ng/mL, 0.65 ± 0.13ng/mL and 13.3 ± 2.9ng/mL; p&lt;0.01), as did CR+Leu (29.9 ±1.9ng/mL, 0.19 ± 0.06ng/mL, 1.7 ± 0.25ng/mL; p&lt;0.01), respectively. CR and CR+Leu did not differ with respect to these parameters. CR+Leu tumors (103.8 ± 18.4mm3) were significantly larger than CR (46.4 ± 13.4mm3, p&lt;0.05), yet were smaller than CON (229.7 ± 40.1mm3, p&lt;0.05). CR significantly reduced tumor burden relative to CON (p&lt;0.0001). CR+Leu tumors also had higher levels of p-mTOR than CR, but not CON. We found that supplementation with L-Leucine blunts the anti-cancer effects of a CR diet in association with increases in mTOR signaling but does not alter other factors typically associated with the protective properties of CR (body composition, insulin sensitivity, and serum hormone levels). Therefore, our findings suggest that excessive protein supplementation using L-Leucine should be used with caution among those at high risk for developing pancreatic cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 809. doi:10.1158/1538-7445.AM2011-809