The complexities of obesity and diabetes with the development and progression of pancreatic cancer

Abstract

Pancreatic cancer (PC) is one of the most lethal malignant diseases with the worst prognosis. It is ranked as the fourth leading cause of cancer-related deaths in the United States. Many risk factors have been associated with PC. Interestingly, large numbers of epidemiological studies suggest that obesity and diabetes, especially type-2 diabetes, are positively associated with increased risk of PC. Similarly, these chronic diseases (obesity, diabetes, and cancer) are also a major public health concern. In the U.S. population, 50 percent are overweight, 30 percent are medically obese, and 10 percent have diabetes mellitus (DM). Therefore, obesity and DM have been considered as potential risk factors for cancers; however, the focus of this article is restricted to PC. Although the mechanisms responsible for the development of these chronic diseases leading to the development of PC are not fully understood, the biological importance of the activation of insulin, insulin like growth factor-1 (IGF-1) and its receptor (IGF-1R) signaling pathways in insulin resistance mechanism and subsequent induction of compensatory hyperinsulinemia has been proposed. Therefore, targeting insulin/IGF-1 signaling with anti-diabetic drugs for lowering blood insulin levels and reversal of insulin resistance could be useful strategy for the prevention and/or treatment of PC. A large number of studies have demonstrated that the administration of anti-diabetic drugs such as metformin and thiazolidinediones (TZD) class of PPAR-γ agonists decreases the risk of cancers, suggesting that these agents might be useful anti-tumor agents for the treatment of PC. In this review article, we will discuss the potential roles of metformin and TZD anti-diabetic drugs as anti-tumor agents in the context of PC and will further discuss the complexities and the possible roles of microRNAs (miRNAs) in the pathogenesis of obesity, diabetes, and PC.

Figure 1

Potential pathways directly linking obesity and diabetes to pancreatic cancer. Obesity and diabetes cause mutiple alterations in glucose and lipid hemastasis, microenvironments, and immune responses, which result in the activation of several oncogenic signaling pathways. These deregulations increase cell survival and proliferation, eventually leading to the development and progression of pancreatic cancer. ROS, reactive oxygen species; IGF-1, insulin-like growth factor-1; IR, insulin receptors; IGF-1R, insulin-like growth factor-1 receptors; TNFR, tumor necrosis factor receptors; TLR, Toll-like receptors; HIF-1α, hypoxia-inducible factor-α1; AMPK, AMP kinase; IKK, IκB kinase; PPAR-γ, peroxisome proliferator-activated receptor-γ; VEGF, vascular endothelial growth factor; MAPK, MAP kinase; mTOR, mammalian target of rapamycin; TSC, tuberous sclerosis complex; Akt, protein kinase B. PI3K, phosphoinositide-3-kinase; STAT3, activator of transcription-3; JNK, c-Jun NH2-terminal kinase.