Cancer-Induced Reprogramming of Host Glucose Metabolism: "Vicious Cycle" Supporting Cancer Progression

Unrestricted cancer growth requires permanent supply of glucose that can be obtained from cancer-mediated reprogramming of glucose metabolism in the cancer-bearing host. The pathological mechanisms by which cancer cells exert their negative influence on host glucose metabolism are largely unknown. This paper proposes a mechanism of metabolic and hormonal changes that may favor glucose delivery to tumor (not host) cells by creating a cancer-host "vicious cycle" whose prolonged action drives cancer progression and promotes host cachexia. To verify this hypothesis, a feedback model of host-cancer interactions that create the "vicious cycle" via cancer-induced reprogramming of host glucose metabolism is proposed. This model is capable of answering some crucial questions as to how anabolic cancer cells can reprogram the systemic glucose metabolism and why these pathways were not observed in pregnancy. The current paper helps to better understanding a pathogenesis of cancer progression and identify hormonal/metabolic targets for anti-cancer treatment.

Insulin resistance is a two-sided mechanism acting under opposite catabolic and anabolic conditions

The survival of multi-cellular organisms depends on the organism ability to maintain glucose homeostasis for time of low/high nutrient availability or high energy needs, and the ability to fight infections or stress. These effects are realized through the insulin controlled transport of blood glucose into the insulin-responsive cells such as muscle, fat and liver cells. Reduction in the ability of these cells to take glucose from the blood in response to normal circulating levels of insulin is known as insulin resistance (IR). Chronic IR is a key pathological feature of obesity, type 2 diabetes, sepsis and cancer cachexia, however temporal IR are widely met in fasting/ hibernation, pregnancy, anti-bacterial immunity, exercise and stress. Paradoxically, a certain part of the IR-cases is associated with catabolic metabolism, whereas the other is related to anabolic pathways. How can this paradoxical IR-response be explained? What is the metabolic basis of this IR variability and its physiological and pathological impacts? An answer to these questions might be achieved through the hypothesis in which IR is considered as a two-sided mechanism acting under opposite metabolic conditions (catabolism and anabolism) but with the common aim to sustain glucose homeostasis in a wide metabolic range. To test this hypothesis, I examined the main metabolic distinctions between the varied IR-cases and their dependence on the blood glucose concentration, level of the IR-threshold, and catabolic/anabolic activation. On the basis of the established interrelations, a simple model of IR-distribution has been developed. The model revealed the «U-type distribution» form with separation into two main IR-groups, each determined in the catabolic or anabolic conditions with one exception - type 2 diabetes and its paradoxical catabolic activation in anabolic conditions. The dual opposing (or complementary) role for the IR opens a new possibility for better understanding the cause and consequences of transition from adaptive IR-responses to its pathological forms.

A View on Pathogenesis of ≪Vicious Cancer Progression Cycle≫

Unrestricted tumor growth requires a permanent supply of glucose that can be obtained from cancer-stimulated hepatic glucose production and/or glucose redirecting from host insulin resistant tissues to cancer cells. This study proposes a mechanism based on metabolic and hormonal changes that may provoke glucose delivery to cancer cells through two interconnected "vicious cycles" whose continuous activity drives cancer progression. As follows from the proposed here feedback model, these "vicious cycles" result from cancer-mediated manipulation of host glucose sensors. The derived conclusions contribute to a better understanding of cancer pathogenesis and identifying potential therapeutic targets.

Glucose-lowering Strategies in Diabetes: Pharmacological Development of New Antidiabetic Drugs

Background:

Insulin increases glucose uptake in muscles and fat and inhibits hepatic glucose production, thus serving as the primary regulator of the blood glucose level. In type 2 diabetes, insufficient insulin release and suppressed insulin action [named insulin resistance] lead to increased glucose production in liver and decreased glucose uptake by muscles and fat tissues, resulting in elevated blood glucose concentration which is dangerous to human health. Therefore, the anti-diabetic therapies are aimed at inhibiting excess blood glucose.

Methods:

A comparative analysis of two distinct glucose-lowering modes was used to develop a new feedback model for the purpose of identification of pharmacological targets in diabetes treatment.

Results:

The current brief opinion proposes an original feedback control of glucose-lowering regulation and its models which allow comparing two distinct strategies of glucose level correction, i.e., one of them allows reducing the increased threshold of insulin resistance, whereas the other allows overcoming this threshold/barrier using exogenous insulin treatment. Also, this analytic research presents selected examples comparing the influence of the two analyzed strategies on the normalization of glucose metabolism, their therapeutic potential and side effects associated with additional weight gain. These models show the pathological mechanism by which exogenous insulin provokes formation of a «vicious cycle» by its side effects associated with additional weight gain.

Conclusion:

The presented model and findings can contribute to the development of new anti-diabetic targets and drugs with minimal side effects.