Modulation of the leptin receptor mediates tumor growth and migration of pancreatic cancer cells

Decoding the Influence of Obesity on Prostate Cancer and Its Transgenerational Impact

In recent decades, the escalating prevalence of metabolic disorders, notably obesity and being overweight, has emerged as a pressing concern in public health. Projections for the future indicate a continual upward trajectory in obesity rates, primarily attributable to unhealthy dietary patterns and sedentary lifestyles. The ramifications of obesity extend beyond its visible manifestations, intricately weaving a web of hormonal dysregulation, chronic inflammation, and oxidative stress. This nexus of factors holds particular significance in the context of carcinogenesis, notably in the case of prostate cancer (PCa), which is a pervasive malignancy and a leading cause of mortality among men. A compelling hypothesis arises from the perspective of transgenerational inheritance, wherein genetic and epigenetic imprints associated with obesity may wield influence over the development of PCa. This review proposes a comprehensive exploration of the nuanced mechanisms through which obesity disrupts prostate homeostasis and serves as a catalyst for PCa initiation. Additionally, it delves into the intriguing interplay between the transgenerational transmission of both obesity-related traits and the predisposition to PCa. Drawing insights from a spectrum of sources, ranging from in vitro and animal model research to human studies, this review endeavors to discuss the intricate connections between obesity and PCa. However, the landscape remains partially obscured as the current state of knowledge unveils only fragments of the complex mechanisms linking these phenomena. As research advances, unraveling the associated factors and underlying mechanisms promises to unveil novel avenues for understanding and potentially mitigating the nexus between obesity and the development of PCa.

Dietary fat and lipid metabolism in the tumor microenvironment

Metabolic reprogramming has been considered a core hallmark of cancer, in which excessive accumulation of lipids promote cancer initiation, progression and metastasis. Lipid metabolism often includes the digestion and absorption of dietary fat, and the ways in which cancer cells utilize lipids are often influenced by the complex interactions within the tumor microenvironment. Among multiple cancer risk factors, obesity has a positive association with multiple cancer types, while diets like calorie restriction and fasting improve health and delay cancer. Impact of these diets on tumorigenesis or cancer prevention are generally studied on cancer cells, despite heterogeneity of the tumor microenvironment. Cancer cells regularly interact with these heterogeneous microenvironmental components, including immune and stromal cells, to promote cancer progression and metastasis, and there is an intricate metabolic crosstalk between these compartments. Here, we focus on discussing fat metabolism and response to dietary fat in the tumor microenvironment, focusing on both immune and stromal components and shedding light on therapeutic strategies surrounding lipid metabolic and signaling pathways.

Decoding the obesity-cancer connection: lessons from preclinical models of pancreatic adenocarcinoma

Obesity is a metabolic state of energy excess and a risk factor for over a dozen cancer types. Because of the rising worldwide prevalence of obesity, decoding the mechanisms by which obesity promotes tumor initiation and early progression is a societal imperative and could broadly impact human health. Here, we review results from preclinical models that link obesity to cancer, using pancreatic adenocarcinoma as a paradigmatic example. We discuss how obesity drives cancer development by reprogramming the pretumor or tumor cell and its micro- and macro-environments. Specifically, we describe evidence for (1) altered cellular metabolism, (2) hormone dysregulation, (3) inflammation, and (4) microbial dysbiosis in obesity-driven pancreatic tumorigenesis, denoting variables that confound interpretation of these studies, and highlight remaining gaps in knowledge. Recent advances in preclinical modeling and emerging unbiased analytic approaches will aid in further unraveling the complex link between obesity and cancer, informing novel strategies for prevention, interception, and therapy in pancreatic adenocarcinoma and other obesity-associated cancers.

Multifaceted effects of obesity on cancer immunotherapies: Bridging preclinical models and clinical data

Obesity, defined by excessive body fat, is a highly complex condition affecting numerous physiological processes, such as metabolism, proliferation, and cellular homeostasis. These multifaceted effects impact cells and tissues throughout the host, including immune cells as well as cancer biology. Because of the multifaceted nature of obesity, common parameters used to define it (such as body mass index in humans) can be problematic, and more nuanced methods are needed to characterize the pleiotropic metabolic effects of obesity. Obesity is well-accepted as an overall negative prognostic factor for cancer incidence, progression, and outcome. This is in part due to the meta-inflammatory and immunosuppressive effects of obesity. Immunotherapy is increasingly used in cancer therapy, and there are many different types of immunotherapy approaches. The effects of obesity on immunotherapy have only recently been studied with the demonstration of an "obesity paradox", in which some immune therapies have been demonstrated to result in greater efficacy in obese subjects despite the direct adverse effects of obesity and excess body fat acting on the cancer itself. The multifactorial characteristics that influence the effects of obesity (age, sex, lean muscle mass, underlying metabolic conditions and drugs) further confound interpretation of clinical data and necessitate the use of more relevant preclinical models mirroring these variables in the human scenario. Such models will allow for more nuanced mechanistic assessment of how obesity can impact, both positively and negatively, cancer biology, host metabolism, immune regulation, and how these intersecting processes impact the delivery and outcome of cancer immunotherapy.

SHP2 regulates adipose maintenance and adipocyte-pancreatic cancer cell crosstalk via PDHA1

Adipocytes are the most abundant cell type in the adipose tissue, and their dysfunction is a significant driver of obesity-related pathologies, such as cancer. The mechanisms that (1) drive the maintenance and secretory activity of adipocytes and (2) mediate the cancer cellular response to the adipocyte-derived factors are not fully understood. To address that gap of knowledge, we investigated how alterations in Src homology region 2-containing protein (SHP2) activity affect adipocyte function and tumor crosstalk. We found that phospho-SHP2 levels are elevated in adipose tissue of obese mice, obese patients, and differentiating adipocytes. Immunofluorescence and immunoprecipitation analyses as well as in-silico protein-protein interaction modeling demonstrated that SHP2 associates with PDHA1, and that a positive association promotes a reactive oxygen species (ROS)-driven adipogenic program. Accordingly, this SHP2-PDHA1-ROS regulatory axis was crucial for adipocyte maintenance and secretion of interleukin-6 (IL-6), a key cancer-promoting cytokine. Mature adipocytes treated with an inhibitor for SHP2, PDHA1, or ROS exhibited an increased level of pro-lipolytic and thermogenic proteins, corresponding to an increased glycerol release, but a suppression of secreted IL-6. A functional analysis of adipocyte-cancer cell crosstalk demonstrated a decreased migration, invasion, and a slight suppression of cell cycling, corresponding to a reduced growth of pancreatic cancer cells exposed to conditioned media (CM) from mature adipocytes previously treated with inhibitors for SHP2/PDHA1/ROS. Importantly, PDAC cell growth stimulation in response to adipocyte CM correlated with PDHA1 induction but was suppressed by a PDHA1 inhibitor. The data point to a novel role for (1) SHP2-PDHA1-ROS in adipocyte maintenance and secretory activity and (2) PDHA1 as a regulator of the pancreatic cancer cells response to adipocyte-derived factors.

Adipose-Tumor Crosstalk contributes to CXCL5 Mediated Immune Evasion in PDAC

Background

CXCR1/2 inhibitors are being implemented with immunotherapies in PDAC clinical trials. Cytokines responsible for stimulating these receptors include CXCL ligands, typically secreted by activated immune cells, fibroblasts, and even adipocytes. Obesity has been linked to poor patient outcome and altered anti-tumor immunity. Adipose-derived cytokines and chemokines have been implicated as potential drivers of tumor cell immune evasion, suggesting a possibility of susceptibility to targeting specifically in the context of obesity.

Methods

RNA-sequencing of human PDAC cell lines was used to assess differential influences on the cancer cell transcriptome after treatment with conditioned media from peri-pancreatic adipose tissue of lean and obese PDAC patients. The adipose-induced secretome of PDAC cells was then assessed by cytokine arrays and ELISAs. Lentiviral transduction and CRISPR-Cas9 was used to knock out CXCL5 from a murine PDAC cell line for orthotopic tumor studies in diet-induced obese, syngeneic mice. Flow cytometry was used to define the immune profiles of tumors. Anti-PD-1 immune checkpoint blockade therapy was administered to alleviate T cell exhaustion and invoke an immune response, while the mice were monitored at endpoint for differences in tumor size.

Results

The chemokine CXCL5 was secreted in response to stimulation of PDAC cells with human adipose conditioned media (hAT-CM). PDAC CXCL5 secretion was induced by either IL-1β or TNF, but neutralization of both was required to limit secretion. Ablation of CXCL5 from tumors promoted an immune phenotype susceptible to PD-1 inhibitor therapy. While application of anti-PD-1 treatment to control tumors failed to alter tumor growth, knockout CXCL5 tumors were diminished.

Conclusions

In summary, our findings show that known adipokines TNF and IL-1β can stimulate CXCL5 release from PDAC cells in vitro. In vivo , CXCL5 depletion alone is sufficient to promote T cell infiltration into tumors in an obese setting, but requires checkpoint blockade inhibition to alleviate tumor burden.

DATA AVAILABILITY STATEMENT

Raw and processed RNAseq data will be further described in the GEO accession database ( awaiting approval from GEO for PRJ number ). Additional raw data is included in the supplemental material and available upon reasonable request.

WHAT IS ALREADY KNOWN ON THIS TOPIC

Obesity is linked to a worsened patient outcome and immunogenic tumor profile in PDAC. CXCR1/2 inhibitors have begun to be implemented in combination with immune checkpoint blockade therapies to promote T cell infiltration under the premise of targeting the myeloid rich TME.

WHAT THIS STUDY ADDS

Using in vitro/ex vivo cell and tissue culture-based assays with in vivo mouse models we have identified that adipose derived IL-1β and TNF can promote tumor secretion of CXCL5 which acts as a critical deterrent to CD8 T cell tumor infiltration, but loss of CXCL5 also leads to a more immune suppressive myeloid profile.

HOW THIS STUDY MIGHT AFFECT RESEARCH PRACTICE OR POLICY

This study highlights a mechanism and emphasizes the efficacy of single CXCR1/2 ligand targeting that could be beneficial to overcoming tumor immune-evasion even in the obese PDAC patient population.

Assessment of the Role of Leptin and Adiponectinas Biomarkers in Pancreatic Neuroendocrine Neoplasms

Data on the possible connection between circulating adipokines and PanNENs are limited. This novel study aimed to assess the serum levels of leptin and adiponectin and their ratio in patients with PanNENs and to evaluate the possible relationship between them and PanNEN's grade or stage, including the presence of metastases. The study group consisted of PanNENs (n = 83), and healthy controls (n = 39). Leptin and adiponectin measurement by an ELISA assay was undertaken in the entire cohort. The serum concentration of adiponectin was significantly higher in the control group compared to the study group (p < 0.001). The concentration of leptin and adiponectin was significantly higher in females than in males (p < 0.01). Anincreased leptin-adiponectin ratio was observed in well-differentiated PanNENs (G1) vs. moderatelydifferentiated PanNENs (G2) (p < 0.05). An increased leptin-adiponectin ratio was found in PanNENs with Ki-67 < 3% vs. Ki-67 ≥ 3% (p < 0.05). PanNENs with distal disease presented lower leptin levels (p < 0.001) and a decreased leptin-adiponectin ratio (p < 0.01) compared with the localized disease group. Leptin, adiponectin, and the leptin-adiponectin ratio may serve as potential diagnostic, prognostic, and predictive biomarkers for PanNENs. Leptin levels and the leptin-adiponectin ratio may play an important role as predictors of malignancy and metastasis in PanNENs.

New insights into the role of adipocytes in pancreatic cancer progression: paving the way towards novel therapeutic targets

Pancreatic cancer (PC) remains one of the most lethal malignancies across the world, which is due to delayed diagnosis and resistance to current therapies. The interactions between pancreatic tumor cells and their tumor microenvironment (TME) allow cancer cells to escape from anti-cancer therapies, leading to difficulties in treating PC. With endocrine function and lipid storage capacity, adipose tissue can maintain energy homeostasis. Direct or indirect interaction between adipocytes and PC cells leads to adipocyte dysfunction characterized by morphological change, fat loss, abnormal adipokine secretion, and fibroblast-like transformation. Various adipokines released from dysfunctional adipocytes have been reported to promote proliferation, invasion, metastasis, stemness, and chemoresistance of PC cells via different mechanisms. Additional lipid outflow from adipocytes can be taken into the TME and thus alter the metabolism in PC cells and surrounding stromal cells. Besides, the trans-differentiation potential enables adipocytes to turn into various cell types, which may give rise to an inflammatory response as well as extracellular matrix reorganization to modulate tumor burden. Understanding the molecular basis behind the protumor functions of adipocytes in PC may offer new therapeutic targets.

Aging augments obesity-induced thymic involution and peripheral T cell exhaustion altering the "obesity paradox"

Introduction

The incidence of obesity, a condition characterized by systemic chronic inflammation, has reached pandemic proportions and is a poor prognostic factor in many pathologic states. However, its role on immune parameters has been diverse and at times contradictory. We have previously demonstrated that obesity can result in what has been called the "obesity paradox" which results in increased T cell exhaustion, but also greater efficacy of immune checkpoint blockade in cancer treatment.

Methods

The role of obesity, particularly in the context of aging, has not been robustly explored using preclinical models. We therefore evaluated how age impacts the immune environment on T cell development and function using diet-induced obese (DIO) mice.

Results

We observed that DIO mice initially displayed greater thymopoiesis but then developed greater thymic involution over time compared to their lean counterparts. Both aging and obesity resulted in increased T cell memory conversion combined with increased expression of T cell exhaustion markers and Treg expansion. This increased T cell immunosuppression with age then resulted in a loss of anti-tumor efficacy by immune checkpoint inhibitors (ICIs) in older DIO mice compared to the younger DIO counterparts.

Discussion

These results suggest that both aging and obesity contribute to T cell dysfunction resulting in increased thymic involution. This combined with increased T cell exhaustion and immunosuppressive parameters affects immunotherapy efficacy reducing the advantage of obesity in cancer immunotherapy responses.

Obesity and endocrine-related cancer: The important role of IGF-1

Obesity is increasingly becoming a global epidemic of concern and is considered a risk factor for several endocrine-related cancers. Moreover, obesity is associated with cancer development and poor prognosis. As a metabolic abnormality, obesity leads to a series of changes in insulin, IGF-1, sex hormones, IGFBPs, and adipokines. Among these factors, IGF-1 plays an important role in obesity-related endocrine cancers. This review describes the role of obesity in endocrine-related cancers, such as prostate cancer, breast cancer and pancreatic cancer, focusing on the mechanism of IGF-1 and the crosstalk with estrogen and adipokines. In addition, this review briefly introduces the current status of IGF-1R inhibitors in clinical practice and shows the prospect of IGF-1R inhibitors in combination with other anticancer drugs.

Palmitoyl Carnitine-Anchored Nanoliposomes for Neovasculature-Specific Delivery of Gemcitabine Elaidate to Treat Pancreatic Cancer

Being the fourth most fatal malignancy worldwide, pancreatic cancer is on track to become the second leading cause of cancer-related deaths in the United States by 2030. Gemcitabine is a first-line chemotherapeutic agent for pancreatic ductal adenocarcinoma (PDAC). Gemcitabine Elaidate (Gem Elaidate) is a lipophilic derivative which allows hENT1-independent intracellular delivery of gemcitabine and better pharmacokinetics and entrapment in a nanocarrier. Cancer cells and neovasculature are negatively charged compared to healthy cells. Palmitoyl-DL-carnitine chloride (PC) is a Protein kinase C (PKC) inhibitor which also provides a cationic surface charge to nanoliposomes for targeting tumor neovasculature and augmented anticancer potency. The objectives of our study are: (a) to develop and characterize a PKC inhibitor-anchored Gem Elaidate-loaded PEGylated nanoliposome (PGPLs) and (b) to investigate the anticancer activity of Gem Elaidate and PGPLs in 2D and 3D models of pancreatic cancer. The optimized PGPLs resulted in a particle size of 80 ± 2.31 nm, a polydispersity index of 0.15 ± 0.05 and a ζ-potential of +31.6 ± 3.54 mV, with a 93.25% encapsulation efficiency of Gem Elaidate in PGPLs. Our results demonstrate higher cellular uptake, inhibition in migration, as well as angiogenesis potential and significant apoptosis induced by PGPLs in 3D multicellular tumor spheroids of pancreatic cancer cells. Hence, PGPLs could be an effective and novel nanoformulation for the neovasculature-specific delivery of Gemcitabine Elaidate to treat PDAC.

Modeling Obesity-Driven Pancreatic Carcinogenesis-A Review of Current In Vivo and In Vitro Models of Obesity and Pancreatic Carcinogenesis

Pancreatic ductal adenocarcinoma (PDAC) is the most common pancreatic malignancy with a 5-year survival rate below 10%, thereby exhibiting the worst prognosis of all solid tumors. Increasing incidence together with a continued lack of targeted treatment options will cause PDAC to be the second leading cause of cancer-related deaths in the western world by 2030. Obesity belongs to the predominant risk factors for pancreatic cancer. To improve our understanding of the impact of obesity on pancreatic cancer development and progression, novel laboratory techniques have been developed. In this review, we summarize current in vitro and in vivo models of PDAC and obesity as well as an overview of a variety of models to investigate obesity-driven pancreatic carcinogenesis. We start by giving an overview on different methods to cultivate adipocytes in vitro as well as various in vivo mouse models of obesity. Moreover, established murine and human PDAC cell lines as well as organoids are summarized and the genetically engineered models of PCAC compared to xenograft models are introduced. Finally, we review published in vitro and in vivo models studying the impact of obesity on PDAC, enabling us to decipher the molecular basis of obesity-driven pancreatic carcinogenesis.

The Role of Adipokines in Pancreatic Cancer

In modern society, inappropriate diets and other lifestyle habits have made obesity an increasingly prominent health problem. Pancreatic cancer (PC), a kind of highly aggressive malignant tumor, is known as a silent assassin and is the seventh leading cause of cancer death worldwide, pushing modern medicine beyond help. Adipokines are coming into notice because of the role of the intermediate regulatory junctions between obesity and malignancy. This review summarizes the current evidence for the relationship between highly concerning adipokines and the pathogenesis of PC. Not only are classical adipokines such as leptin and adiponectin included, but they also cover the recognized chemerin and osteopontin. Through a summary of the biological functions of these adipokines as well as their receptors, it was discovered that in addition to their basic function of stimulating the biological activity of tumors, more studies confirm that adipokines intervene in the progression of PC from the viewpoint of tumor metabolism, immune escape, and reprogramming of the tumor microenvironment (TME). Besides endocrine function, the impact of white adipose tissue (WAT)-induced chronic inflammation on PC is briefly discussed. Furthermore, the potential implication of the acknowledged endocrine behavior of brown adipose tissue (BAT) in relation to carcinogenesis is also explored. No matter the broad spectrum of obesity and the poor prognosis of PC, supplemental research is needed to unravel the detailed network of adipokines associated with PC. Exploiting profound therapeutic strategies that target adipokines and their receptors may go some way to improving the current worrying prognosis of PC patients.

Obesity and Pancreatic Cancer: Recent Progress in Epidemiology, Mechanisms and Bariatric Surgery

More than 30% of people in the United States (US) are classified as obese, and over 50% are considered significantly overweight. Importantly, obesity is a risk factor not only for the development of metabolic syndrome but also for many cancers, including pancreatic ductal adenocarcinoma (PDAC). PDAC is the third leading cause of cancer-related death, and 5-year survival of PDAC remains around 9% in the U.S. Obesity is a known risk factor for PDAC. Metabolic control and bariatric surgery, which is an effective treatment for severe obesity and allows massive weight loss, have been shown to reduce the risk of PDAC. It is therefore clear that elucidating the connection between obesity and PDAC is important for the identification of a novel marker and/or intervention point for obesity-related PDAC risk. In this review, we discussed recent progress in obesity-related PDAC in epidemiology, mechanisms, and potential cancer prevention effects of interventions, including bariatric surgery with preclinical and clinical studies.

TNF-α Antagonizes the Effect of Leptin on Insulin Secretion through FOXO1-Dependent Transcriptional Suppression of LepRb in INS-1 Cells

Proinflammatory cytokines play a causal role in the development of hyperinsulinemia and T2MD. FOXO1, a transcription factor which is known to enhance proinflammation, was recently shown to be involved in obesity-induced β cell dysfunction. However, molecular mechanisms for the association remained elusive. In this study, we first found that both leptin (10 nM) and TNF-α (20 ng/ml) significantly inhibited glucose-stimulated insulin secretion (GSIS) of INS-1E cells. When in combination, the GSIS function of INS-1E cells was significantly increased compared with that of the leptin alone treatment, indicating that TNF-α attenuated the inhibiting effect of leptin on GSIS of INS-1E cells. Similarly, we found that TNF-α has the same inhibitory effect on leptin in regulating insulin synthesis and secretion, and the survival and apoptosis of insulin cells. Further studies showed that TNF-α blocks leptin pathway by reducing the expression of leptin receptor (LepRb, also called OBRb) and inhibiting the activation of STAT3, a key molecule involved in the leptin signaling pathway in INS-1E cells. Besides, the downregulated expression of phosphorylated FOXO1 was found to be involved in the possible mechanism of TNF-α. Overexpression of constitutively active FOXO1 markedly aggravated the LepRb reduction by TNF-α treatment of INS-1E cells, and the endogenous FOXO1 knockdown abolished the effect of TNF-α on INS-1E cells. Furthermore, we have proved that FOXO1 could directly bind to the promoter of LepRb as a negative transcription regulator. Taken together, the results of this study reveal that TNF-α-induced LepRb downregulated in pancreatic β cells and demonstrate that transcriptional reduction of FOXO1 might be the primary mechanism underlying TNF-α promoting INS-1E leptin resistance and β cell dysfunction. Conclusions. Our current studies based on INS-1E cells in vitro indicate that the inflammatory factor TNF-α plays an important role in the development of INS-1E leptin resistance and glucose metabolism disorders, probably through FOXO1-induced transcription reduction of LepRb promoter in pancreatic β cells, and FOXO1 may be a novel target for treating β cell dysfunction in obesity-induced hyperinsulinemia and T2DM.

Synthetic adiponectin-receptor agonist, AdipoRon, induces glycolytic dependence in pancreatic cancer cells

Obesity creates a localized inflammatory reaction in the adipose, altering secretion of adipocyte-derived factors that contribute to pathologies including cancer. We have previously shown that adiponectin inhibits pancreatic cancer by antagonizing leptin-induced STAT3 activation. Yet, the effects of adiponectin on pancreatic cancer cell metabolism have not been addressed. In these studies, we have uncovered a novel metabolic function for the synthetic adiponectin-receptor agonist, AdipoRon. Treatment of PDAC cells with AdipoRon led to mitochondrial uncoupling and loss of ATP production. Concomitantly, AdipoRon-treated cells increased glucose uptake and utilization. This metabolic switch further correlated with AMPK mediated inhibition of the prolipogenic factor acetyl coenzyme A carboxylase 1 (ACC1), which is known to initiate fatty acid catabolism. Yet, measurements of fatty acid oxidation failed to detect any alteration in response to AdipoRon treatment, suggesting a deficiency for compensation. Additional disruption of glycolytic dependence, using either a glycolysis inhibitor or low-glucose conditions, demonstrated an impairment of growth and survival of all pancreatic cancer cell lines tested. Collectively, these studies provide evidence that pancreatic cancer cells utilize metabolic plasticity to upregulate glycolysis in order to adapt to suppression of oxidative phosphorylation in the presence of AdipoRon.

Obesity and Pancreatic Cancer: Insight into Mechanisms

Simple Summary

Obesity is recognized as a chronic progressive disease and risk factor for many human diseases. The high and increasing number of obese people may underlie the expected increase in pancreatic cancer cases in the United States. There are several pathways discussed that link obesity with pancreatic cancer. Adipose tissue and adipose tissue-released factors may thereby play an important role. This review discusses selected mechanisms that may accelerate pancreatic cancer development in obesity.

Abstract

The prevalence of obesity in adults and children has dramatically increased over the past decades. Obesity has been declared a chronic progressive disease and is a risk factor for a number of metabolic, inflammatory, and neoplastic diseases. There is clear epidemiologic and preclinical evidence that obesity is a risk factor for pancreatic cancer. Among various potential mechanisms linking obesity with pancreatic cancer, the adipose tissue and obesity-associated adipose tissue inflammation play a central role. The current review discusses selected topics and mechanisms that attracted recent interest and that may underlie the promoting effects of obesity in pancreatic cancer. These topics include the impact of obesity on KRAS activity, the role of visceral adipose tissue, intrapancreatic fat, adipose tissue inflammation, and adipokines on pancreatic cancer development. Current research on lipocalin-2, fibroblast growth factor 21, and Wnt5a is discussed. Furthermore, the significance of obesity-associated insulin resistance with hyperinsulinemia and obesity-induced gut dysbiosis with metabolic endotoxemia is reviewed. Given the central role that is occupied by the adipose tissue in obesity-promoted pancreatic cancer development, preventive and interceptive strategies should be aimed at attenuating obesity-associated adipose tissue inflammation and/or at targeting specific molecules that mechanistically link adipose tissue with pancreatic cancer in obese patients.

The Adipokine Component in the Molecular Regulation of Cancer Cell Survival, Proliferation and Metastasis

A hormonal imbalance may disrupt the rigorously monitored cellular microenvironment by hampering the natural homeostatic mechanisms. The most common example of such hormonal glitch could be seen in obesity where the uprise in adipokine levels is in virtue of the expanding bulk of adipose tissue. Such aberrant endocrine signaling disrupts the regulation of cellular fate, rendering the cells to live in a tumor supportive microenvironment. Previously, it was believed that the adipokines support cancer proliferation and metastasis with no direct involvement in neoplastic transformations and tumorigenesis. However, the recent studies have reported discrete mechanisms that establish the direct involvement of adipokine signaling in tumorigenesis. Moreover, the individual adipokine profile of the patients has never been considered in the prognosis and staging of the disease. Hence, the present manuscript has focused on the reported extensive mechanisms that culminate the basis of poor prognosis and diminished survival rate in obese cancer patients.

Targeting Adipokines in Obesity-Related Tumors

Obesity, a global epidemic, is an independent risk factor for the occurrence and development of a variety of tumors, such as breast cancer, pancreatic cancer, ovarian cancer and colorectal cancer. Adipocytes are important endocrine cells in the tumor microenvironment of obesity-related tumors, which can secrete a variety of adipokines (such as leptin, adiponectin, estrogen, resistin, MIF and MCP-1, etc.), among which leptin, adiponectin and estrogen are the most in-depth and valuable ones. These adipokines are closely related to tumorigenesis and the progression of tumors. In recent years, more and more studies have shown that under chronic inflammatory conditions such as obesity, adipocytes secrete more adipokines to promote the tumorigenesis and development of tumors. However, it is worth noting that although adiponectin is also secreted by adipocytes, it has an anti-tumor effect, and can cross-talk with other adipokines (such as leptin and estrogen) and insulin to play an anti-tumor effect together. In addition, obesity is the main cause of insulin resistance, which can lead to the increase of the expression levels of insulin and insulin-like growth factor (IGF). As important regulators of blood glucose and lipid metabolism, insulin and IGF also play an important role in the progress of obesity related tumors. In view of the important role of adipokines secreted by adipocytes and insulin/IGF in tumors, this article not only elaborates leptin, adiponectin and estrogen secreted by adipocytes and their mechanism of action in the development of obesity- related tumors, but also introduces the relationship between insulin/IGF, a regulator of lipid metabolism, and obesity related tumors. At the same time, it briefly describes the cancer-promoting mechanism of resistin, MIF and MCP-1 in obesity-related tumors, and finally summarizes the specific treatment opinions and measures for various adipokines and insulin/insulin-like growth factors in recent years.

Leptin and Cancer: Updated Functional Roles in Carcinogenesis, Therapeutic Niches, and Developments

Leptin is an obesity-associated adipokine that is known to regulate energy metabolism and reproduction and to control appetite via the leptin receptor. Recent work has identified specific cell types other than adipocytes that harbor leptin and leptin receptor expression, particularly in cancers and tumor microenvironments, and characterized the role of this signaling axis in cancer progression. Furthermore, the prognostic significance of leptin in various types of cancer and the ability to noninvasively detect leptin levels in serum samples have attracted attention for potential clinical applications. Emerging findings have demonstrated the direct and indirect biological effects of leptin in regulating cancer proliferation, metastasis, angiogenesis and chemoresistance, warranting the exploration of the underlying molecular mechanisms to develop a novel therapeutic strategy. In this review article, we summarize and integrate transcriptome and clinical data from cancer patients together with the recent findings related to the leptin signaling axis in the aforementioned malignant phenotypes. In addition, a comprehensive analysis of leptin and leptin receptor distribution in a pancancer panel and in individual cell types of specific organs at the single-cell level is presented, identifying those sites that are prone to leptin-mediated tumorigenesis. Our results shed light on the role of leptin in cancer and provide guidance and potential directions for further research for scientists in this field.

Noncoding RNAs Associated with Therapeutic Resistance in Pancreatic Cancer

Therapeutic resistance is an inevitable impediment towards effective cancer therapies. Evidence accumulated has shown that the signaling pathways and related factors are fundamentally responsible for therapeutic resistance via regulating diverse cellular events, such as epithelial-to-mesenchymal transition (EMT), stemness, cell survival/apoptosis, autophagy, etcetera. Noncoding RNAs (ncRNAs) have been identified as essential cellular components in gene regulation. The expression of ncRNAs is altered in cancer, and dysregulated ncRNAs participate in gene regulatory networks in pathological contexts. An in-depth understanding of molecular mechanisms underlying the modulation of therapeutic resistance is required to refine therapeutic benefits. This review presents an overview of the recent evidence concerning the role of human ncRNAs in therapeutic resistance, together with the feasibility of ncRNAs as therapeutic targets in pancreatic cancer.

Leptin Receptor (LEPR) promotes proliferation, migration, and invasion and inhibits apoptosis in hepatocellular carcinoma by regulating ANXA7

Background

Leptin Receptor (LEPR) has been suggested to have several roles in cancer metastasis. However, the role of LEPR and its underlying mechanisms in lymphatic metastasis of hepatocarcinoma have not yet been studied.

Methods

We performed bioinformatics analysis, qRT-PCR, western blotting, immunohistochemistry, immunofluorescence, enzyme-linked immunosorbent, coimmunoprecipitation assays and a series of functional assays to investigate the roles of LEPR in hepatocellular carcinoma.

Results

We discovered that LEPR was highly expressed in liver cancer tissues, and the expression of LEPR in Hca-F cells was higher than that in Hca-P cells. Furthermore, LEPR promotes the proliferation, migration and invasion and inhibits the apoptosis of hepatocarcinoma lymphatic metastatic cells. Further studies indicated that LEPR interacts with ANXA7. Mechanistically, LEPR regulated ERK1/2 and JAK2/STAT3 expression via ANXA7 regulation.

Conclusions

These findings unveiled a previously unappreciated role of LEPR in the regulation of lymphatic metastatic hepatocellular carcinoma, assigning ANXA7-LEPR as a promising therapeutic target for liver cancer treatments.

A Study on the Immunohistochemical Expressions of Leptin and Leptin Receptor in Clear Cell Renal Cell Carcinoma

Background

The mechanisms that link obesity and cancer development are not well-defined. Investigation of leptin and leptin receptor expressions may help define some of the mechanisms. These proteins are known for associating with the immune response, angiogenesis and, signalling pathways such as JAK2/STAT3, PI3K, and AKT pathways. Tissue proteins can be easily detected with immunohistochemistry (IHC), a technique widely used both in diagnostic and research laboratories. The identification of altered levels of leptin and leptin receptor proteins in tumour tissues may lead to targeted treatment for cancer.

Objective

The objective of this study was to use IHC to compare leptin and leptin receptor expressions in clear cell renal cell carcinomas (ccRCC) in non-obese and obese patients to determine the association between these proteins with the clinicopathological features and prognosis of ccRCC. Patients and Methods. The study involved 60 patients who underwent nephrectomy of which 34 were obese, as assessed using body mass index (BMI). Nephrectomy samples provided tissues of ccRCC and adjacent non-cancerous kidney. The intensity and localization of leptin and leptin receptor protein expressions were evaluated using IHC and correlated with clinicopathological features and clinical outcomes. Aperio ImageScope morphometry and digital pathology were applied to assess the IHC results. The chi-square test was used to determine if there was any significant association between the proteins and the clinicopathological features. The Kaplan-Meier test was used to determine the overall survival, disease-free survival, and recurrence-free survival. A value of p < 0.05 was considered significant.

Results

There was neither significant difference in the overall cellular and nuclear expressions of leptin and leptin receptor between non-cancerous kidney and ccRCC tissues nor in non-obese and obese individuals with ccRCC.

Conclusion

In this present study, it was revealed that leptin and leptin receptor were not associated with tumour characteristics and progression of ccRCC patients. Interestingly, nuclear expression of leptin was significantly associated with overall survival. However, the significance of these proteins as biomarkers in other RCC histotypes is still unclear.

Leptin Signaling Affects Survival and Chemoresistance of Estrogen Receptor Negative Breast Cancer

Estrogen-receptor-negative breast cancer (BCER-) is mainly treated with chemotherapeutics. Leptin signaling can influence BCER- progression, but its effects on patient survival and chemoresistance are not well understood. We hypothesize that leptin signaling decreases the survival of BCER- patients by, in part, inducing the expression of chemoresistance-related genes. The correlation of expression of leptin receptor (OBR), leptin-targeted genes (CDK8, NANOG, and RBP-Jk), and breast cancer (BC) patient survival was determined from The Cancer Genome Atlas (TCGA) mRNA data. Leptin-induced expression of proliferation and chemoresistance-related molecules was investigated in triple-negative BC (TNBC) cells that respond differently to chemotherapeutics. Leptin-induced gene expression in TNBC was analyzed by RNA-Seq. The specificity of leptin effects was assessed using OBR inhibitors (shRNA and peptides). The results show that OBR and leptin-targeted gene expression are associated with lower survival of BCER- patients. Importantly, the co-expression of these genes was also associated with chemotherapy failure. Leptin signaling increased the expression of tumorigenesis and chemoresistance-related genes (ABCB1, WNT4, ADHFE1, TBC1D3, LL22NC03, RDH5, and ITGB3) and impaired chemotherapeutic effects in TNBC cells. OBR inhibition re-sensitized TNBC to chemotherapeutics. In conclusion, the co-expression of OBR and leptin-targeted genes may be used as a predictor of survival and drug resistance of BCER- patients. Targeting OBR signaling could improve chemotherapeutic efficacy.

Endocrine-Exocrine Signaling Drives Obesity-Associated Pancreatic Ductal Adenocarcinoma

Obesity is a major modifiable risk factor for pancreatic ductal adenocarcinoma (PDAC), yet how and when obesity contributes to PDAC progression is not well understood. Leveraging an autochthonous mouse model, we demonstrate a causal and reversible role for obesity in early PDAC progression, showing that obesity markedly enhances tumorigenesis, while genetic or dietary induction of weight loss intercepts cancer development. Molecular analyses of human and murine samples define microenvironmental consequences of obesity that foster tumorigenesis rather than new driver gene mutations, including significant pancreatic islet cell adaptation in obesity-associated tumors. Specifically, we identify aberrant beta cell expression of the peptide hormone cholecystokinin (Cck) in response to obesity and show that islet Cck promotes oncogenic Kras-driven pancreatic ductal tumorigenesis. Our studies argue that PDAC progression is driven by local obesity-associated changes in the tumor microenvironment and implicate endocrine-exocrine signaling beyond insulin in PDAC development.

Increased Adiposity Enhances the Accumulation of MDSCs in the Tumor Microenvironment and Adipose Tissue of Pancreatic Tumor-Bearing Mice and in Immune Organs of Tumor-Free Hosts

Obesity is associated with increased risk and reduced survival for many types of cancer. Increasing adiposity may affect the balance between immunosuppressive and antitumor mechanisms critical for dictating cancer progression or remission. The goal of the current study was to determine if increased adiposity altered tumor growth, survival, and myeloid-derived suppressor cell (MDSC) accumulation in a subcutaneous murine model of pancreatic cancer. C57BL/6 mice were placed on a 30% kcal calorie-restricted diet, 10% kcal from fat diet fed ad libitum, or 60% kcal from fat diet fed ad libitum for 16 weeks to generate lean, overweight, and obese mice, respectively; followed by subcutaneous injection with 1 × 10⁶ Panc.02 cells. We observed a significant linear relationship between increased adiposity and increased tumor growth and mortality; increased accumulation of Gr-1⁺CD11b⁺ MDSCs; and reduced CD8 T cell:MDSC ratio in multiple tissues, including tumor. Increased adiposity also increased the accumulation of MDSCs in the spleen and lymph node of tumor-free mice. These data suggest adiposity induces MDSC accumulation, which may contribute to an immunosuppressive environment promoting tumor growth. Overall, our findings provide a rationale to prevent or reverse increased body weight as a strategy to reduce the accumulation of immunosuppressive cell types.

Leptin receptor mediates the proliferation and glucose metabolism of pancreatic cancer cells via AKT pathway activation

Pancreatic cancer (PC) is the fourth leading cause of cancer‑related mortality worldwide. Leptin is an adipokine that is significantly increased in obese patients and that functions in various biological processes of cancer, such as tumor growth and metastasis. However, its role in PC cell proliferation and glucose metabolism and the underlying mechanisms remain unclear. In the present study, in vitro leptin treatment significantly promoted cell proliferation and increased glucose uptake and lactate production of human PC and healthy pancreas cells in a dose‑dependent manner, accompanied by increased expression of the glycolytic enzymes hexokinase II and glucose transporter 1. Furthermore, leptin receptor‑specific short hairpin RNAs were used to silence leptin receptor expression in PC cells, which had the opposite effect to leptin stimulation and decreased AKT phosphorylation. In addition, the effects of leptin stimulation were significantly counteracted by the AKT inhibitor LY294002, whereas the effects of leptin silencing were counteracted by AKT activator insulin‑like growth factor 1. The results of the present study suggested that leptin may contribute to cell proliferation and glucose metabolism of human PC cells, which may be through activation of the AKT pathway.

Obesity and pancreatic cancer: An update of epidemiological evidence and molecular mechanisms

Despite advances in therapy and achievements in translational research, pancreatic cancer (PC) remains an invariably fatal malignancy. Risk factors that affect the incidence of PC include diabetes, smoking, obesity, chronic pancreatitis, and diet. The growing worldwide obesity epidemic is associated with an increased risk of the most common cancers, including PC. Chronic inflammation, hormonal effects, circulating adipokines, and adipocyte-mediated inflammatory and immunosuppressive microenvironment are involved in the association of obesity with PC. Herein, we systematically review the epidemiology of PC and the biological mechanisms that may account for this association. Included in this review is a discussion of adipokine-mediated inflammation, lipid metabolism, and the interactions of adipocytes with cancer cells. We consider the influence of bariatric surgery on the risk of PC risk as well as potential molecular targets of therapy. Our review leads us to conclude that targeting adipose tissue to achieve weight loss may represent a new therapeutic strategy for preventing and treating PC.

Obesity-Induced Adipose Tissue Inflammation as a Strong Promotional Factor for Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is expected to soon become the second leading cause of cancer related deaths in the United States. This may be due to the rising obesity prevalence, which is a recognized risk factor for PDAC. There is great interest in deciphering the underlying driving mechanisms of the obesity–PDAC link. Visceral adiposity has a strong correlation to certain metabolic diseases and gastrointestinal cancers, including PDAC. In fact, our own data strongly suggest that visceral adipose tissue inflammation is a strong promoter for PDAC growth and progression in a genetically engineered mouse model of PDAC and diet-induced obesity. In this review, we will discuss the relationship between obesity-associated adipose tissue inflammation and PDAC development, with a focus on the key molecular and cellular components in the dysfunctional visceral adipose tissue, which provides a tumor permissive environment.

Induction of osteoclast-like cell formation by leptin-induced soluble intercellular adhesion molecule secreted from cancer cells

Background:

Leptin is considered a tumorigenic adipokine, suggested to promote tumorigenesis and progression in many cancers. On the other hand, intercellular adhesion molecule-1 (ICAM-1) shows altered expression in a variety of benign and malignant diseases. Histologically, ICAM-1 expression is reported as proportional to cancer stage and considered as a potential diagnosis biomarker. The altered expressions of ICAM-1 and its soluble form in malignant diseases have gained interests in recent years.

Material and methods:

The expression of ICAM-1 and its regulatory signaling were examined by Western blot or flow cytometry. The effect of soluble ICAM-1 on osteoclast formation was investigated by tartrate-resistance acid phosphatase staining of RAW cells and tumor-induced osteolysis in vivo.

Results:

In our study, we found that leptin enhanced soluble ICAM-1 production but not surface ICAM-1 expression in lung and breast cancer cells, and this effect was regulated through leptin receptor (ObR), while silencing ObR abrogated leptin-induced soluble ICAM-1 expression. In addition, we revealed that leptin administration provoked the JAK1/2, STAT3, FAK, ERK, and GSK3αβ signaling cascade, leading to the elevation of ICAM-1 expression. Moreover, soluble ICAM-1 secreted by leptin-stimulated cancer cells synergize with the receptor activator of nuclear factor kappa-B ligand (RANKL) in inducing osteoclast formation. Soluble ICAM also enhanced tumor-induced osteolysis in vivo.

Conclusion:

These findings suggest that soluble ICAM-1 produced under leptin treatment enhances osteoclast formation and is involved in tumor-induced osteolysis.

Leptin plays an important role in physiology in health and diseases. Leptin affects immune responses that may induce inflammation and carcinogenesis. Leptin is also considered as a tumorigenic adipokine suggested to promote tumorigenesis and progression in many cancers. On the other hand, intercellular adhesion molecule-1 (ICAM-1) shows altered expression in a variety of benign and malignant diseases. Histologically, ICAM-1 expression is reported to be proportional to cancer stage and considered as a potential diagnosis biomarker. It has been reported that soluble ICAM-1 allows tumor cells to escape from immune recognition and stimulates angiogenesis and tumor growth. The altered expressions of ICAM-1 and its soluble form in malignant diseases have gained interests in recent years. In our study, we found that leptin enhanced soluble ICAM-1 production but not surface ICAM-1 expression in lung and breast cancer cells, and this effect was regulated through leptin receptor (ObR), while silencing ObR abrogated leptin-induced soluble ICAM-1 expression. In addition, we revealed that leptin administration provoked the JAK1/2, STAT3, FAK, ERK, and GSK3αβ signaling cascade, leading to the elevation of ICAM-1 expression. Moreover, soluble ICAM-1 secreted by leptin-stimulated cancer cells synergize with receptor activator of nuclear factor-kappa B ligand in inducing osteoclast formation. Soluble ICAM also enhanced tumor-induced osteolysis in vivo. These findings suggest that soluble ICAM-1 produced under leptin treatment is possibly involved in lung and breast cancer bone metastasis.

Leptin-induced signaling pathways in cancer cell migration and invasion

BACKGROUND

Increasing evidence indicates that obesity is associated with tumor development and progression. Leptin is an adipocyte-related hormone with a key role in energy metabolism and whose circulating levels are elevated in obesity. The effect of leptin on cancer progression and metastasis and its underlying mechanisms are still unclear. Leptin can impact various steps in tumor metastasis, including epithelial-mesenchymal transition, cell adhesion to the extracellular matrix (ECM), and proteolysis of ECM components. To do so, leptin binds to its receptor (OB-Rb) to activate signaling pathways and downstream effectors that participate in tumor cell invasion as well as distant metastasis.

CONCLUSIONS

In this review, we describe metastasis steps in detail and characterize metastasis-related molecules activated by leptin, which may help to develop a roadmap that guides future work. In addition, we conclude that a profound understanding of the fundamental molecular processes that contribute to leptin-induced metastasis may pave the way for the development of new prognostic molecules and appropriate approaches to the treatment of obesity-related cancers.

The Role of Adipokines in the Establishment and Progression of Head and Neck Neoplasms

Adipokines constitute a family of protein factors secreted by white adipose tissue (WAT), that regulate the functions of WAT and other sites. Leptin, adiponectin and resistin, are the main adipokines present in serum and saliva, targeting several tissues and organs, including vessels, muscles, liver and pancreas. Besides body mass regulation, adipokines affect glucose homeostasis, inflammation, angiogenesis, cell proliferation and apoptosis, and other crucial cell procedures. Their involvement in tumor formation and growth is well established and deregulation of adipokine and adipokine receptors' expression is observed in several malignancies including those located in the head and neck region. Intracellular effects of adipokines are mediated by a plethora of receptors that activate several signaling cascades including Janus kinase/ Signal transducer and activator of transcription (JAK/ STAT pathway), Phospatidylinositol kinase (PI3/ Akt/ mTOR) and Peroxisome proliferator-activated receptor (PPAR). The present review summarizes the current knowledge on the role of adipokines family members in carcinogenesis of the head and neck region. The diagnostic and prognostic significance of adipokines and their potential role as serum and saliva biomarkers are also discussed.

Leptin-Notch axis impairs 5-fluorouracil effects on pancreatic cancer

5-FU chemotherapy is a current strategy to treat pancreatic cancer (PC), but unfortunately chemoresistance is eventually developed in most patients. Obesity is a risk factor for PC that could affect 5-FU effectiveness through the adipokine leptin, which is a known proliferation, survival factor and Notch inducer. We investigated whether leptin signaling affects 5-FU cytotoxicity on PC. To this end, tumorspheres developed from BxPC-3 and MiaPaCa-2 PC cells were treated with 5-FU, leptin, inhibitors for Notch (DAPT) and leptin signaling (IONP-LPrA2) and ATP-binding cassette of proteins (Probenecid). Leptin treatment decreased 5-FU cytotoxicity, and increased cell proliferation, colony forming ability, stem cell, pluripotency, EMT markers, drug efflux proteins (ABCC5, ABCC11) and Notch. In addition, leptin reduced the 5-FU effects on apoptosis by decreasing pro-apoptotic (Bax, Caspase-3 activation and PARP degradation) and increasing anti-apoptotic factors (RIP and Bcl-XL). Leptin's effects on PC tumorspheres treated with 5-FU were reduced by IONP-LPrA2 and were mainly Notch signaling- dependent and more evident in MiaPaCa-2-derived tumorspheres. Present results suggest that leptin could impair 5-FU cytotoxicity and promote chemoresistance. Therefore, targeting the leptin-Notch axis could be a novel way to improve 5-FU therapy for PC patients, especially in obesity context.

Diabetes Mellitus and Obesity as Risk Factors for Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest types of cancer. The worldwide estimates of its incidence and mortality in the general population are eight cases per 100,000 person-years and seven deaths per 100,000 person-years, and they are significantly higher in the United States than in the rest of the world. The incidence of this disease in the United States is more than 50,000 new cases in 2017. Indeed, total deaths due to PDAC are projected to increase dramatically to become the second leading cause of cancer-related deaths before 2030. Considering the failure to date to efficiently treat existing PDAC, increased effort should be undertaken to prevent this disease. A better understanding of the risk factors leading to PDAC development is of utmost importance to identify and formulate preventive strategies. Large epidemiologic and cohort studies have identified risk factors for the development of PDAC, including obesity and type 2 diabetes mellitus. This review highlights the current knowledge of obesity and type 2 diabetes as risk factors for PDAC development and progression, their interplay and underlying mechanisms, and the relation to diet. Research gaps and opportunities to address this deadly disease are also outlined.

Leptin-Notch signaling axis is involved in pancreatic cancer progression

Pancreatic cancer (PC) shows a high death rate. PC incidence and prognosis are affected by obesity, a pandemic characterized by high levels of leptin. Notch is upregulated by leptin in breast cancer. Thus, leptin and Notch crosstalk could influence PC progression. Here we investigated in PC cell lines (BxPC-3, MiaPaCa-2, Panc-1, AsPC-1), derived tumorspheres and xenografts whether a functional leptin-Notch axis affects PC progression and expansion of pancreatic cancer stem cells (PCSC). PC cells and tumorspheres were treated with leptin and inhibitors of Notch (gamma-secretase inhibitor, DAPT) and leptin (iron oxide nanoparticle-leptin peptide receptor antagonist 2, IONP-LPrA2). Leptin treatment increased cell cycle progression and proliferation, and the expression of Notch receptors, ligands and targeted molecules (Notch1-4, DLL4, JAG1, Survivin and Hey2), PCSC markers (CD24/CD44/ESA, ALDH, CD133, Oct-4), ABCB1 protein, as well as tumorsphere formation. Leptin-induced effects on PC and tumorspheres were decreased by IONP-LPrA2 and DAPT. PC cells secreted leptin and expressed the leptin receptor, OB-R, which indicates a leptin autocrine/paracrine signaling loop could also affect tumor progression. IONP-LPrA2 treatment delayed the onset of MiaPaCa-2 xenografts, and decreased tumor growth and the expression of proliferation and PCSC markers. Present data suggest that leptin-Notch axis is involved in PC. PC has no targeted therapy and is mainly treated with chemotherapy, whose efficiency could be decreased by leptin and Notch activities. Thus, the leptin-Notch axis could be a novel therapeutic target, particularly for obese PC patients.

The potential role of leptin in tumor invasion and metastasis

The adipocyte-released hormone-like cytokine/adipokine leptin behaves differently in obesity compared to its functions in the normal healthy state. In obese individuals, elevated leptin levels act as a pro-inflammatory adipokine and are associated with certain types of cancers. Further, a growing body of evidence suggests that higher circulating leptin concentrations and/or elevated expression of leptin receptors (Ob-R) in tumors may be poor prognostic factors. Although the underlying pathological mechanisms of leptin's association with poor prognosis are not clear, leptin can impact the tumor microenvironment in several ways. For example, leptin is associated with a number of biological components that could lead to tumor cell invasion and distant metastasis. This includes interactions with carcinoma-associated fibroblasts, tumor promoting effects of infiltrating macrophages, activation of matrix metalloproteinases, transforming growth factor-β signaling, etc. Recent studies also have shown that leptin plays a role in the epithelial-mesenchymal transition, an important phenomenon for cancer cell migration and/or metastasis. Furthermore, leptin's potentiating effects on insulin-like growth factor-I, epidermal growth factor receptor and HER2/neu have been reported. Regarding unfavorable prognosis, leptin has been shown to influence both adenocarcinomas and squamous cell carcinomas. Features of poor prognosis such as tumor invasion, lymph node involvement and distant metastasis have been recorded in several cancer types with higher levels of leptin and/or Ob-R. This review will describe the current scenario in a precise manner. In general, obesity indicates poor prognosis in cancer patients.

Obesity, Inflammation, and Cancer

Obesity, a worldwide epidemic, confers increased risk for multiple serious conditions, including cancer, and is increasingly recognized as a growing cause of preventable cancer risk. Chronic inflammation, a well-known mediator of cancer, is a central characteristic of obesity, leading to many of its complications, and obesity-induced inflammation confers additional cancer risk beyond obesity itself. Multiple mechanisms facilitate this strong association between cancer and obesity. Adipose tissue is an important endocrine organ, secreting several hormones, including leptin and adiponectin, and chemokines that can regulate tumor behavior, inflammation, and the tumor microenvironment. Excessive adipose expansion during obesity causes adipose dysfunction and inflammation to increase systemic levels of proinflammatory factors. Cells from adipose tissue, such as cancer-associated adipocytes and adipose-derived stem cells, enter the cancer microenvironment to enhance protumoral effects. Dysregulated metabolism that stems from obesity, including insulin resistance, hyperglycemia, and dyslipidemia, can further impact tumor growth and development. This review describes how adipose tissue becomes inflamed in obesity, summarizes ways these mechanisms impact cancer development, and discusses their role in four adipose-associated cancers that demonstrate elevated incidence or mortality in obesity.

Adiponectin receptor agonists inhibit leptin induced pSTAT3 and in vivo pancreatic tumor growth

Obesity is a significant risk factor for pancreatic cancer, harboring a chronic inflammatory condition characterized by dysregulation of the adipokines, leptin and adiponectin, that in turn alter oncogenic signaling pathways. We and others have shown that leptin promotes the proliferation and an invasive potential of pancreatic cancer cells through STAT3 mediated signaling. However, the role of adiponectin on the tumorigenicity of pancreatic cancer has not been elucidated. Adiponectin represents an important negative regulator of cytokines, which acts through two receptors, ADIPOR1 and ADIPOR2, to elicit pro-apoptotic, anti-inflammatory, and anti-angiogenic responses. We show that the level and expression of both adiponectin receptors are decreased in pancreatic tumors relative to normal pancreatic tissue. In vitro stimulation with adiponectin or a small molecule adiponectin receptor agonist, AdipoRon, increases apoptosis while inhibiting pancreatic cancer cell proliferation, colony formation, and anchorage independent growth. In addition, adiponectin receptor agonism inhibits leptin mediated STAT3 activation. In vivo, treatment of mice with AdipoRon inhibits orthotopic pancreatic tumor growth. These results demonstrate that adiponectin receptor activation is a key regulator of pancreatic cancer growth and AdipoRon provides a rational agent for the development of novel therapeutic strategies for pancreatic cancer.

Leptin receptor signaling via Janus kinase 2/Signal transducer and activator of transcription 3 impacts on ovarian cancer cell phenotypes

Ovarian cancer is a leading cause of cancer mortality in women world-wide. Considerable progress has been made to characterize the different subtypes of ovarian cancer, but specific therapies remain limited and prognosis poor. Cytokine signaling via the interleukin-6 receptor (IL-6R) family and related receptors has been implicated in a number of cancers, including those with an ovarian origin. The leptin receptor (LEPR) is structurally related to these receptors and utilizes similar downstream pathways. LEPR has diverse roles in metabolism, appetite and bone formation with obesity linked to both elevated levels of leptin and increased cancer incidence. This study investigated a potential role for LEPR signaling in ovarian cancer. Leptin stimulation led to increased proliferation, survival and migration of LEPR-expressing ovarian cancer cell lines, with the effects shown to be mediated by the downstream Janus kinase 2/Signal transducer and activator of transcription 3 (JAK2/STAT3) pathway. A significant correlation was identified between high co-expression of leptin and LEPR and decreased patient survival. This study collectively suggests that leptin/LEPR signaling via JAK2/STAT3 has the potential to significantly impact on pathogenesis in a subset of ovarian cancer patients who may benefit from strategies that dampen this pathway.

Biological Mechanisms for the Effect of Obesity on Cancer Risk: Experimental Evidence

Multiple epidemiological studies demonstrated that overweight and obesity significantly increase the risk of several types of cancer. As the prevalence of obesity is dramatically rising, it is expected that it will represent one of the major lifestyle-associated risk factors for cancer development in the near future. Numerous recent studies expanded knowledge about key players and pathways, which are deregulated in the obese state and potentially promote cancer initiation, progression and aggressiveness via remote and local effects. These players include (but are not limited to) insulin/IGF, adipokines and inflammatory signaling molecules as well as metabolites. Nevertheless, the detailed mechanisms linking obesity and malignant transformation at the systemic, cellular and molecular level still demand further investigation. Additionally, dysfunctional molecular metabolic pathways appear to be specific for distinct cancer entities, thereby yet precluding definition of a common principle. This chapter will present an overview of the current knowledge of molecular nodes linking obesity and cancer and will briefly touch upon potential therapy options addressing metabolic cancer etiologies.

Prognostic Value of Leptin Receptor Overexpression in Upper Tract Urothelial Carcinomas in Taiwan

OBJECTIVES

Leptin and its receptor (LEPR) are key players in the regulation of energy balance and body weight control and act as a growth factor for specific organs in both normal and disease states. However, LEPR accumulation may be involved in carcinogenesis, progression, and metastasis in many cancers. This study evaluated the clinical significance of LEPR expression in upper tract urothelial carcinoma (UTUC).

MATERIALS AND METHODS

LEPR expression was examined in 110 tissue samples from patients with UTUC, using immunohistochemistry, and an analysis was performed to identify evidence of association between LEPR expression and different clinicopathologic variables.

RESULTS

LEPR expression was significantly correlated with patients with increased body mass index (P < .001) and high serum creatinine levels (P = .005). We found, using the log-rank test, that high LEPR expression was associated with poor recurrence-free (P = .009) and cancer-specific survival (P = .001). This finding was supported by our results using Cox regression analysis, which showed that LEPR expression was an independent predictor of poor recurrence-free survival (hazard ratio = 2.55; P = .011) and cancer-specific survival (hazard ratio = 2.26; P = .006).

CONCLUSIONS

Our findings indicate that LEPR expression is a potential biomarker for predicting patient survival in UTUC. Further study is necessary to investigate the role of LEPR in carcinogenesis of UTUC.

Oncogenic role of leptin and Notch interleukin-1 leptin crosstalk outcome in cancer

Obesity is a global pandemic characterized by high levels of body fat (adiposity) and derived-cytokines (i.e., leptin). Research shows that adiposity and leptin provide insight on the link between obesity and cancer progression. Leptin’s main function is to regulate energy balance. However, obese individuals routinely develop leptin resistance, which is the consequence of the breakdown in the signaling mechanism controlling satiety resulting in the accumulation of leptin. Therefore, leptin levels are often chronically elevated in human obesity. Elevated leptin levels are related to higher incidence, increased progression and poor prognosis of several human cancers. In addition to adipose tissue, cancer cells can also secrete leptin and overexpress leptin receptors. Leptin is known to act as a mitogen, inflammatory and pro-angiogenic factor that induces cancer cell proliferation and tumor angiogenesis. Moreover, leptin signaling induces cancer stem cells, which are involved in cancer recurrence and drug resistance. A novel and complex signaling crosstalk between leptin, Notch and interleukin-1 (IL-1) [Notch, IL-1 and leptin crosstalk outcome (NILCO)] seems to be an important driver of leptin-induced oncogenic actions. Leptin and NILCO signaling mediate the activation of cancer stem cells that can affect drug resistance. Thus, leptin and NILCO signaling are key links between obesity and cancer progression. This review presents updated data suggesting that adiposity affects cancer incidence, progression, and response to treatment. Here we show data supporting the oncogenic role of leptin in breast, endometrial, and pancreatic cancers.

Peroxisome proliferator activated receptors at the crossroad of obesity, diabetes, and pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is the fourth cause of cancer death with an overall survival of 5% at five years. The development of PDAC is characteristically associated to the accumulation of distinctive genetic mutations and is preceded by the exposure to several risk factors. Epidemiology has demonstrated that PDAC risk factors may be non-modifiable risks (sex, age, presence of genetic mutations, ethnicity) and modifiable and co-morbidity factors related to the specific habits and lifestyle. Recently it has become evident that obesity and diabetes are two important modifiable risk factors for PDAC. Obesity and diabetes are complex systemic and intertwined diseases and, over the years, experimental evidence indicate that insulin-resistance, alteration of adipokines, especially leptin and adiponectin, oxidative stress and inflammation may play a role in PDAC. Peroxisome proliferator activated receptor-γ (PPARγ) is a nuclear receptor transcription factor that is implicated in the regulation of metabolism, differentiation and inflammation. PPARγ is a key regulator of adipocytes differentiation, regulates insulin and adipokines production and secretion, may modulate inflammation, and it is implicated in PDAC. PPARγ agonists are used in the treatment of diabetes and oxidative stress-associated diseases and have been evaluated for the treatment of PDAC. PPARγ is at the cross-road of diabetes, obesity, and PDAC and it is an interesting target to pharmacologically prevent PDAC in obese and diabetic patients.