Jieru E. Lin

Antiobesity Pharmacotherapy: New Drugs and Emerging Targets

Obesity is a growing pandemic, and related health and economic costs are staggering. Pharmacotherapy, partnered with lifestyle modifications, forms the core of current strategies to reduce the burden of this disease and its sequelae. However, therapies targeting weight loss have a significant history of safety risks, including cardiovascular and psychiatric events. Here, evolving strategies for developing antiobesity therapies, including targets, mechanisms, and developmental status, are highlighted. Progress in this field is underscored by Belviq (lorcaserin) and Qsymia (phentermine/topiramate), the first agents in more than 10 years to achieve regulatory approval for chronic weight management in obese patients. On the horizon, novel insights into metabolism and energy homeostasis reveal guanosine 3′,5′‐cyclic monophosphate (cGMP) signaling circuits as emerging targets for antiobesity pharmacotherapy. These innovations in molecular discovery may elegantly align with practical off‐the‐shelf approaches, leveraging existing approved drugs that modulate cGMP levels for the management of obesity.

A uroguanylin-GUCY2C endocrine axis regulates feeding in mice

Intestinal enteroendocrine cells are critical to central regulation of caloric consumption, since they activate hypothalamic circuits that decrease appetite and thereby restrict meal size by secreting hormones in response to nutrients in the gut. Although guanylyl cyclase and downstream cGMP are essential regulators of centrally regulated feeding behavior in invertebrates, the role of this primordial signaling mechanism in mammalian appetite regulation has eluded definition. In intestinal epithelial cells, guanylyl cyclase 2C (GUCY2C) is a transmembrane receptor that makes cGMP in response to the paracrine hormones guanylin and uroguanylin, which regulate epithelial cell dynamics along the crypt-villus axis. Here, we show that silencing of GUCY2C in mice disrupts satiation, resulting in hyperphagia and subsequent obesity and metabolic syndrome. This defined an appetite-regulating uroguanylin-GUCY2C endocrine axis, which we confirmed by showing that nutrient intake induces intestinal prouroguanylin secretion into the circulation. The prohormone signal is selectively decoded in the hypothalamus by proteolytic liberation of uroguanylin, inducing GUCY2C signaling and consequent activation of downstream anorexigenic pathways. Thus, evolutionary diversification of primitive guanylyl cyclase signaling pathways allows GUCY2C to coordinate endocrine regulation of central food acquisition pathways with paracrine control of intestinal homeostasis. Moreover, the uroguanylin-GUCY2C endocrine axis may provide a therapeutic target to control appetite, obesity, and metabolic syndrome.

Cyclin D1b protein expression in breast cancer is independent of cyclin D1a and associated with poor disease outcome.

Aberrant expression of cyclin D1 protein is a common feature of breast cancer. However, the CCND1 gene encodes two gene products, cyclin D1a and cyclin D1b, which have discrete mechanisms of regulation and impact on cell behavior. A polymorphism at nucleotide 870 in the CCND1 gene, rs603965, influences the relative production of the encoded proteins and can impart increased risk for tumor development. Here, the impact of both the G/A870 polymorphism and cyclin D1b protein production on breast cancer risk, disease phenotype and patient outcome was analysed. In a large multiethnic case–control study, the G/A870 polymorphism conferred no significant risk for breast cancer overall or by stage or estrogen receptor (ER) status. However, the cyclin D1b protein was found to be upregulated in breast cancer, independent of cyclin D1a levels, and exhibited heterogeneous levels in breast cancer specimens. High cyclin D1a expression inversely correlated with the Ki67 proliferation marker and was not associated with clinical outcome. In contrast, elevated cyclin D1b expression was independently associated with adverse outcomes, including recurrence, distant metastasis and decreased survival. Interestingly, cyclin D1b was particularly associated with poor outcome in the context of ER-negative breast cancer. Thus, specific cyclin D1 isoforms are associated with discrete forms of breast cancer and high cyclin D1b protein levels hold prognostic potential.

Bacterial Heat-Stable Enterotoxins: Translation of Pathogenic Peptides into Novel Targeted Diagnostics and Therapeutics

Heat-stable toxins (STs) produced by enterotoxigenic bacteria cause endemic and traveler’s diarrhea by binding to and activating the intestinal receptor guanylyl cyclase C (GC-C). Advances in understanding the biology of GC-C have extended ST from a diarrheagenic peptide to a novel therapeutic agent. Here, we summarize the physiological and pathophysiological role of GC-C in fluid-electrolyte regulation and intestinal crypt-villus homeostasis, as well as describe translational opportunities offered by STs, reflecting the unique characteristics of GC-C, in treating irritable bowel syndrome and chronic constipation, and in preventing and treating colorectal cancer.

Central and peripheral molecular targets for antiobesity pharmacotherapy.

Obesity has emerged as one of the principal worldwide health concerns of the modern era, and there exists a tremendous unmet clinical need for safe and effective therapies to combat this global pandemic. The prevalence of obesity and its associated comorbidities, including cardiovascular and metabolic diseases, has focused the attention of those in drug discovery and development on generating effective modalities for the treatment and prevention of obesity. Early efforts in the field of obesity pharmacotherapy centered on the development of agents with indeterminate mechanisms of action. This led to treatment paradigms characterized by significant off‐target effects. In the past two decades, new insights have been made into the physiologic regulation of energy balance and the subordinate central and peripheral circuits coordinating appetite, metabolism, and lipogenesis. These studies have revealed previously unrecognized molecular targets for controlling appetite and managing weight from which has emerged a new wave of targeted pharmacotherapies to prevent and control obesity.

Gankyrin activates IL-8 to promote hepatic metastasis of colorectal cancer

Hepatic metastasis is responsible for the majority of colorectal cancer (CRC)-related mortalities. Although Gankyrin (PSMD10) has been implicated in cancer metastasis, its exact role and underlying mechanisms of CRC hepatic metastasis remain largely unknown. Herein, we showed that the expression of Gankyrin was higher in primary CRC with hepatic metastasis compared with CRC without metastasis. RNAi-mediated silencing of Gankyrin expression in highly metastatic human CRC cells impaired their migratory and metastatic capacity in vivo. Genome-wide transcriptome profiling revealed activation of the interleukin (IL)-8 signaling pathway by Gankyrin. Protein levels of IL-8 and cyclin D1 (CCND1), the two important molecules in the IL-8 pathway, were positively correlated with Gankyrin expression in human CRC specimens. Furthermore, genetic deletion of cyclin D1 showed its requirement in Gankyrin-mediated cell migration. Finally, administration of recombinant IL-8 rescued the migratory defect of CRC cells where Gankyrin expression was silenced. Together, our findings highlight the importance of Gankyrin in hepatic metastasis of CRC and point out its candidature as a potential prognostic marker and therapeutic target to improve the clinical management of metastatic CRC.

Obesity pharmacotherapy: What is next?

The increase in obesity in the Unites States and around the world in the last decade is overwhelming. The number of overweight adults in the world surpassed 1 billion in 2008. Health hazards associated with obesity are serious and include heart disease, sleep apnea, diabetes, and cancer. Although lifestyle modifications are the most straightforward way to control weight, a large portion of the population may not be able to rely on this modality alone. Thus, the development of anti-obesity therapeutics represents a major unmet medical need. Historically, anti-obesity pharmacotherapies have been unsafe and minimally efficacious. A better understanding of the biology of appetite and metabolism provides an opportunity to develop drugs that may offer safer and more effective alternatives for weight management. This review discusses drugs that are currently on the market and in development as anti-obesity therapeutics based on their target and mechanism of action. It should serve as a roadmap to establish expectations for the near future for anti-obesity drug development.

Obesity-Induced Colorectal Cancer Is Driven by Caloric Silencing of the Guanylin–GUCY2C Paracrine Signaling Axis

Obesity is a well-known risk factor for colorectal cancer but precisely how it influences risks of malignancy remains unclear. During colon cancer development in humans or animals, attenuation of the colonic cell surface receptor guanylyl cyclase C (GUCY2C) that occurs due to loss of its paracrine hormone ligand guanylin contributes universally to malignant progression. In this study, we explored a link between obesity and GUCY2C silencing in colorectal cancer. Using genetically engineered mice on different diets, we found that diet-induced obesity caused a loss of guanylin expression in the colon with subsequent GUCY2C silencing, epithelial dysfunction, and tumorigenesis. Mechanistic investigations revealed that obesity reversibly silenced guanylin expression through calorie-dependent induction of endoplasmic reticulum stress and the unfolded protein response in intestinal epithelial cells. In transgenic mice, enforcing specific expression of guanylin in intestinal epithelial cells restored GUCY2C signaling, eliminating intestinal tumors associated with a high calorie diet. Our findings show how caloric suppression of the guanylin-GUCY2C signaling axis links obesity to negation of a universal tumor suppressor pathway in colorectal cancer, suggesting an opportunity to prevent colorectal cancer in obese patients through hormone replacement with the FDA-approved oral GUCY2C ligand linaclotide.

Guanylyl cyclase C in colorectal cancer: susceptibility gene and potential therapeutic target

Colorectal cancer is one of the leading causes of tumor-related morbidity and mortality worldwide. While mechanisms underlying this disease have been elucidated over the past two decades, these molecular insights have failed to translate into efficacious therapy. The oncogenomic view of cancer suggests that terminal transformation reflects the sequential corruption of signal transduction circuits regulating key homeostatic mechanisms, whose multiplicity underlies the therapeutic resistance of most tumors to interventions targeting individual pathways. Conversely, the paucity of mechanistic insights into proximal pathophysiological processes that initiate and amplify oncogenic circuits preceding accumulation of mutations and transformation impedes development of effective prevention and therapy. In that context, guanylyl cyclase C (GCC), the intestinal receptor for the paracrine hormones guanylin and uroguanylin, whose early loss characterizes colorectal transformation, has emerged as a component of lineage-specific homeostatic programs organizing spatiotemporal patterning along the crypt-surface axis. Dysregulation of GCC signaling, reflecting hormone loss, promotes tumorigenesis through reprogramming of replicative and bioenergetic circuits and genomic instability. Compensatory upregulation of GCC in response to hormone loss provides a unique translational opportunity for prevention and treatment of colorectal tumors by hormone-replacement therapy.

Colorectal Cancer Is a Paracrine Deficiency Syndrome Amenable to Oral Hormone Replacement Therapy

The most commonly lost gene products in colorectal carcinogenesis include the paracrine hormones guanylin and uroguanylin, the endogenous ligands for guanylyl cyclase C (GCC), the intestinal receptor for diarrheagenic bacterial enterotoxins. Recently, GCC‐cyclic guanosine monophosphate (GMP) signaling has emerged as a principal regulator of proliferation, genetic integrity, and metabolic programming in normal human enterocytes and colon cancer cells. Elimination of GCC in mice produced hyperplasia of the proliferating compartment associated with increases in the rapidly cycling progenitor cells and reprogrammed enterocyte metabolism, with a shift from oxidative phosphorylation to glycolysis. In addition, in the colons of mice carrying mutations in adenomatous polyposis coli gene Apc (ApcMin/+) or exposed to the carcinogen azoxymethane, elimination of GCC increased tumor initiation and promotion by disrupting genomic integrity and releasing cell cycle restriction. These previously unrecognized roles for GCC as a fundamental regulator of intestinal homeostasis and as an intestinal tumor suppressor suggest that receptor dysregulation reflecting paracrine hormone insuffciency is a key event during the initial stages of colorectal tumorigenesis. Together with the uniform overexpression of GCC in human tumors, these novel roles for GCC underscore the potential of oral replacement with GCC ligands for a targeted prevention and therapy of colorectal cancer.