A protein tyrosine kinase receptor, c-RET signaling pathway contributes to the enteric neurogenesis induced by a 5-HT4 receptor agonist at an anastomosis after transection of the gut in rodents

Therapeutic advances of targeting receptor tyrosine kinases in cancer

Receptor tyrosine kinases (RTKs), a category of transmembrane receptors, have gained significant clinical attention in oncology due to their central role in cancer pathogenesis. Genetic alterations, including mutations, amplifications, and overexpression of certain RTKs, are critical in creating environments conducive to tumor development. Following their discovery, extensive research has revealed how RTK dysregulation contributes to oncogenesis, with many cancer subtypes showing dependency on aberrant RTK signaling for their proliferation, survival and progression. These findings paved the way for targeted therapies that aim to inhibit crucial biological pathways in cancer. As a result, RTKs have emerged as primary targets in anticancer therapeutic development. Over the past two decades, this has led to the synthesis and clinical validation of numerous small molecule tyrosine kinase inhibitors (TKIs), now effectively utilized in treating various cancer types. In this manuscript we aim to provide a comprehensive understanding of the RTKs in the context of cancer. We explored the various alterations and overexpression of specific receptors across different malignancies, with special attention dedicated to the examination of current RTK inhibitors, highlighting their role as potential targeted therapies. By integrating the latest research findings and clinical evidence, we seek to elucidate the pivotal role of RTKs in cancer biology and the therapeutic efficacy of RTK inhibition with promising treatment outcomes.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

Enteric neuroimmune interactions coordinate intestinal responses in health and disease

The enteric nervous system (ENS) of the gastrointestinal (GI) tract interacts with the local immune system bidirectionally. Recent publications have demonstrated that such interactions can maintain normal GI functions during homeostasis and contribute to pathological symptoms during infection and inflammation. Infection can also induce long-term changes of the ENS resulting in the development of post-infectious GI disturbances. In this review, we discuss how the ENS can regulate and be regulated by immune responses and how such interactions control whole tissue physiology. We also address the requirements for the proper regeneration of the ENS and restoration of GI function following the resolution of infection.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

Expression and copy number gains of the RET gene in 631 early and mid stage non-small cell lung cancer cases

Background

To identify whether RET is a potential target for NSCLC treatment, we examined the status of the RET gene in 631 early and mid stage NSCLC cases from south central China.

Methods

RET expression was identified by Western blot. RET‐positive expression samples were verified by immunohistochemistry. RET gene mutation, copy number variation, and rearrangement were analyzed by DNA Sanger sequencing, TaqMan copy number assays, and reverse transcription‐PCR. ALK and ROS1 expression levels were tested by Western blot and EGFR mutation using Sanger sequencing.

Results

The RET‐positive rate was 2.5% (16/631). RET‐positive expression was related to poorer tumor differentiation (P < 0.05). In the 16 RET‐positive samples, only two samples of moderately and poorly differentiated lung adenocarcinomas displayed RET rearrangement, both in RET‐KIF5B fusion partners. Neither ALK nor ROS1 translocation was found. The EGFR mutation rate in RET‐positive samples was significantly lower than in RET‐negative samples (P < 0.05).

Conclusion

RET‐positive expression in early and mid stage NSCLC cases from south central China is relatively low and is related to poorer tumor differentiation. RET gene alterations (copy number gain and rearrangement) exist in all RET‐positive samples. RET‐positive expression is a relatively independent factor in NSCLC patients, which indicates that the RET gene may be a novel target site for personalized treatment of NSCLC.

Activation of 5-HT4 receptors facilitates neurogenesis of injured enteric neurons at an anastomosis in the lower gut

Two-photon microscopy (2PM) can enable high-resolution deep imaging of thick tissue by exciting a fluorescent dye and protein at anastomotic sites in the mouse small intestine in vivo. We performed gut surgery and transplanted neural stem cells (NSC) from the embryonic central nervous system after marking them with the fluorescent cell linker, PKH26. We found that neurons differentiated from transplanted NSC (PKH [+]) and newborn enteric neurons differentiated from mobilized (host) NSC (YFP [+]) could be localized within the granulation tissue of anastomoses. A 5-HT₄-receptor agonist, mosapride citrate (MOS), significantly increased the number of PKH (+) and YFP (+) neurons by 2.5-fold (P<0.005). The distribution patterns of PKH (+) neurons were similar to those of YFP (+) neurons. On the other hand, the 5-HT₄-receptor antagonist, SB-207266 abolished these effects of MOS. These results indicate that neurogenesis from transplanted NSC is facilitated by activation of 5-HT₄-receptors. Thus, a combination of drug administration and cell transplantation could be more beneficial than exclusive cell transplantation in treating Hirschsprung's disease and related disorders including post rectal cancer surgery. The underlying mechanisms for its action were explored using immunohistochemistry of the longitudinal mouse ileum and rat rectal preparations including an anastomosis. MOS significantly increased the number of new neurons, but not when co-administered with either of a protein tyrosine kinase receptor, c-RET two inhibitors. The c-RET signaling pathway contributes to enteric neurogenesis facilitated by MOS. In the future, we would perform functional studies of new neurons over the thick granulation tissue at anastomoses, using in vivo imaging with 2PM and double transgenic mice expressing a calcium indicator such as GCaMP6 and channelrhodopsin.

Activation of 5-HT4 receptors facilitates neurogenesis from transplanted neural stem cells in the anastomotic ileum

An orally administered serotonin-4 (5-HT₄) receptor agonist, mosapride citrate (MOS), promotes enteric neurogenesis in anastomoses after gut surgery. We performed gut surgery and transplanted 2 × 10⁵ neural stem cells (NSCs) from the embryonic central nervous system after marking them with the cell linker, PKH26. We found that neurons differentiated from transplanted NSCs (PKH [+]) and newborn enteric neurons differentiated from mobilized (host) NSCs (YFP [+]) in the deep granulation tissue of the anastomotic ileum. MOS significantly increased the number of PKH (+) and YFP (+) neurons by 2.5-fold (P < 0.005) (n = 4). The distribution patterns of PKH (+) neurons and YFP (+) neurons were similar along the depth of the anastomosis. A 5-HT₄ receptor antagonist, SB-207266, abolished these effects of MOS (n = 4). Our results indicate that neurogenesis from transplanted NSCs is potentiated by activation of 5-HT₄ receptors. Thus, a combination of drug administration and cell transplantation could be more beneficial than cell transplantation alone in treating Hirschsprung’s disease and related disorders.