Cancers arising from gastrointestinal epithelial cells are common, aggressive, and difficult to treat. Progress in this area resulted from recognizing that the biological behavior of these cancers is highly dependent on bioactive molecules released by neurocrine, paracrine, and autocrine mechanisms within the tumor microenvironment. For many decades after its discovery as a neurotransmitter, acetylcholine was thought to be synthesized and released uniquely from neurons and considered the sole physiological ligand for muscarinic receptor subtypes, which were believed to have similar or redundant actions. In the intervening years, we learned this former dogma is not tenable. (1) Acetylcholine is not produced and released only by neurons. The cellular machinery required to synthesize and release acetylcholine is present in immune, cancer, and other cells, as well as in lower organisms (e.g., bacteria) that inhabit the gut. (2) Acetylcholine is not the sole physiological activator of muscarinic receptors. For example, selected bile acids can modulate muscarinic receptor function. (3) Muscarinic receptor subtypes anticipated to have overlapping functions based on similar G protein coupling and downstream signaling may have unexpectedly diverse actions. Here, we review the relevant research findings supporting these conclusions and discuss how the complexity of muscarinic receptor biology impacts health and disease, focusing on their role in the initiation and progression of gastric, pancreatic, and colon cancers.

M₃ muscarinic receptor (M₃R) activation stimulates colon cancer cell proliferation, migration, and invasion; M₃R expression is augmented in colon cancer and ablating M₃R expression in mice attenuates colon neoplasia. Several lines of investigation suggest that in contrast to these pro-neoplastic effects of M₃R, M₁R plays an opposite role, protecting colon epithelial cells against neoplastic transformation. To pursue these intriguing findings, we examined the relative expression of M₁R versus M₃R in progressive stages of colon neoplasia and the effect of treating colon cancer cells with selective M₁R agonists. We detected divergent expression of M₁R and M₃R in progressive colon neoplasia, from aberrant crypt foci to adenomas, primary colon cancers, and colon cancer metastases. Treating three human colon cancer cell lines with two selective M₁R agonists, we found that in contrast to the effects of M₃R activation, selective activation of M₁R reversibly inhibited cell proliferation. Moreover, these effects were diminished by pre-incubating cells with a selective M₁R inhibitor. Mechanistic insights were gained using selective chemical inhibitors of post-muscarinic receptor signaling molecules and immunoblotting to demonstrate M₁R-dependent changes in the activation (phosphorylation) of key downstream kinases, EGFR, ERK1/2, and p38 MAPK. We did not detect a role for drug toxicity, cellular senescence, or apoptosis in mediating M₁R agonist-induced attenuated cell proliferation. Lastly, adding M₁R-selective agonists to colon cancer cells augmented the anti-proliferative effects of conventional chemotherapeutic agents. Collectively, these results suggest that selective M₁R agonism for advanced colon cancer, alone or in combination with conventional chemotherapy, is a therapeutic strategy worth exploring.

BACKGROUND: Although there are discrepancies in the development and progression of IBD based on biologic sex, little is known about differences in postoperative outcomes between men and women undergoing surgery for this condition. OBJECTIVE: To compare rates of anastomotic leaks, wound complications, and serious adverse events between men and women undergoing surgery for IBD. DESIGN: This was a retrospective cohort study. SETTINGS: Data were obtained from the American College of Surgeons National Surgical Quality Improvement Program IBD Collaborative database, which includes 15 high-volume IBD surgery centers. PATIENTS: All adult patients undergoing surgery for IBD were included. Participants with missing data for exposure or outcome variables were excluded. MAIN OUTCOME MEASURES: Rates of anastomotic leaks, wound complications, and serious adverse events were compared between women and men. RESULTS: A total of 3143 patients were included. There was a significant association between sex and BMI, IBD type, and preoperative medication use. Women had decreased odds of serious adverse events compared to men (OR 0.73; 95% CI, 0.55–0.96), but there was no significant association between sex and anastomotic leaks or wound complications. IBD type was found to be an effect measure modifier of the relationship between sex and serious adverse events. Among patients with ulcerative colitis, women had a 54% decrease in the odds of serious adverse events compared to men, whereas there was no significant difference between women and men with Crohn’s disease. LIMITATIONS: This study was limited by capturing only 30 days of postoperative outcomes. CONCLUSIONS: Women undergoing surgery for ulcerative colitis had decreased odds of serious adverse events compared to men. Understanding sex-based differences in outcomes allows clinicians to make patient-centered decisions regarding surgical planning and perioperative management for patients with IBD. See Video Abstract. DIFERENCIAS BASADAS EN EL SEXO EN LOS RESULTADOS QUIRÚRGICOS DE LA ENFERMEDAD INFLAMATORIA INTESTINAL: ANTECEDENTES: Aunque existen discrepancias en el desarrollo y la progresión de la enfermedad inflamatoria intestinal según el sexo biológico, se sabe poco sobre las diferencias en los resultados postoperatorios entre hombres y mujeres sometidos a cirugía por esta afección. OBJETIVO: Nuestro objetivo fue comparar las tasas de fugas anastomóticas, complicaciones de las heridas y eventos adversos graves entre hombres y mujeres sometidos a cirugía por enfermedad inflamatoria intestinal. DISEÑO: Este fue un estudio de cohorte retrospectivo. AJUSTES: Los datos se obtuvieron de la base de datos del Programa Nacional de Mejora de la Calidad Quirúrgica del Colegio Americano de Cirujanos para la Enfermedad Inflamatoria Intestinal, que incluye 15 centros de cirugía de enfermedad inflamatoria intestinal de alto volumen. PACIENTES: Se incluyeron todos los pacientes adultos sometidos a cirugía por enfermedad inflamatoria intestinal. Se excluyeron los sujetos a los que les faltaban datos sobre exposición o variables de resultado. PRINCIPALES MEDIDAS DE RESULTADO: Se compararon las tasas de fugas anastomóticas, complicaciones de las heridas y eventos adversos graves entre mujeres y hombres. RESULTADOS: Se incluyeron un total de 3.143 pacientes. Hubo una asociación significativa entre el sexo y el índice de masa corporal, el tipo de enfermedad inflamatoria intestinal y el uso de medicación preoperatoria. Las mujeres tuvieron menores probabilidades de sufrir eventos adversos graves en comparación con los hombres (OR = 0,73; IC del 95 %: 0,55 a 0,96), pero no hubo una relacion significativa entre el sexo y las fugas anastomóticas o las complicaciones de las heridas. Se encontró que el tipo de enfermedad inflamatoria intestinal era un modificador de la medida del efecto de la relación entre el sexo y los eventos adversos graves. Entre los pacientes con colitis ulcerosa, las mujeres tuvieron una disminución del 54 % en las probabilidades de sufrir eventos adversos graves en comparación con los hombres, mientras que no hubo diferencias significativas entre mujeres y hombres con enfermedad de Crohn. LIMITACIONES: Este estudio estuvo limitado al capturar solo 30 días de resultados posoperatorios. CONCLUSIONES: Las mujeres sometidas a cirugía por colitis ulcerosa tuvieron menores probabilidades de sufrir eventos adversos graves en comparación con los hombres. Comprender las diferencias en los resultados basadas en el sexo permite a los médicos tomar decisiones centradas en el paciente con respecto a la planificación quirúrgica y el manejo perioperatorio de los pacientes con enfermedad inflamatoria intestinal. (Traducción—Dr Yolanda Colorado).