Cannabinoid drugs against chemotherapy-induced adverse effects: focus on nausea/vomiting, peripheral neuropathy and chemofog in animal models

Chemotherapy-Induced Neuropathy Affecting the Gastrointestinal Tract

BACKGROUND

Cancer is a major global cause of morbidity and mortality. Survivorship is increasing, bringing new challenges. Cancer treatment, including chemotherapeutic drugs, immunotherapy, and radiotherapy, can have severe and impactful gastrointestinal side effects occurring shortly after treatment (acute toxicity) or persisting for years after treatment ends (late/chronic toxicity).

PURPOSE

The aim of this article is to review the neurotoxic effects of chemotherapy on the enteric nervous system (ENS) and the gut extrinsic innervation. These effects could contribute to the development of long-term gastrointestinal dysfunctions. Research, primarily conducted in animal models, indicates that antitumoral drugs can lead to chemotherapy-induced enteric neuropathy (CIEN). Studies, mainly performed in the myenteric plexus, show that CIEN is characterized by a reduced density of nerve cells and fibers, as well as an imbalanced representation of neuronal subpopulations or their markers, with enteric glial cells also affected. These alterations underlie changes in neuronal activity and gastrointestinal motor function. Although research on the submucosal plexus remains limited, evidence suggests that CIEN affects the entire ENS. Furthermore, scarce studies show that CIEN also occurs in humans. Moreover, emerging experimental data on chemotherapy-induced alterations in visceral sensitivity suggest that the extrinsic innervation of the gut is also affected, but this has received little attention thus far. Nevertheless, this could contribute to the development of chemotherapy-induced brain-gut axis (BGA) disorders in the long term. Cancer chemotherapy (and probably also immunotherapy and radiotherapy) seems to cause neuropathic effects on the intrinsic and extrinsic innervation of the gastrointestinal tract, with an important impact on gastrointestinal and BGA functions. This is a relatively neglected area deserving further investigation.

Neurotoxicity of the antineoplastic drugs: "Doxorubicin" as an example

There is an increased prevalence of cancer, and chemotherapy is widely and routinely utilized to manage the majority of cancers; however, administration of chemotherapeutic drugs has faced limitations concerning the "off-target" cytotoxicity. Chemobrain and impairment of neurocognitive functions have been observed in a significant fraction of cancer patients or survivors and reduce their life quality; this could be ascribed to the ability of chemotherapeutic drugs to alter the structure and function of the brain. Doxorubicin (DOX), an FDA-approved chemotherapeutic drug with therapeutic effectiveness, is commonly used to treat several carcinomas clinically. DOX-triggered neurotoxicity is the most serious adverse reaction after DOX-induced cardiotoxicity which greatly limits its clinical application. DOX-induced neurotoxicity is a net of multiple mechanisms that have been verified in pre-clinical and clinical studies, such as oxidative stress, neuroinflammation, mitochondrial disruption, apoptosis, autophagy, disruption of neurotransmitters, and impairment of neurogenesis. There is a massive need for developing novel therapeutics for both cancer and DOX-associated neurotoxicity; therefore investigating the implicated mechanisms of DOX-induced chemobrain will reveal multi-targets for novel curative strategies. Recently, various neuroprotective mechanisms were employed to mitigate DOX-mediated neurotoxicity. For this purpose, therapeutic interventions using pharmacological compounds were developed to protect healthy "off-target" tissues from DOX-induced toxicity. In addition, nanoplatforms were used to enable target delivery of DOX; to prevent its deposition in non-cancerous tissues. The aim of the current review is to provide some reference value for the future management of DOX-induced neurotoxicity and to summarize the underlying mechanisms of DOX-mediated neurotoxicity and the potential therapeutic interventions.

The Endocannabinoid System of the Nervous and Gastrointestinal Systems Changes after a Subnoxious Cisplatin Dose in Male Rats

Background/Objectives: Cisplatin, a common chemotherapy agent, is well known to cause severe side effects in the gastrointestinal and nervous systems due to its toxic and pro-inflammatory effects. Although pharmacological manipulation of the endocannabinoid system (ECS) can alleviate these side effects, how chemotherapy affects the ECS components in these systems remains poorly understood. Our aim was to evaluate these changes. Methods: Male Wistar rats received cisplatin (5 mg/kg, i.p.) or saline on day 0 (D0). Immediately after, serial X-rays were taken for 24 h (D0). Body weight was recorded (D0, D1, D2 and D7) and behavioural tests were performed on D4. On D7, animals were euthanized, and gastrointestinal tissue, dorsal root ganglia (DRGs) and brain areas were collected. Expression of genes related to the ECS was assessed via Rt-PCR, while LC-MS/MS was used to analyse endocannabinoid and related N-acylethanolamine levels in tissue and plasma. Results: Animals treated with cisplatin showed a reduction in body weight. Cisplatin reduced gastric emptying during D0 and decreased MAGL gene expression in the antrum at D7. Despite cisplatin not causing mechanical or heat sensitivity, we observed ECS alterations in the prefrontal cortex (PFC) and DRGs similar to those seen in other chronic pain conditions, including an increased CB1 gene expression in L4/L5 DRGs and a decreased MAGL expression in PFC. Conclusions: A single dose of cisplatin (5 mg/kg, i.p.), subnoxious, but capable of inducing acute gastrointestinal effects, caused ECS changes in both gastrointestinal and nervous systems. Modulating the ECS could alleviate or potentially prevent chemotherapy-induced toxicity.

Effects of vincristine and monosodium glutamate on gastrointestinal motility and visceral sensitivity

BACKGROUND

Chemotherapy-induced adverse effects are an unresolved nightmare. In preclinical studies in rats, the food additive monosodium glutamate (MSG) improved some of the side effects caused by cisplatin, but its effects in other models of chemotherapy-treated animals are not well known. The aim of this study was to test if MSG may improve some of the adverse effects induced by vincristine in rats.

METHODS

Young male Wistar rats were exposed or not to MSG (4 g L-1 ) in drinking water from week 0 till 1 week after treatment (week 3). Rats received two cycles of five daily intraperitoneal (ip) injections (Monday to Friday, weeks 1 and 2) of either saline (2 mL kg-1 ) or vincristine (0.1 mg kg-1 ). Gastrointestinal motility was measured in vivo by radiological methods after the first and tenth ip administrations. On week 3, the threshold for mechanical somatic and colorectal sensitivity was recorded using Von Frey filaments applied to the paws and an intracolonic balloon, respectively. Finally, samples of the terminal ileum and distal colon were histologically evaluated in sections.

KEY RESULTS

Vincristine reduced body weight gain, food intake, and upper gastrointestinal transit, caused somatic (but not visceral) hypersensitivity and increased the thickness of the submucosal and muscle layers of the small intestine. In vincristine-treated animals, MSG partially prevented gastrointestinal dysmotility and reduced visceral sensitivity but did not improve structural alterations of the small intestine.

CONCLUSIONS & INFERENCES

MSG could be used as an adjuvant to conventional treatments to improve some gastrointestinal dysfunctions caused by chemotherapy.

Contractility of isolated colonic smooth muscle strips from rats treated with cancer chemotherapy: differential effects of cisplatin and vincristine

Background

Certain antineoplastic drugs cause gastrointestinal disorders even after the end of treatment. Enteric neuropathy has been associated with some of these alterations. Our goal was to assess the impact of repeated treatment with cisplatin and vincristine on the contractility of circular and longitudinal muscle strips isolated from the rat colon.

Methods

Two cohorts of male rats were used: in cohort 1, rats received one intraperitoneal (ip) injection of saline or cisplatin (2 mg kg-1 week-1) on the first day of weeks 1-5; in cohort 2, rats received two cycles of five daily ip injections (Monday to Friday, weeks 1-2) of saline or vincristine (0.1 mg kg-1 day-1). Body weight and food and water intake were monitored throughout the study. One week after treatment, responses of colonic smooth muscle strips to acetylcholine (10-9-10-5 M) and electrical field stimulation (EFS, 0.1-20 Hz), before and after atropine (10-6 M), were evaluated in an organ bath.

Results

Both drugs decreased body weight gain. Compared to saline, cisplatin significantly decreased responses of both longitudinal and circular smooth muscle strips to EFS, whereas vincristine tended to increase them, although in a non-significant manner. No differences were observed in the muscle response to acetylcholine. Atropine abolished the contractile responses induced by acetylcholine, although those induced by EFS were only partially reduced in the presence of atropine.

Conclusion

The findings suggest that although both drugs cause the development of enteric neuropathy, this seems to have a functional impact only in cisplatin-treated animals. Understanding the effects of chemotherapy on gastrointestinal motor function is vital for enhancing the quality of life of cancer patients.

Mechanisms of Chemotherapy-Induced Neurotoxicity

Since the first clinical trials conducted after World War II, chemotherapeutic drugs have been extensively used in the clinic as the main cancer treatment either alone or as an adjuvant therapy before and after surgery. Although the use of chemotherapeutic drugs improved the survival of cancer patients, these drugs are notorious for causing many severe side effects that significantly reduce the efficacy of anti-cancer treatment and patients’ quality of life. Many widely used chemotherapy drugs including platinum-based agents, taxanes, vinca alkaloids, proteasome inhibitors, and thalidomide analogs may cause direct and indirect neurotoxicity. In this review we discuss the main effects of chemotherapy on the peripheral and central nervous systems, including neuropathic pain, chemobrain, enteric neuropathy, as well as nausea and emesis. Understanding mechanisms involved in chemotherapy-induced neurotoxicity is crucial for the development of drugs that can protect the nervous system, reduce symptoms experienced by millions of patients, and improve the outcome of the treatment and patients’ quality of life.