Cisplatin-induced neurotoxicity involves the disruption of serotonergic neurotransmission

Neurotoxicity is a frequent side effect of cisplatin (CisPt)-based anticancer therapy whose pathophysiology is largely vague. Here, we exploited C. elegans as a 3R-compliant in vivo model to elucidate molecular mechanisms contributing to CisPt-induced neuronal dysfunction. To this end, we monitored the impact of CisPt on various sensory functions as well as pharyngeal neurotransmission by recording electropharyngeograms (EPGs). CisPt neither affected food and odor sensation nor mechano-sensation, which involve dopaminergic and glutaminergic neurotransmission. However, CisPt reduced serotonin-regulated pharyngeal pumping activity independent of changes in the morphology of related neurons. CisPt-mediated alterations in EPGs were fully rescued by addition of serotonin (5-HT) (≤ 2 mM). Moreover, the CisPt-induced pharyngeal injury was prevented by co-incubation with the clinically approved serotonin re-uptake inhibitory drug duloxetine. A protective effect of 5-HT was also observed with respect to CisPt-mediated impairment of another 5-HT-dependent process, the egg laying activity. Importantly, CisPt-induced apoptosis in the gonad and learning disability were not influenced by 5-HT. Using different C. elegans mutants we found that CisPt-mediated (neuro)toxicity is independent of serotonin biosynthesis and re-uptake and likely involves serotonin-receptor subtype 7 (SER-7)-related functions. In conclusion, by measuring EPGs as a surrogate parameter of neuronal dysfunction, we provide first evidence that CisPt-induced neurotoxicity in C. elegans involves 5-HT-dependent neurotransmission and SER-7-mediated signaling mechanisms and can be prevented by the clinically approved antidepressant duloxetine. The data highlight the particular suitability of C. elegans as a 3R-conform in vivo model in molecular (neuro)toxicology and, moreover, for the pre-clinical identification of neuroprotective candidate drugs.

Use of C. elegans as a 3R-compliant in vivo model for the chemoprevention of cisplatin-induced neurotoxicity

Anticancer therapeutics can provoke severe side effects that impair the patient's quality of life. A frequent dose-limiting side effect of platinum-based anticancer therapy is neurotoxicity. Its pathophysiology is poorly understood, and effective preventive or therapeutic measures are missing. Therefore, elucidation of the molecular mechanism of platinating drug-induced neurotoxicity and the development of preventive strategies is urgently needed. To this end, we aim to use C. elegans as a 3R-compliant in vivo model. The 3R principles were conceived for animal welfare in science concerning animal experiments, which should be replaced, reduced or refined. We can analytically demonstrate dose-dependent uptake of cisplatin (CisPt) in C. elegans, as well as genotoxic and cytotoxic effects based on DNA adduct formation (i.e., 1,2-GpG intrastrand crosslinks), induction of apoptosis, and developmental toxicity. Measuring the impairment of pharyngeal pumping as a marker of neurotoxicity, we found that especially CisPt reduces the pumping frequency at concentrations where basal and touch-provoked movement were not yet affected. CisPt causes glutathione (GSH) depletion and RNAi-mediated knockdown of the glutamate-cysteine ligase GCS-1 aggravates the CisPt-induced inhibition of pharyngeal pumping. Moreover, N-acetylcysteine (NAC) mitigated CisPt-triggered toxicity, indicating that GSH depletion contributes to the CisPt-induced pharyngeal damage. In addition to NAC, amifostine (WR1065) also protected the pharynx of C. elegans from the toxic effects of CisPt. Measuring pharyngeal activity by the electrophysiological recording of neurotransmission in the pharynx, we confirmed that CisPt is neurotoxic in C. elegans and that NAC is neuroprotective in the nematode. The data support the hypothesis that monitoring the pharyngeal activity of C. elegans is a useful surrogate marker of CisPt-induced neurotoxicity. In addition, a low GSH pool reduces the resistance of neurons to CisPt treatment, and both NAC and WR1065 are capable of attenuating platinum-induced neurotoxicity during post-incubation in C. elegans. Overall, we propose C. elegans as a 3R-compliant in vivo model to study the molecular mechanisms of platinum-induced neurotoxicity and to explore novel neuroprotective therapeutic strategies to alleviate respective side effects of platinum-based cancer therapy.