Antiemetic activity of the new 5-HT3 antagonist DAU 6215 in animal models of cancer chemotherapy and radiation

Emesis in dogs: a review

Emesis is a common presenting sign in small animal practice. It requires a rational approach to management that is based upon a sound understanding of pathophysiology combined with logical decision making. This review, which assesses the weight of available evidence, outlines the physiology of the vomiting reflex, causes of emesis, the consequences of emesis and the approach to clinical management of the vomiting dog. The applicability of diagnostic testing modalities and the merit of traditional approaches to management, such as dietary changes, are discussed. The role and usefulness of both traditional and novel anti-emetic drugs is examined, including in specific circumstances such as following cytotoxic drug treatment. The review also examines areas in which common clinical practice is not necessarily supported by objective evidence and, as such, highlights questions worthy of further clinical research.

Efficacy of maropitant for treatment and prevention of emesis caused by intravenous infusion of cisplatin in dogs

OBJECTIVE

To evaluate the efficacy of maropitant, a novel neurokinin-1 receptor antagonist, to treat and prevent emesis caused by IV infusion of a chemotherapeutic dose of cisplatin (70 mg/m(2)) in dogs.

ANIMALS

64 healthy 6-month-old Beagles (32 males and 32 females).

PROCEDURES

To evaluate the effect of maropitant on ongoing emesis, 24 dogs were randomized to 2 treatment groups (12 dogs each). Saline (0.9% NaCl) solution or maropitant (1 mg/kg) was administered once by SC injection immediately following the first emetic event after cisplatin infusion. Dogs were assessed for emesis for 6 hours after initiation of cisplatin infusion. To evaluate the use of maropitant for the prevention of emesis, 40 dogs were randomized to 4 treatment groups (10 dogs each). Placebo or maropitant (1, 2, or 3 mg/kg) was administered PO as a tablet. Cisplatin infusion was initiated at 19 hours after treatment, and dogs were assessed for emesis for 6 hours.

RESULTS

No treatment-related adverse events were observed in either study. For the treatment of ongoing emesis, significantly fewer emetic events were observed for maropitant-treated dogs, compared with placebo-treated dogs (mean, 5.2 vs 15.8), and the mean time to cessation of emesis was significantly shorter (0.65 vs 1.65 hours). In the prevention of emesis, maropitant-treated dogs had significantly fewer emetic events (means, 2.7, 1.1, and 0.5 for maropitant at 1, 2, and 3 mg/kg, respectively), compared with placebo-treated dogs (mean, 20.3).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that maropitant is safe and effective in the treatment and prevention of cisplatin-induced emesis in dogs.

Intravenous itasetron: establishing the effective dose range for the prophylactic control of acute emesis in cancer patients undergoing high-dose cisplatin chemotherapy

Nausea and vomiting induced by chemotherapy are a major cause of distress to patients and reduce compliance with potentially beneficial treatment. Itasetron hydrochloride is a new 5-hydroxytryptamine3 (5-HT3) antagonist with potent antiemetic properties. It is more potent than ondansetron in animal models and in early clinical studies it demonstrates a long half-life and does not undergo hepatic biotransformation before elimination. The aim of this open, uncontrolled study was to establish the effective dose range of itasetron hydrochloride given intravenously (i.v.) to patients due to receive high-dose cisplatin chemotherapy (50-120 mg/m2) for the first time. Thirty-nine patients were enrolled in the trial and received a single i.v. infusion of itasetron hydrochloride at a dose of 17-280 microg/kg body weight before commencing the cisplatin infusion (median dose 90-110 mg/m2). Antiemetic protection was demonstrated by doses in the range of 35-280 microg/kg. The 17 microg/kg dose was not effective. Treatment failure (>5 emetic episodes/24 hours) was reported in only six (16%) of the 38 evaluable patients over all treatment groups. Adverse events were generally mild or moderate and of a similar type and incidence to those of current 5-HT3 antagonists. Physicians' and patients' assessments of efficacy and tolerability of itasetron hydrochloride were similar, the majority rating the treatment as 'good' or 'very good'. In conclusion, itasetron hydrochloride is effective in the dose range 35-280 microg/kg in preventing cisplatin-induced emesis. Taken together with results from a larger dose-finding study, a dose corresponding to 35 microg/kg (equivalent to 2.5 mg itasetron, calculated as free base) has been pursued in Phase III studies with the i.v. formulation.

Methotrexate produces delayed emesis in dogs: a potential model of delayed emesis induced by chemotherapy

We investigated the emetic effects of cisplatin and methotrexate in dogs, the effects of ondansetron on cisplatin-induced vomiting, and the effects of ondansetron, dexamethasone and a combination of the two on the vomiting induced by methotrexate. Ondansetron was administered 30 min before cisplatin administration. Ondansetron, dexamethasone or a combination of the two was administered 8, 24 and 48 h after methotrexate administration. Cisplatin (3 mg/kg, i.v.) induced acute vomiting but failed to induce delayed vomiting. The acute vomiting was markedly inhibited by ondansetron (3 mg/kg, p.o.; 1 mg/kg, i.v.). Methotrexate (2.5 mg/kg, i.v.) caused delayed vomiting, which was partly inhibited by ondansetron (1 mg/kg, i.v.) or dexamethasone (2.5 mg/kg, i.v.). The combination of the two agents was more effective. These results suggest that methotrexate-induced emesis in dogs would be useful for studying delayed emesis.

Therapeutic potential of drugs with mixed 5-HT4 agonist/5-HT3 antagonist action in the control of emesis

Drugs interacting with serotonin (5-hydroxytryptamine, 5-HT) receptors are of value in the treatment of several gastrointestinal disturbances. Selective 5-HT3 receptor antagonists (ondansetron, granisetron, tropisetron) are widely utilized to control emesis induced by chemotherapy and radiation, while agonists at 5-HT4 receptors (cisapride, renzapride, BIMU compounds) are endowed with gastrointestinal prokinetic action. Here we overview the therapeutic potential of drugs with potent mixed 5-HT4 agonist/5-HT3 antagonist properties (i.e. BIMU 1) in the management of anticancer therapy-induced emesis and of intestinal adynamic post-operative conditions associated with vomiting. In the former situation, the agonism at 5-HT4 receptors is expected to be of benefit via two possible mechanism: (i) inhibition of 5-HT release from enterochromaffin cells; (ii) restoration of anally driven peristaltic waves in the upper gastrointestinal tract. Moreover, 5-HT4 receptor-induced prokinetic activity may counteract colonic constipation, an unwanted effect which occurs in a number of patients treated with pure 5-HT3 receptor antagonists. Additionally, the above mentioned drugs might be of value in post-operative conditions associated with intestinal adynamia and emesis sensitive to 5-HT3 receptor blockade.

Effects of DAU 6215, a novel 5-hydroxytryptamine3 (5-HT3) antagonist on electrophysiological properties of the rat hippocampus

1. The aim of the present study was to test the effects of DAU 6215 (endo-N-(8-methyl-8-azabicyclo-[3.2.1]-octo-3-yl)-2,3-dihydro-2-ox o-1H- benzimidazole-1-carboxamide carboxamide hydrochloride), a newly synthesized, selective 5-hydroxytryptamine3 (5-HT3) antagonist, on the cell membrane properties and on characterized 5-HT-mediated responses of pyramidal neurones in the hippocampal CA1 region. 2. Administration of DAU 6215, even at concentrations several hundred fold its Ki, did not affect the cell membrane properties of pyramidal neurones, nor modify extracellularly recorded synaptic potentials, evoked by stimulating the Schaffer's collaterals. 3. Micromolar concentrations (15-30 microM) of 5-HT elicited several responses in pyramidal neurones that are mediated by distinct 5-HT receptor subtypes. DAU 6215 did not antagonize the 5-HT1A-induced membrane hyperpolarization and conductance increase, a response that was blocked by the selective 5-HT1A antagonist NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phtalamido)butyl- piperazine). Similarly, DAU 6215 did not affect the membrane depolarization and decrease in amplitude of the afterhyperpolarization, elicited by the activation of putative 5-HT4 receptors. 4. 5-HT increased the frequency of spontaneous postsynaptic potentials (s.p.s.ps) recorded in pyramidal neurones loaded with chloride. In agreement with previous observations, most of the s.p.s.ps were reversed GABAergic events, produced by the activation of 5-HT3 receptors on interneurones, because they persisted in the presence of the glutamate NMDA and non NMDA antagonists, D-aminophosphonovaleric acid (APV; 50 microM) and 6,7-dinitroquinoxaline-2,3-dione (DNQX; 25 microM), and were elicited by the selective 5-HT3 agonist, 2-methyl-5-HT (2-Me-5-HT, 50 microM). 5. The increase in frequency of s.p.s.ps induced by 5-HT was significantly antagonized by DAU 6215 in 70% of the cases, whereas the 5-HT3 antagonist always suppressed the effect of 2-Me-5-HT, at concentrations as low as 60 nM.6. The antagonistic effect of DAU 6215 was also tested on the 5-HT3-mediated block of induction of long-term potentiation (LTP), elicited by a primed burst (PB) stimulation. Extracellular recordings showed that low concentrations (60 nM) of DAU 6215 suppressed the inhibitory action of 5-HT onPB-induced LTP, without affecting the 5-HTlA-induced reduction in the amplitude of the population spike.7. These results provide evidence that DAU 6215 is an effective antagonist of the 5-HT3-mediated responses in the central nervous system and may offer a cellular correlate for the pharmacological effects of DAU 6215 as an anxiolytic and cognition enhancer.

Gastroprokinetic properties of the benzimidazolone derivative BIMU 1, an agonist at 5-hydroxytryptamine4 and antagonist at 5-hydroxytryptamine3 receptors

We have investigated the in vivo motor stimulating and gastroprokinetic properties of the azabicycloalkyl benzimidazolone derivative BIMU 1 (3-ethyl-2,3-dihydro-N-(8-methyl-8-azabicyclo[3.2.1]oct-3-yl)-2-oxo-1H- benzimidazole-1-carboxamide hydrochloride) and its binding profile at 5-hydroxytryptamine3 and 5-hydroxytryptamine4 receptors, in an attempt to assess the serotonergic mechanism underlying its prokinetic action. BIMU 1 dose-dependently (0.01-0.3 mg/kg i.v.) increased the motility of a denervated pouch of canine stomach. This excitatory action was sensitive to muscarinic blockade. A similar stimulatory effect was exerted by the benzamidic prokinetic agent cisapride (0.03-0.3 mg/kg i.v.) but not by the 5-HT3 receptor antagonist ondansetron (up to 1 mg/kg i.v.). The significance for propulsive efficacy of the motor stimulating activity of BIMU 1 was evaluated in a model of gastric emptying of liquids in the conscious dog. The emptying rate of a non-caloric liquid meal instilled through a gastric fistula was accelerated by both BIMU 1 (0.01-1 mg/kg i.v. and 0.1-3 mg/kg p.o.) and cisapride (0.03-1 mg/kg i.v. and 0.3-10 mg/kg p.o.). Ondansetron (1 mg/kg i.v.) did not show any effect. The activity of the 5-HT4 receptor antagonist DAU 6285 was evaluated in the gastric emptying model per se and in interaction experiments on the accelerating action of BIMU 1 (0.3 mg/kg i.v.).(ABSTRACT TRUNCATED AT 250 WORDS)