BRIEF REPORT ⌬9-Tetrahydrocannabinol and Synthetic Cannabinoids Prevent Emesis Produced by the Cannabinoid CB1 Receptor Antagonist/ Inverse Agonist SR 141716A Nissar A. Darmani, Ph.D. There is substantial clinical evidence that produce emesis via either route of administration. SR ⌬9-tetrahydrocannabinol (⌬9-THC) and its synthetic 141716A at an IP dose of 20 mg/kg was used to induce analogs (nabilone and levonantradol) can prevent emesis in emesis for drug interaction studies. Thus, varying doses of cancer patients receiving chemotherapy. Limited available three different classes of cannabinoid agonists [CP 55, 940 animal studies also support the antiemetic potential of these (0, 0.1, 0.5 and 1 mg/kg), WIN 55, 212-2 (0, 1, 5 and 10 cannabinoids. The present study investigates the mg/kg), and ⌬9-THC (0, 5, 10 and 20 mg/kg)], were mechanism of antiemetic action of cannabinoids in an administered IP to different groups of shrews 10 min prior established animal model of emesis, the least shew to SR 141716A injection. The frequency of emesis was (Cryptotis parva). Since cannabinoid agonists prevent recorded for 30 min following the administration of SR emesis, it was hypothesized that blockade of either the 141716A. The order of potency for redcing both the cannabinoid CB1 receptor or the cannabinoid CB2 receptor frequency of emesis and the percentage of shrews vomiting would induce vomiting. Thus, the emetic potential of SR was CP 55, 940 Ͼ WIN 55, 212-2 Ͼ ⌬9-THC which is 141716A (CB1 receptor antagonist) or SR 144528 (CB2 consistent with an action on the CB1 receptor. These results receptor antagonist) was investigated. Both intraperitoneal suggest that the antiemetic activity of ⌬9-THC and its (0, 1, 2.5, 5, 10 and 20 mg/kg, n ϭ 7–15 per group) and synthetic analogs reside in their ability to stimulate the ϭ subcutaneous (0, 10, 20 and 40 mg/kg, n 6–9 per group) cannabinoid CB1 receptor. Furthermore, the antiemetic ϭ ⌬9 administration of SR 141716A caused emesis (ED50 5.52 potency of CP 55, 940 is 45 times greater than -THC. On Ϯ Ϯ 1.23 and 20.2 1.02 mg/kg, respectively) in the least the other hand, blockade of CB1 receptors can induce shrew in a dose-dependent manner. Indeed, both the vomiting, which implicates an important role for endogenous frequency of emesis and the percentage of animals vomiting cannabinoids in emetic circuits. increased with increasing doses of SR 141716A. Significant [Neuropsychopharmacology 24:198–203, 2001] effects were seen at the 10- and 20-mg/kg doses for the IP © 2000 American College of Neuropsychopharmacology. route, while only the 40-mg/kg dose produced significant Published by Elsevier Science Inc. emesis via the SC route. The CB2 antagonist failed to West Jefferson Street, Kirksville, MO 63501, USA. Tel.: (660) 626- From the Department of Pharmacology, Kirksville College of 2326; Fax: (660) 626-2728. Osteopathic Medicine, Kirksville, Missouri, USA E-mail address: [email protected] Address correspondence to: Dr. Nissar A. Darmani, Department Received April 17, 2000; revised July 14, 2000; accepted August of Pharmacology, Kirksville College of Osteopathic Medicine, 800 21, 2000. NEUROPSYCHOPHARMACOLOGY 2001–VOL. 24, NO. 2 © 2001 American College of Neuropsychopharmacology Published by Elsevier Science Inc. 0893-133X/01/$–see front matter 655 Avenue of the Americas, New York, NY 10010 PII S0893-133X(00)00197-4 NEUROPSYCHOPHARMACOLOGY 2001–VOL. 24, NO. 2 Cannabinoid CB1/Receptor and Emesis 199 KEY WORDS: Marijuana; Delta-9-tetrahydrocannabinol; CP volvement of CB1 receptor appears most likely since 55, 940; WIN 55, 212-2; SR 141716A; SR 144528; Emesis; ⌬9-THC produces most of its effects via this site (Pertwee CB1 receptor; CB2 receptor 1997). If activation of cannabinoid receptors prevent eme- In the early 1970s, accumulating anecdotal reports by sis, then blockade of these receptors may produce vomit- young cancer patients suggested that smoking mari- ing. Thus, the present study investigated: (1) whether ad- juana would alleviate the nausea and vomiting caused ministration of the selective cannabinoid CB1-receptor by chemotherapeutic agents. Since then, both govern- antagonist SR 141716A (Rinaldi-Carmona et al. 1994), or ment- and industry-sponsored clinical trials were initi- the CB2-receptor antagonist SR 144528 (Rinaldi-Carmona ated to test the antiemetic potential of ⌬9-tetrahydro- et al. 1998), can induce emesis in the least shrew (Dar- cannabinol (⌬9-THC) and some of its synthetic analogs mani 1998; Darmani et al. 1999); and (2) whether the in- such as nabilone and levonantradol (Gralla 1999; Voth duced emesis can be blocked by the cannabinoid agonists ⌬9 and Schwartz 1997). This literature suggests that both -THC and its newly introduced synthetic analogs CP ⌬9-THC and its tested analogs are useful antiemetics in 55, 940 and WIN 55, 212-2 (Pertwee 1997). some patients for the prevention of nausea and vomit- ing associated with cancer chemotherapy. Though can- nabinoids appear to be a more efficacious class of anti- MATERIALS AND METHODS emetics than dopamine D2 receptor antagonists for the Animals and Drugs prevention of chemotherapy-induced vomiting, the ef- ficacy of tested cannabinoids to date seems not to be as Shrews (Cryptotis parva) were bred and maintained in the high as the more potent antiemetics such as the selec- animal facilities of the Kirksville College of Osteopathic Medicine, Kirksville, Missouri. Both male and female tive 5-HT3 receptor antagonists (Gralla 1999). However, one interesting advantage of cannabinoids is that many shrews (4–6 g, 45–70 days old) were used throughout of the patients who are protected from the acute phase the study. The animals were kept on a 14:10-h light- of emesis, also respond well during the delayed phase dark cycle at a humidity controlled room temperature of 21 Ϯ 1ЊC with ad lib supply of food and water. The of chemotherapy-induced emesis which 5-HT3 receptor antagonists poorly control (Abrahamov et al. 1995; feeding and maintenance of shrews are fully described Chan et al. 1987; Dalzell et al. 1986). elsewhere (Darmani 1998; Darmani et al. 1999). The fol- Unlike the relatively large body of clinical reports, lowing drugs were purchased from Research Biochemi- ⌬9 ⌬9 only a few published animal studies on the antiemetic cals Inc., Natick, MA: -tetrahydrocannabinol ( - ϩ effects of cannabinoids are available. Several cannab- THC) and R( )-WIN 55, 212-2 mesylate. CP 55, 940 was inoids can block cisplatin- or apomorphine-induced obtained from Pfizer (Groton, CT). SR 141716A and SR emesis in a variety of animal species including the cat, 144528 were generously donated by Professor B.R. Mar- the pigeon and the least shrew (Cryptotis parva) (Mc- tin. All drugs were dissolved in a 1:1:18 solution of eth- Carthy and Borison 1981; McCarthy et al. 1984; London anol: emulphor: 0.9% saline to twice the stated drug et al. 1979; Stark 1982; Darmani 2000). Until recently, an concentrations. These drugs concentrations were fur- animal model of emesis had not been employed for in- ther diluted by the addition of an equal volume of sa- vestigating the cannabinoid receptor involved in the line. This procedure was necessary, because the 1:1:18 antiemetic effect of ⌬9-THC and other cannabinoids. In vehicle mixture can cause emesis in up to 20% of ani- the present study, the least shrew (Cryptotis parva) has mals by itself. The final vehicle mixture induced emesis been used as an animal model of emesis. This species only very rarely. All drugs were administered at a vol- was recently introduced as a new serotonergic (Dar- ume of 0.1 ml/10g of body weight. All animals received mani 1998) and dopaminergic (Darmani et al. 1999) ex- care according to the “Guide for the Care and Use of perimental model of vomiting. The least shrew is a Laboratory Animals,” DHSS Publication, revised, 1985. small insectivore (adult weight 4–6 g) that lives in vari- ous ecological niches in Central and North America. Experimental Protocols The family Soricidae, to which shrews belong, consti- tute over 266 species (Churchfield 1990). Over the last The present protocols were based upon our previous decade, Japanese investigators have established the emesis studies in the least shrew (Darmani 1998; Dar- house musk shrew (Suncus murinus) as an experimen- mani et al. 1999). On the test day, the shrews were tal model for the various emetic stimuli (Matsuki et al. transferred to the experimental room and were allowed 1988; Torii et al. 1991). Suncus murinus is relatively a to acclimate for at least 1 h prior to experimentation. larger animal (adult being 50–100 g in weight) and is To habituate the shrews to the test environment, each endogenous to Asia and Africa. animal was randomly selected and transferred to a 20 ϫ While the antiemetic effects of ⌬9-THC appear to be 18 ϫ 21 cm clean clear plastic cage and offered 4 meal receptor-mediated, it is unclear whether the cannabinoid worms (Tenebrio sp) 30 min prior to experimentation. CB1 and/or CB2 receptors are involved in emesis. In- Different groups of shrews were then injected either in- 200 N.A. Darmani NEUROPSYCHOPHARMACOLOGY 2001–VOL. 24, NO. 2 traperitoneally or subcutaneously with vehicle (n ϭ 11– Statistical Analysis 12) or varying doses of the CB antagonist SR 141716A 1 The data were analyzed by the Kruskal-Wallis nonpara- (1, 2.5, 5, 10 and 20 mg/kg, n ϭ 7–15), or the CB antag- 2 metric one-way analysis of variance (ANOVA) and onist SR 144528 (10, 20 and 40 mg/kg, n ϭ 8–11 per posthoc analysis by Dunn’s multiple comparisons test. group). Immediately following injection, each shrew A p-value of Ͻ.05 was necessary to achieve statistical was placed in the observation cage and the onset la- significance.