Frank C. Tortella et al- Novel Anticonvulsant Analogs of Dextromethorphan: Improved Efficacy,...

8/3/2019 Frank C. Tortella et al- Novel Anticonvulsant Analogs of Dextromethorphan: Improved Efficacy, Potency, Duration a

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____________________metabolism to the PCP-like compound dextrorphan (DX). We evaluated13. ABSTRACT (DMdhamuem00woe the anticonvulsant activity and neurological impairing effects inrats of three novel analogs of ON4 which, based upon their 3-position substituents, would either not be expected to beSf1?oca metabolized to DX, or might do so at a reduced rate. The ONThi'cu aboon OippZoW analogs were determined to be sore potent and more efficacious thanlox j ONlc*~ood3~~1gainst maximal electroshock (lIES) convulsions; tro of thedistribut is unUljmft, analogs, namely AHNl-036 ([+J-3-ethoxy-l7-nethylmorphinan) andAHNI-037 ((+1-3- (2-propoxy) -17-methylsorphinan), were equipotent toDX. AHNl-036 and AHN1-037 exhibited a duration of action (1-2 hrs)

* slightly longer than DX (0.5-1 hr) and similar to 0ON (2-4 hr). Theanticonvulsant effect of AMN649 persisted 4-6 h~rs. Againstflurothyl convulsions 0ON was proconvulsant, DX was anticonvulsant,* and the ON analogs were inactive. In contrast, 14-methyl-D-Aspartate (lNMDA) convulsions were antagonized by pretreatment with014 nd the 014 nalogs, albeit with a potency approximately 10 timesless than that of DX. Results of rotarod performance testingfrhrdistinguished the analogs from 014, OX or the anticonvulsantQUA= drug diazepam (DZ). No behavioral impairment was observed at thehighest doses tested of each of the 014 analogs resulting inprotective indices (i.e. rotarod TD,0/1ES anticonvulsant EDQ)greatly exceeding 014, X or clinical anticonvulsant drugs. Theresults of this study establish these 3-substituted 014 nalogs asnovel anticonvulsants exhibiting improved potency, efficacy,duration and side-effect profiles.

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72S Yoieltstso~. Vol. 268(Franklin and Murray, 1992), while exhibiting low to moderate neurological impairment to determine the PI (Loscher andaffinity for DM and sigma-1 sites (310 and 202 nM, respec- Nolting, 1991) for each of the respective compounds.tively) (Klein and Musacchio, 1989; Walker et al., 1990); 2) thebehavioral profiles (Tortella et al., 1989b; Szekely et al., 1991) Methodsof these drugs are distinct; and 3) similar to what has beenobserved in binding studies (Musacchio eta!i., 1989), the clas- Animals. For all the seizure experiments male Sprague-Dawely ratswere obtained from Zivic-Miller (Pittsburgh, PA). At delivery thesical anticonvulsant drug phenytoin potentiates the anticon- animals were housed individually in a humidity and temperature con-vulsant activity of DM (Tortella and Musacchio, 1986), but not trolled environment on a 12-hr light cycle beginning at 6:00 A.M. Th eDX (Tortella et al., 1988a). Furthermore, it has been shown rats were received at a weight range of 100 to 150 g and permitted foodrecently that DM can be differentiated from PCP ligands like and water ad libitum during their acclimation period which lasted atDX on the basis of their ability to attenuate NMDA- and K* - least 7 to 10 days before testing.evoked increases in cytosolic Ca"* concentrations (Church et Convulsant models. Th e anticonvulsant potency and efficacy ofal., 1991). DM , DX , DZ and three of the DM analogs was determined in the MES

Despite these differences, the fact remains that DM will be test. For these experiments rats (n = 10 per group) weighing 175 to 225> 90% metabolized to DX in humans. Because i* would be g were used. Details of this supramaximal convulsion model of seizurepredicted that DM doses higher than the recommended anti- spread and quantitation of anticonvulsant potency has been describedtussive dose (15-30 mg/kg) would be required, the potential elsewhere (Tortella et al., 1986). Briefly, electrical stimuli were appliedtundsireadose(15-0mgk g w rqualitiesofaDXmetaoirehe wouldtialauricularly via small alligator clip electrodes by using fixed supramax-undesirable PCP-like qualities of a DX metabolite would se- imal current stimulation (150 mA, 2 sec). Th e presence or absence ofverely hamper the future development of this drug as a useful complete tonic hindlimb extension was measured. Anticonvulsant ED,,therapeutic entity for treatment of epilepsy, stroke or central values and 95% CL were calculated from quantal dose-effect curves bynervous system trauma. Indeed, case reports of toxicity in using the method of Litchfield and Wilcoxin (1949) and the computerchildren (Pender and Parks, 1991) and psychotomimetic reac- programs of Tallarida and Murray (1987).tions (Dodds, 1967; Fleming, 1986) associated with high-dose For convulsant thresholds each of the drugs were tested for theirDM ingestion are likely attributable to this metabolite, as is ability to influence the onset to clonic convulsions induced by thethe reported abuse potential in adolescent youths (Rammer et volatile convulsant flurothyl (Adler, 1975; Tortella et al.. 1986). In thisal., 1988; Pender and Parks, 1991). model flurothyl is infused as a 10% solution in 95% ethanol (v/v) to

We have explored recently the possibility of preparing DM groups of rats (n = 8 per group) weighing 225 to 275 g and placedindividually in sealed test chambers. Th e seizure threshold was definedanalogs which are modified in position-3 of the morphinan ring as the time interval between the start of the flurothyl infusion and thesystem, with the intention of developing compounds that would onset to a clonic convulsion. In the case of the DM analogs AHNI-036retain anticonvulsant and neuroprotectant activity without in and AHN1-037, where the amount of drug available for testing wasvivo conversion to DX (Newman et al., 1992). In our first series limited, only a single dose equal to 2 times their respective MESof compounds, three analogs including the aniline (AHN649), anticonvulsant EDso was tested.the O-ethylether (AHN1-036) and the O-isopropyl ether For NMDA convulsions, rats weighing 200 to 250 g were initially(AHN1-037) derivatives of DM (fig. 1) displayed anticonvul- anesthetized with halothane and implanted with an i.c.v, cannula aimedsant potency in rats which was equal to or greater than DM or at the right lateral ventricle. Three to 5 days postsurgery the animalsDX (Newman et al.3, 1992). The purpose of the present study were divided into groups (n = 6 per group) for testing. Previous dose-was to 1) evaluate further the pharmacological properties of response and pharmacological experiments from our laboratory haveestablished 12.5 nM NMDA as a nonlethal, suprathreshold dose forthe respective dose-response curves of these novel analogs for inducing clonic "popcorn" convulsions in the rat via a direct interactionseizure protection in the MES test; 2) extend these findings to with the NMDA receptor complex (Robles et al., 1991). Two indices ofother experimental models of convulsant activity; 3) test for convulsive activity were measured: the latency to onset to NMDAanticonvulsant activity after i.c.v. administration in which me- convulsions and the number of rats per group exhibiting convulsivetabolism to DX is unlikely; and 4) use a rotorod assessment of behavior (i.e., the percentage responding).Rotarod performance. Rotarod experiments were carried out by

NCH3 NCH3 using male Sprague-Dawley rats (260-370 g) obtained from TaconicFarms (Germantown, NY). The animals were trained to remain for 60sec on a rotarod (model RRF, Omnitech Electronics. Columbus, OH)rotating at 6 revolutions/sec. Falling off the rotarod before 60 secresulted in a 3 mA , 3 sec electric footshock. After testing to establishthat the behavior was still intact, the subjects were treated with either

OCH3 OH saline or the test compound. Untreated animals were able to remainon the rod for several minutes. A positive score was given during testingif the rat failed to remain on the rotarod for 60 sec. The TDw valuesand 95% CL for neurologic impairment were calculated from the

NCH3 NCH3 NCH3 quantal dose-effect curves as described above. The rotarod experiments- were first conducted with groups of three or four rats per dose. If there

was no effect (0% failures) at a particular dose level, no further testing%too.. too,.. with that dose was done. If, however, there was an effect then additionalrats were run such that n = 6 was completed for that dose. The onlyexception to this design was for the AHN compounds where six ratswere run at the highest doses reported, but no further increments wereNH2 OCH2CHS OCH(CH 3)2 attempted due to the limited availability of these novel compounds.

Calculation of P1 values and statistics. PI values were calculatedAH N 649 AHN 1-036 AHN 1-037 by dividing the respective rotarod TDw values by the MES anticonvul-

Fig. 1.Chemical structures of (+)-3-substituted morphinan analogs, sant EDo values established for each compound. Statistical analysis of


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1994 Novel Anticonvulsant ODAnalogs 729the dose-response curves for regression and parallelism was accom- 100plished by using procedures 5 and 6 from Tallarida and Murray (1987).Flurothyl seizure thresholds were compared by using the Mann-Whit- 80ney U test (significance level, P < .05). Th e latency to NMDA convul-sions was compared by using a one-way analysis of variance and aStudent's t test (significance level, P < .05). a 60 0 *General protocol. In order to determine the time course of theanticonvulsant activity, compounds were tested at various times post- C.injection by using doses (n = 6 per dose) approximately equal to 2 a 40 0 0times their respective ME S anticonvulsant EDso values. These experi-ments (fig. 3) determined the latency to peak anticonvulsant effect for 20 0DM, DX and the respective analogs to be 30 min after s.c. injection.Therefore, the pretreatment time for the MES, flurothyl and rotorod 0dose-response experiments was 30 min and the route of drug adminis- 1101.. ation was s.c. (in a 1 or 2 ml/kg volume). Fo r the i.c.v. NMDAexperiments, pretreatment times were empirically set at 15 min. Alli.c.v. injections were given as a rapid bolus (1-2 sec) in a 5-,ul volume 00followed by a 4-al vehicle flush. Throughout the study each ra t was / - AHNI-037used only once and all rats were drug and seizure naive before testing. s0All experiments were carried out between 8:30 A.M. and 1:00 P.M. at an DXambient temperature of 23-25C. E - 60 - AHNI-036Drugs. All drug solutions were made fresh by using distilled deion-ized water or saline. When necessary (i.e., with the highest doses of & -m. AHN649DM or AHN649) gentle heating was applied to enhance solubility. DM 0 $ 40was obtained from Sigma Cheinical Co. (St. Louis, X10). NIMDA was 0obtained from Research Biochemicals Inc. (Natick, MA). DX and the c -2- DZDM analogs were synthesized as described previously (Newman et aL.,1992).

0*Results 1 10 100 1000Dose (mg/kg, s.c.)The effect of the various compounds on MES convulsions isshown in figure 2, top. All the compounds tested were anticon- Fig. 2. Top, MES anticonvulsant dose-response curves. %Protection,vulsant, blacking the expression of tonic hindlimb extension in the percentage of rats per group protected from MES-induced tonichindlimb extension. Bottom, rotarod performance dose-response curves.a dose-dependent manner. The dose-response curves for DM , % Failures, the percentage of rats per group failing to remain on theDX an d the respective DM analogs were linear (correlation rotarod for 60 sec.coefficients were DM = [0.961, DX = [0.85], AHN649 -[0.95], AHN1-036 = [0.99] an d AHN 1-037 = [0.99]). Statis- TABLE 1tical comparison of these functions indicated that although the MES anticonvulsant ED , values, rotarod TD M values (95%

dose-response curves for DX and AHN-649 were parallel to confidence intervals) and calculated PI valuesDM, those produced by AHN1-036 and AHN1-037 were sig- Treatelnt MESI Rotorod? Ptnificantly different (P < .05 and P < .01, respectively). With DZ 1.7 (0.6-5) 6.4(3-15) 3.8the exception of DM , all the compounds were highly efficacious. DM 37.8 (20-72) 229 (55-950) 6.0In the case of DM , the highest dose tested (70 mg/kg) resulted DX 4.3(3-7) 20.6 (14-31) 4.8AHN649 21.4 (15-30f >300 >14.0in seizure protection in only 70% of the rats tested. AHN1-036 5.6 (3-11)r >100 >17.9The anticonvulsant ED50 values are shown in table 1. The AHN1-037 3.9 (2-7)r >100 >25.6rank order c.f potency for the respective anticonvulsant drugs values are expressed as milligrams per kilogram.was DZ = AHN1-037 = DX = AHN1-036 > AHN649 = DM . From Newman etal. (1992).At the highest doses tested rats given DZ appeared sedatedwhereas DX-treated rats exhibited mild ataxia. Rats given DM 366 9 to 500 19 sec) at the highest dose tested (50 mg/kg).or the DM analogs appeared behaviorally normal at these doses. In contrast, DM, which at low doses (12.5 and 25 mg/kg) failedTime course experiments showed peak anticonvulsant activ- to influence the convulsant threshold to flurothyl, was procon-ity occurring within 30 min for all the compounds tested (fig. vulsant at higher doses (50 and 75 mg/kg), significantly low-3). Further analysis determined that the aniline analog, ering the seizure threshold to 83 3% of control (from 402 AHN649, retained at least 50% activity for as long as 4-hr 19 to 333 14 sec) at the highest dose tested (75 mg/kg, or 2postinjection. DM was also relatively long acting, producing times its MES anticonvulsant dose). Th e DM analog AHN649seizure protection in 50% of the rats 2-hr postinjection. DX was inactive even at doses equivalent to 2 to 4 times its MESwas the shortest acting anticonvulsant producing a marginal anticonvulsant ED50. When tested at 2 times their MES anti-effect (20% protected) at I-hr postinjection. convulsant ED5 odose, AHNI-036 and AHN1-037 had no effectDM , DX and the analogs were tested for their ability to alter on the seizure threshold to flurothyl-induced convulsions.convulsant thresholds to flurothyl. Over the duration of the These results are summarized in table 2.study control seizure thresholds matched to the various exper- The effect of i.c.v. administrated DM , DX and the respectiveimental groups ranged from 364 9 to 402 19 sec. Only DX DM analogs to antagonize convulsive activity induced bywas anticonvulsant in this seizure model, dose-dependently NMDA is demonstrated in figures 4 and 5. Administration ofincreasing the seizure threshold to 137 5% of control (from 12.5 nM NMDA directly into the brain of control, vehicle-


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730 TYatem etaL Vol. 268100 12 5 - 0

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Fig. 3. T'ime course of drug-induced anticonvulsant activity. % Protection, Dose (pg, i.c.v.)the percentage of rats per group protected from MES-induced tonichNndlimb extension. Doses used are the same as defined in table 2 Fig. 5. Dose-dependent increase in the mean latency to NMDA-inducedrepresenting approximately 2 times the MES anticonvulsant EDo dose convulsions. Latency is determined from the initiation of the injection tofor the respective compounds. the onset of behavioral convulsion. Each of the respective data pointswere analyzed to be significantly different from the control latency (P


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1994 Novel Anticonvulsant DM Analogs 731DM analogs, was capable of increasing the seizure thresholds analogs may be limited. This finding, however, is somewhatto flurothyl convulsions. Unfortunately, the anticonvulsant tempered by our results demonstrating that the DM analogseffects of DX were of relatively short duration and occurred at also protect against NMDA convulsions whereas other clini-doses only slightly bel )w those inducing neurobehavioral im- cally effective compounds which block MES convulsions, suchpairments. All three of the DM analogs studied were either as phenytoin or phenobarbital, are ineffective against NMDAmore potent than DM and/or equipotent to DX against MES (Czuczwar et al., 1985; Leander et al., 1988a). Secondly, theconvulsions. Compared to DM , their lack of effect against proconvulsant effects of DM in the flurothyl seizure test, andflurothyl threshold convulsions probably accounts for their the recognition of proconvulsant effects generally associatedimproved anticonvulsant efficacy. Compared to DX , their with high doses of anticonvulsant drugs such as phenytoin orweaker potency against NMDA convulsions as well as their carbamazepine (Loscher et al., 1991), likely contribute to thelack of rotarod impairing effects likely reflects their relative limited efficacy found with DM in some seizure models. There-lack of affinity for the noncompetitive PCP site of the NMDA fore, as shown in the present study, it is possible that thereceptor complex. Significantly, the PI values for the DM improved efficacy obtained with the DM analogs is related toanalogs greatly exceeded those for DM, or reported for other their failure to negatively influence seizure thresholds. Withinstandard anticonvulsants, in similar testing paradigms in rats this framework it will be important to evaluate the effects of(Loscher and Nolting, 1991). Therefore, the results of this study the DM analogs against kindled seizures and other in vivonot only confirm that DM an d the PCP-like drug DX have (genetically predisposed) and in vitro (cortical or hippocampalprominent anticonvulsant effects in rodent models of experi- slice preparations) models of spontaneous epileptiform activity.mental epilepsy but, more importantly, demonstrate that dra- The efficacy of DM as an antagonist of NMDA convulsionsmatic improvement in potency, efficacy, duration of action and in rodents (Ferkany et aL, 1988; Aram et al., 1989; Apland andsafety can be obtained by modification of the DM molecule. Braitman, 1990), albeit weak, has been confirmed in the presentDM was described originally as an anticonvulsant against study. The i.c.v. administration of DM, while effectively delay-ME S convulsions in rats (Tortella and Musacchio, 1986) and ing the onset to NMDA convulsions, failed to antagonize thesubsequently was shown to possess anticonvulsant activity incidence of NMDA-induced convulsions. This limited effectagainst a variety of preclinical experimental models of seizures of DM to antagonize NMDA convulsions may be explained, in(see Tortella et al., 1989b). Whereas a recent case study de- part, by the results of binding studies which suggest that DMscribed a considerable reduction in seizure frequency with DM interacts with relatively low affinity with glutamate/NMDAin a patient suffering from medically refractory complex partial binding sites (Craviso an d Musacchio, 1983; Tortella et al.,seizures (Wieser and Beck, 1992), the clinical efficacy of DM 1989b), including the glycine modulatory site on the NMDAas a valuable antiepileptic drug in humans remains to be receptor complex (Newman et al., 1992).established (Fisher et al., 1990). Although the PI of DM (table In contrast, the results of other binding analysis and com-1 and Leander et al., 1988b) is well within the range of proto- petition studies have indicated that DM interacts with multipletypical MES-selective anticonvulsant drugs including pheny- high and low affinity DM sites as well as high affinity sigmatoin, carbamazepine, phenobarbital and diazepam (Loscher and sites (Klein and Musacchio, 1989; Zhou and Musacchio, 1991).Nolting, 1991), its usefulness as a therapeutic drug in humans Interestingly, similar to DM other highly selective sigma-1may be severely limited due to its metabolism to the PCP-like ligands such as (+)-3-(hydroxyphenyl)-N-n-propylpiperonedrug DX. Therefore, the importance of developing anticonvul- and (+)-pentazocine (Walker et al., 1990) have been found tosant analogs of DM with PI values -I least similar to standard lower flurothyl seizure thresholds in rats (Echevarria et al.,antiepileptic drugs, but whose mechanism of action is inde- 1990) and induce epileptiform EEG activity at high doses (F.pendent of metabolism to DX and distinct from that of DX or C. Tortella, unpublished observations), suggesting that activa-PCP, is indisputable, tion of a population of sigma receptors may propagate convul-Subjective observations of rat behavior revealed that none of sant responses, rather than mediate anticonvulsant activity.the analogs produced overt sedation or ataxia when adminis- Therefore, in view of the high affinity of DM for sigma-1 sitestered at the highest doses tested. More importantly, even min- (vida infra), it is possible that the proconvulsant effect of DMimal neurological deficit as defined by using the rotarod test measured in the flurothyl experiments and its limited efficacy(Loscher and Nolting, 1991) was nonexistent. Therefore, with against MES and NMDA convulsions, results from an inter-PI values at least 4- to 5-fold greater than any prototypical action at this high affinity sigma-1 binding site. Importantly,anticonvulsant drug currently available one might surmise that other high affinity "anticonvulsant" DM ligands such as car-these analogs represent a new class of safe and effective anti- betapentane and caramiphen (Tortella and Musacchio, 1986;convulsant drugs. A note of caution is warranted, however, as Tortella et al., 1988b; Leander, 1989; Aram et al., 1989; Aplandpreclinical underestimation of neurobehavioral toxicity can and Braitman, 1990) also exhibit high relative affinities forresult from a variety of factors (Loscher and Nolting, 1991), sigma-1 sites (Walker et al., 1990) and, likewise, lower flurothylespecially when determinations of PI values are not based on seizure thresholds (F . C. Tortella, unpublished observations).plasma or brain levels of the drugs in question, as was the case Our assessment of the binding characteristics of DM and thein the present study. DM analogs indicates that a functional relationship may exist

A critical finding of this study was our observation that the between anticonvulsant activity and high affinity DM-siteDM analogs were ineffective against flurothyl threshold con- binding in the brain (Newman et al., 1992). Importantly, thevulsions. This result is important for two reasons. First, because DM analogs have been shown to have negligible affinities forthe flurothyl convulsion model, like the metrazol test (Swin- the ['Hithienylcyclohexylpiperidine or [1H]glycine sites on theyard, 1969), classically screens for anticonvulsant drugs effec- NMDA receptor complex (Newman et al., 1992). Therefore, ittive against the petit mal epilepsies (Adler, 1975), it would is unlikely that their ability to antagonize NMDA convulsionsappear that the anticonvulsant spectrum of action of the DM observed in the present study resulted from interactions with


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732 Torlela et &L Vol. 268noncompetitive NMDA ion channel receptors or the strych- enine-insensitive glycine modulatory site, but rather may be due ADLER, M. A.: Pharmacology of flurothyl: Laboratory and clinical applications.In Current Developments in Psychopharmacology, ed. by W. B. Esbman, pp.to some other modulatory action on the NMDA receptor- 30-61, Spectrum Publications, Ne w York, 1975.complex. Although a definitive determination of the receptor APLAND, J. P. AND BRAITMAN, D. J.: Effects of non-opioid antitussives onepileptiform activity and NMDA responses in hippocampal and olfactory cortexmechanism of action mediating the seizure protective proper- slices. Brain Res. 529: 277-285, 1990.ties of these compounds awaits a more detailed analysis, th e ARAM. J. A., MARTIN. D., TOMCZYK, M., ZEMAN. S.MMILLAR. J., POHLER. (.AN D LODGE, D.: Neocortical epileptogenesis in .an): Studies with N-methyl-results of these binding experiments suggest that a selective D-aspartate, phencyclidine, sigma and dextromethorphan receptor ligands. .1interaction with a high affinity DM site may be responsible. Pharmacol. Exp. Ther. 248: 320-328, 1989.BARNHART, J. W. : The urinary excretion of dextromethorphan and three metab-Additional studies are underway addressing this question, as olites in dogs and humans. Toxicol. Appl. Pharmacol. 55: 43-48, 1980.well as the possible role of intracellular neuronal calcium dy- CARPENTER, C. L., MARKS, S. S.. WATSON. D. L. AND GREENBERG. D. A.:namics (Carpenter et al., 1988; Church et al., 1991; DeCoster et Dextromethorphan and dextrorphan as calcium channel antagonists. BrainRes. 439: 372-375, 1988.a., 1992), in the anticonvulsant mechaniqm of action for DM CHAPMAN, A. G. AN D MELDRUM, B. S.: Non-competitive N-methvl-D-aspartateand the respective DM analogs, antagonists protect against sound-induced seizures in DBA/2 mice. Eur. J.Pharmacol. 168: 210-211, 1989.Several results suggest that metabolism to DX is not a CHURCH, J., LODGE, D. AND BERRY. S.: Differential effects of dextrorphan andprerequisite for anticonvulsant activity. First, DM is anticon- levorphanol on the excitation of rat spinal neurons by amino acids. Eur. J.vuleant in in vitro slice preparations where metabolism to DX Pharmacol. 111: 185-190, 1985.CHURCH, J., SHACKLOCK, J. A. AND BAIMBRIDGE, K. G..:Dextromethorphan andis unlikely (Aram et al , 1989; Apland and Braitman, 1990). phencyclidine receptor ligands: Differential effects on K'- and NMDA-evokedSecond, we have demonstrated in this study that minor modi- increases in cytosolic free Ca` concentration. Neurosci. Lett. 124: 232-234.1991.fications at position-3 of the 17-methylmorphinan molecule, CHOI, D. W.: Dextrorphan and dextromethorphan attenuate glutamate neurotox-producing compounds which might not be expected to be me- icity. Brain Res. 403: 333-336, 1987.

CHOI, D. W., PETERS, S. AND VISESKUL, V.: Dextrorphan and levorphanoltabolized to DX, or do so only at a reduced rate (Newman et selectively block N-methyl-o-aspartate receptor-mediated neurotoxicity on cor-aL, 1992), can significantly improve the anticonvulsant phar- tical neurons. J. Pharmacol. Exp. Ther. 242: 713-720, 1987.macology of DM. Substitution of the 3-methoxy group with the CRAviso, G. L. AND MUSACCHIO, J. M.: High-affinity dextromethorphan bindingsites in guinea pig brain. I1. Competition experiments. Mol. Pharmacol. 23:primary amine (AHN649) only slightly increased the potency 629-640, 1983.of DM, but significantly improved the anticonvulsant efficacy, CZUCZWAR, S. J., FREY, H. H. AND LOSCHER. W.: Antagonism of N-methyl-D-aspartic acid-induced convulsions by antiepileptic drugs and other agents. Eur.duration of action and PI. In turn, addition of sterio bulk to J. Pharmacol. 108: 273-280, 1985.the alkyl side chain as seen with the alkyl ether series of DECOSTER, M. A., KOENIG, M. L., HUNTER, J. C. AND TORTELLA, F. C.: Calciumcompounds (AHN1-036 and AHN1-037) significantly im- dynamics in neurons treated with toxic and non-toxic concentrations of glu-tamate. Neuroreport 3: 773-776, 1992.proved anticonvulsant potency without effecting neurological DODDS, A.: Toxic psychosis due to dextromethorphan [Letteri. Med. J. Austr. 2:function. While it is possible that these alkyl ethers could be 231, 1967.ECHEVARRIA, E., ROBLES, L. AN D TORTELLA, F. C.: Differential profiles ofmetabolized via dealkylation to DX, it is important to recognize putative "dextromethorphan sigma" ligands in experimental seizure models.that 1) none of the analogs were behaviorally similar to DX in Fed. Proc. 4: A311, 1990.FERKANY, J. W. , BOROSKY, S. A., CLISSOLD, D. B. AND PONTECORVO, M. J.:the rat; 2) unlike DX they failed to raise seizure thresholds to Dextromethorphan inhibits NMDA-induced convulsions. Eur. J. Pharmacol.flurothyl; 3) compared to DX, the respective analogs exhibited 151:151-154, 1988.an improved duration of action with ANH649 continuing to FISHER, R. S., CYSYK, B. J., LESSER, R. P.. PONTECORVO. M. J.. FERKANY, J.

T., SCHWERDT, P. R., HART, J. AND GORDON. B.: Dextromethorphan formanifest seizure protection as long as 4-hr postinjection; and treatment of complex partial seizures. Neurology 40: 547-549. 1990.4) all the DM analogs were anticonvulsant after i.c.v. admin- FLEMING, P. M.: Dependence on dextromethorphan hydrobromide. Br. Med. J.293: 597, 1986.istration where metabolism in brain to DX is unlikely. FRANKLIN, P. H. AND MURRAY, T. F.: High affinity (5Hldextrorphan binding in

In conclusion, novel analogs of DM have been synthesized rat brain is localized to a noncompetitive antagonist -ite of the activated N-methyl-D-aspartate receptor-cation channel. Mol. Pharmacol. 41: 134-146.which exhibit in'lproved potency, efficacy, duration of action 1992.and safety as potential anticonvulsant treatments. Because of GEORGE, C. P,, GOLDBERG, M. P., CHOI. D. W. AND STEINBERG. G. K.: Dextro-their efficacy in the MES and NMDA models of experimental methorphan reduces neocortical ischemic neuronal damage in Vim. Brain Res.440: 375-379, 1988.seizures, the DM analogs may represent a novel class of anti- KAMM, J. J., TADDOE, A. B. AND VAN LOON, E. J.: Metabolism and excretion ofepileptic drugs for the treatment of generalized seizures of the tritiated dextromethorphan by the rat. J. Pharmacol. Exp. Ther. 158: 437-444, 1967.grand mal type as well as partial (focal),seizures. Their excellent KLEIN, M. AND MUSACCHIO, J. M. : High affinity dextromethorphan bindingPI values clearly distinguish them from prototypical anticon- sites in guinea pig brain. Effect ofsigma ligands and other agents. J. Pharmacol.vulsant agents currently in clinical use, as well as from PCP- Exp. Ther. 251: 207-2215, 1989.KUKO, T. AND WADA, J. A.: Antiepileptic effect of dextromethorphan on amyg-like anticonvulsant agents including DX, ketamine and MK- daloid-kindled seizures in cats. Epilepsia (Basel) 30: 669. 1989.801. Although the critical issue of tolerance development re- LEANDER, J. D. : Evaluation of dextromethorphan and carbetapentane as anti-convulsants and N-methyl-D-aspartic acid antagonists in mice. Epilepsy Res.mains to be addressed, the results of the present study would 4: 28-33, 1989.seem to establish these DM analogs as potential drug develop- LEANDER, J. D. , LAWSON, R. R., ORNSTEIN, P. L. AND ZIMMERMAN. D. M. : N-methyl-D-aspartic acid lethality in mice: Selective antagonism by phencvcli-ment candidates for the treatment of epilepsy and possibly dine-like drugs. Brain Res. 448: 115-120, 1988a.other neurodegenerative disorders such a stroke or brain/spinal LEANDER, J. D., RATHBUN, R. C. AND ZIMMERMAN, D. M. : Anticonvulsantcord trauma. effects of phencyclid ine-like drugs; relation to N-methyl-D-aspartic acid antag-onism. Brain Res. 454: 368-372, 1988b.Acknowledgments LITCHFIELD, J. T. AND WILCOXIN, F.: A simplified method of evaluating dose-effect experiments. J. Pharmacol. Exp. Ther. 96: 99-113. 1949.The authors wish to thank Mark Ginski and Brian Seidleck for their assistance LosCHER, W. , HONACK, D., FASSBENDER, C. P. AND NOLTING, B.: The role ofin conducting the rotarod experiments and Edward Echevarria and Jonathan technical, biological and pharmacological factors in the laborator' evaluationTaylor for their assistance in conducting various phases of the seizure experi- of anticonvulsant drugs. I11. Pentylenetetrazol seizure models. Epilepsy Res.ments. We also wish to acknowledge Dr. Gregory Galbicka for his editorial and 8:171-189, 1991.computer graphics assistance. LOSCHER, W. AND NOLTING, B.: The role of technical, biological and pharma-


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1994 Novel Anticonwhisant Did An~alogs 733cological factors in the laboratory evaluation of anticonvulsant drugs. IV. phan. a non-opioid antituasive, on development and expression of amygdaloidProtective indices. Epilepsy Res. 9: 1-10, 1991. kindled seizures. Epilepsia (Basel) 31: 496-502, 1990.MONVER. H. AND CHOI, D. W.: Morphinans attenuate cortical neuronal injury TALLARIDA. R_ J. AND M'URRAY, R. B.: Manual of Pharmacologic Calculationsinduced by glucose deprivation in vitro. Brain Ras. 446: 144-148, 198 with Computer Programs. Springer- Verlag, New York, 1987,MURRAY, T. F. AND LEID, M. E.: Interaction of dextrorotatory opioids with ToRTELLA, F. C., FERKANY, J. W. AND PONTECORVO, M. ,J.: Anticonvulsantphencyclidine recognition sites in rat brain membranes. Life Sci. 34: 1899- effects Of dextrorphan in rats: P~ossible involvemen' .ldextromethorphan-1911,1984., induced seizure protection. Life Sci. 42: 2509-251., , )Ms.MVSACCNIO, J.EKLEIN, M. AND PATUHZO, J. J.: Effects of dlextromethorphan TORTELLA, F. C., MARTIN. D. A., ALLOT, C. P.. STEEL, J. A.. BLACKtBURN, T.site liganda and allosteric modifiers on the binding of (+)_[ 3H13-(3-hydroxy- P.. LOVEDAY. B. E. AND RUSSELL, N. J.: Dextromethorphan attenuates post-phenyl)-N.(1-propyl)piperidine. Mol. Pharmacol. 35: 1-5, 1989. iechemic hypoperfusion following incomplete global ischeniia in the anesthe-NEWMAN, A. H., BEVAN, K., BOWERY, N. AND TORTELLA, F. C.: Synthesis and tized rat. Brain Res. 482: 179-183, 1989a.evaluation of 3-substituted 17-methylmorphinan analogs as potential anticon- TORTELLA. F. C. AND MUSACCHIO, J. M. : Dextromethorphan and carbetapen-vulsant agents. J. Med. Chem. 35: 4135-4142. 1992. tane: Centrally acting non-opioid antituasive agents with novel anticonvulsantPENDER, E. S. AND PARKS, B. R.: Toxicity with dextromethorphan -containing properties. Brain Res. 383: 314-318, 1986.preparations: A literature review and report of two additional cases. Pediat. TORTELLA, F. C., PELLICANO, M. AND BOWERtY, N. G3.:Dextromethorphan andEmerg. Care 7:163-165, 1991. neuromodulation: Old drug coughs up new activities. Trends. Pharmacol. Sci,RAMMER, L., HOLMGREN. P. AND SANDLER, H.: Fatal intoxication by dextro- 10: 501-507, 1989b.methrphn: reprtto caes.Fornsi Sci In. 3: 76-76, 188. TORTELLA. F. C.. ROBLES, L. AND HOLADAY. J. H.: U50.488, a highly selectivemethrphn: reortto cses Fornsi Sc. m. 37 76-76, 188. kappa opioid: Anticonvulsant profile in rats. J. Pharmacol. Exp. Ther. 237:ROBLES, L., ECHEVARRIA, E. AND ToRTELLA, F. C.: NMDA convulsions produced 49-53.,1986.by i.c.v. administration in rats: Differential sensitivity to various antagonists. TORTELLA, F. C.. WiTKIN, .J.M. AND MUSACCHiO. J. M.: Caramiphen: a non-Soc. Neurosci. Abst. 17: 588, 1991. opioid antitussive with potent anticonvulsant properties in rats. Eur. J. Phar-ROTHMAN, R. B., MAHBOUBi, A., REID, A. A., Kim. C. H., DECOSTA, B. R., macol. 155: 69-75, 1988b.JACOBSON. A. E. AND RICE, K. C.: [3H11,3-D1(2-tolyl)guanidine labels two WALKER, J. M., BOWEN, W. D., WALKER, F. 0., MATSUMOTO, R. R.. DE COSTA,high affinity binding sites in guinea pig brain: Evidence for allosteric regulation B. AND RICE, K. C.: Sigma receptors: Biology and function. Pharmacol. Re%.by calcium channel blockers and sigma liganda. NIDA Res. Monogr. 105: 335- 42: 355-402, 1990.336, 1991. WIESER, H. (G. AND BECK, H.: Improvement of medically refractory temporalSTEINBERG, G. K., SALEH, J. AND KUNis, D.: Delayed treatment with dextro- lobe epilepsy with dlextromethorphan. J1.Epilepsy 5: 246-247. 1992.methorphan and dlextrorphan reduces cerebral damage after transient focal WONG, B. Y., COULTER, D. A., CHO]. D. W. AND PRINCE, D. A.: Dextrorphanischemia. Neurosci. Lett. 89: 193-197, 1988. and dextromethorphan. common antitussives. are antiepileptic and antagonizeSTEINBERG, G. K., SALEH, J., KUNis, D., DE LA PAZ, R. AND ZARNEGAR, R.: N-methyl-d-aspartate in brain slices. Neuroeci. Lett. 85: 261-266, 1988.Protective effect of N-methyl-D-aspartate antagonists after focal cerebral ZHOU, G. Z. AND MIJSACCHIO, J. M.: Computer-assisted modeling of multipleischemia in rabbits. Stroke 20: 1247-1252, 1989. dextromethorphan and sigma binding sites in guinea pig brain. Eur. J1.Phar-SWINYARDt, E. A.: Laboratory evaluation of antiepileptic drugs. Review of labo- macol. 206: 261-269. 1991.ratory methods. Epilepsia (Baael) 10:107-119, 1969.SZEKELY, J. I., SHARPE, L. G. AND JAFFE, J. H.: Induction of phencyclidine-like Send reprint requests to: Dr. Frank C. Tortella, Chief. Neuropharmacologybehavior in rats by dlextrorphan but no t dextromethorphan. Pharmacol, Branch, Department of Medical Neurosciences. Walter Reed Army Institute ofBiochem. Behav. 40: 381-386, 1991. Research, Washingto., DC 20307-5100.TAKAZA WA, A., ANDERSON. P. AND ABRtAHAM, W. C.: Effects of dlextromethor-

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