Liposomal formulation of mirfentanil hydrochloride.

Mirfentanil hydrochloride, a novel CNS analgesic with a short duration of action, was successfully encapsulated in liposomes having a variety of compositions. The lipid composition of the formulation was varied to optimize the stabilization of liposomes and the encapsulation of solutes. Retention of mirfentanil hydrochloride was evaluated by storing loaded liposomes at several temperatures, and also after the physical stressing of formulations. High efficiency of drug encapsulation was observed in liposomes prepared using dipalmitoyl-L-alpha-phosphatidylcholine (DPPC) and the ternary mixture of dimyristoyl-L-alpha-phosphatidylcholine, cholesterol, and dicetyl phosphate (DMPC/CHOL/DCP), both with and without the further incorporation of monosialoganglioside (GM1). Only 35% of encapsulated drug was lost when the formulations containing GM1 were incubated with human plasma over a 24 hour period, suggesting that liposomal formulations containing GM1 could be used to control drug release in vivo.

New 1-(heterocyclylalkyl)-4-(propionanilido)-4-piperidinyl methyl ester and methylene methyl ether analgesics.

A series of new 1-(heterocyclyalkyl)-4-(propionanilido)-4-piperidinyl methyl esters and methylene methyl ethers have been synthesized and pharmacologically evaluated. In the mouse hot-plate test, the majority of compounds exhibited an analgesia (ED50 less than 1 mg/kg) superior to that of morphine. These studies revealed a pharmacological accommodation for many more structurally diverse and far bulkier aromatic ring systems than the corresponding components of the arylethyl groups of the prototypic methyl ester (carfentanil, 2) and methylene methyl ether (sufentanil, 3 and alfentanil, 4) 4-propionanilido analgesics. Compound 9A (methyl 1-[2-(1H-pyrazol-1-yl)-ethyl]-4-[(1-oxopropyl)phenylamino]-4- piperidinecarboxylate), which exhibited appreciable mu-opioid receptor affinity, was a more potent and short-acting analgesic, than alfentanil with less respiratory depression in the rat. On the other hand, the phthalimides 57A and 57B, which exhibited negligible affinity for opioid receptors associated with the mediation of nociceptive transmission (i.e., mu-, kappa-, and delta-subtypes), displayed analgesic efficacy in all antinociception tests. In addition, while 57B, compared to clinical opioids, showed a superior recovery of motor coordination after regaining of righting reflex from full anesthetic doses in the rat rotorod test, 57A showed significantly less depression of cardiovascular function at supraanalgesic doses in the isoflurane-anesthetized rat.

Synthesis and pharmacological evaluation of a series of new 3-methyl-1,4-disubstituted-piperidine analgesics.

The synthesis and intravenous analgesic activity of a series of 3-methyl-4-(N-phenyl amido)piperidines, entries 34-79, is described. The methoxyacetamide pharmacophore produced a series of compounds with optimal analgesic potency and short duration of action. cis-42 was 13,036 times more potent than morphine and 29 times more potent than fentanyl; however, the corresponding diastereomer 43 was only 2778 and 6 times more potent, respectively. Compounds 40, 43, 47, and 57 are extremely short acting; all had durations of action of about 2 min, which was about 1/5 of that of fentanyl in the mouse hot-plate test at a dose equivalent to 2 times the ED50 analgesic dose. Among the many compounds that displayed exceptional analgesic activity, duration of action was one of the main factors for choosing a candidate for further pharmacological investigation. At present, cis-1-[2-(4-ethyl-4,5-dihydro-5-oxo-1H-tetrazol-1-yl)ethyl]-3-meth yl-4- [N-in equilibrium 2-fluorophenyl)methoxyacetamido]piperidine hydrochloride (40) (Anaquest, A-3331.HCl, Brifentanil) is in clinical evaluation. Opiate analgesics that possess short duration of action are excellent candidates for short surgical procedures in an outpatient setting where a rapid recovery is required.

4-Phenyl- and 4-heteroaryl-4-anilidopiperidines. A novel class of analgesic and anesthetic agents.

The incorporation of the 4-phenylpiperidine pharmacophore found in morphine into 4-anilidopiperidines related to fentanyl (1) led to a novel class of potent opioid analgesic and anesthetic agents with a favorable pharmacological profile. The synthesis, analgesic activity, and anesthetic properties of a series of 4-phenyl-4-anilidopiperidines (13-29) are discussed. Isosteric replacement of the phenyl by various heteroaryl substituents extended the series to include 4-heteroaryl-4-anilidopiperidines (30-53). Within this group, 1-[2-(1H-pyrazol-1-yl)ethyl]-4-(4-methylthiazol-2-yl)-4-(N- phenylpropionamido)piperidine (48), exhibited high analgesic potency, short duration of action, rapid recovery of motor coordination following anesthetic doses, and greater cardiovascular and respiratory safety during anesthesia as compared with opioids fentanyl (1) and alfentanil (2) currently in clinical use. Such analgesics could be of great utility to clinicians in the expanding outpatient surgical arena and for patient-controlled analgesia and computer assisted continuous infusion pain control techniques.

Antinociceptive activity of pentamorphone, a 14-beta-aminomorphinone derivative, compared to fentanyl and morphine.

The analgesic potency of pentamorphone, a 14-beta-aminomorphinone derivative, was compared to that of fentanyl and morphine by examining quantal dose-effect curves generated from data obtained in the mouse hot plate, rabbit tooth-pulp, and dog tail clamp tests. Onset and duration of antinociceptive effects were also compared. The ED50 values (mg/kg) were determined in mice for pentamorphone (0.0039), fentanyl (0.016), and morphine (7.3). In the rabbit tooth pulp test the ED50 values were 0.0009 mg/kg for pentamorphone, 0.0074 mg/kg for fentanyl, and 1.1 mg/kg for morphine; in the dog tail clamp test these values were 0.012 mg/kg for pentamorphone and 0.018 mg/kg for fentanyl. Duration of action (defined as the time until response to tooth pulp stimulation declined to 50% of maximum possible effect [MPE]) was 10 min with twice the IV ED50 for pentamorphone in mice. This duration was similar to that of the equipotent dose of fentanyl but much shorter than the duration of an equipotent potent dose of morphine (60 min). The duration in rabbits of the ED98 (IV) dose of pentamorphone was 65 min compared to 35 min for an equipotent dose of fentanyl and 200 min for morphine. Intramuscular doses of pentamorphone had significantly faster onset and shorter duration times than equipotent doses of morphine in both mice and rabbits. Pretreatment with naloxone in mice and rabbits attenuated the development of the antinociceptive effects of pentamorphone. This study shows that pentamorphone is a potent analgesic with a duration of action similar to that of fentanyl.

Synthesis and pharmacological evaluation of 4,4-disubstituted piperidines.

A new class of piperidine derivatives is added to the increasing family of compounds related to fentanyl and carfentanil. Herein, we describe the synthesis and pharmacology of a number of 1-(arylethyl)-4-(acylamino)-4-[(acyloxy)-methyl]piperidines such as 9, 15, and 23. As expected, many of these congeners of fentanyl are extremely potent narcotic agonists. The aim of the study was to identify short-acting analgesic agents (i.e. less than 6 min in the mouse hot-plate assay) for possible use in the surgical theater. Many of the drugs proved to be of intermediate and long duration (i.e. 6-15 min and greater than 15 min, respectively). In addition to analgesic activity, many of the compounds exhibited anesthetic properties as well. The structure-activity relationship for these entities is presented and discussed.

New 4-(heteroanilido)piperidines, structurally related to the pure opioid agonist fentanyl, with agonist and/or antagonist properties.

A research program based on certain heterocyclic modifications (12-50) of the fentanyl (1) molecule has generated a novel class of opioids. In the mouse hot-plate test, these compounds were weaker analgesics than 1. Two types of antagonists were observed in morphine-treated rabbits: those (e.g., 28) that reversed both respiratory depression and analgesia and those (e.g. 32) that selectively reversed respiratory depression. Evaluation of in vitro binding affinities to rat brain opioid receptors was inconclusive for a common locus of action for the agonist as well as the antagonist component. Further pharmacological evaluation of 32, N-(2-pyrazinyl)-N-(1-phenethyl-4-piperidinyl)-2-furamide, in the rat showed it to be a potent analgesic (ED50 = 0.07 mg/kg, tail-flick test) with little cardiovascular and respiratory depression when compared to fentanyl.

Antinociceptive interactions between alpha 2-adrenergic and opiate agonists at the spinal level in rodents.

This study was undertaken to evaluate the antinociceptive interactions of alpha 2 adrenergic and opiate receptors at the spinal level. Morphine and clonidine were administered intrathecally (i.t.) by lumbar puncture to rats either alone or in the presence of either i.t. yohimbine, an alpha 2 antagonist, or systemic naloxone, an opioid antagonist. The effect of tolerance to systematically administered morphine on responses to i.t. morphine and clonidine was examined in mice. Antinociception was determined by observing the response to a clamp applied to the tail (Haffner test) in mice and by the tail-flick test in rats; log dose-response curves for antinociception were generated for morphine, clonidine, and each drug combination. Morphine and clonidine both produced dose-dependent antinociception when given i.t. in both species. The i.t. administration of yohimbine attenuated the antinociceptive effect of both clonidine and morphine, but naloxone attenuated only the response to morphine. Further, a sub-analgetic dose of i.t. clonidine potentiated the effect of i.t. morphine. In morphine-tolerant mice, i.t. morphine was not efficacious whereas clonidine retained full efficacy, although potency was slightly diminished. Thus, it appears that alpha 2 adrenoceptor-mediated antinociception is independent of opiate receptor mechanisms. Clinical use of intrathecal combinations of alpha 2 adrenergic and opiate receptor agonists to increase analgesia and use of intrathecal alpha 2 agonists for pain relief in patients tolerant to opiates might deserve evaluation.

A comparison of the antinociceptive and behavioral effects of intrathecally administered opiates, alpha-2-adrenergic agonists, and local anesthetics in mice and rats.

This study was undertaken to compare the antinociceptive and behavioral effects of intrathecally administered opiates, alpha-2-adrenergic agonists, and local anesthetics injected by lumbar puncture in the mouse and rat. Antinociception was determined by observing the response to a clamp applied to the tail (Haffner test) of the mouse and by the rat tail-flick test; log dose-response curves for antinociception were generated for each drug in each test. Motor coordination and other behavioral effects were also observed. Morphine and fentanyl (mu-opiate agonists) as well as ethylketocyclazocine (EKC) and U50488H (kappa-opiate agonists), together with buprenorphine (partial mu-opiate agonist) and the alpha-2-adrenergic agonist clonidine, all produced antinociception in both species without causing significant behavioral or motor dysfunctions at antinociceptive doses. Xylazine (also an alpha-2-adrenergic agonist), ketamine, procaine, and lidocaine inhibited responses but only at doses that also produced motor impairment or paralysis. Nalbuphine (mixed opiate agonist-antagonist) was without any effect in both species. These data suggest that the mu- and kappa-opiate agonists and clonidine are the preferred agents for producing antinociception without compromising motor function.

Amnesic effect of the novel anticonvulsant MK-801.

MK-801, a reported N-methyl-D-aspartate (NMDA) antagonist with affinity for the phencyclidine (PCP) receptor, injected intravenously in mice before a training trial in a passive avoidance procedure, produced a similar amnesic effect to that produced by the standard amnesic agent scopolamine. Compared to vehicle-treated mice, each drug produced significant amnesia, yet the potency of MK-801 was 40 times that of scopolamine. This result with the MK-801 is consistent with previous reports that drugs which act at PCP recognition sites within the brain produce memory impairing effects in rodents.

Development of acute tolerance to the cardiorespiratory effects of alfentanil after subsequent bolus injection in conscious rats.

The cardiovascular and respiratory effects of alfentanil in conscious freely moving rats, were evaluated after initial and subsequent injections. Doses of alfentanil (50, 130, 260, and 500 ug/kg) were given to naive rats (n = 4-5) and 1 hour later this dose was repeated. The resultant cardiovascular and respiratory effects were compared. At all doses there was a significant (p less than 0.05) depression of mean arterial pressure and heart rate after the initial dose of alfentanil. At doses of 50, 130, and 260 ug/kg, the second administration elicited significantly less depression of cardiovascular parameters than the initial dose. Maximum changes in respiratory parameters (PaCO2 and PaO2) were also significantly less after the second administration of alfentanil. This difference, in maximum respiratory depression, was not seen at the highest doses (500 ug/kg). These results indicate that tolerance, to the cardiorespiratory side effects seen after alfentanil, can occur in as little as 1 hour after subsequent bolus injections.

Induction and growth of mammary tumors after superior cervical ganglionectomy in sighted and blinded-anosmic rats.

Female rats were subjected to superior cervical ganglionectomy (Gx), blinding and anosmia (BAs) or combined procedures (BAsGx). Onset and growth of dimethylbenz(a)anthracene (DBMA)-induced mammary tumors was studied in these animals and compared to tumorigenesis in intact control rats. Carcinostatic effects were present in all surgically altered animals, as evidenced by a trend toward reduced tumor incidence, reduced final tumor mass, and a significant reduction in mean number of tumors in Gx and BAsGx rats, and increased regression of tumors in BAs rats compared to intact group. Reduced tumorigenesis was paralleled by a trend toward either an increase (BAs) or a decrease (Gx and BAsGx) in the activity of pineal hydroxyindole-O-methyltransferase (HIOMT) compared to intact group. In addition, BAs and BAsGx animals showed a significant reduction in body weight. These results suggest that Gx reduces mammary tumorigenesis in both sighted and BAs rats. They further confirm the findings of others on reduced mammary tumorigenesis in BAs rats. Possible involvement of multiple carcinostatic mechanisms in different animal models is discussed.

Efforts toward combined analgesic/antidepressants: synthesis and evaluation of (3-aryl-2,3-dihydrobenzofuran-3-yl)alkanamines.

Several (3-aryl-2,3-dihydrobenzofuran-3-yl)alkanamines, designed as potential antidepressant agents with analgesic properties, were synthesized and pharmacologically evaluated. While two compounds (1a, 1f) displayed potent antitetrabenazine activity, concomitant antinociceptive activity in the phenylquinone writhing assay was not observed.

3-(1-Indolinyl)benzylamines: a new class of analgesic agents.

An extensive series of 3-(1-indolinyl)benzylamines and related compounds was synthesized and tested for analgesic activity. After a detailed study of structure-activity relationships, 3-(1-indolinyl)benzylamine (2b) was selected for further investigation as the most interesting member of this novel class of compounds. It was active in both the phenylquinone writhing and tail-flick assays for analgesic activity. No motor deficits were observed in the rotorod test, and 2b was found to be free of any other effects on the central nervous system. The compound did not bind to opiate receptors, since it was inactive in inhibiting the stereospecific binding of [3H]naloxone in rat brain homogenates. Thus, 3-(1-indolinyl)benzylamine represents a novel analgesic with an unusual chemical structure and biological profile.

Inhibitory effects of superior cervical ganglionectomy on dimethylbenz(a)anthracene-induced mammary tumors in the rat.

The role of the pineal in regulating the oncogenic processes was explored in Sprague-Dawley female rats by comparing incidence and growth of mammary tumors in animals subjected to superior cervical ganglionectomy (SCGx) or blinding and anosmia (BAs) with that of intact rats treated with 7-12-dimethylbenz(a)anthracene (DMBA). The surgery was performed at the age of 56 days, 1 day following the administration of the carcinogen. Growth of mammary tumors was studied, and 15 weeks later the rats were sacrificed by decapitation and the activity of the pineal hydroxyindole-O-methyltransferase (HIOMT) was determined. Carcinostatic effects of similar magnitude were present in both SCGx and BAs groups as evident from tendency toward reduced tumor incidence and decreased total tumor mass. Ganglionectomized rats developed significantly smaller numbers of tumors than intact control animals. A trend toward reduced tumor number and increased tumor regression was evident in the BAs group. Although there was no significant difference in tumor volumes among the groups, BAs animals showed a distinct trend toward smaller tumor volumes at the termination of the experiment. Despite similar carcinostatic tendencies, SCGx rats had significantly lower HIOMT activity than BAs animals. The possible existence of multiple carcinostatic mechanisms in BAs and SCGx rats is discussed.

Dibenz[b,e]oxepinalkanoic acids as nonsteroidal antiinflammatory agents. 4. Synthesis and evaluation of 4-(4,10-dihydro-10-oxothieno[3,2-c] [1]benzoxepin-8-yl)butanol and -butyric acid and related derivatives.

4,10-Dihydro-10-oxothieno[3,2-c][1]benzoxepin-8-acetic acid (6) was previously reported as a potent antiinflammatory-analgesic agent characterized by an impressive therapeutic ratio in comparison with indomethacin. With the goal of finding compounds that might display even more favorable therapeutic ratios and/or enhanced antiinflammatory/analgesic properties in comparison to 6, we synthesized 4-(4,10-dihydro-10-oxothieno [3,2-c][1]-benzoxepin-8-yl) butanol (4b) and -butyric acid (5a) and a series of related derivatives. All compounds were evaluated for potential analgesic activity in the phenylquinone-induced writhing (PQW) assay, for antiinflammatory activity in the carrageenan-induced paw edema (CPE) model and, where warranted, for gastric irritation (GI) liability. Of the compounds investigated, 4b (HP 573) displays moderate analgesic-like activity in PQW, is approximately half as potent as indomethacin or 6 as an antiinflammatory agent in the CPE, and is characterized by an extremely low propensity to induce GI as reflected by comparison of the therapeutic ratios (GI ED50/CPE ED50: 4b greater than 46, 6 = 9.9, indomethacin = 0.4). Compound 4b was selected for clinical evaluation.

Tricyclics with analgesic and antidepressant activity. 2. [[(Alkylamino)ethyl]thio]dibenzo[b,f]thiepins and 10,11-dihydro derivatives.

A series of [[(alkylamino)ethyl]thio]dibenz[b,f]thiepins (III) and their 10,11-dihydro derivatives (IV) was synthesized and subjected to broad analgesic/CNS screening. Preliminary results indicated a combination of analgesic/antidepressant profiles, similar to that observed for the [[(alkylamino)ethyl]thio]dibenz[b,f]oxepins (I) and their corresponding dihydro derivatives (II). The most active congener from the present series, 10b, shows an antinociceptive potency in the pentazocine range as assessed by phenyl-p-quinone-induced writhing (PQW) and tail flick in mice. It is also more than twice as active as imipramine in preventing tetrabenazine-induced ptosis (TBZ), a test widely recognized to be of predictive value for clinically efficacious antidepressants.

Synthesis and analgesic activity of some 5-(4-hydroxyphenyl)-2-azabicyclo[3.2.1]octanes.

A representative series of 5-(4-hydroxyphenyl)-2-azabicyclo[3.2.1]octanes was synthesized and evaluated in vitro, as well as in vivo, as potential analgetic agents. In general, moderate to good activity (19 twice as active as morphine) was observed in the phenylquinone writhing assay (PQW), while only marginal activity was detected by the tail-flick method. Compounds 19 and 18, being the most active in the PQW model, also demonstrated weak binding affinity for the opiate receptors labeled by [3H]naloxone in rat brain homogenates.