Tissue levels of N-n-propylnorapomorphine after treatment with (-)10,11-methylenedioxy-N-n-propylnoraporphine, an orally long-acting prodrug active at central dopamine receptors

Orally active analogues of the dopaminergic prodrug 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one: synthesis and pharmacological activity

A series of analogues of 6-(N,N-di-n-propylamino)-3,4,5,6,7,8-hexahydro-2H-naphthalen-1-one (6), an enone prodrug of the mixed DA D(1)/D(2) agonist 5,6-diOH-DPAT (2), was synthesized. The pharmacological profiles of these new enones and their in vivo pharmacological activities were investigated in the Ungerstedt rat rotation model for Parkinson's disease. At 0.1 mg kg(-1) po, the N-methyl-N-n-propyl (12) and the N-ethyl-N-propyl (13) analogues induced pronounced and long lasting pharmacological effects. The pharmacological profile of enone 12 was found to be similar to that of 6, while enone 13 was significantly more potent than 6 (p < 0.01). Analyses of rat brains after the administration of (-)-6 and 13 indicated the presence of hydroxylated metabolites of the parent enones. It is speculated that such metabolites are alpha'-hydroxylated enones that may constitute the first step in the formation of the corresponding catechols.

A new type of prodrug of catecholamines: an opportunity to improve the treatment of Parkinson's disease

After decades of research around dopamine agonists, we have found a promising compound in S-PD148903 that represents a new type of prodrug, which in the rat is bioactivated to the catecholamine S-5,6-diOH-DPAT, known to display mixed dopamine D(1)/D(2) receptor agonist properties just like apomorphine. This prodrug has an enone structure which by an oxidative bioactivation mechanism is converted to the corresponding catechol and is delivered enantioselectively into the CNS. This novel concept has the potential to revolutionize the treatment of Parkinson's disease by competing with L-DOPA, the current treatment of choice.

R(-) and S(+) stereoisomers of 11-hydroxy- and 11-methoxy-N-n-propylnoraporphine: central dopaminergic behavioral activity in the rat

R(-)11-Hydroxy-N-n-propylnoraporphine (11-OH-NPa) induced stereotyped behavior in the rat as potently (ED50 = 0.80 mg/kg, i.p.) as R(-)apomorphine (APO) and this effect was blocked by haloperidol; the 11-methoxy congener, R(-)11-MeO-NPa, had a weak effect (ED50 greater than 10 mg/kg) and the S(+) isomers had none. The isomer R(-)11-OH-NPa potentiated locomotion stimulated by apomorphine; S(+)11-OH-NPa inhibited it and the isomers of 11-MeO-NPa were inactive. Catecholaporphines usually are inactive orally, but both R(-) and S(+)11-OH-NPa were similarly potent after oral or parenteral administration. The isomer S(+)11-OH-NPa inhibited spontaneous and apomorphine-induced locomotion (ID50 = 1.8-2.7 mg/kg, p.o. and i.p.) and stereotyped behavior (ID50 = 3 mg/kg, p.o. or i.p.), all without inducing catalepsy. While apomorphine was short-acting (1-2 hr), the effects of R(-)11-OH-NPa persisted up to 6-7 hr and those of the S(+) isomer for at least 2.5 hr; moreover, the efficacy of R(-)11-OH-NPa increased markedly up to 3-4 hr, although its ED50 was independent of time (ED50 = 1.7-1.9 mg/kg, i.p. from 1-3 hr). The total effect of R(-)11-OH-NPa (p.o. or i.p.) over time was more than 10-times greater than that of injected apomorphine. These observations accord with the reported high (nM) affinity of 11-OH-NPa at cerebral DA receptor sites (D2 greater than D1) and weak interactions of the 11-methoxy congener. They support the conclusion that the R(-) and S(+) stereoisomers are neuropharmacologically active, respectively, as DA agonist and apparent antagonist, as was found with the enantiomers of N-n-propylnorapomorphine, perhaps due to the low intrinsic postsynaptic agonist activity of the S(+) isomers. Moreover, 11-OH-NPa was highly bioavailable orally and unusually long-acting; it may be absorbed slowly or have active metabolites. Hydroxy-substitution of aporphines at the 11-position, homologous to the 3-OH of DA, evidently is critical for affinity and activity at the DA receptor. These or other monohydroxyaporphines may represent leads to potentially useful DA agonist or antagonist drugs.

Determination of N-n-propylnorapomorphine in serum and brain tissue by gas chromatography-negative ion chemical ionization mass spectrometry

A method for the determination of the neuroactive compound N-n-propylnorapomorphine (NPA) in biological tissues is described. Isolation of NPA from serum or brain tissue was achieved via liquid-liquid extraction from phosphate-buffered tissue extract (0.25 M, pH 7.2) into ethyl acetate. The NPA, along with a [2H7]NPA analogue serving as internal standard, was converted to the corresponding bis(trifluoroacetyl) ester by treatment with excess trifluoroacetic anhydride at 75 degrees C. The electrophoric derivatives were analyzed by fused-silica capillary gas chromatography-mass spectrometry in the negative ion chemical ionization mode. Selected ion monitoring of the [M-CF3CO]- ions of derivatized NPA (m/z 390) and internal standard [2H7]NPA (m/z 397) permitted the quantitation of NPA in serum and brain samples obtained from rats treated with either free NPA or the prodrug methylenedioxy-NPA (MDO-NPA). Calibration was conducted down to a practical limit of assay sensitivity, at 0.50 ng NPA per ml of serum and 0.50 ng NPA per g of brain. The relative standard deviation for replicate serum samples spiked at 20 ng/ml was 4.2% (n = 5) and for brain samples at 10 ng/g, it was 3.6%. This method revealed differences in the free NPA brain/serum ratios in rats treated separately with the stereoisomers R-(-)-MDO-NPA and S-(+)-MDO-NPA.

High-performance liquid chromatographic separation and electrochemical or spectrophotometric determination of R(-)N-n-propylnorapomorphine and R(-)10,11-methylenedioxy-N-n-propylnoraporphine in primate plasma

The dopamine receptor agonist R(-)N-n-propylnorapomorphine (NPA) and its proposed pro-drug R(-)10,11-methylenedioxy-N-n-propylnoraporphine (MDO-NPA) were isolated simultaneously from monkey plasma using a solid-phase extraction procedure. R(-)Apomorphine (APO) and R(-)10,11-methylenedioxyaporphine (MDO-APO) were added as internal standards, and separation and quantification were by high-performance liquid chromatography with electrochemical or ultraviolet detection of the free catechol and MDO compounds, respectively. The detection limits for NPA and MDO-NPA in plasma were 0.5 and 10 ng/ml and the coefficient of variation (S.D./mean) within assays and between days of assays for both drugs was 5.6% or less. Quantification of plasma levels of NPA and MDO-NPA was possible at ranges of 2-1000 and 40-5000 ng/ml, respectively, including concentrations found after intravenous administration of these agents.

S(+)methylenedioxy-N-n-propylnoraporphine: an orally active inhibitor of dopamine selective for rat limbic system

The 10-11-methylenedioxy (MDO) derivative of S(+)N-n-propylnorapomorphine (NPA) was prepared and tested as a possible active prodrug to S(+)NPA, which we have recently found to exert in vivo activity suggestive of selective antagonism of dopamine receptors in the limbic forebrain but not the extrapyramidal basal ganglia. Like S(+)NPA, S(+)MDO-NPA inhibited the behavioral arousal induced by dopamine injected into nucleus accumbens of the rat, but not the head-turning response to dopamine injected into the corpus striatum. However, only MDO-NPA was orally active and it was somewhat longer-acting than NPA. The activity of S(+)MDO-NPA was prevented by pretreatment with the oxidase inhibitor SKF-525A. These properties are analogous to those of R(-)MDO-NPA, which we had previously reported as an orally active prodrug of the dopamine agonist R(-)NPA. Thus the methylenedioxy derivatives of the two entantiomers of NPA have properties desirable in a potentially clinically useful dopamine agonist and limbic dopamine antagonist, respectively.

Disposition of apomorphine in rat brain areas: relationship to stereotypy

Apomorphine-induced stereotyped behavior and apomorphine levels in plasma, striatum and nucleus accumbens were determined in rats at various intervals after a single i.p. injection of serial doses of apomorphine hydrochloride (0.625, 1.25, 2.5 and 5 mg/kg). Apomorphine disappeared from plasma in a mono-exponential mode with a half-life of about 10 min. In striatum and nucleus accumbens apomorphine concentrations peaked 10 min after administration, declining thereafter with a half-life comparable to that in plasma. Apomorphine was concentrated and distributed similarly in the two brain regions; the brain areas/plasma ratio was approximately seven for all doses tested. The rise of apomorphine levels in brain areas slightly preceded the behavioral response, whereas after the peak effect (20-30 min) the intensity of stereotypy declined almost parallel with the log drug concentrations. Plotting apomorphine levels in the tissues assayed against the drug response at the same interval for individual rats, regardless of dose, indicated a highly significant relation between the degree of behavioral effects and brain apomorphine levels. The threshold apomorphine concentrations for inducing stereotyped behaviour were 108 and 95 ng/g respectively in striatum and nucleus accumbens. These findings show that the time course and magnitude of the behavioral effects of apomorphine corresponded with its brain levels in 'dopaminergic' areas, suggesting that apomorphine-induced stereotyped behavior in rats can be described by a direct mechanism. Reserpine (5 mg/kg s.c.) enhanced the apomorphine stereotypy but did not affect apomorphine's disposition in brain and plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Striatally-mediated response of some structurally rigid analogues of dopamine

The potency of structurally rigid analogues of dopamine (DA) at striatal dopamine receptors was evaluated in rats using three types of assessments: (a) effectiveness in producing rotational and sniffing behaviors by intrastriatal injections (b) inhibition of [3H]-spiroperidol binding and (c) stimulation of adenylate cyclase activity. The compounds included apomorphine (APO) and its analogues, (R)-2,10,11-trihydroxyaporphine (R-THA) and (R)-2-hydroxy-10,11-methylenedioxyaporphine (MDO-APO), 2-amino-6,7-dihydroxyaminotetraline (ADTN) and its analogue, exo-2-amino-6,7-dihydroxybenzonorbornene (exo-amine). (R)-THA produced no stereotypy yet it was a potent inhibitor of [3H]-spiroperidol binding and adenylate cyclase activity. MDO-APO was quite active in inducing stereotypy and stimulating cyclase activity, but it showed low potency in displacing [3H]-spiroperidol. The exo-amine and ADTN were equally potent in enhancing rotation and sniffing intensity, however, the former was completely inactive in biochemical assessments. Except for (R)-THA, all DA analogues studied elicited dopaminomimetic behavioral activities of circling and sniffing. Relationships between the actions of these drugs in the behavioral and biochemical assessments are discussed.

Analysis of N-n-propylnorapomorphine in plasma and tissue by capillary gas chromatography--electron-capture detection

Capillary gas chromatography combined with electron-capture detection (GC-ECD) was applied to the detection and quantitation of N-n-propylnorapomorphine (NPA) and related compounds in serum and tissue using trifluoroacetyl (TFA) derivatives. The detection limits for NPA using GC-ECD of TFA derivative extend into the subpicogram level, but quantitation in serum was limited to levels of 100 ng/ml due to matrix interferences. The method was applied to the analysis of NPA in rat serum after administration of a moderate dose of the drug and was applied to the detection of NPA in rat brain after the peripheral administration of (-)10,11-methylenedioxy-N-n-propylnoraporphine (MDO-NPA). These results support previous proposals that MDO-NPA is a prodrug of NPA, which acts at cerebral dopamine-receptors.