Metabolism, excretion, and pharmacokinetics of [14C]INCB018424, a selective Janus tyrosine kinase 1/2 inhibitor, in humans.

The metabolism, excretion, and pharmacokinetics of 3-(4-(7H-pyrrolo[2,3-d]pyrimidin-4-yl)-1H-pyrazol-1-yl)-3-cyclopentylpropanenitrile (INCB018424), a potent, selective inhibitor of Janus tyrosine kinase1/2 and the first investigational drug of its class in phase III studies for the treatment of myelofibrosis, were investigated in healthy human subjects given a single oral 25-mg dose of [(14)C]INCB018424 as an oral solution. INCB018424 and total radioactivity were absorbed rapidly (mean time to reach the maximal drug concentration <1 h), declining in a monophasic or biphasic fashion (mean t(1/2) of 2.32 and 5.81 h, respectively). Recovery of administered radioactivity was fairly rapid (>70% within 24 h postdose) with 74 and 22% recovered in urine and feces, respectively. Parent compound was the predominant entity in the circulation, representing 58 to 74% of the total radioactivity up to 6 h postdose, indicating that the overall circulating metabolite burden was low (<50% of parent). Two metabolite peaks in plasma (M18 and a peak containing M16/M27, both hydroxylations on the cyclopentyl moiety) were identified as major (30 and 14% of parent based on area under the curve from 0 to 24 h). The exposures of other circulating INCB018424-related peaks were <10% of parent, consisting of mono- and dihydroxylated metabolites. The profiles in urine and feces consisted of hydroxyl and oxo metabolites and subsequent glucuronide conjugates with parent drug accounting for <1% of the excreted dose, strongly suggesting that after an oral dose, INCB018424 was >95% absorbed. In healthy subjects administered daily oral doses of unlabeled INCB018424, there were minimal differences in parent and metabolite concentrations between day 1 and day 10, indicating a lack of accumulation of parent or metabolites between single and multiple dosing.

Using a homology model of cytochrome P450 2D6 to predict substrate site of metabolism.

CYP2D6 is an important enzyme that is involved in first pass metabolism and is responsible for metabolizing ~25% of currently marketed drugs. A homology model of CYP2D6 was built using X-ray structures of ligand-bound CYP2C5 complexes as templates. This homology model was used in docking studies to rationalize and predict the site of metabolism of known CYP2D6 substrates. While the homology model was generally found to be in good agreement with the recently solved apo (ligand-free) X-ray structure of CYP2D6, significant differences between the structures were observed in the B' and F-G helical region. These structural differences are similar to those observed between ligand-free and ligand-bound structures of other CYPs and suggest that these conformational changes result from induced-fit adaptations upon ligand binding. By docking to the homology model using Glide, it was possible to identify the correct site of metabolism for a set of 16 CYP2D6 substrates 85% of the time when the 5 top scoring poses were examined. On the other hand, docking to the apo CYP2D6 X-ray structure led to a loss in accuracy in predicting the sites of metabolism for many of the CYP2D6 substrates considered in this study. These results demonstrate the importance of describing substrate-induced conformational changes that occur upon binding. The best results were obtained using Glide SP with van der Waals scaling set to 0.8 for both the receptor and ligand atoms. A discussion of putative binding modes that explain the distribution of metabolic sites for substrates, as well as a relationship between the number of metabolic sites and substrate size, are also presented. In addition, analysis of these binding modes enabled us to rationalize the typical hydroxylation and O-demethylation reactions catalyzed by CYP2D6 as well as the less common N-dealkylation.

Preclinical characterization of BRL 44408: antidepressant- and analgesic-like activity through selective alpha2A-adrenoceptor antagonism.

Biogenic amines such as norepinephrine, dopamine, and serotonin play a well-described role in the treatment of mood disorders and some types of pain. As alpha2A-adrenoceptors regulate the release of these neurotransmitters, we examined the therapeutic potential of BRL 44408, a potent (Ki=8.5 nM) and selective (>50-fold) alpha2A-adrenoceptor antagonist (K(B)=7.9 nM). In rats, BRL 44408 penetrated the central nervous system resulting in peak brain and plasma concentrations of 586 ng/g and 1124 ng/ml, respectively. In a pharmacodynamic assay, pretreatment with BRL 44408 to rats responding under a fixed-ratio 30 operant response paradigm resulted in a rightward shift of the clonidine dose-response curve, an effect indicative of alpha2-adrenoceptor antagonism in vivo. Consistent with presynaptic autoreceptor antagonism and tonic regulation of neurotransmitter release, acute administration of BRL 44408 elevated extracellular concentrations of norepinephrine and dopamine, but not serotonin, in the medial prefrontal cortex. Additionally, BRL 44408, probably by inhibiting alpha2A heteroceptors, produced a significant increase in cortical levels of acetylcholine. In the forced swim test and schedule-induced polydipsia assay, BRL 44408 produced an antidepressant-like response by dose-dependently decreasing immobility time and adjunctive water intake, respectively, while in a model of visceral pain, BRL 44408 exhibited analgesic activity by decreasing para-phenylquinone (PPQ)-induced abdominal stretching. Finally, BRL 44408 did not produce deficits in overall motor coordination nor alter general locomotor activity. This preclinical characterization of the neurochemical and behavioural profile of BRL 44408 suggests that selective antagonism of alpha2A-adrenoceptors may represent an effective treatment strategy for mood disorders and visceral pain.

Synthesis, potency, and in vivo evaluation of 2-piperazin-1-ylquinoline analogues as dual serotonin reuptake inhibitors and serotonin 5-HT1A receptor antagonists.

On the basis of the previously reported clinical candidate, SSA-426 (1), a series of related 2-piperazin-1-ylquinoline derivatives 3-16 were synthesized and evaluated as dual-acting serotonin (5-HT) reuptake inhibitors and 5-HT1A receptor antagonists. In particular, compound 7 exhibits potent functional activities at both the 5-HT transporter and 5-HT1A receptor, good selectivity over the alpha1-adrenergic and dopaminergic receptors, acceptable pharmacokinetic properties, and a favorable in vivo profile.

Desvenlafaxine and venlafaxine exert minimal in vitro inhibition of human cytochrome P450 and P-glycoprotein activities.

OBJECTIVE: Identification of potential pharmacokinetic drug-drug interactions is an important step in clinical drug development.We assessed and compared the drug-drug interaction potential of desvenlafaxine and venlafaxine, based on their inhibitory potency on human cytochrome P450 (CYP) and P-glycoprotein (P-gp) activities in vitro. METHODS: Reversible inhibition of CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP3A4, and mechanism-based inhibition of CYP2C9, CYP2C19, CYP2D6, and CYP3A activity by desvenlafaxine and venlafaxine were determined in human liver microsomes.Whether these drugs were substrates for efflux or inhibitors of P-gp were determined in Caco-2 monolayers. RESULTS: Desvenlafaxine and venlafaxine showed little or no reversible inhibition of various CYP enzymes (concentration that inhibits 50% [IC50] or inhibition constant [Ki] ~ or >100 muM). In addition, neither drug acted as a mechanism-based inhibitor of CYP2C9, CYP2C19, CYP2D6, or CYP3A as they did not reduce the IC50 value for any of these enzymes in the presence of preincubations with or without a nicotinamide adenine dinucleotide phosphate-regenerating system. Desvenlafaxine and venlafaxine showed little inhibition of P-gp activity (IC50 values >250 muM) and did not act as substrates (efflux ratios <2) for efflux in Caco-2 monolayers. CONCLUSIONS: Considering in vitro and available clinical data, desvenlafaxine and venlafaxine appear to have low potential for pharmacokinetic drug-drug interactions via inhibiting the metabolic clearance of concomitant drugs that are substrates of various CYP enzymes, in particular CYP2D6. In addition, these data suggest that desvenlafaxine and venlafaxine exhibit little potential for pharmacokinetic interactions with concomitant drugs that are substrates or inhibitors of P-gp.