Metabolism, Excretion, and Pharmacokinetics of Selumetinib, an MEK1/2 inhibitor, in Healthy Adult Male Subjects.

PURPOSE: Selumetinib (AZD6244, ARRY-142886), an oral mitogen activated kinase 1/2 inhibitor, is in clinical development for the treatment of a variety of different tumor types. Herein, we report a study that determined the distribution, metabolism, and excretion of selumetinib in healthy male volunteers. METHODS: In this open-label, single-center, Phase I clinical trial, 6 subjects received a single 75-mg dose of [14C]-selumetinib. Blood and excreta samples were collected for pharmacokinetic and radiometric analyses. Tolerability monitoring was performed throughout the study. FINDINGS: The Cmax of plasma selumetinib was 1520 ng/mL at 1 hour postdose and declined with a t1/2 of 13.7 hours. Over a 216-hour postdose collection period, total dose recovery was 93% of the radioactive dose, with 59% recovered from feces and 33% from urine. Circulating drug-related material was primarily associated with plasma, with minimal distribution into red blood cells. Selumetinib was the major circulating drug-related component and accounted for 40% of the plasma radioactivity (mean of AUC0-72h pool). The major circulating metabolite (M2; accounting for 22% of the plasma radioactivity) resulted from multiple biotransformation pathways, including loss of the ethanediol moiety in combination with glucuronidation. A further 6 circulating metabolites were identified, each accounting for between 2% and 7% of plasma radioactivity. Selumetinib was a minor component in urine, accounting for ≤1% of the dose. M2 was the most abundant metabolite in urine, accounting for 10% of the dose, and there were 5 other metabolites accounting for between 1% and 10% of the dose. In feces, selumetinib accounted for a mean of 19% of the dose. Also present were 7 metabolites accounting for between 1% and 9% of the dose. The majority of the dose was recovered as metabolites, indicating that the liver is the major route of drug elimination. There were no tolerability concerns. IMPLICATIONS: The findings from this study will inform the label and will contribute to the understanding of the clinical pharmacology of selumetinib. ClinicalTrials.gov identifier: NCT01931761.

In vitro hepatic metabolism of cediranib, a potent vascular endothelial growth factor tyrosine kinase inhibitor: interspecies comparison and human enzymology.

The in vitro metabolism of cediranib (4-[(4-fluoro-2-methyl-1H-indol-5-yl)oxy]-6-methoxy-7-[3-(1-pyrrolidinyl)propoxy]quinazoline), a vascular endothelial growth factor (VEGF) tyrosine kinase inhibitor (TKI) of all three VEGF receptors in late-stage development for the treatment of colorectal cancer and recurrent glioblastoma was investigated in hepatic proteins from preclinical species and humans using radiolabeled material. In human hepatocyte cultures, oxidative and conjugative metabolic pathways were identified, with pyrrolidine N(+)-glucuronidation being the major route. The primary oxidative pathways were di-and trioxidations and pyrrolidine N-oxidation. All metabolites with the exception of the N(+)-glucuronide metabolite were observed in rat and cynomolgus monkey hepatocyte preparations. Additional metabolism studies in liver microsomes from these or other preclinical species (CD-1 mouse, Han Wistar rat, Dunkin Hartley guinea pig, Göttingen mini-pig, New Zealand White rabbit, beagle dog, and cynomolgus and rhesus monkey) indicated that the N(+)-glucuronide metabolite was not formed in these additional species. Incubations with recombinant flavin-containing monooxygenase (FMO) and UDP-glucuronosyltransferase (UGT) enzymes and inhibition studies using the nonselective cytochrome P450 (P450) chemical inhibitor 1-aminobenzotriazole in human hepatocytes indicated that FMO1 and FMO3 contributed to cediranib N-oxidation, whereas UGT1A4 had a major role in cediranib N(+)-glucuronidation. P450 enzymes had only a minor role in the metabolism of cediranib. In conclusion, species differences in the formation of the N(+)-glucuronide metabolite of cediranib were observed. All other metabolites of cediranib found in humans were also detected in rat and cynomolgus monkey. Non-P450 enzymes are predominantly involved in the metabolism of cediranib, and this suggests that clinical drug interactions involving other coadministered drugs are unlikely.

Utility of long-term cultured human hepatocytes as an in vitro model for cytochrome p450 induction.

Cytochrome P450 (P450) induction may have considerable implications for drug therapy. Therefore, understanding the induction potential of a new chemical entity at an early stage in discovery is crucial to reduce the risk of failure in the clinic and help the identification of noninducing chemical structures. Availability of human viable tissue often limits evaluation of induction potential in human hepatocytes. A solution is to increase the time period during which the hepatocytes remain viable. In this study we have investigated the induction of several P450 isozymes in long-term cultured hepatocytes compared with short-term cultured hepatocytes from the same individuals. Short- and long-term cultured primary hepatocytes isolated from each individual were cultured in a 96-well format and treated for 24 h with a range of prototypical P450 inducers and Merck Research Laboratories compounds. CYP3A4, 1A1, 1A2, 2B6, and 2C9 mRNA levels were measured using quantitative real-time reverse transcriptase-polymerase chain reaction (TaqMan) from the same cultured hepatocyte wells. CYP3A4, 1A1, 1A2, 2B6, and 2C9 were shown to be inducible in long-term cultured hepatocytes. The -fold induction varied between donors, and between short- and long-term cultured hepatocytes from the same donor. However, this variability can be controlled by normalizing data from each hepatocyte preparation to a positive control. The use of long-term cultured hepatocytes on 96-well plates has proven to be sensitive, robust, and convenient for assessing P450 induction potential of new compound entities during the drug discovery process.

3,4-Fused cyclohexyl sulfones as gamma-secretase inhibitors.

The 3,4-fused sulfamides, sulfonamides and sulfone have been identified as highly potent gamma-secretase inhibitors. Evaluation of the SAR of substitution within these series has allowed the identification of a range of compounds which significantly reduce brain A beta in transgenic mouse models and thus have potential as possible treatments for Alzheimer's disease.

In vivo characterization of Abeta(40) changes in brain and cerebrospinal fluid using the novel gamma-secretase inhibitor N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) in the rat.

Plaques in the parenchyma of the brain containing Abeta peptides are one of the hallmarks of Alzheimer's disease. These Abeta peptides are produced by the final proteolytic cleavage of the amyloid precursor protein by the intramembraneous aspartyl protease gamma-secretase. Thus, one approach to lowering levels of Abeta has been via the inhibition of the gamma-secretase enzyme. Here, we report a novel, bioavailable gamma-secretase inhibitor, N-[cis-4-[(4-chlorophenyl)sulfonyl]-4-(2,5-difluorophenyl)cyclohexyl]-1,1,1-trifluoromethanesulfonamide (MRK-560) that displayed oral pharmacokinetics suitable for once-a-day dosing. It was able to markedly reduce Abeta in the brain and cerebrospinal fluid (CSF) in the rat, with ED(50) values of 6 and 10 mg/kg, respectively. Time-course experiments using MRK-560 demonstrated these reductions in Abeta could be maintained for 24 h, and comparable temporal reductions in rat brain and CSF Abeta(40) further suggested that these two pools of Abeta are related. This relationship between the brain and CSF Abeta was maintained when MRK-560 was dosed once a day for 2 weeks, and accordingly, when all the data for the dose-response curve and time courses were correlated, a strong association was observed between the brain and CSF Abeta levels. These results demonstrate that MRK-560 is an orally bioavailable gamma-secretase inhibitor with the ability to markedly reduce Abeta peptide in the brain and CSF of the rat and confirm the utility of the rat for assessing the effects of gamma-secretase inhibitors on central nervous system Abeta(40) levels in vivo.

Quantitative measurement of changes in amyloid-beta(40) in the rat brain and cerebrospinal fluid following treatment with the gamma-secretase inhibitor LY-411575 [N2-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N1-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide].

The efficacy of gamma-secretase inhibitors in vivo has, to date, been generally assessed in transgenic mouse models expressing increased levels of amyloid-beta (Abeta) peptide thereby allowing the detection of changes in Abeta production. However, it is not clear whether the in vivo potency of gamma-secretase inhibitors is independent of the level of amyloid precursor protein expression. In other words, does a gamma-secretase inhibitor have the same effect in nontransgenic physiological animals versus transgenic overexpressing animals? In the present study, an immunoassay has been developed which can detect Abeta(40) in the rat brain, where concentrations are much lower than those seen in transgenic mice such as Tg2576 (c. 0.7 and 25 nM, respectively) and in cerebrospinal fluid (CSF, c. 0.3 nM). Using this immunoassay, the effects of the gamma-secretase inhibitor LY-411575 [N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide] were assessed and robust dose-dependent reductions in rat brain and CSF Abeta(40) levels were observed with ID(50) values of 1.3 mg/kg for both brain and CSF. These values were comparable with those calculated for LY-411575 in transgenic mice. Time course experiments using LY-411575 demonstrated comparable temporal reductions in rat brain and CSF Abeta(40), further suggesting these two pools of Abeta are related. Accordingly, when all the data for the dose-response curve and time course were correlated, a strong association was observed between the brain and CSF Abeta(40) levels. These data demonstrate the utility of the rat as a novel approach for assessing the effects of gamma-secretase inhibitors on central nervous system Abeta(40) levels in vivo.