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Zoptarelin doxorubicin is a fusion molecule of the chemotherapeutic doxorubicin and a luteinizing hormone-releasing hormone receptor (LHRHR) agonist, designed for drug targeting to LHRHR positive tumors. The aim of this study was to establish a physiologically based pharmacokinetic (PBPK) parent-metabolite model of zoptarelin doxorubicin and to apply it for drug–drug interaction (DDI) potential analysis. The PBPK model was built in a two-step procedure. First, a model for doxorubicin was developed, using clinical data of a doxorubicin study arm. Second, a parent-metabolite model for zoptarelin doxorubicin was built, using clinical data of three different zoptarelin doxorubicin studies with a dosing range of 10–267 mg/m2, integrating the established doxorubicin model. DDI parameters determined in vitro were implemented to predict the impact of zoptarelin doxorubicin on possible victim drugs. In vitro, zoptarelin doxorubicin inhibits the drug transporters organic anion-transporting polypeptide 1B3 (OATP1B3) and organic cation transporter 2 (OCT2). The model was applied to evaluate the in vivo inhibition of these transporters in a generic manner, predicting worst-case scenario decreases of 0.5% for OATP1B3 and of 2.5% for OCT2 transport rates. Specific DDI simulations using PBPK models of simvastatin (OATP1B3 substrate) and metformin (OCT2 substrate) predict no significant changes of the plasma concentrations of these two victim drugs during co-administration. The first whole-body PBPK model of zoptarelin doxorubicin and its active metabolite doxorubicin has been successfully established. Zoptarelin doxorubicin shows no potential for DDIs via OATP1B3 and OCT2.

PurposeTo provide whole-body physiologically based pharmacokinetic (PBPK) models of the potent clinical organic anion transporter (OAT) inhibitor probenecid and the clinical OAT victim drug furosemide for their application in transporter-based drug-drug interaction (DDI) modeling.MethodsPBPK models of probenecid and furosemide were developed in PK-Sim®. Drug-dependent parameters and plasma concentration-time profiles following intravenous and oral probenecid and furosemide administration were gathered from literature and used for model development. For model evaluation, plasma concentration-time profiles, areas under the plasma concentration–time curve (AUC) and peak plasma concentrations (Cmax) were predicted and compared to observed data. In addition, the models were applied to predict the outcome of clinical DDI studies.ResultsThe developed models accurately describe the reported plasma concentrations of 27 clinical probenecid studies and of 42 studies using furosemide. Furthermore, application of these models to predict the probenecid-furosemide and probenecid-rifampicin DDIs demonstrates their good performance, with 6/7 of the predicted DDI AUC ratios and 4/5 of the predicted DDI Cmaxratios within 1.25-fold of the observed values, and all predicted DDI AUC and Cmaxratios within 2.0-fold.ConclusionsWhole-body PBPK models of probenecid and furosemide were built and evaluated, providing useful tools to support the investigation of transporter mediated DDIs.

Clarithromycin is a substrate and mechanism-based inhibitor of cytochrome P450 (CYP) 3A4 as well as a substrate and competitive inhibitor of P-glycoprotein (P-gp) and organic anion-transporting polypeptides (OATP) 1B1 and 1B3. Administered concomitantly, clarithromycin causes drug–drug interactions (DDI) with the victim drugs midazolam (CYP3A4 substrate) and digoxin (P-gp substrate). The objective of the presented study was to build a physiologically based pharmacokinetic (PBPK) DDI model for clarithromycin, midazolam, and digoxin and to exemplify dosing adjustments under clarithromycin co-treatment. The PBPK model development included an extensive literature search for representative PK studies and for compound characteristics of clarithromycin, midazolam, and digoxin. Published concentration-time profiles were used for model development (training dataset), and published and unpublished individual profiles were used for model evaluation (evaluation dataset). The developed single-compound PBPK models were linked for DDI predictions. The full clarithromycin DDI model successfully predicted the metabolic (midazolam) and transporter (digoxin) DDI, the acceptance criterion (0.5 ≤ AUCratio,predicted/AUCratio,observed ≤ 2) was met by all predictions. During co-treatment with 250 or 500 mg clarithromycin (bid), the midazolam and digoxin doses should be reduced by 74 to 88% and by 21 to 22%, respectively, to ensure constant midazolam and digoxin exposures (AUC). With these models, we provide highly mechanistic tools to help researchers understand and characterize the DDI potential of new molecular entities and inform the design of DDI studies with potential CYP3A4 and P-gp substrates.

Green tea polyphenols may contribute to the prevention of cancer and other diseases. To learn more about the pharmacokinetics and interindividual variation of green tea polyphenols after oral intake in humans we performed a population nutrikinetic study of standardized green tea extract. 84 healthy participants took green tea extract capsules standardized to 150 mg epigallocatechin-gallate (EGCG) twice a day for 5 days. On day 5 catechin plasma concentrations were analyzed using non-compartmental and population pharmacokinetic methods. A strong between-subject variability in catechin pharmacokinetics was found with maximum plasma concentrations varying more than 6-fold. The AUCs of EGCG, EGC and ECG were 877.9 (360.8–1576.5), 35.1 (8.0–87.4), and 183.6 (55.5–364.6) h*μg/L respectively, and the elimination half lives were 2.6 (1.8–3.8), 3.9 (0.9–10.7) and 1.8 (0.8–2.9) h, respectively. Genetic polymorphisms in genes of the drug transporters MRP2 and OATP1B1 could at least partly explain the high variability in pharmacokinetic parameters. The observed variability in catechin plasma levels might contribute to interindividual variation in benefical and adverse effects of green tea polyphenols. Our data could help to gain a better understanding of the causes of variability of green tea effects and to improve the design of studies on the effects of green tea polyphenols in different health conditions. Trial registration: ClinicalTrials.gov: {"type":"clinical-trial","attrs":{"text":"NCT01360320","term_id":"NCT01360320"}}NCT01360320

Topical application of CYP11B1 inhibitors to reduce cutaneous cortisol is a novel strategy to promote healing of chronic wounds. Pyridyl substituted arylsulfonyltetrahydroquinolines were designed and synthesized resulting in a strong inhibitor 34 (IC50 = 5 nM). It showed no inhibition of CYP17 and CYP19 and no mutagenic effects. It exhibited inverse metabolic stability in plasma (t1/2 ≫ 150 min), which is similar to wound fluid in composition, and in liver S9 fractions (t1/2 = 16 min).

The inhibition of 11β-hydroxylase is a promising strategy for the treatment of Cushing's syndrome, in particular for the recurrent and subclinical cases. To achieve proof of concept in rats, efforts were paid to identify novel lead compounds inhibiting both human and rat CYP11B1. Modifications on a potent promiscuous inhibitor of hCYP11B1, hCYP11B2 and hCYP19 (compound IV) that exhibited moderate rCYP11B1 inhibition led to compound 8 as a new promising lead compound. Significant improvements compared to starting point IV were achieved regarding inhibitory potency against both human and rat CYP11B1 (IC50 values of 2 and 163 nM, respectively) as well as selectivity over hCYP19 (IC50 = 1900 nM). Accordingly, compound 8 was around 7- and 28-fold more potent than metyrapone regarding the inhibition of human and rat CYP11B1 and exhibited a comparable selectivity over hCYP11B2 (SF of 3.5 vs 4.9). With further optimizations on this new lead compound 8, drug candidates with satisfying profiles are expected to be discovered.

Diseases triggered by an abnormally high level of cortisol (hypercortisolism), such as the Cushing's and metabolic syndromes, could be successfully tackled by inhibitors of CYP11B1, a steroidal cytochrome P450 enzyme that catalyzes the last hydroxylation step of the cortisol biosynthesis. Structural optimization of 7-(benzyloxy)-4-(1H-imidazol-1-ylmethyl)-2H-chromen-2-one 2, a selective aromatase inhibitor, afforded the 4-(1H-imidazol-1-ylmethyl)-7-{[3-(trifluoromethoxy)benzyl]oxy}-2H-chromen-2-one 7, with improved inhibitory potency at human CYP11B1 (IC50 = 5 nM) and an enhanced selectivity over human CYP11B2 (SIB = 25) compared to lead compound 2 (IC50 = 72 nM, SIB = 4.0) and metyrapone (IC50 = 15 nM, SIB = 4.8), a non-selective drug used in the therapy of the Cushing's syndrome. Structure–activity relationship studies allowed the design and optimization of a novel series of potent and selective compounds, that can be regarded as open analogues of 2H-chromen-2-one derivatives. Compound 23, 2-(1H-imidazol-1-yl)-1-(4-{[3(trifluoromethoxy)benzyl]oxy}phenyl) ethanone, was the most interesting inhibitor of the series displaying a high potency at CYP11B1 (IC50 = 15 nM), increased selectivities over CYP11B2 (SIB = 33), CYP19 (SIB = 390) and CYP17 (5% inhibition at 2.5 μM concentration).

17β-HSD2 is a promising new target for the treatment of osteoporosis. In this paper, a rational strategy to overcome the metabolic liability in the 2,5-thiophene amide class of 17β-HSD2 inhibitors is described, and the biological activity of the new inhibitors. Applying different strategies, as lowering the cLogP or modifying the structures of the molecules, compounds 27, 31 and 35 with strongly improved metabolic stability were obtained. For understanding biotransformation in the 2,5-thiophene amide class the main metabolic pathways of three properly selected compounds were elucidated.

Estradiol is the most potent estrogen in humans. It is known to be involved in the development and proliferation of estrogen dependent diseases such as breast cancer and endometriosis. The last step of its biosynthesis is catalyzed by 17β-hydroxysteroid dehydrogenase type 1 (17β- HSD1) which consequently is a promising target for the treatment of these diseases. Recently, we reported on bicyclic substituted hydroxyphenylmethanones as potent inhibitors of 17β-HSD1. The present study focuses on rational structural modifications in this compound class with the aim of gaining more insight into its structure-activity relationship (SAR). (4-Hydroxyphenyl)-(5-(3-hydroxyphenylsulfanyl)-thiophen-2-yl)methanone (25) was discovered as a member of a novel potent class of human 17β-HSD1 inhibitors. Computational methods were used to elucidate its interactions with the target protein. The compound showed activity also towards the murine 17β-HSD1 enzyme and thus is a starting point for the design of compounds suitable for evaluation in an animal disease model.

17β-Hydroxysteroid dehydrogenase type 2 (17β-HSD2) is responsible for the oxidation of the highly active estradiol (E2) and testosterone (T) into the less potent estrone (E1) and Δ4-androstene-3,17-dione (Δ4-AD), respectively. As 17β-HSD2 is present in bones and as estradiol and testosterone are able to induce bone formation and repress bone resorption, inhibition of this enzyme could be a new promising approach for the treatment of osteoporosis. Herein, we describe the design, the synthesis and the biological evaluation of 24 new 17β-HSD2 inhibitors in the 5-substituted thiophene-2-carboxamide class. Structure–activity and structure–selectivity relationships have been explored by variation of the sulfur atom position in the central core, exchange of the thiophene by a thiazole, substitution of the amide group with a larger moiety, exchange of the N-methylamide group with bioisosteres like N-methylsulfonamide, N-methylthioamide and ketone, and substitutions at positions 2 and 3 of the thiophene core with alkyl and phenyl groups leading to 2,3,5-trisubstituted thiophene derivatives. The compounds were evaluated on human and mouse enzymes. From this study, a novel highly potent and selective compound in both human and mouse 17β-HSD2 enzymes was identified, compound 21 (IC50(h17β-HSD2) = 235 nM, selectivity factor toward h17β-HSD1 = 95, IC50 (m17β-HSD2) = 54 nM). This new compound 21 could be used for an in vivo proof of principle to demonstrate the true therapeutic efficacy of 17β-HSD2 inhibitors in osteoporosis. New structural insights into the active sites of the human and mouse enzymes were gained.

Potent and selective CYP11B1 inhibitors could be promising therapeutics for the treatment of Cushing’s syndrome. Optimization of Ref 1 (5-((1H-imidazol-1-yl)methyl)-2-phenylpyridine) led to compound 44 (5-((5-methylpyridin-3-yl)methyl)-2-phenylpyridine) with a 50-fold improved IC50 value of 2 nM toward human CYP11B1 and an enhanced inhibition of the rat enzyme (IC50 = 2440 nM) compared to Ref 1 (IC50 > 10000 nM). Furthermore, selectivities over CYP11B2, CYP17, and CYP19 were observed, as well as satisfying metabolic stability not only in human and rat plasma but also in liver S9 fraction. Investigation of cytotoxicity and inhibition of hepatic CYP2A6 and CYP3A4 showed that 44 fulfills first safety criteria and can be considered for further in vivo evaluation in rats.

A small library of both [2,3-h] and [3,2-f] novel pyrroloquinolines equipped with an azolylmethyl group was designed and synthesized as nonsteroidal CYP19 aromatase inhibitors. The results showed that azolylmethyl derivatives 11, 13, 14, 21, and 22 exhibited an inhibitory potency on aromatase comparable to that of letrozole chosen as a reference compound. When assayed on CYP11B1 (steroid-11β-hydroxylase) and CYP17 (17α-hydroxy/17,20-lyase), compound 22 was found to be the best and most selective CYP19 inhibitor of them all. In a panel of nine human cancer cell lines, all compounds were either slightly cytotoxic or not at all. Docking simulations were carried out to inspect crucial enzyme/inhibitor interactions such as hydrophobic interactions, hydrogen bonding, and heme iron coordination. This study, along with the prediction of the pharmacokinetics of compounds 11, 13, 14, 21, and 22, demonstrates that the pyrroloquinoline scaffold represents a starting point for the development of new pyrroloquinoline-based aromatase inhibitors.

We have investigated the mechanism of the changes in the profile of metabolic enzyme expression that occur in association with fast-to-slow transformation of rabbit skeletal muscle. The hypotheses assessed are: do 1) lowered intracellular ATP concentration or 2) reduction of the muscular glycogen stores act as triggers of metabolic transformation? We find that 3 days of decreased cytosolic ATP content have no impact on the investigated metabolic markers, whereas incubation of the cells with little or no glucose leads to decreases in glycogen in conjunction with decreases in glyceraldehyde-3-phosphate dehydrogenase (GAPDH) promoter activity, GAPDH mRNA and specific GAPDH enzyme activity (indicators of the anaerobic glycolytic pathway), and furthermore to increases in mitochondrial acetoacetyl-CoA thiolase (MAT, also known as ACAT) promoter activity, peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) expression and citrate synthase (CS) specific enzyme activity (all indicators of oxidative metabolic pathways). The AMP-activated protein kinase (AMPK) activity under these conditions is reduced compared to controls. In experiments with two inhibitors of glycogen degradation we show that the observed metabolic transformation caused by low glucose takes place even if intracellular glycogen content is high. These findings for the first time provide evidence that metabolic adaptation of skeletal muscle cells from rabbit in primary culture can be induced not only by elevation of intracellular calcium concentration or by a rise of AMPK activity, but also by reduction of glucose supply. Contrary to expectations, neither an increase in phospho-AMPK nor a reduction of muscular glycogen content are crucial events in the glucose-dependent induction of metabolic transformation in the muscle cell culture system studied.

Chymotrypsin-like serine proteases are found in high abundance in mast cell granules. By site-directed mutatgenesis, we have previously shown that basic amino acids in positions 143 and 192 (Arg and Lys respectively) of the human mast cell chymase are responsible for an acidic amino acid residue preference in the P2' position of substrates. In order to study the influence of these two residues in determining the specificity of chymase inhibitors, we have synthesized five different potent inhibitors of the human chymase. The inhibitory effects of these compounds were tested against the wild-type enzyme, against two single mutants Arg143Gln and Lys192Met and against a double mutant, Arg143Gln+Lys192Met. We observed a markedly reduced activity of all five inhibitors with the double mutant, indicating that these two basic residues are involved in conferring the specificity of these inhibitors. The single mutants showed an intermediate phenotype, with the strongest effect on the inhibitor by the mutation in Lys192. The Lys192 and the double mutations also affected the rate of cleavage of angiotensin I but did not seem to affect the specificity in the cleavage of the Tyr(4)-Ile(5) bond. A more detailed knowledge about which amino acids that confer the specificity of an enzyme can prove to be of major importance for development of highly specific inhibitors for the human chymase and other medically important enzymes.