Quantitative evaluation of hepatic and intestinal induction of CYP3A in clinical practice.

This is the first report quantitatively evaluating the clinical induction of CYP3A in the liver and the intestine.To evaluate hepatic induction, we collected literature data on endogenous biomarkers of hepatic CYP3A induction which we then used to calculate the fold-induction (inducer-mediated change in biomarker level). Literature data on decreases in the area under the curve (AUC) of alfentanil, a CYP3A substrate, caused by CYP3A inducers were also collected. We used the hepatic intrinsic clearance of alfentanil to calculate the hepatic induction ratio (inducer-mediated change in intrinsic clearance). For intestinal induction, the intestinal bioavailability (Fg) of alfentanil was used to calculate the intestinal induction ratio. We determined in vivo maximum induction (Emax) and the average unbound plasma concentration (Cav,u) required for half the maximum induction (EC50) for inducers using an Emax model analysis.In our results, fold-induction was comparable to the induction ratio at several inducer concentrations, and almost the maximum induction was achieved by a therapeutic dose. Induction ratios in the intestine were similar to the liver.Our findings suggest that, by knowing only hepatic induction ratios for common inducers, we can quantitatively predict the decreases in the AUC of substrates by CYP3A induction.

Preclinical evaluation of the potential for cytochrome P450 inhibition and induction of the selective ALK inhibitor, alectinib.

1. A novel selective anaplastic lymphoma kinase (ALK) inhibitor, alectinib, has shown remarkable efficacy and safety in patients with ALK-positive non-small-cell lung cancer (NSCLC). The purpose of this study was to evaluate in vitro the potential to inhibit and induce cytochrome P450 (CYP) isoforms for alectinib and its major metabolite M4. 2. Alectinib and M4 did not show the meaningful direct inhibition of six major CYP isoforms (CYP1A2, 2B6, 2C9, 2C19, 2D6 and 3A4) in human liver microsomes (HLM). Alectinib, but not M4, competitively inhibited CYP2C8, by which few marketed drugs are exclusively metabolized, with an inhibition constant of 1.98 µM. 3. Out of the seven CYP isoforms in HLM, alectinib and M4 showed time-dependent inhibition (TDI) of only CYP3A4, which suggests low TDI potential due to low inactivation efficiency. 4. Alectinib exhibited quite smaller induction of mRNA expression of CYP1A2, 2B6 and 3A4 genes in human hepatocytes compared to the respective positive controls, suggesting a low potential of enzyme induction. 5. In summary, the risk of alectinib causing drug-drug interactions with coadministered drugs is expected to be low due to the weak potential of CYP inhibition and induction estimated in the preclinical studies.

A series of nonsecosteroidal vitamin D receptor agonists for osteoporosis therapy.

In an extension of our study on gamma hydroxy carboxylic acid analogs, we explored a series of nonsecosteroidal vitamin D receptor (VDR) agonists in which 1,3-diol of 1,25(OH)2D3 had been replaced by aryl acetic acid. These analogs showed very potent activity in vitro compared with 1,25(OH)2D3. An X-ray analysis of 8d showed that the inserted phenyl ring well mimicked the folded methylene linker of the gamma hydroxy carboxylic acid moiety but the carboxylic acid of 8d interacted with VDR in a different manner from gamma hydroxy carboxylic acids. Through our in vivo screening in an osteoporosis rat model using immature rats, we identified a potent active vitamin D3 analog, compound 7e. In mature rats of the same model, compound 7e also showed good PK profiling and excellent ability to prevent bone mineral density loss without severe hypercalcemia. Our nonsecosteroidal VDR agonist 7e (CH5036249) could be a possible new drug candidate for treating osteoporosis in human.

Quantitative prediction of mechanism-based inhibition caused by mibefradil in rats.

It was previously demonstrated that mibefradil, which shows mechanism-based inhibition in humans, also caused drug-drug interactions (DDIs) with midazolam (MDZ) in rats. In this study, we aimed to quantitatively predict the DDIs observed in rats using a physiologically based pharmacokinetic (PBPK) model from in vitro inactivation parameters. For more precise predictions, contribution ratios of cytochrome P450 (P450) isozymes involved in MDZ metabolism and inactivation parameters of mibefradil against each isozyme were incorporated in the predictive model. The evaluation of metabolic rate using recombinant P450s suggested that CYP3A2 and CYP2C11 contributed to 89 and 11% of MDZ metabolism, respectively. Inactivation studies of mibefradil against the two isozymes showed that the maximal inactivation rate constants (k(inact)) were considerable in both isozymes (0.231-0.565 min(-1)), whereas the inhibitor concentration producing half the k(inact) (K(I, app)) of CYP3A2 (0.263-0.410 µM) was a good deal lower than that for CYP2C11 (6.82-11.4 µM). As a result of predicting the DDIs using the PBPK model, predicted increases in areas under the concentration-time curve of MDZ with coadministration of mibefradil (284 and 510% at 6 and 12 mg/kg mibefradil, respectively) closely corresponded to the observed values (226 and 545%, respectively). From those results, it was thought that the construction of a predictive model for DDIs using the PBPK model in detail would enable us to quantitatively predict in vivo DDIs from in vitro data. This approach to predict DDIs on the basis of the contributing isozymes would be important for predicting clinical DDIs of drugs metabolized by multiple enzymes.

Novel nonsecosteroidal vitamin D3 carboxylic acid analogs for osteoporosis, and SAR analysis.

Novel vitamin D(3) analogs with carboxylic acid were explored, focusing on a nonsecosteroidal analog, LG190178, with a bisphenyl skeleton. From X-ray analysis of these analogs with vitamin D receptor (VDR), the carboxyl groups had very unique hydrogen bonding interactions in VDR and mimicked 1α-hydroxy group and/or 3ß-hydroxy group of 1α,25-dihydroxyvitamin D(3). A highly potent analog, 6a, with good in vitro activity and pharmacokinetic profiles was identified from an SAR study. Compound 6a showed significant prevention of bone loss in a rat osteoporosis model by oral administration.

MHC-associated peptide proteomics enabling highly sensitive detection of immunogenic sequences for the development of therapeutic antibodies with low immunogenicity.

Immunogenicity is a key factor capable of influencing the efficacy and safety of therapeutic antibodies. A recently developed method called MHC-associated peptide proteomics (MAPPs) uses liquid chromatography/mass spectrometry to identify the peptide sequences derived from a therapeutic protein that are presented by major histocompatibility complex class II (MHC II) on antigen-presenting cells, and therefore may induce immunogenicity. In this study, we developed a MAPPs technique (called Ab-MAPPs) that has high throughput and can efficiently identify the MHC II-presented peptides derived from therapeutic antibodies using magnetic nanoparticle beads coated with a hydrophilic polymer in the immunoprecipitation process. The magnetic beads could identify more peptides and sequence regions originating from infliximab and adalimumab in a shorter measurement time than Sepharose beads, which are commonly used for MAPPs. Several sequence regions identified by Ab-MAPPs from infliximab corresponded to immunogenic sequences reported by other methods, which suggests the method's high potential for identifying significant sequences involved in immunogenicity. Furthermore, our study suggests that the Ab-MAPPs method can recognize the difference of a single amino acid residue between similar antibody sequences with different levels of T-cell proliferation activity and can identify potentially immunogenic peptides with high binding affinity to MHC II. In conclusion, Ab-MAPPs is useful for identifying the immunogenic sequences of therapeutic antibodies and will contribute to the design of therapeutic antibodies with low immunogenicity during the drug discovery stage.

HIV-1 protease inhibitor ritonavir potentiates the effect of 1,25-dihydroxyvitamin D3 to induce growth arrest and differentiation of human myeloid leukemia cells via down-regulation of CYP24.

HIV-1 protease inhibitor, ritonavir (RTV) is a potent inhibitor of cytochrome p450 (CYPs) enzymes. This study explored the effects of RTV on CYP24 which converts 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] to its inactive form 1,24,25,(OH)(3). Real-time RT-PCR showed that exposure of HL-60 cells to 1,25(OH)(2)D(3) induced expression of CYP24, and pre-incubation of these cells with RTV decreased this transcripts, resulting in increased intracellular levels of 1,25(OH)(2)D(3) and potentiation of the ability of 1,25(OH)(2)D(3) to induce growth arrest and differentiation of these cells. Taken together, inhibition of CYP24 might open a new paradigm for therapy using Vitamin D compounds.

Prediction of drug-drug interactions based on time-dependent inhibition from high throughput screening of cytochrome P450 3A4 inhibition.

A method of assessing the risk of drug-drug interaction (DDI) caused by mechanism-based inhibition (MBI) was developed for early-stage drug development using cytochrome P450 (CYP) 3A4 inhibition screening data. CYP3A4 inhibition was evaluated using a fluorescent substrate with or without preincubation containing an inhibitor. The results showed that five well-known mechanism-based inhibitors, but not the competitive inhibitor ketoconazole, had lower IC(50) after preincubation, suggesting the utility of the IC(50) shift by preincubation to discern mechanism-based inhibitors. A method to approximately predict the change in the area under the concentration-time curve (AUC) of a co-administered drug by MBI was found using IC(50) shift data and the unbound mean plasma concentration of the inhibitor. From our predictions of change in the AUC for 38 drugs using this method, all mechanism-based inhibitors causing change in the AUC of more than 200% were predicted to be high risk. In conclusion, our method provides a simple assessment of the risk of DDI from mechanism-based inhibitors, especially in the early stages of drug development.

Novel vitamin D3 antipsoriatic antedrugs: 16-En-22-oxa-1alpha,25-(OH)2D3 analogs.

A series of 16-en-22-oxa-derivatives of vitamin D3 based on the structure of maxacalcitol (2) were prepared. Maxacalcitol is currently used topically for the treatment of psoriasis and is recognized as the most successful antedrug of natural vitamin D(3) because it retains the original antiproliferative activity of calcitriol without increased calcemic activity. We introduced 16-olefinic functionality to accelerate the oxidative metabolism of the drug in liver, presumed to be essential for the reduction of calcemic activity, and modified the side-chain moiety by placing the 22-oxygen on the more labile allylic carbon center. Novel 22-oxa analogs (7a-i), carrying either the 24-alkynyl bond or 24-hydroxy functionality in addition to the 16-double bond were synthesized and their pharmacokinetics were evaluated.

Design and evaluation of new antipsoriatic antedrug candidates having 16-en-22-oxa-vitamin D3 structures.

Design, synthesis, and in vitro and in vivo evaluation of a series of antipsoriatic antedrugs having 16-en-22-oxa-vitamin D3 are described. Among the seven compounds examined, two are promising: ester 5c and amide 5f, both of which exhibit greater potent antiproliferation activity with lessened calcemic activity than the presently prescribed maxacalcitol (2).

Ferrocene-based Diels-Alder derivatization for the determination of 1alpha-hydroxyvitamin D3 in rat plasma by high-performance liquid chromatography-electrospray tandem mass spectrometry.

A specific and sensitive liquid chromatography-electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) method has been developed for the determination of 1alpha-hydroxyvitamin D(3) (1alphaOHD(3)) in rat plasma. A new ferrocene-based Cookson-type reagent, 4-ferrocenylmethyl-1,2,4-triazoline-3,5-dione (FMTAD), designed and synthesized to be highly sensitive to vitamin D analogs in ESI, considerably improved the detection limit with 250 fg (359 amol)/injection. 1alphaOHD(3) in rat plasma was extracted with acetonitrile and then purified using Oasis HLB 96-well plates. After the precolumn derivatization with FMTAD, samples were subjected to LC/ESI-MS/MS employing a column-switching system. This method achieved a lower limit of quantitation of 5 pg from 0.1-mL plasma aliquots and 200-fold sensitivity of that without derivatization. The calibration curve (0.05-15 ng/mL) exhibited acceptable linearity (r>0.9966), intraassay precision ranged from 3.8 to 9.6%, interassay precision ranged from 3.0 to 17.0%, and accuracy was within 81.4-112.0%. This FMTAD derivatization method is considered very useful for determination of vitamin D analogs in ESI and applicable for biological samples.