Cocktail Assay Research Articles

An in-vitro cocktail assay for assessing compound-mediated inhibition of six major cytochrome P450 enzymes

An efficient screening assay was developed and validated for simultaneous assessment of compound-mediated inhibition of six major human cytochrome P450 (CYP) enzymes. This method employed a cocktail of six probe substrates (i.e., phenacetin, amodiaquine, diclofenac, S-mephenytoin, dextromethorphan and midazolam for CYP1A2, 2C8, 2C9, 2C19, 2D6 and 3A4, respectively) as well as individual prototypical inhibitors of the six CYP enzymes in human liver microsomes under optimized incubation conditions. The corresponding marker metabolites (i.e., acetaminophen, N-desethylamodiaquine, 4-OH-diclofenac, 4-OH-S-mephenytoin, dextrorphan and 1-OH-midazolam) in the incubates were quantified using LC–MS/MS methods either by an internal standard (IS) calibration curve or a simplified analyte-to-IS peak area ratio approach. The results showed that the IC50 values determined by the cocktail approach were in good agreement with those obtained by the individual substrate approach as well as those reported in the literature. Besides, no remarkable difference was observed between the two quantification approaches. In conclusion, this new cocktail assay can be used for reliable screening of compound-mediated CYP inhibition.

Bright-Field HER2 Dual In Situ Hybridization (DISH) Assay vs Fluorescence In Situ Hybridization (FISH)

To compare the INFORM HER2 bright-field dual in situ hybridization (DISH) DNA probe cocktail assay with the PathVysion fluorescence in situ hybridization (FISH) assay on 103 invasive breast carcinomas with a 2+ score on immunohistochemistry (IHC). The cases were categorized as positive, equivocal, or negative for HER2 gene amplification using the 2007 American Society of Clinical Oncology/College of American Pathologists (ASCO/CAP) HER2:CEP17 ratio criteria and also based on mean HER2 gene copies/cell. The third criterion used a HER2:CEP17 ratio of 2 to categorize cases as positive or negative. The agreement between FISH and DISH was 85% using the 2007 ASCO/CAP ratio criterion, 79% using the mean HER2 gene copies/cell criterion, and 92% using the 2.0 cutoff HER2:CEP17 ratio criterion. In addition, 20 known IHC 3+ breast carcinomas analyzed by DISH showed clusters of the HER2 gene consistent with unequivocal amplification. Despite some technical and interpretational issues associated with DISH, it compares favorably with FISH in this group of challenging breast cancer cases.

Identification of Key Licorice Constituents Which Interact with Cytochrome P450: Evaluation by LC/MS/MS Cocktail Assay and Metabolic Profiling

Licorice has been shown to affect the activities of several cytochrome P450 enzymes. This study aims to identify the key constituents in licorice which may affect these activities. Bioactivity assay was combined with metabolic profiling to identify these compounds in several complex licorice extracts. Firstly, the inhibition potencies of 40 pure licorice compounds were tested using an liquid chromatography/tandem mass spectrometry cocktail method. Significant inhibitors of human P450 isozymes 1A2, 2C9, 2C19, 2D6, and 3A4 were then selected for examination of their structural features by molecular docking to determine their molecular interaction with several P450 isozymes. Based on the present in vitro inhibition findings, along with our previous in vivo metabolic studies and the prevalence of individual compounds in licorice extract, we identified several licorice constituents, viz., liquiritigenin, isoliquiritigenin, together with seven isoprenylated flavonoids and arylcoumarins, which could be key components responsible for the herb-drug interaction between cytochrome P450 and licorice. In addition, hydrophilic flavonoid glycosides and saponins may be converted into these P450 inhibitors in vivo. These studies represent a comprehensive examination of the potential effects of licorice components on the metabolic activities of P450 enzymes.

Selective Inhibition of Cytochrome P450 2D6 by Sarpogrelate and Its Active Metabolite, M-1, in Human Liver Microsomes

The present study was performed to evaluate the in vitro inhibitory potential of sarpogrelate and its active metabolite, M-1, on the activities of nine human cytochrome (CYP) isoforms. Using a cocktail assay, the effects of sarpogrelate on nine CYP isoforms and M-1 were measured by specific marker reactions in human liver microsomes. Sarpogrelate potently and selectively inhibited CYP2D6-mediated dextromethorphan O-demethylation with an IC50 (Ki) value of 3.05 μM (1.24 μM), in a competitive manner. M-1 also markedly inhibited CYP2D6 activity; its inhibitory effect with an IC50 (Ki) value of 0.201 μM (0.120 μM) was more potent than that of sarpogrelate, and was similarly potent as quinidine (Ki, 0.129 μM), a well-known typical CYP2D6 inhibitor. In addition, sarpogrelate and M-1 strongly inhibited both CYP2D6-catalyzed bufuralol 1'-hydroxylation and metoprolol α-hydroxylation activities. However, sarpogrelate and M-1 showed no apparent inhibition of the other following eight CYPs: CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2E1, or CYP3A4/5. Upon 30-minute preincubation of human liver microsomes with sarpogrelate or M-1 in the presence of NADPH, no obvious shift in IC50 was observed in terms of inhibition of the nine CYP activities, suggesting that sarpogrelate and M-1 are not time-dependent inactivators. Sarpogrelate strongly inhibited the activity of CYP2D6 at clinically relevant concentrations in human liver microsomes. These observations suggest that sarpogrelate could have an effect on the metabolic clearance of drugs possessing CYP2D6-catalyzed metabolism as a major clearance pathway, thereby eliciting pharmacokinetic drug-drug interactions.

Potent inhibition of cytochrome P450 2B6 by sibutramine in human liver microsomes

The present study was performed to evaluate the potency and specificity of sibutramine as an inhibitor of the activities of nine human CYP isoforms in liver microsomes. Using a cocktail assay, the effects of sibutramine on specific marker reactions of the nine CYP isoforms were measured in human liver microsomes. Sibutramine showed potent inhibition of CYP2B6-mediated bupropion 6-hydroxylation with an IC50 value of 1.61μM and Ki value of 0.466μM in a competitive manner at microsomal protein concentrations of 0.25mg/ml; this was 3.49-fold more potent than the typical CYP2B6 inhibitor thio-TEPA (Ki=1.59μM). In addition, sibutramine slightly inhibited CYP2C19 activity (Ki=16.6μM, noncompetitive inhibition) and CYP2D6 activity (Ki=15.7μM, noncompetitive inhibition). These observations indicated 35.6- and 33.7-fold decreases in inhibition potency, respectively, compared with that of CYP2B6 by sibutramine. However, no inhibition of CYP1A2, CYP2A6, CYP2C8, CYP2C9, CYP2D6, or CYP2E1 activities was observed. In addition, the CYP2B6 inhibitory potential of sibutramine was enhanced at a lower microsomal protein concentration of 0.05mg/ml. After 30min preincubation of human liver microsomes with sibutramine in the presence of NADPH, no shift in IC50 was observed in terms of inhibition of the activities of the nine CYPs, suggesting that sibutramine is not a time-dependent inactivator. These observations suggest that sibutramine is a selective and potent inhibitor of CYP2B6 in vitro, whereas inhibition of other CYPs is substantially lower. These in vitro data support the use of sibutramine as a well-known inhibitor of CYP2B6 for routine screening of P450 reversible inhibition when human liver microsomes are used as the enzyme source.

A sensitive and specific CYP cocktail assay for the simultaneous assessment of human cytochrome P450 activities in primary cultures of human hepatocytes using LC–MS/MS

A sensitive and specific CYP cocktail assay for simultaneous measurement of the activities of major human cytochrome P450 enzymes (CYP1A2 (phenacetin), CYP3A4/5 (midazolam), CYP2C9 (diclofenac), CYP2C19 (S-mephenytoin) and CYP2D6 (dextromethorphan)) in primary cultures of human hepatocytes, was developed and validated using liquid chromatography–tandem mass spectrometry (LC–MS/MS). Hepatocyte incubation medium was processed by a solid phase extraction (SPE) using Oasis SPE extraction cartridges prior to chromatography. The metabolites derived from each of the substrates were simultaneously quantitated using the corresponding stable isotope-labeled internal standards by a positive electrospray ionization mode using multiple reactions monitoring with a single eight minute run. The mean accuracy was in the range of 98–114%. The interday and intraday precision over the concentration ranges evaluated for all the analytes were lower than 15%, and 14%, respectively. All the generated metabolites were stable under the conditions used for sample analysis. Additionally, the interaction of a cocktail substrate on other CYP substrates was also analyzed. Due to substantial inter-substrate interaction, chlorzoxazone (CYP2E1) and bupropion (CYP2B6) were removed from the initial seven probes CYP cocktail assay. Therefore, the final CYP cocktail assay consisting of five probes provides a robust method to simultaneously measure activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4/5 in primary cultures of human hepatocytes.

Quantification of human hepatocyte cytochrome P450 enzymes and transporters induced by HIV protease inhibitors using newly validated LC‐MS/MS cocktail assays and RT‐PCR

Human immunodeficiency virus (HIV) protease inhibitors (PIs) produce profound and unpredictable drug-drug interactions (DDIs) that cannot be explained fully by their inhibition/inactivation of CYP3A enzymes. Delineating and quantifying the CYPs and transporters inducible by PIs are crucial in developing an integrative mechanistic understanding and prediction of PI-based DDIs. To do so, two LC-MS/MS cocktail assays were modified and validated simultaneously to quantify the CYP activity of CYP3A, 2B6, 2C8, 2C9, 2C19, 1A, 2E1, 2A6 and 2D6 enzymes. These new assays were applied to evaluate the induction potential of eight PIs in microsomes isolated from PI-treated human hepatocytes. The mRNA expression of these CYPs and transporters (OATP1B1, OATP1B3, OATP1A2, MDR1, MRP2 and MRP4) was also evaluated using relative RT-PCR. The majority of PIs were net inducers of CYP3As and 2B6 at both the mRNA and activity level (> 2-fold), while ritonavir, saquinavir, nelfinavir or lopinavir did not induce CYP3A activity (< 2-fold), presumably due to CYP3A inactivation. OATP1B1 and MDR1 were the only two hepatic transporters induced (> 2-fold) by the PIs. Amprenavir was the most potent net inducer. In conclusion, our validated cocktail assays can be implemented to comprehensively quantify CYP activities in human liver microsomes and hepatocyte studies. The results also provide the much needed data on the net induction potential of the PIs for hepatic CYPs and transporters. A qualitative agreement was observed between our results and published PI-based DDIs, suggesting that human hepatocytes are a useful platform for more extensive and quantitative in vitro-in vivo prediction of PI-based DDIs.

P5-11-10: Reproducibility and Robustness of the FDA Approved INFORM HER2 Dual ISH DNA Probe Cocktail Assay.

Abstract Background: Amplification and/or HER2 overexpression is associated with poor clinical outcome for patients with invasive breast carcinoma. Determination of HER2 status dictates eligibility of patients for trastuzumab (Herceptin) therapy, which has been shown to improve prognosis. We present data from the inter-observer reproducibility and robustness studies of the FDA approved INFORM HER2 Dual ISH DNA Probe Cocktail (HER2 Dual ISH) assay, which is an alternative to FISH. The assay is fully automated and is scored using light microscopy providing morphological context. Methods: Ninety-five human invasive breast carcinoma specimens (a mix of amplified and non-amplified cases) were stained in a study, using the HER2 Dual ISH assay. The slides were enumerated by two qualified readers. The same cohort was stained using Path Vysion FISH and read by one qualified reader. To verify the robustness of the HER2 Dual ISH assay, customer selectable options for factors known to impact the staining quality and intensity, which can be varied for troubleshooting, were tested on human invasive breast carcinoma cases and xenografts. The slides were evaluated by one qualified reader. For both studies all assay steps were fully automated on a VENTANA BenchMark XT automated slide stainer using silver metallographic and red colorimetric detections for Dual ISH. Results: In the inter-observer study the first pass staining success rate was &amp;gt;93% for the HER2 Dual ISH assay, while the FISH first pass staining success rate was 59%. Some cases were rescued after a second attempt, which yielded a second pass staining success rate of 80% for FISH and 97% for HER2 Dual ISH. The negative, positive and overall agreement rates and 95% confidence intervals for the 61 clinical samples of this cohort that were enumerable with both FISH and the HER2 Dual ISH assay are 94.7 (75.4−99.1), 95.2 (84.2−98.7), 95.1 (86.5−98.3) and 89.5 (68.6−97.1), 97.6 (87.7−99.6), 95.1 (86.5−98.3) for reader A vs. FISH and reader B vs. FISH respectively. The positive and negative agreement rates for the inter-observer reproducibility of the HER2 Dual ISH assay were 94.7 and 97.6 %, respectively. In robustness testing, the recommended staining protocol was shown to be effective. All conditions tested resulted in appropriate staining (except for mildest cell conditioning and protease options). Conclusion: The fully automated FDA approved INFORM HER2 Dual ISH assay is robust, reproducible and concordant with the manual FISH assay in determining HER2 status in invasive breast carcinoma. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P5-11-10.

The INFORM HER2 Dual ISH assay compared with FISH to determine HER2 gene status in invasive breast carcinoma.

25 Background: The HER2 gene, located on chromosome 17 (Chr17), is amplified in 15-25% of patients with invasive breast carcinoma. Amplification and/or HER2 overexpression is associated with poor clinical outcome for these patients; however prognosis is improved if HER2 status indicates eligibility of patients for trastuzumab therapy. Thus, accurate diagnosis of HER2 status through a companion diagnostic is essential. Here we validated the INFORM HER2 Dual ISH Probe Cocktail (Dual ISH) assay as an alternative to FISH, the current gold standard for HER2 testing. The Dual ISH assay is fully automated and is scored using light microscopy. Methods: A multi-site method comparison and inter-laboratory reproducibility study were performed. 5 sites were used to compare Dual ISH results with FISH (Vysis PathVysion). 510 invasive breast carcinoma cases were stained at 3 clinical sites, FISH staining was performed at a fourth site (central laboratory). IHC status was determined at a fifth site (second central laboratory). In addition, 6 cases were evaluated for inter-site (3 sites), inter-reader (6 readers), inter-run (15 runs) and intra-run (duplicate slides) reproducibility. All assay steps were fully automated on a VENTANA BenchMark XT automated slide stainer, using a HER2 repeat-reduced, dinitrophenyl-labeled probe targeting the HER2 gene, detected with silver metallographic detection, and a digoxigenin-labeled Chr 17 probe, detected by an alkaline phosphatase-driven red chromogenic detection. HER2 and CHR17 signals were enumerated using conventional light microscopy allowing interpretation within the morphological context of the specimen. HER2 status was determined as the ratio of HER2/Chr17, where a ratio &lt;2 is non-amplified and a ratio ≥2 is amplified. Results: The positive and negative agreement rates with FISH (95% CI) were 96% (92.6-97.9) and 92.3% (88.6-94.8), respectively. The HER2 Dual ISH assay also was highly reproducible in determining HER2/Chr17 ratio across sites, days, readers and runs. Conclusions: The fully automated INFORM HER2 Dual ISH assay is reproducible and concordant with the manual FISH assay in determining HER2 status in invasive breast carcinoma.

Clinicopathologic features and treatment outcomes of patients (pts) with HER2-positive (pos) adenocarcinomas (ACA) of the esophagus (E) and gastroesophageal junction (GEJ).

4046 Background: HER2 is overexpressed in 21% of gastric and 33% of GEJ ACA, and pts with advanced HER2pos disease survive longer after chemotherapy and trastuzumab than after chemotherapy alone. This retrospective analysis was undertaken to better define the clinicopathologic features and treatment outcomes in pts with HER2pos ACA of the E and GEJ. Methods: Between 11/99 and 7/06, 156 pts with T3 or N1 or M1a ACA of the E or GEJ were entered on one of two Cleveland Clinic trials. Induction chemoradiation, with 96 hour infusions of cisplatin (20 mg/m2/d) and fluorouracil (1,000 mg/m2/d) beginning on day 1 of radiation (30 Gy at 1.5 Gy bid), was followed by surgery and identical post-operative chemoradiation. 76 pts also received 2 years of oral gefitinib. Pathology was tested for HER2 by immunohistochemistry using PATHWAY anti-HER-2/neu 4B5 Rabbit Monoclonal Primary Antibody (Ventana, Tucson AZ) and in situ hybridization with the INFORM HER2 Dual ISH DNA Probe Cocktail assay (Ventana, Tucson AZ). Baseline characteristics and outcomes after treatment of the HER2pos and negative (neg) pts were compared. Results: Of the 156 pts, 136 pts had either initial biopsy or resection specimen available. HER2 was deemed pos if either was pos. Discordance between biopsy and resection was found in only 6/65 pts (9%). 32 pts (24%) were HER2pos; 27% of 82 pts with GEJ, and 19% of 54 pts with E tumors (p=0.31). There was no statistical difference between HER2pos and neg pts in age, gender, race, stage, or pathological response. The only difference was that HER2neg tumors were more likely poorly differentiated (p<0.001). Locoregional control, distant metastatic control, freedom from recurrence and overall survival were statistically the same in both the entire cohort, and in the gefitinib-treated subset. Conclusions: Except for tumor differentiation, HER2pos and neg pts with ACA of the E and GEJ do not differ in clinicopathologic characteristics and treatment outcomes. Given the demonstrated benefit of trastuzumab in HER2pos gastric cancer and the similar incidence of HER2 overexpression in the E and GEJ, further evaluation of HER2 directed therapy in this disease seems indicated.

Clinicopathologic features and treatment outcomes of patients (pts) with HER2-positive (pos) adenocarcinomas (ACA) of the esophagus (E) and gastroesophageal junction (GEJ).

71 Background: HER2 is overexpressed in 21% of gastric and 33% of GEJ ACA, and pts with advanced HER2pos disease survive longer after chemotherapy and trastuzumab than after chemotherapy alone. This retrospective analysis was undertaken to better define the clinicopathologic features and treatment outcomes in pts with HER2pos ACA of the E and GEJ. Methods: Between 11/99 and 7/06, 156 pts with T3 or N1 or M1a ACA of the E or GEJ were entered on one of two Cleveland Clinic trials. Induction chemoradiation, with 96 hour infusions of cisplatin (20 mg/m2/d) and fluorouracil (1,000 mg/m2/d) beginning on day 1 of radiation (30 Gy at 1.5 Gy bid), was followed by surgery and identical post-operative chemoradiation. 76 pts also received 2 years of oral gefitinib. Pathology was tested for HER2 by immunohistochemistry using PATHWAY anti-HER-2/neu 4B5 rabbit monoclonal primary antibody (Ventana, Tucson AZ) and in situ hybridization with the inform HER2 dual ISH DNA probe cocktail assay (Ventana, Tucson AZ). Baseline characteristics and outcomes after treatment of the HER2pos and negative (neg) pts were compared. Results: Of the 156 pts, 136 pts had either initial biopsy or resection specimen available. HER2 was deemed pos if either was pos. Discordance between biopsy and resection was found in only 6/65 pts (9%). 32 pts (24%) were HER2pos; 27% of 82 pts with GEJ, and 19% of 54 pts with E tumors (p=0.31). There was no statistical difference between HER2pos and neg pts in age, gender, race, stage, or pathological response. The only difference was that HER2neg tumors were more likely poorly differentiated (p&lt;0.001). Locoregional control, distant metastatic control, freedom from recurrence and overall survival were statistically the same in both the entire cohort, and in the gefitinib-treated subset. Conclusions: Except for tumor differentiation, HER2pos and neg pts with ACA of the E and GEJ do not differ in clinicopathologic characteristics and treatment outcomes. Given the demonstrated benefit of trastuzumab in HER2pos gastric cancer and the similar incidence of HER2 overexpression in the E and GEJ, further evaluation of HER2 directed therapy in this disease seems indicated. No significant financial relationships to disclose.

An In Vitro, High Throughput, Seven CYP Cocktail Inhibition Assay for the Evaluation of New Chemical Entities Using LC-MS/MS

A validated method for the simultaneous characterization of xenobiotic compound-mediated inhibition of seven major cytochrome P450 (CYP) enzymes in pooled human liver microsomes through the use of specific CYP probe substrates (cocktail assay) with low protein content, and a rapid, three minute LC-MS/MS analytical method is described. The specific CYP substrates used in this cocktail assay included phenacetin (CYP1A2), bupropion (CYP2B6), amodiaquine (CYP2C8), tolbutamide (CYP2C9), S-mephenytoin (CYP2C19), dextromethorphan (CYP2D6), and midazolam (CYP3A4/5). The LC-MS method incorporated the aforementioned seven CYP substrates along with their respective major metabolites, and one internal standard, labetalol. In a cross-validation analysis, the concentrations of each CYP probe substrate in the assay had minimal effect (i.e., inhibition or activation) on the other CYP activities. Furthermore, the assay conditions for the multiple probe substrate, ie., cocktail assay, were validated against the single probe substrate assay using 18 compounds with known CYP inhibition liabilities and 10 proprietary compounds. The inhibitory constant (Ki) determined with this cocktail assay was highly correlated (R(2) ≥ 0.77 for each individual probe substrate) with that of the single probe substrate assay for all 27 CYP inhibitors. This seven CYP inhibition cocktail assay has increased the efficiency to assess compounds for inhibition of the major CYP isoforms in a high throughput, drug discovery setting.

Profiling Induction of Cytochrome P450 Enzyme Activity by Statins Using a New Liquid Chromatography-Tandem Mass Spectrometry Cocktail Assay in Human Hepatocytes

Human hepatocytes in primary culture are a very useful model to directly assess induction of gene expression by xenobiotics. We developed a cytochrome P450 (P450) activity cocktail assay using model substrates for the seven important P450s 1A2 (phenacetin), 2B6 (bupropion), 2C8 (amodiaquine), 2C9 (tolbutamide), 2C19 (S-mephenytoin), 2D6 (propafenone), and 3A4 (atorvastatin). Metabolite formation was determined by liquid chromatography-tandem mass spectrometry in hepatocyte culture supernatants. Atorvastatin has not been previously assessed as a CYP3A probe drug. We demonstrate highly selective atorvastatin ortho-hydroxylation by CYP3A4 by recombinant P450s. In human liver microsomes ortho-hydroxyatorvastatin formation was highly correlated with CYP3A4 protein content (r(s) = 0.78, p < 0.0001, n = 150). We profiled induction of these P450 activities in primary human hepatocytes after treatment with 30 microM atorvastatin, lovastatin, pravastatin, rosuvastatin, and simvastatin for 24 to 72 h. Except for pravastatin, all statins induced P450 activities to various degrees, approximately in the order atorvastatin > simvastatin > lovastatin > rosuvastatin. Inducibility of P450s followed the order CYP2C8 > CYP3A4 > CYP2C9 > CYP2B6 > CYP2C19 approximately CYP2D6 > CYP1A2. The strongest induction was observed for amodiaquine N-desalkylation, which was induced approximately 20-fold. Quantitative reverse transcription-polymerase chain reaction confirmed corresponding changes on the mRNA level with even more dramatic induction up to almost 100-fold. These data suggest a broader inducing effect of statins on cytochrome P450s and possibly other absorption, distribution, metabolism, and excretion genes than previously known, thus further emphasizing their drug-drug interaction potential. Our cocktail assay should be helpful for economical use of human hepatocytes in the assessment of P450 induction by drugs and drug candidates.

An automated, high-throughput, 384 well Cytochrome P450 cocktail IC 50 assay using a rapid resolution LC–MS/MS end-point

The current study focused on the development of an automated IC 50 cocktail assay in a miniaturized 384 well assay format. This was developed in combination with a significantly shorter high pressure liquid chromatography (HPLC) separation and liquid chromatography–mass spectrometry (LC–MS/MS) run-time; than those currently reported in the literature. The 384-well assay used human liver microsomes in conjunction with a cocktail of probe substrates metabolized by the five major CYPs (tacrine for CYP1A2, diclofenac for CYP2C9, (S)-mephenytoin for CYP2C19, dextromethorphan for CYP2D6 and midazolam for CYP3A4). To validate the usefulness of the automated and analytical methodologies, IC 50 determinations were performed for a series of test compounds known to exhibit inhibition across these five major P450s. Eight compounds (sertraline, disulfuram, ticlopidine fluconazole, fluvoxamine, ketoconazole, miconazole, paroxetine, flunitrazepam) were studied as part of a cocktail assay, and against each CYPs individually. The data showed that the IC 50s generated with cocktail incubations did not differ to a great extent from those obtained in the single probe experiments and hence unlikely to significantly influence the predicted clinical DDI risk. In addition the present method offered a significant advantage over some of the existing cocktail analytical methodology in that separation can be achieved with run times as short as 1 min without compromising data integrity. Although numerous studies have been reported to measure CYP inhibition in a cocktail format the need to support growing discovery libraries not only relies on higher throughput assays but quicker analytical run times. The current study reports a miniaturized high-throughput cocktail IC 50 assay, in conjunction with a robust, rapid resolution LC–MS/MS end-point offered increased sample throughput without compromising analytical sensitivity or analyte resolution.

In vitro interaction cocktail assay for nine major cytochrome P450 enzymes with 13 probe reactions and a single LC/MSMS run: analytical validation and testing with monoclonal anti‐CYP antibodies

A sensitive and rugged LC/MSMS method was developed for a comprehensive in vitro metabolic interaction screening assay with N-in-1 approach reported earlier. A cocktail consisting of ten cytochrome P450 (CYP)-selective probe substrates with known kinetic, metabolic and interaction properties in vivo was incubated in a pool of human liver microsomes, and metabolites of melatonin (CYP1A2), coumarin (CYP2A6), bupropion (CYP2B6), amodiaquine (CYP2C8) tolbutamide (CYP2C9), omeprazole (CYP2C19 and CYP3A4), dextromethorphan (CYP2D6), chlorzoxazone (CYP2E1), midazolam (CYP3A4) and testosterone (CYP3A4) were simultaneously analysed with a single LC/MSMS run. Altogether, 13 metabolites and internal standard phenacetin were analysed in multiple reaction mode. Polarity switching mode was utilized to acquire negative ion mode electrospray data for hydroxychlorzoxazone and positive ionization data for the rest of the analytes. Fast gradient elution was applied, giving total injection cycle of 8 min. The method was modified for two different LC/MSMS systems, and was validated for linear range, detection limit, accuracy and precision for each metabolite. In addition, cocktail inhibition system was further tested using monoclonal anti-CYP antibodies as inhibitors for each probe reaction.

In vitro LC‐MS cocktail assays to simultaneously determine human cytochrome P450 activities

Using liquid chromatography-mass spectrometry (LC-MS), two sensitive cocktail assays were developed, one to simultaneously determine activities of the cytochrome P450 enzymes, CYP1A2 (phenacitin), 2B6 (bupropion), 2C8 (amodiaquine) and 2C19 (omperazole), and the other to determine simultaneously activities of CYP3A4/5 (testosterone), 2C9 (tolbutamide) and 2D6 (dextromethorphan). These cocktail assays are sensitive, require only a small amount of microsomal protein, employ selective and high turnover CYP substrates and do not require post-incubation extraction. In each of these cocktails, no interactions were observed between the substrates. Combining the two cocktails into a single cocktail resulted in significant inhibition of CYP2D6 by amiodiaquine. These assays were used successfully to determine induction of CYP enzymes in microsomes isolated from human hepatocytes treated (72 h) with or without the prototypic inducer, rifampin.

Induction of Cytochrome P450: Assessment in an Immortalized Human Hepatocyte Cell Line (Fa2N4) Using a Novel Higher Throughput Cocktail Assay

Over recent years the application of cocktail studies to measure biological markers has become increasingly popular. The current study investigated a novel approach in assessing cytochrome P450 (P450) enzyme induction in an immortalized cell line using a cocktail of five P450 substrate probes compared with the traditional single-probe approach. The findings reported herein support use of a cocktail approach to assess the induction of the major P450s, namely, CYP3A4, CYP1A2, and CYP2C9. CYP2C19 and CYP2D6 could also be followed as part of the cocktail approach reported. Response to prototypical inducers did not differ to those observed in the presence of the specific probes alone. Consequently, this approach requires significantly fewer sample numbers if screening the induction potential of more than one P450. Moreover, these studies highlight the utility of the immortalized cell line Fa2N4 as a robust model system for induction studies. In conclusion, the current experimental setup is an improvement on current approaches used to assess P450 induction, significantly increasing sample throughput.

Comparison of cytochrome P450 inhibition assays for drug discovery using human liver microsomes with LC–MS, rhCYP450 isozymes with fluorescence, and double cocktail with LC–MS

The disparity of IC50s from CYP450 inhibition assays used to assess drug–drug interaction potential was investigated, in order to have evidence for selecting a reliable in vitro CYP450 inhibition assay to support drug discovery. Three assays were studied: individual rhCYP isozymes and corresponding coumarin derivative-probe substrates with fluorescent detection, human liver microsomes (HLM) and cocktail drug-probe substrates with LC–MS detection, and double cocktail rhCYP isozymes mix and drug-probe mix with LC–MS detection. Data comparisons showed that the rhCYP-fluorescent assay and the cocktail assay with HLM–LC–MS had weak correlation. Detection method and probe substrates were shown to not be the major cause of the disparity in IC50s. However, the enzyme source and composition (HLM versus, rhCYP) caused disparity in IC50s. Specifically, the high concentrations of CYP isozymes often used with HLM-based assays produced high probe substrate conversion and test compound metabolism, which should both contribute to artificially higher IC50s. Non-specific binding of substrate to higher concentration proteins and lipids in the HLM-based assays should also contribute to higher IC50s. The modified double cocktail assay was found to overcome limitations of the other two assays. It uses an rhCYP isozymes mix, drug-probe substrate mix, low protein concentration, and LC–MS detection. The double cocktail assay is sensitive, selective, and high throughout for use in drug discovery to provide an early alert to potential toxicity with regard to drug–drug interaction, prioritize chemical series, and guide structural modification to circumvent CYP450 inhibition.

Multienzyme Profiling of Thermophilic Microorganisms with a Substrate Cocktail Assay

AbstractLabeled substrates for 16 different catalytic activities were combined into a cocktail reagent for multienzyme functional profiling, called PHENOZYMTM. The assay involves a single reaction followed by determination of substrate consumption by HPLC‐analysis. The method allows a rapid identification of multiple enzyme activities, and is compatible with a diversity of growth media and reaction conditions (pH, temperature). The PHENOZYMTM cocktail was used to analyze the activity of 16 enzyme activities in a series of microbial strains, including thermophilic microorganisms. The functional profiles were used for a functional classification of the different microbial strains tested by hierarchical cluster analysis. The resulting “phylo‐enzymatic” tree revealed associations consistent with the known phylogenetic classification of the strains. The influence of the culture medium on the enzyme activity profiles was also apparent.

Isolated extragenital bowenoid papulosis of the neck

We report a case of extragenital bowenoid papulosis (BP) in a healthy immunocompetent 42-year-old man. The lesions occurred on the anterolateral aspects of the neck and were not associated with genital, oral, or periungual lesions. Lesional skin tested positive with the Digene hybrid capture system cocktail assay that identifies infection with a mixture of high to intermediate oncogenic human papillomavirus (HPV) types, including types 16, 18, 31, 33, 35, 45, 51, 52, and 56. This cocktail assay identifies infection with HPV types typically associated with high-grade squamous intraepithelial lesions and invasive carcinoma. This case represents the sixth case of isolated cutaneous BP occurring a significant distance from the genital region. (J Am Acad Dermatol 1999;41:867-70.)