Quantitative analysis of intracellular nucleoside triphosphates and other polar metabolites using ion pair reversed-phase liquid chromatography coupled with tandem mass spectrometry.

Simultaneous, quantitative determination of intracellular nucleoside triphosphates and other polar metabolites using liquid chromatography with electrospray ionization tandem mass spectrometry (LC-MS/MS) represents a bioanalytic challenge because of charged, highly hydrophilic analytes presented at a large concentration range in a complex matrix. In this study, an ion pair LC-MS/MS method using triethylamine (TEA)-hexafluoroisopropanol (HFIP) ion-pair mobile phase was optimized and validated for simultaneous and unambiguous determination of 8 nucleoside triphosphates (including ATP, CTP, GTP, UTP, dATP, dCTP, dGTP, and dTTP) in cellular samples. Compared to the the less volatile ion-pair reagent, triethylammonium acetate (100mM, pH 7.0), the combination of HFIP (100mM) and TEA (8.6mM) increased the MS signal intensity by about 50-fold, while retaining comparable chromatographic resolution. The isotope-labeled internal standard method was used for the quantitation. Lower limits of quantitation were determined at 0.5nM for CTP, UTP, dATP, dCTP, and dTTP, at 1nM for ATP, and at 5nM for GTP and dGTP. The intra- and inter-day precision and accuracy were within the generally accepted criteria for bioanalytical method validation (<15%). While the present method was validated for the quantitation of intracellular nucleoside triphosphates, it had a broad application potential for quantitative profiling of nucleoside mono- and bi-phosphates as well as other polar, ionic metabolic intermediates (including carbohydrate derivatives, carboxylic acid derivatives, co-acyl A derivatives, fatty acyls, and others) in biological samples.

A liquid chromatography with tandem mass spectrometry method for simultaneous determination of UTL-5g and its metabolites in human plasma.

UTL-5g is a novel small-molecule TNF-α inhibitor under investigation as both a chemoprotective and radioprotective agent. Animal studies showed that pretreatment of UTL-5g protected kidney, liver, and platelets from cisplatin-induced toxicity. In addition, UTL-5g reduced liver and lung injuries induced by radiation in vivo. Although a number of preclinical studies have been conducted, a validated bioanalytical method for UTL-5g in human plasma has not been published. In this work, a sensitive and reproducible reverse-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) assay was developed and validated for the determination of UTL-5g and its metabolites, 5-methylisoxazole-3-carboxylic acid (ISOX) and 2,4-dichloroaniline (DCA), in human plasma. The method involves a simple methanol precipitation step followed by injection of the supernatant onto a Waters 2695 HPLC system coupled with a Waters Quattro Micro™ triple quadrupole mass spectrometer. Chromatographic separation was accomplished using a Waters Nova-Pak C18 column maintained at 30°C, running at gradient mode with mobile phase consisting of 0.1% formic acid in water and 0.1% formic acid in methanol at a flow rate of 0.2mL/min. The analytes were monitored under positive electrospray ionization (ESI). Quantitation of these compounds in plasma was linear from 0.05 to 10µM. The lower limit of quantitation (LLOQ) was 0.05, 0.1, and 0.2µM for UTL-5g, ISOX and DCA, respectively. The accuracy and intra-and inter-day precisions were within the generally accepted criteria for bioanalytical method (<15%). This method provides a practical tool to measure and characterize the plasma concentration-time profiles for UTL-5g and its metabolites, ISOX and DCA.

Complex disease-, gene-, and drug-drug interactions: impacts of renal function, CYP2D6 phenotype, and OCT2 activity on veliparib pharmacokinetics.

PURPOSE: Veliparib, a poly (ADP-ribose) polymerase (PARP) inhibitor, undergoes renal excretion and liver metabolism. This study quantitatively assessed the interactions of veliparib with metabolizing enzyme (CYP2D6) and transporter (OCT2) in disease settings (renal impairment). EXPERIMENTAL DESIGN: Veliparib in vitro metabolism was examined in human liver microsomes and recombinant enzymes carrying wild-type CYP2D6 or functional defect variants (CYP2D6*10 and *4). Plasma pharmacokinetics were evaluated in 27 patients with cancer. A parent-metabolite joint population model was developed to characterize veliparib and metabolite (M8) pharmacokinetics and to identify patient factors influencing veliparib disposition. A physiologically based pharmacokinetic model integrated with a mechanistic kidney module was developed to quantitatively predict the individual and combined effects of renal function, CYP2D6 phenotype, and OCT2 activity on veliparib pharmacokinetics. RESULTS: In vitro intrinsic clearance of CYP2D6.1 and CYP2D6.10 for veliparib metabolism were 0.055 and 0.017 µL/min/pmol CYP, respectively. Population mean values for veliparib oral clearance and M8 clearance were 13.3 and 8.6 L/h, respectively. Creatinine clearance was identified as the significant covariate on veliparib oral clearance. Moderate renal impairment, CYP2D6 poor metabolizer, and co-administration of OCT2 inhibitor (cimetidine) increased veliparib steady-state exposure by 80%, 20%, and 30%, respectively. These factors collectively led to >2-fold increase in veliparib exposure. CONCLUSIONS: Renal function (creatinine clearance) is a significant predictor for veliparib exposure in patients with cancer. Although a single factor (i.e., renal impairment, CYP2D6 deficiency, and reduced OCT2 activity) shows a moderate impact, they collectively could result in a significant and potentially clinically relevant increase in veliparib exposure.

A stable isotope-labeled internal standard is essential for correcting for the interindividual variability in the recovery of lapatinib from cancer patient plasma in quantitative LC-MS/MS analysis.

The development and validation of a LC-MS/MS method is often performed using pooled human plasma, which may fail to account for variations in interindividual matrices. Since calibrator standards and quality control samples are routinely prepared in pooled human plasma, variations in the extraction recovery and/or matrix effect between pooled plasma and individual patient plasma can cause erroneous measurements. Using both pooled human plasma as well as individual healthy donor and cancer patient plasma samples, we evaluated the analytical performance of two classes of internal standards (i.e., non-isotope-labeled and isotope-labeled) in the quantitative LC-MS/MS analysis of lapatinib. After exhaustive extraction with organic solvent, the recovery of lapatinib, a highly plasma protein-bound drug, varied up to 2.4-fold (range, 29-70%) in 6 different donors of plasma and varied up to 3.5-fold (range, 16-56%) in the pretreatment plasma samples from 6 cancer patients. No apparent matrix effects were observed for lapatinib in both pooled and individual donor or patient plasma samples. The calibration curve range was 5-5000ng/ml of lapatinib in plasma. Both the non-isotope-labeled (zileuton) and isotope-labeled (lapatinib-d3) internal standard methods showed acceptable specificity, accuracy (within 100±10%), and precision (<11%) in the determination of lapatinib in pooled human plasma. Nevertheless, only the isotope-labeled internal standard could correct for the interindividual variability in the recovery of lapatinib from patient plasma samples. As inter- and intra-patient matrix variability is commonly presented in the clinical setting, this study provides an example underscoring the importance of using a stable isotope-labeled internal standard in quantitative LC-MS/MS analysis for therapeutic drug monitoring or pharmacokinetic evaluation.

Simultaneous determination of 1-(2'-deoxy-2'-fluoro-ß-D-arabinofuranosyl) uracil (FAU) and 1-(2'-deoxy-2'-fluoro-ß-D-arabinofuranosyl) 5-methyluracil (FMAU) in human plasma by liquid chromatography/tandem mass spectrometry.

A liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) assay was developed and validated for simultaneous determination of 1-(2'-deoxy-2'-fluoro-ß-D-arabinofuranosyl) uracil (FAU) and its active metabolite 1-(2'-deoxy-2'-fluoro-ß-D-arabinofuranosyl) 5-methyluracil (FMAU) in human plasma. FAU and FMAU were extracted from plasma samples using solid-phase extraction with Waters Sep-Pak® Vac C18 cartridge. Chromatographic separation was achieved on a Waters Atlantis T3 C18 column with a gradient mobile phase consisting of methanol and water with 0.45% formic acid (v/v) running at a flow rate of 0.2 ml/min. The analytes were monitored by triple quadrupole mass spectrometer under positive ionization mode. The lower limit of quantitation (LLOQ) was 10 and 2 ng/ml for FAU and FMAU in plasma, respectively. Calibration curves were linear over FAU and FMAU plasma concentration range of 10-2000 and 2-1000 ng/ml, respectively. The intra-day and inter-day accuracy and precision were within the generally accepted criteria for bioanalytical method (<15%). The method has been successfully employed to characterize the plasma pharmacokinetics of FAU and FMAU in cancer patients receiving 1-h intravenous infusion of FAU 50 mg/m².

Validation and implementation of a liquid chromatography/tandem mass spectrometry assay for quantitation of the total and unbound RO4929097, a γ-secretase inhibitor targeting Notch signaling, in human plasma.

A reversed-phased liquid chromatography with tandem mass spectrometry (LC-MS/MS) method was developed and validated for quantitation of the total and unbound RO4929097, a γ-secretase inhibitor targeting Notch signaling, in human plasma. Sample preparation involved a liquid-liquid extraction with ethyl acetate. Chromatographic separation was achieved on a Waters X-Terra™ MS C(18) column with an isocratic mobile phase consisting of methanol/0.45% formic acid in water (60:40, v/v) running at a flow rate of 0.2 ml/min for 6 min. The lower limits of quantitation (LLOQs) were 5 ng/ml for the total RO4929097 in plasma and 0.5 ng/ml for the unbound drug in phosphate buffer solution (PBS). Calibration curves were linear over RO4929097 concentration range of 5-2000 ng/ml in plasma for the total drug and 0.5-200 ng/ml in PBS for the unbound drug. The intra-day and inter-day accuracy and precision were within the generally accepted criteria for bioanalytical method (<15%). The method has been successfully employed to characterize the total and unbound plasma pharmacokinetics of RO4929097 after its oral administration in cancer patients.

Simultaneous determination of ABT-888, a poly (ADP-ribose) polymerase inhibitor, and its metabolite in human plasma by liquid chromatography/tandem mass spectrometry.

A reversed-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous determination of ABT-888 and its major metabolite (M8) in human plasma. Sample preparation involved a liquid-liquid extraction by the addition of 0.25 ml of plasma with 10 microl of 1 M NaOH and 1.0 ml ethyl acetate containing 50 ng/ml of the internal standard zileuton. The analytes were separated on a Waters XBridge C(18) column using a gradient mobile phase consisting of methanol/water containing 0.45% formic acid at the flow rate of 0.2 ml/min. The analytes were monitored by tandem mass spectrometry with electrospray positive ionization. Linear calibration curves were generated over the ABT-888 and M8 concentration ranges of 1-2000 ng/ml in human plasma. The lower limits of quantitation (LLOQ) were 1 ng/ml for both ABT-888 and M8 in human plasma. The accuracy and within- and between-day precisions were within the generally accepted criteria for bioanalytical method (<15%). This method was successfully employed to characterize the plasma concentration-time profile of ABT-888 after its oral administration in cancer patients.

Validation and implementation of a liquid chromatography/tandem mass spectrometry assay to quantitate aminoflavone (NSC 686288) in human plasma.

A reverse-phase liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method was developed and validated for determination of aminoflavone (AF) in human plasma. Sample preparation involved a liquid-liquid extraction by the addition of 0.25 mL of plasma with 1.0 mL ethyl acetate containing 50 ng/mL of the internal standard zileuton. The analytes were separated on a Waters X-Terra MS C(18) column using a mobile phase consisting of methanol/water containing 0.45% formic acid (70:30, v/v) and isocratic flow at 0.2 mL/min for 6 min. The analytes were monitored by tandem mass spectrometry with electrospray positive ionization. Linear calibration curves were generated over the AF concentration range of 5-2000 ng/mL in human plasma. The lower limit of quantitation (LLOQ) was 5 ng/mL for AF in human plasma. The accuracy and within- and between-day precisions were within the generally accepted criteria for bioanalytical method (<15%). This method was successfully applied to characterize AF plasma concentration-time profile in the cancer patients in a phase I trial.

Methylation suppresses the proteasome-inhibitory function of green tea polyphenols.

Under physiological conditions, biotransformation reactions, such as methylation, can modify green tea polyphenols (GTPs) and therefore limit their in vivo cancer-preventive activity. Although a recent study suggested that methylated polyphenols are less cancer-protective, the molecular basis is unknown. We previously reported that ester bond-containing GTPs, for example (-)-epigallocatechin-3-gallate [(-)-EGCG] or (-)-epicatechin-3-gallate [(-)-ECG], potently and specifically inhibit the proteasomal chymotrypsin-like activity. In this study, we hypothesize that methylated GTPs have decreased proteasome-inhibitory abilities. To test this hypothesis, methylated (-)-EGCG and (-)-ECG analogs that can be found in vivo were synthesized and studied for their structure-activity relationships (SARs) using a purified 20S proteasome. The addition of a single methyl group on (-)-EGCG or (-)-ECG led to decreased proteasome inhibition and, as the number of methyl groups increased, the inhibitory potencies further decreased. These SARs were supported by our findings from in silico docking analysis published recently. Previously, we synthesized a peracetate-protected (-)-EGCG molecule, Pro-EGCG (1), to enhance its cellular permeability and stability, and current HPLC analysis confirms conversion of Pro-EGCG (1) to (-)-EGCG in cultured human leukemic Jurkat T cells. Furthermore, in this study, peracetate-protected forms of methylated GTPs were added in intact Jurkat T cells to observe the intracellular effects of methylation. Peracetate-protected, monomethylated (-)-EGCG induced greater cellular proteasome inhibition and apoptosis than did peracetate-protected, trimethylated (-)-EGCG, consistent with the potencies of the parent methylated analogs against a purified 20S proteasome. Therefore, methylation on GTPs, under physiological conditions, could decrease their proteasome-inhibitory activity, contributing to decreased cancer-preventive effects of tea consumption.

A phase 1 trial of XK469: toxicity profile of a selective topoisomerase IIbeta inhibitor.

PURPOSE: XK469, a member of the quinoxaline family of antitumor agents, is believed to be unique in its ability to selectively target topoisomerase IIbeta. Based on encouraging pre-clinical data, a phase I trial was conducted to determine the dose limiting toxicity (DLT) and the maximum tolerated dose (MTD). METHODS: A 2B accelerated titration schema was employed. XK469 was administered as a 5 or 20 min IV infusion on days 1-5 every 21 days. The starting dose was 9 mg/m(2). Pharmacokinetics (PK) were conducted in cycles 1-3. RESULTS: 22 patients (21 evaluable, mean age: 56 years, median performance status: 1) were enrolled. At dose level 11 (260 mg/m(2)/daily X 5), 1/6 patients experienced a DLT of grade 4 neutropenia. At 346 mg/m(2)/daily X 5, 2/2 patients experienced DLT's with one episode of febrile neutropenia and one grade 3 infection. The MTD was identified as 260 mg/m(2)/day. XK469 peak plasma levels and systemic exposure were proportional to dose indicating linear pharmacokinetics. However, secondary peaks in the PK profiles and a rapid decline in drug level from 23 to 24 h occurred in some patients. Drug infusion in the afternoon followed by dense sampling of levels during the elimination phase supported the hypothesis that the drug was being sequestered. No anti-tumor activity was identified. CONCLUSIONS: Traditional PK sampling designs were inadequate to describe XK469 disposition. XK469 and related structures work through a unique mechanism of action. A further understanding of the specific mechanism of these compounds might uncover a unique avenue for future drug development.

Phase I clinical trial of BMS-247550, a derivative of epothilone B, using accelerated titration 2B design.

PURPOSE: BMS-247550 is a semisynthetic derivative of epothilone B with mechanism of action analogous to paclitaxel. It has shown impressive antitumor activity in preclinical studies including in taxane-resistant models. We conducted a phase I trial, based on accelerated titration "2B" design, of BMS-247550 given as a 1-hour infusion every 3 weeks. EXPERIMENTAL DESIGN: Seventeen patients (M:F, 10:7; median age, 54 years; performance status, 0-2) were treated on the trial. Forty-five cycles (1-9 cycles) of BMS-247550 were given at dosages ranging from 7.4 to 56 mg/m2. All patients received prophylaxis for hypersensitivity reactions, related to Cremophor-EL, with steroids and histamine antagonists. RESULTS: First-course dose-limiting toxicity (DLT) was observed in two of three patients at 56 mg/m2 (neutropenic sepsis, prolonged grade 4 neutropenia) and in one of six patients at 40 mg/m2. Nonhematologic grade 3 to 4 toxicities observed were emesis and fatigue and they occurred only at 56 mg/m2. Grade 1 to 2 peripheral neuropathy was also observed. Other grade 1 to 2 toxicities were myalgias, arthralgias, rash, hand/foot syndrome, and mucositis. AUC and C(max) seemed proportional to the dose and the DLT. Development of neutropenia with BMS-247550 is related to the duration of drug exposure above a threshold. CONCLUSIONS: The maximum tolerated dose (MTD) of BMS-247550 is 40 mg/m2 given every 3 weeks. Neutropenia is the DLT. The accelerated titration "2B" design may help in determining MTD with fewer patients enrolled and more being treated closer to the MTD. However, the accelerated titration design did not seem to shorten the study duration.

Pharmacokinetics and tissue distribution of cryptophycin 52 (C-52) epoxide and cryptophycin 55 (C-55) chlorohydrin in mice with subcutaneous tumors.

PURPOSE: To compare the pharmacokinetics and tissue distribution (both normal and tumor) of cryptophycin 52 (C-52) and its putative chlorohydrin prodrug cryptophycin 55 (C-55) in a murine model and to investigate a possible mechanism behind the superior activity of C-55. METHODS: Mammary adenocarcinoma 16/c tumor-bearing mice were treated with an i.v. bolus of 11 mg/kg C-52 or 38 mg/kg C-55 in Cremophor-alcohol. At predetermined time intervals, C-52 and C-55 concentrations in plasma, liver, kidney, small intestine and tumors were measured using a previously described HPLC method. Pharmacokinetic parameters were computed using noncompartmental methods. Tissue (both normal and tumor) to plasma ratios as a function of time were also calculated for comparison. RESULTS: Both C-52 and C-55 were rapidly distributed into different tissues including tumors following i.v. administration. However, the affinities of these compounds towards different tissues were different. Thus, the half-lives (minutes) of C-55 were in the decreasing order liver (725), intestine (494), tumor (206), kidney (62) and plasma (44), whereas the AUC values (microg x min/ml) were in the order tumor (9077), liver (7734), kidney (6790), plasma (2372) and intestine (2234). For C-52, the half-lives (minutes) were in the decreasing order liver (1333), kidney (718), intestine (389), tumor (181) and plasma (35), and the AUC values (microg x min/ml) were in the order kidney (1164), liver (609), intestine (487), plasma (457) and tumor (442). The relative exposures to C-52 after i.v. injection of C-55 were plasma 3.9%, tumor 80.8%, kidney 3.4%, liver 1.1% and intestine 2.8%. Although plasma exposure to C-52 following C-55 administration was relatively small, the use of C-55 to deliver C-52 increased the retention of C-52 and its AUC in tumor compared to direct injection of C-52. Simultaneously, this approach shortened C-52 retention in all normal tissues studied. CONCLUSIONS: The distribution of C-55 and its bioconversion to C-52 in different organs and tumor tissue observed in this study suggest the ability of C-55 to target tumor tissue, creating a depot of C-52 in tumor. Increased C-52 exposure of tumor, with concomitant decreased exposure of normal tissue, is a contributing factor to the superior activity of C-55 versus C-52. However, except in the case of tumor tissue in which 81% of C-55 converts to C-52, only a minor amount of C-55 may serve as a prodrug for C-52, whereas the majority is handled by the biosystem through a different route of elimination. Tissue distribution combined with rate of conversion may be an important determinant of the relative effectiveness of other epoxide-chlorohydrin pairs of cryptophycins.

Inhibition of macromolecular synthesis by cryptophycin-52.

Cryptophycin (CP)-52, a synthetic analog of CP-1, possesses potent and selective antiproliferative activity against human solid tumors both and. Based on an algorithm developed in this laboratory using HCT-116 human colon adenocarcinoma cells, CP-52 exhibited a time- and concentration-dependent antiproliferative effect in the clonogenic assay. Inhibition of both DNA and RNA synthesis was observed in the absence of any effect on protein synthesis following a 24-h exposure to CP-52, at a time when proliferating cells were arrested in the G2/M phase of the cell cycle. In summary, we interpret these data to indicate that the selective inhibition of DNA synthesis may be a major causative factor responsible for the antiproliferative activity of CP-52 and subsequent G2/M arrest.