Young G. Shin

Application of Pharmacokinetic-Pharmacodynamic Modeling and Simulation for Antibody-Drug Conjugate Development

ABSTRACTCharacterization and prediction of the pharmacokinetics (PK) and pharmacodynamics (PD) of Antibody-Drug Conjugates (ADCs) is challenging, since it requires simultaneous quantitative understanding about the PK-PD properties of three different molecular species i.e., the monoclonal antibody, the drug, and the conjugate. Mathematical modeling and simulation provides an excellent tool to overcome these challenges, as it can simultaneously integrate the PK-PD of ADCs and their components in a quantitative manner. Additionally, the computational PK-PD models can also serve as a cornerstone for the model-based drug development and preclinical-to-clinical translation of ADCs. To provide an overview of this subject matter, this manuscript reviews the PK-PD models applicable to ADCs. Additionally, the usage of these models during different drug development stages (i.e., discovery, preclinical development, and clinical development) is also emphasized. The importance of PK-PD modeling and simulation in making rationale go/no-go decisions throughout the drug development process is also highlighted. There is an array of PK-PD models available, ranging from the systems models specifically developed for ADCs to the empirical models applicable to all chemotherapeutic agents, which one can employ for ADCs. The decision about which model to choose depends on the questions to be answered, time at hand, and resources available.

Opportunities in low-level radiocarbon microtracing: applications and new technology

14C-radiolabeled (radiocarbon) drug studies are central to defining the disposition of therapeutics in clinical development. Concerns over radiation, however, have dissuaded investigators from conducting these studies as often as their utility may merit. Accelerator mass spectrometry (AMS), originally designed for carbon dating and geochronology, has changed the outlook for in-human radiolabeled testing. The high sensitivity of AMS affords human clinical testing with vastly reduced radiative (microtracing) and chemical exposures (microdosing). Early iterations of AMS were unsuitable for routine biomedical use due to the instruments’ large size and associated per sample costs. The situation is changing with advances in the core and peripheral instrumentation. We review the important milestones in applied AMS research and recent advances in the core technology platform. We also look ahead to an entirely new class of 14C detection systems that use lasers to measure carbon dioxide in small gas cells.

Qualification and application of a liquid chromatography–quadrupole time-of-flight mass spectrometric method for the determination of trastuzumab in rat plasma

An liquid chromatography-quadrupole time-of-flight (QqTOF) mass spectrometric method was developed for the determination of humanized or human monoclonal antibodies in rat plasma at the early drug discovery stage. Trastuzumab was used as a model monoclonal antibody. The method consisted of immunoprecipitation followed by tryptic digestion for sample preparation and LC-TOF-MS/MS analysis of specific signature peptides in the positive ion mode using electrospray ionization for analysis. A stable isotope-labeled signature peptide was also used as internal standard. A quadratic regression (weighted 1/concentration(2) ), with an equation y = ax(2)  + bx + c, was used to fit calibration curves over the concentration range of 0.500-100 µg/mL for trastuzumab. Samples from a pharmacokinetic study in rat were analyzed by this qualified LC-TOF-MS/MS method and concentrations were compared with those generated by enzyme linked immunosorbent assays method. The LC-TOF-MS/MS method was accurate and precise, with quantitative results comparable with those of ELISA. The qualification run met the acceptance criteria of ±25% accuracy and precision values for quality control samples. Within-run accuracy ranged from 1.53 to 9.20% with precision values ≤10.29%. This LC-TOF-MS/MS method approach could be used as a complementary method for humanized or human monoclonal antibodies at the early drug discovery stage.

Comparison of rosiglitazone metabolite profiles in rat plasma between intraperitoneal and oral administration and identifcation of a novel metabolite by liquid chromatography-triple time of flight mass spectrometry

Rosiglitazone metabolites in rat plasma were analyzed after intraperitoneal and oral administration to rats. Seven metabolites (M1-M7) were detected in rat plasma (IP and PO), and the structures were confirmed using liquid chromatography-triple time of flight (TOF) mass spectrometry; as a result, the most abundant metabolite was M5, a de-methylated rosiglitazone. Other minor in vivo metabolites were driven from monooxygenation and demethylation (M2), thiazolidinedione ring-opening (M1, M3), mono-oxygenation (M4, M7), and mono-oxygenation followed by sulfation (M6). Among them, M1 was found to be a 3-{p-[2-(N-methyl-N-2-pyridylamino)ethoxy]phenyl}-2-(methylsulfinyl)propionamide, which is a novel metabolite of rosiglitazone. There was no significant difference in the metabolic profiles resulting from the two administrations. The findings of this study provide the first comparison of circulating metabolite profiles of rosiglitazone in rat after IP and PO administration and a novel metabolite of rosiglitazone in rat plasma.

Replacement of the C-terminal Trp-cage of Exendin-4 with a Fatty Acid Improves Therapeutic Utility

&NA; Exendin‐4, a 39 amino acid peptide isolated from the saliva of the Gila monster, plays an important role in regulating glucose homeostasis, and is used clinically for the treatment of type 2 diabetes. Exendin‐4 shares 53% sequence identity with the incretin hormone glucagon‐like peptide 1 (GLP‐1) but, unlike GLP‐1, is highly resistant to proteolytic enzymes such as dipeptidyl peptidase IV (DPP‐IV) and neutral endopeptidase 24.11 (NEP 24.11). Herein, we focused on the structure and function of the C‐terminal Trp‐cage of exendin‐4, and suggest that it may be structurally required for resistance to proteolysis by NEP 24.11. Using a series of substitutions and truncations of the C‐terminal Trp‐cage, we found that residues 1–33, including the N‐terminal and helical regions of wild‐type (WT) exendin‐4, is the minimum motif required for both high peptidase resistance and potent activity toward the GLP‐1 receptor comparable to WT exendin‐4. To improve the therapeutic utility of C‐terminally truncated exendin‐4, we incorporated various fatty acids into exendin‐4(1–33) in which Ser33 was substituted with Lys for acylation. Exendin‐4(1–32)K‐capric acid exhibited the most well balanced activity, with much improved therapeutic utility for regulating blood glucose and body weight relative to WT exendin‐4.

Prediction of pharmacokinetics and drug-drug interaction potential using physiologically based pharmacokinetic (PBPK) modeling approach: A case study of caffeine and ciprofloxacin

Over the last decade, physiologically based pharmacokinetics (PBPK) application has been extended significantly not only to predicting preclinical/human PK but also to evaluating the drug-drug interaction (DDI) liability at the drug discovery or development stage. Herein, we describe a case study to illustrate the use of PBPK approach in predicting human PK as well as DDI using in silico, in vivo and in vitro derived parameters. This case was composed of five steps such as: simulation, verification, understanding of parameter sensitivity, optimization of the parameter and final evaluation. Caffeine and ciprofloxacin were used as tool compounds to demonstrate the “fit for purpose” application of PBPK modeling and simulation for this study. Compared to caffeine, the PBPK modeling for ciprofloxacin was challenging due to several factors including solubility, permeability, clearance and tissue distribution etc. Therefore, intensive parameter sensitivity analysis (PSA) was conducted to optimize the PBPK model for ciprofloxacin. Overall, the increase in Cmax of caffeine by ciprofloxacin was not significant. However, the increase in AUC was observed and was proportional to the administered dose of ciprofloxacin. The predicted DDI and PK results were comparable to observed clinical data published in the literatures. This approach would be helpful in identifying potential key factors that could lead to significant impact on PBPK modeling and simulation for challenging compounds.

Drug–drug interaction of microdose and regular-dose omeprazole with a CYP2C19 inhibitor and inducer

Purpose A microdose drug–drug interaction (DDI) study may be a valuable tool for anticipating drug interaction at therapeutic doses. This study aimed to compare the magnitude of DDIs at microdoses and regular doses to explore the applicability of a microdose DDI study. Patients and methods Six healthy male volunteer subjects were enrolled into each DDI study of omeprazole (victim) and known perpetrators: fluconazole (inhibitor) and rifampin (inducer). For both studies, the microdose (100 μg, cold compound) and the regular dose (20 mg) of omeprazole were given at days 0 and 1, respectively. On days 2–9, the inhibitor or inducer was given daily, and the microdose and regular dose of omeprazole were repeated at days 8 and 9, respectively. Full omeprazole pharmacokinetic samplings were performed at days 0, 1, 8, and 9 of both studies for noncompartmental analysis. Results The magnitude of the DDI, the geometric mean ratios (with perpetrator/omeprazole only) of maximum concentration (Cmax) and area under the curve to the last measurement (AUCt) of the microdose and the regular dose were compared. The geometric mean ratios in the inhibition study were: 2.17 (micro) and 2.68 (regular) for Cmax, and 4.07 (micro), 4.33 (regular) for AUCt. For the induction study, they were 0.26 (micro) and 0.21 (regular) for Cmax, and 0.16 (micro) and 0.15 (regular) for AUCt. There were no significant statistical differences in the magnitudes of DDIs between microdose and regular-dose conditions, regardless of induction or inhibition. Conclusion Our results may be used as partial evidence that microdose DDI studies may replace regular-dose studies, or at least be used for DDI-screening purposes.

A Highly Sensitive Liquid Chromatography–Electrospray Ionization–Time of Flight/Mass Spectrometric Assay for the Quantitation of 4-Beta-Hydroxycholesterol and Its Application to in vivo Cytochrome P450 3a Induction by AGM-130

A liquid chromatography–electrospray ionization-time-of-flight/mass spectrometry (LC–ESI-TOF/MS) method was developed for the determination of 4-beta-hydroxycholesterol (4β-HC) in rat plasma, to evaluate cytochrome P450 3A (CYP3A) induction liability of a novel cyclin dependent kinases (CDKs) inhibitor, AGM-130. The method consisted of sample preparation without derivatization reagents for high sensitivity such as picolinyl ester, which could be labor-intensive and time consuming. The 4% bovine serum albumin in phosphate-buffered saline as a surrogate matrix was used in the calibration curve and quality control samples for the determination of 4β-HC. Stable isotope-labeled (SIL) 4β-HC (d7-4β-HC) was used as an internal standard. A quadratic regression (weighted 1/concentration), with an equation y = ax2 + bx + c, was used to fit calibration curves over the concentration range of 3.01–2220 ng/mL for 4β-HC. For quality control samples at 15.0, 165, and 1820 ng/mL from the qualification experiment, the within-run accuracy ranged from 95% to 105% with precision values ≤10% for 4β-HC. This novel LC–ESI-TOF/MS method was successfully applied to evaluate the potential of CYP3A induction by 5′-hydroxy-5-nitro-indirubin oxime (AGM-130) in rat.