Drug Metabolism and Pharmacokinetics

The NMR and Drug Metabolism Core has developed rapid and efficient approaches to investigate metabolism, metabolic stability, pharmacokinetics (PK), and chemical structure identification of small molecular weight compounds using liquid chromatography-mass spectrometry (LC-MS and MS/MS). In brief, PK is the study of what the body does to a drug; PK and tissue distribution play important roles in drug development. The half-life of a drug (t_1⁄2), absorption and tissue distribution are important properties for first-pass success of a candidate compounds. Preclinical pharmacokinetic studies can determine the optimal dose for administration, time taken to achieve steady state, and dosage intervals. The DMPK services that we offer include:

Drug and chemical entities analysis

We have developed LC-MS/MS assays for quantitatively measuring a number of drugs and other new chemical entities in various matrix of interest (e.g. plasma, CSF, urine, feces, tissues, etc.).

Tissue bioanalysis

Determining the concentration of compounds of interest in target tissues is essential for the assessment of drug efficacy and safety (e.g., drug concentration in solid tumor tissue, brain, etc.).

Method development

We have state-of-the art LC-MS and technical expertise to meet your needs. Specific analytical methods can be developed, set up, and tailored to your requirements.

Microsomal stability

These assays assist you to understand the stability of your compounds in vitro and to predict in vivo clearance. Both half-life and intrinsic clearance are calculated based on the data from the assay of metabolic stability.

Metabolite identification

We identify drug metabolites from liver microsomes (e.g., mouse, rat, dog, and human) and in vivo studies. Identifying the unstable moieties can help guide the synthetic optimization of lead compounds.

Reaction phenotyping

Identifying the CYP450 enzymes involved in the metabolism of lead compounds is important for predicting potential drug-drug interactions. Recommended inhibitors by FDA and HLM are used for confirmation.

In vivo PK

PK profiles are used for dose translation in pre-clinical disease animal models. Healthy animals are employed to generate time-dependent concentration profiles for calculating clearance and volume of distribution of compounds.

Oral bioavailability

Understanding oral bioavailability can help guide the selection of lead compounds for further development. Intravenous and oral administration are employed to determine the oral bioavailability in rodent models.

Tissue distribution

We can identify drug distribution and concentration in 15 different target organs in rodent models. This information helps to understand drug distribution in the body as well as accumulation in a specific tissue of interest.

Drug metabolism and pharmacokinetics (DMPK) are essential for the process of validation and optimization of compounds prior to licensure by pharmaceutical interests. There are two key elements associated with successful drug development: efficacy and safety. Both depend on drug metabolism. Drug metabolism has become an integral part of the lead optimization phase in drug discovery. Also, identifying the major metabolic enzymes that act on a drug can predict likely drug-drug interactions that should be evaluated in the process of drug development.

Pharmacokinetics (PK) is the study of the time course of drug absorption, distribution, metabolism, and excretion in the body. In brief, PK is the study of what the body does to a drug. PK and tissue distribution also play important roles in drug development. Half-life of a drug (t_1⁄2), absorption and tissue distribution are important properties for first-pass success of a candidate. Preclinical pharmacokinetic studies can determine the optimal dose for administration, time taken to achieve steady state, and dosage intervals.

The liver is the major site of drug metabolism. Approximately 60 percent of marketed drugs are metabolized by hepatic CYP450s. Human liver microsomes (HLM) are an important in vitro experimental model for the evaluation of drug metabolism. HLM are subcellular fractions derived from the endoplasmic reticulum of hepatic cells and are prepared by homogenization of liver. In addition, microsomes are pooled from multiple donors, which minimize the effect of variability between individuals. These subcellular fractions are a rich source of many drug-metabolizing enzymes like cytochrome P450s (CYP450s), flavin monooxygenases, carboxyl esterases, epoxide hydrolases, and UDP glucuronyl transferases. Therefore, they are widely used as an in vitro model system to investigate the metabolic fate of xenobiotics, their stability, and metabolite identification. Additionally, recombinant P450s (E. coli expressed recombinant enzymes) can be employed to determine the specific enzymes involved in drug metabolism (e.g., CYP1A2, 2C8, 2C9, 2C19, and CYP3A4). Metabolism in liver microsomes can generate the major metabolites and identify the ‘soft spots’ of a drug. This information can be used to optimize the structures of lead compounds, resulting in more suitable pharmacological properties and reduced possible toxicity.

We have developed rapid and efficient approaches to investigate metabolism, metabolic stability, pharmacokinetics, and chemical structure identification of small molecular weight compounds using liquid chromatography-mass spectrometry (LC-MS and MS/MS).

All users are required to sign up on iLabs to request services and to provide charge sources for core fees. Sample submission and preparation for analysis by the core must be accompanied by a completed sample submission form. Baylor investigators may complete and submit the form online (iLab) electronic copy.

Use permanent markers (e.g. Sharpie) to directly label tubes since labels may fall off when frozen. Send an electronic document containing sample information—preferably in advance of sending the samples. Send the completed xl file to core director. All Samples should be shipped frozen and on dry ice. Tubes should be clearly labeled with sample identifiers and include a hard copy of the list of samples. Please include all available sample information when you submit the samples, excluding any patient identifiers. For pharmacokinetic studies, investigators should provide serum or plasma. In case of submitting samples in person, after submitting the samples please send a follow-up e-mail to core directors and notify the name of the person who received your samples.

5-10 mg of pure tested compounds in Eppendorf or glass vials. 1 ml of 5 mM stock solution in DMSO or MeOH in glass vial is acceptable as well. Provide the formula, structures, purity, solubility, storage conditions. 50 ul of serum/ plasma at each time point, the information of administrate routes and dose are required for pharmacokinetics. 50 mg of tissue samples at each time point is required. 1.0 ml of blank serum/plasma or 1.0 g of tissue (no drug treatment) is needed for standard curve creation. All the serum/plasma and tissue samples should be submitted on dry ice.

Li, F., et al., Metabolomic analysis reveals novel isoniazid metabolites and hydrazones in human urine. Drug Metab Pharmacokinet. 2011, 26(6):569-576.

Li, F., et al., CYP3A4-mediated α-hydroxyaldehyde formation in saquinavir metabolism. Drug Metab Dispos, 2014, 42(2):213-220.

Liu X. et al., Metabolomics reveals the formation of aldehydes and iminium in gefitinib metabolism. Biochem Pharmacol., 2015, 97, 111-121.

Liu X. et al., Characterizing novel metabolic pathways of melatonin receptors agonist agomelatine using metabolomics approaches. Biochem. Pharmacol., 2016, 109, 70-82.