In Vitro ADME Screening Studies

In Vitro ADME (Absorption, Distribution, Metabolism, and Excretion) studies are an essential part of drug discovery and development. These studies involve the use of In Vitro models and assays to assess the pharmacokinetic properties of potential drug candidates before they are tested in animal models or humans. In Vitro ADME screening studies provide valuable information about a drugs absorption, distribution within the body, metabolism, and elimination, helping researchers make informed decisions about the drug's viability and potential dosing regimens.

Key Components of In Vitro ADME Studies

Absorption Studies

Absorption refers to the process by which a drug enters the bloodstream from the site of administration. In Vitro, absorption studies assess parameters such as permeability across biological barriers (e.g., intestinal epithelium or skin), transporter interactions, and drug dissolution and solubility. Techniques like Caco-2 cell monolayers, PAMPA (Parallel Artificial Membrane Permeability Assay), or intestinal tissue slices can be used to evaluate drug absorption.

Distribution Studies

Distribution studies investigate how a drug is distributed within the body after it enters the bloodstream. In Vitro drug screening, techniques like plasma protein binding assays determine the extent to which a drug binds to proteins in the blood, affecting its distribution and availability. Additionally, cell-based models or organ-on-a-chip systems can be employed to study drug uptake and transport across specific tissue barriers, such as the blood-brain barrier.

Metabolism Studies

Metabolism refers to the enzymatic transformation of a drug in the body. In Vitro metabolism studies aim to identify and characterize the metabolic pathways involved in drug biotransformation. Techniques such as liver microsomal assays, hepatocyte cultures, or recombinant enzyme systems (e.g., cytochrome P450 enzymes) help assess drug metabolism, including oxidation, reduction, conjugation, or hydrolysis reactions. Metabolite identification and profiling are crucial for understanding the potential of a drug for drug-drug interactions or toxicity.

Excretion Studies

Excretion involves eliminating drugs and their metabolites from the body, primarily through the kidneys and liver. In Vitro excretion studies focus on renal and hepatic clearance, assessing factors such as drug transporters, renal tubular reabsorption, or biliary excretion. Techniques like kidney cell monolayers or Hepatocyte cultures can be used to study drug excretion processes.

TheraIndx In Vitro ADME Assays

Solubility

Solubility influences bioavailability for orally delivered compounds. The assay measures the aqueous solubility of compounds in aqueous solutions at different pH.

Stability in biological fluids-plasma, GI fluids

The extreme pH range in the gastro- intestinal tract can affect the solubility and stability of small molecules. Low and high pH may degrade the molecules. Thus if molecules are unstable at low and high pH their absorption and bioavailability will be low. This assay measures the stability of molecules in simulated GI fluids and plasma.

Plasma Protein Binding (Mouse, Rat, Dog, Human)

Both endogenous and exogenous molecules bind to plasma proteins present in the blood. Binding to plasma proteins influences the PK and efficacy of molecules. This assay measures the binding of molecules to plasma proteins from different species.

Permeability (PAMPA, CaCo2-Unidirectional, Bidirectional)

Permeability across plasma membranes influences the distribution and oral bioavailability of compounds. These assays measure permeability across artificial membranes (PAMPA) or across intestinal cells (CaCo2).

Microsomal Metabolic Stability ( Mouse, Rat, Dog, Human)

Molecules undergo metabolic transformations following entry into the body. The liver is the primary site of metabolism. It has phase 1 and phase 2 drug-metabolizing enzymes (DME). The microsomes are a fraction of the endoplasmic reticulum of cells which harbour phase 1 DMEs. This assay measures the metabolic stability of molecules in microsomes from different species.

Hepatocyte Metabolic Stability (Mouse, Rat, Dog, Human)

This assay measures the metabolic stability of molecules in hepatocytes from different species. Hepatocytes are intact liver cells carrying both phase 1 and phase 2 DMEs.

Human CYP450 assays

Inhibition, Isoform Phenotyping The CYP450 family of enzymes is a class of DMEs that is responsible for the metabolism of most drugs on the market. Inhibition of CYP450s, induction of CYP450s can lead to significant drug-drug interactions that can cause sub-pharmacological exposures or toxicities. Therefore it is essential to understand the potential to inhibit or induce CYP450s for compounds. The inhibition and induction assays measure the extent of inhibition or induction of the major CYP450 DMEs. In Isoform phenotyping assays, the DME which primarily metabolizes the molecule is Measured.

Cytotoxicity (HepG2, A549, MDCK cell lines)

Molecules that are toxic to human cells In Vitro screening are predicted to show toxicity in the body. Cytotoxicity assays in cell lines measure the potency and magnitude of toxicity of molecules.