On the Way to the Clinic

Abstract

This chapter walks through the essential preclinical drug development steps to ensure that the compound has optimal pharmacological features. Robust and reproducible preclinical pharmacology studies must demonstrate the desired on-target effect; drug formulation and route of administration must be established; pharmacokinetics must be characterized; and preclinical safety studies must be conducted to predict potential drug toxicities and establish safe dosing ranges. We also consider the great genetic variation among humans when developing a drug. Early evaluation of these characteristics will increase the probability that clinical trials will succeed.

Daria Mochly-Rosen, Ed, Kevin Grimes, Ed.

Key Terms and Abbreviations

Key Terms

• Absorption, Distribution, Metabolism, and Excretion (ADME): PK parameters that measure how the body processes drugs.

• Active Pharmaceutical Ingredient (API): The ingredient that produces the intended effects, also called drug substance.

• Adverse Drug Reactions (ADRs): Unwanted or dangerous side effects caused by the administration of a drug.

• Alzet® Pumps: Miniature osmotic infusion pumps for continuous dosing of a drug to a laboratory animal.

• Ames Test: An assay performed in bacteria that tests whether a compound causes mutations in the DNA of the test organism.

• Area Under the Plasma Drug Concentration vs. Time Curve (AUC): Plasma concentration of a drug integrated over time after dosing.

• Artificial Intelligence (AI): The use of a machine/computer to mimic human intelligence by executing tasks normally performed by humans.

• Arylamine N-Acetyltransferase (NAT): A polymorphic enzyme that catalyzes the transfer of an acetyl group (from acetyl-CoA) to a xenobiotic acceptor containing aromatic amines. Acetylation of drugs enhances excretion.

• Bio-Betters: New formulations of biologic therapeutics to improve dosing schedule or route of administration.

• Bioavailability: Based on the route of administration, the fraction (or percent) of the dose of chemically unchanged drug reaching systemic circulation.

• Bolus: A single dose of an injected drug given over a short period of time.

• Buccal: In the mouth.

• Carboxylesterase (CES): A class of enzymes that catalyze the hydrolysis of esters, amides, thioesters, and carbamates. Their most common drug substrates are ester prodrugs, though they can also convert xenobiotics into inactive metabolites.

• Center for Drug Evaluation and Research (CDER): Center within the US Food and Drug Administration (FDA) responsible for the regulation of over-the-counter and prescription drugs (including some biological therapeutics and generic drugs).

• Compartmental Modeling: Requires log transformation of the plasma concentration data. Each linear elimination phase is ascribed to a fictive compartment (e.g., one phase = 1-Comp model). A mathematical model is developed to describe the log-transformed plasma concentrations. Assuming linear PK, this model can be used to simulate different doses and/or schedules.

• Cytochrome P450 (CYP): A class of heme-containing enzymes (monooxygenases) involved in drug metabolism. Genetic polymorphisms exist in subpopulations with altered abilities to metabolize xenobiotics (e.g., poor metabolizers).

• Depot: A drug formulation injected into the body that serves as a reservoir allowing drug release over an extended period of time, measured in days to months.

• Drug–Gene Interactions (DGI): The relationship between a drug and the genetic makeup of an individual that may affect the patient’s response to the drug.

• Endpoints: Measurements (e.g., weight or tumor size) or observations (e.g., motor control or healthiness) used in a study to evaluate the effectiveness or safety of a treatment.

• Enteral: Routes for drug absorption through the gastrointestinal tract.

• European Medicines Agency (EMA): An agency of the European Union responsible for the evaluation, supervision, and safety of medicinal products. EMA and US FDA have similar missions to ensure that medical products are both safe and efficacious before they are approved for marketing.

• Excipients: Inactive materials (e.g., fillers, binders, coatings) included in the drug product formulation.

• Extended-Release (XR): An oral formulation that releases its API over 1 day.

• First in Human (FIH): A clinical trial in which a treatment is tested in humans for the first time.

• Flavin-Containing Monooxygenase (FMO): A class of enzymes that adds molecular oxygen to lipophilic xenobiotics, enhancing solubility and rapid elimination of the molecule.

• Good Laboratory Practice (GLP): Extensive documentation of each procedural step to ensure high quality, reproducible studies.

• Good Manufacturing Practice (GMP): Exacting procedures and documentation of quality assurance carried out at a certified drug manufacturing facility (sometimes referred to as “cGMP” for “current” practice).

• Human Equivalent Dose (HED): A calculated dose predicted to achieve the same exposure in humans as in a relevant animal model. This is a species-dependent ratio based on body surface area that generalizes how a given dose in that species will convert to a corresponding human dose. These ratios can be found in the FDA guidance document on First in Human Testing.

• Human Ether-á-Go-Go-Related Gene (hERG) Channel: A potassium ion channel that is important for normal electrical activity of the heart. Inhibition of this channel can lead to sometimes fatal cardiac arrhythmias.

• International Committee on Harmonization (ICH): Joint effort of European, Japanese, and US regulatory authorities and pharmaceutical industries to provide uniform standards and guidance for drug development.

• Intranasal: In the nose.

• Intraperitoneal (ip): Within the peritoneum (abdominal cavity).

• Intravenous (IV): Within a vein.

• Investigational New Drug Application (IND): Document filed with FDA prior to initiating research on human subjects using any drug that has not been previously approved for the proposed clinical indication, dosing regimen, or patient population.

• Maximum Concentration (C_max): The maximum concentration a drug achieves in a given body fluid or tissue (most often plasma) after the drug has been administered.

• Monoamine Oxidase (MAO): A family of enzymes that catalyze the oxidation of monoamines, implicated in brain metabolite clearance (serotonin, dopamine, norepinephrine).

• New Drug Application (NDA): Application to obtain FDA approval for the sale and marketing of a new drug in the US.

• New Molecular Entity (NME): A novel drug that has not been previously approved for human use.

• Noncompartmental Analysis (NCA): A type of PK analysis commonly used in drug development. This method is often used for assessing clearance, half-lives, and distribution.

• Oral (po): By mouth.

• Orphan Indication: An FDA designation of a disease or condition that affects less than 200,000 people per year in the US or for a treatment that is not expected to recoup its research and development (R&D) costs due to pricing constraints.

• P-Value: A statistical measure of the probability of obtaining a result at least as extreme as the one observed. Although there is no experimental basis for doing so, it is routinely accepted that if the p-value is less than the significance level (usually 0.05 or 0.01), one rejects the null hypothesis that there is no treatment effect. The “requirement” for studies to achieve p < 0.05 is a major contributor to research waste (Begley and Snapinn 2021).

• Parenteral: Routes for drug absorption outside the gastrointestinal tract.

• Pharmacodynamics (PD): Measurements of drug action in the body (e.g., target inhibition/activation, cell killing, change in blood pressure).

• Pharmacogenomics (PGx): The field that studies variations in genes that code for drug metabolizing enzymes and drug transporters.

• Pharmacokinetics (PK): Measurements of what the body does to a drug (absorption, distribution, metabolism, and excretion).

• Pharmacokinetics/Pharmacodynamics (PK/PD): Interplay of pharmacokinetics and pharmacodynamics that ultimately determines the biologic impact of a drug (i.e., whether a drug will be safe and efficacious for the disease indication as dosed).

• Preclinical Animal Studies: Animal studies performed to validate a disease target and test the performance of a molecule prior to moving into human testing.

• Single Dose Pharmacokinetics (SDPK): A dosing regimen in which a single dose of a compound is administered and PK is measured. SDPK can provide a relatively robust understanding of the PK/PD relationship of a compound’s effect on its target.

• Single Nucleotide Polymorphism (SNP): A single DNA nucleotide base change in the genome that contributes to genetic variation.

• Slow-Release (SR): An oral formulation that releases its API over a period of hours. SR formulated drugs are often dosed every 12 h.

• Structure–Activity Relationship (SAR): The relationship between the chemical structure of a molecule and its biological activity. During lead optimization, iterative chemical modifications are made to a molecule and the impact on various biological parameters is assessed.

• Subcutaneous (sc): Beneath the skin.

• Sublingual: Under the tongue.

• Therapeutic Index: The ratio of the toxic dose to the effective dose; a larger therapeutic index suggests a larger safety window.

• Time of Maximum Plasma Concentration (T_max): The time at which the drug reaches its maximum concentration after administration.

• Topical: Routes for drug absorption at the site of application, usually the skin or mucosal membranes.

• UDP-Glucuronosyltransferase (UGT): A class of enzymes that conjugate glucuronic acid to lipophilic xenobiotics, which enhances solubility and rapid elimination of the molecule.

• US Food and Drug Administration (FDA): A US federal agency responsible for protecting public health by assuring the safety and efficacy of drugs, biological products, medical devices, and other products.

• Xenobiotic: A substance foreign to the body.

Key Abbreviations

ANOVA:

Analysis of Variance

CPNDS:

Canadian Pharmacogenomics Network for Drug Safety

CNS:

Central Nervous System

CEO:

Chief Executive Officer

CSO:

Chief Scientific Officer

CDSS:

Clinical Decision Support Systems

CPIC:

Clinical Pharmacogenetics Implementation Consortium

cDNA:

Complementary DNA

DPWG;:

Dutch Pharmacogenetics Working Group

ESI:

Ethical Legal and Societal Issues

RNPGx:

French National Network of Pharmacogenetics

GWAS:

Genome-Wide Association Studies

HIV:

Human Immunodeficiency Virus

I-PWG:

Industry Pharmacogenomics Working Group

KAP:

Knowledge, Attitudes, and Practices

NGS:

Next Generation Sequencing

NOD:

Non-Obese Diabetic

PCR-RFLP:

PCR-Restriction Fragment Length Polymorphism

PM:

Poor Metabolizer

R&D:

Research and Development

RT-PCR:

Reverse Transcription-PCR

VUS:

Variants of Unknown Clinical Significance

WHO:

World Health Organization