Basic principles of non-clinical development

The toxicology studies aim to address how toxic the medicinal product is:

• Single-dose toxicity.
• Repeated-dose toxicity.
• Genotoxicity (damage within a cell that causes changes or mutations in the genes).
• Carcinogenicity (can it cause cancer?).
• Development and reproductive toxicity (DART)

It should be noted that:

• When researchers have a special cause for concern or when the medicine is for long-term use, then the researchers must assess the risk of developing cancer (the drug’s carcinogenic potential).
• Other non-clinical studies should be carried out on a case-by-case basis, as appropriate. These include for example phototoxicity studies, immunotoxicity studies, juvenile animal toxicity studies and abuse potential studies.

Single dose and dose-range finding (DRF) studies

First, these studies are done in rodents (mice or rats), and then in a larger animal species (for example dogs and usually non-primates).

The purpose of the studies is to find out how toxic the developmentcandidate is. This is based on:

• The maximum tolerated dose (MTD). The MDT is the highest dose that does not cause unacceptable side effects.
• The non-observed adverse effect level (NOAEL). The NOAEL is the highest dose level that does not produce a significant increase in adverse effects in comparison to the control group.
• The target organ(s) in which toxicity is seen.
• The doses for future toxicology studies or first-in-human studies.

In the DRF/toleration studies, the animals are monitored as the dose is increased and until the dose is found where adverse effects are first seen in one or few animals. Such studies will help define the so-called toxicological dose–response profile (usually for the first time for a medicinal product in development). The studies will include cage side observations (for physical and behavioural effects), drug exposure analysis, blood chemistry, haematology (the study of blood and blood-forming tissues), pathology (the study of the causes and effects of disease or injury mostly through analysis of tissue, cell, and body fluid samples) and histopathology (the study of diseased cells and tissues using a microscope).

Repeated dose toxicology studies

A repeated dose toxicology study will often be carried out in specific animal species. The purpose of this is to confirm the dose levels that will later be used in GLP toxicology and Safety Pharmacology studies.

In general, repeated dose toxicity studies shall be done in two species of mammals.  One of these species must be a non-rodent.

The goal is to:

• Find the toxicity profile (MTD, NOAEL) when given repeatedly over a period of time.
• Identify target organ(s) in which toxicity is seen.
• Find out if adverse effects can be reversed.
• Find the dose(s) for future toxicology studies or clinical trials.

Their standard duration is:

• Sub-chronic: 7, 14 and 28 days and 3 months
• Chronic: 6, 9 and 12 months.

Genotoxicity studies

The purpose of these studies is to find out if the medicinal product potentially affects DNA or chromosomes because this may lead to gene mutation and/or chromosomal damage.

The standard genotoxicity tests (or test battery) include:

• In-vitro bacterial mutation (Ames test).
• In-vitro mammalian cell chromosomal aberration (e.g. Human peripheral blood lymphocytes HPBL).
• In-vivo mammalian cell chromosomal aberration (e.g. rodent micronucleus).

Carcinogenicity studies

Carcinogenicity studies include:

• 2-year mouse or 26-week transgenic mouse (a mouse where the genes have been changed by inserting genes from another species).
• 2-year rat bioassay.

Development and reproductive toxicology studies

Development and reproductive toxicology (DART) studies include:

• Fertility (typically rat)
• Teratology (typically rat and rabbit)
• Peri- and post-natal (typically rat)