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FDA Guidelines For Developmental and Reproductive Toxicology (DART) Studies for Small Molecules. Author-Writer: Stephen J. Williams, Ph.D.

This posting is a follow-up on the Report on the Fall Mid-Atlantic Society of Toxicology Meeting “Reproductive Toxicology of Biologics: Challenges and Considerations post and gives a brief synopsis of the current state of FDA regulatory guidelines with respect to DART studies on small molecule (non-biological based) therapeutics.    The following is adapted from the book Principles and Methods of Toxicology by Dr. A Wallace Hayes (1) and is an excellent reference on reproductive toxicology and testing methods.

Chemical insult occurs to the human reproductive system at a multitude of stages in development and the life cycle, leading to the extensive testing which must be performed to diligently the reproductive and development toxicity of a chemical/drug.  Abnormalities and toxic manifestations in the offspring may result from insult to the adult reproductive (either female or male) and neuroendocrine systems, as well as damage to the embryo resulting in embryolethality, fetus at any period during organogenesis, juvenile development or, in the case of certain antibody therapies, immune system development.  The latter, toxic insult to the developing immune system could possibly be manifested as either an immune defect in the newborn or, later in life, as tolerance to said therapy.  It is estimated that exposure to the pregnant woman, of either environmental contaminants or drug, is significant.  It is estimated that a mother may be taking an average of 8-9 different drug preparations, mostly over the counter preparations such as antacids, vitamin preparations, cathartics etc. with the maximal drug intake occurring between 24 and 36 weeks of gestation.

Toxic insult to the developing embryo is dependent on

• Fetal development stage during drug/chemical exposure
• Maternal/placental xenobiotic metabolism
• Pharmacokinetic parameters affecting bioavailability and fetal/maternal drug binding

The following table shows the dependency of developmental stage to teratogenicity: adapted from J. Manson, H. Zenick, and R.D. Costlow from Principles and Methods of Toxicology.

Developmental Stage	Major Susceptibility
Preimplantation	Embryolethality
Organogenesis	Births defects; embryolethality
Fetal	Growth retardation, fetal death, functional deficits
Neonatal	Growth retardation, nervous system alterations, immune and endocrine systems

It is not generally accepted that there is a dose dependency of teratogenesis however most teratogens have specific mechanisms of action and teratogenic effects occur at much lower doses than result in maternal toxicity.   However, the developmental toxicity may be manifested later in life, including as reproductive toxicity affecting adult fertility and familial generations.

FDA Guidelines for DART Studies on Non-Biologics (Small Molecule Therapeutics)

The basic design for DART studies incorporate the aforementioned principles of tetralogy:

• developmental stage of fetal exposure
• parental effects on reproduction and development
• toxicity may be manifested over multiple generations including fertility rates

Therefore two designs are generally used for DART studies

1. exposure across several generations
2. exposure during one generation

FDA requires one control group and two treatment groups, and evaluation of at least two species.  However, most studies will use two rodent and one nonrodent species.

Multigenerational Design

Multigenerational DART studies are conducted for compounds likely to concentrate in the body following long-term exposure.  Examples of types of compounds include pesticides and food additives.

Figure 1.  General Design of a Multigenerational DART study.  Weanlings (30-30 days of age) from the parental generation are treated for a period up to 60 days. At 100-120 days of parental generation, animals are mated.  F_x = filial_x .

Three Segment, Single Generation Tests

The single generation design is more suitable for DART studies on drugs, as most therapeutic would be taken over short periods (during pregnancy) and have relatively short half-lives in the body.  FDA guidelines separate these studies in three phases:

I.            Phase I: evaluation of fertility and general reproductive performance

II.            Phase II: assessment of teratogenicity and embryotoxicity

III.            Phase III: peri- and postnatal evaluations.

All figures are adapted from Principles and Methods of Toxicology.(1)

FDA guidelines Guidance for Industry Reproductive and Developmental Toxicities —Integrating Study Results to Assess Concerns can be found at: http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm079240.pdf

FDA Guideline for reproductive toxicity testing for small molecule therapeutics can be found at:

http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/ucm074950.pdf

1.            Hayes, A. W. (1986) Principles and Methods of Toxicology, Raven Press, New York

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