The FDA expects preclinical testing for large molecule drugs (biologics) to be tailored to the drug's characteristics, intended clinical use, and risk profile. These studies are designed to ensure the investigational drug is reasonably safe for human testing and to provide data supporting the initiation of clinical trials under an Investigational New Drug (IND) application. The key preclinical testing requirements include the following:

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1. Toxicology Studies

• Purpose: Toxicology studies aim to identify potential toxic effects, determine target organs of toxicity, and establish a margin of safety between clinical and toxic doses. These studies are critical for determining the safe starting dose for human trials.
• Study Design:
  • Typically conducted in both rodent and non-rodent species, with nonhuman primates often used when they are the most relevant species ¹⁹.
  • Repeat-dose toxicity studies are required, often lasting one month in both rodent and non-rodent species before initiating clinical trials ¹¹²¹.
  • For monoclonal antibodies and other biologics, the FDA recommends following the ICH S6(R1) guidance, which includes toxicology studies in relevant animal models ¹¹¹⁶.
  • Toxicological endpoints include clinical signs, body weight, hematology, blood chemistry, urinalysis, organ weights, gross pathology, and histopathology ¹¹¹⁵.
  • The No-Observed-Adverse-Effect Level (NOAEL) is used to derive the starting dose for clinical trials, typically not exceeding 1/50 of the NOAEL in the most sensitive species ¹⁹.
• Flexibility: For exploratory IND studies or microdose studies, which involve limited human exposure, less extensive toxicology data may suffice ¹⁵²³.

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2. Pharmacology Studies

• Purpose: These studies evaluate the drug's mechanism of action (MOA), pharmacokinetics (PK), and pharmacodynamics (PD) to predict therapeutic activity and guide dose selection.
• Key Requirements:
  • In vitro studies assess binding to receptors, enzyme activity, and other pharmacological parameters ¹²¹⁵.
  • In vivo studies evaluate efficacy and safety, including mechanistically based endpoints such as receptor saturation or enzyme inhibition ¹⁵¹⁹.
  • Pharmacokinetic studies assess absorption, distribution, metabolism, and excretion (ADME) of the drug. Scaling from animals to humans using body surface area or PK/PD modeling is acceptable ¹⁵.

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3. Safety Pharmacology and Genetic Toxicology

• Safety Pharmacology: These studies evaluate the drug's effects on vital organ systems (e.g., cardiovascular, respiratory, and central nervous systems). However, for biologics, safety pharmacology studies may not always be necessary ¹⁵.
• Genetic Toxicology: Routine genetic toxicology testing (e.g., in vitro cytogenetic studies, in vivo mouse micronucleus assays) is generally not required for biologics, especially for single-dose or microdose studies, as these exposures are considered low risk ³¹⁵¹⁹.

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4. Reproductive and Developmental Toxicology

• Purpose: These studies assess the drug's effects on fertility, embryo-fetal development, and prenatal/postnatal development, especially if the drug will be tested in women of childbearing potential.
• Timing: Some reproductive toxicology studies may be conducted in parallel with clinical trials, provided adequate precautions are taken to prevent pregnancy during the trials ²¹²⁵.

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5. Analytical and Manufacturing Considerations

• Batch Consistency: The biologic used in preclinical studies should be manufactured using the same methods intended for clinical trials. Any changes in the product or manufacturing process must be documented and justified to ensure consistency and safety ⁹¹⁸.
• Compatibility with Delivery Devices: If a delivery device is used, compatibility studies must ensure the drug maintains its strength, potency, and purity under clinical conditions (e.g., formulation, dose range, infusion volume, and temperature) ²⁶.

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6. Special Considerations for Biologics

• Species Selection: The choice of animal species is critical. For biologics, species must be scientifically justified as the most relevant model for the drug's intended clinical use. In some cases, a single species may suffice ²¹⁹.
• Immunogenicity and Species-Specific Responses: Biologics often require tailored preclinical testing approaches due to their immunogenicity and species-specific activity. These factors influence the choice of animal models and study design ²⁹¹¹.
• Exploratory IND Studies: For early-phase exploratory IND studies, which involve limited human exposure, the FDA permits reduced preclinical testing requirements, enabling sponsors to move forward more efficiently with promising candidates ⁸¹²²³.

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7. Regulatory Flexibility

• The FDA provides flexibility in preclinical testing requirements based on the drug's characteristics, the goals of the proposed investigation, and the expected risks. Sponsors are encouraged to tailor their submissions and consult the FDA during pre-IND meetings to discuss specific requirements ¹³¹⁶.

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8. Compliance with Good Laboratory Practices (GLP)

• Toxicology studies must comply with GLP regulations under 21 CFR Part 58. However, the FDA recognizes that some biologics may require exemptions from GLP due to unique animal care requirements or technical expertise needed for certain disease models ¹¹¹⁴.

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Summary

The FDA expects preclinical testing for large molecule drugs to include toxicology, pharmacology, and safety studies tailored to the drug's unique properties and intended use. These studies must comply with GLP and focus on the drug's mechanism of action, immunogenicity, and species-specific responses. Flexibility is provided for exploratory IND studies and biologics with low-risk profiles. Sponsors are encouraged to consult FDA guidance documents, such as ICH S6(R1) and ICH M3, and engage in pre-IND discussions to ensure their preclinical program meets regulatory expectations ^{1257911131415161921232526}.