Opportunities And Challenges Of Mini Pigs As A Nonclinical Large Animal Species

From anatomical and physiological perspectives, miniature pigs share significant similarities with humans in their cardiovascular, urinary, dermatological, and digestive systems. Pigs have been utilized in drug efficacy, pharmacokinetics (PK), toxicology, and medical device evaluation for decades. However, traditional domestic pigs' large size has posed operational challenges, leading to the development of smaller breeds, or miniature pigs, which are easier to handle, safer, and more cost-effective. Common miniature pig breeds include Yucatan, Hanford, Sinclair, and Gottingen. Additionally, genetically engineered miniature pigs carrying human heavy-chain γ1, γ4, and light-chain κ genes have been developed to reduce immunogenicity risks for fully human or humanized antibodies.

Compared to dogs and nonhuman primates (NHPs) like cynomolgus monkeys, the use of miniature pigs in nonclinical drug development has been limited, primarily for transdermal drug delivery studies. Research as early as 2010 suggested miniature pigs could replace dogs or NHPs in nonclinical toxicology studies. By 2014, their use was primarily restricted to small-molecule transdermal delivery and cardiovascular safety assessments. The limited application in biologics can be attributed to the lack of background data, reagents, biomarkers, and limited applicability in developmental toxicity studies.

However, a 2020 survey revealed that 80% of companies considered miniature pigs for small-molecule nonclinical safety testing, and many also evaluated their use in biologics projects. The COVID-19 pandemic highlighted challenges in NHP supply and cost, leading to increased interest in miniature pigs. In 2022, the FDA issued guidelines suggesting alternative nonrodent species for general toxicology studies if scientifically justified. From an animal ethics standpoint, miniature pigs are also a preferred choice over NHPs.

Current Trends and Industry Insights

A recent study, published in Opportunities and Challenges for Use of Minipigs in Nonclinical Pharmaceutical Development, surveyed 21 companies from 2017–2022. Findings indicated that around 50% of companies used miniature pigs in pharmacodynamic studies, while over 75% employed them in PK and toxicology studies-a significant increase compared to earlier surveys.

Miniature pigs are predominantly used in small-molecule research, followed by peptides and small proteins, and least in large proteins or antibody drugs.

Key challenges with miniature pigs include:

• Test Article Requirements: Miniature pigs require 60% more test article than Beagle dogs for dose-range finding and IND-enabling studies, and up to twice as much for long-term toxicology studies. However, for many projects, this is not prohibitive due to sufficient clinical sample preparation.

• Lack of Specific Reagents: The scarcity of reagents for immune toxicity or molecular pathology studies can delay evaluations, although companies are increasingly developing reagents tailored for miniature pigs.

• Background Data Deficiency: Historical control data for miniature pigs are less comprehensive than for dogs or cynomolgus monkeys. However, the increasing use of miniature pigs is gradually alleviating this issue.

• Placental Transfer Challenges: Large molecules generally do not cross the placenta in miniature pigs, complicating reproductive toxicity studies. Potential solutions include studies in genetically engineered rodents or alternative molecular approaches.

Advantages

Despite challenges, miniature pigs offer several advantages:

• Physiological Similarities: Their cardiovascular, metabolic, dermatological, and gastrointestinal systems closely mimic those of humans, making them suitable for various human disease studies.

• Ethical Considerations: Miniature pigs are more ethically acceptable compared to NHPs.

• Practicality in Juvenile Toxicology: Their larger litter sizes and faster sexual maturity (4–7 months) reduce the demand for pregnant animals.

• Application in Novel Therapies: Miniature pigs have been successfully used in human organ transplantation trials, including cardiac and skin grafts.

Several successful applications of miniature pigs in nonclinical studies highlight their versatility:

• Small-Molecule Drug for Atherosclerosis: After Beagle dogs showed adrenal cortical atrophy due to species-specific factors, and cynomolgus monkeys failed to achieve adequate exposure, miniature pigs were used as the primary nonrodent species, receiving regulatory approval.

• Dual-Function Insulin/PCSK9 Inhibitor: Miniature pigs demonstrated better tolerance and higher exposure than cynomolgus monkeys, becoming the preferred species for toxicology studies.

• Recombinant Protein Therapy: Miniature pigs showed similar pharmacological activity to humans and rodents, supporting their selection as the primary nonrodent species despite regulatory scrutiny.

Conclusion

While miniature pigs have limitations, such as higher test article requirements and limited historical data, their physiological similarities to humans and practical advantages make them a promising alternative in nonclinical research. Building a robust research platform for miniature pigs can establish a competitive advantage and pave the way for broader adoption in the future.