Assessing the viability of in vitro and in vivo oral bioavailability screening techniques

Wyatt James Roth, Purdue University

Abstract

Improving pharmaceutical research and development (R&D) strategies to increase productivity and reduce expenditures is one of the most important issues facing the pharmaceutical industry today. With heightened pressure from regulatory agencies, loss of revenue due to patent expirations, and an evolving healthcare system, companies must become more efficient at bringing new molecules to the market. Currently, a considerable amount of emphasis is being placed on improving efficiency and productivity in the early stages of discovery and development with an aim to decrease attrition rates of compounds in late-stage clinical development. Compounds that fail at this stage generally do so because of poor oral bioavailability (Phase I), lack of efficacy in vivo (Phase II and III), or unexpected toxicity that was not predicted or observed based on animal models (Phase II and III). In order to reduce the number of failures, better in vitro and in vivo models are needed in preclinical development to characterize the properties and predict the developability of new molecular entities (NMEs). The need for improving preclinical testing by focusing on translation/prediction of clinical outcomes has long been considered an area of critical need for the pharmaceutical industry. This dissertation focuses on the optimization and utilization of two preclinical models that can be used to screen NMEs for optimal development properties. The first section (Chapters 1 and 2) discusses the use of the Caco-2 cell line as an in vitro model to predict the absorption of orally administered drugs. Chapter 1 primarily focuses on background information and explains the major advantages and limitations of utilizing the Caco-2 model in preclinical studies. Chapter 2 discusses the problem of variability associated with the Caco-2 cell line with a specific emphasis on variability associated with cell culture conditions, an issue that often limits inter- and sometimes intra-laboratory comparisons. A detailed study is presented in which two Caco-2 sources, were cultured with different growth media. Differences in drug transporter and metabolizing enzyme mRNA expression and functional transport data as a function of source and media were determined. The second section of this dissertation (Chapters 3, 4, and 5) focuses on the utilization of the porcine model as a potential in vivo screening tool for preclinical pharmacokinetic (PK) testing. Chapter 3 explains the rationale behind utilizing pigs as preclinical animal models, including a comparison of the gastrointestinal tracts of various mammalian species that are currently used during pharmaceutical testing. Additionally, Chapter 3 examines PK testing and analysis of the antibiotic rifampin in both adult and juvenile pigs. Results indicated significant similarities between the PK of pigs and humans. Furthermore, age-based changes in porcine PK correlated well with age-based changes in human PK. Based on these similarities, we hypothesized that juvenile pigs could be used as preclinical surrogates for human children during pediatric drug development and PK testing. Consequently, Chapters 4 and 5 discuss the development, optimization, and in vivo characterization in juvenile pigs of novel pediatric dosage forms of rifampin. Chapter 4 examines the feasibility of orally disintegrating films (ODFs), while Chapter 5 focuses on orally disintegrating tablets (ODTs) of rifampin. Finally, Chapter 6 provides brief concluding remarks and offers future perspectives on the projects presented in this dissertation. It is our laboratory's working hypothesis that a better understanding of the advantages and limitations of preclinical models will allow pharmaceutical scientists to increase efficiency and decrease compound attrition during drug development.

Degree

Ph.D.

Advisors

Knipp, Purdue University.

Subject Area

Pharmaceutical sciences

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