Metabolic factors determining outcome in chemotherapy : studies with pazopanib

• Main Author: Sharp, Stephanie Lora
• Other Authors: Wolf, C.; Henderson, Colin
• Published: University of Dundee 2014
• Subjects: 616.99
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.613591

Understanding of human pathology has been greatly advanced by the use of ‘model organisms’, such as yeast and Drosophila. While these models have led to great advances in the treatment of human disease, they are limited by variations in physiology, metabolism, and genetic background. The development of humanised mice, in which the gene or genes of interest have been excised from the genome and replaced with the functional human counterpart, may have the potential to bridge the gap between preclinical mouse models and human disease. The work carried out in this thesis utilises a number of transgenic-animal models where the metabolic pathways involved in the metabolism of drugs have either been deleted or humanised in order to delineate the impact that such systems have on drug metabolism, distribution, and efficacy. These pathways include the cytochrome P450-dependent monooxygenase system and the constitutive androstane and pregnane X nuclear receptors. The aims of this work were to assess whether these humanised mouse models better represented human drug metabolism and pharmacokinetics compared to wild-type animals. Using a novel anti-cancer agent pazopanib as a test substrate, the work detailed in this thesis assesses differences in the pharmacokinetic profile of pazopanib in various humanised and knock out animal models, as well as differences in toxicological responses. Furthermore, this project looks at variations in the efficacy of pazopanib in syngeneic tumours in humanised and wild-type mice. The techniques used in this work include liver microsome preparations and drugstability assays in vitro, pharmacokinetic profiling of drugs, and syngeneic tumourgrowth studies in vivo. Drug stability studies in vitro identified a species difference in pazopanib metabolism between wild-type mouse and human liver microsomes. Furthermore, this difference was attenuated in humanised CYP3A4/3A7 mouse liver microsomes when compared with human liver microsomes, suggesting that humanised mice represent a better model for human pazopanib metabolism in vitro. This species difference in metabolism was reflected in in vivo pharmacokinetic studies with humanised CYP3A4/3A7/hCAR/hPXR mice exhibiting significantly decreasedmaximum plasma concentration, clearance and half-life of pazopanib compared to wild-type mice. Finally, this work addresses the efficacy of pazopanib in a mouse derived B16 melanoma tumour growth study in vivo. Pazopanib retarded the growth of melanoma tumours in both wild-type and humanised CYP3A4/3A7/hCAR/hPXR mice. Overall survival was reduced in animals which has been induced using Aroclor-1254, which suggests that induction of the cytochrome P450 system does induce the turnover of pazopanib thereby reducing bioavailability and efficacy in vivo.