Stephanie van Hoppe

175 Summary Membrane transporters are key players in the regulation of homeostasis, cell integrity and metabolism in organisms. The ATP-binding cassette (ABC) efflux transporters and Organic Anion-transporting Polypeptide (OATP) influx transporters are two main superfamilies that are expressed in pharmacologically important organs such as the liver, small intestine, kidney and the blood-brain barrier (BBB). These transporters can transport endogenous and exogenous molecules and thereby are important in the absorption, disposition, elimination and toxicity of many drugs. In this thesis we delved deeper into the pharmacological functions of ABCB1 and ABCG2 in vitro and in vivo for several anti-cancer drugs using specialized cell lines and various knockout and transgenic mouse models. We additionally looked into the pharmacological impact of CYP3A proteins which form one of the main metabolic enzyme complexes. We used various knockout and humanized mouse models to study its effects on a subset of anti- cancer drugs. In chapter 1 of this thesis we provide a brief introduction to the ABC transporters and their tissue localization and their pharmacologic role in the distribution of their substrates. We also introduced the Cytochrome P450 enzymes and the tyrosine kinase inhibitors (TKIs). We gave further insight at the end of the chapter into what we believe would be a more desirable approach for the future, i.e. the development of TKIs that are not substantially transported by ABC transporters. Chapter 2 focusses on the role ABCB1 and ABCG2 play in the distribution of the irreversible TKI afatinib. We have shown that ABCB1 and ABCG2 transport afatinib in vitro , and that in vivo they limit the oral bioavailability and brain accumulation of afatinib. We additionally showed that the liver distribution is not affected heavily by these ABC transporters. In chapter 3 we demonstrated the importance of these ABC transporters, especially ABCB1, for brain accumulation of the irreversible TKI osimertinib and its main active metabolite AZ5104. However, the bioavailability or liver distribution of these compounds was not noticeably affected by these ABC transporters. In chapter 4 we investigated the roles ABCB1 and ABCG2, as well as CYP3A, play in the disposition of the irreversible TKI ibrutinib and its main metabolite, ibrutinib-DiOH. We found that ABCB1 and ABCG2 do not play a significant role in the oral bioavailability of ibrutinib. On the other hand, we showed that CYP3A does restrict the bioavailability of ibrutinib. The brain distribution of ibrutinib as well as ibrutinib-DiOH was clearly limited by ABCB1 activity, whereas the relative distribution to a range of other tissues did not seem to be much affected by either the ABC transporters or CYP3A. Chapter 5 describes the effects of theABC transporters andCYP3Aon thedistribution of ponatinib and its main metabolite, DMP. We demonstrated that ABCB1 and ABCG2 both transport ponatinib in vitro , and that together they affect its brain disposition, but