© Copyright 2019 Savannah Jane Kerr McFeely Clinical Significance and Regulatory Framework for the Evaluation of Organic Anion Transporting Polypeptide 1B-Based Drug-Drug Interactions Savannah Jane Kerr McFeely A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2019 Reading Committee: Isabelle Ragueneau-Majlessi, Chair Jashvant Unadkat Bhagwat Prasad Program Authorized to Offer Degree: Pharmaceutics University of Washington Abstract Clinical Significance and Regulatory Framework for the Evaluation of Organic Anion Transporting Polypeptide 1B-Based Drug-Drug Interactions Savannah Jane Kerr McFeely Chair of the Supervisory Committee: Dr. Isabelle Ragueneau-Majlessi Department of Pharmaceutics This dissertation research aims to conduct a comprehensive analysis of the clinical role of organic anion transporting polypeptides (OATPs) 1B1 and 1B3 and the regulatory approach for their evaluation. The work included here has identified the most relevant clinical substrates and inhibitors. Additionally, the contributing factors in the variability of in vitro inhibition constants as well as real-world implications for OATP1B1/1B3 drug-drug interactions are discussed. In Chapter 2, six compounds were identified as potential clinical markers of OATP1B1/1B3 activity through the use of a novel indexing system. These drugs were identified from a list of 34 clinical substrates identified from a thorough analysis of the available in vitro and in vivo data. These findings also suggest that the risk for comedication interactions involve drugs from multiple therapeutic areas showing a reliance on hepatic uptake via the OATP transporters. Chapters 3 seeks to better understand the variability of in vitro inhibition data. By analyzing available OATP1B1/1B3 IC50 values, the primary contributing factors to in vitro variability were identified as the cell system used and inclusion of a preincubation with the inhibitor. The variability of the overall dataset (highest IC50 relative to the lowest) was reduced from 12.35 to 5.23 when both factors were considered. This variability, however, did not directly translate to clinical predictions and the calculated R-values did not show a significant shift relative to the FDA cut-off of 1.1 when these parameters were considered. The goal of Chapter 4 was to identify clinical inhibitors of OATP1B1/1B3 and potential regulatory index drugs. Through the analysis of available clinical and preclinical data, 13 drugs and nine combination treatments were found to be clinical inhibitors. From these clinical inhibitors, two drugs were identified as potential clinical index inhibitors. While no novel index inhibitors were found, this work supports the inclusion of rifampin and cyclosporine as selective and broad-spectrum inhibitors, respectively, and again illustrates the broad range of therapeutic areas that should be considered for comedication studies. The impact of OATP1B1/1B3 inhibition on patients, specifically those in low income countries, is discussed in Chapter 5. As the potent OATP1B1/1B3 inhibitor rifampin is part of the recommended treatment regimen for tuberculosis, this chapter evaluated the complexities of DDI management from pharmacological standpoints and illustrated the unique barriers to effective management of DDIs, such as the challenges of co- infection and treatment settings. The use of modeling and simulation techniques are discussed, as they can facilitate the implementation of optimal treatments for infectious diseases at the individual patient level. This dissertation research has improved our understanding of the clinical relevance of OATP1B1/1B3. The implications of the broad-reaching OATP1B1/1B3 interaction profile was discussed using rifampin to illustrate the complications that can arise from comedication scenarios. Overall, this data can be used to improve the evaluation of OATP1B1/1B3 in drug disposition and potentially mitigate the risk of DDIs that could compromise patient safety and drug efficacy. TABLE OF CONTENTS Chapter 1. Introduction ................................................................................................................... 9 1.1 Background ..................................................................................................................... 9 1.1.1 Introduction ................................................................................................................. 9 1.1.2 Expression and Function ............................................................................................. 9 1.1.3 Substrate and Inhibitor Specificity............................................................................ 11 1.1.4 Pharmacogenetics ..................................................................................................... 12 1.1.5 Drug-Drug and Food-Drug Interactions ................................................................... 13 1.1.6 Current Regulatory Perspective ................................................................................ 16 1.2 Hypothesis and Specific Aims ...................................................................................... 17 Chapter 2. Identification and Evaluation of Clinical Substrates of Organic Anion Transporting Polypeptides 1B1 and 1B3 ............................................................................................................ 23 2.1 Methods......................................................................................................................... 24 2.1.1 Clinical Substrate Determination .............................................................................. 24 2.1.2 Data Refinement ....................................................................................................... 26 2.1.3 Clinical Substrate Rank Ordering ............................................................................. 27 2.2 Results ........................................................................................................................... 29 2.2.1 In Vitro Substrates of OATP1B1/1B3 ...................................................................... 29 2.2.2 Clinical DDIs Potentially Attributable to OATP1B1/1B3 ....................................... 30 2.2.3 SLCO1B1 and SLCO1B3 PGx studies ...................................................................... 30 2.2.4 Clinical Impact of OATP1B1/1B3 Inhibition ........................................................... 31 i 2.2.5 Clinical Marker Substrate Identification ................................................................... 33 2.2.6 Comparison of Clinical Substrates to ECCS Classification ..................................... 34 2.3 Discussion ..................................................................................................................... 34 Chapter 3. Variability In In Vitro Oatp1B1/1B3 Inhibition Data: Impact Of Incubation Conditions On Variability And Subsequent Drug Interaction Predictions ................................... 47 3.1 Introduction ................................................................................................................... 47 3.2 Methods......................................................................................................................... 47 3.3 Results ........................................................................................................................... 48 3.3.1 IC50 Variability.......................................................................................................... 48 3.3.2 R-Value Variability ................................................................................................... 50 3.4 Discussion ..................................................................................................................... 51 Chapter 4. Inhibitors of Organic Anion Transporting Polypeptides 1B1 and 1B3 – Clinical Relevance and Regulatory Perspective ......................................................................................... 73 4.1 Introduction ................................................................................................................... 73 4.2 Methods......................................................................................................................... 74 4.2.1 In Vitro Data ............................................................................................................. 74 4.2.2 Clinical DDI Data ..................................................................................................... 74 4.2.3 In Vitro to In Vivo Predictions .................................................................................. 75 4.2.4 Clinical Data Refinement .......................................................................................... 75 4.2.5 Identification of Clinical Index Inhibitors ................................................................ 76 4.3 Results ........................................................................................................................... 77 4.3.1 In Vitro Inhibitors of OATP1B1/1B3 ....................................................................... 77 ii 4.3.2 Identification of Clinical Inhibitors of OATP1B1/1B3 ............................................ 78 4.3.3 Clinical Index Inhibitors of OATP1B1/1B3 ............................................................. 80 4.4 Discussion ....................................................................................................................