My remarks today and the information contained in these slides do not necessarily reflect the official views of FDA.

Possible Criteria that Warrant In Vivo P-Glycoprotein Glycoprotein-Mediated Drug Interaction Studies Based on In Vitro Assessment Lei Zhang, Ph.D. Office of Clinical Pharmacology Office of Translational Sciences Center for Drug Evaluation and Research Food and Drug Administration Disclaimer My remarks today and the information contained in these slides do not necessarily reflect the official views of FDA. 2 1

Outline P-gp substrate Decision i tree Inhibitor considerations P-gp inhibitor Decision tree On-going activities ities P-gp inducer 3 P-gp Substrate Decision Tree 4 2

Decision tree to determine whether an investigational drug is a substrate for P-gp and whether an in vivo drug interaction study with a P-gp inhibitor is needed Bi-directional transport assay Net flux Ratio > 2 Net flux ratio < 2 Is efflux significantly inhibited by 1 or more P-gp inhibitors Poor or non-substrate YES Likely a P-gp substrate NO Other efflux transporters are responsible An in vivo interaction study with a P-gp inhibitor may be warranted Note exceptions BCRP Zhang L et.al., Xenobiotica, 38: 709 724, 2008 5 Selection of Inhibitors Overlap of P-gp and CYP3A inhibitors Inhibition potentcy for either P-gp or CYP3A may not be equal If an NME is a dual substrate Select potent/strong inhibitors for both for worst case scenario 6 3

Overlap of CYP3A and P-gp Inhibitors Strong CYP3A Inhibitors (>5-fold change in AUC) Ritonavir (22%) Voriconazole (15%) Conivaptan (44%) Nefazodone Telithromycin (positive case report) Itraconazole Clarithromycin Ketoconazole* Lopinavir/RIT* Potent P-gp Inhibitors (>50% change in AUC) Moderate CYP3A Inhibitors: Erythromycin Verapamil Weak CYP3A Inhibitors: Amiodarone Quinidine Azithromycin Ranolazine Felodipine In vivo potency for P-gp unknown: Indinavir Troleandomycin Nelfinavir Saquinavir In vivo potency for CYP3A unknown: Carvedilol Data Source: UW DIDB 7 P-gp Inhibitor Decision Tree 8 4

Decision tree to determine whether an investigational drug is an inhibitor of P-gp and whether an in vivo drug interaction study with a P-gp substrate is needed (updated version) Bi-directional transport assay Ntfl Net flux with Ntfl Net flux with [drug] [drug] Determine K i or IC 50 Poor or non-inhibitor [I] 1 /IC 50 (or K i ) > 0.1 [I] 1 /IC 50 (or K i ) < 0.1 or and [I] 2 /IC 50 (or K i ) > 10 [I] 2 /IC 50 (or K i ) < 10 An in vivo interaction study with a P-gp substrate (e.g., digoxin) is recommended An in vivo interaction study with a P-gp substrate is not needed 9 P-gp Inhibition Data Collection Digoxin, a narrow index therapeutic drug, is the recommended probe substrate in the guidance. A database for drugs that have both in vitro and in vivo interaction ti data with digoxin was created. 10 5

In Vivo Data In vivo interaction data with digoxin were collected from literature or NDA packages. Significant in vivo inhibition on oral digoxin pharmacokinetics was defined as an increase of C max or AUC by > 25%. 11 In Vitro Data In vitro IC 50 data for inhibiting digoxin transport t were collected. Two [I]/IC 50 ratios were calculated for each drug, where [I] was: [I] 1 = Total C max at steady-state [I] 2 = Dose divided by a volume of 250 ml 12 6

Drugs that showed significant in vivo inhibition on digoxin (1) Compound % Increase in C max % Increase in AUC [I] 1 /IC 50 [I] 2 /IC 50 Cyclosporin 44% - 1.75 729 Itraconazole 34% 68% 0.73 872 Quinidine 44% - 0.28 64 Zhang L et.al., Xenobiotica, 38(7 8): 709 724, 2008 >0.1 >10 13 Drugs that showed significant in vivo inhibition on digoxin (2) Compound % Increase in C max % Increase in AUC [I] 1 /IC 50 [I] 2 /IC 50 Clarithromycin 83% 64% <0.026 <13.4 0.65 326 Verapamil 44% 50% 0.022 119 Diltiazem 37% 51% 0.024 76 Ranolazine 46% 60% 0.043 47.5 Zhang L et.al., Xenobiotica, 38(7 8): 709 724, 2008 <0.1 >10 14 7

Drugs that did not show significant in vivo inhibition on digoxin Compound % Increase in C max % Increase in AUC [I] 1 /IC 50 [I] 2 /IC 50 Atorvastatin 20% 15% < 0.00049 < 2.65 Rosuvastatin 4% 4% <0.00017 <1.60 Losartan 13% 6% 0.0031 2.78 Omeprazole 10% 10% 0.022 2.32 Sitagliptin 18% 11% < 0.0019 < 1.53 Zhang L et.al., Xenobiotica, 38(7 8): 709 724, 2008 <0.1 <10 15 Results Drugs that had [I] 1 /IC50 > 0.1 or [I] 2 /IC50 >10 showed significant interaction with digoxin. Drugs that had [I] 1 /IC50 < 0.1 and [I] 2 /IC50 <10 did not show significant interaction with digoxin. Three false negatives: talinolol, captopril, and felodipine Zhang L, et.al., Xenobiotica, 38: 709 724, 2008 Fenner K, et al., CPT 85, 173-181, 2009 16 8

False Negatives Compound Talinolol % Increase in Cmax C max 45% % Increase in AUC [I] 1 /IC 50 [I] 2 /IC 50 18% 0.0024 4.17 Felodipne 34% 18% 0.001 3.59 Captopril* 59% 39% < 0.0046 < 2.30 * In healthy young males, there in no interaction with digoxin (Digoxin Label). Need further attention: Mechanisms of inhibition involving other transporters? - Digoxin is also a substrate of OATP 17 False Positives Fenner K, et al., CPT 85, 173-181, 2009 The inhibition effect is canceled out by induction? Troglitazone is a CYP3A inducer and PXR activator (likely a P-gp inducer?) Nicardipine is a PXR activator (likely a P-gp inducer?) 18 9

Limitations Only consider P-gp inhibition. No interplay between metabolism and P-gp or induction could be projected. In vitro IC 50 determination may be different from different labs which could impact the I/IC 50 ratios. Only for immediate-release formulation. May not work for investigator drugs that are prodrugs. 19 200 ** [I] 2 /IC 50 Ratios: < 5 > 5 150 IC (µm) 50 100 Digoxin NSF Caco-2 50 Digoxin ER caco-2 Cal-AM MDCK-MDR1 Digoxin B-A MDCK-MDR1 Cal-AM MDCK-MDR1 GSK (B-A) Digoxin LLC-GA5-COL150-MDR1 Caco-2 Digoxin 0 Amiodarone asd Cyclosporin Diltiazem Itraconazole Ketoconazole Nitrendipine Quinidine Ritonavir Talinolol Verapamil Nicardipine Carvedilol R123 NIH-3T3-G185 MDCK-MDR1 Dig Caco-2 2Di Dig **Talinolol there are two IC50 values that lie beyond the Y axis scale) 20 Caroline Lee, et. al. (Poster #1012) 10

How good is the prediction based on the Decision Tree? [I] 1 /IC50 > 0.1 or [I] 2 /IC50 >10 for positive P-gp inhibition False negative: 19% (3/16) False positive: 27% (3/11) Zhang L et.al., Xenobiotica, 38: 709 724, 2008 Fenner et al., CPT 85 (2), 173-181, 2009 21 How well do we predict P450 inhibition using I max /Ki > 0.1? False Negative: 37% (15/41) False Positive: 33% (3/9) ) Data Source: Ito et al., AAPS PharmSci 2002; 4 (3), Article 20 22 11

How well do we predict P450 inhibition using I in, max, u /Ki? False Negative: 17% %(7/41) False Positive: 44% (4/9) Data Source: Ito et al., AAPS PharmSci 2002; 4 (3), Article 20 23 On-going Activities (1) Following DIA/FDA Critical Path Transporter workshop, a working group is formed to further study IC 50 for P-gp inhibition Led by Caroline Lee Interested scientists from industry and FDA Caco-2 MDR1-LLCPK MDR1-MDCK Vesicle 24 12

On-going Activities (2) Study the same panel of 16 compounds on digoxin transport inhibition P-gp OATP? Determine the potential for inhibiting OATP as well? IC 50 calculation methods 25 P-gp Inducer Evaluation Methods for in vitro evaluation for P-gp induction are not well understood. The P-gp induction potential of an investigational drug can only be evaluated in vivo. Because of similarities in the mechanism of CYP3A and P-gp induction, information from test of CYP3A inducibility can inform decisions about P-gp. 26 13

P-gp Inducer Evaluation (Cont d) If an investigational drug is found not to induce CYP3A in vitro, no further tests of CYP3A and P- gp induction in vivo are necessary. If a study of the investigational drug s effect on CYP3A activity in vivo is indicated from a positive in vitro screen, but the drug is shown not to induce CYP3A in vivo, then no further test of P-gp induction in vivo is necessary. However, if the in vivo CYP3A induction test t is positive, then an additional study of the investigation drug s effect on a P-gp probe substrate is recommended. 27 Summary The criteria proposed in the decision trees provide a starting point for identifying compounds having a potential to interact with P-gp. Collect more data to further evaluate these prediction criteria. In vitro IC 50 determination needs to be standardized. Appropriate controls are needed to compare results from different laboratories. 28 14

Acknowledgments Drs. Shiew-Mei Huang and Larry Lesko International Drug Transporter Working Group Members 29 Backup slides 30 15

Drug interaction Number Recent Data Sugiyama (Xenobiotica, in press) Our decision tree: DIN>2.5 L 31 Recent Data CYP3A4 inhibitors with a DIN below 2.8 L have a low risk of interacting with substrates t which h exhibit intestinal ti firstpass metabolism and those with a DIN above 9.4 L have a high risk P-gp inhibitors with a DIN below 10.8 L have a low risk of interacting with P-gp substrates and those with a DIN above 27.9 L have a high risk; The DIN indexes 2.8 L and 9.4 L for CYP3A4 and 10.8 L and 27.9 L for P-gp, were validated by data from dual CYP3A4/P-gp substrates Sugiyama (Xenobiotica, in press) 32 16

Sugiyama (Xenobiotica, in press) 33 False Negatives 34 17

False Positives Fenner K, et al., CPT 85, 173-181, 2009 35 Differences in IC 50 values may caused by using different substrate, t cell system, calculation method, etc. Despite the varying IC 50 values reported in the literature, in general, compounds cluster in either the unshaded region (predict interaction) or the shaded region (predict no interaction) 36 18

Alternative In Vitro Assay Vesicles may be used to evaluate the role of efflux transporters such as P- gp as an alternative method if molecules show low permeability. 37 How well do we predict P450 inhibition using I max, u /Ki? False Negative: 66% (27/41) False Positive: 11% (1/9) 38 19

60 50 ** [I]/IC 50 Ratios: < 0.1 > 0.1 IC 50 (µm M) 40 30 20 10 Digoxin NSF Caco-2 Digoxin ER caco-2 Cal-AM MDCK-MDR1 MDR1 Digoxin B-A MDCK-MDR1 Cal-AM MDCK-MDR1 GSK (B-A) Digoxin LLC-GA5-COL150-MDR1 Caco-2 Digoxin R123 NIH-3T3-G185 MDCK-MDR1 Dig Caco-2 Dig 0 sfg Amiodarone Amiodarone Cyclosporin Cyclosporin Diltiazem Diltiazem Itraconazole Itraconazole Ketoconazole Ketoconazole Nitrendipine Nitrendipine Quinidine Quinidine Ritonavir Ritonavir Talinolol Talinolol Verapamil Verapamil Nicardipine Nicardipine Carvedilol Carvedilol **Talinolol there are two IC50 values that lie beyond the Y axis scale) 39 Courtesy: Caroline Lee (Poster) Draft Guidance (http://www.fda.gov/cder/guidance/6695dft.pdf): Decision tree to determine whether an investigational drug is an inhibitor of P-gp and whether an in vivo drug interaction study with a P-gp substrate is needed Bi-directional transport assay Net flux with [drug] Net flux [drug] with Determine K i or IC 50 Poor or non-inhibitor [I]/IC 50 (or K i ) > 0.1 [I]/IC 50 (or K i ) < 0.1 An in vivo interaction study with a P-gp substrate (e.g., digoxin) is recommended An in vivo interaction study with a P-gp substrate is not needed 40 20