# Presentation: 723643

## Transporters:  Focus on OATP1B1 and Selected Renal Transporters

**Kathy Giacomini**
**University of California, San Francisco**

## OCTs

- OCTNs OATs

- PEPT1
- PEPT2

*Organic *
*Ions*

- CNT1
- CNT2
- CNT3

*Nucleosides*

- ENT1
- ENT2

*Nucleosides*

- DAT
- NET
- GAT1
- SERT

*Neurotransmitters*

- OATPs

*Organic Anions *

- NRAMP1
- DMT1
- IREG1

*Oligopeptides*

*Fe**+++** *

- MATE1-2

- MDR1
- MDR3
- BSEP

- MRP1-4

*Hydrophobic Cations*

*Hydrophobic Anions*

*Organic Cations*

- VMAT
- VAChT

**Selected Membrane Transporters in Human Genome**

- ABC Family ~ 50

- SLC Family ~ 300

## Transporters in the Liver

**Transporters in the Liver**

**OAT2**

**OATP**
**1B1, 1B3**
** ****2B1**

**NTCP**

**OCT1**

**MRP1,3**

**BCRP**

**BSEP**

**MRP2**

**MDR1,3**

**Hepatocyte**

**Bile**

**Blood**

## Is OATP1B1 Important for Drug-Drug Interactions?

- What is the evidence?
-  In vitro evidence
-  In vivo evidence

## Selected Substrates of OATPs

- nateglinide, repaglinide, rifampin
_**OATP1B3:**_  digoxin, fexofenadine,
- fluvastatin, pravastatin,methotrexate,
- paclitaxel, rifampin
_**OATP2B1:**_  benzylpenicillin, fexofenadine, fluvastatin,
- pravastatin

**Selected Substrates of OATPs**

**OATP**
**1B3**

**OATP**
**2B1**

**OATP**
**1B1**

## Is OATP1B1 Important for Drug-Drug Interactions?

- What is the evidence?
-  In vitro evidence
-  In vivo evidence

## In Vivo Evidence

**Genetic Studies**
-  Knockout/transgenic Mice
-  Polymorphisms in Humans
**Chemical Inhibition Studies**

## In Vivo Evidence

**Genetic Studies**
-  Knockout Mice: Not applicable
-  Polymorphisms in Humans
**Chemical Inhibition Studies:** Specific inhibitors
- 			not available

## Individuals with Polymorphisms of OATP1B1

**Have Higher Plasma Levels of Repaglinide**

- Niemi M. et al, Clin Pharmacol Ther 2005; 77:468-78

**Homozygous 521CC**

**Homozygous 521TT**

## Individuals with Polymorphisms of ABCB1

**Individuals with Polymorphisms of ABCB1**
**Have Similar Plasma Levels of Repaglinide**

- Niemi M. et al, Clin Pharmacol Ther 2005; 77:468-78

## Individuals with Polymorphisms of CYP3A5

- Niemi M. et al, Clin Pharmacol Ther 2005; 77:468-78

**Individuals with Polymorphisms of CYP3A5**
**Have Similar Plasma Levels of Repaglinide**

## Individuals with Polymorphisms of OATP1B1

- Niemi M. et al, British Journal of Clinical Pharmacology 2005, 59: 602-604

**Individuals with Polymorphisms of OATP1B1**
**Have Higher Plasma Levels of Fexofenadine**

**Homozygous 521CC**

**Homozygous 521TT**

## Individuals with Polymorphisms of OATP1B1

- Niemi M. et al, Pharmacogenetics. 2004 Jul;14(7):429-40.

**Individuals with Polymorphisms of OATP1B1**
**Have Higher Plasma Levels of Pravastatin**

**11187GA**

**11187GG**

## Individuals with Polymorphisms of OATP1B1

- Niemi M. et al, Pharmacogenetics. 2004 Jul;14(7):429-40.

**Individuals with Polymorphisms of OATP1B1**
**Have Higher Plasma Levels of Pravastatin**

**521CC**

**521TC**

**521TT**

## Individuals with Polymorphisms of OATP1B1

- Niemi M. et al, Pharmacogenetics. 2004 Jul;14(7):429-40.

**Individuals with Polymorphisms of OATP1B1**
**Have Higher Plasma Levels of Pravastatin**

***17 Heterozygotes**

## OATP1B1

**Genetic Studies:**  Compelling Evidence that
- 	OATP1B1 Plays a Role in Drug Disposition
**Chemical Inhibition Studies:** Specific inhibitors
- 			not available

## Drug-Drug Interactions with Repaglinide

- Itraconazole: CYP3A4 inhibitor P-gp inhibitor
- Gemfibrozil: CYP2C8 and OATP1B1 inhibitor

- Niemi M. et al, Diabetologia. 2003 Mar;46(3):347-51.

## Increase in Plasma Levels of Repaglinide by Trimethoprim, A CYP2C8 Inhibitor

**+trimethoprim**

- Trimethoprim: CYP2C8 inhibitor

- Niemi M. et al, Br J Clin Pharmacol. 2004 Apr;57(4):441-7

**Increase in Plasma Levels of Repaglinide by Trimethoprim, A CYP2C8 Inhibitor**

## OATP1B1

**Genetic Studies:**  Compelling evidence that
- 	OATP1B1 plays a role in drug disposition
**Chemical Inhibition Studies:** Inhibitor studies are
- 	suggestive, but not definitive.

## Recommendations to Consider

-   Perform in vitro studies in cells expressing   	OATP1B1- Assess if NME is substrate/inhibitor
-   If *in vitro* data show evidence of interaction
- with OATP1B1
-   Substrate:  Possibly perform clinical Interaction study    with gemfibrozil or rifampicin as inhibitor of NME
-   Inhibitor:  Possibly perform clinical Interaction study
- 	with NME as inhibitor of fexofenadine (no metabolism)
- 	or atorvastatin/pravastatin

## Selected Membrane Transporters in Human Genome

- OATs

- PEPT1
- PEPT2

*Organic *
*Ions*

- CNT1
- CNT2
- CNT3

*Nucleosides*

- ENT1
- ENT2

*Nucleosides*

- DAT
- NET
- GAT1
- SERT

*Neurotransmitters*

- OATPs

*Organic Anions *

- NRAMP1
- DMT1
- IREG1

*Oligopeptides*

*Fe**+++** *

- MATE1-2

- MDR1
- MDR3
- BSEP

- MRP1-4

*Hydrophobic Cations*

*Hydrophobic Anions*

*Organic Cations*

- VMAT
- VAChT

**Selected Membrane Transporters in Human Genome**

- ABC Family ~ 50

- SLC Family ~ 300

## Renal Drug Transporters

**Renal Drug Transporters**

- Li M *et al. Expert Opin Drug Metab Toxicol* 2006

**Urine **

**Blood **

**Notes:**
Almost all of the clinical drug-drug interactions for which specific renal drug transporters have been implicated are substrates of OCTs or OATs.  This is not surprising, given that these are the most extensively studied drug transporters in the kidney.  (Except MDR1, which although it is expressed in kidney, has not been shown to have a major influence of renal drug elimination.)

## Expression of Various Renal Transporters in Human Kidney

## OCT2, OAT1 and OAT3:  Important for Drug-Drug Interactions?

- What is the evidence?
-  In vitro evidence
-  In vivo evidence

## Selected Substrates of OATs and OCTs

**OAT1:****  acyclovir, adefovir, cidofovir, methotrexate**
**OAT3:**  **estrone sulfate, methotrexate, cimetidine, tetracycline**
**OCT2:****  ****amantadine, memantine, cimetidine, metformin**

**Selected Substrates of OATs and OCTs**

**OAT3**

**OAT1**

**OCT2**

**Notes:**
OAT1 substrates: acyclovir and ganciclovir(hOAT1 stable S2 cells, Takeda et al. JPET 2002); adefovir and cidofovir (hOAT1 stable CHO cells, Ho and Cihlar papers); methotrexate (OAT1-injected oocytes, Uwai et al. FEBS Lett 1998)
OAT3 substrates: estrone sulfate, methotrexate, cimetidine (OAT3-injected oocytes, Cha et al. Mol Pharmacol 2001); tetracycline (hOAT3 stable S2 cells, Babu et al. Jpn J Pharmacol 2002)
OCT2 substrates: amantadine, memantine (hOCT2-injected oocytes, Busch et al. Mol Pharmacol 1998); cimetidine (hOCT2 stable HEK293 cells, Urakami et al. J Am Soc Nephrol 2002); metformin (oocytes, Dresser et al. Pharm Res 2002)

## In Vivo Evidence

- Genetic Studies
-  Knockout/transgenic Mice: Available
-  Polymorphisms in Humans
- Chemical Inhibition Studies: Selective
- but not specific inhibitors are available

## Knockout Mouse Models

**Oat1-/- Mice**
-   Decreased CLR of para-aminohippurate,  furosemide, endogenous organic anions   (Eraly et al. J Biol Chem 2006)
**Oat3-/- Mice**
-   Reduced uptake of para-aminohippurate,    estrone sulfate in kidney slices and choroid plexus    (Sweet et al. J Biol Chem 2002 ; Sykes et al. AJP    Ren Physiol 2004)
**Oct1/2-/- Mice**
-   Complete loss of active secretion of  tetraethylammonium  (Jonker et al. Mol Cell Biol 2003)

## Preliminary Data on Cefotaxime and GeneticVariants of OAT3: Unpublished Data

**Preliminary Data on Cefotaxime and Genetic****Variants of OAT3: Unpublished Data**

## Preliminary Data on Gabapentin and GeneticVariants of OCTN1: Unpublished Data

**Preliminary Data on Gabapentin and Genetic****Variants of OCTN1: Unpublished Data**

**Cells**

**Clinical**

## Preliminary Data on Gabapentin and GeneticVariants of OCTN1: Unpublished Data

**Preliminary Data on Gabapentin and Genetic****Variants of OCTN1: Unpublished Data**

**Cells**

**Clinical**

## In Vivo Evidence

- Genetic Studies
-  Knockout/transgenic Mice: Available
-  Polymorphisms in Humans
- Chemical Inhibition Studies: Selective
- but not specific inhibitors are available

**Drug-Drug Interactions Related**** to Renal Drug Transporters**

- Organic Anion Transporters (OATs):
- Cefazolin/Probenecid (~38% ↓ cefazolin CLR)
- (Spina *et al. Ann Pharmacother* 2003, Sakurai *et al. Pharm Res* 2004)
- Organic Cation Transporters (OCTs):
- Procainamide/Cimetidine (42% ↓ procainamide CLR)
- (Somogyi *et al. Eur J Clin Pharmacol* 1983)
- Metformin/Cimetidine (28% ↓ metformin CLR)
- (Somogyi *et al. Br J Clin Pharmacol* 1987)

**Notes:**
Our understanding of drug-drug interactions operating at the level of renal transport is slowly maturing, and is based on the synthesis of clinical pharmacokinetic information and data obtained from in vitro studies of specific cloned renal transporters.
Coadministration with probenecid results in roughly 2-fold increased half-life of cefazolin, increasing exposure and improving therapeutic effect; this is believed to be due to inhibition of OAT3, since cefazolin is not an OAT1 substrate
Similarly, inhibition of OATs is thought to explain the decreased renal clearance of cidofovir on coadministration with probenecid; here, the interaction is also used for therapeutic benefit – however, instead of increasing efficacy (as with cefazolin), the interaction causes a decrease in cidofovir nephrotoxicity.  This is explained by the fact that OAT1 (and OAT3) is (are) basolateral uptake transporters, so that inhibition of OATs by probenecid decreases accumulation of cidofovir in the site of toxicity despite increasing overall systemic exposure to the drug.
Procainamide renal clearance is decreased by 42% on coadministration of cimetidine, a nonspecific inhibitor of OCTs (and OAT3); however, only OCT2 is both a) expressed abundantly in human kidney, and b) accepts procainamide as a substrate.
Metformin renal clearance is decreased 28% on coadminstration of cimetidine.  Metformin is a substrate of OCT2, which is the predominant OCT isoform in human kidney.

## Other DDIs Potentially Resulting From Renal Transporter Interactions

- Methotrexate/NSAIDs
- Furosemide/Probenecid
- Pindolol/Cimetidine
- Amiloride/Cimetidine
- Procainamide/Trimethoprim

**Charge Specific**
**Inhibitors**

**Notes:**
Other drug-drug interactions are more complex, and can involve interactions at the level of intestinal absorption, metabolism, and/or protein binding as well as renal drug transport.

## Recommendations to Consider

**Recommendations to Consider**

-  Perform in vitro studies in cells expressing  OAT1, OAT3 or OCT2- Assess if NME is substrate/inhibitor
-   If *in vitro* data show evidence of interaction with   OCT2, OAT1 or OAT3
-   Substrate of OCT2: Cimetidine inhibition
-   Inhibitor of OCT2:  Metformin
-   Substrate of OATs:  Probenecid
-   Inhibitor of OATs:  Cefazolin