Tamoxifen, Endoxifen, and CYP2D6

Sally Usdin Yasuda, MS, PharmDSenior Reviewer, Division of Clinical Pharmacology 1 Office of Clinical PharmacologyCenter for Drug Evaluation and Research Food and Drug Administration

Clinical Pharmacology Subcommittee October 18, 2006Rockville, Maryland

Outline

Exposure to tamoxifen and metabolites Exposure to tamoxifen and metabolites after administration of tamoxifenafter administration of tamoxifen

Pharmacology of tamoxifen, endoxifen, Pharmacology of tamoxifen, endoxifen, and other metabolitesand other metabolites

CYP2D6-mediated metabolism of CYP2D6-mediated metabolism of tamoxifen and formation of endoxifen tamoxifen and formation of endoxifen in vitroin vitro

Role of CYP2D6 in formation of Role of CYP2D6 in formation of endoxifen endoxifen in vivoin vivo– CYP2D6 genotypeCYP2D6 genotype– Strong Inhibitors of CYP2D6Strong Inhibitors of CYP2D6

Case Report

45 year-old woman presented with 45 year-old woman presented with intense, intolerable hot flashes after intense, intolerable hot flashes after being prescribed 20 mg of tamoxifen per being prescribed 20 mg of tamoxifen per day for a week.day for a week.

Placed on 10 mg per day of paroxetine Placed on 10 mg per day of paroxetine for depressionfor depression

Resolution of hot flashes within a weekResolution of hot flashes within a week Hot flashes resumed when taken off Hot flashes resumed when taken off

paroxetineparoxetine

Personal Communication from David Flockhart

Classic Understanding of Tamoxifen Pharmacology

Estradiol (E2)

E2-ER

ERE

Tamoxifen

4OH-Tam-ER

4OH-Tam2D6

Antagonism:BreastCNS

Agonism:BoneLiverUterus

Hypothesis: CYP2D6 inhibition interferes with formation of 4-OH-tamoxifen 12 women with hx of breast cancer 12 women with hx of breast cancer

receiving tamoxifen (20 mg/day) as receiving tamoxifen (20 mg/day) as adjuvant treatment for at least 4 adjuvant treatment for at least 4 weeks before starting the studyweeks before starting the study– History of troublesome hot flashes for History of troublesome hot flashes for

which treatment with a non-hormonal which treatment with a non-hormonal agent was considered to be appropriateagent was considered to be appropriate

Blood samples collected before and Blood samples collected before and after 4 weeks of co-administration of after 4 weeks of co-administration of tamoxifen with 10 mg/day paroxetinetamoxifen with 10 mg/day paroxetine

Paroxetine Administration Decreased the Concentration of One Metabolite

Before

After

4OHTam

X

X

As modified from Stearns et al.

JNCI 2003: 95:1758-1764.

X

X

Separated, purified, identified and synthesized metabolite X:

4-hydroxy-N-desmethyl tamoxifen(Endoxifen)

Concentration of endoxifen is ~ 10x > 4-OH-tamoxifen

Paroxetine and CYP2D6 genotype change the plasma concentrations of endoxifen (but not of tamoxifen, N-desmethyl, or 4-hydroxy-tamoxifen )

from Stearns et al. JNCI 2003: 95:1758-1764, as communicated by D. Flockhart

Endoxifen

0

10

20

30

40

50

60

70

Before After

En

do

xife

n (

nM

)

p = 0.004

4-OH Tamoxifen

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Before After

4-O

H T

am

ox

ife

n (

nM

)

What is the relative pharmacological

activity of tamoxifen and its metabolites? Tamoxifen and N-desmethyl-tamoxifen Tamoxifen and N-desmethyl-tamoxifen

have similar pharmacologic activityhave similar pharmacologic activity11

4-OH-tamoxifen is 30-100 times more 4-OH-tamoxifen is 30-100 times more potent as antiestrogen than tamoxifenpotent as antiestrogen than tamoxifen22

Endoxifen is equipotent to 4-OH-tamoxifen (and has 5-10x higher concentration)

1Nolvadex (Tamoxifen Citrate) label. 9-27-2005. Wilmington, Delaware, AstraZeneca Pharmaceuticals LP. 2Coezy E, Borgna JL, and Rochefort H. Cancer Res. 1982;4:317-23.

Antiestrogen (M)plus 2nM FluormoneTM

1e-9

2e-9

5e-9

1e-8

2e-8

5e-8

1e-7

2e-7

5e-7

1e-6

Pol

ariz

atio

n (u

nits

)

100

150

200

250

300

4OH NDes tam4OH tamTamoxifen

4-OH-Tamoxifen and 4-OH-N-Des-Tamoxifen have equal affinities for Estrogen Receptor α

Johnson MD, et al. Breast Cancer Research and Treatment, 2004; 85:151-159.

Endoxifen and 4-OH-Tamoxifen are Equipotent as Inhibitors of Estrogen Stimulated Cell Proliferation in MCF7 Cells

Stearns V et al. JNCI 2003; 95:1758-64

In vitro studies suggest N-desmethyl-TAM accounts for majority of primary TAM oxidation

Desta et al. JPET 2004; 310:1062-1075

0

0.5

1

1.5

2

2.5

3

3.5

HG23 HG112 HG06

HLMs

Cli

nt

(mM

/min

/mg

pro

tein

)

0

20

40

60

80

100

120

140

160

CY

P2

D6

ac

tiv

ity

(p

mo

l/m

in/m

g p

rote

in)

Clint (Vmax/Km)

CYP2D6 activity

Desta et al. JPET 2004; 310:1062-1075 and personal communication from D. Flockhart

CYP2D6 is the principal route of metabolism to Endoxifen

modified from Stearns et al. JNCI 2003: 95:1758-1764

CYP3A4

Pharmacogenetics of CYP2D6 (debriosquine metabolic ratio)

Alvan G, Bertilsson L, Dahl M.-L., Ingleman-Sundber M, and Sjöqvist F. Drug Metab Sip 2001; 29:580-585

CYP2D6 Genotype, CYP2D6 Inhibitors, and Tamoxifen Exposure 80 pre- and postmenopausal women with newly 80 pre- and postmenopausal women with newly

diagnosed breast cancer starting tamoxifen (20 diagnosed breast cancer starting tamoxifen (20 mg/day) as adjuvant therapymg/day) as adjuvant therapy

Blood samples for determination of tamoxifen and Blood samples for determination of tamoxifen and metabolites in plasmametabolites in plasma

Genotype functional and variant alleles of:Genotype functional and variant alleles of:– CYP3A5 (*1, *3)CYP3A5 (*1, *3)– CYP2D6 (*1, *3, *4, *5, *6)CYP2D6 (*1, *3, *4, *5, *6)– CYP2C9 (*1, *2, *3)CYP2C9 (*1, *2, *3)– SULT1A1 (*1,*2)SULT1A1 (*1,*2)

No statistically significant associations of candidate No statistically significant associations of candidate genotypes with tamoxifen or metabolite exposure genotypes with tamoxifen or metabolite exposure except for CYP2D6except for CYP2D6

Jin Y et al. JNCI 2005; 97:30-39

Jin Y et al. JNCI 2005; 97:30-39

CYP2D6 Vt/Vt genotype has decreased endoxifen exposure

CYP2D6 inhibitors decrease endoxifen exposure

Strong: paroxetine, fluoxetineWeak: amiodarone, sertralineOther: metoclopramide, citalopram

Jin Y et al. JNCI 2005; 97:30-39

Commonly used antidepressants and endoxifen concentrations

Jin Y et al. JNCI 2005; 97:30-39

CYP2D6 inhibitor:Strong: ParoxetineWeak: Sertraline

Effect of CYP2D6 genotype on endoxifen/NDM ratio and endoxifen plasma concentration (n=158)

Endoxifen/N-desmethyltamoxifen plasma concentration ratio

0.0 0.1 0.2 0.3 0.4 0.5 0.6

CY

P2

D6

Ge

no

typ

e

*10/PM*10/PM

*41/PM*41/PM*41/PM

PM/PMPM/PMPM/PMPM/PMPM/PMPM/PMPM/PM

IM/IMIM/IMIM/IMIM/IM

EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10

EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41

EM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PM

EM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EM

*41/*41xn*41/*41xn

UM/EMUM/EMUM/EMUM/EMUM/EMUM/EMUM/EM

EM/*41xn

*9/PM

EM/*9

EM/*29

EMxn/PM

*

*

*

Endoxifen plasma concentration (nM)

0 20 40 60 80 100 120 140 160 180 200

CY

P2

D6

Ge

no

typ

e

PM/PMPM/PMPM/PMPM/PMPM/PMPM/PMPM/PM

*41/PM*41/PM*41/PM

*10/PM*10/PM

IM/IMIM/IMIM/IMIM/IM

EM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PMEM/PM

EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41EM/*41

EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10EM/*10

EM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EMEM/EM

UM/EMUM/EMUM/EMUM/EMUM/EMUM/EMUM/EM

*41/*41xn*41/*41xn

EM/*41xn

EM/*29

EMxn/PM

*9/PM

EM/*9

*

*

*

*, P < 0.001 *, P < 0.01

Borges S et al. Clin Pharmacol Ther 2006; 80:61-74.

Conclusions

Endoxifen is an active metabolite of Endoxifen is an active metabolite of tamoxifen, present in patients at tamoxifen, present in patients at 5-105-10 x x greater concentration than 4-OH-tamoxifengreater concentration than 4-OH-tamoxifen

In vitro In vitro studies demonstrate the primary role studies demonstrate the primary role of CYP2D6 in the formation of endoxifen.of CYP2D6 in the formation of endoxifen.

Potent inhibitors of CYP2D6 reduce endoxifen Potent inhibitors of CYP2D6 reduce endoxifen concentrations in patients taking tamoxifenconcentrations in patients taking tamoxifen

CYP2D6 genotype correlates with endoxifen CYP2D6 genotype correlates with endoxifen concentrations in patients taking tamoxifenconcentrations in patients taking tamoxifen

AcknowledgementsAcknowledgements

Larry Lesko, PhDLarry Lesko, PhD Shiew Mei Huang, PhDShiew Mei Huang, PhD NAM Atiqur Rahman, PhDNAM Atiqur Rahman, PhD Felix Frueh, PhDFelix Frueh, PhD Myong-Jin Kim, PharmDMyong-Jin Kim, PharmD Todd Skaar, PhDTodd Skaar, PhD David Flockhart, MD, PhDDavid Flockhart, MD, PhD