Targeted Bioavailability : Mechanisms Influencing the ...

Targeted Bioavailability : Mechanisms Influencing the Tissue Distribution of Drugs

June 8, 2005 The New England Drug Metabolism

Discussion Group Summer Symposium University of Massachusetts Medical School

Shrewsbury, Massachusetts

William F. Elmquist, Pharm.D., Ph.D. Department of Pharmaceutics

University of Minnesota-Twin Cities

brain

Outline

Background

1) Drug transport proteins in the body and the CNS drug disposition (overview)

Experimental Studies 2) Delivery of Anti-tumor Agents (Gleevec) to CNS

Summary

3) CNS drug delivery program and efflux transporters

Variability in Drug Response in the CNS

- variability in distribution central - variability in receptors

- variability in elimination and metabolism peripheral - variability in absorption

Why study drug transporters in the CNS barriers?

Bioavailability Definitions:

FDA - “the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action. For drug products that are not intended to be absorbed into the bloodstream, bioavailability may be assessed by measurements intended to reflect the rate and extent to which the active ingredient or active moiety becomes available at the site of action.”

21CFR320.1 Code of Federal Regulations, Title 21, Volume 5, Parts 300 to 499, 1999. ; Guidance for Industry, CDER, FDA, Bioavailability and Bioequivalence Studies for Orally Administered Drug Products – General Considerations, 2003.

Commonly accepted definition: Typically, one modifies this definition to limit the delivery path from the site of administration to the bloodstream, i.e., the term bioavailability is “the fraction of the oral dose that actually reaches the systemic circulation”, and “commonly applied to both the rate and extent of drug input into the systemic circulation”.

Explain variability in drug response to PK and PD

Genetic Factors - drug targets - drug transporters - drug metabolizing enzymes

Environmental Factors - induction - inhibition

Physiological Factors - age, disease, etc.

Sources of Variability in Drug Response Variability Cycle

“Locations” of Variability in Drug Response

Presystemic bioavailability questions (“traditional” bioavailability)

Site-specific bioavailability questions (drug targeting)

Oral dosage form

Systemic circulation

Drug action

Targeted Bioavailability

Intestinal absorption

Liver metabolism

Cellular delivery

Intestinal metabolism

Tissue distribution Target site

Physicochemical Properties Ph

ysio

logy

/ Pa

thol

ogy Drug

Metabolism Receptor Affinity

Protein Binding

Membrane Permeability

Drug Transport

Gene Regulation

Targeted

Bioavailability

Dosage R

egimen

Protein Expression

Pharmacological / Toxicological Response




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Mechanisms influencing intestinal absorption: - solubility - permeability - transit time - carrier-mediated influx and efflux - stability - dosage form performance (disintegration, dissolution)




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Mechanisms influencing the intestinal first-pass metabolism : - carrier-mediated transport - phase I metabolism (e.g., CYP3A4) - phase II metabolism (e.g., UGTs) - enzyme induction - enzyme inhibition - locations of windows of absorption - intestinal motility / transit time - genetic expression patterns




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Mechanisms influencing the intestinal first-pass metabolism :

- carrier-mediated transport influx and efflux transporters - phase I (e.g., CYP3A4) - phase II (e.g., UGTs) - enzyme induction - enzyme inhibition - blood flow - protein binding - genetic expression patterns




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Systemic clearance

Mechanisms that influence the fraction of the drug in the systemic circulation that is available for distribution to target tissue and the exposure of the tissue to the drug

- distribution of blood flow - ratio of total clearance to a distributional clearance

Distributional clearance - membrane permeability, carrier-mediated transport (influx or efflux), protein-binding, intracellular metabolism, tissue transit time, capillary structure Total clearance – will affect the availability of the drug in the blood to distribute to the tissue




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Mechanisms that influence cellular delivery - membrane permeability - carrier-mediated transport

(influx / efflux) - intracellular metabolism - receptor-mediated transport - binding




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Mechanisms influencing the drug action at the target site - intracellular signaling - intracellular transport - expression of target receptors - receptor affinity - availability of cofactors




Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Examine a location

Physicochemical Properties Ph

ysio

logy

/ Pa

thol

ogy

Drug Metabolism

Receptor Affinity

Protein Binding

Membrane Permeability

Drug Transport

Gene Regulation

Targeted

Bioavailability

Dosage R

egimen

Protein Expression

Pharmacological / Toxicological Response

Examine a location considering the interplay between external factors and mechanism

Mechanisms

Targeting modalities

100 mg

20 mg

20 mg

80 mg 60 mg

30 mg

30 mg

F = .80 x .75 x .5 = 0.3

Fg = 0.75 Fa = 0.80 Fh = 0.50

“Traditional Bioavailability” F = Fa x Fg x Fh

Influence of fruit juices on oral bioavailability “traditional bioavailability”

At each location, several mechanisms at play:

F = fa x fg x fh

basolateral apical intracellular

Complexity of the Transporter Problem at Various Barriers

Many processes can be occurring simultaneously!

PSin

PSout

PSout

PSin

Carrier in Carrier in

Carrier out

Carrier out

Bidirectional

Bidirectional

“Targeted” Bioavailability F = Fa x Fg x Fh and Fd , Fc , Ft



Oral dosage form


Drug action



Liver metabolism

Cellular delivery



Fa Fg Fh Fd Fc Ft

Importance of Transporters in the Disposition of Drugs

From Lee and Gottesmann. Journal of Clinical Investigation, 1998 illustration by Naba Bora, Medical College of Georgia.

Compartmental model for solute exchange in the brain

Adapted from Quentin Smith

Pardridge, 1998

Transgenic mice

Microdialysis

Blood-Brain Barrier (BBB)

Basolateral membrane

Apical membrane

Cooray et al., 2002 NeuroReport

microvessel from normal brain stained for GLUT-1 and BCRP

GLUT-1 on both inner and outer walls of the microvessel

BCRP shows a more narrow distribution

Apical -- blood

Basolateral -- brain

MCT1

BBB endothelial cell

OATP2

OATP2

MCT1

Background Selected Drug transport systems in BBB and BCSFB

MCT1-- monocarboxylate transporter OATP2-- organic anion transport protein 2 MRP -- multidrug resistant-associated protein (ABCCX) P-gp -- p-glycoprotein (ABCB1) BCRP – breast cancer resistance protein (ABCG2)

?

?

?

P-gp MRP1, MRP4, MRP5

BCRP

Murakami, 2000

PS (in situ perf) versus logP(MW- ½)

Efflux

Barriers to Drug Delivery



Oral dosage form


Drug action



Liver metabolism

Cellular delivery



location of variability

location of variability

Outline

Background

1) Drug transport proteins in CNS drug disposition (overview)

Experimental Studies 2) Delivery of Anti-tumor Agents to CNS

Summary

3) CNS drug delivery program and efflux transporters

CNS Delivery of Anti-tumor Agents 1) Brain Around Tumor - BAT (growing edge) 2) Membrane permeability vs. efflux transport 3) Tumor vasculature 4) Primary and secondary tumors (metastases)

CH3SO3H

N

N

N NH

NH

O

N

N

STI-571 (GleevecTM)

Recently approved for chronic myelogenous leukemia (CML) Several clinical trials currently underway for glioma

Mechanism of Action of STI-571

“Molecularly Targeted” Therapy

Kaplan-Meier survival plots intracerebral human glioma nude mice STI-571 txt bid PO 50 mg/kg/day

Kilic, et al., Canc.Res., 2001

Ras transformed negative control

PDGF

glioma

qd dosing

8 hours

Fur

Intestinal content

1 hour

SpleenKidney Pineal glandBrown fatSkin

7 days

Eye

Fur

From Novartis Pharma

5 min.

Pineal glandLungAdrenal gland

Pituitary glandIntestinal mucosa Liver

Whole-body Autoradiography of Pigmented Rats

Methods •  The directional flux of STI-571 was

studied in MDCKII epithelial cell monolayers, using Transwell inserts. The effect of P-glycoprotein inhibition on the directional flux was also determined.

•  In vivo brain distribution studies were done using wild-type and mdr-1a/b (-/-) knockout mice. Mice were administered 25 mg/kg 14C-STI-571 orally, or STI-571 intravenously and brain-to-plasma concentration ratios of STI-571 were determined 30, 60 and 120 minutes post dose. RP-HPLC was used to determine the radioactivity associated with parent drug or LC-MS was used .

wild type mice mdr 1a/b (-/-) knockout mice

In Vitro Experiment

Figure 1. Directional flux of STI-571 Across MDCKII Monolayers July 31, 2001

Time (minutes)0 30 60 90 120 150 180

% F

lux

of S

TI-5

71 a

cros

s e

pith

elia

l cel

l mon

olay

er

0

10

20

30

40 A to B flux wild-type cells n=5A to B flux mdr1 cells n=5B to A flux wild-type cells n=4B to A flux mdr1 cells n=4

mean + stdev

directional flux mdckII jul 31-01.JNB

STI-571 Flux Across MDCKII Cell Monolayer(31 July 2001)

% F

lux

of S

TI-5

71 A

cros

s M

DC

KII

Mon

olay

ers

(at 1

80 m

in)

0

10

20

30

40

50

A to BWT cells

B to AWT cells

A to BMDR cells

B to AMDR cells

(mean + S.D., n = 4-5)

5.4 folddifference

24.3 folddifference

enhancement due to MDR-transfection = 4.5 fold

STI-571 Flux MDR1-transfected MDCKII epithelium

“Corrected” flux = (B-to-A / A-to-B)mdr (B-to-A / A-to-B)wt

Corrected flux ratio

4.5-fold

In Vitro Experiment

Figure XX. Directional flux of STI-571 Across MDCKII Monolayers September 11, 2001

(effect of 1µM LY335979)

Time (minutes)0 30 60 90 120 150 180

% F

lux

of S

TI-5

71 a

cros

s e

pith

elia

l cel

l mon

olay

er

0

5

10

15

20

25

A to B flux control mdr1 cells, n = 4B to A flux control mdr1 cells, n = 4A to B flux txt LY335979, n = 5B to A flux txt LY335979, n = 5

mean + stdev

STI directional flux mdckII sept-11-01 w-979.JNB

Effect of Specific P-gp inhibition on STI-571 Flux

Directional flux of STI-571 Across MDCKII Monolayers

Time (minutes)0 20 40 60 80 100 120 140 160 180 200

% F

lux

of S

TI-5

71 a

cros

s e

pith

elia

l cel

l mon

olay

er

0

10

20

30

40

WT a2b pgp a2b WT b2a Pgp b2a

The directional flux of 14C-STI-571 was studied in MDCKII epithelial cell monolayers.

Effe

ctiv

e P

erm

eabi

lity

of S

TI-

571

(Pef

f)(c

m/m

in)

0.0000

0.0002

0.0004

0.0006

0.0008

0.0010

A to BWT cells

B to AWT cells

A to BMDR cells

B to AMDR cells

B

***

***

RESULTS

WT MDR

Bra

in/P

lasm

a R

atio

(% ra

dioe

quiv

alen

ts)

0

1

2

3

4

5

3H-Inulin14C-STI-571

Figure 6. Brain to plasma ratio of tritiated inulin (10 min post tail vein injection) and carbon-14 STI-571 (90 min and 120 min post oral dose, 25 mg/kg) in

wild-type mice. (dual label liquid scintillation counting, total levels, not corrected for residual volume (inulin space))

14C-STI-571(90 min post PO)

3H-Inulin 3H-Inulin 14C-STI-571(120 min post PO)

14,15 nov mice inulin sti.jnb

mean + stdev

Bra

in/P

lasm

a R

atio

(%

radi

oact

ivity

)

0

1

2

3

4

P-gp KnockoutWild-type Wild-typeP-gp Modulator

Figure XX. Brain to Plasma Ratio of STI-571 Radioequivalents 60 minutes post oral dose (25 mg/kg) in wild-type mice, p-gp knockout mice, and wild-type mice treated with potent p-gp modulator.

Bra

in/P

lasm

a R

atio

(% ra

dioa

ctiv

ity)

0

1

2

3

4

5

Wild-type miceP-gp knockout mice

30 minutespostdose

60 minutespostdose

120 minutespostdose

Figure 4. Brain to plasma ratio of STI-571 radioequivalents post oral dose(25 mg/kg) at various times postdose. (mean + SD, n = 4 at each time point)

corrected for residual vascular volume (inulin space)18 sept mice wt ko 30 60 120.jnb mean + stdev

Radiopurity of 14C-STI-571 (GleevecTM)

Time (minutes)0 5 10 15 20 25

dpm

in e

fflue

nt

0

2000

4000

6000

8000

10000

12000

14000retention time of parentSTI-571 by UV detection

Tracer STI-571 injected on column

Plasma Radioactivity Profile Wild-type Mice 1-4Sept. 18, 2001 plasma collected 60 min post 14C-STI-571 dose

retention time (min)0 5 10 15 20 25

Pla

sma

Rad

ioac

tivity

(dp

m)

0

1000

2000

3000

4000

wild-type #1wild-type #2wild-type #4wild-type #3

Polar metabolites

Parent STI-571

Brai

n to

Pla

sma

Rat

io %

dpm

ass

ocia

ted

with

STI

-571

0

2

4

6

8

10

12

Wild-type Mice mdr 1 a/b (-/-) Mice

Brain-to-Plasma Ratio at 60 minutes postdose

Brain/Plasma ratio KO = 11.2 fold opportunity for Brain/Plasma ratio WT targeted bioavailability

Gleevec Brain Distribution

Time (minutes)20 40 60 80 100 120 140

Pla

sma

STI

-571

Con

cent

ratio

n(n

g/m

l)

0

2000

4000

6000

8000

Mdr 1 a/b (-/-) mice Wild type mice

A

Time (minutes)20 40 60 80 100 120 140

Bra

in S

TI-5

71 C

once

ntra

tion

(ng/

gram

bra

in ti

ssue

)

0

2000

4000

6000

8000

Mdr 1 a/b (-/-) mice Wild type mice

B

Rat

io o

f STI

-571

bra

in p

enet

ratio

n (m

dr 1

a/b

(-/-)

mic

e / w

ild ty

pe m

ice)

0

2

4

6

8

10

12

30 60 120

C

Time postdose (minutes)

A – Plasma STI-571 conc vs time B – Brain STI-571 conc vs. time

C – increase in STI-571 brain penetration in the P-gp knockout

enhanced: 6-8 fold !

“targeted bioavailability”

Brain and Plasma Concentrations (LC-MS)

A) mice developed neurological symptoms while on imatinib

B) pathological evidence of macrophage brain and meningeal masses

(50 mg/kg am, 100 mg/kg pm orally) C) brain and spinal cord B-lymphoid cell staining

D) laser dissected regions compared using PCR primers specific for P210 Bcr/Abl normal brain brain lesion

PCR products

Wolff et al., Blood 2003 The CNS is a sanctuary for leukemic cells in mice receiving imatinib mesylate for BCR/Abl induced leukemia

Drug Metabolite

ng/ml µM ng/ml µM

Concentration

Plasma (average)

6958 (± 2082)

11.8 (± 3.5)

611 (± 179)

1.0 (± 0.3)

CSF (pooled)

45 0.08 0 0

Plasma/CSF ratio

155 NA

(n = 9)

from Wolff et al., CSF/ Plasma STI571 concentrations in the mouse model

STI

-571

con

cent

ratio

n(n

g/m

l)

0

1000

2000

3000

4000

5000

CSF Plasma

IC50

Simultaneous STI-571 Concentrations in Four Patientswith CML Lymphoid Blast Crisis

Leis et al., Low penetration of imatinib (STI571) into the CSF indicates need for standard CNS prophylaxis in patients with CML lymphoid blast crisis and Philadelphia Chromosome Positive ALL. Abstract, American Society of Hematology, December 8, 2001

improved cellular activity

provided tyrosine kinase activity

abolished protein kinase-c inhibitory activity

increased solubility and oral bioavailability

Capdeville et al., Glivec (STI571, Imatinib), a rationally developed, targeted anticancer drug.

Nature Reviews Drug Discovery, July 2002.

P-gp substrate pharmacophore model and Gleevec aligned. Blue features (hydrophobes) and green features (hydrogen bond acceptors) with vector in the direction of the putative hydrogen bond donor. (Ekins et al, Molecular Pharmacology, vol. 61, 2002)

basolateral apical intracellular

Complexity of the Transporter Problem at Various Barriers

Many processes can be occurring simultaneously !

PSin

PSout

PSout

PSin

Carrier in Carrier in

Carrier out

Carrier out Pgp

Drug delivery across barrier

Bidirectional

Bidirectional Carrier out BCRP

Cancer Res 2005; 65:(7). April 1, 2005

Breedveld et al. (BCRP and Imatinib CNS Penetration)

Cancer Res 2005; 65:(7). April 1, 2005

[A] Imatinib Brain penetration - BCRP, P-gp [B] Imatinib Brain penetration - control mice w/inhibitor

From Tsuji, 2000.

Transport Mechanisms at the Blood- Brain Barrier

X

Barriers to Drug Delivery



Oral dosage form


Drug action



Liver metabolism

Cellular delivery



X

Biochemistry and molecular biology

Program for CNS drug delivery evaluation

In Vitro cellular barriers (transfected cell lines and isolated brain cellular barriers)

In Vivo techniques (BUI, intravenous injection, in situ perfusion)

Specialized in vivo techniques (microdialysis, transgenic animals)

Strategies to Improve the CNS Delivery of Drugs

1) improve physiochemical properties 2) use existing influx transport systems 3) reduce affinity for efflux transporters

problem: multidrug resistance 4) temporary breakdown of the BBB

hyperosmotic (mannitol) inflammatory mediators (RMP-7)

5) drug delivery systems implants/direct delivery polymeric carriers nanoparticles peptide vectors immunodirected vectors efflux inhibitors

CNS Drug Distribution in the Future The role of various drug efflux proteins in the blood-brain and blood-CSF barriers in CNS targeting can be examined using a variety of complimentary experimental approaches. These include:

- biochemical and molecular biological methods (expression of functional protein and RNA message)

- in vitro models using transfected cell cultures

- in vitro models using cell cultures of CNS barriers

- in vivo models using novel sampling techniques

- in vivo models that have been genetically engineered

These approaches will allow a specific quantitative analysis of the biological determinants of drug action in the CNS that are related to drug delivery across the cellular barriers in the CNS.

Acknowledgements Haiying Sun Hua Yang Qin Wang Michele Fontaine Tim Spitzenberger Christine Brandquist Haiqing Dai Ying Chen Dr. Mini Kurumboor Naveed Shaik Dr. Paul Stemmer Dr. Donald Miller

Dr. Alexander Kabanov Dr. Elena Batrakova Tanya Bronich

Lilly Cancer Research Dr. Anne Dantzig Dr. James Starling

Funding National Institutes of Health Lilly Cancer Research Laboratories Novartis Pharma UNMC Graduate Fellowship

Yale University Dr. Alan Sartorelli Dr. Rick Finch

Novartis Pharma Dr. Michel Lemaire Dr. Peter Marbach

Center for Neurovirology Dr. Howard Gendelman Dr. Yuri Persidsky

Alfred Schinkel

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