WHAT IS THE QUESTION?:

Thoughts for PK/PD experts from a clinical immunotherapist

Richard P Junghans, PhD, MD

Associate Professor of MedicineBoston University School of MedicineDirector, Biotherapeutics Development LabRoger Williams Medical CenterProvidence, RI, USA

No commercial relationships to disclose.

ABSTRACT:

The classic two-compartment model for pharmacokinetics transformed the understanding of drug delivery more than 50 years ago. Since this time, the recognition of drug interactions with the host has led to new complexity in these models. The best modeling is based on mechanisms and not merely on model independent curve-fitting. Mechanism driven modeling allows the use of clinical data for hypothesis testing to probe those postulated mechanisms. In this presentation, I will pose the questions that we as clinical therapists would like to see addressed with the help of PK/PD modeling in the particular interest areas of antibodies, cytokines and adoptive cellular therapies.

Modeling

o Linear models– Assume all drug movement is scale

independent• Low dose and high dose behave the same

• Tested by PK with different doses

o Non-linear models– Allow for drug interactions

Utility

o Dose scheduling

o Predicting blood concentrations

o BUT is this all there is?

o Can we mine PK data for more?

o Can we gain information on processes?

Pitfalls

o Understand assay and units– How they may be flawed

• Interfering substances

• In vivo versus in vitro state of agent (e.g., IL15 vs IL15-IL15Ra)

– What questions to ask

o Understand the biological system– Examples to follow…

Example 1: Antibodies

o Macromolecules: 150 kDao Regulated catabolismo Restricted extravascular

penetrationo Key property: interacts with

specific and non-specific ligands/receptors

What is the question?

o What is the half life?o Two-compartment modeling

– Alpha phase 1-2d

– Beta phase 23d

– Vd 6L (1:1 intravascular to extravascular)

o Dosing once per 2-3w: maintains plasma levelso Is that the real question?.... NO.o What is effective concentration at the site of action?

What is the question?

o What is effective concentration at the site of action?

o What does it mean to have a Vd of 6 L? – 3L IV + 3L EV

– Total ECF = 15L, 3L IV + 12L EV

– Can you infer concentration in EV space?• PK models say peak EV conc ~0.5 of C0

• Yet 0.5 C0 > 3L/12L C0

– What is distribution in the tissues?– Measurements needed

What is question?

o “What is effective concentration at the site of action?”

o In vitro testing gives concentration values for effects (receptor blockade, apoptosis, ADCC)

o In vivo infer effective systemic levels by doses in escalation

o Correspondence? Not truly known: studies needed!

What is question?o “When is effective concentration NOT effective

concentration?”

o Soluble Antigen– May not affect Ab catabolism/blood levels

– May render Ab inactive

o Antigen Target Load– May reduce free Ab below levels sufficient for blockade

– Less important for tracer distribution (radioAb)

o May be different in different clinical settings

Soluble antigen generation

Soluble Ag binds and block Ab

Modeling of binding and activity

Inputs: PK [Ab], [Ag], d[Ag]/dt, Ka binding affinity

Co-model complex interactions and their PK

Antibody may look okay, but not be okay…

Ab Ag

What is question?o “When is effective concentration NOT effective

concentration?”

o Soluble Antigen– May not affect Ab catabolism/blood levels

– May render Ab inactive

o Antigen Target Load– May reduce free Ab below levels sufficient for blockade

– Less important for tracer distribution (radioAb)

o May be different in different clinical settings

Patient specific PK differences

Two leukemia patients, same 50 mg dose of 111In-anti-Tac

Hypothesis: Tumor load affects PK

Estimating Burden of Tumor Ag

Disappearance at 2 days correlated with tumor Ag burden

Divergence of PK from model may reveal processes

Example 2: Cellular therapies

o “Living drugs”o Complex interactions

– Suppression– Activation– Growth factors

o Effectiveness may increase with doseo Means needed to quantify

– At site of action!

T cells

What is the question?o PK: “What is disappearance from blood”o Administration IVo Can be followed in blood (flow cytometry)

– Rapid disappearance– Engraftment protocols

o What is the REAL question?– “What is T cell concentration at site of action?” – “What is T cell activity status at site of action?”

o Not measured routinely: biopsy, imaging– Studies needed!

TCR

Gene-Modified TCR

Anti-Cancer T Cell Gene Therapy

Pharmacokinetics“Drug disappearance in the body”

Rapid Systemic Loss…

Response: Proof-of-principle

Increasing pain

Pain resolved

1600

1400

1200

1000

800

600

400

200

0-28 -21 -14 -7 0 7 14 21 28

Day of Treatment

CE

A (

NG

/ML

)

T Cells CEA

BUT! Time-Limited in Duration…

Phase I Trial in Prostate Cancer

Ex vivo gene therapy

T Cell Harvest

Hematologic Recovery

Tumor Response

Anti-PSMA designer T cells

Non-myeloablative (NMA) Conditioning

CD3+

CIR+

CIR+

+IL2 low dose (outpatient)

Phase I dose escalation:10^9 cells10^10 cells 10^11 cells

Peripheral Blood Recovery

o Chemo d-8 to d-2o T cells d0o IL2 start d0 x 28do ANC=0 for 5-8 d

– Recovery by d8 to d10

ANC and ALC Counts per uL over Time

0

1000

2000

3000

4000

5000

6000

-8 0 8 16 24

days

Co

un

ts p

er

uL

ANC

ALC

CFSE stained total T cells

Rhodamine staining of IgTCR+ T cells

Total and IgTCR-modified T cells

CD8V5+ cell per uL of blood

0 0 0 0 0 0 0 2

9

33

1115

05

101520253035

time: one month

CD

8V

5+

cell

s p

er

uL

of

blo

od

PK for JN

Modified CD8V5+

1.1%

CD3

2.5%

EngraftmentBlood sample

Day +14

Dose

61%

7.3%

CIR+

CIR+

CD3+

What is the question?o PK: what are dTc levels?

o Measured in blood…

o Calculations:– Estimate 10^12 T cells in body

• Never measured!!! Need this.

– 10% x 10^12 T cells = 10^11 cells– 10^9 dose =>100x expansion

o But are dTc everywhere? Or just where we measure? Bone marrow, LN, spleen, etc.– Important to calculation of ??

o What is concentration at site of action??? (Tumor)– Data needed (biopsy, imaging)

Response

Dose-Response

o Response in low dose, not high doseo Numbers small (2/3 PR low dose; 0/2 PR high dose)

o Against expectationo With 50-70% PSA reduction in low dose, one could hope for

100% PSA reduction in high dose

o Unclear difference between responders and non-responderso Age, disease stage, PS, renal function, prior therapies…

o During data analysis, became apparent IL2 levels differed

Example 3: Cytokine

o Mainly small proteins (e.g., IL2, 15 kDa)

o Growth factors for T cells

o Renal filtration dTc need IL2

What is the question?

o Administration: Bolus versus continuous infusiono T1/2 1-3 hro Vd 8L

o What is the REAL question?o “What is concentration at site of action?”o “What is persistence of activity at site of action?”

IL2 via Continuous Infusion

IL2 of JN

0

200

400

600

800

1000

1200

1400

1600

1800

2000

prescr

een

prein

fusi

on

post- 0

hr

post –1 h

r

post –3 h

r

post –8 h

r

post –24

hr

post –48

hr

post-day

5

post-day

7

post-day

14

post-day

21

post-day

28

IL2

(pg

/ml)

20 IU/ml

75,000 IU/kg/d

~ 3 MIU/m2/d

IL2 levels pts 1-5

Significance:

1 Cetus unit IL2 = ½ max stimulation of aTc6 IU ~ 1 Cetus unit

[know your units and their meaning?]

30 IU/ml = 5x ½ max stim3-6 IU/ml =< ½ max stim (and lower in tumor…)

[what is level in tumor??]

Therefore, the range plausible for difference in therapeutic activity

0

500

1000

1500

2000

2500

Pre

-Scre

en-1

po

st-0

hr

po

st –

3 h

r

po

st –

24

hr

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st-d

ay 3

po

st-d

ay 1

0

We

ek 3

Co

nc

en

tra

tio

n o

f IL

2 in

pg

/ml

Time

Concentration of IL2 - (Patient: 4)

0

500

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2500

pre

scre

en

pre

infu

sio

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po

st –

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r

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48

hr

po

st-d

ay 7

po

st-d

ay 2

1

po

st 3

mo

nth

s

(sam

ple

…

Co

nc

en

tra

tio

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f IL

2 in

pg

/ml

Time

Concentration of IL2 (Patient: 2)

0

500

1000

1500

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2500

pre

scre

en

po

st-0

hr

po

st –

3 h

r

po

st –

24

hr

po

st-d

ay 5

po

st-d

ay 1

4

po

st-d

ay 2

8

po

st 6

mo

nth

s

(sam

ple

s

…

Co

nc

en

tra

tio

n o

f IL

2 in

pg

/ml

Time

Concentration of IL2 (Patient:1)

0

500

1000

1500

2000

2500

Pre

-Scre

en-1

pre

infu

sio

n

po

st –

1 h

r

po

st –

8 h

r

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48

hr

po

st-d

ay 7

We

ek 2

We

ek 4

Co

nc

en

tra

tio

n o

f IL

2 in

pg

/ml

Time

Concentration of IL2 (Patient: 3)

IL2 held/ resumed

0

500

1000

1500

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2500

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-Scre

en-1

po

st –

1 h

r

po

st –

8 h

r

po

st –

day 2

po

st-w

ee

k 1

po

st-w

ee

k 3

Co

ncen

trati

on o

f IL

2 in

pg

/ml

Time

Concentration of IL2 - (Patient: 5)

30 IU/ml

30 IU/ml

3 IU/ml

3IU/ml

6IU/ml

Response versus IL2

RESPONSE

NO YES

LOW 3 0

IL2

HIGH 0 2

P = 0.1 by Fischer exact test (ns)

[underpowered = too few samples]

Causes for Low IL2o Artifact?

– Repeat assays together instead of sequential– Mixing assays to rule out ELISA inhibitor

o Delivery problems?– Pharmacy verified pumps function normal – Cassette volumes appropriately depleted

o Bioactivity problem?– Novartis confirmed bioactivity nominal for all lots– Same lot used for patients 2 (hi IL2) and 3 (lo IL2)

o Catabolic rates differ between individuals?– Would need 10-fold difference in rates; no precedent

o CONCLUDE: IL2 levels genuinely differento WHY THEN?

– Only dose sizes are variables between patients…– Maybe the T cells?

Hypothesis: T Cells Depleting IL2?

o Hypothesis: Are high levels of engrafted activated T cells (aTc) binding and reducing IL2 to too low a level?

o Calculation: • Total body 10^12 T cells [NEVER MEASURED!!]• 10% engraftment = 10^11 T cells

– 100-fold expansion from 10^9 T cells [DISTRIBUTION UNPROVEN!]

• 1000 IL2R per T cell => 10^14 R (~2 nmole) [NOT MEASURED!!]– bind 3 ug IL2 vs total 16 ug at steady state (10 ug/h) , 19% reduction– 50% engraftment => 95% reduction

– Plausible, in range: depending on several factors: actual IL2R, internalization/cycling rates, number of T cells, etc.

– SO MANY UNCERTAINTIES! (“plausible is not data”)

Estimating Cell Load for IL2 Binding

o Infused T cells are all activated T cells (aTc), with elevated IL2R – Modified = dTc, CAR+

– Unmodified = CAR-

o Recovering T cells = endogenous (non-activated) + infused (activated)

o Recovery complete by 2 weeks

o To estimate relative cell load, use fractional engraftment of aTc

o Calculate total aTc from dTc using the original modified dose fraction

Dose

61%CAR+

7.3%

CAR+

CD3+

CAR+

Blood

Deriving Fraction of aTc in Engraftment

IL2 versus aTc Engraftment

Summary of Datao Higher dTc doses NOT higher response

– Against expectation– High engraftments of aTc => non-response

o Low IL2 correlates with high engraftment

o Non-response correlates with low IL2

o Plausible: – MDI sufficient for low engraftment– MDI insufficient for high engraftment

o Results affect plan:– Benefit of higher doses of dTc will be realized with adequate IL2 (use high

dose IL2) [BUT I WISH I KNEW TISSUE LEVELS…]– Instead of 50-70% PSA reductions, may obtain 100% PSA reductions

Summary:What are the questions?

o What is concentration of drug at site of action?

o What are mechanisms of action in vivo?

o What is activity state of drug at the site?

o What are interactions that can impact the drug activity?

Summary: The Final Questiono “What makes a good pharmacometricist?”o Be more than your training

– Be a good chemist: be critical about assay data

– Be a good biologist: know what agent does

– Be a good clinician: know patients and their diseases

o Learn about the processes and the clinical settingo Engage in the topic (it’s more fun!!)o Ask lots of questions!

– [you don’t have to do the bench research, but you can motivate it!]

o Teach! We need your help to pose the questions!

T cells homing in on target

THE

END

LiteratureAntibodies and metabolism:

Junghans RP, Anderson CL. The protection receptor for IgG catabolism is the β2-microglobulin-containing neonatal intestinal transport receptor. Proc Natl Acad Sci USA 1996;93:5512-6.

Junghans RP. Finally! The Brambell receptor (FcRB): Mediator of transmission of immunity and protection from catabolism for IgG. Immunol Res 1997;16:29-57.

Antibodies and soluble antigen:

Junghans RP, Waldmann TA. Metabolism of Tac (IL2Rα): Physiology of cell surface shedding and renal elimination, and suppression of catabolism by antibody binding. J Exp Med 1996;183:1587-602.

 

Junghans RP, Carrasquillo JA, Waldmann TA. Impact of antigenemia on the bioactivity of infused anti-Tac antibody: implications for dose selection in antibody immunotherapies. Proc Natl Acad Sci USA 1998;95:1752-7.

Scheinberg DA, Sgouros G, Junghans RP. Antibody-based immunotherapies in cancer. (Chapter 29) In: Chabner BA, Longo DL, eds. Cancer Chemo-therapy and Biotherapy. 3nd Edition Philadelphia: Lippincott, 2001, pp. 850-90.

Literature (cont.)Antibodies and fixed antigen (tumor) overload:

Junghans RP. Leukemia is a disease of the marrow. Images in Clinical Medicine. N Engl J Med 1998;339:1375.

Koon HB, Severy P, Hagg DS, Butler K, Hill T, Jones AG, Waldman TA, Junghans RP. Anti-leukemic effect of daclizumab in CD25 high-expressing leukemias and impact of tumor burden on antibody dosing. Leuk Res 2006;30:190-203.

Designer T cells:

Nolan KF, Yun CO, Akamatsu Y, Beecham EJ, Murphy JC, Leung S, Junghans RP. Bypassing immunization: Optimized design of 'designer T cells' against carcinoembryonic antigen (CEA)-expressing tumors, and lack of suppression by soluble CEA. Clin Cancer Res 1999;5:3928-41.

Ma QZ, Gonzalo-Daganzo R, Junghans RP. Genetically engineered T cells as adoptive immunotherapy of cancer. (Chapter 15) In Giaccone R, Schlinsky R, Sondel P (eds) Cancer Chemotherapy & Biological Response Modifiers - Annual 20 Oxford: Elsevier Science, 2002, pp. 319-45.

Ma QZ, Safar M, Holmes E, Wang YW, Boynton AL, Junghans RP. Anti-prostate specific membrane antigen designer T cells for prostate cancer therapy. The Prostate 2004:61:12-25.

Literature (cont.)

IL2 cytokine and T cells:

Safar AM, Junghans RP. Interleukin 2 maintains its biologic stability over prolonged time. Immunopharmacology 2000;49:419-23.

Emtage PCR, Lo ASY, Gomes EM, Liu DL, Gonzalo-Daganzo R, Junghans RP. 2nd generation anti-CEA designer T cells resist activation-induced cell death, proliferate on tumor contact, secrete cytokines and exhibit superior anti-tumor activity in vivo: a preclinical evaluation. Clin Cancer Res 2008;14:8112-22.

 

Lo ASY, Ma Q, Liu DL, Junghans RP. Anti-GD3 chimeric sFv-CD28/T cell receptor zeta designer T cells for treatment of metastatic melanoma and other neuroectodermal tumors. Clin Cancer Res 2010;16:2769-80.