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WHAT IS THE QUESTION?: Thoughts for PK/PD experts from a clinical immunotherapist Richard P Junghans, PhD, MD Associate Professor of Medicine Boston University.

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Presentation on theme: "WHAT IS THE QUESTION?: Thoughts for PK/PD experts from a clinical immunotherapist Richard P Junghans, PhD, MD Associate Professor of Medicine Boston University."— Presentation transcript:

1 WHAT IS THE QUESTION?: Thoughts for PK/PD experts from a clinical immunotherapist Richard P Junghans, PhD, MD Associate Professor of Medicine Boston University School of Medicine Director, Biotherapeutics Development Lab Roger Williams Medical Center Providence, RI, USA No commercial relationships to disclose.

2 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.

3 Modeling oLinear models –Assume all drug movement is scale independent Low dose and high dose behave the same Tested by PK with different doses oNon-linear models –Allow for drug interactions

4 Utility oDose scheduling oPredicting blood concentrations oBUT is this all there is? oCan we mine PK data for more? oCan we gain information on processes?

5 Pitfalls oUnderstand 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 oUnderstand the biological system –Examples to follow…

6 Example 1: Antibodies oMacromolecules: 150 kDa oRegulated catabolism oRestricted extravascular penetration oKey property: interacts with specific and non-specific ligands/receptors

7 What is the question? oWhat is the half life? oTwo-compartment modeling –Alpha phase 1-2d –Beta phase 23d –Vd 6L (1:1 intravascular to extravascular) oDosing once per 2-3w: maintains plasma levels oIs that the real question?.... NO. oWhat is effective concentration at the site of action?

8 What is the question? oWhat is effective concentration at the site of action? oWhat 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

9 What is question? o“What is effective concentration at the site of action?” oIn vitro testing gives concentration values for effects (receptor blockade, apoptosis, ADCC) oIn vivo infer effective systemic levels by doses in escalation oCorrespondence? Not truly known: studies needed!

10 What is question? o“When is effective concentration NOT effective concentration?” oSoluble Antigen –May not affect Ab catabolism/blood levels –May render Ab inactive oAntigen Target Load –May reduce free Ab below levels sufficient for blockade –Less important for tracer distribution (radioAb) oMay be different in different clinical settings

11 Soluble antigen generation

12 Soluble Ag binds and block Ab

13 Modeling of binding and activity Inputs: PK [Ab], [Ag], d[Ag]/dt, Ka binding affinity

14 Co-model complex interactions and their PK

15 Antibody may look okay, but not be okay… AbAg

16 What is question? o“When is effective concentration NOT effective concentration?” oSoluble Antigen –May not affect Ab catabolism/blood levels –May render Ab inactive oAntigen Target Load –May reduce free Ab below levels sufficient for blockade –Less important for tracer distribution (radioAb) oMay be different in different clinical settings

17 Patient specific PK differences

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

19 Hypothesis: Tumor load affects PK

20

21 Estimating Burden of Tumor Ag

22 Disappearance at 2 days correlated with tumor Ag burden Divergence of PK from model may reveal processes

23 Example 2: Cellular therapies o“Living drugs” oComplex interactions –Suppression –Activation –Growth factors oEffectiveness may increase with dose oMeans needed to quantify –At site of action!

24 T cells

25 What is the question? oPK: “What is disappearance from blood” oAdministration IV oCan be followed in blood (flow cytometry) –Rapid disappearance –Engraftment protocols oWhat is the REAL question? –“What is T cell concentration at site of action?” –“What is T cell activity status at site of action?” oNot measured routinely: biopsy, imaging –Studies needed!

26 TCR Gene-Modified TCR Anti-Cancer T Cell Gene Therapy

27 Pharmacokinetics “Drug disappearance in the body” Rapid Systemic Loss…

28 Response: Proof-of-principle Increasing pain Pain resolved Day of Treatment CEA (NG/ML) T Cells CEA BUT! Time-Limited in Duration…

29 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+ +IL2 low dose (outpatient) Phase I dose escalation: 10^9 cells 10^10 cells 10^11 cells

30 Peripheral Blood Recovery oChemo d-8 to d-2 oT cells d0 oIL2 start d0 x 28d oANC=0 for 5-8 d –Recovery by d8 to d10

31 CFSE stained total T cells

32 Rhodamine staining of IgTCR+ T cells

33 Total and IgTCR-modified T cells

34 PK for JN Modified CD8V5+

35 1.1% CD3 2.5 % Engraftment Blood sample Day +14 Dose 61% 7.3% CIR+ CD3+

36 What is the question? oPK: what are dTc levels? oMeasured in blood… oCalculations: –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 oBut are dTc everywhere? Or just where we measure? Bone marrow, LN, spleen, etc. –Important to calculation of ?? oWhat is concentration at site of action??? (Tumor) –Data needed (biopsy, imaging)

37 Response

38 Dose-Response oResponse in low dose, not high dose oNumbers small (2/3 PR low dose; 0/2 PR high dose) oAgainst expectation oWith 50-70% PSA reduction in low dose, one could hope for 100% PSA reduction in high dose oUnclear difference between responders and non-responders oAge, disease stage, PS, renal function, prior therapies… oDuring data analysis, became apparent IL2 levels differed

39 Example 3: Cytokine oMainly small proteins (e.g., IL2, 15 kDa) oGrowth factors for T cells oRenal filtration dTc need IL2

40 What is the question? oAdministration: Bolus versus continuous infusion oT1/2 1-3 hr oVd 8L oWhat is the REAL question? o“What is concentration at site of action?” o“What is persistence of activity at site of action?”

41 IL2 via Continuous Infusion 20 IU/ml 75,000 IU/kg/d ~ 3 MIU/m2/d

42 IL2 levels pts 1-5 Significance: 1 Cetus unit IL2 = ½ max stimulation of aTc 6 IU ~ 1 Cetus unit [know your units and their meaning?] 30 IU/ml = 5x ½ max stim 3-6 IU/ml =< ½ max stim (and lower in tumor…) [what is level in tumor??] Therefore, the range plausible for difference in therapeutic activity

43 Response versus IL2 RESPONSE NOYES LOW 3 0 IL2 HIGH 0 2 P = 0.1 by Fischer exact test (ns) [underpowered = too few samples]

44 Causes for Low IL2 oArtifact? –Repeat assays together instead of sequential –Mixing assays to rule out ELISA inhibitor oDelivery problems? –Pharmacy verified pumps function normal –Cassette volumes appropriately depleted oBioactivity problem? –Novartis confirmed bioactivity nominal for all lots –Same lot used for patients 2 (hi IL2) and 3 (lo IL2) oCatabolic rates differ between individuals? –Would need 10-fold difference in rates; no precedent oCONCLUDE: IL2 levels genuinely different oWHY THEN? –Only dose sizes are variables between patients… –Maybe the T cells?

45 Hypothesis: T Cells Depleting IL2? oHypothesis: Are high levels of engrafted activated T cells (aTc) binding and reducing IL2 to too low a level? oCalculation: 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”)

46 Estimating Cell Load for IL2 Binding oInfused T cells are all activated T cells (aTc), with elevated IL2R –Modified = dTc, CAR+ –Unmodified = CAR- oRecovering T cells = endogenous (non- activated) + infused (activated) oRecovery complete by 2 weeks oTo estimate relative cell load, use fractional engraftment of aTc oCalculate total aTc from dTc using the original modified dose fraction Dose 61%CAR % CAR+ CD3+ CAR+ Blood

47 Deriving Fraction of aTc in Engraftment

48 IL2 versus aTc Engraftment

49 Summary of Data oHigher dTc doses NOT higher response –Against expectation –High engraftments of aTc => non-response oLow IL2 correlates with high engraftment oNon-response correlates with low IL2 oPlausible: –MDI sufficient for low engraftment –MDI insufficient for high engraftment oResults 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

50 Summary: What are the questions? oWhat is concentration of drug at site of action? oWhat are mechanisms of action in vivo? oWhat is activity state of drug at the site? oWhat are interactions that can impact the drug activity?

51 Summary: The Final Question o“What makes a good pharmacometricist?” oBe 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 oLearn about the processes and the clinical setting oEngage in the topic (it’s more fun!!) oAsk lots of questions! –[you don’t have to do the bench research, but you can motivate it!] oTeach! We need your help to pose the questions!

52 T cells homing in on target THE END

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

54 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: 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: 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 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.

55 Literature (cont.) IL2 cytokine and T cells: Safar AM, Junghans RP. Interleukin 2 maintains its biologic stability over prolonged time. Immunopharmacology 2000;49: Emtage PCR, Lo ASY, Gomes EM, Liu DL, Gonzalo-Daganzo R, Junghans RP. 2 nd 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: 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:


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