Steady-State Plasma Imatinib Levels in 142 GIST Patients Distribution, Dose, Dose Escalation, and Response Laura K Nolden 1, Linyee Shum 2, Amaury Dumont 1, Shreyaskumar Patel 1, Dejka M Araujo 1, Joseph A Ludwig 1, Vinod Ravi 1, Suzanne George 3, Saroj Vadhan-Raj 1, Robert S Benjamin 1, Jonathan C Trent 1 1 UT-MD Anderson Cancer Center, Department of Sarcoma Medical Oncology and the Sarcoma Research Center; Houston, Texas, United States; 2 Avantix Laboratories, Inc., New Castle, Delaware, United States; 3 Dana-Farber Cancer Institute, Center for Sarcoma and Bone Oncology, Boston, Massachusetts, United States Laura K Nolden 1, Linyee Shum 2, Amaury Dumont 1, Shreyaskumar Patel 1, Dejka M Araujo 1, Joseph A Ludwig 1, Vinod Ravi 1, Suzanne George 3, Saroj Vadhan-Raj 1, Robert S Benjamin 1, Jonathan C Trent 1 1 UT-MD Anderson Cancer Center, Department of Sarcoma Medical Oncology and the Sarcoma Research Center; Houston, Texas, United States; 2 Avantix Laboratories, Inc., New Castle, Delaware, United States; 3 Dana-Farber Cancer Institute, Center for Sarcoma and Bone Oncology, Boston, Massachusetts, United States

Background Several studies from patients with GIST and CML suggest a correlation between imatinib steady-state plasma trough levels and patient outcomes Demetri, G et al. J Clin Oncol; 2009 Larson, RA et al. Blood; 2008 Picard, S et al. Blood; 2007

Rationale Variability in imatinib plasma levels could occur for several reasons: Gastrectomy Unadjusted dosing (weight, BSA) Race, gender, age Duration of therapy Concomitant medications Blanke CD et al. J Clin Oncol, 2008 Judson I et al. Cancer Chemother Pharmacol. 2005

Objectives To determine the distribution of plasma imatinib levels in patients with GIST To determine factors that correlate with plasma imatinib level To determine the incremental effects of imatinib dose escalation To explore the median plasma levels and outcomes of patients with KIT exon 9 mutation

Patient Response Assessment Response was assessed within the first 4 months of imatinib exposure Response was classified according to Choi criteria: –CR, no radiographic evidence of GIST –PR, > 10% decrease in GIST size or > 15% decrease in GIST radiodensity –SD, less than 10% decrease or increase in GIST size and does not meet criteria of PR by radiodensity –PD, > 10% increase in GIST size –ND, patient underwent resection and no response could be assessed Response was assessed within the first 4 months of imatinib exposure Response was classified according to Choi criteria: –CR, no radiographic evidence of GIST –PR, > 10% decrease in GIST size or > 15% decrease in GIST radiodensity –SD, less than 10% decrease or increase in GIST size and does not meet criteria of PR by radiodensity –PD, > 10% increase in GIST size –ND, patient underwent resection and no response could be assessed

Plasma Imatinib Level Determination 5/ /2009, observational, retrospective study 142 GIST patients underwent therapeutic drug monitoring at M.D. Anderson Cancer Center Plasma imatinib levels were determined using a validated liquid chromatography-tandem mass spectrometry assay by Avantix Laboratories, Newark, DE. The steady-state level of imatinib was calculated: Adj-C min = C measured *exp (0.041 Δt) 5/ /2009, observational, retrospective study 142 GIST patients underwent therapeutic drug monitoring at M.D. Anderson Cancer Center Plasma imatinib levels were determined using a validated liquid chromatography-tandem mass spectrometry assay by Avantix Laboratories, Newark, DE. The steady-state level of imatinib was calculated: Adj-C min = C measured *exp (0.041 Δt) Wang Y et al. Ther Drug Monit; Oct 2009

Patient Characteristics Characteristicn ( % ) Female65 ( 45.8 ) Male77 ( 54.2 ) Caucasian118 ( 83.1 ) African American 12 ( 8.5 ) Hispanic7 ( 4.9 ) Asian5 ( 3.5 ) Mean (stdev) Median (range) Age at Diagnosis (yrs) 54.8 (12.5) 55 (19, 87) Mean BSA 2.0 (0.3) 2.0 (1.3, 2.8)

Tumor Characteristics

Treatment Characteristics Gastrectomyn ( % ) Total gastrecomy4( 2.8 ) Gastrectomy, partial, proximal29( 20.4 ) Gastrectomy, partial, distal16( 11.3 ) none93( 65.5 ) Dosen ( % ) < 400 mg5( 3.5 ) 400 mg91( 64.1 ) 600 mg18( 12.7 ) 800 mg27( 19.0 ) 1200 mg1( 0.7 )

Plasma Level Distribution

Plasma Level Distribution Imatinib Dose

Imatinib Plasma Level Correlative Characteristics Significant factors Age p = Gender p = Imatinib dose p = < Non-significant factors BSA Gastrectomy Significant factors Age p = Gender p = Imatinib dose p = < Non-significant factors BSA Gastrectomy Duration of imatinib Race Duration of imatinib Race

Plasma Level Distribution Choi Response (4 months)

p = 0.009

Imatinib Plasma Level Individual Dose Escalation p = mean 867 ng/mL mean 1762 ng/mL 100 mg imatinib 296 ng/mL plasma level

KIT Mutations Predict Overall Survival (on imatinib; independent of dose) KIT exon 9 (n=22) No kinase mutation (n=9) KIT exon 11 (n=85) P-value= Days Overall Survival (%) Heinrich et al, J Clin Oncol 2007

Progression-Free Survival KIT Genotype p = 0.08 p = 0.32

Imatinib Plasma Levels Kit Genotype Genotype Median Imatinib Dose (mg) Range (mg) Average Imatinib Plasma Level (ng/mL) Range (ng/mL) Exon Exon Wild-type Other

Summary Imatinib plasma levels in our patients ranged from 256 – 4582 with a first quartile cutoff of 851ng/mL, lower than the published literature. Imatinib plasma levels correlated with age, gender, imatinib dose and Choi response Dose escalation of imatinib by 100 mg resulted in an average 296 ng/mL plasma level increase. Patients with KIT exon 9 mutation were treated with higher dose of imatinib, had higher plasma levels, and had a PFS similar to that of patients with exon 11 mutation Imatinib plasma levels in our patients ranged from 256 – 4582 with a first quartile cutoff of 851ng/mL, lower than the published literature. Imatinib plasma levels correlated with age, gender, imatinib dose and Choi response Dose escalation of imatinib by 100 mg resulted in an average 296 ng/mL plasma level increase. Patients with KIT exon 9 mutation were treated with higher dose of imatinib, had higher plasma levels, and had a PFS similar to that of patients with exon 11 mutation

Randomized Study of Imatinib Plasma SARC-019 Advanced GIST on Imatinib 400mg/day (N=400) Measure Imatinib Plasma Level <1100 ng/mL (N=100)>1100 ng/mL (N=300) Randomize Arm A Imatinib 400mg/day Plasma Level Testing No Dose Adjustment Arm B Imatinib 600mg/day Plasma Level Testing Adjust Dose Arm C Imatinib 400mg/day Plasma Level Testing No Dose Adjustment Arm D (Exon 9) Imatinib 4-800mg/day Plasma Level Testing No Dose Adjustment Control Cohort (N=50) KIT Genotype PIs Suzanne George and Jon Trent

Acknowledgements Robert Benjamin Shreyaskumar Patel Dejka Araujo Joseph Ludwig Vinod Ravi Alex Lazar Robert Benjamin Shreyaskumar Patel Dejka Araujo Joseph Ludwig Vinod Ravi Alex Lazar Supported by a grant from the Institute for Personalized Cancer Therapy at M. D. Anderson Cancer Center Suzanne George Linyee Shum Saroj Vadhan-Raj Wei Qiao Jon Trent Billy Wang Suzanne George Linyee Shum Saroj Vadhan-Raj Wei Qiao Jon Trent Billy Wang

Concomitant Medications Cyp3A4 inhibitors may increase TKIs –ketoconazole, itraconazole, erythromycin, and clarithromycin, grapefruit, star fruit CYP3A4 inducer may decrease TKIs –dexamethasone, phenytoin, carbamazepine, rifampin (80%), phenobarbital or St. John's Wort CYP3A4, CYP2C8, CYP2C9, CYP2D6 are competitively inhibited by TKIs –Warfarin, midazolam, macrolides, caffeine Cyp3A4 inhibitors may increase TKIs –ketoconazole, itraconazole, erythromycin, and clarithromycin, grapefruit, star fruit CYP3A4 inducer may decrease TKIs –dexamethasone, phenytoin, carbamazepine, rifampin (80%), phenobarbital or St. John's Wort CYP3A4, CYP2C8, CYP2C9, CYP2D6 are competitively inhibited by TKIs –Warfarin, midazolam, macrolides, caffeine