Steady-State Imatinib Trough Levels as Well as Dose Interruptions Are Associated with Clinical Response (CCyR and MMR) and Adverse Events (AEs) in Patients with Chronic Myeloid Leukemia (CML) Receiving IM as Frontline Therapy.

Correlations between IM trough plasma levels (Cmin) and clinical response have been previously reported [Picard et al. Blood 2007; Larson et al. (IRIS) Blood 2008; Guilhot et al. (TOPS) ASH 2008]. This analysis correlates IM Cmin on Day 29 of initial treatment with complete cytogenetic response (CCyR) and major molecular responses (MMR) at 12 months and with cumulative Grade 3&4 toxicity over 12 months based on data pooled from 2 studies, IRIS (400 mg qd) and TOPS (400 mg bid (800 mg/daily) vs 400 mg qd), in newly diagnosed, previously untreated, Ph+ CML-CP.

Steady-state Cmin was defined as predose blood level collected within ±3 hours of the scheduled dosing time on Day 29 without any dose interruptions within 5 days prior to PK sampling. The correlation between IM Cmin and CCyR and MMR at 12 months was studied by two approaches: 1) analysis of outcomes by quartile groups based on patients' IM Cmin levels; 2) logistic regression analysis with Cmin as a continuous variable plus Sokal risk scores and cumulative days with any dose interruptions during the initial 12 months. Safety parameters included Grade 3&4 AEs, as well as all frequently-occurring (>10%) AEs of any grade that occurred during the 12 months. Patients with missing covariates were excluded.

Steady-state IM Cmin trough levels were available in 526 patients: 319 in IRIS and 207 from TOPS. At the time of assessment most patients received either 400 mg or 800 mg; 8 patients received reduced doses (6 at 300 mg; 2 at 600 mg). The median IM Cmin [25-75% quartiles] for 400 mg in the pooled dataset was 943 ng/mL [688-1280 ng/mL], and that for 800 mg was 2910 ng/mL [2333-3900 ng/mL]. IM Cmin showed large inter-patient variability for both 400 mg and 800 mg dose groups (52.7% and 39.9%, respectively). Both CCyR and MMR rates at 12 months were significantly correlated with IM Cmin on Day 29. Besides Cmin on Day 29, Sokal risk scores and cumulative dose interruptions (due either to treatment-related toxicities or non-adherence) were significant covariates for 12 month CCyR and MMR. Patients with high Sokal scores (H) had lower CCyR and MMR rates than those with low Sokal scores (L), 64% (H), 69% (intermediate (I)), and 83% (L), respectively, for CCyR, and 37%, 48%, and 59%, respectively, for MMR. Response rates at 12 months were significantly lower for patients with cumulative dose interruptions > 28 days (in the first 12 months): 45% vs 76% for CCyR, and 27% vs 48% for MMR. Modeling predicts that at a Cmin level of 1000 ng/mL and assuming no or minimal dose interruptions, the CCyR at 12 months would be 85%, 78%, and 68% for L, I, and H Sokal risk patients, respectively, and for MMR 55%, 45% and 36%, respectively. If the Cmin were 2000 ng/mL, the CCyR at 12 months would be 93%, 89%, and 83% for L, I, and H Sokal risk patients, respectively, and for MMR 65%, 55% and 44%, respectively. The predicted CCyR and MMR would be lower if there were dose interruptions. Patients who had Grade 3&4 AEs over first 12 months period (n=136) had a higher IM Cmin on Day 29 (median [25-75% quartiles], 1985 [982-2943] ng/mL vs 1010 [728-1468] ng/mL, P<0.001), than those without (n=390) as well as longer cumulative dose interruptions (20 [8-41] days vs 0 [0-2] days, P<0.001), lower CCyR rate (66%; 77/117 vs 75%; 277/369, P=0.05), and lower MMR rate (37%; 49/131 vs 48%; 155/323, P=0.006). Most Grade 3&4 AEs were treatment-related hematologic AEs with median times to onset between 50-63 days. Regression analysis showed the correlation between hematologic Grade 3&4 AEs and IM Cmin level for the population (Figure). Among all-grade non-hematologic AEs, rash and vomiting were associated with higher IM Cmin levels.

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IRIS+TOPS pooled data confirmed earlier findings that higher steady-state IM levels correlate with better CCyR and MMR responses but also with more Grade 3&4 treatment-related toxicities. Dose interruptions compromise CCyR and MMR rates at 12 months. IM Cmin levels provide additional information together with clinical response and tolerability to inform dose changes for individual patients.

Larson:Novartis: Consultancy, Honoraria, Research Funding. Chia:Novartis: Employment. Granvil:Novartis: Employment. Guilhot:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria. Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. O'Brien:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Wyeth: Research Funding. Baccarani:Novartis Pharma: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Mayer Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau. Hughes:Bristol-Myers Squibb: Advisor, Honoraria, Research Funding; Novartis: Advisor, Honoraria, Research Funding. Nedelman:Novartis: Employment, Equity Ownership. Wang:Novartis: Employment, Equity Ownership.