Abstract
Dasatinib (SPRYCEL®) is an effective BCR-ABL inhibitor that is 325-fold more potent than imatinib and 16-fold more potent than nilotinib in vitro against unmutated BCR-ABL. Across a series of phase II and III trials, dasatinib has demonstrated durable efficacy in patients with CML following resistance, suboptimal response, or intolerance to imatinib. BCR-ABL mutations are an important cause of imatinib failure and suboptimal response. Here, the efficacy of dasatinib in patients with CML-CP who had baseline BCR-ABL mutations following imatinib treatment was analyzed using data from three trials (CA180-013, -017, and -034). Mutational assessment of the BCR-ABL kinase domain was performed using RT-PCR and direct sequencing of peripheral blood cell mRNA. Hematologic, cytogenetic, and molecular response rates were reported after ≥24 mos of follow-up. Duration of response, progression-free survival (PFS), and overall survival (OS; in 013/034) were calculated using Kaplan-Meier analysis, and rates were estimated at the 24-mo time point. Of 1,150 patients with CML-CP who received dasatinib, 1,043 had a baseline mutational assessment and were analyzed further. Of these, 402 patients (39%) had a BCR-ABL mutation, including 8% of 238 imatinib-intolerant and 48% of 805 imatinib-resistant patients. Excluding known polymorphisms, 64 different BCR-ABL mutations were detected affecting 49 amino acids, with G250 (n=61), M351 (n=54), M244 (n=46), F359 (n=42), H396 (n=37), Y253 (n=26), and E255 (n=25) most frequently affected. Dasatinib treatment in patients with or without a baseline BCR-ABL mutation, respectively, resulted in high rates of major cytogenetic response (MCyR; 56% vs 65%), complete cytogenetic response (CCyR; 44% vs 56%), major molecular response (MMR; 33% vs 45%); PFS (70% vs 83%), and OS (89% vs 94%) (Table). After 24 mos, CCyRs in patients with or without a BCR-ABL mutation had been maintained by 84% vs 85%, respectively, of those achieving this response. Among patients with mutations who received dasatinib 100 mg once daily, which has a more favorable clinical safety profile, efficacy and durability were similar (MCyR: 55%; CCyR: 41%; MMR: 36%; PFS: 73%; OS: 90%). In general, high response rates and durable responses were observed in patients with different mutation types, including highly imatinib-resistant mutations in amino acids L248, Y253, E255, F359, and H396. When responses were analyzed according to dasatinib cellular IC50 for individual BCR-ABL mutations, dasatinib efficacy was observed in 44 patients who had any of 5 imatinib-resistant mutations with a dasatinib cellular IC50 >3 nM (Q252H, E255K/V, V299L, and F317L, excluding T315I), including MCyR in 34%, CCyR in 25%, MMR in 18%, PFS in 48%, and OS in 81%. Among patients whose mutations had a dasatinib IC50 ≤3 nM (n=254) or unknown IC50 (n=83), responses and durability were comparable to patients with no BCR-ABL mutation. As expected, few patients with a T315I mutation (IC50 >200 nM; n=21) achieved a response. Among 70 patients with >1 mutation, a MCyR was achieved in 53% and a CCyR in 37%. Among patients with mutational analysis at last follow-up (n=162), 42 (26%) retained a BCR-ABL mutation (20 retained a mutation with IC50 >3 nM), 42 (26%) lost a mutation (5 lost a mutation with IC50 >3 nM), and 44 (27%) developed a new mutation (39 developed a mutation with IC50 >3 nM), with some patients counted in more than one category. Overall, this analysis demonstrates that dasatinib has broad efficacy against all BCR-ABL mutations except for T315l. For patients with BCR-ABL mutations, dasatinib treatment is associated with durable responses and favorable long-term outcomes.
Table
Analysis by dasatinib IC50 No BCR-ABL mutation BCR-ABL mutation BCR-ABL mutation treated with 100 mg QD >3 nM (excl. T315I) 3 nM* Unknown IC50** Some patients had >1 mutation. *Excluding patients with a concurrent mutation with dasatinib IC50 >3 nM. **Excluding patients with a concurrent mutation with known dasatinib IC50. Patients, n 641 402 49 44 254 83 Response rates (≥24 mos of follow-up), % CHR 93 90 90 82 94 96 MCyR 65 56 55 34 58 73 CCyR 56 44 41 25 47 54 MMR 45 33 36 18 34 43 Median time to MCyR, mos 2.8 2.9 2.8 5.7 2.9 2.8 Median time to CcyR, mos 3.0 5.3 3.0 5.7 5.4 3.4 24-mo PFS (95% CI), % 83 (79.8–86.5) 70 (65.3–75.2) 73 (60.1–86.3) 48 (31.2–64.7) 73 (66.6–78.9) 89 (82.3–96.3) 24-mo OS (95% CI), % 94 (91.4– 95.7) 89 (85.1– 92.1) 90 (81.2– 98.3) 81 (68.8– 93.8) 90 (85.8– 94.2) 96 (91.2–100)
Efficacy of nilotinib in a patient in late chronic phase CML, intolerant to imatinib and resistant to dasatinib