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Abstract 4362 Midostaurin (PKC412) is a multi-targeted tyrosine kinase inhibitor (TKI) of several receptors, including wild-type and mutant variants of KIT and the FMS-like tyrosine kinase 3 (FLT3) receptor, and has known roles in hematopoiesis and leukemia. Midostaurin has demonstrated activity in acute myeloid leukemia (AML) and myelodysplastic syndrome in phase 1 and 2 trials, and is currently under investigation in a randomized phase 3 AML study at 50mg twice daily (bid) in combination with chemotherapy and a phase 2 monotherapy study of aggressive systemic mastocytosis (ASM) at 100mg bid. Despite the absence of specific midostaurin-related cardiac toxicity issues, we conducted a dedicated phase 1 study to directly investigate the effect of midostaurin on QTc interval. Healthy subjects were randomized to 3 treatment arms: placebo; midostaurin administered orally at 75mg bid on days 1 and 2 and once daily (od) on day 3; or an active control arm of moxifloxacin administered orally at 400mg od on day 3. The primary variable was QTcF interval on day 3 corrected for baseline and placebo in the midostaurin and moxifloxacin treatment arms. Drug exposure levels at each time point were confirmed for moxifloxacin, midostaurin, and its two metabolites – CGP62221 and CGP52421. Of 192 subjects enrolled, 166 completed the study. 24 of 80 subjects discontinued in the midostaurin arm: 19 (23%) due to adverse events (AEs), 17 of which encompassed expected gastrointestinal events. No patients were discontinued for AEs in the other 2 treatment groups. Discontinued patients were not included in the ECG analysis. In time-matched analysis of QTcF interval change, the maximum mean change in the midostaurin arm corrected for baseline and placebo was 0.72ms with a 90% confidence interval (CI) upper bound of 4.71ms, which excluded 10ms. At each nominal time point, the mean change from baseline placebo-corrected for midostaurin was 30ms or >480ms change from baseline for QTcF or QTcI. For QTcB the only occurrences of change were in the 30–60ms category: 1 (1.3%) of the subjects on midostaurin met this non-specific outlier criterion; 7 (15.9%) on moxifloxacin; and 1 (1.5%) on placebo. 1 new U-wave abnormality was noted in the moxifloxacin group. The peak plasma concentration of midostaurin achieved in the present study (mean 2273ng/mL) covered the peak and trough plasma exposure observed at 50mg bid (2220ng/mL and 1005ng/mL, respectively) in AML patients. The peak level achieved for midostaurin was also above the steady-state trough level of 1060ng/mL, but below the peak concentration of 3500ng/mL, for the 100mg bid dose. Midostaurin was safe and generally well tolerated: 97% of the AEs noted in subjects while on study drug (n=61; 40%) were reported as grade 1. No grade 3/4 AEs were reported. While some TKIs exert pharmacologic effects on QTc interval, this carefully conducted trial demonstrates that midostaurin at 75mg bid has no effect on heart rate, AV conduction, or cardiac depolarization. The midostaurin exposure achieved in this study exceeds the peak and trough levels for the 50mg bid dose regimen under investigation in the AML phase 3 trial. The midostaurin exposure achieved also exceeds the steady state trough level, but not the peak level, of the 100mg bid dose regimen under investigation in the phase 2 ASM trial. Further, the effects of the long-acting metabolite CGP52421 cannot be fully addressed by this short study. Due to the lack of QT prolongation observed in this trial, we recommend reduced but continued ECG monitoring and omission of QT-related exclusion criteria in future midostaurin clinical trials. Disclosures: del Corral: Novartis Pharmaceuticals Corporation: Employment. Dutreix:Novartis Pharmaceuticals Corporation: Employment. Huntsman Labed:Novartis Pharmaceuticals Corporation: Employment. Rai:Novartis Pharmaceuticals Corporation: Employment. Grosch:Novartis Pharmaceuticals Corporation: Employment. Morganroth:eResearchTechnology Inc: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees; Novartis Pharmaceuticals Corporation: Consultancy, Research Funding. Wang:Novartis Pharmaceuticals Corporation: Employment, Equity Ownership.

Abstract 634 FLT3, a transmembrane receptor tyrosine kinase constitutively activated via mutation in blasts of patients (pts) with AML, is an important therapeutic target. Blasts from approximately 25% of pts have a length or internal tandem duplication (ITD) mutation in the juxtamembrane region or tyrosine kinase domain (TKD1) of FLT3, which is associated with reduced disease-free survival and overall survival (OS), particularly in pts with normal cytogenetics. Blasts from 5–10% of pts have a point mutation (typically D835Y) in the tyrosine kinase domain (TKD); the effect of this mutation on prognosis is uncertain. Midostaurin (PKC412) is a multi-targeted kinase inhibitor with demonstrated clinical activity in FLT3-mutant (FLT3–mut) and FLT3-wild-type (FLT3–wt) AML (peripheral blood blast reduction in 70% and 30% of pts, respectively) but rarely produces complete remissions). Preclinical studies demonstrated synergy between FLT3 inhibitors and chemotherapy. We conducted a Phase 1b trial to investigate the feasibility of administering daunorubicin (60 mg/m2 IV, days 1–3) and cytarabine (100 mg/m2 IVCI, days 1–7) induction and high-dose cytarabine post-remission therapy (3 gm/m2 over 3h every 12h, days 1, 3, and 5 for 3 cycles) plus oral midostaurin at 100 mg or 50 mg each twice daily on days 8–21 (sequentially) or days 1–7, 15–21 (concomitantly) with all chemo cycles in newly diagnosed pts under age 61 with de novo AML. Whereas 100 mg of midostaurin plus induction chemotherapy was poorly tolerated due to nausea and vomiting, the 40 pts who received 50 mg of midostaurin orally twice daily ( 20 each on the sequential and concomitant schedules; 27 FLT3–wt; 13 FLT3–mut [9 with an ITD]), tolerated the combination well. Median midostaurin exposure was 133 days (range 21–975) for the FLT3–mut pts and 90 days (range 7–1016) for FLT3–wt pts. Maintenance therapy with midostaurin was allowed with investigator discretion and was received by 5 pts (3 FLT3–mut, 2 FLT–wt). The median ages for the FLT3–wt and FLT3–mut pts were 50 years (range 25–60) and 46 years (range 20–65), respectively. 77% of the FLT3–mut pts displayed normal, 15% adverse and 8% other intermediate cytogenetics compared with 18.5%, 26%, and 26%, respectively, for FLT3-wt (also 18.5% favorable; 11% unknown). Complete response occurred in 32/40 (80%) of all pts (20/27 [74%] of FLT3–wt patients, 12/13 [92%] of FLT3–mut pts). Patients were censored at the last date they were known to be alive with a median post treatment follow-up for FLT3-mut pts of 1059 days and 1086 days for FLT3-wt. Even accounting for their differing cytogenetics and ages, the OS of the FLT3–mut subgroup was expected to be inferior to that of the FLT3–wt subgroup. However, we report that the 1 and 2 year OS for the pts with FLT3–mut AML was 85% and 62%, respectively, and was comparable to that of the FLT3–wt subgroup (81% and 59%, respectively). Although based on small numbers and not stratified for type of FLT3 mutation (TKD, ITD, ITD length, location, or allelic ratio), these long-term results suggest that combination therapy with a FLT3 inhibitor and chemotherapy might be effective enough to obviate the perceived need for allogeneic stem cell transplantation for FLT3–mut AML pts in first complete remission. Moreover, these data support the rationale for the ongoing international phase 3 study of induction, post-remission intensification, and maintenance with midostaurin (50 mg po bid) or placebo. Disclosures: Stone: Novartis: Research Funding, ad hoc consultancy; Cephalon: ad hoc consultancy. Off Label Use: midostaurin with chemothereapy for AML. Paquette:Novartis: Honoraria, Research Funding, Speakers Bureau. Schiller:Novartis: Research Funding, Speakers Bureau; Millenium: Research Funding, Speakers Bureau; Genzyme: Research Funding; Vion: Research Funding; Centocor: Research Funding; Eli Lilly: Research Funding; Celgene: Research Funding. Schiffer:Novartis: Consultancy, Research Funding; Genzyme: Consultancy. Ehninger:Novartis: Honoraria, Research Funding. Cortes:Novartis: Research Funding; Bristol-Myers Squibb: Research Funding; Wyeth: Research Funding. Kantarjian:Novartis: Research Funding. DeAngelo:Bristol-Myers Squibb: Speakers Bureau; Celgene: Speakers Bureau; Enzon: Speakers Bureau; Novartis: Speakers Bureau. Huntsman-Labed:Novartis: Employment, Equity Ownership. Dutreix:Novartis: Employment, Equity Ownership. Rai:Novartis: Employment, Equity Ownership. Giles:Novartis: Research Funding; Merck: Research Funding; Bristol-Myers Squibb: Research Funding; Vion: Research Funding.