a Phase 1b/2 Study of TAK-659, an Investigational Dual SYK and FLT-3 Inhibitor, in Patients (Pts) with Relapsed or Refractory Acute Myelogenous Leukemia (R/R AML)

Background

Spleen tyrosine kinase (SYK) is a nonreceptor cytoplasmic protein kinase and a key mediator of immunoreceptor signaling that has been shown to play an important role in the pathogenesis of both B-cell and myeloid malignancies. SYK has also been shown to directly bind and activate FMS-like tyrosine kinase 3 (FLT-3), a Class III receptor tyrosine kinase that is commonly mutated in approximately 30% of pts with AML (Puissant et al. Cancer Cell 2014;25:226-42). TAK-659 is an investigational, reversible, and potent dual inhibitor of SYK and FLT-3. Preclinical studies with TAK-659 have demonstrated growth inhibition of cell lines and xenograft tumor models of B-cell lymphoma or AML origin. Moreover, TAK-659 has exhibited antitumor activity in lymphoma pts in an ongoing clinical trial (Petrich et al. Blood 2015;126:2693). The primary objectives of the phase 1b dose-finding portion of this study are to evaluate the safety, tolerability, and maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D) of TAK-659, as well as preliminary efficacy in the phase 2 expansion study. Secondary objectives include evaluation of TAK-659 pharmacokinetics (PK) in this pt population.

Methods

During dose escalation using a 3x3 schema, adult pts with R/R AML received oral TAK-659 daily (QD) in 28-d cycles (C) starting with a dose of 60 mg. Adverse events (AEs) were assessed per NCI-CTCAE v4.03. Response per IWG criteria for AML was assessed between d22 and d28 of C1, C2, and C4. Blood samples for plasma pharmacokinetic (PK) assessments were collected pre-dose and at multiple times post-dose on d1 and d15 of C1. The pharmacodynamic effect of TAK-659 was assessed at multiple time points by measuring the phosphorylation of ribosomal protein S6 (pS6) in peripheral AML blasts using flow cytometry. FLT-3 mutation status (wild type [FLT-3-WT], FLT-3-ITD, or point mutation [FLT-3-D835Y]) was assessed using a PCR-based assay at a central laboratory. The effect of TAK-659 treatment on FLT-3-ITD phosphorylation was evaluated using a plasma inhibitory assay (PIA) as previously described (Levis et al. Blood 2006;108:3477-83).

Results

At data cut-off (June 9, 2016), 15 pts had been enrolled at TAK-659 QD 60 mg (n=4), 100 mg (n=7), or 120 mg (n=4). No dose-limiting toxicity per protocol has been observed. Dose escalation is currently ongoing at 160 mg QD. In the safety population (n=13), median age was 67 yrs (range 25-86), 69% of pts were male, and 38% had received ≥4 prior lines of therapy. Baseline mutation data was available for 12 pts: 6 pts were FLT-3-WT, 3 pts had FLT-3-ITD, 1 pt had FLT-3-D835Y, and 2 pts had concurrent FLT-3-ITD/D835Y mutations. In the safety population, all-grade drug-related AEs occurred in 12 (92%) pts overall; the most common were elevated AST (31%), ALT (23%), and amylase levels (23%). Grade ≥3 drug-related AEs occurred in 7 (54%) pts including: increased ALT, AST, and amylase levels, cataract, positive fungal test, macular fibrosis, pancreatitis, pneumocystis jirovecii pneumonia, rash, and fungal sinusitis (each 1pt). Blood LDH levels were increased in almost all pts (significance unknown).

Three pts discontinued TAK-659 due to AEs and 3 pts died on study; none of these events were considered related to the study drug. Preliminary plasma PK of TAK-659 (n=11, 60-100 mg) was characterized by rapid absorption (median T_max of 2 hours), moderate variability in steady-state exposures (42% coefficient of variation for C1 d15 dose-normalized AUC_tau), and mean accumulation of 2.1-fold after repeated QD dosing for 15 days. Of 9 pts evaluated to date, pS6 was detected at baseline and reduced after dosing in 4 pts (2 FLT-3-ITD; 2 FLT-3-WT). At 60 mg and 100 mg TAK-659, up to 70% inhibition of FLT-3-ITD phosphorylation was observed as assessed by PIA. Early signs of clinical activity were observed, with decreases in peripheral blood myeloblasts observed in some pts. Assessment is ongoing and preliminary efficacy data will be presented.

Conclusions

TAK-659 has a unique mechanism of action with dual inhibition of SYK and FLT-3. Dose escalation to determine the MTD/RP2D is ongoing. TAK-659 exhibits an acceptable PK profile in R/R AML pts, supporting continuous oral QD dosing.