RESUMEN
Acute myeloid leukemia (AML) is associated with dysregulated hematopoietic cell proliferation and increased bone marrow angiogenesis, each regulated by signaling through receptor tyrosine kinases (RTKs). SU5416 is a small molecule inhibitor of VEGF receptors, c-kit and FLT3 and therefore provides a novel opportunity to target both angiogenesis and proliferation in AML. SU5416 was assessed in a phase II hematological malignancy trial in the US, where partial responses were observed in two of 33 patients. Since AML provides a unique platform to evaluate mechanism of action of small molecule inhibitors, investigation of the effect of SU5416 on FLT3 expression and phosphorylation in blood and bone marrow was an additional focus of this trial. Phosphorylated FLT3 was detected by immunoprecipitation/Western analysis in peripheral blood samples from 17 of 22 patients, and seven exhibited strong inhibition of phosphorylation immediately following a 1h SU5416 infusion, demonstrating that SU5416 can modulate RTK phosphorylation in humans. Although no clear correlation with clinical response was observed, analysis of patient plasma drug levels suggested that a threshold SU5416 concentration of 15 microM was associated with FLT3 inhibition. This observation was supported by data from an ex vivo model where AML cells were spiked into human blood, established to mimic the clinical setting and enable more rigorous analysis of effect of SU5416. In addition, FLT3 protein levels were downregulated in patient bone marrow samples, analyzed by an RIA assay. To identify putative predictors of response, patient plasma was analyzed for levels of secreted ligands of SU5416 targets; SCF and FLT3 ligand. Baseline levels of SCF in patients with stable or progressive disease were significantly higher than those in normal donors, whereas FLT3 ligand levels in patients who exhibited progressive disease were significantly lower than those in normal donors. The translational and clinical analyses described in this report provide some insights into the mechanism and duration of action of SU5416.
Asunto(s)
Indoles/farmacología , Leucemia Mieloide/tratamiento farmacológico , Proteínas Proto-Oncogénicas/efectos de los fármacos , Pirroles/farmacología , Proteínas Tirosina Quinasas Receptoras/efectos de los fármacos , Enfermedad Aguda , Adulto , Anciano , Médula Ósea/química , Regulación hacia Abajo/efectos de los fármacos , Femenino , Humanos , Indoles/uso terapéutico , Leucemia Mieloide/sangre , Leucemia Mieloide/patología , Masculino , Proteínas de la Membrana/sangre , Persona de Mediana Edad , Mutación , Fosforilación/efectos de los fármacos , Proteínas Tirosina Quinasas/antagonistas & inhibidores , Proteínas Proto-Oncogénicas/sangre , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Pirroles/uso terapéutico , Proteínas Tirosina Quinasas Receptoras/sangre , Proteínas Tirosina Quinasas Receptoras/genética , Proteínas Tirosina Quinasas Receptoras/metabolismo , Factor de Células Madre/sangre , Tirosina Quinasa 3 Similar a fmsRESUMEN
PURPOSE: Obtaining direct and rapid proof of molecular activity in early clinical trials is critical for optimal clinical development of novel targeted therapies. SU11248 is an oral multitargeted kinase inhibitor with selectivity for fms-related tyrosine kinase 3/Flk2 (FLT3), platelet-derived growth factor receptor alpha/beta, vascular endothelial growth factor receptor 1/2, and KIT receptor tyrosine kinases. FLT3 is a promising candidate for targeted therapy in acute myeloid leukemia (AML), because activating mutations occur in up to 30% of patients. We conducted an innovative single-dose clinical study with a primary objective to demonstrate inhibition of FLT3 phosphorylation by SU11248 in AML. EXPERIMENTAL DESIGN: Twenty-nine AML patients each received a single dose of SU11248, escalated from 50 to 350 mg, in increments of 50 mg and cohorts of three to six patients. FLT3 phosphorylation and plasma pharmacokinetics were evaluated at seven time points over 48 h after SU11248 administration, and FLT3 genotype was determined. Study drug-related adverse events occurred in 31% of patients, mainly grade 1 or 2 diarrhea and nausea, at higher dose levels. RESULTS: Inhibition of FLT3 phosphorylation was apparent in 50% of FLT3-wild-type (WT) patients and in 100% of FLT3-mutant patients. FLT3 internal tandem duplication (ITD) mutants showed increased sensitivity relative to FLT3-WT, consistent with preclinical predictions. The primary end point, strong inhibition of FLT3 phosphorylation in >50% patients, was reached in 200 mg and higher dose cohorts. Downstream signaling pathways were also inhibited; signal transducer and activator of transcription 5 (STAT5) was reduced primarily in internal tandem duplication patients and at late time points in FLT3-WT patients, whereas extracellular signal-regulated kinase (ERK) activity was reduced in the majority of patients, independent of FLT3 inhibition. CONCLUSIONS: This novel translational study bridges preclinical models to the patient setting and provides the first evidence of anti-FLT3 activity in patients. Proof of target inhibition accomplishes a crucial milestone in the development of novel oncology therapeutics.
Asunto(s)
Indoles/toxicidad , Leucemia Mieloide Aguda/tratamiento farmacológico , Proteínas Proto-Oncogénicas/antagonistas & inhibidores , Pirroles/toxicidad , Proteínas Tirosina Quinasas Receptoras/antagonistas & inhibidores , Administración Oral , Adulto , Anciano , Crisis Blástica/patología , Inhibidores Enzimáticos/administración & dosificación , Inhibidores Enzimáticos/sangre , Inhibidores Enzimáticos/toxicidad , Femenino , Genotipo , Humanos , Indoles/administración & dosificación , Indoles/sangre , Leucemia Mieloide Aguda/patología , Masculino , Tasa de Depuración Metabólica , Persona de Mediana Edad , Proteínas Quinasas Activadas por Mitógenos/metabolismo , Fosforilación , Pirroles/administración & dosificación , Pirroles/sangre , Sunitinib , Tirosina Quinasa 3 Similar a fmsRESUMEN
Increased bone marrow angiogenesis and vascular endothelial growth factor (VEGF) levels are adverse prognostic features in patients with acute myeloid leukemia (AML) or myelodysplastic syndromes (MDSs). VEGF is a soluble circulating angiogenic molecule that stimulates signaling via receptor tyrosine kinases (RTKs), including VEGF receptor 2 (VEGFR-2). AML blasts may express VEGFR-2, c-kit, and FLT3. SU5416 is a small molecule RTK inhibitor (RTKI) of VEGFR-2, c-kit, and both wild-type and mutant FLT3. A multicenter phase 2 study of SU5416 was conducted in patients with refractory AML or MDS. For a median of 9 weeks (range, 1-55 weeks), 55 patients (33 AML: 10 [30%] primary refractory, 23 [70%] relapsed; 22 MDS: 15 [68%] relapsed) received 145 mg/m2 SU5416 twice weekly intravenously. Grade 3 or 4 drug-related toxicities included headaches (14%), infusion-related reactions (11%), dyspnea (14%), fatigue (7%), thrombotic episodes (7%), bone pain (5%), and gastrointestinal disturbance (4%). There were 11 patients (20%) who did not complete 4 weeks of therapy (10 progressive disease, 1 adverse event); 3 patients (5%) who achieved partial responses; and 1 (2%) who achieved hematologic improvement. Single agent SU5416 had biologic and modest clinical activity in refractory AML/MDS. Overall median survival was 12 weeks in AML patients (range, 4-41 weeks) and not reached in MDS patients. Most observed toxicities were attributable to drug formulation (polyoxyl 35 castor oil or hyperosmolarity of the SU5416 preparation). Studies of other RTKI and/or other antiangiogenic approaches, with correlative studies to examine biologic effects, may be warranted in patients with AML/MDS.
Asunto(s)
Indoles/farmacología , Leucemia Mieloide/tratamiento farmacológico , Síndromes Mielodisplásicos/tratamiento farmacológico , Pirroles/farmacología , Enfermedad Aguda , Adulto , Anciano , Antineoplásicos/administración & dosificación , Antineoplásicos/farmacología , Antineoplásicos/toxicidad , Apoptosis/efectos de los fármacos , Células de la Médula Ósea/efectos de los fármacos , Examen de la Médula Ósea , Humanos , Indoles/administración & dosificación , Indoles/toxicidad , Leucemia Mieloide/complicaciones , Leucemia Mieloide/patología , Persona de Mediana Edad , Síndromes Mielodisplásicos/complicaciones , Síndromes Mielodisplásicos/patología , Necrosis , Farmacocinética , Proteínas Tirosina Quinasas/antagonistas & inhibidores , Pirroles/administración & dosificación , Pirroles/toxicidad , Inducción de Remisión/métodos , Terapia RecuperativaRESUMEN
FLT3 (fms-related tyrosine kinase/Flk2/Stk-2) is a receptor tyrosine kinase (RTK) primarily expressed on hematopoietic cells. In blasts from acute myelogenous leukemia (AML) patients, 2 classes of FLT3 activating mutations have been identified: internal tandem duplication (ITD) mutations in the juxtamembrane domain (25%-30% of patients) and point mutations in the kinase domain activation loop (7%-8% of patients). FLT3-ITD mutations are the most common molecular defect identified in AML and have been shown to be an independent prognostic factor for decreased survival. FLT3-ITD is therefore an attractive molecular target for therapy. SU11248 is a recently described selective inhibitor with selectivity for split kinase domain RTKs, including platelet-derived growth factor receptors, vascular endothelial growth factor receptors, and KIT. We show that SU11248 also has potent activity against wild-type FLT3 (FLT3-WT), FLT3-ITD, and FLT3 activation loop (FLT3-Asp835) mutants in phosphorylation assays. SU11248 inhibits FLT3-driven phosphorylation and induces apoptosis in vitro. In addition, SU11248 inhibits FLT3-induced VEGF production. The in vivo efficacy of SU11248 was investigated in 2 FLT3-ITD models: a subcutaneous tumor xenograft model and a bone marrow engraftment model. We show that SU11248 (20 mg/kg/d) dramatically regresses FLT3-ITD tumors in the subcutaneous tumor xenograft model and prolongs survival in the bone marrow engraftment model. Pharmacokinetic and pharmacodynamic analysis in subcutaneous tumors showed that a single administration of an efficacious drug dose potently inhibits FLT3-ITD phosphorylation for up to 16 hours following a single dose. These results suggest that further exploration of SU11248 activity in AML patients is warranted.