YM155 sensitivity in pediatric acute lymphoblastic leukemia.

Abstract

9555 Background: Despite advances in treatment and outcomes in pediatric acute lymphoblastic leukemia, there continue to be subsets of patients that are refractory to standard intensive chemotherapy. Therefore, novel agents are needed to further advance treatment for this disease. YM155 (Astellas) is a selective suppressant of survivin expression. Survivin has been shown to be over-expressed in malignant cells and in relapsed ALL. Early adult phase I/II studies show promise in both tolerability and possible efficacy in B-cell malignancies. Methods: Fresh diagnostic leukemic patient samples, ALL cell lines, and xenograft samples were obtained and subjected to YM155 at doses ranging from 1nM to 10µM. Samples were then tested for viability using standard methane-thiosulfate, apoptosis using Guava nexin Annexin V binding, protein expression using immunoblot, and P53 activation with phospho-flow cytometry. Results: The median IC50 for viability and apoptosis for the samples are: NCI standard risk ALL 5.3nM ±3.47, NCI high risk ALL 91.76 nM ±93.42, T-ALL 336.6nM ±147.7, AML 333.6nM ±489, Ph+ALL xenografts 3.8nM ±1.04, and ALL cell lines 18.5nM ±135. Ph+ALL samples, including primary patient, xenograft, and dasatinib (BMS) resistant samples remain significantly sensitive to YM155. For dasatinib sensitive samples, combination therapy suggests an additive effect by isobologram analysis. Immunoblot and RT2-PCR Arrays (Qiagen) identify that multiple protein expression are decreased with YM155 treatment. Conclusions: Our data supports the model of the use of YM155 as a treatment for ALL including an added benefit in combination with dasatinib in Ph+ALL. Although initial studies suggested that YM155 is a selective suppressant of survivin, subsequent studies are beginning to identify off target effects. These off target effects may enhance the drugs potential for activating cell death. Finally, we show that screening primary samples with YM155 has the potential to select a target population that is more sensitive to YM155 treatment. Future studies will be designed to develop YM155 as an additional therapeutic agent for pediatric acute lymphoblastic leukemia.