ALBERT

Description: Abstract 784 Background: In vitro studies have suggested that CML stem cells are resistant to tyrosine kinase inhibitors (TKIs), but in vivo effects in patients have not been prospectively assessed. Furthermore, the inter-individual variation of the leukemic stem cell pool at diagnosis and its possible prognostic value is unknown. Patients: 46 newly diagnosed CML-CP patients were randomized 1:1 to receive either dasatinib 100 mg or imatinib 400 mg QD. The primary endpoint was a comparison of the proportion of Ph+ cells in CD34+CD38− and CD34+CD38+ compartment at 6 months between the study arms. Key secondary endpoints were the fraction of Ph+ cells in the stem cell compartments at 1 and 3 months, and molecular and cytogenetic responses at 3, 6, 12 and 18 months. Experimental endpoints included the percentage of Ph+ cells in the stem cell compartment at diagnosis and its correlation with therapeutic response. Results: One patient in the imatinib arm and none in the dasatinib arm progressed to blast crisis within first 12 months. 4/22 of dasatinib patients have discontinued the treatment due to side-effects (mainly pleural effusion) and 1 patient due to insufficient response. 3/24 imatinib patients have discontinued the therapy (1 blast crisis, 1 side-effects, 1 other malignancy). Early cytogenetic responses were superior in the dasatinib arm: the median percentage of Ph+ cells in the bone marrow was 81% (imatinib) vs. 70% (dasatinib) at 1 month (p=0.15) and 5% vs. 0% at 3 months (p=0.0085). At 12 months all dasatinib (n=20) and 19/20 imatinib patients were in CCyR (results based on patients on treatment at 12 months). MMR rate was significantly higher in the dasatinib arm already at 6 months (70% vs. 20%, p=0.002) and similarly at 9 (75 vs. 26%, p=0.004) and 12 months (88% vs. 40%, p=0.009). Undetectable BCR-ABL1 transcripts (at least CMR4) were observed in 20% of the dasatinib patients at 6 months compared to none in the imatinib arm (p=0.11) and 44% in the dasatinib arm at 12 months compared to 7% in the imatinib arm (p=0.037). The median percentage of Ph+ cells, as measured by FISH (1000 cells analyzed), in the CD34+CD38− fraction at diagnosis was 79% (range 1–100%) compared to 96% (range 50–100%) in CD34+CD38+ fraction. The proportion of Ph+ cells in CD34+CD38− fraction correlated with WBC count (r=0.50, p

Description: Abstract 4427 Imatinib and other tyrosine kinase inhibitors (TKIs) are the standard first-line treatment for patients with chronic myeloid leukemia (CML) and have dramatically improved disease outcome. However, a proportion of patients fails to achieve optimal molecular response (major molecular response, MMR, or better) to TKI treatment and has a marked residual disease even after years of therapy start. The reasons for suboptimal imatinib response are unclear and these patients might benefit from treatment with more potent and broad spectrum 2nd generation TKIs (dasatinib and nilotinib) already from the diagnosis to prevent disease progression. By using a phosphoproteomic approach, we aimed to identify predictive markers for imatinib failure or suboptimal response, which could be used to guide treatment selection already at the time of diagnosis. The study consisted of 9 CML patients in chronic phase with optimal and 10 patients with suboptimal response to imatinib. Patients with suboptimal response had complete cytogenetic response, but no MMR after 18 months of therapy, whereas all patients with optimal response were at least in MMR at 18 months. 7 of 19 patients belonged to intermediate Sokal risk group (5/10 in suboptimal and 2/9 in optimal group) and 12 patients to low Sokal risk group. One additional failure patient without any cytogenetic response to any of the available TKIs was also analyzed (patient had M351T imatinib resistant mutation). Bone marrow mononuclear cells (BM MNC) were collected at the time of diagnosis prior to any TKI therapy and were analyzed for 46 kinase phosphorylation sites central in the pathogenesis of CML (R&D Human Phospho-Kinase Array Kit). BM MNCs from 3 healthy controls and the K562 Ph+ cell line were used as controls. Quantitative analyses of the phosphoproteins were performed by measurement of array spot densities with CellProfiler2.0. In K562 cell line, the protein phosphorylation was most prominent in pSTAT5b Y699 and only modest in pSTAT5a Y694. In diagnostic BM samples, pSTAT5b and pSTAT5a levels showed marked variability within individual patients. Src Y419 (P