Analysis of Bone Marrow Microenviroment Factors As Early Markers of Response in Patients with Newly Diagnosed Bcr-Abl Positive CML in Chronic Phase Treated with Nilotinib.

Abstract 2795

In the era of molecular target therapy, whereas Imatinib has shown an overall survival rate of 85% and an estimated event-free survival of 55% in a 8 year result update of IRIS trial, several in vitro data have confirmed that Ph+ stem cells housed within BM niches are resistant to TKI treatments. Second generation TKI Nilotinib has been designed with improved target specificity over Imatinib. Its efficacy in the treatment of patients with CML who are resistant to or intolerant to Imatinib led to the registration of a clinical trial CAMN107EIC01, a phase IIIb, multicentre, open-label study applying Nilotinib in the treatment of newly diagnosed CML. The aim of the current study (CAMN107EIC01 sub-study N10) is to define BM microenvironment markers that nurture and determine leukemic stem cell fate in the BM niches of Nilotinib treated patients. We enrolled 37 patients involving 21 Italian centers, from whom written informed consent has been obtained for sub-study N10. Patients have been monitored by Real Time RT-PCR (RT-qPCR) for the expression of the fusion mRNA BCR-ABL, as specified by the core protocol. Major Molecular Response (MMR) is defined as detectable disease ≤0.1% BCR-ABL according to the international scale (^IS). Plasma and mononuclear cells have been collected from BM and PB samples of the enrolled patients at the screening visit (V0) and after 3 months of treatment (V4). We purified total RNA from BM and PB mononuclear cells of the enrolled patients to screen by RT-qPCR the expression of 10 genes (ARF, cKIT, CXCR4, FLT3, LIF, NANOg, PML, PRAME, SET and TIE), involved in the regulation of the stemness and survival signaling of hematopoietic stem cells. RT-qPCR results were normalized by the expression of ABL mRNA (Normalized mRNA copy Number: NCN). Moreover, we evaluated by multiplex ELISA assay BioPlex, the BM plasma concentration level of 20 cytokines (IL1a, IL1b, IL3, IL6, IL7, IL8, IL10, IL12, IL15, G-CSF, M-CSF, SCF, SDF1, TRAIL, HGF, PDGFbb, GM-CSF, MIP-1a, TNFa and VEGF), known to be key factors in the interaction of Ph+ stem cells to BM microenvironment. The interim analysis of MMR until the 12^th month is available in 26 out of 37 enrolled patients. We observed that MMR is achieved during the first 12 months of treatments in 17 out of 26 (65%) patients. Molecular analysis showed that the expression of two genes involved in the regulation of stem cell pluripotency (NANOg) and cytokine signaling (SET) were significantly down-regulated at V0 in PB mononuclear cells of patients achieving MMR in comparison to cells from non-responding patients (4vs21 NANOg NCN, p=0.05; 8vs32 SET NCN, p=0.05). These data were also confirmed on BM patient's sample. Moreover, we investigated the concentration level of the above-mentioned soluble factors in BM plasma samples of all 37 enrolled patients at both V0 and V4. We observed that the BM plasma level of several cytokines produced by leukemic cells significantly decreased during the first 3 months of Nilotinib treatment: IL3 (54vs3ng/ml; p=0.02), M-CSF (56vs12 ng/ml; p=0.005), SCF (170vs104 ng/ml; p=0.007), HGF (7565vs705 ng/ml; p<10-5), IL10 (67vs28 ng/ml; p=0.02), IL12 (167vs73 ng/ml; p=0.03) and VEGF (1326vs404 ng/ml; p= 0.0003). Whereas the plasma level of a stroma-derived cytokine SDF1, playing an important role in regulating the retention of hematopoietic progenitor cells within the BM microenvironment, was significantly increased at V4 respect to V0 (171vs390 ng/ml; p= 0.0004). Also, we observed that SCF and HGF concentration levels were significantly lower in the plasma of patients at V4 that achieved MMR compared to those in non- responding patients (71vs134 ng/ml, p=0.02; 421vs737 ng/ml, p=0.01; respectively). These data indicate that expression analysis of genes involved in cell pluripotency (NANOg) and cell signaling (SET), as well as measurement of the plasma concentration level of several soluble factors produced by leukemic progenitor cells and stroma cells (SCF and HGF) may assist in the early prediction of molecular response in patients treated with Nilotinib. Moreover, further studies need to be conducted to evaluate the functional role of stroma secreted cytokines, such as SDF1 and VEGF, in the regulation of TKI responsiveness in these subset of CML patients, since it may be plausible that the same factors that modulate hematopoiesis promote also leukemogenesis, enhance blast survival and make them resistant to treatment within the BM microenvironment.