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Chronic myeloid leukemia (CML) is specifically associated with the t(9;22)(q34;q11) reciprocal translocation giving rise to the Philadelphia chromosome and the subsequent formation of the BCR/ABL1 fusion gene, encoding a constitutively active tyrosine kinase. Advances in targeted therapies in chronic phase CML, notably the use of tyrosine kinase inhibitors (TKIs) such as imatinib mesylate (IM), have achieved successful treatment outcomes. However, some patients fail to achieve optimal response, and a substantial proportion of patients develop resistance to IM, which is frequently associated with mutations in the ABL kinase domain. Although BCR/ABL1 fusion oncogene is a key molecular marker involved in the pathogenesis and the clinical course of CML, molecular or cellular events that initiate leukemogenesis or drive translocation of the BCR/ABL1 genes are incompletely understood and little is known about individual susceptibility to this disease. Moreover, it is still unclear whether BCR/ABL1 oncoprotein alone is sufficient to explain the full range of clinical responses to ITKs. There is mounting evidence that genetic factors may play an important role in susceptibility to CML and variability in drug responsiveness. Polymorphic variants of several genes are linked to variations in expression, function, drug disposition and drug response and are potential factors accounting for susceptibility to complex diseases or drug resistance as they can uniquely influence the quality and quantity of gene product. Association studies have been performed to identify genetic variants associated with CML susceptibility and progression, but data are lacking for Argentina. In the present study, we determined the distribution of polymorphisms on TP53 tumor suppressor gene, drug transporter (ABCB1) and drug-metabolizing (glutathione-S-transferases, GSTs) genes to identify markers of susceptibility and pharmacogenetic response in Argentinian patients with CML. Genomic DNA samples from peripheral blood of 141 patients (69 females/72 males, median age 50.8 ± 1.3 years,) treated with IM and 141 age and sex matched healthy controls were evaluated. IM therapy failure was defined by cytogenetics and qRT-PCR in 2 consecutive studies, finding 76 cases that fail treatment. All individuals provided their informed consent according to institutional guidelines and the study was approved by the Ethics Committee of our Institution. GSTM1 and GSTT1 gene deletion polymorphisms and single nucleotide polymorphisms (SNPs) in GSTP1 (313A> G), TP53 (215C> G) and ABCB1 (3435C> T, 1236 C> T and 2677G>T/A) were determined using PCR-based methods. BCR/ABL1 transcript level was analyzed using RT-PCR and ABL1 mutations were identified by RT-PCR and sequencing. Comparison of genotypes between patients and controls as well as regarding clinical parameters was performed by logistic regression. The Kaplan-Meier curves were analyzed using the log-rank test. The level of significance was p Disclosures Moiraghi: Bristol Myers Squibb: Speakers Bureau; Novartis: Speakers Bureau. Bengio:Novartis: Speakers Bureau; Bristol Myers Squibb: Speakers Bureau.

Philadelphia (Ph) chromosome in acute lymphoblastic leukemia (ALL) is found nearly in 20-30% adults and 5% children. Ph chromosome results from the reciprocal translocation t(9;22)(q34;q11) joining the tyrosine kinase c-ABL1 proto-oncogene on chromosome 9 to BCR gene on chromosome 22. The majority of Ph breakpoint in ALL occurs in the minor breakpoint cluster region at first intron of the BCR gene, and results in the fusion of BCR exon 1 to ABL1 exon 2 (e1a2) generating the oncoprotein p190BCR-ABL1. Ph+ ALL patients present an aggressive disease with a poor prognosis. Current treatment includes potent chemotherapy and tyrosine kinase inhibitors, such as imatinib. The aim of this study was to quantify BCR-ABL1 transcripts in ALL Ph+ patients at different stages of treatment in order to evaluate the kinetics of the tumor clone in response to treatment. We reported a preliminary analysis of the clinical trial GATLA LLA-Ph+2011 (Grupo Argentino de Tratamiento de la Leucemia Aguda LLA-Ph+) that includes patients from 1 to 21 years old newly diagnosed Ph+ ALL. Written informed consent was obtained from all subjects. Diagnosis of Ph+ALL was confirmed by the presence of Ph chromosome and/or positive molecular analysis for detection of BCR-ABL1 fusion transcripts. All patients received induction treatment consisting of vincristine, daunorubicin, prednisolone, asparaginase, and metrotexate. Imatinib was administered 300 mg/m2/day from day 15 of induction until the initiation of conditioning for alloHSCT or to the end of maintenance therapy. The clinical protocol consist in an induction IA (33 days) and IB (28 days), consolidation RA1, RA2 and RA3, re-induction (Protocol II A and B, 36 days each) and maintenance to complete 2 years of treatment. Eligible patients are transplanted after the third block. Minimal residual disease (MRD) monitoring was performed by one-step quantitative RT-PCR assays in bone marrow and/or peripheral blood, using RotorGene® Qiagen; at the end of induction AI, previous RA1, RA2, RA3 and protocol II Fase IIA, IIB and during maintenance or post-alloHSCT. BCR-ABL1 quantification was expressed relative to the amount of ABL1 mRNA. We studied a control group of pediatrics positive P190 isoform bone marrow samples at diagnosis in order to establish our basal reference to estimate the logarithmic reduction of BCR-ABL1 transcripts for our cohort. The obtained mean value of BCR-ABL1(e1a2)/ABL1 in the control group was 55.5% (range 29% - 92%). The molecular response was defined as optimal (OMR, OMR-undetectable) if the BCR-ABL1/ABL1 ratio was lower than 0.055%. A total of 25 subjects (male: female = 16: 9) were enrolled into the study from November 2011 to July 2014. The median age was 7 (range 2 - 19) years old. Type of BCR breakpoint was minor (e1a2) in 96% of patients, and only one present a rearrangement corresponding to major BCR (b3a2). During the follow up (median: 15 months), five patients (20%) died: 3 by sepsis, 1 by post alloHCT complications, and 1 due to disease progression. Two patients had to rotate to dasatinib because of disease relapse: one in central nervous system and the other post alloHCT. Our preliminary results showed that the overall survival was 79%±10% and the survival free of event (death, molecular and disease relapse) was 67%±10% at 12 months. We serially measured BCR-ABL1 at different trial stage (AI, RA1, RA2, RA3, Protocol II) and OMR was 13.3%, 41.2%, 33.3%, 45.5% and 76.9%, respectively. Among 17 evaluable patients on maintenance and post alloHCT, 88% (15/17) obtained OMR values, and among them, 87% (13/15) presented OMR-undetectable values. We evaluated the kinetics of the tumor clone under treatment regarding prognostic factors. Patients older than 10 years showed a higher rate of OMR at RA1 (83% vs 27%, p=0.05). However, all evaluated younger patients reached an OMR at protocol II stage (100% vs 33%, p=0.045), showing a sustained and deeper molecular response. Other evaluated parameters did not show a relationship with OMR at different stages. Our preliminary data showed that BCR-ABL1 quantification may be a good marker to evaluate response to treatment in Ph+ positive ALL patients. BCR–ABL1 transcripts dropped to undetectable levels in 76% (13/17) of evaluable cases at the later stage of treatment. Also, 77% of patients achieved an OMR at Protocol II not only might provide a better chance for receiving alloHSCT but also might contribute to durable remissions. Disclosures No relevant conflicts of interest to declare.

Abstract 4877 Chronic Myeloid Leukemia (CML) is a clonal myeloproliferative disorder characterized by the reciprocal chromosomal translocation between chromosome 9 and 22, t(9;22)(q34;q11), known as Philadelphia chromosome. At molecular level, this cytogenetic aberration associates with a chimeric BCR-ABL fusion gene responsible for the pathogenesis of the disease. Targeting BCR-ABL with tyrosine kinase inhibitors (TKIs) has led to a rapid clinical response in most CML cases; however, harboring of point mutations within the kinase domain (KD) of BCR-ABL is the most common mechanism responsible for acquired resistance to therapy. The objective of this work was to evaluate the expression profiles of 4 different genes involved in proliferation, differentiation or cell survival, in order to study their association with acquired missense mutations within the KD of BCR-ABL. Due to its clear involvement in cell proliferation and apotosis the following genes were analyzed. CAMKIIγ (Ca2+ /calmodulin dependent protein kinase IIγ) is a critical regulator of multiple signalling networks regulating the proliferation in myeloid leukaemia. HSP70 (Heat Shock protein 70) is a chaperone protein that protects cells from apoptotic and necrotic stimuli. HSP90 (Heat Shock protein 90) is a chaperone that facilitates folding of client proteins such as BCR-ABL. Ki-67 is a nuclear antigen associated with cellular proliferation and ribosomal RNA transcription. Total RNA was extracted from 50 TKI-resistant CML-patient's PBMC samples; by quantitative real time-PCR (QRT-PCR) (SybrGreen method, melting analysis and β2-microglobulin as an endogenous control reference gene) we measured the gene expression of CaMKIIγ, Ki67, HSP70, HSP90 and BCR-ABL. All patients were treated with TKIs (26 imatinib, 13 nilotinib, 11 dasatinib) and showed primary lack or loss of haematological and/or cytogenetic response according to the ELN (European Leukaemia Net) criteria. To characterize TKI-resistant mutations within the KD of the chimeric BCR-ABL gene, ABL exons 4, 5, 6 and 7 were subjected to automated DNA sequencing following a nested- BCR-ABL-specific PCR. Mutations were observed in 27/50 cases at 15 different residues: 1 L248V, 1 G250E, 1 Y253H, 5 E255K/V, 1 E279K, 1 V289F, 4 T315I, 2 F317L, 1 L348M, 3 M351T, 1 E355G, 1 N358S, 2 F359V/C, 2 L387M and 1 L389V. Remaining 23 CML cases did not show mutations (detection limit 10–20%). Our results showed a significant increase in the expression of CaMKIIγ and HSP70 and decrease of HSP90 in mutated patients (MT) with respect to cases without mutations (WT) (p Taking into account these results we design a score (TKI-MT) to estimate the likelihoods for a patient to harbor TKI-resistance mutations using the transcript normalised expression of CaMKIIγ, HSP70 and HSP90 as follows: [Log10(CaMKIIγ) + Log10(HSP70) – Log10(HSP90)]. TKI-MT scores from 27 and 23 patients from the MT and WT groups respectively were analysed by use of ROC curves in order to find an optimal cut-off value to classify new unstudied cases. We found that patients with TKI-MT scores over a cut-off value of −0.79 showed 4.8 times more probabilities to present TKI-resistance mutations than those below −0.79 (OR 4.8, CI95% 1.3–17.6, P We concluded that the expression of CaMKIIγ, HSP70 and HSP90 allowed prediction of mutations in the ABL tyrosine kinase domain with 82% of specificity in CML patients treated with TKIs and associated with lack or loss of response. Disclosures: No relevant conflicts of interest to declare.