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Human bone marrow stromal cells (hBMSCs) may contribute to the growth of tyrosine kinase inhibitor (TKI)-resistant chronic myelogenous leukemia (CML). However, there are certain differences in biology between CML and Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL). Little is known about the role and mechanism of hBMSCs on the growth of TKI-resistant Ph+ ALL. The current study co-cultured hBMSCs with the TKI-resistant SUP-B15. Next, the proliferation of SUP-B15 was detected using a Cell Counting Kit-8. Additionally, quantitative polymerase chain reaction and flow cytometry were used to detect the expression of the associated genes and proteins. The present study explores the role and mechanism of hBMSCs on the growth of TKI-resistant Ph+ ALL. The current study showed that hBMSCs promoted the proliferation of TKI-resistant Ph+ ALL. This was shown by the increase in cells in the S+G2-M phase of the cell cycle. It was also found that the expression of cyclins A, C, D1 and E was increased. Apoptosis was inhibited through upregulation of anti-apoptotic genes [B-cell lymphoma-2 (BCL-2) and BCL-extra large] and downregulation of apoptotic genes (BCL-XS, BCL-2-associated X protein, and caspases 3, 7 and 9). Expression of the breakpoint cluster region (BCR)-Abelson murine leukemia viral oncogene homolog 1 (ABL) gene, Wnt5a, and Wnt signaling pathway-associated genes (glycogen synthase kinase-3β, β-catenin, E-cadherin and phosphoinositide 3-kinase) and transcription factors (c-myc, ephrin type-B2, fibroblast growth factor 20 and matrix metalloproteinase 7) was also increased. Furthermore, the expression of drug resistance genes (low-density lipoprotein receptor, multidrug resistance-associated protein and multi-drug resistance gene) was increased and the expression of anti-oncogenes (death-associated protein kinase and interferon regulatory factor-1) was decreased. It was concluded that hBMSCs promote the growth of TKI-resistant Ph+ ALL by these aforementioned mechanisms. Therefore, targeting hBMSCs may be a promising approach for preventing the growth of TKI-resistant Ph+ ALL.

The discovery of Philadelphia (Ph) chromosome in 1959 was a landmark moment in the history of targeted therapies for cancer. The BCR-ABL fusion gene formed as a result of this translocation is the key pathogenetic event of chronic myeloid leukemia (CML) and Ph-positive acute lymphoblastic leukemia (ALL). Currently, there are five tyrosine kinase inhibitors (TKIs) available in the clinic to target the BCR-ABL kinase. The last one to be added to the list is ponatinib. Ponatinib is highly effective even in the presence of mutations such as T315I that render all other TKIs ineffective. The initial enthusiasm following the impressive results from the Ponatinib Ph-positive ALL and CML Evaluation (PACE) trial was dampened by the emergence of arterial occlusive events. With a dose-adapted strategy, the drug seems to be ready for a comeback. We review the drug ponatinib, including the history, chemistry, mechanism of action, pharmacokinetics, clinical trial data, ongoing clinical trials, and adverse events.

BCR-ABL fusion gene t(9;22)(q34;q11) occurs in only 3% of pediatric acute lymphoblastic leukemia (ALL) cases. Previously, less than 40% of Philadelphia-positive ALL patients were cured with intensive chemotherapy. The use of imatinib (340 mg/m2/day) added to an intensive chemotherapy regimen has improved the outcome in this population at 3 years to an event-free survival of 80%. Imatinib treatment alone was administered after remission induction chemotherapy to a patient with Philadelphia-positive ALL who presented with serious chemotherapy toxicity, so that intensive chemotherapy could not be maintained. This is the only patient in the literature who survived remission for more than 2.5 years with imatinib treatment only. Copyright © 2011 S. Karger AG, Basel.

Philadelphia-positive acute lymphoblastic leukemia (Ph+ ALL) still represents a major challenge. We report the experience of the Italian Association of Pediatric Hematology and Oncology (AIEOP) with allogeneic hematopoietic stem cell transplantation (HSCT) in children with Ph+ ALL from 1990 to 2008. Sixty-nine patients received HSCT from either a related (37, 54%) or an unrelated (32,46%) donor. Twenty-five patients (36%) underwent transplantation before 2000 and 44 (64%) after 2000. Twenty-three patients (33%) received lmatinib mesylate treatment before HSCT and seven (10%) after HSCT. After a median follow-up of 56 months, the overall survival (OS) probability was 51% (95% confidence interval [Cl], 38-63), the leukemia-free survival (LFS) was 47% (95% CI, 34-59), transplantation-related mortality (TRM) was 17% (95% CI, 10-30), and relapse incidence (RI) was 36% (95% CI, 26-50). Transplantation in first complete remission, female gender, and lower WBC count at diagnosis were associated with a better LFS in both univariate and multivariate analyses. Patients with p210 transcript had a trend for a worse prognosis compared with those who had the p190 transcript. Our series confirms the role of HSCT in the eradication of Ph+ ALL. Early HSCT is recommended once morphologic remission is obtained. Biol Blood Marrow Transplant 18: 852-860 (2012) (C) 2012 American Society for Blood and Marrow Transplantation

Background: Deletions of IKZF1 gene, encoding for a regulator of lymphocyte differentiation, occur in more than 80% of adult patients (pts) with Ph+ ALL and significantly affect the prognosis. The deletions either involve the entire IKZF1 locus, resulting in loss of function, or delete an internal subset of exons, resulting in the expression of dominant negative isoforms. To better stratify Ph+ ALL pts according to IKZF1 status, we set up, validate and assess the routine applicability of a IKZF1 deletion screening strategy based on a multiplex-PCR. Patients and methods: We studied 87 adult BCR-ABL1+ ALL pts. For each type of common IKZF1 deletion (D4-7, D2-7, D4-8) an appropriate pair of primers will be designed using Primer 3 (http://frodo.wi.mit.edu/primer3/). Their ability to efficiently amplify the deletion was tested. PCR amplifications was performed using 50 ng genomic DNA as template for each reaction and a FastStart Taq DNA Polymerase (Roche Diagnostics). For each patient 3 amplicons were generated and sequenced (amplicon A for D4-7, amplicon B for D2-7 and amplicon C for D4-8). Moreover, a multiplex amplification strategy was assessed and a forth amplicon was generated and sequenced (forward primers were localized on intron 1 and 3, the reverse ones in the intron 7 and at the end of the gene, after the exon 8). The size of amplicons depends on the positions of the breakpoints in the IKZF1 gene and on the number of nucleotides added at the conjunction. It was in the range of 450-600 nucleotides. A positive control was used for each run. Results: On 87 pts previously analyzed by SNPs array, we identify IKZF1 deletions in 69/89 (78%) samples. Deletions were: 51 D4-7, 12 D2-7 and 4 D4-8; in 2 cases the deletion was extended to all gene, and 2 pts presented two breakpoints simultaneously. Multiplex PCR and subsequent sequencing were performed for most common deletions on 40 pts confirming previous results and indentifying the precise genomic positions of breakpoints and the nucleotides added at the conjunction. This rearrangement has been used to strictly monitor Minimal Residual Disease (MDR) during the follow-up and at relapse to confirm the clonal fidelity. Conclusions: We set-up a method rapid sensitive and with less amount of DNA sample, to screen Ph+ ALL pts at diagnosis and to monitor MRD during the treatment. Supported by: European LeukemiaNet, AIL, AIRC, FIRB 2006, Fondazione del Monte di Bologna e Ravenna, Strategico di Ateneo, GIMEMA Onlus.

Loss of CDKN2A, encoding p16/INK4A and p14/ARF tumor suppressors, has been associated with poorer survival and higher leukemia-initiating- cell-frequency in xenograft models (Notta F et al. Nature 2011). Recently, using genome-wide single nucleotide polymorphisms arrays and gene candidate deep exon sequencing, we identified CDKN2A deletions in 29% (29/101) adult newly diagnosed Ph+ ALL patients and in 47% relapsed cases. Accordingly, here we aimed to investigate the functional consequences of genomic deletions and their prognostic value. By quantitative real-time PCR a significant difference in the expression of CDKN2A was observed among cases with heterozygous (p = 0.04) and homozygous (p = 0.01) loss compared to normal cases, suggesting that deletions lead to CDKN2A haploinsufficiency. In order to investigate their clinical implications, data were collected from 81 patients (median follow-up: 25.2 months- range 2.1-148.1; median age at diagnosis: 54 years- range, 18-76; CDKN2A loss in 29, 36%, cases). 72 patients (89%) were enrolled in the GIMEMA clinical trials (12 patients in GIMEMA LAL0201-B protocol, 13 in LAL2000 and 47 in LAL1205 protocols), while 9 patients (11%) were enrolled into institutional protocols. By univariate analysis a shorter overall survival (OS) and disease-free survival (DFS) were found in patients with CDKN2A deletion compared with those wild-type (OS: 27.7 v 38.2 months, respectively, p = 0.0206; DFS: 10.1 vs 56.1 months, respectively, p = 0.0010). Moreover, a higher cumulative incidence of relapse for patients with CDKN2A deletion (73.3 vs 38.1; p = 0.0014) was also recognized. The multivariate analysis confirmed the negative prognostic impact of CDKN2A deletion on DFS (p = 0051). These results show that there are genetically distinct Ph+ ALL patients with a different risk of leukemia relapse and that testing for CDKN2A alterations at diagnosis may help in risk stratification. Furthermore, since the loss of CDKN2A eliminates the critical tumor surveillance mechanism and allows proliferation, cell growth and tumor formation by the action of MDM2 and CDK4/6, attractive drugs to prevent disease recurrence could be represented by the inhibitors of MDM2 and CDK4/ CDK6. These drugs are currently under investigation in in vitro studies by our group. Supported by: ELN, AIL, AIRC, Fondazione Del Monte di Bologna e Ravenna, FIRB 2006, PRIN 2008, Ateneo RFO grants, Project of integreted program, Programma di Ricerca Regione – Università 2007 – 2009.

Checkpoint kinase 1 (Chk1) and 2 (Chk2) are serine/threonine kinases regulated by Ataxia-Telangiectasia and Rad3-related (ATR) kinases and involved in the DNA damage response and in the regulation of cell cycle progression at S-G2 phase. Deregulation of these pathways has been previously described in BCR-ABL positive cells and involved in chemoresistance. Based on the potential utility of DNA checkpoint inhibition in enhancing tumor cell death, in this study we aimed to investigate the preclinical activity of PF-0477736 (Pfizer), a potent and selective Chk1/2 inhibitor, in Ph+ ALL and to determine potential biomarkers of functional inhibition. We first examined Chk1 and Chk2 mRNA expression levels in 45 newly diagnosed Ph+ ALL patients, in their paired remission samples, in 14 relapsed cases and in 3 Ph+ cell lines (BV-173, SUPB-15 and K562) by Fluidigm Dynamic Array real-time qPCR assay (Fluidigm Corporation). Higher transcript levels of Chk1 but not Chk2 were found in newly diagnosed patients compared to remission samples (p = 0.0009 for Chk1 and p= 0.8183 for Chk2). Chk1 transcript levels were comparable between diagnosis and relapsed cases (p = 0.5728), suggesting that the ATR-Chk1 pathway is strongly activated in Bcr-Abl-positive cells. This was confirmed by phosphorylation of Chk1 Ser317 by western blotting analysis in Ph+ cell lines. We then evaluated the effect of PF-0477736 as single agent on cell viability using the Cell Proliferation Reagent WST-1 (Roche). BV-173, SUPB-15 and K562 cell lines were incubated with increasing concentration of PF-0477736 (0.005-2 μM) for 24, 48 and 72 hours. PF-0477736 inhibition of Chk1 resulted in dose and time-dependent cytotoxicity with IC50 at 24 hours of 0.1–0.5 μM, with BV-173 being the most sensitive, while K562 the most resistant. These results were confirmed in primary blasts cells from a Ph+ ALL patient with wild-type Bcr-Abl and from 3 cases harboring the T315I Bcr-Abl mutation found to be insensitive to the available TKIs (IC50 ranged from 0.1–0.5 μM at 48 hours). Consistent with the WST-1 results, Annexin V/Propidium Iodide staining analysis showed a significant increase of apoptosis at 24 and 48 hours in both cell lines and primary cells. To test whether increased apoptosis resulted from Chk1 inhibition, we assessed the changes in phosphorylation of Cdc25c phosphatase, which is inactivated by Chk1 to prevent mitotic entry, and of {gamma}H2AX, which is increased in response to DNA damage. Western blot analysis showed that PF-0477736 decreases the inhibitory phosphorylation of Cdc25c Ser216 and increases levels of {gamma}H2AX. Since multiple studies reported a higher activity of PF-0477736 against p53-defective cancer cells, we performed a mutational screening by amplification and subsequent sequencing of all coding exons of p53. All cell lines except for K562 and primary leukemia cells lacked mutations in the p53 gene, demonstrating that in Ph+ ALL PF-0477736 is highly effective also on p53 wild-type tumor cells. Finally, in order to elucidate the mechanisms of action of PF-0477736 and to determine biomarkers of response, gene expression profiling analysis (Affymetrix GeneChip Human Gene 1.0 ST) was performed on 3 treated Ph+ cell lines and their untreated counterparts. Consistent with a specific Chk1-mechanism of action, treatment resulted in differential expression (p < 0.05) of 211 genes including those involved in apoptosis and cell cycle (CEBPB, CUL1, Histone H1-H2A, 2B family clusters, Histone H4, DHX15, SNCB, FOS) and DNA damage, such as DNA-damage-inducible transcript 3 (DDIT3) and growth-arrest and DNA damage-inducible proteins GADD34 and GADD45a, suggesting that PF-0477736 contributes to a checkpoint abrogation and to an activation of DNA damage response in Ph+ ALL cells. In conclusion, for the first time we demonstrate in a large cohort of Ph+ ALL patients an over-expression of Chk1, providing a strong rational for its inhibition. In vitro treatment of Ph+ ALL cells with PF-0477736 alone resulted in reduction of inhibitory phosphorylation of Cdc25c, inhibition of proliferation and induction of biomarkers of DNA damage and apoptosis, suggesting that single-agent Chk1/2 inhibition may be an effective treatment strategy for Ph+ ALL.

Introduction. Little is known about alterations of cyclin dependent kinase inhibitors p15INK4B, p16INK4A and p14ARF due to single nucleotide polymorphisms (SNPs) located within the CDKN2A/B genes and/or neighbouring loci. In order to investigate the potential involvement of such common DNA sequence variants in leukemia susceptibility, an association study was performed. Methods. 23 SNPs spanning the MTAP, CDKN2A/Band CDKN2BAS loci, as well as relative intergenic regions were genotyped in a case-control cohort made up of 149 leukemia patients, including Philadelphia positive (Ph+) acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML) samples, and 183 healthy controls. 6 SNPs were selected on the basis of their previous association with several diseases, such as coronary artery disease (rs2891168, rs518394, rs564398, rs10757278), type 2 diabetes mellitus (rs564398), frailty (rs2811712). The remaining 17 SNPs were selected to deepen the SNPs coverage for the examined region. Genotyping was performed using iPLEX Gold technology and MassARRAY high-throughput DNA analysis with Matrix-assisted laser desorption/ionization timeof-flight (MALDI-TOF) mass spectrometry (Sequenom, Inc., San Diego, CA). Results. A total of 17 SNPs, spanning the 9p genomic interval that encompasses the MTAP, CDKN2A/B and CDKN2BAS loci, were successfully genotyped and used for investigating their potential associations with the leukemia phenotypes. Five SNPs (rs1012713, rs10965179, rs34011899, rs3731232, rs3218010) with MAF 20% missing call rates, were instead excluded from the association analysis and potential population stratification affecting the control sample was ruled out as its genotypes distribution satisfies the Hardy-Weinberg equilibrium criterion. Among the 17 SNPs, rs564398, mapping to the CDKN2BAS locus that encodes for ANRIL antisense non-coding RNA, showed a statistically significant correlation with the ALL phenotype, with a risk pattern that was compatible with an overdominant model of disease susceptibility and a OR of 2 (95% CI, 1.20 to 3.33; P=7.1¥103). Conclusions. Since a co-ordinated regulation of ANRIL and p14/ARF, p16/CDKN2A, p15/CDKN2B transcription has been already observed in both physiologic and pathologic conditions, we hypothesized that rs564398 association reflects a condition of high linkage disequilibrium between such polymorphism and a causative variant that is able to alter CDKN2A/B expression profiles by changing ANRIL dosage, thus leading to abnormal proliferative boosts and consequent increased ALL susceptibility. Supported by European LeukemiaNet, AIL, AIRC, FIRB 2006, PRIN 2008, Ateneo RFO grants, Project of integrated program (PIO), Programma di Ricerca Regione - Università 2007-2009.

Abstract 575 Incorporation of the tyrosine kinase inhibitor (TKI) imatinib in the frontline treatment of Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL) patients (pts) has significantly improved the anti-leukemic efficacy of induction therapy. In contrast to chronic myeloid leukemia (CML), however, responses are short-lived and relapse is frequently associated with the selection of Bcr-Abl kinase domain (KD) mutations, fostered by the high genetic instability of Ph+ ALL cells. The advent of the 2nd-generation TKIs dasatinib and nilotinib has brought additional treatment options both for newly diagnosed and for imatinib-resistant pts. To analyze the changes they have brought in mutation frequency and type, we have reviewed the database recording the results of BCR-ABL KD mutation analyses done in our laboratory from January 2004 to June 2011. Overall, 781 tests on 258 Ph+ ALL pts (number of tests per pt, range: 1–15) were performed by denaturing high-performance liquid chromatography (D-HPLC) followed by direct sequencing of D-HPLC-positive cases. One hundred and fourty-three pts were analyzed because of imatinib resistance. One hundred and one out of 143 (71%) pts scored positive for one or more KD mutations. Similarly to what is know to occur in CML, hematologic and cytogenetic resistance were by far more frequently associated with mutations than molecular resistance (Bcr-Abl transcript increase as assessed by RT-Q-PCR). Overall, mutations at thirteen residues were detected. In contrast to what can be observed in CML, three mutations were by far the most frequent, accounting for almost 75% of the mutated cases: T315I (n=38 pts, 37%), E255K/V (n=19 pts, 18%) and Y253H (n=19 pts, 18%). The other mutations were, in order of frequency: F359V/I, M244V, M351T, F317L, G250E, Q252H, L387M, D276G, L248R, E279K. Nine out of 103 (9%) pts had two mutations, in the same (2 pts) or in different (7 pts) subclones. In 84 pts who were analyzed because they were reported to have developed resistance to dasatinib (n=72) or nilotinib (n=12) as 2nd- or 3rd-line TKIs, 65 (77%) had newly acquired mutations (57/72 dasatinib-resistant pts and 8/12 nilotinib-resistant pts). The most frequent newly acquired mutation in this setting was the T315I, detected in 35/57 (61%) cases acquiring mutations on dasatinib and in 2/8 cases acquiring mutations on nilotinib. Other recurrent newly acquired mutations were F317L, V299L, T315A in dasatinib-resistant pts and Y253H and E255K in nilotinib-resistant pts. Thirty out of 65 pts (46%) were positive for multiple mutations (2 to 4 mutations, in the same or in different subclones or both) that emerged under the same TKI in 11 cases (37%) and accumulated as a consequence of multiple lines of TKI therapy in the remaining 19 (63%) cases. Mutation analysis was also performed in 15 resistant pts enrolled in a clinical trial of dasatinib as first-line treatment for Ph+ ALL. Twelve pts were positive for mutations; 11/12 had a T315I. Sixty-one pts were analyzed at the time of diagnosis in order to assess whether TKI-resistant mutations could already be detectable. Only two pts (3%) were positive for mutations: one patient had an F311L that disappeared after one month of nilotinib treatment; an additional patient was positive only by D-HPLC, but not by the less sensitive direct sequencing – most likely for the T315I mutation that shortly after the start of dasatinib treatment outgrew and led to resistance. Taking advantage of the recent availability of a next-generation sequencing platform (Roche 454), allowing high sensitivity (0.01%) mutation scanning of the KD, samples collected at the time of diagnosis and during follow-up from selected Ph+ ALL cases who developed mutations and resistance to TKI therapy were retrospectively analyzed – but the mutations were not always already detectable at diagnosis. In conclusion: a) although 2nd generation TKIs may ensure a more rapid debulking of the neoplastic clone and have much fewer insensitive mutations, long-term disease control remains a problem and the T315I becomes an even tougher enemy; b) the clinical usefulness of mutation screening of Ph+ ALL pts at diagnosis before TKI start, even with highly sensitive approaches is low – not all mutations pre-exist since genetic instability remains high and fosters mutational events anytime during treatment. Supported by PRIN, FIRB, AIL and AIRC. Disclosures: Soverini: ARIAD: Consultancy; Novartis: Consultancy; Bristol-Myers Squibb: Consultancy. Luppi:CELGENE CORPORATION: Research Funding. Foà:Bristol-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees. Baccarani:Bristol-Meyers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Martinelli:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Pfizer: Consultancy.

Abstract 3580 Introduction: Although treatment with tyrosine kinase inhibitors (TKIs) has revolutionized the management of adult patients with BCR-ABL1 -positive acute lymphoblastic leukemia (ALL) and significantly improved response rates, relapse is still an expected and early event in the majority of them. It is usually attributed to the emergence of resistant clones with mutations in BCR-ABL1 kinase domain or to BCR-ABL1 -independent pathways but many questions remain unresolved about the genetic abnormalities responsible for relapse after TKI and chemotherapy-based regimens. Patients and methods: In an attempt to better understand the genetic mechanisms responsible for this phenomenon, we have analyzed matched diagnosis-relapse samples from 30 adult BCR-ABL1 -positive ALL patients using high resolution Affymetrix single nucleotide polymorphism (SNP) arrays (GeneChip® Human Mapping 250K NspI, n=15 pairs and Genome-Wide Human SNP 6.0, n= 15 pairs). Genetic differences were analyzed in terms of copy number changes and loss of heterozygosity (LOH) events. 20 patients were enrolled in clinical trials of GIMEMA AL Working Party and treated with imatinib alone or in combination with conventional chemotherapy (40%) or dasatinib as frontline therapy (60%). The median age at diagnosis was 54 years (range 23–74) and the median blast cell count was 97% (range 60–99). The median time to relapse was 27 months (range, 9–104). 10 patients were treated according to the GMALL trials, a high-dose chemotherapy based protocol in combination with imatinib. The median age at diagnosis was 65 years (range 19–79) and the median leucocyte count was 37300/μl (range 5000 – 220000/μl). The median time to relapse was 9.8 months (range, 3 – 25). Results: First, we compared diagnosis and relapse samples for the presence of macroscopic (> 1.5 MB) copy number alterations (CNA). Novel acquired macroscopic CNAs were detected in 7/20 (35%) TKI relapse cases and included losses of 3p12-p14, 5q34, 9q34, 10q24 and 12p13-p12 and gains of 1q, 9q34-q33 and 22q and in 4/10 (40%) chemotherapy-relapse cases and included losses of 9p21 and 12q21–22 and gains of all chromosome 8 or part of it in 2 patients. Since no common patterns of acquired alterations were observed, it is likely that relapse may be due to a more generalized genetic instability rather than to specific mechanisms. Moreover, chemotherapy did not select resistant clones with higher number of alterations. 8/20 (40%) TKI resistant cases and 4/10 chemotherapy resistant patients harbored the same CNAs present in the matched diagnosis sample (losses of 9p21 in 7 cases, 7p and 22q11 in single cases and gains of chromosomes 1q, 4, 8q, 17q and 21), indicating a common clonal origin. In contrast, in 5/20 (25%) TKI resistant cases and 4/10 (40%) chemotherapy resistant patients macroscopic CNAs present at diagnosis were lost at relapse (losses of chromosomes 7, 11q, 14q, 15q, 16q and 19p and gains of 5q, 8q, 9q34 and 22q11). Thereafter, we compared diagnosis and relapse samples for microscopic CNAs (< 1.5 MB). The alteration most frequently acquired at relapse was loss of the tumor suppressor CDKN2A (53% vs 33 % of diagnosis). Other common acquired CNAs at relapse included gains of ABC transporter genes, such as ABCC1, ABCC6 (1q41) and BCL8 (15q11); losses affected EBF1 (5q33) and IGLL3 (22q11) genes involved in B-cell development, BTG1 (12q21) involved in cell cycle regulation and CHEK2 (22q12) involved in DNA repair. Interestingly, for all relapse cases analysis of IKZF1 deletions, identified in 80% of patients, demonstrated a clonal relationship between diagnostic and relapse samples, suggesting that this alteration is not acquired with relapse but it is maintained with fidelity from diagnosis working as a marker of disease. The majority (92%) of relapse samples harbored at least some of the CNAs present in the matched diagnosis sample, indicating a common clonal origin. Conclusions: Genomic copy number changes evolving from diagnosis to relapse have been identified demonstrating that a diversity of alterations contributes to relapse and with the most common alterations targeting key regulators of tumor suppression, cell cycle control, and lymphoid/B cell development. Supported by European LeukemiaNet, AIL, AIRC, Fondazione Del Monte di Bologna e Ravenna, FIRB 2006, PRIN 2009, Ateneo RFO grants, PIO program, Programma di Ricerca Regione – Università 2007 – 2009. Disclosures: Soverini: Novartis: Consultancy; ARIAD: Consultancy; Bristol-Myers Squibb: Consultancy. Baccarani:Pfizer Oncology: Consultancy; Novartis: Consultancy; BMS: Consultancy; Ariad: Consultancy; Novartis: Research Funding; Pfizer Oncology: Honoraria; Novartis: Honoraria; BMS: Honoraria; Ariad: Honoraria; Novartis: Membership on an entity's Board of Directors or advisory committees; BMS: Membership on an entity's Board of Directors or advisory committees; Ariad: Membership on an entity's Board of Directors or advisory committees. Ottmann:Novartis Corporation: Consultancy, Honoraria, Research Funding, Speakers Bureau. Martinelli:Novartis: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Pfizer: Consultancy.

In Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) patients (pts) treated with tyrosine kinase inhibitors (TKIs), responses are generally short-lived and relapse is most often accompanied by selection of point mutations in the Bcr-Abl kinase domain (KD). In order to assess whether mutations are already present at the time of diagnosis, we analyzed RNA samples from 13 pts with newly diagnosed Ph+ ALL enrolled on the GIMEMA LAL1205 protocol – designed to assess activity, safety and tolerability of dasatinib monotherapy as first-line treatment for adult Ph+ ALL. The pts investigated (males/ females: 6/7; median age: 56 years, range 30–73) included 6 pts who subsequently relapsed with dasatinib-resistant mutations, 2 pts who relapsed without evidence of mutations as assessed by direct sequencing and 5 pts in persistent remission. Screening for low level mutations was performed by cloning the entire Bcr-Abl KD (amino acid 206 through 524) in a bacterial vector and sequencing 150 to 200 independent clones for each pt. All pts, irrespective of their subsequent response to dasatinib, had evidence of aberrant KD sequences due to point mutations (13/13 pts), small insertions (2/13 pts) or small deletions (1/13 pts). Two to five point mutations were detectable for each pt. In some cases, multiple mutations could be found to co-exist in the same cloned fragment. A total of 45 different point mutations (including 18 silent mutations, 4 nonsense mutations and 23 missense mutations) were observed. Base substitutions were scattered all over the KD and there were no mutation hotspots. Thirty-nine out of 45 (87%) mutations were transitions: G>A (n=14), A>G (n=10), C>T (n=9), T>C (n=6). Such a high prevalence of transitions (which normally occur 1.4 times more frequently than transversions) suggests that a specific mechanism generating mutations is predominant. Activation-induced cytidine deaminase (AID) has been recently shown to be aberrantly expressed in a proportion of Ph+ ALLs and has been implicated in the development of at least some Bcr-Abl mutations; correlation with AID expression will be presented. Mutations were detected in no more than three independent clones, suggesting that they were present at low levels. Mutations detected in less than two clones were considered only if independently validated by a specifically designed ASO-PCR assay run on the original cDNA sample. The majority of point mutations detected have never been reported in association with TKI resistance. However, three pts were found to harbor known imatinib- or dasatinib-resistant mutations, including two T315I mutations that were later on selected and led to relapse. This supports the theory that mutations randomly arise as a consequence of a high genetic instability and very few of them will confer a growth advantage under the selective pressure of TKIs. Six samples from newly diagnosed chronic phase CML (CP-CML) pts were screened for comparison with the same cloning approach, including 2 pts who later progressed with evidence of KD mutations after 3 and 6 months from the start of imatinib, respectively, and 4 pts who achieved a stable molecular response on imatinib. Both pts who experienced early relapse on imatinib had low level mutations detectable at the time of diagnosis, whereas none of the clones from CP-CML imatinib responders had evidence of KD mutations. The results herein presented support the concept that Ph+ ALL cells have a particularly high genomic instability that allows early escape from TKI inhibitor therapy. Only a fraction of CML cases share this feature. Our data highlight the importance of understanding the mechanism(s) responsible for this ‘mutator’ phenotype, as well as how to interfere therapeutically with it.