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Introduction: Tyrosine kinase inhibitors (TKIs) dramatically improved the prognosis of chronic myelogenous leukemia (CML), as nearly half of CML patients presenting with a deep molecular response (DMR) over several years could achieve treatment-free remission. DASISION study reported dasatinib (DAS), a second-generation TKI was superior to imatinib to achieve faster and deeper response in treating newly-diagnosed chronic CML. However, standard initial dosage of 100 mg DAS/day might be too potent for patients aged >70 years with CML, possibly owing to the presence of other health conditions that threaten the life spans (e.g., lung and cardiovascular disease), thereby preventing TKI continuation. In this open-label, multicenter, single-arm, phase 2 study (DAVLEC), we evaluated the efficacy and safety of a reduced initial dose of DAS (20 mg/day) in the elderly with chronic CML. Patients and Methods: We included CML patients aged >70 years with an ECOG performance status of 0-2 and adequate organ function. After diagnosis, they began orally taking 20 mg of DAS per day. BCR-ABL mRNA values were measured and aligned to an international scale at a central laboratory to evaluate the drug's efficacy at 3, 6, 9, and 12 mo of therapy, per recommendations by European LeukemiaNet. The dosage was maintained in case of the optimal, increased by 20 mg/day when the warning appeared and could be decreased when an adverse event (AE) > grade 3 appeared. Patients were excluded if the respond was the failure or disease progression was detected. Primary endpoint was the cumulative major molecular response (MMR) rate at 12 mo. Secondary endpoints included the rates of the cumulative DMR, treatment discontinuation due to AEs, and failure to DAS treatment or disease progression. The non-inferiority of primary endpoint MMR (non-inferiority limit of 38%) was evaluated by binomial test with normal approximation. Other differences were investigated by Mann-Whitney tests, with p < 0.05 indicating significance. Results: Among the 56 patients enrolled from 25 centers, 4 declined participation, and so 52 (median age, 77.5 years) began taking 20 mg/day of DAS. In total, 73.1% of the patients had comorbidities. Median BCR-ABL values at 3, 6, and 12 mo were 1.47%, 0.23%, and 0.03%, respectively; cumulative MMR rate at 3, 6, 9, and 12 mo were 11.5%, 36.5%, 40.4%, and 59.6%, respectively. Calculated MMR at 12 mo was higher than 38%, a value selected based upon findings from the DASISION trial, accounting for a non-inferiority margin of 10% (p=0.047). At 12 mo, among the 31 patients achieving MMR, 23 were only given 20 mg DAS/day, and 14 and 7 respectively achieved MR4.0 and 4.5. Patients discontinued the study due to treatment failure (n=3), content withdrawal (n=2), drug-related AEs (Long QT Syndrome; n=1), or others (n=2). No patient discontinued it due to disease progression. Treatment-related AEs of all grades were noted in 96.2%and that of grade 3 or 4 events in 23.1% of the patients. Median dose interruptions for a median of 7 days (range: 5-36) were respectively noted in 3 and 2 patients due to hematological and non-hematological AEs. Furthermore, 4 patients experienced pleural effusion < grade 2, and 1 had lymphocytosis. Patients who achieved MMR at 12 mo (n=31) had a significantly lower BCR-ABL value at 3 mo (0.41% vs. 4.26%, p=0.0020) and a lower halving time from diagnosis to 3 mo (11.35 vs. 18.34 days, p=0.0050) than those who did not (n=21). Patients who achieved MMR by 12 mo with only 20 mg/day of DAS (n=23) had lower BCR-ABL values at 1 and 3 mo (25.51 vs. 63.63 %, p=0.00028; 0.33 vs. 5.89%, p Patients who achieved MMR at 12 mo (n=31) had higher plasma DAS concentration (23.5 vs. 8.0 ng/mL, p Conclusion: This study discovered that prescribing a starting very-low dose DAS (20 mg/day) while monitoring IS and AEs was a successful initial therapeutic strategy for the elderly with chronic CML comparable to previous studies using standard-dose. Notably, rapid BCR-ABL downregulation, early molecular responses at 1 and 3 mo, a shortened halving time from diagnosis to 3 mo, and sufficient increase in plasma DAS concentrations 2 h post-intake after 12 mo of treatment were key indicators for successful low-dose therapy. Disclosures Kumagai: Bristol-Myers Squibb: Honoraria; Novartis: Honoraria, Speakers Bureau; Pfizer: Honoraria; Otsuka Pharmaceuticals: Honoraria, Speakers Bureau. Murai: Bristol Myers Squibb: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; Novartis Pharma: Honoraria; Pfizer: Honoraria; CHUGAI Pharmaceutical Co., Ltd.: Honoraria; TAKEDA Pharmaceutical Co., Ltd.: Honoraria; DAIICHI SANKYO COMPANY, LIMITED.: Honoraria; ONO PHARMACEUTICAL CO., LTD.: Honoraria; Asahi Kasei Pharma Corporation.: Honoraria. Tanaka: Bristol-Myers Squibb: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; Otsuka Pharmaceuticals: Honoraria. Nishiwaki: Kyowa-Kirin: Research Funding; Alexion: Honoraria. Inokuchi: Bristol-Myers Squibb: Research Funding. Yoshida: Bristol-Myers Squibb: Honoraria, Research Funding; Novartis KK,: Honoraria; Pfizer Japan Inc.: Honoraria; Otsuka Pharmaceutical.: Honoraria; AbbVie GK: Honoraria; Janssen Pharmaceutical KK: Honoraria; Nippon Shinyaku: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria. Uoshima: Janssen: Honoraria; Eisai: Honoraria. Usuki: MSD K.K.: Research Funding, Speakers Bureau; Eisai Co., Ltd.: Speakers Bureau; Alexion Pharmaceuticals, Inc.: Research Funding, Speakers Bureau; Pfizer Japan Inc.: Research Funding, Speakers Bureau; Kyowa-Kirin Co., Ltd.: Research Funding, Speakers Bureau; Nippon-Shinyaku Co., Ltd.: Research Funding, Speakers Bureau; Amgen-Astellas Biopharma K.K.: Research Funding; Mundipharma K.K.: Research Funding; Nippon-Boehringer-Ingelheim Co., Ltd.: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding, Speakers Bureau; Celgene K.K.: Research Funding, Speakers Bureau; Janssen Pharmaceutical K.K.: Research Funding; Ono Pharmaceutical Co., Ltd.: Research Funding, Speakers Bureau; Novartis Pharma K.K.: Research Funding, Speakers Bureau; Otsuka Pharmaceutical Co., Ltd.: Research Funding, Speakers Bureau; Sumitomo-Dainippon Pharma Co., Ltd.: Research Funding; Daiichi Sankyo Co., Ltd.: Research Funding, Speakers Bureau; SymBio Pharmaceuticals Ltd.: Research Funding, Speakers Bureau; Gilead Sciences, Inc.: Research Funding; AbbVie GK: Research Funding, Speakers Bureau; Astellas Pharma Inc.: Research Funding, Speakers Bureau; PharmaEssentia Japan KK: Research Funding, Speakers Bureau; Yakult Honsha Co., Ltd.: Research Funding, Speakers Bureau; Bristol-Myers-Squibb K.K.: Research Funding, Speakers Bureau; Apellis Pharmaceuticals, Inc.: Research Funding; Incyte Biosciences Japan G.K.: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding, Speakers Bureau; Sanofi K.K.: Speakers Bureau; Amgen K.K.: Research Funding. Kuroda: Otsuka Pharmaceutical: Honoraria, Research Funding; Astellas Pharma: Honoraria, Research Funding; Takeda: Honoraria, Research Funding; Celgene: Consultancy, Honoraria, Research Funding; MSD: Research Funding; Abbvie: Consultancy, Honoraria; Ono Pharmaceutical: Honoraria, Research Funding; Eisai: Honoraria, Research Funding; Sysmex: Research Funding; Pfizer: Honoraria, Research Funding; Fujimoto Pharmaceutical: Current Employment, Honoraria, Research Funding; Taiho Pharmaceutical: Research Funding; Asahi Kasei: Research Funding; Shionogi: Research Funding; Nippon Shinyaku: Honoraria, Research Funding; Janssen Pharmaceutical K.K: Consultancy; Bristol-MyersSquibb: Consultancy, Honoraria, Research Funding; Chugai Pharmaceutical: Honoraria, Research Funding; Dainippon Sumitomo Pharma: Honoraria, Research Funding; Daiichi Sankyo: Honoraria, Research Funding; Sanofi: Consultancy, Honoraria, Research Funding; Kyowa Kirin: Honoraria, Research Funding. Ono: Chugai Pharmaceutical Co., Ltd.: Honoraria, Research Funding; Kyowa Kirin Co., Ltd.: Honoraria, Research Funding; Novartis Pharma KK: Honoraria; Otsuka Pharmaceutical Co., Ltd.: Honoraria; DAIICHI SANKYO COMPANY, LIMITED.: Honoraria; Mundipharma K.K.: Honoraria; TAIHO PHARMACEUTICAL CO., LTD.: Research Funding; Merck Sharp & Dohme: Honoraria, Research Funding; Astellas Pharma Inc.: Honoraria; Eisai Co., Ltd.: Honoraria; Janssen Pharmaceutical K.K: Honoraria; Takeda Pharmaceutical Company Limited.: Honoraria; ONO PHARMACEUTICAL CO., LTD.: Honoraria, Research Funding; Pfizer Japan Inc.: Honoraria; Bristol-Myers Squibb Company: Honoraria; Celgene: Honoraria, Research Funding. Fujimaki: CSL Behring K.K.: Honoraria; Mundipharma K.K.: Honoraria; Takeda Pharmaceutical Company Limited: Honoraria; Meiji Seika Pharma Co., Ltd.: Honoraria; Janssen Pharmaceutical KK: Honoraria; AbbVie GK: Honoraria; Bristol-Myers Squibb: Honoraria; Novartis KK: Honoraria; Nippon Shinyaku: Honoraria; Chugai Pharmaceutical Co., Ltd.: Honoraria; Pfizer Japan Inc.: Honoraria; Otsuka Pharmaceutical.: Honoraria. Shibayama: Chugai: Research Funding; Eizai: Speakers Bureau; Nippon Shinyaku: Speakers Bureau; Kyowa Kirin: Speakers Bureau; AbbVie: Research Funding; Celgene: Research Funding; Novartis: Research Funding, Speakers Bureau; Ono: Research Funding, Speakers Bureau; Janssen: Research Funding, Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Mundi Pharma: Speakers Bureau; Otsuka: Speakers Bureau; Sanofi: Research Funding, Speakers Bureau; AstraZeneca: Research Funding, Speakers Bureau; Takeda: Speakers Bureau. Kondo: Abbvie: Honoraria; Astellas Pharma Inc.: Consultancy, Honoraria; Otsuka Pharmaceutical: Consultancy, Honoraria, Research Funding; Novartis Pharma KK: Honoraria; Bristol-Myers Squibb Company: Honoraria; Sumitomo Dainippon Pharma: Honoraria; Sanwa Kagaku Kenkyusho CO.,LTD: Consultancy; Pfizer: Honoraria. Minami: Bristol-Myers Squibb Company: Honoraria; Novartis Pharma KK: Honoraria; Pfizer Japan Inc.: Honoraria; Takeda: Honoraria; Astellas: Honoraria; Ono: Research Funding; CMIC: Research Funding. Kimura: Eisai: Speakers Bureau; Kyowa-Kirin: Research Funding, Speakers Bureau; PharmaEssentia: Speakers Bureau; Astellas: Speakers Bureau; Sanifi: Speakers Bureau; Gilead: Research Funding; Nippon-Boehringer-Ingelheim: Research Funding; Celgene: Research Funding, Speakers Bureau; Sumitomo-Dainippon: Research Funding; Chugai: Research Funding, Speakers Bureau; Mundi: Research Funding; Yakult: Research Funding, Speakers Bureau; MSD: Research Funding, Speakers Bureau; Ono: Research Funding, Speakers Bureau; SymBio: Research Funding, Speakers Bureau; Daiichi-Sankyo: Research Funding, Speakers Bureau; Janssen: Research Funding; Astellas-Amgen-Biopharma: Research Funding; Takeda: Research Funding, Speakers Bureau; Nippon-Shinyaku: Research Funding, Speakers Bureau; Amgen: Research Funding; Alexion: Research Funding, Speakers Bureau; Incyte: Research Funding; Novartis: Honoraria, Research Funding, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding, Speakers Bureau; Otsuka Pharmaceutical: Honoraria, Research Funding, Speakers Bureau; Ohara Pharmaceutical: Research Funding; Astellas Pharma: Research Funding; AbbVie: Research Funding, Speakers Bureau; Apellis: Research Funding.

Transient thrombocytopenia is common after autologous peripheral blood stem cell transplantation (auto-PBSCT). Although patients underwent auto-PBSCT usually show the recovery of peripheral leukocytes and platelets counts within a couple of weeks after auto-PBSCT, delayed platelet engraftment (DPE) is occasionally observed despite prompt neutrophil engraftment. However, there are few studies evaluating the risk factors for DPE. In this study, to investigate the association between clinical characteristics and duration required for post-auto-PBSCT platelet engraftment, we retrospectively analyzed 144 patients with B-cell non-Hodgkin lymphomas who underwent auto-PBSCT between January 2000 and December 2017 at 5 independent institutes involved in the Kyoto Clinical Hematology Study Group. Platelet recovery was defined as a recovery of platelet count greater than 50.0 × 109/L without transfusion support for 3 consecutive days, and the first day of 3 consecutive days was regarded as the day of platelet engraftment. The median observation period was 930 days (range, 25 - 5272 days). Median age at auto-PBSCT was 61, and 144 patients included 109 diffuse large B cell lymphoma, 11 follicular lymphoma, 22 mantle cell lymphoma. Ninety one patients were in complete remission at the time of auto-PBSCT. The mobilization regimens for stem cell collection were chemotherapy such as high-dose VP16 (46.5%), CHASE (cyclophosphamide, AraC, VP16, and dexamethasone) (40.3%), and high-dose AraC (8.3%) followed by G-CSF. All 144 patients except one achieved neutrophil engraftment with the median engraftment day of 10 days (range, 4-41 days), and 139 patients achieved platelet engraftment with the median engraftment day of 19 days (range, 10-1125 days). Multivariate analysis showed that infused CD34-positive cell number (≥ 2.0 × 106/kg vs. < 2.0 ×106/kg: HR 3.06: P < 0.001), pre-apheresis absolute lymphocyte count (PA-ALC), which was the mean number of lymphocytes during aphaeresis procedure (≥ 1.0 × 109/L vs. < 1.0 × 109/L: HR 2.62: P < 0.001), and the days required for apheresis procedure (≥ 3 days vs. 1 or 2 days: HR 0.49: P = 0.02) were independently associated with the duration for platelet engraftment after auto-PBSCT. Age, gender, diagnosis, Ann Arbor stages, previous history of bone marrow infiltration, performance status, international prognostic index (IPI)-defined disease risk, disease status at the time of transplant, the number of chemotherapy regimens, and mobilization regimen were not associated with platelet engraftment period. On the basis of these results, we next tried to create a new prediction system for post-transplant platelet recovery by incorporating the three factors, i.e., infused CD34-positive cell number, PA-ALC, and days required for apheresis procedure. Risk groups were determined by the sum of predictive factors for platelet recovery: favorable (3 factors), intermediate (2 factors), unfavorable (1 factor), and very unfavorable (no factor). As the results, the median duration for platelet engraftment with favorable, intermediate, unfavorable, and very unfavorable groups were 15, 19, 31, and 148 days, respectively (P < 0.001) (Figure). Furthermore, 14 of 144 patients did not achieve platelet engraftment by day 80 after auto-PBSCT. We defined those as patients with DPE. Median duration for platelet engraftment in patients with DPE was 137 days (range, 82-1125 days), while that for neutrophil engraftment was 11 days. Intriguingly, PA-ALC was less than 1.0 × 109/L in all 14 patients with DPE, while 6 required apheresis for ≥3 days, and 5 received Figure Figure. Disclosures Kuroda: Chugai Pharma: Honoraria, Research Funding.

[Introduction] Multiple myeloma (MM) remains mostly incurable despite major advances in treatment strategies. The complex interplay among various cell-intrinsic and -extrinsic molecular mechanisms confers inter-patients diversity and intraclonal heterogeneity in MM. However, as the universal and relevant therapeutic target molecule against MM, we have recently identified that 3-phosphoinositide-dependent protein kinase 1 (PDPK1) and its major downstream substrate RSK2 were universally active in MM (Shimura Y, Mol Caner Ther 2012; Chinen Y, Cancer Res 2014), while we also identified that the repression of miR-375 was found to be the universal underlying mechanism for the overexpression/activation of PDPK1 in MM (Tatekawa S, ASH meeting 2015). In this study, we further extended our study to assess the clinical relevance of miR-375 repression and the molecular mechanisms for the miR-375 repression in MM for the future clinical translation of miR-375/PDPK1/RSK2 signaling axis in the diagnosis and treatment development for MM. [Methods] The miR-375 expression level was analyzed by the quantitative RT-PCR in 11 HMCLs and 113 patient-derived myeloma cells isolated by CD138-positive cell sorting (normal plasma cells; N=10, MGUS; N=30, newly diagnosed MM (NDMM); N=34, relapsed/refractory (RRMM); N=39). The level of miR-375 expression was calculated with 2-ΔΔCt methods. Human U6 snRNA was examined as the reference and cDNA of RPMI8226 was used as a calibrator sample. The methylation status of miR-375 upstream regions including promoter site were analyzed by methylation-specific PCR (MSP) and bisulfite sequence. Chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) was performed to examine the histone modification status in miR-375 upstream regions. The circulating plasma RNA samples were converted to cDNA libraries followed by sequencing using the multiplex small RNA library primer set. This study was conducted in accordance with the Declaration of Helsinki and with the approval of the Institutional Review Boards. Patient-derived samples were obtained with informed consent. [Result] When compared to normal plasma cells, the miR-375 expression was significantly decreased in CD138 positive plasma cells from MGUS (p [Conclusion and Discussion] This study revealed that the expression level of miR-375 decreased specifically in clonal plasma cells from MGUS to RRMM patients, and the repression of miR-375 was caused by the overlapping epigenetic dysregulations. The abnormal repression of miR-375 which is the major causative for the constitutive hyperactivation of the PDPK1/RSK2 signaling axis in MM is likely to be involved in the myelomagenesis in MGUS as well as the disease progression in MM, and the epigenetic deregulations may be a novel therapeutic target for MM. Disclosures Iida: Celgene: Honoraria, Research Funding; Janssen Pharmaceuticals: Honoraria, Research Funding. Kuroda:Celgene: Honoraria, Research Funding; Bristol Myers Squibb: Honoraria, Research Funding; Astra Zeneca: Research Funding; Janssen: Honoraria.

Follicular lymphoma (FL) is the most prevalent among indolent subtypes of non-Hodgkin lymphomas. While the histologic transformation associates with disease aggressiveness in variant FL, a minor population of non-transformed FL patients also shows a shorter period for disease control despite the use of rituximab (Rit) immunochemotherapy. In this study, we investigated the clinical and genetic features of high-risk non-transformed FL. With the median follow-up period of 61 months for 103 consecutively treated patients with histologically non-transformed FL including 85 patients treated with the first-line Rit-containing therapies and 18 with watch and wait, the 5-year overall survival (OS) and progression-free survival (PFS) of the entire cohort were 93.3% and 54.4%, respectively. Chemotherapy was initiated according to the GELF criteria. Although neither FLIPI nor FLIPI2 sufficiently predicted the risks for either OS or PFS, the presence of two extranodal involvements, including peripheral blood (PB) (N=7, p=0.006) and/or bone (N=6, p=0.007), at diagnosis were found to be significantly associated with poor PFS, but not OS, in our cohort. Indeed, 13 high-risk patients with PB and/or bone involvements at diagnosis showed a significantly shorter median PFS of 27.2 months compared with that of the 90 standard-risk patients, who have not yet reached the median (pTG substitution to be the most common mutational signature, while there was no difference with regard to the composition of the signature between the high- and standard-risk FLs. "Kataegis", a pattern of clustered hypermutations, was observed mostly in the target motif of activation-induced cytidine deaminase (AID), recurrently on chromosome 2p12 (involving the IGK locus), 14q32 (IGH), 18q21 (BCL2), 21p11, and 22q11 (IGLL). The mean number of C>T mutations in the AID-motif was significantly increased in the high-risk FLs over that in the standard-risk FLs (17 vs. 11, p=0.02), whereas there was no difference in the mean number of mutations in the target motif of APOBEC, which is considered to be the major driving agent responsible for kataegis in various solid cancers, between the two risk groups (8 vs. 7, p=0.49). For functional assessment of mutated genes, CREBBP and TNFRSF14 mutations were identified as the driver mutations of FL regardless of the disease risk using background mutation rate analysis. Hypergeometric test on all of the non-synonymous mutated genes from 14 FLs resulted in 71 significantly enriched gene ontologies (GOs), including the terms "cell development and differentiation", "regulation of cell death", "immunity mediated by lymphocytes, including B cells", "hematopoiesis", and "differentiation of leukocytes, including lymphocytes". In addition, pathway analysis demonstrated that mutated genes were enriched in the Notch and B cell receptor signaling pathways. However, we were not able to identify GOs or signaling pathways specific to the high-risk FL patients that could explain the different outcomes of the disease. Non-synonymous mutations in the high-risk FLs were found in genes, such as MEF2B and FUBP1, and were suggested to be associated with cancer aggressiveness, but not with the AID pathway. Overall, our results suggested that genomic instability, which allows for the emergence of distinct mutations not only by kataegis due to AID activity but also by additional mechanisms that increase mutations, underlies development of the high-risk phenotype in FLs. Disclosures Kuroda: Bristol Myers Squibb: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Astra Zeneca: Research Funding; Janssen: Honoraria.

[Introduction] Multiple myeloma (MM) is a cytogenetically/molecularly heterogeneous hematologic malignancy that remains mostly incurable, and the identification of a universal and relevant therapeutic target molecule is essential for the further development of therapeutic strategy. We have recently identified that 3-phosphoinositide-dependent protein kinase 1 (PDPK1), a serine threonine kinase, and its major downstream substrate RSK2, a member of the 90 kDa ribosomal S6 kinase family of serine threonine kinases, were universally active in eleven human MM-derived cell lines (HMCLs) examined regardless of the type of cytogenetic abnormality, the mutation state of RAS, RAF and FGFR3 genes and myeloma cells of approximately 90% of symptomatic patients at diagnosis. Our study also disclosed that PDPK1/RSK2 signaling axis played pivotal roles in myeloma pathophysiology by regulating series of downstream molecules, such as c-MYC, IRF4, D-type cyclins, or PLK1, while the inactivation of either PDPK1 or N-terminal domain of RSK2 resulted in the induction of apoptosis in myeloma cells which was accompanied by the activation of BH3-only proteins BIM and BAD (Shimura Y, Mol Caner Ther 2012; Chinen Y, Cancer Res 2014). Here we assessed the underlying mechanism for PDPK1 overexpression in MM. [Methods] The miR-375 expression level was analyzed by the quantitative RT-PCR in 11 HMCLs and 92 patient-derived myeloma cells isolated by CD138-positive cell sorting (normal plasma cells (N=10), MGUS (N=21), newly diagnosed MM (NDMM) (N=27), relapsed/refractory (RRMM) (N=34). The pre-miR-375 precursor molecule (miR-375 mimics), the siRNA targeted against PDPK1, or a negative control RNA-oligonucleotides was transfected into 8 cell lines by utilizing Hemagglutinating Virus of Japan (HVJ)-envelope vector. The copy number abnormality of PDPK1 gene was assessed by double-color FISH for PDPK1 gene and the centromere of chromosome 16. The methylation status of miR-375 promoter site was analyzed by methylation-specific PCR (MSP). This study was conducted in accordance with the Declaration of Helsinki and with the approval of the Institutional Review Boards. Patient-derived samples were obtained with informed consent, and normal bone marrow plasma cells were obtained from volunteers who were not affected by hematologic disease. [Result] The level of miR-375 expression was calculated with 2-ΔCt methods. Human U6 snRNA was examined as the reference. The median log102-ΔCt ± SD of normal plasma cells, MGUS, NDMM, RRMM and HMCLs were -2.46 ± 0.67, -3.64 ± 0.68, -4.23 ± 0.95, -3.92 ± 1.24 and -3.69 ± 0.29 respectively. When compared to normal plasma cells, the miR-375 expression was significantly decreased in NDMM and RRMM (p [Conclusion and Discussion] PDPK1 is activated by autophosphorylation and, therefore, its expression level is the crucial determinant for its activity, Because our study revealed the miR-375 expression as the major regulator of PDPK1 expression, it is suggested that the abnormally repressed miR-375 is the major causative for the constitutive hyperactivation of the PDPK1/RSK2 signaling axis in MM. Moreover, since the decreased miR-375 expression was observed in plasma cells of MGUS and was more pronounced in MM, miR-375 repression by epigenetic deregulation may be involved in both disease development and progression of MM. Disclosures No relevant conflicts of interest to declare.

Multiple myeloma (MM) is a highly molecularly heterogeneous hematologic malignancy and remains mostly incurable despite recent improvement of treatment outcome by novel agents. Therefore, the identification of novel and universal targetable therapeutic molecules is a core component for the therapeutic development. Herein, we identified that 3-phosphoinositide-dependent protein kinase 1 (PDPK1), a member of serine threonine kinase, is a rationalistic candidate of a novel therapeutic target against MM. PDPK1 is universally phosphorylated in all eleven MM-derived cell lines examined regardless of type of cytogenetic/genetic abnormalities or the activation/mutation state of FGFR3, RAS, ERK and AKT. PDPK1 promotes the cell proliferation of myeloma cells by activating RSK2Ser227 at N-terminal kinase domain which is a pivotal regulator of molecules that are essential for myelomagenesis, such as c-MYC, IRF4, or Cyclin Ds (Shimura Y, Mol Cancer Ther 2011), and AKTThr308. In contrast, PDPK1 inhibition by a selective inhibitor, BX-912, caused G2/M arrest, which was accompanied by the inactivation of PLK1, and resulted in cell death via induction of apoptosis which was accompanied by the activation of pro-apoptotic BH3-only proteins, BIM and BAD, in myeloma-derived cell lines. These molecular and cytological effects of PDPK1 inhibition in myeloma cells were also validated by gene knockdown by means of RNA interference using two different siRNAs specific for PDPK1. In addition, the cytotoxic effect of BX-912 was not hampered in two cell lines acquiring resistance to bortezomib (BTZ) (Ri M, Leukemia 2010), and PDPK1 inhibition by BX-912 showed additive to synergistic in vitro cytotoxic effects on myeloma cells with melphalan, etoposide, bortezomib or BAY11-7085, an inhibitor for NF-κB. BX-912 also induced cell death in eleven patient-derived primary myeloma cells those were positively isolated by CD138-labelling from bone marrow aspirates, while normal peripheral lymphocytes were significantly less sensitive to PDPK1 inhibitor compared with MM cells. In the clinical setting, PDPK1 was active in myeloma cells of 57 of 65 (87.7%) symptomatic MM patients at diagnosis. While patients backgrounds, such as age, gender, and the type of M-protein, were not significantly different between PDPK1-negative (PDPK1(-)) and PDPK1-positive (PDPK1(+)) patients, patients with the disease stage III according to International Staging System were significantly more frequent in the PDPK1(+) cohort compared with PDPK1(-) cohort. The PDPK1(-) patients tended to exhibit longer overall survival (OS) than the patients with PDPK1(+) (median OS: 2925 days vs. 2155 days, p=0.069) with a median follow-up period of 1310 days (range: 228–3317 days). Of particular, the 8-year OS of PDPK1(-) patients was statistically significantly more favorable than those of PDPK1(+) patients (83% vs. 17%, p=0.041). In addition, when we analyzed the impact of PDPK1 activity on the treatment outcome of patients treated by BTZ and dexamethasone therapy (BD), our results revealed that progression free survival (PFS) of patients with PDPK1(-) was a significantly longer than those of patients with PDPK1(+) (median PFS: PDPK1(-) vs. PDPK1(+), not reached vs. 167 days, p=0.049). The PFS of PDPK1(-) patients treated by high-dose therapy/autologous stem cell transplantation (HDT/ASCT) tended to be longer than those of PDPK1(+) (median PFS: PDPK1(-) vs. PDPK1(+), 972 days vs. 567 days, p=0.125). In conclusion, our study provides the rationale for PDPK1 as a possible universal molecular target for MM with various molecular/cytogenetic features. Especially, PDPK1 is a potential therapeutic target for not only newly diagnosed patients but also patients who are resistant or refractory to currently available anti-myeloma therapies. This study was conducted in accordance with the Declaration of Helsinki and with the approval of the Institutional Review Board. Patient-derived samples were obtained with informed consent. Disclosures No relevant conflicts of interest to declare.

Background Cell signaling mediated by the JAK2-STAT (Janus kinase 2-signal transducer and activator of transcription) pathway plays a critical role in hematopoiesis, and its aberrant activation is associated with the progression of hematological malignancies. For instance, somatic mutations in the JAK2 gene that lead to constitutive activation of STATs are involved in the pathogenesis of myeloproliferative neoplasms (MPN) and refractory anemia with ringed sideroblasts with thrombocytosis, one of the myelodysplastic/myeloproliferative neoplasms, unclassifiable (MDS/MPN, U). In addition, insufficient inactivation of the JAK-STAT pathway due to repression of SOCS-1 (suppressor of cytokine signaling 1) through hypermethylation of the SOCS-1 gene is involved in the disease progression of high-risk myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) (Brakensiek et al.; Br. J. Haematol. 2005;130:209). These observations prompted us to investigate the effect of the JAK2-selective inhibitor NS-018, which is in an early-phase clinical trial for MPN, on the colony formation by bone marrow hematopoietic progenitor cells from high-risk de novo MDS patients and the phosphorylation status of STAT3 in these cells. Methods Bone marrow mononuclear cells (BMMNCs) from six MDS patients and three healthy volunteers were collected with informed consent in accordance with the Declaration of Helsinki and with the approval of the Institutional Review Board. The MDS subtypes of the six patients included two RCMD, three RAEB-1 and one RAEB-2 according to the WHO classification. All MDS patients had complex cytogenetic abnormalities and their prognostic risks were defined to be high (N=1) or very high (N=5) in the IPSS-R. Commercially available normal human CD34+ BM cells were also examined for comparison. Cells were incubated in methylcellulose medium containing cytokines with or without NS-018. Burst forming unit-erythroid (BFU-E) and colony forming unit-granulocyte/macrophage (CFU-GM) were scored on day 14 of culture. Colony-forming cells were then collected and subjected to western blotting analysis. Results We first examined the colony-formation capacity of MDS-derived BMMNCs. CFU-GM colony formation was observed in four of six MDS samples, although the absolute CFU-GM numbers from MDS BMMNCs were less than those from normal BMMNCs and normal CD34+BM cells. MDS-derived BMMNCs produced larger numbers of CFU-GM colonies (78–99% of total colonies) than BFU-E, similar to the findings usually observed in AML, whereas normal BMMNCs and normal CD34+BM cells formed virtually the same numbers of CFU-GM colonies and BFU-E colonies. These results suggest that BMMNCs from four of the MDS patients enrolled in this study had characteristics similar to AML BMMNCs, although they showed less proliferation than AML BMMNCs. We next examined the effect of NS-018 on CFU-GM colony formation. NS-018 treatment decreased the numbers of CFU-GM colonies from MDS-derived BMMNCs in a dose-dependent manner, and this effect was significantly more potent against MDS-derived than against normal cells (57.2% inhibition in MDS cells vs. 12.8% inhibition in normal cells at 0.5 mM NS-018; see Figure). These results indicate that NS-018 is preferentially efficacious in inhibiting CFU-GM formation from BMMNCs from high risk MDS. In addition, the level of phospho-STAT3 in MDS-derived colony-forming cells was twice as high as in colony-forming cells from normal BMMNCs, and 1.0 mM NS-018 completely suppressed the phosphorylation of STAT3 in CFU-GM colony-forming cells from MDS. Conclusion Our results show for the first time that a JAK2 inhibitor, NS-018, potently suppresses the formation of MDS colonies. NS-018 could be a new therapeutic option for high-risk MDS patients. Disclosures: Kodama: Nippon Shinyaku: Employment. Naito:Nippon Shinyaku: Employment. Nakaya:Nippon Shinyaku: Employment. Taniwaki:Novartis: Honoraria.

Little is known about the molecular pathogenesis of acute myeloid leukemia (AML) with high-level DNA amplifications commonly defined as the presence of double minutes (dmins) and/or homogeneously staining regions (hsr), although dmins and hsr are found in nearly 1% of karyotypically abnormal AML and myelodysplastic syndromes (MDS). It is sometimes difficult to precisely assign dmins, hsr, and marker chromosomes (mars) to specific chromosomal bands, while most of them consist of an amplified segment from chromosome band 8q24 or 11q23. In AML, the 8q24 amplicon has been previously identified in a commonly involved segment of about 4 Mb, which contains several genes such as TRIB1 (C8FW), NSMCE2 (non-SMC element 2), PVT1, and MYC. To further define the pathogenetic lesions of 8q24 amplicons in AML, we performed comprehensive molecular studies on leukemic cells from a patient with AML (patient 1) with two mars and leukemic cell lines HL60 and K562, identifying two novel chimeric transcripts, PVT1-NSMCE2 and BF104016-NSMCE2. Regarding PVT1-NSMCE2 fusion transcripts, PVT1 exon 1a fused to NSMCE2 exon 3 in patient 1, PVT1 exon 3a to NSMCE2 exon 4 in patient 2, and PVT1 exon 4b to NSMCE2 exon 4 in K562. Patient 2 was identified from the screening of an additional 50 patients with AML or MDS by RT-PCR. As for BF104016-NSMCE2 fusion transcript, BF104016 exon 1 fused to NSMCE2 exon 6 in HL60 harboring hsr and dmins. BF104016 is located inside the CCDC26 gene, sharing the same exon of CCDC26. In patient 1, fluorescence in situ hybridization identified the amplification of 5’PVT1 on the mars and dmins, and the amplification of NSMCE2 only on the mars. In HL60, PVT1 and NSMCE2 were amplified on dmins. Although real-time quantitative PCR showed the amplification of the aberrant NSMCE2 chimeric transcripts, western blot analysis demonstrated the depletion of NSMCE2 protein. High-resolution oligonucleotide array analysis demonstrated two amplicons at 8q24 commonly found in patient 1 and HL60. Furthermore, the coding directions of these three fusion genes were different at the 8q24; NSMCE2 and PVT1 are transcribed from centromere toward telomere, opposite to the direction of transcription of the CCDC26 gene. These results suggest that the chimeric formation of these genes were caused by chromothripsis. PVT1 and CCDC26 were known as large intervening non-coding RNAs, both of which were considered to be associated with the oncogenesis. NSMCE2 is known as a small ubiquitin-like modifier (SUMO) E3 ligase and is required for DNA repair. Functional analysis of NSMCE2 chimeric transcripts with PVT1 or CCDC26 will contribute to understanding of the leukemogenesis in AML harboring 8q24 amplicons. Disclosures: Taniwaki: Novartis: Honoraria.

Abstract 2945 Background: Despite recent advances of therapeutic strategies, multiple myeloma (MM) still remains mostly incurable due to its drug resistance by both various cell intrinsic molecular abnormalities and the supports of myeloma microenvironment factors. The search for new therapeutic target molecule upon which various MM-promoting signalings converge is essential for the development of more effective therapy for MM. RSK2 is a member of the 90 kDa ribosomal S6 kinases (RSKs) family of serine (Ser) /threonine (Thr) kinases and lies downstream of RAS/ERK-1/2 signaling cascade. In MM, it has been shown that RSK2 mediates signaling initiated by FGFR3 activation for cell survival, but the functional role and the value as the therapeutic target of RSK2 have not been clearly defined. In this study, we precisely studied the association with RSK2 activation and chromosomal status, especially focusing on RSK2Ser227, which is responsible for downstream signaling phosphorylation, and the value of RSK2 as the therapeutic target in MM. Methods: Twelve human myeloma-derived cell lines and primary MM cells were utilized in this study. The use of human samples was approved by the ethical review board of our institute. Cell killing assay was performed using flow cytometry. Growth inhibitory assay was performed with modified MTT assay. Protein levels were examined by Western blotting. BI-D1870, a RSK2 inhibitor, was purchased from Symansis Limited (Auckland, New Zealand). RNA interference for RSK2 was performed by transfection of small interfering RNA (siRNA) into NCI-H929 cells by means of CLB-Transfection Kit (Lonza, Swiss) with protocol 9. Drug combination assays were evaluated with CalcuSyn software (Biosoft, Cambridge, UK). Results: RSK2Ser227 was shown to be phosphorylated in all 12 MM cell lines and 6 of 9 primary MM cells. t(4;14) involving IgH/FGFR3 was detected only in 7 cell lines and high FGFR3 expression was identified only in 6 cell lines. RSK2Ser227 was phosphorylated even in the absence of ERK1/2 or RSK2Tyr529 phosphorylation in several MM cell lines, indicating that their activation was not mandatory to RSK2Ser227 phosphorylation. Our study also did not show any positive relationship between RSK2Ser227 phosphorylation and other so-called “high-risk” cytogenetic abnormalities, such as 13q-, t(11;14), t(8;14), t(14;16), 1q21+, or 17p-. Treatment with BI-D1870 (RSK2 inhibitor) resulted in complete dephosphorylation of RSK2Ser227, but not RSK2Tyr529. The phosphorylation status of ERK1/2, or related signaling kinases, such as AKT, p38 MAPK, or JNK was also not affected. BI-D1870 showed dose-dependent growth inhibition effect in 6 MM-derived cell lines by inducing apoptosis. At molecular level, Mcl-1, p21WAF1/CIP1, cyclin D2 and c-Myc was significantly down-regulated and Bim was up-regulated by BI-D1870 intervention in NCI-H929 cell. BI-D1870 didn't modulate expression level of IRF-4. These change were also observed in other MM cell lines (KMS-34, AMO-1). To exclude the possibility that above BI-D1870 induced changes in protein expression and cell death are due to its off-target effects, we performed gene knockdown experiments of RSK2. Transient gene knockdown of RSK2 by means of RNAi caused downregulation of cyclin D2, p21WAF1/CIP1, c-Myc, while it induced cell death in NCI-H929 cells. In contrast, Bim expression was not altered by RSK2 knockdown. Lenalidomide (LEN) is the most powerful currently available IMiD for MM treatment. While cell death induction by LEN (100μM) was partly prevented by IL-6 (50ng/ml) in NCI-H929 cells, co-administration of BI-D1870 (0.2 μM, at the degree of low concentration not to affect cell viability when used solely) overcame the resistance to LEN induced by IL-6. KMS-11/BTZ were highly resistant to bortezomib (BTZ)-induced cell death, by contrast, it showed the similar sensitivities to BI-D1870-induced cell death when compared with their parental cells. And more, BI-D1870 showed synergistic or additive effects with upcoming new anti-MM agents, such as RAD001, MS-275 and ABT-263 in MM cell lines. Conclusions: RSK2, especially RSK2Ser227, may be a universal therapeutic target for MMs with diverse molecular signatures. Disclosures: Iida: Janssen Pharmaceutical K.K.: Honoraria.

Abstract 3744 [Introduction] Tyrosine kinase inhibitors (TKIs) for BCR-ABL have dramatically improved the treatment outcome of chronic myelogenous leukemia (CML) during this decade, however, the resistance to TKIs due to various molecular mechanisms, such as BCR-ABL mutations, dysfunction of cell killing mechanisms like BIM deregulation, or the supports by leukemia microenvironment factors, has remained to be overcome. We have identified that BIM, a member of BH3-only proteins, is the essential pro-apoptotic mediator under the blockade of BCR-ABL signaling (Kuroda J, PNAS, 2006). One of the attractive therapeutic strategies for complete eradication of CML cells by simultaneously targeting both TKI-sensitive and TKI-resistant CML cells may be the use of agents that can activate BIM as well as other pro-apoptotic BH3-only protein which is not utilized in apoptosis by TKIs. In this study, we assessed the therapeutic potential of the protein phosphatase 2A (PP2A) activator Fingolimod (FTY720), an immunosuppressive agent currently used for multiple sclerosis, in CML. [Materials and methods] Human CML-derived cell lines, K562, MYL, KBM5, KCL22, and their various subclones, were utilized in this study. Murine Ba/F3 lymphoid cells were transfected with either wild type or mutated bcr-abl gene. FTY720 was purchased from Cayman Chemical (Ann Arbor, MI). Cell death analyses were performed using flow cytometry. Protein levels were determined by conventional Western blotting. [Result and discussion] Treatment with FTY720 impairs phosphorylation of BCR-ABL and its downstream targets, AKT, ERK and STAT5, and inhibited the growth of CML cell lines through the induction of apoptosis. The apoptosis induced by FTY720 was accompanied by the activation of both caspase-8 and caspase-9, while enforced expression of either BCL2 or dominant-negative protein of FADD (FADD.DN) by gene introduction partly protected K562 cells from apoptosis by FTY720, indicating the involvement of both cell extrinsic and intrinsic apoptosis pathways in FTY720-induced apoptosis. FTY720 treatment resulted in the activation of Bim as well as the processing of Bid into tBid, a BH3-only protein which plays crucial role in accelerating death-receptor-mediated extrinsic apoptosis pathway and is not utilized in apoptosis by TKIs. Importantly, gene knockdown of either BIM or BID partly protected K562 cells from apoptosis by FTY720, but the degrees of cell protection by those were not as much as the degree of cell protection by overexpression of either BCL2 or FADD.DN. Moreover, double knockdown of BIM and BID did not further protect K562 cells from apoptosis by FTY720, when compared with single knockdown of BIM. These results indicate that BIM and BID compensate each other for promoting apoptosis by FTY720 in CML cells, especially when either of them is functionally disturbed. Through these mechanisms, FTY720 overcomes TKI resistance by various mechanisms, such as ABL kinase domain (KD) mutations in BCR-ABL-transfected Ba/F3 cells (T315I, G250E, E255K or H396P) and in KBM5 cells with T315I. FTY720 also overcomes TKI resistance due to dysfunction of BIM by gene deletion polymorphism in KCL22 cells. Also, although galectin-3 overexpression has been shown to mediate bone marrow environment-mediated drug resistance in CML cells (Yamamoto-Sugitani M, PNAS, 2011), the addition of FTY720 to imatinib overcomes resistance to imatinib in galectin-3 overexpressing K562 cells and MYL cells. In conclusion, FTY720 induces apoptotic cell death in CML via dual activation of both BIM and BID, and is potent in overcoming various types of cell intrinsic and tumor microenvironment-mediated resistance to TKI. Disclosures: No relevant conflicts of interest to declare.

Abstract 4450 In B-cell malignancies, the genes implicated in B-cell differentiation, germinal center formation, apoptosis, and cell cycle regulation are juxtaposed to immunoglobulin loci through chromosomal translocations. In the present study, we have identified BTB and CNC homology 2 (BACH2) as a novel translocation partner gene of the immunoglobulin heavy chain (IGH) locus, resulting in chimeric Cδ-BACH2 gene in a patient with MYC-IGH-positive highly aggressive B-cell lymphoma/leukemia carrying der(14)t(8;14) and del(6)(q15). A 71-year-old male was diagnosed as having highly aggressive B-cell lymphoma/leukemia. SKY analysis revealed the representative karyotype of tumor cells as 45,X,-Y,der(3)t(3;X)(p21.2;q24),del(6)(q15),der(14)t(8;14)(q24;q32),del(16)(q22),der(20) t(3;20)(q21;p13). FISH and long-distance PCR analyses identified a fusion of MYC with Cγ. FISH analysis also detected a small IGH signal on del(6), and a VH on del(6)(q15). Genome copy number analysis using SNP-array detected an approximately 60Mb deletion in 6q15–25 region, and its centromeric breakpoint within BACH2 gene. The cDNA bubble PCR using BACH2 primers detected multiple PCR products, and sequence analysis has revealed that one of the products contained a sequence of the first exon of IGHCδ fused to 5’ untranslated region of BACH2 exon 2. Genomic fusion point of Cδ-BACH2, was within intron 1 of Cδ and intron 1 of BACH2. Cδ-BACH2 fusion transcript consisted of exon 1 of Cδ and exons 2 to 9 of BACH2, indicating that whole coding region of BACH2 was fused to Cδ. This suggested that Cδ-BACH2 fusion cause constitutive activation of BACH2. We next analyzed the expression levels of BACH2, MYC, PRDM1, and IRF4 genes in the patient using real-time PCR and compared them with those of several hematologic malignancy cell lines, including 14 non-Hodgkin's lymphoma (NHL), 10 multiple myeloma (MM), and 3 B-lineage acute lymphoblastic leukemia, and 3 EB-virus transformed B-cell lines from normal healthy volunteers. IGH-MYC-positive MM cell lines showed increased levels of MYC expression compared with the other cell lines. The MYC expression level in our patient was lower than those in IGH-MYC-positive MM cell lines; however, it was similar to 5 IGH-MYC-positive NHL cell lines [3 Burkitt lymphoma (BL) and 2 diffuse large B-cell lymphoma (DLBCL)]. On the other hand, BACH2 expression levels were higher in NHL cell lines, especially in BL cell lines, but not correlated with the IGH-MYC translocation status. Our IGH-BACH2-positive case also showed a higher level of BACH2 expression. The expression levels of IRF4 and PRDM1 were higher in MM cell lines than in other cell lines. PRDM1 is activated by MYC through IRF4, and the MYC is negatively regulated by activated PRDM1. In MM cell lines with IGH-MYC translocation, MYC was highly expressed regardless of high expression of PRDM1, indicating that MYC activated by IGH translocation could not be inhibited by PRDM1. Unexpectedly, the expression levels of PRDM1 and IRF4 were very low in NHL including our patient, suggesting that the regulation of MYC in NHL is different from that in MM. BACH2 is a B cell-specific transcription repressor, and is specifically required for class switch recombination, somatic hypermutation, and germinal center formation. One of the target genes of BACH2 is PRDM1 at 6q21-q22.1 that is required for plasma cell differentiation. In this patient, deletion of 6q15–25 was found, indicating loss of one PRDM1 allele. It was reported that PRDM1 is inactivated by chromosomal alterations in 24% of activated B cell–like DLBCL, suggesting that PRDM1 acts as a tumor suppressor gene, and its inactivation may contribute to lymphomagenesis by blocking post–GC differentiation. The combination of BACH2 and MYC in double IGH translocations is unique and consistent with previous reports demonstrating that each partner gene found in double or multiple IGH translocations is exclusively specific to certain types of B-cell lymphoma. These results suggest that the promoter of IGHCδ and/or Eμ enhancer of IGH activate the expression of BACH2, and that BACH2 may act as oncogene in some cases with B-cell lymphoma. Although the IGH-BACH2 translocation is rare in NHL, our data suggest that the BACH2 plays a critical role in B-cell lymphomagenesis through not only IGH translocation but also activation by some other mechanisms. Disclosures: No relevant conflicts of interest to declare.

The AML1/RUNX1 gene is frequently rearranged by chromosomal translocations in acute leukemia. To date, more than 10 fusion genes involving AML1 have been cloned, such as AML1-MTG8 in acute myeloid leukemia (AML) with t(8;21), AML1-EVI1/MDS1 in therapy-related AML/myelodysplastic syndrome with t(3;21), and TEL/ETV6-AML1 in B precursor ALL with t(12;21). We analyzed a pediatric patient having T-cell acute lymphoblastic leukemia (T-ALL) with t(2;21)(q11;q22), and identified that the LAF4 gene on 2q11.2–12 was fused to the AML1 gene on 21q22 using the bubble PCR method for cDNA. The genomic breakpoints were within intron 7 of AML1 and intron 7 of LAF4 resulting in the in-frame fusion of exon 7 of AML1 and exon 8 of LAF4. LAF4 gene is a member of the AF4/FMR2 family, and was previously identified as a fusion partner of MLL in B-precursor ALL with t(2;11)(q11;q23), although AML1-LAF4 was in T-ALL. LAF4 is the first gene fused with both AML1 and MLL in acute leukemia. These findings provide new insights into the common mechanism of AML1 and MLL fusion proteins in the pathogenesis of ALL. In this study, we first applied the panhandle PCR method that is usually used for cloning the fusion partners of MLL or NUP98; however, no fusion transcripts could be obtained. Therefore, we searched for another method for cloning the fusion transcripts and successfully adapted the bubble PCR method for cloning the novel AML1-LAF4 fusion transcript. To date, bubble PCR has been performed for cloning unknown genomic fusion points but not fusion cDNAs. Using double-strand cDNA, we could apply the bubble PCR method for cloning fusion cDNA with rare non-specific products. Bubble PCR for cDNA could amplify in both 5′ to 3′ and 3′ to 5′ directions of the gene or transcript and handle any exons fused to unknown partners for amplification easily. This method will contribute to identifying numerous novel translocation partners more easily, and these findings may help to clarify the role of the fusion proteins in leukemogenesis.