Profiling of drug-metabolizing enzymes/transporters in CD33+ acute myeloid leukemia patients treated with Gemtuzumab-Ozogamicin and Fludarabine, Cytarabine and Idarubicin.

Genetic heterogeneity in drug-metabolizing enzyme/transporter (DMET) genes affects specific drug-related cancer phenotypes. To investigate the relationships between genetic variation and response to treatment in acute myeloid leukemia (AML), we genotyped 1931 variants on DMET genes in 94 CD33-positive AML patients enrolled in a phase III multicenter clinical trial combining Gemtuzumab-Ozogamicin (GO) with Fludarabine-Cytarabine-Idarubicin (FLAI) regimen, with the DMET Plus platform. Two ADH1A variants showed statistically significant differences (odds ratio (OR)=5.68, P=0.0006; OR=5.35, P=0.0009) in allele frequencies between patients in complete/partial remission and patients without response, two substitutions on CYP2E1 (OR=0.13, P=0.001; OR=0.09, P=0.003) and one on SLCO1B1 (OR=4.68, P=0.002) were found to differently influence liver toxicity, and two nucleotide changes on SULTB1 and SLC22A12 genes correlated with response to GO (OR=0.24, P=0.0009; OR=2.75, P=0.0029). Genetic variants were thus found for the first time to be potentially associated with differential response and toxicity in AML patients treated with a combination of GO-FLAI regimen.

Therapeutic targeting of CK2 in acute and chronic leukemias.

CK2 is a ubiquitously expressed, constitutively active Ser/Thr protein kinase, which is considered the most pleiotropic protein kinase in the human kinome. Such a pleiotropy explains the involvement of CK2 in many cellular events. However, its predominant roles are stimulation of cell growth and prevention of apoptosis. High levels of CK2 messenger RNA and protein are associated with CK2 pathological functions in human cancers. Over the last decade, basic and translational studies have provided evidence of CK2 as a pivotal molecule driving the growth of different blood malignancies. CK2 overexpression has been demonstrated in nearly all the types of hematological cancers, including acute and chronic leukemias, where CK2 is a key regulator of signaling networks critical for cell proliferation, survival and drug resistance. The findings that emerged from these studies suggest that CK2 could be a valuable therapeutic target in leukemias and supported the initiation of clinical trials using CK2 antagonists. In this review, we summarize the recent advances on the understanding of the signaling pathways involved in CK2 inhibition-mediated effects with a particular emphasis on the combinatorial use of CK2 inhibitors as novel therapeutic strategies for treating both acute and chronic leukemia patients.

Therapeutic potential of targeting sphingosine kinases and sphingosine 1-phosphate in hematological malignancies.

Sphingolipids, such as ceramide, sphingosine and sphingosine 1-phosphate (S1P) are bioactive molecules that have important functions in a variety of cellular processes, which include proliferation, survival, differentiation and cellular responses to stress. Sphingolipids have a major impact on the determination of cell fate by contributing to either cell survival or death. Although ceramide and sphingosine are usually considered to induce cell death, S1P promotes survival of cells. Sphingosine kinases (SPHKs) are the enzymes that catalyze the conversion of sphingosine to S1P. There are two isoforms, SPHK1 and SPHK2, which are encoded by different genes. SPHK1 has recently been implicated in contributing to cell transformation, tumor angiogenesis and metastatic spread, as well as cancer cell multidrug-resistance. More recent findings suggest that SPHK2 also has a role in cancer progression. This review is an overview of our understanding of the role of SPHKs and S1P in hematopoietic malignancies and provides information on the current status of SPHK inhibitors with respect to their therapeutic potential in the treatment of hematological cancers.

Cytotoxic activity of the casein kinase 2 inhibitor CX-4945 against T-cell acute lymphoblastic leukemia: targeting the unfolded protein response signaling.

Constitutively active casein kinase 2 (CK2) signaling is a common feature of T-cell acute lymphoblastic leukemia (T-ALL). CK2 phosphorylates PTEN (phosphatase and tensin homolog) tumor suppressor, resulting in PTEN stabilization and functional inactivation. Downregulation of PTEN activity has an impact on PI3K/Akt/mTOR signaling, which is of fundamental importance for T-ALL cell survival. These observations lend compelling weight to the application of CK2 inhibitors in the therapy of T-ALL. Here, we have analyzed the therapeutic potential of CX-4945-a novel, highly specific, orally available, ATP-competitive inhibitor of CK2α. We show that CX-4945 treatment induced apoptosis in T-ALL cell lines and patient T lymphoblasts. CX-4945 downregulated PI3K/Akt/mTOR signaling in leukemic cells. Notably, CX-4945 affected the unfolded protein response (UPR), as demonstrated by a significant decrease in the levels of the main UPR regulator GRP78/BIP, and led to apoptosis via upregulation of the ER stress/UPR cell death mediators IRE1α and CHOP. In vivo administration of CX-4945 to a subcutaneous xenotransplant model of human T-ALL significantly delayed tumor growth. Our findings indicate that modulation of the ER stress/UPR signaling through CK2 inhibition could be exploited for inducing apoptosis in T-ALL cells and that CX-4945 may be an efficient treatment for those T-ALLs displaying upregulation of CK2α/PI3K/Akt/mTOR signaling.

Activity of the pan-class I phosphoinositide 3-kinase inhibitor NVP-BKM120 in T-cell acute lymphoblastic leukemia.

Constitutively active phosphoinositide 3-kinase (PI3K) signaling is a common feature of T-cell acute lymphoblastic leukemia (T-ALL), where it upregulates cell proliferation, survival and drug resistance. These observations lend compelling weight to the application of PI3K inhibitors in the therapy of T-ALL. Here, we have analyzed the therapeutic potential of the pan-PI3K inhibitor NVP-BKM120 (BKM120), an orally bioavailable 2,6-dimorpholino pyrimidine derivative, which has entered clinical trials for solid tumors, on both T-ALL cell lines and patient samples. BKM120 treatment resulted in G2/M phase cell cycle arrest and apoptosis, being cytotoxic to a panel of T-ALL cell lines and patient T lymphoblasts, and promoting a dose- and time-dependent dephosphorylation of Akt and S6RP. BKM120 maintained its pro-apoptotic activity against Jurkat cells even when cocultured with MS-5 stromal cells, which mimic the bone marrow microenvironment. Remarkably, BKM120 synergized with chemotherapeutic agents currently used for treating T-ALL patients. Moreover, in vivo administration of BKM120 to a subcutaneous xenotransplant model of human T-ALL significantly delayed tumor growth, thus prolonging survival time. Taken together, our findings indicate that BKM120, either alone or in combination with chemotherapeutic drugs, may be an efficient treatment for T-ALLs that have aberrant upregulation of the PI3K signaling pathway.

c-Myb and its target Bmi1 are required for p190BCR/ABL leukemogenesis in mouse and human cells.

Expression of c-Myb is required for normal hematopoiesis and for proliferation of myeloid leukemia blasts and a subset of T-cell leukemia, but its role in B-cell leukemogenesis is unknown. We tested the role of c-Myb in p190(BCR/ABL)-dependent B-cell leukemia in mice transplanted with p190(BCR/ABL)-transduced marrow cells with a c-Myb allele (Myb(f/d)) and in double transgenic p190(BCR/ABL)/Myb(w/d) mice. In both models, loss of a c-Myb allele caused a less aggressive B-cell leukemia. In p190(BCR/ABL)-expressing human B-cell leukemia lines, knockdown of c-Myb expression suppressed proliferation and colony formation. Compared with c-Myb(w/f) cells, expression of Bmi1, a regulator of stem cell proliferation and maintenance, was decreased in pre-B cells from Myb(w/d) p190(BCR/ABL) transgenic mice. Ectopic expression of a mutant c-Myb or Bmi1 enhanced the proliferation and colony formation of Myb(w/d) p190(BCR/ABL) B-cells; by contrast, Bmi1 downregulation inhibited colony formation of p190(BCR/ABL)-expressing murine B cells and human B-cell leukemia lines. Moreover, c-Myb interacted with a segment of the human Bmi1 promoter and enhanced its activity. In blasts from 19 Ph(1) adult acute lymphoblastic leukemia patients, levels of c-Myb and Bmi1 showed a positive correlation. Together, these findings support the existence of a c-Myb-Bmi1 transcription-regulatory pathway required for p190(BCR/ABL) leukemogenesis.

Application of the whole-transcriptome shotgun sequencing approach to the study of Philadelphia-positive acute lymphoblastic leukemia.

Although the pathogenesis of BCR-ABL1-positive acute lymphoblastic leukemia (ALL) is mainly related to the expression of the BCR-ABL1 fusion transcript, additional cooperating genetic lesions are supposed to be involved in its development and progression. Therefore, in an attempt to investigate the complex landscape of mutations, changes in expression profiles and alternative splicing (AS) events that can be observed in such disease, the leukemia transcriptome of a BCR-ABL1-positive ALL patient at diagnosis and at relapse was sequenced using a whole-transcriptome shotgun sequencing (RNA-Seq) approach. A total of 13.9 and 15.8 million sequence reads was generated from de novo and relapsed samples, respectively, and aligned to the human genome reference sequence. This led to the identification of five validated missense mutations in genes involved in metabolic processes (DPEP1, TMEM46), transport (MVP), cell cycle regulation (ABL1) and catalytic activity (CTSZ), two of which resulted in acquired relapse variants. In all, 6390 and 4671 putative AS events were also detected, as well as expression levels for 18 315 and 18 795 genes, 28% of which were differentially expressed in the two disease phases. These data demonstrate that RNA-Seq is a suitable approach for identifying a wide spectrum of genetic alterations potentially involved in ALL.

Different isoforms of the B-cell mutator activation-induced cytidine deaminase are aberrantly expressed in BCR-ABL1-positive acute lymphoblastic leukemia patients.

The main reason for the unfavorable clinical outcome of BCR-ABL1-positive acute lymphoblastic leukemia (ALL) is genetic instability. However, how normal B-cell precursors acquire the genetic changes that lead to transformation has not yet been completely defined. We investigated the expression of the activation-induced cytidine deaminase (AID) and its role in clinical outcome in 61 adult BCR-ABL1-positive ALL patients. AID expression was detected in 36 patients (59%); it correlated with the BCR-ABL1 transcript levels and disappeared after treatment with tyrosine kinase inhibitors. Different AID splice variants were identified: full-length isoform; AIDDeltaE4a, with a 30-bp deletion of exon 4; AIDDeltaE4, with the exon 4 deletion; AIDins3, with the retention of intron 3; AIDDeltaE3-E4 isoform without deaminase activity. AID-FL predominantly showed cytoplasmic localization, as did the AID-DeltaE4a and AID-DeltaE3E4 variants, whereas the C-terminal-truncated AID-DeltaE4 showed a slightly increased nuclear localization pattern. AID expression correlated with a higher number of copy number alterations identified in genome-wide analysis using a single-nucleotide polymorphism array. However, the expression of AID at diagnosis was not associated with a worse prognosis. In conclusion, BCR-ABL1-positive ALL cells aberrantly express different isoforms of AID that may act as mutators outside the immunoglobulin (Ig) gene loci in promoting genetic instability.