BCR/ABL and leukemia

CX‑5461 potentiates imatinib‑induced apoptosis in K562 cells by stimulating KIF1B expression

The selective RNA polymerase I inhibitor CX-5461 has been shown to be effective in treating some types of leukemic disorders. Emerging evidence suggests that combined treatments with CX-5461 and other chemotherapeutic agents may achieve enhanced effectiveness as compared with monotherapies. Currently, pharmacodynamic properties of the combination of CX-5461 with tyrosine kinase inhibitors remain to be explored. The present study tested whether CX-5461 could potentiate the effect of imatinib in the human chronic myeloid leukemia cell line K562, which is p53-deficient. It was demonstrated that CX-5461 at 100 nM, which was non-cytotoxic in K562 cells, potentiated the pro-apoptotic effect of imatinib. Mechanistically, the present study identified that the upregulated expression of kinesin family member 1B (KIF1B) gene might be involved in mediating the pro-apoptotic effect of imatinib/CX-5461 combination. Under the present experimental settings, however, neither CX-5461 nor imatinib alone exhibited a significant effect on KIF1B expression. Moreover, using other leukemic cell lines, it was demonstrated that regulation of KIF1B expression by imatinib/CX-5461 was not a ubiquitous phenomenon in leukemic cells and should be studied in a cell type-specific manner. In conclusion, the results suggested that the synergistic interaction between CX-5461 and imatinib may be of potential clinical value for the treatment of tyrosine kinase inhibitor-resistant chronic myeloid leukemia.

STS-1 and STS-2, Multi-Enzyme Proteins Equipped to Mediate Protein-Protein Interactions

STS-1 and STS-2 form a small family of proteins that are involved in the regulation of signal transduction by protein-tyrosine kinases. Both proteins are composed of a UBA domain, an esterase domain, an SH3 domain, and a PGM domain. They use their UBA and SH3 domains to modify or rearrange protein-protein interactions and their PGM domain to catalyze protein-tyrosine dephosphorylation. In this manuscript, we discuss the various proteins that have been found to interact with STS-1 or STS-2 and describe the experiments used to uncover their interactions.

Determination of cDNA encoding BCR/ABL fusion gene in patients with chronic myelogenous leukemia using a novel FRET-based quantum dots-DNA nanosensor

In the present study, we developed a sensitive method based on fluorescence resonance energy transfer (FRET) for the determination of the BCR/ABL fusion gene, which is used as a biomarker to confirm the clinical diagnosis of both chronic myelogenous leukemia (CML) and acute lymphocytic leukemia (ALL). For this purpose, CdTe quantum dots (QDs) were conjugated to amino-modified 18-mer oligonucleotide ((N)DNA) to form the QDs-(N)DNA nanosensor. In the presence of methylene blue (MB) as an intercalator, the hybridization of QDs-(N)DNA with the target BCR/ABL fusion gene (complementary DNA), brings the MB (acceptor) at close proximity of the QDs (donor), leading to FRET upon photoexcitation of the QDs. The enhancement in the emission intensity of MB was used to follow up the hybridization, which was linearly proportional to concentration of the target complementary DNA in a range from 1.0 × 10^-9 to 1.25 × 10^-7 M. The detection limit of the proposed method was obtained to be 1.5 × 10^-10 M. Finally, the feasibility and selectivity of the proposed nanosensor was evaluated by the analysis of derived nucleotides from both mismatched sequences and clinical samples of patients with leukemia as real samples.

Regulators of carcinogenesis: emerging roles beyond their primary functions

Cancers are characterized by aberrant cell signaling that results in accelerated proliferation, suppressed cell death, and reprogrammed metabolism to provide sufficient energy and intermediate metabolites for macromolecular biosynthesis. Here, we summarize the emerging "unconventional" roles of these regulators based on their newly identified interaction partners, different subcellular localizations, and/or structural variants. For example, the epidermal growth factor receptor (EGFR) regulates DNA synthesis, microRNA maturation and drug resistance by interacting with previously undescribed partners; cyclins and cyclin-dependent kinases (CDKs) crosstalk with multiple canonical pathways by phosphorylating novel substrates or by functioning as transcriptional factors; apoptosis executioners play extensive roles in necroptosis, autophagy, and in the self-renewal of stem cells; and various metabolic enzymes and their mutants control carcinogenesis independently of their enzymatic activity. These recent findings will supplement the systemic functional annotation of cancer regulators and provide new rationales for potential molecular targeted cancer treatments.

Elevated β-arrestin1 expression correlated with risk stratification in acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the main subtype of childhood leukemia. Risk stratification is pivotal for ALL prognosis and individualized therapy. The current factors for risk stratification include clinical and laboratory features, cytogenetic characteristics of the blast, early response to chemotherapy, and genetic factors. Analyses of gene expression are becoming increasingly important in ALL risk stratification. β-Arrestin1, a multifunctional scaffold protein mediating many intracellular signaling networks, has been shown to be involved in many tumors. However, little is known of β-arrestin1 in leukemia. In this study, we found that β-arrestin1 was significantly elevated in 155 newly diagnosed ALL patients, compared with 51 controls. Further analysis showed that β-arrestin1 expression was positively related with risk classification and white blood cell count in ALL. Moreover, expression of Notch1, an essential gene for developing hematological cells and T-ALL, was found to be negatively correlated with β-arrestin1 in ALL. In conclusion, β-arrestin1 may be a useful predictor of risk stratification and prognosis of ALL, and thus of potential use in the design of individualized therapy strategies.

Activation of protein kinase A (PKA) by 8-Cl-cAMP as a novel approach for antileukaemic therapy

Activation of PKA by cAMP agonists, such as 8-Cl-cAMP activation, selectively causes rapid apoptosis in v-abl transformed fibroblasts by inhibiting the Raf-1 kinase. Here we investigated whether 8-Cl-cAMP is useful for the treatment of chronic myelogenous leukaemia (CML), which is hallmarked by the expression of the p210^bcr/abl oncogene. Autologous bone marrow transplantation is a feasible alternative for patients with no suitable donor, but hampered by the risk of relapse due to the persistence of leukaemia cells in the transplant. To study the effects of 8-Cl-cAMP on primary leukaemic cells, bone marrow cells (BMCs) from eight CML patients (one at diagnosis, three in chronic and four in accelerated phase) were treated. Ex vivo treatment of BMCs obtained in chronic phase of CML with 100 μM 8-Cl-cAMP for 24–48 h led to the selective purging of Philadelphia Chromosome (Ph1 chromosome) without toxic side effects on BMCs from healthy donors as measured by colony-forming unit (CFU) assays. BMCs from patients in accelerated phase showed selective, but incomplete elimination of Ph1 chromosome positive colony forming cells. The mechanism of 8-Cl-cAMP was investigated in FDCP-mix cells transformed by p210^bcr/abl, a cell culture model for CML. The results showed that 8-Cl-cAMP reduced DNA synthesis and viability independent of Raf inhibition as Raf inhibitors had no effect. MEK inhibitors interfered with DNA synthesis, but not with viability. In summary, our results indicate that 8-Cl-cAMP could be useful to purge malignant cells from the bone marrow of patients with CML and certain other forms of leukaemias.

Alpha-interferon improves survival and remission duration in P-190BCR-ABL positive adult acute lymphoblastic leukemia

Treatment of P190BCR-ABL+ acute lymphoblastic leukemia (ALL) patients remains problematic: one possibility is to use biologic response modifiers such as alpha-interferon (alpha-IFN), which is known to be active in chronic myeloid leukemia (CML). We used alpha-IFN to treat 10 adult P190BCR-ABL+ ALL patients (eight newly diagnosed; two in first relapse). All received a remission induction chemotherapy (modified L-20 protocol). Patients achieving morphological, immunological and cytogenetic complete remission (CR) were then submitted to a rotational consolidation regimen lasting 6 months. When no HLA-identical donor was available, patients aged <55 years underwent stem cell harvest followed by autologous transplantation; patients aged >/=55 years received standard maintenance treatment for 6 months. In the second year, maintenance treatment (all ages) was based on cycles of alpha-IFN (3 MU three times a week for 6 weeks) alternated with methotrexate/6-mercaptopurine continuously for up to 2 years from first demonstration of CR. Thereafter, patients maintaining CR had the same schedule of alpha-IFN (6 weeks on, 6 off). Eight patients (6/8 first diagnosis, 2/2 relapsed) obtained morphological, immunological and cytogenetic CR with persistent molecular positivity. Two with an HLA-identical donor had allogeneic bone marrow transplantation. Six proceeded with chemotherapy: one experienced early relapse, three were autotransplanted, and two received maintenance. Five patients then received alpha-IFN as scheduled. All five are in continuous morphological and cytogenetic CR, with a longer mean duration of maintained morphological CR (mean 46 months; range: 20-88) than in previous reports of Ph+ ALL patients treated with chemotherapy regimens (excluding allogeneic BMT). alpha-IFN thus appears effective in this poor-risk subset of patients. This well-tolerated IFN-containing maintenance treatment could be considered to reinforce intensified programs based on autologous stem cell transplantation as an alternative to allogeneic transplantation in P190BCR-ABL+ ALL patients (and by extension for Ph+ ALL patients) lacking an HLA-matched donor. Leukemia (2000) 14, 22-27.

Inhibition of bcr-abl oncogene expression by novel deoxyribozymes (DNAzymes)

Deoxyribozymes, or DNA enzymes (DNAzymes), are novel nucleic acids that have the ability to bind to specific sequences of RNA, and to cleave the target site catalytically. DNAzymes are smaller and more efficient enzymatically than ribozymes (RZs), which are catalytic nucleic acids synthesized from ribonucleotides. We have designed three DNAzymes that specifically target the two variants of the p210 bcr-abl gene (splice 1, b3a2; splice 2, b2a2) and the p190 variant (ela2). The cleavage sites for these DNAzymes are located 5 nucleotides (nt) 5' from the fusion site for b3a2, and only 1 nt 5' from the fusion sites for b2a2 and e1a2. We have shown in cell-free in vitro cleavage assays that these DNAzymes efficiently cleave their respective substrates. Mutated DNAzymes, in which only one critical base has been altered, do not cleave these targets. We have used a serum-resistant cytofectin (GS 2888; Gilead) to transfect the DNAzymes into target K562 cells, which express p210bcr-abl. In short-term transfection assays, the DNAzymes specifically inhibited p210bcr-abl protein expression by K562 cells by about 40%, and inhibited cell growth by more than 50% in a 6-day liquid culture assay. We have also transfected freshly isolated CD34+ bone marrow cells from patients with CML with the DNAzymes, which specifically inhibited the growth of bcr-abl-positive CFU-Mix colonies by 53-80%. The potential advantages of anti-bcr-abl DNAzymes over RZs include the following: DNAzymes are much less expensive to synthesize; they are more resistant to serum; and the anti-b2a2 DNAzyme cleaves at a site only 1 nt away from the fusion site, whereas its hammerhead RZ counterpart cleaves this target at a site 8 nt 3' to the fusion site, well within abl exon 2. DNAzymes are novel RNA-cleaving molecules that may significantly improve our ability to inhibit bcr-abl oncogene expression in Ph-positive target cells.

Amplification of BCR-ABL rearrangement in atypical Philadelphia chromosome: a new variant detected by fluorescence in situ hybridization in one case of acute lymphoblastic leukemia

We report on a 67-year-old woman with acute lymphoblastic leukemia (ALL) who was supposed to have a variant Philadelphia (Ph) translocation identified by conventional cytogenetic techniques. Fluorescence in situ hybridization (FISH) analysis demonstrated the presence of an amplification of BCR-ABL rearrangement at locus 22q11. This is the first observation, to our knowledge, of a duplicated BCR-ABL chimeric gene within the derived chromosome 22 in ALL. Our observation supports the possibility of detecting a variant Ph chromosome at the single-cell level by FISH analysis.