Therapeutic potential of MEK inhibition in acute myelogenous leukemia: rationale for "vertical" and "lateral" combination strategies.

In hematological malignancies, constitutive activation of the RAF/MEK/ERK pathway is frequently observed, conveys a poor prognosis, and constitutes a promising target for therapeutic intervention. Here, we investigated the molecular and functional effects of pharmacological MEK inhibition in cell line models of acute myeloid leukemia (AML) and freshly isolated primary AML samples. The small-molecule, ATP-non-competitive, MEK inhibitor PD0325901 markedly inhibited ERK phosphorylation and growth of several AML cell lines and approximately 70 % of primary AML samples. Growth inhibition was due to G(1)-phase arrest and induction of apoptosis. Transformation by constitutively active upstream pathway elements (HRAS, RAF-1, and MEK) rendered FDC-P1 cells exquisitely prone to PD0325901-induced apoptosis. Gene and protein expression profiling revealed a selective effect of PD0325901 on ERK phosphorylation and compensatory upregulation of the RAF/MEK and AKT/p70( S6K ) kinase modules, potentially mediating resistance to drug-induced growth inhibition. Consequently, in appropriate cellular contexts, both "vertical" (i.e., inhibition of RAF and MEK along the MAPK pathway) and "lateral" (i.e., simultaneous inhibition of the MEK/ERK and mTOR pathways) combination strategies may result in synergistic anti-leukemic effects. Overall, MEK inhibition exerts potent growth inhibitory and proapoptotic activity in preclinical models of AML, particularly in combination with other pathway inhibitors. Deeper understanding of the molecular mechanisms of action of MEK inhibitors will likely translate into more effective targeted strategies for the treatment of AML.

Adult acute lymphoblastic leukemia / Leucemia linfoblástica do adulto

This review focuses on the most recent advances in the diagnostic and prognostic work-up of adult acute lymphoblastic leukemia (ALL), and on their implications in the clinical management of the disease. Over the years, information obtained through extensive immunophenotyping, karyotyping, molecular genetics, multidrug resistance and, more recently, genomic profiling is progressively contributing to a better understanding of the biology of this complex disease, to the identification of subgroups of patients with different clinical outcomes, to a more precise monitoring of minimal residual disease, to the use of different therapeutic protocols based on prognostic indicators and, finally, to the design of innovative and specific treatment strategies. The next few years will tell us if this biologically-guided approach, which is progressively individualizing the management of adult ALL patients, will ultimately impact on the prognosis of a disease that has stagnated over many decade.

Esta revisão focaliza os mais recentes avanços no diagnóstico e prognóstico da leucemia linfoblástica aguda do adulto e suas implicações no manuseio clínico desta doença. Com o passar dos anos, informações obtidas através de extensa pesquisa em imunofenotipagem, citogenética, genética molecular, resistência a múltiplas drogas e, mais recentemente, perfil genômico têm contribuído progressivamente para o melhor entendimento da biologia desta doença complexa, na identificação de sub grupos de pacientes com evolução clínica distintas, no mais preciso monitoramento da doença residual mínima, no uso de diferentes protocolos baseados em indicadores prognósticos e, mais recentemente, também no desenho de tratamentos inovativos e específicos. Os próximos anos nos dirão se abordagens baseadas guiadas biologicamente, que será uma individualização progressiva do manuseio dos pacientes adultos com LLA podem causar um impacto favorável em uma doença estagnada há várias décadas.

Identification of different Ikaros cDNA transcripts in Philadelphia-positive adult acute lymphoblastic leukemia by a high-throughput capillary electrophoresis sizing method.

BACKGROUND: Ikaros is the prototypic member of a Kruppel-like zinc finger transcription factor subfamily that is required for normal hematopoietic cell differentiation and proliferation, particularly in the lymphoid lineages. Alternative splicing can generate multiple Ikaros isoforms that lack different numbers of exons and have different functions. Shorter isoforms, which lack the amino-terminal domain that mediates sequence-specific DNA binding, exert a dominant negative effect and inhibit the ability of longer heterodimer partners to bind DNA. DESIGN AND METHODS: In this study, we developed a high-throughput capillary electrophoresis sizing method to detect and quantify different Ikaros cDNA transcripts. RESULTS: We demonstrated that Philadelphia chromosome-positive acute lymphoblastic leukemia cells expressed high levels of the non-DNA-binding isoform Ik6 that was generated following IKZF1 genomic deletions (19/46 patients, 41%). Furthermore, a recurring 60 bp insertion immediately upstream of exon 5, at the exon 3/exon 5 junction, was frequently detected in the Ik2 and Ik4 isoforms. This insertion occurred either alone or together with an in-frame ten amino acid deletion that was due to a 30 bp loss at the end of exon 7. Both the alterations are due to the selection of alternative cryptic splice sites and have been suggested to cause impaired DNA-binding activity. Non-DNA-binding isoforms were localized in the cytoplasm whereas the DNA-binding isoforms were localized in the nucleus. CONCLUSIONS: Our findings demonstrate that both aberrant splicing and genomic deletion leading to different non-DNA-binding Ikaros cDNA transcripts are common features of Philadelphia chromosome-positive acute lymphoblastic leukemia.

FLT3 inhibition in t(4;11)+ adult acute lymphoid leukaemia.

The present study was designed to investigate, in t(4;11)+ adult lymphoid leukaemia (ALL) blast cells, the pathogenetic role of the FLT3 protein, its level of mRNA and protein expression, the degree of constitutive phosphorylation, the possible presence of mutations of the sequence, the capacity of signal transduction and the potential therapeutic role of specific inhibitors. We evaluated nine adult ALL patients carrying this translocation. The increased FLT3 mRNA levels, determined by oligonucleotide microarray analysis, was in agreement with the increased protein expression evaluated by Western blot. The protein was constitutively phosphorylated in all cases analysed. Polymerase chain reaction detected no internal tandem duplication or point mutations. The signal transduction apparatus, after stimulation with the specific ligand, was preserved. We then investigated the effect of specific FLT3 inhibition on signal transduction and survival. The PKC412 inhibitor specifically inhibited ligand-induced phosphorylation; the same inhibitor reduced the survival of leukaemic cells when compared with untreated cells. These data indicate that the FLT3 protein might play a role in this subgroup of ALL with a particularly poor prognosis. Specific inhibition of the kinase receptor must be hypothesised as an innovative therapeutic tool for t(4;11)+ ALL patients.