cytidylyl-3--5--guanosine and Leukemia--Myeloid

Frequent genetic alterations in hematopoietic neoplasias (chromosomal translocations, point mutations, etc.) have provided biologic targets for the development of effective novel therapies. A rapidly increasing body of knowledge provides evidence also for multiple epigenetic alterations in these disorders, which can complement or even precede genetic aberrations. Gene inactivation ('silencing') of tumor suppressor and growth inhibitory genes (e.g. the cyclin-dependent kinase inhibitors p16, p15, p21) is frequently mediated by DNA methylation of gene promoters. The acetylation state of histones (functionally linked to the DNA methylation state by the methylcytosine binding protein 2, recruiting histone deacetylases) provides a second major epigenetic silencing mechanism. Therapeutic reversal strategies are being developed for acute leukemias, myelodysplastic syndromes and malignant lymphomas. Since the discovery of the DNA methyltransferase (Dnmt) inhibitory activity of two azanucleosides (5-azacytidine, 5-aza-2'-deoxycytidine/decitabine) even at doses with minimal nonhematologic toxicity, both have been clinically studied in several myeloid neoplasias, particularly in elderly patients unable to tolerate aggressive treatment. Further development of agents counteracting aberrant methylation is directed at more targeted approaches, for example, antisense molecules against Dnmts. Histone deacetylases (HDACs) can be inhibited by numerous compounds (sodium phenylbutyrate, valproic acid, novel compounds such as depsipeptide), which have entered the clinical arena in similar indications as Dnmt inhibitors. Impressive effects of HDAC inhibition in acute promyelocytic leukemia models (PML/RARA expression) translate the finding of HDAC recruitment by this chimeric transcription factor to its target genes. The recent discovery of recruitment by PML/RARA also of Dnmt activity to the retinoic acid receptor-beta promoter makes it an interesting candidate for Dnmt inhibitors. Studies combining a 're-expressor' strategy with inhibitors of Dnmts and HDACs are underway. Thus, resensitization to biological agents such as retinoids, colony-stimulating factors and other differentiation inducers may be envisioned.

Topics: Dinucleoside Phosphates; DNA Methylation; Gene Silencing; Humans; Leukemia, Myeloid; Mutation; Neoplasms; Point Mutation; Promoter Regions, Genetic; Translocation, Genetic

Patterns of DNA methylation are substantially altered in malignancies compared to normal tissue, with both genome-wide hypomethylation and regional increase of cytosine methylation at dinucleotides of cytosine and guanine, i.e., CpG dinucleotides. While genome-wide hypomethylation renders chromosomes instable, hypermethylation of CpGs in promoter regions is generally associated with transcriptional silencing, e.g., of tumor suppressor genes. To investigate whether disease-specific methylation profiles exist for different entities of acute leukemia, a microarray-based DNA methylation analysis simultaneously assessing 249 CpG dinucleotides originating from 57 genes was employed. Hereby, samples from precursor B-cell acute lymphoblastic leukemia (ALL) could be distinguished from cases of acute myeloid leukemia by virtue of N33, EGR4, CDC2, CCND2, or MOS hypermethylation in ALL.

Topics: Acute Disease; Base Sequence; Classification; Diagnosis, Differential; Dinucleoside Phosphates; DNA Methylation; Humans; Leukemia, Myeloid; Neoplasm Proteins; Oligonucleotide Array Sequence Analysis; Precursor B-Cell Lymphoblastic Leukemia-Lymphoma; Precursor Cell Lymphoblastic Leukemia-Lymphoma; Promoter Regions, Genetic

Topics: Acute Disease; Apoptosis Regulatory Proteins; Burkitt Lymphoma; Calcium-Calmodulin-Dependent Protein Kinases; Death-Associated Protein Kinases; Dinucleoside Phosphates; DNA Methylation; HL-60 Cells; Humans; Leukemia, B-Cell; Leukemia, Myeloid; Research Design; Tumor Cells, Cultured

The restriction endonucleases HpaII and MspI both cleave the nucleotide sequence CCGG, but the action of HpaII is inhibited if the internal cytosine is methylated. HpaII and MspI were used on fixed chromosomes from bone marrow cells of individuals suffering from chronic myelogenous leukemia and healthy individuals. We found that MspI acts with the same efficiency on all chromosome samples, whereas HpaII extracts more DNA from the chromosomes of leukemic individuals than from the chromosomes of nonleukemic individuals. We postulate that demethylation of cytosine in the CpG dinucleotide of leukemic cell DNA accounts for our findings.

Topics: Cytidine Monophosphate; Cytosine Nucleotides; Deoxyribonuclease HpaII; Dinucleoside Phosphates; DNA Restriction Enzymes; DNA, Neoplasm; Guanosine; Humans; Karyotyping; Leukemia, Myeloid; Staining and Labeling