Altered ligand binding and transcriptional regulation by mutations in the PML/RARα ligand-binding domain arising in retinoic acid–resistant patients with acute promyelocytic leukemia

Pharmacogenomic analysis of acute promyelocytic leukemia cells highlights CYP26 cytochrome metabolism in differential all-trans retinoic acid sensitivity

Disease relapse sometimes occurs after acute promyelocytic leukemia (APL) therapy with all-trans retinoic acid (ATRA). Among the diagnostic parameters predicting relapse, heterogeneity in the in vitro differentiation rate of blasts is an independent factor. To identify biologic networks involved in resistance, we conducted pharmacogenomic studies in APL blasts displaying distinct ATRA sensitivities. Although the expression profiles of genes invested in differentiation were similarly modulated in low- and high-sensitive blasts, low-sensitive cells showed higher levels of transcription of ATRA-target genes, transcriptional regulators, chromatin remodelers, and transcription factors. In opposition, only high-sensitive blasts expressed the CYP26A1 gene, encoding the p450 cytochrome which is known to be involved in retinoic acid catabolism. In NB4 cells, ATRA treatment activates a novel signaling pathway, whereby interleukin-8 stimulates the expression of the homeobox transcription factor HOXA10v2, an effective enhancer of CYP26A1 transcription. These data were corroborated in primary APL cells, as maturation levels correlated with CYP26A1 expression. Treatment with a retinoic acid metabolism blocking agent (RAMBA) results in high-nucleoplasmic concentrations of retinoid and growth of NB4-resistant subclones. Hence, for APL blasts associated with poor prognosis, the low CYP26A1 expression may explain high risk of resistance installation, by increased retinoid pressure. Pharmacogenomic profiles of genes involved in retinoid acid metabolism may help to optimize anticancer therapies, including retinoids.

The clinical application of targeting cancer through histone acetylation and hypomethylation

Methods of gene inactivation include genetic events such as mutations or deletions. Epigenetic changes, heritable traits that are mediated by changes in DNA other than nucleotide sequences, play an important role in gene expression. Two epigenetic events that have been associated with transcriptional silencing include methylation of CpG islands located in gene promoter regions of cancer cells and changes in chromatin conformation involving histone acetylation. Recent evidence demonstrates that these processes form layers of epigenetic silencing. Reversal of these epigenetic processes and up-regulation of genes important to prevent or reverse the malignant phenotype has therefore become a new therapeutic target in cancer treatment.