adarotene and Leukemia--Myeloid

ST1926 is an atypical retinoid and a promising anti-tumour agent with selective apoptotic activity on the leukaemic blast. The anti-tumour activity of the compound has been associated with its capacity to induce DNA double stranded breaks. Target profiling by affinity chromatography coupled to mass spectrometry led to the identification of histone H2A.Z as a protein capable of binding ST1926 specifically. The result was confirmed by studies involving Surface Plasmon Resonance (SPR). This indicates that H2A.Z is a primary target of ST1926 and links the perturbations of the histone pathway observed by microarray analysis to the DNA damage and apoptotic responses caused by the atypical retinoid. Comparison of the whole-genome gene-expression profiles of the ST1926-sensitive NB4 and the ST1926-resistant NB4.437r cell lines demonstrated differential expression of numerous genes. Network analysis of the data indicated enrichment of the cellular pathways controlling cAMP (cyclic adenosine-monophosphate)-dependent signal transduction, proteasome-dependent protein degradation and nuclear histones in NB4.437r cells. Pharmacological inhibition of cAMP-dependent protein kinase A with H89 partially reverted resistance of NB4.437r cells to ST1926. Conversely, inhibition of the proteasome with MG132 or bortezomib blocked the apoptotic response afforded by ST1926 in the NB4 cell line. This last effect was associated with a dramatic reduction in the DNA damage caused by the atypical retinoid. The results corroborate the idea that DNA damage is an important determinant of ST1926 apoptotic activity. More importantly, they demonstrate a proactive role of the proteasome in the DNA damaging and ensuing apoptotic response observed upon the challenge of acute myeloid leukaemia cells with ST1926.

Topics: Acute Disease; Adamantane; Apoptosis; Blotting, Western; Cell Line, Tumor; Cell Survival; Cinnamates; Cyclic AMP-Dependent Protein Kinases; Drug Resistance, Neoplasm; Enzyme Inhibitors; Gene Expression Profiling; Gene Expression Regulation, Leukemic; Histones; Humans; Isoquinolines; Leukemia, Myeloid; Leupeptins; Oligonucleotide Array Sequence Analysis; Proteasome Endopeptidase Complex; Protein Binding; Signal Transduction; Sulfonamides; Surface Plasmon Resonance

Retinoid-related molecules (RRMs) are derivatives of retinoic acid and promising antileukemic agents with a mechanism of action different from that of other common chemotherapeutics. Here, we describe a novel chemical series designed against the RRM prototype, CD437. This includes molecules with apoptotic effects in acute promyelocytic leukemia and other myelogenous leukemia cell lines, as well as ST2065, an RRM with antagonistic properties. The most interesting apoptotic agent is ST1926, a compound more powerful than CD437 in vitro and orally active in vivo on severe combined immunodeficiency (SCID) mice that received transplants of NB4 cells. ST1926 has the same mechanism of action of CD437, as indicated by the ability to trans-activate retinoic acid receptor gamma, to induce the phosphorylation of p38 and JNK, and to down-regulate the expression of many genes negatively modulated by CD437. ST1926 causes an immediate increase in the cytosolic levels of calcium that are directly related to the apoptotic potential of the RRMs considered. The intracellular calcium elevation is predominantly the result of an inhibition of the mitochondrial calcium uptake. The phenomenon is blocked by the ST2065 antagonist, the intracellular calcium chelator BAPTA (1,2 bis (2-aminophenoxy) ethane-N, N, N',N'-tetraacetic acid tetrakis (acetoxymethyl ester), and by high concentrations of calcium blockers of the dihydropyridine type, compounds that suppress ST1926-induced apoptosis.

Topics: Adamantane; Antineoplastic Agents; Apoptosis; Calcium; Cell Line, Tumor; Chelating Agents; Cinnamates; Dihydropyridines; Egtazic Acid; Gene Expression; HeLa Cells; Homeostasis; Humans; Intracellular Fluid; JNK Mitogen-Activated Protein Kinases; Leukemia, Myeloid; Mitochondria; Mitogen-Activated Protein Kinases; p38 Mitogen-Activated Protein Kinases; Receptors, Retinoic Acid; Retinoic Acid Receptor gamma; Retinoids