4-(2-(5-6-7-8-tetrahydro-5-5-8-8-tetramethyl-2-naphthalenyl)-1-propenyl)benzoic-acid and Leukemia--Promyelocytic--Acute

Twofold sila-substitution (C/Si exchange) in the saturated ring of the tetrahydronaphthalene skeleton of the retinoid agonists TTNPB (1 a) and 3-methyl-TTNPB (2 a) leads to disila-TTNPB (1 b) and disila-3-methyl-TTNPB (2 b), respectively. The silicon compounds 1 b and 2 b were synthesized in multiple steps, and their identities were established by elemental analyses, multinuclear NMR experiments, and single-crystal X-ray diffraction studies. Like TTNPB (1 a) and 3-methyl-TTNPB (2 a), the analogous silicon-based arotinoids 1 b and 2 b are strong pan-RAR agonists and display the same strong differentiation and apoptosis-inducing activity in NB4 promyelocytic leukemia cells as the parent carbon compounds. These results are in keeping with the nearly isomorphous structures of 1 a and 1 b bound to the complex of the RARbeta ligand-binding domain with the nuclear receptor (NR) box 2 peptide of the SRC-1 coactivator. The contacts within the ligand-binding pocket are identical except for helix H11, for which two turns are shifted in the disila-TTNPB (1 b) complex. This study represents the first comprehensive structure-function analysis of a carbon/silicon switch in a signaling molecule and demonstrates that silicon analogues can have the same biological functionalities and conserved structures as their parent carbon compounds, and it illustrates at the same time that silicon analogues of biologically active compounds have the potential to induce alternative allosteric effects, as in the case of helix H11, which might allow for novel options in drug design.

Topics: Apoptosis; Benzoates; Cell Differentiation; Cell Line, Tumor; Cell Nucleus; Humans; Leukemia, Promyelocytic, Acute; Magnetic Resonance Spectroscopy; Models, Chemical; Models, Molecular; Molecular Conformation; Naphthalenes; Organosilicon Compounds; Protein Conformation; Protein Structure, Tertiary; Retinoids; Silicon

New structure-activity relationships of a series of methylene or side chain modified retinoids on NB4 acute promyelocytic leukemia cells are investigated. The differentiation- and apoptosis-inducing potential of these compounds is analyzed on the basis of their selective retinoic acid receptor binding profile.

Topics: Cell Death; Cell Differentiation; Cell Line, Tumor; Humans; Hydrocarbons; Leukemia, Promyelocytic, Acute; Methane; Retinoids; Structure-Activity Relationship

In the NB4 model of acute promyelocytic leukemia (APL), ATRA, 9-cis retinoic acid (9-cis RA), the pan-RAR and RARalpha-selective agonists, TTNPB and AM580, induce growth inhibition, granulocytic differentiation and apoptosis. By contrast, two RXR agonists, a RARbeta agonist and an anti-AP1 retinoid have very limited activity, ATRA- and AM580-dependent effects are completely inhibited by RAR antagonistic blockade, while 9-cis RA-induced cell-growth-inhibition and apoptosis are equally inhibited by RAR and RXR antagonists. ATRA, 9-cis RA and AM580 cause upregulation of the mRNAs coding for pro-caspase-1, -7, -8, and -9, which, however, results in increased synthesis of only pro-caspase-1 and -7 proteins. These phenomena are associated with activation of pro-caspase-6, -7 and -8, cytochrome c release from the mitochondria, inversion of Bcl-2/Bax ratio and degradation of PML-RARalpha. Caspase activation is fundamental for retinoid-induced apoptosis, which is suppressed by the caspase-inhibitor z-VAD.

Topics: Alitretinoin; Antineoplastic Agents; Apoptosis; Benzoates; Caspases; Cell Differentiation; Cell Division; Enzyme Activation; Gene Expression; Humans; Leukemia, Promyelocytic, Acute; Receptors, Retinoic Acid; Retinoid X Receptors; Retinoids; Tetrahydronaphthalenes; Transcription Factors; Tretinoin; Tumor Cells, Cultured

All-trans retinoic acid (t-RA) administration leads to complete remission in acute promyelocytic leukemia (APL) patients by inducing growth arrest and differentiation of the leukemic clone. In the present study, we show that t-RA treatment dramatically induced type II transglutaminase (type II TGase) expression in cells carrying the t(15;17) translocation and expressing the PML-RARalpha product such as the APL-derived NB4 cell line and fresh leukemic cells from APL patients. This induction correlated with t-RA-induced growth arrest, granulocytic differentiation, and upregulation of the leukocyte adherence receptor beta subunit (CD18) gene expression. The increase in type II TGase was not abolished by cycloheximide treatment, suggesting that synthesis of a protein intermediate was not required for the induction. t-RA did not significantly alter the rate of growth arrest and did not stimulate differentiation and type II TGase activity in NB4.306 cells, a t-RA-resistant subclone of the NB4 cell line, or in leukemic cells derived from two patients morphologically defined as APL but lacking the t(15;17). However, in NB4.306 cells, t-RA treatment was able to increase CD18 mRNA expression in a manner similar to NB4 cells. The molecular mechanisms involved in the induction of these genes were investigated. In NB4 cells, using novel receptor-selective ligands such as 9-cis-RA, TTNPB, AM580, and SR11217, we found that RAR- and RARalpha-selective retinoids were able to induce growth arrest, granulocytic differentiation, and type II TGase, whereas the RXR-selective retinoid SR11217 was inactive. Moreover, an RAR alpha-antagonist completely inhibited the expression of type II TGase and CD18 induced by these selective retinoids in NB4 cells. In NB4.306 cells, an RARalpha-dependent signaling pathway was found involved in the modulation of CD18 expression. In addition, expression of the PML-RARalpha gene in myeloid U937 precursor cells resulted in the ability of these cells to induce type II TGase in response to t-RA. On the basis of these results we hypothesize a specific involvement of a signaling pathway involving PML-RAR alpha for the induction of growth arrest, granulocytic differentiation, and type II TGase by retinoids in APL cells.

Topics: Apoptosis; Benzoates; CD18 Antigens; Cell Differentiation; Chromosomes, Human, Pair 15; Chromosomes, Human, Pair 17; Cytosol; Drug Resistance, Neoplasm; Enzyme Induction; Fenretinide; Gene Expression Regulation, Leukemic; Humans; Isoenzymes; Leukemia, Promyelocytic, Acute; Neoplasm Proteins; Neoplastic Stem Cells; Oncogene Proteins, Fusion; Protein Multimerization; Receptors, Retinoic Acid; Retinoids; Signal Transduction; Tetrahydronaphthalenes; Transglutaminases; Translocation, Genetic; Tretinoin; Tumor Cells, Cultured