sr-11217 and Leukemia--Promyelocytic--Acute

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

Retinoids, such as all-trans-retinoic acid and 9-cis-retinoic acid, are naturally occurring ligands of the nuclear retinoic acid receptors (RARs). In concert with binding of ligand, these receptors from heterodimers with the retinoic X receptor (RXR) and transactivate RAR/RXR-responsive genes. Retinoids can differentiate leukemic cell lines in vitro and induce clinically complete remissions in patients with acute promyelocytic leukemia. Synthetic ligands to the RAR and RXR receptors have been developed that selectively bind and activate RAR/RXR (TTAB) and RXR/RXR dimers (SR11217). We investigated the affect of these ligands, either alone or in combination, on in vitro growth and differentiation of cells from the HL-60, KG-1, THP-1, and WEHI-3 myeloid cell lines as well as on clonal growth of fresh myeloid leukemic blasts from patients. Clonal inhibition of proliferation of these cells was studied in soft agar cultures. Cells were plated in the presence of either one or a combination of retinoids at concentrations of 10(-5) to 10(-10) mol/L. TTAB inhibited 50% clonal growth at an effective dose (ED50) that was about 1,000-fold lower than the concentration of SR11217 required to achieve an ED50 for the same leukemic cells. Combination of both ligands at a variety of concentrations showed no synergistic effects. Superoxide production (nitroblue tetrazolium reduction) and CD11b expression as parameters of differentiation of HL-60 cells were also examined. Results paralleled those of clonal growth, with SR11217 being markedly less potent than TTAB. These results show that the ligand selective for RXR-homodimers has little effect on either inducing differentiation or inhibiting clonal growth of leukemic cells. The differentiating and antiproliferative effects of retinoids are mainly induced through RAR/RXR heterodimers, and development of therapeutic analogs should focus on this category of retinoids.

Topics: Animals; Cell Differentiation; Cell Division; Humans; Leukemia, Promyelocytic, Acute; Mice; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid; Retinoid X Receptors; Retinoids; Transcription Factors; Tumor Cells, Cultured