Novel treatment of acute promyelocytic leukemia: As₂O₃, retinoic acid and retinoid pharmacology.

Acute promyelocytic leukemia(APL), a specific characteristic of t(15;17) chromosome translocation, represents 5% to 15% of cases of acute nonlymphocytic leukemia. An alternative approach is to consider retinoic acid(all-trans RA, ATRA or 13-cis RA or 9-cis RA) plus chemotherapy or RA plus As₂O₃ regimens as now novel therapy. Molecular gene analyses are conclusive in vivo evidence that oncogenic PML/RARa plays a crucial role in APL leukemogenesis. As a novel approach to APL treatment, one possible the action of RA, A consense sequence (5'-TCAGGTCATGACCTGA-3') has been postulated for the thyroid hormone (TRE) and retinoic acid responsive element (RARE) containing half palindromes, which located in the promoter region of target genes. High dose (100-fold) of RA-RARE-PML/RARa complex in intracellular localization appears to relieve repressor from DNA binding, including corepressors N-CoR, SMRT and HDACs, release PML/RARa- mediated transcriptional repression, and release histone deacetylase activity from PMLRARa. The resulting PML/RARa oncoprotein proteolytic degradation through the autophagy-lysosome pathway and the ubiquitin SUMO-proteasome system (UPS), as well as caspase 3 (cleavage site Asp522 within a-helics region of PML component of the fusion protein) or neutrophil elastase, or lysosomal protease enzyme induction. PML protein relocalizes into the wild-type nuclear body (PML-NB) configuration or/and wild-type RARa upregulated. An effect to relieve the blockade (inhibition) of PML/RARA-mediated RA dependent promyelocytic differentiation, and retinoic acid in APL therapy (see Figure in the full text, George Zhu, 1991). Here, like v-erbA, PML/RARa is a (strong) transcriptional repressor of the RA receptor (RAR) complex, and PML/RARa fusion receptor gene act as conditional oncogenic receptor (translocated chimeric retinoic acid a signaling) or oncogenic PML/RARa may participate in leukemogenesis of APL through blocking RA-mediated promyelocytic differentiation. This is first described in eukaryotes.