[Mechanism of action of retinoids in a new therapeutic approach to acute promyelocytic leukemia].

Vitamin A (retinol) and retinoic acid, its natural derivative, play an important role in the growth, differentiation and development of known normal tissues. Retinoids have recently become of interest to research in areas as diverse as dermatology, embryonal development and cancer research. Retinol is the major retinoid transported in the blood and tissues by its specific carrier retinol binding protein (RBP). The normal level of retinol in plasma is regulated very precisely by retinol homeostasis. RBP-retinol circulation supplies target cells, which then activate retinol into retinoic acid (RA) if they possess the NAD-dependent enzymatic oxidation system. RA, which is one of the most active metabolites of retinol, is also present in low concentration in the blood and the RA rate formation varies from tissues depending on specific need of the cell. The cellular transport and biological activity of retinoids may be mediated by their specific cytoplasmic binding proteins cellular retinol binding protein (CRBP) and the cellular retinoic acid binding protein (CRABP) which may function as shuttles targetting RA to nucleosol fraction and/or as regulator of cellular concentration of RA. The nuclear proteins RARs (retinoic acid receptors), which are members of the nuclear receptor superfamily are likely to be the final transducers of the RA signal at the gene expression. All-trans retinoic acid (ATRA) is able to specifically differentiate the malignant cells from leukemic patients with APL in short-term culture. For this reason, APL patients were successfully treated with ATRA (Chinese and French results). Acute promyelocytic leukemia M3 (French-American-British FAB classification) is a rare disease (10% of AML), characterized by a reciprocal chromosome 15-17 translocation. It has been shown that the chromosome 17 breakpoint of the translocation is localized within the RAR alpha gene. Due to the t(15;17) RAR alpha gene translocated to a gene PML on chromosome 15 resulting in synthesis of PML/RAR alpha fusion messenger RNA. Detection of PML/RAR alpha transcript is now a molecular marker of the disease. The abnormal PML/RAR alpha protein exhibits altered transcription activation properties when compared with RAR alpha. Clinical trials have demonstrated that ATRA is extremely efficient in inducing complete remission in APL patients. The morphologic finding of maturing elements in the bone marrow and peripheral blood during retinoic acid treatment indicates that the remission is obtained without hypoplasia and suggests that a differentiating mechanism is involved.(ABSTRACT TRUNCATED AT 400 WORDS)