ALL-TRANS RETINOIC ACID (ATRA) THERAPEUTIC EFFECT IN ACUTE PROMYELOCYTIC LEUKEMIA

All-trans retinoic acid (ATRA) is able to specifically differentiate acute promyelocytic leukemic cells (APL) in short-term culture. Patients with APL achieved complete remission within 1-3 months by a progressive maturation of leukemic cells. The advantages of this differentiation therapy are the rapid disappearance of the bleeding disorders and the absence of aplastic phase avoiding the early deaths occurring in 15-30% of patients with conventional chemotherapy. However, relapses occurred when ATRA alone was maintained. For this reason, a chemotherapy is added after complete remission obtained by ATRA. A pilot study on 27 patients was proposed with the sequential combination of ATRA and chemotherapy. A European trial randomizes conventional therapy to the sequential ATRA-chemotherapy protocol. Retinoic acid receptor (RARa) is rearranged by the specific translocation t(15;17) of APL; a PCR technique was developed in order to ensure the diagnosis and to follow the minimal residual disease. Transfection experiment of the chimaeric gene inhibits the transactivation of the natural RAR. ATRA is able to revert the arrest of maturation perhaps through an increase of the expression of the normal allele of RAR, which could overpass the impairment induced by the chimaeric protein on target responsive elements. One of the steps of the repair is the modulation of programmed cell death (PCD). Bc1-2, a gene involved in the PCD, is modulated in in vitro studies, arguing for the engagement of the cell in the natural death. The beneficial effect of differentiation therapy is probably due to the induction of the natural death of the malignant cell.