Mutations in the E-domain of RARα portion of the PML/RARα chimeric gene may confer clinical resistance to all-trans retinoic acid in acute promyelocytic leukemia

The binding of all-trans retinoic acid (ATRA) to the ligand-binding region in the E-domain of retinoic acid receptor-alpha (RAR alpha) modifies the transcriptional activity of RAR alpha protein. ATRA probably induces differentiation of acute promyelocytic leukemia (APL) cells by binding to the E-domain of the RAR alpha portion (RAR alpha/E-domain) of PML/RAR alpha chimeric protein. Therefore, molecular alteration in the RARa/E-domain of the chimeric gene is one mechanism by which patients with APL may acquire resistance to ATRA therapy. In this study using reverse transcription polymerase chain reaction and single-strand conformation polymorphism, DNA segments amplified from the RAR alpha/E-domain in fresh APL cells of 23 APL patients (8 males and 15 females from 4 to 76 years of age) were screened for mutations. Of those patients, 3 patients (1 with de novo and 2 with relapse) had clinical resistance to ATRA therapy. We found mutations in the RAR alpha/E-domain of PML/RAR alpha chimeric gene exclusively in the 2 patients who exhibited ATRA-resistance at relapse, whereas the mutations were not detected at their initial onset. Interestingly, these patients received a prolonged or intermittent administration of ATRA before relapse with ATRA-resistance. The mutations lead to the change of amino acid in the ligand-binding region of RAR alpha/E domain, Arg272Gln, or Met297Leu according to the amino acid sequence of RAR alpha, respectively. Further study demonstrated that the in vitro ligand-dependent transcriptional activity of the mutant PML/RAR alpha protein was significantly decreased as compared with that of wild type PML/RAR alpha. These findings suggest that mutations in the RAR alpha/E domain of the PML/RAR alpha chimeric gene may confer clinical resistance to ATRA therapy in patients with APL. (C) 1998 by The American Society of Hematology.