LEUKEMIC CELLULAR RETINOIC ACID RESISTANCE AND MISSENSE MUTATIONS IN THE PML-RAR-ALPHA FUSION GENE AFTER RELAPSE OF ACUTE PROMYELOCYTIC LEUKEMIA FROM TREATMENT WITH ALL-TRANS-RETINOIC ACID AND INTENSIVE CHEMOTHERAPY

This study evaluated whether relapse of acute promyelocytic leukemia ( APL) patients from clinical remissions achieved and/or maintained with all-trans retinoic acid (RA) in combination with intensive chemothera py is associated with leukemic cellular resistance to WA and with alte rations in the PML-RAR alpha fusion gene. We studied matched pretreatm ent and relapse specimens from 12 patients who received variable amoun ts of WA, primarily in nonconcurrent combination with daunorubicin and cytarabine (DA) on Eastern Cooperative Oncology Group (ECOG) protocol E2491, and from 8 patients who received DA only on protocol E2491. Of 10 RA-treated patients evaluable for a change in APL cell sensitivity to RA-induced differentiation in vitro, 8 showed diminished sensitivi ty at relapse, whereas, of 6 evaluable patients treated with DA alone, only 1 had marginally reduced sensitivity. From analysis of sequences encoding the principal functional domains of the PML and RAR alpha po rtions of PML-RAR alpha, we found missense mutations in relapse specim ens from 3 of 12 RA-treated patients and 0 of 8 DA-treated patients. A ll 3 mutations were located in the ligand binding domain (LBD) of the RAR alpha region of PML-RAR alpha. Relative to normal RAR alpha 1, the mutations were Leu290Val, Arg394Trp, and Met413Thr. All pretreatment analyses were normal except for a C to T base change in the 3'-untrans lated (UT) region of 1 patient that was also present after relapse fro m DA therapy. No mutations were detected in the corresponding sequence s of the normal RAR alpha or PML (partial) alleles. Minor additional P ML-RAR alpha isoforms encoding truncated PML proteins were detected in 2 cases. We conclude that APL cellular resistance occurs with high in cidence after relapse from RA + DA therapy administered in a nonconcur rent manner and that mutations in the RAR alpha region of the PML-RAR alpha gene are present in and likely mechanistically involved in RA re sistance in a subset of these cases. (C) 1998 by The American Society of Hematology.