Mutation in the Unrearranged PML Allele Confers Resistance to Arsenic Trioxide in Acute Promyelocytic Leukemia.

Arsenic trioxide (ATO) is able to selectively target and degrade the disease-causing PML::RARα (P/R) oncoprotein in acute promyelocytic leukemia (APL) for curing the disease. However, some relapsed patients develop resistance to ATO due to mutations in the promyelocytic leukemia (PML) part of the PML::RARα fusion gene. A relapsed APL patient had shown resistance to ATO and chemotherapy and was identified to harbor a point mutation (A216V) in the unrearranged PML allele rather than the PML::RARα fusion gene. Here, we report that mutations in the unrearranged PML allele impede the ATO-induced destabilization and degradation of the wild-type P/R oncoprotein. Deletion of the coiled-coil domain in a PML mutant completely reversed wild-type P/R protein resistance to ATO by abolishing the interaction between PML and P/R proteins. Collectively, our findings reveal that a point mutation in the unrearranged PML allele can confer ATO resistance through a protein-protein interaction. Therefore, the unrearranged PML allele should also be screened for drug-resistant mutations in relapsed APL patients.