Missense mutations in PML-RARA are critical for the lack of responsiveness to arsenic trioxide treatment

Arsenic trioxide (As2O3) is a highly effective treatment for patients with refractory/relapsed acute promyelocytic leukemia (APL), but resistance to As2O3 has recently been seen. In the present study, we report the findings that 2 of 15 patients with refractory/relapsed APL treated with As2O3 were clinically As2O3 resistant. Leukemia cells from these 2 patients harbored missense mutations in promyelocytic leukemia gene-retinoic acid receptor-alpha gene (PML-RARA) transcripts, resulting in amino acid substitutions of A216V and L218P in the PML B2 domain. When wild-type or mutated PML-RARA (PR-WT and PR-B/L-mut, respectively) were overexpressed in HeLa cells, immunoblotting showed SUMOylated and/or oligomerized protein bands in PR-WT but not in PR-B/L-mut after As2O3 treatment. Protein-localization analysis indicated that PR-WT in the soluble fraction was transferred to the insoluble fraction after treatment with As2O3, but PR-B/L-mut was stably detected in fractions both with and without As2O3. Immunofluorescent microscopy analysis showed PR-WT localization as a microgranular pattern in the cytoplasm without As2O3 and as a macrogranular pattern with As2O3. PR-B/L-mut was diffusely observed in the cytoplasm with and without As2O3. Nearly identical localization patterns were observed in patients' primary cells. Therefore, B2 domain mutations may play an important role in aberrant molecular responses to As2O3 and may be critical for As2O3 resistance in APL. (Blood. 2011;118(6):1600-1609)