Varying Responses of PML-Rara with Different Genetic Mutations to Arsenic Trioxide

Resistance to arsenic and/or ATRA is a challenging problem in the clinical management of acute promyelocytic leukemia (APL). Acquired genetic mutations in the PML moiety of the PML-RARA fusion gene have been found to exist virtually in APL patients at relapse. While C212/C213 mutations in the PML B2 domain of PML-RARA were shown to be capable of abolishing the effect of arsenic on target proteins in vitro, A216V and L218P mutations in the PML portion of PML-RARA were detectable in two APL patients resistant to arsenic therapy. More recently, we identified a panel of point mutations (including previously reported A216V and, newly identified S214L, A216T, L217F and S220G) from nine of 13 APL patients with arsenic resistance. These findings indicated the existence of a mutational hotspot (S214-S220) within the PML-RARA oncoprotein among APL patients at relapse. Whether each of the identified point mutations plays a role and functions distinctly in the mechanism underlying the resistance to arsenic therapy is of particular interest.

Here, we performed in vitro functional analyses in both the hematopoietic irrelevant and relevant cells, and a retrospective analysis of APL patients to investigate the effect of PML-RARA mutations on mediating the resistance to arsenic trioxide. Among the five point mutations in the PML part of PML-RARA identified in patients with relapsed APL, we found that A216V, S214L and A216T mutations could attenuate the negative regulation of arsenic on PML-RARA, which resulted in the retention of oncoproteins. In contrast, L217F and S220G mutations function weakly in this context. Furthermore, we demonstrated that high concentration of As₂O₃could overcome the primary arsenic resistance driven by the indicated point mutations in PML-RARA. In addition to providing more evidence to reinforce the correlation of genetic mutations in PML-RARA with arsenic efficacy, we provide a novel insight into the functional difference of acquired mutations of PML-RARA both in vitro and in the clinical setting. Our findings may help predict the prognosis and select more effective strategies during APL therapy.