The Impact of the Epigenetic Cancer Drug Azacitidine on Host Immunity: The Role of Myelosuppression, Iron Overload and tp53 Mutations in a Zebrafish Model.

The unsatisfactory real-world efficacy of the hypomethylating agent azacitidine in treating myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) has prompted us to investigate the hematological adverse events and host variables that may compromise the use of this epigenetic drug. Using the zebrafish, we found that azacitidine destroyed their myeloid precursors and impaired myeloid function by inhibiting antigen processing, allogeneic response and phagocytic activity, resulting in increased susceptibility to infection even by the normal flora E. coli. In addition, iron overload, a MDS-associated condition following repeated transfusions, exacerbated bacterial infection especially by V. vulnificus with known iron dependence. Furthermore, we show that the tp53 mutant zebrafish survived longer than the wild-type (WT) when challenged with bacteria following azacitidine treatment. This was attributed to the mutant's hematopoietic cells rather than its general genetic background, since the WT animals reconstituted with the tp53 mutant kidney marrow became more resistant to bacterial infection following treatment with azacitidine. The clinical relevance of our findings was indicated by a MDS case with severe azacitidine-induced bone marrow suppression and by the association of hyperferritinemia with bacteremia in azacitidine-treated patients, while tp53-mediated resistance to azacitidine-induced myelosuppression may explain the survival advantage of malignant MDS and AML clones over their normal counterparts under azacitidine treatment. Together, we propose that myelosuppression, iron overload and TP53 mutations may represent the host variables that compromise the azacitidine efficacy.