5-Azacytidine prevents relapse and produces long-term complete remissions in leukemia xenografts treated with Moxetumomab pasudotox
Menée à l'aide de xénogreffes de leucémie traitée par moxetumomab pasudotox, cette étude montre qu'un traitement par 5-azacytidine prévient le risque de récidive et engendre une rémission complète à long terme
Moxetumomab pasudotox is a fusion protein of an anti-CD22 Fv and Pseudomonas exotoxin. It is highly active against leukemia in vitro but acute lymphoblastic leukemia (ALL) patients often are resistant. Studies with cultured cells showed resistance is caused by reduced diphthamide, the intracellular target of Pseudomonas exotoxin, but diphthamide is not reduced in most cells from most ALL patients. To study how resistance develops in animals, we injected ALL cells into mice and found that resistant cells occur in discrete bone marrow niches and contain major chromosomal and transcriptional changes. Mice pretreated with 5-azacytidine show greatly improved responses, supporting a trial of the combination in leukemia patients.Moxetumomab pasudotox (Moxe) is a chimeric protein composed of an anti-CD22 Fv fused to a portion of Pseudomonas exotoxin A and kills CD22-expressing leukemia cells. It is very active in hairy-cell leukemia, but many children with relapsed/refractory acute lymphoblastic leukemia (ALL) either respond transiently or are initially resistant. Resistance to Moxe in cultured cells is due to low expression of diphthamide genes (DPH), but only two of six ALL blast samples from resistant patients had low DPH expression. To develop a more clinically relevant model of resistance, we treated NSG mice bearing KOPN-8 or Reh cells with Moxe. More than 99.9% of the cancer cells were killed by Moxe, but relapse occurred from discrete bone marrow sites. The resistant cells would no longer grow in cell culture and showed major chromosomal changes and changes in phenotype with greatly decreased CD22. RNA deep sequencing of resistant KOPN-8 blasts revealed global changes in gene expression, indicating dedifferentiation toward less-mature B cell precursors, and showed an up-regulation of myeloid genes. When Moxe was combined with 5-azacytidine, resistance was prevented and survival increased to over 5 months in the KOPN-8 model and greatly improved in the Reh model. We conclude that Moxe resistance in mice is due to a new mechanism that could not be observed using cultured cells and is prevented by treatment with 5-azacytidine.