Page 92 - Haematologica - Vol. 105 n. 6 - June 2020

N. Maslah et al.
was probably due to the very high proportion of mutant progenitor cells that grew in these conditions, as no wild- type colonies could be discerned even in the absence of treatment. An in vivo evaluation of the change in the TP53 allelic burden in patients treated by the combination would be relevant to address the question of mutant TP53 selectivity. A clinical trial (clinicaltrials.gov identifier: 03745716) testing the association of APR and AZA in TP53-mutant MDS/AML is ongoing and may help answer this question.
The molecular mechanism underlying the efficacy of the association between AZA and APR remains unknown. AZA is a DNA demethylating agent and APR is an agent that reactivates the transcription factor p53. Both drugs may act by modulating gene expression. Thus, we sought to study differences in gene expression profiles between cells treated by the single agents or with the drug combi- nation. The results of the transcriptomic analysis provide further evidence that APR, even at low doses, reactivates the p53 pathway and that it results in activation of an apoptotic program. We also found that genes involved in FLT3 signaling were down-regulated by the combination of APR and AZA. The relevance of this observation was confirmed as the addition of FLT3 ligand reversed the inhi- bition of cell proliferation by the APR + AZA combina- tion. Interestingly none of the cell lines tested had FLT3
mutations or duplications,41 suggesting that the drug com- bination effect is not dependent on the presence of such molecular alterations. However, it would be interesting to test this drug combination in cell lines with FLT-3 muta- tions or duplications. In addition to providing clues for a specific mechanism of action of the drug combination through a synthetic lethality process involving the FLT3 pathway, our observations indicate that the addition of FLT3-inhibitors to the APR + AZA combination could be of relevance in TP53-mutated MDS/AML.42
In conclusion, our results suggest that APR exhibits promising synergistic effects when combined with con- ventional AZA therapy in the high-risk subgroup of TP53- mutated MDS/AML. Promising preliminary results of a phase I/II clinical trial combining AZA and APR in TP53- mutated MDS/AML, and activated at US centers and our center, have been reported.29
Acknowledgments
We thank the animal facility of the Institut Universitaire d’Hématologie of Hôpital Saint-Louis, Paris, for technical assis- tance and the Genomic Platform at the Cochin Institute for assis- tance with the transcriptomic analysis. This study was supported by the Groupe Francophone des Myélodysplasies (GFM). We are indebted to Aprea Therapeutics and Celgene for supplying the APR and AZA, respectively.
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