Page 88 - Haematologica - Vol. 105 n. 6 - June 2020

N. Maslah et al.
only 26% when FLT3-L was added (Figure 7E). These results suggest that the synergistic effect observed with the APR + AZA combination on proliferation and apopto- sis correlates with downregulation of the FLT3 pathway.
Discussion
APR has been shown to have efficacy on its own as well as when combined with other drugs in solid tumors19,20,23-25 and lymphoid tumors.21,27,28,36 In this study, we observed that APR inhibited the proliferation of sev- eral TP53-mutated myeloid cell lines, as previously sug-
gested by other studies on myeloid26,34 and lymphoid cell lines.27,28 Of note, the additive/synergistic impact of the combination was more robust with regards to apoptosis compared to cell cycle arrest, suggesting that most of the anti-proliferative effect may be mediated by hypomethy- lating agent (AZA) while the pro-apoptotic effects of the combination was clearly due to APR.
These inhibitory effects were more pronounced in the TP53-mutated MDS-derived SKM1 cell line, and may be related to the structure of the mutant protein in the differ- ent cell lines. Indeed, APR binding to the cysteine residues of the DBD has been associated with the reformation of an active structure by p.R175H and p.R273H mutant p53
AB
CD
EF
Figure 4. Effects of PRIMA-1Met (APR-246, APR) on primary cells from TP53 wild-type or mutated myelodysplastic syndromes (MDS) / acute myeloid leukemia (AML) patients and healthy donors. (Left) Relative proliferation of CD34+ cells treated with 1 μM APR, 1 μM AZA or the combination APR + AZA at these concentra- tions. (Right) Percentages of Annexin V-positive cells at day 3 post treatment with 1 μM APR, 1 μM of AZA or the combination APR + AZA at these concentrations. (A) TP53-mutated MDS/AML samples (n=3), (B) Wild-type TP53 MDS/AML samples (n=3), and (C) healthy donors (n=3). *P<0.05.
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