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Figure 3. Impact of dexamethasone on chemoresistance. (A) Leukemia long-term culture initiating cell (L-LTC-IC) frequency in acute myeloid leukemia (AML) samples upon dexamethasone treatment (#38 to 49, Online Supplementary Table S8). (B) Expression of CD34 and CD38 upon dexamethasone treatment in co-culture with AML samples and MS-5 stromal cells. (C) Expression of lineage and CD14/11b markers upon dexamethasone treatment in co-culture with AML samples and MS-5 stromal cells. (D) Seven AML cell lines incubated in a co-culture system with MS-5 stromal cells were treated for 1 week with vehicle, dexamethasone, cytarabine, or dexamethasone plus cytarabine. (E) Gene ontology enrichment analysis of down-regulated and up-regulated genes from RNA expression profiles of viable AML cells following cytarabine versus vehicle-treated AML-patient-derived xenograft (PDX) mice, by 1.5-fold or more. (F and G) Gene-to-small molecule associations that are sig- nificantly enriched within residual post-cytarabine AML cells (Figure 3F and Online Supplementary Table S5) or in relapse (compared to pairwise diagnosis, Figure 3G and Online Supplementary Table S6) using a data-mining algorithm (Genomatix) from GSE9763119 or GSE6652520 publicly accessible transcriptomic databases, respectively. These two graphs shown a gene signature ranking assessed by the number of observed versus expected genes significantly modulated in transcrip- tomes after treatment with diverse small molecules and significantly enriched in AML transcriptomes of residual post-cytarabine AML cells or of relapse. (H) Treatment of PDX models from 2 AML samples collected at diagnosis (black dots: normal karyotype, NPM1 mutation, wild-type for FLT3-ITD, DNMT3A-exon23, CEBPA, IDH1, and IDH2, red dots: normal karyotype, NPM1 mutation, DNMT3A-exon23 mutation, FLT3 wild type) with vehicle, dexamethasone (10 mg/kg/day, 5 days), cytarabine (30 mg/kg/day, 5 days), or dexamethasone plus cytarabine. At day 8, the reduction of the total AML cell burden was assessed by the absolute quantifi- cation of the hCD45+hCD33+mCD45.1- cell population in bone marrow and spleen. Mann Whitney test: ****P<0.0001; ***P<0.001; **P<0.01; *P<0.05; ns: not significant.
Dexamethasone in AML
We thus explored the impact of dexamethasone treatment in the OCI-AML3 xenotransplantation model (Online Supplementary Figure S3B). Dexamethasone treatment resulted in a significant survival advantage compared to vehicle. Moreover, the combination of dexamethasone
plus cytarabine significantly improved mouse survival compared to that following cytarabine treatment alone (Figure 4B). We then tested the in vitro activity of dexam- ethasone against primary samples from patients with or without an NPM1 mutation. Primary AML samples with
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