We found that chemorefractory blasts from leukemias with varied genetic backgrounds expressed a common transcriptional program. shRNA knockdown experiments demonstrated that the viability of primary AML cells, but not normal CD34+ cells, depended on FOXM1 expression. The refractory gene signature was highly enriched with targets of the transcription factor FOXM1. However, the proportion of immunophenotypically defined LSCs appeared to decrease following treatment, with implications for the targeting of these cells on the basis of cell surface antigen expression. Resistant blasts also appeared less differentiated and expressed leukemia stem cell (LSC) maintenance genes. Remarkably, the gene expression signature suggested that post-chemotherapy blasts were more proliferative than those at presentation. Despite the genetic heterogeneity of the leukemias studied, transcriptional analysis found concerted changes in gene expression in resistant blasts. Immunophenotypic characterisation found leukemia-associated immunophenotypes in all cases that persisted following treatment.

Molecular genetic analysis revealed early clonal selection occurring after induction chemotherapy. Lentiviral vectors expressing short hairpin RNAs were used to assess the effect of FOXM1 knockdown on colony forming capacity, proliferative capacity and apoptosis in cell lines, primary AML cells and CD34+ cells from healthy donors. Sorted blasts were subjected to RNA sequencing. Fluorescence in situ hybridization (FISH), targeted genetic sequencing and detailed immunophenotypic analysis were used to confirm that sorted cells were leukemic. Leukemic blasts were isolated by fluorescence-activated cell sorting. We sought to characterise in vivo chemoresistant blasts by studying the transcriptional and genetic features of blasts from before and shortly after induction chemotherapy using paired samples from six patients with primary refractory AML.

However, further treatment responses are often seen following relapse, suggesting that most blasts remain chemosensitive. To date, attempts to define the characteristics of in vivo resistant blasts have focused on comparisons between leukemic cells at presentation and relapse. Disease relapse remains common following treatment of acute myeloid leukemia (AML) and is due to chemoresistance of leukemia cells with disease repopulating potential.

Fischer pool table serial number lookup