HIF1-Alpha and MYC Transcription Factor Signatures in B-Cell Acute Lymphoblastic Leukemia Are Associated with Positive Minimal Residual Disease Status: Therapeutic Implications

Precursor B-cell lymphoblastic leukemia (B-ALL) in adults remains a challenging clinical problem due to higher relapse rate and worse prognosis than in children. Although most of adult patients respond to standard induction therapy and complete remissions (CR) are typically achieved in 90% of patients, the majority of them eventually relapse. Our previous studies indicate that the minimal residual disease (MRD) status after induction therapy is the most important risk factor of relapse in adult B-ALL patients [Br J Haematol 2008;142:227-37]. We hypothesized that the survival of B-ALL blasts after induction therapy is a result of intrinsic characteristics of the tumor cells that determine resistance to chemotherapeutics. Therefore, we sought to identify the molecular background of B-ALL cells resistance to daunorubicin.

To identify potential mechanisms responsible for drug-resistant phenotype, we utilized gene expression data from previous studies that assessed transcriptional profiles of drug-sensitive and drug-resistant cells. Using gene set enrichment analysis (GSEA) of daunorubicin-sensitive versus -resistant phenotypes of B-ALL cells we identified differential expression HIF1α and MYC transcription factors target genes (p=0.002, FDR=0.144; p<0.001; FDR=0.171, respectively). To verify these in silico findings, we compared the expression of a panel of MYC and HIF1α target genes in 41 newly diagnosed adult B-ALL patients who subsequently underwent standard induction therapy according to Polish Adult Leukemia Group PALG-ALL6 protocol. Expression of MYC and HIF1α signature genes was significantly higher in patients with positive (>0.1%) MRD status after completion of the induction therapy. Among studied HIF1α and MYC targets, lactate dehydrogenase A (LDHA) expression was the best predictor differentiating MRD+ versus MRD- patients (p=0.0019, FDR=0.005). It was of particular interest, since tumor stem cells are typically characterized by MYC and HIF1α transcriptional signatures, which rewire cellular metabolism towards aerobic glycolysis. We next assessed the effect of LDHA inhibition with a small molecule inhibitor, GSK2837808A, on proliferation and clonogenicity of human B-ALL cell lines. GSK2837808A markedly reduced lactate production in B-ALL cell lines (RS4;11, SEM-K2 and NALM-6) and decreased proliferation and colony formation in semi-solid medium in a dose-dependent fashion.

Taken together, we show that adult B-ALL patients with positive MRD status after induction therapy exhibit concordant upregulation of HIF1α and MYC signature genes. Expression of LDHA, a target gene regulated by both HIF1α and MYC transcription factors was significantly higher in MRD-positive patients. Finally, inhibition of LDHA markedly decreased proliferation and clonogenicity of B-ALL cell lines, indicating that LDHA might be a therapeutic target in B-ALL.