The Hedgehog pathway as targetable vulnerability with 5-azacytidine in myelodysplastic syndrome and acute myeloid leukemia

J Hematol Oncol. 2015 Oct 20;8:114. doi: 10.1186/s13045-015-0211-8.


Background: Therapy and outcome for elderly acute myeloid leukemia (AML) patients has not improved for many years. Similarly, there remains a clinical need to improve response rates in advanced myelodysplastic syndrome (MDS) patients treated with hypomethylating agents, and few combination regimens have shown clinical benefit. We conducted a 5-azacytidine (5-Aza) RNA-interference (RNAi) sensitizer screen to identify gene targets within the commonly deleted regions (CDRs) of chromosomes 5 and 7, whose silencing enhances the activity of 5-Aza.

Methods and results: An RNAi silencing screen of 270 genes from the CDRs of chromosomes 5 and 7 was performed in combination with 5-Aza treatment in four AML cell lines (TF-1, THP-1, MDS-L, and HEL). Several genes within the hedgehog pathway (HhP), specifically SHH, SMO, and GLI3, were identified as 5-Aza sensitizing hits. The smoothened (SMO) inhibitors LDE225 (erismodegib) and GDC0449 (vismodegib) showed moderate single-agent activity in AML cell lines. Further studies with erismodegib in combination with 5-Aza demonstrated synergistic activity with combination index (CI) values of 0.48 to 0.71 in seven AML lines. Clonogenic growth of primary patient samples was inhibited to a greater extent in the combination than with single-agent erismodegib or 5-Aza in 55 % (6 of 11) primary patient samples examined. There was no association of the 5-Aza/erismodegib sensitization potential to clinical-cytogenetic features or common myeloid mutations. Activation of the HhP, as determined by greater expression of HhP-related genes, showed less responsiveness to single-agent SMO inhibition, while synergy between both agents was similar regardless of HhP gene expression. In vitro experiments suggested that concurrent dosing showed stronger synergy than sequential dosing.

Conclusions: Inhibition of the HhP with SMO inhibitors in combination with the hypomethylating agent 5-Aza demonstrates synergy in vitro and inhibits long-term repopulation capacity ex vivo in AML and MDS. A clinical trial combining 5-Aza with LDE225 (erismodegib) in MDS and AML is ongoing based on these results as well as additional publications suggesting a role for HhP signaling in myeloid disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acute Disease
  • Aged
  • Aged, 80 and over
  • Anilides / pharmacology
  • Anilides / therapeutic use
  • Antimetabolites, Antineoplastic / pharmacology
  • Antimetabolites, Antineoplastic / therapeutic use
  • Azacitidine / pharmacology*
  • Azacitidine / therapeutic use
  • Biphenyl Compounds / pharmacology
  • Biphenyl Compounds / therapeutic use
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Cell Survival / genetics
  • Chromosomes, Human, Pair 5 / genetics
  • Chromosomes, Human, Pair 7 / genetics
  • Drug Synergism
  • Female
  • HL-60 Cells
  • Hedgehog Proteins / genetics*
  • High-Throughput Nucleotide Sequencing / methods
  • Humans
  • Leukemia, Myeloid / drug therapy*
  • Leukemia, Myeloid / genetics
  • Leukemia, Myeloid / pathology
  • Male
  • Myelodysplastic Syndromes / drug therapy*
  • Myelodysplastic Syndromes / genetics
  • Myelodysplastic Syndromes / pathology
  • Pyridines / pharmacology
  • Pyridines / therapeutic use
  • RNA Interference
  • Signal Transduction / drug effects*
  • Signal Transduction / genetics


  • Anilides
  • Antimetabolites, Antineoplastic
  • Biphenyl Compounds
  • Hedgehog Proteins
  • HhAntag691
  • Pyridines
  • sonidegib
  • Azacitidine