Inhibition of SP1 by the mithramycin analog EC-8042 efficiently targets tumor initiating cells in sarcoma

Oncotarget. 2016 May 24;7(21):30935-50. doi: 10.18632/oncotarget.8817.


Tumor initiating cells (TICs), responsible for tumor initiation, and cancer stem cells (CSCs), responsible for tumor expansion and propagation, are often resistant to chemotherapeutic agents. To find therapeutic targets against sarcoma initiating and propagating cells we used models of myxoid liposarcoma (MLS) and undifferentiated pleomorphic sarcoma (UPS) developed from human mesenchymal stromal/stem cells (hMSCs), which constitute the most likely cell-of-origin for sarcoma. We found that SP1-mediated transcription was among the most significantly altered signaling. To inhibit SP1 activity, we used EC-8042, a mithramycin (MTM) analog (mithralog) with enhanced anti-tumor activity and highly improved safety. EC-8042 inhibited the growth of TIC cultures, induced cell cycle arrest and apoptosis and upregulated the adipogenic factor CEBPα. SP1 knockdown was able to mimic the anti-proliferative effects induced by EC-8042. Importantly, EC-8042 was not recognized as a substrate by several ABC efflux pumps involved in drug resistance, and, opposite to the chemotherapeutic drug doxorubicin, repressed the expression of many genes responsible for the TIC/CSC phenotype, including SOX2, C-MYC, NOTCH1 and NFκB1. Accordingly, EC-8042, but not doxorubicin, efficiently reduced the survival of CSC-enriched tumorsphere sarcoma cultures. In vivo, EC-8042 induced a profound inhibition of tumor growth associated to a strong reduction of the mitotic index and the induction of adipogenic differentiation and senescence. Finally, EC-8042 reduced the ability of tumor cells to reinitiate tumor growth. These data suggest that EC-8042 could constitute an effective treatment against both TIC and CSC subpopulations in sarcoma.

Keywords: DIG-MSK; cancer stem cells; mesenchymal stem cells; mithralog EC-8042; myxoid liposarcoma.

MeSH terms

  • ATP-Binding Cassette Transporters / metabolism
  • Animals
  • Antineoplastic Agents / pharmacokinetics
  • Antineoplastic Agents / therapeutic use*
  • Apoptosis / drug effects
  • Cell Cycle Checkpoints / drug effects
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Doxorubicin / pharmacokinetics
  • Drug Resistance, Neoplasm
  • Female
  • Fluorescent Antibody Technique
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Humans
  • Mice, Inbred NOD
  • Mice, SCID
  • NF-kappa B p50 Subunit / metabolism
  • Neoplastic Stem Cells / drug effects*
  • Plicamycin / analogs & derivatives*
  • Plicamycin / pharmacokinetics
  • Plicamycin / therapeutic use
  • Proto-Oncogene Proteins c-myc / metabolism
  • Receptor, Notch1 / metabolism
  • SOXB1 Transcription Factors / metabolism
  • Sarcoma, Experimental / drug therapy*
  • Sarcoma, Experimental / genetics
  • Sarcoma, Experimental / metabolism
  • Signal Transduction / drug effects
  • Sp1 Transcription Factor / metabolism*
  • Xenograft Model Antitumor Assays


  • ATP-Binding Cassette Transporters
  • Antineoplastic Agents
  • MYC protein, human
  • NF-kappa B p50 Subunit
  • NFKB1 protein, human
  • NOTCH1 protein, human
  • Proto-Oncogene Proteins c-myc
  • Receptor, Notch1
  • SOX2 protein, human
  • SOXB1 Transcription Factors
  • Sp1 Transcription Factor
  • Sp1 protein, human
  • demycarosyl-3D-digitoxosylmithramycin SK
  • Doxorubicin
  • Plicamycin