Targeting non-canonical activation of GLI1 by the SOX2-BRD4 transcriptional complex improves the efficacy of HEDGEHOG pathway inhibition in melanoma

Oncogene. 2021 Jun;40(22):3799-3814. doi: 10.1038/s41388-021-01783-9. Epub 2021 May 6.

Abstract

Despite the development of new targeted and immune therapies, the prognosis of metastatic melanoma remains bleak. Therefore, it is critical to better understand the mechanisms controlling advanced melanoma to develop more effective treatment regimens. Hedgehog/GLI (HH/GLI) signaling inhibitors targeting the central pathway transducer Smoothened (SMO) have shown to be clinical efficacious in skin cancer; however, several mechanisms of non-canonical HH/GLI pathway activation limit their efficacy. Here, we identify a novel SOX2-BRD4 transcriptional complex driving the expression of GLI1, the final effector of the HH/GLI pathway, providing a novel mechanism of non-canonical SMO-independent activation of HH/GLI signaling in melanoma. Consistently, we find a positive correlation between the expression of GLI1 and SOX2 in human melanoma samples and cell lines. Further, we show that combined targeting of canonical HH/GLI pathway with the SMO inhibitor MRT-92 and of the SOX2-BRD4 complex using a potent Proteolysis Targeted Chimeras (PROTACs)-derived BRD4 degrader (MZ1), yields a synergistic anti-proliferative effect in melanoma cells independently of their BRAF, NRAS, and NF1 mutational status, with complete abrogation of GLI1 expression. Combination of MRT-92 and MZ1 strongly potentiates the antitumor effect of either drug as single agents in an orthotopic melanoma model. Together, our data provide evidence of a novel mechanism of non-canonical activation of GLI1 by the SOX2-BRD4 transcriptional complex, and describe the efficacy of a new combinatorial treatment for a subset of melanomas with an active SOX2-BRD4-GLI1 axis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology
  • Cell Cycle Proteins / antagonists & inhibitors*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Dipeptides / administration & dosage
  • Dipeptides / pharmacology*
  • Drug Synergism
  • Female
  • Guanidines / administration & dosage
  • Guanidines / pharmacology*
  • Hedgehog Proteins / antagonists & inhibitors*
  • Hedgehog Proteins / metabolism
  • Heterocyclic Compounds, 3-Ring / administration & dosage
  • Heterocyclic Compounds, 3-Ring / pharmacology*
  • Humans
  • Melanoma / drug therapy*
  • Melanoma / metabolism
  • Melanoma / pathology
  • Mice
  • Mice, Nude
  • Molecular Targeted Therapy
  • SOXB1 Transcription Factors / metabolism*
  • Signal Transduction / drug effects
  • Smoothened Receptor / antagonists & inhibitors
  • Spheroids, Cellular
  • Transcription Factors / antagonists & inhibitors*
  • Xenograft Model Antitumor Assays
  • Zinc Finger Protein GLI1 / metabolism*

Substances

  • BRD4 protein, human
  • Cell Cycle Proteins
  • Dipeptides
  • GLI1 protein, human
  • Guanidines
  • Hedgehog Proteins
  • Heterocyclic Compounds, 3-Ring
  • MRT-92
  • MZ1 compound
  • SMO protein, human
  • SOX2 protein, human
  • SOXB1 Transcription Factors
  • Smoothened Receptor
  • Transcription Factors
  • Zinc Finger Protein GLI1