Small molecule inhibitors block Gas6-inducible TAM activation and tumorigenicity

Sci Rep. 2017 Mar 8;7:43908. doi: 10.1038/srep43908.

Abstract

TAM receptors (Tyro-3, Axl, and Mertk) are a family of three homologous type I receptor tyrosine kinases that are implicated in several human malignancies. Overexpression of TAMs and their major ligand Growth arrest-specific factor 6 (Gas6) is associated with more aggressive staging of cancers, poorer predicted patient survival, acquired drug resistance and metastasis. Here we describe small molecule inhibitors (RU-301 and RU-302) that target the extracellular domain of Axl at the interface of the Ig-1 ectodomain of Axl and the Lg-1 of Gas6. These inhibitors effectively block Gas6-inducible Axl receptor activation with low micromolar IC50s in cell-based reporter assays, inhibit Gas6-inducible motility in Axl-expressing cell lines, and suppress H1299 lung cancer tumor growth in a mouse xenograft NOD-SCIDγ model. Furthermore, using homology models and biochemical verifications, we show that RU301 and 302 also inhibit Gas6 inducible activation of Mertk and Tyro3 suggesting they can act as pan-TAM inhibitors that block the interface between the TAM Ig1 ectodomain and the Gas6 Lg domain. Together, these observations establish that small molecules that bind to the interface between TAM Ig1 domain and Gas6 Lg1 domain can inhibit TAM activation, and support the further development of small molecule Gas6-TAM interaction inhibitors as a novel class of cancer therapeutics.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Body Weight / drug effects
  • Carcinogenesis / drug effects*
  • Cell Line, Tumor
  • Humans
  • Intercellular Signaling Peptides and Proteins / chemistry
  • Intercellular Signaling Peptides and Proteins / metabolism*
  • Isoxazoles / pharmacology*
  • Mice
  • Mice, Inbred NOD
  • Mice, SCID
  • Neoplasms / drug therapy
  • Neoplasms / metabolism
  • Neoplasms / pathology
  • Piperazines / pharmacology*
  • Protein Kinase Inhibitors / metabolism*
  • Protein Kinase Inhibitors / pharmacology
  • Protein Kinase Inhibitors / therapeutic use
  • Proto-Oncogene Proteins / chemistry
  • Proto-Oncogene Proteins / metabolism*
  • Receptor Protein-Tyrosine Kinases / chemistry
  • Receptor Protein-Tyrosine Kinases / metabolism*
  • Transplantation, Heterologous
  • c-Mer Tyrosine Kinase / chemistry
  • c-Mer Tyrosine Kinase / metabolism*

Substances

  • Intercellular Signaling Peptides and Proteins
  • Isoxazoles
  • Piperazines
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins
  • RU-301
  • RU-302
  • growth arrest-specific protein 6
  • MERTK protein, human
  • Receptor Protein-Tyrosine Kinases
  • TYRO3 protein, human
  • axl receptor tyrosine kinase
  • c-Mer Tyrosine Kinase