Application of a MYC degradation screen identifies sensitivity to CDK9 inhibitors in KRAS-mutant pancreatic cancer

Sci Signal. 2019 Jul 16;12(590):eaav7259. doi: 10.1126/scisignal.aav7259.

Abstract

Stabilization of the MYC oncoprotein by KRAS signaling critically promotes the growth of pancreatic ductal adenocarcinoma (PDAC). Thus, understanding how MYC protein stability is regulated may lead to effective therapies. Here, we used a previously developed, flow cytometry-based assay that screened a library of >800 protein kinase inhibitors and identified compounds that promoted either the stability or degradation of MYC in a KRAS-mutant PDAC cell line. We validated compounds that stabilized or destabilized MYC and then focused on one compound, UNC10112785, that induced the substantial loss of MYC protein in both two-dimensional (2D) and 3D cell cultures. We determined that this compound is a potent CDK9 inhibitor with a previously uncharacterized scaffold, caused MYC loss through both transcriptional and posttranslational mechanisms, and suppresses PDAC anchorage-dependent and anchorage-independent growth. We discovered that CDK9 enhanced MYC protein stability through a previously unknown, KRAS-independent mechanism involving direct phosphorylation of MYC at Ser62 Our study thus not only identifies a potential therapeutic target for patients with KRAS-mutant PDAC but also presents the application of a screening strategy that can be more broadly adapted to identify regulators of protein stability.

Publication types

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

MeSH terms

  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Cell Proliferation / genetics
  • Cyclin-Dependent Kinase 9 / antagonists & inhibitors*
  • Cyclin-Dependent Kinase 9 / metabolism
  • Drug Screening Assays, Antitumor / methods*
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Molecular Structure
  • Mutation
  • Pancreatic Neoplasms / genetics*
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology
  • Phosphorylation / drug effects
  • Protein Kinase Inhibitors / chemistry
  • Protein Kinase Inhibitors / pharmacology*
  • Protein Stability
  • Proteolysis
  • Proto-Oncogene Proteins c-myc / genetics
  • Proto-Oncogene Proteins c-myc / metabolism*
  • Proto-Oncogene Proteins p21(ras) / genetics*
  • Proto-Oncogene Proteins p21(ras) / metabolism
  • Small Molecule Libraries / chemistry
  • Small Molecule Libraries / pharmacology

Substances

  • KRAS protein, human
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins c-myc
  • Small Molecule Libraries
  • CDK9 protein, human
  • Cyclin-Dependent Kinase 9
  • Proto-Oncogene Proteins p21(ras)