The prolyl oligopeptidase inhibitor SUAM-14746 attenuates the proliferation of human breast cancer cell lines in vitro

Breast Cancer. 2017 Sep;24(5):658-666. doi: 10.1007/s12282-017-0752-5. Epub 2017 Jan 9.


Background: Prolyl oligopeptidase (POP, EC is a serine peptidase that hydrolyzes post-proline peptide bonds in peptides that are <30 amino acids in length. We previously reported that POP inhibition suppressed the growth of NB-1 human neuroblastomas cells and KATO III human gastric cancer cells. POP activity is commonly elevated in many cancers, which includes breast cancer. However, the effect of POP inhibition as a candidate breast cancer therapy is unknown.

Methods: The effects of POP inhibition and knockdown on the proliferation of cultured human estrogen receptor-positive (ER+) MCF7 and T47D, and ER-negative (ER-) MDA-MB-231 breast cancer cell lines and the MCF12A non-tumorigenic epithelial cell line were tested by analyzing their influence on cell proliferation (WST-1 assay), cell viability (trypan blue exclusion assay), and cell cycle arrest (cell cycle analysis, cell cycle regulator proteins expression).

Results: POP-specific inhibitors 3-({4-[2-(E)-styrylphenoxy]butanoyl}-L-4-hydroxyprolyl)-thiazolidine (SUAM-14746) and benzyloxycarbonyl-thiopropyl-thioprolinal and RNAi-mediated POP knockdown inhibited the proliferation of MCF7 cells without inducing cell death. SUAM-14746-induced growth inhibition was also observed in T47D and MDA-MB-231 cells, but not in MCF12A cells. This growth inhibition was associated with G1 phase arrest; reduced cyclin D1 and D3, cyclin-dependent kinase 4 (CDK4), E2F1, and retinoblastoma protein (pRb) expression; and increased cyclin-dependent kinase inhibitor 1B (p27kip1) expression. Moreover, the SUAM-14746-mediated cell cycle arrest of MCF7 cells was associated with increased pRb2/p130 protein expression and an increase in the number of cells in the quiescent G0 state, as defined by low RNA levels.

Conclusions: SUAM-14746 inhibited breast cancer cell growth in a cytostatic manner without inducing lethality, and POP-specific inhibitors may be an effective treatment against ER+ and ER- breast cancer.

Keywords: Cell cycle arrest; Human breast cancer cell lines; Prolyl oligopeptidase; Quiescent G0 state; SUAM-14746.

MeSH terms

  • Breast Neoplasms / drug therapy*
  • Breast Neoplasms / pathology
  • Cell Line, Tumor
  • Cell Proliferation / drug effects*
  • Cell Survival / drug effects
  • Cyclin D1 / metabolism
  • Cyclin D3 / metabolism
  • Cyclin-Dependent Kinase 4 / antagonists & inhibitors
  • Cyclin-Dependent Kinase 4 / metabolism
  • Cyclin-Dependent Kinase Inhibitor p27 / pharmacology
  • E2F1 Transcription Factor / metabolism
  • Female
  • G1 Phase Cell Cycle Checkpoints / drug effects*
  • Gene Knockdown Techniques
  • Humans
  • Proline / analogs & derivatives*
  • Proline / pharmacology
  • Proline / therapeutic use
  • Prolyl Oligopeptidases
  • Protease Inhibitors / therapeutic use
  • RNA Interference
  • RNA, Small Interfering / metabolism
  • Receptors, Estrogen / metabolism
  • Retinoblastoma Binding Proteins / metabolism
  • Serine Endopeptidases / genetics
  • Serine Endopeptidases / metabolism*
  • Thiazolidines / pharmacology*
  • Thiazolidines / therapeutic use
  • Ubiquitin-Protein Ligases / metabolism


  • 3-((4-(2-styrylphenoxy)butanoyl)-4-hydroxyprolyl)thiazolidine
  • CCND1 protein, human
  • CCND3 protein, human
  • Cyclin D3
  • E2F1 Transcription Factor
  • E2F1 protein, human
  • Protease Inhibitors
  • RB1 protein, human
  • RNA, Small Interfering
  • Receptors, Estrogen
  • Retinoblastoma Binding Proteins
  • Thiazolidines
  • Cyclin D1
  • Cyclin-Dependent Kinase Inhibitor p27
  • Proline
  • Ubiquitin-Protein Ligases
  • CDK4 protein, human
  • Cyclin-Dependent Kinase 4
  • Serine Endopeptidases
  • PREPL protein, human
  • Prolyl Oligopeptidases