A Small Molecule Inhibitor Selectively Induces Apoptosis in Cells Transformed by High Risk Human Papilloma Viruses

PLoS One. 2016 Jun 9;11(6):e0155909. doi: 10.1371/journal.pone.0155909. eCollection 2016.

Abstract

A phenotypic high-throughput cell culture screen was performed to identify compounds that prevented proliferation of the human Papilloma virus type 16 (HPV-16) transformed cell line Ca Ski. A series of quinoxaline compounds exemplified by Compound 1 was identified. Testing against a panel of cell lines demonstrated that Compound 1 selectively inhibited replication of all HPV-16, HPV-18, and HPV-31 transformed cell lines tested with 50% Inhibitory Concentration (IC50) values of 2 to 8 μM relative to IC50 values of 28 to 73 μM in HPV-negative cell lines. Treatment with Compound 1 resulted in a cascade of multiple apoptotic events, including selective activation of effector caspases 3 and 7, fragmentation of cellular DNA, and PARP (poly(ADP-ribose) polymerase) cleavage in HPV-positive cells relative to HPV-negative cells. Unregulated proliferation of HPV transformed cells is dependent on the viral oncogenes, E6 and E7. Treatment with Compound 1 resulted in a decrease in HPV E7 protein in Ca Ski cells. However, the timing of this reduction relative to other effects of compound treatment suggests that this was a consequence, rather than a cause, of the apoptotic cascade. Likewise, compound treatment resulted in no obvious effects on the E6- and E7- mediated down regulation of p53 and Rb, or their downstream effectors, p21 or PCNA. Further investigation of apoptotic signals induced by Compound 1 revealed cleavage of Caspase-8 in HPV-positive cells as early as 2 hours post-treatment, suggesting the compound initiates apoptosis through the extrinsic, death receptor-mediated, pathway of cell death. These studies provide proof of concept that cells transformed by oncogenic Papillomaviruses can be selectively induced to undergo apoptosis by compound treatment.

MeSH terms

  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins / metabolism
  • Cell Transformation, Viral / drug effects*
  • Female
  • Humans
  • Papillomaviridae / drug effects*
  • Papillomavirus E7 Proteins / metabolism
  • Papillomavirus Infections / drug therapy
  • Papillomavirus Infections / pathology*
  • Papillomavirus Infections / virology
  • Retinoblastoma Protein / metabolism
  • Small Molecule Libraries / pharmacology*
  • Tumor Cells, Cultured
  • Tumor Suppressor Protein p53 / metabolism
  • Uterine Cervical Neoplasms / drug therapy
  • Uterine Cervical Neoplasms / pathology*
  • Uterine Cervical Neoplasms / virology

Substances

  • Apoptosis Regulatory Proteins
  • Papillomavirus E7 Proteins
  • Retinoblastoma Protein
  • Small Molecule Libraries
  • Tumor Suppressor Protein p53

Grants and funding

Bristol-Myers Squibb Company provided support in the form of salaries for all the authors at the time this work was carried out, and the authors designed, collected and analyzed data, and prepared the manuscript as employees of Bristol-Myers Squibb. Bristol-Myers Squibb Company approved the decision to disclose this work. The specific roles of the authors are articulated in the 'author contributions' section.