Reduced proficiency in homologous recombination underlies the high sensitivity of embryonal carcinoma testicular germ cell tumors to Cisplatin and poly (adp-ribose) polymerase inhibition

PLoS One. 2012;7(12):e51563. doi: 10.1371/journal.pone.0051563. Epub 2012 Dec 12.

Abstract

Testicular Germ Cell Tumors (TGCT) and patient-derived cell lines are extremely sensitive to cisplatin and other interstrand cross-link (ICL) inducing agents. Nevertheless, a subset of TGCTs are either innately resistant or acquire resistance to cisplatin during treatment. Understanding the mechanisms underlying TGCT sensitivity/resistance to cisplatin as well as the identification of novel strategies to target cisplatin-resistant TGCTs have major clinical implications. Herein, we have examined the proficiency of five embryonal carcinoma (EC) cell lines to repair cisplatin-induced ICLs. Using γH2AX staining as a marker of double strand break formation, we found that EC cell lines were either incapable of or had a reduced ability to repair ICL-induced damage. The defect correlated with reduced Homologous Recombination (HR) repair, as demonstrated by the reduction of RAD51 foci formation and by direct evaluation of HR efficiency using a GFP-reporter substrate. HR-defective tumors cells are known to be sensitive to the treatment with poly(ADP-ribose) polymerase (PARP) inhibitor. In line with this observation, we found that EC cell lines were also sensitive to PARP inhibitor monotherapy. The magnitude of sensitivity correlated with HR-repair reduced proficiency and with the expression levels and activity of PARP1 protein. In addition, we found that PARP inhibition strongly enhanced the response of the most resistant EC cells to cisplatin, by reducing their ability to overcome the damage. These results point to a reduced proficiency of HR repair as a source of sensitivity of ECs to ICL-inducing agents and PARP inhibitor monotherapy, and suggest that pharmacological inhibition of PARP can be exploited to target the stem cell component of the TGCTs (namely ECs) and to enhance the sensitivity of cisplatin-resistant TGCTs to standard treatments.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Cell Line, Tumor
  • Cisplatin / pharmacology*
  • DNA Damage
  • DNA Repair / drug effects
  • DNA-Binding Proteins / metabolism
  • Drug Screening Assays, Antitumor
  • Embryonal Carcinoma Stem Cells / enzymology*
  • Embryonal Carcinoma Stem Cells / pathology
  • Endonucleases / metabolism
  • Enzyme Inhibitors / pharmacology*
  • Enzyme Inhibitors / therapeutic use
  • Homologous Recombination / drug effects*
  • Humans
  • Inhibitory Concentration 50
  • Male
  • Mice
  • Neoplasm Proteins / metabolism
  • Neoplasms, Germ Cell and Embryonal / drug therapy
  • Neoplasms, Germ Cell and Embryonal / enzymology*
  • Neoplasms, Germ Cell and Embryonal / genetics
  • Neoplasms, Germ Cell and Embryonal / pathology
  • Phthalazines / pharmacology
  • Phthalazines / therapeutic use
  • Piperazines / pharmacology
  • Piperazines / therapeutic use
  • Poly(ADP-ribose) Polymerase Inhibitors*
  • Poly(ADP-ribose) Polymerases / metabolism
  • Testicular Neoplasms / drug therapy
  • Testicular Neoplasms / enzymology*
  • Testicular Neoplasms / genetics
  • Testicular Neoplasms / pathology

Substances

  • DNA-Binding Proteins
  • Enzyme Inhibitors
  • Neoplasm Proteins
  • Phthalazines
  • Piperazines
  • Poly(ADP-ribose) Polymerase Inhibitors
  • xeroderma pigmentosum group F protein
  • Poly(ADP-ribose) Polymerases
  • ERCC1 protein, human
  • Endonucleases
  • Cisplatin
  • olaparib

Grant support

This work was supported by Associazione Italiana per la Ricerca sul Cancro (AIRC) grant n. 4765 to MB) and from Ministry of Education, Universities and Research of Italy (Cooperlink grant 2011, n. CII11RLETZ, to MB). FC was supported by AIRC Fellowship for abroad 2010, and Byrne Foundation. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.