Reduced Proficiency in Homologous Recombination Underlies the High Sensitivity of Embryonal Carcinoma Testicular Germ Cell Tumors to Cisplatin and Poly (ADP-Ribose) Polymerase Inhibition

Francesca Cavallo,Cristina Antinozzi,George J Bosl,Jane Houldsworth,Marco Barchi,Mary Ellen Moynahan,Darren R Feldman,Maria Jasin,Raju S K Chaganti,Grazia Graziani,Michael Lichten

doi:10.1371/journal.pone.0051563

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.

Highlights

Testicular germ cell tumors (TGCTs) develop from premalignant intratubular germ cell neoplasia and are histologically distinguished in seminomas and nonseminomas
embryonal carcinoma (EC) cell lines were sensitive to cisplatin compared with MCF10A and U2OS but displayed a wide range of response
These results indicate that, they appear more sensitive to cisplatin than somatic tumor cells, EC cell lines differ from each other, suggesting that resistant cells may have acquired specific molecular characteristics that render them less responsive to treatment

Summary

Introduction

Testicular germ cell tumors (TGCTs) develop from premalignant intratubular germ cell neoplasia and are histologically distinguished in seminomas and nonseminomas. TGCTs are highly curable with approximately 95% of newly diagnosed patients in 2012 expected to be rendered long-term disease-free This includes more than 70% of patients with advanced (metastatic) disease, distinguishing TGCTs from most other solid tumors. Multiple studies have identified the presence of vascular invasion and the concomitant presence of ECdominant tumors, as additive-risk factors for tumor recurrence in stage 1 non-seminoma TGCTs [5,6]. This is likely, because the invading element is commonly, the EC component [7]. The development of new therapeutic strategies to target ECs, and platinum-resistant TGCTs represents a clinical priority

Methods

Results

Conclusion