Impairment of lysosomal activity as a therapeutic modality targeting cancer stem cells of embryonal rhabdomyosarcoma cell line RD

PLoS One. 2014 Oct 20;9(10):e110340. doi: 10.1371/journal.pone.0110340. eCollection 2014.

Abstract

Rhabdomyosarcoma is the most frequent soft tissue sarcoma in children and adolescents, with a high rate of relapse that dramatically affects the clinical outcome. Multiagent chemotherapy, in combination with surgery and/or radiation therapy, is the treatment of choice. However, the relapse rate is disappointingly high and identification of new therapeutic tools is urgently needed. Under this respect, the selective block of key features of cancer stem cells (CSC) appears particularly promising. In this study, we isolated rhabdomyosarcoma CSC with stem-like features (high expression of NANOG and OCT3/4, self-renewal ability, multipotency). Rhabdomyosarcoma CSC showed higher invasive ability and a reduced cytotoxicity to doxorubicin in comparison to native cells, through a mechanism unrelated to the classical multidrug resistance process. This was dependent on a high level of lysosome acidity mediated by a high expression of vacuolar ATPase (V-ATPase). Since it was not associated with other paediatric cancers, like Ewing's sarcoma and neuroblastoma, V-ATPase higher expression in CSC was rhabdomyosarcoma specific. Inhibition of lysosomal acidification by the V-ATPase inhibitor omeprazole, or by specific siRNA silencing, significantly enhanced doxorubicin cytoxicity. Unexpectedly, lysosomal targeting also blocked cell growth and reduced the invasive potential of rhabdomyosarcoma CSC, even at very low doses of omeprazole (10 and 50 µM, respectively). Based on these observations, we propose lysosome acidity as a valuable target to enhance chemosensitivity of rhabdomyosarcoma CSC, and suggest the use of anti-V-ATPase agents in combination with standard regimens as a promising tool for the eradication of minimal residual disease or the prevention of metastatic disease.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cell Line, Tumor
  • Cell Movement / drug effects
  • Doxorubicin / pharmacology
  • Humans
  • Hydrogen-Ion Concentration
  • Lysosomes / chemistry
  • Lysosomes / drug effects*
  • Lysosomes / metabolism
  • Molecular Targeted Therapy / methods*
  • Neoplasm Invasiveness
  • Neoplastic Stem Cells / drug effects*
  • Neoplastic Stem Cells / pathology*
  • Proton Pump Inhibitors / pharmacology
  • Proton Pump Inhibitors / therapeutic use
  • Rhabdomyosarcoma, Embryonal / drug therapy
  • Rhabdomyosarcoma, Embryonal / pathology*
  • Vacuolar Proton-Translocating ATPases / metabolism

Substances

  • Proton Pump Inhibitors
  • Doxorubicin
  • Vacuolar Proton-Translocating ATPases

Grant support

This work was supported by a FIRB grant (RBAP10447J to N.B.) from the Italian Ministry of Education, University and Research; from the Italian Association for Cancer Research (AIRC 11426 to N.B.); and by the Italian Ministry of the Health, Financial Support for Scientific Research “5 per mille 2010”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.