A switch between cytoprotective and cytotoxic autophagy in the radiosensitization of breast tumor cells by chloroquine and vitamin D

Horm Cancer. 2011 Oct;2(5):272-85. doi: 10.1007/s12672-011-0081-7.

Abstract

Calcitriol or 1,25-dihydroxyvitamin D3, the hormonally active form of vitamin D, as well as vitamin D analogs, has been shown to increase sensitivity to ionizing radiation in breast tumor cells. The current studies indicate that the combination of 1,25-dihydroxyvitamin D3 with radiation appears to kill p53 wild-type, estrogen receptor-positive ZR-75-1 breast tumor cells through autophagy. Minimal apoptosis was observed based on cell morphology by DAPI and TUNEL staining, annexin/PI analysis, caspase-3, and PARP cleavage as well as cell cycle analysis. Induction of autophagy was indicated by increased acridine orange staining, RFP-LC3 redistribution, and detection of autophagic vesicles by electron microscopy, while autophagic flux was monitored based on p62 degradation. The autophagy inhibitors, chloroquine and bafilomycin A1, as well as genetic suppression of the autophagic signaling proteins Atg5 or Atg 7 attenuated the impact of the combination treatment of 1,25 D3 with radiation. In contrast to autophagy mediating the effects of the combination treatment, the autophagy induced by radiation alone was apparently cytoprotective in that either pharmacological or genetic inhibition increased sensitivity to radiation. These studies support the potential utility of vitamin D for improving the impact of radiation for breast cancer therapy, support the feasibility of combining chloroquine with radiation for the treatment of breast cancer, and demonstrate the existence of an "autophagic switch" from cytoprotective autophagy with radiation alone to cytotoxic autophagy with the 1,25 D3-radiation combination.

Publication types

  • Evaluation Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autophagy / drug effects*
  • Autophagy / genetics
  • Autophagy-Related Protein 5
  • Autophagy-Related Protein 7
  • Breast Neoplasms / drug therapy
  • Breast Neoplasms / genetics
  • Breast Neoplasms / pathology*
  • Breast Neoplasms / radiotherapy
  • Carcinoma / drug therapy
  • Carcinoma / genetics
  • Carcinoma / pathology*
  • Carcinoma / radiotherapy
  • Cell Survival / drug effects
  • Cell Survival / genetics
  • Cell Survival / radiation effects
  • Cellular Senescence / drug effects
  • Cellular Senescence / genetics
  • Cellular Senescence / radiation effects
  • Chloroquine / pharmacology*
  • Cytoprotection / drug effects*
  • Cytoprotection / genetics
  • Cytotoxins / pharmacology
  • Feasibility Studies
  • Female
  • Genes, Switch / drug effects
  • Genes, Switch / physiology
  • Humans
  • Microtubule-Associated Proteins / antagonists & inhibitors
  • Microtubule-Associated Proteins / genetics
  • RNA, Small Interfering / pharmacology
  • Radiation Tolerance / drug effects
  • Radiation Tolerance / genetics
  • Radiation-Sensitizing Agents / pharmacology
  • Tumor Cells, Cultured
  • Ubiquitin-Activating Enzymes / antagonists & inhibitors
  • Ubiquitin-Activating Enzymes / genetics
  • Vitamin D / pharmacology*

Substances

  • ATG5 protein, human
  • Autophagy-Related Protein 5
  • Cytotoxins
  • Microtubule-Associated Proteins
  • RNA, Small Interfering
  • Radiation-Sensitizing Agents
  • Vitamin D
  • Chloroquine
  • Atg7 protein, human
  • Autophagy-Related Protein 7
  • Ubiquitin-Activating Enzymes