Inhibition of autophagy sensitizes cancer cells to Photofrin-based photodynamic therapy

BMC Cancer. 2018 Feb 20;18(1):210. doi: 10.1186/s12885-018-4126-y.


Background: Accumulating evidence suggest that autophagy plays a pivotal role in various anticancer therapies, including photodynamic therapy (PDT), acting as a pro-death or pro-survival mechanism in a context-dependent manner. Therefore, we aimed to determine the role of autophagy in Photofrin-based PDT.

Methods: In vitro cytotoxic/cytostatic effects of PDT were evaluated with crystal violet cell viability assay. Autophagy induction was analyzed by immunoblotting and immunofluorescence using anti-LC3 antibody. Autophagy was inhibited by shRNA-mediated ATG5 knockdown or CRISPR/Cas9-mediated ATG5 knockout. Apoptosis was assessed by flow cytometry analysis of propidium iodide and anexin V-positive cells as well as by detection of cleaved PARP and caspase 3 proteins using immunoblotting. Protein carbonylation was evaluated by the 2,4-dinitrophenylhydrazine (DNPH) method.

Results: Photofrin-PDT leads to robust autophagy induction in two cancer cell lines, Hela and MCF-7. shRNA-mediated knockdown of ATG5 only partially blocks autophagic response and only marginally affects the sensitivity of Hela and MCF-7 cells to PDT. ATG5 knockout in HeLa cell line utilizing CRISPR/Cas9 genome editing results in increased PDT-mediated cytotoxicity, which is accompanied by an enhanced apoptotic response and increased accumulation of carbonylated proteins.

Conclusions: Altogether, these observations imply that autophagy contributes to Photofrin-PDT resistance by enabling clearance of carbonylated and other damaged proteins. Therefore, autophagy inhibition may serve as a strategy to improve PDT efficacy.

Keywords: ATG5; Autophagy; CRISR/Cas-9; Photodynamic therapy; Photofrin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Autophagy / drug effects*
  • Autophagy / genetics
  • Autophagy / radiation effects*
  • Autophagy-Related Protein 5 / genetics
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Cell Survival / radiation effects
  • Dihematoporphyrin Ether / pharmacology*
  • Gene Expression
  • Gene Knockdown Techniques
  • Gene Targeting
  • Humans
  • Light
  • Photochemotherapy
  • Photosensitizing Agents / pharmacology*
  • RNA Interference
  • RNA, Small Interfering / genetics


  • ATG5 protein, human
  • Antineoplastic Agents
  • Autophagy-Related Protein 5
  • Photosensitizing Agents
  • RNA, Small Interfering
  • Dihematoporphyrin Ether