title: Methylene blue photodynamic therapy induces selective and massive cell death in human breast cancer cells.
abstract: Breast cancer is the main cause of mortality among women. The disease presents high recurrence mainly due to incomplete efficacy of primary treatment in killing all cancer cells. Photodynamic therapy (PDT), an approach that causes tissue destruction by visible light in the presence of a photosensitizer (Ps) and oxygen, appears as a promising alternative therapy that could be used adjunct to chemotherapy and surgery for curing cancer. However, the efficacy of PDT to treat breast tumours as well as the molecular mechanisms that lead to cell death remain unclear.
  
  
  
  In this study, we assessed the cell-killing potential of PDT using methylene blue (MB-PDT) in three breast epithelial cell lines that represent non-malignant conditions and different molecular subtypes of breast tumours. Cells were incubated in the absence or presence of MB and irradiated or not at 640 nm with 4.5 J/cm2. We used a combination of imaging and biochemistry approaches to assess the involvement of classical autophagic and apoptotic pathways in mediating the cell-deletion induced by MB-PDT. The role of these pathways was investigated using specific inhibitors, activators and gene silencing.
  
  
  
  We observed that MB-PDT differentially induces massive cell death of tumour cells. Non-malignant cells were significantly more resistant to the therapy compared to malignant cells. Morphological and biochemical analysis of dying cells pointed to alternative mechanisms rather than classical apoptosis. MB-PDT-induced autophagy modulated cell viability depending on the cell model used. However, impairment of one of these pathways did not prevent the fatal destination of MB-PDT treated cells. Additionally, when using a physiological 3D culture model that recapitulates relevant features of normal and tumorous breast tissue morphology, we found that MB-PDT differential action in killing tumour cells was even higher than what was detected in 2D cultures.
  
  
  
  Finally, our observations underscore the potential of MB-PDT as a highly efficient strategy which could use as a powerful adjunct therapy to surgery of breast tumours, and possibly other types of tumours, to safely increase the eradication rate of microscopic residual disease and thus minimizing the chance of both local and metastatic recurrence.
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Ancély F
authors.initials: AF
authors.lastname: Dos Santos
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Letícia F
authors.initials: LF
authors.lastname: Terra
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Rosangela A M
authors.initials: RA
authors.lastname: Wailemann
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Talita C
authors.initials: TC
authors.lastname: Oliveira
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Vinícius de Morais
authors.initials: VM
authors.lastname: Gomes
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Marcela Franco
authors.initials: MF
authors.lastname: Mineiro
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Flávia Carla
authors.initials: FC
authors.lastname: Meotti
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Bruni-Cardoso
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil. baptista@iq.usp.br.
authors.forename: Maurício S
authors.initials: MS
authors.lastname: Baptista
authors.affiliation: Biochemistry Department, Chemistry Institute, University of São Paulo, São Paulo, 05508-000, SP, Brazil. labriola@iq.usp.br.
authors.forename: Leticia
authors.identifier: 0000-0003-3899-6088
authors.initials: L
authors.lastname: Labriola
mesh_terms: D017209:Apoptosis; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D061986:MCF-7 Cells; D008751:Methylene Blue / Q000008:administration & dosage* / Q000494:pharmacology; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage* / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D017319:Photosensitizing Agents; D020169:Caspases; D008751:Methylene Blue
keywords: Breast cancer; Methylene blue; Photodynamic therapy; Selectivity