title: Photochemical internalization (PCI)-mediated enhancement of bleomycin cytotoxicity by liposomal mTHPC formulations in human head and neck cancer cells.
abstract: OBJECTIVE
  Photodynamic therapy (PDT) with photosensitizers that locate in endocytic vesicles of cancer cells can be exploited to promote the intracellular release of anticancer drugs entrapped in endolysosomal vesicles. This new approach is commonly referred to as Photochemical Internalization (PCI). Here we report on the PCI effects of three different formulations (Foscan, Foslip, and Fospeg) of the clinically approved photosensitizer, meta-tetrahydroxyphenyl chlorin (mTHPC) on the anticancer drug bleomycin (BLM) in the head and neck cancer cell lines.
  
  
  METHODS
  Uptake and localization of Foscan, Foslip, and Fospeg in head and neck cancer cells were evaluated by fluorescence spectrophotometry and fluorescence microscopy. Photodynamic efficacy of Foscan, Foslip, and Fospeg were compared with cell proliferation assay. Moreover, PCI effects of Foscan, Foslip, and Fospeg on BLM were compared using protocols in which PDT was applied after or before BLM treatment.
  
  
  RESULTS
  Cellular uptake of Foscan, Foslip, and Fospeg increased in a dose-dependent fashion with consistent higher uptakes of Foslip and Fospeg than Foscan. Fluorescence microscopy showed diffuse intracellular localization pattern for Foscan, Foslip, and Fospeg similar to that of a specific ER probe. However, the subcellular localization pattern of the Rhodamine-labelled same type of pegylated liposomes as Fospeg was similar to that of a specific endolysosomal probe, suggesting that Fospeg uptake appeared to initially proceed via endolysosomal trafficking. Foscan, Foslip, and Fospeg showed no apparent PCI-mediated cytotoxicity when PDT was performed after BLM treatment. However, significantly increased cytotoxicity of BLM (P < 0.05) was observed for both Foslip and Fospeg when PDT was performed before BLM treatment. The observed differences of PCI-mediated cytotoxicity between these two timing protocols appears to be related to the differential intracellular trafficking and localization of Foscan, Foslip, and Fospeg.
  
  
  CONCLUSIONS
  Liposomal formulations of mTHPC may be candidates for developing mTHPC-based PCI protocols to enhance the efficacy of anticancer drugs entrapped in endolysosomal vesicles.
authors.affiliation: Department of Oral & Maxillofacial Surgery, University of Groningen, University Medical Center Groningen, The Netherlands.
authors.forename: Wei
authors.initials: W
authors.lastname: Peng
authors.forename: Douwe F
authors.initials: DF
authors.lastname: Samplonius
authors.forename: Sebastiaan
authors.initials: S
authors.lastname: de Visscher
authors.forename: Jan L N
authors.initials: JL
authors.lastname: Roodenburg
authors.forename: Wijnand
authors.initials: W
authors.lastname: Helfrich
authors.forename: Max J H
authors.initials: MJ
authors.lastname: Witjes
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001761:Bleomycin / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004305:Dose-Response Relationship, Drug; D006258:Head and Neck Neoplasms / Q000188:drug therapy*; D006801:Humans; D008081:Liposomes; D008652:Mesoporphyrins / Q000494:pharmacology*; D008856:Microscopy, Fluorescence; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D008081:Liposomes; D008652:Mesoporphyrins; D017319:Photosensitizing Agents; D001761:Bleomycin; C072269:temoporfin
keywords: Foscan; Foslip; Fospeg; bleomycin; head and neck cancer; mTHPC; photochemical internalization; photodynamic therapy