title: Early apoptotic responses in transgenic mouse mammary carcinoma for photodynamic therapy.
abstract: BACKGROUND
  Male transgenic mice expressing the human RAS gene on an FVB strain background develop adenocarcinoma of the breast between 7 and 8 weeks of age. We have utilized this mammary tumour model to investigate apoptotic responses following photodynamic therapy (PDT) with a chlorin-based, water-soluble photosensitizer.
  
  
  METHODS
  Detection of apoptosis was accomplished by use of the antibody M30 against a neo-epitope of caspase-cleaved cytokeratin 18 that becomes available at an early stage of the apoptotic cascade. Mice bearing multiple tumours were injected with the photosensitizer intraperitoneally, and following a drug-light interval of 96h, 40J/cm(2) of 652nm laser light was applied to one tumour per animal, while the other tumours were protected from light to serve as host controls. The M30 antibody was used for standard immunohistochemistry of tumour sections and flow cytometric detection of epitope expression coupled to cell cycle analysis in tumour cell populations retrieved from paraffin blocks.
  
  
  RESULTS
  M30 staining was significantly increased within 2h following light treatment and persisted until 96h after treatment. Flow cytometric analysis for the S-phase fraction (SPF) of tumour cells post-PDT showed a substantial decrease in SPF at 2h post PDT, and recovery of SPF within 96h.
  
  
  CONCLUSIONS
  Cytokeratin 18 cleavage seems to be both an early and ongoing event during the cellular response to PDT. Calculating the M30/SPF ratio at both 2h and 96h suggested distinct cellular dynamics at early and late time points, and we propose the M30/SPF ratio as a tumour dynamic index (TDI) to monitor events post PDT.
authors.affiliation: Research Division of Gynaecology, Department of Obstetrics and Gynaecology, University Hospital, Zurich, CH-8091, Switzerland.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Walt
authors.affiliation: Department of Pathology, Atrium Heerlen Medical Centre, Heerlen, CX, 4446 6401, The Netherlands.
authors.forename: Marius
authors.initials: M
authors.lastname: Nap
authors.affiliation: The Jackson Laboratory, Bar Harbor, ME 04609, USA.
authors.forename: Ann M
authors.initials: AM
authors.lastname: Dorward
authors.affiliation: Department of Pathology, Atrium Heerlen Medical Centre, Heerlen, CX, 4446 6401, The Netherlands.
authors.forename: Mathie P G
authors.initials: MP
authors.lastname: Leers
authors.affiliation: The Jackson Laboratory, Bar Harbor, ME 04609, USA.
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Tennent
authors.affiliation: Department of Pathology, University Hospital, Zurich, CH-8091, Switzerland.
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Varga
authors.affiliation: Department of Pathology, University Hospital, Zurich, CH-8091, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Stallmach
authors.affiliation: Cancer Council, Bromma, SE 16762, Sweden.
authors.forename: Viveka
authors.initials: V
authors.lastname: Björklund
authors.affiliation: The Jackson Laboratory, Bar Harbor, ME 04609, USA.
authors.forename: Wesley G
authors.initials: WG
authors.lastname: Beamer