title: Photodynamic therapy of DNA mismatch repair-deficient and -proficient tumour cells.
abstract: Loss of DNA mismatch repair is a common finding in hereditary nonpolyposis colon cancer as well as in many types of sporadic human tumours. DNA mismatch repair-deficient cells have been reported to be resistant to many chemotherapeutic agents and to radiotherapy, and to have the potential of rapidly acquiring additional mutations leading to tumour progression. Photodynamic therapy is a new treatment modality using light to activate a photosensitiser that preferentially localises in tumour cells. An oxygen dependent photochemical reaction ensues, resulting in selective tumour necrosis. The effect of loss of DNA mismatch repair activity on the sensitivity to photodynamic therapy was tested using pairs of cell lines proficient or deficient in mismatch repair due to loss of either MLH1 or MSH2 protein function. Cells were incubated with the photosensitiser 5,10,15,20-meta-tetra(hydroxyphenyl)chlorin and exposed to laser light at 652 nm with various optical doses ranging from 0-1 J cm(-2). Cell survival was assessed using the clonogenic assay. Loss of MLH1 or MSH2 function was not associated with resistance to photodynamic therapy. MCF-7 cells repeatedly treated with photodynamic therapy expressed parental levels of MLH1, MSH2, MSH6, and PMS2. DNA mismatch repair-deficient and -proficient cells showed similar subcellular distributions of meta-tetra(hydroxyphenyl)chlorin as analysed by laser scanning and fluorescence microscopy. Therefore, repeated exposure of tumour cells to photodynamic therapy does not seem to result in loss of DNA mismatch repair, and loss of mismatch repair, in turn, does not seem to contribute to resistance to photodynamic therapy. Our results suggest recommending photodynamic therapy as a strategy for circumventing resistance due to loss of DNA mismatch repair.
authors.affiliation: Department of Obstetrics and Gynaecology, Division of Gynaecology, University Hospital of Zurich, CH-8091 Zurich, Switzerland.
authors.forename: V A
authors.initials: VA
authors.lastname: Schwarz
authors.forename: R
authors.initials: R
authors.lastname: Hornung
authors.forename: A
authors.initials: A
authors.lastname: Fedier
authors.forename: M K
authors.initials: MK
authors.lastname: Fehr
authors.forename: H
authors.initials: H
authors.lastname: Walt
authors.forename: U
authors.initials: U
authors.lastname: Haller
authors.forename: D
authors.initials: D
authors.lastname: Fink
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000230:Adenocarcinoma / Q000473:pathology; D020137:Base Pair Mismatch; D001943:Breast Neoplasms / Q000473:pathology; D002352:Carrier Proteins; D015179:Colorectal Neoplasms / Q000473:pathology; D004260:DNA Repair; D004268:DNA-Binding Proteins; D019008:Drug Resistance, Neoplasm; D006801:Humans; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D009687:Nuclear Proteins; D010778:Photochemotherapy; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics*; D014407:Tumor Cells, Cultured
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C497172:MSH2 protein, human; D000070957:MutL Protein Homolog 1; D051718:MutS Homolog 2 Protein