All cell lines used in the experiments form well-defined individual colonies when seeded sparsely on standard tissue culture plates. Reagents The porphyrin-based photosensitiser 5,10,15,20-meta-tetra (hydroxyphenyl)chlorin (m-THPC, Foscan?) with a molecular selleck products weight of 680 Daltons was provided by SCOTIA Pharmaceuticals Ltd (Stirling, UK). This second-generation photosensitiser has recently been approved by the European Medicine Evaluation Agency for treatment of head and neck cancer. The absorption maximum of m-THPC is at 652nm. m-THPC was dissolved in a recommended solution of ethanol:polyethylene-glycol:water (20:30:50) to a concentration of 5mg per 10ml, and stored at 4��C in the dark. 6-Thioguanine was purchased from Sigma (Buchs, Switzerland) and dissolved immediately before use in 0.

9% saline. PDT experiments PDT experiments were carried out under dimmed room light as follows. Cells growing in log phase were harvested with EDTA-trypsin and washed with phosphate-buffered saline (PBS). Either 2000 MLH1-proficient or -deficient cells (HCT116), or 10000 MSH2-proficient or -deficient cells (HEC59) from a single-cell suspension were seeded into 60mm tissue culture dishes. After 24h, 0.1��gml?1m-THPC diluted in tissue culture medium was added to the dishes and cells were incubated with m-THPC for 24h. Cells not exposed to either m-THPC or laser light were used as controls. Then, cells were exposed to laser light at a wavelength of 652nm generated by a diode laser (Applied Optronics Corp., South Plainfield, NJ, USA) and an energy of 25mW as verified by a power meter (Fieldmaster Coherent Inc.

, Santa Clara, USA). The light was conducted through a laser fibre terminated by a front lens light diffuser to the site of irradiation. The optical dose (J cm?2) is defined as the fluence rate (W cm?2) multiplied by the exposure time in seconds. Irradiation times for the colorectal and the endometrial cancer cells were 0, 7, 14, 28, 42 or 56s, resulting in optical doses of 0, 0.125, 0.25, 0.5, 0.75 or 1Jcm?2 at a fluence rate of 36mWcm?2. The cells were then washed, fresh medium was added and the cells were allowed to proliferate for 10 days. Repetitive PDT exposure of MCF-7 cells MCF-7 breast cancer cells (106) growing in log phase were seeded into 60mm tissue culture dishes. After 24h, m-THPC was added to a final concentration of 0.

1��gml?1 and incubated for 24h in the dark, followed by illumination for 5min with a fluence rate of 25mWcm?2 resulting in an optical dose of 2.12Jcm?2. This PDT dose resulted in a survival fraction of approximately 10?4. Surviving cells were allowed to proliferate to Anacetrapib a density of 106cells, and the experiment was repeated for a total of five times. The repetition was restricted to five times due to the fact that from the clinician’s point of view it is very unlikely that recurrent tumours will be treated more than five times with the same treatment modality.