Response of Photofrin®-sensitised mesothelioma xenografts to photodynamic therapy with 514 nm light

We have studied the response of human mesothelioma xenografts in nude mice to Photofrin-sensitised photodynamic therapy with 514 nm light. Delays in tumour regrowth following four different 514 nm irradiation regimens were compared with results obtained with the more commonly used 630 nm light. One of these 514 nm regimens, which consisted of 1 h of irradiation at an incident fluence rate of 20 mW cm-2 and a second hour at a fluence rate of 28 mW cm-2, produced tumour volume doubling times that were statistically indistinguishable from results that were observed when tumours were irradiated for 2 h with 630 nm light at an incident fluence rate of 50 mW cm-2. The three other 514 nm light protocols tested were found to be less effective than the 630 nm regimen. The 514 nm treatment protocols were devised on the basis of attempts to equate the photodynamic dose and the dose rate at these two wavelengths, with photodynamic dose defined as the number of photons absorbed by the sensitiser. Photosensitiser extinction coefficients, photon energies and tissue optical properties were considered in these attempts. Our results indicate that, under certain conditions, photodynamic therapy performed with 514 nm light can provide tumour control that is similar to that achieved with 630 nm, with potential for diminished normal tissue damage.