Photodynamic therapy of 4T1 tumors in NOD-SCID mice.

Background: Promising results for mammary carcinoma treatment with photodynamic therapy (PDT) presuppose a careful selection of irradiation light wavelength. Methods: 4T1 tumors implanted in NOD-SCID mice were treated with Metvix-PDT under 625 nm, 660 nm and their combination light, for a fixed radiant exposure. The therapeutic outcome was assessed through Monte Carlo based computational simulations along with a preliminary in vivo study, where fluorescence, size and temperature measurements were conducted. Results: The light source combination protocol presents great potential, since it results in high cytotoxic products levels and reduced treatment times; while the in vivo findings, regarding the harvested tumor mass, also support this hypothesis. The irradiation with 625 nm beam alone presented better results for most of the in vivo measured parameters. The mouse treated with only the 660 nm light source had the highest un-photobleached photosensitizer (PS) signal, the lowest body temperature, the heaviest harvested tumor and the lowest estimated concentration of PDT cytotoxic products. Conclusions: The use of 625 nm irradiation light matches the PS excitation band but is preferable only for treatment of superficial tumors. For deeper laying masses, the simultaneous use of longer wavelengths enhances the therapeutic outcome due to their increased penetration depth.