In-vivo investigations on dye-enhanced photothermal tumor therapy with a naphthalocyanine derivative.

Chromophore-enhanced photothermal therapy involves the application of an exogenous chromophore in combination with irradiation, using an appropriate wavelength, exposure duration and sufficient irradiances. The chromophore palladium(II) octabutoxynaphthalocyanine (PdNc(OBu)8) accumulates at satisfactory concentrations and with good selectivity between both tumor and muscle and tumor and skin in tumor-bearing mice. In an attempt to thermally damage tumor tissue with concurrent sparing of adjacent normal tissue, the potential of PdNc(OBu)8 for photothermal therapy was investigated. Using a Balb/c mouse model with subcutaneously implanted EMT6 adenocarcinoma, 90-100 hours after intraperitoneal application of PdNc(OBu)8, the tumor and surrounding tissue were irradiated with a 826nm continuous-wave diode laser. The thermal effects on tumor and normal tissue were evaluated histologically. Our results indicate that after PdNc(OBu)8 administration and tumor irradiation using 5W/cm-for 100 seconds, pronounced selective heating of the tumor was achieved in mice, while in control animals merely an unspecific and marginal overall increase in temperature over the entire irradiation area was observed. Histological evaluation of treated areas indicated that the PdNc(OBu)8-targeted tumor tissue showed severe thermal damage while peripheral tissue like skin and muscle remained largely unaffected. This study shows the potential of creating localized thermal effects by using PdNc(OBu)8 and continuous-wave light for chromophore-enhanced photothermal therapy.