Photochemotherapy of experimental colonic tumours with intra-tumorally applied methylene blue

Abstract

Introduction: Phototoxicity of intra-tumoral injected methylene blue (MB⁺) was studied in 48 experimental colonic tumours in comparison with photosan-3, Zn-phthalocyanine and tetrasulphanated ClAl-phthalocyanine. Methods: In mice, xenotransplanted subcutaneous tumours about 1 cm in diameter were treated photodynamically twice, with different sensitisers. The irradiation was performed at the sensitiser-specific wavelength, and a densitiy of 100 mW/cm² and a dose of 100 J/cm². Results: Light alone without sensitiser did not induce any effect in mice tumours. Surprisingly, Al-phthalocyanine could only be used for intratumoral injections because of toxic effects after intravenous applications in nude mice. Using MB⁺ (1%), 75% of the tumours were destroyed by a single photodynamic treatment (PDT). In addition, toxicity of MB⁺ was most intense when compared with Zn-phthalocyanine and photosan-3. However, after the second PDT, there was no statistically significant difference among these sensitisers. Dark toxicity of MB⁺ (1%) could be well demonstrated by sufficient sensitiser incorporation without irradiation, which led to a stationary tumour volume up to 3 weeks after injection. Conclusion: Intra-tumoral MB⁺ PDT is a potential treatment for inducing necrosis in vivo. With regard to tumour tissue, the selectivity of MB⁺ is high and depends on a precise local injection of the dye.