Photodynamic therapy using methylene blue in lung adenocarcinoma xenograft and hamster cheek pouch induced squamous cell carcinoma

BackgroundPhotodynamic therapy (PDT) is used to treat early proximal bronchial cancer during a flexible bronchoscopy. The technique relies on the excitation of a photosensitizer by an appropriate wavelength, which is delivered into the bronchus in close contact with the tumor.ObjectiveTo assess methylene blue (MB) as a PDT agent for the treatment of respiratory tract cancer in animal models.MethodsMB-induced PDT was performed on 7 subcutaneous NCI-H460 lung adenocarcinoma xenografts in nude mice and 9 induced squamous cell cancer in the hamster cheek pouch model. In mice, PDT was carried out on right-sided tumors after intratumoral injection of methylene blue 1% (w/v) and illumination at 630 nm at 200 J/cm (Diomed PDT 630), with the left tumor used as control (illumination alone or MB alone). The tumoral volume was assessed before and 15 days after PDT.ResultsFourteen xenografts were treated in mice, including seven treated with MB-PDT, producing a 52% mean tumor volume regression (1568 mm³ vs. 544 mm³) compared to seven control cases in which tumor volume increased (p = 0.007; Mann-Whitney test). Nine cheek pouch induced carcinomas were treated in the hamster group, with a mean volume decrease of 85.8% (from 44.8% to 100%) (initial mean volume = 210 mm³ vs. post PDT mean volume = 97 mm³). Histology analysis showed 4/9 complete responses.ConclusionIntratumoral MB appears efficient as PDT agent for cancer treatment in animal models. Further studies are needed to assess the safety and efficacy of MB-associated PDT for the treatment of lung cancer in humans.