Photodynamic therapy of human lung cancer xenografts in mice

BackgroundThere is a need to develop novel therapies for non-small cell lung cancer (NSCLC). Photodynamic therapy has been used successfully for endobronchial palliation of NSCLC, and its role in early stages of disease is being explored. We hypothesized that a novel photosensitizer, PS1, would be more effective than the standard agent, porfimer sodium (Photofrin or PFII), in treating human lung cancer xenografts in mice.Materials and methodsPatient-derived NSCLC xenografts were established subcutaneously in severe combined immune deficiency mice. Two groups of five mice were injected with PS1 (3-[1′-m-iodobenzyloxy]ethyl-3-devinylpyropheophorbide-a), a chlorophyll-a derivative, or PFII (a purified version of hematoporphyrin derivative) and then treated with nonthermal laser light. Four mice were treated with laser light without photosensitizer and six mice received no treatment at all. All mice were then observed for tumor growth. The tumor growth end point, time-to-1000 mm3, was evaluated using standard Kaplan–Meier methods and the log-rank test. Tumor hematoxylin and eosin and caspase 3 staining was done to evaluate necrosis and apoptosis.ResultsThe median time-to-1000 mm3 was 12, 12, 26, and 52 d for the control, light only, PFII, and PS1 groups. There was a significant association between the tumor growth end point and treatment (P < 0.05). Hematoxylin and eosin staining revealed <1%, 0%, 67%, and 80% necrosis, and caspase 3 positivity was 2%, <1%, 17%, and 39%, respectively, in the same four groups.ConclusionsThe mice treated with PS1 exhibited a longer time for tumor regrowth and showed more tumor necrosis and apoptosis compared with the other treatment groups. Thus, the novel photosensitizer, PS1, was demonstrated to be more effective than porfimer sodium in this preclinical pilot study.