Efficient Synthesis of Chlorin e6 and its Potential Photodynamic Immunotherapy in Mouse Melanoma by the Abscopal Effect

Abstract

Abstract Background Photodynamic therapy (PDT) can eradicate not only cancer cells but also stimulate an anti-tumor immune response. Herein, we describe two efficient synthetic methodologies for the preparation of the second generation of photosensitizer Chlorin e6 (Ce6) from Spirulina platensis in higher yield and purity, and we address the phototoxic effect of Ce6 in vitro along with anti-tumor activity due to photodynamic therapy in vivo. Methods The use of different solvents, the duration of extraction/reaction, and the yield were analyzed and compared between the two methods during the synthesis of Ce6. The synthesized Ce6 was evaluated by TLC, HPLC, LC/MS, NMR, and studied for the anti-tumor activity of melanoma in vitro and in vivo. Melanoma B16F10 cells were seeded and phototoxicity was monitored by the MTT assay. C57BL/6 mice were transplanted with B16F10 cells for the tumor allograft model. The mice were subcutaneously inoculated on the left and right flank with 0.1 mL of B16F10 cells (1×106 cells/mL). The treated mice were intravenously injected with Ce6 of 2.5 mg/kg and then exposed to red light (660 nm) on the left flank tumors at 3 h after the injection. Results Our results revealed that the tumor was suppressed not only in the left flank but also in the right flank, where no PDT was given. The immune response was also studied by analyzing Interferon-gamma (IFN-γ), Tumor necrosis factor-alpha (TNF-α), and Interleukin-2 (IL-2) of the right flank tumors through qPCR. The upregulated expression of IFN-γ, TNF-α, and IL-2 revealed the local anti-tumor immunity due to Ce6-PDT. Conclusion The finding of this study suggest an efficient methodology of Ce6 preparation and the efficacy of Ce6-PDT as a promising anti-tumor immune response.