Photodynamic therapy by lysosomal-targeted drug delivery using talaporfin sodium incorporated into inactivated virus particles.

Background: Photodynamic therapy (PDT), a minimally invasive cancer treatment involving the activation of photosensitizer by a specific wavelength of light, is considered to be a promising treatment option for drug-resistant prostate cancer. Hemagglutinating virus of Japan envelope (HVJ-E) has the potential to serve as a highly effective cancer therapy through selective drug delivery and enhancement of the anti-tumor immune response.

Objectives: To improve therapeutic efficacy and selective accumulation of photosensitizer into tumor cells, we developed a novel photosensitizer, Laserphyrin^®-HVJ-E (L-HVJ-E), by incorporating talaporfin sodium (Laserphyrin^®, Meiji Seika Pharma) into HVJ-E.

Materials and methods: The therapeutic effect of PDT with Laserphyrin^® or L-HVJ-E was evaluated in the human prostate cancer cell line PC-3 in vitro. The subcellular localizations of Laserphyrin^® and L-HVJ-E were observed by confocal microscopy. Apoptosis or necrosis following PDT was detected by annexin V-fluorescein/propidium iodide double staining.

Results: The cytotoxic effect of Laserphyrin^®- and L-HVJ-E-mediated PDT were determined by evaluating cell survival rate and production of reactive oxygen species. The cytotoxicity of L-HVJ-E-mediated PDT was dependent on drug concentration and light dose. Laserphyrin^® and L-HVJ-E gradually entered cells as incubation time increased, and both agents tended to be distributed in lysosomes rather than mitochondria. Time and dose dependent increase in ROS production was observed, and induction of both apoptotic and necrotic cell death was confirmed.

Conclusions: Laserphyrin^® and L-HVJ-E were distributed mainly in lysosomes and induced cell death by both apoptosis and necrosis. Furthermore, L-HVJ-E-mediated PDT effectively killed cultured PC-3 cells and exerted higher photocytotoxicity than Laserphyrin^®-mediated PDT.