Anti-cancer effects of oncolytic viral therapy combined with photodynamic therapy in human pancreatic cancer cell lines

Background: Oncolytic viral therapy and photodynamic therapy are potential therapies for inoperable or advanced pancreatic cancer. Our aim was to investigate the anti-cancer killing effects of reovirus therapy combined with protoporphyrin IX (PpIX)-mediated photodynamic therapy on a variety of human pancreatic cancer cell lines. Methods: Pancreatic cancer cell lines (PsPC-1 and BXPC-3) and a non-cancer control cell line (HEK293) were infected with reovirus serotype 3 strain Dearing (T3D) at 0, 0·1, 1, and 10 plaque-forming units (PFU) per cell for 48 h. Cells were incubated with PpIX pro-drug 5-aminolevulinic acid (5-ALA) at 0, 1, 2, 3, and 4 mM for 4 h. Then, cells were photo-irradiated for 15 min with visible red light-emitting diodes with a light-fluence of 0·54 J/cm2 of 653 nm (PpIX optimal excitation wavelength). The killing effects of reovirus combined with PpIX-mediated photodynamic therapy were analysed in methylthiazoltetrazolium (MTT) and trypan blue assays. The effect of adding reovirus after photodynamic therapy was also assessed. The statistical significance of the difference between groups was assessed with the two-tailed Student's t test. p<0·05 was considered statistically significant. Findings: Reovirus monotherapy induced cell death in the two pancreatic lines (mean 57% [SE 10·2] at 10 PFU per cell). PpIX-mediated PDT monotherapy induced cell death in a dose-dependent manner (mean 10% [SE 2·2], 30 [6·4], 50 [8·2], and 70 [13·2] after 1, 2, 3, and 4 mM 5-ALA, respectively). Reovirus with PpIX-mediated photodynamic therapy resulted in a significantly increased cytotoxic effect compared with reovirus monotherapy and photodynamic therapy (p=0·042) with 100% cell death observed across pancreatic cell lines with 10 PFU per cell combined with 1 and 2 mM 5-ALA. There was no difference in cytotoxicity observed between added reovirus before or after photodynamic therapy. Interpretation: To our knowledge, this is the first in-vitro study to combine reovirus oncolytic viral therapy with PpIX-mediated photodynamic therapy to treat pancreatic cancer. These results show a significant additive effect in cell killing and they provide initial evidence for a novel combined therapeutic intervention.