Background: The propagation of injury ("bystander effect") from directly damaged cells to other cells has been observed in cancer therapies. Some experiments suggested that this phenomenon was also detected in photodynamic therapy (PDT). The present study was undertaken to evaluate the bystander response in cells co-cultured with PDT- or heat-injured cells.
Material/methods: Human ovary cancer cells (OVP10) were co-cultivated with PDT- and heat-damaged cells under various conditions. Fluorescence and light microscopy, shear test, clonogenic assays, and RT-PCR were used to estimate the vital functions of intact cells.
Results: In the shear test, the addition of damaged cells to a monolayer of uninjured OVP10 cells resulted in a significant cell detachment of up to 87% for PDT-treated cells and 74% for heat-treated cells. Cells that were co-cultured with their PDT-injured counterparts in a proportion of 50% showed progressive decreases in density by 7% and 38% (significant) after 24 and 48 h, respectively. In co-culture with heat-damaged cells, the density decreased significantly by 21% and 28% after 24 and 48 h. "Bystander" growth arrest is attributed to a significant decrease in mitotic activity at 24 h and a lower expression of the focal adhesion kinase gene (FAK). Neither PDT- nor heat-damaged cells induced changes in mRNA expressions for GADD45, P21(WAF/cip1), C-JUN, C-FOS, and BAX in the bystander cells.
Conclusions: Bystander response may modulate the growth and adhesion of cells co-cultured with their PDT- and heat-injured counterparts in vitro.