Role of NF-kB/Snail/RKIP in the response of tumour cells to photodynamic therapy

Background and Objective: Photodynamic therapy (PDT) is a therapeutic modality whose efficacy depends on several factors including type of photosensitizer, light fluence and cellular response. Cell recurrence is one of the problems still unsolved in PDT. In this work we found that in B78-H1 murine amelanotic melanoma cells there is a correlation between cell recurrence and the NF-kappa B/Snail/RKIP loop. Materials and Methods: Proliferation and migration of surviving cells were analyzed by MTT and wound-scratch assays. The levels of ROS/NO in B78-H1 melanoma cells treated with pheophorbide a (Pba) and light (Pba/PDT) were measured by FACS, while expression of NF-kappa B, Snail and RKIP were determined by Western blots. The mechanism of cell death was investigated by caspase and microscopy assays. Results: Our data show that after a low-dose Pba/PDT treatment, B78-H1 cells are able to recover. This correlates with a low level of NO production, which blocks apoptosis via NF-kappa B pathway. Western blot analyses showed that a low-dose Pba/PDT increases the expression of NF-kappa B and anti-apoptotic Snail, but reduces the expression of pro-apoptotic RKIP. The role played by NF-kappa B in the modulation of Snail and RKIP was investigated using DHMEQ: a NF-kappa B inhibitor which behaves as NO donor. DHMEQ caused a decrease of Snail and an increase of RKIP expression. When B78-H1 cells were treated with a low dose Pba/PDT and DHMEQ, the NO level strongly increased, with the result that Snail was down-regulated and RKIP was upregulated, as observed with a high-dose Pba/PDT. Conclusion: One major problem in PDT is the cellular rescue occurring in tissue regions receiving a low-dose PDT. To minimize this problem and sensitize cancer cells to PDT we propose a combined treatment in which the photosensitizer is delivered with a donor of NO acting on the NF-kappa B/Snail/RKIP loop.