The role of p53 in the efficiency of photodynamic therapy with hypericin and subsequent long-term survival of colon cancer cells.

Photodynamic therapy with hypericin (HY-PDT) is known as an efficient modality for treatment of various cancerous and non-cancerous diseases. Although the role of p53 protein in cell death signaling is well established, relatively little is known of its impact on the efficiency of HY-PDT. Comparison of sensitivity and long-term survival of p53-null versus wt-p53-expressing HCT-116 cells is reported here. The lack of p53 function did not affect cell proliferation or attenuate the initial phases of programmed cell death. However, analyses of apoptosis in the final stages revealed suppression of its incidence and delayed activation of caspase-3 in p53-null cells. Significantly higher clonogenic ability, especially in hypoxia, was identified in the case of p53-null cells. Induction of Mcl-1 and Bax levels were more prominent in wt-pt53 cells. Interestingly, the level of Bcl-2 did not react to HY-PDT at all, in both cell lines. Bringing the evidence together, we prove that despite insignificant impact on overall toxicity, expression of p53 affects the clonogenic efficiency of HCT-116 cells. Since destruction of tumor tissue and its vascular system by PDT tends to lead to hypoxia, superior survival of p53-deficient tumor cells under given conditions might result in recurrence of cancer diseases.