Photodynamic therapy with 5-aminolaevulinic acid and DNA damage: unravelling roles of p53 and ABCG2

Abstract

Objectives: In spite of high sensitivity of A549 cells (p53+/+) to lethal effects of photodynamic therapy with 5-aminolaevulinic acid (5-ALA/PDT), DNA damage was observed only in H1299 cells (p53−/−), suggesting that p53 may exert a protective effect. Studies on human colon adenocarcinoma cell lines HCT-116, and their cognate knockouts for p53, were not entirely consistent with the assumption above. Exploring alternative explanations for such conflicting behaviour, we observed that expression of the ATP-binding cassette G2 (ABCG2), a regulator of cell component efflux, had important effects on PDT-generated DNA injury in PC3 cells (prostate) which are p53−/− and positive for ABCG2. Addition of an ABCG2 inhibitor in ABCG2 positive A549 (p53+/+) and PC3 (p53−/−) cells eliminated resistance to DNA damage. Materials and methods: All cell lines investigated were incubated with 5-ALA and irradiated. Effects of PDT were evaluated assessing residual cell viability, cell-cycle profiles, PpIX localization, comet assay and Western blotting. Identical measurements were made in the presence of ABCG2 inhibitor, in cells expressing the transporter. Results: Our data show that cell aptitude to defend its DNA from PDT-induced injury was mainly ruled by ABCG2 expression. These findings, while providing helpful information in predicting effectiveness of 5-ALA/PDT, may indicate a way to shift PDT from a palliative to a more effective approach in anti-cancer therapy.