Tumour-targeting photosensitisers for one- and two-photon activated photodynamic therapy

Despite the advantages of photodynamic therapy (PDT) over chemotherapy or radiotherapy such as low side effects, lack of treatment resistance and spatial selectivity inherent to light activation of the drug, several limitations especially related to the photosensitiser (PS) prevent PDT from becoming widespread in oncology. Herein, new folic acid- and biotin-conjugated PSs for tumour-targeting PDT are reported, with promising properties related to PDT such as intense absorption following one-photon excitation in the red or two-photon excitation in the near-infrared, and also high singlet oxygen quantum yield (close to 70% in DMSO). Cellular studies demonstrated that both targeted PSs induced phototoxicity, the folate-targeted PS being the most effective one with 80% of cell death following 30 min of irradiation and a phototoxicity four times higher than that of the non-targeted PS. This result is in accordance with the uptake of the folate-targeted PS in HeLa cells, mediated by the folate receptors. Moreover, this folate-targeted PS was also phototoxic following two-photon excitation at 920 nm, opening new perspectives for highly selective PDT treatment of small and deep tumours.