Near-infrared photosensitive dyes based on red fluorescence protein chromophore analogue for photodynamic therapy and two-photon fluorescence imaging

Abstract

In this paper, two photosensitizers RFP-OH and RFP-Ac based on red fluorescent protein chromophore analogue with NIR emission was synthesized for photodynamic therapy (PDT) in A-549 cells and zebrafish. After the introduction of p-hydroxystyrene and acryloyl ester, the emission wavelengths of RFP-OH and RFP-Ac were red-shifted to the NIR band, which were 721 nm and 758 nm, respectively. And the stokes shift of RFP-OH and RFP-Ac was as large as 228 nm and 260 nm, respectively. The singlet oxygen yield of RFP-OH and RFP-Ac was 35.6% and 28.8%, respectively. Tumor cells are rich in biological thiols, such as Cys. After RFP-Ac encountered with Cys, the singlet oxygen yield of the products increased to 34.1%. In addition, DFT calculations showed that RFP-OH can transition to triplet state through intersystem crossing after being excited to singlet state, thereby enhancing the singlet oxygen yield. Both RFP-OH and RFP-Ac showed low dark toxicity (≥91.02%), high photo toxicity, and good PDT effects in A-549 cells and zebrafish. More importantly, RFP-OH exhibited superior two-photon fluorescence imaging properties in zebrafish. In a word, considering to the positive results of the experiments, RFP-OH and RFP-Ac had a great potential for PDT in anti-cancer therapy.