Enhancing Photodynamic Therapy through Resonance Energy Transfer Constructed Near-Infrared Photosensitized Nanoparticles

Abstract

Photodynamic therapy (PDT) is an important cancer treatment modality due to its minimally invasive nature. However, the efficiency of existing PDT drug molecules in the deep-tissue-penetrable near-infrared (NIR) region has been the major hurdle that has hindered further development and clinical usage of PDT. Thus, herein a strategy is presented to utilize a resonance energy transfer (RET) mechanism to construct a novel dyad photosensitizer which is able to dramatically boost NIR photon utility and enhance singlet oxygen generation. In this work, the energy donor moiety (distyryl-BODIPY) is connected to a photosensitizer (i.e., diiodo-distyryl-BODIPY) to form a dyad molecule (RET-BDP). The resulting RET-BDP shows significantly enhanced absorption and singlet oxygen efficiency relative to that of the acceptor moiety of the photosensitizer alone in the NIR range. After being encapsulated with biodegradable copolymer pluronic F-127-folic acid (F-127-FA), RET-BDP molecules can form uniform and small organic nanoparticles that are water soluble and tumor targetable. Used in conjunction with an exceptionally low-power NIR LED light irradiation (10 mW cm^-2 ), these nanoparticles show superior tumor-targeted therapeutic PDT effects against cancer cells both in vitro and in vivo relative to unmodified photosensitizers. This study offers a new method to expand the options for designing NIR-absorbing photosensitizers for future clinical cancer treatments.

Keywords: bodipy; nanoparticles; near-infrared radiation; photodynamic therapy; resonance energy transfer.

Figure 1

a) UV–V is absorption spectra of compounds B-1, B-2, and RET-BDP in toluene; b) emission spectra of compounds B-1, B-2, and RET-BDP, λ_ex = 610 nm, c = 10 μM in toluene at 20 °C.

Figure 2

a) Dynamic light scattering of RET-BDP-TNM in deionized water; b) UV–V is absorption spectrum of RET-BDP-TNM nanomicelles; c) plot of change in optical density of DPBF at 415 nm against irradiation time, with RET-BDP-TNM as the photosensitizer, in PBS with 10% THF, excitation range is 600–800 nm, and power intensity is 10 mW cm⁻².

Figure 3

Different cancer cell lines' (HeLa, KP7B, and 4T1) viability after treatment with different concentrations of RET-BDP-TNM and B2-TNM with or without irradiation, as measured by MTT assay: a) HeLa cells; b) KP7B cells; and c) 4T1 cells. Red columns: without PSs and NIR; green columns: only NIR; blue columns: B2-TNM and NIR; cyan columns: RET-BDP-TNM and NIR. NIR 600–800 nm, 10 mW cm⁻²). d) Confocal fluorescence microscopy observed with RET-BDP-TNM-mediated (10 μg mL⁻¹) PDT with PI staining for dead cells, λ_ex = 514 nm, capture wavelength 580–620 nm; e) DCFH-DA verified singlet-oxygen generation in RET-BDP-TNM-mediated PDT (10 μg mL⁻¹), λ_ex = 476 nm, capture wavelength 485–520 nm, scale bar represents 30 μm.

Figure 4

Specific targeted NIR-fluorescence tumor imaging in vivo. a) Time-dependent in vivo NIR fluorescence images of 4T1 tumor-bearing mice after intravenous injection of 50 μg mL⁻¹, 150 μL: RET-BDP-TNM as the positive group and RET-BDP-NNM as the negative group. b) Normalized fluorescence intensity of RET-BDP-TNM and RET-BDP-NNM in 4T1 tumors at 8, 24, 48, and 96 h. Data are mean ±s.e.m (n = 3 mice).

Figure 5

a) Tumor-growth inhibition by RET-BDP-TNM-mediated PDT in 4T1 tumors; PDT was performed 24 h after RET-BDP-TNM injection (50 μg mL⁻¹, 150 μL). Values are means ± s.e.m. (n = 4 mice per group); b) digital photos of tumors for the four groups of mice. c) H&E staining of tumor-tissue sections from different treatment groups after 10 days of treatment, scale bar represents 50 μm.

Scheme 1

Schematic illustration of RET-photosensitizer-mediated PDT (RET-BDP-TNM; TNM = targeted nanomicelle) and the molecular structure of RET-BDP.