Enhanced Intracellular IR780 Delivery by Acidity-Triggered PEG-Detachable Hybrid Nanoparticles to Augment Photodynamic and Photothermal Combination Therapy for Melanoma Treatment

Abstract

The PEGylation of drug-carrying nanoparticles has often been used to prolong blood circulation and improve drug deposition at tumor sites. Nevertheless, the PEG-rich hydrophilic surfaces retard the release of the payloads and internalization of therapeutic nanoparticles by cancer cells, thus lowering the anticancer efficacy. To boost the anticancer potency of the combined photodynamic therapy (PDT) and photothermal therapy (PTT) against melanoma by conquering the PEG dilemma, herein, the hybrid PEGylated chitosan-covered polydopamine (PDA) nanoparticles (PCPNs) with acidity-elicited PEG detachment ability were fabricated as carriers of IR780, a small-molecule photosensitizer used for PTT and PDT. The IR780@PCPNs displayed a uniform, solid-like spherical shape and sound colloidal stability. Under near-infrared (NIR) irradiation, the IR780@PCPNs showed prominent photothermal conversion efficiency (ca. 54.6%), robust photothermal stability, reduced IR780 photobleaching, sufficient singlet oxygen (¹O₂) production, and glutathione-depleting ability. Moreover, with the environmental pH being reduced from 7.4 to 5.0 at 37 °C, the decreased interactions between IR780 and PCPNs due to the increased protonation of phenolic hydroxyl residues within PDA and primary amine groups of chitosan accelerated the release of IR780 species from IR780@PCPNs. Importantly, the cellular uptake of IR780@PCPNs by B16F10 melanoma was remarkably promoted in a weakly acidic milieu upon PEG detachment driven by the disintegration of acid-labile benzoic imine. With NIR irradiation, the internalized IR780@PCPNs generated hyperthermia and ¹O₂ to damage mitochondria, thereby effectively inhibiting the proliferation of B16F10 cells. Collectively, our findings present a practical strategy for amplifying the anticancer efficacy of PTT combined with PDT using PEG-detachable IR780@PCPNs.

Keywords: IR780; PEG detachment; benzoic imine bond; melanoma treatment; photothermal and photodynamic therapy.

Scheme 1. Illustrative Diagram of (a) Fabrication of IR780@PCPNs and (b) Their PTT/PDT-Based Anticancer Effect Enhanced by Acid-Activated PEG Detachment

Figure 1

(a) FT-IR spectra of chitosan, mPEG-CHO, PEGylated chitosan, PDA, and PCPNs. (b) ¹H NMR spectra of chitosan, mPEG-CHO, and PEGylated chitosan in D₂O.

Figure 2

(a) UV/vis absorption spectra of DA monomers, PDA particles, free IR780 molecules, PCPNs, and IR780@PCPNs in pH 7.4 aqueous solution. (b) Particle size distribution profiles of PCPNs and IR780@PCPNs dispersed in pH 7.4 PBS. N 1s XPS spectra of (c) PEGylated chitosan adducts and (d) PCPNs. (e) Zeta potential values of PDA particles, PCPNs, and IR780@PCPNs at pH 7.4, 6.5, and 5.0. (f) Zeta potential values of IR780@PCPNs in aqueous solutions at pH 7.4 and 5.0 at different time intervals.

Figure 3

(a) SEM images of (i) PCPNs and (iii) IR780@PCPNs. TEM images of (ii) PCPNs and (iv) IR780@PCPNs. Scale bars: 200 nm. (b) Angle-dependent DLS (black square) and SLS (blue circle) measurements performed on IR780@PCPNs in pH 7.4 PBS. (c) Particle size distribution profiles of IR780@PCPNs dispersed in 10% FBS-containing pH 7.4 PBS at various intervals. (d) Cumulative IR780 release performance of IR780@PCPNs in aqueous pH 7.4, 6.5, and 5.0 solutions at 37 °C.

Figure 4

(a) Heating curves of IR780 molecules, PCPNs, and IR780@PCPNs in pH 7.4 PBS exposed to NIR laser irradiation. Photothermal performance and plot fitting of cooling time versus the negative natural logarithm of the driving force temperature during the cooling process of (b) IR780@PCPN solution and (c) free IR780 molecules (IR780 concentration: 22.2 μM). (d) Photothermal performance test for aqueous solutions of IR780 molecules, PCPNs, or IR780@PCPNs receiving three laser on/off cycles (808 nm, 1.0 W/cm²). UV/vis spectra of (e) the IR780 solution and (f) the IR780@PCPN solution receiving repeated laser irradiation. Inset: Photos of IR780 solution and IR780@PCPN solution before and after the first laser on/off cycle (808 nm, 1.0 W/cm²).

Figure 5

(a) UV/vis absorption spectra of DPBF in IR780@PCPNs-containing aqueous solution receiving 808 nm laser irradiation at different times. (b) Normalized absorbance of DPBF in aqueous solutions of IR780, PCPNs, and IR780@PCPNs, respectively, exposed to 808 nm laser irradiation at different times. (c) UV/vis absorption spectra of DTNB in a GSH solution treated with IR780@PCPNs for different time intervals. (d) Residual content of GSH treated with PCPNs and IR780@PCPNs for various time intervals.

Figure 6

(a) CLSM images and (b) intracellular mean IR780 fluorescence intensity of B16F10 cells incubated with free IR780 molecules at pH 7.4 or IR780@PCPNs at pH 7.4 or 6.5 for 0.5 and 4 h, respectively, at 37 °C (IR780 = 2.5 μM). Scale bars: 15 μm. (c) DCF fluorescence images of B16F10 cells receiving different treatments. Scale bars: 50 μm.

Figure 7

(a) JC-1 staining images and (b) ratio of green and red fluorescence intensities of B16F10 cells subjected to different treatments. Scale bars: 50 μm. Viability of B16F10 cells treated with PCPNs, IR780@PCPNs at pH 7.4 or 6.5, or free IR780 molecules at pH 7.4 without laser irradiation (c) or laser irradiation (d).