Near-Infrared Fluorescent Hydroxyapatite Nanoparticles for Targeted Photothermal Cancer Therapy

Abstract

Near-infrared (NIR) fluorophores have attracted great attention due to their excellent optical and photothermal properties. Among them, a bone-targeted NIR fluorophore (named P800SO3) contains two phosphonate groups, which play important roles in binding with hydroxyapatite (HAP) as the main mineral component of bones. In this study, biocompatible and NIR fluorescent HAP nanoparticles functionalized with P800SO3 and polyethylene glycol (PEG) were readily prepared for tumor-targeted imaging and photothermal therapy (PTT). The PEGylated HAP nanoparticle (HAP800-PEG) demonstrated improved tumor targetability with high tumor-to-background ratios (TBR). Moreover, the HAP800-PEG also showed excellent photothermal properties, and the temperature of tumor tissue reached 52.3 °C under NIR laser irradiation, which could completely ablate the tumor tissue without recurrence. Therefore, this new type of HAP nanoparticle has great potential as a biocompatible and effective phototheranostic material, which enables the use of P800SO3 for targeted photothermal cancer treatment.

Keywords: P800SO3; hydroxyapatite; near-infrared fluorescence imaging; photothermal therapy; targeted nanoparticles.

Figure 1

Preparation scheme of NIR fluorescent HAP nanoparticles for targeted NIR fluorescence imaging and PTT.

Figure 2

(a) Absorption and fluorescence emission spectra of P800SO3, HAP, HAP800, and HAP800-PEG measured in PBS, with a pH of 7.4. (b) Size distributions and (c) zeta potential of HAP nanoparticles measured in DW.

Figure 3

In vivo HT-29 tumor targeting efficiency and biodistribution of P800SO3 and HAP800. (a) NIR fluorescence imaging 48 h after injection of P800SO3 and HAP800, respectively. The arrowheads indicate the tumor area. Scale bars = 1 cm. (b) Resected organs and tumor tissue were imaged at 4 h post-injection of HAP800. Abbreviations: Du, duodenum; He, heart; In, intestines; Ki, kidneys; Li, liver; Lu, lungs; Mu, muscle; Pa, pancreas; Sp, spleen; Tu, tumor; PI, post-injection. The representative images were selected from each treatment group.

Figure 4

In vivo HT-29 tumor targeting efficiency and biodistribution of HAP800-BSA and HAP800-PEG. (a) NIR fluorescence imaging 48 h after injection of HAP800-BSA and HAP800-PEG. The arrowheads indicate the tumor area. Scale bars = 1 cm. (b) Time-dependent fluorescence intensities at the tumor sites targeted by HAP800-BSA and HAP800-PEG. (c) Tumor-to-background ratio (TBR) of HAP800-BSA and HAP800-PEG were observed for 48 h post-injection. TBR was considered between the fluorescence signals of the tumor and the neighboring area. The representative images were selected from each treatment group.

Figure 5

(a) In vitro thermal images of the HAP800-PEG and PBS solutions irradiated with an 808 nm laser with 1.0 W/cm² power density for 1 min. The infrared thermal imager was used to monitor the maximum temperature in real time. (b) Temperature changes in the HAP800-PEG and PBS solutions were observed for 60 s of laser irradiation. (c) Photobleaching test of the HAP800-PEG solution (100 μM) during 3 cycles of laser irradiation. (d) In vivo thermal images at the tumor area 5 min post-irradiation of the 808 nm laser with 1.0 W/cm² power density after 24 h of the injections of the HAP800-PEG and PBS solutions. (e) Temperature changes of tumors treated with the HAP800-PEG and PBS for 5 min of laser irradiation with 1.0 W/cm² power density. The representative images were selected from each treatment group.

Figure 6

(a) Photos of HT-29 tumor-bearing mice observed for 9 days in each treatment group. The tumors were irradiated with an 808 nm laser with 1.0 W/cm² power density for 5 min after 24 h of injections of PBS, HAP800, or HAP800-PEG. The arrowheads indicate the tumor area. Scale bars = 1 cm. (b) Tumor growth rates (inset: the gross photo of tumors harvested from each treatment group at day 9) and (c) body weights of each treatment group were observed during the course of different treatments. (d) Histological observation of tumor slides after staining with H&E in each treatment group. Scale bars = 100 μm. The representative images were selected from each treatment group.