An injectable hydrogel co-loading with cyanobacteria and upconversion nanoparticles for enhanced photodynamic tumor therapy

https://doi.org/10.1016/j.colsurfb.2021.111640Get rights and content

Highlights

  • Red blood cell membrane doped hydrogel system co-loaded with UCNPs, RB, and S. 7942 was constructed (UCNPs/S7942/RB-RHY).

  • Cyanobacteria were used to produce oxygen for alleviating tumor hypoxia microenvironment.

  • UCNPs could convert 980 nm light to visible light, which further activated the RB for PDT.

Abstract

Photodynamic therapy (PDT) is an exceedingly promising cancer treatment. However, the hypoxic environment in tumor and the low penetration efficiency of short-wavelength light limit the effects of PDT. In this paper, an injectable red blood cell membrane doped hydrogel system (UCNPs/S7942/RB-RHY) containing upconversion nanoparticles (UCNPs), a photosensitizer (Rose Bengal) and a strain of cyanobacteria Synechococcus elongatus PCC 7942 (S. 7942) was developed to improve the PDT effects with a good biocompatibility and biosafety. In the system, S. 7942 was capable of inexhaustibly generating oxygen triggered by the 640 nm laser irradiation for alleviating hypoxic tumor microenvironment. In addition, UCNPs converted near-infrared light to visible light upon excitation by a 980 nm laser, which further activated the photosensitizer to release reactive singlet oxygen to eradicate tumors. In vivo experiments showed that the tumor volume in the UCNPs/S7942/RB-RHY combined 640 nm with 980 nm light group was 496.9 mm3, in compared with 955.5 mm3 of the tumor volume in the group without irradiation. The results demonstrated that UCNPs/S7942/RB-RHY was able to not only dramatically alleviate tumor hypoxia but also achieve a more efficient PDT treatment. The oxygen-generating system described here provides a new idea for hypoxia-resistant cancer therapy in the future.

Introduction

As a non-invasive cancer treatment, photodynamic therapy (PDT) has been successfully used in the treatment of various malignant tumors in the clinic due to its safety and lack of initiating resistance [[1], [2], [3]]. A typical PDT process includes three key components: light, photosensitizer (PS) and oxygen [4,5]. A photosensitizer is excited by light with specific wavelength to transform energy to oxygen, further generating large amounts of cytotoxic reactive oxygen species (ROS) to kill cancer cells. However, due to the hypoxic microenvironment at the tumor sites (pO2 values≤2.5 mmHg), effects of PDT are greatly limited [6]. In addition, poor light penetration of short-wavelength also restrict the activation efficiency of the photosensitizer thus negatively impact the PDT effects [7].

To improve the oncotherapy, great efforts have been made to combat the ineffectiveness of hypoxia-mediated PDT [8,9]. For example, endogenous H2O2 decomposition and oxygen transportation were used to modulate tumor hypoxia [10,11]. However, both H2O2 existing in tumor tissues and the oxygen loaded in the nanosystem were limited [12], depending on repeated administration to maintain the therapy. To address these issues, it’s necessary to build a sustaining oxygen-production system. Notably, cyanobacteria are the only prokaryotes performing oxygenic photosynthesis, enabling oxygen generation when exposed to light [13]. Thus injection of a hydrogel containing cyanobacteria into the tumor site could provide a rich source of oxygen to address the limitations of PDT in hypoxia conditions [14]. Several recent studies have demonstrated the biosafety of cyanobacteria especially Synechococcus on animals, providing promising strategy for PDT optimization [15]. Meanwhile, upconversion nanoparticles (UCNPs) with anti-stokes luminescence properties are able to convert long-wavelength light into short-wavelength light. Therefore, it can be applied to address the poor tissue penetration issue of short-wavelength laser [[16], [17], [18], [19]]. Further, Rose Bengal (RB) is a photosensitizer approved by the U.S. Food and Drug Administration (FDA) for PDT, which has the advantage of high photon yield and safety [[20], [21], [22], [23]]. The combination of RB and UCNPs excited by 980 nm laser has been suggested as a promising method for PDT [[24], [25], [26]].

To achieve an optimized PDT and reduce dosing frequency, in this study, a hydrogel system co-loading with UCNPs, RB, and cyanobacteria Synechococcus elongatus PCC 7942 (hereafter S. 7942) was constructed. To reduce the toxic side effects on animals, S. 7942 were encapsulated and the residual hydrogels after tumor treatment was removed. Detailly, UCNPs, RB, and S. 7942 were encapsulated in an injectable hydrogel system and the process was divided into three parts as described in Fig. 1: i) The hydrogel system, which was formed by red blood cell membrane and alginate scaffolds to improve the biocompatibility [27], which could be subcutaneously injected into the tumor site; ii) The hydrogel injected site was irradiated by 640 nm laser to support the survival of S. 7942 and oxygen generation, thereby alleviating hypoxic tumor microenvironment; iii) UCNPs were exposed to 980 nm laser to produce green light (548 nm), which further stimulated the photosensitizer RB to produce ROS for oncotherapy. The system presented here were demonstrated to significantly enhance the effect of PDT and provided new ideas for addressing the hypoxia and light penetrability problems in clinically hypoxia-resistant cancer therapy.

Section snippets

Materials

Rose Bengal sodium salt (RB) and 3-[4,5-dimethylthiazol-`2-yl]-2,5-diphenyltetrazolium-bromide (MTT) were bought from Sigma-Aldrich (MO, USA). Propidium iodide (PI), Hoechst 33342, Calcein-AM and Tetraethylorthosilicate (TEOS) were obtained from Aladdin (Shanghai, China). Ethanol, Dimethyl sulfoxide (DMSO), sodium chloride, methanol and Sodium chloride were obtained from Yuan Li (Tianjin, China). Annexin V-FITC Apoptosis Detection Kit, Reactive Oxygen Species Assay Kit and BCA protein Assay kit

Characterization of upconversion nanoparticles (UCNPs) for PDT

Synthesized UCNPs-photosensitizer (UCNPs-PS) nanocomplexes mediated PDT allowed effective resonance energy transfer from donors to acceptors using near-infrared light (NIR). Notably, various studies about UCNPs-based PDT have been published in recent years, suggesting its feasibility [19]. In this work, UCNPs excited by NIR were used as energy donors to activate RB approved by the U.S. FDA for generating ROS (Fig. 2A). As shown in Fig. 2B, green UCNPs were synthesized with particle size of

Discussion

Hypoxia is one of the hallmarks of solid tumors, which especially limits the clinical application of PDT. Besides, the traditional PDT is usually irradiated by ultraviolet or white light, which is usually used for skin cancer treatment due to its shallow tissue penetration. Therefore, the application of PDT in the treatment of other deep tissue tumors has been plagued by some key issues, such as the inability to achieve excitation light penetration, and the lack of oxygen in deep tissue tumors [

Conclusions

To alleviate hypoxia in tumor tissue and address the question of the poor light penetration using short-wavelength for PDT, in this study, we prepared an injectable hydrogel system loaded with UCNPs, photosensitizers and cyanobacteria for enhanced photodynamic oncotherapy. Due to the oxygen production from S. 7942, the hypoxia at the tumor site was successfully alleviated, followed by the improved PDT effects in mice. In addition, this hydrogel system showed good biocompatibility and biosafety.

CRediT authorship contribution statement

Xinyu Zhang: Writing - review & editing, Methodology. Yingying Zhang: Writing - review & editing, Methodology. Chaonan Zhang: Writing - review & editing, Investigation. Chun Yang: Methodology. Ran Tian: Methodology. Tao Sun: Methodology, Investigation. Weiwen Zhang: Supervision. Jin Chang: Supervision. Hanjie Wang: Supervision, Methodology, Writing - review & editing.

Declaration of Competing Interest

The authors report no declarations of interest.

Acknowledgements

This work was sponsored by National Key Research and Development Program of China (2019YFA0906500 and 2017YFA0205104), National Natural Science Foundation of China (31971300, 817719709 and 51873150), Tianjin Natural Science Foundation (19JCYBJC28800), Young Elite Scientists Sponsorship Program by Tianjin and the Key project of Tianjin Foundational Research (JingJinJi) Program, China (19JCZDJC64100).

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