Targeted photodynamic therapy with a novel photosensitizer cercosporin encapsulated multifunctional copolymer
Graphical abstract
A multifunctional copolymer has been encapsulated with a novel photoactivated perylenequinone photosensitizer, cercosporin to exhibit strong targeting ability and high PDT efficiency for cancer treatment.
Introduction
Cercosporin, first isolated in the 1950s from the soybean pathogen Cercospora kikuchii, has been considered a light-activated perylenequinone toxin that plays an important role in fungal pathogenicity. It is toxic in mice, bacteria, fungi as well as plants [[1], [2], [3], [4]]. This light-activated toxin is a photosensitizer that can generate superoxide radical (O2•−) and singlet oxygen (1O2), which is the potent reactive oxygen species (ROS) after light initiated reaction with oxygen [3,[5], [6], [7]]. 1O2 can cause cell death by indiscriminately damaging cellular components, including nucleic acids, proteins, lipids and membranes [3,8]. Cercosporin is a promising photosensitizer for photodynamic therapy (PDT) as it has a higher 1O2 quantum yield (0.81) compared to other photosensitizers such as porphyrins, chlorophyll and porphyrin-related compounds [2,5,9]. PDT, a medical treatment based on 1O2 produced by photosensitizer, is used for treatment of non-malignant and malignant disease [10,11]. The poor water solubility, selectivity and toxicity of photosensitizers limit the applications of PDT in cancer treatment [12]. The incorporation of photosensitizers into nanomaterials is a promising means to improve specificity with tumor cells, enhance the PDT efficiency and minimize undesired systemic toxicity [13,14]. Recent theranostic delivery systems that combine PDT with different therapy are advantageous for cancer treatment [[15], [16], [17], [18]].
Long chain amphiphilic polymers can help to improve the solubility and reduce the toxicity of small molecules [19]. Based on our previous work, galactose ligands have been proved the targeting ability to the asialoglycoprotein receptors (ASGPRs), which are overexpressed on hepatocellular carcinoma cell membrane [20]. Here, we encapsulate cercosporin into our hepatocellular carcinoma targeting multifunctional copolymer, which is galactose modified rhodamine B-based poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) with poly(3-azido-2-hydroxypropyl methacrylate) (PGMA-N3) copolymer nanocarrier (Gal-polymer) (Scheme 1a) [20,21]. Cercosporin is loaded into the Gal-polymer via hydrophobic interactions with PGMA-N3 segments and released in the acidic tumor microenvironment via PDMAEMA protonation [[22], [23], [24]]. Galactose ligands enhance cellular uptake on hepatocellular carcinoma cell surfaces, which provide the cercosporin with selectivity (Scheme 1b) [[25], [26], [27]]. Rhodamine B (RhB) end-labeling facilitates real-time imaging [28,29]. Cercosporin loaded Gal-polymer (Cer@Gal-polymer) not only improved water solubility, stability and biocompatibility, but also allowed for targeting delivery of cercosporin to HepG2 cells for PDT and tracking.
Section snippets
Synthesis of gal-polymer and glc-polymer
RhB-based initiator for atom transfer radical polymerization (ATRP) and monomer 3-azido-2-hydroxypropyl methacrylate (GMA-N3) were synthesized as previously reported (Figure S1, S2) [[30], [31], [32]]. Then, RhB modified PDMAEMA/PGMA-N3 copolymers were polymerized under typical ATRP protocol (Figure S3) [33,34]. The structures were confirmed by 1NMR (Figure S4) and GPC with similar details reported in our previous literature [20]. The Gal- and Glc-polymers were synthesized by copper catalyzed
Conclusions
We describe the first encapsulated copolymer system to encapsulate cercosporin for targeted PDT against hepatocellular carcinoma cells. Cer@Gal-polymer is internalized by HepG2 cells via galactose-ASGPR-mediated endocytosis. Upon release of the nanoparticles in the acidic tumor cell microenvironment, the cercosporin escaped from endosomal compartments into the cytoplasm. High yielding 1O2 generation induces enhanced photodynamic cell damage. The Cer@Gal-polymer targets cercosporin delivery that
Preparation of cercosporin loaded Gal-polymer (Cer@Gal-polymer) and Glc-polymer (Cer@Glc-polymer)
Cercosporin (4.0 mg, 7.5 mmol) was added to DMSO (0.5 mL), and stirred for 2 h at 25 °C. Gal-polymer or Glc-polymer (10 mg) were added to DMSO (0.5 mL) and then mixed with cercosporin independently. After water (5 mL) was added for 10 min under vigorous stirring, the mixture solutions were stirred for 2 h. Then the mixture were dialyzed (MWCO 2000) against water for 2 days with exchange of water every 6 h. After the solutions were filtered through microporous filter (0.45 μm), Cer@Gal-polymer
Declaration of Competing Interest
None.
Acknowledgements
We are grateful for financial support from National Natural Science Foundation of China (31700706, 21877052), Natural Science Foundation of Jiangsu Province (BK20180030), and the Fundamental Research Funds for the Central Universities (JUSRP51712B), and Max Planck Society International Partner Group Program, High-end Foreign Experts Recruitment Program, the Thousand Talents Plan (Young Professionals), and the China Scholarship Council.
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These authors contributed equally.