Porphyrin-based nanocomposites for tumor photodynamic therapy
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Introduction For decades, cancer has been recognized as a significant cause of mortality.1,2 Conventional cancer treatment strategies, including surgery, radiotherapy, and chemotherapy, are widely used in clinical settings. However, these treatments have many problems, such as high cancer recurrence rates, systemic side effects, and cumulative radiation dose.3 A safe, potent, and cost-effective treatment modality needs to be developed and is highly desired. Photodynamic therapy (PDT) has been considered as a promising strategy for cancer treatment due to its noninvasive nature, high therapeutic efficiency, and low systemic toxicity.4,5 In general, PDT contains three functional elements: photosensitizers, visible light, and oxygen. Photosensitizers effectively kill tumor cells by absorbing light and converting oxygen (O2) to cytotoxic singlet oxygen (1O2).6 Porphyrin photosensitizers, which are chromophores that exist in nature, are widely used in biomedical applications, especially for PDT of tumors due to their well-known photosensitizing properties. Nevertheless, low aqueous solubility and photostability, and lack of tumor targeting limit their in vivo bioapplications. Over the past few decades, the rapid development of nanotechnology has resulted in new opportunities for improving the in vivo applications of porphyrin-based PDT. Nanotechnology not only improves water solubility and photostability of porphyrin, but also significantly increases accumulation in the
tumor by passive (enhanced permeability and retention effect [EPR]) or active targeting (antibody or targeted peptide modification) strategies.7 In this article, we first summarize the strategies for porphyrin delivery, including encapsulation, covalent conjugation, and self-assembly for PDT (Figure 1).8–17 Next, we describe the characterization methods for singlet oxygen (1O2) and the latest developments in multifunctional porphyrin-based nanoparticles for improving cancer PDT efficacy, such as increasing the tissue penetration depth of light, tumor hypoxia relief, and multimodal imaging guidance. Finally, the challenges and prospects of porphyrin-based nanocomposites in PDT of tumors are discussed.
Delivery strategies for nanoparticle-mediated porphyrin photosensitizers Encapsulation For inorganic nanoparticles, porphyrin photosensitizers can be effectively delivered to tumor tissues by using their specific mesoporous or hollow structures. For instance, Zhao et al.8 synthesized porphyrin-doped mesoporous silica-coated gold nanorods and found these nanocomposites could be easily dispersed in an aqueous solution. This unique design facilitates the generation and release of 1O2 from the matrix, enhancing production efficiency to greater than that for pure porphyrin.8 Lin et al.9 used nanoscale metal–organic frameworks (NMOFs)
Weitao Yang, Institute of Photomedicine, Shanghai Skin Disease Hospital, The Institute for Biomedical Engineering and Nano Science, Tongji University School of Medicine, China; [email protected] Bingbo Zhang, Institute of P
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