Critical discussion of the applications of metal complexes for 2-photon photodynamic therapy
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MINI REVIEW
Critical discussion of the applications of metal complexes for 2‑photon photodynamic therapy Johannes Karges1 · Hui Chao2 · Gilles Gasser3 Received: 3 September 2020 / Accepted: 18 October 2020 © Society for Biological Inorganic Chemistry (SBIC) 2020
Abstract Photodynamic therapy is a light-activated medical technique, which has received increasing attention within the last decade to treat various diseases including bacterial, viral or fungal infections as well as cancer. To overcome the limitations of the currently clinically applied photosensitizers based on a tetrapyrrolic scaffold, metal complexes are sought to be an interesting alternative. While these complexes show attractive photophysical and biological properties, the majority of these compounds are excited using visible light, which is associated with a poor tissue penetration. To circumvent this drawback, increasing attention has been devoted towards the use of 2-Photon instead of 1-Photon irradiation. In this mini-review, the metal complexes prepared in view of 2P-PDT are reviewed and the requirements these compounds need to fulfil to be of interest are critically discussed. Graphic abstract
Keywords Bioinorganic chemistry · Medicinal inorganic chemistry · Metals in medicine · Photodynamic therapy · Photosensitizers * Johannes Karges [email protected]
Introduction
* Hui Chao [email protected]
During the last decades, scientists from all over the world have worked towards the development of novel medical techniques to treat challenging or uncurable diseases. Among other techniques, photodynamic therapy (PDT) has expanded the range of treatment opportunities for cancer
* Gilles Gasser [email protected] http://www.gassergroup.com Extended author information available on the last page of the article
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patients, although this technique is still under used for reasons sometimes independent of efficacy (e.g., costs not refunded by the national health systems, medical doctors not willing to learn new techniques, etc.). PDT is a clinically approved medical procedure to treat various diseases including bacterial, viral or fungal infections, various topological skin diseases as well as cancer (e.g., lung, neck, bladder, oesophageal, brain cancer) [1–3]. We note that nearly all articles published so far on the use of metal complexes as 2P-PDT PSs were aimed for cancer treatment. However, we would like to highlight that various kinds of PSs were designed for applications in antimicrobial [4–6], viral [7–9] and fungal [10–12] therapy. A PDT treatment consists of two phases. In the first phase, a light activatable agent, a socalled photosensitizer (PS), is either systemically or locally injected. In the second phase, the PS is activated upon irradiation to photo-catalytically generate reactive oxygen species (ROS) or singlet oxygen (1O2) to cause cellular damage [13–16]. The vast majority of clinically applied PSs are based on a tetrapyrrolic scaffold (i.e., porphyrin, phthalocyanine, chlorine)
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