2.3 Application of porphyrins in PDT of cancer
Cancer has become a huge threat to human health, with millions of patients dying from cancer every year, making it the second leading cause of death in the world after cardiovascular disease(Bouramtane et al. 2019). Traditional cancer treatments are divided into three main types, surgical treatment, physical therapy and chemotherapy, but all of them have many side effects. Therefore, breakthroughs in novel cancer treatments have become the main goal of scientists. The key roles of porphyrins in light energy capture and oxygen molecule transport in the human body have been described earlier in this paper, respectively. The excellent light trapping properties and good biocompatibility in human tissues make it possible for porphyrins to be applied as photosensitizers for cancer therapy.
As medicine continues to evolve, so do cancer treatment strategies. PDT is considered to be a safer cancer treatment with fewer side effects(Luo et al. 2017). With the development of PDT, impressive progress has been made in the research of preparing photosensitizers, especially porphyrin-based photosensitizers(Lin et al. 2020). Most of the photosensitizers used for cancer therapy have a porphyrin-based macrocyclic backbone(M. 1997; Martinez De Pinillos Bayona et al. 2017; Morgan and Oseroff 2001), and the main advantages of porphyrins in photodynamic studies include: (1) stability of aromatic compounds; (2) effective absorption of visible light; (3) high yield of reactive oxygen species; (4) easy functionalization modifications and structural diversity; (5) long triplet state lifetime and low dark toxicity(Ethirajan et al. 2011; Xiong et al. 2019). Hematoporphyrin (HPD) was first used by Dougherty in 1978 for the treatment of gastrointestinal cancers(Dougherty et al. 1978; Habermeyer and Guilard 2018). Clinical studies have shown that PDT has been increasingly used in the treatment of solid tumors, including tumors of the brain, head and neck, skin, esophagus, lung, gastrointestinal tract, pancreas, bladder, prostate, breast, cervix, and ovary, as well as basal cell carcinoma(Banerjee et al. 2017; Dobson et al. 2018; Fan and Andrén-Sandberg 2007; Felsher 2003; Li et al. 2018). Sodium porphyrin (Fig. 4) is the world’s first approved photosensitizer for the treatment of cancer(Lin et al. 2020) that is not only reusable but also has virtually no side effects and does not develop resistance to the drug.
Fig. 4 Structure of sodium porphyrin.