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.