4.2 Metal-modified porphyrin photosensitizers enhance light
energy capture efficiency to enhance PDT
Metal-porphyrins are widely present in nature and their ability to
cleave DNA nucleases has attracted significant attention in the last few
years. Thus, combining porphyrins with metals not only provides
additional antitumor activity and tumor selectivity, but also allows
tracking the biodistribution of metals inside and outside tumor
cells(Lovejoy and Lippard 2009). Due to paramagnetic effects, the
photocatalytic activity of metal complexes is heavily dependent on the
central metal(Zhang et al. 2019c). Therefore, many researchers have
inserted metals into porphyrin rings to maintain the stability and
photophysical properties of the porphyrin ring. In addition, the
structure of β-substituted porphyrins is closer to that of natural
porphyrins and has been widely used in biological research(Zhou et al.
1996). In these studies, some transition metal compounds, such as
iridium, ruthenium, rhenium, and osmium compounds, were investigated to
have good antitumor activity, especially in the field of
photodynamics(Imberti et al. 2020; Xie et al. 2021; Zhang et al. 2019a;
Zhu et al. 2019c). Ru is less toxic to normal cells and its use in PDT
is very attractive(Schmitt et al. 2008; Schmitt et al. 2009).
Schmitt and co-workers synthesized four aromatic Ru(II) derivatives (the
aromatics are C6H5Me orp -PriC6H4Me),
Mononuclear 5-(4-pyridyl)-10,15,20-triphenylporphyrin,
5-(3-pyridyl)-10,15,20-triphenylporphyrin, tetranuclear
5,10,15,20-tetra(4-pyridyl)porphyrin (tetra-4-pp),
5,10,15,20-tetra(3-pyridyl) porphyrin) (tetra-3-pp) and evaluated them
as potential dual photosensitizers and chemotherapeutic agents against
human melanoma cells Me300(Schmitt et al. 2009). The results showed that
the uptake and high photosensitizing activity of metal Ru on human
melanoma cell models were promoted under red light (652 nm) irradiation
at only 5 J/cm2. In another study, Zhang and
co-workers synthesized porphyrin derivatives containing Ru(II)
polypyridyl porphyrins and zinc(II) porphyrin structures and evaluated
their cytotoxicity against human nasopharyngeal carcinoma HK-1 and
cervical cancer HeLa cells(Zhang et al. 2011). The results showed that
the porphyrins containing Ru had high1O2 quantum yields, rapid cellular
uptake, low dark cytotoxicity and potent photocytotoxicity (80% of
Ru-L-containing incubated HK-1 cells were killed at a concentration of 1
μM and a yellow light dose of 3 J/cm2).