Сборник содержит материалы научной мультиконференции «Биотех- нология медицине будущего»

EPR studies of complexes of photosensitizers with albumin promising
in photodynamic therapy of cancer
Timofeev I.O.
1
, Spitsina A.S.
2
, Lebedeva N.Sh.
3
, Koifman O.I.
3
, Chubarov A.S.
4
, Fedin M.V.
1
, 
Bagraynskaya E.G.
2
, Krumkacheva O.A.
1
1
International Tomography Center SB RAS, Russia 
2
N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Russia 
3
G. A. Krestov Institute of Solution Chemistry, Russia 
4
Institute of Chemical Biology and Fundamental Medicine SB RAS
Many photosensitizers promising for photodynamic therapy are lipophilic substances with 
low solubility in water. Therefore, the effective delivery of such photosensitizers requires the 
use of special transport systems. Human serum albumin (HSA) is a natural transport protein 
with multiple ligand binding sites, making it a promising carrier for the delivery of lipophilic 
drugs. HSA is able to bind with some photosensitizers with high efficiency and to accumulate 
in malignant and inflamed tissues. Photophysical properties of photosensitizers bound to HSA 
depend on its localization at the protein. In order to create new efficient agents for photody-
namic treatment it is necessary to investigate the structure of such complexes.
In this paper, we for the first time applied various methods of electron paramagnetic 
resonance (EPR) spectroscopy to study complexes of human serum albumin (HSA) with 
porphyrin derivatives. As a result, we obtained the distribution functions for the distances 
between the photoexcited triplet of photosensitizers and the nitroxyl radical selectively intro-
duced at HSA. This allowed us to establish binding sites on HSA for various porphyrins. We 
estimated also the accessibility of the photosensitizer triplet to solvent molecules in complex 
with protein. In addition, the effect of binding to HSA on the singlet oxygen generation 
efficiency and on the distribution of the electron spin density in the porphyrin triplet molecules 
was evaluated. 
It was shown that tetra (hydroxyphenyl) porphyrin forms a complex with HSA in 
two binding sites located in domains IIa and IIIa. In these sites, porphyrin has practically 
no access to solvent molecules, but demonstrates effective production of singlet oxygen. In 
contrast to this, EPR methods have showed binding of cationic porphyrin (5,10,15,20-tetrakis 
(4-N-methylpyridyl porphyrin) mainly in one site in domain 1B of HSA, in which porphyrin 
is highly accessible to solvent molecules. The significant decrease in the efficiency of singlet 
oxygen generation is observed for this porphyrin in complex with HSA, despite the fact that 
according to EPR data the formation of a complex does not affect the quantum yield of the 
triplet state and the structure of porphyrin.
The work was supported by the RSF № 18-73-00292

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Всероссийская мультиконференция с международным участием «Биотехнология – медицине будущего»
29 июня - 2 июля 2019 г., г. Новосибирск, Россия
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