TY - JOUR

T1 - Application of EPR to porphyrin-protein agents for photodynamic therapy

AU - Sannikova, Natalya E.

AU - Timofeev, Ivan O.

AU - Chubarov, Alexey S.

AU - Lebedeva, Natalya Sh

AU - Semeikin, Aleksandr S.

AU - Kirilyuk, Igor A.

AU - Tsentalovich, Yuri P.

AU - Fedin, Matvey V.

AU - Bagryanskaya, Elena G.

AU - Krumkacheva, Olesya A.

N1 - Copyright © 2020 Elsevier B.V. All rights reserved.

PY - 2020/10/1

Y1 - 2020/10/1

N2 - Recently, a new type of spin labels based on photoexcited triplet molecules was proposed for nanometer scale distance measurements by pulsed dipolar electron paramagnetic resonance (PD EPR). However, such molecules are also actively used within biological complexes as photosensitizers for photodynamic therapy (PDT) of cancer. Up to date, the idea of using the photoexcited triplets simultaneously as PDT agents and as spin labels for PD EPR has never been employed. In this work, we demonstrate that PD EPR in conjunction with other methods provides valuable information on the structure and function of PDT candidate complexes, exemplified here with porphyrins bound to human serum albumin (HSA). Two distinct porphyrins with different properties were used: amphiphilic meso-tetrakis(4-hydroxyphenyl)porphyrin (mTHPP) and water soluble cationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4); HSA was singly nitroxide-labeled to provide a second tag for PD EPR measurements. We found that TMPyP4 locates in a cavity at the center of the four-helix bundle of HSA subdomain IB, close to the interface with solvent, thus being readily accessible to oxygen. As a result, the photolysis of the complex leads to photooxidation of HSA by generated singlet oxygen and causes structural perturbation of the protein. Contrary, in case of mTHPP porphyrin, the binding occurs at the proton-rich pocket of HSA subdomain IIIA, where the access of oxygen to a photosensitizer is hindered. Structural data of PD EPR were supported by other EPR techniques, laser flash photolysis and protein photocleavage studies. Therefore, pulsed EPR on complexes of proteins with photoexcited triplets is a promising approach for gaining structural and functional insights into such PDT agents.

AB - Recently, a new type of spin labels based on photoexcited triplet molecules was proposed for nanometer scale distance measurements by pulsed dipolar electron paramagnetic resonance (PD EPR). However, such molecules are also actively used within biological complexes as photosensitizers for photodynamic therapy (PDT) of cancer. Up to date, the idea of using the photoexcited triplets simultaneously as PDT agents and as spin labels for PD EPR has never been employed. In this work, we demonstrate that PD EPR in conjunction with other methods provides valuable information on the structure and function of PDT candidate complexes, exemplified here with porphyrins bound to human serum albumin (HSA). Two distinct porphyrins with different properties were used: amphiphilic meso-tetrakis(4-hydroxyphenyl)porphyrin (mTHPP) and water soluble cationic meso-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP4); HSA was singly nitroxide-labeled to provide a second tag for PD EPR measurements. We found that TMPyP4 locates in a cavity at the center of the four-helix bundle of HSA subdomain IB, close to the interface with solvent, thus being readily accessible to oxygen. As a result, the photolysis of the complex leads to photooxidation of HSA by generated singlet oxygen and causes structural perturbation of the protein. Contrary, in case of mTHPP porphyrin, the binding occurs at the proton-rich pocket of HSA subdomain IIIA, where the access of oxygen to a photosensitizer is hindered. Structural data of PD EPR were supported by other EPR techniques, laser flash photolysis and protein photocleavage studies. Therefore, pulsed EPR on complexes of proteins with photoexcited triplets is a promising approach for gaining structural and functional insights into such PDT agents.

KW - DEER/PELDOR

KW - Distance measurements

KW - EPR spectroscopy

KW - Photodynamic treatment

KW - Porphyrin

KW - Spin labels

KW - TRIPLET-STATE

KW - HUMAN SERUM-ALBUMIN

KW - PHOTOSENSITIZERS

KW - DAMAGE

KW - MOLECULES

KW - DISTANCE MEASUREMENTS

KW - MELANOMA

KW - SINGLET OXYGEN

KW - GENERATION

KW - BINDING

UR - http://www.scopus.com/inward/record.url?scp=85090595579&partnerID=8YFLogxK

U2 - 10.1016/j.jphotobiol.2020.112008

DO - 10.1016/j.jphotobiol.2020.112008

M3 - Article

C2 - 32932136

AN - SCOPUS:85090595579

VL - 211

JO - Journal of Photochemistry and Photobiology B: Biology

JF - Journal of Photochemistry and Photobiology B: Biology

SN - 1011-1344

M1 - 112008

ER -