Page 171 - SRPSKO DRUŠTVO ISTRAŽIVAČA RAKA

SDIRSACR Oncology Insights

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Overcoming oxygen heterogeneity in cancer photodynamic therapy to boost cytotoxicity

Alexey Bogdanov, Vladimir Klimenko, Vladimir Moiseyenko

N.P. Napalkov Saint Petersburg Clinical Research and Practical Center of Specialized Types of Medical Care (Oncological), Saint
Petersburg, Russia

Keywords: cancer, control of oxygenation, photodynamic therapy, pulse-mode irradiation

Background: Photodynamic therapy (PDT) represents an important addition to traditional cancer treatment
methods. However, tumor hypoxia and oxygen heterogeneity significantly limit its clinical effectiveness. The
development of strategies to overcome these limitations is a pressing issue. The aim of this study was to
evaluate the impact of metabolic oxygen consumption in tumor spheroids formed from mouse CT26 colon
adenocarcinoma cells on the formation of hypoxic zones and the efficacy of photodynamic action (PDA).
Materials and Methods: Tumor spheroids were formed by seeding CT26 cells into low-adhesion round-
bottom plates. A chlorin e6-based photosensitizer was used, and irradiation was performed using a 662
nm laser. Modeling of oxygen concentration changes within 650 µm diameter spheroids was carried out
using COMSOL Multiphysics, taking into account cellular metabolic oxygen consumption. Assessment of
photochemical oxygen consumption was conducted using a macroscopic model of singlet oxygen generation.
Results: It was shown that cellular metabolic activity leads to the formation of an oxygen gradient and the
establishment of a hypoxic zone (with oxygen concentration below 1 µM) in the center of the spheroid. Spheroids
were classified by size: small (100–400 µm), medium (400–650 µm), and large (650–1200 µm). Hypoxic tumor
zones demonstrated protection against PDA at an irradiation dose of 15 J/cm², which affected cytotoxic efficacy
and promoted spheroid regrowth. Medium-sized spheroids exhibited the highest resistance. Growth suppression
in large spheroids was achieved after PDA with a dose of 15 J/cm² and an average power density of 12.5 mW/
cm². Mathematical modeling showed that metabolic oxygen consumption reduces oxygen concentration at the
spheroid surface to 70–80 µM, forming hypoxic zones in the center. During PDA, an increased oxygen consumption
rate and reduced surface oxygen concentration were observed. The viable cell zone protected from PDA was
located at the boundary adjacent to the necrotic core, where oxygen concentration ranged from 1 to 10 µM.
Conclusions: To enhance PDT efficacy, it is crucial to account for tumor oxygen levels as low as 1–10 µM, caused by
high metabolic consumption and limited diffusion. Computational modeling of singlet oxygen generation supports
experimental findings and underscores the need for optimized irradiation protocols to overcome hypoxia and improve
treatment outcomes.

Acknowledgments and funding: This work was supported by the Health Committee of Saint Petersburg state
assignment for N.P. Napalkov Saint Petersburg Clinical Research and Practical Center of Specialized Types of Medical
Care (Oncological).

P85

Targeting glycolysis with 2-Deoxy-D-Glucose and lysosomal integrity with L-Leucyl-L-Leucine methyl ester
as antimelanoma strategy

Mihajlo Bošnjak , Milica Kosić , Miloš Mandić , Ljubica Vučićević , Maja Misirkić Marjanović , Vladimir Perović , Verica
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Paunović , Danijela Stevanović , Kristina Janjetović , Aleksandar Paunić , Aleksandra Aničin , Vladimir Trajković ,
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Ljubica Harhaji Trajković 2
1Institute of Microbiology and Immunology, Faculty of Medicine, University of Belgrade, Belgrade, Serbia
2Institute for Biological Research “Siniša Stanković” – National Institute of the Republic of Serbia, University of Belgrade, Belgrade,
Serbia
Keywords: lysosomes, cathepsins, melanoma, glycolysis, energy metabolism
Background: Malignant melanomas are characterized by enhanced glycolysis, which supplies energy and biosynthetic
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