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Indocyanine Green as a Theragnostic Agent in MCF-7 Breast Cancer Cells
by
, , and
Wiktoria Mytych
1
,
Dorota Bartusik-Aebisher
2
,
Piotr Oleś
3,
Aleksandra Kawczyk-Krupka
3, 
David Aebisher
4,*
and
Gabriela Henrykowska
5,* 1
English Division Science Club, Collegium Medicum, Faculty of Medicine, University of Rzeszów, 35-310 Rzeszów, Poland
2
Department of Biochemistry and General Chemistry, Collegium Medicum, Faculty of Medicine, University of Rzeszów, 35-310 Rzeszów, Poland
3
Department of Internal Diseases, Angiology and Physical Medicine, Center for Laser Diagnostics and Therapy, Medical University of Silesia, Batorego 15, 41-902 Bytom, Poland
4
Department of Photomedicine and Physical Chemisry, Collegium Medicum, Faculty of Medicine, University of Rzeszów, 35-310 Rzeszów, Poland
5
Department of Epidemiology and Public Health, Faculty of Medicine, Medical University of Lodz, Tadeusza Kosciuszki 4, 90-419 Lodz, Poland
*
Authors to whom correspondence should be addressed.
Molecules 2026, 31(3), 520; https://doi.org/10.3390/molecules31030520
Submission received: 31 December 2025
/
Revised: 26 January 2026
/
Accepted: 30 January 2026
/
Published: 2 February 2026
(This article belongs to the Special Issue Design, Synthesis and Biological Evaluation of Medicinal Potential Compounds—2nd Edition)
Simple Summary
Indocyanine green (ICG) is a clinically approved near-infrared dye already used for tumor imaging. This study explores whether the same molecule, when activated by safe 780 nm light, can also effectively kill breast cancer cells through photodynamic therapy (PDT) while sparing healthy breast cells. Using both traditional flat (2D) cultures and three-dimensional (3D) collagen-based models that partially mimic tumor ECM barriers of human MCF-7 breast cancer cells, we show that ICG photodynamic therapy selectively destroys cancer cells, generates high amounts of toxic singlet oxygen, and works better in 2D than in 3D (as expected from diffusion limitations that mimic real tumors). Healthy breast cells remain almost unaffected, giving a therapeutic safety margin of approximately 5:1. These findings suggest that ICG could become a simple, low-cost “see-and-treat” agent for breast cancer with minimal side effects.
Abstract
Background/Objectives: Indocyanine green (ICG) is an FDA-approved, near-infrared fluorescent dye widely used for tumor imaging. This study aimed to evaluate the photodynamic efficacy and selectivity of ICG as a photosensitizer in photodynamic therapy (PDT) against MCF-7 breast cancer cells in 2D monolayers and 3D collagen-embedded cell cultures that simulate ECM diffusion, and to confirm direct generation of singlet oxygen (1O2) as the primary cytotoxic species. Methods: MCF-7 breast adenocarcinoma cells and HMEC normal mammary epithelial cells were cultured in 2D monolayers, with MCF-7 cells additionally grown in 3D collagen type I matrices to mimic tumor environments. Cells were incubated with 50 µM ICG for 30 min, washed, and irradiated with a 780 nm diode laser at 39.8 mW/cm2. Cell viability was quantified using the Muse® Count & Viability assay at multiple time points, while ICG uptake and penetration were assessed via flow cytometry, fluorescence microscopy, and confocal imaging. Direct 1O2 production was measured through its characteristic 1270 nm phosphorescence using time-resolved near-infrared spectrometry. Results: ICG-PDT reduced MCF-7 viability to 58.3 ± 7.4% in 2D cultures (41.7% cell kill, p < 0.0001) and 70.2 ± 10.7% in 3D cultures (29.8% cell kill, p = 0.0002). In contrast, normal HMECs maintained 91.0 ± 1.3% viability (only 9% reduction, p = 0.08), resulting in a therapeutic index of approximately 4.6. IC50 values in 2D MCF-7 cultures decreased over time from 51.4 ± 3.0 µM at 24 h to 27.3 ± 3.0 µM at 72 h. ICG uptake was higher in 2D (78%) than in 3D (65%) MCF-7 cultures, with diffusion in 3D collagen exhibiting linear depth-dependent penetration. Notably, the singlet-oxygen phosphorescence signal, though weak and requiring highly sensitive detectors, provided direct evidence of efficient 1O2 generation. Conclusions: ICG as a photosensitizer in photodynamic therapy using clinically compatible parameters is highly cytotoxic to MCF-7 breast cancer cells while largely sparing HMECs in 2D cell culture. Direct spectroscopic evidence confirms efficient 1O2 generation, which contributes significantly to the cytotoxicity. The reduced efficacy in 3D versus 2D models highlights the importance of penetration barriers also present in solid tumors. These results support further preclinical and clinical investigation of ICG as a dual imaging-and-therapy (theragnostic) agent for selective photodynamic treatment of breast cancer.
