Basic Study
Copyright ©The Author(s) 2022. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Clin Oncol. Nov 24, 2022; 13(11): 880-895
Published online Nov 24, 2022. doi: 10.5306/wjco.v13.i11.880
Folate receptor-targeted near-infrared photodynamic therapy for folate receptor-overexpressing tumors
Winn Aung, Atsushi B Tsuji, Kenjiro Hanaoka, Tatsuya Higashi
Winn Aung, Atsushi B Tsuji, Tatsuya Higashi, Department of Molecular Imaging and Theranostics, Institute for Quantum Medical Science, National Institutes for Quantum and Radiological Science and Technology, Chiba 263-8555, Japan
Kenjiro Hanaoka, Faculty of Pharmacy and Graduate School of Pharmaceutical Sciences, Keio University, Tokyo 105-8512, Japan
Author contributions: Aung W designed the study, conducted most of the experiments, analyzed the data, and wrote the manuscript; Hanaoka K, designed, synthesized, and provided the folate-Si-rhodamine-1; Tsuji AB and Higashi T coordinated the research and contributed to manuscript preparation; all authors critically reviewed and approved the final version of the article.
Supported by a Grant-in-Aid for Scientific Research (C) from the Japan Society for the Promotion of Science, No. 21K07740 (to Aung W).
Institutional animal care and use committee statement: This study was reviewed and approved by the Institutional Review Board of National Institute for Quantum and Radiological Science and Technology, No. 13-1022-9.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
Data sharing statement: All relevant data were presented in the manuscript. Further information is available from the corresponding author.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Corresponding author: Winn Aung, MBBS, PhD, Senior Researcher, Department of Molecular Imaging and Theranostics, Institute for Quantum Medical Science, National Institutes for Quantum and Radiological Science and Technology, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan.
Received: August 3, 2022
Peer-review started: August 3, 2022
First decision: August 29, 2022
Revised: September 12, 2022
Accepted: October 18, 2022
Article in press: October 18, 2022
Published online: November 24, 2022

Photodynamic therapy (PDT) is a minimally invasive form of cancer therapy, and the development of a novel photosensitizer (PS) with optimal properties is important for enhancing PDT efficacy. Folate receptor (FR) membrane protein is frequently overexpressed in 40% of human cancer and a good candidate for tumor-specific targeting. Specific active targeting of PS to FR can be achieved by conjugation with the folate moiety. A folate-linked, near-infrared (NIR)-sensitive probe, folate-Si-rhodamine-1 (FolateSiR-1), was previously developed and is expected to be applicable to NIR-PDT.


To investigate the therapeutic efficacy of NIR-PDT induced by FolateSiR-1, a FR-targeted PS, in preclinical cancer models.


FolateSiR-1 was developed by conjugating a folate moiety to the Si-rhodamine derivative through a negatively charged tripeptide linker. FR expression in the designated cell lines was examined by western blotting (WB). The selective binding of FolateSiR-1 to FR was confirmed in FR overexpressing KB cells (FR+) and tumors by fluorescence microscopy and in vivo fluorescence imaging. Low FR expressing OVCAR-3 and A4 cell lines were used as negative controls (FR-). The NIR light (635 ± 3 nm)-induced phototoxic effect of FolateSiR-1 was evaluated by cell viability imaging assays. The time-dependent distribution of FolateSiR-1 and its specific accumulation in KB tumors was determined using in vivo longitudinal fluorescence imaging. The PDT effect of FolateSiR-1 was evaluated in KB tumor-bearing mice divided into four experimental groups: (1) FolateSiR-1 (100 μmol/L) alone; (2) FolateSiR-1 (100 μmol/L) followed by NIR irradiation (50 J/cm2); (3) NIR irradiation (50 J/cm2) alone; and (4) no treatment. Tumor volume measurement and immunohistochemical (IHC) and histological examinations of the tumors were performed to analyze the effect of PDT.


High FR expression was observed in the KB cells by WB, but not in the OVCAR-3 and A4 cells. Substantial FR-specific binding of FolateSiR-1 was observed by in vitro and in vivo fluorescence imaging. Cell viability imaging assays showed that NIR-PDT induced cell death in KB cells. In vivo longitudinal fluorescence imaging showed rapid peak accumulation of FolateSiR-1 in the KB tumors 2 h after injection. In vivo PDT conducted at this time point caused tumor growth delay. The relative tumor volumes in the PDT group were significantly reduced compared to those in the other groups [5.81 ± 1.74 (NIR-PDT) vs 12.24 ± 2.48 (Folate-SiR-1), vs 11.84 ± 3.67 (IR), vs 12.98 ± 2.78 (Untreated), at Day 16, P < 0.05]. IHC analysis revealed reduced proliferation marker Ki-67-positive cells in the PDT treated tumors, and hematoxylin-eosin staining revealed features of necrotic- and apoptotic cell death.


FolateSiR-1 has potential for use in PDT, and FR-targeted NIR-PDT may open a new effective strategy for the treatment of FR-overexpressing tumors.

Keywords: Photodynamic therapy, Near-infrared, Photosensitizer, Folate receptor, Fluorescence, Cancer

Core Tip: Photodynamic therapy (PDT) is a minimally invasive cancer therapy and photosensitizers (PS) with optimal properties are crucial for enhancing the efficacy of PDT. We evaluated the therapeutic efficacy of a folate receptor (FR)-targeted, near-infrared (NIR)-sensitive PS (FolateSiR-1). FolateSiR-1 showed FR specificity in vitro and in vivo and functions as a tumor-damaging PS by inducing necrosis, apoptosis, and cell growth inhibition upon activation with NIR light. Our findings suggest that FolateSiR-1 is effective in FR-targeted NIR-PDT with low side effects and has potential for presenting new and effective treatment options for FR-overexpressing tumors.