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
Research background

Photodynamic therapy (PDT) is one of the emerging options to combat cancer and it requires photosensitizer (PS) and corresponding light irradiation. The tumor selectivity of the photosensitizer improves tumor localization in PDT, enhances tumor destruction, and reduces side effects due to off-target localization. Folate receptor (FR) membrane protein is frequently overexpressed in human cancer and specific active targeting of PS to FR can be achieved by conjugation with the folate moiety.

Research motivation

We previously developed a folate-linked, near-infrared (NIR)-sensitive probe folate-Si-rhodamine-1 (FolateSiR-1). The feasibility of NIR-PDT using FolateSiR-1 and appropriate light irradiation had not been determined and reqired elucidation.

Research objectives

The aim of this study was to evaluate the photodynamic therapeutic efficacy of FolateSiR-1 in a preclinical cancer model and determine the cell death mode induced by FolateSiR-1-based PDT.

Research methods

FolateSiR-1 was synthesized by conjugating a folate moiety to the Si-rhodamine derivative through a negatively charged tripeptide linker. Utilizing FR-overexpressing cell line KB and low FR-expressing cell lines OVCAR-3 and A4, selective binding of FolateSiR-1 to FR was evaluated by fluorescence microscopy. Cell viability imaging assays was exploited to assess the phototoxic effect of FolateSiR-1. In vivo longitudinal fluorescence imaging was conducted to examine the time-dependent biodistribution of FolateSiR-1 and its specific accumulation in KB tumors. To evaluate PDT efficacy of FolateSiR-1, KB tumor-bearing mice were divided into four groups: (1) FolateSiR-1 alone; (2) FolateSiR-1 followed by NIR irradiation; (3) NIR irradiation alone; and (4) no treatment. Tumor volume measurement, as well as immunohistochemical (IHC) and histological examinations of tumors were performed to determine the effect of PDT.

Research results

FR-specific binding of FolateSiR-1 was observed by fluorescence microscopy and in vivo fluorescence imaging. Cell viability imaging assays indicated that NIR-PDT induced cell death. In vivo longitudinal fluorescence imaging showed rapid peak accumulation of FolateSiR-1 in KB tumors 2 h after injection. The tumor volumes in the PDT group were significantly reduced compared to the other groups (P < 0.05). IHC analysis revealed reduced numbers of proliferation marker Ki-67-positive cells in PDT treated tumors, and hematoxylin-eosin staining revealed features of necrotic- and apoptotic cell death.

Research conclusions

FolateSiR-1 may be effectively utilized in PDT with low side effects, and the FR-targeted NIR-PDT can potentially reveal new strategies for the treatment of FR-overexpressing tumors.

Research perspectives

The fascinating features of FolateSiR-1, including specificity to FR, cytotoxicity in combination with NIR irradiation and relatively fast clearance implying low toxicity, prompted the development of an alternative PS for NIR-PDT. The therapeutic effect was significant after a single dose of irradiation and may be optimized to achieve patient-specific clinical effects. Moreover, fluorescence emission from FolateSiR-1 may be used for real time cancer detection and patient screening for treatment selection. Further research may elucidate these additional details of these processes.