A next-generation bifunctional photosensitizer with improved water-solubility for photodynamic therapy and diagnosis.

Hirotada Nishie,Noriyuki Hayashi,Akihiro Nomoto,Jun-Ichi Kikuchi,Shigenobu Yano,Hiromi Kataoka,Eiji Kubota,Takashi Joh,Atsushi Narumi

doi:10.18632/oncotarget.12366

Abstract

Photodynamic therapy (PDT) exploits light interactions and photosensitizers to induce cytotoxic reactive oxygen species. Photodynamic diagnosis (PDD) uses the phenomenon of photosensitizer emitting fluorescence to distinguish some tumors from normal tissue. The standard photosensitizer used for PDD is 5-aminolevulinic acid (5-ALA), although it is not entirely satisfactory. We previously reported glucose-conjugated chlorin (G-chlorin) as a more effective photosensitizer than another widely used photosensitizer, talaporfin sodium (TS); however, G-chlorin is hydrophobic. We synthesized oligosaccharide-conjugated chlorin (O-chlorin) with improved water-solubility. We report herein on its accumulation and cytotoxicity. O-chlorin was synthesized and examined for solubility. Flow cytometric analysis was performed to evaluate O-chlorin accumulation in cancer cells. To evaluate the intracellular localization of photosensitizer, cells were stained with O-chlorin and organelle-specific fluorescent probes. We then measured the in vitro fluorescence of various photosensitizers and the half-maximal inhibitory concentrations to evaluate effects in PDD and PDT, respectively. Xenograft tumor models were established, and antitumor and visibility effects were analyzed. O-chlorin was first shown to be hydrophilic. Flow cytometry then revealed a 20- to 40-times higher accumulation of O-chlorin in cancer cells than of TS, and a 7- to 23-times greater fluorescence than 5-ALA. In vitro, the cytotoxicity of O-chlorin PDT was stronger than that of TS PDT, and O-chlorin tended to accumulate in lysosomes. In vivo, O-chlorin showed the best effect in PDT and PDD compared to other photosensitizers.O-chlorin was hydrophilic and showed excellent tumor accumulation and fluorescence. O-chlorin is promising as a next-generation bifunctional photosensitizer candidate for both PDT and PDD.

Highlights

Photosensitizers are molecules that undergo photochemical reactions in response to specific light irradiation to emit fluorescence
In this study we proved that newly developed O-chlorin Photodynamic therapy (PDT) was superior to talaporfin sodium (TS) PDT, the secondgeneration PDT widely used in Japan, due to increased tumor accumulation and cytotoxicity
We previously reported that conjugating sugar chains onto photosensitizer compounds increases their cellular uptake and antitumor effect, glycoconjugated chlorin reagents should achieve more effective PDT than TS PDT

Summary

Introduction

Photosensitizers are molecules that undergo photochemical reactions in response to specific light irradiation to emit fluorescence. Photodynamic therapy (PDT) exploits this phenomenon to generate reactive oxygen species (ROS) such as singlet oxygen [1, 2], and is an established treatment for cancer and some nonmalignant diseases [2,3,4,5,6]. The same photosensitizers can be used for photodynamic diagnosis (PDD) based on the emission of fluorescence when irradiated in the presence of specific abnormal cells. The first is a direct toxicity action due to ROS generation inside the tumor; the second is a shutdown effect induced by starving the surrounding vessels, leading to tumor infarction; and, the third is a normal immunological mechanism activated via the tumor response to PDT [1, 2, 7, 8]. The photosensitizer, 5-aminolevulinic acid (5ALA), which is converted at the tissue level to its active compound protoporphyrin IX, has been used historically for PDD in many medical fields because it accumulates strongly in tumor cells rather than in normal tissue due to their difference cellular metabolisms [9,10,11,12,13]

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Conclusion