Date Published: December 19, 2017
Publisher: John Wiley and Sons Inc.
Author(s): Ilkoo Noh, DaeYong Lee, Heegon Kim, Chan‐Uk Jeong, Yunsoo Lee, Jung‐Oh Ahn, Hoon Hyun, Ji‐Ho Park, Yeu‐Chun Kim.
A noninvasive and selective therapy, photodynamic therapy (PDT) is widely researched in clinical fields; however, the lower efficiency of PDT can induce unexpected side effects. Mitochondria are extensively researched as target sites to maximize PDT effects because they play crucial roles in metabolism and can be used as cancer markers due to their high transmembrane potential. Here, a mitochondria targeting photodynamic therapeutic agent (MitDt) is developed. This photosensitizer is synthesized from heptamethine cyanine dyes, which are conjugated or modified as follows. The heptamethine meso‐position is conjugated with a triphenylphosphonium derivative for mitochondrial targeting, the N‐alkyl side chain is modified for regulation of charge balance and solubility, and the indolenine groups are brominated to enhance reactive oxygen species generation (ROS) after laser irradiation. The synthesized MitDt increases the cancer uptake efficiency due to the lipo‐cationic properties of the triphenylphosphonium, and the PDT effects of MitDt are amplified after laser irradiation because mitochondria are susceptible to ROS, the response to which triggers an apoptotic anticancer effect. Consequently, these hypotheses are demonstrated by in vitro and in vivo studies, and the results indicate strong potential for use of MitDts as efficient single‐molecule‐based PDT agents for cancer treatment.
Phototherapy methods, including photodynamic therapy (PDT), have been intensively studied in clinical fields as a method to solve drug resistance, frequent relapses, and toxicity, which are problems associated with the use of conventional therapeutic agents.1, 2 PDT is a process by which a photosensitizer (PS) absorbs light energy and then converts oxygen to singlet oxygen or free radicals, resulting in programmed cell death.1 The therapeutic effect of PDT is achieved by the formation of singlet oxygen and free radicals after laser irradiation; it thus has characteristics other than those of other therapeutic agents. The advantages of PDT are that it is a noninvasive treatment and the generated reactive oxygen species (ROS) have a short lifetime and diffusion range (0.1 µm); treatment at restricted sites is therefore possible.2, 3 However, PDT also has some drawbacks as a first‐line therapy because its effectiveness is reduced when the oxygen supply is lowered in tumors due to their microvessel structure and microcirculation, and because of oxygen consumption by the PDT process.4 In addition, PDT agents may cause genetic variation when they are taken up by organelles such as the nucleus.5 In order to overcome these drawbacks, research has been conducted to develop a PS target site where there is a mechanism for action by PDT.6
In summary, MitDt‐1 was developed in this work as a PDT agent capable of targeting cancerous mitochondria. Synthesis of this photodynamic therapeutic agent was based on cyanine dye, and the agent was composed of a TPP moiety, quaternary ammonium, and brominated indolenine groups. The photochemical properties of the synthesized dye indicated (and were confirmed) to be sensitive to a wavelength in the NIR region, and the brominated dye group had a high singlet oxygen production rate. Moreover, MitDt‐1 accumulated in the mitochondria of the human cancer cell lines (NCI‐H460 and MCF‐7) via charge and lipocationic properties at TPP sites. We could also confirm that ROS production was amplified according to the on–off state of the 662 nm single laser, proving that intensive and effective photodynamic therapy is possible for the target cancer in vitro and in vivo by mitochondria destabilization apoptosis. Consequently, MitDt‐1 allowed outstanding phototherapy and is a promising structure for a cyanine dye based PDT system for cancer therapy.
Materials: N,N‐dimethylformamide anhydrous, 1,3‐propane sultone, 3‐bromopropionic acid, 2,3,3‐trimethylindolenine, (3‐bromopropyl)trimethylammonium bromide, phosphorus pentachloride, acetic acid, 4‐bromophenylhydrazine hydrochloride, DPBS (10 × 10−3m, pH 7.4), and DMEM were obtained from Sigma‐Aldrich. Triphenylphosphine, toluene anhydrous, methyl tert‐butyl ether, 3‐bromopropylamine hydrobromide, acetonitrile anhydrious, and triethylamine were obtained from alfa‐aesar. Aniline and cyclohexanone were obtained from Tokyo Chemical Industry. Ethanol, methanol, diethyl ether, sodium acetate, tetrahydrofuran, n‐hexane, and ethyl acetate were obtained Daejung chemical and metal. All chemicals were used without further purification. All reactions were performed under argon and monitored by thin layer chromatography.
The authors declare no conflict of interest.