Red and Near-Infrared Absorbing DicyanomethyleneSquaraine Cyanine Dyes: PhotophysicochemicalProperties and Anti-Tumor Photosensitizing Effects.

Tiago D Martins,Paulo Almeida,Lucinda V Reis,Diana Ferreira,Renato E Boto,José R Fernandes,Eurico Lima,Luis F V Ferreira,Amélia M Silva

doi:10.3390/ma13092083

Abstract

Photodynamic therapy is a medical modality developed for the treatment of several diseases of oncological and non-oncological etiology that requires the presence of a photosensitizer, light and molecular oxygen, which combined will trigger physicochemical reactions responsible for reactive oxygen species production. Given the scarcity of photosensitizers that exhibit desirable characteristics for its potential application in this therapeutic strategy, the main aims of this work were the study of the photophysical and photochemical properties and the photobiological activity of several dicyanomethylene squaraine cyanine dyes. Thus, herein, the study of their aggregation character, photobleaching and singlet oxygen production ability, and the further application of the previously synthesized dyes in Caco-2 and HepG2 cancer cell lines, to evaluate their phototherapeutic effects, are described. Dicyanomethylene squaraine dyes exhibited moderate light-stability and, despite the low singlet oxygen quantum yields, were a core of dyes that exhibited relevant in vitro photodynamic activity, as there was an evident increase in the toxicity of some of the tested dyes exclusive to radiation treatments.

Highlights

Photodynamic therapy is a successful and clinically approved medical technique used in the treatment of oncological and non-oncological diseases [1,2], which is based on the interaction between a photosensitizer compound, light stimuli and molecular oxygen [3]
Thespecies ground state absorption spectra strategy of the squaraine dyes 1–5 were studied in dimethyl
1–5 were studied in dimethyl sulfoxide sulfoxide (Figure 2), reaching values between 678 and 689 nm

Summary

Introduction

Photodynamic therapy is a successful and clinically approved medical technique used in the treatment of oncological and non-oncological diseases [1,2], which is based on the interaction between a photosensitizer compound, light stimuli and molecular oxygen [3]. The discovery of novel, more efficient photosensitizers, presenting fewer side effects, namely squaraine cyanine dyes, has been explored by several research groups [7,8,9], since the photosensitizers hitherto marketed, mainly porphyrins and their derivatives, have several disadvantages, for instance, poor light absorption and cutaneous photosensitivity [10] For this purpose, there are some required characteristics to be considered as an ideal photosensitizer, namely: the ability to selectively accumulate in the target tissue, light absorption at high wavelengths, more precisely within the “phototherapeutic window” (600–850 nm); to be innocuous in the absence of radiation; to have a high singlet oxygen quantum yield; and to be eliminated from the body [11,12]

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