Influence of Polymer Charge on the Localization and Dark- and Photo-Induced Toxicity of a Potential Type I Photosensitizer in Cancer Cell Models.

Mikael Lindgren,Lena Chen,Monica Siksjø,Tom A Hansen,Bastien Mettra,Cyrille Monnereau,Odrun A Gederaas,Chantal Andraud

doi:10.3390/molecules25051127

Abstract

A current trend within photo-dynamic therapy (PDT) is the development of molecular systems targeting hypoxic tumors. Thus, type I PDT sensitizers could here overcome traditional type II molecular systems that rely on the photo-initiated production of toxic singlet oxygen. Here, we investigate the cell localization properties and toxicity of two polymeric anthracene-based fluorescent probes (neutral Ant-PHEA and cationic Ant-PIm). The cell death and DNA damage of Chinese hamster ovary cancer cells (CHO-K1) were characterized as combining PDT, cell survival studies (MTT-assay), and comet assay. Confocal microscopy was utilized on samples incubated together with either DRAQ5, Lyso Tracker Red, or Mito Tracker Deep Red in order to map the localization of the sensitizer into the nucleus and other cell compartments. While Ant-PHEA did not cause significant damage to the cell, Ant-PIm showed increased cell death upon illumination, at the cost of a significant dark toxicity. Both anthracene chromophores localized in cell compartments of the cytosol. Ant-PIm showed a markedly improved selectivity toward lysosomes and mitochondria, two important biological compartments for the cell’s survival. None of the two anthracene chromophores showed singlet oxygen formation upon excitation in solvents such as deuterium oxide or methanol. Conclusively, the significant photo-induced cell death that could be observed with Ant-PIm suggests a possible type I PDT mechanism rather than the usual type II mechanism.

Highlights

IntroductionMolecules 2020, 25, 1127 reactive oxygen species upon illumination (type II photo-dynamic therapy (PDT)) alternative photo-redox mechanisms exist (type I) [2]
We report on a comparative study on the localization of the polycationic imidazolium-substituted probe (Ant-PIm) vs. the hydroxyl-substituted probe (Ant-PHEA) with structures shown in Figure 1, and on their respective dark and light-induced cytotoxicity’s in CHO-K1 cells
The two photo-sensitizers showed very similar absorption spectra but the emission of Ant-PIm shifted by approx. 15 nm in water or physiological serum. This is a direct consequence of the ionic nature of the polymer chain, which reinforces the polarity of the chromophore’s local environment, thereby affecting the excited state relaxation processes

Summary

Introduction

Molecules 2020, 25, 1127 reactive oxygen species upon illumination (type II PDT) alternative photo-redox mechanisms exist (type I) [2]. While most PDT probes developed either in the context of fundamental research and clinical applications focus on a type II PDT mechanism (i.e., energy transfer to triplet molecular oxygen, resulting in the build-up of cytotoxic 1 O2 within the cell), tumor micro-environments are often hypoxic, which may limit the success of this therapeutic approach, especially in the case of advanced cancers [3]. The development of complementary strategies relying on type I PDT (direct redox mechanism between the excited state of the PS and its environment such as water or biomolecules) is a valuable alternative to circumvent this limitation [4,5]. After or during PDT, cells undergo apoptosis or necrosis.

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Conclusion