Flavylium-Based Hypoxia-Responsive Probe for Cancer Cell Imaging.

Thitima Pewklang,Anyanee Kamkaew,Sirawit Wet-Osot,Rung-Yi Lai,Kantapat Chansaenpak,Sirilak Wangngae,Mongkol Sukwattanasinitt,Chuthamat Duangkamol,Utumporn Ngivprom,Parinya Noisa

doi:10.3390/molecules26164938

Abstract

A hypoxia-responsive probe based on a flavylium dye containing an azo group (AZO-Flav) was synthesized to detect hypoxic conditions via a reductase-catalyzed reaction in cancer cells. In in vitro enzymatic investigation, the azo group of AZO-Flav was reduced by a reductase in the presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH) followed by fragmentation to generate a fluorescent molecule, Flav-NH2. The response of AZO-Flav to the reductase was as fast as 2 min with a limit of detection (LOD) of 0.4 μM. Moreover, AZO-Flav displayed high enzyme specificity even in the presence of high concentrations of biological interferences, such as reducing agents and biothiols. Therefore, AZO-Flav was tested to detect hypoxic and normoxic environments in cancer cells (HepG2). Compared to the normal condition, the fluorescence intensity in hypoxic conditions increased about 10-fold after 15 min. Prolonged incubation showed a 26-fold higher fluorescent intensity after 60 min. In addition, the fluorescence signal under hypoxia can be suppressed by an electron transport process inhibitor, diphenyliodonium chloride (DPIC), suggesting that reductases take part in the azo group reduction of AZO-Flav in a hypoxic environment. Therefore, this probe showed great potential application toward in vivo hypoxia detection.

Highlights

Solid tumor growth is restricted by vascularization, which requires oxygen and nutrient supply
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The results showed that the fluorescence signals of the reduction product (Flav-NH2) were quite stable in the acidic to neutral pH range, whereas the emission intensity dropped about 10–20% in the basic solution

Summary

Introduction

Solid tumor growth is restricted by vascularization, which requires oxygen and nutrient supply. It has been reported that the median oxygen concentration is around 4% in some solid tumors and can be decreased to as low as 0% in a certain area [1,2]. Such low oxygen conditions in tumors are known as hypoxia, which is primarily due to variations in microcirculation and temporary disturbance in oxygen perfusion [3]. Hypoxia could regulate the expression of several genes by the stabilization of hypoxia-inducible factor 1α (HIF-1α), leading to various biological phenomena [6]. The detection of hypoxia is an important approach to investigate its biological effects

Methods

Results

Conclusion