Abstract
We developed a pH dependent amino heptamethine cyanine based theranostic probe (I2-IR783-Mpip) that can be activated by near infrared light. I2-IR783-Mpip, in acidic condition, exhibited an intense, broad NIR absorption band (820–950 nm) with high singlet oxygen generation upon exposure to NIR light (~850 nm). Theoretical calculations showed that the protonation of the probe in an acidic environment decreased the molecular orbital energy gaps and increased the intramolecular charge transfer efficiency. I2-IR783-Mpip exhibited good photodynamic efficiency towards liver hepatocellular carcinoma cells under physiological and slightly acidic conditions while normal human embryonic kidney cells remained alive under the same conditions. Detection of intracellular reactive oxygen species (ROS) in cells treated with I2-IR783-Mpip after NIR light exposure confirmed PDT efficiency of the probe in acidic environment. Moreover, I2-IR783-Mpip also demonstrated efficient phototoxicity under deep-seated tumour cell system. We believed this is the first PDT agent that possesses intrinsic tumour binding and selectively eradicate tumour in acidic environment under 850 nm NIR lamp.
Highlights
Photodynamic therapy (PDT) is an attractive non-invasive technique for treating cancers
Hcyanine derivative IR783 was selected as a NIR fluorophore because of its good biocompatibility, optimized emission wavelength and intracellular uptake via organic anion-transporting polypeptides (OATPs)
At neutral pH, the fluorescence of I2-IR783-Mpip is expected to be quenched by the effect from the nitrogen lone pair electrons of N-methylpiperazine moiety through a photoinduced electron transfer (PeT) process[19]
Summary
Photodynamic therapy (PDT) is an attractive non-invasive technique for treating cancers. IR2 was reported as a pH switchable NIR fluorescence and photothermal agent by adjusting the intramolecular charge transfer (ICT) efficiency using dimethylamine group. We developed a Hcyanine based theranostic probe (I2-IR783-Mpip) for NIR fluorescent imaging and PDT that aimed to target cancer cells via OATPs and the protonation in acidic tumour environment. Our probe showed remarkably red-shifted NIR absorbance in acidic pH, which has not been reported elsewhere These phenomena are beneficial for activating such PDT agent using long wavelength of light, i.e. 850 nm, to reach highest possible penetration depth in NIR-I region[6] while high fluorescence is still remained
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