In-Vivo Optical Monitoring of the Efficacy of Epidermal Growth Factor Receptor Targeted Photodynamic Therapy: The Effect of Fluence Rate.

Wei Peng,Dominic J Robinson,Timo L M Ten Hagen,Max J H Witjes,Henriette S De Bruijn,Go M Van Dam,Kristian Berg,Jan L N Roodenburg

doi:10.3390/cancers12010190

Abstract

Targeted photodynamic therapy (PDT) has the potential to improve the therapeutic effect of PDT due to significantly better tumor responses and less normal tissue damage. Here we investigated if the efficacy of epidermal growth factor receptor (EGFR) targeted PDT using cetuximab-IRDye700DX is fluence rate dependent. Cell survival after treatment with different fluence rates was investigated in three cell lines. Singlet oxygen formation was investigated using the singlet oxygen quencher sodium azide and singlet oxygen sensor green (SOSG). The long-term response (to 90 days) of solid OSC-19-luc2-cGFP tumors in mice was determined after illumination with 20, 50, or 150 mW·cm−2. Reflectance and fluorescence spectroscopy were used to monitor therapy. Singlet oxygen was formed during illumination as shown by the increase in SOSG fluorescence and the decreased response in the presence of sodium azide. Significantly more cell death and more cures were observed after reducing the fluence rate from 150 mW·cm−2 to 20 mW·cm−2 both in-vitro and in-vivo. Photobleaching of IRDye700DX increased with lower fluence rates and correlated with efficacy. The response in EGFR targeted PDT is strongly dependent on fluence rate used. The effectiveness of targeted PDT is, like PDT, dependent on the generation of singlet oxygen and thus the availability of intracellular oxygen.

Highlights

Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) that after exposure to light, and in the presence of oxygen, leads to the formation of reactive oxygen species, predominantly singlet oxygen [1]
Our results show that the response to epidermal growth factor receptor (EGFR) targeted photodynamic therapy (PDT) is the result of singlet oxygen formation, that this response is dependent on the fluence rate used, and that in-vivo optical monitoring of IRDye700DX fluorescence photobleaching has potential for predicting therapeutic efficacy
The effect of fluence rate on the cell survival was investigated on the three head and neck cell lines OSC-19-luc2-cGFP, scc-U2 and scc-U8 with an EGFR expression relative to the expression in the OSC-19-luc2-cGFP of 66% in scc-U8 and 70% in scc-U2 as previously determined [23]

Summary

Introduction

Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) that after exposure to light, and in the presence of oxygen, leads to the formation of reactive oxygen species, predominantly singlet oxygen [1]. The efficacy of the treatment is dependent on many factors. Ground state oxygen is needed for formation of singlet oxygen, which means that tissue oxygenation strongly influences treatment efficacy [2]. Illumination with high fluence rates can deplete oxygen levels in both tumor and normal tissue, limiting efficacy [3,4]. Vascular responses that can occur during PDT, such as constriction and thrombus formation, can decrease tumor oxygenation and negatively affect the PDT response [5,6,7,8].

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Results

Conclusion