Measurement of Cyanine Dye Photobleaching in Photosensitizer Cyanine Dye Conjugates Could Help in Optimizing Light Dosimetry for Improved Photodynamic Therapy of Cancer

Abstract

Photodynamic therapy (PDT) of cancer is dependent on three primary components: photosensitizer (PS), light and oxygen. Because these components are interdependent and vary during the dynamic process of PDT, assessing PDT efficacy may not be trivial. Therefore, it has become necessary to develop pre-treatment planning, on-line monitoring and dosimetry strategies during PDT, which become more critical for two or more chromophore systems, for example, PS-CD (Photosensitizer-Cyanine dye) conjugates developed in our laboratory for fluorescence-imaging and PDT of cancer. In this study, we observed a significant impact of variable light dosimetry; (i) high light fluence and fluence rate (light dose: 135 J/cm2, fluence rate: 75 mW/cm2) and (ii) low light fluence and fluence rate (128 J/cm2 and 14 mW/cm2 and 128 J/cm2 and 7 mW/cm2) in photobleaching of the individual chromophores of PS-CD conjugates and their long-term tumor response. The fluorescence at the near-infrared (NIR) region of the PS-NIR fluorophore conjugate was assessed intermittently via fluorescence imaging. The loss of fluorescence, photobleaching, caused by singlet oxygen from the PS was mapped continuously during PDT. The tumor responses (BALB/c mice bearing Colon26 tumors) were assessed after PDT by measuring tumor sizes daily. Our results showed distinctive photobleaching kinetics rates between the PS and CD. Interestingly, compared to higher light fluence, the tumors exposed at low light fluence showed reduced photobleaching and enhanced long-term PDT efficacy. The presence of NIR fluorophore in PS-CD conjugates provides an opportunity of fluorescence imaging and monitoring the photobleaching rate of the CD moiety for large and deeply seated tumors and assessing PDT tumor response in real-time.

A Pyropheophorbide Analogue Containing a Fused Methoxy Cyclohexenone Ring System Shows Promising Cancer‐Imaging Ability

“…To further confirm the differencei ns inglet oxygen producing ability of chlorins 2 and 4 under physiological conditions, the PSs were dissolved in albumin-containing aqueous solutions, and these formulations were subjected to in vitro PDT efficacy and photobleaching studies. Photobleaching [24] is the destruction of the fluorophore caused by the photochemical reaction of singlet oxygen resulting in compounds that either no longer fluoresce or have fluorescencec haracteristics that are altered.T his occurs either by cleavage of certainc ovalent bonds or nonspecific reactions between the ROS (e.g.,s inglet oxygen) and the molecule. [25,26] Therefore, the rate of photobleachingo ft he PS depends on:1 )the availability of oxygen, 2) the photostabilityo ft he PS, and 3) the singlet oxygen (or other ROS).…”

Cationic High Molecular Weight Lignin Polymer: A Flocculant for the Removal of Anionic Azo-Dyes from Simulated Wastewater

“…The filtrates were collected and the concentration of dye remaining in the filtrates was measured using the calibration formula listed in Table 2 by a UV/Vis spectrophotometer (Genesys 10s). The dye removal was calculated based on equation 1 [20,40,41]: (1) Where A0 and A are the absorbance of the dye solutions before and after the addition of lignin-METAC. The chemical oxygen demand (COD) of the simulated dye solutions (100 mg/L of dye concentration) was measured before and after the addition of lignin-METAC using YSI CR2200 COD thermo reactor.…”

Safety and delivery efficiency of a photodynamic treatment of the lungs using indocyanine green and extracorporeal near infrared illumination

“…Since photobleaching is an indication of the presence of the photodynamic reaction, detecting its presence and demonstrating the integrity of the tissue provides proof of the safety of the protocol. [13] 2 | MATERIALS AND METHODS…”