Buhong Li

Photosensitized singlet oxygen generation and detection: Recent advances and future perspectives in cancer photodynamic therapy

Photodynamic therapy (PDT) uses photosensitizers and visible light in combination with molecular oxygen to produce reactive oxygen species (ROS) that kill malignant cells by apoptosis and/or necrosis, shut down the tumor microvasculature and stimulate the host immune system. The excited singlet state of oxygen (1 O2 ) is recognized to be the main cytotoxic ROS generated during PDT for the majority of photosensitizers used clinically and for many investigational new agents, so that maximizing its production within tumor cells and tissues can improve the therapeutic response, and several emerging and novel approaches for this are summarized. Quantitative techniques for 1 O2 production measurement during photosensitization are also of immense importance of value for both preclinical research and future clinical practice. In this review, emerging strategies for enhanced photosensitized 1 O2 generation are introduced, while recent advances in direct detection and imaging of 1 O2 luminescence are summarized. In addition, the correlation between cumulative 1 O2 luminescence and PDT efficiency will be highlighted. Meanwhile, the validation of 1 O2 luminescence dosimetry for PDT application is also considered. This review concludes with a discussion on future demands of 1 O2 luminescence detection for PDT dosimetry, with particular emphasis on clinical translation. Eye-catching color image for graphical abstract.

Pattern recognition of multiple excitation autofluorescence spectra for colon tissue classification

OBJECTIVES The aim of this study was to explore the usefulness of multiple excitation autofluorescence (AF) and a spectral feature-based pattern recognition in classification of colon tissues. MATERIALS AND METHODS Under four different excitation wavelengths (337, 375, 405 and 460 nm), AF spectra of freshly excised normal and adenocarcinoma colon tissues were measured. Pattern recognition method including features extraction, data reduction using principal component analysis (PCA) and Fishers discriminant analysis (FDA) were performed for classification. RESULTS There was a significantly difference between spectral patterns of normal and adenocarcinoma tissues. Compared with the other three excitation wavelengths, the AF spectra obtained under 337 nm excitation provided more diagnostic information, but also more sensitive to the trivial change resulted from neoplastic transformation. For discriminating normal from adenocarcinoma tissues, the sensitivity, specificity and accuracy using 337 nm excitation in the present study were 88.9%, 80.0% and 83.9%, respectively. Compared these values with those determined from multispectral data analysis, our findings indicate that the latter has higher specificity while maintaining the same sensitivity (sensitivity 88.9% vs. 88.9%, specificity 91.4% vs. 80.0%, and accuracy 90.3% vs. 83.9%). CONCLUSION This study suggests that the pattern recognition of the multiple excitation AF spectra is an effective algorithm for improving the diagnostic accuracy of adenocarcinoma.

Detection system for singlet oxygen luminescence in photodynamic therapy

Singlet oxygen (1O2) is widely considered to play a major role in photodynamic therapy (PDT), and thus an increasing attention has been focused on the direct detection of 1O2 near-infrared luminescence around 1270 nm for PDT dosimetry. A new sensitive detection system is developed to directly measure the temporal and spectral resolved 1O2 luminescence spectra. The triplet state and 1O2 lifetimes of Rose Bengal as a model photosensitizer in different solvents are determined, and the obtained results agree well with the published data. Our detection system has the potential application in 1O2 luminescence-based PDT dosimetry.

Direct imaging of singlet oxygen luminescence generated in blood vessels during photodynamic therapy

Singlet oxygen (1O2) is commonly recognized to be a major phototoxic component for inducing the biological damage during photodynamic therapy (PDT). In this study, a novel configuration of a thermoelectrically-cooled near-infrared sensitive InGaAs camera was developed for imaging of photodynamically-generated 1O2 luminescence. The validation of 1O2 luminescence images for solution samples was performed with the model photosensitizer Rose Bengal (RB). Images of 1O2 luminescence generated in blood vessels in vivo in a well-controlled dorsal skinfold window chamber model were also recorded during PDT. This study demonstrated the capacity of the newly-developed imaging system for imaging of 1O2 luminescence, and the first reported images of 1O2 luminescence in blood vessels in vivo. This system has potential for elucidating the mechanisms of vascular targeted PDT.

Advanced optical techniques for monitoring dosimetric parameters in photodynamic therapy

Photodynamic therapy (PDT) is based on the generation of highly reactive singlet oxygen through interactions of photosensitizer, light and molecular oxygen. PDT has become a clinically approved, minimally invasive therapeutic modality for a wide variety of malignant and nonmalignant diseases. The main dosimetric parameters for predicting the PDT efficacy include the delivered light dose, the quantification and photobleaching of the administrated photosensitizer, the tissue oxygen concentration, the amount of singlet oxygen generation and the resulting biological responses. This review article presents the emerging optical techniques that in use or under development for monitoring dosimetric parameters during PDT treatment. Moreover, the main challenges in developing real-time and noninvasive optical techniques for monitoring dosimetric parameters in PDT will be described.

Characterizing autofluorescence generated from endogenous porphyrins in cancerous tissue of human colon: case studies

The aim of this case study was to explore the relationship between porphyrins and colon adenocarcinoma, and to examine the potential of porphyrin-induced fluorescence for the diagnosis of colon cancer. Further studies were carried on 8 cases ex vivo colon adenocarcinoma samples which exceptionally exhibited 635 nm fluorescence emission under 405 nm excitation. The time-resolved fluorescence spectra at 635 nm emission under 405 nm excitation were also measured and two-exponential decay fitting was performed to determine the fluorescence lifetime at 635 nm emission. Significant difference was observed between the spectra of normal and cancer tissues, which included an emission peak at 635 nm under the excitation wavelengths of 405 nm. There was also a significant difference between the fluorescence lifetimes of 635 nm emission of the normal tissue and cancer tissue (P<0.05). These results demonstrate that the spectroscopic analysis method allows a selective detection of adenocarcinoma tissues. This spectral profile and lifetime of the red fluorescence resemble that of porphyrins, which suggests that porphyrin fluorescence may be a useful biomarker for characterizing colon cancers of certain patient populations.

Discriminant analysis for classification of colonic tissue autofluorescence spectra

This study evaluates the potential of a discriminant analysis to classify colonic mucosa from autofluorescence spectral characteristics. With 337 nm excitation, the autofluorescence spectra of colonic tissues were measured using a FLS920 spectrofluorimeter. Principal component analysis (PCA) combined with Fishers discriminant analysis was performed for tissue classification. As a result, the sensitivity and specificity of the discriminant analysis is 92.3% and 90.5%, respectively. The results suggest the relative concentrations of collagen and nicotinamide adenine dinucleotide (NADH) are the potential diagnostic biomarkers for colonic tissue classification using autofluorescence spectroscopy, and the discriminant analysis based on PCA is useful to differentiate adenocarcinoma from normal tissue.

Illumination and projection optics for spatial frequency domain fluorescence imaging

A digital micromirror device (DMD) based structural illumination and projection optical system were designed and evaluated for fluorescence imaging and diffuse reflectance imaging of tissue in spatial frequency domain, respectively. Light emitting diodes (LEDs) at discrete wavelengths (532, 620, 656 nm) provided illumination for the diffuse reflectance imaging while a 532 nm laser diode (LD) was used as excitation light source of photosensitizer (PS) fluorescence. Both the LEDs and LD light were collimated, homogenized and converged on a DMD to generate the structural illumination. A projection lens was also designed to project a rectangular structural illumination spot on target tissue. The designed optical system could be applied to provide variable frequency structural illumination for depth sensitive excitation of PS and diffuse reflectance imaging.

Structural and functional imaging for vascular targeted photodynamic therapy

Vascular targeted photodynamic therapy (V-PDT) has been widely used for the prevention or treatment of vascular-related diseases, such as localized prostate cancer, wet age-related macular degeneration, port wine stains, esophageal varices and bleeding gastrointestinal mucosal lesions. In this study, the fundamental mechanisms of vascular responses during and after V-PDT will be introduced. Based on the V-PDT treatment of blood vessels in dorsal skinfold window chamber model, the structural and functional imaging, which including white light microscopy, laser speckle imaging, singlet oxygen luminescence imaging, and fluorescence imaging for evaluating vascular damage will be presented, respectively. The results indicate that vessel constriction and blood flow dynamics could be considered as the crucial biomarkers for quantitative evaluation of vascular damage. In addition, future perspectives of non-invasive optical imaging for evaluating vascular damage of V-PDT will be discussed.

Detection techniques for singlet oxygen production during photodynamic therapy(Conference Presentation)

Singlet oxygen is widely considered to be the major cytotoxic reactive oxygen species (ROS) generated during photodynamic therapy (PDT). This talk summarizes recent advances and future perspectives in detection techniques for singlet oxygen production, and the advantages and limitations of each technique will be presented. In addition, our custom developed novel configuration of a near-infrared sensitive camera and adaptive optics for in vivo fast imaging of singlet oxygen luminescence around 1270 nm will be highlighted. For clinical PDT application, the challenges for direct measrement of singlet oxygen luminescence will be discussed.