Porphyrin Bleaching and PDT-induced Spectral Changes are Irradiance Dependent in ALA-sensitized Normal Rat Skin In Vivo¶

NIR-II Ratiometric Chemiluminescent/Fluorescent Reporters for Real-Time Monitoring and Evaluating Cancer Photodynamic Therapy Efficacy

The development of probes for early monitoring tumor therapy response may greatly benefit the promotion of photodynamic therapy (PDT) efficacy. Singlet oxygen (¹ O₂ ) generation is a typical indicator for evaluating PDT efficacy in cancer. However, most existing probes cannot quantitatively detect ¹ O₂ in vivo due to the high reactivity and transient state, and thus have a poor correlation with PDT response. Herein, a ¹ O₂ -responsive theranostic platform comprising thiophene-based small molecule (2SeFT-PEG) and photosensitizer Chlorin e6 (Ce6) micelles for real-time monitoring PDT efficacy is developed. After laser irradiation, the Ce6-produced ¹ O₂ could simultaneously kill cancer and trigger 2SeFT-PEG to produce increased chemiluminescence (CL) and decreased fluorescence (FL) signals variation at 1050 nm in the second near-infrared (NIR-II, 950-1700 nm) window. Significantly, the ratiometric NIR-II CL/FL imaging at 1050 nm could effectively quantify and monitor the concentration of ¹ O₂ and O₂ consumption or recovery, so as to evaluate the therapeutic efficacy of PDT in vivo. Hence, this ¹ O₂ activated NIR-II CL/FL probe provides an efficient ratiometric optical imaging platform for real-time evaluating PDT effect and precisely guiding the PDT process in vivo.

Mass Spectrometric Analysis of the Photobleaching of Protoporphyrin IX Used in Photodynamic Diagnosis and Therapy of Cancer

Photobleaching and photoproduct formations are considered essential phenomena in improving the efficacy of photodynamic diagnosis and therapy (PDD and PDT). We investigated the photobleaching of protoporphyrin IX (PpIX) by measuring its concentration with mass spectrometry (MS). The reduction in the concentration of PpIX dissolved in dimethyl sulfoxide was measured during PDD and PDT conditions using lasers with wavelengths of 405 and 635 nm, respectively, at a power density of 10, 50 or 100 mW/cm² . The obtained results were compared with the results of conventional fluorescence spectroscopy and previously reported results. Our results demonstrate the variation in the MS-based photobleaching coefficient of PpIX with the power density, while the fluorescence-based photobleaching coefficient was independent of the power density. The results of MS also show faster photobleaching of PpIX in comparison with that obtained from fluorescence. The difference may be attributed to the change in the fluorescence quantum yield of PpIX with its concentration and the effect of fluorescence emission from the PpIX photoproducts. Thus, an MS-based investigation of the photobleaching poses to be a more stable investigation form. Our finding highlights the importance of recognizing the potential significance of these discoveries in the PDD and PDT dosimetry and efficacy.

In vivo Spectroscopic Evaluation of the Intraperitoneal Cavity in Canines

As part of a preclinical trial for the treatment of peritoneal carcinomatosis (PC) with photodynamic therapy (PDT), we have assessed changes in optical properties, tissue oxygenation and drug concentration as a result of benzoporphyrin derivative (BPD)-mediated PDT using diffuse reflectance and fluorescence measurements. PDT can effectively treat superficial disease spread, but treatment efficacy is influenced by physical properties of the treated tissue which can change over the treatment time. In this study, healthy canines were given BPD and irradiated with 690 nm light during a partial bowel resection, and spectroscopic and fluorescence measurements were made using an in-house built spectroscopic probe. Hemoglobin concentration, oxygenation and optical properties were determined to be highly heterogeneous between canines and at different anatomical locations within the same subject, so further development of PDT dosimetry systems will need to address this patient and location-specific dose optimization. Compared to other photosensitizers, we found no apparent BPD photobleaching after PDT.

Squaraine Dyes: Molecular Design for Different Applications and Remaining Challenges

Squaraine dyes are a class of organic dyes with strong and narrow absorption bands in the near-infrared. Despite high molar absorptivities and fluorescence quantum yields, these dyes have been less explored than other dye scaffolds due to their susceptibility to nucleophilic attack. Recent strategies in probe design including encapsulation, conjugation to biomolecules, and new synthetic modifications have seen squaraine dyes emerging into the forefront of biomedical imaging and other applications. Herein, we provide a concise overview of (1) the synthesis of symmetrical and unsymmetrical squaraine dyes, (2) the relationship between structure and photophysical properties of squaraine dyes, and (3) current applications of squaraine dyes in the literature. Given the recent successes at overcoming the limitations of squaraine dyes, they show high potential in biological imaging, in photodynamic and photothermal therapies, and as molecular sensors.

Advances in nanomaterials for photodynamic therapy applications: Status and challenges

Photodynamic therapy (PDT), as a non-invasive therapeutic modality that is alternative to radiotherapy and chemotherapy, is extensively investigated for cancer treatments. Although conventional organic photosensitizers (PSs) are still widely used and have achieved great progresses in PDT, the disadvantages such as hydrophobicity, poor stability within PDT environment and low cell/tissue specificity largely limit their clinical applications. Consequently, nano-agents with promising physicochemical and optical properties have emerged as an attractive alternative to overcome these drawbacks of traditional PSs. Herein, the up-to-date advances in the fabrication and fascinating applications of various nanomaterials in PDT have been summarized, including various types of nanoparticles, carbon-based nanomaterials, and two-dimensional nanomaterials, etc. In addition, the current challenges for the clinical use of PDT, and the corresponding strategies to address these issues, as well as future perspectives on further improvement of PDT have also been discussed.

PDT dose dosimetry for Photofrin-mediated pleural photodynamic therapy (pPDT)

Photosensitizer fluorescence excited by photodynamic therapy (PDT) treatment light can be used to monitor the in vivo concentration of the photosensitizer and its photobleaching. The temporal integral of the product of in vivo photosensitizer concentration and light fluence is called PDT dose, which is an important dosimetry quantity for PDT. However, the detected photosensitizer fluorescence may be distorted by variations in the absorption and scattering of both excitation and fluorescence light in tissue. Therefore, correction of the measured fluorescence for distortion due to variable optical properties is required for absolute quantification of photosensitizer concentration. In this study, we have developed a four-channel PDT dose dosimetry system to simultaneously acquire light dosimetry and photosensitizer fluorescence data. We measured PDT dose at four sites in the pleural cavity during pleural PDT. We have determined an empirical optical property correction function using Monte Carlo simulations of fluorescence for a range of physiologically relevant tissue optical properties. Parameters of the optical property correction function for Photofrin fluorescence were determined experimentally using tissue-simulating phantoms. In vivo measurements of photosensitizer fluorescence showed negligible photobleaching of Photofrin during the PDT treatment, but large intra- and inter-patient heterogeneities of in vivo Photofrin concentration are observed. PDT doses delivered to 22 sites in the pleural cavity of 8 patients were different by 2.9 times intra-patient and 8.3 times inter-patient.

Irradiation-induced enhancement of Pc 4 fluorescence and changes in light scattering are potential dosimeters for Pc 4-PDT

Phthalocyanine 4 (Pc 4) is a promising photosensitizer currently in clinical trials. Photobiological responses to Pc 4 photodynamic therapy (Pc 4-PDT) have been characterized extensively, but relatively little has been done to evaluate dose metrics for this sensitizer. We describe an irradiation-induced increase in fluorescence in tumor cell monolayers. This increase is due solely to enhanced fluorescence from Pc 4, as confirmed by confocal spectroscopy. In EMT6 cells incubated with 250 nM Pc 4 for 24 h, the maximum increase in fluorescence is approximately 3.7-fold above baseline levels. This increase occurs over a range of fluences, 0.05-0.6 J cm(-2), where clonogenic survival decreases by 3 orders of magnitude. Light scattering measurements performed on similarly treated EMT6 cells in suspension suggested a Pc 4-PDT-mediated mitochondrial swelling of approximately 13% at 0.6 J cm(-2), where fluorescence enhancement saturates under these treatment conditions. Fluorescence imaging and light scattering experiments performed at a five-fold lower Pc 4 incubation concentration revealed a reduced fluorescence enhancement at a five-fold higher fluence, which produced comparable mitochondrial swelling. Taken together, these data suggest that Pc 4 is initially aggregated at high local concentration in mitochondria and that irradiation relaxes the quenching of Pc 4 fluorescence through a mechanism that may involve mitochondrial swelling.