A feasibility study of singlet oxygen explicit dosmietry (SOED) of PDT by intercomparison with a singlet oxygen luminescence dosimetry (SOLD) system

Detection of singlet oxygen luminescence for experimental corneal rose bengal photodynamic antimicrobial therapy

Rose bengal photodynamic antimicrobial therapy (RB-PDAT) treats corneal infection by activating rose bengal (RB) with green light to produce singlet oxygen (¹O₂). Singlet oxygen dosimetry can help optimize treatment parameters. We present a ¹O₂ dosimeter for detection of ¹O₂ generated during experimental RB-PDAT. The system uses a 520 nm laser and an InGaAs photoreceiver with bandpass filters to detect ¹O₂ luminescence during irradiation. The system was validated in RB solutions and ex vivo in human donor eyes. The results demonstrate the feasibility of ¹O₂ dosimetry in an experimental model of RB-PDAT in the cornea.

Multispectral singlet oxygen and photosensitizer luminescence dosimeter for continuous photodynamic therapy dose assessment during treatment

SIGNIFICANCE

Photodynamic therapy (PDT) involves complex light-drug-pathophysiology interactions that can be affected by multiple parameters and often leads to large variations in treatment outcome from patient to patient. Direct PDT dosimetry technologies have been sought to optimize the control variables (e.g., light dose, drug administration, tissue oxygenation, and patient conditioning) for best patient outcomes. In comparison, singlet oxygen (O21) dosimetry has been tested in various forms to provide an accurate and perhaps comprehensive prediction of the treatment efficacy.

AIM

We discuss an advanced version of this approach provided by a noninvasive, continuous wave dosimeter that can measure near-infrared spectrally resolved luminescence of both photosensitizer (PS) and O21 generated during PDT cancer treatment.

APPROACH

This dosimetry technology uses an amplified, high quantum efficiency InGaAs detector with spectroscopic decomposition during the light treatment to continuously extract the maximum signal of O21 phosphorescence while suppressing the strong PS luminescence background by spectrally fitting the data points across nine narrow band wavelengths. O21 and PS luminescence signals were measured in vivo in FaDu xenograft tumors grown in mice during PDT treatment using Verteporfin as the PS and a continuous laser treatment at 690 nm wavelength.

RESULTS

A cohort of 19 mice was used and observations indicate that the tumor growth rate inhibition showed a stronger correlation with O21 than with just the PS signal.

CONCLUSIONS

These results suggest that O21 measurement may be a more direct dosimeter of PDT damage, and it has potential value as a definitive diagnostic for PDT treatment, especially with spectral separation of the background luminescence and online estimation of the PS concentration.

Use of photodynamic inactivation for in vitro reduction of prevalent bacteria in Fournier's Gangrene

Fournier's Gangrene (FG) is an infectious disease caused by several synergic microbes, with high morbidity and mortality rates; therefore, the search for new less invasive and mutilating treatments, with faster recovery, has been proposed. Surgical intervention, the use of several systemic and topic antibiotics, and hyperbaric oxygen therapy are currently the best approach for the treatment of these patients. The use of Photodynamic Inactivation (PDI) aims to lower morbidity and mortality, by reducing bacterial microbiota and speeding wound healing. In the present study, viable bacteria were separated in four groups: Group L-/F- (no irradiation with red laser and absence of methylene blue photosensitizer), Group L-/F+ (no irradiation with red laser and presence of methylene blue), Group L+/F- (irradiation with red laser and absence of methylene blue) and L+/F+ (irradiation with red laser associated to methylene blue). In all groups, exposure time to treatment was 5, 10 and 15 minutes. The concentration of methylene blue photosensitizer was 0.1mg/L, and the dose of red laser (660nm wave length) was 176.9mW/cm². Following irradiation, the reduction of number of bacteria was evaluated, and the results were expressed in colony forming units (CFU) and as exponential reduction. As the main results, in the L+/F+ group, there were no Clostridium perfringens and Staphylococcus aureus CFUs and there was a reduction of Escherichia coli that was not observed in the other groups.

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.