The influence of different illumination parameters on protoporphyrin IX induced cell death in squamous cell carcinoma cells

Photodynamic Therapy Using a Rose-Bengal Photosensitizer for Hepatocellular Carcinoma Treatment: Proposition for a Novel Green LED-Based Device for In Vitro Investigation

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Despite new treatments, the HCC rate remains important, making it necessary to develop novel therapeutic strategies. Photodynamic therapy (PDT) using a Rose-Bengal (RB) photosensitizer (RB-PDT) could be a promising approach for liver tumor treatment. However, the lack of standardization in preclinical research and the diversity of illumination parameters used make comparison difficult across studies. This work presents and characterizes a novel illumination device based on one green light-emitting diode (CELL-LED-550/3) dedicated to an in vitro RB-PDT. The device was demonstrated to deliver a low average irradiance of 0.62 mW/cm2 over the 96 wells of a multi-well plate. Thermal characterization showed that illumination does not cause cell heating and can be performed inside an incubator, allowing a more rigorous assessment of cell viability after PDT. An in vitro cytotoxic study of the RB-PDT on an HCC cell line (HepG2) demonstrated that RB-PDT induces a significant decrease in cell viability: almost all the cells died after a light dose irradiation of 0.3 J/cm2 using 75 µM of RB (<10% of viability). In conclusion, the RB-PDT could be a therapeutic option to treat unresectable liver lesions and subclinical disease remaining in the post-resection tumor surgical margin.

On the need for standardized reporting of photophysical parameters of in vitro photodynamic therapy studies

In vitro dose escalation experiments are one of the first gatekeepers in therapeutic evaluation and development. This also holds for evaluating novel photosensitizers (PS) and Photodynamic Therapy (PDT) co-therapies as needed to provide dose response guidelines before engaging in further pre-clinical studies. The dose needed to achieve 50% cell kill (LD₅₀) is a standard metric to report the potency of a therapeutic agents that is widely accepted for single-drug therapies. In reporting results of PDT experiments, which involve delivery of both drug and light, it is inherently more complicated to identify such a convenient dose response metric that actually captures the larger space of treatment parameters. In addition to ubiquitous sources of biological variability that apply broadly in biomedical research, PDT treatment efficacy is determined by multiple key parameters that may or may not have been documented, including PS concentration and light fluence, where the latter is itself a function of the spectral properties of the light source used (often not described), not to mention dose rate, fractionation and other parameters that potentially vary between individual studies. It is impossible to compare results between two study when, for example one reports LD₅₀ PS concentration without providing essential light dosimetry details. Motivated by this challenge in comparing outcomes and establishing reproducibility of in vitro PDT studies, we endeavored to perform a meta-analysis of the reporting of PDT results by converting, where possible, the disparately reported experimental details into a consistent metric that could be used to compare across studies. In this context we adopt here the number of photons absorbed by photosensitizers per unit volume to affect a 50% decline in cell survival as a standardized metric. By choosing this metric one can acknowledge the quantum-based generation of cytotoxins. While this metric does not cover every possible source of variability between any two studies, for a PS with known optical properties, this does encapsulate PS concentration as well as irradiance and spectral properties of light delivered. For the sake of focus we adopt this approach for study of reported results with two photosensitizers, Protoporphyrin IX, either synthesized in the cells by aminolevulinic acid or administered exogenously, and Chlorin e6. A literature search was performed to identify in vitro studies with these two photosensitizers and collect necessary information to calculate the absorbed photon LD₅₀ threshold for each study. Only approximately 1/10 of the manuscripts reporting on in vitro studies provide the minimum required information to calculate the threshold values. While the majority of the determined threshold values are within a factor of 10, the range of threshold values spanned close to 7 orders of magnitude for both photosensitizers. To contrast with single-agent therapies, a similar exercise was performed for chemotherapeutic drugs targeting cellular mitosis or tyrosine kinase inhibitors resulted in an LD₅₀ or IC₅₀ range of 1-2 orders of magnitude, with LD₅₀ or IC₅₀ values for a single cell line being within a factor of 5. This review underscores challenges in the reporting of in vitro PDT efficacy. In many cases it takes considerable effort to extract the necessary methodology information to make meaningful comparison between PDT studies. Only when results between studies can be compared is it possible to begin to assess reproducibility which, as shown here, can be a major issue. Hence, guidelines need to be developed and enforced through the peer review process for meaningful reporting of preclinical PDT results in order for the most promising sensitizers and co-therapies to be identified and translated into the clinic.

Identification and pharmacological modification of resistance mechanisms to protoporphyrin-mediated photodynamic therapy in human cutaneous squamous cell carcinoma cell lines

BACKGROUND

Photodynamic therapy (PDT) is clinically approved to treat neoplastic skin diseases such as precursors of cutaneous squamous cell carcinoma (cSCC). In PDT, 5-aminolevulinic acid (5-ALA) drives the selective formation of the endogenous photosensitizer protoporphyrin IX (PpIX). Although 5-ALA PDT is clinically highly effective, resistance might occur due to decreased accumulation of PpIX in certain tumors. Such resistance may be caused by any fundamental step of PpIX accumulation: 5-ALA uptake, PpIX synthesis and PpIX efflux.

METHODS

We investigated PpIX accumulation and photodynamically induced cell death in PDT refractory SCC-13, PDT susceptible A431, and normal human epidermal keratinocytes (NHEK). Expression of genes associated with cellular PpIX kinetics was investigated on mRNA and protein level. PpIX accumulation and cell death upon illumination were pharmacologically manipulated using drugs targeting 5-ALA uptake, PpIX synthesis or efflux.

RESULTS

The experiments indicate that taurine transporter (SLC6A6) is the major pathway for 5-ALA uptake in cSCC cells, while being less important in NHEK. Downregulation of PpIX synthesis enzymes in SCC-13 was counteracted by methotrexate (MTX) treatment, which restored PpIX formation and cell death. PpIX efflux inhibitors targeting ABC transporters led to significantly increased PpIX accumulation in SCC-13, thereby fully overcoming resistance.

CONCLUSIONS

The results indicate a conserved threshold for PpIX accumulation with respect to PDT-resistance. Cells showed increased viability after PDT at PpIX concentrations below 1.5 nM. Selective uptake of 5-ALA via taurine transporter SLC6A6 in cutaneous tumor cells is novel but unrelated to resistance. MTX can partially abrogate resistance by PpIX synthesis enzyme induction, while efflux mechanisms via ABC transporters seem the main driving force and promising drug targets.

Two-step irradiance schedule for condyloma acuminatum and the influencing factors of analgesic effect: A prospective randomized study

BACKGROUND

The two-step irradiance schedule in photodynamic therapy (PDT) is an emerging treatment method with a remarkable analgesic effect. We evaluated the influencing factors of pain in condyloma acuminate (CA) treatment with a two-step irradiance schedule.

METHODS

All patients were randomly divided into a two-step irradiance group and control group. The two-step irradiance group used 40 mW/cm² for the first 8min, followed by 80 mW/cm² for 16 min, while the control group used 80 mW/cm² for 20 min. The Numerical Rating Scale (NRS) scores and pain-influencing factors were recorded accordingly.

RESULTS

In the two-step irradiance and control groups, 64 and 63 patients completed the treatment, respectively. The NRS scores of the two-step irradiance group were significantly lower than that of the control group (p < .001), with a low fluence rate inducing less pain compared with a high fluence rate (p < .001). Moreover, when the total fluence accumulated to 57.6 J/cm² , the pain experienced by patients reached its peak. The NRS score of the urethral orifice group was the highest, and the male external genitalia group was the lowest. The NRS score was at its lowest in the first session and highest in the second session. There was a linear relationship between pain and wart size. Among these influencing factors, the fluence rate had the greatest impact on pain.

CONCLUSION

The two-step irradiance schedule provides better analgesic effects than standard treatment irradiation while showing similar treatment efficacy. Factors that influence pain include high fluence rate, CA at the urethral orifice, second therapy session, wart size, and the interval between CO₂  laser and ALA-PDT.

Systematic Review and Meta-Analysis of In Vitro Anti-Human Cancer Experiments Investigating the Use of 5-Aminolevulinic Acid (5-ALA) for Photodynamic Therapy

5-Aminolevulinic acid (5-ALA) is an amino acid derivative and a precursor of protoporphyrin IX (PpIX). The photophysical feature of PpIX is clinically used in photodynamic diagnosis (PDD) and photodynamic therapy (PDT). These clinical applications are potentially based on in vitro cell culture experiments. Thus, conducting a systematic review and meta-analysis of in vitro 5-ALA PDT experiments is meaningful and may provide opportunities to consider future perspectives in this field. We conducted a systematic literature search in PubMed to summarize the in vitro 5-ALA PDT experiments and calculated the effectiveness of 5-ALA PDT for several cancer cell types. In total, 412 articles were identified, and 77 were extracted based on our inclusion criteria. The calculated effectiveness of 5-ALA PDT was statistically analyzed, which revealed a tendency of cancer-classification-dependent sensitivity to 5-ALA PDT, and stomach cancer was significantly more sensitive to 5-ALA PDT compared with cancers of different origins. Based on our analysis, we suggest a standardized in vitro experimental protocol for 5-ALA PDT.

Split-face study comparing conventional MAL photodynamic therapy in multiple actinic keratosis with complete time vs. half-time red light LED conventional illumination

BACKGROUND

Conventional photodynamic therapy (PDT) with methylaminolevulinic acid (MAL) and daylight PDT have demonstrated similar efficacy in the treatment of actinic keratosis (AK). The reason for the use of daylight is to reduce pain during illumination but daylight has the limitation of the weather conditions. The difference in the doses of red light applied between these two methods suggests that an intermediate dose with red light conventional illumination could be effective in PDT of AK.

OBJECTIVE

To compare the efficiency of conventional MAL-PDT with half-time conventional red light illumination in patients with multiple AK.

MATERIAL AND METHODS

Adult patients with more than five symmetrically distributed AK were selected. After randomization, one area was treated with conventional PDT (Aktilite^® , 630 nm, 37 J/cm² , 8 min), while the contralateral was illuminated half time (Aktilite^® , 630 nm, 37 J/cm² , 4 min). Patients evaluated pain in each different side. Patients were evaluated at baseline, 3 and 6 months after PDT treatment by a blinded dermatologist. A questionnaire to be done at home 24 h after completing treatment was deliver to the patients to evaluate any side-effects.

RESULTS

A total of 774 lesions were treated, 385 with conventional PDT and 389 with half-time PDT (P > 0.05). Conventional PDT was 85% of complete response of AK (327/385) at 3 months, and half-time PDT was 82% (319/389). At 6 months, conventional PDT was 70% (268/385) of complete response and half-time PDT was 65% (252/389). Pain during illumination was significantly lower in the VAS with the half-time protocol with a mean of 5.59 (SD 1.48) vs. 6.41 (SD 1.66) in conventional PDT. No difference in adverse effects was found between protocols.

CONCLUSION

Conventional PDT with half-time illumination in multiple actinic keratosis is as effective as complete time illumination and decreased pain significantly.

Modeling PpIX effective light fluence at depths into the skin for PDT dose comparison

BACKGROUND

Daylight-activated PDT has seen increased support in recent years as a treatment method for actinic keratosis and other non-melanoma skin cancers. The inherent variability observed in broad-spectrum light used in this methodology makes it difficult to plan and monitor light dose, or compare to lamp light doses.

METHODS

The present study expands on the commonly used PpIX-weighted effective surface irradiance metric by introducing a Monte Carlo method for estimating effective fluence rates into depths of the skin. The fluence rates are compared between multiple broadband and narrowband sources that have been reported in previous studies, and an effective total fluence for various treatment times is reported. A dynamic estimate of PpIX concentration produced during pro-drug incubation and treatment is used with the fluence estimates to calculate a photodynamic dose.

RESULTS

Even when there is up to a 5x reduction between the effective surface irradiance of the broadband light sources, the effective fluence below 250 μm depth is predicted to be relatively equivalent. An effective threshold fluence value (0. 70Jeff/cm2) is introduced based on a meta-analysis of previously published ALA-PpIX induced cell death. This was combined with a threshold PpIX concentration (50 nM) to define a threshold photodynamic dose of 0.035 u M Jeff/cm2.

CONCLUSIONS

The threshold was used to generate lookup tables to prescribe minimal treatment times to achieve depth-dependent cytotoxic effect based on incubation times and irradiance values for each light source.

Thermal photodynamic therapy increases apoptosis and reactive oxygen species generation in cutaneous and mucosal squamous cell carcinoma cells

Thermal photodynamic therapy (PDT) is an emerging modality to optimize treatment of pre-cancerous squamous cell carcinoma (SCC) lesions, known as actinic keratoses. Thermal PDT involves heating the tissue, skin, or mucosa above normal skin temperature during 5-aminolevulinic (5-ALA) incubation and irradiating with blue light, which leads to cell apoptosis and reactive oxygen species (ROS) generation. To our knowledge, thermal PDT has not been studied for the treatment of cutaneous or mucosal SCC. We incubated two SCC cell lines with 5-ALA for 30 minutes at temperatures between 21 °C and 42 °C and then irradiated cells with 1000 seconds of blue light. We measured changes in apoptosis, necrosis, and ROS. At 36 °C, there was a dose-dependent increase in apoptosis and ROS generation. Thermal incubation of 5-ALA at 39° and 42 °C followed by blue light increased cell apoptosis and ROS generation compared to untreated control samples incubated at the same temperatures. Thermal PDT may represent a new treatment option for cutaneous and mucosal SCC cancer. Thermal PDT is associated with an increase in SCC cellular apoptosis and is associated with an upregulation in ROS. Clinical trials are required to determine optimal thermal PDT treatment parameters and efficacy for cutaneous and mucosal SCC.

An In Vitro Approach to Photodynamic Therapy

Photodynamic therapy (PDT) is a medical procedure that involves incubation of an exogenously applied photosensitizer (PS) followed by visible light photoactivation to induce cell apoptosis. The Federal Drug Administration has approved PDT for the treatment of actinic keratosis, and clinical guidelines recommend PDT as a treatment for certain non-melanoma skin cancers and acne vulgaris. PDT is an advantageous therapeutic modality as it is low cost, non-invasive, and associated with minimal adverse events and scaring. In the first step of PDT, a PS is applied and allowed to accumulate intracellularly. Subsequent light irradiation induces reactive oxygen species formation, which may ultimately lead to cell apoptosis, membrane disruption, mitochondrial damage, immune modulation, keratinocyte proliferation, and collagen turnover. Herein, we present an in vitro method to study PDT in an adherent cell line. This treatment protocol is designed to simulate PDT and may be adjusted to studying the use of PDT with various cell lines, photosensitizers, incubation temperatures, or photoactivation wavelengths. Squamous cell carcinoma cells were incubated with 0, 0.5, 1.0, and 2 mM 5-aminolevulinic acid (5-ALA) for 30 min and photoactivated with 417 nm blue light for 1,000 s. The primary outcome measure was apoptosis and necrosis, as measured by annexin-V and 7-aminoactinomycin D flow cytometry. There was a dose-dependent increase in cell apoptosis following thirty-minute incubation of 5-ALA. To achieve high inter-test validity, it is important to maintain consistent incubation and light parameters when performing in vitro PDT experiments. PDT is a useful clinical procedure and in vitro research may allow for the development of novel PSs, optimization of protocols, and new indications for PDT.