Photodynamic therapy--aspects of pain management

Riboflavin-Vancomycin Conjugate Enables Simultaneous Antibiotic Photo-Release and Photodynamic Killing against Resistant Gram-Positive Pathogens

Decades of antibiotic misuse have led to alarming levels of antimicrobial resistance, and the development of alternative diagnostic and therapeutic strategies to delineate and treat infections is a global priority. In particular, the nosocomial, multidrug-resistant "ESKAPE" pathogens such as Gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus spp (VRE) urgently require alternative treatments. Here, we developed light-activated molecules based on the conjugation of the FDA-approved photosensitizer riboflavin to the Gram-positive specific ligand vancomycin to enable targeted antimicrobial photodynamic therapy. The riboflavin-vancomycin conjugate proved to be a potent and versatile antibacterial agent, enabling the rapid, light-mediated, killing of MRSA and VRE with no significant off-target effects. The attachment of riboflavin on vancomycin also led to an increase in antibiotic activity against S. aureus and VRE. Simultaneously, we evidenced for the first time that the flavin subunit undergoes an efficient photoinduced bond cleavage reaction to release vancomycin, thereby acting as a photoremovable protecting group with potential applications in drug delivery.

RNA-Seq-based transcriptomics analysis during the photodynamic therapy of primary cells in secondary hyperparathyroidism

BACKGROUND

The aim of this study was to identify changes in gene expression before and after 5-aminolevulinic acid-mediated photodynamic therapy (5-ALA-PDT) and to investigate the potential mechanism of 5-ALA-PDT based on ribonucleic acid sequencing (RNA-Seq) analysis.

METHODS

Secondary hyperparathyroidism (SHPT) primary cells were isolated from surgically excised specimens and exposed to laser light. The transcription profiles of SHPT primary cells were identified through RNA-Seq. Differentially expressed genes (DEGs) were identified. Enrichment of functions and signaling pathway analysis were performed based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Quantitative real-time polymerase chain reaction (RT-qPCR) and western blot analysis were used to validate genes based on RNA-Seq results.

RESULTS

In total, 1320 DEGs were identified, of which 1019 genes were upregulated and 301 genes were downregulated. GO and KEGG pathway analyses identified significantly enriched pathways in DEGs, including TGF beta in extracellular matrix (ECM), negative regulation of triglyceride biosynthetic process, protein heterodimerization activity, systemic lupus erythematosus, ECM-receptor interaction, focal adhesion and protein digestion and absorption. Protein-protein interaction (PPI) network analyses identified potential heat shock protein (HSP) interactions among the DEGs. Eight HSP genes were also identified that were most likely involved in 5-ALA-PDT, which were further validated by RT-qPCR and western blotting.

CONCLUSIONS

The findings of this descriptive study reveal changes in the transcriptome profile during 5-ALA-PDT, suggesting that gene expression and mutation, signaling pathways, and the molecular network are altered in SHPT primary cells. The above findings provide new insight for further studies on the mechanisms underlying 5-ALA-PDT in SHPT.

Hemodynamic changes during conventional and daylight photodynamic therapy of actinic keratoses - a randomized controlled trial

BACKGROUND

Photodynamic therapy (PDT) is an effective treatment for actinic keratosis (AK). However, pain and hypertension are important side effects of conventional PDT (c-PDT). Several studies have demonstrated that daylight PDT (dl-PDT) is less painful while being as effective as c-PDT.

OBJECTIVE

To observe the effect of c-PDT and dl-PDT on different hemodynamic parameters (systolic blood pressure and diastolic blood pressure, pulse rate, and peripheral oxygen saturation).

METHODS

Fifty patients with AK on the head were enrolled into this prospective, randomized, controlled study and treated with c-PDT or dl-PDT in a 1:1 ratio. Hemodynamic parameters were measured at four different time points during treatment. Pain was quantified using a visual analog scale. AK was counted before treatment and after one month.

RESULTS

C-PDT is associated with significantly more pain, a significant increase in blood pressure and a higher rate of patients with grade 3 hypertension. Whereas dl-PDT is almost painless and does not lead to any changes in hemodynamic parameters. For both treatments, a similar lesion response rate was found after one month.

CONCLUSIONS

dl-PDT has a better tolerability while being as effective as c-PDT and therefore may be the more favorable treatment option in certain patient groups.

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.

Dermatological Conditions Inducing Acute and Chronic Pain

Pain is a common condition in dermatology. The aim of this review is to analyse the characteristics of pain in dermatology. Some skin diseases are conventionally known to cause pain; e.g. ulcers, pyoderma gangrenosum and herpes zoster. Common dermatoses, such as psoriasis or atopic dermatitis, can also cause significant pain. Some conditions are characterized by neuropathic pain and/or pruritus, without visible primary lesions: e.g. the neurocutaneous diseases, including small fibre neuropathies. Patients often fear pain in skin surgery; however, surgical procedures are rather well tolerated and any pain is mainly due to administration of local anaesthetic. Some therapies may also be uncomfortable for the patient, such as photodynamic therapy or aesthetic procedures. Thus, pain in dermatology is common, and its aetiology and characteristics are very varied. Knowledge of the different situations that cause pain will enable dermatologists to propose suitable analgesic solutions.

Ablative Fractional Laser-assisted Low-irradiance Photodynamic Therapy for Treatment of Actinic Keratoses in Organ Transplant Recipients: A Prospective, Randomized, Intraindividual Controlled Trial

Pain and inferior efficacy are major limiting factors of conventional photodynamic therapy for the field treatment of actinic keratoses in immunosuppressed organ transplant recipients. This prospective randomized controlled study evaluates the efficacy and tolerability of ablative fractional laser system pretreatment combined with low-irradiance photodynamic therapy (18.5 mW/cm2) compared with conventional photodynamic therapy (61.67 mW/cm2) in the treatment of actinic keratoses on the face and scalp in organ transplant recipients, using a red light-emitting diode lamp at a total light dose of 37 J/cm2. Low-irradiance photodynamic therapy combined with Er:YAG pretreatment achieved a significantly superior lesion response rate (mean ± standard deviation 77.3 ± 23.6%) compared with conventional photodynamic therapy (61.8 ± 21.4%; p = 0.025) in intra-individual fields at 3 months without negatively impacting pain (p = 0.777) or cosmetic outcome (p = 0.157).

Two Beats One: Osteosarcoma Therapy with Light-Activated and Chemo-Releasing Keratin Nanoformulation in a Preclinical Mouse Model

Osteosarcoma treatment is moving towards more effective combination therapies. Nevertheless, these approaches present distinctive challenges that can complicate the clinical translation, such as increased toxicity and multi-drug resistance. Drug co-encapsulation within a nanoparticle formulation can overcome these challenges and improve the therapeutic index. We previously synthetized keratin nanoparticles functionalized with Chlorin-e6 (Ce6) and paclitaxel (PTX) to combine photo (PDT) and chemotherapy (PTX) regimens, and the inhibition of osteosarcoma cells growth in vitro was demonstrated. In the current study, we generated an orthotopic osteosarcoma murine model for the preclinical evaluation of our combination therapy. To achieve maximum reproducibility, we systematically established key parameters, such as the number of cells to generate the tumor, the nanoparticles dose, the design of the light-delivery device, the treatment schedule, and the irradiation settings. A 60% engrafting rate was obtained using 10 million OS cells inoculated intratibial, with the tumor model recapitulating the histological hallmarks of the human counterpart. By scheduling the treatment as two cycles of injections, a 32% tumor reduction was obtained with PTX mono-therapy and a 78% reduction with the combined PTX-PDT therapy. Our findings provide the in vivo proof of concept for the subsequent clinical development of a combination therapy to fight osteosarcoma.

Nanoparticle-Mediated Photothermal Therapy Limitation in Clinical Applications Regarding Pain Management

The development of new effective cancer treatment methods has attracted much attention, mainly due to the limited efficacy and considerable side effects of currently used cancer treatment methods such as radiation therapy and chemotherapy. Photothermal therapy based on the use of plasmonically resonant metallic nanoparticles has emerged as a promising technique to eradicate cancer cells selectively. In this method, plasmonic nanoparticles are first preferentially uptaken by a tumor and then selectively heated by exposure to laser radiation with a specific plasmonic resonant wavelength, to destroy the tumor whilst minimizing damage to adjacent normal tissue. However, several parameters can limit the effectiveness of photothermal therapy, resulting in insufficient heating and potentially leading to cancer recurrence. One of these parameters is the patient's pain sensation during the treatment, if this is performed without use of anesthetic. Pain can restrict the level of applicable laser radiation, cause an interruption to the treatment course and, as such, affect its efficacy, as well as leading to a negative patient experience and consequential general population hesitancy to this type of therapy. Since having a comfortable and painless procedure is one of the important treatment goals in the clinic, along with its high effectiveness, and due to the relatively low number of studies devoted to this specific topic, we have compiled this review. Moreover, non-invasive and painless methods for temperature measurement during photothermal therapy (PTT), such as Raman spectroscopy and nanothermometry, will be discussed in the following. Here, we firstly outline the physical phenomena underlying the photothermal therapy, and then discuss studies devoted to photothermal cancer treatment concerning pain management and pathways for improved efficiency of photothermal therapy whilst minimizing pain experienced by the patient.

Novel Water-Soluble Chlorin-Based Photosensitizer for Low-Fluence Photodynamic Therapy

Photodynamic therapy (PDT), performed with low-fluence rates, can improve antitumor responses and prevent adverse effects. However, photosensitizers (PSs) for low-fluence PDT treatment are rarely reported. Herein, we exploited an amphiphilic chlorin-based PS, named DYSP-C34, which has a variety of beneficial biological properties, such as improved water solubility, better cellular permeability, specific localization and enhanced phototoxicity under low light dose irradiation. In addition, DYSP-C34 could effectively accumulate in a mouse subcutaneous xenograft tumor and exhibit substantial tumor regression after irradiation with an extremely low light fluence (6 J/cm2). Meanwhile, the excellent phototoxicity could stimulate the host immune system and lead to a strong inhibition of tumor growth synergistically. These results indicated the potential value of DYSP-C34 as a chlorin-type PS for low-fluence PDT application.

iQbD: a TRL-indexed Quality-by-Design Paradigm for Medical Device Engineering

Risk assessment is a critical step in the roadmap of medical device development. Failure modes, effects and criticality analysis is a common approach based on declarative prior information that proved beneficial in the risk assessment of well established processes. But at early steps of development when innovative materials or technologies are embedded, the lack of experience on those innovations introduces too much subjectivity in FMECA for a robust risk assessment. Since mid-2000, the Quality-by-Design guideline has been proposed within the pharmaceutical industry as a proactive engineering approach of drug development. This paradigm enables a data-driven risk assessment throughout the development workflow, which completes risk assessment provided by FMECA. Nevertheless, its implementation guide is unclear and not flexible enough to be efficiently applied to the development of medical devices. To address this issue, a new QbD paradigm indexed on the technological readiness level of the innovative product is proposed. It covers the development of medical devices throughout the whole preclinical phase and is composed of at least nine learning cycles. The first part of this medical device QbD layout, composed of three consecutive risk assessment cycles, is evaluated through a real study case with the objective to demonstrate the proof of concept of a photobleaching controller in photodynamic therapy. Beyond this experimental result, this application has confirmed practical ability of the iQbD approach to complete FMECA and to provide an alternative solution to risk assessment when prior knowledge on the technological innovation is not available.

Photodynamic therapy for squamous cell carcinoma of the head and neck: narrative review focusing on photosensitizers

This narrative review aimed to evaluate the effectiveness of PDT in early or advanced squamous cell carcinoma of the head and neck (SCCHN). Scopus, MEDLINE/PubMed, and Embase were searched electronically following the PRISMA protocol. Quality assessment was performed according to JBI, NIH, and AMSTAR protocols. The main outcomes evaluated were treatment response, recurrence, survival, and adverse effects. A total of 49 articles met the search criteria: 43 case series, two cohort studies, two prospective before-after clinical trials, one systematic review, and one meta-analysis. Data from 2121 SCCHN patients were included. The response to PDT was variable according to the type of photosensitizer, tumor location, and tumor stage. In general, higher complete responses rated were observed in T1/T2 SCCHN, mainly with mTHPC-mediated PDT. With regard to T3/T4 or advanced SCCHN tumors, there is no compelling evidence suggesting the effectiveness of PDT. Any adverse effects reported were well tolerated by patients. The present review suggests that PDT is a promising treatment modality for early-stage SCCHN. Although there are limitations due to the low level of evidence of the included studies, we believe that the present review could help to design robust clinical trials to determine the efficacy of PDT in SCCHN.

Antitumor Immune Response Triggered by Metal-Based Photosensitizers for Photodynamic Therapy: Where Are We?

Metal complexes based on transition metals have rich photochemical and photophysical properties that are derived from a variety of excited state electronic configurations triggered by visible and near-infrared light. These properties can be exploited to produce powerful energy and electron transfer processes that can lead to oxygen-(in)dependent photobiological activity. These principles are the basis of photodynamic therapy (PDT), which is a clinically approved treatment that offers a promising, effective, and noninvasive complementary treatment or even an alternative to treat several types of cancers. PDT is based on a reaction involving a photosensitizer (PS), light, and oxygen, which ultimately generates cytotoxic reactive oxygen species (ROS). However, skin photosensitivity, due to the accumulation of PSs in skin cells, has hampered, among other elements, its clinical development and application. Therefore, these is an increasing interest in the use of (metal-based) PSs that are more specific to tumor cells. This may increase efficacy and corollary decrease side-effects. To this end, metal-containing nanoparticles with photosensitizing properties have recently been developed. In addition, several studies have reported that the use of immunogenic/immunomodulatory metal-based nanoparticles increases the antitumor efficacy of immune-checkpoint inhibitor-based immunotherapy mediated by anti-PD-(L)1 or CTLA-4 antibodies. In this review, we discuss the main metal complexes used as PDT PSs. Lastly, we review the preclinical studies associated with metal-based PDT PSs and immunotherapies. This therapeutic association could stimulate PDT.

Overcoming barriers in photodynamic therapy harnessing nano-formulation strategies

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

Codelivery of Anticancer Drug and Photosensitizer by PEGylated Graphene Oxide and Cell Penetrating Peptide Enhanced Tumor-Suppressing Effect on Osteosarcoma

Objective: Graphene oxide (GO) has been widely used for various biological and biomedical applications due to its unique physiochemical properties. This study aimed to investigate the effects of cell penetrating peptide (CPP) modified and polyethylene-glycol- (PEG-) grafted GO (pGO) loaded with photosensitive agent 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-alpha (HPPH) and Epirubicin (EPI) (HPPH/EPI/CPP-pGO) on tumor growth in osteosarcoma. Methods: The HPPH/EPI/CPP-pGO were prepared, and then in vitro drug release assay was conducted. The detection of singlet oxygen (¹O₂) and cellular uptake of HPPH was performed as well. Next, the effects of control (saline solution), CPP-pGO, EPI, HPPH, HPPH/CPP-pGO, EPI/CPP-pGO, HPPH/EPI/pGO, and HPPH/EPI/CPP-pGO were evaluated by MTT assay, colony-forming assay, and cell apoptosis assay in MG-63 cells. Furthermore, the antitumor effects of HPPH/EPI/CPP-pGO on osteosarcoma xenograft mice were unraveled. Results: The ¹O₂ generation and cellular uptake of HPPH were significantly increased after CPP and pGO modification compared with free HPPH. In addition, compared with control cells, CPP-pGO treatment had low cytotoxicity in MG-63 cells. Compared with free HPPH or EPI, HPPH/CPP-pGO or EPI/CPP-pGO treatment significantly inhibited cell viability and colony forming number, as well as inducing cell apoptosis. HPPH/EPI-pGO treatment showed stronger inhibition effects on MG-63 cells than HPPH/CPP-pGO or EPI/CPP-pGO, and HPPH/EPI/CPP-pGO was the most effective one. Similarly, in vivo experiments revealed that, compared with control group, the tumor size and weight of osteosarcoma xenograft mice were obviously decreased after free HPPH or EPI treatment, which were further reduced in other groups, especially in HPPH/EPI/CPP-pGO group. Conclusion: HPPH/EPI/CPP-pGO had superior tumor-inhibiting effects in vitro and in vivo on osteosarcoma.

Alternative Pathway Involvement in Protoporphyria Patients Related to Sun Exposure

The homeostasis of tissues in a chronic disease is an essential function of the alternative pathway (AP) of the complement system (CS). However, if not controlled, it may also be detrimental to healthy cells with a consequent aggravation of symptoms. The protoporphyria (PP) is a rare chronic disease that causes phototoxicity in visible light with local skin pain and general malaise. In order to establish if there is a systemic involvement of the CS during sun exposure, we designed a non-invasive method with a serum collection in winter and summer from 19 PP and 13 controls to detect the levels of CS protein: Properdin, Factor H (FH), and C5. Moreover, the global radiation data were collected from the regional agency of environmental protection (ARPA). The results show growing values for every protein in patients with PP, compared to control, in both seasons, in particular in summer compared to winter. To reinforce the evidence, we have estimated the personal exposure of patients based on the global radiation data. The main factors of the AP increased over the season, confirming the involvement of the AP in relation to light exposure. The systemic response could justify the general malaise of patients after long light exposure and can be exploited to elucidate new therapeutic approaches.

The Role of NIR Fluorescence in MDR Cancer Treatment: From Targeted Imaging to Phototherapy

BACKGROUND

Multidrug Resistance (MDR) is defined as a cross-resistance of cancer cells to various chemotherapeutics and has been demonstrated to correlate with drug efflux pumps. Visualization of drug efflux pumps is useful to pre-select patients who may be insensitive to chemotherapy, thus preventing patients from unnecessary treatment. Near-Infrared (NIR) imaging is an attractive approach to monitoring MDR due to its low tissue autofluorescence and deep tissue penetration. Molecular NIR imaging of MDR cancers requires stable probes targeting biomarkers with high specificity and affinity.

OBJECTIVE

This article aims to provide a concise review of novel NIR probes and their applications in MDR cancer treatment.

RESULTS

Recently, extensive research has been performed to develop novel NIR probes and several strategies display great promise. These strategies include chemical conjugation between NIR dyes and ligands targeting MDR-associated biomarkers, native NIR dyes with inherent targeting ability, activatable NIR probes as well as NIR dyes loaded nanoparticles. Moreover, NIR probes have been widely employed for photothermal and photodynamic therapy in cancer treatment, which combine with other modalities to overcome MDR. With the rapid advancing of nanotechnology, various nanoparticles are incorporated with NIR dyes to provide multifunctional platforms for controlled drug delivery and combined therapy to combat MDR. The construction of these probes for MDR cancers targeted NIR imaging and phototherapy will be discussed. Multimodal nanoscale platform which integrates MDR monitoring and combined therapy will also be encompassed.

CONCLUSION

We believe these NIR probes project a promising approach for diagnosis and therapy of MDR cancers, thus holding great potential to reach clinical settings in cancer treatment.

Possibilities of pain management during photodynamic therapy

The authors consider the possibilities of pain management during photodynamic therapy (PDT) of visible tumors based on the observation of 102 patients. Of the total number of patients, 62 had verified basal cell skin cancer, 10 people - squamous cell skin cancer, another 10 - oral and oropharynx mucosa cancer, 8 - oral leukoplakia and dysplasia, in 6 - lower lip cancer, in 4 - breast cancer, in 2 - other localizations of neoplasms. In 15 patients, nonsteroidal anti-inflammatory drugs (NSAID) were used as pain management, in 69 - a combination of NSAID with tramadol, in 14 - nerve block anesthesia, in 4 - PDT was performed under general anesthesia. The intensity of pain syndrome during laser irradiation of the tumor was assessed on the verbal rating scale (VRS). The absence of pain was recorded in 9% of cases. Mild pain was noted by 58% of patients, moderate pain - 20%, severe pain - 10%, very severe pain was noted by 3% of patients.

The degree of expression of pain syndrome during PDT depends on the incidence of a lesion, histological form of tumor, and method of anesthesia. NSAID alone, or in combination with an opioid analgesic, allows effective control of pain syndrome in PDT of basal cell skin cancer in 89%, in PDT of squamous cell skin cancer in 66% of observations. Nerve block anesthesia allows stoping pain syndrome during PDT of oropharyngeal tumors.

Management of keratinocyte carcinoma - Special considerations in the elderly

Keratinocyte carcinomas (KCs) are now an epidemic in The United States of America, especially in elderly patients. KCs, including basal cell carcinoma and squamous cell carcinoma, can lead to disfigurement and occasionally death. However, the lower mortality rate associated with KC compared with melanoma allows for increased flexibility in the selection of treatment. Flexibility in treatment is particularly important in the elderly given that this patient population often has medical comorbidities that should be considered. These patients may have multiple KCs, higher risk tolerance to recurrence, and different concerns about cosmetic outcomes compared with their younger counterparts. We review treatment options for KCs and how the selection of each option may affect the elderly patient.

[Current aspects of pain management during and after dermatologic surgery]

The project "Pain-free Hospital" was the first attempt to improve the level of postoperative care by standardizing pain therapy standards (concepts) in the individual surgical disciplines. Dermatosurgery is no exception. In addition to drug therapy, it is also important to consider biopsychosocial aspects of the symptom pain, as this is the only way to prevent chronification of acute pain in the further course of a disease. Drug therapy should not only be adapted to the classic WHO system (only considering pain intensity), but should also address aspects of pain quality. In this article, we discuss these aspects in more detail and present our treatment concept for dermatosurgery.

Early and Late Onset Side Effects of Photodynamic Therapy

Photodynamic Therapy (PDT) is a non-invasive treatment successfully used for neoplastic, inflammatory and infectious skin diseases. One of its strengths is represented by the high safety profile, even in elderly and/or immuno-depressed subjects. PDT, however, may induce early and late onset side effects. Erythema, pain, burns, edema, itching, desquamation, and pustular formation, often in association with each other, are frequently observed in course of exposure to the light source and in the hours/days immediately after the therapy. In particular, pain is a clinically relevant short-term complication that also reduces long-term patient satisfaction. Rare complications are urticaria, contact dermatitis at the site of application of the photosensitizer, and erosive pustular dermatosis. Debated is the relationship between PDT and carcinogenesis: the eruptive appearance of squamous cell carcinoma (SCC) in previously treated areas has been correlated to a condition of local and/or systemic immunosuppression or to the selection of PDT-resistant SCC. Here we review the literature, with particular emphasis to the pathogenic hypotheses underlying these observations.

Photosensitization in Porphyrias and Photodynamic Therapy Involves TRPA1 and TRPV1

Photosensitization, an exaggerated sensitivity to harmless light, occurs genetically in rare diseases, such as porphyrias, and in photodynamic therapy where short-term toxicity is intended. A common feature is the experience of pain from bright light. In human subjects, skin exposure to 405 nm light induced moderate pain, which was intensified by pretreatment with aminolevulinic acid. In heterologous expression systems and cultured sensory neurons, exposure to blue light activated TRPA1 and, to a lesser extent, TRPV1 channels in the absence of additional photosensitization. Pretreatment with aminolevulinic acid or with protoporphyrin IX dramatically increased the light sensitivity of both TRPA1 and TRPV1 via generation of reactive oxygen species. Artificial lipid bilayers equipped with purified human TRPA1 showed substantial single-channel activity only in the presence of protoporphyrin IX and blue light. Photosensitivity and photosensitization could be demonstrated in freshly isolated mouse tissues and led to TRP channel-dependent release of proinflammatory neuropeptides upon illumination. With antagonists in clinical development, these findings may help to alleviate pain during photodynamic therapy and also allow for disease modification in porphyria patients.

SIGNIFICANCE STATEMENT

Cutaneous porphyria patients suffer from burning pain upon exposure to sunlight and other patients undergoing photodynamic therapy experience similar pain, which can limit the therapeutic efforts. This study elucidates the underlying molecular transduction mechanism and identifies potential targets of therapy. Ultraviolet and blue light generates singlet oxygen, which oxidizes and activates the ion channels TRPA1 and TRPV1. The disease and the therapeutic options could be reproduced in models ranging from isolated ion channels to human subjects, applying protoporphyrin IX or its precursor aminolevulinic acid. There is an unmet medical need, and our results suggest a therapeutic use of the pertinent antagonists in clinical development.

Oncologic Photodynamic Therapy: Basic Principles, Current Clinical Status and Future Directions

Photodynamic therapy (PDT) is a clinically approved cancer therapy, based on a photochemical reaction between a light activatable molecule or photosensitizer, light, and molecular oxygen. When these three harmless components are present together, reactive oxygen species are formed. These can directly damage cells and/or vasculature, and induce inflammatory and immune responses. PDT is a two-stage procedure, which starts with photosensitizer administration followed by a locally directed light exposure, with the aim of confined tumor destruction. Since its regulatory approval, over 30 years ago, PDT has been the subject of numerous studies and has proven to be an effective form of cancer therapy. This review provides an overview of the clinical trials conducted over the last 10 years, illustrating how PDT is applied in the clinic today. Furthermore, examples from ongoing clinical trials and the most recent preclinical studies are presented, to show the directions, in which PDT is headed, in the near and distant future. Despite the clinical success reported, PDT is still currently underutilized in the clinic. We also discuss the factors that hamper the exploration of this effective therapy and what should be changed to render it a more effective and more widely available option for patients.

Pain management in photodynamic therapy using a nitrous oxide/oxygen mixture: a prospective, within-patient, controlled clinical trial

BACKGROUND

Photodynamic therapy is an effective treatment for actinic keratoses. Nevertheless, severe pain during the procedure is a serious adverse effect, which leads to interruption or even termination. Complete pain relief remains a difficult challenge.

OBJECTIVE

To evaluate the effect of a nitrous oxide/oxygen mixture on pain intensity during photodynamic therapy.

METHODS

This clinical trial has been designed as a prospective, single-centre, explorative, controlled, observational study.

RESULTS

We were able to detect a significant overall pain reduction of 55.2% after application of a nitrous oxide/oxygen mixture by means of an intra-individual comparison. Furthermore, the total number of therapy interruption significantly decreased by 82% after the inhalation analgesia. Additionally, treatment satisfaction ranged from 'extremely to very satisfied'.

CONCLUSIONS

This study shows that analgesia by means of a nitrous oxide/oxygen mixture is a very effective and well-tolerated method for achieving significant pain reduction during photodynamic therapy.

Pain reduction in patients after applying a nitrous oxide/oxygen mixture (Livopan) during photodynamic therapy: study protocol for an observational study (Livopan study)

INTRODUCTION

Photodynamic therapy (PDT) is an effective treatment option for extensively photodamaged skin with multiple actinic kerastosis. However, the main drawback of PDT is the intensive pain experienced during its application, which makes it frequently necessary to interrupt or even terminate the process resulting in incomplete treatment. Several strategies for controlling pain during PDT have been studied but few effective methods are currently available. Alternative options are urgently needed. Livopan, a nitrous oxide/oxygen mixture, is indicated for the treatment of short-term pain conditions when rapid analgesic onset and offset effects are wanted. But so far, there are no studies evaluating the effect of Livopan on pain intensity during PDT. Therefore, it remains unclear whether patients benefit from this inhalation analgesia. Within the Livopan study, this issue will be evaluated for the first time.

METHODS AND ANALYSIS

The Livopan study is a prospective, single-centre, explorative, controlled, observational study to investigate the pain reduction in patients after applying a nitrous oxide/oxygen mixture (Livopan) during PDT according to the visual analogue scale in 60 patients.

ETHICS AND DISSEMINATION

Ethics approval was provided by the ethics committee of the medical faculty of the University of Heidelberg. Ethics approval number S-169/2014.

TRIAL REGISTRATION NUMBER

German Clinical Trial Register (DRKS): DRKS00006054.