Artificial daylight photodynamic therapy with "non-inflammatory" doses of hexyl aminolevulinate only marginally delays SCC development in UV-exposed hairless mice

NLRP3 Inflammasome Mediated Interleukin-1β Production in Cancer-Associated Fibroblast Contributes to ALA-PDT for Cutaneous Squamous Cell Carcinoma

Background

Long-term tumor control following PDT is a result of its direct effect on tumor and vasculature in combination with induction of inflammatory-reactions upregulating the immune system. When PDT induces necrosis of tumors and vascular system, an immune cascade can be initiated to release all kinds of cytokines including IL1β. This further leads to the activation of inflammatory-cells and hence death of tumor cells.

Methods

Ultraviolet irradiation was used to induce cSCC mice model, gene chip was used to screen inflammatory cytokines, qPCR, ELISA and implanted tumor mice model were used to verify the changes and important role of interleukin-1β, and WB preliminarily explored the production mechanism of interleukin-1β.

Results

Inflammatory cytokines and receptors transcript screening identify IL1r1 as the top4. After ALA-PDT, IL1r1 and IL1β increased in patients' biopsies, principally in mesenchymal cells. In vivo, the inhibition of ALA-PDT on tumor growth of cutaneous squamous cell carcinoma (cSCC) mice in the group with intralesional injection of anti-IL1β mAb or caspase1-inhibitor was significantly weaker than the control groups. Furthermore, NLRP3-inflammasome and p-p65/p65 were elevated after ALA-PDT mediated IL1β production in cancer-associated-fibroblasts.

Discussion

By means of activating NLRP3-inflammasome with IL1β production in CAFs, PDT stimulates local acute-inflammatory-response, which further promotes PDT effect for cSCC.

Enhancement of Photodynamic Cancer Therapy by Physical and Chemical Factors

The viable use of photodynamic therapy (PDT) in cancer therapy has never been fully realized because of its undesirable effects on healthy tissues. Herein we summarize some physicochemical factors that can make PDT a more viable and effective option to provide future oncological patients with better-quality treatment options. These physicochemical factors include light sources, photosensitizer (PS) carriers, microwaves, electric fields, magnetic fields, and ultrasound. This Review is meant to provide current information pertaining to PDT use, including a discussion of in vitro and in vivo studies. Emphasis is placed on the physicochemical factors and their potential benefits in overcoming the difficulty in transitioning PDT into the medical field. Many advanced techniques, such as employing X-rays as a light source, using nanoparticle-loaded stem cells and bacteriophage bio-nanowires as a photosensitizer carrier, as well as integration with immunotherapy, are among the future directions.

The background and philosophy behind daylight photodynamic therapy

Conventional photodynamic therapy (PDT) is associated with side effects, primarily related to the waiting time between pretreatment with application of photosensitizer and illumination. Pain during illumination is a major issue for the patients and options for effective pain relief are limited. Post-treatment inflammation can often be severe and cause inconvenient down-time for the patients and their employers. To avoid the problems of pain and patients crowding in the clinic we eliminated red light treatment of high PpIX concentration and introduced illumination in daylight which may be performed at home. We also investigated if protoporphyrin IX (PpIX) could be activated continuously during its formation which might reduce pain and inflammation. Continuous activation of PpIX during its formation turned out to minimize pain as single PpIX molecules are activated continuously without accumulation of PpIX in the skin. PpIX molecules are formed in the mitochondria and the photodynamic effect only takes place in the mitochondria when continuously activated. This results primarily in apoptosis with little inflammation. Continuous activation of PpIX can be obtained by performing photodynamic therapy in daylight, as well as with daylight-emitting light sources of appropriate wavelengths. Use of daylight prevents the patients from crowding in the clinic. Daylight-PDT completely fulfils the purpose of minimizing pain and inflammation, as well as limiting the strain on the clinic treating the patients.