Photodynamic therapy for enhancing antitumour immunity

Three in One: In Vitro and In Vivo Evaluation of Anticancer Activity of a Theranostic Agent that Combines Magnetic Resonance Imaging, Optical Bioimaging, and Photodynamic Therapy Capabilities

Cancer treatment is a crucial area of research and development, as current chemotherapeutic treatments can have severe side effects or poor outcomes. In the constant search for new strategies that are localized and minimally invasive and produce minimal side effects, photodynamic therapy (PDT) is an exciting therapeutic modality that has been gaining attention. The use of theranostics, which combine diagnostic and therapeutic capabilities, can further improve treatment monitoring through image guidance. This study explores the potential of a theranostic agent consisting of four Gd(III) DTTA complexes (DTTA: diethylenetriamine-N,N,N″,N″-tetraacetate) grafted to a meso-tetraphenylporphyrin core for PDT, fluorescence, and magnetic resonance imaging (MRI). The agent was first tested in vitro on both nonmalignant TIB-75 and MRC-5 and tumoral CT26 and HT-29 cell lines and subsequently evaluated in vivo in a preclinical colorectal tumor model. Advanced MRI and optical imaging techniques were employed with engineered quantitative in vivo molecular imaging based on dynamic acquisition sequences to track the biodistribution of agents in the body. With 3D quantitative volume computed by MRI and tumoral cell function assessed by bioluminescence imaging, we could demonstrate a significant impact of the molecular agent on tumor growth following light application. Further exhaustive histological analysis confirmed these promising results, making this theranostic agent a potential drug candidate for cancer.

Cancer treatment therapies: traditional to modern approaches to combat cancers

As far as health issues are concerned, cancer causes one out of every six deaths around the globe. As potent therapeutics are still awaited for the successful treatment of cancer, some unconventional treatments like radiotherapy, surgery, and chemotherapy and some advanced technologies like gene therapy, stem cell therapy, natural antioxidants, targeted therapy, photodynamic therapy, nanoparticles, and precision medicine are available to diagnose and treat cancer. In the present scenario, the prime focus is on developing efficient nanomedicines to treat cancer. Although stem cell therapy has the capability to target primary as well as metastatic cancer foci, it also has the ability to repair and regenerate injured tissues. However, nanoparticles are designed to have such novel therapeutic capabilities. Targeted therapy is also now available to arrest the growth and development of cancer cells without damaging healthy tissues. Another alternative approach in this direction is photodynamic therapy (PDT), which has more potential to treat cancer as it does minimal damage and does not limit other technologies, as in the case of chemotherapy and radiotherapy. The best possible way to treat cancer is by developing novel therapeutics through translational research. In the present scenario, an important event in modern oncology therapy is the shift from an organ-centric paradigm guiding therapy to complete molecular investigations. The lacunae in anticancer therapy may be addressed through the creation of contemporary and pertinent cancer therapeutic techniques. In the meantime, the growth of nanotechnology, material sciences, and biomedical sciences has revealed a wide range of contemporary therapies with intelligent features, adaptable functions, and modification potential. The development of numerous therapeutic techniques for the treatment of cancer is summarized in this article. Additionally, it can serve as a resource for oncology and immunology researchers.

Insight into the Prospects for Tumor Therapy Based on Photodynamic Immunotherapy

Malignancy is one of the common diseases with high mortality worldwide and the most important obstacle to improving the overall life expectancy of the population in the 21st century. Currently, single or combined treatments, including surgery, chemotherapy, and radiotherapy, are still the mainstream regimens for tumor treatment, but they all present significant side effects on normal tissues and organs, such as organ hypofunction, energy metabolism disorders, and various concurrent diseases. Based on this, theranostic measures for the highly selective killing of tumor cells have always been a hot area in cancer-related fields, among which photodynamic therapy (PDT) is expected to be an ideal candidate for practical clinical application due to its precise targeting and excellent safety performance, so-called PDT refers to a therapeutic method mainly composed of photosensitizers (PSs), laser light, and reactive oxygen species (ROS). Photoimmunotherapy (PIT), a combination of PDT and immunotherapy, can induce systemic antitumor immune responses and inhibit continuing growth and distant metastasis of residual tumor cells, demonstrating a promising application prospect. This article reviews the types of immune responses that occur in the host after PDT treatment, including innate and adaptive immunity. To further help PIT-related drugs improve their pharmacokinetic properties and bioavailability, we highlight the potential improvement of photodynamic immunotherapy from three aspects: immunostimulatory agents, tumor-associated antigens (TAAs) as well as different immune cells. Finally, we focus on recent advances in various strategies and shed light on their corresponding mechanisms of immune activation and possible clinical applications such as cancer vaccines. Having discovered the inherent potential of PDT and the mechanisms that PDT triggers host immune responses, a variety of immunotherapeutic strategies have been investigated in parallel with approaches to improve PDT efficiency. However, it remains to be further elucidated under what conditions the immune effect induced by PDT can achieve tumor immunosuppression and to what extent PDT-induced antitumor immunity will lead to complete tumor rejection. Currently, PIT presents several outstanding intractable challenges, such as the aggregation ability of PSs locally in tumors, deep tissue penetration ability of laser light, immune escape, and biological toxicity, and it is hoped that these issues raised will help to point out the direction of preclinical research on PIT and accelerate its transition to clinical practice.

Recent advances in noble metal complex based photodynamic therapy

Photodynamic therapy (PDT) utilizes light-activated photosensitizers (PSs) to generate toxic species for therapeutics. It has become an emerging solution for cancer treatment because of its specific spatiotemporal selectivity and minimal invasiveness. Noble metal (Ru, Ir and Pt) complexes are of increasing interest as photosensitizers for their excellent photophysical, photochemical, and photobiological properties. In this review, we highlight recent advancements in the development of noble metal complex photosensitizers for PDT during the last 5 years. We will summarize the design strategies of noble metal complexes for efficient and precise PDT, including increasing the light penetration depth, reducing the oxygen-dependent nature and improving target ability. Finally, we summarize recent efforts for the development of noble-based PSs and discuss the limitations of such PSs in clinical application and future perspectives in this field, such as the combination of PDT with other treatment modalities.

Current Strategies for Tumor Photodynamic Therapy Combined With Immunotherapy

Photodynamic therapy (PDT) is a low invasive antitumor therapy with fewer side effects. On the other hand, immunotherapy also has significant clinical applications in the treatment of cancer. Both therapies, on their own, have some limitations and are incapable of meeting the demands of the current cancer treatment. The efficacy of PDT and immunotherapy against tumor metastasis and tumor recurrence may be improved by combination strategies. In this review, we discussed the possibility that PDT could be used to activate immune responses by inducing immunogenic cell death or generating cancer vaccines. Furthermore, we explored the latest advances in PDT antitumor therapy in combination with some immunotherapy such as immune adjuvants, inhibitors of immune suppression, and immune checkpoint blockade.

Could Photodynamic Therapy Be a Promising Therapeutic Modality in Hepatocellular Carcinoma Patients? A Critical Review of Experimental and Clinical Studies

Simple Summary

Hepatocellular Carcinoma (HCC) is one of the leading causes of cancer-associated mortality worldwide. With a limited number of therapeutic options available and a lack of effective anti-tumoral immune responses by the therapies, there is a dire need to search for new translational treatment options. Photodynamic Therapy (PDT), in recent years, has proven itself as an effective anti-cancer therapy. In this review, we discuss the mechanism of PDT, its evolution as an anti-cancer modality, with a special focus on HCC. We also highlight the immune response generated by PDT and how it could be essential in HCC treatment. Finally, we proposed an intraoperative procedure for the treatment of HCC by combining hepatectomy with PDT.

Abstract

Photodynamic Therapy (PDT) relies on local or systemic administration of a light-sensitive dye, called photosensitizer, to accumulate into the target site followed by excitation with light of appropriate wavelength and fluence. This photo-activated molecule reacts with the intracellular oxygen to induce selective cytotoxicity of targeted cells by the generation of reactive oxygen species. Hepatocellular carcinoma (HCC), one of the leading causes of cancer-associated mortality worldwide, has insufficient treatment options available. In this review, we discuss the mechanism and merits of PDT along with its recent developments as an anti-cancerous therapy. We also highlight the application of this novel therapy for diagnosis, visualization, and treatment of HCC. We examine the underlying challenges, some pre-clinical and clinical studies, and possibilities of future studies associated with PDT. Finally, we discuss the mechanism of an active immune response by PDT and thereafter explored the role of PDT in the generation of anti-tumor immune response in the context of HCC, with an emphasis on checkpoint inhibitor-based immunotherapy. The objective of this review is to propose PDT as a plausible adjuvant to existing therapies for HCC, highlighting a feasible combinatorial approach for HCC treatment.

Machine learning for real-time optical property recovery in interstitial photodynamic therapy: a stimulation-based study

With the continued development of non-toxic photosensitizer drugs, interstitial photodynamic therapy (iPDT) is showing more favorable outcomes in recent clinical trials. IPDT planning is crucial to further increase the treatment efficacy. However, it remains a major challenge to generate a high-quality, patient-specific plan due to uncertainty in tissue optical properties (OPs), µ a and µ s . These parameters govern how light propagates inside tissues, and any deviation from the planning-assumed values during treatment could significantly affect the treatment outcome. In this work, we increase the robustness of iPDT against OP variations by using machine learning models to recover the patient-specific OPs from light dosimetry measurements and then re-optimizing the diffusers' optical powers to adapt to these OPs in real time. Simulations on virtual brain tumor models show that reoptimizing the power allocation with the recovered OPs significantly reduces uncertainty in the predicted light dosimetry for all tissues involved.

Long-term results of ERCP- or PTCS-directed photodynamic therapy for unresectable hilar cholangiocarcinoma

BACKGROUND

Photodynamic therapy (PDT) can be performed as palliative therapy for cholangiocarcinoma, while there is currently insufficient evidence for the efficacy. The aim of this study was to explore the clinical efficacy and safety of endoscopic retrograde cholangiopancreatography (ERCP)- or percutaneous transhepatic cholangioscopy (PTCS)-directed PDT combined with stent placement for unresectable hilar cholangiocarcinoma.

METHODS

A retrospective analysis was conducted on 62 patients with unresectable hilar cholangiocarcinoma. Thirty patients received PDT using hematoporphyrin combined with biliary stent placement (PDT+stent group), including 22 receiving ERCP-directed PDT and 8 receiving PTCS-directed PDT. Survival time, quality of life, and postoperative adverse events were compared to 32 patients receiving biliary stent placement alone (Stent-only group).

RESULTS

After 42 months of follow-up, median survival time was significantly longer in the PDT+stent group than the Stent-only group (14.2 vs. 9.8 months, P = 0.003). In the PDT+stent group, the median survival time was longer in the 6 patients with recurrence after surgical resection than the 24 patients without prior surgical resection (20.0 vs. 13.0 months, P = 0.017). The QOL total scores was significantly higher in the PDT+stent group than the Stent-only group at postoperative 6, 9, and 12 months (P<0.05). There was no significant difference in the incidence of postoperative adverse events between the two groups (24 [38.7%] vs. 20 [29.0%], P = 0.239).

CONCLUSION

ERCP- or PTCS-directed PDT + stent placement can prolong the survival of patients with unresectable hilar cholangiocarcinoma, especially those with recurrence and improve quality of life without increasing adverse events.

Synergistic effect of glycated chitosan and photofrin photodynamic therapy on different breast tumor model

Metastases and recurrence of cancer are the main causes of failure and death. Induction of a long-term tumor specific immunity seems to be a great strategy to deal with this challenge. Laser immunotherapy (LIT), using immunomodulatory techniques in combination with photodynamic therapy (PDT), so as to enhance an already robust immune response, has been proposed and investigated by numerous researchers. In our study, mice bearing EMT6 breast tumors and 4T1 metastatic breast tumors were addressed in various permutations of the different components in LIT. The survival rates and the tumor growth curve of EMT6 breast tumors bearing mice were analyzed. We compared the level of inflammatory reaction, cell apoptosis and activated immune cells infiltration of local tumors. We validated the systemic effect of LIT through the 4T1 metastatic breast tumors bearing mice. The results not only proved that concomitant with Glycated chitosan (GC) can improve the effect of inhibiting the tumor growth, improving survival, enhancing local inflammatory reaction and attracting acted immune cells to tumor by photodynamic therapy with Photofrin, but also intuitively proved the systemic effect and long-term effect of LIT.

Outcomes of patients with advanced non-small cell lung cancer and airway obstruction treated with photodynamic therapy and non-photodynamic therapy ablation modalities

Background

Non-small cell lung cancer (NSCLC) patients with central airway obstruction (CAO) may have better survival on systemic therapy if the airway patency is successfully restored by bronchoscopic interventions. It remains unclear which therapeutic bronchoscopic modality [laser, stenting, external beam radiation, brachytherapy and photodynamic therapy (PDT)] used for restoring airway patency positively affects outcomes in these patients. We analyzed the effectiveness of PDT in terms of mortality, and time to subsequent treatments in patients with stage III and IV NSCLC.

Methods

Study used Surveillance, Epidemiology, and End Results (SEER) Medicare linked data. We categorized NSCLC patients diagnosed between 2000 and 2011 and with stage III and IV, into three treatment groups: PDT + radiation ± chemotherapy, non-PDT ablation therapy + radiation ± chemotherapy, and radiation + chemotherapy. We analyzed all-cause and cause-specific mortality using Cox proportional hazard models with an inverse probability weighted propensity score adjustment. Time to subsequent treatment was analyzed using GLM model.

Results

For the PDT group, hazard for all-cause and cause-specific mortality was comparable to the radiation + chemotherapy group (HR =1.03, 95% CI: 0.73-1.45; and HR =1.04, 95% CI: 0.71-1.51, respectively). The non-PDT ablation group had higher hazard for all-cause (HR =1.22, 95% CI: 1.13-1.33) and cause-specific mortality (HR =1.10, 95% CI: 1.01-1.20), compared to the radiation + chemotherapy group. The PDT group had longer time to follow-up treatment, compared to non-PDT ablation group.

Conclusions

In our exploratory study of stage III and IV NSCLC patients with CAO, addition of PDT demonstrated hazard of mortality comparable to radiation + chemotherapy group. However, addition of non-PDT ablation showed higher mortality compared to the radiation + chemotherapy group. Future studies should investigate the efficacy and effectiveness of multimodal therapy including radiation, chemo, immunotherapy and bronchoscopic interventions.

Synthesis of carboxylated silicon phthalocyanine photosensitive microspheres with controllable etching

Using a new kind of alkenyl silicon phthalocyanine, styrene (St) and methacrylic acid as monomers and potassium persulfate as an initiator, carboxylated silicon phthalocyanine photosensitive microspheres were synthesized by in-situ emulsion copolymerization. The structure and morphology of the microspheres were characterized by Fourier transform infrared spectroscopy (FT-IR)and scanning electron microscopy. Fluorescence spectrometer was used to characterize the optical property of the microspheres. The experimental results show that silicon phthalocyanine molecules with flexible unsaturated side chains have good compatibility with styrene. With the presence of carboxyl groups, the as-prepared photosensitive microspheres show high monodispersity and stability. On the basis of this, 9,10-diphenylanthracene (DPA) as singlet oxygen indicator was used to evaluate the photosensitivity of the microspheres. In addition, we report a novel phenomenon that the microspheres can be controllable etched by light irradiation with the presence of DPA in a specific solvent.

Photodynamic therapy reduces the inhibitory effect of osteosarcoma cells on dendritic cells by upregulating HSP70

Osteosarcoma is the most common primary bone tumor and predominantly affects children and adolescents. The prognosis for patients with osteosarcoma is poor. Therefore, the development of novel treatments for osteosarcoma is required. Photodynamic therapy (PDT) is a disease site-specific treatment that utilizes a photosensitizing agent along with light to kill cancer cells. This agent only works following activation by certain wavelengths of light. After the agent is absorbed by the cancer cells, light is then applied to the area to be treated. The light causes the drug to react with oxygen, which produces radical and reactive oxygen species that kill the cells. However, the immune reaction that occurs following PDT remains unknown. The present study demonstrated that the necrosis of osteosarcoma cells inhibited the function of dendritic cells. However, treatment of osteosarcoma cells with PDT restored the function of dendritic cells by upregulating heat shock protein 70. Taken together, the results of the present study provided insight into the subsequent molecular reaction following PDT treatment of osteosarcoma at the molecular level.

Polymeric Nanoparticles for Cancer Photodynamic Therapy

In chemotherapy a fine balance between therapeutic and toxic effects needs to be found for each patient, adapting standard combination protocols each time. Nanotherapeutics has been introduced into clinical practice for treating tumors with the aim of improving the therapeutic outcome of conventional therapies and of alleviating their toxicity and overcoming multidrug resistance. Photodynamic therapy (PDT) is a clinically approved, minimally invasive procedure emerging in cancer treatment. It involves the administration of a photosensitizer (PS) which, under light irradiation and in the presence of molecular oxygen, produces cytotoxic species. Unfortunately, most PSs lack specificity for tumor cells and are poorly soluble in aqueous media, where they can form aggregates with low photoactivity. Nanotechnological approaches in PDT (nanoPDT) can offer a valid option to deliver PSs in the body and to solve at least some of these issues. Currently, polymeric nanoparticles (NPs) are emerging as nanoPDT system because their features (size, surface properties, and release rate) can be readily manipulated by selecting appropriate materials in a vast range of possible candidates commercially available and by synthesizing novel tailor-made materials. Delivery of PSs through NPs offers a great opportunity to overcome PDT drawbacks based on the concept that a nanocarrier can drive therapeutic concentrations of PS to the tumor cells without generating any harmful effect in non-target tissues. Furthermore, carriers for nanoPDT can surmount solubility issues and the tendency of PS to aggregate, which can severely affect photophysical, chemical, and biological properties. Finally, multimodal NPs carrying different drugs/bioactive species with complementary mechanisms of cancer cell killing and incorporating an imaging agent can be developed. In the following, we describe the principles of PDT use in cancer and the pillars of rational design of nanoPDT carriers dictated by tumor and PS features. Then we illustrate the main nanoPDT systems demonstrating potential in preclinical models together with emerging concepts for their advanced design.

Evaluation of the effects of systemic photodynamic therapy in a rat model of acute myeloid leukemia

Systemic PDT (SPDT) approach is developed to treat a variety of hematological diseases, including cancers and blood-borne infections. We evaluated the efficacy of an SPDT method for treating leukemia using a Brown Norway myeloid leukemia (BNML) rat model with the LT12 cells engineered to express GFP. The survival times of animals receiving SPDT at 5 (early-SPDT) and 10 (mid-SPDT) days post-LT12 injection were prolonged by 2 days, the rats in the late-SPDT group (15 days) exhibited a 6-day increase in life span (p<0.05). The percentages of GFP-LT12 cells in the bone marrow of the late-SPDT rats decreased from 61.6% to 56.5% on day 17. Likewise, there was a decrease in the serum expression levels of IL-1β, IL-10, TNF-α, and IFN-γ in the late-SPDT rats (p<0.05). Our findings indicate that SPDT could be an effective method for the treatment of leukemia, and that antitumor immunity may play a key role in this process.

Opportunities and challenges of radiotherapy for treating cancer

The past 20 years have seen dramatic changes in the delivery of radiation therapy, but the impact of radiobiology on the clinic has been far less substantial. A major consideration in the use of radiotherapy has been on how best to exploit differences between the tumour and host tissue characteristics, which in the past has been achieved empirically by radiation-dose fractionation. New advances are uncovering some of the mechanistic processes that underlie this success story. In this Review, we focus on how these processes might be targeted to improve the outcome of radiotherapy at the individual patient level. This approach would seem a more productive avenue of treatment than simply trying to increase the radiation dose delivered to the tumour.

Sasanquasaponin from Camellia oleifera Abel. induces apoptosis via Bcl-2, Bax and caspase-3 activation in HepG2 cells

The present study aimed to elucidate the molecular mechanisms underlying the induction of cytotoxic effects by sasanquasaponin (SQS) in HepG2 cells. Following SQS treatment, time- and dose-dependent increases in the apoptotic rate were observed. The induction of cell death by SQS mainly occurs via programmed cell death, as indicated by Annexin V-fluorescein isothiocyanate and propidium iodide staining, where up to 30% apoptotic cells were detected following 12 h SQS treatment. Reverse transcription-polymerase chain reaction analysis demonstrated that SQS treatment upregulated B-cell lymphoma-2 (Bcl-2)-associated x protein and caspase-3 mRNA expression and downregulated Bcl-2 mRNA expression. Greater alterations in Bax, Bcl-2 and caspase-3 expression were observed with increasing treatment duration. The decrease in Bcl-2, increase in Bax and, finally, the activation of caspase-3 in HepG2 cells indicated that the apoptotic process induced by SQS was irreversible. The results of the present study therefore suggested that SQS induced HepG2 cell apoptosis via the activation of mitochondrial apoptotic pathways.

Photodynamic therapy for intractable bronchial lung cancer

OBJECTIVE

To investigate the effectiveness and side effects of photofrin-photodynamic therapy (PDT) for intractable bronchial lung cancer.

METHODS

Thirty patients were classified as stage II-IV intractable bronchial lung cancer with lumen obstruction after they failed previous treatment regimens such as surgery, radiotherapy and chemotherapy. PDT was performed with 630 nm laser light (Diomed) delivered through cylinder diffusing tip quartz fibers that was passed through the biopsy channel of a flexible endoscope 48 h after intravenous injection of the photosensitizer photofrin (2mg/kg body weight). 72 h after the first irradiation, the endoscopic procedure was repeated, necrotic tissues were mechanically removed and the deep original lesions and newly exposed cancer lesions were re-treated, and, if necessary, the areas were cleaned repeatedly.

RESULTS

The total response rate CR+PR was 86.7%, and the mean percentage of obstruction due to tumors at different treated sites decreased from 90% to 16.7% at discharge after PDT. The KPS score was significantly improved after PDT.

CONCLUSIONS

PDT of intractable bronchial lung cancer effectively reduces the amount of lumen obstruction, and improves the patient's quality of life. It may be an effective palliative treatment with minor side effects on patients with advanced bronchial lung cancer.

In vitro and in vivo clearance of Rose Bengal Acetate-PhotoDynamic Therapy-induced autophagic and apoptotic cells

This study focuses on the clearance of Rose Bengal Acetate (RBAc)-PhotoDynamic Therapy (PDT)-generated apoptotic and autophagic HeLa cells by murine and human macrophages. Indeed, phagocytosis of dead cells drives the therapeutic efficacy of PDT through both efficient removal of dead/dying cells and macrophages response evoked during engulfment and, up to now, clearance of dying photosensitized cells has been less investigated than PDT mechanisms of cell death induction. RBAc-PDT ensures a long onset of cytotoxicity and a time-related cell death of HeLa cells by signals originating from or converging on almost all intracellular organelles. On this basis, to clarify whether the efficacious cell death commitment is followed by an efficient clearance mechanism, we primarily focused on the analysis of 'eat me' signals exposure and 'find me' signals release, and then investigated the migration, recognition, engulfment and response of murine Raw 264.7 and human blood isolated macrophages. Dead cells secreted 'find me' signals, i.e. fractalkine and Heat Shock Protein 70 (HSP 70), to recruit macrophages and promote their fast phagocytosis. Macrophages phagocytosed apoptotic and autophagic PDT-treated cells more efficiently than the respective positive controls, i.e. puromycin-induced apoptotic and Earle's balanced salt solution-starved autophagic cells. Phagocytosis depends on the glycans exposed on dead cells. The macrophages internalization of photokilled cells elicits the production of Interleukin-10, Transforming Growth Factor-β and Tumour Necrosis Factor-α by macrophages. TNFα production, along with HSP70 release and plasma membrane translocation on dead cells, suggest an immunogenic impact of RBAc-PDT. In fact, macrophages, activated fibroblasts and endothelial cells colonized the inoculum site of photosensitized cells in rat calf muscles, endorsing the hypothesis of immunogenic elicitation of RBAc-PDT.

Hypericin-photodynamic therapy leads to interleukin-6 secretion by HepG2 cells and their apoptosis via recruitment of BH3 interacting-domain death agonist and caspases

Photodynamic therapy (PDT) has emerged as a capable therapeutic modality for the treatment of cancer. PDT is a targeted cancer therapy that reportedly leads to tumor cell apoptosis and/or necrosis by facilitating the secretion of certain pro-inflammatory cytokines and expression of multiple apoptotic mediators in the tumor microenvironment. In addition, PDT also triggers oxidative stress that directs tumor cell killing and activation of inflammatory responses. However, the cellular and molecular mechanisms underlying the role of PDT in facilitating tumor cell apoptosis remain ambiguous. Here, we investigated the ability of PDT in association with hypericin (HY) to induce tumor cell apoptosis by facilitating the induction of reactive oxygen species (ROS) and secretion of Th1/Th2/Th17 cytokines in human hepatocellular liver carcinoma cell line (HepG2) cells. To discover if any apoptotic mediators were implicated in the enhancement of cell death of HY-PDT-treated tumor cells, selected gene profiling in response to HY-PDT treatment was implemented. Experimental results showed that interleukin (IL)-6 was significantly increased in all HY-PDT-treated cells, especially in 1 μg/ml HY-PDT, resulting in cell death. In addition, quantitative real-time PCR analysis revealed that the expression of apoptotic genes, such as BH3-interacting-domain death agonist (BID), cytochrome complex (CYT-C) and caspases (CASP3, 6, 7, 8 and 9) was remarkably higher in HY-PDT-treated HepG2 cells than the untreated HepG2 cells, entailing that tumor destruction of immune-mediated cell death occurs only in PDT-treated tumor cells. Hence, we showed that HY-PDT treatment induces apoptosis in HepG2 cells by facilitating cytotoxic ROS, and potentially recruits IL-6 and apoptosis mediators, providing additional hints for the existence of alternative mechanisms of anti-tumor immunity in hepatocellular carcinoma, which contribute to long-term suppression of tumor growth following PDT.

Immunogenic cell death: can it be exploited in PhotoDynamic Therapy for cancer?

Immunogenic Cell Death (ICD) could represent the keystone in cancer management since tumor cell death induction is crucial as well as the control of cancer cells revival after neoplastic treatment. In this context, the immune system plays a fundamental role. The concept of Damage-Associated Molecular Patterns (DAMPs) has been proposed to explain the immunogenic potential of stressed or dying/dead cells. ICD relies on DAMPs released by or exposed on dying cells. Once released, DAMPs are sensed by immune cells, in particular Dendritic Cells (DCs), acting as activators of Antigen-Presenting Cells (APCs), that in turn stimulate both innate and adaptive immunity. On the other hand, by exposing DAMPs, dying cancer cells change their surface composition, recently indicated as vital for the stimulation of the host immune system and the control of residual ill cells. It is well established that PhotoDynamic Therapy (PDT) for cancer treatment ignites the immune system to elicit a specific antitumor immunity, probably linked to its ability in inducing exposure/release of certain DAMPs, as recently suggested. In the present paper, we discuss the DAMPs associated with PDT and their role in the crossroad between cancer cell death and immunogenicity in PDT.