Enhancement of anti-tumor immunity by photodynamic therapy

Direct and indirect photodynamic therapy effects on the cellular and molecular components of the tumor microenvironment

Photodynamic therapy (PDT) is a novel cancer treatment. It involves the activation of a photosensitizer (PS) with light of specific wavelength, which interacts with molecular oxygen to generate singlet oxygen and other reactive oxygen species (ROS) that lead to tumor cell death. When a tumor is treated with PDT, in addition to affect cancer cells, the extracellular matrix and the other cellular components of the microenvironment are altered and finally this had effects on the tumor cells survival. Furthermore, the heterogeneity in the availability of nutrients and oxygen in the different regions of a tridimensional tumor has a strong impact on the sensitivity of cells to PDT. In this review, we summarize how PDT affects indirectly to the tumor cells, by the alterations on the extracellular matrix, the cell adhesion and the effects over the immune response. Also, we describe direct PDT effects on cancer cells, considering the intratumoral role that autophagy mediated by hypoxia-inducible factor 1 (HIF-1) has on the efficiency of the treatment.

Photodynamic therapy-generated cancer vaccine elicits acute phase and hormonal response in treated mice

Photodynamic therapy (PDT)-generated cancer vaccines have shown promising results in preclinical studies and are being introduced in the clinics. Using an SCCVII mouse squamous cell carcinoma-based whole-cell autologous PDT vaccine model developed in our previous work, we have examined systemic effects in vaccinated mice that could be related to the induction of acute phase response. The upregulation of gene encoding serum amyloid P component (prototypic mouse acute phase reactant) was detected in the liver and to a lesser degree in the tumor of vaccinated mice at 24 h post-PDT vaccine treatment. A strong upregulation of gene for heat shock protein 70 was found in both the liver and tumor of mice at 4 h after their PDT vaccine treatment. Changes in the expression of genes for glucocorticoid-induced leucine zipper and serum- and glucocorticoid-regulated kinase 1 that are highly responsive to glucocorticoid modulation were uncovered in both the tumor and liver of vaccinated mice. A rise in the levels of serum corticosterone was detected in mice at 24 h after PDT vaccine treatment. The results indicate that a sudden appearance of a large number of PDT vaccine cells elicits host responses for securing their optimized clearance, which in addition to producing seminal acute phase reactants includes the engagement of glucocorticoid hormones. It is becoming increasingly clear that a consummate execution of this process of PDT vaccine cell removal is critical for tumor antigen recognition and the attainment of potent antitumor immune response.

IL-6 potentiates tumor resistance to photodynamic therapy (PDT)

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) is an anticancer modality approved for the treatment of early disease and palliation of late stage disease. PDT of tumors results in the generation of an acute inflammatory response. The extent and duration of the inflammatory response is dependent upon the PDT regimen employed and is characterized by rapid induction of proinflammatory cytokines, such as IL-6, and activation and mobilization of innate immune cells. The importance of innate immune cells in long-term PDT control of tumor growth has been well defined. In contrast the role of IL-6 in long-term tumor control by PDT is unclear. Previous studies have shown that IL-6 can diminish or have no effect on PDT antitumor efficacy.

STUDY DESIGN/MATERIALS AND METHODS

In the current study we used mice deficient for IL-6, Il6(-/-) , to examine the role of IL-6 in activation of antitumor immunity and PDT efficacy by PDT regimens known to enhance antitumor immunity.

RESULTS

Our studies have shown that elimination of IL-6 had no effect on innate cell mobilization into the treated tumor bed or tumor draining lymph node (TDLN) and did not affect primary antitumor T-cell activation by PDT. However, IL-6 does appear to negatively regulate the generation of antitumor immune memory and PDT efficacy against murine colon and mammary carcinoma models. The inhibition of PDT efficacy by IL-6 appears also to be related to regulation of Bax protein expression. Increased apoptosis was observed following treatment of tumors in Il6(-/-) mice 24 hours following PDT.

CONCLUSIONS

The development of PDT regimens that enhance antitumor immunity has led to proposals for the use of PDT as an adjuvant treatment. However, our results show that the potential for PDT induced expression of IL-6 to enhance tumor survival following PDT must be considered.

Angiogenesis inhibition for the improvement of photodynamic therapy: the revival of a promising idea

Photodynamic therapy (PDT) is a minimally invasive form of treatment, which is clinically approved for the treatment of angiogenic disorders, including certain forms of cancer and neovascular eye diseases. Although the concept of PDT has existed for a long time now, it has never made a solid entrance into the clinical management of cancer. This is likely due to secondary tissue reactions, such as inflammation and neoangiogenesis. The recent development of clinically effective angiogenesis inhibitors has lead to the initiation of research on the combination of PDT with such angiostatic targeted therapies. Preclinical studies in this research field have shown promising results, causing a revival in the field of PDT. This review reports on the current research efforts on PDT and vascular targeted combination therapies. Different combination strategies with angiogenesis inhibition and vascular targeting approaches are discussed. In addition, the concept of increasing PDT selectivity by targeted delivery of photosensitizers is presented. Furthermore, the current insights on sequencing the therapy arms of such combinations will be discussed in light of vascular normalization induced by angiogenesis inhibition.

The effect of photodynamic therapy on tumor cell expression of major histocompatibility complex (MHC) class I and MHC class I-related molecules

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) is FDA-approved anti-cancer modality for elimination of early disease and palliation in advanced disease. PDT efficacy depends in part on elicitation of a tumor-specific immune response that is dependent on cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. The cytolytic potential of CTLs and NK cells is mediated by the ability of these cells to recognize major histocompatibility complex (MHC) class I and MHC class I-related molecules. The MHC class I-related molecules MICA and MICB are induced by oxidative stress and have been reported to activate NK cells and co-stimulate CD8(+) T cells. The purpose of this study was to examine the effect of PDT on tumor cell expression of MHC classes I and II-related molecules in vivo and in vitro.

STUDY DESIGN/MATERIALS AND METHODS

Human colon carcinoma Colo205 cells and murine CT26 tumors were treated with 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH)-PDT at various doses. MHC classes I and I-related molecule expression following treatment of Colo205 cells was temporally examined by flow cytometry using antibodies specific for components of MHC class I molecules and by quantitative PCR using specific primers. Expression of MHC class I-related molecules following HPPH-based PDT (HPPH-PDT) of murine tumors was monitored using a chimeric NKG2D receptor.

RESULTS

In vitro HPPH-PDT significantly induces MICA in Colo205 cells, but had no effect on MHC class I molecule expression. PDT also induced expression of NKG2D ligands (NKG2DL) following in vivo HPPH-PDT of a murine tumor. Induction of MICA corresponded to increased NK killing of PDT-treated tumor cells.

CONCLUSIONS

PDT induction of MICA on human tumor cells and increased expression of NKG2DL by murine tumors following PDT may play a role in PDT induction of anti-tumor immunity. This conclusion is supported by our results demonstrating that tumor cells have increased sensitivity to NK cell lysis following PDT.

Feasibility and safety of long-term photodynamic therapy (PDT) in the palliative treatment of patients with hilar cholangiocarcinoma

Background and Aim

PDT is an important palliative option for patients with unresectable extrahepatic cholangiocarcinoma (CC). However, the results published to date reported on studies with no more than 6 (mostly up to 4) PDT procedures. Furthermore, the clinical experience of PDT in combination with chemotherapy is limited. The purpose of this retrospective analysis was to evaluate the feasibility and safety of multiple (4 to 14) settings of PDT, combined with biliary drainage, and (in some cases) with chemotherapy.

Methods

Ten patients with unresectable extrahepatic CC were treated with biliary stenting and at least 4 PDT procedures in our department between 10/2005 and 08/2010.

Results

Ten patients (male/female = 5/5), mean age 68.8 years (range, 54 - 81 years) who received at least 4 PDT procedures were analyzed. All patients underwent endoscopic biliary drainage. Nine patients received metallic stents and one patient a plastic stent. In 4 patients (40%) bilateral metal stenting (JoStent SelfX^®) was performed. The mean number of PDT sessions was 7.9 ± 3.9 (range: 4 - 14). Eight patients had elevated bilirubin levels with a mean bilirubin at admission of 9.9 ± 11.3 mg/dL, which had decreased to an average minimum of 1.2 ± 0.9 mg/dL after 3 months. No severe toxicity was noted. Two patients received concomitant chemotherapy (GEMCIS as 1^st line, GEMOX plus cetuximab as 2^nd line). The median overall survival has not been reached, whereas the estimated survival of all patients was 47.6 months, 95% CI 25.9 - 48.1.

Conclusion

Long-term PDT in patients with extrahepatic CC is feasible and effective and is accompanied - at least in this cohort- by a survival time of more than 2 years.

Photodynamic therapy in the management of pre-malignant head and neck mucosal dysplasia and microinvasive carcinoma

The management of head and neck mucosal dysplasia and microinvasive carcinoma is an appealing strategy to prevent the development of invasive carcinomas. While surgery remains the standard of care, photodynamic therapy (PDT) offers several advantages including the ability to provide superficial yet wide field mucosal ablative treatment. This is particularly attractive where defining the extent of the dysplasia can be difficult. PDT can also retreat the mucosa without any cumulative fibrotic complications affecting function. To date, clinical experience suggests that this treatment approach can be effective in obtaining a complete response for the treated lesion but long term follow-up is limited. Further research efforts are needed to define not only the risk of malignant transformation with PDT but also to develop site specific treatment recommendations that include the fluence, fluence rate and light delivery technique.

Photodynamic therapy for malignant pleural mesothelioma: the future of treatment?

Malignant pleural mesothelioma is a deadly incurable cancer, with a median survival of approximately 9 months. The best available chemotherapy, arguably the standard of care, only yields a 40% response rate and an 11-week extension in median survival. Surgery, the modality most likely to be associated with prolonged remission, remains investigational and must always be combined with other modalities in an effort to treat the microscopic disease that will remain even after the most aggressive operations. One such modality, photodynamic therapy, is a light-based cancer treatment that has features making it particularly well suited as a component of a surgery-based multimodal treatment plan. Utilizing intraoperative photodynamic therapy has enabled development of a less drastic surgical procedure that is also yielding some encouraging survival results. A unique aspect of photodynamic therapy is its stimulation of a tumor-directed immune response, a feature that offers promise for designing future treatments.

Induction of immune mediators in glioma and prostate cancer cells by non-lethal photodynamic therapy

Background

Photodynamic therapy (PDT) uses the combination of photosensitizing drugs and harmless light to cause selective damage to tumor cells. PDT is therefore an option for focal therapy of localized disease or for otherwise unresectable tumors. In addition, there is increasing evidence that PDT can induce systemic anti-tumor immunity, supporting control of tumor cells, which were not eliminated by the primary treatment. However, the effect of non-lethal PDT on the behavior and malignant potential of tumor cells surviving PDT is molecularly not well defined.

Methodology/Principal Findings

Here we have evaluated changes in the transcriptome of human glioblastoma (U87, U373) and human (PC-3, DU145) and murine prostate cancer cells (TRAMP-C1, TRAMP-C2) after non-lethal PDT in vitro and in vivo using oligonucleotide microarray analyses. We found that the overall response was similar between the different cell lines and photosensitizers both in vitro and in vivo. The most prominently upregulated genes encoded proteins that belong to pathways activated by cellular stress or are involved in cell cycle arrest. This response was similar to the rescue response of tumor cells following high-dose PDT. In contrast, tumor cells dealing with non-lethal PDT were found to significantly upregulate a number of immune genes, which included the chemokine genes CXCL2, CXCL3 and IL8/CXCL8 as well as the genes for IL6 and its receptor IL6R, which can stimulate proinflammatory reactions, while IL6 and IL6R can also enhance tumor growth.

Conclusions

Our results indicate that PDT can support anti-tumor immune responses and is, therefore, a rational therapy even if tumor cells cannot be completely eliminated by primary phototoxic mechanisms alone. However, non-lethal PDT can also stimulate tumor growth-promoting autocrine loops, as seen by the upregulation of IL6 and its receptor. Thus the efficacy of PDT to treat tumors may be improved by controlling unwanted and potentially deleterious growth-stimulatory pathways.

Novel development of 5-aminolevurinic acid (ALA) in cancer diagnoses and therapy

Early detection and intervention are needed for optimal outcomes in cancer therapy. Improvements in diagnostic technology, including endoscopy, photodynamic diagnosis (PDD), and photodynamic therapy (PDT), have allowed substantial progress in the treatment of cancer. 5-Aminolevulinic acid (ALA) is a natural, delta amino acid biosynthesized by animal and plant mitochondria. ALA is a precursor of porphyrin, heme, and bile pigments, and it is metabolized into protoporphyrin IX (PpIX) in the course of heme synthesis. PpIX preferentially accumulates in tumor cells resulting in a red fluorescence following irradiation with violet light and the formation of singlet oxygen. This reaction, utilized to diagnose and treat cancer, is termed ALA-induced PDD and PDT. In this review, the biological significance of heme metabolites, the mechanism of PpIX accumulation in tumor cells, and the therapeutic potential of ALA-induced PDT alone and combined with hyperthermia and immunotherapy are discussed.

Low dose hypericin-PDT induces complete tumor regression in BALB/c mice bearing CT26 colon carcinoma

BACKGROUND

Successful tumor eradication with photodynamic therapy (PDT) in vivo depends on the optimal combination of treatment parameters. (Low-dose) PDT may additionally induce antitumoral immune responses. Since the naturally occurring hypericin (Hyp) is a promising photosensitizer for PDT, the aim of the study was to investigate phototoxic and immunologic effects of a low-dose Hyp-PDT on murine tumors in contrast to commonly used Hyp-PDT conditions.

METHODS

BALB/c mice bearing CT26 colon carcinoma received hypericin intravenously and were irradiated with red light 0.5-4h later. Tumor development was recorded. Mice were then re-challenged 60 days after the first tumor cell inoculation to investigate an antitumoral immune response.

RESULTS

Different results of tumor/host responses were obtained, ranging from mice exitus over delayed tumor growth to complete tumor regression according to different treatment protocols. PDT with common doses and a 4h drug-light-interval resulted in a four times delayed tumor growth compared to the control groups. PDT with relatively low doses and a drug-light-interval of 0.5h led to 100% tumor eradication. Re-challenge of these mice with CT26 mouse colon carcinoma cells prevented new tumor growth.

CONCLUSIONS

Not only drug concentrations and light doses seem to determine the efficiency of tumor eradication, but also the localization of hypericin at the time of irradiation. Targets in our low-dose PDT protocol are exclusively the vessels. The advantage of this low-dose PDT beside less drug and light exposure of the animals is reduced skin damage, faster healing of the lesions and induction of an antitumoral immune response.

Recent advances in the prevention and treatment of skin cancer using photodynamic therapy

Photodynamic therapy (PDT) is a noninvasive procedure that involves a photosensitizing drug and its subsequent activation by light to produce reactive oxygen species that specifically destroy target cells. Recently, PDT has been widely used in treating non-melanoma skin malignancies, the most common cancer in the USA, with superior cosmetic outcomes compared with conventional therapies. The topical 'photosensitizers' commonly used are 5-aminolevulinic acid (ALA) and its esterified derivative methyl 5-aminolevulinate, which are precursors of the endogenous photosensitizer protoporphyrin IX. After treatment with ALA or methyl 5-aminolevulinate, protoporphyrin IX preferentially accumulates in the lesion area of various skin diseases, which allows not only PDT treatment but also fluorescence diagnosis with ALA-induced porphyrins. Susceptible lesions include various forms of non-melanoma skin cancer such as actinic keratosis, basal cell carcinoma and squamous cell carcinoma. The most recent and promising developments in PDT include the discovery of new photosensitizers, the exploitation of new drug delivery systems and the combination of other modalities, which will all contribute to increasing PDT therapeutic efficacy and improving outcome. This article summarizes the main principles of PDT and its current clinical use in the management of non-melanoma skin cancers, as well as recent developments and possible future research directions.

Cancer vaccines generated by photodynamic therapy

The development of photodynamic therapy (PDT)-generated cancer vaccines is potentially one of the most significant achievements in the field of PDT. Employing vaccine protocols optimizes the capacity of PDT of inducing a strong immune response against treated tumor due to the establishment of highly favourable conditions for maximizing the avidity of the immune reaction while sustaining and prolonging its tumor-destroying attack. While the introduction of PDT vaccines into the clinics and testing on patients is still in a very early phase, much work can still be done on further improvement of the potency of PDT vaccines. Considerable advances can be expected by identifying the most effective adjuvants to be used with PDT vaccines, which will most likely be different with different types of cancerous lesions.

DAMPs and PDT-mediated photo-oxidative stress: exploring the unknown

Damage-associated molecular patterns (DAMPs) or cell death associated molecular patterns (CDAMPs) are a subset of endogenous intracellular molecules that are normally hidden within living cells but become either passively released by primary and secondary necrotic cells or actively exposed and secreted by the dying cells. Once released, DAMPs are sensed by the innate immune system and act as activators of antigen-presenting cells (APCs) to stimulate innate and adaptive immunity. Cancer cells dying in response to a subset of conventional anticancer modalities exhibit a particular composition of DAMPs at their cell surface, which has been recently shown to be vital for the stimulation of the host immune system and the control of residual disease. Photodynamic therapy (PDT) for cancer has long been shown to be capable of killing malignant cells and concomitantly stimulate the host immune system, properties that are likely linked to its ability of inducing exposure/release of certain DAMPs. PDT, by evoking oxidative stress at specific subcellular sites through the light activation of organelle-associated photosensitizers, may be unique in incorporating tumour cells destruction and antitumor immune response in one therapeutic paradigm. Here we review the current knowledge about mechanisms and signalling cascades leading to the exposure of DAMPs at the cell surface or promoting their release, the cell death mechanism associated to these processes and its immunological consequences. We also discuss how certain PDT paradigms may yield therapies that optimally stimulate the immune system and lead to the discovery of new DAMPs.

Molecular enzymology of 5-aminolevulinate synthase, the gatekeeper of heme biosynthesis

Pyridoxal-5'-phosphate (PLP) is an obligatory cofactor for the homodimeric mitochondrial enzyme 5-aminolevulinate synthase (ALAS), which controls metabolic flux into the porphyrin biosynthetic pathway in animals, fungi, and the α-subclass of proteobacteria. Recent work has provided an explanation for how this enzyme can utilize PLP to catalyze the mechanistically unusual cleavage of not one but two substrate amino acid α-carbon bonds, without violating the theory of stereoelectronic control of PLP reaction-type specificity. Ironically, the complex chemistry is kinetically insignificant, and it is the movement of an active site loop that defines k(cat) and ultimately, the rate of porphyrin biosynthesis. The kinetic behavior of the enzyme is consistent with an equilibrium ordered induced-fit mechanism wherein glycine must bind first and a portion of the intrinsic binding energy with succinyl-Coenzyme A is then utilized to perturb the enzyme conformational equilibrium towards a closed state wherein catalysis occurs. Return to the open conformation, coincident with ALA dissociation, is the slowest step of the reaction cycle. A diverse variety of loop mutations have been associated with hyperactivity, suggesting the enzyme has evolved to be purposefully slow, perhaps as a means to allow for rapid up-regulation of activity in response to an as yet undiscovered allosteric type effector. Recently it was discovered that human erythroid ALAS mutations can be associated with two very different diseases. Mutations that down-regulate activity can lead to X-linked sideroblastic anemia, which is characterized by abnormally high iron levels in mitochondria, while mutations that up-regulate activity are associated with X-linked dominant protoporphyria, which in contrast is phenotypically identified by abnormally high porphyrin levels. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.

Photodynamic therapy: illuminating the road from cell death towards anti-tumour immunity

Photodynamic therapy (PDT) utilizes the destructive power of reactive oxygen species generated via visible light irradiation of a photosensitive dye accumulated in the cancerous tissue/cells, to bring about their obliteration. PDT activates multiple signalling pathways in cancer cells, which could give rise to all three cell death modalities (at least in vitro). Simultaneously, PDT is capable of eliciting various effects in the tumour microenvironment thereby affecting the tumour-associated/-infiltrating immune cells and by extension, leading to infiltration of various immune cells (e.g. neutrophils) into the treated site. PDT is also associated to the activation of different immune phenomena, e.g. acute-phase response, complement cascade and production of cytokines/chemokines. It has also come to light that, PDT is capable of activating 'anti-tumour adaptive immunity' in both pre-clinical as well as clinical settings. Although the ability of PDT to induce 'anti-cancer vaccine effect' is still debatable, yet it has been shown to be capable of inducing exposure/release of certain damage-associated molecular patterns (DAMPs) like HSP70. Therefore, it seems that PDT is unique among other approved therapeutic procedures in generating a microenvironment suitable for development of systemic anti-tumour immunity. Apart from this, recent times have seen the emergence of certain promising modalities based on PDT like-photoimmunotherapy and PDT-based cancer vaccines. This review mainly discusses the effects exerted by PDT on cancer cells, immune cells as well as tumour microenvironment in terms of anti-tumour immunity. The ability of PDT to expose/release DAMPs and the future perspectives of this paradigm have also been discussed.

Antitumor efficacy of a photodynamic therapy-generated dendritic cell glioma vaccine

The objective of this study is to generate dendritic cell (DC) vaccines by exposing DCs to C6 glioma cancer cell antigenic (tumor) peptides following the exposure of C6 cells to photodynamic therapy (PDT) and acid elution. Effects of these DCs on host immunity were assessed by measuring cytokine induction (following adaptive transfer into rats) and assessing DC-induced cytotoxic T lymphocyte (CTL)-mediated lysis of C6 target cells. Precursor dendritic cells were purified from rat bone marrow and matured in vitro. C6 cells were stimulated with PDT, and adherent cells were acid-eluted to obtain cell surface antigens, whole cell antigens were also isolated from supernatants. C6 cells not stimulated with PDT were also used to isolate antigens by acid elution or freeze-thaw methods for comparison purposes. The isolated antigens from the respective purification methods were used to sensitize DCs for the generation of DC vaccines subsequently transferred into SD rats. Following adoptive transfer, the changes in interleukin (IL)-12, IL-10, and TNF-α expression were measured in rat serum by ELISA. CTL-mediated lysis was assessed using the MTT assay. PDT-generated antigens further purified by acid elution had the greatest stimulatory effect on DCs based on the elevated serum IL-12 and TNF-α levels and decreased serum IL-10 levels. CTL activity in this group was also highest (percent lysis 95.5% ± 0.016) compared with that elicited by PDT-supernatants, acid elution, and freeze-thawing (or the control group), which had 90.2% ± 0.024, 73.3% ± 0.027, 63.6% ± 0.049, or 0.4% ± 0.063 lysis, respectively. PDT significantly enhanced tumor cell immunogenicity. These data suggested that DC vaccines prepared by treating tumor cells with PDT to generate antigen-specific CTL responses can be developed as novel cancer immunotherapeutic strategies.

Targeted Therapy of Cancer Using Photodynamic Therapy in Combination with Multi-faceted Anti-Tumor Modalities

Photodynamic therapy (PDT) has emerged as one of the important therapeutic options in the management of cancer and other diseases. PDT involves a tumor-localized photosensitizer (PS), which when appropriately illuminated by visible light converts oxygen into cytotoxic reactive oxygen species (ROS), that attack key structural entities within the targeted cells, ultimately resulting in necrosis or apoptosis. Though PDT is a selective modality, it can be further enhanced by combining other targeted therapeutic strategies that include the use of synthetic peptides and nanoparticles for selective delivery of photosensitizers. Another potentially promising strategy is the application of targeted therapeutics that exploit a myriad of critical pathways involved in tumorigenesis and metastasis. Vascular disrupting agents that eradicate tumor vasculature during PDT and anti-angiogenic agents that targets specific molecular pathways and prevent the formation of new blood vessels are novel therapeutic approaches that have been shown to improve treatment outcome. In addition to the well-documented mechanisms of direct cell killing and damage to the tumor vasculature, PDT can also activate the body's immune response against tumors. Numerous pre-clinical studies and clinical observations have demonstrated the immuno-stimulatory capability of PDT. Herein, we aim to integrate the most important findings with regard to the combination of PDT and other novel targeted therapy approaches, detailing its potential in cancer photomedicine.