Choice of oxygen-conserving treatment regimen determines the inflammatory response and outcome of photodynamic therapy of tumors

Preoperative mapping of nonmelanoma skin cancer using spatial frequency domain and ultrasound imaging

RATIONALE AND OBJECTIVES

The treatment of nonmelanoma skin cancer (NMSC) is usually by surgical excision or Mohs micrographic surgery and alternatively may include photodynamic therapy (PDT). To guide surgery and to optimize PDT, information about the tumor structure, optical parameters, and vasculature is desired.

MATERIALS AND METHODS

Spatial frequency domain imaging (SFDI) can map optical absorption, scattering, and fluorescence parameters that can enhance tumor contrast and quantify light and photosensitizer dose. High frequency ultrasound (HFUS) imaging can provide high-resolution tumor structure and depth, which is useful for both surgery and PDT planning.

RESULTS

Here, we present preliminary results from our recently developed clinical instrument for patients with NMSC. We quantified optical absorption and scattering, blood oxygen saturation (StO2), and total hemoglobin concentration (THC) with SFDI and lesion thickness with ultrasound. These results were compared to histological thickness of excised tumor sections.

CONCLUSIONS

SFDI quantified optical parameters with high precision, and multiwavelength analysis enabled 2D mappings of tissue StO2 and THC. HFUS quantified tumor thickness that correlated well with histology. The results demonstrate the feasibility of the instrument for noninvasive mapping of optical, physiological, and ultrasound contrasts in human skin tumors for surgery guidance and therapy planning.

IL-17 promotes neutrophil entry into tumor-draining lymph nodes following induction of sterile inflammation

Blood-borne neutrophils are excluded from entering lymph nodes across vascular portals termed high endothelial venules (HEVs) because of lack of expression of the CCR7 homeostatic chemokine receptor. Induction of sterile inflammation increases neutrophil entry into tumor-draining lymph nodes (TDLNs), which is critical for induction of antitumor adaptive immunity following treatments such as photodynamic therapy (PDT). However, the mechanisms controlling neutrophil entry into TDLNs remain unclear. Prior evidence that IL-17 promotes neutrophil emigration to sites of infection via induction of CXCL2 and CXCL1 inflammatory chemokines raised the question of whether IL-17 contributes to chemokine-dependent trafficking in TDLNs. In this article, we demonstrate rapid accumulation of IL-17-producing Th17 cells in the TDLNs following induction of sterile inflammation by PDT. We further report that nonhematopoietic expression of IL-17RA regulates neutrophil accumulation in TDLNs following induction of sterile inflammation by PDT. We show that HEVs are the major route of entry of blood-borne neutrophils into TDLNs through interactions of l-selectin with HEV-expressed peripheral lymph node addressin and by preferential interactions between CXCR2 and CXCL2 but not CXCL1. CXCL2 induction in TDLNs was mapped in a linear pathway downstream of IL-17RA-dependent induction of IL-1β. These results define a novel IL-17-dependent mechanism promoting neutrophil delivery across HEVs in TDLNs during acute inflammatory responses.

Vascular targeting to the SST2 receptor improves the therapeutic response to near-IR two-photon activated PDT for deep-tissue cancer treatment

BACKGROUND

Broader clinical acceptance of photodynamic therapy is currently hindered by (a) poor depth efficacy, and (b) predisposition towards establishment of an angiogenic environment during the treatment. Improved depth efficacy is being sought by exploiting the NIR tissue transparency window and by photo-activation using two-photon absorption (2PA). Here, we use two-photon activation of PDT sensitizers, untargeted and targeted to SST2 receptors or EGF receptors, to achieve deep tissue treatment.

METHODS

Human tumor lines, positive or negative for SST2r expression were used, as well as murine 3LL cells and bovine aortic endothelial cells. Expression of SST2 receptors on cancer cells and tumor vasculature was evaluated in vitro and frozen xenograft sections. PDT effects on tumor blood flow were followed using in vivo scanning after intravenous injection of FITC conjugated dextran 150K. Dependence of the PDT efficacy on the laser pulse duration was evaluated. Effectiveness of targeting to vascular SST2 receptors was compared to that of EGF receptors, or no targeting.

RESULTS

Tumor vasculature stained for SST2 receptors even in tumors from SST2 receptor negative cell lines, and SST2r targeted PDT led to tumor vascular shutdown. Stretching the pulse from ~120fs to ~3ps led to loss of the PDT efficacy especially at greater depth. PDT targeted to SST2 receptors was much more effective than untargeted PDT or PDT targeted to EGF receptors.

GENERAL SIGNIFICANCE

The use of octreotate to target SST2 receptors expressed on tumor vessels is an excellent approach to PDT with few recurrences and some long term cures.

Apoptosis in cancer cells induced by photodynamic treatment – a methodological approach

Photodynamic therapy (PDT) is approved for clinical indications including several (pre-) cancers of the skin and solid tumors of the brain and the gastrointestinal tract. It operates by an acute cellular response caused by oxidation of cell components following light-induced and photosensitizer-mediated generation of reactive oxygen species. By this, PDT is capable of inducing the major types of cytotoxic responses: autophagy, apoptosis, and necrosis. As excited photosensitizer molecules react rather non-specifically with neighboring molecules, we suggest that with PDT and most (if not any) cell-localizing photosensitizers, all kinds of cellular responses can be provoked — following a strict dose-dependency, i.e. a transition from survival, over apoptosis to necrosis depending on the applied photosensitizer concentration or light dose. In this review, we briefly discuss (i) the types of cell death induced by PDT focusing on apoptosis induction, (ii) a simple experimental approach to quickly assess the dose-dependent phototoxic responses based on viability assays, and (iii) an overview of in vitro apoptosis detection methods for further in depth analyses. With this conceptual framework, we attempt to provide a rational experimental approach for initial in vitro, cell-based characterization of newly synthesized photosensitizers or formulations thereof — thus to plug the gap between subsequent in vivo evaluation and the preceding fundamental (physico-)chemical work devoted to the improvement of photosensitizing drugs based on mainly porphyrins, phthalocyanines and their derivatives.

Photodynamic therapy of a 2-methoxyestradiol tumor-targeting drug delivery system mediated by Asn-Gly-Arg in breast cancer

Fullerene (C60) has shown great potential in drug delivery. In this study we exploited modified fullerene (diadduct malonic acid-fullerene-Asn-Gly-Arg peptide [DMA-C60-NGR]) as an antitumor drug carrier in order to build a new tumor-targeting drug delivery system. We also investigated the synergistic enhancement of cancer therapy using photodynamic therapy (PDT) induced by DMA-C60-NGR and 2-methoxyestradiol (2ME). Cytotoxicity tests indicated that DMA-C60-NGR had no obvious toxicity, while our drug delivery system (DMA-C60-2ME-NGR) had a high inhibition effect on MCF-7 cells compared to free 2ME. The tumor-targeting drug delivery system could efficiently cross cell membranes, and illumination induced the generation of intracellular reactive oxygen species and DNA damage. Furthermore, DMA-C60-2ME-NGR with irradiation had the highest inhibition effect on MCF-7 cells compared to the other groups. DMA-C60-NGR combined with 2ME showed a good synergistic photosensitization effect for inhibiting the growth of MCF-7 cells, demonstrating that DMA-C60-2ME-NGR may be promising for high treatment efficacy with minimal side effects in future therapy.

Nicotinamide reduces photodynamic therapy-induced immunosuppression in humans

BACKGROUND

The immune suppressive effects of topical photodynamic therapy (PDT) are potential contributors to treatment failure after PDT for nonmelanoma skin cancer. Nicotinamide (vitamin B(3) ) prevents immune suppression by ultraviolet radiation, but its effects on PDT-induced immunosuppression are unknown.

OBJECTIVES

To determine the effects of topical and oral nicotinamide on PDT-induced immunosuppression in humans.

METHODS

Twenty healthy Mantoux-positive volunteers received 5% nicotinamide lotion or vehicle to either side of the back daily for 3 days. Another group of 30 volunteers received 500 mg oral nicotinamide or placebo twice daily for 1 week in a randomized, double-blinded, crossover design. In each study, methylaminolaevulinate cream was applied to discrete areas on the back, followed by narrowband red light irradiation (37 J cm(-2) ) delivered at high (75 mW cm(-2) ) or low (15 mW cm(-2) ) irradiance rates. Adjacent, nonirradiated sites served as controls. Delayed-type hypersensitivity (Mantoux) reactions were assessed at treatment and control sites to determine immunosuppression.

RESULTS

High irradiance rate PDT with vehicle or with placebo caused significant immunosuppression (equivalent to 48% and 50% immunosuppression, respectively; both P < 0·0001); topical and oral nicotinamide reduced this immunosuppression by 59% and 66%, respectively (both P < 0·0001). Low irradiance rate PDT was not significantly immunosuppressive in the topical nicotinamide study (15% immunosuppression, not significant), but caused 22% immunosuppression in the oral study (placebo arm; P = 0·006); nicotinamide reduced this immunosuppression by 69% (P = 0·045).

CONCLUSIONS

While the clinical relevance of these findings is currently unknown, nicotinamide may provide an inexpensive means of preventing PDT-induced immune suppression and enhancing PDT cure rates.

Confocal fluorescence imaging enables noninvasive quantitative assessment of host cell populations in vivo following photodynamic therapy

We report the use of optical imaging strategies to noninvasively examine photosensitizer distribution and physiological and host responses to 2-[1-hexyloxyethyl]-2 devinyl pyropheophorbide-a (HPPH)-mediated photodynamic therapy (PDT) of EMT6 tumors established in the ears of BALB/c mice. 24 h following intravenous (IV) administration of 1 μmol kg(-1) HPPH, wide-field fluorescence imaging reveals tumor selectivity with an approximately 2-3-fold differential between tumor and adjacent normal tissue. Confocal microscopy demonstrates a relatively homogeneous intratumor HPPH distribution. Labeling of host cells using fluorophore-conjugated antibodies allowed the visualization of Gr1(+)/CD11b(+) leukocytes and major histocompatibility complex class II (MHC-II)(+) cells in vivo. Imaging of the treated site at different time-points following irradiation shows significant and rapid increases in Gr1(+) cells in response to therapy. The maximum accumulation of Gr1(+) cells is found at 24 h post-irradiation, followed by a decrease at the 48 h time-point. Using IV-injected FITC-conjugated dextran as a fluorescent perfusion marker, we imaged tissue perfusion at different times post-irradiation and found that the reduced Gr1(+ )cell density at 48 h correlated strongly with functional damage to the vasculature as reported via decreased perfusion status. Dual color confocal imaging experiments demonstrates that about 90% of the anti-Gr1 cell population co-localized with anti-CD11b labeling, thus indicating that majority of the Gr1-labeled cells were neutrophils. At 24 h post-PDT, an approximately 2-fold increase in MHC-II+ cells relative to untreated control is also observed. Co-localization analysis reveals an increase in the fraction of Gr1(+) cells expressing MHC-II, suggesting that HPPH-PDT is stimulating neutrophils to express an antigen-presenting phenotype.

Novel methods to incorporate photosensitizers into nanocarriers for cancer treatment by photodynamic therapy

OBJECTIVE

A hydrophobic photosensitizer, 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH), was loaded into nontoxic biodegradable amine functionalized polyacrylamide (AFPAA) nanoparticles using three different methods (encapsulation, conjugation, and post-loading), forming a stable aqueous dispersion. Each formulation was characterized for physicochemical properties as well as for photodynamic performance so as to determine the most effective nanocarrier formulation containing HPPH for photodynamic therapy (PDT).

MATERIALS AND METHODS

HPPH or HPPH-linked acrylamide was added into monomer mixture and polymerized in a microemulsion for encapsulation and conjugation, respectively. For post-loading, HPPH was added to an aqueous suspension of pre-formed nanoparticles. Those nanoparticles were tested for optical characteristics, dye loading, dye leaching, particle size, singlet oxygen production, dark toxicity, in vitro photodynamic cell killing, whole body fluorescence imaging and in vivo PDT.

RESULTS

HPPH was successfully encapsulated, conjugated or post-loaded into the AFPAA nanoparticles. The resultant nanoparticles were spherical with a mean diameter of 29 ± 3 nm. The HPPH remained intact after entrapment and the HPPH leaching out of nanoparticles was negligible for all three formulations. The highest singlet oxygen production was achieved by the post-loaded formulation, which caused the highest phototoxicity in in vitro assays. No dark toxicity was observed. Post-loaded HPPH AFPAA nanoparticles were localized to tumors in a mouse colon carcinoma model, enabling fluorescence imaging, and producing a similar photodynamic tumor response to that of free HPPH in equivalent dose.

CONCLUSIONS

Post-loading is the promising method for loading nanoparticles with hydrophobic photosensitizers to achieve effective in vitro and in vivo PDT.

Antiangiogenesis agents avastin and erbitux enhance the efficacy of photodynamic therapy in a murine bladder tumor model

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) has been established as an alternative therapy for the treatment of various types of malignant disorders, including oesophageal, lung, and bladder cancer. However, one of the limitations of PDT is treatment-induced hypoxia that triggers angiogenesis. The objective of this study was to evaluate the effects of combination therapy with PDT and an antiangiogenic protocol using monoclonal antibodies against both vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR).

MATERIALS AND METHODS

In vitro angiogenesis assays and in vivo matrigel assay were performed to understand the inhibitory effects of the antiangiogenic agents. Tumor bearing mice were assigned to six different categories: Control, PDT only, Avastin + Erbitux, PDT + Avastin, PDT + Erbitux, and PDT + Avastin and Erbitux. Treated and control tumors were monitored for recurrence for up to 90 days.

RESULTS

In vitro results provided valuable insight into the dynamics of endothelial cells in response to angiogenic stimulants and inhibitors to assess the angiogenesis processes. Addition of VEGF increased the migration of bladder cancer cells and addition of Avastin and Erbitux decreased cell migration significantly. Both inhibitors were also able to suppress invasion and tube formation in human umbilical vein endothelial cells (HUVEC). The in vivo tumor response for PDT with single inhibitor (Avastin or Erbitux) and double inhibitor (Avastin + Erbitux) was comparable; however, targeting both VEGF and EGFR pathways along with PDT resulted in more rapid response. Downregulation of VEGF and EGFR were observed in tumors treated with PDT in combination with Avastin and Erbitux respectively.

CONCLUSION

Our results show that blocking the VEGF or EGFR pathway along with PDT can effectively suppress tumor growth and the combination of both VEGF and EGFR inhibitors along with PDT could be used to treat more aggressive tumors to achieve rapid 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.

Photodynamic therapy of cervical intraepithelial neoplasia 1-3 and human papilloma virus (HMV) infection with methylaminolevulinate and hexaminolevulinate--a double-blind, dose-finding study

INTRODUCTION

Cervical intraepithelial neoplasia (CIN) 1-3 is the precursor of invasive cervical cancer and associated with human papillomavirus infection. Standard treatment is surgical and may be associated with subsequent pregnancy complications. Photodynamic therapy (PDT) of CIN may be an interesting alternative.

MATERIAL AND METHODS

Patients were treated by PDT using hexaminolevulinate (HAL) and methylaminolevulinate in six dose and light groups and two incubation periods in a double-blind setting. Follow-up examinations were performed after 3, 6, and 12 months with histology, cytology, and HPV testing.

RESULTS

We included eight patients with CIN1, 23 with CIN2, and 36 with CIN3. Treatment was well tolerated. HAL 40 mM with 3-hour application turned out to be the most-effective group with 67% (10/15) complete response rate. The combined complete and partial response for patients with CIN2 was 83% (20/24).

CONCLUSION

PDT with CIN may be a safe and effective procedure for CIN treatment.

The effects of combined treatment with ionizing radiation and indocyanine green-mediated photodynamic therapy on breast cancer cells

This study was undertaken to evaluate the effects of indocyanine green as a sensitizer in both photodynamic and radiation therapy on MCF-7 human breast cancer cells line. The cells were incubated with indocyanine green at different concentrations for 24h and were then exposed in the independent treatment groups to a non-coherent light at different fluence rates and X-ray ionizing radiation at different dose rates. In addition, combination effects of this chemo, photo, and radiotherapy were evaluated. The percentage of the cell survival was investigated using the MTT assay. The results showed that indocyanine green had no significant cytotoxic effects up to 100 μM but as a photosensitizer had a strong cytotoxic effect on cancer cells. Despite, indocyanine green could not act as a radiosensitizer. Furthermore, it is surprising to find that 50 μM of indocyanine green in combination with light at 60 J/cm(2) and 4 Gy of X-ray radiation astonishingly killed cancer cells and reduced the percentage of viable cancer cells to be 3.42%. According to the findings, we observed the same efficacy of treatment by adding a low dose of radiation and reducing light fluence rate. In fact, it appears from our data that the adverse effects of photodynamic therapy can be partially abated without reducing the efficacy of treatment. Obviously, this new therapeutic avenue in breast cancer therapy could be worth further investigation and elucidation and should be tested in vivo models for being applied in human therapy.

NADH fluorescence as a photobiological metric in 5-aminolevlinic acid (ALA)-photodynamic therapy

Photodynamic therapy (PDT) dosimetry is complex as many factors are involved and varied interdependently. Monitoring the biological consequence of PDT such as cell death is the most direct approach to assess treatment efficacy. In this study, we performed 5-aminolevlinic acid (ALA)-PDT in vitro to induce different cell death modes (i.e., slight cell cytotoxicity, apoptosis, and necrosis) by a fixed fluence rate of 10 mW/cm(2) and varied fluences (1, 2, and 6 J/cm(2)). Time course measurements of cell viability, caspase-3 activity, and DNA fragmentation were conducted to determine the mode of cell death. We demonstrated that NADH fluorescence lifetime together with NADH fluorescence intensity permit us to detect apoptosis and differentiate it from necrosis. This feature will be unique in the use of optimizing apoptosis-favored treatments such as metronomic PDT.

Polymorphonuclear neutrophils and cancer: intense and sustained neutrophilia as a treatment against solid tumors

Polymorphonuclear neutrophils (PMN) are the most abundant circulating immune cells and represent the first line of immune defense against infection. This review of the biomedical literature of the last 40 years shows that they also have a powerful antitumoral effect under certain circumstances. Typically, the microenvironment surrounding a solid tumor possesses many of the characteristics of chronic inflammation, a condition considered very favorable for tumor growth and spread. However, there are many circumstances that shift the chronic inflammatory state toward an acute inflammatory response around a tumor. This shift seems to convert PMN into very efficient anticancer effector cells. Clinical reports of unexpected antitumoral effects linked to the prolonged use of granulocyte colony-stimulating factor, which stimulates an intense and sustained neutrophilia, suggest that an easy way to fight solid tumors would be to encourage the development of intense peritumoral PMN infiltrates. Specifically designed clinical trials are urgently needed to evaluate the safety and efficacy of such drug-induced neutrophilia in patients with solid tumors. This antitumoral role of neutrophils may provide new avenues for the clinical treatment of cancer.

Photodynamic therapy augments the efficacy of oncolytic vaccinia virus against primary and metastatic tumours in mice

Background:

Therapies targeted towards the tumour vasculature can be exploited for the purpose of improving the systemic delivery of oncolytic viruses to tumours. Photodynamic therapy (PDT) is a clinically approved treatment for cancer that is known to induce potent effects on tumour vasculature. In this study, we examined the activity of PDT in combination with oncolytic vaccinia virus (OVV) against primary and metastatic tumours in mice.

Methods:

The effect of 2-[1-hexyloxyethyl-]-2-devinyl pyropheophorbide-a (HPPH)-sensitised-PDT on the efficacy of oncolytic virotherapy was investigated against subcutaneously implanted syngeneic murine NXS2 neuroblastoma and human FaDu head and neck squamous cell carcinoma xenografts in nude mice. Treatment efficacy was evaluated by monitoring tumour growth and survival. The effects of combination treatment on vascular function were examined using magnetic resonance imaging (MRI) and immunohistochemistry, whereas viral replication in tumour cells was analysed by a standard plaque assay. Normal tissue phototoxicity following PDT-OV treatment was studied using the mouse foot response assay.

Results:

Combination of PDT with OVV resulted in inhibition of primary and metastatic tumour growth compared with either monotherapy. PDT-induced vascular disruption resulted in higher intratumoural viral titres compared with the untreated tumours. Five days after delivery of OVV, there was a loss of blood flow to the interior of tumour that was associated with infiltration of neutrophils. Administration of OVV did not result in any additional photodynamic damage to normal mouse foot tissue.

Conclusion:

These results provide evidence into the usefulness of PDT as a means of enhancing intratumoural replication and therapeutic efficacy of OV.

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 of cancer: an update

Photodynamic therapy (PDT) is a clinically approved, minimally invasive therapeutic procedure that can exert a selective cytotoxic activity toward malignant cells. The procedure involves administration of a photosensitizing agent followed by irradiation at a wavelength corresponding to an absorbance band of the sensitizer. In the presence of oxygen, a series of events lead to direct tumor cell death, damage to the microvasculature, and induction of a local inflammatory reaction. Clinical studies revealed that PDT can be curative, particularly in early stage tumors. It can prolong survival in patients with inoperable cancers and significantly improve quality of life. Minimal normal tissue toxicity, negligible systemic effects, greatly reduced long-term morbidity, lack of intrinsic or acquired resistance mechanisms, and excellent cosmetic as well as organ function-sparing effects of this treatment make it a valuable therapeutic option for combination treatments. With a number of recent technological improvements, PDT has the potential to become integrated into the mainstream of cancer treatment.

Aminolevulinic acid-photodynamic therapy combined with topically applied vascular disrupting agent vadimezan leads to enhanced antitumor responses

The tumor vascular-disrupting agent (VDA) vadimezan (5,6-dimethylxanthenone-4-acetic acid, DMXAA) has been shown to potentiate the antitumor activity of photodynamic therapy (PDT) using systemically administered photosensitizers. Here, we characterized the response of subcutaneous syngeneic Colon26 murine colon adenocarcinoma tumors to PDT using the locally applied photosensitizer precursor aminolevulinic acid (ALA) in combination with a topical formulation of vadimezan. Diffuse correlation spectroscopy (DCS), a noninvasive method for monitoring blood flow, was utilized to determine tumor vascular response to treatment. In addition, correlative CD31-immunohistochemistry to visualize endothelial damage, ELISA to measure induction of tumor necrosis factor-alpha (TNF-α) and tumor weight measurements were also examined in separate animals. In our previous work, DCS revealed a selective decrease in tumor blood flow over time following topical vadimezan. ALA-PDT treatment also induced a decrease in tumor blood flow. The onset of blood flow reduction was rapid in tumors treated with both ALA-PDT and vadimezan. CD31-immunostaining of tumor sections confirmed vascular damage following topical application of vadimezan. Tumor weight measurements revealed enhanced tumor growth inhibition with combination treatment compared with ALA-PDT or vadimezan treatment alone. In conclusion, vadimezan as a topical agent enhances treatment efficacy when combined with ALA-PDT. This combination could be useful in clinical applications.

PDT-induced inflammatory and host responses

Photodynamic therapy (PDT) is used in the management of neoplastic and nonmalignant diseases. Its unique mechanisms of action include direct cytotoxic effects exerted towards tumor cells, destruction of tumor and peritumoral vasculature and induction of local acute inflammatory reaction. The latter develops in response to (1) damage to tumor and stromal cells that leads to the release of cell death-associated molecular patterns (CDAMs) or damage associated molecular patterns (DAMPs), (2) early vascular changes that include increased vascular permeability, vascular occlusion, and release of vasoactive and proinflammatory mediators, (3) activation of alternative pathway of complement leading to generation of potent chemotactic factors, and (4) induction of signaling cascades and transcription factors that trigger secretion of cytokines, matrix metalloproteinases, or adhesion molecules. The majority of studies indicate that induction of local inflammatory response contributes to the antitumor effects of PDT and facilitates development of systemic immunity. However, the degree of PDT-induced inflammation and its subsequent contribution to its antitumor efficacy depend on multiple parameters, such as chemical nature, concentration and subcellular localization of the photosensitizers, the spectral characteristics of the light source, light fluence and fluence rate, oxygenation level, and tumor type. Identification of detailed molecular mechanisms and development of therapeutic approaches modulating PDT-induced inflammation will be necessary to tailor this treatment to particular clinical conditions.

Photodynamic therapy enhancement of anti-tumor immunity

Photodynamic therapy (PDT) is an FDA-approved modality for the treatment of early-stage disease and palliation of late-stage disease. Pre-clinical studies using mouse models and clinical studies in patients have demonstrated that PDT is capable of influencing the immune system. The effect of PDT on the generation of anti-tumor immunity is regimen-dependent and is tightly linked to the degree and nature of inflammation induced by PDT. However, the precise mechanism underlying PDT-regulated adaptive anti-tumor immunity remains unclear. This review will focus on the current knowledge of immune regulation by PDT.

Photodynamic therapy-induced immunosuppression in humans is prevented by reducing the rate of light delivery

Photodynamic therapy (PDT) of non-melanoma skin cancers currently carries failure rates of 10-40%. The optimal irradiation protocol is as yet unclear. Previous studies showed profound immunosuppression after PDT, which may compromise immune-mediated clearance of these antigenic tumors. Slower irradiation prevents immunosuppression in mice, and may be at least as effective as high-fluence-rate PDT in preliminary clinical trials. The photosensitizers 5-aminolaevulinic acid and/or methyl aminolaevulinate were applied to discrete areas on the backs of healthy Mantoux-positive volunteers, followed by narrowband red light irradiation (632 nm) at varied doses and fluence rates. Delayed type hypersensitivity (Mantoux) reactions were elicited at test sites and control sites to determine immunosuppression. Human ex vivo skin received low- and high-fluence-rate PDT and was stained for oxidative DNA photolesions. PDT caused significant, dose-responsive immunosuppression at high (75 mW cm(-2)) but not low (15 or 45 mW cm(-2)) fluence rates. DNA photolesions, which may be a trigger for immunosuppression, were observed after high-fluence-rate PDT but not when light was delivered more slowly. This study demonstrates that the current clinical PDT protocol (75 mW cm(-2)) is highly immunosuppressive. Simply reducing the rate of irradiation, while maintaining the same light dose, prevented immunosuppression and genetic damage and may have the potential to improve skin cancer outcomes.

Stimulation of anti-tumor immunity by photodynamic therapy

Photodynamic therapy (PDT) is a rapidly developing cancer treatment that utilizes the combination of nontoxic dyes and harmless visible light to destroy tumors by generating reactive oxygen species. PDT produces tumor-cell destruction in the context of acute inflammation that acts as a 'danger signal' to the innate immune system. Activation of the innate immune system increases the priming of tumor-specific T lymphocytes that have the ability to recognize and destroy distant tumor cells and, in addition, lead to the development of an immune memory that can combat recurrence of the cancer at a later point in time. PDT may be also successfully combined with immunomodulating strategies that are capable of overcoming or bypassing the escape mechanisms employed by the progressing tumor to evade immune attack. This article will cover the role of the immune response in PDT anti-tumor effectiveness. It will highlight the milestones in the development of PDT-mediated anti-tumor immunity and emphasize the combination strategies that may improve this therapy.

Increasing damage to tumor blood vessels during motexafin lutetium-PDT through use of low fluence rate

Photodynamic therapy (PDT) with low light fluence rate has rarely been studied in protocols that use short drug-light intervals and thus deliver illumination while plasma concentrations of photosensitizer are high, creating a prominent vascular response. In this study, the effects of light fluence rate on PDT response were investigated using motexafin lutetium (10 mg/kg) in combination with 730 nm light and a 180-min drug-light interval. At 180 min, the plasma level of photosensitizer was 5.7 ng/microl compared to 3.1 ng/mg in RIF tumor, and PDT-mediated vascular effects were confirmed by a spasmodic decrease in blood flow during illumination. Light delivery at 25 mW/cm(2) significantly improved long-term tumor responses over that at 75 mW/cm(2). This effect could not be attributed to oxygen conservation at low fluence rate, because 25 mW/cm(2) PDT provided little benefit to tumor hemoglobin oxygen saturation. However, 25 mW/cm(2) PDT did prolong the duration of ischemic insult during illumination and was correspondingly associated with greater decreases in perfusion immediately after PDT, followed by smaller increases in total hemoglobin concentration in the hours after PDT. Increases in blood volume suggest blood pooling from suboptimal vascular damage; thus the smaller increases after 25 mW/cm(2) PDT provide evidence of more widespread vascular damage, which was accompanied by greater decreases in clonogenic survival. Further study of low fluence rate as a means to improve responses to PDT under conditions designed to predominantly damage vasculature is warranted.

Substrate affinity of photosensitizers derived from chlorophyll-a: the ABCG2 transporter affects the phototoxic response of side population stem cell-like cancer cells to photodynamic therapy

Photosensitizers (PS) synthesized with the aim of optimizing photodynamic therapy (PDT) of tumors do not always fulfill their potential when tested in vitro and in vivo in different tumor models. The ATP-dependent transporter ABCG2, a multidrug resistant pump expressed at variable levels in cancerous cells, can bind and efflux a wide range of structurally different classes of compounds including several PS used preclinically and clinically such as porphyrins and chlorins. ABCG2 may lower intracellular levels of substrate PS below the threshold for cell death in tumors treated by PDT, leaving resistant cells to repopulate the tumor. To determine some of the structural factors that affect substrate affinity of PS for ABCG2, we used an ABCG2-expressing cell line (HEK 293 482R) and its nonexpressing counterpart, and tyrosine kinase ABCG2 inhibitors in a simple flow cytometric assay to identify PS effluxed by the ABCG2 pump. We tested a series of conjugates of substrate PS with different groups attached at different positions on the tetrapyrrole macrocycle to examine whether a change in affinity for the pump occurred and whether such changes depended on the position or the structure/type of the attached group. PS without substitutions including pyropheophorbides and purpurinimides were generally substrates for ABCG2, but carbohydrate groups conjugated at positions 8, 12, 13, and 17 but not at position 3 abrogated ABCG2 affinity regardless of structure or linking moiety. At position 3, affinity was retained with the addition of iodobenzene, alkyl chains and monosaccharides, but not with disaccharides. This suggests that structural characteristics at position 3 may offer important contributions to requirements for binding to ABCG2. We examined several tumor cell lines for ABCG2 activity, and found that although some cell lines had negligible ABCG2 activity in bulk, they contained a small ABCG2-expressing side population (SP) thought to contain cells which are responsible for initiating tumor regrowth. We examined the relevance of the SP to PDT resistance with ABCG2 substrates in vitro and in vivo in the murine mammary tumor 4T1. We show for the first time in vivo that the substrate PS HPPH (2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a) but not the nonsubstrate PS HPPH-Gal (a galactose conjugate of HPPH) selectively preserved the SP which was primarily responsible for regrowth in vitro. The SP could be targeted by addition of imatinib mesylate, a tyrosine kinase inhibitor which inhibits the ATPase activity of ABCG2, and prevents efflux of substrates. A PDT resistant SP may be responsible for recurrences observed both preclinically and clinically. To prevent ABCG2 mediated resistance, choosing nonsubstrate PS or administering an ABCG2 inhibitor alongside a substrate PS might be advantageous when treating ABCG2-expressing tumors with PDT.

Compartmental targeting for mTHPC-based photodynamic treatment in vivo: Correlation of efficiency, pharmacokinetics, and regional distribution of apoptosis

PURPOSE

The present study investigates the efficacy of compartmental targeting in xenografted tumors treated by meta-tetra(hydroxyphenyl)chlorin (mTHPC)-mediated photodynamic therapy (PDT). The therapeutic efficacy was, furthermore, related to a regional photoinduced distribution of apoptosis and an mTHPC biodistribution profile.

METHODS AND MATERIALS

Mice bearing EMT6 tumors were subjected to a single irradiation (10 J/cm(2)) of red laser light (652 nm) at different intervals after a single- (0.3 mg/kg or 0.15 mg/kg) or double-intravenous (2 × 0.15 mg/kg) injection(s) of mTHPC. Efficiency of the treatment was evaluated by monitoring tumor regrowth. mTHPC pharmacokinetics were assessed by high-performance liquid chromatography analysis of excised organs. The regional distribution of apoptosis in tumor sections was investigated with a newly developed colabelling immunohistochemistry technique.

RESULTS

A fractionated double-injection protocol of mTHPC with 24-h and 3-h drug-light intervals (DLI) yielded 100% tumor cure, with tumors presenting a massive apoptosis of neoplastic cells along with a distortion of vessels. The best efficiency for a single injection (0.3 mg/kg) was about 54% tumor cure and corresponded to a DLI of 3 h. At this DLI, tumors showed apoptosis of endothelial cells in residual vessels. Concentrations of mTHPC observed in plasma and tumor for the fractionated injection were not statistically different and were less than the total drug dose in each compartment.

CONCLUSIONS

The present work suggests that clinical PDT protocols with mTHPC could be greatly improved by fractionation of the drug administration. Time points should be chosen based on the intratumoral spatiotemporal drug distribution.

Enhancement of anti-tumor immunity by photodynamic therapy

Photodynamic therapy (PDT) is an FDA-approved modality that rapidly eliminates local tumors, resulting in cure of early disease and palliation of advanced disease. PDT was originally considered to be a local treatment; however, both pre-clinical and clinical studies have shown that local PDT treatment of tumors can enhance systemic anti-tumor immunity. The current state of investigations into the ability of PDT to enhance anti-tumor immunity, the mechanisms behind this enhancement and the future of PDT as an immunotherapy are addressed in this review.

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.

Standard-fluence versus low-fluence photodynamic therapy in chronic central serous chorioretinopathy: a nonrandomized clinical trial

PURPOSE

To evaluate the efficacy of low-fluence compared with standard-fluence rate photodynamic therapy (PDT) for treating chronic central serous chorioretinopathy.

DESIGN

Prospective, multicenter, investigator-masked, nonrandomized clinical trial.

METHODS

Forty-two eyes (42 patients) with chronic central serous chorioretinopathy were enrolled; 19 eyes received indocyanine green angiography-guided standard-fluence PDT (50 J/cm(2)) and 23 eyes received indocyanine green angiography-guided low-fluence PDT (25 J/cm(2)). Primary outcome measures were the changes in mean logarithm of the minimal angle of resolution best-corrected visual acuity and the rate of eyes with complete subretinal fluid reabsorption. Secondary outcomes were the changes in central foveal thickness and choroidal perfusion.

RESULTS

Mean logarithm of the minimal angle of resolution best-corrected visual acuity improved significantly at all time points (P < .01), in the standard-fluence group from 0.43 to 0.24 at 12 months and in the low-fluence-group from 0.46 to 0.16, without significant difference between the 2 groups. At 12 months, a complete subretinal fluid reabsorption was seen in 15 standard-fluence-treated and 21 low-fluence-treated eyes (79% vs 91%; P = .5). In 1 standard-fluence eye, choroidal neovascularization developed at 3 months, and this eye received further PDT; in the other eyes, at 12 months, a moderate-significant choriocapillaris nonperfusion was seen in 8 standard-fluence-treated and 0 low-fluence-treated eyes (44% vs 0%; P = .002).

CONCLUSIONS

In most of the eyes, both standard-fluence PDT and low-fluence PDT resulted in complete subretinal fluid reabsorption with visual acuity improvement. Choroidal hypoperfusion related to PDT could be reduced by low-fluence PDT.

Evaluation of hypericin-mediated photodynamic therapy in combination with angiogenesis inhibitor bevacizumab using in vivo fluorescence confocal endomicroscopy

Photodynamic therapy (PDT) is an alternative cancer treatment modality that offers localized treatment using a photosensitizer and light. However, tumor angiogenesis is a major concern following PDT-induced hypoxia as it promotes recurrence. Bevacizumab is a monoclonal antibody that targets vascular endothelial growth factor (VEGF), thus preventing angiogenesis. The combination of PDT with antiangiogenic agents such as bevacizumab has shown promise in preclinical studies. We use confocal endomicroscopy to study the antiangiogenic effects of PDT in combination with bevacizumab. This technique offers in vivo surface and subsurface fluorescence imaging of tissue. Mice bearing xenograft bladder carcinoma tumors were treated with PDT, bevacizumab, or PDT and bevacizumab combination therapy. In tumor regression experiments, combination therapy treated tumors show the most regression. Confocal fluorescence endomicroscopy enables visualization of tumor blood vessels following treatment. Combination therapy treated tumors show the most posttreatment damage with reduced cross-sectional area of vessels. Immunohistochemistry and immunofluorescence studies show that VEGF expression is significantly downregulated in the tumors treated by combination therapy. Overall, combining PDT and bevacizumab is a promising cancer treatment approach. We also demonstrate that confocal endomicroscopy is useful for visualization of vasculature and evaluation of angiogenic response following therapeutic intervention.

Low-fluence-rate photodynamic therapy to treat subfoveal choroidal neovascularization in pathological myopia. A study of efficacy and safety

BACKGROUND

To evaluate the efficacy and safety of low-fluence-rate photodynamic therapy (LFPDT) to treat choroidal neovascularisation (CNV) secondary to pathological myopia (PM).

METHODS

Twenty-five eyes with CNV in PM underwent LFPDT, with a standard dose of verteporfin and timing but adopting fluence and irradiance rates reduced to 25 mJ/cm2 and 300 mW/cm2, respectively. Best corrected visual acuity (BCVA) was measured and biomicroscopy and fluorescein angiography (FA) were evaluated. Particular attention was paid to choroidal hypoperfusion, and to changes (depigmentation/atrophy) at the RPE level in areas exposed to laser light.

RESULTS

After a mean follow-up of 13.4+/-2.46 months (range: 12-21), and 1.37+/-0.66 treatments (range: 1-3), BCVA was stable in 29 (91%) eyes. Two (6%) patients gained more than three lines and one (3%) eye lost more than three lines. Mean greatest linear dimension did not change significantly (p=0.08) at the end of follow-up. RPE depigmentation was present in six eyes (18%) and no patient showed RPE atrophy.

CONCLUSIONS

LFPDT is effective and safe for CNV secondary to PM treatment, stabilizing visual acuity and lesion size and determining only mild RPE changes. Further controlled studies are needed to demonstrate the long-term efficacy and safety of this treatment option.

Targeting EGFR with photodynamic therapy in combination with Erbitux enhances in vivo bladder tumor response

BACKGROUND

Photodynamic therapy (PDT) is a promising cancer treatment modality that involves the interaction of the photosensitizer, molecular oxygen and light of specific wavelength to destroy tumor cells. Treatment induced hypoxia is one of the main side effects of PDT and efforts are underway to optimize PDT protocols for improved efficacy. The aim of this study was to investigate the anti-tumor effects of PDT plus Erbitux, an angiogenesis inhibitor that targets epidermal growth factor receptor (EGFR), on human bladder cancer model. Tumor-bearing nude mice were assigned to four groups that included control, PDT, Erbitux and PDT plus Erbitux and tumor volume was charted over 90-day period.

RESULTS

Our results demonstrate that combination of Erbitux with PDT strongly inhibits tumor growth in the bladder tumor xenograft model when compared to the other groups. Downregulation of EGFR was detected using immunohistochemistry, immunofluorescence and western blotting. Increased apoptosis was associated with tumor inhibition in the combination therapy group. In addition, we identified the dephosphorylation of ErbB4 at tyrosine 1284 site to play a major role in tumor inhibition. Also, at the RNA level downregulation of EGFR target genes cyclin D1 and c-myc was observed in tumors treated with PDT plus Erbitux.

CONCLUSION

The combination therapy of PDT and Erbitux effectively inhibits tumor growth and is a promising therapeutic approach in the treatment of bladder tumors.

Drug and light dose responses to focal photodynamic therapy of single blood vessels in vivo

As part of an ongoing program to develop two-photon (2-gamma) photodynamic therapy (PDT) for treatment of wet-form age-related macular degeneration (AMD) and other vascular pathologies, we have evaluated the reciprocity of drug-light doses in focal-PDT. We targeted individual arteries in a murine window chamber model, using primarily the clinical photosensitizer Visudyne/liposomal-verteporfin. Shortly after administration of the photosensitizer, a small region including an arteriole was selected and irradiated with varying light doses. Targeted and nearby vessels were observed for a maximum of 17 to 25 h to assess vascular shutdown, tapering, and dye leakage/occlusion. For a given end-point metric, there was reciprocity between the drug and light doses, i.e., the response correlated with the drug-light product (DLP). These results provide the first quantification of photosensitizer and light dose relationships for localized irradiation of a single blood vessel and are compared to the DLP required for vessel closure between 1-gamma and 2-gamma activation, between focal and broad-beam irradiation, and between verteporfin and a porphyrin dimer with high 2-gamma cross section. Demonstration of reciprocity over a wide range of DLP is important for further development of focal PDT treatments, such as the targeting of feeder vessels in 2-gamma PDT of AMD.

Fluence rate-dependent intratumor heterogeneity in physiologic and cytotoxic responses to Photofrin photodynamic therapy

Photodynamic therapy (PDT) can lead to the creation of heterogeneous, response-limiting hypoxia during illumination, which may be controlled in part through illumination fluence rate. In the present report we consider (1) regional differences in hypoxia, vascular response, and cell kill as a function of tumor depth and (2) the role of fluence rate as a mediator of depth-dependent regional intratumor heterogeneity. Intradermal RIF murine tumors were treated with Photofrin PDT using surface illumination at an irradiance of 75 or 38 mW cm(-2). Regional heterogeneity in tumor response was examined through comparison of effects in the surface vs. base of tumors, i.e. along a plane parallel to the skin surface and perpendicular to the incident illumination. 75 mW cm(-2) PDT created significantly greater hypoxia in tumor bases relative to their surfaces. Increased hypoxia in the tumor base could not be attributed to regional differences in Photofrin concentration nor effects of fluence rate distribution on photochemical oxygen consumption, but significant depth-dependent heterogeneity in vascular responses and cytotoxic response were detected. At a lower fluence rate of 38 mW cm(-2), no detectable regional differences in hypoxia or cytotoxic responses were apparent, and heterogeneity in vascular response was significantly less than that during 75 mW cm(-2) PDT. This research suggests that the benefits of low-fluence-rate PDT are mediated in part by a reduction in intratumor heterogeneity in hypoxic, vascular and cytotoxic responses.

Enhanced systemic immune reactivity to a Basal cell carcinoma associated antigen following photodynamic therapy

PURPOSE

Numerous preclinical studies have shown that local photodynamic therapy (PDT) of tumors enhances systemic antitumor immunity. However, other than single-case and anecdotal reports, this phenomenon has not been examined following clinical PDT. To determine whether PDT in a clinical setting enhances systemic recognition of tumor cells, we examined whether PDT of basal cell carcinoma resulted in an increased systemic immune response to Hip1, a tumor antigen associated with basal cell carcinoma.

EXPERIMENTAL DESIGN

Basal cell carcinoma lesions were either treated with PDT or surgically removed. Blood was collected from patients immediately before or 7 to 10 days following treatment. Peripheral blood leukocytes were isolated from HLA-A2-expressing patients and reactivity to a HLA-A2-restricted Hip1 peptide was measured by INF-gamma ELISpot assay.

RESULTS

Immune recognition of Hip1 increased in patients whose basal cell carcinoma lesions were treated with PDT. This increase in reactivity was significantly greater than reactivity observed in patients whose lesions were surgically removed. Patients with superficial lesions exhibited greater enhancement of reactivity compared with patients with nodular lesions. Immune reactivity following PDT was inversely correlated with treatment area and light dose.

CONCLUSIONS

These findings show for the first time that local tumor PDT can enhance systemic immune responses to tumors in patients, and validate previous preclinical findings.