Cellular targets and molecular responses associated with photodynamic therapy

Radiovaccination Strategy for Cancer Treatment Integrating Photodynamic Therapy-Generated Vaccines with Radiotherapy

Therapeutic cancer vaccines have become firmly established as a reliable and proficient form of tumor immunotherapy. They represent a promising approach for substantial advancements in the successful treatment of malignant diseases. One attractive vaccine strategy is using, as the vaccine material, the whole tumor cells treated ex vivo by rapid tumor ablation therapies that instigate stress signaling responses culminating in immunogenic cell death (ICD). One such treatment is photodynamic therapy (PDT). The underlying mechanisms and critical elements responsible for the potency of these vaccines are discussed in this review. Radiotherapy has emerged as a suitable component for the combined therapy protocols with the vaccines. Arguments and prospects for optimizing tumor control using a radiovaccination strategy involving X-ray irradiation plus PDT vaccines are presented, together with the findings supporting its validity.

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.

Feasibility of photodynamic therapy for secondary hyperparathyroidism in chronic renal failure rats

BACKGROUND

Feasibility of photodynamic therapy (PDT) for secondary hyperparathyroidism (SHPT) was examined in a rat model of SHPT.

METHODS

A photosensitizer, 5-aminolevulinic acid (5-ALA), was injected intraperitoneally, and the parathyroid glands were irradiated either after surgical exposure with 385-nm light or transdermally with 630-nm light from a light-emitting diode (LED) lamp.

RESULTS

PDT with high 5-ALA and irradiation doses caused severe hypoparathyroidism in SHPT rats within two days. Low-dose invasive PDT reduced intact parathyroid hormone (iPTH) levels in all rats from 748.9 ± 462.6 pg/mL at baseline to 138.7 ± 117.5 pg/mL at week 6, followed by a further decrease to 80.5 ± 54.0 pg/mL at week 9 in 60 % of rats or an increase to 970.0 ± 215.6 pg/mL at week 9 in 40 % of rats. Low-dose noninvasive PDT reduced iPTH levels from 1612.5 ± 607.8 pg/mL at baseline to 591.9 ± 480.1 pg/mL at week 4 in all rats. Thereafter, iPTH levels remained low in 43 % of rats and were 233.7 ± 51.6 pg/mL at week 9, whereas 57 % showed an increase, reaching 3305.9 ± 107.3 pg/mL at week 9. Control SHPT rats had iPTH levels of 2487.8 ± 350.9 and 2974.6 ± 372.1 pg/mL at week 4 and 9, respectively. The parathyroid glands of the rats with low iPTH levels were atrophied and had few parathyroid cells surrounded by fibrotic materials and no recognizable blood vessels. Those of the rats with high iPTH levels showed well-preserved gland structure, clusters of parathyroid cells, and blood vessels.

CONCLUSION

These results demonstrate that 5-ALA-mediated PDT for SHPT is feasible.

Tumor response to mTHPC-mediated photodynamic therapy exhibits strong correlation with extracellular release of HSP70

BACKGROUND AND OBJECTIVE

We investigated the relationship among heat shock protein 70 (hsp70) promoter activation, extracellular HSP70 protein levels, and tumor cure in an animal model of meso-tetrahydroxyphenyl chlorin (mTHPC; Foscan®)-mediated photodynamic therapy (PDT).

MATERIALS AND METHODS

Using Western blot analysis, we compared HSP70 protein levels in control and PDT-treated EMT6 cells with the amplitude of hsp70-promoter driven green fluorescent protein (GFP) expression in identically treated, stably transfected hsp70-GFP/EMT6 cells. A clonogenic survival assay was performed to assess the relationship among promoter activation, HSP70 levels, and cell survival in vitro. Tumor growth studies with this transfected cell line were performed to examine responses to fluences from 0.1 to 10 J cm(-2) , which ranged from sub-curative to curative. In vivo stereofluorescence and confocal fluorescence imaging were used to assess the temporal kinetics in hsp70 activation in tumors subjected to these fluences and the intratumor spatial correlation between hsp70 induction and extracellular levels of HSP70, respectively.

RESULTS

Maximum GFP expression and HSP protein levels in cells were observed at PDT doses that corresponded to 30% cell survival. The relative changes in GFP and HSP70 protein accumulation as analyzed using Western immunoblots agreed very well, thereby confirming the validity of fluorescent reporter assessment of gene expression in our studies. In vivo imaging revealed that hsp70 promoter-driven GFP expression and accumulation of extracellular HSP70 in PDT-treated tumors subjected to non-curative doses exhibit minimal spatial correlation. There is a strong correlation between mTHPC-PDT doses that result in long-term tumor cure and those that cause high levels of surface exposed or extracellularly released HSP70s.

CONCLUSION

Treatment conditions that induce strong promoter activation do not correspond to tumor cure. PDT doses that result in long-term tumor growth control also produce significant accumulation of extracellular HSP70.

Tumor cell apoptosis induced by nanoparticle conjugate in combination with radiation therapy

Semiconductor nanoparticles conjugated to photosensitizers have been shown to increase tumor cell death with ionizing radiation but the mechanism, particularly the role of photodynamic therapy in the process, was unknown. We used a molecular probe to measure production of (1)O(2) to quantify the component of photodynamic cell-killing in an in vitro system. The intracellular distribution of the nanoparticle conjugate (NC) was determined by the co-localization of nanoparticles and the lysotracker. Induction of apoptosis was measured by the TUNEL assay and western blot analysis of the cleaved caspase-3. As a result, dose-dependent (1)O(2) production was observed with 48 nm NC after irradiating with 6 MV x-rays. A high geometrical coincidence between the fluorescence emission of the nanoparticle and lysotracker was observed using confocal microscopy. Finally, apoptosis, as indicated by the TUNEL stain and cleavage of the caspase-3, was observed in cells treated by both the NC and 6 Gy of radiation but not in cells treated with radiation alone. In conclusion, the cell death induced by the NC in combination with radiation is consistent with a supra-additive effect to radiation-or NC-alone-killing and is mediated by an NC-induced photodynamic therapy mechanism, which is distinctly different from that for radiation-killing alone. By providing a second distinct cell-killing mechanism, this nanoparticle conjugate has great promise as a targeted physical radiosensitizer aimed at overcoming radioresistant tumor clonogens or/and reducing normal tissue toxicity by using a lower ionizing radiation dose.

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.

Photodynamic therapy for treatment of solid tumors--potential and technical challenges

Photodynamic therapy (PDT) involves the administration of photosensitizer followed by local illumination with visible light of specific wavelength(s). In the presence of oxygen molecules, the light illumination of photosensitizer can lead to a series of photochemical reactions and consequently the generation of cytotoxic species. The quantity and location of PDT-induced cytotoxic species determine the nature and consequence of PDT. Much progress has been seen in both basic research and clinical application in recent years. Although the majority of approved PDT clinical protocols have primarily been used for the treatment of superficial lesions of both malignant and non-malignant diseases, interstitial PDT for the ablation of deep-seated solid tumors are now being investigated worldwide. The complexity of the geometry and non-homogeneity of solid tumor pose a great challenge on the implementation of minimally invasive interstitial PDT and the estimation of PDT dosimetry. This review will discuss the recent progress and technical challenges of various forms of interstitial PDT for the treatment of parenchymal and/or stromal tissues of solid tumors.

Utility of biomarkers in prediction of response to ablative therapy in Barrett's esophagus

BACKGROUND & AIMS

Photodynamic therapy (PDT) has been shown to be effective in the treatment of high-grade dysplasia (HGD)/mucosal carcinoma in Barrett's esophagus (BE). Substantial proportions of patients do not respond to PDT or progress to carcinoma despite PDT. The role of biomarkers in predicting response to PDT is unknown. We aimed to determine if biomarkers known to be associated with neoplasia in BE can predict loss of dysplasia in patients treated with ablative therapy for HGD/intramucosal cancer.

METHODS

Patients with BE and HGD/intramucosal cancer were studied prospectively from 2002 to 2006. Biomarkers were assessed using fluorescence in situ hybridization performed on cytology specimens, for region-specific and centromeric probes. Patients were treated with PDT using cylindric diffusing fibers (wavelength, 630 nm; energy, 200 J/cm fiber). Univariate and multiple variable logistic regression was performed to determine predictors of response to PDT.

RESULTS

A total of 126 consecutive patients (71 who underwent PDT and 55 patients who did not undergo PDT and were under surveillance, to adjust for the natural history of HGD), were included in this study. Fifty (40%) patients were responders (no dysplasia or carcinoma) at 3 months after PDT. On multiple variable analysis, P16 allelic loss (odds ratio [OR], 0.32; 95% confidence interval [CI], 0.10-0.96) predicted decreased response to PDT. BE segment length (OR, 0.71; 95% CI, 0.59-0.85), and performance of PDT (OR, 7.17; 95% CI, 2.50-20.53) were other independent predictors of loss of dysplasia.

CONCLUSIONS

p16 loss detected by fluorescence in situ hybridization can help predict loss of dysplasia in patients with BE and HGD/mucosal cancer. Biomarkers may help in the selection of appropriate therapy for patients and improve treatment outcomes.

The physics, biophysics and technology of photodynamic therapy

Photodynamic therapy (PDT) uses light-activated drugs to treat diseases ranging from cancer to age-related macular degeneration and antibiotic-resistant infections. This paper reviews the current status of PDT with an emphasis on the contributions of physics, biophysics and technology, and the challenges remaining in the optimization and adoption of this treatment modality. A theme of the review is the complexity of PDT dosimetry due to the dynamic nature of the three essential components -- light, photosensitizer and oxygen. Considerable progress has been made in understanding the problem and in developing instruments to measure all three, so that optimization of individual PDT treatments is becoming a feasible target. The final section of the review introduces some new frontiers of research including low dose rate (metronomic) PDT, two-photon PDT, activatable PDT molecular beacons and nanoparticle-based PDT.

Peptide-Induced Inflammatory Increase in Vascular Permeability Improves Photosensitizer Delivery and Intersubject Photodynamic Treatment Efficacy

Photodynamic therapy (PDT) treatment can exhibit high intersubject variability due to the inherent differences in drug delivery within the tissue to be treated. In this study, the increased perfusion of the lipid-associated photosensitizer verteporfin was studied using substance P, a peptide known to increase vascular permeability. The transvascular permeability coefficient was quantified before and after administration of substance P, and the mean value increased from 0.026 to 0.043 microm/s with the induced inflammation. Correspondingly, there was a 40-50% increase in uptake of verteporfin in the tumor parenchyma in tumors injected with substance P compared to those without. This increased drug uptake resulted in a modest increase in tumor doubling time from 4 days with regular PDT to 6.2 days with substance P and PDT. There was also a significant reduction in the interindividual variability in with substance P plus PDT from 64% to 13%. The resulting treatment was therefore more effective and there was less variability in dose between subjects.

Milestones in the development of photodynamic therapy and fluorescence diagnosis

Many reviews on PDT have been published. This field is now so large, and embraces so many sub-specialties, from laser technology and optical penetration through diffusing media to a number of medical fields including dermatology, gastroenterology, ophthalmology, blood sterilization and treatment of microbial-viral diseases, that it is impossible to cover all aspects in a single review. Here, we will concentrate on a few basic aspects, all important for the route of development leading PDT to its present state: early work on hematoporphyrin and hematoporphyrin derivative, second and third generation photosensitizers, 5-aminolevulinic acid and its derivatives, oxygen and singlet oxygen, PDT effects on cell organelles, mutagenic potential, the basis for tumour selectivity, cell cooperativity, photochemical internalization, light penetration into tissue and the significance of oxygen depletion, photobleaching of photosensitizers, optimal light sources, effects on the immune system, and, finally, future trends.

Hypericin-mediated photodynamic therapy elicits differential interleukin-6 response in nasopharyngeal cancer

Cytokines induce inflammatory and immune responses in tumors after photodynamic therapy (PDT). Since there are no reports of IL-6 in nasopharyngeal cancer (NPC) cells following PDT, we evaluated IL-6 expression in two different NPC tumors after hypericin mediated PDT. Interleukin-6 transcription was significantly upregulated in PDT-treated CNE-2 poorly differentiated cells but not in HK1 well differentiated cells. In vivo, IL-6 mRNA expression was elevated in PDT-treated CNE-2 tumors but not in HK1 tumors. In conclusion, the study elucidated that the cell type, degree of histological differentiation and the basal expression of the cytokine influence the cytokine response following PDT.

Potential applications of photodynamic therapy in regenerative medicine

Photodynamic therapy (PDT) is an emerging field that uses light-activated drugs to produce specific biological effects in cells and tissues. Its particular strengths arise from the ability to spatially localize the biological responses by the way the light is applied; the range of possible mechanisms of action at the cell, tissue, and organism levels; and the combination of novel molecular and optical technologies. This paper presents the basic principles of PDT and considers some of the possible applications in regenerative medicine.

Comparison of the cellular molecular stress responses after treatments used in bladder cancer

OBJECTIVE

To investigate the molecular stress responses related to the quality of recovery of normal tissue after various treatments for bladder cancer, i.e. hyperthermia, ionizing radiation, mitomycin-C and 5-aminolaevulinic acid photodynamic therapy (ALA-PDT).

MATERIALS AND METHODS

The study focused particularly on intracellular fibroblast levels of heat-shock protein-47 (HSP47) and HSP72, which are associated with collagen metabolism and the development of tolerance to repeated treatment, respectively. Iso-effective treatment doses (50% clonogenic cell survival) of each method were delivered to a 3T6 murine fibroblast model. Intracellular extracts were analysed at 3, 6, 9, 12 and 24 h after treatment, using Western blot analysis to compare the levels of HSP47 and HSP72. Time-matched treatment and control groups were quantified by comparison with actin and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression using appropriate software.

RESULTS

There were various changes in levels of HSP expression with treatment method; HSP47 levels were significantly higher after hyperthermia and radiation but not with mitomycin-C or ALA-PDT. HSP72 levels were significantly higher with all methods except ALA-PDT.

CONCLUSIONS

Hyperthermia and ionizing radiation are associated with early increases in levels of HSP47 (a marker of collagen metabolism), in contrast to ALA-PDT and mitomycin-C. These findings are compatible with clinical findings where fibrosis/scarring is common with the first two but not the last two methods. In addition, all methods except ALA-PDT are associated with an increase in HSP 72 (a protein associated with cellular tolerance) and this may help to explain, at a cellular level, why resistance to repeated ALA-PDT treatments does not seem to occur.

Localization of tetra(m-hydroxyphenyl)chlorin (Foscan) in human healthy tissues and squamous cell carcinomas of the upper aero-digestive tract, the esophagus and the bronchi: a fluorescence microscopy study

To date, little is known about precise time-dependent distribution and histological localization of tetra(m-hydroxyphenyl)chlorin (mTHPC) in human healthy tissues and squamous cell malignancies in the upper aero-digestive tract. A fluorescence microscopy study was performed on 50 healthy tissue biopsies and on 13 tumors (graded from Tis to T1 SCC) from 30 patients. Tissue samples were taken between 4 h and 11 days following injection of 0.15 mg/kg mTHPC. A fairly comparable distribution pattern in various tissues was observed over time in different patients. Vascular localization of mTHPC fluorescence predominates at a short delay, whereas the dye is essentially located in the tumoral and healthy mucosa after longer delays. A much lower uptake and retention of mTHPC fluorescence was noted in striated muscle and cartilage as compared to neoplastic lesions. No significant selectivity was found between healthy and tumoral mucosa. The obtained data are important to confirm drug-light interval that have been selected for effective PDT for early SCC malignancies while minimizing the risks of over- or under-treatment. The low fluorescence level in striated muscle provides the opportunity to develop interstitial PDT as a treatment modality for invasive SCC of unfavorable locations in the oral cavity or pharynx, such as the base of the tongue.

Interaction between photodynamic therapy and BCG immunotherapy responsible for the reduced recurrence of treated mouse tumors

Subcutaneous mouse EMT6 tumors were treated by individual or combined regimens of a single Bacillus Calmette-Guérin (BCG) vaccine administration and photodynamic therapy (PDT). Six clinically relevant photosensitizers characterized by different action mechanisms were used: Photofrin, benzoporphyrin derivative, tetra(m-hydroxyphenyl)chlorin (foscan), mono-L-aspartylchlorin e6, lutetium texaphyrin or zinc phthalocyanine. Irrespective of the type of photosensitizer used, the optimized BCG protocols improved the cure rate of PDT-treated tumors. This indicates that the interaction does not take place during the early phase of tumor ablation but at later events involved in preventing tumor recurrence. Beneficial effects on tumor cure were observed even when the BCG injection was delayed to 7 days after PDT. The accumulation of activated myeloid cells that markedly increases in tumors treated by Photofrin-based PDT was not additionally affected by BCG treatment. However, the incidence of immune memory T cells in tumor-draining lymph nodes that almost doubled at 6 days after Photofrin-PDT further increased close to three-fold with adjuvant BCG. This suggests that BCG immunotherapy amplifies the T-lymphocyte-mediated immune response against PDT-treated tumors. Since both these modalities are established for the treatment of superficial bladder carcinomas, use of their combination for this condition should be clinically tested.

Antitumor effect of photodynamic therapy with zincphyrin, zinc-coproporphyrin III, in mice

We studied the antitumor effects of photodynamic therapy (PDT) with Zincphyrin, coproporphyrin III with zinc, derived from Streptomyces sp. AC8007, in vitro and in vivo. The photokilling effect of Zincphyrin in the presence of 0.78-100 microg/ml with visible light of 27.2 mW x min/cm2 for 10 min was lower than the hematoporphyrin (Hp) used as a control with L5178Y or sarcoma-180 cells. On the other hand, Zincphyrin apparently reduced tumor growth after intraperitoneal injection at doses of 12.5-50 mg/kg with light irradiation of 75.48 mW x min/cm2 for 10 min in sarcoma-180-bearing mice. Although no mice treated with Zincphyrin died, Hp did cause the death of mice. In B-16 melanoma-bearing mice, both Zincphyrin and Hp had a similar phototherapic effect. Further improvement of the phototherapic effect was observed with the continuous administration of Zincphyrin at 12.5 mg/kg per day for 3 days. The concentration of Zincphyrin in the serum reached a maximum level of 16 microg/ml within 20 min, and the concentration remained at 4.2 microg/ml at 1 hour after the onset of treatment, indicating its rapid action in the body. No animals died after the intraperitoneal administration of Zincphyrin at 100 mg/kg plus exposure to light of 10 mW x min/cm2 for 2 hours, and the body weight of the mice did not decrease. In contrast, all animals receiving 100 mg/kg of Hp under the same conditions died. These results indicate that Zincphyrin would be a useful photosensitizer with low phototoxicity.

Photodynamic therapy

Photodynamic therapy involves administration of a tumor-localizing photosensitizing agent, which may require metabolic synthesis (i.e., a prodrug), followed by activation of the agent by light of a specific wavelength. This therapy results in a sequence of photochemical and photobiologic processes that cause irreversible photodamage to tumor tissues. Results from preclinical and clinical studies conducted worldwide over a 25-year period have established photodynamic therapy as a useful treatment approach for some cancers. Since 1993, regulatory approval for photodynamic therapy involving use of a partially purified, commercially available hematoporphyrin derivative compound (Photofrin) in patients with early and advanced stage cancer of the lung, digestive tract, and genitourinary tract has been obtained in Canada, The Netherlands, France, Germany, Japan, and the United States. We have attempted to conduct and present a comprehensive review of this rapidly expanding field. Mechanisms of subcellular and tumor localization of photosensitizing agents, as well as of molecular, cellular, and tumor responses associated with photodynamic therapy, are discussed. Technical issues regarding light dosimetry are also considered.