Dynamics and mechanism of HSP70 translocation induced by photodynamic therapy treatment

Cyanine dyes in the mitochondria-targeting photodynamic and photothermal therapy

Mitochondrial dysregulation plays a significant role in the carcinogenesis. On the other hand, its destabilization strongly represses the viability and metastatic potential of cancer cells. Photodynamic and photothermal therapies (PDT and PTT) target mitochondria effectively, providing innovative and non-invasive anticancer therapeutic modalities. Cyanine dyes, with strong mitochondrial selectivity, show significant potential in enhancing PDT and PTT. The potential and limitations of cyanine dyes for mitochondrial PDT and PTT are discussed, along with their applications in combination therapies, theranostic techniques, and optimal delivery systems. Additionally, novel approaches for sonodynamic therapy using photoactive cyanine dyes are presented, highlighting advances in cancer treatment.

Modulation of heat shock protein expression and cytokine levels in MCF-7 cells through photodynamic therapy

In this study, we assess the impact of photodynamic therapy (PDT) using aluminum phthalocyanine tetrasulfonate (AlPcS4) on the viability and cellular stress responses of MCF-7 breast cancer cells. Specifically, we investigate changes in cell viability, cytokine production, and the expression of stress-related genes. Experimental groups included control cells, those treated with AlPcS4 only, light-emitting diode (LED) only, and combined PDT. To evaluate these effects on cell viability, cytokine production, and the expression of stress-related genes, techniques such as 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, enzyme-linked immunosorbent assays (ELISA), and real-time quantitative PCR (RT‒qPCR) were employed. Our findings reveal how PDT with AlPcS4 modulates mitochondrial activity and cytokine responses, shedding light on the cellular pathways essential for cell survival and stress adaptation. This work enhances our understanding of PDT's therapeutic potential and mechanisms in treating breast cancer.

Revealing the Effect of Photothermal Therapy on Human Breast Cancer Cells: A Combined Study from Mechanical Properties to Membrane HSP70

Hyperthermia-induced overexpression of heat shock protein 70 (HSP70) leads to the thermoresistance of cancer cells and reduces the efficiency of photothermal therapy (PTT). In contrast, cancer cell-specific membrane-associated HSP70 has been proven to activate antitumor immune responses. The dual effect of HSP70 on cancer cells inspires us that in-depth research of membrane HSP70 (mHSP70) during PTT treatment is essential. In this work, a PTT treatment platform for human breast cancer cells (MCF-7 cells) based on a mPEG-NH₂-modified polydopamine (PDA)-coated gold nanorod core-shell structure (GNR@PDA-PEG) is developed. Using the force-distance curve-based atomic force microscopy (FD-based AFM), we gain insight into the PTT-induced changes in the morphology, mechanical properties, and mHSP70 expression and distribution of individual MCF-7 cells with high-resolution at the single-cell level. PTT treatment causes pseudopod contraction of MCF-7 cells and generates a high level of intracellular reactive oxygen species, which severely disrupt the cytoskeleton, leading to a decrease in cellular mechanical properties. The adhesion maps, which are recorded by aptamer A8 functional probes using FD-based AFM, reveal that PTT treatment causes a significant upregulation of mHSP70 expression and it starts to exhibit a partial aggregation distribution on the MCF-7 cell surface. This work not only exemplifies that AFM can be a powerful tool for detecting changes in cancer cells during PTT treatment but also provides a better view for targeting mHSP70 for cancer therapy.

Triggering anti-GBM immune response with EGFR-mediated photoimmunotherapy

BACKGROUND

Surgical resection followed by chemo-radiation postpones glioblastoma (GBM) progression and extends patient survival, but these tumours eventually recur. Multimodal treatment plans combining intraoperative techniques that maximise tumour excision with therapies aiming to remodel the immunologically cold GBM microenvironment could improve patients' outcomes. Herein, we report that targeted photoimmunotherapy (PIT) not only helps to define tumour location and margins but additionally promotes activation of anti-GBM T cell response.

METHODS

EGFR-specific affibody molecule (ZEGFR:03115) was conjugated to IR700. The response to ZEGFR:03115-IR700-PIT was investigated in vitro and in vivo in GBM cell lines and xenograft model. To determine the tumour-specific immune response post-PIT, a syngeneic GBM model was used.

RESULTS

In vitro findings confirmed the ability of ZEGFR:03115-IR700 to produce reactive oxygen species upon light irradiation. ZEGFR:03115-IR700-PIT promoted immunogenic cell death that triggered the release of damage-associated molecular patterns (DAMPs) (calreticulin, ATP, HSP70/90, and HMGB1) into the medium, leading to dendritic cell maturation. In vivo, therapeutic response to light-activated conjugate was observed in brain tumours as early as 1 h post-irradiation. Staining of the brain sections showed reduced cell proliferation, tumour necrosis, and microhaemorrhage within PIT-treated tumours that corroborated MRI T2*w acquisitions. Additionally, enhanced immunological response post-PIT resulted in the attraction and activation of T cells in mice bearing murine GBM brain tumours.

CONCLUSIONS

Our data underline the potential of ZEGFR:03115-IR700 to accurately visualise EGFR-positive brain tumours and to destroy tumour cells post-conjugate irradiation turning an immunosuppressive tumour environment into an immune-vulnerable one.

Photodynamic priming with triple-receptor targeted nanoconjugates that trigger T cell-mediated immune responses in a 3D in vitro heterocellular model of pancreatic cancer

Photodynamic priming (PDP), a collateral effect of photodynamic therapy, can transiently alter the tumor microenvironment (TME) beyond the cytotoxic zone. Studies have demonstrated that PDP increases tumor permeability and modulates immune-stimulatory effects by inducing immunogenic cell death, via the release of damage-associated molecular patterns and tumor-associated antigens. Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest of cancers with a stubborn immunosuppressive TME and a dense stroma, representing a challenge for current molecular targeted therapies often involving macromolecules. We, therefore, tested the hypothesis that PDP's TME modulation will enable targeted therapy and result in immune stimulation. Using triple-receptor-targeted photoimmuno-nanoconjugate (TR-PINs)-mediated PDP, targeting epidermal growth factor receptor, transferrin receptor, and human epidermal growth factor receptor 2 we show light dose-dependent TR-PINs mediated cytotoxicity inhuman PDA Ccells (MIAPaCa-2),co-cultured with human pancreatic cancer-associated fibroblasts (PCAFs) in spheroids. Furthermore, TR-PINs induced the expression of heat shock proteins (Hsp60, Hsp70), Calreticulin, and high mobility group box 1 in a light dose and time-dependent manner.TR-PINs-mediated T cell activation was observed in co-cultures of immune cells with the MIA PaCa-2-PCAF spheroids. Both CD4⁺ T and CD8⁺ T cells showed light dose and time-dependant antitumor reactivity by upregulating degranulation marker CD107a and interferon-gamma post-PDP. Substantial tumor cell death in immune cell-spheroid co-cultures by day 3 shows the augmentation by antitumor T cell activation and their ability to recognize tumors for a light dose-dependent kill. These data confirm enhanced destruction of heterogeneous pancreatic spheroids mediated by PDP-induced phototoxicity, TME modulation and increased immunogenicity with targeted nanoconstructs.

Growing tool-kit of photosensitizers for clinical and non-clinical applications

Photosensitizers are photosensitive molecules utilized in clinical and non-clinical applications by taking advantage of light-mediated reactive oxygen generation, which triggers local and systemic cellular toxicity. Photosensitizers are used for diverse biological applications such as spatio-temporal inactivation of a protein in a living system by chromophore-assisted light inactivation, localized cell photoablation, photodynamic and immuno-photodynamic therapy, and correlative light-electron microscopy imaging. Substantial efforts have been made to develop several genetically encoded, chemically synthesized, and nanotechnologically driven photosensitizers for successful implementation in redox biology applications. Genetically encoded photosensitizers (GEPS) or reactive oxygen species (ROS) generating proteins have the advantage of using them in the living system since they can be manipulated by genetic engineering with a variety of target-specific genes for the precise spatio-temporal control of ROS generation. The GEPS variety is limited but is expanding with a variety of newly emerging GEPS proteins. Apart from GEPS, a large variety of chemically- and nanotechnologically-empowered photosensitizers have been developed with a major focus on photodynamic therapy-based cancer treatment alone or in combination with pre-existing treatment methods. Recently, immuno-photodynamic therapy has emerged as an effective cancer treatment method using smartly designed photosensitizers to initiate and engage the patient's immune system so as to empower the photosensitizing effect. In this review, we have discussed various types of photosensitizers, their clinical and non-clinical applications, and implementation toward intelligent efficacy, ROS efficiency, and target specificity in biological systems.

Near-Infrared Light-Triggered Photodynamic Therapy and Apoptosis Using Upconversion Nanoparticles With Dual Photosensitizers

Elucidation of upconversion nanoparticles (UCNPs) that can be excited by near-infrared (NIR) light is an interesting topic in the field of photodynamic therapy (PDT). However, the PDT efficiency of conventional UCNPs is limited due to the low quantum yield and overheating effect of the 980 nm light source. In this study, a light source with a wavelength of 808 nm was used as an excitation source for Nd-doped UCNPs to solve the overheating effect. UCNPs with a core@shell structure (NaYF₄:Yb,Er,Nd@NaYF₄:Yb,Nd) were synthesized to increase the upconversion emission efficiency. Dual-color emitting Er-doped UCNPs and dual photosensitizers (Chlorin e6 and Rose Bengal) were used for enhanced PDT. Each photosensitizer could absorb red and green emissions of the UCNPs to generate reactive oxygen species (ROS), respectively. The ROS generation in a dual photosensitizer system is significantly higher than that in a single photosensitizer system. Additionally, PDT induces immunogenic apoptosis. In this study, by utilizing a highly efficient PDT agent, PDT-induced apoptosis was studied by biomarker analysis.

Nanotechnology-based photoimmunological therapies for cancer

Phototherapy is a non-invasive or minimally invasive therapeutic strategy. Immunotherapy uses different immunological approaches, such as antibodies, vaccines, immunoadjuvants, and cytokines to stimulate the host immune system to fight against diseases. In cancer treatment, phototherapy not only destroys tumor cells, but also induces immunogenic tumor cell death to initiate a systemic anti-tumor immune response. When combined with immunotherapy, the effectiveness of phototherapy can be enhanced. Because of their special physical, chemical, and sometimes immunological properties, nanomaterials have also been used to enhance phototherapy. In this article, we review the recent progress in nanotechnology-based phototherapy, including nano-photothermal therapy, nano-photochemical therapy, and nano-photoimmunological therapy in cancer treatment. Specifically, we focus on the immunological responses induced by nano-phototherapies.

Graphitic carbon nitride nanosheets as a multifunctional nanoplatform for photochemical internalization-enhanced photodynamic therapy

Photodynamic therapy (PDT) has been widely used as a noninvasive and moderate technique in precision cancer therapy by destroying cancer cells via light-induced reactive oxygen species (ROS). However, the overproduction of heat shock protein 70 (HSP70) induced by ROS will contribute to the cell survival under harsh conditions, finally leading to decreased PDT efficiency. To overcome this issue, herein, for the first time, we have prepared an HSP70 inhibitor (2-phenylethynesulfonamide (PES))-loaded graphitic carbon nitride nanosheet (GCNS) as a multifunctional nanoplatform (GCNS-PES) for enhanced PDT. By taking advantage of commendable PDT efficiency, strong blue fluorescence, satisfactory drug loading capacity and good water dispersity, the GCNS can simultaneously serve as a photosensitizer, an imaging agent and a drug carrier. Moreover, when the nanoplatform is restricted in the endo/lysosome vesicles through endocytosis, the GCNS can generate ROS effectively under visible light irradiation to promote the lipid peroxidation of endo/lysosomal membranes and accelerate the liberation of GCNS and PES into the cytoplasm. Finally, the tolerance of cancer cells to ROS is decreased by PES-induced HSP70 inactivation, and therefore the efficiency of PDT is significantly enhanced. As a result, GCNS-PES can serve as a promising therapeutic nanoplatform for photo-controlled cancer therapy.

Photodynamic Efficiency of Xanthene Dyes and Their Phototoxicity against a Carcinoma Cell Line: A Computational and Experimental Study

The aim of this study is to assess the insights of molecular properties of the xanthene dyes [fluorescein (FL), Rose Bengal (RB), erythrosin B (EB), and eosin Y (EY)] to correlate systematically their photodynamic efficiency as well as their phototoxicity against a carcinoma cell line. The phototoxicity was evaluated by comparing the values of the medium inhibitory concentration (IC50) upon HEp-2 cells with the xanthene corresponding photodynamic activity using the uric acid as a chemical dosimeter and their octanol-water partition coefficient (log⁡P). RB was the more cytotoxic dye against HEp-2 cell line and the most efficient photosensitizer in causing photoxidation of uric acid; nevertheless it was the only one characterized as being hydrophobic among the xanthenes studied here. On the other hand, it was observed that the halogen substituents increased the hydrophilicity and photodynamic activity, consistent with the cytotoxic experiments. Furthermore, the reactivity index parameters, electric dipole moment, molecular volume, and the frontier orbitals were also obtained by the Density Functional Theory (DFT). The lowest dipole moment and highest molecular volume of RB corroborate with its highest hydrophobicity due to heavy atom substituents like halogens, while the halogen substituents did not affect expressively the electronic features at all.

Targeting Antitumor Immune Response for Enhancing the Efficacy of Photodynamic Therapy of Cancer: Recent Advances and Future Perspectives

Photodynamic therapy (PDT) is a minimally invasive therapeutic strategy for cancer treatment, which can destroy local tumor cells and induce systemic antitumor immune response, whereas, focusing on improving direct cytotoxicity to tumor cells treated by PDT, there is growing interest in developing approaches to further explore the immune stimulatory properties of PDT. In this review we summarize the current knowledge of the innate and adaptive immune responses induced by PDT against tumors, providing evidence showing PDT facilitated-antitumor immunity. Various immunotherapeutic approaches on different cells are reviewed for their effectiveness in improving the treatment efficiency in concert with PDT. Future perspectives are discussed for further enhancing PDT efficiency via intracellular targetable drug delivery as well as optimized experimental model development associated with the study of antitumor immune response.

Effects of combination of melatonin and laser irradiation on ovarian cancer cells and endothelial lineage viability

The main goal of anti-cancer therapeutic approaches is to induce apoptosis in tumor masses but not in the normal tissues. Nevertheless, the combination of photodynamic irradiation with complementary oncostatic agents contributes to better therapeutic performance. Here, we applied two different cell lines; SKOV3 ovarian carcinoma cells and HUVECs umbilical cord cells as in vitro models to pinpoint whether pharmacological concentration of melatonin in combination with photodynamic therapy induces cell cytotoxicity. The cells were separately treated with various concentrations of melatonin (0 to 10 mM) and photodynamic irradiation alone or in combination. Cells were preliminary exposed to increasing concentrations of melatonin for 24 h and subsequently underwent laser irradiation for 60 s with an output power of 80 mW in continuous mode at 675 nm wavelength and a total light dose of 13.22 J/cm². Cell viability, apoptosis/necrosis rates, and reactive oxygen species levels as well as heat shock protein 70 expression were monitored after single and combined treatments. A statistical analysis was performed by applying one-way analysis of variance (ANOVA) and post hoc Tukey's test. Combination treatment of both cell lines caused a marked increase in apoptosis/necrosis rate, reactive oxygen species generation, and heat shock protein 70 expression compared to incubation of the cells with each agent alone (p < 0.05). SKOV3 cancer cells expressed higher level of heat shock protein 70 under experimental procedure as compared to HUVECs (p < 0.05). Our results introduce melatonin as a potent stimulus for enhancing the efficacy of laser on induction of apoptosis in tumor cells.

Mitochondrial Malfunctioning, Proteasome Arrest and Apoptosis in Cancer Cells by Focused Intracellular Generation of Oxygen Radicals

Photofrin/photodynamic therapy (PDT) at sub-lethal doses induced a transient stall in proteasome activity in surviving A549 (p53^+/+) and H1299 (p53^−/−) cells as indicated by the time-dependent decline/recovery of chymotrypsin-like activity. Indeed, within 3 h of incubation, Photofrin invaded the cytoplasm and localized preferentially within the mitochondria. Its light activation determined a decrease in mitochondrial membrane potential and a reversible arrest in proteasomal activity. A similar result is obtained by treating cells with Antimycin and Rotenone, indicating, as a common denominator of this effect, the ATP decrease. Both inhibitors, however, were more toxic to cells as the recovery of proteasomal activity was incomplete. We evaluated whether combining PDT (which is a treatment for killing tumor cells, per se, and inducing proteasome arrest in the surviving ones) with Bortezomib doses capable of sustaining the stall would protract the arrest with sufficient time to induce apoptosis in remaining cells. The evaluation of the mitochondrial membrane depolarization, residual proteasome and mitochondrial enzymatic activities, colony-forming capabilities, and changes in protein expression profiles in A549 and H1299 cells under a combined therapeutic regimen gave results consistent with our hypothesis.

Rose Bengal acetate photodynamic therapy (RBAc-PDT) induces exposure and release of Damage-Associated Molecular Patterns (DAMPs) in human HeLa cells

The new concept of Immunogenic Cell Death (ICD), associated with Damage Associated Molecular Patterns (DAMPs) exposure and/or release, is recently becoming very appealing in cancer treatment. In this context, PhotoDynamic Therapy (PDT) can give rise to ICD and to immune response upon dead cells removal. The list of PhotoSensitizers (PSs) able to induce ICD is still short and includes Photofrin, Hypericin, Foscan and 5-ALA. The goal of the present work was to investigate if Rose Bengal Acetate (RBAc), a powerful PS able to trigger apoptosis and autophagy, enables photosensitized HeLa cells to expose and/or release pivotal DAMPs, i.e. ATP, HSP70, HSP90, HMGB1, and calreticulin (CRT), that characterize ICD. We found that apoptotic HeLa cells after RBAc-PDT exposed and released, early after the treatment, high amount of ATP, HSP70, HSP90 and CRT; the latter was distributed on the cell surface as uneven patches and co-exposed with ERp57. Conversely, autophagic HeLa cells after RBAc-PDT exposed and released HSP70, HSP90 but not CRT and ATP. Exposure and release of HSP70 and HSP90 were always higher on apoptotic than on autophagic cells. HMGB1 was released concomitantly to secondary necrosis (24 h after RBAc-PDT). Phagocytosis assay suggests that CRT is involved in removal of RBAc-PDT generated apoptotic HeLa cells. Altogether, our data suggest that RBAc has all the prerequisites (i.e. exposure and/or release of ATP, CRT, HSP70 and HSP90), that must be verified in future vaccination experiments, to be considered a good PS candidate to ignite ICD. We also showed tha CRT is involved in the clearance of RBAc photokilled HeLa cells. Interestingly, RBAc-PDT is the first cancer PDT protocol able to induce the translocation of HSP90 and plasma membrane co-exposure of CRT with ERp57.

Cancer phototherapy via selective photoinactivation of respiratory chain oxidase to trigger a fatal superoxide anion burst

AIMS

Here, we develop a novel cancer treatment modality using mitochondria-targeting, high-fluence, low-power laser irradiation (HF-LPLI) in mouse tumor models and explore the mechanism of mitochondrial injury by HF-LPLI.

RESULTS

We demonstrated that the initial reaction after photon absorption was photosensitization of cytochrome c oxidase (COX), to inhibit enzymatic activity of COX in situ and cause respiratory chain superoxide anion (O2(-•)) burst. We also found that HF-LPLI exerted its main tumor killing effect through mitochondrial O2(-•) burst via electron transport chain (ETC). These phenomena were completely absent in the respiration-deficient cells and COX knockdown cells. With a carefully selected irradiation protocol, HF-LPLI could efficaciously destroy tumors. The inhibition of enzymatic activity of COX and generation of O2(-•) by HF-LPLI in vivo were also detected.

INNOVATION

It is the first time that the mechanism involved in the interaction between light and its photoacceptor under HF-LPLI treatment is clarified. Our results clearly indicate that HF-LPLI initiates its effects via targeted COX photoinactivation and that the tumor-killing efficacy is dependent of the subsequent mitochondrial O2(-•) burst via ETC.

CONCLUSION

Based on both in vitro and in vivo results, we conclude that HF-LPLI can selectively photoinactivate respiratory chain oxidase to trigger a fatal mitochondrial O2(-•) burst, producing oxidative damage on cancer cells. This study opens up the possibilities of applications of HF-LPLI as a mitochondria-targeting cancer phototherapy.

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

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

PDT-induced HSP70 externalization up-regulates NO production via TLR2 signal pathway in macrophages

We studied the molecular mechanism underlying PDT-induced apoptosis-dependent macrophage activation, particularly through NO production. We demonstrate that NO production is initially induced by HSP70 on the apoptotic cell surface, and is further enhanced by macrophage phagocytosis. Additionally, we found that apoptotic cells, through TLR2, could activate PI3K, and this could be either dependent or independent of the activation of MyD88. These results reveal a novel pathway linking innate immune signalling to apoptotic cells and point at HSP70 as an important antitumor immunostimulant. They also indicate that PDT-induced apoptosis has an important role in macrophage innate immunity.

Effects of Iron Oxide Nanoparticle Labeling on Human Endothelial Cells

Iron oxide nanoparticles (INOPS) are a potential contrast agent for magnetic resonance (MR) tracking of transplanted endothelial cells. The objective of this study was to examine the effect of INOPS labeling on endothelial cells. The mixture of INOPS and poly-l-lysine (PLL) was used to label human endothelial cells. Labeling efficiency was examined by Prussian blue staining, transmission electron microscopy, and atomic absorption spectrometry. The effect of iron oxide concentration on cell viability and proliferation were determined. The correlation of reactive oxygen species (ROS) and apoptosis was also examined. In vitro MRI scanning was carried out using a 1.5T MR system. INOPS-PLL could be readily taken up by endothelial cells and subsequently induce MRI signal intensity changes. However, higher labeling concentration (>50 μg/ml) and longer incubation (48 h) can affect cell viability and proliferation. Mitochondrial damage, apoptosis, and autolysosmes were observed under high INOPS-PLL concentrations, which were correlated to ROS production. INOPS-PLL nanoparticles can be used to label transplanted endothelial cells. However, high concentration of INOPS can impair cell viability, possibly through ROS-mediated apoptosis and autophagy.

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.

Mitochondria-targeting photoacoustic therapy using single-walled carbon nanotubes

In vitro photoacoustic therapy using modified single-walled carbon nanotubes (SWNTs) as "bomb" agents is a newly reported approach for cancer. Herein, a mitochondria-targeting photoacoustic modality using unmodified SWNTs and its in vitro and in vivo antitumor effect are reported. Unmodified SWNTs can be taken up into cancer cells due to a higher mitochondrial transmembrane potential in cancerous cells than normal cells. Under the irradiation of a 1064 nm pulse laser, 79.4% of cancer cells with intracellular SWNTs die within 20 s, while 82.3% of normal cells without SWNTs remain alive. This modality kills cancer cells mainly by triggering cell apoptosis that initiates from mitochondrial damage, through the depolarization of mitochondria and the subsequent release of cytochrome c after photoacoustic therapy. It is very effective in suppressing tumor growth by selectively destroying tumor tissue without causing epidermis injury. Taken together, these discoveries provide a new method using mitochondria-localized SWNTs as photoacoustic transducers for cancer treatment.

Hypericin-based photodynamic therapy induces surface exposure of damage-associated molecular patterns like HSP70 and calreticulin

Surface-exposed HSP70 and calreticulin are damage-associated molecular patterns (DAMPs) crucially involved in modulating the success of cancer therapy. Photodynamic therapy (PDT) involves the administration of a photosensitising (PTS) agent followed by visible light-irradiation. The reactive oxygen species that are thus generated directly kill tumours by damaging their microvasculature and inducing a local inflammatory reaction. PDT with the PTS photofrin is associated with DAMPs exposure, but the same is not true for other PTSs. Here, we show that when cancer cells are treated with hypericin-based PDT (Hyp-PDT), they surface-expose both HSP70 and calreticulin (CRT). Induction of CRT exposure was not accompanied by co-exposure of ERp57, but this did not compromise the ability of the exposed CRT to regulate the phagocytosis of Hyp-PDT-treated cancer cells by dendritic cells. Interestingly, we found that Hyp-PDT-induced CRT exposure (in contrast to anthracycline-induced CRT exposure) was independent of the presence of ERp57. Our results indicate that Hyp-PDT is a potential anti-cancer immunogenic modality.

Haematoporphyrin based photodynamic therapy combined with hyperthermia provided effective therapeutic vaccine effect against colon cancer growth in mice

Photodynamic therapy (PDT) has become an attractive option used in tumor treatment via its direct tumoricidal activities or its immune-boosting activities. On the other hand, heat shock protein 70 has been found to be largely associated with the establishment of anti-tumor activities offered by hyperthermia treated tumor cells. In the present study, we found that injection of tumor-bearing mice with colon cancer cell line CT-26 treated with haematoporphyrin based photodynamic therapy (hematoporphyrin monomethyl ether based PDT, HMME-PDT) together with hyperthermia demonstrated the most effective therapeutic effects against tumor growth, followed by cells treated by hyperthermia alone. CT-26 cells treated only with HMME-PDT failed to provide any therapeutic effects, although significant cell death was induced by HMME-PDT. Compared to hyperthermia treatment, HMME-PDT induced more efficient surface localization of HSP70 on CT-26 cells which correlated with efficient activation of cytolytic CD8 T cells and with effective anti-tumor responses. Thus, our study demonstrated that the surface expression of HSP70 may play a more important role than the total expression or release of this molecule in the activation of immune responses. And our study offered a novel modified PDT approach to the treatment of tumor cells intrinsically low on HSP70 expression.

Label-free nondestructive discrimination of colon carcinoma sublines and biomolecular insights into their differential Hsp70 expression: DNA/RNA nucleobase specific changes

Hsp70 is biologically relevant for its chaperon functions. The CX(-) and CX(+) sublines, which derive from the parental colon carcinoma CX2 cell line, are accordingly very similar. They have been reported to be specifically different only in Hsp70 membrane expression, which is associated with immunostimulatory effects. CX(-) /CX(+) have been phenotypically characterized by immunofluorescence studies and Raman spectroscopy combined with robust clustering and multivariate analysis. With the latter we address the potential of overall characterization for CX(-) /CX(+) discrimination and gain molecular insights into Hsp70 differential expression. Due to their strong resemblance, CX(-) and CX(+) show similar mean Raman spectra, which look indiscernible at first. Interestingly, their rather protein-dominated Raman spectra reveal, besides changes in protein and amino acids, very specific changes in DNA/RNA nucleotides involving pyrimidine ring Raman hypochromic effects. Therefore, discriminating CX(-) from CX(+) is ultimately achieved based on principal component scores. Because CX(-) /CX(+) are associated with the same lipid marker, changes in proteins support lipid interactions with regulatory proteins. More importantly, changes observed in nucleobases, which are indicative of DNA/RNA-protein binding interactions, suggest transcription deregulations as participating precursor onsets of different transport mechanisms that lead to Hsp70 differential expression and associated phenotypic variation. Besides immunofluorescence, we have used Raman spectroscopy combined with multivariate analysis within an autologous tumor system for label-free nondestructive cell-subline discrimination, and demonstrate, to our knowledge, the first overall phenotypic monitoring with insights into Hsp70 differential expression. This might well prove to be useful for Raman label-free cell-sorting of the CX(-) /CX(+) sublines.

Heat shock protein 70 is acute phase reactant: response elicited by tumor treatment with photodynamic therapy

Oxidative stress in photodynamic therapy (PDT)-treated tumor cells is known to instigate a strong upregulation of the expression of heat shock proteins. However, the treatment of mouse Lewis lung carcinoma (LLC) cells with Photofrin™ PDT resulted in the upregulation of heat shock protein 70 (Hsp70) gene not only in these cells but also in co-incubated untreated Hepa 1-6 cells. To investigate whether this phenomenon extends in vivo, LLC tumors growing in C57BL/6 mice were treated with Photofrin™ PDT. The tumors and the livers from the mice were collected at 4, 8, or 24 h after therapy for quantitative reverse transcriptase polymerase chain reaction-based analysis of Hsp70 gene expression. Increased Hsp70 gene expression was detected in both the tumor and liver tissues and was most pronounced at 4 h after PDT. This effect was inhibited by treatment of host mice with glucocorticoid synthesis inhibitor metyrapone. Hsp70 protein levels in the livers of mice bearing PDT-treated tumors gradually decreased after therapy while serum levels increased at 4 h after therapy and then continually decreased. The exposure of in vitro PDT-treated LLC cells to Hsp70 and subsequent flow cytometry analysis revealed binding of this protein to cells that was dependent on PDT dose and more pronounced with dying than viable cells. Thus, following the induction of tumor injury by PDT, Hsp70 can be produced in the liver and spleen as acute phase reactant and released into circulation, from where it can be rapidly sequestered to damaged tumor tissue to facilitate the disposal of dying cells.

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.

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.

Study on ASTC-a-1 cells labeled with superparamagnetic iron oxide and its magnetic resonance imaging

The aim of this preliminary study is to explore the feasibility of incorporating superparamagnetic iron oxide (SPIO) with poly-L-lysine (PLL) for labeling and magnetic resonance imaging (MRI) of human lung adenocarcinoma cells. Endorem (5-200 microg/mL) was incubated with ASTC-a-1 cells in the presence of PLL (1.5 microg/mL) for 0.5-24 h. The presence of SPIO in labeled cells was examined by Prussian blue stain. The effects of SPIO on cell proliferation, reactive oxygen species (ROS) generation and the mitochondria were also examined. In vitro MRI of SPIO-PLL-labeled cells was performed using a clinical 1.5 T MRI system. The labeling efficiency of >99% could be achieved after incubating for 0.5 h with 25 microg/mL of SPIO in the presence of PLL (1.5 microg/mL). Higher concentrations of SPIO (e.g. >50 microg/mL) could induce significant cell death, which might be mediated by changes in intracellular ROS level and mitochondrial membrane potential. In vitro MRI showed the decrease in MRI signal intensity on T(1)WI, T(2)WI and T(2)*WI sequences. In conclusion, MRI can trace SPIO-labeled cancer cells according to changes in T(1)WI, T(2)WI and T(2)*WI sequences. It should be noted that at higher concentrations, SPIO can cause cell damage.

Regulation of HSP70 on activating macrophages using PDT-induced apoptotic cells

Although anti-tumor immunological responses have been mainly associated with necrosis, apoptosis-associated immune responses have been recently suggested as well. In this study, we investigated anti-tumor immune responses and regulatory mechanisms of HSP70 using apoptotic cells induced by photodynamic therapy (PDT). The relationships between HSP70 release, HSP70 translocation and macrophage responses were studied using confocal fluorescence microscopy, FACS and ELISA. Macrophages incubated with apoptotic cells as well as necrotic tumor cells showed a high level of TNFalpha secretion. Apoptotic cells but not the apoptotic cell supernatants induced TNFalpha secretion. During both necrosis and apoptosis processes, the TNFalpha production was diminished drastically when HSP70 or TLR-2 was inhibited. After the PDT treatment, cytoplasmic HSP70 was released from the necrotic cells, while HSP70 rapidly translocated to the surface of the apoptotic cells. Furthermore, the TNFalpha secretion and the tumor cytotoxicity of splenocytes from mice immunized with apoptotic cells appeared similar to that of splenocytes immunized with necrotic cells. Our in vitro and in vivo results show that apoptosis can potentially have higher impact in inducing immunological responses, hence clarifying the immunological regulatory mechanisms of HSP70 under cell apoptosis and necrosis induced by PDT treatment. These findings could lead to an optimal PDT treatment based on immunological responses.