Molecular Effectors of Photodynamic Therapy-Mediated Resistance to Cancer Cells

Nrf2-Mediated Antioxidant Response and Drug Efflux Transporters Upregulation as Possible Mechanisms of Resistance in Photodynamic Therapy of Cancers

Photodynamic therapy (PDT) is a groundbreaking approach involving the induction of cytotoxic reactive oxygen species (ROS) within tumors through visible light activation of photosensitizers (PS) in the presence of molecular oxygen. This innovative therapy has demonstrated success in treating various cancers. While PDT proves highly effective in most solid tumors, there are indications that certain cancers exhibit resistance, and some initially responsive cancers may develop intrinsic or acquired resistance to PDT. The molecular mechanisms underlying this resistance are not fully understood. Recent evidence suggests that, akin to other traditional cancer treatments, the activation of survival pathways, such as the KEAP1/Nrf2 signaling pathway, is emerging as an important mechanism of post-PDT resistance in many cancers. This article explores the dual role of Nrf2, highlighting evidence linking aberrant Nrf2 expression to treatment resistance across a range of cancers. Additionally, it delves into the specific role of Nrf2 in the context of photodynamic therapy for cancers, emphasizing evidence that suggests Nrf2-mediated upregulation of antioxidant responses and induction of drug efflux transporters are potential mechanisms of resistance to PDT in diverse cancer types. Therefore, understanding the specific role(s) of Nrf2 in PDT resistance may pave the way for the development of more effective cancer treatments using PDT.

Photodynamic therapy for cancer: mechanisms, photosensitizers, nanocarriers, and clinical studies

Photodynamic therapy (PDT) is a temporally and spatially precisely controllable, noninvasive, and potentially highly efficient method of phototherapy. The three components of PDT primarily include photosensitizers, oxygen, and light. PDT employs specific wavelengths of light to active photosensitizers at the tumor site, generating reactive oxygen species that are fatal to tumor cells. Nevertheless, traditional photosensitizers have disadvantages such as poor water solubility, severe oxygen-dependency, and low targetability, and the light is difficult to penetrate the deep tumor tissue, which remains the toughest task in the application of PDT in the clinic. Here, we systematically summarize the development and the molecular mechanisms of photosensitizers, and the challenges of PDT in tumor management, highlighting the advantages of nanocarriers-based PDT against cancer. The development of third generation photosensitizers has opened up new horizons in PDT, and the cooperation between nanocarriers and PDT has attained satisfactory achievements. Finally, the clinical studies of PDT are discussed. Overall, we present an overview and our perspective of PDT in the field of tumor management, and we believe this work will provide a new insight into tumor-based PDT.

Comparative response to PDT with methyl-aminolevulinate and temoporfin in cutaneous and oral squamous cell carcinoma cells

Cutaneous and Head and Neck squamous cell carcinoma (CSCC, HNSCC) are among the most prevalent cancers. Both types of cancer can be treated with photodynamic therapy (PDT) by using the photosensitizer Temoporfin in HNSCC and the prodrug methyl-aminolevulinate (MAL) in CSCC. However, PDT is not always effective. Therefore, it is mandatory to correctly approach the therapy according to the characteristics of the tumour cells. For this reason, we have used cell lines of CSCC (A431 and SCC13) and HNSCC (HN5 and SCC9). The results obtained indicated that the better response to MAL-PDT was related to its localization in the plasma membrane (A431 and HN5 cells). However, with Temoporfin all cell lines showed lysosome localization, even the most sensitive ones (HN5). The expression of mesenchymal markers and migratory capacity was greater in HNSCC lines compared to CSCC, but no correlation with PDT response was observed. The translocation to the nucleus of β-catenin and GSK3β and the activation of NF-κβ is related to the poor response to PDT in the HNSCC lines. Therefore, we propose that intracellular localization of GSK3β could be a good marker of response to PDT in HNSCC. Although the molecular mechanism of response to PDT needs further elucidation, this work shows that the most MAL-resistant line of CSCC is more sensitive to Temoporfin.

Photodynamic Therapy and Immunological View in Gastrointestinal Tumors

Gastrointestinal cancers are a specific group of oncological diseases in which the location and nature of growth are of key importance for clinical symptoms and prognosis. At the same time, as research shows, they pose a serious threat to a patient's life, especially at an advanced stage of development. The type of therapy used depends on the anatomical location of the cancer, its type, and the degree of progression. One of the modern forms of therapy used to treat gastrointestinal cancers is PDT, which has been approved for the treatment of esophageal cancer in the United States. Despite the increasingly rapid clinical use of this treatment method, the exact immunological mechanisms it induces in cancer cells has not yet been fully elucidated. This article presents a review of the current understanding of the mode of action of photodynamic therapy on cells of various gastrointestinal cancers with an emphasis on colorectal cancer. The types of cell death induced by PDT include apoptosis, necrosis, and pyroptosis. Anticancer effects are also a result of the destruction of tumor vasculature and activation of the immune system. Many reports exist that concern the mechanism of apoptosis induction, of which the mitochondrial pathway is most often emphasized. Photodynamic therapy may also have a beneficial effect on such aspects of cancer as the ability to develop metastases or contribute to reducing resistance to known pharmacological agents.

Cancer Metabolism: The Role of ROS in DNA Damage and Induction of Apoptosis in Cancer Cells

Cancer is a huge challenge for people worldwide. High reactive oxygen species (ROS) levels are a recognized hallmark of cancer and an important aspect of cancer treatment research. Abnormally elevated ROS levels are often attributable to alterations in cellular metabolic activities and increased oxidative stress, which affects both the development and maintenance of cancer. Moderately high levels of ROS are beneficial to maintain tumor cell genesis and development, while toxic levels of ROS have been shown to be an important force in destroying cancer cells. ROS has become an important anticancer target based on the proapoptotic effect of toxic levels of ROS. Therefore, this review summarizes the role of increased ROS in DNA damage and the apoptosis of cancer cells caused by changes in cancer cell metabolism, as well as various anticancer therapies targeting ROS generation, in order to provide references for cancer therapies based on ROS generation.

Autophagy Regulation Using Multimodal Chlorin e6-Loaded Polysilsesquioxane Nanoparticles to Improve Photodynamic Therapy

Photodynamic therapy (PDT) is a promising anticancer noninvasive technique that relies on the generation of reactive oxygen species (ROS). Unfortunately, PDT still has many limitations, including the resistance developed by cancer cells to the cytotoxic effect of ROS. Autophagy, which is a stress response mechanism, has been reported as a cellular pathway that reduces cell death following PDT. Recent studies have demonstrated that PDT in combination with other therapies can eliminate anticancer resistance. However, combination therapy is usually challenged by the differences in the pharmacokinetics of the drugs. Nanomaterials are excellent delivery systems for the efficient codelivery of two or more therapeutic agents. In this work, we report on the use of polysilsesquioxane (PSilQ) nanoparticles for the codelivery of chlorin-e6 (Ce6) and an autophagy inhibitor for early- or late-stage autophagy. Our results, obtained from a reactive oxygen species (ROS) generation assay and apoptosis and autophagy flux analyses, demonstrate that the reduced autophagy flux mediated by the combination approach afforded an increase in the phototherapeutic efficacy of Ce6-PSilQ nanoparticles. We envision that the promising results in the use of multimodal Ce6-PSilQ material as a codelivery system against cancer pave the way for its future application with other clinically relevant combinations.

Up-regulation of ABCG2 by MYBL2 deletion drives Chlorin e6-mediated photodynamic therapy resistance in colorectal cancer

OBJECTIVE

Photodynamic therapy (PDT) is an effective therapeutic strategy for colorectal cancer at an early stage. However, malignant cells' resistance to photodynamic agents can lead to treatment failure. MYBL2 (B-Myb) is an oncogene in colorectal carcinogenesis and development, for which little research has focused on its effect on drug resistance.

MATERIALS AND METHODS

In the present work, a colorectal cancer cell line with a stable knockdown of MYBL2 (ShB-Myb) was constructed first. Chlorin e6 (Ce6) was utilized to induced PDT. The anti-cancer efficacy was measured by CCK-8, PI staining, and Western blots. The drug uptake of Ce6 was assayed by flow cytometry and confocal microscopy. The ROS generation was detected by the CellROX probe. DDSB and DNA damage were assayed through comet experiment and Western blots. The over-expression of MYBL2 was conducted by MYBL2 plasmid.

RESULTS

The findings indicated that the viability of ShB-Myb treated with Ce6-PDT was not decreased compared to control SW480 cells (ShNC), which were resistant to PDT. Further investigation revealed reduced photosensitizer enrichment and mitigated oxidative DNA damage in colorectal cancer cells with depressed MYBL2. It turned out that SW480 cells knocking down MYBL2 showed phosphorylation of NF-κB and led to up-regulation of ABCG2 expression thereupon. When MYBL2 was replenished back in MYBL2-deficient colorectal cancer cells, phosphorylation of NF-κB was blocked and ABCG2 expression up-regulation was suppressed. Additionally, replenishment of MYBL2 also increased the enrichment of Ce6 and the efficacy of PDT.

CONCLUSION

In summary, MYBL2 absence in colorectal cancer contributes to drug resistance by activating NF-κB to up-regulate ABCG2 and thereby leading to photosensitizer Ce6 efflux. This study provides a novel theoretical basis and strategy for how to effectively improve the anti-tumor efficacy of PDT.

Precision Killing of M2 Macrophages with Phage-Displayed Peptide-Photosensitizer Conjugates

Among the immunosuppressive cells recruited to the tumor microenvironment, macrophages are particularly abundant and involved in angiogenesis, metastasis, and resistance to current cancer therapies. A strategy that simultaneously targets tumor cells and macrophages, particularly pro-tumoral M2 macrophages, would have significant clinical impact for various types of solid malignancies. By the use of phage display technology, we have recently developed a synthetic peptide, named NW, which binds to M1 and M2 macrophages with high affinity. Additional affinity selection on M2 macrophages identified only dominant peptides whose binding motifs are similar to that of the NW peptide. To reduce the frequency of selecting such dominating peptides, the peptide library was affinity selected on M2 macrophages blocked with NW peptide. This approach resulted in the selection of peptides that bind to M2, but not M1 macrophages. To explore the therapeutic potential of the selected peptides, the M13 phage-displayed peptides were conjugated to the photosensitizer IR700, which has been used for cancer photoimmunotherapy. The phage displaying a dominant peptide (SPILWLNAPPWA) killed both M1 and M2 macrophages, while those displaying the M2-specific peptides killed M2 macrophages only upon near-infrared light exposure. A significant fraction of the M2 macrophages were also killed with the untargeted M13 phage-IR700 conjugates. Hence, M2 macrophages can also be selectively targeted by the wild type M13 phage, which displayed a significant tropism to these cells. The benefits of this photoimmunotherapy include an automatic self-targeting ability of the wild type M13 phage, and the option of genetic manipulation of the phage genome to include tumor targeting peptides, allowing the killing of both M2 macrophages and cancer cells.

5-aminolevulinic acid photodynamic therapy combined with carbon dioxide laser therapy is a safe and effective treatment for vaginal intraepithelial neoplasia

BACKGROUND

Vaginal intraepithelial neoplasia (VaIN) is a precursor of vaginal carcinoma that is often treated with CO₂ laser therapy. However, recurrence after laser therapy is common, so new approaches are needed to enhance treatment effectiveness. The aim of this study was to investigate the efficacy and safety of combining 5- aminolevulinic acid photodynamic therapy (5-ALA-PDT) with CO₂ laser therapy for the treatment of VaIN.

METHODS

Clinical data from 40 VaIN patients who received CO2 laser therapy with or without ALA-PDT were retrospectively analyzed. Cytology, human papillomavirus (HPV) status, colposcopic images, and histopathology before and after treatment were compared, and treatment efficacy, adverse reactions, and patient prognosis were assessed.

RESULTS

There was no significant difference in the cure rate between the CO2 laser group and the CO2 laser+5-ALA-PDT group after 12 months of follow-up. The difference in HPV clearance rate between the CO₂ laser only group and the CO₂ laser + 5-ALA-PDT group was significant at 6 and 12 months after treatment but not at 3 months after treatment. 10% patients in the CO₂ laser only group experienced adverse events, while no serious adverse events were observed in the CO₂ laser + 5-ALA-PDT group.

CONCLUSIONS

5-ALA-PDT combined with CO₂ laser therapy appears to be a safe and effective treatment for VaIN that results in a high rate of HPV clearance with few side effects.

The oxidative stress, mitochondrial pathway apoptosis, and the antagonistic effects of chrysophanol in SH-SY5Y cells via DTPP-induced photodynamic therapy

BACKGROUND

To investigate the susceptibility of SH-SY5Y cells to DTPP-based photodynamic therapy (PDT) and the antagonistic effects of chrysophanol (Chr) on PDT.

METHODS

PDT photocytotoxicity to cells was quantified and determined by exposing increasing concentrations of DTPP between 2.5 to 20 μg/mL to radiation with energy densities of 1.2-9.6 J/cm² at 630-nm wavelength. Sodium azide (SA, NaN₃) and d-mannitol (DM) were employed to study the reaction type of PDT. The photodynamic stress after PDT was assessed by superoxide dismutase (SOD), malondialdehyde (MDA), and total antioxidative capacity (T-AOC) assays. The apoptosis pathway of SH-SY5Y cells after PDT was studied by the determination of JC-1 and caspase-9/Caspase-3 concentrations. MTT and double fluorescence staining assays were applied to study the effect of Chr on cell survival and apoptosis rate in PDT, respectively. PI was used to detect the effect of Chr on cell membrane integrity after DTPP-PDT treatment.

RESULTS

The dose-dependent killing effect of high DTPP concentrations and irradiation doses were identified. Cell apoptosis is mediated by a mitochondrial pathway with a total apoptosis rate of 33.8% at 10 μg/mL of DTPP after irradiation with 2.4 J/cm². Oxidative stress was produced by ROS in PDT and non-reversible cell oxidative damage appeared due to the cells' modulation of the oxidative stress balance during the PDT response. Chr had a- effect on ROS capture and an inhibitory effect on the PDT-induced destruction of cell membranes.

CONCLUSIONS

SH-SY5Y cells were susceptible to DTPP-PDT, resulting in a mitochondrial apoptosis pathway. There is an antagonistic effect of Chr on PDT in SH-SY5Y neuroblastoma cells.

The response of the canine mammary simple carcinoma and carcinosarcoma cells to 5-aminolaevulinic acid-based photodynamic therapy: An in vitro study

BACKGROUNDS

Canine mammary gland tumors (CMGTs) are heterogeneous tumors and share many similar features with human breast cancer. Despite the improvement of current treatment options, new treatment modalities are required to effectively kill tumor cells without general toxicity in the treatment of CMGTs. Photodynamic therapy (PDT) is a promising method for cancer treatment. However, there is a limited study evaluating the therapeutic efficacy of PDT in the treatment of CMGTs.

METHODS

In this context, we, for the first time, investigated the therapeutic potential of 5-aminolaevulinic acid (5-ALA) mediated PDT at 6 and 12 J/cm² in two different subtypes [Tubulopapillary carcinoma (TPC) and carcinosarcoma (CS)] cells via different molecular analysis. The cytotoxic effects of 5-ALA/PDT on these cells were analyzed by intracellular PpIX level, WST-1 and ROS analysis. Furthermore, the underlying moleculer mechanism of 5-ALA/PDT mediated apoptotic effects on TPC and CS cells were evaluated Annexin V, AO/PI, RT-PCR and western blot analysis.

RESULTS

The 5-ALA/PDT treatment upon irradiation considerably inhibited the viability of both TPC and CS cells (p<0.01) and caused apoptotic death through elevated ROS levels, the activation of Caspase-9, and Caspase-3, and the overexpression of Bax. However, the response of TPC and CS cells to 5-ALA/PDT was different.

CONCLUSIONS

Our preliminary in vitro findings provide novel insights into the molecular mechanisms underlying 5-ALA/PDT mediated apoptosis in both TPC and CS cells. However, the therapeutic response of CMGT cells to 5-ALA/PDT is limited.

Targeting mitochondria in cancer therapy: Insight into photodynamic and photothermal therapies

Mitochondria are critical multifunctional organelles in cells that generate power, produce reactive oxygen species, and regulate cell survival. Mitochondria that are dysfunctional are eliminated via mitophagy as a way to protect cells under moderate stress and physiological conditions. However, mitophagy is a double-edged sword and can trigger cell death under severe stresses. By targeting mitochondria, photodynamic (PD) and photothermal (PT) therapies may play a role in treating cancer. These therapeutic modalities alter mitochondrial membrane potential, thereby affecting respiratory chain function and generation of reactive oxygen species promotes signaling pathways for cell death. In this regard, PDT, PTT, various mitochondrion-targeting agents and therapeutic methods could have exploited the vital role of mitochondria as the doorway to regulated cell death. Targeted mitochondrial therapies would provide an excellent opportunity for effective mitochondrial injury and accurate tumor erosion. Herein, we summarize the recent progress on the roles of PD and PT treatments in regulating cancerous cell death in relation to mitochondrial targeting and the signaling pathways involved.

Bibliometric Analysis of Global Research on Cancer Photodynamic Therapy: Focus on Nano-Related Research

A growing body of research has illuminated that photodynamic therapy (PDT) serves as an important therapeutic strategy in oncology and has become a hot topic in recent years. Although numerous papers related to cancer PDT (CPDT) have been published, no bibliometric studies have been conducted to summarize the research landscape, and highlight the research trends and hotspots in this field. This study collected 5,804 records on CPDT published between 2000 and 2021 from Web of Science Core Collection. Bibliometric analysis and visualization were conducted using VOSviewer, CiteSpace, and one online platform. The annual publication and citation results revealed significant increasing trends over the past 22 years. China and the United States, contributing 56.24% of the total publications, were the main driving force in this field. Chinese Academy of Sciences was the most prolific institution. Photodiagnosis and Photodynamic Therapy and Photochemistry and Photobiology were the most productive and most co-cited journals, respectively. All keywords were categorized into four clusters including studies on nanomaterial technology, clinical applications, mechanism, and photosensitizers. “nanotech-based PDT” and “enhanced PDT” were current research hotspots. In addition to several nano-related topics such as “nanosphere,” “nanoparticle,” “nanomaterial,” “nanoplatform,” “nanomedicine” and “gold nanoparticle,” the following topics including “photothermal therapy,” “metal organic framework,” “checkpoint blockade,” “tumor microenvironment,” “prodrug” also deserve further attention in the near future.

Ultrasound Triggers Hypericin Activation Leading to Multifaceted Anticancer Activity

The use of ultrasound (US) in combination with a responsive chemical agent (sonosensitizer) can selectively trigger the agent's anticancer activity in a process called sonodynamic therapy (SDT). SDT shares some properties with photodynamic therapy (PDT), which has been clinically approved, but sets itself apart because of its use of US rather than light to achieve better tissue penetration. SDT provides anticancer effects mainly via the sonosensitizer-mediated generation of reactive oxygen species (ROS), although the precise nature of the underpinning mechanism is still under debate. This work investigates the SDT anticancer activity of hypericin (Hyp) in vitro in two- (2D) and three-dimensional (3D) HT-29 colon cancer models, and uses PDT as a yardstick due to its well-known Hyp phototoxicity. The cancer cell uptake and cellular localization of Hyp were investigated first to determine the proper noncytotoxic concentration and incubation time of Hyp for SDT. Furthermore, ROS production, cell proliferation, and cell death were evaluated after Hyp was exposed to US. Since cancer relapse and transporter-mediated multidrug resistance (MDR) are important causes of cancer treatment failure, the US-mediated ability of Hyp to elicit immunogenic cell death (ICD) and overcome MDR was also investigated. SDT showed strong ROS-mediated anticancer activity 48 h after treatment in both the HT-29 models. Specific damage-associated molecular patterns that are consistent with ICD, such as calreticulin (CRT) exposure and high-mobility group box 1 protein (HMGB1) release, were observed after SDT with Hyp. Moreover, the expression of the ABC transporter, P-glycoprotein (P-gp), in HT-29/MDR cells was not able to hinder cancer cell responsiveness to SDT with Hyp. This work reveals, for the first time, the US responsiveness of Hyp with significant anticancer activity being displayed, making it a full-fledged sonosensitizer for the SDT of cancer.

Which cell death modality wins the contest for photodynamic therapy of cancer?

Photodynamic therapy (PDT) was discovered more than 100 years ago. Since then, many protocols and agents for PDT have been proposed for the treatment of several types of cancer. Traditionally, cell death induced by PDT was categorized into three types: apoptosis, cell death associated with autophagy, and necrosis. However, with the discovery of several other regulated cell death modalities in recent years, it has become clear that this is a rather simple understanding of the mechanisms of action of PDT. New observations revealed that cancer cells exposed to PDT can pass through various non-conventional cell death pathways, such as paraptosis, parthanatos, mitotic catastrophe, pyroptosis, necroptosis, and ferroptosis. Nowadays, immunogenic cell death (ICD) has become one of the most promising ways to eradicate tumor cells by activation of the T-cell adaptive immune response and induction of long-term immunological memory. ICD can be triggered by many anti-cancer treatment methods, including PDT. In this review, we critically discuss recent findings on the non-conventional cell death mechanisms triggered by PDT. Next, we emphasize the role and contribution of ICD in these PDT-induced non-conventional cell death modalities. Finally, we discuss the obstacles and propose several areas of research that will help to overcome these challenges and lead to the development of highly effective anti-cancer therapy based on PDT.

Synthesis, characterization, and evaluation of chloroaluminium phthalocyanine incorporated in poly(ε-caprolactone) nanoparticles for photodynamic therapy

BACKGROUND

The use of nanotechnology has been widely used in biomedical science, which consists of orthopedic implants, tissue engineering, cancer therapy and drug elution from nanoparticle systems, such as poly-caprolactone (PCL) nanoparticles, which stand out mainly for their biocompatibility, being considered as effective carriers for photosensitizing drugs (PS) in photodynamic therapy (PDT) protocols.

METHODS

This manuscript describes the synthesis and characterization of PCL nanoparticles for controlled release of the drug chloro-aluminum phthalocyanine (ClAlPc) as a photosensitizer for application in PDT. The PCL-ClAlPc nanoparticles were developed by the nanoprecipitation process. The structure and morphology of the nanoparticles were studied with scanning electron microscopy (SEM) and with Fourier transform infrared (FTIR). The size of nanomaterials was studied using the Dynamic Light Scattering (DLS) method. Photophysical and photochemical characterizations were performed. Subsequently, photobiological studies were also used to characterize the system.

RESULTS

The nanoparticles had an average diameter of 384.7 ± 138.6 nm and a polydispersity index of 0.153. SEM analysis revealed that the system formed a spherical shape typical of these delivery systems. Charging efficiency was 82.1% ± 1.2%. The phthalocyanine-loaded PCL nanoparticles maintained their photophysical behavior after encapsulation. Cell viability was determined after the dark toxicity test, and it was possible to observe that there was no evidence of toxicity in the dark, for all concentrations tested. The assay also revealed that adenocarcinoma cells treated with free ClAlPc and in the nanoformulation showed 100% cell death when subjected to PDT protocols. The intracellular location of the photosensitizer indicated a high potential for accumulation in the cytoplasm and nucleus.

CONCLUSIONS

From the photophysical, photochemical and photobiological analyzes obtained, it was possible to observe that the development of PCL nanoparticles encapsulated with ClAlPc, by the nanoprecipitation method was adequate and that the in vivo release study is efficient to reduce the release rate and attenuate the burst of PS loaded on PCL nanoparticles. The results reinforce that the use of this system as drug delivery systems is useful in PDT protocols.

Reactive Oxygen Species and Folate Receptor-Targeted Nanophotosensitizers Composed of Folic Acid-Conjugated and Poly(ethylene glycol)-Chlorin e6 Tetramer Having Diselenide Linkages for Targeted Photodynamic Treatment of Cancer Cells

Folic acid-conjugated nanophotosensitizers composed of folic acid (FA), poly(ethylene glycol) (PEG) and chlorin e6 (Ce6) tetramer were synthesized using diselenide linkages for reactive oxygen species (ROS)- and folate receptor-specific delivery of photosensitizers. Ce6 was conjugated with 3-[3-(2-carboxyethoxy)-2,2-bis(2-carboxyethoxymethyl)propoxy]propanoic acid (tetra acid, or TA) to make Ce6 tetramer via selenocystamine linkages (TA-sese-Ce6 conjugates). In the carboxylic acid end group of the TA-sese-Ce6 conjugates, FA-PEG was attached again using selenocystamine linkages to make FA-PEG/TA-sese-Ce6 conjugates (abbreviated as FAPEGtaCe6 conjugates). Nanophotosensitizers were fabricated by a dialysis procedure. In the morphological observations, they showed spherical shapes with small diameters of less than 200 nm. Stability of the aqueous FAPEGtaCe6 nanophotosensitizer solution was maintained (i.e., their particle sizes were not significantly changed until 7 days later). When H₂O₂ was added to the nanophotosensitizer solution, the particle size distribution was changed from a monomodal pattern to a multimodal pattern. In addition, the fluorescence intensity and Ce6 release rate from the nanophotosensitizers were also increased by the addition of H₂O₂. These results indicated that the nanophotosensitizers had ROS-sensitive properties. In an in vitro cell culture study, an FAPEGtaCe6 nanophotosensitizer treatment against cancer cells increased the Ce6 uptake ratio, ROS generation and light-irradiated cytotoxicity (phototoxicity) compared with Ce6 alone against various cancer cells. When the folic acid was pretreated to block the folate receptors of the Y79 cells and KB cells (folate receptor-overexpressing cells), the intracellular Ce6 uptake, ROS generation and thereby phototoxicity were decreased, while the MCF-7 cells did not significantly respond to blocking of the folate receptors. These results indicated that they could be delivered by a folate receptor-mediated pathway. Furthermore, an in vivo pulmonary metastasis model using Y79 cells showed folate receptor-specific delivery of FAPEGtaCe6 nanophotosensitizers. When folic acid was pre-administered, the fluorescence intensity of the lungs was significantly decreased, indicating that the FAPEGtaCe6 nanophotosensitizers had folate receptor specificity in vitro and in vivo. We suggest that FAPEGtaCe6 nanophotosensitizers are promising candidates for a targeted photodynamic therapy (PDT) approach against cancer cells.