Enhanced efficacy of photodynamic therapy via a sequential targeting protocol

Photodynamic priming modulates cellular ATP levels to overcome P-glycoprotein-mediated drug efflux in chemoresistant triple-negative breast cancer

P-glycoprotein (P-gp, ABCB1) is a well-researched ATP-binding cassette (ABC) drug efflux transporter linked to the development of cancer multidrug resistance (MDR). Despite extensive studies, approved therapies to safely inhibit P-gp in clinical settings are lacking, necessitating innovative strategies beyond conventional inhibitors or antibodies to reverse MDR. Photodynamic therapy is a globally approved cancer treatment that uses targeted, harmless red light to activate non-toxic photosensitizers, confining its cytotoxic photochemical effects to disease sites while sparing healthy tissues. This study demonstrates that photodynamic priming (PDP), a sub-cytotoxic photodynamic therapy process, can inhibit P-gp function by modulating cellular respiration and ATP levels in light accessible regions. Using chemoresistant (VBL-MDA-MB-231) and chemosensitive (MDA-MB-231) triple-negative breast cancer cell lines, we showed that PDP decreases mitochondrial membrane potential by 54.4% ± 30.4 and reduces mitochondrial ATP production rates by 94.9% ± 3.46. Flow cytometry studies showed PDP can effectively improve the retention of P-gp substrates (calcein) by up to 228.4% ± 156.3 in chemoresistant VBL-MDA-MB-231 cells, but not in chemosensitive MDA-MB-231 cells. Further analysis revealed that PDP did not alter the cell surface expression level of P-gp in VBL-MDA-MB-231 cells. These findings indicate that PDP can reduce cellular ATP below the levels that is required for the function of P-gp and improve intracellular substrate retention. We propose that PDP in combination with chemotherapy drugs, might improve the efficacy of chemotherapy and overcome cancer MDR.

Carrier-Free, Amorphous Verteporfin Nanodrug for Enhanced Photodynamic Cancer Therapy and Brain Drug Delivery

Glioblastoma (GBM) is hard to treat due to cellular invasion into functioning brain tissues, limited drug delivery, and evolved treatment resistance. Recurrence is nearly universal even after surgery, chemotherapy, and radiation. Photodynamic therapy (PDT) involves photosensitizer administration followed by light activation to generate reactive oxygen species at tumor sites, thereby killing cells or inducing biological changes. PDT can ablate unresectable GBM and sensitize tumors to chemotherapy. Verteporfin (VP) is a promising photosensitizer that relies on liposomal carriers for clinical use. While lipids increase VP's solubility, they also reduce intracellular photosensitizer accumulation. Here, a pure-drug nanoformulation of VP, termed "NanoVP", eliminating the need for lipids, excipients, or stabilizers is reported. NanoVP has a tunable size (65-150 nm) and 1500-fold higher photosensitizer loading capacity than liposomal VP. NanoVP shows a 2-fold increase in photosensitizer uptake and superior PDT efficacy in GBM cells compared to liposomal VP. In mouse models, NanoVP-PDT improved tumor control and extended animal survival, outperforming liposomal VP and 5-aminolevulinic acid (5-ALA). Moreover, low-dose NanoVP-PDT can safely open the blood-brain barrier, increasing drug accumulation in rat brains by 5.5-fold compared to 5-ALA. NanoVP is a new photosensitizer formulation that has the potential to facilitate PDT for the treatment of GBM.

Ir(III) Half-Sandwich Photosensitizers with a π-Expansive Ligand for Efficient Anticancer Photodynamic Therapy

One approach to reduce the side effects of chemotherapy in cancer treatment is photodynamic therapy (PDT), which allows spatiotemporal control of the cytotoxicity. We have used the strategy of coordinating π-expansive ligands to increase the excited state lifetimes of Ir(III) half-sandwich complexes in order to facilitate the generation of 1O2. We have obtained derivatives of formulas [Cp*Ir(C∧N)Cl] and [Cp*Ir(C∧N)L]BF4 with different degrees of π-expansion in the C∧N ligands. Complexes with the more π-expansive ligand are very effective photosensitizers with phototoxic indexes PI > 2000. Furthermore, PI values of 63 were achieved with red light. Time-dependent density functional theory (TD-DFT) calculations nicely explain the effect of the π-expansion. The complexes produce reactive oxygen species (ROS) at the cellular level, causing mitochondrial membrane depolarization, cleavage of DNA, nicotinamide adenine dinucleotide (NADH) oxidation, as well as lysosomal damage. Consequently, cell death by apoptosis and secondary necrosis is activated. Thus, we describe the first class of half-sandwich iridium cyclometalated complexes active in PDT.

Critical PDT Theory V: What it Takes

First evidence for an apoptotic response to photodamage provided by Oleinick's group in 1991.

Esterase-Activated, pH-Responsive, and Genetically Targetable Nano-Prodrug for Cancer Cell Photo-Ablation

Activatable prodrugs have drawn considerable attention for cancer cell ablation owing to their high specificity in drug delivery systems. However, phototheranostic prodrugs with dual organelle-targeting and synergistic effects are still rare due to low intelligence of their structures. Besides, the cell membrane, exocytosis, and diffusional hindrance by the extracellular matrix reduce drug uptake. Moreover, the up-regulation of heat shock protein and short singlet-oxygen lifetime in cancer cells hamper photo-ablation efficacy, especially in the mono-therapeutic model. To overcome those obstacles, we prepare an esterase-activated DM nano-prodrug, which is conjugated by diiodine-substituted fluorogenic malachite green derivative (MG-2I) and phototherapeutic agent DPP-OH via hydrolyzable ester linkage, having pH-responsiveness and genetically targetable activity for dual organelles-targeting to optimize photo-ablation efficacy. The DM nanoparticles (NPs) present improved pH-responsive photothermal/photodynamic property by the protonation of diethylaminophenyl units in acidic environment. More importantly, the MG-2I and DPP-OH moieties can be released from DM nano-prodrug through overexpressed esterase; then specifically target lysosomes and mitochondria in CT-26 Mito-FAP cells. Hence, near-infrared DM NPs can trigger parallel damage in dual-organelles with strong fluorescence and effective phototoxicity, thus inducing serious mitochondrial dysfunction and apoptotic death, showing excellent photo-ablation effect based on esterase-activated, pH-responsive, and genetically targetable activities.

Photodynamic and Photothermal Therapies: Synergy Opportunities for Nanomedicine

Tumoricidal photodynamic (PDT) and photothermal (PTT) therapies harness light to eliminate cancer cells with spatiotemporal precision by either generating reactive oxygen species or increasing temperature. Great strides have been made in understanding biological effects of PDT and PTT at the cellular, vascular and tumor microenvironmental levels, as well as translating both modalities in the clinic. Emerging evidence suggests that PDT and PTT may synergize due to their different mechanisms of action, and their nonoverlapping toxicity profiles make such combination potentially efficacious. Moreover, PDT/PTT combinations have gained momentum in recent years due to the development of multimodal nanoplatforms that simultaneously incorporate photodynamically- and photothermally active agents. In this review, we discuss how combining PDT and PTT can address the limitations of each modality alone and enhance treatment safety and efficacy. We provide an overview of recent literature featuring dual PDT/PTT nanoparticles and analyze the strengths and limitations of various nanoparticle design strategies. We also detail how treatment sequence and dose may affect cellular states, tumor pathophysiology and drug delivery, ultimately shaping the treatment response. Lastly, we analyze common experimental design pitfalls that complicate preclinical assessment of PDT/PTT combinations and propose rational guidelines to elucidate the mechanisms underlying PDT/PTT interactions.

Photodynamic Priming Overcomes Per- and Polyfluoroalkyl Substance (PFAS)-Induced Platinum Resistance in Ovarian Cancer†

Per- and polyfluoroalkyl substances (PFAS) are widespread environmental contaminants linked to adverse outcomes, including for female reproductive biology and related cancers. We recently reported, for the first time, that PFAS induce platinum resistance in ovarian cancer, potentially through altered mitochondrial function. Platinum resistance is a major barrier in the management of ovarian cancer, necessitating complementary therapeutic approaches. Photodynamic therapy (PDT) is a light-based treatment modality that reverses platinum resistance and synergizes with platinum-based chemotherapy. The present study is the first to demonstrate the ability of photodynamic priming (PDP), a low-dose, sub-cytotoxic variant of PDT, to overcome PFAS-induced platinum resistance. Comparative studies of PDP efficacy using either benzoporphyrin derivative (BPD) or 5-aminolevulinic acid-induced protoporphyrin IX (PpIX) were conducted in two human ovarian cancer cell lines (NIH:OVCAR-3 and Caov-3). BPD and PpIX are clinically approved photosensitizers that preferentially localize to, or are partly synthesized in, mitochondria. PDP overcomes carboplatin resistance in PFAS-exposed ovarian cancer cells, demonstrating the feasibility of this approach to target the deleterious effects of environmental contaminants. Decreased survival fraction in PDP + carboplatin treated cells was accompanied by decreased mitochondrial membrane potential, suggesting that PDP modulates the mitochondrial membrane, reducing membrane potential and re-sensitizing ovarian cancer cells to carboplatin.

Critical PDT Theory III: Events at the Molecular and Cellular Level

Photodynamic therapy (PDT) is capable of eradicating neoplastic cells that are accessible to sufficient light and oxygen. There is adequate information now available for assessing conditions where PDT might be the therapy of choice, but limited access to clinical facilities and impediments to regulatory approval of new agents have limited clinical usage. Early reports mainly involved clinical data with few thoughts towards finding death pathways. In 2022, there is a clear understanding of the determinants of successful tumor eradication. While PDT may be the optimal method for many clinical indications, support for this approach has lagged. This report provides a commentary on some elements of recent progress in PDT at the molecular and cellular levels, along with a discussion of some of the limitations in current research efforts.

Photodynamic Therapy: Critical PDT Theory

Photodynamic therapy can be useful for eradication of malignant cells at sites that are accessible to light delivery. There are few adverse effects, with many clinical reports indicating that PDT has curative potential. Patients with minimal disease, where success is more likely, are also sought by those promoting other protocols. New photosensitizing agents that initiate light-catalyzed reactions continue to be discovered. Reports describing advances in understanding fundamental aspects of photobiology are always of interest. But implications for treatment of neoplasia and other diseases are not always justified, especially when poorly-penetrating wavelengths of light are employed, often at very high light doses. Efficacy is sometimes estimated by protocols that may not accurately measure photokilling. Many reports claiming potential clinical relevance for in vitro observations are based on a limited understanding of the determinants of clinical efficacy. The future of photodynamic therapy depends on an appreciation of what can be accomplished, especially when used with other modalities, but will also depend on the goals and interests of granting agencies, pharmaceutical groups and clinical personnel. This commentary is intended to provide some thoughts on current research efforts, especially where clinical implications are suggested, hinted at or otherwise implied.

Photosensitized Oxidation of Intracellular Targets: Understanding the Mechanisms to Improve the Efficiency of Photodynamic Therapy

The development of improved photosensitizers is a key aspect in the establishment of photodynamic therapy (PDT) as a reliable treatment modality. In this chapter, we discuss how molecular design can lead to photosensitizers with higher selectivity and better efficiency, with focus on the importance of specific intracellular targeting in determining the cell death mechanism and, consequently, the PDT outcome.

Co-Encapsulation of Methylene Blue and PARP-Inhibitor into Poly(Lactic-Co-Glycolic Acid) Nanoparticles for Enhanced PDT of Cancer

The development of resistance against photodamage triggered by photodynamic therapy (PDT) is ascribed mainly to the cellular redox defenses and repair. If the tumor tissue is not promptly eliminated by the first few PDT sessions, PDT-resistance can be favored, challenging the efficacy of the treatment. Although the mechanism of PDT resistance is still unclear, in vitro assays have evidenced that it can be developed through the PARP damage-repair signaling pathway. Therefore, inhibition of poly(adenosine diphosphate (ADP)-ribose) polymerase (PARP) has the potential to increase PDT efficacy. This work reports on the synthesis of a controlled release system of a photosensitizer, methylene blue (MB) and a PARP-inhibitor, the veliparib. MB and veliparib were co-encapsulated in poly(lactic-co-glycolic acid) (PLGA) nanoparticles (VMB-NPs). A colloidal stable aqueous suspension of nanoparticles was obtained. The average hydrodynamic diameter was 90 nm and a narrow size distribution was obtained, with a polydispersity index (PDI) of 0.08. The release kinetics of MB and veliparib from VMB-NPs showed an initial burst of 8.7% and 58.3% release of the total amounts of MB and veliparib respectively, in the first 6 h, and a delayed release of up to 11.3% and 70%, in 19 days, for MB and veliparib, respectively. The VMB-NPs showed no cytotoxicity in the dark but the viability of B16F10-Nex2 cells decreased by 36% when the cells were irradiated (102 J/cm², 660 nm) and treated with VMB-NPs containing 1.0 µM of MB and 8.3 µM of veliparib. Considering the increased photoactivity even at low MB and veliparib concentrations and the absence of cytotoxicity in dark, the co-encapsulation of MB and veliparib was shown to be a promising strategy to improve the PDT efficacy.

Photodestruction of Stromal Fibroblasts Enhances Tumor Response to PDT in 3D Pancreatic Cancer Coculture Models

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of human cancers. The dismal response of PDAC to virtually all therapeutics is associated, in part, with a characteristically dense fibrotic stroma. This stroma not only acts as a barrier to drug perfusion, but also promotes tumor survival through paracrine crosstalk and biophysical interactions. Photodynamic therapy (PDT) is being explored for PDAC treatment, though the impact of tumor-promoting stromal crosstalk on PDT response in PDAC is not well-characterized. The current study assesses the effect of tumor-stroma interactions on response to PDT or chemotherapy in heterocellular 3D cocultures using PDAC cells and two different fibroblastic cell types (pancreatic stellate cells, PSCs, and a normal human fibroblast cell line, MRC5) embedded in extracellular matrix (ECM). While stromal fibroblasts promote resistance to chemotherapy as expected, PDAC 3D nodules in coculture with fibroblasts exhibit increased response to PDT relative to homotypic cultures. These results point to the potential for PDT to overcome tumor-promoting stromal interactions associated with poor therapeutic response in PDAC.

Autophagy Regulation and Photodynamic Therapy: Insights to Improve Outcomes of Cancer Treatment

Cancer is considered an age-related disease that, over the next 10 years, will become the most prevalent health problem worldwide. Although cancer therapy has remarkably improved in the last few decades, novel treatment concepts are needed to defeat this disease. Photodynamic Therapy (PDT) signalize a pathway to treat and manage several types of cancer. Over the past three decades, new light sources and photosensitizers (PS) have been developed to be applied in PDT. Nevertheless, there is a lack of knowledge to explain the main biochemical routes needed to trigger regulated cell death mechanisms, affecting, considerably, the scope of the PDT. Although autophagy modulation is being raised as an interesting strategy to be used in cancer therapy, the main aspects referring to the autophagy role over cell succumbing PDT-photoinduced damage remain elusive. Several reports emphasize cytoprotective autophagy, as an ultimate attempt of cells to cope with the photo-induced stress and to survive. Moreover, other underlying molecular mechanisms that evoke PDT-resistance of tumor cells were considered. We reviewed the paradigm about the PDT-regulated cell death mechanisms that involve autophagic impairment or boosted activation. To comprise the autophagy-targeted PDT-protocols to treat cancer, it was underlined those that alleviate or intensify PDT-resistance of tumor cells. Thereby, this review provides insights into the mechanisms by which PDT can be used to modulate autophagy and emphasizes how this field represents a promising therapeutic strategy for cancer treatment.

Expanding the Limits of Photodynamic Therapy: The Design of Organelles and Hypoxia-Targeting Nanomaterials for Enhanced Photokilling of Cancer

Photodynamic therapy (PDT) is a minimally invasive clinical protocol that combines a nontoxic photosensitizer (PS), appropriate visible light, and molecular oxygen for cancer treatment. This triad generates reactive oxygen species (ROS) in situ, leading to different cell death pathways and limiting the arrival of nutrients by irreversible destruction of the tumor vascular system. Despite the number of formulations and applications available, the advancement of therapy is hindered by some characteristics such as the hypoxic condition of solid tumors and the limited energy density (light fluence) that reaches the target. As a result, the use of PDT as a definitive monotherapy for cancer is generally restricted to pretumor lesions or neoplastic tissue of approximately 1 cm in size. To expand this limitation, researchers have synthesized functional nanoparticles (NPs) capable of carrying classical photosensitizers with self-supplying oxygen as well as targeting specific organelles such as mitochondria and lysosomes. This has improved outcomes in vitro and in vivo. This review highlights the basis of PDT, many of the most commonly used strategies of functionalization of smart NPs, and their potential to break the current limits of the classical protocol of PDT against cancer. The application and future perspectives of the multifunctional nanoparticles in PDT are also discussed in some detail.

Photodynamic therapy: autophagy and mitophagy, apoptosis and paraptosis

Macroautophagy/autophagy can play a cytoprotective role after photodynamic damage to malignant cells, depending on the site of subcellular damage initiated by reactive oxygen species. There is evidence for such protection when mitochondria are among the targets. Targeting lysosomes has been reported to be more effective for photokilling, perhaps because autophagy offers no cytoprotection. Photodynamic damage to both lysosomes and mitochondria can, however, markedly enhance the overall level of photokilling. Two mechanisms have been proposed to account for this result. Lysosomal photodamage leads to the release of calcium ions, resulting in the activation of the protease CAPN (calpain). CAPN then cleaves ATG5 to a fragment (tATG5) capable of interacting with mitochondria to enhance pro-apoptotic signals. It has also been proposed that targeting lysosomes for photodynamic damage can impair mitophagy, a process that could mitigate the pro-apoptotic effects of mitochondrial targeting. The level of lysosomal photodamage required for suppression of mitophagy is unclear. The "tATG5 route" involves the catalytic action of CAPN, activated by a degree of lysosomal photodamage barely detectible by a viability assay. ER photodamage can also initiate paraptosis, a death pathway functional even in cell types with impaired apoptosis and apparently unaffected by autophagy. Abbreviations: ALLN: N-acetyl-Leu-Leu-norleucinal (cell-permeable inhibitor of calpain); ATG: autophagy related; BPD: benzoporphyrin derivative (Visudyne); ER: endoplasmic reticulum; EtNBS: 5-ethylamino-9-diethyl-aminobenzo[a]phenothiazinium chloride; MTT: a tetrazolium dye; NPe6: mono N-aspartyl chlorin e6; PDT: photodynamic therapy; ROS: reactive oxygen species.

Photodynamic therapy, priming and optical imaging: Potential co-conspirators in treatment design and optimization - a Thomas Dougherty Award for Excellence in PDT paper

Photodynamic therapy is a photochemistry-based approach, approved for the treatment of several malignant and non-malignant pathologies. It relies on the use of a non-toxic, light activatable chemical, photosensitizer, which preferentially accumulates in tissues/cells and, upon irradiation with the appropriate wavelength of light, confers cytotoxicity by generation of reactive molecular species. The preferential accumulation however is not universal and, depending on the anatomical site, the ratio of tumor to normal tissue may be reversed in favor of normal tissue. Under such circumstances, control of the volume of light illumination provides a second handle of selectivity. Singlet oxygen is the putative favorite reactive molecular species although other entities such as nitric oxide have been credibly implicated. Typically, most photosensitizers in current clinical use have a finite quantum yield of fluorescence which is exploited for surgery guidance and can also be incorporated for monitoring and treatment design. In addition, the photodynamic process alters the cellular, stromal, and/or vascular microenvironment transiently in a process termed photodynamic priming, making it more receptive to subsequent additional therapies including chemo- and immunotherapy. Thus, photodynamic priming may be considered as an enabling technology for the more commonly used frontline treatments. Recently, there has been an increase in the exploitation of the theranostic potential of photodynamic therapy in different preclinical and clinical settings with the use of new photosensitizer formulations and combinatorial therapeutic options. The emergence of nanomedicine has further added to the repertoire of photodynamic therapy's potential and the convergence and co-evolution of these two exciting tools is expected to push the barriers of smart therapies, where such optical approaches might have a special niche. This review provides a perspective on current status of photodynamic therapy in anti-cancer and anti-microbial therapies and it suggests how evolving technologies combined with photochemically-initiated molecular processes may be exploited to become co-conspirators in optimization of treatment outcomes. We also project, at least for the short term, the direction that this modality may be taking in the near future.

High-power light-emitting diode array design and assembly for practical photodynamic therapy research

SIGNIFICANCE

Commercial lasers, lamps, and light-emitting diode (LED) light sources have stimulated the clinical translation of photodynamic therapy (PDT). Yet, the continued exploration of new photosensitizers (PSs) for PDT often requires separate activation wavelengths for each agent being investigated. Customized light sources for such research frequently come at significant financial or technical cost, especially when compounded over many agents and wavelengths.

AIM

LEDs offer potential as a cost-effective tool for new PS and multi-PS photodynamic research. A low-cost-per-wavelength tool leveraging high-power LEDs to facilitate efficient and versatile research is needed to further accelerate research in the field.

APPROACH

We developed and validated a high-power LED array system for benchtop PDT with a modular design for efficient switching between wavelengths that overcome many challenges in light source design. We describe the assembly of a low-cost LED module plus the supporting infrastructure, software, and protocols to streamline typical in vitro PDT experimentation.

RESULTS

The LED array system is stable at intensities in excess of 100  mW  /  cm2 with 2.3% variation across the illumination field, competitive with other custom and commercial devices. To demonstrate efficacy and versatility, a primary ovarian cancer cell line was treated with two widely used PSs, aminolevulinic acid and verteporfin, using the LED modules at a clinically relevant 50  J  /  cm2 light dose that induced over 90% cell death for each treatment.

CONCLUSIONS

Our work provides the community with a tool for new PS and multi-PS benchtop photodynamic research that, unlike most commercial light sources, affords the user a low barrier to entry and low-cost-per-wavelength with the goal of illuminating new insights at the forefront of PDT.

Photodynamic Therapy and the Biophysics of the Tumor Microenvironment

Targeting the tumor microenvironment (TME) provides opportunities to modulate tumor physiology, enhance the delivery of therapeutic agents, impact immune response and overcome resistance. Photodynamic therapy (PDT) is a photochemistry-based, nonthermal modality that produces reactive molecular species at the site of light activation and is in the clinic for nononcologic and oncologic applications. The unique mechanisms and exquisite spatiotemporal control inherent to PDT enable selective modulation or destruction of the TME and cancer cells. Mechanical stress plays an important role in tumor growth and survival, with increasing implications for therapy design and drug delivery, but remains understudied in the context of PDT and PDT-based combinations. This review describes pharmacoengineering and bioengineering approaches in PDT to target cellular and noncellular components of the TME, as well as molecular targets on tumor and tumor-associated cells. Particular emphasis is placed on the role of mechanical stress in the context of targeted PDT regimens, and combinations, for primary and metastatic tumors.

The Course of Immune Stimulation by Photodynamic Therapy: Bridging Fundamentals of Photochemically Induced Immunogenic Cell Death to the Enrichment of T-Cell Repertoire

Photodynamic therapy (PDT) is a potentially immunogenic and FDA-approved antitumor treatment modality that utilizes the spatiotemporal combination of a photosensitizer, light and oftentimes oxygen, to generate therapeutic cytotoxic molecules. Certain photosensitizers under specific conditions, including ones in clinical practice, have been shown to elicit an immune response following photoillumination. When localized within tumor tissue, photogenerated cytotoxic molecules can lead to immunogenic cell death (ICD) of tumor cells, which release damage-associated molecular patterns and tumor-specific antigens. Subsequently, the T-lymphocyte (T cell)-mediated adaptive immune system can become activated. Activated T cells then disseminate into systemic circulation and can eliminate primary and metastatic tumors. In this review, we will detail the multistage cascade of events following PDT of solid tumors that ultimately lead to the activation of an antitumor immune response. More specifically, we connect the fundamentals of photochemically induced ICD with a proposition on potential mechanisms for PDT enhancement of the adaptive antitumor response. We postulate a hypothesis that during the course of the immune stimulation process, PDT also enriches the T-cell repertoire with tumor-reactive activated T cells, diversifying their tumor-specific targets and eliciting a more expansive and rigorous antitumor response. The implications of such a process are likely to impact the outcomes of rational combinations with immune checkpoint blockade, warranting investigations into T-cell diversity as a previously understudied and potentially transformative paradigm in antitumor photodynamic immunotherapy.

Effectiveness of ZnPc and of an amine derivative to inactivate Glioblastoma cells by Photodynamic Therapy: an in vitro comparative study

Glioblastoma multiforme is considered to be one of the most aggressive types of tumors of the central nervous system, with a poor prognosis and short survival periods of ~ one year. The current protocol for glioblastoma treatment includes the surgical excision of the primary tumor followed by radio and chemotherapy. Photodynamic therapy (PDT) is considered a promising strategy for the treatment of several types of tumors. Phthalocyanines (Pcs) are good photosensitizers (PSs) for PDT because they induce cell death in several cellular models. ZnPc (Zn(II)phthalocyanine) is a well-known Pc, extensively tested in different cells and tumor models, but its evaluation on a glioblastoma model has been poorly studied. Herein, we compare the capacity of ZnPc and one of its derivatives, Zn(II)tetraminephthalocyanine (TAZnPc), to photoinactivate glioblastoma cells (T98G, MO59, LN229 and U87-MG) in culture. We measured the cellular uptake, the toxicity in the dark and the subcellular localization of the different Pcs, as well as the clonogenic capacity of surviving cells after PDT. The mechanism of cell death induced after PDT was determined by measuring caspase 3 activation, DNA fragmentation, phosphatidylserine externalization, mitochondrial morphological changes and loss of mitochondrial membrane potential as well as lysosomal membrane integrity. Overall, ZnPc and TAZnPc present good properties to be used as PSs with photoinactivation capacity on glioblastoma cells.

Parallel damage in mitochondria and lysosomes is an efficient way to photoinduce cell death

Cells challenged by photosensitized oxidations face strong redox stresses and rely on autophagy to either survive or die. However, the use of macroautophagy/autophagy to improve the efficiency of photosensitizers, in terms of inducing cell death, remains unexplored. Here, we addressed the concept that a parallel damage in the membranes of mitochondria and lysosomes leads to a scenario of autophagy malfunction that can greatly improve the efficiency of the photosensitizer to cause cell death. Specific damage to these organelles was induced by irradiation of cells pretreated with 2 phenothiazinium salts, methylene blue (MB) and 1,9-dimethyl methylene blue (DMMB). At a low concentration level (10 nM), only DMMB could induce mitochondrial damage, leading to mitophagy activation, which did not progress to completion because of the parallel damage in lysosome, triggering cell death. MB-induced photodamage was perceived almost instantaneously after irradiation, in response to a massive and nonspecific oxidative stress at a higher concentration range (2 µM). We showed that the parallel damage in mitochondria and lysosomes activates and inhibits mitophagy, leading to a late and more efficient cell death, offering significant advantage (2 orders of magnitude) over photosensitizers that cause unspecific oxidative stress. We are confident that this concept can be used to develop better light-activated drugs. Abbreviations: ΔΨm: mitochondrial transmembrane inner potential; AAU: autophagy arbitrary units; ATG5, autophagy related 5; ATG7: autophagy related 7; BAF: bafilomycin A1; BSA: bovine serum albumin; CASP3: caspase 3; CF: carboxyfluorescein; CTSB: cathepsin B; CVS: crystal violet staining; DCF: dichlorofluorescein; DCFH2: 2',7'-dichlorodihydrofluorescein; DMMB: 1,9-dimethyl methylene blue; ER: endoplasmic reticulum; HaCaT: non-malignant immortal keratinocyte cell line from adult human skin; HP: hydrogen peroxide; LC3B-II: microtubule associated protein 1 light chain 3 beta-II; LMP: lysosomal membrane permeabilization; LTG: LysoTracker™ Green DND-26; LTR: LysoTracker™ Red DND-99; 3-MA: 3-methyladenine; MB: methylene blue; mtDNA: mitochondrial DNA; MitoSOX™: red mitochondrial superoxide probe; MTDR: MitoTracker™ Deep Red FM; MTO: MitoTracker™ Orange CMTMRos; MT-ND1: mitochondrially encoded NADH:ubiquinone oxidoreductase core subunit 1; MTT: methylthiazolyldiphenyl-tetrazolium bromide; 1O2: singlet oxygen; OH. hydroxil radical; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; PBS: phosphate-buffered saline; PI: propidium iodide; PDT: photodynamic therapy; PS: photosensitizer; QPCR: gene-specific quantitative PCR-based; Rh123: rhodamine 123; ROS: reactive oxygen species RTN: rotenone; SQSTM1/p62: sequestosome 1; SUVs: small unilamellar vesicles; TBS: Tris-buffered saline.

A Combination of Visudyne and a Lipid-anchored Liposomal Formulation of Benzoporphyrin Derivative Enhances Photodynamic Therapy Efficacy in a 3D Model for Ovarian Cancer

A major objective in developing new treatment approaches for lethal tumors is to reduce toxicity to normal tissues while maintaining therapeutic efficacy. Photodynamic therapy (PDT) provides a mechanistically distinct approach to treat tumors without the systemic toxicity of chemotherapy drugs. PDT involves the light-based activation of a small molecule, a photosensitizer (PS), to generate reactive molecular species (RMS) that are toxic to target tissue. Depending on the PS localization, various cellular and subcellular components can be targeted, causing selective photodamage. It has been shown that targeted lysosomal photodamage followed by, or simultaneous with, mitochondrial photodamage using two different PS results in a considerable enhancement in PDT efficacy. Here, two liposomal formulations of benzoporphyrin derivative (BPD): (1) Visudyne (clinically approved) and (2) an in-house formulation entrapping a lipid conjugate of BPD are used in combination with direct PS localization to mitochondria, endoplasmic reticulum and lysosomes, enabling simultaneous photodamage to all three organelles using a single wavelength of light. Building on findings by our group, and others, this study demonstrates, for the first time in a 3D model for ovarian cancer, that BPD-mediated photodestruction of lysosomes and mitochondria/ER significantly enhances PDT efficacy at lower light doses than treatment with either PS formulation alone.

Photodynamic therapy: Promoting in vitro efficacy of photodynamic therapy by liposomal formulations of a photosensitizing agent

OBJECTIVE

A relatively low level of lysosomal photodamage has been shown capable of promoting the efficacy of photodamage simultaneously or subsequently directed to mitochondrial/ER sites. The procedure has hitherto involved the use of two photosensitizing agents that require irradiation at two different wavelengths and different formulation techniques. This, together with different pharmacokinetic profiles of the photosensitizers, adds a layer of complexity to a protocol that we have sought to circumvent. In this study, liposomal formulations were used to direct photodamage created by benzoporphyrin derivative (BPD, Verteporfin) to lysosomes, mitochondria and the ER. This resulted in the development of an optimal targeting profile using a single agent and a single wavelength of activating irradiation.

MATERIALS/METHODS

These studies were carried out in monolayer cultures of OVCAR5 tumor cells. BPD localization was modified by lipid anchoring and formulation in liposomes, and was assessed by fluorescence microscopy. Irradiation was carried out at 690 ± 10 nm with photodamage assessed also using fluorescent probes and microscopy.

RESULTS

BPD normally localizes in a wide variety of sub-cellular loci that include both mitochondria and the ER, but lysosomes are spared from photodamage. Using a liposomal formulation containing BPD anchored to a lipid resulted in the targeting of lysosomes. A mixture of liposomes containing "free" and "anchored" BPD was shown to significantly promote photokilling. Eliminating cholesterol from the formulation of the anchored product enhanced lysosomal photodamage; prior studies had revealed that excess cholesterol can have a cytoprotective effect when lysosomes are the PDT target.

DISCUSSION

The ability of a liposomal formulation to change localization patterns permits directing photodynamic therapy toward specific sub-cellular loci, thereby promoting photokilling. Incorporating chemotherapeutic agents into such formulations could represent a logical next step in assessing the ability of directed photodamage to enhance tumor eradication. Lasers Surg. Med. 50:499-505, 2018. © 2018 Wiley Periodicals, Inc.

Effects of Combined Lysosomal and Mitochondrial Photodamage in a Non-small-Cell Lung Cancer Cell Line: The Role of Paraptosis

We previously reported that a low level of lysosomal photodamage potentiated the phototoxic effect of subsequent mitochondrial photodamage mediated by the benzoporphyrin derivative (BPD) in murine hepatoma 1c1c7 cells. This was attributed to release of Ca²⁺ from damaged lysosomes and a calpain-mediated conversion of the autophagy-related protein ATG5 to a pro-apoptotic fragment. We now report a comparison of these results with those obtained with the human non-small-cell lung cancer A549 cell line. A549 cells contained lower levels of ATG5 and were less responsive than 1c1c7 cultures to the PDT combination. A rapid appearance of caspase 3/7 activation together with formation of condensed chromatin indicated initiation of apoptosis in both cell lines, but to a lesser extent in A549 cultures. Both cell lines became highly vacuolated within 16 h of combination PDT or an equivalent phototoxic dose from BPD alone. The vacuole periphery was labeled with a fluorescent probe for the endoplasmic reticulum (ER), and vacuole formation was prevented by presence of the protein synthesis inhibitor cycloheximide. These effects are characteristics of a caspase-independent death mode termed paraptosis previously associated with ER stress. These studies suggest that paraptosis may be a more frequent outcome of PDT than has hitherto been realized.

Iron Chelators and Exogenic Photosensitizers. Synergy through Oxidative Stress Gene Expression

In non-invasive anticancer photodynamic therapy (PDT), a nontoxic photosensitizer (PS), which is activated by visible light, is used as a magic bullet that selectively destroys cancer cells. Recently, we described the combined therapy of 5-aminolevulinic acid (ALA-PDT) with thiosemicarbazone (TSC), i.e. an iron-chelating agent. This resulted in a strong synergistic effect. Herein, we investigated a novel strategy using a combination of PDT consist of the xenobiotic-porphyrin type PS with TSC. We observed a synergistic effect for all of the pairs of TSC-PS. This approach can be rationalized by the fact that both chlorin and TSC can affect the generation of reactive oxygen species (ROS). In order to elucidate the plausible mechanism of action, we also combined the investigated PSs with DFO, which forms complexes that are redox inactive. We detected a slight antagonism or additivity for this combination. This may suggest that the ability of an iron chelator (IC) to participate in the production of ROS and the generation of oxidative stress is important.

Subcellular Targeting as a Determinant of the Efficacy of Photodynamic Therapy

In prior studies, we have identified the ability of low-level lysosomal photodamage to potentiate the phototoxic effect of subsequent photodamage to mitochondria. The mechanism involves calpain-mediated cleavage of the autophagy-associated protein ATG5 to form a proapoptotic fragment (tATG5). In this report, we explore the permissible time lag between the two targeting procedures along with the effect of simultaneously targeting both lysosomes and mitochondria. This was found to be as effective as the sequential protocol with no gap between the irradiation steps. Inhibition of calpain reversed the enhanced efficacy of the "simultaneous" protocol. It appears that even a minor level of lysosomal photodamage can have a significant effect on the efficacy of subsequent mitochondrial photodamage. We propose that these results may explain the efficacy of Photofrin, a photosensitizing product that also targets both lysosomes and mitochondria for photodamage.

Beyond the Barriers of Light Penetration: Strategies, Perspectives and Possibilities for Photodynamic Therapy

Photodynamic therapy (PDT) is a photochemistry based treatment modality that involves the generation of cytotoxic species through the interactions of a photosensitizer molecule with light irradiation of an appropriate wavelength. PDT is an approved therapeutic modality for several cancers globally and in several cases has proved to be effective where traditional treatments have failed. The key parameters that determine PDT efficacy are 1. the photosensitizer (nature of the molecules, selectivity, and macroscopic and microscopic localization etc.), 2. light application (wavelength, fluence, fluence rate, irradiation regimes etc.) and 3. the microenvironment (vascularity, hypoxic regions, stromal tissue density, molecular heterogeneity etc.). Over the years, several groups aimed to monitor and manipulate the components of these critical parameters to improve the effectiveness of PDT treatments. However, PDT is still misconstrued to be a surface treatment primarily due to the limited depths of light penetration. In this review, we present the recent advances, strategies and perspectives in PDT approaches, particularly in cancer treatment, that focus on increasing the 'damage zone' beyond the reach of light in the body. This is enabled by a spectrum of approaches that range from innovative photosensitizer excitation strategies, increased specificity of phototoxicity, and biomodulatory approaches that amplify the biotherapeutic effects induced by photodynamic action. Along with the increasing depth of understanding of the underlying physical, chemical and physiological mechanisms, it is anticipated that with the convergence of these strategies, the clinical utility of PDT will be expanded to a powerful modality in the armamentarium for the management of cancer.

PLGA nanoparticle encapsulation reduces toxicity while retaining the therapeutic efficacy of EtNBS-PDT in vitro

Photodynamic therapy regimens, which use light-activated molecules known as photosensitizers, are highly selective against many malignancies and can bypass certain challenging therapeutic resistance mechanisms. Photosensitizers such as the small cationic molecule EtNBS (5-ethylamino-9-diethyl-aminobenzo[a]phenothiazinium chloride) have proven potent against cancer cells that reside within acidic and hypoxic tumour microenvironments. At higher doses, however, these photosensitizers induce "dark toxicity" through light-independent mechanisms. In this study, we evaluated the use of nanoparticle encapsulation to overcome this limitation. Interestingly, encapsulation of the compound within poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PLGA-EtNBS) was found to significantly reduce EtNBS dark toxicity while completely retaining the molecule's cytotoxicity in both normoxic and hypoxic conditions. This dual effect can be attributed to the mechanism of release: EtNBS remains encapsulated until external light irradiation, which stimulates an oxygen-independent, radical-mediated process that degrades the PLGA nanoparticles and releases the molecule. As these PLGA-encapsulated EtNBS nanoparticles are capable of penetrating deeply into the hypoxic and acidic cores of 3D spheroid cultures, they may enable the safe and efficacious treatment of otherwise unresponsive tumour regions.

Promotion of Proapoptotic Signals by Lysosomal Photodamage: Mechanistic Aspects and Influence of Autophagy

Prior studies demonstrated that a low level (LD10-15 ) of lysosomal photodamage can sensitize cells to the apoptotic death that results from subsequent mitochondrial photodamage. We have proposed that this process occurs via a calpain-catalyzed cleavage of the autophagy-associated protein ATG5 to form a proapoptotic fragment. In this report, we provide evidence for the postulated ATG5 cleavage and show that the sequential photodynamic therapy (PDT) protocol can also partly overcome the adverse effect of hypoxia on the initiation of apoptosis. While autophagy can offer cytoprotection after mitochondrial photodamage, this does not appear to apply when lysosomes are the target. This may account for the ability of very low PDT doses directed at lysosomes to evoke ATG5 cleavage. The resulting proapoptotic effect overcomes intrinsic cytoprotection from mitochondrial photodamage along with a further stimulation of phototoxicity.

Photodynamic therapy: Promotion of efficacy by a sequential protocol

Photodynamic therapy (PDT) offers a new approach to selective tumor eradication. Modifications designed to increase and optimize efficacy continue to emerge. Selective photodamage to malignant cells and their environment can bring about tumor cell destruction, shutdown of the tumor vasculature, stimulation of immunologic anti-tumor effects and potentiation of other therapeutic effects. Current development of combination protocols may provide a better rationale for integration of PDT into clinical practice. An example described here is the ability of a sequential (two-sensitizer) PDT protocol to enhance the efficacy of photokilling. The first step involves low-level lysosomal photodamage that has been shown to promote the apoptotic response to subsequent photodynamic effects directed at mitochondria. In this report, we demonstrate the ability of Photofrin, an FDA-approved photosensitizing agent, to serve as either the first or second element of the sequential protocol.

Photodynamic therapy as an effective therapeutic approach in MAME models of inflammatory breast cancer

Photodynamic therapy (PDT) is a minimally invasive, FDA-approved therapy for treatment of endobronchial and esophageal cancers that are accessible to light. Inflammatory breast cancer (IBC) is an aggressive and highly metastatic form of breast cancer that spreads to dermal lymphatics, a site that would be accessible to light. IBC patients have a relatively poor survival rate due to lack of targeted therapies. The use of PDT is underexplored for breast cancers but has been proposed for treatment of subtypes for which a targeted therapy is unavailable. We optimized and used a 3D mammary architecture and microenvironment engineering (MAME) model of IBC to examine the effects of PDT using two treatment protocols. The first protocol used benzoporphyrin derivative monoacid A (BPD) activated at doses ranging from 45 to 540 mJ/cm(2). The second PDT protocol used two photosensitizers: mono-L-aspartyl chlorin e6 (NPe6) and BPD that were sequentially activated. Photokilling by PDT was assessed by live-dead assays. Using a MAME model of IBC, we have shown a significant dose-response in photokilling by BPD-PDT. Sequential activation of NPe6 followed by BPD is more effective in photokilling of tumor cells than BPD alone. Sequential activation at light doses of 45 mJ/cm(2) for each agent resulted in >90 % cell death, a response only achieved by BPD-PDT at a dose of 360 mJ/cm(2). Our data also show that effects of PDT on a volumetric measurement of 3D MAME structures reflect efficacy of PDT treatment. Our study is the first to demonstrate the potential of PDT for treating IBC.

Photodynamic Efficiency: From Molecular Photochemistry to Cell Death

Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.

The role of photodynamic therapy in overcoming cancer drug resistance

Many modalities of cancer therapy induce mechanisms of treatment resistance and escape pathways during chronic treatments, including photodynamic therapy (PDT). It is conceivable that resistance induced by one treatment might be overcome by another treatment. Emerging evidence suggests that the unique mechanisms of tumor cell and microenvironment damage produced by PDT could be utilized to overcome cancer drug resistance, to mitigate the compensatory induction of survival pathways and even to re-sensitize resistant cells to standard therapies. Approaches that capture the unique features of PDT, therefore, offer promising factors for increasing the efficacy of a broad range of therapeutic modalities. Here, we highlight key preclinical findings utilizing PDT to overcome classical drug resistance or escape pathways and thus enhance the efficacy of many pharmaceuticals, possibly explaining the clinical observations of the PDT response to otherwise treatment-resistant diseases. With the development of nanotechnology, it is possible that light activation may be used not only to damage and sensitize tumors but also to enable controlled drug release to inhibit escape pathways that may lead to resistance or cell proliferation.

More Adventures in Photodynamic Therapy

Photodynamic therapy is a procedure that can provide a selective eradication of neoplastic disease if sufficient drug, light, and oxygen are available. As this description suggests, it involves the photosensitization of malignant tissues to irradiation with photons in the visible range. While not suitable for tumors at unknown loci, it can be of use for eradication of cancer at surgical margins and therapy at sites where substantial surgery might otherwise be involved. Drug development has been delayed by several factors including the reluctance of major pharmaceutical firms in the United States to invest in this technology along with some unwise approaches in the past.

Promotion of Proapoptotic Signals by Lysosomal Photodamage

We previously reported that low-level lysosomal photodamage enhanced the efficacy of subsequent mitochondrial photodamage, resulting in a substantial promotion of apoptotic cell death. We now extend our analysis of the sequential PDT protocol to include two additional lysosomal-targeting photosensitizers. These agents, because of enhanced permeability, are more potent than the agent (N-aspartyl chlorin E6, NPe6) used in the initial study. Addition of the cell-permeable cysteine protease inhibitor E-64d and calcium chelator BAPTA-AM almost completely suppressed sequential PDT-induced loss of mitochondrial membrane potential and activation of procaspases-3 and -7. These inhibitors did not, however, suppress the proapoptotic effect of a BH3 mimetic or mitochondrial photodamage. Knockdowns of ATG7 or ATG5, proteins normally associated with autophagy, suppressed photodamage induced by the sequential PDT protocol. These effects appear to be independent of the autophagic process as pharmacological inhibition of autophagy offered no such protection. Effects of ATG7 and ATG5 knockdowns may reflect the role that ATG7 plays in regulating lysosome permeability, and the likelihood that a proteolytic fragment of ATG5 amplifies mitochondrial proapoptotic processes. Our results suggest that low-dose photodamage that sequentially targets lysosomes and mitochondria may offer significant advantages over the use of single photosensitizers.

Apoptosis and associated phenomena as a determinants of the efficacy of photodynamic therapy

Failure of neoplastic cells to respond to conventional chemotherapy is usually associated with factors that limit access of drugs to subcellular sites, differences in cell-cycle kinetics or mutations leading to loss of drug-activation pathways or other processes that govern response factors. For PDT, efficacy depends mainly on selective uptake of photosensitizers by neoplastic cells, oxygenation levels, the suitable direction of irradiation and the availability of pathways to cell death that are highly conserved among mammalian cell types. While it is possible to engineer PDT-resistant cell types, current evidence suggests that the major obstacles to cancer control relate to drug, light and oxygen distribution. This review discusses some of the factors that can govern PDT-induced cell death.

A Novel Exploration of a Combination of Gambogic Acid with TiO₂ Nanofibers: The Photodynamic Effect for HepG2 Cell Proliferation

As a good photosensitizer, TiO₂ nanomaterials show potential biomedical applications, such as drug carriers or enhancers in photodynamic therapy. In this contribution, novel nanocomposites through the blending of TiO₂ nanofibers with the active compound, gambogic acid (GA), were explored, and the results showed that GA could inhibit cancer cell proliferation in a time-dependent and dose-dependent manner, inducing apoptosis and cell cycle arrest at the G0/G1 phase in HepG2 cells. It is evident that after the GA-TiO₂ nanocomposites were cultured with the cancer cells, the cooperation effect could effectively enhance the cytotoxicity of GA for HepG2 cells. Meanwhile, if activated by UV irradiation, under the presence of GA-TiO₂ nanocomposites, this would lead to significant apoptosis and necrosis for HepG2 cells with a photodynamic therapy (PDT) effect. Associated with the controlled drug-release from these nanocomposites, TiO₂ nanofibers could readily cut down the drug consumption in HepG2 cells and reduce the side-effect for the normal cells and tissue, which may be further utilized in the therapeutic alliance for cancer therapy.

The "Nano" World in Photodynamic Therapy

Photodynamic Therapy (PDT) is an externally activated, photochemistry-based approach that generates cytotoxic reactive molecular species (RMS), which kill or modulate biological targets. PDT provides unique opportunities for applications of nanotechnology where light activation can trigger both direct RMS-mediated cytotoxic activity and the release of contents within the nanoconstructs (Figure 1). This process allows several species, working via different mechanisms and molecular targets to be activated or released in the right place and time, thus providing a distinctive approach to combination therapy. With advances in the development of miniaturized, even biodegradable, light sources and delivery systems, exciting possibilities of anatomical reach with PDT are being made possible. This brief article introduces aspects of interfaces of PDT and nanotechnology but, due to space constraints, makes no attempt to be a comprehensive review.