In Vitro Low-Fluence Photodynamic Therapy Parameter Screening Using 3D Tumor Spheroids Shows that Fractionated Light Treatments Enhance Phototoxicity

Computational modelling of the therapeutic outputs of photodynamic therapy on spheroid-on-chip models

Photodynamic therapy (PDT) is a medical radio chemotherapeutic method that uses light, photosensitizing agents, and oxygen to produce cytotoxic compounds, which eliminate malignant cells. Recently, Microfluidic systems have been used to analyse photosensitizers (PSs) due to their potential to replicate in vivo environments. While prior studies have established a strong correlation between reacted singlet oxygen concentration and PDT-induced cellular death, the effects that the ambient fluid flow might have on the concentration of oxygen and PS have been disregarded in many, which limits the reliability of the results. Herein, we coupled the transport of oxygen and PS throughout the ambient medium and within the spheroidal multicellular aggregate to initially study the profiles of oxygen and PS concentration alongside PDT-induced cellular death throughout the spheroid before and after radiation. The attained results indicate that the PDT-induced cellular death initiates on the surface of the spheroids and subsequently spreads to the neighbouring regions, which is in great accordance with experimental results. Afterward, the effects that drug-light interval (DLI), fluence rate, PS composition, microchannel height, and inlet flow rate have on the therapeutic outcomes are studied. The findings show that adequate DLI is critical to ensure uniform distribution of PS throughout the medium, and a value of 5 h was found to be sufficient. The composition of PS is critical, as ALA-PpIX induces earlier cell death but accelerates oxygen consumption, especially in the outer layers, depriving the inner layers of oxygen necessary for PDT, which in turn disrupts and prolongs the exposure time compared to mTHPC and Photofrin. Despite the fluence rate directly influencing the singlet oxygen generation rate, increasing the fluence rate by 189 mW/cm2 would not significantly benefit us. Microwell height and inlet flow rate involve competing phenomena-increasing height or decreasing flow reduces oxygen supply and increases PS "washout" and its concentration.

Assays on 3D tumor spheroids for exploring the light dosimetry of photodynamic effects under different gaseous conditions

The multifaceted nature of photodynamic therapy (PDT) requires a throughout evaluation of a multitude of parameters when devising preclinical protocols. In this study, we constructed MCF-7 human breast tumor spheroid assays to infer PDT irradiation doses at four gradient levels for violet light at 408 nm and red light at 625 nm under normal and hypoxic oxygen conditions. The compacted three-dimensional (3D) tumor models conferred PDT resistance as compared to monolayer cultures due to heterogenous distribution of photosensitizers along with the presence of internal hypoxic region. Cell viability results indicated that the violet light was more efficient to kill cells in the spheroids under normal oxygen conditions, while cells exposed to the hypoxic microenvironment exhibited minimal PDT-induced death. The combination of 3D tumor spheroid assays and the multiparametric screening platform presented a solid framework for assessing PDT efficacy across a wide range of different physiological conditions and therapeutic regimes.

Enhancing Fractionated Cancer Therapy: A Triple-Anthracene Photosensitizer Unleashes Long-Persistent Photodynamic and Luminous Efficacy

Conventional photodynamic therapy (PDT) is often limited in treating solid tumors due to hypoxic conditions that impede the generation of reactive oxygen species (ROS), which are critical for therapeutic efficacy. To address this issue, a fractionated PDT protocol has been suggested, wherein light irradiation is administered in stages separated by dark intervals to permit oxygen recovery during these breaks. However, the current photosensitizers used in fractionated PDT are incapable of sustaining ROS production during the dark intervals, leading to suboptimal therapeutic outcomes (Table S1). To circumvent this drawback, we have synthesized a novel photosensitizer based on a triple-anthracene derivative that is designed for prolonged ROS generation, even after the cessation of light exposure. Our study reveals a unique photodynamic action of these derivatives, facilitating the direct and effective disruption of biomolecules and significantly improving the efficacy of fractionated PDT (Table S2). Moreover, the existing photosensitizers lack imaging capabilities for monitoring, which constraints the fine-tuning of irradiation parameters (Table S1). Our triple-anthracene derivative also serves as an afterglow imaging agent, emitting sustained luminescence postirradiation. This imaging function allows for the precise optimization of intervals between PDT sessions and aids in determining the timing for subsequent irradiation, thus enabling meticulous control over therapy parameters. Utilizing our novel triple-anthracene photosensitizer, we have formulated a fractionated PDT regimen that effectively eliminates orthotopic pancreatic tumors. This investigation highlights the promise of employing long-persistent photodynamic activity in advanced fractionated PDT approaches to overcome the current limitations of PDT in solid tumor treatment.

Multi-charged nanoemulsion for photodynamic treatment of glioblastoma cell line in 2D and 3D in vitro models

Multi-charged nanoemulsions (NE) were designed to deliver Cannabidiol (CBD), Indocyanine green (ICG), and Protoporphyrin (PpIX) to treat glioblastoma (GBM) through Photodynamic Therapy (PDT). The phase-inversion temperature (PIT) method resulted in a highly stable NE that can be scaled easily, with a six-month shelf-life. We observed the quasi-spherical morphology of the nanoemulsions without any unencapsulated material and that 89% (± 5.5%) of the material was encapsulated. All physicochemical properties were within the expected range for a nanostructured drug delivery system, making these multi-charged nanoemulsions promising for further research and development. NE-PIC (NE-Protoporphyrin + Indocyanine + CBD) was easily internalized on GBM cells after three hours of incubation. Nanoemulsion (NE and NE-PIC) did not result in significant cytotoxicity, even for GBM or non-tumorigenic cell lines (NHF). Phototoxicity was significantly higher for the U87MG cell than the T98G cell when exposed to: visible (430 nm) and infrared (810 nm) laser light, with a difference of about 20%. From 50 mJ.cm-2, the viability of GBM cell lines decreases significantly, ranging from 65% to 85%. The NE-PIC was also effective for inhibiting cell proliferation into a 3D spheroidal GBM cell model, which is promising for mimicking the tumor cell environment. Irradiation at 810 nm was more effective in treating spheroid due to its deeper penetration in complex structures. NE-PIC has the potential as a drug delivery system for photoinactivation and photo diagnostic of GBM cell lines, taking advantage of the versatility of its active components.

Are tumour-associated carbonic anhydrases genuine therapeutic targets for photodynamic therapy?

INTRODUCTION

Photodynamic therapy (PDT) is a reactive oxygen species (ROS)-dependent treatment modality which has emerged as an alternative cancer therapy strategy. However, in solid tumors, the therapeutic efficacy of PDT is strongly reduced by hypoxia, a typical feature of many such tumors. The tumor-associated carbonic anhydrases IX (hCA IX) and XII (hCA XII), which are overexpressed under hypoxia are attractive, validated anticancer drug targets in solid tumors. Current challenges in therapeutic design of effective PDT systems aim to overcome the limitation of hypoxia by developing synergistic CA-targeted therapies combining photosensitizers and hCA IX/XII inhibitors.

AREA COVERED

In this review, the current literature on the use of hCA IX/XII inhibitors (CAi) for targeting photosensitizing chemical systems useful for PDT against hypoxic solid tumors is summarized, along with recent progress, challenges, and future prospects.

EXPERT OPINION

hCA IX/XII-focused photosensitizers have recently provided new generation of compounds of considerable potential. Proof of concept of in vivo efficacy studies suggested enhanced efficacy for CAi-PDT hybrid systems. Further research is needed to deepen our understanding of how hCA IX/hCA XII inhibition can enhance PDT and for obtaining more effective such derivatives.

Metronomic Photodynamic Therapy with Conjugated Polymer Nanoparticles in Glioblastoma Tumor Microenvironment

Alternative therapies such as photodynamic therapy (PDT) that combine light, oxygen and photosensitizers (PSs) have been proposed for glioblastoma (GBM) management to overcome conventional treatment issues. An important disadvantage of PDT using a high light irradiance (fluence rate) (cPDT) is the abrupt oxygen consumption that leads to resistance to the treatment. PDT metronomic regimens (mPDT) involving administering light at a low irradiation intensity over a relatively long period of time could be an alternative to circumvent the limitations of conventional PDT protocols. The main objective of the present work was to compare the effectiveness of PDT with an advanced PS based on conjugated polymer nanoparticles (CPN) developed by our group in two irradiation modalities: cPDT and mPDT. The in vitro evaluation was carried out based on cell viability, the impact on the macrophage population of the tumor microenvironment in co-culture conditions and the modulation of HIF-1α as an indirect indicator of oxygen consumption. mPDT regimens with CPNs resulted in more effective cell death, a lower activation of molecular pathways of therapeutic resistance and macrophage polarization towards an antitumoral phenotype. Additionally, mPDT was tested in a GBM heterotopic mouse model, confirming its good performance with promising tumor growth inhibition and apoptotic cell death induction.

Mesenchymal Stem Cell Membrane-Coated TPCS2a-Loaded Nanoparticles for Breast Cancer Photodynamic Therapy

Despite substantial improvements in breast cancer (BC) treatment there is still an urgent need to find alternative treatment options to improve the outcomes for patients with advanced-stage disease. Photodynamic therapy (PDT) is gaining a lot of attention as a BC therapeutic option because of its selectivity and low off-target effects. However, the hydrophobicity of photosensitizers (PSs) impairs their solubility and limits the circulation in the bloodstream, thus representing a major challenge. The use of polymeric nanoparticles (NPs) to encapsulate the PS may represent a valuable strategy to overcome these issues. Herein, we developed a novel biomimetic PDT nanoplatform (NPs) based on a polymeric core of poly(lactic-co-glycolic)acid (PLGA) loaded with the PS meso-tetraphenylchlorin disulfonate (TPCS_2a). TPCS_2a@NPs of 98.89 ± 18.56 nm with an encapsulation efficiency percentage (EE%) of 81.9 ± 7.92% were obtained and coated with mesenchymal stem cells-derived plasma membranes (mMSCs) (mMSC-TPCS_2a@NPs, size of 139.31 ± 12.94 nm). The mMSC coating armed NPs with biomimetic features to impart long circulation times and tumor-homing capabilities. In vitro, biomimetic mMSC-TPCS_2a@NPs showed a decrease in macrophage uptake of 54% to 70%, depending on the conditions applied, as compared to uncoated TPCS_2a@NPs. Both NP formulations efficiently accumulated in MCF7 and MDA-MB-231 BC cells, while the uptake was significantly lower in normal breast epithelial MCF10A cells with respect to tumor cells. Moreover, encapsulation of TPCS_2a in mMSC-TPCS_2a@NPs effectively prevents its aggregation, ensuring efficient singlet oxygen (¹O₂) production after red light irradiation, which resulted in a considerable in vitro anticancer effect in both BC cell monolayers (IC₅₀ < 0.15 µM) and three-dimensional spheroids.

Anti-Hypoxia Nanoplatforms for Enhanced Photosensitizer Uptake and Photodynamic Therapy Effects in Cancer Cells

Photodynamic therapy (PDT) holds great promise in cancer eradication due to its target selectivity, non-invasiveness, and low systemic toxicity. However, due to the hypoxic nature of many native tumors, PDT is frequently limited in its therapeutic effect. Additionally, oxygen consumption during PDT may exacerbate the tumor's hypoxic condition, which stimulates tumor proliferation, metastasis, and invasion, resulting in poor treatment outcomes. Therefore, various strategies have been developed to combat hypoxia in PDT, such as oxygen carriers, reactive oxygen supplements, and the modulation of tumor microenvironments. However, most PDT-related studies are still conducted on two-dimensional (2D) cell cultures, which fail to accurately reflect tissue complexity. Thus, three-dimensional (3D) cell cultures are ideal models for drug screening, disease simulation and targeted cancer therapy, since they accurately replicate the tumor tissue architecture and microenvironment. This review summarizes recent advances in the development of strategies to overcome tumor hypoxia for enhanced PDT efficiency, with a particular focus on nanoparticle-based photosensitizer (PS) delivery systems, as well as the advantages of 3D cell cultures.

Novel Water-Soluble Chlorin-Based Photosensitizer for Low-Fluence Photodynamic Therapy

Photodynamic therapy (PDT), performed with low-fluence rates, can improve antitumor responses and prevent adverse effects. However, photosensitizers (PSs) for low-fluence PDT treatment are rarely reported. Herein, we exploited an amphiphilic chlorin-based PS, named DYSP-C34, which has a variety of beneficial biological properties, such as improved water solubility, better cellular permeability, specific localization and enhanced phototoxicity under low light dose irradiation. In addition, DYSP-C34 could effectively accumulate in a mouse subcutaneous xenograft tumor and exhibit substantial tumor regression after irradiation with an extremely low light fluence (6 J/cm²). Meanwhile, the excellent phototoxicity could stimulate the host immune system and lead to a strong inhibition of tumor growth synergistically. These results indicated the potential value of DYSP-C34 as a chlorin-type PS for low-fluence PDT application.

Recent Advances in Strategies for Addressing Hypoxia in Tumor Photodynamic Therapy

Photodynamic therapy (PDT) is a treatment modality that uses light to target tumors and minimize damage to normal tissues. It offers advantages including high spatiotemporal selectivity, low side effects, and maximal preservation of tissue functions. However, the PDT efficiency is severely impeded by the hypoxic feature of tumors. Moreover, hypoxia may promote tumor metastasis and tumor resistance to multiple therapies. Therefore, addressing tumor hypoxia to improve PDT efficacy has been the focus of antitumor treatment, and research on this theme is continuously emerging. In this review, we summarize state-of-the-art advances in strategies for overcoming hypoxia in tumor PDTs, categorizing them into oxygen-independent phototherapy, oxygen-economizing PDT, and oxygen-supplementing PDT. Moreover, we highlight strategies possessing intriguing advantages such as exceedingly high PDT efficiency and high novelty, analyze the strengths and shortcomings of different methods, and envision the opportunities and challenges for future research.

Morphological Response in Cancer Spheroids for Screening Photodynamic Therapy Parameters

Photodynamic therapy (PDT) is a treatment which uses light-activated compounds to produce reactive oxygen species, leading to membrane damage and cell death. Multicellular cancer spheroids are a preferable alternative for PDT evaluation in comparison to monolayer cell cultures due to their ability to better mimic in vivo avascular tumour characteristics such as hypoxia and cell-cell interactions, low cost, and ease of production. However, inconsistent growth kinetics and drug responsiveness causes poor experimental reproducibility and limits their usefulness. Herein, we used image analysis to establish a link between human melanoma C8161 spheroid morphology and drug responsiveness. Spheroids were pre-selected based on sphericity, area, and diameter, reducing variation in experimental groups before treatment. Spheroid morphology after PDT was analyzed using AnaSP and ReViSP, MATLAB-based open-source software, obtaining nine different parameters. Spheroids displayed a linear response between biological assays and morphology, with area (R² = 0.7219) and volume (R² = 0.6138) showing the best fit. Sphericity, convexity, and solidity were confirmed as poor standalone indicators of spheroid viability. Our results indicate spheroid morphometric parameters can be used to accurately screen inefficient treatment combinations of novel compounds.