Increasing the efficiency of photodynamic therapy by improved light delivery and oxygen supply using an anticoagulant in a solid tumor model

Photodynamically Tumor Vessel Destruction Amplified Tumor Targeting of Nanoparticles for Efficient Chemotherapy

Efficient tumor-targeted drug delivery is still a challenging and currently unbreakable bottleneck in chemotherapy for tumors. Nanomedicines based on passive or active targeting strategy have not yet achieved convincing chemotherapeutic benefits in the clinic due to the tumor heterogeneity. Inspired by the efficient inflammatory-cell recruitment to acute clots, we constructed a two-component nanosystem, which is composed of an RGD-modified pyropheophorbide-a (Ppa) micelle (PPRM) that mediates the tumor vascular-targeted photodynamic reaction to activate local coagulation and subsequently transmits the coagulation signals to the circulating clot-targeted CREKA peptide-modified camptothecin (CPT)-loaded nanodiscs (CCNDs) for amplifying tumor targeting. PPRM could effectively bind with the tumor vasculature and induce sufficient local thrombus by a photodynamic reaction. Local photodynamic reaction-induced tumor target amplification greatly increased the tumor accumulation of CCND by 4.2 times, thus significantly enhancing the chemotherapeutic efficacy in the 4T1 breast tumor model. In other words, this study provides a powerful platform to amplify tumor-specific drug delivery by taking advantage of the efficient crosstalk between the PPRM-activated coagulation cascade and clot-targeted CCND.

Effects of Nanobubbles on Photochemical Processes of Levofloxacin Photosensitizer

Photodynamic therapy (PDT) stands as an efficacious modality for the treatment of cancer and various diseases, in which optimization of the electron transfer and augmentation of the production of lethal reactive oxygen species (ROS) represent pivotal challenges to enhance its therapeutic efficacy. Empirical investigations have established that the spontaneous initiation of redox reactions associated with electron transfer is feasible and is located in the gas-liquid interfaces. Meanwhile, nanobubbles (NBs) are emerging as entities capable of furnishing a plethora of such interfaces, attributed to their stability and large surface/volume ratio in bulk water. Thus, NBs provide a chance to expedite the electron-transfer kinetics within the context of PDT in an ambient environment. In this paper, we present a pioneering exploration into the impact of nitrogen nanobubbles (N2-NBs) on the electron transfer of the photosensitizer levofloxacin (LEV). Transient absorption spectra and time-resolved decay spectra, as determined through laser flash photolysis, unequivocally reveal that N2-NBs exhibit a mitigating effect on the decay of the LEV excitation triplet state, thereby facilitating subsequent processes. Of paramount significance is the observation that the presence of N2-NBs markedly accelerates the electron transfer of LEV, albeit with a marginal inhibitory influence on its energy-transfer reaction. This observation is corroborated through absorbance measurements and offers compelling evidence substantiating the role of NBs in expediting electron transfer within the ambit of PDT. The mechanism elucidated herein sheds light on how N2-NBs intricately influence both electron-transfer and energy-transfer reactions in the photosensitizer LEV. These findings not only contribute to a nuanced understanding of the underlying processes but also furnish novel insights that may inform the application of NBs in the realm of photodynamic therapy.

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.

Iridium oxide nanoparticles mediated enhanced photodynamic therapy combined with photothermal therapy in the treatment of breast cancer

Photodynamic therapy (PDT) of tumor has achieved good results, but the treatment efficiency is not high due to the lack of effective photosensitizers and tumor hypoxia. In this study, iridium dioxide nanoparticles (IrO₂ NPs) with excellent photothermal/photodynamic effects and catalase like activity were synthesized by a simple method. The combination of glucose oxidase (GOx) and IrO₂ NPs is formed by hyaluronic acid (HA), which have the activities of glucose oxidase and catalase, can target tumor sites and form in situ amplifiers in tumor microenvironment (IrO₂-GOx@HA NPs). Firstly, GOx convert the high levels of glucose in the tumor to hydrogen peroxide (H₂O₂), and then IrO₂ NPs convert H₂O₂ to oxygen (O₂), which can enhance the type II of PDT. IrO₂ NPs also can be used as a thermosensitive agent for photothermal therapy (PTT). In cancer cells, IrO₂-GOx@HA NPs-mediated amplifier enhances the effect of type II of PDT, aggravating the apoptosis of breast cancer (4T1) cells and cooperating with its own PTT to further improve the overall treatment effect. Under simulated hypoxic conditions of tumor tissue, it was found that IrO₂-GOx@HA NPs treatment can effectively relieve hypoxia inside tumor tissue. In addition, the results in vivo further proved that, IrO₂-GOx@HA NPs can enhance the role of II PDT and cooperate with PTT to treat breast cancer effectively. The results highlight the prospect of IrO₂-GOx@HA NPs in controlling and regulating tumor hypoxia to overcome the limitations of current cancer therapy.

A Photosensitive Polymeric Carrier with a Renewable Singlet Oxygen Reservoir Regulated by Two NIR Beams for Enhanced Antitumor Phototherapy

Photodynamic therapy (PDT), which utilizes photosensitizer to convert molecular oxygen into singlet oxygen (¹ O₂ ) upon laser irradiation to ablate tumors, will exacerbate the already oxygen shortage of most solid tumors and is thus self-limiting. Herein, a sophisticated photosensitive polymeric material (An-NP) that allows sustained ¹ O₂ generation and sufficient oxygen supply during the entire phototherapy is engineered by alternatively applying PDT and photothermal therapy (PTT) controlled by two NIR laser beams. In addition to a photosensitizer that generates ¹ O₂ , An-NP consists of two other key components: a molecularly designed anthracene derivative capable of trapping/releasing ¹ O₂ with superior reversibility and a dye J-aggregate with superb photothermal performance. Thus, in 655 nm laser-triggered PDT process, An-NP generates abundant ¹ O₂ with extra ¹ O₂ being trapped via the conversion into EPO-NP; while in the subsequent 785 nm laser-driven PTT process, the converted EPO-NP undergoes thermolysis to liberate the captured ¹ O₂ and regenerates An-NP. The intratumoral oxygen level can be replenished during the PTT cycle for the next round of PDT to generate ¹ O₂ . The working principle and phototherapy efficacy are preliminarily demonstrated in living cells and tumor-bearing mice, respectively.

Nanomedicine-Based Strategies Assisting Photodynamic Therapy for Hypoxic Tumors: State-of-the-Art Approaches and Emerging Trends

Since the first clinical cancer treatment in 1978, photodynamic therapy (PDT) technologies have been largely improved and approved for clinical usage in various cancers. Due to the oxygen-dependent nature, the application of PDT is still limited by hypoxia in tumor tissues. Thus, the development of effective strategies for manipulating hypoxia and improving the effectiveness of PDT is one of the most important area in PDT field. Recently, emerging nanotechnology has benefitted progress in many areas, including PDT. In this review, after briefly introducing the mechanisms of PDT and hypoxia, as well as basic knowledge about nanomedicines, we will discuss the state of the art of nanomedicine-based approaches for assisting PDT for treating hypoxic tumors, mainly based on oxygen replenishing strategies and the oxygen dependency diminishing strategies. Among these strategies, we will emphasize emerging trends about the use of nanoscale metal-organic framework (nMOF) materials and the combination of PDT with immunotherapy. We further discuss future perspectives and challenges associated with these trends in both the aspects of mechanism and clinical translation.

Tumor microenvironment-responsive polymer with chlorin e6 to interface hollow mesoporous silica nanoparticles-loaded oxygen supply factor for boosted photodynamic therapy

Cancer treatment has always been a big problem for people. With the application of photodynamic therapy, the problem has been alleviated. However, the problem of tumor hypoxia affecting photodynamic therapy has been waiting to be resolved. Therefore, we report here that a redox nanocarrier (called RN) is prepared by hollow mesoporous silica sphere (HMSNs) and a redox-responsive polymer ligand. The nanocarrier is loaded with metformin and catalase, and the polymer is linked to the photosensitizer chlorin e6 (Ce6). Metformin inhibits the mitochondrial respiration of cancer cells, reducing the activity of cancer cells and increasing the oxygen concentration required for photodynamic therapy. Not only the effect of photodynamic therapy is enhanced, but also the effect of chemotherapy is increased to achieve super additive treatment. These RNs exhibit not only low cytotoxicity but also high biocompatibility in vitro experiments. In vitro Ce6 release studies have shown a higher release in the presence of glutathione (GSH). Confocal microscopy can further indicate that the nanoparticles are carried to the area around the nucleus of the cancer cells. In addition, treatment with a mouse tumor model demonstrated that RN has an effective therapeutic effect on tumors.

A Phototheranostic Strategy to Continuously Deliver Singlet Oxygen in the Dark and Hypoxic Tumor Microenvironment

Continuous irradiation during photodynamic therapy (PDT) inevitably induces tumor hypoxia, thereby weakening the PDT effect. In PDT-induced hypoxia, providing singlet oxygen from stored chemical energy may enhance the cell-killing effect and boost the therapeutic effect. Herein, we present a phototheranostic (DPPTPE@PEG-Py NPs) prepared by using a 2-pyridone-based diblock polymer (PEG-Py) to encapsulate a semiconducting, heavy-atom-free pyrrolopyrrolidone-tetraphenylethylene (DPPTPE) with high singlet-oxygen-generation ability both in dichloromethane and water. The PEG-Py can trap the 1 O2 generated from DPPTPE under laser irradiation and form a stable intermediate of endoperoxide, which can then release 1 O2 in the dark, hypoxic tumor microenvironment. Furthermore, fluorescence-imaging-guided phototherapy demonstrates that this phototheranostic could completely inhibit tumor growth with the help of laser irradiation.

Ultrasonically sculpted virtual relay lens for in situ microimaging

We demonstrate in situ non-invasive relay imaging through a medium without inserting physical optical components. We show that a virtual optical graded-index (GRIN) lens can be sculpted in the medium using in situ reconfigurable ultrasonic interference patterns to relay images through the medium. Ultrasonic wave patterns change the local density of the medium to sculpt a graded refractive index pattern normal to the direction of light propagation, which modulates the phase front of light, causing it to focus within the medium and effectively creating a virtual relay lens. We demonstrate the in situ relay imaging and resolving of small features (22 µm) through a turbid medium (optical thickness = 5.7 times the scattering mean free path), which is normally opaque. The focal distance and the numerical aperture of the sculpted optical GRIN lens can be tuned by changing the ultrasonic wave parameters. As an example, we experimentally demonstrate that the axial focal distance can be continuously scanned over a depth of 5.4 mm in the modulated medium and that the numerical aperture can be tuned up to 21.5%. The interaction of ultrasonic waves and light can be mediated through different physical media, including turbid media, such as biological tissue, in which the ultrasonically sculpted GRIN lens can be used for relaying images of the underlying structures through the turbid medium, thus providing a potential alternative to implanting invasive endoscopes.

Ultrasonically Steerable Graded-Index Optical Waveguides for Deep Tissue Light Delivery: Theory and Applications

Graded-index (GRIN) fibers have been used as implantable optical waveguides to guide light and relay images through the depth of the tissue. We have recently shown that non-invasive ultrasound can generate refractive index gradients within the tissue that form virtual GRIN lenses for imaging and photostimulation deep into the tissue. Here we present the theory behind this idea by analyzing the coupled acoustic-photonic system that models the interaction of light with the ultrasonically modulated medium. We will discuss how changing the parameters of ultrasound will change the confinement and guiding of light within the modulated medium. We will also demonstrate that using a custom-designed cylindrical ultrasonic array, the pressure interference can be controlled to sculpt complex patterns of light in the medium, such as dipole and quadrupole shapes, suitable for multisite imaging. Finally, we will discuss experimental results corroborating the theoretical predictions to generate single and multisite in situ virtual lenses that can be used for fluorescent imaging of mouse brain tissue that expresses green fluorescent protein (GFP).

Evolution of Nanoparticle-Mediated Photodynamic Therapy: From Superficial to Deep-Seated Cancers

Enthusiasm for photodynamic therapy (PDT) as a potential therapeutic intervention for cancer has increased exponentially in recent decades. Photodynamic therapy constitutes a clinically approved, minimally invasive treatment modality that uses a photosensitizer (light absorbing molecule) and light to kill cancer cells. The principle of PDT is, when irradiated with a light of a suitable wavelength, a photosensitizer absorbs the light energy and generates cytotoxic free radicals through various mechanisms. The overall efficiency of PDT depends on characteristics of activation light and in-situ dosimetry, including the choice of photosensitizer molecule, wavelength of the light, and tumor location and microenvironment, for instance, the use of two-photon laser or an X-ray irradiator as the light source increases tissue-penetration depth, enabling it to achieve deep PDT. In this mini-review, we discuss the various designs and strategies for single, two-photon, and X-ray-mediated PDT for improved clinical outcomes.

Photosensitizers with Aggregation-Induced Emission: Materials and Biomedical Applications

Photodynamic therapy is arising as a noninvasive treatment modality for cancer and other diseases. One of the key factors to determine the therapeutic function is the efficiency of photosensitizers (PSs). Opposed to traditional PSs, which show quenched fluorescence and reduced singlet oxygen production in the aggregate state, PSs with aggregation-induced emission (AIE) exhibit enhanced fluorescence and strong photosensitization ability in nanoparticles. Here, the design principles of AIE PSs and their biomedical applications are discussed in detail, starting with a summary of traditional PSs, followed by a comparison between traditional and AIE PSs to highlight the various design strategies and unique features of the latter. Subsequently, the applications of AIE PSs in photodynamic cancer cell ablation, bacteria killing, and image-guided therapy are discussed using charged AIE PSs, AIE PS molecular probes, and AIE PS nanoparticles as examples. These studies have demonstrated the great potential of AIE PSs as effective theranostic agents to treat tumor or bacterial infection. This review hopefully will spur more research interest in AIE PSs for future translational research.

Protein Corona around Gold Nanorods as a Drug Carrier for Multimodal Cancer Therapy

A single nanodevice based on gold nanorods (NRs) coloaded with a photosensitizer, Chlorin e6 (Ce6), and a chemotherapeutic, Doxorubicin (Dox), on its endogenously formed human serum (HS) protein corona, i.e., NR-HS-Ce6-Dox was developed with the aim of performing multimodal cancer therapy: photodynamic (PDT), photothermal (PTT) and chemotherapy (CTX) simultaneously upon irradiation with a single 665 nm laser. Here, the excitation of NRs and Ce6 resulted in photothermal ablation (PTT), and production of reactive oxygen species (ROS) to kill Cal 27 oral squamous cell carcinoma (OSCC) cells by oxidative stress (PDT) respectively, while the laser-triggered release of Dox intercalated into the DNA of cancer cells to result in DNA damage and cell death (CTX). High laser-triggered Dox release efficiency of 71.5% and strong plasmonic enhancement of ROS production by Ce6 (4.8-fold increase compared to free Ce6) was observed. Uptake of both Ce6 and Dox by Cal 27 cells was greatly enhanced, with 3.3 and 52 times higher intracellular Dox and Ce6 fluorescence observed, respectively, 6 h after dosing with NR-HS-Ce6-Dox compared to free drugs. The simultaneous trimodal therapy achieved a near complete eradication of cancer cells (98.7% cell death) with an extremely low dose of 15 pM NR-HS-Ce6-Dox loaded with just 1.26 nM Ce6 and 12.5 nM Dox due to strong synergistic enhancement in cancer cell kill compared to individual therapies performed separately. No dark toxicities were observed. These drug concentrations were far lower than any previously reported in vitro, thus eliminating any potential systemic toxicity of these agents.

Manipulating tumor hypoxia toward enhanced photodynamic therapy (PDT)

This mini-review summarizes various methods for overcoming or utilizing hypoxia for enhanced PDT.

Exploiting the protein corona around gold nanorods for low-dose combined photothermal and photodynamic therapy

A nanodevice comprising human serum (HS) protein corona coated gold nanorods (NRs) has been developed to perform both photothermal therapy (PTT) and photodynamic therapy (PDT) simultaneously at a very low dose under irradiation by a single laser. Here, we exploit the protein corona to load a photosensitizer, chlorin e6 (Ce6), to form NR-HS-Ce6, whose excitation wavelength matches with the longitudinal surface plasmon resonance (LSPR) of NRs. When excited by a single laser, the NRs caused photothermal ablation of cancer cells while Ce6 simultaneously produced reactive oxygen species (ROS) to kill cancer cells through oxidative stress in PDT. We found that the protein corona did not affect the photothermal heating of NRs and observed more than 5-fold increase in ROS generation when Ce6 was loaded on NR-HS compared to free HS-Ce6 dissolved in HS. The uptake of Ce6 by Cal 27 oral squamous cell carcinoma (OSCC) cells also increased 57-fold when loaded on NR-HS compared to free HS-Ce6. While both PDT and PTT have established modest success in reducing cancer cell viability on their own, we have shown that the combined therapy can achieve near complete eradication (95.2% cell kill) of cancer cells even at an extremely low dose of 50 pM of NR-HS-Ce6 containing an equivalent of 7.67 μg mL^-1 Au and 4.83 nM Ce6. This near complete cell kill at such a low dose has not been reported previously. The advantages of this nanoscale delivery system showcase the application of protein corona in cancer treatment instead of considering it as an undesirable biological artefact.

Reactive oxygen species generating systems meeting challenges of photodynamic cancer therapy

The reactive oxygen species (ROS)-mediated mechanism is the major cause underlying the efficacy of photodynamic therapy (PDT). The PDT procedure is based on the cascade of synergistic effects between light, a photosensitizer (PS) and oxygen, which greatly favors the spatiotemporal control of the treatment. This procedure has also evoked several unresolved challenges at different levels including (i) the limited penetration depth of light, which restricts traditional PDT to superficial tumours; (ii) oxygen reliance does not allow PDT treatment of hypoxic tumours; (iii) light can complicate the phototherapeutic outcomes because of the concurrent heat generation; (iv) specific delivery of PSs to sub-cellular organelles for exerting effective toxicity remains an issue; and (v) side effects from undesirable white-light activation and self-catalysation of traditional PSs. Recent advances in nanotechnology and nanomedicine have provided new opportunities to develop ROS-generating systems through photodynamic or non-photodynamic procedures while tackling the challenges of the current PDT approaches. In this review, we summarize the current status and discuss the possible opportunities for ROS generation for cancer therapy. We hope this review will spur pre-clinical research and clinical practice for ROS-mediated tumour treatments.

A Bifunctional Photosensitizer for Enhanced Fractional Photodynamic Therapy: Singlet Oxygen Generation in the Presence and Absence of Light

The photosensitized generation of singlet oxygen within tumor tissues during photodynamic therapy (PDT) is self-limiting, as the already low oxygen concentrations within tumors is further diminished during the process. In certain applications, to minimize photoinduced hypoxia the light is introduced intermittently (fractional PDT) to allow time for the replenishment of cellular oxygen. This condition extends the time required for effective therapy. Herein, we demonstrated that a photosensitizer with an additional 2-pyridone module for trapping singlet oxygen would be useful in fractional PDT. Thus, in the light cycle, the endoperoxide of 2-pyridone is generated along with singlet oxygen. In the dark cycle, the endoperoxide undergoes thermal cycloreversion to produce singlet oxygen, regenerating the 2-pyridone module. As a result, the photodynamic process can continue in the dark as well as in the light cycles. Cell-culture studies validated this working principle in vitro.

Antiproliferative effect of pheophorbide a-mediated photodynamic therapy and its synergistic effect with doxorubicin on multiple drug-resistant uterine sarcoma cell MES-SA/Dx5

Prolonged cancer chemotherapy is associated with the development of multidrug resistance (MDR), which is a major cause of treatment failure. Photodynamic therapy (PDT) has been applied as anticancer therapy and a means of circumventing MDR. The antiproliferative effect of pheophorbide a-mediated photodynamic therapy (Pa-PDT) has been demonstrated in several human cancer cell lines, including the uterine sarcoma cell line, MES-SA. This study set out to evaluate, first, the therapeutic potential of Pa-PDT on MES-SA/Dx5 uterine sarcoma cells and, subsequently, the effectiveness of combination therapy using Pa-PDT with doxorubicin (Dox). Our results showed that Pa-PDT was able to circumvent MDR in the P-glycoprotein (P-gp) overexpressing human uterine sarcoma cell line, MES-SA/Dx5. Intracellular accumulation of Pa and Pa-PDT-induced cell death was not abrogated by MDR phenotype, when compared to the parental cell line, MES-SA. Combined therapy using Pa-PDT and Dox, a common chemotherapeutic drug, was found to be synergistic in the cell line, MES-SA/Dx5. Both activity and expression of MDR1 and P-gp were reduced by Pa-PDT treatment and such reductions were attenuated by α-tocopherol, the scavenger of reactive oxygen species (ROS), suggesting that the effect of Pa-PDT was mediated by the generation of intracellular ROS. In conclusion, our findings demonstrated the therapeutic potential of Pa-PDT alone or in combination with Dox in combating multidrug-resistant malignancies.

Advance in photosensitizers and light delivery for photodynamic therapy

The brief history of photodynamic therapy (PDT) research has been focused on photosensitizers (PSs) and light delivery was introduced recently. The appropriate PSs were developed from the first generation PS Photofrin (QLT) to the second (chlorins or bacteriochlorins derivatives) and third (conjugated PSs on carrier) generations PSs to overcome undesired disadvantages, and to increase selective tumor accumulation and excellent targeting. For the synthesis of new chlorin PSs chlorophyll a is isolated from natural plants or algae, and converted to methyl pheophorbide a (MPa) as an important starting material for further synthesis. MPa has various active functional groups easily modified for the preparation of different kinds of PSs, such as methyl pyropheophorbide a, purpurin-18, purpurinimide, and chlorin e6 derivatives. Combination therapy, such as chemotherapy and photothermal therapy with PDT, is shortly described here. Advanced light delivery system is shown to establish successful clinical applications of PDT. Phtodynamic efficiency of the PSs with light delivery was investigated in vitro and/or in vivo.

Novel dual-control poly(N-isopropylacrylamide-co-chlorophyllin) nanogels for improving drug release

AIM

How to overcome insufficient drug release is an important issue in the drug-delivery system.

MATERIALS & METHODS

Here, a novel temperature and UV dual-control poly(N-isopropylacrylamide [PNIPAM]-co-chlorophyllin) nanogel was prepared via the surfactant-free emulsion polymerization.

RESULTS

The introduction of hydrophilic chlorophyllin to the PNIPAM chain backbone led to a narrow size of poly[NIPAM-co-CHLN nanogel (D ∼180 nm) confirmed by atomic force microscopy and transmission electron microscopy. This nanogel had a lower critical solution temperature (∼35°C), observed by dynamic laser light scattering. After the phase transition, the size under UV light (50 nm) was much smaller than that induced by temperature (90 nm). The inhomogeneous collapse was attributed to the temperature-gradient generated from the gel surface to the core with a surrounding dense PNIPAM layer. The obstacles that strongly inhibited 5-fluorouracil release was successfully overcome by light irradiation via a large drug diffusion coefficient.

CONCLUSION

Consequently, the novel dual functional nanogel is potent for improving the drug-release profile.