Cytochrome P450 enzyme-mediated auto-enhanced photodynamic cancer therapy of co-nanoassembly between clopidogrel and photosensitizer

Enzyme-responsive design combined with photodynamic therapy for cancer treatment

Photodynamic therapy (PDT) is a noninvasive cancer treatment that has garnered significant attention in recent years. However, its application is still hampered by certain limitations, such as the hydrophobicity and low targeting of photosensitizers (PSs) and the hypoxia of the tumor microenvironment. Nevertheless, the fusion of enzyme-responsive drugs with PDT offers novel solutions to overcome these challenges. Utilizing the attributes of enzyme-responsive drugs, PDT can deliver PSs to the target site and selectively release them, thereby enhancing therapeutic outcomes. In this review, we spotlight recent advances in enzyme-responsive materials for cancer treatment and primarily delineate their application in combination with PDT.

Recent Progress in Carrier-Free Nanomedicine for Tumor Phototherapy

Safe and effective strategies are urgently needed to fight against the life-threatening diseases of various cancers. However, traditional therapeutic modalities, such as radiotherapy, chemotherapy and surgery, exhibit suboptimal efficacy for malignant tumors owing to the serious side effects, drug resistance and even relapse. Phototherapies, including photodynamic therapy (PDT) and photothermal therapy (PTT), are emerging therapeutic strategies for localized tumor inhibition, which can produce a large amount of reactive oxygen species (ROS) or elevate the temperature to initiate cell death by non-invasive irradiation. In consideration of the poor bioavailability of phototherapy agents (PTAs), lots of drug delivery systems have been developed to enhance the tumor targeted delivery. Nevertheless, the carriers of drug delivery systems inevitably bring biosafety concerns on account of their metabolism, degradation, and accumulation. Of note, carrier-free nanomedicine attracts great attention for clinical translation with synergistic antitumor effect, which is characterized by high drug loading, simplified synthetic method and good biocompatibility. In this review, the latest advances of phototherapy with various carrier-free nanomedicines are summarized, which may provide a new paradigm for the future development of nanomedicine and tumor precision therapy.

Molecularly engineering a dual-drug nanoassembly for self-sensitized photodynamic therapy via thioredoxin impairment and glutathione depletion

Photodynamic therapy (PDT) has been extensively investigated as a spatiotemporally noninvasive and controllable modality for cancer treatment. However, the intracellular antioxidant systems mainly consisting of thioredoxin (Trx) and glutathione (GSH) significantly counteract and prevent reactive oxygen species (ROS) accumulation, resulting in a serious loss of PDT efficiency. To address this challenge, we propose that PDT can be improved by precisely blocking antioxidant systems. After molecular engineering and synergistic cytotoxic optimization, a DSPE-PEG_2K-modified dual-drug nanoassembly (PPa@GA/DSPE-PEG_2K NPs) of pyropheophorbide a (PPa) and gambogic acid (GA) is successfully constructed. Interestingly, GA can effectively destroy intracellular antioxidant systems by simultaneously inhibiting Trx and GSH. Under laser irradiation, the cell-killing effects of PPa is significantly enhanced by GA-induced inhibition of the antioxidant systems. As expected, PPa@GA/DSPE-PEG_2K nanoparticles demonstrate potent antitumor activity in a 4T1 breast tumor-bearing BALB/c mouse xenograft model. Such a carrier-free self-sensitized nanotherapeutic offers a novel co-delivery strategy for effective PDT.

Carrier-free supramolecular nanoassemblies of pure LSD1 inhibitor for effective anti-tumor therapy

The LSD1 protein is an oxidase that regulates protein methylation, which regulates gene expression and triggers tumors. Previously, inhibiting LSD1 has been found to be an effective treatment strategy for opposing tumors caused by overexpression of LSD1. Our recent study found that compound 17i was a suitable LSD1 inhibitor with potential anti-tumor activity. However, its extremely insoluble nature limits further validation of its anti-tumor activity at the clinical level. In this study, a unique carrier-free supramolecular nanoassemblies of pure compound 17i is expected to enhance therapeutic efficacy. Aqueous-insoluble compound 17i was mixed with a small quantity of DSPE-PEG₂₀₀₀ into an organic solvent and was prepared as nanoassemblies in water via the one-step nanoprecipitation method. The 17i nanoassemblies have a similar effect on its cytotoxicity when compared with 17i solution in vitro. Importantly, the PEGylated 17i nanoassemblies exhibit significant superiorities over 17i solutions in therapeutic efficiency, anti-tumor immune response and systemic toxicity in BALB/c mice bearing CT-26 colorectal tumors. We envision that the fabrication of pure drug nanoassemblies offers an efficient platform for reforming the undesirable characteristics of drug-like compounds to potentiate the anti-tumor therapeutic effect.

Molecularly Self-Engineered Nanoamplifier for Boosting Photodynamic Therapy via Cascade Oxygen Elevation and Lipid ROS Accumulation

Photodynamic therapy (PDT) has been extensively explored as a noninvasive cancer treatment modality. However, the dilemma of tumor hypoxia and short half-life of singlet oxygen (¹O₂) severely restrict the therapeutic efficacy of PDT. Herein, we develop a facile three-in-one PDT nanoamplifier (AA@PPa/Hemin NPs) assembled by pyropheophorbide a (PPa), hemin, and arachidonic acid (AA). Interestingly, AA not only acts as an enabler to facilitate the assembly of PPa and hemin in the construction of ternary hybrid nanoassemblies but also acts as a lipid reactive oxygen species (ROS) amplifier for robust PDT. In tumor cells, hemin plays the role of a catalase-like catalyst that accelerates the production of oxygen (O₂) from hydrogen peroxide (H₂O₂), significantly alleviating tumor hypoxia. Under laser irradiation, vast amounts of ¹O₂ generated by PPa trigger the peroxidation of AA to produce large amounts of cytotoxic lipid ROS, immensely amplifying the efficiency of PDT by promptly eliciting cellular oxidative stress. As expected, AA@PPa/Hemin NPs exert potent antitumor activity in a 4T1 breast-tumor-bearing BALB/c mice xenograft model. Such a cascade nanohybrid amplifier provides a novel codelivery platform for accurate and effective PDT of cancer.

Cu-Hemin Nanosheets and Indocyanine Green Co-Loaded Hydrogel for Photothermal Therapy and Amplified Photodynamic Therapy

Near-infrared (NIR) organic small molecule indocyanine green (ICG) could respond well to 808 nm laser to promote local high temperature and ROS generation for realizing photothermal therapy (PTT)/photodynamic therapy (PDT). However, the high content of GSH in the tumor microenvironment (TME) limited the further therapeutic performance of ICG. Herein, injectable agarose in situ forming NIR-responsive hydrogels (CIH) incorporating Cu-Hemin and ICG were prepared for the first time. When CIH system was located to the tumor tissue through local injection, the ICG in the hydrogel could efficiently convert the light energy emitted by the 808 nm laser into thermal energy, resulting in the heating and softening of the hydrogel matrix, which releases the Cu-Hemin. Then, the over-expressed GSH in the TME could also down-regulated by Cu-Hemin, which amplified ICG-mediated PDT. In vivo experiments validated that ICG-based PDT/PTT and Cu-Hemin-mediated glutathione depletion could eliminate cancer tissues with admirable safety. This hydrogel-based GSH-depletion strategy is instructive to improve the objective response rate of PDT.

Stable high-oxidation-state complex in situ Mn(V)-Mn(III) transition to achieve highly efficient cervical cancer therapy

Designing metal complexes to target the vulnerable redox balance in cancer cells is a promising strategy to realize successful cancer therapy. The synthesized stable nitridomanganese(V) complex Mn^V(N) (salen) not only reacts with GSH to achieve in situ Mn(V)-Mn(III) transformation to down-regulate the antioxidant system, but also catalyzes H₂O₂ to higher oxidation capacity ROS to up-regulate the intracellular oxidative level, finally resulting in cancer cell death.

Elaborately Engineering a Self-Indicating Dual-Drug Nanoassembly for Site-Specific Photothermal-Potentiated Thrombus Penetration and Thrombolysis

Thrombotic cardio-cerebrovascular diseases seriously threaten human health. Currently, conventional thrombolytic treatments are challenged by the low utilization, inferior thrombus penetration, and high off-target bleeding risks of most thrombolytic drugs, resulting in unsatisfactory treatment outcomes. Herein, it is proposed that these challenges can be overcome by precisely integrating the conventional thrombolytic strategy with photothermal therapy. After co-assembly engineering optimization, a fibrin-targeting peptide-decorated nanoassembly of DiR (a photothermal probe) and ticagrelor (TGL, an antiplatelet drug) is prepared for thrombus-homing delivery, abbreviated as FT-DT NPs. The elaborately engineered nanoassembly shows multiple advantages, including simple preparation with high drug co-loading capacity, synchronous delivery of two drugs with long systemic circulation, thrombus-targeted accumulation with self-indicating function, as well as photothermal-potentiated thrombus penetration and thrombolysis with high therapeutic efficacy. As expected, FT-DT NPs not only show bright fluorescence signals in the embolized vessels, but also perform photothermal/antiplatelet synergistic thrombolysis in vivo. This study offers a simple and versatile co-delivery nanoplatform for imaging-guided photothermal/antiplatelet dual-modality thrombolysis.

Pure drug nano-assemblies: A facile carrier-free nanoplatform for efficient cancer therapy

Nanoparticulate drug delivery systems (Nano-DDSs) have emerged as possible solution to the obstacles of anticancer drug delivery. However, the clinical outcomes and translation are restricted by several drawbacks, such as low drug loading, premature drug leakage and carrier-related toxicity. Recently, pure drug nano-assemblies (PDNAs), fabricated by the self-assembly or co-assembly of pure drug molecules, have attracted considerable attention. Their facile and reproducible preparation technique helps to remove the bottleneck of nanomedicines including quality control, scale-up production and clinical translation. Acting as both carriers and cargos, the carrier-free PDNAs have an ultra-high or even 100% drug loading. In addition, combination therapies based on PDNAs could possibly address the most intractable problems in cancer treatment, such as tumor metastasis and drug resistance. In the present review, the latest development of PDNAs for cancer treatment is overviewed. First, PDNAs are classified according to the composition of drug molecules, and the assembly mechanisms are discussed. Furthermore, the co-delivery of PDNAs for combination therapies is summarized, with special focus on the improvement of therapeutic outcomes. Finally, future prospects and challenges of PDNAs for efficient cancer therapy are spotlighted.

Cytochrome P450 Enzymes and Drug Metabolism in Humans

Human cytochrome P450 (CYP) enzymes, as membrane-bound hemoproteins, play important roles in the detoxification of drugs, cellular metabolism, and homeostasis. In humans, almost 80% of oxidative metabolism and approximately 50% of the overall elimination of common clinical drugs can be attributed to one or more of the various CYPs, from the CYP families 1–3. In addition to the basic metabolic effects for elimination, CYPs are also capable of affecting drug responses by influencing drug action, safety, bioavailability, and drug resistance through metabolism, in both metabolic organs and local sites of action. Structures of CYPs have recently provided new insights into both understanding the mechanisms of drug metabolism and exploiting CYPs as drug targets. Genetic polymorphisms and epigenetic changes in CYP genes and environmental factors may be responsible for interethnic and interindividual variations in the therapeutic efficacy of drugs. In this review, we summarize and highlight the structural knowledge about CYPs and the major CYPs in drug metabolism. Additionally, genetic and epigenetic factors, as well as several intrinsic and extrinsic factors that contribute to interindividual variation in drug response are also reviewed, to reveal the multifarious and important roles of CYP-mediated metabolism and elimination in drug therapy.

Disulfur-bridged polyethyleneglycol/DOX nanoparticles for the encapsulation of photosensitive drugs: a case of computational simulations on the redox-responsive chemo-photodynamic drug delivery system

Tumor redox stimulus-responsive nanoparticulate drug delivery systems (nano-DDSs) have attracted considerable attention due to their thermodynamically stable microstructures and well-controlled drug release properties. However, drug-loading nanoparticle conformation and redox-triggered drug release mechanisms at the molecular level remain unclear. Herein, doxorubicin-conjugated polymers were constructed using disulfide bonds as linkages (PEG–SS–DOX), which loaded photosensitizer chlorin e6 (Ce6). We integrated multiple scale dynamic simulations (density functional theory (DFT) calculation, atomistic molecular dynamics (MD) simulation and dissipative particle dynamics (DPD) simulations) to elucidate the assembly/drug release dynamic processing. First, it was revealed that the emergence of the calculated bond flexible angle of disulfide bonds facilitated the assembly behavior and improved the stability of conformation. Sorted by the binding model, hydrogen bonding accounted for the major interactions between polymers and photosensitive drugs. DPD simulations were further delved into to acquire knowledge regarding the drug-free self-aggregation and Ce6-loaded assembly mechanism. The results show that nano-assembly conformation not only depended on the concentration of polymers, but also were associated with the polymer–drug ratio. Different from dicarbon bond-bridging polymers, disulfide bonds would contribute to the breakage of the polymer and the rapid release of DOX and Ce6. Our findings provide deep insights into the influence of redox-responsive chemical linkages and offer theoretical guidance to the rational design of specific stimulus-responsive nano-DDSs for cancer therapy.

Schematic of disulfide/dicarbide-bridged DOX polymer-encapsulated photosensitive drugs Ce6: a case of computational simulations on the redox-responsive chemo-photodynamic drug delivery system.

Enzyme-Responsive Materials as Carriers for Improving Photodynamic Therapy

Photodynamic therapy (PDT) is a mini-invasive therapy on malignancies via reactive oxygen species (ROS) induced by photosenitizer (PS) upon light irradiation. However, poor target of PS to tumor limits the clinical application of PDT. Compared with normal tissues, tumor tissues have a unique enzymatic environment. The unique enzymatic environment in tumor tissues has been widely used as a target for developing smart materials to improve the targetability of drugs to tumor. Enzyme-responsive materials (ERM) as a smart material can respond to the enzymes in tumor tissues to specifically deliver drugs. In PDT, ERM was designed to react with the enzymes highly expressed in tumor tissues to deliver PS in the target site to prevent therapeutic effects and avoid its side-effects. In the present paper, we will review the application of ERM in PDT and discuss the challenges of ERM as carriers to deliver PS for further boosting the development of PDT in the management of malignancies.

Glutathione-Depleting Nanomedicines for Synergistic Cancer Therapy

Cancer cells frequently exhibit resistance to various molecular and nanoscale drugs, which inevitably affects the drugs' therapeutic outcomes. Overexpression of glutathione (GSH) has been observed in many cancer cells, and solid evidence has corroborated the resulting tumor resistance to a variety of anticancer therapies, suggesting that this biochemical characteristic of cancer cells can be developed as a potential target for cancer treatments. The single treatment of GSH-depleting agents can potentiate the responses of the cancer cells to different cell death stimuli; therefore, as an adjunctive strategy, GSH depletion is usually combined with mainstream cancer therapies for enhancing the therapeutic outcomes. Propelled by the rapid development of nanotechnology, GSH-depleting agents can be readily constructed into anticancer nanomedicines, which have shown a steep rise over the past decade. Here, we review the common GSH-depleting nanomedicines which have been widely applied in synergistic cancer treatments in recent years. Some current challenges and future perspectives for GSH depletion-based cancer therapies are also presented. With the understanding of the structure-property relationship and action mechanisms of these biomaterials, we hope that the GSH-depleting nanotechnology will be further developed to realize more effective disease treatments and even achieve successful clinical translations.

Photosensitizer-driven nanoassemblies of homodimeric prodrug for self-enhancing activation and synergistic chemo-photodynamic therapy

Carrier-free prodrug-nanoassemblies have emerged as promising nanomedicines. In particular, the self-assembled nanoparticles (NPs) composed of homodimeric prodrugs with ultrahigh drug loading have attracted broad attention. However, most homodimeric prodrugs show poor self-assembly ability due to their symmetric structures. Herein, we developed photosensitizer-driven nanoassemblies of homodimeric prodrug for self-enhancing activation and chemo-photodynamic synergistic therapy.

Methods: In this work, a pyropheophorbide a (PPa)-driven nanoassemblies of an oxidation-responsive cabazitaxel homodimer (CTX-S-CTX) was fabricated (pCTX-S-CTX/PPa NPs). The assembly mechanisms, aggregation-caused quenching (ACQ) effect alleviation, singlet oxygen generation, self-enhancing prodrug activation, cellular uptake, intracellular reactive oxygen species (ROS) generation and synergistic cytotoxicity of pCTX-S-CTX/PPa NPs were investigated in vitro. Moreover, the pharmacokinetics, ex vivo biodistribution and in vivo therapeutic efficacy of pCTX-S-CTX/PPa NPs were studied in mice bearing 4T1 tumor.

Results: Interestingly, PPa was found to drive the assembly of CTX-S-CTX, which cannot self-assemble into stable NPs alone. Multiple intermolecular forces were found to be involved in the assembly process. Notably, the nanostructure was destroyed in the presence of endogenous ROS, significantly relieving the ACQ effect of PPa. In turn, ROS generated by PPa under laser irradiation together with the endogenous ROS synergistically promoted prodrug activation. As expected, the nanoassemblies demonstrated potent antitumor activity in a 4T1 breast cancer BALB/c mice xenograft model.

Conclusion: Our findings offer a simple strategy to facilitate the assembly of homodimeric prodrugs and provide an efficient nanoplatform for chemo-photodynamic therapy.

Tumor cell-activated "Sustainable ROS Generator" with homogeneous intratumoral distribution property for improved anti-tumor therapy

Photodynamic therapy (PDT) holds a number of advantages for tumor therapy. However, its therapeutic efficiency is limited by non-sustainable reactive oxygen species (ROS) generation and heterogeneous distribution of photosensitizer (PS) in tumor. Herein, a "Sustainable ROS Generator" (SRG) is developed for efficient antitumor therapy. Methods: SRG was prepared by encapsulating small-sized Mn₃O₄-Ce6 nanoparticles (MC) into dendritic mesoporous silica nanoparticles (DMSNs) and then enveloped with hyaluronic acid (HA). Due to the high concentration of HAase in tumor tissue, the small-sized MC could be released from DMSNs and homogeneously distributed in whole tumor. Then, the released MC would be uptaken by tumor cells and degraded by high levels of intracellular glutathione (GSH), disrupting intracellular redox homeostasis. More importantly, the released Ce6 could efficiently generate singlet oxygen (¹O₂) under laser irradiation until the tissue oxygen was exhausted, and the manganese ion (Mn²⁺) generated by degraded MC would then convert the low toxic by-product (H₂O₂) of PDT to the most harmful ROS (·OH) for sustainable and recyclable ROS generation. Results: MC could be homogeneously distributed in whole tumor and significantly reduced the level of intracellular GSH. At 2 h after PDT, obvious intracellular ROS production was still observed. Moreover, during oxygen recovery in tumor tissue, ·OH could be continuously produced, and the nanosystem could induce 82% of cell death comparing with 30% of cell death induced by free Ce6. For in vivo PDT, SRG achieved a complete inhibition on tumor growth. Conclusion: Based on these findings, we conclude that the designed SRG could induce sustainable ROS generation, homogeneous intratumoral distribution and intracellular redox homeostasis disruption, presenting an efficient strategy for enhanced ROS-mediated anti-tumor therapy.

Targeted Manganese doped silica nano GSH-cleaner for treatment of Liver Cancer by destroying the intracellular redox homeostasis

Background: Glutathione (GSH), the primary antioxidant in cells, could fight against oxidative stress. Tumor cells display a higher GSH level than normal cells for coping with the hyperoxidative state, which meets the requirements of enhanced metabolism and vicious proliferation. Therefore, the consumption of GSH will lead to cell redox imbalance and impede life activities. Herein, targeted sorafenib (SFB) loaded manganese doped silica nanoparticle (FaPEG-MnMSN@SFB) was constructed, which could destroy the intracellular redox homeostasis by consuming GSH. Methods: In this study, MnMSN was prepared by an optimized one-pot Stober's method for loading SFB, and FaPEG chain was modified on the surface of MnMSN to achieve long circulation and targeted delivery. The anticancer efficacy and mechanism of the designed FaPEG-MnMSN@SFB were assessed both in vitro and in vivo.Results: FaPEG-MnMSN@SFB exhibited efficient antitumor activity by dual depleting intracellular GSH (the degradation of MnMSN would consume intracellular GSH and the SFB would inhibit the effect of Xc- transport system to inhibit GSH synthesis). Moreover, disruption of redox balance would lead to apoptosis and reactive oxygen species (ROS)-dependent ferroptosis of tumor cells. Conclusion: Such a GSH-starvation therapeutic strategy would cause multi-path programmed cell death and could be a promising strategy for cancer therapy.

Versatile Nanoplatforms with enhanced Photodynamic Therapy: Designs and Applications

As an emerging antitumor strategy, photodynamic therapy (PDT) has attracted intensive attention for the treatment of various malignant tumors owing to its noninvasive nature and high spatial selectivity in recent years. However, the therapeutic effect is unsatisfactory on some occasions due to the presence of some unfavorable factors including nonspecific accumulation of PS towards malignant tissues, the lack of endogenous oxygen in tumors, as well as the limited light penetration depth, further hampering practical application. To circumvent these limitations and improve real utilization efficiency, various enhanced strategies have been developed and explored during the past years. In this review, we give an overview of the state-of-the-art advances progress on versatile nanoplatforms for enhanced PDT considering the enhancement from targeting or responsive, chemical and physical effect. Specifically, these effects mainly include organelle-targeting function, tumor microenvironment responsive release photosensitizers (PS), self-sufficient O2 (affinity oxygen and generating oxygen), photocatalytic water splitting, X-rays light stimulate, surface plasmon resonance enhancement, and the improvement by resonance energy transfer. When utilizing these strategies to improve the therapeutic effect, the advantages and limitations are addressed. Finally, the challenges and prospective will be discussed and demonstrated for the future development of advanced PDT with enhanced efficacy.