The role of hypoxia-activated prodrugs in cancer therapy

A light-activatable theranostic combination for ratiometric hypoxia imaging and oxygen-deprived drug activity enhancement

While performing oxygen-related tumour treatments such as chemotherapy and photodynamic therapy, real-time monitoring hypoxia of tumour is of great value and significance. Here, we design a theranostic combination for light-activated ratiometric hypoxia imaging, hypoxia modulating and prodrug activation. This combination consisted of an oxygen-sensitive near-infrared-emitting ratiometric phosphorescence probe and a hypoxia-activated prodrug-loaded covalent organic framework. In this combination, the probe plays two roles, including quantitative monitoring of oxygen concentration by ratiometric imaging and consuming the oxygen of tumour under light excitation by photodynamic therapy. Meanwhile, the enhanced hypoxia microenvironment of tumour can raise the cytotoxicity of prodrug loaded in covalent organic framework, resulting in boosting antitumour therapeutic effects in vivo. This theranostic combination can precisely provide therapeutic regime and screen hypoxia-activated prodrugs based on real-time tumour hypoxia level, offering a strategy to develop hypoxia mediated tumour theranostics with hypoxia targeted prodrugs.

Nature-Inspired Thylakoid-Based Photosynthetic Nanoarchitectures for Biomedical Applications

"Drawing inspiration from nature" offers a wealth of creative possibilities for designing cutting-edge materials with improved properties and performance. Nature-inspired thylakoid-based nanoarchitectures, seamlessly integrate the inherent structures and functions of natural components with the diverse and controllable characteristics of nanotechnology. These innovative biomaterials have garnered significant attention for their potential in various biomedical applications. Thylakoids possess fundamental traits such as light harvesting, oxygen evolution, and photosynthesis. Through the integration of artificially fabricated nanostructures with distinct physical and chemical properties, novel photosynthetic nanoarchitectures can be catalytically generated, offering versatile functionalities for diverse biomedical applications. In this article, an overview of the properties and extraction methods of thylakoids are provided. Additionally, the recent advancements in the design, preparation, functions, and biomedical applications of a range of thylakoid-based photosynthetic nanoarchitectures are reviewed. Finally, the foreseeable challenges and future prospects in this field is discussed.

Nanotechnological strategies to increase the oxygen content of the tumor

Hypoxia is a negative prognostic indicator of solid tumors, which not only changes the survival state of tumors and increases their invasiveness but also remarkably reduces the sensitivity of tumors to treatments such as radiotherapy, chemotherapy and photodynamic therapy. Thus, developing therapeutic strategies to alleviate tumor hypoxia has recently been considered an extremely valuable target in oncology. In this review, nanotechnological strategies to elevate oxygen levels in tumor therapy in recent years are summarized, including (I) improving the hypoxic tumor microenvironment, (II) oxygen delivery to hypoxic tumors, and (III) oxygen generation in hypoxic tumors. Finally, the challenges and prospects of these nanotechnological strategies for alleviating tumor hypoxia are presented.

Carbohydrate ligands-directed active tumor targeting of combinatorial chemotherapy/phototherapy-based nanomedicine: A review

Phototherapies or light mediated therapies, including mutually photothermal and photodynamic therapy that encompass irradiation of the target organs with light, have been widely employed as minimally invasive approach associated with negligible drug resistance for eradicating multiple tumors with minimal hazards to normal organs. Despite all these advantages, many obstacles in phototherapy hinder progress toward clinical application. Therefore, researchers have developed nano-particulate delivery systems integrated with phototherapy and therapeutic cytotoxic drugs to overcome these obstacles and achieve maximum efficacy in cancer treatment. Active targeting ligands were integrated into their surfaces to improve the selectivity and tumor targeting ability, enabling easy binding and recognition by cellular receptors overexpressed on the tumor tissue compared to normal ones. This enhances intratumoral accumulation with minimal toxicity on the adjacent normal cells. Various active targeting ligands, including antibodies, aptamers, peptides, lactoferrin, folic acid and carbohydrates, have been explored for the targeted delivery of chemotherapy/phototherapy-based nanomedicine. Among these ligands, carbohydrates have been applied due to their unique features that ameliorate the bioadhesive, noncovalent conjugation to biological tissues. In this review, the up-to-date techniques of employing carbohydrates active targeting ligands will be highlighted concerning the surface modification of the nanoparticles for ameliorating the targeting ability of the chemo/phototherapy.

Engineering lactate-modulating nanomedicines for cancer therapy

Lactate in tumors has long been considered "metabolic junk" derived from the glycolysis of cancer cells and utilized only as a biomarker of malignancy, but is presently believed to be a pivotal regulator of tumor development, maintenance and metastasis. Indeed, tumor lactate can be a "fuel" for energy supply and functions as a signaling molecule, which actively contributes to tumor progression, angiogenesis, immunosuppression, therapeutic resistance, etc., thus providing promising opportunities for cancer treatment. However, the current approaches for regulating lactate homeostasis with available agents are still challenging, which is mainly due to the short half-life, low bioavailability and poor specificity of these agents and their unsatisfactory therapeutic outcomes. In recent years, lactate modulation nanomedicines have emerged as a charming and efficient strategy for fighting cancer, which play important roles in optimizing the delivery of lactate-modulating agents for more precise and effective modulation and treatment. Integrating specific lactate-modulating functions in diverse therapeutic nanomedicines may overcome the intrinsic restrictions of different therapeutic modalities by remodeling the pathological microenvironment for achieving enhanced cancer therapy. In this review, the most recent advances in the engineering of functional nanomedicines that can modulate tumor lactate for cancer therapy are summarized and discussed, and the fundamental mechanisms by which lactate modulation benefits various therapeutics are elucidated. Finally, the challenges and perspectives of this emerging strategy in the anti-tumor field are highlighted.

Hypoxia-Triggered Bioreduction of Poly(N-oxide)-Drug Conjugates Enhances Tumor Penetration and Antitumor Efficacy

PEGylation prolongs the blood circulation time of drugs; however, it simultaneously reduces the tumor penetration of drugs due to the nonfouling function and bulky hydrodynamic volume of PEG, leading to unsatisfactory outcomes in the treatment of solid tumors. Herein, we report the in situ growth of a bioreducible polymer of poly(N-oxide) from an important protein drug of interferon alpha (IFN) to generate site-specific IFN-poly(N-oxide) conjugates with higher bioactivity than a clinically used PEGylated IFN of PEGASYS. An IFN-poly(N-oxide) conjugate is screened out to have a circulating half-life as long as 51 h, which is similar to that of PEGASYS but 96-fold greater than that of IFN. However, the conjugate greatly outperforms PEGASYS and IFN in tumor penetration and antitumor efficacy in mice bearing melanoma. This enhanced tumor penetration is ascribed to the adsorption-mediated transcytosis of the conjugate whose poly(N-oxide) is biologically reduced into poly(tertiary amine), under hypoxia, which can be further protonated in the acidic tumor microenvironment. These novel findings demonstrate that poly(N-oxide)s are not only long-circulating but also bioreducible under hypoxia and are of great promise as next-generation carriers to deliver drugs into the interior of solid tumors to enhance their antitumor efficacy.

Recent Developments in the Study of the Microenvironment of Cancer and Drug Delivery

Cancer is characterized by disrupted molecular variables caused by cells that deviate from regular signal transduction. The uncontrolled segment of such cancerous cells annihilates most of the tissues that contact them. Gene therapy, immunotherapy, and nanotechnology advancements have resulted in novel strategies for anticancer drug delivery. Furthermore, diverse dispersion of nanoparticles in normal stroma cells adversely affects the healthy cells and disrupts the crosstalk of tumour stroma. It can contribute to cancer cell progression inhibition and, conversely, to acquired resistance, enabling cancer cell metastasis and proliferation. The tumour's microenvironment is critical in controlling the dispersion and physiological activities of nano-chemotherapeutics which is one of the targeted drug therapy. As it is one of the methods of treating cancer that involves the use of medications or other substances to specifically target and kill off certain subsets of malignant cells. A targeted therapy may be administered alone or in addition to more conventional methods of care like surgery, chemotherapy, or radiation treatment. The tumour microenvironment, stromatogenesis, barriers and advancement in the drug delivery system across tumour tissue are summarised in this review.

Tumor hypoxia: From basic knowledge to therapeutic implications

Diminished oxygen availability, termed hypoxia, within solid tumors is one of the most common characteristics of cancer. Hypoxia shapes the landscape of the tumor microenvironment (TME) into a pro-tumorigenic and pro-metastatic niche through arrays of pathological alterations such as abnormal vasculature, altered metabolism, immune-suppressive phenotype, etc. In addition, emerging evidence suggests that limited efficacy or the development of resistance towards antitumor therapy may be largely due to the hypoxic TME. This review will focus on summarizing the knowledge about the molecular machinery that mediates the hypoxic cellular responses and adaptations, as well as highlighting the effects and consequences of hypoxia, especially for angiogenesis regulation, cellular metabolism alteration, and immunosuppressive response within the TME. We also outline the current advances in novel therapeutic implications through targeting hypoxia in TME. A deep understanding of the basics and the role of hypoxia in the tumor will help develop better therapeutic avenues in cancer treatment.

A neutrophil-biomimic platform for eradicating metastatic breast cancer stem-like cells by redox microenvironment modulation and hypoxia-triggered differentiation therapy

Metastasis accounts for 90% of breast cancer deaths, where the lethality could be attributed to the poor drug accumulation at the metastatic loci. The tolerance to chemotherapy induced by breast cancer stem cells (BCSCs) and their particular redox microenvironment further aggravate the therapeutic dilemma. To be specific, therapy-resistant BCSCs can differentiate into heterogeneous tumor cells constantly, and simultaneously dynamic maintenance of redox homeostasis promote tumor cells to retro-differentiate into stem-like state in response to cytotoxic chemotherapy. Herein, we develop a specifically-designed biomimic platform employing neutrophil membrane as shell to inherit a neutrophil-like tumor-targeting capability, and anchored chemotherapeutic and BCSCs-differentiating reagents with nitroimidazole (NI) to yield two hypoxia-responsive prodrugs, which could be encapsulated into a polymeric nitroimidazole core. The platform can actively target the lung metastasis sites of triple negative breast cancer (TNBC), and release the escorted drugs upon being triggered by the hypoxia microenvironment. During the responsiveness, the differentiating agent could promote transferring BCSCs into non-BCSCs, and simultaneously the nitroimidazole moieties conjugated on the polymer and prodrugs could modulate the tumor microenvironment by depleting nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) and amplifying intracellular oxidative stress to prevent tumor cells retro-differentiation into BCSCs. In combination, the BCSCs differentiation and tumor microenvironment modulation synergistically could enhance the chemotherapeutic cytotoxicity, and remarkably suppress tumor growth and lung metastasis. Hopefully, this work can provide a new insight in to comprehensively treat TNBC and lung metastasis using a versatile platform.

Strategies and progresses for enhancing targeted antibiotic delivery

Antibiotic resistance is a global health issue and a potential risk for society. Antibiotics administered through conventional formulations are devoid of targeting effect and often spread to various undesired body sites, leading to sub-lethal concentrations at the site of action and thus resulting in emergence of resistance, as well as side effects. Moreover, we have a very slim antibiotic pipeline. Drug-delivery systems have been designed to control the rate, time, and site of drug release, and innovative approaches for antibiotic delivery provide a glint of hope for addressing these issues. This review elaborates different delivery strategies and approaches employed to overcome the limitations of conventional antibiotic therapy. These include antibiotic conjugates, prodrugs, and nanocarriers for local and targeted antibiotic release. In addition, a wide range of stimuli-responsive nanocarriers and biological carriers for targeted antibiotic delivery are discussed. The potential advantages and limitations of targeted antibiotic delivery strategies are described along with possible solutions to avoid these limitations. A number of antibiotics successfully delivered through these approaches with attained outcomes and potentials are reviewed.

Assessing the therapeutic response of tumors to hypoxia-targeted prodrugs with an in silico approach

Tumor hypoxia is commonly recognized as a condition stimulating the progress of the aggressive phenotype of tumor cells. Hypoxic tumor cells inhibit the delivery of cytotoxic drugs, causing hypoxic areas to receive insufficient amounts of anticancer agents, which results in adverse treatment responses. Being such an obstruction to conventional therapies for cancer, hypoxia might be considered a target to facilitate the efficacy of treatments in the resistive environment of tumor sites. In this regard, benefiting from prodrugs that selectively target hypoxic regions remains an effective approach. Additionally, combining hypoxia-activated prodrugs (HAPs) with conventional chemotherapeutic drugs has been used as a promising strategy to eradicate hypoxic cells. However, determining the appropriate sequencing and scheduling of the combination therapy is also of great importance in obtaining favorable results in anticancer therapy. Here, benefiting from a modeling approach, we study the efficacy of HAPs in combination with chemotherapeutic drugs on tumor growth and the treatment response. Different treatment schedules have been investigated to see the importance of determining the optimal schedule in combination therapy. The effectiveness of HAPs in varying hypoxic conditions has also been explored in the study. The model provides qualitative conclusions about the treatment response, as the maximal benefit is obtained from combination therapy with greater cell death for highly hypoxic tumors. It has also been observed that the antitumor effects of HAPs show a hypoxia-dependent profile.

In vitro radiosensitization of breast cancer with hypoxia-activated prodrugs

KP167 is a novel hypoxia‐activated prodrug (HAP), targeting cancer cells via DNA intercalating and alkylating properties. The single agent and radiosensitizing efficacy of KP167 and its parental comparator, AQ4N, were evaluated in 2D and 3D cultures of luminal and triple negative breast cancer (TNBC) cell lines and compared against DNA damage repair inhibitors. 2D normoxic treatment with the DNA repair inhibitors, Olaparib or KU‐55933 caused, as expected, substantial radiosensitization (sensitiser enhancement ratio, SER_0.01 of 1.60–3.42). KP167 induced greater radiosensitization in TNBC (SER_0.01 2.53 in MDAMB‐231, 2.28 in MDAMB‐468, 4.55 in MDAMB‐436) and luminal spheroids (SER_0.01 1.46 in MCF‐7 and 1.76 in T47D cells) compared with AQ4N. Significant radiosensitization was also obtained using KP167 and AQ4N in 2D normoxia. Although hypoxia induced radioresistance, radiosensitization by KP167 was still greater under 2D hypoxia, yielding SER_0.01 of 1.56–2.37 compared with AQ4N SER_0.01 of 1.13–1.94. Such data show KP167 as a promising single agent and potent radiosensitiser of both normoxic and hypoxic breast cancer cells, with greater efficacy in TNBCs.

The Role of Imaging Biomarkers to Guide Pharmacological Interventions Targeting Tumor Hypoxia

Hypoxia is a common feature of solid tumors that contributes to angiogenesis, invasiveness, metastasis, altered metabolism and genomic instability. As hypoxia is a major actor in tumor progression and resistance to radiotherapy, chemotherapy and immunotherapy, multiple approaches have emerged to target tumor hypoxia. It includes among others pharmacological interventions designed to alleviate tumor hypoxia at the time of radiation therapy, prodrugs that are selectively activated in hypoxic cells or inhibitors of molecular targets involved in hypoxic cell survival (i.e., hypoxia inducible factors HIFs, PI3K/AKT/mTOR pathway, unfolded protein response). While numerous strategies were successful in pre-clinical models, their translation in the clinical practice has been disappointing so far. This therapeutic failure often results from the absence of appropriate stratification of patients that could benefit from targeted interventions. Companion diagnostics may help at different levels of the research and development, and in matching a patient to a specific intervention targeting hypoxia. In this review, we discuss the relative merits of the existing hypoxia biomarkers, their current status and the challenges for their future validation as companion diagnostics adapted to the nature of the intervention.

Hybrid theranostic microbubbles for ultrasound/photoacoustic imaging guided starvation/low-temperature photothermal/hypoxia-activated synergistic cancer therapy

Constructing a theranostic agent for high-contrast multimodality imaging-guided synergistic therapy with long-term tumor retention and minimum systemic side effects still remains a major challenge. Herein, a hybrid microbubble-based theranostic platform was developed for dual-modality ultrasound (US) and enhanced photoacoustic (PA) imaging-guided synergistic tumor therapy by combining starvation therapy, low-temperature photothermal therapy (PTT), and hypoxia-activated therapy, based on polydopamine (PDA) doped poly(vinyl alcohol) microbubbles loaded with glucose oxidase (GOx) (PDA-PVAMBs@GOx) and hypoxia-activated prodrug (HAP) tirapazamine (TPZ). For dual-modality US/enhanced PA imaging, PDA-PVAMBs provided 6.5-fold amplified PA signals relative to freely dispersed PDA nanoparticles (PDA NPs). For synergistic cancer therapy, oxygen (O₂) carried by PDA-PVAMBs@GOx was first released to promote starvation therapy by loaded GOx. Then, moderate near-infrared (NIR) laser irradiation triggered PTT and improved enzymatic activity of GOx with its optimal activity around 47 °C. Subsequently, GOx-mediated tumor starvation depleted O₂ and exacerbated the hypoxia environment, thereby activating the toxicity of TPZ in the tumor site. Through dual-modality US/PA imaging monitoring, PDA-PVAMBs@GOx with long-term retention (∼7 days) combined with PTT and TPZ significantly inhibited the growth of solid tumors with minimum systemic side effects, which might be a powerful tool for effective tumor treatment.

Effects of hypoxia and nanocarrier size on pH-responsive nano-delivery system to solid tumors

One of the special features of solid tumors is the acidity of the tumor microenvironment, which is mainly due to the presence of hypoxic regions. Therefore, pH-responsive drug delivery systems have recently been highly welcomed. In the present study, a comprehensive mathematical model is presented based on extravascular drug release paradigm. Accordingly, drug delivery system using pH-responsive nanocarriers is taken into account to examine the impacts of hypoxic regions as well as the size of nanocarriers for cancerous cell-death. The extent of hypoxic regions is controlled by vascular density. This means that regions with very low vascular density represent regions of hypoxia. Using this mathematical model, it is possible to simulate the extracellular and intracellular concentrations of drug by considering the association/disassociation of the free drug to the cell-surface receptors and cellular uptake. Results show that nanocarriers with smaller sizes are more effective due to higher accumulation in the tumor tissue interstitium. The small size of the nanocarriers also allows them to penetrate deeper, so they can expose a larger portion of the tumor to the drug. Additionally, the presence of hypoxic regions in tumor reduces the fraction of killed cancer cells due to reduced penetration depth. The proposed model can be considered for optimizing and developing pH-sensitive delivery systems to reduce both cost and time of the process.

From oxygen sensing to angiogenesis: Targeting the hypoxia signaling pathway in metastatic kidney cancer

PURPOSE

This article summarizes examples of current and emerging therapies that target the hypoxia and angiogenesis signaling pathways in the clear cell type of renal cell cancer (RCC), with an emphasis on the hypoxia signaling pathway.

SUMMARY

Mammalian cells transduce signals of decreased oxygen to hypoxia inducible factor (HIF), an intracellular heterodimer that mediates the adaptation of normal and tumor cells to oxygen deprivation. HIF is frequently overexpressed in cancer cells and is involved in the transcriptional activation of many genes essential for cell invasion, migration, survival, and angiogenesis (including vascular endothelial growth factor [VEGF]). Moreover, HIF confers resistance to cytotoxic chemotherapy and radiation therapy and is associated with poor prognosis in patients with cancer. Blocking the activity of HIF inhibits the expression of VEGF and oncogenic pathways, resulting in the inhibition of tumor growth. Interestingly, activation of oncogenes and/or inactivation of tumor suppressor genes (eg, the gene encoding von Hippel-Lindau [VHL] tumor suppressor protein) can activate tumorigenesis even with normal levels of oxygen, providing support for the notion that the HIF-VHL-VEGF axis is amenable to targeted therapies for the treatment of RCC. This article highlights the current understanding of the hypoxia signaling pathway and its relevance to RCC development. Pharmacologic agents targeting the hypoxia and angiogenesis signaling pathways are discussed.

CONCLUSION

Development of novel therapeutic agents that target the hypoxia and angiogenesis signaling pathways holds promise in the management of metastatic clear cell RCC.

Pieces of the Complex Puzzle of Cancer Cell Energy Metabolism: An Overview of Energy Metabolism and Alternatives for Targeted Cancer Therapy

Over the past decades, several advances in cancer cell biology have led to relevant details about a phenomenon called the 'Warburg effect'. Currently, it has been accepted that the Warburg effect is not compatible with all cancer cells, and thus the process of aerobic glycolysis is now challenged by the knowledge of a large number of cells presenting mitochondrial function. The energy metabolism of cancer cells is focused on the bioenergetic and biosynthetic pathways in order to meet the requirements of rapid proliferation. Changes in the metabolism of carbohydrates, amino acids and lipids have already been reported for cancer cells and this might play an important role in cancer progression. To the best of our knowledge, these changes are mainly attributed to genetic reprogramming which leads to the transformation of a healthy into a cancerous cell. Indeed, several enzymes that are highly relevant for cellular energy are targets of oncogenes (e.g. PI3K, HIF1, and Myc) and tumor suppressor proteins (e.g. p53). As a consequence of extensive studies on cancer cell metabolism, some new therapeutic strategies have appeared that aim to interrupt the aberrant metabolism, in addition to influencing genetic reprogramming in cancer cells. In this review, we present an overview of cancer cell metabolism (carbohydrate, amino acid, and lipid), and also describe oncogenes and tumor suppressors that directly affect the metabolism. We also discuss some of the potential therapeutic candidates which have been designed to target and disrupt the main driving forces associated with cancer cell metabolism and proliferation.

Anesthesia Medications and Interaction with Chemotherapeutic Agents

Cancer is now a leading health concern worldwide. In an effort to provide these patients with adequate care, coordination between anesthesiologists and surgeons is crucial. In cancer-related treatment, it is very clear that radio-chemotherapy and medical procedures are important. There are some obstacles to anesthesia when dealing with cancer treatment, such as physiological disturbances, tumor-related symptoms, and toxicity in traditional chemotherapy treatment. Therefore, it is important that a multisystemic, multidisciplinary and patient-centered approach is used to preserve perioperative homeostasis and immune function integrity. Adding adjuvants can help increase patient safety and satisfaction and improve clinical efficacy. Correctly paired anesthetic procedures and medications will reduce perioperative inflammatory and immune changes that could potentially contribute to improved results for future cancer patients. Further research into best practice strategies is required which will help to enhance the acute and long-term effects of cancer care in clinical practice.

Design, Synthesis and In-Vitro Biological Evaluation of Antofine and Tylophorine Prodrugs as Hypoxia-Targeted Anticancer Agents

Phenanthroindolizidines, such as antofine and tylophorine, are a family of natural alkaloids isolated from different species of Asclepiadaceas. They are characterized by interesting biological activities, such as pronounced cytotoxicity against different human cancerous cell lines, including multidrug-resistant examples. Nonetheless, these derivatives are associated with severe neurotoxicity and loss of in vivo activity due to the highly lipophilic nature of the alkaloids. Here, we describe the development of highly polar prodrugs of antofine and tylophorine as hypoxia-targeted prodrugs. The developed quaternary ammonium salts of phenanthroindolizidines showed high chemical and metabolic stability and are predicted to have no penetration through the blood-brain barrier. The designed prodrugs displayed decreased cytotoxicity when tested under normoxic conditions. However, their cytotoxic activity considerably increased when tested under hypoxic conditions.

Protein-Based Nanomedicine for Therapeutic Benefits of Cancer

Proteins, a type of natural biopolymer that possess many prominent merits, have been widely utilized to engineer nanomedicine for fighting against cancer. Motivated by their ever-increasing attention in the scientific community, this review aims to provide a comprehensive showcase on the current landscape of protein-based nanomedicine for cancer therapy. On the basis of role differences of proteins in nanomedicine, protein-based nanomedicine engineered with protein therapeutics, protein carriers, enzymes, and composite proteins is introduced. The cancer therapeutic benefits of the protein-based nanomedicine are also discussed, including small-molecular therapeutics-mediated therapy, macromolecular therapeutics-mediated therapy, radiation-mediated therapy, reactive oxygen species-mediated therapy, and thermal effect-mediated therapy. Lastly, future developments and potential challenges of protein-based nanomedicine are elucidated toward clinical translation. It is believed that protein-based nanomedicine will play a vital role in the battle against cancer. We hope that this review will inspire extensive research interests from diverse disciplines to further push the developments of protein-based nanomedicine in the biomedical frontier, contributing to ever-greater medical advances.

Application of Advanced Mass Spectrometry-Based Proteomics to Study Hypoxia Driven Cancer Progression

Cancer is one of the largest contributors to the burden of chronic disease in the world and is the second leading cause of death globally. It is associated with episodes of low-oxygen stress (hypoxia or ischemia/reperfusion) that promotes cancer progression and therapeutic resistance. Efforts have been made in the past using traditional proteomic approaches to decipher oxygen deprivation stress-related mechanisms of the disease initiation and progression and to identify key proteins as a therapeutic target for the treatment and prevention. Despite the potential benefits of proteomic in translational research for the discovery of new drugs, the therapeutic outcome with this approach has not met expectations in clinical trials. This is mainly due to the disease complexity which possess a multifaceted molecular pathology. Therefore, novel strategies to identify and characterize clinically important sets of modulators and molecular events for multi-target drug discovery are needed. Here, we review important past and current studies on proteomics in cancer with an emphasis on recent pioneered labeling approaches in mass spectrometry (MS)-based systematic quantitative analysis to improve clinical success. We also discuss the results of the selected innovative publications that integrate advanced proteomic technologies (e.g. MALDI-MSI, pSILAC/SILAC/iTRAQ/TMT-LC-MS/MS, MRM-MS) for comprehensive analysis of proteome dynamics in different biosystems, including cell type, cell species, and subcellular proteome (i.e. secretome and chromatome). Finally, we discuss the future direction and challenges in the application of these technological advancements in mass spectrometry within the context of cancer and hypoxia.

State-of-the-art advances of copper-based nanostructures in the enhancement of chemodynamic therapy

Chemodynamic therapy (CDT) is a new emerging strategy for the in situ treatment of tumors. In the microenvironment of tumor cells, CDT may be achieved through the generation of reactive oxygen species (ROS), e.g., hydroxyl radicals (˙OH) and singlet oxygen (¹O₂), which induce the death of tumor cells. Copper (Cu) or other transition-metal ions catalyze the production of ˙OH by hydrogen peroxide (H₂O₂) through Fenton or Fenton-like reactions. With the development of advanced nanotechnology, nanotherapeutic systems with Cu-based nanostructures have received extensive attention and have been demonstrated for their wide applications in the design and construction of nanotherapeutic systems for CDT, along with multimodal synergistic therapy. Herein, the cutting-edge developments of Cu-based nanostructures in CDT are reviewed and discussed, by focusing on the monotherapy of CDT as well as synergistic treatments by hyphenating CDT with various therapeutic protocols, e.g., photothermal therapy (PTT), photodynamic therapy (PDT), sonodynamic therapy (SDT), and so on. In addition, the potential challenges and future perspectives are described in the improvement of CDT therapeutic efficacy, the enhancement of targeting capability, and mechanistic investigations on CDT therapy.

Microbial nitroreductases: A versatile tool for biomedical and environmental applications

Nitroreductases, enzymes found mostly in bacteria and also in few eukaryotes, use nicotinamide adenine dinucleotide (NADH) or nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor for their activity and metabolize an enormous list of a diverse nitro group-containing compounds. Nitroreductases that are capable of metabolizing nitroaromatic and nitro heterocyclic compounds have drawn great attention in recent years owing to their biotechnological, biomedical, environmental, and human impact. These enzymes attracted medicinal chemists and pharmacologists because of their prodrug selectivity for activation/reduction of nitro compounds that wipe out pathogens/cancer cells, leaving the host/normal cells unharmed. It is applied in diverse fields of study like prodrug activation in treating cancer and leishmaniasis, designing fluorescent probes for hypoxia detection, cell imaging, ablation of specific cell types, biodegradation of nitro-pollutants, and interpretation of mutagenicity of nitro compounds. Keeping in view the immense prospects of these enzymes and a large number of research contributions in this area, the present review encompasses the enzymatic reaction mechanism, their role in antibiotic resistance, hypoxia sensing, cell imaging, cancer therapy, reduction of recalcitrant nitro chemicals, enzyme variants, and their specificity to substrates, reaction products, and their applications.

Nanoplatform-based cascade engineering for cancer therapy

Various therapeutic techniques have been studied for treating cancer precisely and effectively, such as targeted drug delivery, phototherapy, tumor-specific catalytic therapy, and synergistic therapy, which, however, evoke numerous challenges due to the inherent limitations of these therapeutic modalities and intricate biological circumstances as well. With the remarkable advances of nanotechnology, nanoplatform-based cascade engineering, as an efficient and booming strategy, has been tactfully introduced to optimize these cancer therapies. Based on the designed nanoplatforms, pre-supposed cascade processes could be triggered under specific conditions to generate/deliver more therapeutic species or produce stronger tumoricidal effects inside tumors, aiming to achieve cancer therapy with increased anti-tumor efficacy and diminished side effects. In this review, the recent advances in nanoplatform-based cascade engineering for cancer therapy are summarized and discussed, with an emphasis on the design of smart nanoplatforms with unique structures, compositions and properties, and the implementation of specific cascade processes by means of endogenous tumor microenvironment (TME) resources and/or exogenous energy inputs. This fascinating strategy presents unprecedented potential in the enhancement of cancer therapies, and offers better controllability, specificity and effectiveness of therapeutic functions compared to the corresponding single components/functions. In the end, challenges and prospects of such a burgeoning strategy in the field of cancer therapy will be discussed, hopefully to facilitate its further development to meet the personalized treatment demands.

Controlled anti-cancer drug release through advanced nano-drug delivery systems: Static and dynamic targeting strategies

Advances in nanomedicine, including early cancer detection, targeted drug delivery, and personalized approaches to cancer treatment are on the rise. For example, targeted drug delivery systems can improve intracellular delivery because of their multifunctionality. Novel endogenous-based and exogenous-based stimulus-responsive drug delivery systems have been proposed to prevent the cancer progression with proper drug delivery. To control effective dose loading and sustained release, targeted permeability and individual variability can now be described in more-complex ways, such as by combining internal and external stimuli. Despite these advances in release control, certain challenges remain and are identified in this research, which emphasizes the control of drug release and applications of nanoparticle-based drug delivery systems. Using a multiscale and multidisciplinary approach, this study investigates and analyzes drug delivery and release strategies in the nanoparticle-based treatment of cancer, both mathematically and clinically.

Combining hypoxia-activated prodrugs and radiotherapy in silico: Impact of treatment scheduling and the intra-tumoural oxygen landscape

Hypoxia-activated prodrugs (HAPs) present a conceptually elegant approach to not only overcome, but better yet, exploit intra-tumoural hypoxia. Despite being successful in vitro and in vivo, HAPs are yet to achieve successful results in clinical settings. It has been hypothesised that this lack of clinical success can, in part, be explained by the insufficiently stringent clinical screening selection of determining which tumours are suitable for HAP treatments. Taking a mathematical modelling approach, we investigate how tumour properties and HAP-radiation scheduling influence treatment outcomes in simulated tumours. The following key results are demonstrated in silico: (i) HAP and ionising radiation (IR) monotherapies may attack tumours in dissimilar, and complementary, ways. (ii) HAP-IR scheduling may impact treatment efficacy. (iii) HAPs may function as IR treatment intensifiers. (iv) The spatio-temporal intra-tumoural oxygen landscape may impact HAP efficacy. Our in silico framework is based on an on-lattice, hybrid, multiscale cellular automaton spanning three spatial dimensions. The mathematical model for tumour spheroid growth is parameterised by multicellular tumour spheroid (MCTS) data.

Recent Advances in Nanostrategies Capable of Overcoming Biological Barriers for Tumor Management

Engineered nanomaterials have been extensively employed as therapeutics for tumor management. Meanwhile, the complex tumor niche along with multiple barriers at the cellular level collectively hinders the action of nanomedicines. Here, the advanced strategies that hold promise for overcoming the numerous biological barriers facing nanomedicines are summarized. Starting from tumor entry, methods that promote tissue penetration of nanomedicine and address the hypoxia issue are also highlighted. Then, emphasis is given to the significance of overcoming both physical barriers, such as membrane-associated efflux pumps, and biological features, such as resistance to apoptosis. The pros and cons for an individual approach are presented. In addition, the associated technical problems are discussed, along with the importance of balancing the therapeutic merits and the additional cost of sophisticated nanomedicine designs.

Blackboard to Bedside: A Mathematical Modeling Bottom-Up Approach Toward Personalized Cancer Treatments

Cancers present with high variability across patients and tumors; thus, cancer care, in terms of disease prevention, detection, and control, can highly benefit from a personalized approach. For a comprehensive personalized oncology practice, this personalization should ideally consider data gathered from various information levels, which range from the macroscale population level down to the microscale tumor level, without omission of the central patient level. Appropriate data mined from each of these levels can significantly contribute in devising personalized treatment plans tailored to the individual patient and tumor. Mathematical models of solid tumors, combined with patient-specific tumor profiles, present a unique opportunity to personalize cancer treatments after detection using a bottom-up approach. Here, we discuss how information harvested from mathematical models and from corresponding in silico experiments can be implemented in preclinical and clinical applications. To conceptually illustrate the power of these models, one such model is presented, and various pertinent tumor and treatment scenarios are demonstrated in silico. The presented model, specifically a multiscale, hybrid cellular automaton, has been fully validated in vitro using multiple cell-line-specific data. We discuss various insights provided by this model and other models like it and their role in designing predictive tools that are both patient, and tumor specific. After refinement and parametrization with appropriate data, such in silico tools have the potential to be used in a clinical setting to aid in treatment protocols and decision making.

A Novel Model System for Understanding Anticancer Activity of Hypoxia-Activated Prodrugs

Reports on the comprehensive factors for design considerations of hypoxia-activated prodrugs (HAPs) are rare. We introduced a new model system composed of a series of highly water-soluble HAPs, providing a platform to comprehensively understand the interaction between HAPs and hypoxic biosystems. Specifically, four kinds of new HAPs were designed and synthesized, containing the same biologically active moiety but masked by different bioreductive groups. Our results demonstrated that the activity of the prodrugs was strongly dependent on not only the molecular structure but also the hypoxic tumor microenvironment. We found the presence of a direct linear relationship between cytotoxicity of the HAPs and the reduction potential of whole molecule/oxygen concentration/reductase expression. Moreover, limited blood vasculature in hypoxic regions was also a critical barrier for effective activation of the HAPs. This study offers a comprehensive insight into understanding the design factors required for HAPs.

A novel multifunctional 2-nitroimidazole-based bioreductive linker and its application in hypoxia-activated prodrugs

Tumor hypoxia has been widely explored over the years as a diagnostic and therapeutic marker. Herein, we designed, optimized and synthesized a new multifunctional bioreductive linker (12) containing an alkynyl group (potential click chemistry fragment); the linker is based on 2-nitroimidazole which was expected to simultaneously overcome the drawbacks of hypoxia-activated prodrugs (poor selectivity and unsatisfactory water solubility). Furthermore, a hypoxia-activated, water-soluble SN-38 prodrug was obtained, and it was stable under physiological conditions and was rapidly released as an active drug under hypoxic conditions.

Cellular adaptation to hypoxia through hypoxia inducible factors and beyond

Molecular oxygen (O2) sustains intracellular bioenergetics and is consumed by numerous biochemical reactions, making it essential for most species on Earth. Accordingly, decreased oxygen concentration (hypoxia) is a major stressor that generally subverts life of aerobic species and is a prominent feature of pathological states encountered in bacterial infection, inflammation, wounds, cardiovascular defects and cancer. Therefore, key adaptive mechanisms to cope with hypoxia have evolved in mammals. Systemically, these adaptations include increased ventilation, cardiac output, blood vessel growth and circulating red blood cell numbers. On a cellular level, ATP-consuming reactions are suppressed, and metabolism is altered until oxygen homeostasis is restored. A critical question is how mammalian cells sense oxygen levels to coordinate diverse biological outputs during hypoxia. The best-studied mechanism of response to hypoxia involves hypoxia inducible factors (HIFs), which are stabilized by low oxygen availability and control the expression of a multitude of genes, including those involved in cell survival, angiogenesis, glycolysis and invasion/metastasis. Importantly, changes in oxygen can also be sensed via other stress pathways as well as changes in metabolite levels and the generation of reactive oxygen species by mitochondria. Collectively, this leads to cellular adaptations of protein synthesis, energy metabolism, mitochondrial respiration, lipid and carbon metabolism as well as nutrient acquisition. These mechanisms are integral inputs into fine-tuning the responses to hypoxic stress.

Enhanced selectivity, cellular uptake, and in vitro activity of an intrinsically fluorescent copper-tirapazamine nanocomplex for hypoxia targeted therapy in prostate cancer

In the present work, a copper-tirapazamine (TPZ) nanocomplex [Cu(TPZ)₂] was synthesized for selective hypoxia-targeted therapy. The nanocomplex revealed a crystalline form, and exhibited higher lipophilicity, compared to TPZ. Furthermore, its stability was confirmed in different media, with minimum dissociation in serum (∼20% up to 72 h). In contrast to other hypoxia-targeted agents, our intrinsically fluorescent nanocomplex offered an invaluable tool to monitor its cellular uptake and intracellular distribution under both normoxia and hypoxia. The conferred higher cellular uptake of the nanocomplex, especially under hypoxia, and its biocompatible reductive potential resulted in superior hypoxia selectivity in two prostate cancer (PC) cell lines. More promisingly, the nanocomplex showed higher potency in three-dimensional tumor spheroids, compared to TPZ, due to its slower metabolism, and probably deeper penetration in tumor spheroids. Interestingly, the nuclear localization of the intact nanocomplex, combined with its higher DNA binding affinity, as evidenced by the DNA binding assay, resulted in significant S-phase cell-cycle arrest, followed by apoptosis in the three-dimensional spheroid model. In conclusion, the presented findings suggested that the Cu(TPZ)₂ nanocomplex can be a promising hypoxia-targeted therapeutic, which could potentiate the efficacy of the existing chemo- and radiotherapy in PC.

Design, synthesis and evaluation of targeted hypoxia-activated prodrugs applied to chondrosarcoma chemotherapy

The tumor microenvironment in chondrosarcoma (CHS), a chemo- and radio-resistant cancer provides unique hallmarks for developing a chondrosarcoma targeted drug-delivery system. Tumor targeting could be achieved using a quaternary ammonium function (QA) as a ligand for aggrecan, the main high negative charged proteoglycan of the extracellular matrix of CHS, and a 2-nitroimidazole as trigger that enables hypoxia-responsive drug release. In a previous work, ICF05016 was identified as efficient proteoglycan-targeting hypoxia-activated prodrug in a human extraskeletal myxoid chondrosarcoma model in mice and a first study of the structure-activity relationship of the QA function and the alkyl linker length was conducted. Here, we report the second part of the study, namely the modification of the nitro-aromatic trigger and the position of the proteoglycan-targeting ligand at the aromatic ring as well as the nature of the alkylating mustard. Synthetic approaches have been established to functionalize the 2-nitroimidazole ring at the N-1 and C-4 positions with a terminal tertiary alkyl amine, and to perform the phosphorylation step namely through the use of an amine borane complex, leading to phosphoramide and isophosphoramide mustards and also to a phosphoramide mustard bearing four 2-chloroethyl chains. In a preliminary study using a reductive chemical activation, QA-conjugates, except the 4-nitrobenzyl one, were showed to undergo efficient cleavage with release of the corresponding mustard. However N,N,N-trimethylpropylaminium tethered to the N-1 or C-4 positions of the imidazole seemed to hamper the enzymatic reduction of the prodrugs and all tested compounds featured moderate selectivity toward hypoxic cells, likely not sufficient for application as hypoxia-activated prodrugs.

Multigram scale synthesis of polycyclic lactones and evaluation of antitumor and other biological properties

An efficient four-step synthesis of tetracyclic lactones from 1,4-benzodioxine-2-carboxylic acid was developed. Ellipticine derivatives exhibit antitumor activity however only a few derivatives without carbazole subunit have been studied to date. Herein, several tetracyclic lactones were synthesized and biologically evaluated. Several compounds (2a, 3a, 4a and 5a) were found to be inhibitors of the Kras-Wnt pathway. The lactone 2a also exerted a potent inhibition of Tau protein translation and was shown to have capacity for CYP1A1-bioactivation. The results obtained are further evidence of the therapeutic potential of tetracyclic lactones related to ellipticine. Molecular modeling studies showed that compound 2a is inserted between helix α3 and α4 of the KRas protein making interactions with the hydrophobic residues Phe90, Glu91, Ile9364, Hie94, Leu133 and Tyr137and a hydrogen bond with residue Arg97.

Hypoxia-responsive nanoparticle based drug delivery systems in cancer therapy: An up-to-date review

Hypoxia is a salient feature observed in most solid malignancies that holds a pivotal role in angiogenesis, metastasis and resistance to conventional cancer therapeutic approaches, and thus enables cancer progression. However, the typical characteristics of hypoxic cells such as low oxygen levels and highly bio-reductive environment can offer stimuli-responsive drug release to aid in tumor-specific chemo, radio, photodyanamic and sonodynamic therapies. This approach based on targeting the poorly oxygenated tumor habitats offers the prospective to overcome the difficulties that arises due to heterogenic nature of tumor and could be possibly used in the design of diagnostic as well as therapeutic nanocarriers for targeting various types of solid cancers. Consequently, hypoxia triggered nanoparticle based drug delivery systems is a rapidly progressing research area in developing effective strategies to combat drug-resistance in solid tumors. The present review presents the recent advances in the development of hypoxia-responsive nanovehicles for drug delivery to heterogeneous tumors. The initial sections of the article provides insights into the development of hypoxia in growing cancer and its role in disease progression. The current limitations and the future prospective of hypoxia-stimulated nanomachines for cancer treatment are also discussed.

Platelet-Mimicking Biotaxis Targeting Vasculature-Disrupted Tumors for Cascade Amplification of Hypoxia-Sensitive Therapy

Tumorous vasculature plays key roles in sustaining tumor growth. Vascular disruption is accompanied by internal coagulation along with platelet recruitment and the resulting suppression of oxygen supply. We intend to artificially create this physiological process to establish the mutual feedback between vascular disruption and platelet-mimicking biotaxis for the cascade amplification of hypoxia-dependent therapy. To prove this concept, mesoporous silica nanoparticles are co-loaded with a hypoxia-activated prodrug (HAP) and a vessel-disruptive agent and then coated with platelet membranes. Upon entering into tumors, our nanotherapeutic can disrupt local vasculature for tumor inhibition. This platelet membrane-coated nanoplatform shares the hemorrhage-tropic function with parental platelets and can be persistently recruited by the vasculature-disrupted tumors. In this way, the intratumoral vascular disruption and tumor targeting are biologically interdependent and mutually reinforced. Relying on this mutual feedback, tumorous hypoxia was largely promoted by more than 20-fold, accounting for the effective recovery of the HAP's cytotoxicity. Consequently, our bioinspired nanodesign has demonstrated highly specific and effective antitumor potency via the biologically driven cooperation among intratumoral vascular disruption, platelet-mimicking biotaxis, cascade hypoxia amplification, and hypoxia-sensitive chemotherapy. This study offers a paradigm of correlating the therapeutic design with the physiologically occurring events to achieve better therapy performance.

Experimental and theoretical charge density, intermolecular interactions and electrostatic properties of metronidazole

Metronidazole is a radiosensitizer; it crystallizes in the monoclinic system with space group P2₁/c. The crystal structure of metronidazole has been determined from high-resolution X-ray diffraction measurements at 90 K with a resolution of (sin θ/λ)_max = 1.12 Å^-1. To understand the charge-density distribution and the electrostatic properties of metronidazole, a multipole model refinement was carried out using the Hansen-Coppens multipole formalism. The topological analysis of the electron density of metronidazole was performed using Bader's quantum theory of atoms in molecules to determine the electron density and the Laplacian of the electron density at the bond critical point of the molecule. The experimental results have been compared with the corresponding periodic theoretical calculation performed at the B3LYP/6-31G** level using CRYSTAL09. The topological analysis reveals that the N-O and C-NO₂ exhibit less electron density as well as negative Laplacian of electron density. The molecular packing of crystal is stabilized by weak and strong inter- and intramolecular hydrogen bonding and H...H interactions. The topological analysis of O-H...N, C-H...O and H...H intra- and intermolecular interactions was also carried out. The electrostatic potential of metronidazole, calculated from the experiment, predicts the possible electrophilic and nucleophilic sites of the molecule; notably, the hydroxyl and the nitro groups exhibit large electronegative regions. The results have been compared with the corresponding theoretical results.

Triggering Sequential Catalytic Fenton Reaction on 2D MXenes for Hyperthermia-Augmented Synergistic Nanocatalytic Cancer Therapy

The unique characteristics of a tumor microenvironment (TME) enable the development of new tumor-therapeutic modalities with high efficiency, biosafety, and tumor specificity. In this work, we report on the construction of photothermal-enhanced and nanocatalyst-enabled sequential catalytic reaction for TME-specific cancer therapy. This conceptual advance is achieved by engineering the surface of two-dimensional Ti₃C₂ MXene with two separate catalysts, including natural glucose oxidase (GOD) as glucose catalysts and superparamagnetic iron oxide nanoparticles (IONPs) as Fenton-reaction nanocatalysts. A sequential catalytic reaction is triggered by using GOD for catalyzing the tumor-overtaken glucose to generate large amounts of hydrogen peroxide molecules. Subsequently IONPs can catalyze the transformation of pregenerated hydrogen peroxide into large amounts of highly toxic hydroxyl radicals to kill the cancer cells subsequently in TME-enabled acidity condition. The two-dimensional (2D) Ti₃C₂ MXene matrix efficiently converts the near-infrared light into thermal energy to synergistically enhance the catalytic efficiency of this sequential catalytic reaction and therefore achieve the high synergistic cancer-therapeutic outcome, accompanied with the high biocompatibility of the constructed composite nanocatalysts. Both in vitro cancer-cell evaluation and in vivo tumor xenograft on nude mice with complete tumor eradication demonstrate the high synergistic efficiency of photothermal-enhanced sequential nanocatalytic cancer therapy. Therefore, this work substantially broadens the biomedical applications of 2D MXenes to nanocatalytic cancer therapy by enhancing the Fenton reaction-based nanocatalytic therapy via converting the near-infrared light into thermal energy and subsequently elevating the local Fenton-reaction temperature.

Role of hypoxia in cancer therapy by regulating the tumor microenvironment

AIM

Clinical resistance is a complex phenomenon in major human cancers involving multifactorial mechanisms, and hypoxia is one of the key components that affect the cellular expression program and lead to therapy resistance. The present study aimed to summarize the role of hypoxia in cancer therapy by regulating the tumor microenvironment (TME) and to highlight the potential of hypoxia-targeted therapy.

METHODS

Relevant published studies were retrieved from PubMed, Web of Science, and Embase using keywords such as hypoxia, cancer therapy, resistance, TME, cancer, apoptosis, DNA damage, autophagy, p53, and other similar terms.

RESULTS

Recent studies have shown that hypoxia is associated with poor prognosis in patients by regulating the TME. It confers resistance to conventional therapies through a number of signaling pathways in apoptosis, autophagy, DNA damage, mitochondrial activity, p53, and drug efflux.

CONCLUSION

Hypoxia targeting might be relevant to overcome hypoxia-associated resistance in cancer treatment.

Nitrogen Mustards as Anticancer Chemotherapies: Historic Perspective, Current Developments and Future Trends

Nitrogen mustards, a family of DNA alkylating agents, marked the start of cancer pharmacotherapy. While traditionally characterized by their dose-limiting toxic effects, nitrogen mustards have been the subject of intense research efforts, which have led to safer and more effective agents. Even though the alkylating prodrug mustards were first developed decades ago, active research on ways to improve their selectivity and cytotoxic efficacy is a currently active topic of research. This review addresses the historical development of the nitrogen mustards, outlining their mechanism of action, and discussing the improvements on their therapeutic profile made through rational structure modifications. A special emphasis is made on discussing the nitrogen mustard prodrug category, with Cyclophosphamide (CPA) serving as the main highlight. Selected insights on the latest developments on nitrogen mustards are then provided, limiting such information to agents that preserve the original nitrogen mustard mechanism as their primary mode of action. Additionally, future trends that might follow in the quest to optimize these invaluable chemotherapeutic medications are succinctly suggested.

Programmable Therapeutic Nanodevices with Circular Amplification of H2 O2 in the Tumor Microenvironment for Synergistic Cancer Therapy

Tumor microenvironment activated nanodevices have remarkable superiority to enhance therapeutic efficacy and minimize side effects, but their practical applications are dramatically reduced by the low abundance and heterogeneous distribution of specific stimuli at the tumor site. Herein, programmable vesicular nanodevices based on the triblock copolymer containing poly(ethylene glycol) (PEG) and poly(caprolactone) (PCL) with peroxalate esters (PO) as hydrogen peroxide-responsive linkage (PEG-PO-PCL-PO-PEG), are developed for co-delivery of hypoxia-activated prodrug (AQ4N) and glucose oxidase (GOD). The obtained nanodevices (PAG) can be activated by the high level of H₂ O₂ in tumor microenvironment to improve the permeability of membranes for glucose entrance. Afterward, the oxidation of glucose catalyzed by GOD produces amplified H₂ O₂ amounts which in turn induce complete destruction of PAG for fast release of AQ4N and GOD. Ultimately, the PAG can exert programmable therapeutic effects from the following aspects: 1) starvation therapy by cutting off the energy supply from glucose through GOD catalysis; 2) oxidative cytotoxicity after H₂ O₂ amplification; 3) chemotherapy of AQ4N activated by the intensified tumor hypoxia microenvironment after oxygen consumption. The stimuli amplification, controlled drug release, synergistic therapy, and corresponding mechanisms of PAG are demonstrated. Therefore, the presented work could provide significant new insights for cancer treatment.

Perfluorocarbon regulates the intratumoural environment to enhance hypoxia-based agent efficacy

Hypoxia-based agents (HBAs), such as anaerobic bacteria and bioreductive prodrugs, require both a permeable and hypoxic intratumoural environment to be fully effective. To solve this problem, herein, we report that perfluorocarbon nanoparticles (PNPs) can be used to create a long-lasting, penetrable and hypoxic tumour microenvironment for ensuring both the delivery and activation of subsequently administered HBAs. In addition to the increased permeability and enhanced hypoxia caused by the PNPs, the PNPs can be retained to further achieve the long-term inhibition of intratumoural O₂ reperfusion while enhancing HBA accumulation for over 24 h. Therefore, perfluorocarbon materials may have great potential for reigniting clinical research on hypoxia-based drugs.

Hypoxia-based agents need permeable and hypoxic intratumour environment to be effective. Here, the authors show that perfluorocarbon nanoparticles promote increased permeability and sustained hypoxia to improve accumulation of hypoxia-based agents, and inhibit intratumour oxygen reperfusion.

Enzyme-Activated Generation of Reactive Oxygen Species from Heterocyclic N-Oxides under Aerobic and Anaerobic Conditions and Its Relevance to Hypoxia-Selective Prodrugs

Enzymatic one-electron reduction of heterocyclic N-oxides can lead to the intracellular generation of reactive oxygen species via several different chemical pathways. These reactions may be relevant to hypoxia-selective anticancer drugs, antimicrobial agents, and unwanted toxicity of heterocylic nitrogen compounds.

Overcoming Radioresistance: Small Molecule Radiosensitisers and Hypoxia-activated Prodrugs

The role of hypoxia in radiation resistance is well established and many approaches to overcome hypoxia in tumours have been explored, with variable success. Two small molecule strategies for targeting hypoxia have dominated preclinical and clinical efforts. One approach has been the use of electron-affinic nitroheterocycles as oxygen-mimetic sensitisers. These agents are best exemplified by the 5-nitroimidazole nimorazole, which has limited use in conjunction with radiotherapy in head and neck squamous cell carcinoma. The second approach seeks to leverage tumour hypoxia as a tumour-specific address for hypoxia-activated prodrugs. These prodrugs are selectively activated by reductases under hypoxia to release cytotoxins, which in some instances may diffuse to kill surrounding oxic tumour tissue. A number of these hypoxia-activated prodrugs have been examined in clinical trial and the merits and shortcomings of recent examples are discussed. There has been an evolution from delivering DNA-interactive cytotoxins to molecularly targeted agents. Efforts to implement these strategies clinically continue today, but success has been elusive. Several issues have been identified that compromised these clinical campaigns. A failure to consider the extravascular transport and the micropharmacokinetic properties of the prodrugs has reduced efficacy. One key element for these 'targeted' approaches is the need to co-develop biomarkers to identify appropriate patients. Hypoxia-activated prodrugs require biomarkers for hypoxia, but also for appropriate activating reductases in tumours, as well as markers of intrinsic sensitivity to the released drug. The field is still evolving and changes in radiation delivery and the impact of immune-oncology will provide fertile ground for future innovation.

Nitroimidazole derivative incorporated liposomes for hypoxia-triggered drug delivery and enhanced therapeutic efficacy in patient-derived tumor xenografts

Hypoxia is not merely a tumor microenvironment byproduct, but rather an active participant in tumor development, invasion, and metastasis. Hypoxia contributes to poor outcomes in tumor treatment and has currently emerged as an important therapeutic target. In this work, a facile hypoxia-responsive liposomal drug delivery system was developed by incorporating derivatized nitroimidazole into liposome membranes. Under hypoxic conditions, hypoxia-induced reductive metabolism of the nitroimidazole derivative facilitated disassembly of the liposomes for triggered drug release. The liposomes showed high sensitivity to hypoxia, even at the cellular level, and could release payload in an oxygen-dependent manner, leading to high cytotoxicity in hypoxic conditions. In vivo fluorescence imaging revealed that there was a selective release of the liposomes at the hypoxic tumor site. As a result, the liposomes exhibited enhanced therapeutic efficacy in treating a hypoxic tumor in both cell line-derived and clinically relevant patient-derived xenograft models. Thus, hypoxia-responsive liposomes are a promising drug delivery system for hypoxia targeted tumor therapy. STATEMENT OF SIGNIFICANCE: 1. A facile but smart hypoxia-responsive liposomal drug delivery system is developed by incorporating nitroimidazole derivative, one of representative hypoxia-responsive moieties, into phospholipid bilayer of the liposomes. 2. The liposomes show extremely high sensitivity to hypoxia and can selectively release payload in hypoxic cells and hypoxic tumor. 3. The liposomes show enhanced therapeutic efficacy not only in cell line-derived xenograft model but also in clinically relevant patient-derived xenograft model, indicating their promising prospect in clinical application.

Endoplasmic reticulum-targeted two-photon turn-on fluorescent probe for nitroreductase in tumor cells and tissues

Hypoxia conditions could increase the activity of intracellular nitroreductase (NTR) and lead to many malignant diseases. Therefore, monitoring the activity of NTR is of great significance to study the related diseases. Organelles play crucial roles in the metabolism of living cells. In these organelles, the endoplasmic reticulum (ER) possesses single membrane structure, and it is the largest organelle in the cell. ER performs the synthesis, processing and modification of proteins and lipid, stabilizing the intracellular Ca²⁺ concentration and other physiological functions in living cells. Therefore, it is of great significance to develop ER-target probes in living system. Toward this goal, a new endoplasmic reticulum-targeted two-photon fluorescence turn-on NTR probe Na-NTR-ER is designed and synthesized. Probe Na-NTR-ER has been proved to display high sensitivity (36 ng/mL) and selectivity to NTR. Particularly, probe Na-NTR-ER has been successfully applied for the monitoring of NTR in ER with a high the Pearson's colocalization coefficient as 0.90 in HeLa cells and cancerous mouse tissues up to the depth of 100 μm with significant fluorescence signals.