Targeting Hypoxia: Hypoxia-Activated Prodrugs in Cancer Therapy

U-Shape Pillar Strip for 3D Cell-Lumped Organoid Model (3D-COM) Mimicking Lung Cancer Hypoxia Conditions in High-Throughput Screening (HTS)

Hypoxia is a representative tumor characteristic associated with malignant progression in clinical patients. Engineered in vitro models have led to significant advances in cancer research, allowing for the investigation of cells in physiological environments and the study of disease mechanisms and processes with enhanced relevance. In this study, we propose a U-shape pillar strip for a 3D cell-lumped organoid model (3D-COM) to study the effects of hypoxia on lung cancer in a high-throughput manner. We developed a U-pillar strip that facilitates the aggregation of PDCs mixed with an extracellular matrix to make the 3D-COM in 384-plate array form. The response to three hypoxia-activated prodrugs was higher in the 3D-COM than in the 2D culture model. The protein expression of hypoxia-inducible factor 1 alpha (HIF-1α) and HIF-2α, which are markers of hypoxia, was also higher in the 3D-COM than in the 2D culture. The results show that 3D-COM better recapitulated the hypoxic conditions of lung cancer tumors than the 2D culture. Therefore, the U-shape pillar strip for 3D-COM is a good tool to study the effects of hypoxia on lung cancer in a high-throughput manner, which can efficiently develop new drugs targeting hypoxic tumors.

New-generation advanced PROTACs as potential therapeutic agents in cancer therapy

Proteolysis-targeting chimeras (PROTACs) technology has garnered significant attention over the last 10 years, representing a burgeoning therapeutic approach with the potential to address pathogenic proteins that have historically posed challenges for traditional small-molecule inhibitors. PROTACs exploit the endogenous E3 ubiquitin ligases to facilitate degradation of the proteins of interest (POIs) through the ubiquitin-proteasome system (UPS) in a cyclic catalytic manner. Despite recent endeavors to advance the utilization of PROTACs in clinical settings, the majority of PROTACs fail to progress beyond the preclinical phase of drug development. There are multiple factors impeding the market entry of PROTACs, with the insufficiently precise degradation of favorable POIs standing out as one of the most formidable obstacles. Recently, there has been exploration of new-generation advanced PROTACs, including small-molecule PROTAC prodrugs, biomacromolecule-PROTAC conjugates, and nano-PROTACs, to improve the in vivo efficacy of PROTACs. These improved PROTACs possess the capability to mitigate undesirable physicochemical characteristics inherent in traditional PROTACs, thereby enhancing their targetability and reducing off-target side effects. The new-generation of advanced PROTACs will mark a pivotal turning point in the realm of targeted protein degradation. In this comprehensive review, we have meticulously summarized the state-of-the-art advancements achieved by these cutting-edge PROTACs, elucidated their underlying design principles, deliberated upon the prevailing challenges encountered, and provided an insightful outlook on future prospects within this burgeoning field.

Prodrug-conjugated tumor-seeking commensals for targeted cancer therapy

Prodrugs have been explored as an alternative to conventional chemotherapy; however, their target specificity remains limited. The tumor microenvironment harbors a range of microorganisms that potentially serve as tumor-targeting vectors for delivering prodrugs. In this study, we harness bacteria-cancer interactions native to the tumor microbiome to achieve high target specificity for prodrug delivery. We identify an oral commensal strain of Lactobacillus plantarum with an intrinsic cancer-binding mechanism and engineer the strain to enable the surface loading of anticancer prodrugs, with nasopharyngeal carcinoma (NPC) as a model cancer. The engineered commensals show specific binding to NPC via OppA-mediated recognition of surface heparan sulfate, and the loaded prodrugs are activated by tumor-associated biosignals to release SN-38, a chemotherapy compound, near NPC. In vitro experiments demonstrate that the prodrug-loaded microbes significantly increase the potency of SN-38 against NPC cell lines, up to 10-fold. In a mouse xenograft model, intravenous injection of the engineered L. plantarum leads to bacterial colonization in NPC tumors and a 67% inhibition in tumor growth, enhancing the efficacy of SN-38 by 54%.

Improving drug delivery to the brain: the prodrug approach

INTRODUCTION

The prodrug approach has been thought to be a simple solution to improve brain drug delivery for decades. Nevertheless, it still comes as a surprise that there is relatively little success in the field. The best example anti-parkinsonian drug levodopa has been serendipitously discovered to be a transporter-utilizing brain-delivered prodrug rather than a rationally developed one.

AREAS COVERED

The lack of success can mainly be explained by the insufficient understanding of the role of membrane proteins that can facilitate drug delivery at dynamic barriers, such as the blood-brain barrier (BBB), but also by the sparse knowledge of prodrug bioconverting enzymes in the brain. This review summarizes the current status of the prodrug attempts that have been developed in the past to improve brain drug delivery.

EXPERT OPINION

With the expandingly improved analytical and computational technologies, it is anticipated that enhanced brain drug delivery will be eventually achieved for most of the central nervous system (CNS) acting drugs. However, this requires that carrier-mediated (pro)drug delivery methods are implemented in the very early phases of the drug development processes and not as a last step to survive a problematic investigational drug candidate.

The landscape of small-molecule prodrugs

Prodrugs are derivatives with superior properties compared with the parent active pharmaceutical ingredient (API), which undergo biotransformation after administration to generate the API in situ. Although sharing this general characteristic, prodrugs encompass a wide range of different chemical structures, therapeutic indications and properties. Here we provide the first holistic analysis of the current landscape of approved prodrugs using cheminformatics and data science approaches to reveal trends in prodrug development. We highlight rationales that underlie prodrug design, their indications, mechanisms of API release, the chemistry of promoieties added to APIs to form prodrugs and the market impact of prodrugs. On the basis of this analysis, we discuss strengths and limitations of current prodrug approaches and suggest areas for future development.

Hypoxia-Activated Theragnostic Prodrugs (HATPs): Current State and Future Perspectives

Hypoxia is a significant feature of solid tumors and frequently poses a challenge to the effectiveness of tumor-targeted chemotherapeutics, thereby limiting their anticancer activity. Hypoxia-activated prodrugs represent a class of bio-reductive agents that can be selectively activated in hypoxic compartments to unleash the toxic warhead and thus, eliminate malignant tumor cells. However, their applicability can be further elevated by installing fluorescent modalities to yield hypoxia-activated theragnostic prodrugs (HATPs), which can be utilized for the simultaneous visualization and treatment of hypoxic tumor cells. The scope of this review is to summarize noteworthy advances in recent HATPs, highlight the challenges and opportunities for their further development, and discuss their potency to serve as personalized medicines in the future.

Medicinal Chemistry of Drugs with N-Oxide Functionalities

Molecules with N-oxide functionalities are omnipresent in nature and play an important role in Medicinal Chemistry. They are synthetic or biosynthetic intermediates, prodrugs, drugs, or polymers for applications in drug development and surface engineering. Typically, the N-oxide group is critical for biomedical applications of these molecules. It may provide water solubility or decrease membrane permeability or immunogenicity. In other cases, the N-oxide has a special redox reactivity which is important for drug targeting and/or cytotoxicity. Many of the underlying mechanisms have only recently been discovered, and the number of applications of N-oxides in the healthcare field is rapidly growing. This Perspective article gives a short summary of the properties of N-oxides and their synthesis. It also provides a discussion of current applications of N-oxides in the biomedical field and explains the basic molecular mechanisms responsible for their biological activity.

Regulation of Hypoxia Dependent Reprogramming of Cancer Metabolism: Role of HIF-1 and Its Potential Therapeutic Implications in Leukemia

Metabolic reprogramming occurs to meet cancer cells' high energy demand. Its function is essential to the survival of malignancies. Comparing cancer cells to non-malignant cells has revealed that cancer cells have altered metabolism. Several pathways, particularly mTOR, Akt, PI3K, and HIF-1 (hypoxia-inducible factor-1) modulate the metabolism of cancer. Among other aspects of cancer biology, gene expression in metabolism, survival, invasion, proliferation, and angiogenesis of cells are controlled by HIF-1, a vital controller of cellular responsiveness to hypoxia. This article examines various cancer cell metabolisms, metabolic alterations that can take place in cancer cells, metabolic pathways, and molecular aspects of metabolic alteration in cancer cells placing special attention on the consequences of hypoxia-inducible factor and summarising some of their novel targets in the treatment of cancer including leukemia. A brief description of HIF-1α's role and target in a few common types of hematological malignancies (leukemia) is also elucidated in the present article.

Stem Cell Theory of Cancer: Clinical Implications for Cellular Metabolism and Anti-Cancer Metabolomics

Although Otto Warburg may be right about the role of glycolysis versus OXPHOS in cancer metabolism, it remains unclear whether an altered metabolism is causative or correlative and is the main driver or a mere passenger in the pathogenesis of cancer. Currently, most of our successful treatments are designed to eliminate non-cancer stem cells (non-CSCs) such as differentiated cancer cells. When the treatments also happen to control CSCs or the stem-ness niche, it is often unintended, unexpected, or undetected for lack of a pertinent theory about the origin of cancer that clarifies whether cancer is a metabolic, genetic, or stem cell disease. Perhaps cellular context matters. After all, metabolic activity may be different in different cell types and their respective microenvironments-whether it is in a normal progenitor stem cell vs. progeny differentiated cell and whether it is in a malignant CSC vs. non-CSC. In this perspective, we re-examine different types of cellular metabolism, e.g., glycolytic vs. mitochondrial, of glucose, glutamine, arginine, and fatty acids in CSCs and non-CSCs. We revisit the Warburg effect, an obesity epidemic, the aspartame story, and a ketogenic diet. We propose that a pertinent scientific theory about the origin of cancer and of cancer metabolism influences the direction of cancer research as well as the design of drug versus therapy development in cancer care.

Tumour response to hypoxia: understanding the hypoxic tumour microenvironment to improve treatment outcome in solid tumours

Hypoxia is a common feature of solid tumours affecting their biology and response to therapy. One of the main transcription factors activated by hypoxia is hypoxia-inducible factor (HIF), which regulates the expression of genes involved in various aspects of tumourigenesis including proliferative capacity, angiogenesis, immune evasion, metabolic reprogramming, extracellular matrix (ECM) remodelling, and cell migration. This can negatively impact patient outcomes by inducing therapeutic resistance. The importance of hypoxia is clearly demonstrated by continued research into finding clinically relevant hypoxia biomarkers, and hypoxia-targeting therapies. One of the problems is the lack of clinically applicable methods of hypoxia detection, and lack of standardisation. Additionally, a lot of the methods of detecting hypoxia do not take into consideration the complexity of the hypoxic tumour microenvironment (TME). Therefore, this needs further elucidation as approximately 50% of solid tumours are hypoxic. The ECM is important component of the hypoxic TME, and is developed by both cancer associated fibroblasts (CAFs) and tumour cells. However, it is important to distinguish the different roles to develop both biomarkers and novel compounds. Fibronectin (FN), collagen (COL) and hyaluronic acid (HA) are important components of the ECM that create ECM fibres. These fibres are crosslinked by specific enzymes including lysyl oxidase (LOX) which regulates the stiffness of tumours and induces fibrosis. This is partially regulated by HIFs. The review highlights the importance of understanding the role of matrix stiffness in different solid tumours as current data shows contradictory results on the impact on therapeutic resistance. The review also indicates that further research is needed into identifying different CAF subtypes and their exact roles; with some showing pro-tumorigenic capacity and others having anti-tumorigenic roles. This has made it difficult to fully elucidate the role of CAFs within the TME. However, it is clear that this is an important area of research that requires unravelling as current strategies to target CAFs have resulted in worsened prognosis. The role of immune cells within the tumour microenvironment is also discussed as hypoxia has been associated with modulating immune cells to create an anti-tumorigenic environment. Which has led to the development of immunotherapies including PD-L1. These hypoxia-induced changes can confer resistance to conventional therapies, such as chemotherapy, radiotherapy, and immunotherapy. This review summarizes the current knowledge on the impact of hypoxia on the TME and its implications for therapy resistance. It also discusses the potential of hypoxia biomarkers as prognostic and predictive indictors of treatment response, as well as the challenges and opportunities of targeting hypoxia in clinical trials.

Tumor microenvironment-responsive degradable silica nanoparticles: design principles and precision theranostic applications

Silica nanoparticles have emerged as promising candidates in the field of nanomedicine due to their remarkable versatility and customizable properties. However, concerns about their potential toxicity in healthy tissues and organs have hindered their widespread clinical translation. To address this challenge, significant attention has been directed toward a specific subset of silica nanoparticles, namely degradable silica nanoparticles, primarily because of their excellent biocompatibility and responsive biodegradability. In this review, we provide a comprehensive understanding of degradable silica nanoparticles, categorizing them into two distinct groups: inorganic species-doped and organic moiety-doped silica nanoparticles based on their framework components. Next, the recent progress of tumor microenvironment (TME)-responsive degradable silica nanoparticles for precision theranostic applications is summarized in detail. Finally, current bottlenecks and future opportunities of theranostic nanomedicines based on degradable silica nanoparticles in clinical applications are also outlined and discussed. The aim of this comprehensive review is to shed light on the potential of degradable silica nanoparticles in addressing current challenges in nanomedicine, offering insights into their design, applications in tumor diagnosis and treatment, and paving the way for future advancements in clinical theranostic nanomedicines.

Cobalt(III)-py2en systems as potential carriers of β-ketoester-based ligands

Two cobalt(III) complexes containing different β-ketoesters, namely [CoIII(L1)(py2en)](ClO4)2·H2O (1) and [CoIII(L2)(py2en)](ClO4)2 (2) (py2en = N,N'-bis(pyridin-2-ylmethyl)ethylenediamine; L1- = methylacetoacetate; L2- = ethyl 4-chloroacetoacetate) have been prepared and investigated as prototypes of bioreductive prodrugs. The presence of β-ketoester and py2en ligands in 1 and 2, as well as the perchlorate counterions, was supported by IR spectroscopy and CHN elemental analysis. The composition molecular structure of both complexes was confirmed by NMR spectroscopy and ESI mass spectrometry. Structural information was also obtained for 2via X-ray diffraction analysis. The redox properties indicate that 1 and 2 are suitable for reduction under biological conditions. Investigation of DNA-interacting suggest that 1 and 2 bind DNA via electrostatic forces. Both complexes may be employed as possible platforms for the delivery of biologically active compounds, since their reaction with ascorbic acid in PBS at pH 6.2 and 7.4 at 37°C results in the release of the β-ketoester ligands upon Co(III)/Co(II) reduction.

Substitution Kinetics, Albumin and Transferrin Affinities, and Hypoxia All Affect the Biological Activities of Anticancer Vanadium(V) Complexes

Limited stability of most transition-metal complexes in biological media has hampered their medicinal applications but also created a potential for novel cancer treatments, such as intratumoral injections of cytotoxic but short-lived anticancer drugs. Two related V(V) complexes, [VO(Hshed)(dtb)] (1) and [VO(Hshed)(cat)] (2), where H2shed = N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine, H2dtb = 3,5-di-tert-butylcatechol, and H2cat = 1,2-catechol, decomposed within minutes in cell culture medium at 310 K (t1/2 = 43 and 9 s for 1 and 2, respectively). Despite this, both complexes showed high antiproliferative activities in triple-negative human breast cancer (MDA-MB-231) cells, but the mechanisms of their activities were radically different. Complex 1 formed noncovalent adducts with human serum albumin, rapidly entered cells via passive diffusion, and was nearly as active in a short-term treatment (IC50 = 1.9 ± 0.2 μM at 30 min) compared with a long-term treatment (IC50 = 1.3 ± 0.2 μM at 72 h). The activity of 1 decreased about 20-fold after its decomposition in cell culture medium for 30 min at 310 K. Complex 2 showed similar activities (IC50 ≈ 12 μM at 72 h) in both fresh and decomposed solutions and was inactive in a short-term treatment. The activity of 2 was mainly due to the reactions among V(V) decomposition products, free catechol, and O2 in cell culture medium. As a result, the activity of 1 was less sensitive than that of 2 to the effects of hypoxic conditions that are characteristic of solid tumors and to the presence of apo-transferrin that acts as a scavenger of V(V/IV) decomposition products in blood serum. In summary, complex 1, but not 2, is a suitable candidate for further development as an anticancer drug delivered via intratumoral injections. These results demonstrate the importance of fine-tuning the ligand properties for the optimization of biological activities of metal complexes.

Cascade strategy for glucose oxidase-based synergistic cancer therapy using nanomaterials

Nanomaterial-based cancer therapy faces significant limitations due to the complex nature of the tumor microenvironment (TME). Starvation therapy is an emerging therapeutic approach that targets tumor cell metabolism using glucose oxidase (GOx). Importantly, it can provide a material or environmental foundation for other diverse therapeutic methods by manipulating the properties of the TME, such as acidity, hydrogen peroxide (H2O2) levels, and hypoxia degree. In recent years, this cascade strategy has been extensively applied in nanoplatforms for ongoing synergetic therapy and still holds undeniable potential. However, only a few review articles comprehensively elucidate the rational designs of nanoplatforms for synergetic therapeutic regimens revolving around the conception of the cascade strategy. Therefore, this review focuses on innovative cascade strategies for GOx-based synergetic therapy from representative paradigms to state-of-the-art reports to provide an instructive, comprehensive, and insightful reference for readers. Thereafter, we discuss the remaining challenges and offer a critical perspective on the further advancement of GOx-facilitated cancer treatment toward clinical translation.

Carbon Ions for Hypoxic Tumors: Are We Making the Most of Them?

Hypoxia, which is associated with abnormal vessel growth, is a characteristic feature of many solid tumors that increases their metastatic potential and resistance to radiotherapy. Carbon-ion radiation therapy, either alone or in combination with other treatments, is one of the most promising treatments for hypoxic tumors because the oxygen enhancement ratio decreases with increasing particle LET. Nevertheless, current clinical practice does not yet fully benefit from the use of carbon ions to tackle hypoxia. Here, we provide an overview of the existing experimental and clinical evidence supporting the efficacy of C-ion radiotherapy in overcoming hypoxia-induced radioresistance, followed by a discussion of the strategies proposed to enhance it, including different approaches to maximize LET in the tumors.

Hypoxia signaling in hepatocellular carcinoma: Challenges and therapeutic opportunities

Hepatocellular carcinoma (HCC) is one of the most common cancers with a relatively high cancer-related mortality. The uncontrolled proliferation of HCC consumes a significant amount of oxygen, causing the development of a hypoxic tumor microenvironment (TME). Hypoxia-inducible factors (HIFs), crucial regulators in the TME, activate several cancer hallmarks leading to the hepatocarcinogenesis of HCC and resistance to current therapeutics. As such, HIFs and their signaling pathways have been explored as potential therapeutic targets for the future management of HCC. This review discusses the current understanding of the structure and function of HIFs and their complex relationship with the various cancer hallmarks. To address tumor hypoxia, this review provides an insight into the various potential novel therapeutic agents for managing HCC, such as hypoxia-activated prodrugs, HIF inhibitors, nanomaterials, antisense oligonucleotides, and natural compounds, that target HIFs/hypoxic signaling pathways in HCC. Because of HCC's relatively high incidence and mortality rates in the past decades, greater efforts should be put in place to explore novel therapeutic approaches to improve the outcome for HCC patients.

Mechanisms of HIF-driven immunosuppression in tumour microenvironment

Hypoxia arises due to insufficient oxygen delivery to rapidly proliferating tumour cells that outpace the available blood supply. It is a characteristic feature of most solid tumour microenvironments and plays a critical role in regulating anti-tumour immunity, enhancing tumoral heterogeneity, and promoting therapeutic resistance and poor clinical outcomes. Hypoxia-inducible factors (HIFs) are the major hypoxia-responsive transcription factors that are activated under low oxygenation conditions and have been identified to drive multifunctional roles in tumour immune evasion. The HIF signalling network serves as an attractive target for targeted therapeutic approaches. This review aims to provide a comprehensive overview of the most crucial mechanisms by which HIF controls the expression of immunosuppressive molecules and immune checkpoints, disrupts cancer immunogenicity, and induces immunotherapeutic resistance.

The Development of Nonthermal Plasma and Tirapazamine as a Novel Combination Therapy to Treat Melanoma In Situ

Although melanoma accounts for only 5.3% of skin cancer, it results in >75% of skin-cancer-related deaths. To avoid disfiguring surgeries on the head and neck associated with surgical excision, there is a clear unmet need for other strategies to selectively remove cutaneous melanoma lesions. Mohs surgery is the current treatment for cutaneous melanoma lesions and squamous and basal cell carcinoma. While Mohs surgery is an effective way to remove melanomas in situ, normal tissue is also excised to achieve histologically negative margins. This paper describes a novel combination therapy of nonthermal plasma (NTP) which emits a multitude of reactive oxygen species (ROS) and the injection of a pharmaceutical agent. We have shown that the effects of NTP are augmented by the DNA-damaging prodrug, tirapazamine (TPZ), which becomes a free radical only in conditions of hypoxemia, which is often enhanced in the tumor microenvironment. In this study, we demonstrate the efficacy of the combination therapy through experiments with B16-F10 and 1205 Lu metastatic melanoma cells both in vitro and in vivo. We also show the safety parameters of the therapy with no significant effects of the therapy when applied to porcine skin. We show the need for the intratumor delivery of TPZ in combination with the surface treatment of NTP and present a model of a medical device to deliver this combination therapy. The importance of functional gap junctions is indicated as a mechanism to promote the therapeutic effect. Collectively, the data support a novel therapeutic combination to treat melanoma and the development of a medical device to deliver the treatment in situ.

Genome editing and cancer therapy: handling the hypoxia-responsive pathway as a promising strategy

The precise characterization of oxygen-sensing pathways and the identification of pO2-regulated gene expression are both issues of critical importance. The O2-sensing system plays crucial roles in almost all the pivotal human processes, including the stem cell specification, the growth and development of tissues (such as embryogenesis), the modulation of intermediate metabolism (including the shift of the glucose metabolism from oxidative to anaerobic ATP production and vice versa), and the control of blood pressure. The solid cancer microenvironment is characterized by low oxygen levels and by the consequent activation of the hypoxia response that, in turn, allows a complex adaptive response characterized mainly by neoangiogenesis and metabolic reprogramming. Recently, incredible advances in molecular genetic methodologies allowed the genome editing with high efficiency and, above all, the precise identification of target cells/tissues. These new possibilities and the knowledge of the mechanisms of adaptation to hypoxia suggest the effective development of new therapeutic approaches based on the manipulation, targeting, and exploitation of the oxygen-sensor system molecular mechanisms.

Drug-Eluting Embolic Loaded with Tyrosine Kinase Inhibitor Targeted Therapies for Transarterial Chemoembolization in a VX2 Model

Drug-eluting embolic transarterial chemoembolization (DEE-TACE) improves the overall survival of hepatocellular carcinoma (HCC), but the agents used are not tailored to HCC. Our patented liposomal formulation enables the loading and elution of targeted therapies onto DEEs. This study aimed to establish the safety, feasibility, and pharmacokinetics of sorafenib or regorafenib DEE-TACE in a VX2 model. DEE-TACE was performed in VX2 hepatic tumors in a selective manner until stasis using liposomal sorafenib- or regorafenib-loaded DEEs. The animals were euthanized at 1, 24, and 72 h timepoints post embolization. Blood samples were taken for pharmacokinetics at 5 and 20 min and at 1, 24, and 72 h. Measurements of sorafenib or regorafenib were performed in all tissue samples on explanted hepatic tissue using the same mass spectrometry method. Histopathological examinations were carried out on tumor tissues and non-embolized hepatic specimens. DEE-TACE was performed on 23 rabbits. The plasma concentrations of sorafenib and regorafenib were statistically significantly several folds lower than the embolized liver at all examined timepoints. This study demonstrates the feasibility of loading sorafenib or regorafenib onto commercially available DEEs for use in TACE. The drugs eluted locally without release into systemic circulation.

Application of tumor pH/hypoxia-responsive nanoparticles for combined photodynamic therapy and hypoxia-activated chemotherapy

Introduction: Cancer selectivity, including targeted internalization and accelerated drug release in tumor cells, remains a major challenge for designing novel stimuli-responsive nanocarriers to promote therapeutic efficacy. The hypoxic microenvironment created by photodynamic therapy (PDT) is believed to play a critical role in chemoresistance. Methods: We construct dual-responsive carriers (^DANP_CT) that encapsulate the photosensitizer chlorin e6 (Ce6) and hypoxia-activated prodrug tirapazamine (TPZ) to enable efficient PDT and PDT-boosted hypoxia-activated chemotherapy. Results and discussion: Due to TAT masking, ^DANP_CT prolonged payload circulation in the bloodstream, and selective tumor cell uptake occurred via acidity-triggered TAT presentation. PDT was performed with a spatially controlled 660-nm laser to enable precise cell killing and exacerbate hypoxia. Hypoxia-responsive conversion of the hydrophobic NI moiety led to the disassembly of ^DANP_CT, facilitating TPZ release. TPZ was reduced to cytotoxic radicals under hypoxic conditions, contributing to the chemotherapeutic cascade. This work offers a sophisticated strategy for programmed chemo-PDT.

Toward nanotechnology-enabled application of bilirubin in the treatment and diagnosis of various civilization diseases

Bilirubin, an open chain tetrapyrrole, has powerful antioxidant, anti-inflammatory, immuno-suppressive, metabolic-modulating and anti-proliferative activities. Bilirubin is a natural molecule that is produced and metabolized within the human body, making it highly biocompatible and well suited for clinical use. However, the use of bilirubin has been hampered by its poor water solubility and instability. With advanced construction strategies, bilirubin-derived nanoparticles (BRNPs) have not only overcome the disadvantages of bilirubin but also enhanced its therapeutic effects by targeting damaged tissues, passing through physiological barriers, and ensuring controlled sustained release. We review the mechanisms underlying the biological activities of bilirubin, BRNP preparation strategies and BRNP applications in various disease models. Based on their superior performance, BRNPs require further exploration of their efficacy, biodistribution and long-term biosafety in nonhuman primate models that recapitulate human disease to promote their clinical translation.

Targeting Hypoxia-Inducible Factor-1α for the Management of Hepatocellular Carcinoma

Hypoxia-inducible factor 1 alpha (HIF-1α) is a transcription factor that regulates the cellular response to hypoxia and is upregulated in all types of solid tumor, leading to tumor angiogenesis, growth, and resistance to therapy. Hepatocellular carcinoma (HCC) is a highly vascular tumor, as well as a hypoxic tumor, due to the liver being a relatively hypoxic environment compared to other organs. Trans-arterial chemoembolization (TACE) and trans-arterial embolization (TAE) are locoregional therapies that are part of the treatment guidelines for HCC but can also exacerbate hypoxia in tumors, as seen with HIF-1α upregulation post-hepatic embolization. Hypoxia-activated prodrugs (HAPs) are a novel class of anticancer agent that are selectively activated under hypoxic conditions, potentially allowing for the targeted treatment of hypoxic HCC. Early studies targeting hypoxia show promising results; however, further research is needed to understand the effects of HAPs in combination with embolization in the treatment of HCC. This review aims to summarize current knowledge on the role of hypoxia and HIF-1α in HCC, as well as the potential of HAPs and liver-directed embolization.

PROTACs: Emerging Targeted Protein Degradation Approaches for Advanced Druggable Strategies

A potential therapeutic strategy to treat conditions brought on by the aberrant production of a disease-causing protein is emerging for targeted protein breakdown using the PROTACs technology. Few medications now in use are tiny, component-based and utilize occupancy-driven pharmacology (MOA), which inhibits protein function for a short period of time to temporarily alter it. By utilizing an event-driven MOA, the proteolysis-targeting chimeras (PROTACs) technology introduces a revolutionary tactic. Small-molecule-based heterobifunctional PROTACs hijack the ubiquitin-proteasome system to trigger the degradation of the target protein. The main challenge PROTAC's development facing now is to find potent, tissue- and cell-specific PROTAC compounds with favorable drug-likeness and standard safety measures. The ways to increase the efficacy and selectivity of PROTACs are the main focus of this review. In this review, we have highlighted the most important discoveries related to the degradation of proteins by PROTACs, new targeted approaches to boost proteolysis' effectiveness and development, and promising future directions in medicine.

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.

Hypoxia, a Targetable Culprit to Counter Pancreatic Cancer Resistance to Therapy

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer, and it is a disease of dismal prognosis. While immunotherapy has revolutionized the treatment of various solid tumors, it has achieved little success in PDAC. Hypoxia within the stroma-rich tumor microenvironment is associated with resistance to therapies and promotes angiogenesis, giving rise to a chaotic and leaky vasculature that is inefficient at shuttling oxygen and nutrients. Hypoxia and its downstream effectors have been implicated in immune resistance and could be contributing to the lack of response to immunotherapy experienced by patients with PDAC. Paradoxically, increasing evidence has shown hypoxia to augment genomic instability and mutagenesis in cancer, suggesting that hypoxic tumor cells could have increased production of neoantigens that can potentially enable their clearance by cytotoxic immune cells. Strategies aimed at relieving this condition have been on the rise, and one such approach opts for normalizing the tumor vasculature to reverse hypoxia and its downstream support of tumor pathogenesis. An important consideration for the successful implementation of such strategies in the clinic is that not all PDACs are equally hypoxic, therefore hypoxia-detection approaches should be integrated to enable optimal patient selection for achieving improved patient outcomes.

Spatial Transcriptomic Analysis of a Diverse Patient Cohort Reveals a Conserved Architecture in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive disease that disproportionately affects African American (AA) women. Limited targeted therapeutic options exist for patients with TNBC. Here, we employ spatial transcriptomics to interrogate tissue from a racially diverse TNBC cohort to comprehensively annotate the transcriptional states of spatially resolved cellular populations. A total of 38,706 spatial features from a cohort of 28 sections from 14 patients were analyzed. Intratumoral analysis of spatial features from individual sections revealed heterogeneous transcriptional substructures. However, integrated analysis of all samples resulted in nine transcriptionally distinct clusters that mapped across all individual sections. Furthermore, novel use of join count analysis demonstrated nonrandom directional spatial dependencies of the transcriptionally defined shared clusters, supporting a conserved spatio-transcriptional architecture in TNBC. These findings were substantiated in an independent validation cohort comprising 17,861 spatial features representing 15 samples from 8 patients. Stratification of samples by race revealed race-associated differences in hypoxic tumor content and regions of immune-rich infiltrate. Overall, this study combined spatial and functional molecular analyses to define the tumor architecture of TNBC, with potential implications in understanding TNBC disparities.

SIGNIFICANCE

Spatial transcriptomics profiling of a diverse cohort of triple-negative breast cancers and innovative informatics approaches reveal a conserved cellular architecture across cancers and identify proportional differences in tumor cell composition by race.

Prospects for hypoxia-based drug delivery platforms for the elimination of advanced metastatic tumors: From 3D modeling to clinical concepts

Hypoxia is a unique characteristic of the solid tumor microenvironment. Hypoxia contributes to multi-drug resistance, metastasis and cancer relapse through numerous molecular pathways, but at the same time provides an opportunity for the development of novel drugs or modalities specifically targeting hypoxic tumor regions. Given the high significance of tumor hypoxia in therapeutic results, we here discuss a variety of hypoxia-adopted strategies, and their potential and utility in the treatment of deep-seated hypoxic tumor cells. We discuss the merits and demerits of these approaches, as well as their combination with other approaches such as photodynamic therapy. We also survey the currently available 3D hypoxia modeling systems, in particular organoid-based microfluidics. Finally, we discuss the potential and the current status of preclinical tumor hypoxia approaches in clinical trials for advanced cancer. We believe that multi-modal imaging and therapeutic hypoxia adopted drug delivery platforms could provide better efficacy and safety profiles, and more importantly personalized therapy. Determining the hypoxia status of tumors could offer a second chance for the clinical translation of hypoxia-based agents, such as hypoxia activated prodrugs (HAPs) from bench to bedside.

Targeting DNA topoisomerase IIα (TOP2A) in the hypoxic tumour microenvironment using unidirectional hypoxia-activated prodrugs (uHAPs)

The hypoxic tumour microenvironment (hTME), arising from inadequate and chaotic vascularity, can present a major obstacle for the treatment of solid tumours. Hypoxic tumour cells compromise responses to treatment since they can generate resistance to radiotherapy, chemotherapy and immunotherapy. The hTME impairs the delivery of a range of anti-cancer drugs, creates routes for metastasis and exerts selection pressures for aggressive phenotypes; these changes potentially occur within an immunosuppressed environment. Therapeutic strategies aimed at the hTME include targeting the molecular changes associated with hypoxia. An alternative approach is to exploit the prevailing lack of oxygen as a principle for the selective activation of prodrugs to target cellular components within the hTME. This review focuses on the design concepts and rationale for the use of unidirectional Hypoxia-Activated Prodrugs (uHAPs) to target the hTME as exemplified by the uHAPs AQ4N and OCT1002. These agents undergo irreversible reduction in a hypoxic environment to active forms that target DNA topoisomerase IIα (TOP2A). This nuclear enzyme is essential for cell division and is a recognised chemotherapeutic target. An activated uHAP interacts with the enzyme-DNA complex to induce DNA damage, cell cycle arrest and tumour cell death. uHAPs are designed to overcome the shortcomings of conventional HAPs and offer unique pharmacodynamic properties for effective targeting of TOP2A in the hTME. uHAP therapy in combination with standard of care treatments has the potential to enhance outcomes by co-addressing the therapeutic challenge presented by the hTME.

Bone Marrow Microenvironment as a Source of New Drug Targets for the Treatment of Acute Myeloid Leukaemia

Acute myeloid leukaemia (AML) is a heterogeneous disease with one of the worst survival rates of all cancers. The bone marrow microenvironment is increasingly being recognised as an important mediator of AML chemoresistance and relapse, supporting leukaemia stem cell survival through interactions among stromal, haematopoietic progenitor and leukaemic cells. Traditional therapies targeting leukaemic cells have failed to improve long term survival rates, and as such, the bone marrow niche has become a promising new source of potential therapeutic targets, particularly for relapsed and refractory AML. This review briefly discusses the role of the bone marrow microenvironment in AML development and progression, and as a source of novel therapeutic targets for AML. The main focus of this review is on drugs that modulate/target this bone marrow microenvironment and have been examined in in vivo models or clinically.

Visualization of hypoxia in cancer cells from effusions in animals and cancer patients

Objective

Tumor hypoxia is frequently observed in primary solid malignancies, but the hypoxic status of tumor cells floating in body cavity effusions is largely unknown, especially in patients. This study was to observe the hypoxia and proliferation status of cancer cells floating in effusions in mice and patients.

Methods

The distribution of hypoxia in cancer cells floating in ascites was first studied in nude mice. Hypoxia was detected by immunofluorescent visualization of pimonidazole and GLUT-1. For cancer patients, we retrospectively collected 21 ascites and 7 pleural effusion sample blocks of cancer patients, which were confirmed to contain tumor cells. Immunohistochemistry was performed to detect the expression of endogenous hypoxic markers HIF-1α and GLUT-1, proliferation index Ki-67. ¹⁸F-FDG PET/CT was performed to detect the glucose metabolism status of tumor cells in effusions.

Results

The tumor cells collected from ascites were positive for pimonidazole and GLUT-1, which suggesting that the cancer cells floating in ascites were hypoxic. Patterns of tumor hypoxia in human patients are similar to those observed in animal. HIF-1α and GLUT-1 were expressed by tumor cells in nearly all 28 cytological cases. For Ki-67 index, ascites tumor cells had a relatively low expression level compared with their corresponding primary or its metastatic lesions. Tumor cells in effusions showed high ¹⁸F-FDG uptake indicated the enhanced activity of glucose metabolism.

Conclusion

Tumor cells in body cavity effusions, as a unique subgroup of tumor, are in a state of hypoxia and low proliferation, which would be one of the driven causes of chemo-radiotherapy resistance. Novel therapeutic interventions are urgently needed to overcome tumor hypoxia.

Tumor microenvironment: barrier or opportunity towards effective cancer therapy

Tumor microenvironment (TME) is a specialized ecosystem of host components, designed by tumor cells for successful development and metastasis of tumor. With the advent of 3D culture and advanced bioinformatic methodologies, it is now possible to study TME’s individual components and their interplay at higher resolution. Deeper understanding of the immune cell’s diversity, stromal constituents, repertoire profiling, neoantigen prediction of TMEs has provided the opportunity to explore the spatial and temporal regulation of immune therapeutic interventions. The variation of TME composition among patients plays an important role in determining responders and non-responders towards cancer immunotherapy. Therefore, there could be a possibility of reprogramming of TME components to overcome the widely prevailing issue of immunotherapeutic resistance. The focus of the present review is to understand the complexity of TME and comprehending future perspective of its components as potential therapeutic targets. The later part of the review describes the sophisticated 3D models emerging as valuable means to study TME components and an extensive account of advanced bioinformatic tools to profile TME components and predict neoantigens. Overall, this review provides a comprehensive account of the current knowledge available to target TME.

Hypoxia signaling: Challenges and opportunities for cancer therapy

Hypoxia is arguably the first recognized cancer microenvironment hallmark and affects virtually all cellular populations present in tumors. During the past decades the complex adaptive cellular responses to oxygen deprivation have been largely elucidated, raising hope for new anti cancer agents. Despite undeniable preclinical progress, therapeutic targeting of tumor hypoxia is yet to transition from bench to bedside. This review focuses on new pharmacological agents that exploit tumor hypoxia or interfere with hypoxia signaling and discusses strategies to maximize their therapeutic impact.

Controversial Role of Transferrin in the Transport of Ruthenium Anticancer Drugs

Ruthenium complexes are at the forefront of developments in metal-based anticancer drugs, but many questions remain open regarding their reactivity in biological media, including the role of transferrin (Tf) in their transport and cellular uptake. A well-known anticancer drug, KP1019 ((IndH)[Ru^IIICl₄(Ind)₂], where Ind = indazole) and a reference complex, [Ru^III(nta)₂]^3- (nta = nitrilotriacetato(3-)) interacted differently with human apoTf, monoFeTf, or Fe₂Tf. These reactions were studied by biolayer interferometry (BLI) measurements of Ru-Fe-Tf binding to recombinant human transferrin receptor 1 (TfR1) in conjunction with UV-vis spectroscopy and particle size analysis. Cellular Ru uptake in human hepatoma (HepG2) cells was measured under the conditions of the BLI assays. The mode of Tf binding and cellular Ru uptake were critically dependent on the nature of Ru complex, availability of Fe(III) binding sites of Tf, and the presence of proteins that competed for metal binding, particularly serum albumin. Cellular uptake of KP1019 was not Tf-mediated and occurred mostly by passive diffusion, which may also be suitable for treatments of inoperable cancers by intratumoral injections. High cellular Ru uptake from a combination of [Ru^III(nta)₂]^3- and Fe₂Tf in the absence of significant Ru-Tf binding was likely to be due to trapping of Ru(III) species into the endosome during TfR1-mediated endocytosis of Fe₂Tf.

Novel Design Strategies to Enhance the Efficiency of Proteolysis Targeting Chimeras

Despite the success of drug discovery over the past decades, many potential drug targets still remain intractable for small molecule modulation. The development of proteolysis targeting chimeras (PROTACs) that trigger degradation of the target proteins provides a conceptually novel approach to address drug targets that remained previously elusive. Currently, the main challenge of PROTAC development is the identification of efficient, tissue- and cell-selective PROTAC molecules with good drug-likeness and favorable safety profiles. This review focuses on strategies to enhance the effectiveness and selectivity of PROTACs. We provide a comprehensive summary of recently reported PROTAC design strategies and discuss the advantages and disadvantages of these strategies. Future perspectives for PROTAC design will also be discussed.

Electrochemical Detection of a Novel Pt(IV) Prodrug with the Metronidazole Axial Ligand in the Hypoxic Area

We report herein a Pt(IV) prodrug with metronidazole in axial positions Pt-Mnz. The nitroaromatic axial ligand was conjugated with a cisplatin scaffold to irreversibly reduce under hypoxic conditions, thereby retaining the Pt(IV) prodrug in the area of hypoxia. X-ray near-edge adsorption spectroscopy (XANES) on dried drug-preincubated tumor cell samples revealed a gradual release of cisplatin from the Pt-Mnz prodrug instead of rapid intracellular degradation. The ability of the prodrug to penetrate into three-dimensional (3D) spheroid cellular cultures was evaluated by a novel electrochemical assay via a platinum-coated carbon nanoelectrode, capable of single-cell measurements. Using a unique technique of electrochemical measurements in single tumor spheroids, we were able to both detect the real-time response of the axial ligand to hypoxia and establish the depth of penetration of the drug into the tumor model.

The measurement and modification of hypoxia in colorectal cancer: overlooked but not forgotten

Tumour hypoxia is the inevitable consequence of a tumour's rapid growth and disorganized, inefficient vasculature. The compensatory mechanisms employed by tumours, and indeed the absence of oxygen itself, hinder the ability of all treatment modalities. The clinical consequence is poorer overall survival, disease-free survival, and locoregional control. Recognizing this, clinicians have been attenuating the effect of hypoxia, primarily with hypoxic modification or with hypoxia-activated pro-drugs, and notable success has been demonstrated. However, in the case of colorectal cancer (CRC), there is a general paucity of knowledge and evidence surrounding the measurement and modification of hypoxia, and this is possibly due to the comparative inaccessibility of such tumours. We specifically review the role of hypoxia in CRC and focus on the current evidence for the existence of hypoxia in CRC, the majority of which originates from indirect positron emission topography imaging with hypoxia selective radiotracers; the evidence correlating CRC hypoxia with poorer oncological outcome, which is largely based on the measurement of hypoxia inducible factor in correlation with clinical outcome; the evidence of hypoxic modification in CRC, of which no direct evidence exists, but is reflected in a number of indirect markers; the prognostic and monitoring implications of accurate CRC hypoxia quantification and its potential in the field of precision oncology; and the present and future imaging tools and technologies being developed for the measurement of CRC hypoxia, including the use of blood-oxygen-level-dependent magnetic resonance imaging and diffuse reflectance spectroscopy.

Effect of lncRNA00511 on Non-Small Cell Lung Cancer by Regulating miR-29b-3p

This study assessed the effect of LINC00511 on NSCLC cells through regulating miR-29b-3p/DRAM1 axis. LINC00511 expression in NSCLC tissue and para-carcinoma tissue was analyzed and its correlation with TNM stage was assessed. Lung carcinoma cells as A549 cells were cultivated in vitro and transfected with LINC00511 siRNA or plasmid with DRAM1 overexpression followed by analysis of LINC00511 and miR-184 expression by RT-PCR, cell proliferation and invasion, Bcl-2, Bax and DRAM1 expression by Western Blot. LINC00511 was significantly upregulated in NSCLC tissue and positively correlated with the TNM staging. However, miR-29b-3p was significantly downregulated in NSCLC tissue. The miR-29b-3p was a target of LINC00511. The DRAM1 was a target of miR-29b-3p. Downregulation of LINC00511 restrained proliferation and invasion of A549 cells and promoted cell apoptosis. The development of NSCLC could be prompted by increasing the presentation of LINC00511 through increasing presentation of DRAM1 and being targeted with miR-29b-3p. It could be restrained through reducing the presentation of LINC00511.

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.

Significance of Specific Oxidoreductases in the Design of Hypoxia-Activated Prodrugs and Fluorescent Turn Off–On Probes for Hypoxia Imaging

Simple Summary

Hypoxia-activated prodrugs (HAPs), selectively reduced by specific oxidoreductases under hypoxic conditions, form cytotoxic agents damaging the local cancer cells. On the basis of the reported clinical data concerning several HAPs, one can draw conclusions regarding their preclinical attractiveness and, regrettably, the low efficacy of Phase III clinical trials. Clinical failure may be explained, inter alia, by the lack of screening of patients on the basis of tumor hypoxia and low availability of specific oxidoreductases involved in HAP activation. There is surprisingly little information on the quantification of these enzymes in cells or tissues, compared to the advanced research associated with the use of HAPs. Our knowledge about the expression and activity of these enzymes in various cancer cell lines under hypoxic conditions is inadequate. Only in a few cases were researchers able to demonstrate the differences in the expression or activity of selected oxidoreductases, depending on the oxygen concentration. Additionally, it was cell line dependent. More systematic studies are required. The optical probes, based on turning on the fluorescence emission upon irreversible reduction catalyzed by the overexpressed oxidoreductases, can be helpful in this type of research. Ultimately, such sensors can estimate both the oxidoreductase activity and the degree of oxygenation in one step. To achieve this goal, their response must be correlated with the expression or activity of enzymes potentially involved in turning on their emissions, as determined by biochemical methods. In conclusion, the incorporation of biomarkers to identify hypoxia is a prerequisite for successful HAP therapies. However, it is equally important to assess the level of specific oxidoreductases required for their activation.

Abstract

Hypoxia is one of the hallmarks of the tumor microenvironment and can be used in the design of targeted therapies. Cellular adaptation to hypoxic stress is regulated by hypoxia-inducible factor 1 (HIF-1). Hypoxia is responsible for the modification of cellular metabolism that can result in the development of more aggressive tumor phenotypes. Reduced oxygen concentration in hypoxic tumor cells leads to an increase in oxidoreductase activity that, in turn, leads to the activation of hypoxia-activated prodrugs (HAPs). The same conditions can convert a non-fluorescent compound into a fluorescent one (fluorescent turn off–on probes), and such probes can be designed to specifically image hypoxic cancer cells. This review focuses on the current knowledge about the expression and activity of oxidoreductases, which are relevant in the activation of HAPs and fluorescent imaging probes. The current clinical status of HAPs, their limitations, and ways to improve their efficacy are briefly discussed. The fluorescence probes triggered by reduction with specific oxidoreductase are briefly presented, with particular emphasis placed on those for which the correlation between the signal and enzyme expression determined with biochemical methods is achievable.

Improving Tirapazamine (TPZ) to Target and Eradicate Hypoxia Tumors by Gold Nanoparticle Carriers

Tumor hypoxia is a hallmark of solid tumors and emerged as the therapeutic target for cancer treatments, such as a prodrug Tirapazamine (TPZ) activated in hypoxia. To increase tumor accumulation, gold nanoparticles (GNPs) were selected to conjugate with TPZ. In this study, we successfully formulated and assessed the biochemical and therapeutic roles of the conjugated gold nanoparticles–Tirapazamine (GNPs–TPZ) on therapeutic assessments of MKN45-induced xenograft animal model. The results indicated that GNPs–TPZ was a potential nanomedicine for selectively targeting hypoxia tumors coupled with decreased side effects on healthy tissue or organs. TPZ significantly reduced cell viability of hypoxic gastric cancer MKN45 cells, but not in cells incubated in normoxia condition. For improving tumor targeting efficiency, furthermore, the GNPs drug carrier was conjugated to TPZ via biding mediator bovine serum albumin (BSA), and we demonstrated that this conjugated GNPs–TPZ retained the unique characteristics of hypoxic toxin and possessed the adequate feature of systemic bio-distributions in animals. GNPs–TPZ nanoparticles revealed their superior affinity to hypoxia tumors in the MKN45 xenograft. Moreover, GNPs–TPZ treatments did not significantly alter the biochemical parameters of blood samples acquired from animals. Taken together, TPZ, a prodrug activated by hypoxia, was conjugated with GNPs, whereas BSA severed as an excellent binding agent for preparing the conjugated GNPs–TPZ nanomedicines. We demonstrated that GNPs–TPZ enhanced tumor targeting, resulting in higher therapeutic efficacy compared to TPZ. We suggest that it may sever as an adjuvant treatment or combined therapy with other chemotherapeutics for the treatment of cancer patients in the future.

Monitoring and modulation of the tumor microenvironment for enhanced cancer modeling

Cancer treatments utilizing biologic or cytotoxic drugs compose the frontline of therapy, and though gains in treatment efficacy have been persistent in recent decades, much work remains in understanding cancer progression and treatment. Compounding this situation is the low rate of success when translating preclinical drug candidates to the clinic, which raises costs and development timelines. This underperformance is due in part to the poor recapitulation of the tumor microenvironment, a critical component of cancer biology, in cancer model systems. New technologies capable of both accurately observing and manipulating the tumor microenvironment are needed to effectively model cancer response to treatment. In this review, conventional cancer models are summarized, and a primer on emerging techniques for monitoring and modulating the tumor microenvironment is presented and discussed.

Targeting HIF-2α in the Tumor Microenvironment: Redefining the Role of HIF-2α for Solid Cancer Therapy

Inadequate oxygen supply, or hypoxia, is characteristic of the tumor microenvironment and correlates with poor prognosis and therapeutic resistance. Hypoxia leads to the activation of the hypoxia-inducible factor (HIF) signaling pathway and stabilization of the HIF-α subunit, driving tumor progression. The homologous alpha subunits, HIF-1α and HIF-2α, are responsible for mediating the transcription of a multitude of critical proteins that control proliferation, angiogenic signaling, metastasis, and other oncogenic factors, both differentially and sequentially regulating the hypoxic response. Post-translational modifications of HIF play a central role in its behavior as a mediator of transcription, as well as the temporal transition from HIF-1α to HIF-2α that occurs in response to chronic hypoxia. While it is evident that HIF-α is highly dynamic, HIF-2α remains vastly under-considered. HIF-2α can intensify the behaviors of the most aggressive tumors by adapting the cell to oxidative stress, thereby promoting metastasis, tissue remodeling, angiogenesis, and upregulating cancer stem cell factors. The structure, function, hypoxic response, spatiotemporal dynamics, and roles in the progression and persistence of cancer of this HIF-2α molecule and its EPAS1 gene are highlighted in this review, alongside a discussion of current therapeutics and future directions.

A tumor microenvironment-responsive poly(amidoamine) dendrimer nanoplatform for hypoxia-responsive chemo/chemodynamic therapy

BACKGROUND

Chemodynamic therapy is a promising cancer treatment with specific therapeutic effect at tumor sites, as toxic hydroxyl radical (·OH) could only be generated by Fenton or Fenton-like reaction in the tumor microenvironment (TME) with low pH and high level of endogenous hydrogen peroxide. However, the low concentration of catalytic metal ions, excessive glutathione (GSH) and aggressive hypoxia at tumor site seriously restrict the curative outcomes of conventional chemodynamic therapy.

RESULTS

In this study, polyethylene glycol-phenylboronic acid (PEG-PBA)-modified generation 5 (G5) poly(amidoamine) (PAMAM) dendrimers were synthesized as a targeted nanocarrier to chelate Cu(II) and then encapsulate hypoxia-sensitive drug tirapazamine (TPZ) by the formation of hydrophobic Cu(II)/TPZ complex for hypoxia-enhanced chemo/chemodynamic therapy. The formed G5.NHAc-PEG-PBA@Cu(II)/TPZ (GPPCT) nanoplatform has good stability and hemocompatibility, and could release Cu(II) ions and TPZ quickly in weakly acidic tumor sites via pH-sensitive dissociation of Cu(II)/TPZ. In vitro experiments showed that the GPPCT nanoplatforms can efficiently target murine breast cancer cells (4T1) cells overexpressing sialic acid residues, and show a significantly enhanced inhibitory effect on hypoxic cells by the activation of TPZ. The excessive GSH in tumors could be depleted by the reduction of Cu(II) to Cu(I), and abundant of toxic ·OH would be generated in tumor cells by Fenton reaction for chemodynamic therapy. In vivo experiments demonstrated that the GPPCT nanoplatform could specifically accumulate at tumors, effectively inhibit the growth and metastasis of tumors by the combination of CDT and chemotherapy, and be metabolized with no systemic toxicity.

CONCLUSIONS

The targeted GPPCT nanoplatform may represent an effective model for the synergistic inhibition of different tumor types by hypoxia-enhanced chemo/chemodynamic therapy.

Leukemic Stem Cells: From Leukemic Niche Biology to Treatment Opportunities

Acute myeloid leukemia (AML) is one of the most common types of leukemia in adults. While complete remission can be obtained with intensive chemotherapy in young and fit patients, relapse is frequent and prognosis remains poor. Leukemic cells are thought to arise from a pool of leukemic stem cells (LSCs) which sit at the top of the hierarchy. Since their discovery, more than 30 years ago, LSCs have been a topic of intense research and their identification paved the way for cancer stem cell research. LSCs are defined by their ability to self-renew, to engraft into recipient mice and to give rise to leukemia. Compared to healthy hematopoietic stem cells (HSCs), LSCs display specific mutations, epigenetic modifications, and a specific metabolic profile. LSCs are usually considered resistant to chemotherapy and are therefore the drivers of relapse. Similar to their HSC counterpart, LSCs reside in a highly specialized microenvironment referred to as the “niche”. Bidirectional interactions between leukemic cells and the microenvironment favor leukemic progression at the expense of healthy hematopoiesis. Within the niche, LSCs are thought to be protected from genotoxic insults. Improvement in our understanding of LSC gene expression profile and phenotype has led to the development of prognosis signatures and the identification of potential therapeutic targets. In this review, we will discuss LSC biology in the context of their specific microenvironment and how a better understanding of LSC niche biology could pave the way for new therapies that target AML.