Targeting hypoxic tumour cells to overcome metastasis

Enhancing tumor immunotherapy via photodynamic therapy with a cascade reaction of reactive oxygen species and sustaining nutrient supply

Photo-immunotherapy is a promising strategy for the treatment of malignancies; however, its efficacy is often limited by the low tumor immunogenicity and immunosuppressive tumor microenvironment (TME). TME is typically deficient in L-arginine (L-Arg), which negatively impacts T cell survival and function. To address this issue, we developed a novel drug delivery system based on the multi-vesicular liposomes (MVLs) loaded with photosensitizer indocyanine green (ICG) and L-Arg (R), named R-ICG@MVLs. Under near-infrared (NIR) light irradiation, the PDT-mediated cascade reaction of reactive oxygen species (ROS) could oxidize a portion of L-Arg to generate NO, thereby inducing immunogenic tumor cell death (ITCD) and stimulating anti-tumor immune responses, including antigen-presenting cells (APCs) recruitment and T cells activation. Subsequently, R-ICG@MVLs continued to release L-Arg, which improved the immunosuppressive TME, providing nutritional support for the tumor-infiltrating T cells and thus enhancing their anti-tumor efficacy. Additionally, the photo-thermal effect of ICG could accelerate the membrane rearrangement of R-ICG@MVLs and produce multiple drug-loaded nanovesicles, thus enabling the NIR-controlled accelerated drug release. The formation of drug-loaded nanovesicles led to deeper penetration and widened the range of ICD and TME improvement, achieving a "shrapnel effect". In conclusion, our strategy realized the dual effects of immune activation and nutrition support, which might provide a clinically applicable reference for tumor immunotherapy.

MFN2 deficiency promotes cardiac response to hypobaric hypoxia by reprogramming cardiomyocyte metabolism

AIM

Under hypobaric hypoxia (HH), the heart triggers various defense mechanisms including metabolic remodeling against lack of oxygen. Mitofusin 2 (MFN2), located at the mitochondrial outer membrane, is closely involved in the regulation of mitochondrial fusion and cell metabolism. To date, however, the role of MFN2 in cardiac response to HH has not been explored.

METHODS

Loss- and gain-of-function approaches were used to investigate the role of MFN2 in cardiac response to HH. In vitro, the function of MFN2 in the contraction of primary neonatal rat cardiomyocytes under hypoxia was examined. Non-targeted metabolomics and mitochondrial respiration analyses, as well as functional experiments were performed to explore underlying molecular mechanisms.

RESULTS

Our data demonstrated that, following 4 weeks of HH, cardiac-specific MFN2 knockout (MFN2 cKO) mice exhibited significantly better cardiac function than control mice. Moreover, restoring the expression of MFN2 clearly inhibited the cardiac response to HH in MFN2 cKO mice. Importantly, MFN2 knockout significantly improved cardiac metabolic reprogramming during HH, resulting in reduced capacity for fatty acid oxidation (FAO) and oxidative phosphorylation, and increased glycolysis and ATP production. In vitro data showed that down-regulation of MFN2 promoted cardiomyocyte contractility under hypoxia. Interestingly, increased FAO through palmitate treatment decreased contractility of cardiomyocyte with MFN2 knockdown under hypoxia. Furthermore, treatment with mdivi-1, an inhibitor of mitochondrial fission, disrupted HH-induced metabolic reprogramming and subsequently promoted cardiac dysfunction in MFN2-knockout hearts.

CONCLUSION

Our findings provide the first evidence that down-regulation of MFN2 preserves cardiac function in chronic HH by promoting cardiac metabolic reprogramming.

Chronic Obstructive Pulmonary Disease Is Associated with Worse Oncologic Outcomes in Early-Stage Resected Pancreatic and Periampullary Cancers

Pancreatic ductal adenocarcinoma (PDAC) is the 3rd leading cause of cancer mortality in the United States. Hypoxic and hypercapnic tumor microenvironments have been suggested to promote tumor aggressiveness. The objective of this study was to evaluate the association between chronic obstructive pulmonary disease (COPD) and oncologic survival outcomes in patients with early-stage PDAC and periampullary cancers. In this case-control study, patients who underwent a pancreaticoduodenectomy during 2014-2021 were assessed. Demographic, perioperative, histologic, and oncologic data were collected. A total of 503 PDAC and periampullary adenocarcinoma patients were identified, 257 males and 246 females, with a mean age of 68.1 (±9.8) years and a mean pre-operative BMI of 26.6 (±4.7) kg/m². Fifty-two percent of patients (N = 262) reported a history of smoking. A total of 42 patients (8.3%) had COPD. The average resected tumor size was 2.9 ± 1.4 cm and 65% of the specimens (N = 329) were positive for lymph-node involvement. Kaplan-Meier analysis showed that COPD was associated with worse overall and disease-specific survival (p < 0.05). Cox regression analysis showed COPD to be an independent prognostic factor (HR = 1.5, 95% CI 1.0-2.3, p = 0.039) along with margin status, lymphovascular invasion, and perineural invasion (p < 0.05 each). A 1:3 nearest neighbor propensity score matching was also employed and revealed COPD to be an independent risk factor for overall and disease-specific survival (OR 1.8 and OR 1.6, respectively; p < 0.05 each). These findings may support the rationale posed by in vitro laboratory studies, suggesting an important impact of hypoxic and hypercapnic tumor respiratory microenvironments in promoting therapy resistance in cancer.

Optimized Carbohydrate-Based Nanogel Formulation to Sensitize Hypoxic Tumors

Solid tumors are often poorly vascularized, which impairs oxygen supply and drug delivery to the cells. This often leads to genetic and translational adaptations that promote tumor progression, invasion, metastasis, and resistance to conventional chemo-/radiotherapy and immunotherapy. A hypoxia-directed nanosensitizer formulation of a hypoxia-activated prodrug (HAP) was developed by encapsulating iodoazomycin arabinofuranoside (IAZA), a 2-nitroimidazole nucleoside-based HAP, in a functionally modified carbohydrate-based nanogel, facilitating delivery and accrual selectively in the hypoxic head and neck and prostate cancer cells. Although IAZA has been reported as a clinically validated hypoxia diagnostic agent, recent studies have pointed to its promising hypoxia-selective anti-tumor properties, which make IAZA an excellent candidate for further exploration as a multimodal theranostic of hypoxic tumors. The nanogels are composed of a galactose-based shell with an inner core of thermoresponsive (di(ethylene glycol) methyl ethyl methacrylate) (DEGMA). Optimization of the nanogels led to high IAZA-loading capacity (≅80-88%) and a slow time-controlled release over 50 h. Furthermore, nanoIAZA (encapsulated IAZA) displayed superior in vitro hypoxia-selective cytotoxicity and radiosensitization in comparison to free IAZA in the head and neck (FaDu) and prostate (PC3) cancer cell lines. The acute systemic toxicity profile of the nanogel (NG1) was studied in immunocompromised mice, indicating no signs of toxicity. Additionally, growth inhibition of subcutaneous FaDu xenograft tumors was observed with nanoIAZA, demonstrating that this nanoformulation offers a significant improvement in tumor regression and overall survival compared to the control.

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.

Carbon Dot@MXene Nanozymes with Triple Enzyme-Mimic Activities for Mild NIR-II Photothermal-Amplified Nanocatalytic Therapy

Nanozymes have shown promising potential in disease treatment owing to the advantages of low-cost, facile fabrication, and high stability. However, the highly complex tumor microenvironment (TME) and inherent low catalytic activity severely restrict the clinical applications of nanozymes. Herein, a novel mild hyperthermia-enhanced nanocatalytic therapy platform based on Z-scheme heterojunction nanozymes by depositing N-doped carbon dots (CDs) onto Nb₂ C nanosheets is constructed. CD@Nb₂ C nanozymes not only display outstanding photothermal effects in the safe and efficient NIR-II window but also possess triple enzyme-mimic activities to obtain amplified ROS levels. The triple enzyme-mimic activities and NIR-II photothermal properties of CD nanozymes are enhanced by the construction of Z-scheme heterojunctions owing to the accelerated carrier transfer process. More importantly, the introduction of mild hyperthermia can further improve the peroxidase-mimic and catalase-mimic activities as well as the glGSH depletion abilities of CD@Nb₂ C nanozymes, thereby producing more ROS to efficiently inhibit tumor growth. The combined therapy effect of CD@Nb₂ C nanozymes through mild NIR-II photothermal-enhanced nanocatalytic therapy can achieve complete tumor eradication. This work highlights the efficient tumor therapy potential of heterojunction nanozymes.

Hypoxia signaling in cancer: Implications for therapeutic interventions

Hypoxia is a persistent physiological feature of many different solid tumors and a key driver of malignancy, and in recent years, it has been recognized as an important target for cancer therapy. Hypoxia occurs in the majority of solid tumors due to a poor vascular oxygen supply that is not sufficient to meet the needs of rapidly proliferating cancer cells. A hypoxic tumor microenvironment (TME) can reduce the effectiveness of other tumor therapies, such as radiotherapy, chemotherapy, and immunotherapy. In this review, we discuss the critical role of hypoxia in tumor development, including tumor metabolism, tumor immunity, and tumor angiogenesis. The treatment methods for hypoxic TME are summarized, including hypoxia-targeted therapy and improving oxygenation by alleviating tumor hypoxia itself. Hyperoxia therapy can be used to improve tissue oxygen partial pressure and relieve tumor hypoxia. We focus on the underlying mechanisms of hyperoxia and their impact on current cancer therapies and discuss the prospects of hyperoxia therapy in cancer treatment.

Transiently hypoxic tumour cell turnover and radiation sensitivity in human tumour xenografts

BACKGROUND

Solid tumour perfusion can be unstable, creating transiently hypoxic cells that can contribute to radiation resistance. We investigated the in vivo lifetime of transiently hypoxic tumour cells and chronically hypoxic tumour cells during tumour growth and following irradiation.

METHODS

Hypoxic cells in SiHa and WiDr human tumour xenografts were labelled using pimonidazole and EF5, and turnover was quantified as the loss of labelled cells over time. The perfusion-modifying drug pentoxifylline was used to reoxygenate transiently hypoxic cells prior to hypoxia marker administration or irradiation.

RESULTS

Chronically hypoxic cells constantly turnover in SiHa and WiDr tumours, with half-lives ranging from 42-82 h and significant numbers surviving >96 h. Transiently hypoxic cells constitute 26% of the total hypoxic cells in WiDr tumours. These transiently hypoxic cells survive at least 24 h, but then rapidly turnover with a half-life of 34 h and are undetectable 72 h after labelling. Transiently hypoxic cells are radiation-resistant, although vascular dysfunction induced by 10 Gy of ionising radiation preferentially kills transiently hypoxic cells.

CONCLUSIONS

Transiently hypoxic tumour cells survive up to 72 h in WiDr tumours and are radiation-resistant, although transiently hypoxic cells are sensitive to vascular dysfunction induced by high doses of ionising radiation.

Recent advances in ZnO-based photosensitizers: Synthesis, modification, and applications in photodynamic cancer therapy

Zinc oxide nanoparticles (ZnO NPs) are important semiconductor materials with interesting photo-responsive properties. During the past, ZnO-based NPs have received considerable attention for photodynamic therapy (PDT) due to their biocompatibility and excellent potential of generating tumor-killing reactive oxygen species (ROS) through gentle photodynamic activation. This article provides a comprehensive review of the recent developments and improvements in optical properties of ZnO NPs as photosensitizers for PDT. The optical properties of ZnO-based photosensitizers are significantly dependent on their charge separation, absorption potential, band gap engineering, and surface area, which can be adjusted/tuned by doping, compositing, and morphology control. Here, we first summarize the recent progress in the charge separation capability, absorption potential, band gap engineering, and surface area of nanosized ZnO-based photosensitizers. Then, morphology control that is closely related to their synthesis method is discussed. Following on, the state-of-art for the ZnO-based NPs in the treatment of hypoxic tumors is comprehensively reviewed. Finally, we provide some outlooks on common targeted therapy methods for more effective tumor killing, including the attachment of small molecules, antibodies, ligands molecules, and receptors to NPs which further improve their selective distribution and targeting, hence improving the therapeutic effectiveness. The current review may provide useful guidance for the researchers who are interested in this promising dynamic cancer treatment technology.

Multifunctional nanoprobes combined with radiotherapy and hypoxia-activated therapy synergistically improve antitumor efficacy

The developed nanoprobes show a high level of biocompatibility, efficient radiosensitisation and anti-tumour efficacy at the cellular and tissue level.

Recent advances in active targeting of nanomaterials for anticancer drug delivery

One of the challenges in cancer chemotherapy is the low target to non-target ratio of therapeutic agents which incur severe adverse effect on the healthy tissues. In this regard, nanomaterials have tremendous potential for impacting cancer therapy by altering the toxicity profile of the drug. Some of the striking advantages provided by the nanocarriers mediated targeted drug delivery are relatively high build-up of drug concentration at the tumor site, improved drug content in the formulation and enhanced colloidal stability. Further, nanocarriers with tumor-specific moieties can be targeted to the cancer cell through cell surface receptors, tumor antigens and tumor vasculatures with high affinity and accuracy. Moreover, it overcomes the bottleneck of aimless drug biodistribution, undesired toxicity and heavy dosage of administration. This review discusses the recent developments in active targeting of nanomaterials for anticancer drug delivery through cancer cell surface targeting, organelle specific targeting and tumor microenvironment targeting strategies. Special emphasis has been given towards cancer cell surface and organelle specific targeting as delivery of anticancer drugs through these routes have made paradigm change in cancer management. Further, the current challenges and future prospects of nanocarriers mediated active drug targeting are also demonstrated.

Large-Volume Hyperthermia for Safe and Cost-Effective Targeted Drug Delivery Using a Clinical Ultrasound-Guided Focused Ultrasound Device

Lyso-thermosensitive liposomes (LTSLs) are specifically designed to release chemotherapy agents under conditions of mild hyperthermia. Preclinical studies have indicated that magnetic resonance (MR)-guided focused ultrasound (FUS) systems can generate well-controlled volumetric hyperthermia using real-time thermometry. However, high-throughput clinical translation of these approaches for drug delivery is challenging, not least because of the significant cost overhead of MR guidance and the much larger volumes that need to be heated clinically. Using an ultrasound-guided extracorporeal clinical FUS device (Chongqing HAIFU, JC200) with thermistors in a non-perfused ex vivo bovine liver tissue model with ribs, we present an optimised strategy for rapidly inducing (5-15 min) and sustaining (>30 min) mild hyperthermia (ΔT <+4°C) in large tissue volumes (≤92 cm³). We describe successful clinical translation in a first-in-human clinical trial of targeted drug delivery of LTSLs (TARDOX: a phase I study to investigate drug release from thermosensitive liposomes in liver tumours), in which targeted tumour hyperthermia resulted in localised chemo-ablation. The heating strategy is potentially applicable to other indications and ultrasound-guided FUS devices.

Enhancing the efficacy of immunotherapy using radiotherapy

Recent clinical breakthroughs in cancer immunotherapy, especially with immune checkpoint blockade, offer great hope for cancer sufferers - and have greatly changed the landscape of cancer treatment. However, whilst many patients achieve clinical responses, others experience minimal benefit or do not respond to immune checkpoint blockade at all. Researchers are therefore exploring multimodal approaches by combining immune checkpoint blockade with conventional cancer therapies to enhance the efficacy of treatment. A growing body of evidence from both preclinical studies and clinical observations indicates that radiotherapy could be a powerful driver to augment the efficacy of immune checkpoint blockade, because of its ability to activate the antitumor immune response and potentially overcome resistance. In this review, we describe how radiotherapy induces DNA damage and apoptosis, generates immunogenic cell death and alters the characteristics of key immune cells in the tumor microenvironment. We also discuss recent preclinical work and clinical trials combining radiotherapy and immune checkpoint blockade in thoracic and other cancers. Finally, we discuss the scheduling of immune checkpoint blockade and radiotherapy, biomarkers predicting responses to combination therapy, and how these novel data may be translated into the clinic.

Recent progress of hypoxia-modulated multifunctional nanomedicines to enhance photodynamic therapy: opportunities, challenges, and future development

Hypoxia, a salient feature of most solid tumors, confers invasiveness and resistance to the tumor cells. Oxygen-consumption photodynamic therapy (PDT) suffers from the undesirable impediment of local hypoxia in tumors. Moreover, PDT could further worsen hypoxia. Therefore, developing effective strategies for manipulating hypoxia and improving the effectiveness of PDT has been a focus on antitumor treatment. In this review, the mechanism and relationship of tumor hypoxia and PDT are discussed. Moreover, we highlight recent trends in the field of nanomedicines to modulate hypoxia for enhancing PDT, such as oxygen supply systems, down-regulation of oxygen consumption and hypoxia utilization. Finally, the opportunities and challenges are put forward to facilitate the development and clinical transformation of PDT.

Perfluorocarbon nanodroplets stabilized with cisplatin-prodrug-constructed lipids enable efficient tumor oxygenation and chemo-radiotherapy of cancer

Concurrent chemo-radiotherapy has been widely applied for the treatment of a wide range of cancers, but its therapeutic efficacy against most solid tumors is severely impaired by their intrinsic hypoxic microenvironments. Utilizing the high oxygen loading capacity of perfluoro-15-crown-5-ether (PFCE), herein, we prepare PFCE nanodroplets with cisplatin prodrug (cisPt(iv)) conjugated phospholipids and other commercial lipids as the stabilizer to enable tumor targeted oxygen shuttling. The obtained PFCE@cisPt(iv)-Lip shows high physiological stability and efficient oxygen loading capacity. As vividly visualized under an in vivo photoacoustic imaging system, tumors on the mice with intravenous injection of such PFCE@cisPt(iv)-Lip show effective tumor oxygenation. Together with X-ray exposure, such PFCE@cisPt(iv)-Lip upon intravenous injection could induce severe DNA damage of cells, thereby remarkably suppressing the tumor growth and significantly prolonging their survival time without causing obvious toxic side effects. This work highlights PFCE@cisPt(iv)-Lip as an adjuvant nanomedicine for enhanced chemo-radiotherapy of tumors by attenuating hostile tumor hypoxia, indicating its promising potential for future clinical translation ascribed to its straightforward synthesis and notable tumor growth inhibition at a safe dose.

Advances in nanomaterials for treatment of hypoxic tumor

The hypoxic tumor microenvironment is characterized by disordered vasculature and rapid proliferation of tumors, resulting from tumor invasion, progression and metastasis. The hypoxic conditions restrict efficiency of tumor therapies, such as chemotherapy, radiotherapy, phototherapy and immunotherapy, leading to serious results of tumor recurrence and high mortality. Recently, research has concentrated on developing functional nanomaterials to treat hypoxic tumors. In this review, we categorize such nanomaterials into (i) nanomaterials that elevate oxygen levels in tumors for enhanced oxygen-dependent tumor therapy and (ii) nanomaterials with diminished oxygen dependence for hypoxic tumor therapy. To elevate oxygen levels in tumors, oxygen-carrying nanomaterials, oxygen-generating nanomaterials and oxygen-economizing nanomaterials can be used. To diminish oxygen dependence of nanomaterials for hypoxic tumor therapy, therapeutic gas-generating nanomaterials and radical-generating nanomaterials can be used. The biocompatibility and therapeutic efficacy of these nanomaterials are discussed.

High-throughput screening in multicellular spheroids for target discovery in the tumor microenvironment

INTRODUCTION

Solid tumors are highly influenced by a complex tumor microenvironment (TME) that cannot be modeled with conventional two-dimensional (2D) cell culture. In addition, monolayer culture conditions tend to induce undesirable molecular and phenotypic cellular changes. The discrepancy between in vitro and in vivo is an important factor accounting for the high failure rate in drug development. Three-dimensional (3D) multicellular tumor spheroids (MTS) more closely resemble the in vivo situation in avascularized tumors.

AREAS COVERED

This review describes the use of MTS for anti-cancer drug discovery, with an emphasis on high-throughput screening (HTS) compatible assays. In particular, we focus on how these assays can be used for target discovery in the context of the TME.

EXPERT OPINION

Arrayed MTS in microtiter plates are HTS compatible but remain more expensive and time consuming than their 2D culture counterpart. It is therefore imperative to use assays with multiplexed readouts, in order to maximize the information that can be gained with the screen. In this context, high-content screening allowing to uncover microenvironmental dependencies is the true added value of MTS-based screening compared to 2D culture-based screening. Hit translation in animal models will, however, be key to allow a broader use of MTS-based screening in industry.

Engineering Targeting Materials for Therapeutic Cancer Vaccines

Therapeutic cancer vaccines constitute a valuable tool to educate the immune system to fight tumors and prevent cancer relapse. Nevertheless, the number of cancer vaccines in the clinic remains very limited to date, highlighting the need for further technology development. Recently, cancer vaccines have been improved by the use of materials, which can strongly enhance their intrinsic properties and biodistribution profile. Moreover, vaccine efficacy and safety can be substantially modulated through selection of the site at which they are delivered, which fosters the engineering of materials capable of targeting cancer vaccines to specific relevant sites, such as within the tumor or within lymphoid organs, to further optimize their immunotherapeutic effects. In this review, we aim to give the reader an overview of principles and current strategies to engineer therapeutic cancer vaccines, with a particular focus on the use of site-specific targeting materials. We will first recall the goal of therapeutic cancer vaccination and the type of immune responses sought upon vaccination, before detailing key components of cancer vaccines. We will then present how materials can be engineered to enhance the vaccine's pharmacokinetic and pharmacodynamic properties. Finally, we will discuss the rationale for site-specific targeting of cancer vaccines and provide examples of current targeting technologies.

Tumor microenvironment targeted nanotherapeutics for cancer therapy and diagnosis: A review

Recent findings suggest that the cellular and extracellular materials surrounding the cancerous cells from an atypical tumor microenvironment (TM) play a pivotal role in the process of tumor initiation and progression. TM comprises an intricate system involving diverse cell types including endothelial cells, pericytes, smooth muscle cells, fibroblasts, various inflammatory cells, dendritic cells, and cancer stem cells (CSCs). The TM-forming cells dynamically interact with the cancerous cells through various signaling mechanisms and pathways. The existence of this dynamic cellular communication is responsible for creating an environment suitable for sustaining a reasonably high cellular proliferation. Presently, researchers are showing interest to use these TM conditions to mediate effective targeting measures for cancer therapy. The use of nanotherapeutics-based combination therapy; stimuli-responsive nanotherapeutics targeting acidic pH, hypoxic environment; and nanoparticle-induced hyperthermia are some of the approaches that are under intense investigation for cancer therapy. This review discusses TM and its role in cancer progression and crosstalk understanding, opportunities, and epigenetic modifications involved therein to materialize the capability of nanotherapeutics to target cancer by availing TM. STATEMENT OF SIGNIFICANCE: This article presents various recent reports, proof-of-concept studies, patents, and clinical trials on the concept of tumor microenvironment for mediating the cancer-specific delivery of nanotechnology-based systems bearing anticancer drug and diagnostics. We highlight the potential of tumor microenvironment; its role in disease progression, opportunities, challenges, and allied treatment strategies for effective cancer therapy by conceptual understanding of tumor microenvironment and epigenetic modifications involved. Specifically, nanoparticle-based approaches to target various processes related to tumor microenvironment (pH responsive, hypoxic environment responsive, targeting of specific cells involved in tumor microenvironment, etc.) are dealt in detail.

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.

Improving cancer therapy through the nanomaterials-assisted alleviation of hypoxia

Hypoxia, resulting from the imbalance between oxygen supply and consumption is a critical component of the tumor microenvironment. It has a paramount impact on cancer growth, metastasis and has long been known as a major obstacle for cancer therapy. However, none of the clinically approved anticancer therapeutics currently available for human use directly tackles this problem. Previous clinical trials of targeting tumor hypoxia with bioreductive prodrugs have failed to demonstrate satisfactory results. Therefore, new ideas are needed to overcome the hypoxia barrier. The method of modulating hypoxia to improve the therapeutic activity is of great interest but remains a considerable challenge. One of the emerging concepts is to supply or generate oxygen at the tumor site to increase the partial oxygen pressure and thereby reverse the hypoxia and its effects. In this review, we present an overview of the recent progress in the development of novel nanomaterials for the alleviation of hypoxic microenvironment. Two main strategies for hypoxia augmentation, i) direct delivery of O₂ into the tumor, and ii) in situ O₂ generations in the tumor microenvironment through different methods such as catalytic decomposition of endogenous hydrogen peroxide (H₂O₂) and light-triggered water splitting are discussed in detail. At present, these emerging nanomaterials are in their early phase and expected to grow rapidly in the coming years. Despite the promising start, there are several challenges needed to overcome for successful clinical translation.

A signature of hypoxia-related factors reveals functional dysregulation and robustly predicts clinical outcomes in stage I/II colorectal cancer patients

Background

The hypoxic tumor microenvironment accelerates the invasion and migration of colorectal cancer (CRC) cells. The aim of this study was to develop and validate a hypoxia gene signature for predicting the outcome in stage I/II CRC patients that have limited therapeutic options.

Methods

The hypoxic gene signature (HGS) was constructed using transcriptomic data of 309 CRC patients with complete clinical information from the CIT microarray dataset. A total of 1877 CRC patients with complete prognostic information in six independent datasets were divided into a training cohort and two validation cohorts. Univariate and multivariate analyses were conducted to evaluate the prognostic value of HGS.

Results

The HGS consisted of 14 genes, and demarcated the CRC patients into the high- and low-risk groups. In all three cohorts, patients in the high-risk group had significantly worse disease free survival (DFS) compared with those in the low risk group (training cohort—HR = 4.35, 95% CI 2.30–8.23, P < 0.001; TCGA cohort—HR = 2.14, 95% CI 1.09–4.21, P = 0.024; meta-validation cohort—HR = 1.91, 95% CI 1.08–3.39, P = 0.024). Compared to Oncotype DX, HGS showed superior predictive outcome in the training cohort (C-index, 0.80 vs 0.65) and the validation cohort (C-index, 0.70 vs 0.61). Pathway analysis of the high- and low-HGS groups showed significant differences in the expression of genes involved in mTROC1, G2-M, mitosis, oxidative phosphorylation, MYC and PI3K–AKT–mTOR pathways (P < 0.005).

Conclusion

Hypoxic gene signature is a satisfactory prognostic model for early stage CRC patients, and the exact biological mechanism needs to be validated further.

Exosomal miR-155 Derived from Hepatocellular Carcinoma Cells Under Hypoxia Promotes Angiogenesis in Endothelial Cells

PURPOSE

In this study, we aim to clarify whether exosomes secreted from hepatocellular carcinoma (HCC) cells under hypoxia affect angiogenesis in endothelial cells.

METHODS

Exosomes derived from human liver cancer cell lines were cultured under hypoxic or normoxic conditions for 24 h, isolated using ExoQuick-TC^®, and co-cultured with HUVECs to evaluate angiogenic activity. We also evaluated the expression of miR-155 in the exosomes from 40 patients with HCC.

RESULTS

Exosomes under hypoxia remarkably enhanced tube formation of HUVECs. Both cellular and exosomal miR-155 were significantly up-regulated under hypoxic conditions. Knockdown of miR-155 in HCC cells attenuated the promotion of tube formation by exosomes under hypoxia in HUVECs, and high expression of exosomal miR-155 in preoperative plasma was significantly correlated with early recurrence.

CONCLUSION

These results suggest that exosomes derived from HCC cells under hypoxia induce tube formation of HUVECs and that exosomal miR-155 may affect angiogenic activity in HCC.

Mitochondria-targeting cyclometalated iridium(iii) complexes for tumor hypoxic imaging and therapy

The organometallic anthraquinone iridium(iii) complexes display an efficient turn-on phosphorescence response to hypoxia. The complexes can induce cell apoptosis in HeLa cells via mitochondrial dysfunction and caspase-3 activation making them excellent candidates as theranostic agents for hypoxic cancer cells.

Tumor Microenvironment Targeted Nanotherapy

Recent developments in nanotechnology have brought new approaches to cancer diagnosis and therapy. While enhanced permeability and retention effect promotes nano-chemotherapeutics extravasation, the abnormal tumor vasculature, high interstitial pressure and dense stroma structure limit homogeneous intratumoral distribution of nano-chemotherapeutics and compromise their imaging and therapeutic effect. Moreover, heterogeneous distribution of nano-chemotherapeutics in non-tumor-stroma cells damages the non-tumor cells, and interferes with tumor-stroma crosstalk. This can lead not only to inhibition of tumor progression, but can also paradoxically induce acquired resistance and facilitate tumor cell proliferation and metastasis. Overall, the tumor microenvironment plays a vital role in regulating nano-chemotherapeutics distribution and their biological effects. In this review, the barriers in tumor microenvironment, its consequential effects on nano-chemotherapeutics, considerations to improve nano-chemotherapeutics delivery and combinatory strategies to overcome acquired resistance induced by tumor microenvironment have been summarized. The various strategies viz., nanotechnology based approach as well as ligand-mediated, redox-responsive, and enzyme-mediated based combinatorial nanoapproaches have been discussed in this review.

Liposomal Formulations to Modulate the Tumour Microenvironment and Antitumour Immune Response

Tumours are complex systems of genetically diverse malignant cells that proliferate in the presence of a heterogeneous microenvironment consisting of host derived microvasculature, stromal, and immune cells. The components of the tumour microenvironment (TME) communicate with each other and with cancer cells, to regulate cellular processes that can inhibit, as well as enhance, tumour growth. Therapeutic strategies have been developed to modulate the TME and cancer-associated immune response. However, modulating compounds are often insoluble (aqueous solubility of less than 1 mg/mL) and have suboptimal pharmacokinetics that prevent therapeutically relevant drug concentrations from reaching the appropriate sites within the tumour. Nanomedicines and, in particular, liposomal formulations of relevant drug candidates, define clinically meaningful drug delivery systems that have the potential to ensure that the right drug candidate is delivered to the right area within tumours at the right time. Following encapsulation in liposomes, drug candidates often display extended plasma half-lives, higher plasma concentrations and may accumulate directly in the tumour tissue. Liposomes can normalise the tumour blood vessel structure and enhance the immunogenicity of tumour cell death; relatively unrecognised impacts associated with using liposomal formulations. This review describes liposomal formulations that affect components of the TME. A focus is placed on formulations which are approved for use in the clinic. The concept of tumour immunogenicity, and how liposomes may enhance radiation and chemotherapy-induced immunogenic cell death (ICD), is discussed. Liposomes are currently an indispensable tool in the treatment of cancer, and their contribution to cancer therapy may gain even further importance by incorporating modulators of the TME and the cancer-associated immune response.

Novel microtubule inhibitor MPT0B098 inhibits hypoxia-induced epithelial-to-mesenchymal transition in head and neck squamous cell carcinoma

Background

Tumor hypoxia-induced epithelial–mesenchymal transition (EMT) is critical in promoting cancer metastasis. We recently discovered a novel microtubule inhibitor, MPT0B098, that employs a novel antitumor mechanism. It destabilizes hypoxia-inducible factor (HIF)-1α mRNA by blocking the function of human antigen R. Thus, we proposed that MPT0B098 modulates hypoxia-induced EMT.

Methods

In vitro IC₅₀ values were determined through the methylene blue dye assay. To investigate molecular events, reverse transcriptase-polymerase chain reaction, Western blotting, immunofluorescence staining, and wound healing assay were employed.

Results

MPT0B098 significantly inhibited HIF-1α expression, epithelial-to-mesenchymal morphology changes, and migratory ability in the human head and neck squamous cell carcinoma cell line OEC-M1. Furthermore, after MPT0B098 treatment, the expression of two mesenchymal markers, vimentin and N-cadherin, was downregulated under hypoxic conditions. Moreover, MPT0B098 suppressed hypoxia-induced EMT in part by inhibiting EMT-activating transcription factors, Twist and SNAI2/Slug. In addition, the inhibition of hypoxia-induced F-actin rearrangement and focal adhesion kinase phosphorylation may have contributed to suppression of EMT by MPT0B098in OEC-M1 cells. MPT0B098 significantly inhibited transforming growth factor(TGF)-β-induced phosphorylation of receptor-associated Smad2/3 by downregulating TGF-β mRNA and protein expression.

Conclusions

Taken together, this study provides a novel insight into the role of MPT0B098 in inhibiting hypoxia-induced EMT, suggesting its potential use for treating head and neck cancers.

Electronic supplementary material

The online version of this article (10.1186/s12929-018-0432-6) contains supplementary material, which is available to authorized users.

Tumor oxygenation and cancer therapy-then and now

In 2012, cancer affected 14.1 million people worldwide and was responsible for 8.2 million deaths. The disease predominantly affects aged populations and is one of the leading causes of death in most western countries. In tumors, the aggressive growth of the neoplastic cell population and associated overexpression of pro-angiogenic factors lead to the development of disorganized blood vessel networks that are structurally and functionally different from normal vasculature. A disorganized labyrinth of vessels that are immature, tortuous and hyperpermeable typifies tumor vasculature. Functionally, the ability of the tumor vasculature to deliver nutrients and remove waste products is severely diminished. A critical consequence of the inadequate vascular networks in solid tumors is the development of regions of hypoxia [low oxygen tensions typically defined as oxygen tensions (pO₂ values) < 10 mm Hg]. Tumor cells existing in such hypoxic environments have long been known to be resistant to anticancer therapy, display an aggressive phenotype, and promote tumor progression and dissemination. This review discusses the physiological basis of hypoxia, methods of detection, and strategies to overcome the resulting therapy resistance.

Oxygen Sensing with Perfluorocarbon-Loaded Ultraporous Mesostructured Silica Nanoparticles

Oxygen homeostasis is important in the regulation of biological function. Disease progression can be monitored by measuring oxygen levels, thus producing information for the design of therapeutic treatments. Noninvasive measurements of tissue oxygenation require the development of tools with minimal adverse effects and facile detection of features of interest. Fluorine magnetic resonance imaging (¹⁹F MRI) exploits the intrinsic properties of perfluorocarbon (PFC) liquids for anatomical imaging, cell tracking, and oxygen sensing. However, the highly hydrophobic and lipophobic properties of perfluorocarbons require the formation of emulsions for biological studies, though stabilizing these emulsions has been challenging. To enhance the stability and biological loading of perfluorocarbons, one option is to incorporate perfluorocarbon liquids into the internal space of biocompatible mesoporous silica nanoparticles. Here, we developed perfluorocarbon-loaded ultraporous mesostructured silica nanoparticles (PERFUMNs) as ¹⁹F MRI detectable oxygen-sensing probes. Ultraporous mesostructured silica nanoparticles (UMNs) have large internal cavities (average = 1.8 cm³ g^-1), facilitating an average 17% loading efficiency of PFCs, meeting the threshold fluorine concentrations needed for imaging studies. Perfluoro-15-crown-5-ether PERFUMNs have the highest equivalent nuclei per PFC molecule and a spin-lattice (T₁) relaxation-based oxygen sensitivity of 0.0032 mmHg^-1 s^-1 at 16.4 T. The option of loading PFCs after synthesizing UMNs, rather than traditional in situ core-shell syntheses, allows for use of a broad range of PFC liquids from a single material. The biocompatible and tunable chemistry of UMNs combined with the intrinsic properties of PFCs makes PERFUMNs a MRI sensor with potential for anatomical imaging, cell tracking, and metabolic spectroscopy with improved stability.

Modulating tumor hypoxia by nanomedicine for effective cancer therapy

Hypoxia, a characteristic feature of tumors, is indispensable to tumor angiogenesis, metastasis, and multi drug resistance. Hypoxic avascular regions, deeply embedded inside the tumors significantly hinder delivery of therapeutic agents. The low oxygen tension results in resistance to the current applied anti-cancer therapeutics including radiotherapy, chemotherapy, and photodynamic therapy, the efficacy of which is firmly tied to the level of tumor oxygen supply. However, emerging data indicate that nanocarriers/nanodrugs can offer substantial benefits to improve the efficacy of current therapeutics, through modulation of tumor hypoxia. This review aims to introduce the most recent advances made in nanocarrier mediated targeting of tumor hypoxia. The first part is dedicated to the approaches by which nanocarriers could be designed to target/leverage hypoxia. These approaches include i) inhibiting Hypoxia Inducer Factor (HIF-1α); ii) hypoxia activated prodrugs/linkers; and iii) obligate anaerobe mediated targeting of tumor hypoxia. The second part, details novel nanosystems proposed to modulate tumor hypoxia through tumor oxygenation. These methods seek to lessen tumor hypoxia through vascular normalization, or reoxygenation therapy. The reoxygenation of tumor could be accomplished by: i) generation of oxygen filled nanocarriers; ii) natural/artificial oxygen nanocarriers; and iii) oxygen generators. The efficacy of each approach and their potential in cancer therapy is further discussed.

Hybrid Manganese Dioxide Nanoparticles Potentiate Radiation Therapy by Modulating Tumor Hypoxia

Hypoxia in the tumor microenvironment (TME) mediates resistance to radiotherapy and contributes to poor prognosis in patients receiving radiotherapy. Here we report the design of clinically suitable formulations of hybrid manganese dioxide (MnO₂) nanoparticles (MDNP) using biocompatible materials to reoxygenate the TME by reacting with endogenous H₂O₂ MDNP containing hydrophilic terpolymer-protein-MnO₂ or hydrophobic polymer-lipid-MnO₂ provided different oxygen generation rates in the TME relevant to different clinical settings. In highly hypoxic murine or human xenograft breast tumor models, we found that administering either MDNP formulation before radiotherapy modulated tumor hypoxia and increased radiotherapy efficacy, acting to reduce tumor growth, VEGF expression, and vascular density. MDNP treatment also increased apoptosis and DNA double strand breaks, increasing median host survival 3- to 5-fold. Notably, in the murine model, approximately 40% of tumor-bearing mice were tumor-free after a single treatment with MDNPs plus radiotherapy at a 2.5-fold lower dose than required to achieve the same curative treatment without MDNPs. Overall, our findings offer a preclinical proof of concept for the use of MDNP formulations as effective radiotherapy adjuvants. Cancer Res; 76(22); 6643-56. ©2016 AACR.

Chemokines, cytokines and exosomes help tumors to shape inflammatory microenvironment

Relationship between inflammation and cancer is now well-established and represents a paradigm that our immune response does not necessarily serves solely to protect us from infections and cancer. Many specific mechanisms that link chronic inflammation to cancer promotion and metastasis have been uncovered in the recent years. Here we are focusing on the effects that tumors may exert on inflammatory cascades, tuning the immune system ability to cause tumor promotion or regression. In particular, we discuss the contributions of chemokines, cytokines and exosomes to the processes such as induction of inflammation and tumorigenesis. Overall, tumor-elicited inflammation is a key driver of tumor progression and an essential component of tumor microenvironment.

Catalase-Loaded TaOx Nanoshells as Bio-Nanoreactors Combining High-Z Element and Enzyme Delivery for Enhancing Radiotherapy

A novel type of bio-nanoreactor with catalase loaded inside TaOx hollow nanoshells is fabricated via a mild one-step method. Such bio-nanoreactors could efficiently improve the tumor oxygenation by supplying oxygen via decomposition of endogenic H2 O2 in a tumor microenvironment, and thus synergistically enhance the efficacy of cancer radiotherapy by both depositing radiation energy within the tumor and overcoming hypoxia-induced radiotherapy resistance.

A phase 1 'window-of-opportunity' trial testing evofosfamide (TH-302), a tumour-selective hypoxia-activated cytotoxic prodrug, with preoperative chemoradiotherapy in oesophageal adenocarcinoma patients

Background

Neo-adjuvant chemoradiotherapy followed by surgery is the standard treatment with curative intent for oesophageal cancer patients, with 5-year overall survival rates up to 50 %. However, patients’ quality of life is severely compromised by oesophagectomy, and eventually many patients die due to metastatic disease.

Most solid tumours, including oesophageal cancer, contain hypoxic regions that are more resistant to chemoradiotherapy. The hypoxia-activated prodrug evofosfamide works as a DNA-alkylating agent under these hypoxic conditions, which directly kills hypoxic cancer cells and potentially minimizes resistance to conventional therapy. This drug has shown promising results in several clinical studies when combined with chemotherapy. Therefore, in this phase I study we investigate the safety of evofosfamide added to the chemoradiotherapy treatment of oesophageal cancer.

Methods/Design

A phase I, non-randomized, single-centre, open-label, 3 + 3 trial with repeated hypoxia PET imaging, will test the safety of evofosfamide in combination with neo-adjuvant chemoradiotherapy in potentially resectable oesophageal adenocarcinoma patients. Investigated dose levels range from 120 mg/m2 to 340 mg/m2. Evofosfamide will be administered one week before the start of chemoradiotherapy (CROSS-regimen) and repeated weekly up to a total of six doses. PET/CT acquisitions with hypoxia tracer ¹⁸F-HX4 will be made before and after the first administration of evofosfamide, allowing early assessment of changes in hypoxia, accompanied with blood sampling to measure hypoxia blood biomarkers. Oesophagectomy will be performed according to standard clinical practice.

Higher grade and uncommon non-haematological, haematological, and post-operative toxicities are the primary endpoints according to the CTCAEv4.0 and Clavien-Dindo classifications. Secondary endpoints are reduction in hypoxic fraction based on ¹⁸F-HX4 imaging, pathological complete response, histopathological negative circumferential resection margin (R0) rate, local and distant recurrence rate, and progression free and overall survival.

Discussion

This is the first clinical trial testing evofosfamide in combination with chemoradiotherapy. The primary objective is to determine the dose limiting toxicity of this combined treatment and herewith to define the maximum tolerated dose and recommended phase 2 dose for future clinical studies. The addition of non-invasive repeated hypoxia imaging (‘window-of-opportunity’) enables us to identify the biologically effective dose. We believe this approach could also be used for other hypoxia targeted drugs.

Trial registration

ClinicalTrials.gov Identifier: NCT02598687.

Hypoxia-inducible factor 1α (HIF-1α) and reactive oxygen species (ROS) mediates radiation-induced invasiveness through the SDF-1α/CXCR4 pathway in non-small cell lung carcinoma cells

Radiotherapy is an important procedure for the treatment of inoperable non-small cell lung cancer (NSCLC). However, recent evidence has shown that irradiation can promote the invasion and metastasis of several types of cancer, and the underlying mechanisms are not fully understood. This study aimed to investigate the molecular mechanism by which radiation enhances the invasiveness of NSCLC cells. We found that after irradiation, hypoxia-inducible factor 1α (HIF-1α) was increased and translocated into the nucleus, where it bound to the hypoxia response element (HRE) in the CXCR4 promoter and promoted the transcription of CXCR4. Furthermore, reactive oxygen species (ROS) also plays a role in the radiation-induced expression of CXCR4. Our results revealed that 2 Gy X-ray irradiation promoted the metastasis and invasiveness of H1299, A549 and H460 cells, which were significantly enhanced by SDF-1α treatment. Blocking the SDF-1α/CXCR4 interaction could suppress the radiation-induced invasiveness of NSCLC cells. The PI3K/pAkt and MAPK/pERK1/2 pathways were found to be involved in radiation-induced matrix metalloproteinase (MMP) expression. In vivo, irradiation promoted the colonization of H1299 cells in the liver and lung, which was mediated by CXCR4. Altogether, our findings have elucidated the underlying mechanisms of the irradiation-enhanced invasiveness of NSCLC cells.

Cyclometalated Ruthenium(II) Anthraquinone Complexes Exhibit Strong Anticancer Activity in Hypoxic Tumor Cells

Hypoxia is the critical feature of the tumor microenvironment that is known to lead to resistance to many chemotherapeutic drugs. Six novel ruthenium(II) anthraquinone complexes were designed and synthesized; they exhibit similar or superior cytotoxicity compared to cisplatin in hypoxic HeLa, A549, and multidrug-resistant (A549R) tumor cell lines. Their anticancer activities are related to their lipophilicity and cellular uptake; therefore, these physicochemical properties of the complexes can be changed by modifying the ligands to obtain better anticancer candidates. Complex 1, the most potent member of the series, is highly active against hypoxic HeLa cancer cells (IC50 =0.53 μM). This complex likely has 46-fold better activity than cisplatin (IC50 =24.62 μM) in HeLa cells. This complex tends to accumulate in the mitochondria and the nucleus of hypoxic HeLa cells. Further mechanistic studies show that complex 1 induced cell apoptosis during hypoxia through multiple pathways, including those of DNA damage, mitochondrial dysfunction, and the inhibition of DNA replication and HIF-1α expression, making it an outstanding candidate for further in vivo studies.

The hypoxic tumor microenvironment: driving the tumorigenesis of non-small-cell lung cancer

Since the application of molecular biology in cancer biology, lung cancer research has classically focused on molecular drivers of disease. One such pathway, the hypoxic response pathway, is activated by reduced local oxygen concentrations at the tumor site. Hypoxia-driven gene and protein changes enhance epithelial-to-mesenchymal transition, remodel the extracellular matrix, drive drug resistance, support cancer stem cells and aid evasion from immune cells. However, it is not the tumor cells alone which drive this response to hypoxia, but rather their interaction with a complex milieu of supporting cells. This review will focus on recent advances in our understanding of how these cells contribute to the tumor response to hypoxia in non-small-cell lung cancer.

Spatio-Temporal Dynamics of Hypoxia during Radiotherapy

Tumour hypoxia plays a pivotal role in cancer therapy for most therapeutic approaches from radiotherapy to immunotherapy. The detailed and accurate knowledge of the oxygen distribution in a tumour is necessary in order to determine the right treatment strategy. Still, due to the limited spatial and temporal resolution of imaging methods as well as lacking fundamental understanding of internal oxygenation dynamics in tumours, the precise oxygen distribution map is rarely available for treatment planing. We employ an agent-based in silico tumour spheroid model in order to study the complex, localized and fast oxygen dynamics in tumour micro-regions which are induced by radiotherapy. A lattice-free, 3D, agent-based approach for cell representation is coupled with a high-resolution diffusion solver that includes a tissue density-dependent diffusion coefficient. This allows us to assess the space- and time-resolved reoxygenation response of a small subvolume of tumour tissue in response to radiotherapy. In response to irradiation the tumour nodule exhibits characteristic reoxygenation and re-depletion dynamics which we resolve with high spatio-temporal resolution. The reoxygenation follows specific timings, which should be respected in treatment in order to maximise the use of the oxygen enhancement effects. Oxygen dynamics within the tumour create windows of opportunity for the use of adjuvant chemotherapeutica and hypoxia-activated drugs. Overall, we show that by using modelling it is possible to follow the oxygenation dynamics beyond common resolution limits and predict beneficial strategies for therapy and in vitro verification. Models of cell cycle and oxygen dynamics in tumours should in the future be combined with imaging techniques, to allow for a systematic experimental study of possible improved schedules and to ultimately extend the reach of oxygenation monitoring available in clinical treatment.

Carving out its niche: A role for carbonic anhydrase IX in pre-metastatic niche development

Primary tumor-associated hypoxia stimulates the production of secreted factors that mobilize bone marrow-derived cells, including immunomodulatory myeloid-derived suppressor cells (MDSCs) to pre-metastatic niches. We recently found that the hypoxia-induced enzyme carbonic anhydrase IX (CAIX) promotes metastasis by stimulating the G-CSF dependent mobilization of granulocytic MDSCs to the lung pre-metastatic niche.