Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

Hypoxia-selective prodrug restrains tumor cells through triggering mitophagy and inducing apoptosis

Hypoxia is a common feature of various solid tumors, which reduces the sensitivity of tumor cells to both radiotherapy and chemotherapy. However, hypoxia also presents an opportunity for tumor-selective therapy. The prodrug strategy, leveraging the hypoxic nature of the tumor microenvironment, shows significant potential for clinical application. Here we present CHD-1, a hypoxia-activated antitumor prodrug that activates in hypoxic environments, effectively inhibiting hypoxic tumor cells while exhibiting no toxicity to normoxic cells. CHD-1 impairs mitochondrial morphology and membrane potential of hypoxic tumor cells, further triggers excessive mitophagy and induces apoptosis. Moreover, prodrug CHD-1 significantly inhibits HeLa xenograft growth in vivo, and shows lower toxicity than parent molecule in an acute toxicity assessment in animal models. This study introduces a promising hypoxia-activated antitumor prodrug with strong potential for further development in hypoxic tumor therapy.

Novel Prodrug Strategies for the Treatment of Tuberculosis

The emergence of drug-resistant strains of Mycobacterium tuberculosis (M.tb), the causative agent of tuberculosis, is on the rise and increasing antimicrobial resistance is a global threat. This phenomenon necessitates new drug design methods such as a prodrug strategy to develop novel antitubercular agents. The prodrug strategy is a viable and useful means to improve the absorption, distribution, metabolism, excretion and toxicity (ADMET) profiles of pharmacologically active agents. Granulomas are a pathological hallmark of M.tb infection and bear a remarkable resemblance to the tumour microenvironment, including regions of hypoxia. The hypoxic environment observed in the two structures offer an exceptional opportunity to deliver antitubercular agents selectively in a similar manner to hypoxia activated prodrugs in cancer therapy. Nitroimidazoles have been studied extensively as bioactivated prodrugs of cancer, and their suitability as substrates for mammalian reductases highlight their huge potential. This review will discuss the mechanism of action and resistance mechanisms of the current prodrugs used for the treatment of tuberculosis. It will also highlight the potential advantages and challenges of using hypoxia activated prodrugs as a viable strategy to target latent M.tb in hypoxic regions of granulomas.

AQ4N nanocomposites for hypoxia-associated tumor combination therapy

Hypoxia in solid tumors increases their invasiveness and resistance to therapy, presenting a formidable obstacle in tumor therapy. The hypoxia prodrug banoxantrone (AQ4N) undergoes conversion into its topoisomerase II inhibitor form AQ4 under hypoxic conditions, which inhibits tumor cells while leaving normal cells unharmed. Numerous studies have found that AQ4N significantly enhances the tumor effect while minimizing toxicity to normal tissues when combined with other drugs or therapeutic approaches. Thus, to maximize AQ4N's effectiveness, co-delivery of AQ4N with other therapeutic agents to the tumor site is paramount, leading to the development of multifunctional multicomponent AQ4N nanocomposites thereby emerging as promising candidates for combination therapy in tumor treatment. However, currently there is a lack of systematic analysis and reviews focusing on AQ4N. Herein, this review provides a comprehensive retrospect and analysis of the recent advancements in AQ4N nanocomposites. Specifically, we discuss the synergistic effects observed when AQ4N is combined with chemotherapeutic drugs, radiotherapy, phototherapy, starvation, sonodynamic therapy and immunotherapy in preclinical models. Moreover, the advantages, limitations, and future perspectives of different AQ4N nanocomposites are highlighted, providing researchers from diverse fields with novel insights into tumor treatment.

The third generation AKR1C3-activated prodrug, ACHM-025, eradicates disease in preclinical models of aggressive T-cell acute lymphoblastic leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that expresses high levels of the enzyme aldo-keto reductase family 1 member C3 (AKR1C3). To exploit this finding, we developed a novel prodrug, ACHM-025, which is selectively activated by AKR1C3 to a nitrogen mustard DNA alkylating agent. We show that ACHM-025 has potent in vivo efficacy against T-ALL patient-derived xenografts (PDXs) and eradicated the disease in 7 PDXs. ACHM-025 was significantly more effective than cyclophosphamide both as a single agent and when used in combination with cytarabine/6-mercaptopurine. Notably, ACHM-025 in combination with nelarabine was curative when used to treat a chemoresistant T-ALL PDX in vivo. The in vivo efficacy of ACHM-025 directly correlated with AKR1C3 expression levels, providing a predictive biomarker for response. Together, our work provides strong preclinical evidence highlighting the potential of ACHM-025 as a targeted and effective therapy for aggressive forms of T-ALL.

Aptamer functionalized hypoxia-potentiating agent and hypoxia-inducible factor inhibitor combined with hypoxia-activated prodrug for enhanced tumor therapy

Triple-negative breast cancer (TNBC) is the most lethal subtype of breast cancer. Hypoxia-activated prodrugs (HAPs) have shown promise as potential therapeutic agents for TNBC. While increasing hypoxia levels may promote the HAP activation, it raises concerns regarding HIF1α-dependent drug resistance. It is desirable to develop a targeted approach that enhances tumor hypoxia for HAP activation without promoting HIF1α-dependent drug resistance in TNBC treatment. Herein, we proposed a multi-responsive carrier-free self-assembled nanomedicine named AQ4N@CA4T1ASO. This nanomedicine first targeted tumors by the TNBC-targeting aptamers (T1), and then disassembled in the reductive and acidic conditions within tumors. The released Combretastatin 4 (CA4) could exacerbate hypoxia, thereby promoting the conversion of inactive Banoxantrone (AQ4N) to its active form, AQ4. Simultaneously, the released antisense oligonucleotide (ASO) could attenuate hypoxia-induced HIF1α mRNA expression, thereby sensitizing the tumor to chemotherapy. Overall, this smart nanomedicine represents a profound targeted therapy strategy, combining "hypoxia-potentiating, hypoxia-activated, chemo-sensitization" approaches for TNBC treatment. In vivo study demonstrated significant suppression of tumor growth, highlighting the promising potential of this nanomedicine for future clinical translation.

Recent advances for enhanced photodynamic therapy: from new mechanisms to innovative strategies

Photodynamic therapy (PDT) has been developed as a potential cancer treatment approach owing to its non-invasiveness, spatiotemporal control and limited side effects. Currently, great efforts have been made to improve the PDT effect in terms of safety and efficiency. In this review, we highlight recent advances in innovative strategies for enhanced PDT, including (1) the development of novel radicals, (2) design of activatable photosensitizers based on the TME and light, and (3) photocatalytic NADH oxidation to damage the mitochondrial electron transport chain. Additionally, the new mechanisms for PDT are also presented as an inspiration for the design of novel PSs. Finally, we discuss the current challenges and future prospects in the clinical practice of these innovative strategies. It is hoped that this review will provide a new angle for understanding the relationship between the intratumoural redox environment and PDT mechanisms, and new ideas for the future development of smart PDT systems.

Recent Advances in the Application of Nitro(het)aromatic Compounds for Treating and/or Fluorescent Imaging of Tumor Hypoxia

This review delves into recent advancements in the field of nitro(het)aromatic bioreductive agents tailored for hypoxic environments. These compounds are designed to exploit the low-oxygen conditions typically found in solid tumors, making them promising candidates for targeted cancer therapies. Initially, this review focused on their role as gene-directed enzyme prodrugs, which are inert until activated by specific enzymes within tumor cells. Upon activation, these prodrugs undergo chemical transformations that convert them into potent cytotoxic agents, selectively targeting cancerous tissue while sparing healthy cells. Additionally, this review discusses recent developments in prodrug conjugates containing nitro(het)aromatic moieties, designed to activate under low-oxygen conditions within tumors. This approach enhances their efficacy and specificity in cancer treatment. Furthermore, this review covers innovative research on using nitro(het)aromatic compounds as fluorescent probes for imaging hypoxic tumors. These probes enable non-invasive visualization of low-oxygen regions within tumors, providing valuable insights for the diagnosis, treatment planning, and monitoring of therapeutic responses. We hope this review will inspire researchers to design and synthesize improved compounds for selective cancer treatment and early diagnostics.

Sonodynamic and sonomechanical effect on cellular stemness and extracellular physicochemical environment to potentiate chemotherapy

BACKGROUND

Hypoxia-activated prodrug (HAP) is a promising candidate for highly tumor-specific chemotherapy. However, the oxygenation heterogeneity and dense extracellular matrix (ECM) of tumor, as well as the potential resistance to chemotherapy, have severely impeded the resulting overall efficacy of HAP.

RESULTS

A HAP potentiating strategy is proposed based on ultrasound responsive nanodroplets (PTP@PLGA), which is composed of protoporphyrin (PpIX), perfluoropropane (PFP) and a typical HAP, tirapazamine (TPZ). The intense vaporization of PFP upon ultrasound irradiation can magnify the sonomechanical effect, which loosens the ECM to promote the penetration of TPZ into the deep hypoxic region. Meanwhile, the PpIX enabled sonodynamic effect can further reduce the oxygen level, thus activating the TPZ in the relatively normoxic region as well. Surprisingly, abovementioned ultrasound effect also results in the downregulation of the stemness of cancer cells, which is highly associated with drug-refractoriness.

CONCLUSIONS

This work manifests an ideal example of ultrasound-based nanotechnology for potentiating HAP and also reveals the potential acoustic effect of intervening cancer stem-like cells.

TH-4000, a hypoxia-activated pan-HER inhibitor, shows excellent preclinical efficacy for the treatment of HER2+ breast cancer

Human epidermal growth factor receptor 2-positive (HER2+) breast cancer is correlated with poor prognosis, the current treatment of which is still based on surgery and adjuvant targeted therapy with monoclonal antibody. Problems of drug resistance hinder the use of monoclonal antibodies. Subsequently, tyrosine kinase inhibitors (TKIs) have been noticed, TKIs have the advantages of multi-targets and reduced drug resistance. However, TKIs that target HER family proteins often cause adverse effects such as liver damage and diarrhea. Thus, TKIs with high selectivity are being developed. TH-4000, a prodrug that generated an active form TH-4000Effector (TH-4000E) under hypoxic condition, was evaluated in this research. We found that TH-4000E ([(E)-4-[[4-(3-bromo-4-chloroanilino)pyrido[3,4-d]pyrimidin-6-yl]amino]-4-oxobut-2-enyl]-dimethyl-[(3-methyl-5-nitroimidazol-4-yl)methyl]azanium) (1-1000 nM) had potent and highly selective toxic effects on HER2+ breast cancer cells and inhibited the phosphorylation of HER family kinases at lower doses than that of Lapatinib and Tucatinib. TH-4000E activated Caspase-3 and induced apoptosis through a reactive oxygen species (ROS)-dependent pathway. The prodrug TH-4000 ([(E)-4-[[4-(3-bromo-4-chloroanilino)pyrido[3,4-d]pyrimidin-6-yl]amino]-4-oxobut-2-enyl]-dimethyl-[(3-methyl-5-nitroimidazol-4-yl)methyl]azanium;bromide) (50 mg/kg) effectively suppressed the tumor growth with less liver damage in mouse tumor models. This hypoxia-targeted strategy has possessed advantage in avoiding drug-induced liver damage, TH-4000 could be a promising drug candidate for the treatment of HER2+ breast cancer.

Novel quinazolines bearing 1,3,4-thiadiazole-aryl urea derivative as anticancer agents: design, synthesis, molecular docking, DFT and bioactivity evaluations

A novel series of 1-(5-((6-nitroquinazoline-4-yl)thio)-1,3,4-thiadiazol-2-yl)-3-phenylurea derivatives 8 were designed and synthesized to evaluate their cytotoxic potencies. The structures of these obtained compounds were thoroughly characterized by IR, 1H, and 13C NMR, MASS spectroscopy and elemental analysis methods. Additionally, their in vitro anticancer activities were investigated using the MTT assay against A549 (human lung cancer), MDA-MB231 (human triple-negative breast cancer), and MCF7 (human hormone-dependent breast cancer). Etoposide was used as a reference marketed drug for comparison. Among the compounds tested, compounds 8b and 8c demonstrated acceptable antiproliferative activity, particularly against MCF7 cells. Considering the potential VEGFR-2 inhibitor potency of these compounds, a molecular docking study was performed for the most potent compound, 8c, to determine its probable interactions. Furthermore, computational investigations, including molecular dynamics, frontier molecular orbital analysis, Fukui reactivity descriptor, electrostatic potential surface, and in silico ADME evaluation for all compounds were performed to illustrate the structure-activity relationship (SAR).

Design and synthesis of bioreductive prodrugs of class I histone deacetylase inhibitors and their biological evaluation in virally transfected acute myeloid leukemia cells

Although histone deacetylase (HDAC) inhibitors show promise in treating various types of hematologic malignancies, they have some limitations, including poor pharmacokinetics and off-target side effects. Prodrug design has shown promise as an approach to improve pharmacokinetic properties and to improve target tissue specificity. In this work, several bioreductive prodrugs for class I HDACs were designed based on known selective HDAC inhibitors. The zinc-binding group of the HDAC inhibitors was masked with various nitroarylmethyl residues to make them substrates of nitroreductase (NTR). The developed prodrugs showed weak HDAC inhibitory activity compared to their parent inhibitors. The prodrugs were tested against wild-type and NTR-transfected THP1 cells. Cellular assays showed that both 2-nitroimidazole-based prodrugs 5 and 6 were best activated by the NTR and exhibited potent activity against NTR-THP1 cells. Compound 6 showed the highest cellular activity (GI50  = 77 nM) and exhibited moderate selectivity. Moreover, activation of prodrug 6 by NTR was confirmed by liquid chromatography-mass spectrometry analysis, which showed the release of the parent inhibitor after incubation with Escherichia coli NTR. Thus, compound 6 can be considered a novel prodrug selective for class I HDACs, which could be used as a good starting point for increasing selectivity and for further optimization.

Exploring chronic and transient tumor hypoxia for predicting the efficacy of hypoxia-activated pro-drugs

Hypoxia, a low level of oxygen in the tissue, arises due to an imbalance between the vascular oxygen supply and oxygen demand by the surrounding cells. Typically, hypoxia is viewed as a negative marker of patients' survival, because of its implication in the development of aggressive tumors and tumor resistance. Several drugs that specifically target the hypoxic cells have been developed, providing an opportunity for exploiting hypoxia to improve cancer treatment. Here, we consider combinations of hypoxia-activated pro-drugs (HAPs) and two compounds that transiently increase intratumoral hypoxia: a vasodilator and a metabolic sensitizer. To effectively design treatment protocols with multiple compounds we used mathematical micro-pharmacology modeling and determined treatment schedules that take advantage of heterogeneous and dynamically changing oxygenation in tumor tissue. Our model was based on data from murine pancreatic cancers treated with evofosfamide (as a HAP) and either hydralazine (as a vasodilator), or pyruvate (as a metabolic sensitizer). Subsequently, this model was used to identify optimal schedules for different treatment combinations. Our simulations showed that schedules of HAPs with the vasodilator had a bimodal distribution, while HAPs with the sensitizer showed an elongated plateau. All schedules were more successful than HAP monotherapy. The three-compound combination had three local optima, depending on the HAPs clearance from the tissue interstitium, each two-fold more effective than baseline HAP treatment. Our study indicates that the three-compound therapy administered in the defined order will improve cancer response and that designing complex schedules could benefit from the use of mathematical modeling.

Cellular signaling in the hypoxic cancer microenvironment: Implications for drug resistance and therapeutic targeting

The rewiring of cellular metabolism is a defining characteristic of cancer, as tumor cells adapt to acquire essential nutrients from a nutrient-poor environment to sustain their viability and biomass. While hypoxia has been identified as a major factor depriving cancer cells of nutrients, recent studies have revealed that cancer cells distant from supporting blood vessels also face nutrient limitations. To overcome this challenge, hypoxic cancer cells, which heavily rely on glucose as an energy source, employ alternative pathways such as glycogen metabolism and reductive carboxylation of glutamine to meet their energy requirements for survival. Our preliminary studies, alongside others in the field, have shown that under glucose-deficient conditions, hypoxic cells can utilize mannose and maltose as alternative energy sources. This review aims to comprehensively examine the hypoxic cancer microenvironment, its association with drug resistance, and potential therapeutic strategies for targeting this unique niche. Furthermore, we will critically evaluate the current literature on hypoxic cancer microenvironments and explore state-of-the-art techniques used to analyze alternate carbohydrates, specifically mannose and maltose, in complex biological fluids. We will also propose the most effective analytical methods for quantifying mannose and maltose in such biological samples. By gaining a deeper understanding of the hypoxic cancer cell microenvironment and its role in drug resistance, novel therapeutic approaches can be developed to exploit this knowledge.

Hypoxia stabilizes SETDB1 to maintain genome stability

Von Hippel-Lindau (VHL) is a tumor suppressor that functions as the substrate recognition subunit of the CRL2VHL E3 complex. While substrates of VHL have been identified, its tumor suppressive role remains to be fully understood. For further determination of VHL substrates, we analyzed the physical interactome of VHL and identified the histone H3K9 methyltransferase SETBD1 as a novel target. SETDB1 undergoes oxygen-dependent hydroxylation by prolyl hydroxylase domain proteins and the CRL2VHL complex recognizes hydroxylated SETDB1 for ubiquitin-mediated degradation. Under hypoxic conditions, SETDB1 accumulates by escaping CRL2VHL activity. Loss of SETDB1 in hypoxia compared with that in normoxia escalates the production of transposable element-derived double-stranded RNAs, thereby hyperactivating the immune-inflammatory response. In addition, strong derepression of TEs in hypoxic cells lacking SETDB1 triggers DNA damage-induced death. Our collective results support a molecular mechanism of oxygen-dependent SETDB1 degradation by the CRL2VHL E3 complex and reveal a role of SETDB1 in genome stability under hypoxia.

Radiation Therapy for Gestational Trophoblastic Neoplasia: Forward-Looking Lessons Learnt

Gestational trophoblastic neoplasia (GTN) includes several rare malignant diseases occurring after pregnancy: invasive moles, choriocarcinoma, placental site trophoblastic tumours, and epithelioid trophoblastic tumours. Multidisciplinary protocols including multi-agent chemotherapy, surgery, and occasionally radiotherapy achieve good outcomes for some high-risk metastatic patients. In this narrative review of the published studies on the topic, we have tried to identify the role of radiotherapy. The available studies are mainly small, old, and retrospective, with incomplete data regarding radiotherapy protocols delivering low doses (which can make this disease appear radioresistant in some cases despite high response rates with palliative doses) to wide fields (whole-brain, whole-liver, etc.), which can increase toxicity. Studies considering modern techniques are needed to overcome these limitations and determine the full potential of radiotherapy beyond its antihemorrhagic and palliative roles.

Strategic Design of Conquering Hypoxia in Tumor for Advanced Photodynamic Therapy

Photodynamic therapy (PDT), with its advantages of high targeting, minimally invasive, and low toxicity side effects, has been widely used in the clinical therapy of various tumors, especially superficial tumors. However, the tumor microenvironment (TME) presents hypoxia due to the low oxygen (O2 ) supply caused by abnormal vascularization in neoplastic tissues and high O2 consumption induced by the rapid proliferation of tumor cells. The efficacy of oxygen-consumping PDT can be hampered by a hypoxic TME. To address this problem, researchers have been developing advanced nanoplatforms and strategies to enhance the therapeutic effect of PDT in tumor treatment. This review summarizes recent advanced PDT therapeutic strategies to against the hypoxic TME, thus enhancing PDT efficacy, including increasing O2 content in TME through delivering O2 to the tumors and in situ generations of O2 ; decreasing the O2 consumption during PDT by design of type I photosensitizers. Moreover, recent synergistically combined therapy of PDT and other therapeutic methods such as chemotherapy, photothermal therapy, immunotherapy, and gas therapy is accounted for by addressing the challenging problems of mono PDT in hypoxic environments, including tumor resistance, proliferation, and metastasis. Finally, perspectives of the opportunities and challenges of PDT in future clinical research and translations are provided.

Hypoxia-activated prodrugs of phenolic olaparib analogues for tumour-selective chemosensitisation

Poly(ADP-ribose)polymerase inhibitors (PARPi) are used for treatment of tumours with a defect in homologous recombination (HR) repair. Combination with radio- or chemotherapy could broaden their applicability but a major hurdle is enhancement of normal tissue toxicity. Development of hypoxia-activated prodrugs (HAPs) of PARPi has potential to restrict PARP inhibition to tumours thereby avoiding off-target toxicity. We have designed and synthesised phenolic derivatives of olaparib (termed phenolaparibs) and corresponding ether-linked HAPs. Phenolaparib cytotoxicity in HR-proficient and deficient cell lines was consistent with inhibition of PARP-1. Prodrugs were deactivated relative to phenolaparibs in biochemical PARP-1 inhibition assays, and cell culture. Prodrug 7 was selectively converted to phenolaparib 4 under hypoxia and demonstrated hypoxia-selective cytotoxicity, including chemosensitisation of HR-proficient cells in combination with temozolomide. This work demonstrates the feasibility of a HAP approach to PARPi for use in combination therapies.

Lighting Up the Fire in the Microenvironment of Cold Tumors: A Major Challenge to Improve Cancer Immunotherapy

Immunotherapy includes immune checkpoint inhibitors (ICI) such as antibodies targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) or the programmed cell death protein/programmed death ligand 1 (PD-1/PD-L1) axis. Experimental and clinical evidence show that immunotherapy based on immune checkpoint inhibitors (ICI) provides long-term survival benefits to cancer patients in whom other conventional therapies have failed. However, only a minority of patients show high clinical benefits via the use of ICI alone. One of the major factors limiting the clinical benefits to ICI can be attributed to the lack of immune cell infiltration within the tumor microenvironment. Such tumors are classified as "cold/warm" or an immune "desert"; those displaying significant infiltration are considered "hot" or inflamed. This review will provide a brief summary of different tumor properties contributing to the establishment of cold tumors and describe major strategies that could reprogram non-inflamed cold tumors into inflamed hot tumors. More particularly, we will describe how targeting hypoxia can induce metabolic reprogramming that results in improving and extending the benefit of ICI.

Hypoxia-targeting therapy for intestinal T-cell lymphoma in dogs: Preclinical study using 3D in vitro models

The transcription factor hypoxia-inducible factor 1α (HIF-1α) is activated in response to oxygen deficiency, and is expressed in several cancers under intratumoral hypoxic stress that arises during pathogenic processes. Hypoxic stimulation enhanced the growth potential of canine lymphoma cells by activating the HIF-1α signalling pathway in a previously reported study. The aim of this study was to establish a molecular design strategy for a novel hypoxia-targeting therapy for intestinal T-cell lymphoma (ITL) in dogs. We assessed the relationship between immunohistochemistry-based HIF-1α expression and clinical information, including signalment, tumour area, clinical signs, systemic diseases, treatment protocol, follow-up information, chemotherapy response and overall survivals (OS), using 48 tissue samples from dogs with ITL. We investigated the effects of hypoxic stimulation on the biological behaviour of cell lines from three different types of canine ITL. We assessed the effects of evofosfamide (Evo; hypoxia-activated prodrug) on cell lines cultured under hypoxic conditions. Our data showed that treatment response and overall survival might be significantly decreased in dogs with higher HIF-1α expression than in those with lower HIF-1α expression. Hypoxic culture (1% O₂ , 72 h) enhanced the invasiveness of cell lines and decreased their sensitivity to CCNU, resulting in hypoxia-dependent aggressive behaviour. Sensitivity to Evo significantly increased in cell lines cultured under hypoxia compared with those cultured under normoxia, which exhibited hypoxia-dependent apoptosis. Additionally, Evo downregulated HIF-1α expression in cell lines cultured under hypoxia, suggesting that Evo might inhibit cell growth by inactivating HIF-1α-dependent cell signalling. Our results revealed the preclinical antitumor activity of Evo and provide a rationale for treatment strategies for dogs with ITL.

In situ forming oxygen/ROS-responsive niche-like hydrogel enabling gelation-triggered chemotherapy and inhibition of metastasis

Though the development of the diverse hypoxia-activated prodrugs (HAPs) has made great progresses in the last several decades, current cancer therapy based on HAPs still suffers many obstacles, e.g., poor therapeutic outcome owing to hard deep reaching to hypoxic region, and the occurrence of metastasis due to hypoxia. Inspired by engineered niches, a novel functional chitosan polymer (CS-FTP) is synthesized for construction of a hydrogel-based bio-niche (CS-FTP-gel) in aiming at remodeling tumor hypoxic microenvironment. The CS-FTP polymers are crosslinked to form a niche-like hydrogel via enzyme-mediated oxygen-consumable dimerization after injected into tumor, in which a HAP (i.e., AQ4N) could be physically encapsulated, resulting in enhanced tumor hypoxia to facilitate AQ4N-AQ4 toxic transformation for maximizing efficacy of chemotherapy. Furthermore, Pazopanib (PAZ) conjugated onto the CS backbone via ROS-sensitive linker undergoes a stimuli-responsive release behavior to promote antiangiogenesis for tumor starvation, eventually contributing to the inhibition of lung metastasis and synergistic action with AQ4N-based chemotherapy for an orthotopic 4T1 breast tumor model. This study provides a promising strategy for hypoxia-based chemotherapy and demonstrates an encouraging clinical potential for multifunctional hydrogel applicable for antitumor treatment.

•

CS-FTP shows enzyme-mediated hypoxia-inducible gelation and reactive oxygen species (ROS)-responsive drug release.

•

CS-FTP gel formed intratumorally can be used as a bio-niche to enhance tumor hypoxic microenvironment.

•

In vivo PET/CT directly monitors the tumor hypoxia changes and confirm the ability of CS-FTP to enhance tumor hypoxia.

•

Oxygen-consumable gelation of ROS-responsive CS-FTP triggers chemotherapy and starvation therapy for antimetastasis.

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.

Cytotoxic Activity of Herbal Medicines as Assessed in Vitro: A Review

Since time immemorial, human beings have sought natural medications for treatment of various diseases. Weighty evidence demonstrates the use of chemical methodologies for sensitive evaluation of cytotoxic potentials of herbal agents. However, due to the ubiquitous use of cytotoxicity methods, there is a need for providing updated guidance for the design and development of in vitro assessment. The aim of this review is to provide practical guidance on common cell-based assays for suitable assessment of cytotoxicity potential of herbal medicines and discussing their advantages and disadvantages Relevant articles in authentic databases, including PubMed, Web of Science, Science Direct, Scopus, Google Scholar and SID, from 1950 to 2022 were collected according to selection criteria of in vitro cytotoxicity assays and protocols. In addition, the link between cytotoxicity assay selection and different factors such as the drug solvent, concentration and exposure duration were discussed.

Notch signaling, hypoxia, and cancer

Notch signaling is involved in cell fate determination and deregulated in human solid tumors. Hypoxia is an important feature in many solid tumors, which activates hypoxia-induced factors (HIFs) and their downstream targets to promote tumorigenesis and cancer development. Recently, HIFs have been shown to trigger the Notch signaling pathway in a variety of organisms and tissues. In this review, we focus on the pro- and anti-tumorigenic functions of Notch signaling and discuss the crosstalk between Notch signaling and cellular hypoxic response in cancer pathogenesis, including epithelia-mesenchymal transition, angiogenesis, and the maintenance of cancer stem cells. The pharmacological strategies targeting Notch signaling and hypoxia in cancer are also discussed in this review.

Assessment of hypoxia-targeting therapy for gastrointestinal lymphoma in dogs: Preclinical test using murine models

The transcription factor hypoxia-inducible factor 1α (HIF-1α) is expressed in several cancers under intratumoral hypoxic stress that arises during pathogenic processes, resulting in malignant progression. We previously reported that hypoxic stimulation enhances the growth potential of canine lymphoma cells by activating the HIF-1α signaling pathway. In contrast, evofosfamide (Evo) releases a DNA-alkylating moiety within hypoxic tumor regions, suggesting that Evo could serve as a hypoxia-targeting drug in canine lymphoma. This study aimed to use Evo to evaluate hypoxia-targeted therapy in dogs with gastrointestinal lymphoma (GIL) and investigate how Evo affects antitumor efficacy and adverse events in three type of murine xenograft models using T-cell GIL cells. In vitro tests, the sensitivity to Evo of three T-cell GIL cell lines under hypoxic culture was significantly higher than that under normoxic culture. Our metabolic analysis suggested that the three murine models might have high reproducibility as clinical cases in canine GIL. Our data showed that Evo showed significantly higher tumor growth potential and fewer adverse events in three type of murine models compared to lomustine; CeeNu (CCNU). Additionally, Evo suppressed the expression of HIF-1α protein in tumor tissues, suggesting that it may preferentially target and inhibit tumor cells in a hypoxic region. The evidence presented here supports the favorable preclinical evaluation that Evo may be effective for GIL in dogs.

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.

A carbon monoxide releasing metal organic framework nanoplatform for synergistic treatment of triple-negative breast tumors

BACKGROUND

Carbon monoxide (CO) is an important signaling molecule participating in multiple biological functions. Previous studies have confirmed the valuable roles of CO in cancer therapies. If the CO concentration and distribution can be controlled in tumors, new cancer therapeutic strategy may be developed to benefit the patient survival.

RESULTS

In this study, a UiO-67 type metal-organic framework (MOF) nanoplatform was produced with cobalt and ruthenium ions incorporated into its structure (Co/Ru-UiO-67). Co/Ru-UiO-67 had a size range of 70-90 nm and maintained the porous structure, with cobalt and ruthenium distributed uniformly inside. Co/Ru-UiO-67 was able to catalyze carbon dioxide into CO upon light irradiation in an efficient manner with a catalysis speed of 5.6 nmol/min per 1 mg Co/Ru-UiO-67. Due to abnormal metabolic properties of tumor cells, tumor microenvironment usually contains abundant amount of CO₂. Co/Ru-UiO-67 can transform tumor CO₂ into CO at both cellular level and living tissues, which consequently interacts with relevant signaling pathways (e.g. Notch-1, MMPs etc.) to adjust tumor microenvironment. With proper PEGylation (pyrene-polyacrylic acid-polyethylene glycol, Py-PAA-PEG) and attachment of a tumor-homing peptide (F3), functionalized Co/Ru-UiO-67 could accumulate strongly in triple-negative MDA-MB-231 breast tumors, witnessed by positron emission tomography (PET) imaging after the addition of radioactive zirconium-89 (⁸⁹Zr) into Co-UiO-67. When applied in vivo, Co/Ru-UiO-67 could alter the local hypoxic condition of MDA-MB-231 tumors, and work synergistically with tirapazamine (TPZ).

CONCLUSION

This nanoscale UiO-67 MOF platform can further our understanding of CO functions while produce CO in a controllable manner during cancer therapeutic administration.

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.

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

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

In vitro radiosensitization of breast cancer with hypoxia-activated prodrugs

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

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

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

PET/CT features of a novel gallium-68 labelled hypoxia seeking agent in patients diagnosed with tuberculosis: a proof-of-concept study

INTRODUCTION

Positron emission tomography/computed tomography (PET/CT) in infection and inflammation has yielded promising results across a range of radiopharmaceuticals. In particular, PET/CT imaging of tuberculosis (TB) allows for a better understanding of this complex disease by providing insights into molecular processes within the TB microenvironment. TB lesions are hypoxic with research primarily focussed on cellular processes occurring under hypoxic stress. With the development of hypoxia seeking PET/CT radiopharmaceuticals, that can be labelled in-house using a germanium-68/gallium-68 (68Ge/68Ga) generator, a proof-of-concept for imaging hypoxia in TB is presented.

METHODS

Ten patients diagnosed with TB underwent whole-body PET/CT imaging, 60-90 min after intravenous administration of 74-185 MBq (2-5 mCi) 68Ga-nitroimidazole. No oral or intravenous contrast was administered. Images were visually and semiquantitatively assessed for abnormal 68Ga-uptake in the lungs.

RESULTS

A total of 28 lesions demonstrating hypoxic uptake were identified. Low- to moderate-uptake was seen in nodules, areas of consolidation and cavitation as well as effusions. The mean standard uptake value (SUVmean) of the lesions was 0.47 (IQR, 0.32-0.82) and SUVmax was 0.71 (IQR, 0.41-1.11). The lesion to muscle ratio (median, 1.70; IQR, 1.15-2.31) was higher than both the left ventricular and the aorta lesion to blood ratios.

CONCLUSION

Moving towards the development of unique host-directed therapies (HDT), modulation of oxygen levels may improve therapeutic outcome by reprogramming TB lesions to overcome hypoxia. This proof-of-concept study suggests that hypoxia in TB lesions can be imaged and quantified using 68Ga-nitroimidazole PET/CT. Subsequently, hypoxic load can be estimated to inform personalised treatment plans of patients diagnosed with TB.

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.

Key Players of the Immunosuppressive Tumor Microenvironment and Emerging Therapeutic Strategies

The tumor microenvironment (TME) is a complex, dynamic battlefield for both immune cells and tumor cells. The advent of the immune checkpoint inhibitors (ICI) since 2011, such as the anti-cytotoxic T-lymphocyte associated protein (CTLA)-4 and anti-programmed cell death receptor (PD)-(L)1 antibodies, provided powerful weapons in the arsenal of cancer treatments, demonstrating unprecedented durable responses for patients with many types of advanced cancers. However, the response rate is generally low across tumor types and a substantial number of patients develop acquired resistance. These primary or acquired resistance are attributed to various immunosuppressive elements (soluble and cellular factors) and alternative immune checkpoints in the TME. Therefore, a better understanding of the TME is absolutely essential to develop therapeutic strategies to overcome resistance. Numerous clinical studies are underway using ICIs and additional agents that are tailored to the characteristics of the tumor or the TME. Some of the combination treatments are already approved by the Food and Drug Administration (FDA), such as platinum-doublet chemotherapy, tyrosine kinase inhibitor (TKI) -targeting vascular endothelial growth factor (VEGF) combined with anti-PD-(L)1 antibodies or immuno-immuno combinations (anti-CTLA-4 and anti-PD-1). In this review, we will discuss the key immunosuppressive cells, metabolites, cytokines or chemokines, and hypoxic conditions in the TME that contribute to tumor immune escape and the prospect of relevant clinical trials by targeting these elements in combination with ICIs.

Cytotoxic and Radiosensitising Effects of a Novel Thioredoxin Reductase Inhibitor in Brain Cancers

The thioredoxin (Trx) system, a key antioxidant pathway, represents an attractive target for cancer therapy. This study investigated the chemotherapeutic and radiosensitising effects of a novel Trx reductase (TrxR) inhibitor, IQ10, on brain cancer cells and the underlying mechanisms of action. Five brain cancer cell lines and a normal cell type were used. TrxR activity and expression were assessed by insulin reduction assay and Western blotting, respectively. IQ10 cytotoxicity was evaluated using growth curve, resazurin reduction and clonogenic assays. Radiosensitivity was examined using clonogenic assay. Reactive oxygen species levels were examined by flow cytometry and DNA damage assessed by immunofluorescence. Epithelial-mesenchymal transition (EMT)-related gene expression was examined by RT-PCR array. IQ10 significantly inhibited TrxR activity but did not affect Trx system protein expression in brain cancer cells. The drug exhibited potent anti-proliferative and cytotoxic effects against brain cancer cells under both normoxic and hypoxic conditions in both 2D and 3D systems, with IC₅₀s in the low micromolar range. It was up to ~ 1000-fold more potent than temozolomide. IQ10 substantially sensitised various brain cancer cells to radiation, with such effect being due, in part, to functional inhibition of TrxR, making cells less able to deal with oxidative stress and leading to increased oxidative DNA damage. IQ10 significantly downregulated EMT-associated gene expression suggesting potential anti-invasive and antimetastatic properties. This study suggests that IQ10 is a potent anticancer agent and could be used as either a single agent or combined with radiation, to treat brain cancers.

Recent advances in targeted drug delivery for the treatment of pancreatic ductal adenocarcinoma

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) has become a serious health problem with high impact worldwide. The heterogeneity of PDAC makes it difficult to apply drug delivery systems (DDS) used in other cancer models, for example, the poorly developed vascular system makes anti-angiogenic therapy ineffective. Due to its various malignant pathological changes, drug delivery against PDAC is a matter of urgent concern. Based on this situation, various drug delivery strategies specially designed for PDAC have been generated.

AREAS COVERED

This review will briefly describe how delivery systems can be designed through nanotechnology and formulation science. Most research focused on penetrating the stromal barrier, exploiting and alleviating the hypoxic microenvironment, targeting immune cells, or designing vaccines, and combination therapies. This review will summarize the ways to reverse the malignant pathological features of PDAC and hopefully provide ideas for subsequent studies.

EXPERT OPINION

Drug delivery systems designed to achieve penetrating functions or to alleviate hypoxia and activate immunity have achieved good therapeutic results in animal models in several studies. In future studies, there is a need to deliver PDAC therapeutics in a more precise manner, or the use of drug carriers for multiple functions simultaneously, are potential therapeutic strategy.

DNA Origami-Anthraquinone Hybrid Nanostructures for In Vivo Quantitative Monitoring of the Progression of Tumor Hypoxia Affected by Chemotherapy

Hypoxia is a well-known feature of malignant solid tumors. To explain the misinterpretation of tumor hypoxia variation during chemotherapy, we developed a DNA origami-based theranostic nanoplatform with an intercalated anticancer anthraquinone as both the chemotherapeutic drug and the photoacoustic contrast agent. The size distribution of the DNA origami nanostructure is 44.5 ± 2.3 nm, whereas the encapsulation efficiency of the drug is 90.7 ± 1.0%, and the drug loading content is 92.2 ± 0.1%. The controlled cumulative release rates were measured in vitro, showing an acidic environment induced rapid drug release. The values of free energy of binding between the drugs and the DNA double helix were calculated through molecular simulations. The cell viability assay was used to characterize cytotoxicity, and fluorescence confocal cell imaging illustrates the biodistribution of the probe in vitro. Photoacoustic and fluorescence imaging were used to indicate drug delivery, release, and biodistribution to predict the drug's chemotherapeutic effect in vivo, whereas the photoacoustic signals were compared with those of deoxygenated/oxygenated hemoglobin to represent the tissue hypoxia/normoxia maps during the chemotherapeutic process and indicate alleviated tumor hypoxia. Staining of tissue sections taken from organs and tumors was used to verify the results of photoacoustic imaging. Our results suggest that photoacoustic imaging can visualize this DNA origami-based theranostic nanoplatform and reveal the mechanisms of chemotherapy on tumor hypoxia.

Multifaceted Interplay between Hormones, Growth Factors and Hypoxia in the Tumor Microenvironment

Hormones and growth factors (GFs) are signaling molecules implicated in the regulation of a variety of cellular processes. They play important roles in both healthy and tumor cells, where they function by binding to specific receptors on target cells and activating downstream signaling cascades. The stages of tumor progression are influenced by hormones and GF signaling. Hypoxia, a hallmark of cancer progression, contributes to tumor plasticity and heterogeneity. Most solid tumors contain a hypoxic core due to rapid cellular proliferation that outgrows the blood supply. In these circumstances, hypoxia-inducible factors (HIFs) play a central role in the adaptation of tumor cells to their new environment, dramatically reshaping their transcriptional profile. HIF signaling is modulated by a variety of factors including hormones and GFs, which activate signaling pathways that enhance tumor growth and metastatic potential and impair responses to therapy. In this review, we summarize the role of hormones and GFs during cancer onset and progression with a particular focus on hypoxia and the interplay with HIF proteins. We also discuss how hypoxia influences the efficacy of cancer immunotherapy, considering that a hypoxic environment may act as a determinant of the immune-excluded phenotype and a major hindrance to the success of adoptive cell therapies.

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.

Silk fibroin-capped metal-organic framework for tumor-specific redox dyshomeostasis treatment synergized by deoxygenation-driven chemotherapy

Disturbance in redox homeostasis always leads to oxidative damages to cellular components, which inhibits cancer cell proliferation and causes tumor regression. Therefore, synergistic effects arising from cellular redox imbalance together with other treatment modalities are worth further investigation. Herein, a metal-organic framework nanosystem (NMOF) based on coordination between Fe (III) and 4,4,4,4-(porphine-5,10,15,20-tetrayl) tetrakis (benzoic acid) (TCPP) was synthesized through a one-pot method. After surface capping of silk fibroin (SF) to form NMOF@SF nanoparticles (NPs), this nanoplatform can serve as an eligible nanocarrier to deliver tirapazamine (TPZ), a hypoxia-activated precursor. As-developed NS@TPZ (NST) NPs remained inactive in the normal tissue, whereas became highly active upon endocytosis by tumor cells via glutathione (GSH)-mediated reduction of Fe (III) into Fe (II), further enabling Fe (II)-mediated chemodynamic therapy (CDT). Upon optical laser irradiation, TCPP-mediated photodynamic therapy (PDT) coordinated with CDT to aggravate intracellular oxidative stress. Thus, such reactive oxygen species accumulation and GSH deprivation contributed to a deleterious redox dyshomeostasis. On the other hand, local deoxygenation caused by PDT can increase the cytotoxicity of released TPZ, which significantly improved the integral therapeutic effectiveness relying on the combined redox balance disruption and bioreductive chemotherapy. More importantly, severe immunogenic cell death can be triggered by the combinatorial treatment modalities and the presence of SF, which facilitated an almost complete tumor eradication in vivo. Taken together, this paradigm provides an insightful strategy for tumor-specific redox dyshomeostasis treatment synergized by deoxygenation-driven chemotherapy, which can remarkably enhance antitumor efficacy with negligible adverse effects. STATEMENT OF SIGNIFICANCE: Recently, silk fibroin (SF) has been demonstrated to be effective in activating antitumor immune system through polarization tumor-associated macrophages into M1 subtype. However, engineering SF into multifunctional nanocomposites is seldom reported for combination tumor therapy. In another aspect, disruption of redox homeostasis becomes increasingly attractive for tumor suppression with high clinical-relevance. Herein, we established a newfashioned NMOF nanosystem, named as NST, for tumor-specific redox dyshomeostasis treatment synergized by deoxygenation-driven chemotherapy. This platform takes advantages of Fe²⁺/Fe³⁺ coupled Fenton-like reaction and GSH depletion, as well as TCPP-mediated photosensitization for admirable redox unbalancing, which further initiates hypoxia-relevant toxin of TPZ for chemotherapy. Finally, combinatorial treatments and the presence of SF could trigger ICD for rendering a complete tumor eradication in vivo.

Targeted Anti-Cancer Provascular Therapy Using Ultrasound, Microbubbles, and Nitrite to Increase Radiotherapy Efficacy

Hypoxia is an important mechanism of resistance to radiation therapy in many human malignancies including prostate cancer. It has been recently shown that ultrasound targeted microbubble cavitation (UTMC) can increase blood perfusion in skeletal muscle by triggering nitric oxide signaling. Interestingly, this effect was amplified with a sodium nitrite coinjection. Since sodium nitrite has been shown to synergize with radiotherapy (RT), we hypothesized that UTMC with a sodium nitrite coinjection could further radiosensitize solid tumors by increasing blood perfusion and thus reduce tumor hypoxia. We evaluated (1) the ability of UTMC with and without nitrite to increase perfusion in muscle (mouse hindlimbs) and human prostate tumors using different pulse lengths and pressure; (2) the efficacy of this approach as a provascular therapy given directly before RT in the human prostate subcutaneous xenografts PC3 tumor model. Using long pulses with various pressures, in muscle, the provascular response following UTMC was strong (6.61 ± 4.41-fold increase in perfusion post-treatment). In tumors, long pulses caused an increase in perfusion (2.42 ± 1.38-fold) at lower mechanical index (MI = 0.25) but not at higher MI (0.375, 0.5, and 0.750) when compared to control (no UTMC). However, when combined with RT, UTMC with long pulses (MI = 0.25) did not improve tumor growth inhibition. With short pulses, in muscle, the provascular response following UTMC (SONOS) + nitrite was strong (13.74 ± 8.60-fold increase in perfusion post-treatment). In tumors, UTMC (SONOS) + nitrite also caused a provascular response (1.94 ± 1.20-fold increase in perfusion post-treatment) that lasted for at least 10 min, but not with nitrite alone. Interestingly, the blunted provascular response observed for long pulses at higher MI without nitrite was reversed with the addition of nitrite. UTMC (SONOS) with and without nitrite caused an increase in perfusion in tumors. The provascular response observed for UTMC (SONOS) + nitrite was confirmed by histology. Finally, there was an improved growth inhibition for the 8 Gy RT dose + nitrite + UTMC group vs 8 Gy RT + nitrite alone. This effect was not significant with mice treated by UTMC + nitrite and receiving doses of 0 or 2 Gy RT. In conclusion, UTMC + nitrite increased blood flow leading to an increased efficacy of higher doses of RT in our tumor model, warranting further study of this strategy.

Development and Evaluation of 2-Amino-7-Fluorophenazine 5,10-Dioxide Polymeric Micelles as Antitumoral Agents for 4T1 Breast Cancer

2-Amino-7-fluorophenazine 5,10-dioxide (FNZ) is a bioreducible prodrug, poorly soluble in water, with potential anticancer activity on hypoxic-tumors. This poor solubility limits its potential applications in clinic. Amphiphilic pristine polymeric micelles (PMs) based on triblock copolymers Pluronic® and Tetronic®, glycosylated derivatives and their mixtures with preformed-liposomes (LPS), were analyzed as strategies to improve the bioavailability of FNZ. FNZ encapsulations were performed and the obtaining nanostructures were characterized using UV-visible spectroscopy (UV-VIS), Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS). The most promising nanoformulations were analyzed for their potential toxicity and pharmacologically, at 20 mg/kg FNZ-doses, in a stage-IV murine metastatic-breast tumor model. The results revealed that the solubility of the encapsulated-FNZ increased up to 14 times and the analysis (UV-VIS, DLS and TEM) confirmed the interaction between vehicles and FNZ. In all the cases appropriate encapsulation efficiencies (greater than 75%), monodisperse nanometric particle sizes (PDI = 0.180-0.335), adequate Z-potentials (-1.59 to -26.4 mV), stabilities and spherical morphologies were obtained. The in vitro profile of FNZ controlled releases corresponded mainly to a kinetic Higuchi model. The in vitro/in vivo biological studies revealed non-toxicity and relevant tumor-weight diminution (up to 61%).