Tumor Hypoxia Research Articles

A thiourea-bridged 99mTc(CO)3-dipicolylamine-2-nitroimidazole complex for targeting tumor hypoxia: Utilizing metabolizable thiourea-bridge to improve pharmacokinetics.

The 2-nitroimidazole based 99mTc-radiopharmaceuticals are widely explored for imaging tumor hypoxia. Radiopharmaceuticals for targeting hypoxia are often lipophilic and therefore, show significant uptake in liver and other vital organs. In this context, lipophilic radiopharmaceuticals with design features enabling faster clearance from liver may be more desirable. A dipicolylamine-NCS bifunctional chelator that could generate a thiourea-bridge up on conjugation to primary amine bearing molecule was used to synthesize a 2-nitroimidazole-dipicolyl amine ligand for radiolabeling with 99mTc(CO)3 core. Corresponding Re(CO)3-analogue was prepared to establish the structure of 2-nitroimidazole-99mTc(CO)3 complex prepared in trace level. The 2-nitroimidazole-99mTc(CO)3 complex showed a hypoxic to normoxic ratio of ~2.5 in CHO cells at 3 h. In vivo, the complex showed accumulation and retention in tumor with high tumor to blood and tumor to muscle ratio. The study demonstrated the utility of metabolizable thiourea-bridge in 2-nitroimidazole-99mTc(CO)3 complex in inducing faster clearance of the radiotracer from liver. The dipicolylamine-NCS bifunctional chelator reported herein can also be used for radiolabeling other class of target specific molecules with 99mTc(CO)3 core.

Regulation of Tumor Microenvironment through YAP/TAZ under Tumor Hypoxia.

In solid tumors such as hepatocellular carcinoma (HCC), hypoxia is one of the important mechanisms of cancer development that closely influences cancer development, survival, and metastasis. The development of treatments for cancer was temporarily revolutionized by immunotherapy but continues to be constrained by limited response rates and the resistance and high costs required for the development of new and innovative strategies. In particular, solid tumors, including HCC, a multi-vascular tumor type, are sensitive to hypoxia and generate many blood vessels for metastasis and development, making it difficult to treat HCC, not only with immunotherapy but also with drugs targeting blood vessels. Therefore, in order to develop a treatment strategy for hypoxic tumors, various mechanisms must be explored and analyzed to treat these impregnable solid tumors. To date, tumor growth mechanisms linked to hypoxia are known to be complex and coexist with various signal pathways, but recently, mechanisms related to the Hippo signal pathway are emerging. Interestingly, Hippo YAP/TAZ, which appear during early tumor and normal tumor growth, and YAP/TAZ, which appear during hypoxia, help tumor growth and proliferation in different directions. Peculiarly, YAP/TAZ, which have different phosphorylation directions in the hypoxic environment of tumors, are involved in cancer proliferation and metastasis in various carcinomas, including HCC. Analyzing the mechanisms that regulate the function and expression of YAP in addition to HIF in the complex hypoxic environment of tumors may lead to a variety of anti-cancer strategies and combining HIF and YAP/TAZ may develop the potential to change the landscape of cancer treatment.

Baseline SUVmax is correlated with tumor hypoxia and patient outcomes in nasopharyngeal carcinoma

To evaluate the prognostic significance of the maximum standardized uptake value (SUVmax) in nasopharyngeal carcinoma (NPC), establish a gene signature that correlates with SUVmax, and explore the underlying biological behaviors associated with these correlations for the prediction of clinical outcomes. A cohort of 726 patients with NPC was examined to identify correlations between SUVmax and various clinical variables. RNA sequencing was performed to identify genes related to SUVmax, and these genes were used to develop an SUV signature. Additionally, transcriptome enrichment analysis was conducted to investigate the potential biological behaviors underlying the observed correlations. Higher SUVmax was associated with an increased tumor burden and worse prognosis. The SUV signature, which consisted of 10 genes, was positively correlated with SUVmax, and it predicted worse survival outcomes. This signature was highly expressed in malignant epithelial cells and associated with hypoxia and resistance to radiotherapy. Additionally, the signature was negatively correlated with immune function. SUVmax is a valuable prognostic indicator in NPC, with higher values predicting worse outcomes. The SUV signature offers further prognostic insights, linking glucose metabolism to tumor aggressiveness, treatment resistance, and immune function, and it could represent a potential biomarker for NPC.

Direct inhibition of tumor hypoxia response with synthetic transcriptional repressors.

Many oncogenic transcription factors (TFs) are considered to be undruggable because of their reliance on large protein-protein and protein-DNA interfaces. TFs such as hypoxia-inducible factors (HIFs) and X-box-binding protein 1 (XBP1) are induced by hypoxia and other stressors in solid tumors and bind to unfolded protein response element (UPRE) and hypoxia-induced response element (HRE) motifs to control oncogenic gene programs. Here, we report a strategy to create synthetic transcriptional repressors (STRs) that mimic the basic leucine zipper domain of XBP1 and recognize UPRE and HRE motifs. A lead molecule, STR22, binds UPRE and HRE DNA sequences with high fidelity and competes with both TFs in cells. Under hypoxia, STR22 globally suppresses HIF1α binding to HRE-containing promoters and enhancers, inhibits hypoxia-induced gene expression and blocks protumorigenic phenotypes in triple-negative breast cancer (TNBC) cells. In vivo, intratumoral and systemic STR22 treatment inhibited hypoxia-dependent gene expression, primary tumor growth and metastasis of TNBC tumors. These data validate a novel strategy to target the tumor hypoxia response through coordinated inhibition of TF-DNA binding.

29: Plasma proteomic profiling of bladder cancer patients with hypoxic tumours undergoing radiotherapy.

29: Plasma proteomic profiling of bladder cancer patients with hypoxic tumours undergoing radiotherapy.

Micronuclear collapse from oxidative damage.

Chromosome-containing micronuclei are a hallmark of aggressive cancers. Micronuclei frequently undergo irreversible collapse, exposing their enclosed chromatin to the cytosol. Micronuclear rupture catalyzes chromosomal rearrangements, epigenetic abnormalities, and inflammation, yet mechanisms safeguarding micronuclear integrity are poorly understood. In this study, we found that mitochondria-derived reactive oxygen species (ROS) disrupt micronuclei by promoting a noncanonical function of charged multivesicular body protein 7 (CHMP7), a scaffolding protein for the membrane repair complex known as endosomal sorting complex required for transport III (ESCRT-III). ROS retained CHMP7 in micronuclei while disrupting its interaction with other ESCRT-III components. ROS-induced cysteine oxidation stimulated CHMP7 oligomerization and binding to the nuclear membrane protein LEMD2, disrupting micronuclear envelopes. Furthermore, this ROS-CHMP7 pathological axis engendered chromosome shattering known to result from micronuclear rupture. It also mediated micronuclear disintegrity under hypoxic conditions, linking tumor hypoxia with downstream processes driving cancer progression.

2847: Regulatory role of miRNAs at different tumor hypoxia levels in prostate cancer patients

2847: Regulatory role of miRNAs at different tumor hypoxia levels in prostate cancer patients

Galectin-9 Mediates the Functions of Microglia in the Hypoxic Brain Tumor Microenvironment.

Galectin-9 is a multifaceted regulator of various pathophysiological processes that exerts positive or negative effects in a context-dependent manner. Here, we elucidated the distinctive functional properties of galectin-9 on myeloid cells within the brain tumor microenvironment. Galectin-9-expressing cells were abundant at the hypoxic tumor edge in the tumor-bearing ipsilateral hemisphere compared to the contralateral hemisphere in an intracranial mouse brain tumor model. Galectin-9 was highly expressed in microglia and macrophages in tumor-infiltrating cells. In primary glia, both the expression and secretion of galectin-9 were influenced by tumors. Analysis of a human glioblastoma bulk RNA-sequencing dataset and a single-cell RNA-sequencing dataset from a murine glioma model revealed a correlation between galectin-9 expression and glial cell activation. Notably, the galectin-9high microglial subset was functionally distinct from the galectin-9neg/low subset in the brain tumor microenvironment. Galectin-9high microglia exhibited properties of inflammatory activation and higher rates of cell death, whereas galectin-9neg/low microglia displayed a superior phagocytic ability against brain tumor cells. Blockade of galectin-9 suppressed tumor growth and altered the activity of glial and T cells in a mouse glioma model. Additionally, glial galectin-9 expression was regulated by Hif-2α in the hypoxic brain tumor microenvironment. Myeloid-specific Hif-2α deficiency led to attenuated tumor progression. Together, these findings reveal that galectin-9 on myeloid cells is an immunoregulator and putative therapeutic target in brain tumors.

Hypoxia-Targeted Immunotherapy with PD-1 Blockade in Head and Neck Cancer.

Intratumoral hypoxia is associated with tumor progression, aggressiveness, and therapeutic resistance in several cancers. Hypoxia causes cancer cells to experience replication stress, thereby activating DNA damage and repair pathways. MutT homologue-1 (MTH1, also known as NUDT1), a member of the Nudix family, maintains the genomic integrity and viability of tumor cells in the hypoxic tumor microenvironment. Although hypoxia is associated with poor prognosis and can cause therapeutic resistance by regulating the microenvironment, it has not been considered a treatable target in cancer. This study aimed to investigate whether hypoxia-induced MTH1 is a useful target for immunotherapy and whether hypoxic conditions influence the antitumor activity of immune cells. Our results showed that MTH1 expression was elevated under hypoxic conditions in head and neck cancer cell lines. Furthermore, we identified a novel MTH1-targeting epitope peptide that can activate peptide-specific CD4+ helper T cells with cytotoxic activity. The proliferation and cytotoxic activity of T cells were maintained under hypoxic conditions, and PD-1 blockade further augmented the cytotoxicity. These results indicate that MTH1-targeted immunotherapy combined with checkpoint blockade can be an effective strategy for the treatment of hypoxic tumors.

Platinum-Metformin Conjugates Acting as Promising PD-L1 Inhibitors through the AMP-Activated Protein Kinase Mediated Lysosomal Degradation Pathway.

With the development of metalloimmunology, the potential of platinum drugs in cancer immunotherapy has attracted extensive attention. Although immunochemotherapy combining PD-1/PD-L1 antibodies with platinum drugs has achieved great success in the clinic, combination therapy commonly brings new problems. Herein, we have developed a platinum-metformin conjugate as a promising alternative to antibody-based PD-L1 inhibitors, not only disrupting PD-1/PD-L1 axis on cell surface but also down-regulating the total PD-L1 levels in non-small cell lung cancer (NSCLC) cells comprehensively, thus achieving highly efficient immunochemotherapy by a single small molecule. Mechanism studies demonstrate that Pt-metformin conjugate can selectively accumulate in lysosomes, promote lysosomal-dependent PD-L1 degradation via the AMPK-TFEB pathway, and modulate the upstream regulatory proteins related to PD-L1 expression (e.g. HIF-1α and NF-κB), eventually decreasing the total abundance of PD-L1 in NSCLC, overcoming tumor hypoxia, and activating anti-tumor immunity in vivo. This work suggests an AMPK-mediated lysosomal degradation pathway of PD-L1 for the first time and provides a unique design perspective for the development of novel platinum drugs for immunochemotherapy.

Docetaxel-Encapsulated Catalytic Pt/Au Nanotubes for Synergistic Chemo-Photothermal Therapy of Triple-Negative Breast Cancer.

The combination of photothermal therapy with chemotherapy has emerged as a promising therapeutic modality for addressing triple-negative breast cancer (TNBC). This manuscript describes a novel hybrid nanoplatform comprising ultrathin catalytic platinum/gold (Pt/Au) nanotubes encapsulated with docetaxel and phase-change materials (PCMs) for the photoacoustic imaging-guided synergistic chemo-photothermal therapy of TNBC. Upon irradiation of near-infrared laser, the photothermal heating of nanotubes converts solid-state PCM into liquid, triggering the controlled release of the encapsulated docetaxel. The thin Pt layer within nanotubes enhances the nanotube's thermal stability, thus prolonging the photothermal ablation of tumors. Furthermore, platinum effectively mitigates tumor hypoxia by catalyzing the decomposition of hydrogen peroxides to generate oxygen in the tumor microenvironment, thus improving the efficiency of chemotherapy. It is demonstrated that the drug-loaded nanotubes achieve significant tumor inhibition rates of 75.4% in vivo on 4T1 tumor-bearing mice, significantly surpassing control groups. These nanotubes also notably extend survival, attributable to the synergistic effects of prolonged photothermal therapy facilitated by platinum and oxygenation-enhanced chemotherapy. This combination leverages the unique properties of the Pt/Au NTs-DTX/PCM nanoplatform, optimizing therapeutic outcomes. It is envisioned that this nanoplatform may find important applications in managing superficial malignant solid tumors in general.

A comprehensive landscape analysis of autophagy in cancer development and drug resistance.

Autophagy plays important roles in cancer progression and therapeutic resistance, and the autophagy underlying the tumor pathogenesis and further mechanisms of chemoresistance emergence remains unknown. In this study, via the single-sample gene set enrichment analysis (ssGSEA) method, an autophagy 45-gene list was identified to evaluate samples' autophagy activity, verified through six GEO datasets with a confirmed autophagy phenotype. It was further utilized to distinguish tumors into autophagy score-high and score-low subtypes, and analyze their transcriptome landscapes, including survival analysis, correlation analysis of autophagy- and resistance-related genes, biological functional enrichment, and immune- and hypoxia-related and genomic heterogeneity comparison, in TCGA pan-cancer datasets. Furthermore, we performed an analysis of autophagy status in breast cancer chemoresistance combined with multiple GEO datasets and in vitro experiments to validate the mechanisms of potential anticancer drugs for reversing chemoresistance, including CCK-8 cell viability assays, RT-qPCR, and immunofluorescence. The 45-gene list was used to identify autophagy score-high and score-low subtypes and further analyze their multi-dimensional features. We demonstrated that cancer autophagy status correlated with significantly different prognoses, molecular alterations, biological process activations, immunocyte infiltrations, hypoxia statuses, and specific mutational processes. The autophagy score-low subtype displayed a more favorable prognosis compared with the score-high subtype, associated with their immune-activated features, manifested as high immunocyte infiltration, including high CD8+T, Tfh, Treg, NK cells, and tumor-associated macrophages M1/M2. The autophagy score-low subtype also showed a high hypoxia score, and hypoxic tumors showed a significantly differential prognosis in different autophagy statuses. Therefore, "double-edged" cell fates triggered by autophagy might be closely correlated with the immune microenvironment and hypoxia induction. Results demonstrated that dysregulated autophagy was involved in many cancers and their therapeutic resistance and that the autophagy was induced by the resistance-reversing drug response, in five breast cancer GEO datasets and validated by in vitro experiments. In vitro, dihydroartemisinin and artesunate could reverse breast cancer doxorubicin resistance, through inducing autophagy via upregulating LC3B and ATG7. Our study provided a comprehensive landscape of the autophagy-related molecular and tumor microenvironment patterns for cancer progression and resistance, and highlighted the promising potential of drug-induced autophagy in the activation of drug sensitivity and reversal of resistance.

Tumor microenvironment-like conditions alter pancreatic cancer cell metabolism and behavior.

The tumor microenvironment is complex and dynamic, characterized by poor vascularization, limited nutrient availability, hypoxia, and an acidic pH. This environment plays a critical role in driving cancer progression. However, standard cell culture conditions used to study cancer cell biology in vitro fail to replicate the in vivo environment of tumors. Recently, "physiological" cell culture media that closely resemble human plasma have been developed (e.g., Plasmax, HPLM), along with more frequent adoption of physiological oxygen conditions (1%-8% O2). Nonetheless, further refinement of tumor-specific culture conditions may be needed. In this study, we describe the development of a tumor microenvironment medium (TMEM) based on murine pancreatic ductal adenocarcinoma (PDAC) tumor interstitial fluid. Using RNA-sequencing, we show that murine PDAC cells (KPCY) cultured in tumor-like conditions (TMEM, pH 7.0, 1.5% O2) exhibit profound differences in gene expression compared with plasma-like conditions (mouse plasma medium, pH 7.4, 5% O2). Specifically, the expression of genes and pathways associated with cell migration, biosynthesis, angiogenesis, and epithelial-to-mesenchymal transition were altered, suggesting tumor-like conditions promote metastatic phenotypes and metabolic remodeling. Using functional assays to validate RNA-seq data, we confirmed increased motility at 1.5% O2/TMEM, despite reduced cell proliferation. Moreover, a hallmark shift to glycolytic metabolism was identified via measurement of glucose uptake/lactate production and mitochondrial respiration. Taken together, these findings demonstrate that growth in 1.5% O2/TMEM alters several biological responses in ways relevant to cancer biology, and more closely models hallmark cancerous phenotypes in culture. This highlights the importance of establishing tumor microenvironment-like conditions in standard cancer research. NEW & NOTEWORTHY Standard cell culture conditions do not replicate the complex tumor microenvironment experienced by cells in vivo. Although currently available plasma-like media are superior to traditional supraphysiological media, they fail to model tumor-like conditions. Using RNA-seq analysis and functional metabolic and migratory assays, we show that tumor microenvironment medium (TMEM), used with representative tumor hypoxia, better models cancerous phenotypes in culture. This emphasizes the critical importance of accurately modeling the tumor microenvironment in cancer research.

A versatile nanoplatform carrying cascade Pt nanozymes remodeling tumor microenvironment for amplified sonodynamic/chemo therapy of thyroid cancer

Thyroid cancer is increasing globally, with anaplastic thyroid carcinoma (ATC) being the most aggressive type and having a poor prognosis. Current clinical treatments for thyroid cancer present numerous challenges, including invasiveness and the necessity of lifelong medication. Furthermore, a significant portion of patients with ATC experience cancer recurrence and metastasis. To overcome this dilemma, we developed a pH-responsive biomimetic nanocarrier (CLP@HP-A) through the incorporation of Chlorin e6 (Ce6) and Lenvatinib (Len) within hollow polydopamine nanoparticles (HP) that were further modified with platinum nanoparticles (Pt), enabling synergistic chemotherapy and sonodynamic therapy. The CLP@HP-A nanocarriers exhibited specific binding with galectin-3 receptors, facilitating their internalization through receptor-mediated endocytosis for targeted drug delivery. Upon exposure to ultrasound (US) irradiation, Ce6 rapidly generated reactive oxygen species (ROS) to induce significant oxidative stress and trigger apoptosis in tumor cells. Additionally, Pt not only alleviated tumor hypoxia by catalyzing the conversion of H2O2 to oxygen (O2) but also augmented intracellular ROS levels through the production of hydroxyl radicals (•OH), thereby enhancing the efficacy of sonodynamic therapy. Moreover, Len demonstrated a potent cytotoxic effect on thyroid cancer cells through the induction of apoptosis. Transcriptomics analysis findings additionally corroborated that CLP@HP-A effectively triggered cancer cell apoptosis, thereby serving as a crucial mechanism for its cytotoxic effects. In conclusion, the integration of sonodynamic/chemo combination therapy with targeted drug delivery systems offers a novel approach to the management of malignant tumors.

Molecular Engineering of Pure Superoxide Radical Photogenerator for Hypoxia-Tolerant Tumor Theranostics.

Photodynamic therapy (PDT) is a promising cancer treatment, but limited oxygen supply in tumors (hypoxia) can hinder its effectiveness. This is because traditional PDT relies on Type-II reactions that require oxygen. Type-I photosensitizers (PSs) offer a promising approach to overcome the limitations of tumor photodynamic therapy (PDT) in hypoxic environments. To leverage the advantages of Type-I PDT, the design and evaluation of a series of Type-I PSs for developing pure Type-1 PSs, by incorporating benzene, thiophene, or bithiophene into the donor-acceptor molecular skeleton are reported. Among them, CTTI (with bithiophene) shows the best performance, generating the most superoxide radical (O2 •-) upon light irradiation. Importantly, CTTI exclusively produced superoxide radicals, avoiding the less effective Type-II pathway. This efficiency is due to CTTI's energy gap and low reduction potential, which favor electron transfer to oxygen for O2 •- generation. Finally, CTTI NPs are successfully fabricated by encapsulating CTTI into liposomes, and validated to be effective in killing tumor cells, even under hypoxic conditions, making them promising hypoxia-tolerant tumor phototheranostic agents in both in vitro and in vivo applications.

Ultrasmall iridium-encapsulated porphyrin metal-organic frameworks for enhanced photodynamic/catalytic therapy by producing reactive oxygen species storm

Transition metal-coordinated porphyrin metal-organic frameworks (MOFs) were perspective in photodynamic therapy (PDT) and catalytic therapy. However, the tumor hypoxia and the insufficient endogenous hydrogen peroxide (H2O2) seriously limited their efficacies. Herein, by encapsulating ultrasmall iridium (Ir) and modifying glucose oxidase (GOx), an iron-coordinated porphyrin MOF (Fe-MOF) nanoplatform (Fe-MOF@Ir/GOx) was designed to strengthen PDT/catalytic therapy by producing reactive oxygen species (ROS) storm. In this nanoplatform, Fe-MOF showed glutathione (GSH)-responsive degradation, by which porphyrin, GOx and ultrasmall Ir were released. Moreover, ultrasmall Ir possessed dual-activities of catalase (CAT)-like and peroxidase (POD)-like, which provided sufficient oxygen (O2) to enhance PDT efficacy, and hydroxyl radical (·OH) production was also improved by combining Fenton reaction of Fe2+. Further, GOx catalyzed endogenous glucose produced H2O2, also reduced pH value, which accelerated Fenton reaction and resulted in generation of ROS storm. Therefore, the developed Fe-MOF@Ir/GOx nanoplatform demonstrated enhanced PDT/catalytic therapy by producing ROS storm, and also provided a promising strategy to promote degradation/metabolism of inorganic nanoplatforms.

Pt/Pd dual-modified porphyrin metal-organic frameworks for NIR-II photothermal-enhanced photodynamic/catalytic therapy

Photodynamic therapy (PDT) and catalytic therapy were promising treatment modes, but tumor hypoxia and poor catalytic activity severely limited their efficacies. Herein, using a porphyrin metal–organic framework (PCN-224) as nanocarrier, a platinum/palladium (Pt/Pd) dual-modified PCN-224 nanoprobe (PCN-224-Pt@Pd) with strong peroxidase (POD)/catalase (CAT)-like activities was developed, achieving photothermal-promoted PDT/catalytic therapy. Compared with single ultrasmall Pt modifying, CAT-like activity of Pt/Pd dual-modifying increased oxygen concentration from 6.24 to 9.35 mg/L, which improved singlet oxygen (1O2) yield from 63.8 % to 82.9 %. Moreover, POD-like activity of Pt/Pd dual-modifying significantly accelerated hydroxyl radicals (·OH) generation. Importantly, PCN-224-Pt@Pd possessed near-infrared II (NIR-II) photothermal effect with a high efficiency (55.6 %), which further promoted ·OH production. Under combined therapy of PCN-224-Pt@Pd, the cell survival rate greatly reduced to 5.8 %, and the tumors were cured, suggesting NIR-II photothermal-enhanced PDT/catalytic therapy.

Vacancy-engineered Mn-doped iron oxide nano-crystals for enhanced sonodynamic therapy through self-supplied oxygen

Sonodynamic therapy (SDT) is a minimally invasive therapeutic approach, that uses ultrasound activating sonosensitizers to generate reactive oxygen species (ROS) for inducing the tumor cell death. However, the SDT is always limited by the dissatisfactory performance of sonosensitizers and hypoxic tumor microenvironment (TME). Nano iron oxide is a narrow bandgap semiconductor material with good biocompatibility. The doping of manganese into iron oxide (Mn-doped iron oxide nano-crystals named Mn-Fe2O3 NCs) not only reduced the band gap of iron oxide and altered the valence band position of iron oxide, but also introduced more oxygen vacancies and inhibited the complexation of electrons (e-) and holes (h+), significantly enhancing the ability to generate ROS. The Mn-Fe2O3 NCs improved the hypoxic TME by self-generating oxygen and consuming endogenous glutathione (GSH), which amplified oxidative stress and further enhanced the SDT. The therapeutic results showed that the prepared Mn-Fe2O3 NCs could efficiently inhibit the triple-negative breast cancer (TNBC) cells by SDT (80.49 % inhibition ratio in vivo). Overall, we propose a simple method to design inorganic sonosensitizers for enhancing efficient sonodynamic therapy.

Hypoxia-induced complement component 3 promotes aggressive tumor growth in the glioblastoma microenvironment.

Glioblastoma (GBM) is the most aggressive form of glioma with a high rate of relapse despite intensive treatment. Tumor recurrence is tightly linked to radio-resistance, which in turn is associated with hypoxia. Here, we discovered a strong link between hypoxia and local complement signaling using publicly available bulk, single-cell, and spatially resolved transcriptomic data from patients with GBM. Complement component 3 (C3) and the receptor C3AR1 were both associated with aggressive disease and shorter survival in human glioma. In a genetically engineered mouse model of GBM, we found C3 specifically in hypoxic tumor areas. In vitro, we found an oxygen level-dependent increase in C3 and C3AR1 expression in response to hypoxia in several GBM and stromal cell types. C3a induced M2 polarization of cultured microglia and macrophages in a C3aR-dependent fashion. Targeting C3aR using the antagonist SB290157 prolonged survival of glioma-bearing mice both alone and in combination with radiotherapy while reducing the number of M2-polarized macrophages. Our findings establish a strong link between hypoxia and complement pathways in GBM and support a role of hypoxia-induced C3a/C3aR signaling as a contributor to glioma aggressiveness by regulating macrophage polarization.

Prolonged inhibition of intratumoral mast cells enhances efficacy of low-dose antiangiogenic therapy.

Low-dose antiangiogenic therapies have demonstrated the ability to enhance normalization of tumor vessels, consequently improving hypoxia levels, drug delivery, and promoting anticancer immune responses. Mast cells have been identified as contributors to resistance against antiangiogenic therapy and facilitators of abnormal neoangiogenesis. In this study, we demonstrate that by simultaneously targeting intratumoral mast cells with Imatinib and administering low-dose anti-VEGFR2 therapy, antitumor efficacy can be enhanced in preclinical models. Thus, combinatory treatment overcomes therapy resistance, while concurrently promoting tumor vessel normalization. Notably, histomorphometric analysis of tumor sections revealed that vessel perfusion could be improved through mast cell inhibition and, despite a significantly reduced microvessel density, the combination treatment did not result in elevated tumor hypoxia levels compared to anti-VEGFR2 therapy alone. Short-term Imatinib application effectively increased antitumor efficacy, and by prolonging the application of Imatinib tumor vessel normalization was additionally improved. The combination of mast cell depletion and antiangiogenic treatments has not been investigated in detail and promises to help overcoming therapy resistance. Further studies will be required to explore their impact on other treatment approaches, and subsequently to validate these findings in a clinical setting.