Hypoxic Tumor Regions Research Articles

Autonomous In Vivo Computation in Internet of Nano Bio Things

Different natural biological processes are possible because of the collaboration among simple living cells. Similarly computerized systems such as multi-agent systems (MAS) rely on multiple interacting agents with simplified and reduced capability, to collectively solve difficult problems that are impossible for individual agents to solve on their own. This work highlights an autonomous tumor sensitization strategy in complex human vasculature, where target detection is achieved through swarm coordination mechanism, with no prior knowledge of tumor location. We propose that small-scale biocompatible organisms such as nanoparticles, can perform deterministic tasks following the simple principles of aggregation and migration. We aim to show through computational experiments that tumor-triggered bio-physical gradients can be leveraged by nanoparticles to collectively move towards the potential tumor hypoxic regions. Although individual nanoparticles have no target-directed locomotion ability due to limited communication and computation capability, we demonstrate that once passive collaboration is achieved, they can successfully avoid obstacles and detect the tumor. Numerical experiments demonstrate that the overall targeting efficiency could improve considerably from 10% to 90% through passive collaboration among nanoparticles. Furthermore, with the introduction of noisy search space and mobile obstacles, the targeting performance would reduce by 25%. Such self-regulating particles can be used as homing agents for target amplification, and hence can assist in early cancer detection through contrast-enhanced medical imaging. We believe that our work will motivate self-dependent and non-centralized approach for magnification of tumor location.

Improving the Therapeutic Efficiency of Hypoxic-Activated Prodrugs by Enhancing Hypoxia in Solid Tumors.

The low sensitivity of hypoxic regions in solid tumors to radiotherapy and chemotherapy remains a major obstacle to cancer treatment. By taking advantage of hypoxic-activated prodrugs, tirapazamine (TPZ), generating cytotoxic reductive products and the glucose oxidase (GOx)-based glucose oxidation reaction, we designed a nanodrug-loading system that combined TPZ-induced chemotherapy with GOx-mediated cancer-orchestrated starvation therapy and cancer oxidation therapy. In this work, we first prepared mesoporous silica (MSN) loaded with TPZ. Then, in order to prevent the leakage of TPZ in advance, the surface was coated with a layer of carMOF formed by Fe3+ and carbenicillin (car), and GOx was adsorbed on the outermost layer to form the final nanosystem MSN-TPZ@carMOF-GOx (MT@c-G). GOx could effectively consume oxygen and catalyzed glucose into gluconic acid and hydrogen peroxide. First, the generated gluconic acid lowered the pH of tumor tissues, promoted the decomposition of carMOF, and released TPZ. Second, oxygen consumption could improve the degree of hypoxia in tumor tissues, so that enhanced the activity of TPZ. Furthermore, GOx could generate cancer-orchestrated starvation/oxidation therapy. Therefore, our study provided a new strategy that TPZ combined with GOx achieved starvation/oxidation/chemotherapy for enhancing anticancer effects in hypoxic regions.

GLUT3/SLC2A3 Is an Endogenous Marker of Hypoxia in Prostate Cancer Cell Lines and Patient-Derived Xenograft Tumors.

The microenvironment of solid tumors is dynamic and frequently contains pockets of low oxygen levels (hypoxia) surrounded by oxygenated tissue. Indeed, a compromised vasculature is a hallmark of the tumor microenvironment, creating both spatial gradients and temporal variability in oxygen availability. Notably, hypoxia associates with increased metastasis and poor survival in patients. Therefore, to aid therapeutic decisions and better understand hypoxia’s role in cancer progression, it is critical to identify endogenous biomarkers of hypoxia to spatially phenotype oncogenic lesions in human tissue, whether precancerous, benign, or malignant. Here, we characterize the glucose transporter GLUT3/SLC2A3 as a biomarker of hypoxic prostate epithelial cells and prostate tumors. Transcriptomic analyses of non-tumorigenic, immortalized prostate epithelial cells revealed a highly significant increase in GLUT3 expression under hypoxia. Additionally, GLUT3 protein increased 2.4-fold in cultured hypoxic prostate cell lines and was upregulated within hypoxic regions of xenograft tumors, including two patient-derived xenografts (PDX). Finally, GLUT3 out-performs other established hypoxia markers; GLUT3 staining in PDX specimens detects 2.6–8.3 times more tumor area compared to a mixture of GLUT1 and CA9 antibodies. Therefore, given the heterogeneous nature of tumors, we propose adding GLUT3 to immunostaining panels when trying to detect hypoxic regions in prostate samples.

Proteolysis of a histone acetyl reader, ATAD2, induces chemoresistance of cancer cells under severe hypoxia by inhibiting cell cycle progression in S phase.

Cancer cells acquire chemoresistance in hypoxic regions of solid tumors, which is suggested to be at least partly due to reduction of their proliferative activity. However, molecular mechanisms behind it have not been fully elucidated. Here, we revealed the importance of active proteolysis of a histone acetylation reader, ATPase family AAA domain containing 2 (ATAD2), under hypoxia. We found that inactivation of an O2/Fe2+/α-ketoglutarate-dependent dioxygenase triggered ATAD2 proteolysis by the proteasome system upon severe hypoxia in a hypoxia-inducible factors (HIFs)-independent manner. Consistently, ATAD2 expression levels were markedly lower in perinecrotic hypoxic regions in both xenografted and clinical tumor tissues. The ATAD2 proteolysis was accompanied by a decrease in the amount of acetylated histone H3 lysine 27 and inhibited cell cycle progression from the early to late S phase under severe hypoxia. The retardation of S phase progression induced chemoresistance, which was blocked by overexpression of ATAD2. Together, these results indicate that ATAD2 proteolysis upon severe hypoxia induces chemoresistance of cancer cells through heterochromatinization and the subsequent retardation of S phase progression; therefore, inhibition of ATAD2 proteolysis is expected to be a strategy to overcome chemoresistance of hypoxic tumor cells.

In Situ Hypoxia-Induced Supramolecular Perylene Diimide Radical Anions in Tumors for Photothermal Therapy with Improved Specificity.

Considering that hypoxia is closely associated with tumor proliferation, invasion, metastasis, and drug resistance, it is of great significance to overcome hypoxia in tumor treatment. Herein, we report a hypoxia-induced specific photothermal therapy (PTT) based on the photothermal agent of supramolecular perylene diimide radical anions. Hypoxic regions in various tumors display strong reductive ability, and in such environments the supramolecular complex of a perylene diimide derivative and cucurbit[7]uril could be reduced to supramolecular perylene diimide radical anions. Benefiting from the strong NIR absorption and good photothermal conversion performance of the in situ generated supramolecular perylene diimide radical anions, the hypoxia-induced PTT strategy exhibits excellent photothermal therapeutic efficiency as well as good specificity and biological safety. Moreover, hypoxia inducible factor expression of tumors decreases to the normal level after PTT treatment. It is anticipated that such a hypoxia-induced specific PTT strategy opens new horizons for photothermal therapy against hypoxic tumors with improved specificity and safety.

TRIB1 regulates tumor growth via controlling tumor-associated macrophage phenotypes and is associated with breast cancer survival and treatment response

Molecular mechanisms that regulate tumor-associated macrophage (TAM) phenotype and function are incompletely understood. The pseudokinase TRIB1 has been reported as a regulator of macrophage phenotypes, both in mouse and human systems.Methods: Bioinformatic analysis was used to investigate the link between TRIB1 expression in breast cancer and therapeutic response to chemotherapy. In vivo models of breast cancer included immune-competent mice to characterize the consequences of altered (reduced or elevated) myeloid Trib1 expression on tumor growth and composition of stromal immune cell populations.Results: TRIB1 was highly expressed by TAMs in breast cancer and high TRIB1 expression correlated with response to chemotherapy and patient survival. Both overexpression and knockout of myeloid Trib1 promote mouse breast tumor growth, albeit through different molecular mechanisms. Myeloid Trib1 deficiency led to an early acceleration of tumor growth, paired with a selective reduction in perivascular macrophage numbers in vivo and enhanced oncogenic cytokine expression in vitro. In contrast, elevated levels of Trib1 in myeloid cells led to an increased late-stage mammary tumor volume, coupled with a reduction of NOS2 expressing macrophages and an overall reduction of macrophages in hypoxic tumor regions. In addition, we show that myeloid Trib1 is a previously unknown, negative regulator of the anti-tumor cytokine IL-15, and that increased myeloid Trib1 expression leads to reduced IL-15 levels in mammary tumors, with a consequent reduction in the number of T-cells that are key to anti-tumor immune responses.Conclusions: Together, these results define a key role for TRIB1 in chemotherapy responses for human breast cancer and provide a mechanistic understanding for the importance of the control of myeloid TRIB1 expression in the development of this disease.

Magnetotactic bacteria AMB-1 with active deep tumor penetrability for magnetic hyperthermia of hypoxic tumors.

Tumor hypoxia is a great physiological barrier for tumor treatment. The development of efficient detection and treatment methods for tumor hypoxia has great scientific and clinical significance. In this work, we investigated the potential of magnetotactic bacteria AMB-1 for magnetic resonance imaging (MRI)-guided magnetic hyperthermia treatment of hypoxic tumors. Our investigations reveal that AMB-1 bacteria can selectively migrate to the hypoxic regions of solid tumors due to their anaerobic characteristics, showing active deep tumor penetrability. Moreover, AMB-1 bacteria exhibit high MRI contrast and magnetic heating performances because of the excellent magnetic performance of their magnetosomes. In vivo studies demonstrate that AMB-1 can not only generate T2-weighted contrast signals in tumor tissue, but also efficiently ablate hypoxic solid tumors through the magnetic hyperthermia effect. We believe that this novel microbial therapy can be a potential weapon for hypoxic tumor treatment.

Detection and impact of hypoxic regions in multicellular tumor spheroid cultures formed by head and neck squamous cell carcinoma cells lines.

In solid tumors like head and neck cancer (HNC), chronic and acute hypoxia have serious adverse clinical consequences including poorer overall patient prognosis, enhanced metastasis, increased genomic instability, and resistance to radiation-, chemo-, or immuno-therapies. However, cells in the two-dimensional monolayer cultures typically used for cancer drug discovery experience 20%-21% O2 levels (normoxic) which are 4-fold higher than O2 levels in normal tissues and ≥10-fold higher than in the hypoxic regions of solid tumors. The oxygen electrodes, exogenous bio-reductive markers, and increased expression of endogenous hypoxia-regulated proteins like HIF-1α generally used to mark hypoxic regions in solid tumors are impractical in large sample numbers and longitudinal studies. We used a novel homogeneous live-cell permeant HypoxiTRAK™ (HPTK) molecular probe compatible with high content imaging detection, analysis, and throughput to identify and quantify hypoxia levels in live HNC multicellular tumor spheroid (MCTS) cultures over time. Accumulation of fluorescence HPTK metabolite in live normoxic HNC MCTS cultures correlated with hypoxia detection by both pimonidazole and HIF-1α staining. In HNC MCTSs, hypoxic cytotoxicity ratios for the hypoxia activated prodrugs (HAP) evofosfamide and tirapazamine were much smaller than have been reported for uniformly hypoxic 2D monolayers in gas chambers, and many viable cells remained after HAP exposure. Cells in solid tumors and MCTSs experience three distinct O2 microenvironments dictated by their distances from blood vessels or MCTS surfaces, respectively; oxic, hypoxic, or intermediate levels of hypoxia. These studies support the application of more physiologically relevant in vitro 3D models that recapitulate the heterogeneous microenvironments of solid tumors for preclinical cancer drug discovery.

Immunofluorescence-Based Method to Assess Cancer Biomarker in the Hypoxic Region of the Tumor.

The development of novel imaging technologies allows the analysis of the expression and spatial distribution of multiple markers simultaneously, providing necessary information about a cellular identity and the surrounding microenvironment. This chapter describes the utilization of immunofluorescence to identify such biomarkers in fixed tissue from prostate cancer (PCa) xenografts. One such marker detectable by immunofluorescence is pimonidazole, which has been utilized to locate areas of low oxygen (hypoxia). Pimonidazole, in combination with other biomarkers, could be utilized to identify "niches" in the microenvironment harboring more aggressive cells both within and outside hypoxic areas. Specifically, we describe the method to use pimonidazole for the identification of hypoxic regions in PCa xenograft tumors along with CPT1A (carnitine palmitoyltransferase 1A) expression, an indicator of β-oxidation. This approach could be useful to characterize various biomarkers in the complex hypoxic tumor microenvironment.

Radiomics outperforms semantic features for prediction of response to stereotactic radiosurgery in brain metastases

BackgroundBrain metastases show different patterns of contrast enhancement, potentially reflecting hypoxic and necrotic tumor regions with reduced radiosensitivity. An objective evaluation of these patterns might allow a prediction of response to radiotherapy. We therefore investigated the potential of MRI radiomics in comparison with the visual assessment of semantic features to predict early response to stereotactic radiosurgery in patients with brain metastases. Patients and methodsIn this retrospective study, 150 patients with 308 brain metastases from solid tumors (NSCLC in 53% of patients) treated by stereotactic radiosurgery (single dose of 17–20 Gy) were evaluated. The response of each metastasis (partial or complete remission vs. stabilization or progression) was assessed within 180 days after radiosurgery. Patterns of contrast enhancement in the pre-treatment T1-weighted MR images were either visually classified (homogenous, heterogeneous, necrotic ring-like) or subjected to a radiomics analysis. Random forest models were optimized by cross-validation and evaluated in a hold-out test data set (30% of metastases). ResultsIn total, 221/308 metastases (72%) responded to radiosurgery. The optimal radiomics model comprised 10 features and outperformed the model solely based on semantic features in the test data set (AUC, 0.71 vs. 0.56; accuracy, 69% vs. 54%). The diagnostic performance could be further improved by combining semantic and radiomics features resulting in an AUC of 0.74 and an accuracy of 75% in the test data set. ConclusionThe developed radiomics model allowed prediction of early response to radiosurgery in patients with brain metastases and outperformed the visual assessment of patterns of contrast enhancement.

A Self-Driven Bioreactor Based on Bacterium-Metal-Organic Framework Biohybrids for Boosting Chemotherapy via Cyclic Lactate Catabolism.

The excessive lactate in the tumor microenvironment always leads to poor therapeutic outcomes of chemotherapy. In this study, a self-driven bioreactor (defined as SO@MDH, where SO is Shewanella oneidensis MR-1 and MDH is MIL-101 metal-organic framework nanoparticles/doxorubicin/hyaluronic acid) is rationally constructed via the integration of doxorubicin (DOX)-loaded metal-organic framework (MOF) MIL-101 nanoparticles with SO to sensitize chemotherapy. Owing to the intrinsic tumor tropism and electron-driven respiration of SO, the biohybrid SO@MDH could actively target and colonize hypoxic and eutrophic tumor regions and anaerobically metabolize lactate accompanied by the transfer of electrons to Fe3+, which is the key component of the MIL-101 nanoparticles. As a result, the intratumoral lactate would undergo continuous catabolism coupled with the reduction of Fe3+ to Fe2+ and the subsequent degradation of MIL-101 frameworks, leading to an expeditious drug release for effective chemotherapy. Meanwhile, the generated Fe2+ will be promptly oxidized by the abundant hydrogen peroxide in the tumor microenvironment to reproduce Fe3+, which is, in turn, beneficial to circularly catabolize lactate and boost chemotherapy. More importantly, the consumption of intratumoral lactic acid could significantly inhibit the expression of multidrug resistance-related ABCB1 protein (also named P-glycoprotein (P-gp)) for conquering drug-resistant tumors. SO@MDH demonstrated here holds high tumor specificity and promising chemotherapeutic efficacy for suppressing tumor growth and overcoming multidrug resistance, confirming its potential prospects in cancer therapy.

Role of autophagy in cholangiocarcinoma: An autophagy-based treatment strategy.

Cholangiocarcinomas (CCAs) are diverse biliary epithelial tumours involving the intrahepatic, perihilar and distal parts of the biliary tree. The three entirely variable entities have distinct epidemiology, molecular characteristics, prognosis and strategy for clinical management. However, many cholangiocarcinoma tumor-cells appear to be resistant to current chemotherapeutic agents. The role of autophagy and the therapeutic value of autophagy-based therapy are largely unknown in CCA. The multistep nature of autophagy offers a plethora of regulation points, which are prone to be deregulated and cause different human diseases, including cancer. However, it offers multiple targetable points for designing novel therapeutic strategies. Tumor cells have evolved to use autophagy as an adaptive mechanism for survival under stressful conditions such as energy imbalance and hypoxic region of tumors within the tumor microenvironment, but also to increase invasiveness and resistance to chemotherapy. The purpose of this review is to summarize the current knowledge regarding the interplay between autophagy and cholangiocarcinogenesis, together with some preclinical studies with agents that modulate autophagy in order to induce tumor cell death. Altogether, a combinatorial strategy, which comprises the current anti-cancer agents and autophagy modulators, would represent a positive CCA patient approach.

Myoglobin Protects Breast Cancer Cells Due to Its ROS and NO Scavenging Properties.

Myoglobin (MB) is an oxygen-binding protein usually found in cardiac myocytes and skeletal muscle fibers. It may function as a temporary storage and transport protein for O2 but could also have scavenging capacity for reactive oxygen and nitrogen species. In addition, MB has recently been identified as a hallmark in luminal breast cancer and was shown to be robustly induced under hypoxia. Cellular responses to hypoxia are regulated by the transcription factor hypoxia-inducible factor (HIF). For exploring the function of MB in breast cancer, we employed the human cell line MDA-MB-468. Cells were grown in monolayer or as 3D multicellular spheroids, which mimic the in vivo avascular tumor architecture and physiology with a heterogeneous cell population of proliferating cells in the rim and non-cycling or necrotic cells in the core region. This central necrosis was increased after MB knockdown, indicating a role for MB in hypoxic tumor regions. In addition, MB knockdown caused higher levels of HIF-1α protein after treatment with NO, which also plays an important role in cancer cell survival. MB knockdown also led to higher reactive oxygen species (ROS) levels in the cells after treatment with H2O2. To further explore the role of MB in cell survival, we performed RNA-Seq after MB knockdown and NO treatment. 1029 differentially expressed genes (DEGs), including 45 potential HIF-1 target genes, were annotated in regulatory pathways that modulate cellular function and maintenance, cell death and survival, and carbohydrate metabolism. Of these target genes, TMEFF1, TREX2, GLUT-1, MKNK-1, and RAB8B were significantly altered. Consistently, a decreased expression of GLUT-1, MKNK-1, and RAB8B after MB knockdown was confirmed by qPCR. All three genes of interest are often up regulated in cancer and correlate with a poor clinical outcome. Thus, our data indicate that myoglobin might influence the survival of breast cancer cells, possibly due to its ROS and NO scavenging properties and could be a valuable target for cancer therapy.

Hemoglobin microbubbles for in vivo blood oxygen level dependent imaging: Boldly moving beyond MRI

Microbubbles are gas-filled, micron-sized particles stabilized by lipid, protein, or polymer shells. They scatter ultrasound energy efficiently due to their compressible gas cores, making them excellent blood pool contrast agents in ultrasound imaging. In this project, we have developed a novel oxygen-sensitive hemoglobin-shell microbubble designed to acoustically detect blood oxygen levels in vivo. We hypothesized that structural changes in the hemoglobin in response to varying oxygen levels will alter the mechanical properties of the bubble shell, resulting in detectable changes in the bubble acoustic signature. In this project, we have (1) optimized the hemoglobin bubble formulation for in vivo circulation, (2) demonstrated that the hemoglobin shell is still responsive to oxygen after formulation, and (3) characterized the acoustic response of the microbubbles at varying oxygen levels. Our preliminary results show a strong correlation between the oxygen concentration in the solution and the acoustic response of bubbles, suggesting that they would serve as excellent oxygen sensors. If successful, in vivo sensing of oxygen levels would have numerous benefits, including evaluating the hypoxic regions in tumors and in the brain, among other blood-oxygen-level-dependent (BOLD) imaging applications.

MCP-1-Functionalized, Core-Shell Gold Nanorod@Iron-Based Metal-Organic Framework (MCP-1/GNR@MIL-100(Fe)) for Photothermal Therapy.

The low vessel density and oxygen concentration in hypoxia are the main causes of reduced efficiency of anticancer therapeutics and can stimulate the tumor's relapse. Research showed that macrophages could cross the blood-vessel barriers and reach the hypoxic regions of tumors. Using macrophages in a drug delivery system has been a promising method for tumor targeting in recent years. In this work, we successfully modified monocyte chemoattractant protein-1 (MCP-1) and iron-based metal-organic framework (MIL-100(Fe)) on the photothermal agent, gold nanorods (GNRs) (i.e., MCP-1/GNR@MIL-100(Fe)), to increase cellular uptake and biocompatibility. The results of TEM, UV-vis, and FTIR all confirmed that we'd synthesized MCP-1/GNR@MIL-100(Fe) successfully, and the MCP-1/GNR@MIL-100(Fe) also showed good biocompatibility. A transwell migration assay illustrated that our material attracted macrophages, and the material uptake amount was increased by 1.5 times after MCP-1 functionalization. It also indicated that the macrophages have a tumor-targeting ability. In the in vivo experiment, we subcutaneously implanted U251 MG cells in nude mice as a xenograft model to demonstrate the photothermal activity of MCP-1/GNR@MIL-100(Fe). With successive NIR treatment, the tumor growth could be controlled, and the tumor volume still remained below 100 mm3 after laser treatment. MCP-1/GNR@MIL-100(Fe) combined with the laser treatment showed an excellent antitumor efficacy from the histology of tumor tissues, survival rates, and bioluminescence imaging.

First Comparison between [18f]-FMISO and [18f]-Faza for Preoperative Pet Imaging of Hypoxia in Lung Cancer.

Simple SummaryThe definition of the tumor hypoxia is important in oncology because this characteristic is linked to a poor prognosis. In this context, we compared two hypoxia tracers, FMISO and FAZA, before surgery for lung cancer. Hypoxia tracers correlate well with each other and FMISO is superior to FAZA in defining the hypoxia volume of lung cancers. However, there is no correlation with immunohistochemical findings (GLUT-1, CAIX, LDH-5, and HIF1-Alpha).Hypoxic areas are typically resistant to treatment. However, the fluorine-18-fluoroazomycin-arabinoside (FAZA) and fluorine 18 misonidazole (FMISO) tracers have never been compared in non small cell lung cancer (NSCLC). This study compares the capability of 18F-FAZA PET/CT with that of 18F-FMISO PET/CT for detecting hypoxic tumour regions in early and locally advanced NSCLC patients. We prospectively evaluated patients who underwent preoperative PET scans before surgery for localised NSCLC (i.e., fluorodeoxyglucose (FDG)-PET, FMISO-PET, and FAZA-PET). The PET data of the three tracers were compared with each other and then compared to immunohistochemical analysis (GLUT-1, CAIX, LDH-5, and HIF1-Alpha) after tumour resection. Overall, 19 patients with a mean age of 68.2 ± 8 years were included. There were 18 lesions with significant uptake (i.e., SUVmax >1.4) for the F-MISO and 17 for FAZA. The mean SUVmax was 3 (±1.4) with a mean volume of 25.8 cc (±25.8) for FMISO and 2.2 (±0.7) with a mean volume of 13.06 cc (±13.76) for FAZA. The SUVmax of F-MISO was greater than that of FAZA (p = 0.0003). The SUVmax of F-MISO shows a good correlation with that of FAZA at 0.86 (0.66–0.94). Immunohistochemical results are not correlated to hypoxia PET regardless of the staining. The two tracers show a good correlation with hypoxia, with FMISO being superior to FAZA. FMISO, therefore, remains the reference tracer for defining hypoxic volumes.

The Use of Bionic Prodrugs for the Enhancement of Low Dose Radiotherapy.

Radiotherapy (RT) is a standard treatment strategy for many cancer types, but the need to frequently apply high doses of ionizing radiation in order to achieve therapeutic efficacy can cause severe harm to healthy tissues, leading to adverse patient outcomes. In an effort to minimize these toxic side effects, we herein sought to design a novel approach to the low-dose RT treatment of hypoxic tumors using a Tirapazamine (TPZ)-loaded exosome (EXO) nanoplatform (MT). This MT platform was synthesized via loading EXOs with TPZ, which is a prodrug that is activated when exposed to hypoxic conditions. MT application was able to achieve effective tumor inhibition at a relatively low RT dose (2 Gy) that was superior to standard high-dose (6 Gy) RT treatment with specific targeting to the hypoxic region of tumor. RT-mediated oxygen consumption further aggravated hypoxic conditions to improve TPZ activation and treatment efficacy. Together, our findings demonstrate the clinical promise of this MT platform as a novel tool for the efficient radiosensitization and treatment of cancer patients.

Polyethylenimine (PEI)-modified poly (lactic-co-glycolic) acid (PLGA) nanoparticles conjugated with tumor-homing bacteria facilitate high intensity focused ultrasound-mediated tumor ablation

The acoustic propagation characteristic of ultrasound determines that the energy of ultrasound beam will decrease with the increase of its propagation depth in the body. Similarly, the energy of High Intensity Focused Ultrasound (HIFU) will be attenuated with the increase of HIFU propagation depth in the body. Ensuring sufficient ultrasound energy deposition in the HIFU ablation region for tumor ablation is usually achieved by increasing the ultrasound irradiation power or prolonging the ultrasound ablation time. However, these two methods may damage the normal tissue adjacent to the HIFU ablation region. Herein, we constructed the nanoparticles conjugated with tumor-homing bacteria as the biological tumor-homing synergist to facilitate HIFU-mediated tumor ablation avoiding the potential safety risk. In our strategy, Bifidobacterium bifidum (B.bifidum) was selectively colonized in the hypoxic region of solid tumors after been injected into 4T1 breast cancer bearing-BALB/c mice via the tail vein due to its anaerobic growth characteristic. The amount of B. bifidum with negative surface potential in the hypoxic region of solid tumors was increased by its anaerobic proliferation. Polyethylenimine (PEI) -modified Poly (lactic-co-glycolic) acid nanoparticles loaded sodium bicarbonate (PEI-PLGA-NaHCO3-NPs) with positive surface potential injected into 4T1 breast cancer bearing-BALB/c mice via the tail vein displayed the tumor-homing ability by the electrostatic adsorption with B. bifidum colonized solid tumors. PEI-PLGA-NaHCO3-NPs could release NaHCO3 to produce carbon dioxide (CO2) as cavitation nuclei inside the acidic microenvironment of solid tumors. When HIFU irradiated solid tumors contained with more cavitation nuclei, the ultrasound energy deposition at the tumor region was increased to destroy the tumors more effectively. Meanwhile, the improved efficiency of HIFU-mediated tumor ablation reduced the dependence of the tumor ablation on the ultrasound energy dose, which improved the safety of HIFU-mediated tumor ablation to the non-targeted ablation tissue. This tumor-homing synergist shows the potential application value on the HIFU-mediated tumor ablation in the clinical.

Abstract 1613: A hypoxia-driven transcriptional program characterizes acquired resistance to immune checkpoint inhibitors in lung cancer

Abstract Immune checkpoint inhibitors (ICIs) that block negative regulators of T cell function can generate lasting responses in lung cancer patients, yet only a minority of tumors respond to therapy and ~50% of patients whose tumors initially respond eventually develop acquired resistance. Mechanisms of acquired resistance to ICIs in lung cancer are not fully understood and strategies to overcome resistance are lacking. To address this challenge, we developed a new mouse model of acquired resistance to ICIs by knocking out the DNA mismatch repair gene Msh2 in Kras mutant mouse lung adenocarcinoma cells, leading to a higher mutation burden in these cells. Unlike Msh2 WT controls, Msh2 KO tumors transplanted into syngeneic mice are sensitive to ICIs. Importantly, chronic treatment with αPD-1 or αPD-1 + αCTLA-4 led to Msh2 KO tumors that initially responded to therapy but then developed acquired resistance. Tumors remained resistant to ICIs upon transplantation to new hosts, suggesting that tumor-intrinsic programs drive resistance. Gene set enrichment analysis (GSEA) of single cell RNA sequencing data revealed that tumors with acquired resistance to ICIs downregulated antigen processing and presentation gene signatures compared to tumors that were regressing on therapy. Specifically, tumor cells with acquired resistance downregulated expression of MHC class II, which was confirmed by flow cytometry, and this was accompanied by a decrease in expression of Stat1, Irf1, and Ciita, which drive MHC-II expression in response to IFNγ. Depletion of CD4+ T cells during αPD-1 + αCTLA-4 treatment abrogated the response to therapy, suggesting a functional role for tumor cell MHC-II expression. GSEA also revealed that tumors with acquired resistance to ICIs upregulated hypoxia and glycolysis gene signatures compared to tumors responding to therapy. Consistent with these results, resistant tumor cells had increased hypoxia, detected by pimonidazole staining, compared to tumor cells responding to therapy. Tumor infiltrating lymphocytes have been shown to be excluded from hypoxic tumor regions, suggesting that hypoxia in the tumor microenvironment may contribute to acquired resistance to ICIs by excluding T cells from these regions. Moreover, we found that Msh2 KO tumor cells upregulated MHC-II in response to IFNγ under normoxic in vitro conditions, but had lower MHC-II expression under hypoxia. Our data suggest that tumor hypoxia may contribute to both tumor-cell intrinsic transcriptional programs, such as alterations in antigen processing and presentation machinery, as well as tumor-cell extrinsic effects, such as exclusion of T cells from the tumor microenvironment, which together may impact the development of acquired resistance to immune checkpoint blockade. Our results can inform strategies to overcome acquired resistance, addressing a critical unmet need in cancer therapy. Citation Format: Camila Robles-Oteiza, Katherine Hastings, Susan M. Kaech, Katerina Politi. A hypoxia-driven transcriptional program characterizes acquired resistance to immune checkpoint inhibitors in lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1613.

Replication catastrophe induced by cyclic hypoxia leads to increased APOBEC3B activity.

Tumor heterogeneity includes variable and fluctuating oxygen concentrations, which result in the accumulation of hypoxic regions in most solid tumors. Tumor hypoxia leads to increased therapy resistance and has been linked to genomic instability. Here, we tested the hypothesis that exposure to levels of hypoxia that cause replication stress could increase APOBEC activity and the accumulation of APOBEC-mediated mutations. APOBEC-dependent mutational signatures have been well-characterized, although the physiological conditions which underpin them have not been described. We demonstrate that fluctuating/cyclic hypoxic conditions which lead to replication catastrophe induce the expression and activity of APOBEC3B. In contrast, stable/chronic hypoxic conditions which induce replication stress in the absence of DNA damage are not sufficient to induce APOBEC3B. Most importantly, the number of APOBEC-mediated mutations in patient tumors correlated with a hypoxia signature. Together, our data support the conclusion that hypoxia-induced replication catastrophe drives genomic instability in tumors, specifically through increasing the activity of APOBEC3B.