Identification of Surface Markers and Functional Characterization of Myeloid Derived Suppressor Cell-Like Adherent Cells

Myeloid-derived suppressor cell (MDSC)-like adherent cells (MLACs) are a recently identified CD11b+ F4/80- myeloid cell subset that can infiltrate tumors early in development and promote their growth. Because of these functions, MLACs play an important role in establishing an immunosuppressive tumor microenvironment (TME). However, the lack of MLAC-specific markers has hampered further characterization of this cell type. This study identifies the gene signature of MLACs by analyzing RNA-sequencing (RNA-seq) and public single-cell RNA-seq data, revealing that MLACs are an independent cell population that are distinct from other intratumoral myeloid cells. After combining proteome analysis of membrane proteins with RNA-seq data, H2-Ab1 and CD11c are indicated as marker proteins that can support the isolation of MLAC subsets from CD11b+ F4/80- myeloid cells by fluorescence-activated cell sorting. The CD11b+ F4/80- H2-Ab1+ and CD11b+ F4/80- CD11c+ MLAC subsets represent approximately half of the MLAC population that is isolated based on their adhesion properties and possess gene signatures and functional properties similar to those of the MLAC population. Additionally, membrane proteome analysis suggests that MLACs express highly heterogeneous surface proteins. This study facilitates an integrated understanding of heterogeneous intratumoral myeloid cells, as well as the molecular and cellular details of the development of an immunosuppressive TME.

Secretory GFP reconstitution labeling of neighboring cells interrogates cell-cell interactions in metastatic niches

Cancer cells inevitably interact with neighboring host tissue-resident cells during the process of metastatic colonization, establishing a metastatic niche to fuel their survival, growth, and invasion. However, the underlying mechanisms in the metastatic niche are yet to be fully elucidated owing to the lack of methodologies for comprehensively studying the mechanisms of cell-cell interactions in the niche. Here, we improve a split green fluorescent protein (GFP)-based genetically encoded system to develop secretory glycosylphosphatidylinositol-anchored reconstitution-activated proteins to highlight intercellular connections (sGRAPHIC) for efficient fluorescent labeling of tissue-resident cells that neighbor on and putatively interact with cancer cells in deep tissues. The sGRAPHIC system enables the isolation of metastatic niche-associated tissue-resident cells for their characterization using a single-cell RNA sequencing platform. We use this sGRAPHIC-leveraged transcriptomic platform to uncover gene expression patterns in metastatic niche-associated hepatocytes in a murine model of liver metastasis. Among the marker genes of metastatic niche-associated hepatocytes, we identify Lgals3, encoding galectin-3, as a potential pro-metastatic factor that accelerates metastatic growth and invasion.

Tissue-resident macrophages are major tumor-associated macrophage resources, contributing to early TNBC development, recurrence, and metastases

Triple-negative breast cancer (TNBC) is an aggressive and highly heterogenous disease with no well-defined therapeutic targets. Treatment options are thus limited and mortality is significantly higher compared with other breast cancer subtypes. Mammary gland tissue-resident macrophages (MGTRMs) are found to be the most abundant stromal cells in early TNBC before angiogenesis. We therefore aimed to explore novel therapeutic approaches for TNBC by focusing on MGTRMs. Local depletion of MGTRMs in mammary gland fat pads the day before TNBC cell transplantation significantly reduced tumor growth and tumor-associated macrophage (TAM) infiltration in mice. Furthermore, local depletion of MGTRMs at the site of TNBC resection markedly reduced recurrence and distant metastases, and improved chemotherapy outcomes. This study demonstrates that MGTRMs are a major TAM resource and play pivotal roles in the growth and malignant progression of TNBC. The results highlight a possible novel anti-cancer approach targeting tissue-resident macrophages.

AGE/RAGE axis regulates reversible transition to quiescent states of ALK-rearranged NSCLC and pancreatic cancer cells in monolayer cultures

Cancer recurrence due to tumor cell quiescence after therapy and long-term remission is associated with cancer-related death. Previous studies have used cell models that are unable to return to a proliferative state; thus, the transition between quiescent and proliferative states is not well understood. Here, we report monolayer cancer cell models wherein the human non-small cell lung carcinoma cell line H2228 and pancreatic cancer cell line AsPC-1 can be reversibly induced to a quiescent state under hypoxic and serum-starved (HSS) conditions. Transcriptome and metabolome dual-omics profiles of these cells were compared with those of the human lung adenocarcinoma cell line A549, which was unable to enter a quiescent state under HSS conditions. The quiescence-inducible cells had substantially lower intracellular pyruvate and ATP levels in the quiescent state than in the proliferative state, and their response to sudden demand for energy was dramatically reduced. Furthermore, in quiescence-inducible cells, the transition between quiescent and proliferative states of these cells was regulated by the balance between the proliferation-promoting Ras and Rap1 signaling and the suppressive AGE/RAGE signaling. These cell models elucidate the transition between quiescent and proliferative states, allowing the development of drug-screening systems for quiescent tumor cells.

In Vivo Label-Free Observation of Tumor-Related Blood Vessels in Small Animals Using a Newly Designed Photoacoustic 3D Imaging System

Photoacoustic (PA) technology can be used for non-invasive imaging of blood vessels. In this paper, we report on our prototype PA imaging system with a newly designed ultrasound sensor and its visualization performance of microvascular in animal. We fabricated an experimental system for animals using a high-frequency sensor. The system has two modes: still image mode by wide scanning and moving image mode by small rotation of sensor array. Optical test target, euthanized mice and rats, and live mice were used as objects. The results of optical test target showed that the spatial resolution was about two times higher than that of our conventional prototype. The image performance in vivo was evaluated in euthanized healthy mice and rats, allowing visualization of detailed blood vessels in the liver and kidneys. In tumor-bearing mice, different results of vascular induction were shown depending on the type of tumor and the method of transplantation. By utilizing the video imaging function, we were able to observe the movement of blood vessels around the tumor. We have demonstrated the feasibility of the system as a less invasive animal experimental device, as it can acquire vascular images in animals in a non-contrast and non-invasive manner.

Droplet-based valveless microfluidic system for phage-display screening against spheroids

In this study, we proposed a droplet-based valveless microfluidic system that has the necessary functions to perform the binding, washing, eluting, and collecting processes of phage-display screening against spheroids, which can be expected to present a similar repertoire and number of membrane proteins as in vivo. Although spheroids have much larger sizes than single cells, spheroids are difficult to manipulate through manual operation. The proposed microfluidic system actively controls the position and velocity of droplets using a camera, three air pumps, and three liquid pumps to perform the processes for phage-display screening. The cross section of the microchannel is large in width and height for the passage of spheroids. Valves that can close such a large cross-sectional microchannel are not readily available. Thus, we proposed valveless flow control using liquid pumps. In addition, the proposed microfluidic system involves complex flow channels with airflow subchannels to perform phage-display screening. For washing, nonspecific-binding phages remaining in the flow channels must be minimized. The proposed microfluidic system can perform selective blocking and flush washing. Selective blocking can prevent the airflow channels from becoming hydrophilic with blocking liquid, and flush washing can flush phages remaining in the flow channel. We experimentally verified the functions of the developed microfluidic device based on the proposed system.

In Vivo Imaging of Oxidative and Hypoxic Stresses in Mice Model of Amyotrophic Lateral Sclerosis

Oxidative and hypoxic stresses are associated with the degeneration of both motor neurons and skeletal muscles in amyotrophic lateral sclerosis (ALS). In vivo bioluminescent imaging is used to monitor cellular responses to oxidative and hypoxic stresses in living ALS model mice bearing G93A-human Cu/Zn superoxide dismutase (SOD1) longitudinally using the IVIS spectrum imaging system. Double transgenic mice bearing both Keap1-dependent oxidative stress detector No-48 (OKD48) and G93A-SOD1 are useful for in vivo imaging of oxidative stress in ALS. We developed a bioluminescence resonance energy transfer (BRET) probe that is regulated by HIF-1α-specific ubiquitin-proteasome system. G93A-SOD1 mice injected with the BRET probe are useful to investigate the spatiotemporal responses to hypoxic stress in ALS. In this chapter, we introduce a practical protocol of in vivo imaging of both oxidative and hypoxic stress in ALS model mice.

Antibody-guided design and identification of CD25-binding small antibody mimetics using mammalian cell surface display

Small antibody mimetics that contain high-affinity target-binding peptides can be lower cost alternatives to monoclonal antibodies (mAbs). We have recently developed a method to create small antibody mimetics called FLuctuation-regulated Affinity Proteins (FLAPs), which consist of a small protein scaffold with a structurally immobilized target-binding peptide. In this study, to further develop this method, we established a novel screening system for FLAPs called monoclonal antibody-guided peptide identification and engineering (MAGPIE), in which a mAb guides selection in two manners. First, antibody-guided design allows construction of a peptide library that is relatively small in size, but sufficient to identify high-affinity binders in a single selection round. Second, in antibody-guided screening, the fluorescently labeled mAb is used to select mammalian cells that display FLAP candidates with high affinity for the target using fluorescence-activated cell sorting. We demonstrate the reliability and efficacy of MAGPIE using daclizumab, a mAb against human interleukin-2 receptor alpha chain (CD25). Three FLAPs identified by MAGPIE bound CD25 with dissociation constants of approximately 30 nM as measured by biolayer interferometry without undergoing affinity maturation. MAGPIE can be broadly adapted to any mAb to develop small antibody mimetics.

Reconstitution of an Anti-HER2 Antibody Paratope by Grafting Dual CDR-Derived Peptides onto a Small Protein Scaffold

Target-binding small proteins are promising alternatives to conventional monoclonal antibodies (mAbs), offering advantages in terms of tissue penetration and manufacturing costs. Recently, a design strategy to create small proteins called fluctuation-regulated affinity proteins (FLAPs) consisting of a structurally immobilized peptide from the complementarity-determining region (CDR) loops of mAbs (CDR-derived peptide) and a protein scaffold was developed. Because mAb paratopes are usually composed of multiple CDRs, FLAPs with multiple binding peptides may have an enhanced target-binding capability. Here, a strategy to create FLAPs bearing dual CDR-derived peptides (D-FLAPs) using the anti-human epithelial growth factor receptor type 2 (HER2) mAb trastuzumab as a basis is developed. Computationally selected CDR-derived peptides are first grafted onto two adjacent loops of the fibronectin type III domain (FN3) scaffold, yielding 80 D-FLAP candidates. After computational screening based on their similarity to the parental mAb with regard to the conformation of paratope residues, two candidates are selected. After further evaluation with ELISA, one D-FLAP with HYTTPP and GDGFYA peptides from CDR-L3 and CDR-H3 of the parental mAb, respectively, is found to bind HER2 with a dissociation constant of 58 nm. This method applies to various mAb drugs and allows the rational design of small protein alternatives.

Abstract LB-006: In vivo imaging of HIF-active cells in tumors using transgenic mice with a HIF-dependent reporter gene

Hypoxia inducible factor (HIF) is a transcription factor essential for hypoxia adaptation. In tumors, cells increase HIF activity through excess growth factor stimulation and oncogene activation as well as hypoxia, leading to the expression of many genes involved in malignancy. Since elevated HIF activity is one of the key features of malignancy, changes based on HIF activity can be very important therapeutic targets for cancer therapy, especially in the treatment of refractory cancer. Therefore, understanding HIF-active cells in tumors during tumor development and malignant progression is important in developing cancer treatment strategies.Various types of immune cells such as lymphocytes, neutrophils and monocytes infiltrate into tumors at different times. These immune cells have antitumor functions, but have also been reported to promote tumor immunosuppression and malignant progression. Although HIF activation in these cells has been suggested to play a key role in these events, it is not yet clear how and when the HIF activity is involved in the process.We have been developing transgenic mice (Tg) to monitor HIF activity by in vivo imaging. So far, however, no Tg can achieve enough sensitivity to detect cell-based HIF activity by in vivo imaging. Recently, we have constructed a new Tg (HVA-Tg) with a reporter transgene that exresses AkaLuc and Venus proteins in a HIF activity-dependent manner. AkaLuc [1] is a mutant firefly luciferase that achieves 100- - 1000-fold higher detection sensitivity with artificial luciferin AkaLumine-HCl [2] compared to natural firefly luciferase and D-luciferin combination. The bioluminescence produced by AkaLuc and AkaLumine-HCl is called AkaBLI and has a peak emission at 670-680 nm, in the near infrared region, leading to much higher biopermeability compared to the firefly luciferase-D-luciferin system, whose bioluminescence peak is 560 nm.In this study, we monitored HIF activity in tumors syngenically transplanted into HVA-Tg: E0771 (a breast cancer cell line) was orthotopically transplanted and bioluminescence form the tumors were monitored by in vivo imaging overtime. As expected, the host derived luminescence ware detected from the tumor site at two weeks post transplantation. Ex vivo imaging confirmed that this signal was generated from the tumor. Immunohistochemical analysis of tumor sections revealed that AkaLuc was detected in the same cells as Gr-1 and F4/80-positive cells. These data suggest that HVA-Tg is a useful tool to investigate HIF activity in tumor stromal cells, and its analysis will provide useful information to further explore the mechanism how HIF activity contributes to tumor immunosuppression.[1] Iwano S, Kuchimaru T, Kizaka-Kondoh S, et al. Science 359:935-939 (2018).[2] Kuchimaru T., Kadonosono T., Kizaka-Kondoh S. et al. Nat Commun, 7, 11856 (2016).

Citation Format: Hitomi Miyabara, Ryuichiro Hirano, Takahiro Kuchimaru, Tetsuya Kadonosono, Hitomi Watanabe, Gen Kondoh, Shinae Kizaka-Kondoh. In vivo imaging of HIF-active cells in tumors using transgenic mice with a HIF-dependent reporter gene [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-006.

Abstract 2713: Elucidation of bone metastasis using a caudal artery injection mouse model and Akaluc-AkaLumine near-infrared bioluminescence technology

Bone is one of the most common sites of metastasis for various primary tumors including breast, prostate and lung cancers. We have addressed molecular basis underlying bone metastasis using newly developed murine model of bone metastasis and near-infrared bioluminescence technologies. Our new murine model overcomes several limitations in the current standard model by intra-cardiac (IC) injection of cancer cells [1]. We found that the caudal artery is a new pathway to predominantly deliver cancer cells to the bone marrow of hind limbs in mice. Intra-caudal arterial (CA) injection is technically as easy as tail vein injection [2]. In addition, CA injection delivered cancer cells >10-fold more efficiently than IC injection. This accelerated the development of bone metastasis in hind limbs with wide variety of cell lines. We have combined the CA injection model with near-infrared bioluminescence imaging. Bioluminescence imaging (BLI) with firefly luciferases and its natural substrate D-luciferin has been indispensable to noninvasively monitor metastasis development in mice. To improve deep-tissue imaging, synthetic luciferin AkaLumine has successfully extended the wavelength of firefly bioluminescence to the near-infrared region where tissue is more transparent to light [3]. More recently, our collaborators created an engineered luciferase Akaluc that displays high catalytic activity in reaction with AkaLumine [4]. AkaLumine-Akaluc bioluminescence imaging (AkaBLI) is capable of noninvasive visualization of single cancer cells deep inside mice. Combining the CA injection model with AkaBLI technology is a powerful tool for elucidating the mechanism of bone metastasis in small animals. References [1] Kuchimaru et al. Nat Commun 2018, 9, 2918 [2] http://sites.google.com/view/takahirokuchimaru/protocol [3] Kuchimaru et al. Nat Commun 2016, 7, 11856 [4] Iwano et al. Science 2018, 359, 935

Citation Format: Takahiro Kuchimaru, Misa Minegishi, Shinae Kizaka-Kondoh. Elucidation of bone metastasis using a caudal artery injection mouse model and Akaluc-AkaLumine near-infrared bioluminescence technology [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2713.

Slicing Spheroids in Microfluidic Devices for Morphological and Immunohistochemical Analysis

Microfluidic devices utilizing spheroids play important roles in in vitro experimental systems to closely simulate morphological and biochemical characteristics of the in vivo tumor microenvironment. For the observation and analysis of the inner structure of spheroids, sectioning is an efficient approach. However, conventional microfluidic devices are difficult for sectioning, and therefore, spheroids inside the microfluidic channels have not been sliced well. We proposed a microfluidic device created from embedding resin for sectioning. Spheroids were cultured, embedded by resin, and sectioned in the microfluidic device. Slices of the sectioned spheroids yielded clear images at the cellular level. According to morphological and immunohistochemical analyses of the slices of the spheroid, specific protein distribution was observed.

[Semi-rational Design of Target-binding Small Proteins for Cancer Treatment]

Small proteins that have a high affinity for cancer cell surface markers can be promising cheap alternatives to antibodies (antibody mimetics). Various types of antibody mimetics have thus been extensively developed. We recently found that a target-binding peptide binds to its target molecule more strongly when it is structurally constrained. To apply this finding to the development of chemically synthesizable small antibody mimetics, we have established an efficient method of creating such proteins, named fluctuation-regulated affinity proteins (FLAPs). To identify desirable scaffolds, first, 13 human proteins (46-104 aa) were selected from the Protein Data Bank. Then, thirteen graft acceptor (GA) sites that efficiently immobilize the grafted peptide structure were identified from six small protein scaffolds using molecular dynamics simulation. To assess the designed antibody mimetics in vitro, human epidermal growth factor receptor 2 (HER2)-binding peptides were selected from the anti-HER2 antibody drugs trastuzumab and pertuzumab by calculating the binding energy, and these were then grafted into the GA sites of scaffolds to create 65 FLAP candidates. The FLAP candidates were expressed in bacteria as fusion proteins with Renilla luciferase (Rluc), and their relative binding affinity to HER2 was easily determined by measuring the Rluc bioluminescence intensity without protein purification. Finally, four out of the 65 showed specific binding to HER2 with a dissociation constant (K_D) of 24-65 nM, and these were used for the detection of HER2-expressing cancer cells. Our design strategy will promote the development of antibody mimetics for the effective treatment of cancers and other diseases.

Design Strategy to Create Antibody Mimetics Harbouring Immobilised Complementarity Determining Region Peptides for Practical Use

Monoclonal antibodies (mAbs) are attractive therapeutics for treating a wide range of human disorders, and bind to the antigen through their complementarity-determining regions (CDRs). Small stable proteins containing structurally retained CDRs are promising alternatives to mAbs. In this report, we present a method to create such proteins, named fluctuation-regulated affinity proteins (FLAPs). Thirteen graft acceptor (GA) sites that efficiently immobilise the grafted peptide structure were initially selected from six small protein scaffolds by computational identification. Five CDR peptides extracted by binding energy calculations from mAbs against breast cancer marker human epithelial growth factor receptor type 2 (HER2) were then grafted to the selected scaffolds. The combination of five CDR peptides and 13 GA sites in six scaffolds revealed that three of the 65 combinations showed specific binding to HER2 with dissociation constants (K_D) of 270–350 nM in biolayer interferometry and 24–65 nM in ELISA. The FLAPs specifically detected HER2-overexpressing cancer cells. Thus, the present strategy is a promising and practical method for developing small antibody mimetics.

Strategic design to create HER2-targeting proteins with target-binding peptides immobilized on a fibronectin type III domain scaffold

Tumor-binding peptides such as human epidermal growth factor receptor 2 (HER2)-binding peptides are attractive therapeutic and diagnostic options for cancer. However, the HER2-binding peptides (HBPs) developed thus far are susceptible to proteolysis and lose their affinity to HER2 in vivo. In this report, a method to create a HER2-binding fluctuation-regulated affinity protein (HBP-FLAP) consisting of a fibronectin type III domain (FN3) scaffold with a structurally immobilized HBP is presented. HBPs were selected by phage-library screening and grafted onto FN3 to create FN3-HBPs, and the HBP-FLAP with the highest affinity (HBP sequence: YCAHNM) was identified after affinity maturation of the grafted HBP. HBP-FLAP containing the YCAHNM peptide showed increased proteolysis-resistance, binding to HER2 with a dissociation constant (K_D) of 58 nM in ELISA and 287 nM in biolayer interferometry and specifically detects HER2-expressing cancer cells. In addition, HBP-FLAP clearly delineated HER2-expressing tumors with a half-life of 6 h after intravenous injection into tumor-bearing mice. FN3-based FLAP is an excellent platform for developing target-binding small proteins for clinical applications.

A HER2-binding protein, HBP-FLAP, developed by peptide immobilization specifically binds to HER2 and has improved resistance to proteases.

Characterization and Biodistribution Analysis of Oxygen-Doped Single-Walled Carbon Nanotubes Used as in Vivo Fluorescence Imaging Probes

Single-walled carbon nanotubes (SWCNTs) show strong fluorescence in the 1000-1700 nm second near-infrared (NIR-II) wavelength range and are considered promising candidates for angiographic imaging probes. Oxygen-doped SWCNTs coated with phospholipid-polyethylene glycol (o-SWCNT-PEG) show exceptional potential, as they emit fluorescence at ∼1300 nm through excitation with 980 nm light. Here, with the aim of putting o-SWCNTs to practical use as an angiographic agent in animal experiments, the retention time after intravenous administration in the vasculature of mice and the biodistribution were studied. To provide bio affinity, the o-SWCNTs were coated with phospholipid polyethylene glycol. The intravenously injected o-SWCNT-PEG circulated within the vasculature for 3 h and cleared within 1 day. There was prominent fluorescence and Raman signals from the SWCNTs in the liver and spleen early in the experiment; the signals remained for 1 month. No apparent abnormalities in weight or appearance were observed after 2 months, suggesting low toxicity of o-SWCNT-PEG. These characteristics of o-SWCNT-PEG would make it useful as an angiographic imaging probe in the NIR-II wavelength range.

Microfluidic High-Migratory Cell Collector Suppressing Artifacts Caused by Microstructures

The small number of high-migratory cancer cells in a cell population make studies on high-migratory cancer cells difficult. For the development of migration assays for such cancer cells, several microfluidic devices have been developed. However, they measure migration that is influenced by microstructures and they collect not only high-migratory cells, but also surrounding cells. In order to find high-migratory cells in cell populations while suppressing artifacts and to collect these cells while minimizing damages, we developed a microfluidic high-migratory cell collector with the ability to sort cancer cells according to cellular migration and mechanical detachment. High-migratory cancer cells travel further from the starting line when all of the cells are seeded on the same starting line. The high-migratory cells are detached using a stretch of cell adhesive surface using a water-driven balloon actuator. Using this cell collector, we selected high-migratory HeLa cells that migrated about 100m in 12 h and collected the cells.

A reliable murine model of bone metastasis by injecting cancer cells through caudal arteries

Although the current murine model of bone metastasis using intracardiac (IC) injection successfully recapitulates the process of bone metastasis, further progress in the study of bone metastasis requires a new model to circumvent some limitations of this model. Here, we present a new murine model of bone metastasis achieved by injecting cancer cells through the intra-caudal arterial (CA). This model does not require high technical proficiency, predominantly delivers cancer cells to bone marrow of hind limbs with much higher efficiency than IC injection, and greatly shortens the period of overt bone metastasis development. Moreover, CA injection barely causes acute death of mice, enabling us to inject a larger number of cancer cells to further accelerate the development of bone metastasis with a wide variety of cell lines. Our model may open a new avenue for understanding the bone metastatic processes and development of drugs preventing bone metastasis and recurrence.

Blockage of the mevalonate pathway overcomes the apoptotic resistance to MEK inhibitors with suppressing the activation of Akt in cancer cells

With increasing clinical demands for MEK inhibitors in cancer treatment, overcoming the resistance to MEK inhibitors is an urgent problem to be solved. Numerous reports have shown that MEK inhibition results in the activation of PI3K-Akt signaling, which may confer apoptotic resistance to MEK inhibitors. We here demonstrate that the blockade of the mevalonate pathway using the antilipidemic drug statins represses Akt activation following MEK inhibition and induces significant apoptosis when co-treated with CH5126766 or trametinib. These events were clearly negated by the addition of mevalonate or geranylgeranyl pyrophosphate, indicating that the protein geranylgeranylation is implicated in the apoptotic resistance to MEK inhibitors. Furthermore, mechanistically, the combined treatment of CH5126766 with statins upregulated TNF-related apoptosis-inducing ligand (TRAIL), which was dependent on inhibition of the mevalonate pathway and is involved in apoptosis induction in human breast cancer MDA-MB-231 cells. The present study not only revealed that the mevalonate pathway could be targetable to enhance the efficacy of MEK inhibitors, but also proposes that combinatorial treatment of MEK inhibitors with statins may be a promising therapeutic strategy to sensitize cancer cells to apoptosis.

Novel adherent CD11b+ Gr-1+ tumor-infiltrating cells initiate an immunosuppressive tumor microenvironment

The immunosuppressive tumor microenvironment is a hallmark of cancer. Myeloid-derived suppressor cells (MDSCs) are CD11b⁺ Gr-1⁺ tumor-infiltrating immature myeloid cells that strongly mediate tumor immunosuppression. The CD11b⁺ Gr-1⁺ cells are a heterogeneous cell population, and the impacts of each subpopulation on tumor progression are not yet completely understood. In the present study, we identified a novel subpopulation of CD11b⁺ Gr-1⁺ cells from murine lung carcinoma tumors according to their strongly adherent abilities. Although strong adherent activity is a unique property of macrophages, their marker expression patterns are similar to those of MDSCs; thus, we named this novel subpopulation MDSC-like adherent cells (MLACs). Unlike known MDSCs, MLACs lack the ability to suppress cytotoxic T lymphocytes and differentiate into tumor-associated macrophages (TAMs), but could still directly facilitate tumor growth and angiogenesis through secreting CCL2, CXCL1/2/5, PAI-1, MMPs, and VEGFA. Furthermore, MLACs recruited MDSCs via the secretion of CCL2/5 and CXCL1/2/5, thereby enhancing the immunosuppressive tumor microenvironment and promoting TAMs-mediated tumor progression. Our findings suggest that MLACs may function as an initiator of the immunosuppressive tumor microenvironment and highlight a new therapeutic target to prevent the onset or delay malignant progression.

Domain architecture of vasohibins required for their chaperone-dependent unconventional extracellular release

Vasohibins (VASH1 and VASH2) are recently identified regulators of angiogenesis and cancer cell functions. They are secreted proteins without any classical secretion signal sequences, and are thought to be secreted instead via an unconventional protein secretion (UPS) pathway in a small vasohibin-binding protein (SVBP)-dependent manner. However, the precise mechanism of SVBP-dependent UPS is poorly understood. In this study, we identified a novel UPS regulatory system in which essential domain architecture (VASH-PS) of VASHs, comprising regions VASH1_91-180 and VASH2_80-169 , regulate the cytosolic punctate structure formation in the absence of SVBP. We also demonstrate that SVBP form a complex with VASH1 through the VASH1_274-282 (SIa), VASH1_139-144 (SIb), and VASH1_133-137 (SIc), leading to the dispersion in the cytosol and extracellular release of VASH1. The amino acid sequences of VASH-SIa and VASH-PS, containing SIb and SIc, are highly conserved among VASH family members in vertebrates, suggesting that SVBP-dependent UPS may be common within the VASH family. This novel UPS regulatory system may open up new avenues for understanding fundamental protein secretion in vertebrates.

A novel injectable BRET-based in vivo imaging probe for detecting the activity of hypoxia-inducible factor regulated by the ubiquitin-proteasome system

The ubiquitin-proteasome system (UPS) is a selective protein degradation system that plays a critical role in many essential biological processes by regulating the existence of various cellular proteins. The target proteins of UPS are recognized and tagged with polyubiquitin chains by E3 ubiquitin ligases, which have high substrate-specific activities. Here we present a novel injectable imaging probe POL-N that can detect the UPS-regulated hypoxia-inducible factor (HIF) activity in vivo. Because the luciferase is fused to the E3 ligase-recognition domain of the HIF-1α, POL-N is intact only in the HIFα-overexpressing cells, that is, HIF-active cells, generating signals via an intramolecular bioluminescence resonance energy transfer (BRET) between luciferase and a near-infrared (NIR) fluorescent dye at the C-terminal end of the probe. Off-target signals of the NIR-BRET were so low that we could achieve highly sensitive and fast detection of intratumoral HIF-activity. Notably, we successfully detected hypoxic liver metastasis, which is extremely difficult to detect by injectable imaging probes due to strong off-target signals, as early as 1 h after systemic injection of POL-N. Our probe design can be widely adapted to UPS-target proteins and may contribute to the exploration of their roles in animal disease models.

Hypoxia-inducible factor-targeting prodrug TOP3 combined with gemcitabine or TS-1 improves pancreatic cancer survival in an orthotopic model

Pancreatic cancer is one of the most lethal digestive system cancers with a 5‐year survival rate of 4–7%. Despite extensive efforts, recent chemotherapeutic regimens have provided only limited benefits to pancreatic cancer patients. Gemcitabine and TS‐1, the current standard‐of‐care chemotherapeutic drugs for treatment of this severe cancer, have a low response rate. Hypoxia is one of the factors contributing to treatment resistance. Specifically, overexpression of hypoxia‐inducible factor, a master transcriptional regulator of cell adaption to hypoxia, is strongly correlated with poor prognosis in many human cancers. TAT‐ODD‐procaspase‐3 (TOP3) is a protein prodrug that is specifically processed and activated in hypoxia‐inducible factor‐active cells in cancers, leading to cell death. Here, we report combination therapies in which TOP3 was combined with gemcitabine or TS‐1. As monotherapy, gemcitabine and TS‐1 showed a limited effect on hypoxic and starved pancreatic cancer cells, whereas co‐treatment with TOP3 successfully overcame this limitation in vitro. Furthermore, combination therapies of TOP3 with these drugs resulted in a significant improvement in survival of orthotopic pancreatic cancer models involving the human pancreatic cancer cell line SUIT‐2. Overall, our study indicates that the combination of TOP3 with current chemotherapeutic drugs can significantly improve treatment outcome, offering a promising new therapeutic option for patients with pancreatic cancer.

A metal carbonyl-protein needle composite designed for intracellular CO delivery to modulate NF-κB activity

Carbon monoxide (CO) has been recognized as a messenger for signal transduction in living cells and tissues. For intracellular CO delivery, several metal carbonyl complexes have been used as CO-releasing molecules (CO-RMs). To improve the properties of CO-RMs, such as the stability and the CO release rate, ligands and carriers of the metal complexes have been exploited. Here we report the development of an efficient intracellular CO delivery system using a protein scaffold. We used a protein needle reconstructed from gene product 5 of bacteriophage T4, which has high cellular permeability and stability. When ruthenium carbonyl complexes are conjugated to the needle using a His-tag triad at the C-terminus, the resulting composite has a significantly higher cellular uptake efficiency of Ru carbonyl and a 12-fold prolonged CO release rate relative to Ru(CO)3Cl(glycinate), a widely used CO-RM. We demonstrate that CO delivered by the composite activates the transcriptional factor nuclear factor-kappaB (NF-κB), which in turn leads to significant induction of expression of its target genes, HO1, NQO1, and IL6, through generation of reactive oxygen species (ROS). The signaling pathway is distinct from that of tumor necrosis factor (TNF)-α-induced activation of NF-κB. The protein needle-based CO-RM can be exploited to elucidate the biological functions of CO and used in the development of protein-based organometallic tools for modulation of cellular signaling.

Preparation of a cross-linked porous protein crystal containing Ru carbonyl complexes as a CO-releasing extracellular scaffold

Protein crystals generally are stable solid protein assemblies. Certain protein crystals are suitable for use as nanovessels for immobilizing metal complexes. Here we report the preparation of ruthenium carbonyl-incorporated cross-linked hen egg white lysozyme crystals (Ru·CL-HEWL). Ru·CL-HEWL retains a Ru carbonyl moiety that can release CO, although a composite of Ru carbonyl-HEWL dissolved in buffer solution (Ru·HEWL) does not release CO. We found that treatment of cells with Ru·CL-HEWL significantly increased nuclear factor kappa B (NF-κB) activity as a cellular response to CO. These results demonstrate that Ru·CL-HEWL has potential for use as an artificial extracellular scaffold suitable for transport and release of a gas molecule.

A fluorescent protein scaffold for presenting structurally constrained peptides provides an effective screening system to identify high affinity target-binding peptides

Peptides that have high affinity for target molecules on the surface of cancer cells are crucial for the development of targeted cancer therapies. However, unstructured peptides often fail to bind their target molecules with high affinity. To efficiently identify high-affinity target-binding peptides, we have constructed a fluorescent protein scaffold, designated gFPS, in which structurally constrained peptides are integrated at residues K131-L137 of superfolder green fluorescent protein. Molecular dynamics simulation supported the suitability of this site for presentation of exogenous peptides with a constrained structure. gFPS can present 4 to 12 exogenous amino acids without a loss of fluorescence. When gFPSs presenting human epidermal growth factor receptor type 2 (HER2)-targeting peptides were added to the culture medium of HER2-expressing cells, we could easily identify the peptides with high HER2-affinity and -specificity based on gFPS fluorescence. In addition, gFPS could be expressed on the yeast cell surface and applied for a high-throughput screening. These results demonstrate that gFPS has the potential to serve as a powerful tool to improve screening of structurally constrained peptides that have a high target affinity, and suggest that it could expedite the one-step identification of clinically applicable cancer cell-binding peptides.

Bone resorption facilitates osteoblastic bone metastatic colonization by cooperation of insulin-like growth factor and hypoxia

Bone metastasis is a multistep process that includes cancer cell dissemination, colonization, and metastatic growth. Furthermore, this process involves complex, reciprocal interactions between cancer cells and the bone microenvironment. Bone resorption is known to be involved in both osteolytic and osteoblastic bone metastasis. However, the precise roles of the bone resorption in the multistep process of osteoblastic bone metastasis remain unidentified. In this study, we show that bone resorption plays important roles in cancer cell colonization during the initial stage of osteoblastic bone metastasis. We applied bioluminescence/X-ray computed tomography multimodal imaging that allows us to spatiotemporally analyze metastasized cancer cells and bone status in osteoblastic bone metastasis models. We found that treatment with receptor activator of factor-κB ligand (RANKL) increased osteoblastic bone metastasis when given at the same time as intracardiac injection of cancer cells, but failed to increase metastasis when given 4 days after cancer cell injection, suggesting that RANKL-induced bone resorption facilitates growth of cancer cells colonized in the bone. We show that insulin-like growth factor-1 released from the bone during bone resorption and hypoxia-inducible factor activity in cancer cells cooperatively promoted survival and proliferation of cancer cells in bone marrow. These results suggest a mechanism that bone resorption and hypoxic stress in the bone microenvironment cooperatively play an important role in establishing osteoblastic metastasis.

The protective role of the transmembrane thioredoxin-related protein TMX in inflammatory liver injury

AIMS

Accumulating evidence indicates that oxidative stress is associated with inflammation, and the cellular redox status can determine the sensitivity and the final outcome in response to inflammatory stimuli. To control the redox balance, mammalian cells contain a variety of oxidoreductases belonging to the thioredoxin superfamily. The large number of these enzymes suggests a complex mechanism of redox regulation in mammals, but the precise function of each family member awaits further investigations.

RESULTS

We generated mice deficient in transmembrane thioredoxin-related protein (TMX), a transmembrane oxidoreductase in the endoplasmic reticulum (ER). When exposed to lipopolysaccharide (LPS) and d-(+)-galactosamine (GalN) to induce inflammatory liver injury, mutant mice were highly susceptible to the toxicants and developed severe liver damage. LPS-induced production of inflammatory mediators was equivalent in both wild-type and TMX(-/-) mice, whereas neutralization of the proinflammatory cytokine tumor necrosis factor-α suppressed the toxic effects of LPS/GalN in the mutant mice. Liver transcriptional profiles revealed enhanced activation of the p53-signaling pathway in the TMX(-/-) mice after LPS/GalN treatment. Furthermore, TMX deficiency also caused increased sensitivity to thioacetamide, which exerts its hepatotoxicity through the generation of reactive oxygen species.

INNOVATION

The present study is the first to address the role of the oxidoreductase TMX in inflammatory liver injury. The phenotype of mice deficient in TMX suggests a functional link between redox regulation in the ER and susceptibility to oxidative tissue damage.

CONCLUSION

We conclude that TMX plays a major role in host defense under the type of inflammatory conditions associated with oxidative stress.

Development of a hypoxia-selective near-infrared fluorescent probe for non-invasive tumor imaging

A near-infrared fluorochrome, GPU-311, was designed, synthesized and evaluated for its application in non-invasive imaging of tumor hypoxia. Efficient synthesis was achieved by nucleophilic substitution and click chemistry ring using the bifunctional tetraethylene glycol linker 2 containing thiol and azide groups for the conjugation of the propargylated nitroimidazole 1 and the heptamethine cyanine dye 3 bearing a 2-chloro-1-cyclohexenyl ring. GPU-311 exhibited long excitation and emission wavelength (Ex/Em=785/802 nm) and a decent quantum yield (0.05). The water solubility and hydrophilicity of GPU-311 increased. After in vitro treatment of SUIT-2/HRE-Luc pancreatic cancer cells with GPU-311, a higher level of fluorescence was observed selectively in hypoxia than in normoxia. However, in vivo fluorescence imaging of a mouse xenograft model after GPU-311 administration revealed inadequate accumulation of GPU-311 in tumors due to its rapid elimination through the liver.

2-Nitroimidazole-tricarbocyanine conjugate as a near-infrared fluorescent probe for in vivo imaging of tumor hypoxia

We developed a novel near-infrared (NIR) fluorescent probe, GPU-167, for in vivo imaging of tumor hypoxia. GPU-167 comprises a tricarbocyanine dye as an NIR fluorophore and two 2-nitroimidazole moieties as exogenous hypoxia markers that undergo bioreductive activation and then selective entrapment in hypoxic cells. After treatment with GPU-167, tumor cells contained significantly higher levels of fluorescence in hypoxia than in normoxia. In vivo fluorescence imaging specifically detected GPU-167 in tumors 24 h after administration. Ex vivo analysis revealed that fluorescence showed a strong correlation with hypoxia inducible factor (HIF)-1 active hypoxic regions. These data suggest that GPU-167 is a promising in vivo optical imaging probe for tumor hypoxia.

Detection of the onset of ischemia and carcinogenesis by hypoxia-inducible transcription factor-based in vivo bioluminescence imaging

An animal model for the early detection of common fatal diseases such as ischemic diseases and cancer is desirable for the development of new drugs and treatment strategies. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that regulates oxygen homeostasis and plays key roles in a number of diseases, including cancer. Here, we established transgenic (Tg) mice that carry HRE/ODD-luciferase (HOL) gene, which generates bioluminescence in an HIF-1-dependent manner and was successfully used in this study to monitor HIF-1 activity in ischemic tissues. To monitor carcinogenesis in vivo, we mated HOL mice with rasH2 Tg mice, which are highly sensitive to carcinogens and are used for short-term carcinogenicity assessments. After rasH2-HOL Tg mice were treated with N-methyl-N-nitrosourea, bioluminescence was detected noninvasively as early as 9 weeks in tissues that contained papillomas and malignant lesions. These results suggest that the Tg mouse lines we established hold significant potential for monitoring the early onset of both ischemia and carcinogenesis and that these lines will be useful for screening chemicals for carcinogenic potential.

Evaluation of [125I]IPOS as a molecular imaging probe for hypoxia-inducible factor-1-active regions in a tumor: comparison among single-photon emission computed tomography/X-ray computed tomography imaging, autoradiography, and immunohistochemistry

To image hypoxia-inducible factor-1 (HIF-1)-active tumors, we previously developed a chimeric protein probe ([(123/125) I]IPOS) that is degraded in the same manner as HIF-1α under normoxic conditions. In the present study, we aim to show that the accumulation of radioiodinated POS reflects the expression of HIF-1. In vivo single-photon emission computed tomography (SPECT)/X-ray CT (CT) imaging, autoradiography, and double-fluorescent immunostaining for HIF-1α and pimonidazole (PIMO) were carried out 24 h after the injection of [(125) I]IPOS. Tumor metabolite analysis was also carried out. A tumor was clearly visualized by multi-pinhole, high-resolution SPECT/CT imaging with [(125) I]IPOS. The obtained images were in accordance with the corresponding autoradiograms and with the results of ex vivo biodistribution. A metabolite analysis revealed that 77% of the radioactivity was eluted in the macromolecular fraction, suggesting that the radioactivity mainly existed as [(125) I]IPOS in the tumors. Immunohistochemistry revealed that the HIF-1α-positive areas and PIMO-positive areas were not always identical, only some of the regions were positive for both markers. The areas showing [(125) I]IPOS accumulation were positively and significantly correlated with the HIF-1α-positive areas (R = 0.75, P < 0.0001). The correlation coefficient between [(125) I]IPOS-accumulated areas and HIF-1α-positive areas was significantly greater than that between the [(125) I]IPOS-accumulated areas and the PIMO-positive areas (P < 0.01). These findings indicate that [(125) I]IPOS accumulation reflects HIF-1 expression. Thus, [(123/125) I]IPOS can serve as a useful probe for the molecular imaging of HIF-1-active tumors.

Pathophysiological response to hypoxia - from the molecular mechanisms of malady to drug discovery:hypoxia-inducible factor-1 (HIF-1)-active cells as a target for cancer therapy

The microenvironment of solid tumors is characterized by low pO(2) that is well below physiological levels. Intratumoral hypoxia is a major factor contributing to cancer progression and is exacerbated as a result of oxygen consumption by rapidly proliferating tumor cells near blood vessels, poor lymphatic drainage resulting in high interstitial pressure, and irregular blood supply through immature tumor vasculature. Hypoxia-inducible factor-1 (HIF-1) is the main transcription factor that regulates cellular responses to hypoxia. Cellular changes induced by HIF-1 are extremely important targets for cancer therapy. Therefore, targeting strategies to counteract HIF-1-active cells are essential for cancer therapy. In this study, we introduce a novel strategy for targeting HIF-1-active cells.

In vivo imaging of HIF-active tumors by an oxygen-dependent degradation protein probe with an interchangeable labeling system

Hypoxia-inducible factor (HIF) functions as a master transcriptional regulator for adaptation to hypoxia by inducing adaptive changes in gene expression for regulation of proliferation, angiogenesis, apoptosis and energy metabolism. Cancers with high expression of the alpha subunit of HIF (HIFα) are often malignant and treatment-resistant. Therefore, the development of a molecular probe that can detect HIF activity has great potential value for monitoring tumor hypoxia. HIF prolyl hydroxylases (HPHDs) act as oxygen sensors that regulate the fate of HIFα protein through its oxygen-dependent degradation (ODD) domain. We constructed a recombinant protein PTD-ODD-HaloTag (POH) that is under the same ODD regulation as HIFα and contains protein transduction domain (PTD) and an interchangeable labeling system. Administration of near-infrared fluorescently labeled POH (POH-N) to mouse models of cancers allowed successful monitoring of HIF-active regions. Immunohistochemical analysis for intratumoral localization of POH probe revealed its specificity to HIF-active cells. Furthermore, lack of the PTD domain or a point mutation in the ODD domain abrogated the specificity of POH-N to HIF-active cells. Overall results indicate that POH is a practical probe specific to HIF-active cell in cancers and suggest its large potential for imaging and targeting of HIF-related diseases.

Early protective effect of bone marrow mononuclear cells against ischemic white matter damage through augmentation of cerebral blood flow

BACKGROUND AND PURPOSE

To investigate the efficacy of bone marrow mononuclear cell (BMMNC) treatment against ischemic white matter (WM) damage in a hypoperfused brain.

METHODS

Mice were administered intravenous treatment of vehicle, spleen-derived marrow mononuclear cells (MNCs), or BMMNCs (5 × 10⁶ cells) obtained from enhanced green fluorescent protein transgenic mice 24 hours after bilateral common carotid artery stenosis (BCAS), and then euthanized at either 1 day or 30 days after treatment.

RESULTS

Laser speckle perfusion imaging analyses revealed marked recovery of cerebral blood flow (CBF) in the early phase after BMMNC treatment (6 hours after administration), before histological evidence of angiogenesis was assessed by fluorescein-isothiocyanate-dextran perfusion assay. BMMNC treatment induced an increase in vascular endothelial growth factor and Ser1177 phosphorylated endothelial nitric oxide synthase levels in the BCAS-induced mouse brains at 1 day after the treatment. BCAS-induced ischemic WM lesions were significantly improved 30 days after BMMNC treatment despite any evidence of direct structural incorporation of donor BMMNCs into endothelial cells and oligodendrocytes. Instead, enhanced green fluorescent protein-positive donor cells with morphological features of pericytes were observed in the vessel walls. Post-BMMNC administration of an NOS inhibitor abolished early CBF recovery and produced protective effects against ischemic WM damage.

CONCLUSIONS

BMMNC treatment provides marked protection against ischemic WM damage, enhancing CBF in the early phase and in subsequent angiogenesis, both of which involve nitric oxide synthase activation. These findings suggest promise for the application of BMMNCs for subcortical ischemic vascular dementia.

Noninvasive tracking of donor cell homing by near-infrared fluorescence imaging shortly after bone marrow transplantation

Background

Many diseases associated with bone marrow transplantation (BMT) are caused by transplanted hematopoietic cells, and the onset of these diseases occurs after homing of donor cells in the initial phase after BMT. Noninvasive observation of donor cell homing shortly after transplantation is potentially valuable for improving therapeutic outcomes of BMT by diagnosing the early stages of these diseases.

Methodology/Principal Findings

Freshly harvested near-infrared fluorescence-labeled cells were noninvasively observed for 24 h after BMT using a photon counting device to track their homing process. In a congenic BMT model, the homing of Alexa Fluor 750-labeled donor cells in the tibia was detected less than 1 h after BMT. In addition, subsequent cell distribution in an intraBM BMT model was successfully monitored for the first time using this method. In the allogeneic BMT model, T-cell depletion decreased the near-infrared fluorescence (NIRF) signals of the reticuloendothelial system.

Conclusions/Significance

This approach in several murine BMT models revealed that the transplanted cells homed within 24 h after transplantation. NIRF labeling is useful for tracking transplanted cells in the initial phase after BMT, and this approach can contribute to in vivo studies aimed at improving the therapeutic outcomes of BMT.

Functional molecular imaging of ILK-mediated Akt/PKB signaling cascades and the associated role of beta-parvin

Visualization and quantification of the dynamics of protein-protein interactions in living cells can be used to explore the macromolecular events involved in signal transduction processes. In this study, functional molecular imaging using a luciferase-based complementation method demonstrated how the integrin-linked kinase (ILK)-mediated protein complex controls downstream signals. The luciferase complementation assay showed that Akt1 preferentially binds to beta-parvin rather than to ILK within the complex. Moreover, photon flux from the interaction between beta-parvin and Akt1 increased following serum stimulation, and the beta-parvin-Akt1 interaction was dependent on phosphoinositide 3-kinase. Intriguingly, small interfering (si)RNA-mediated beta-parvin knockdown increased photon flux from the interaction between ILK and Akt1, leading to stabilization of hypoxia-inducible factor-1alpha and increased expression of vascular endothelial growth factor-A. These data from functional molecular imaging demonstrated that beta-parvin plays a regulatory role in the ILK-mediated Akt (also called protein kinase B) signaling cascades, suggesting that beta-parvin might be a crucial modulator of cell survival.

Rapid detection of hypoxia-inducible factor-1-active tumours: pretargeted imaging with a protein degrading in a mechanism similar to hypoxia-inducible factor-1alpha

PURPOSE

Hypoxia-inducible factor-1 (HIF-1) plays an important role in malignant tumour progression. For the imaging of HIF-1-active tumours, we previously developed a protein, POS, which is effectively delivered to and selectively stabilized in HIF-1-active cells, and a radioiodinated biotin derivative, (3-(123)I-iodobenzoyl)norbiotinamide ((123)I-IBB), which can bind to the streptavidin moiety of POS. In this study, we aimed to investigate the feasibility of the pretargeting method using POS and (123)I-IBB for rapid imaging of HIF-1-active tumours.

METHODS

Tumour-implanted mice were pretargeted with POS. After 24 h, (125)I-IBB was administered and subsequently, the biodistribution of radioactivity was investigated at several time points. In vivo planar imaging, comparison between (125)I-IBB accumulation and HIF-1 transcriptional activity, and autoradiography were performed at 6 h after the administration of (125)I-IBB. The same sections that were used in autoradiographic analysis were subjected to HIF-1alpha immunohistochemistry.

RESULTS

(125)I-IBB accumulation was observed in tumours of mice pretargeted with POS (1.6%ID/g at 6 h). This result is comparable to the data derived from (125)I-IBB-conjugated POS-treated mice (1.4%ID/g at 24 h). In vivo planar imaging provided clear tumour images. The tumoral accumulation of (125)I-IBB significantly correlated with HIF-1-dependent luciferase bioluminescence (R=0.84, p<0.01). The intratumoral distribution of (125)I-IBB was heterogeneous and was significantly correlated with HIF-1alpha-positive regions (R=0.58, p<0.0001).

CONCLUSION

POS pretargeting with (123)I-IBB is a useful technique in the rapid imaging and detection of HIF-1-active regions in tumours.

Abstract 5230: In vivo imaging of tumor malignancy with near-infrared fluorescence probes specific to HIF-active cells

In solid tumors, the distribution of oxygen pressure is not homogenous because of the uncontrolled tumor growth and immature blood vessels during angiogenesis, which generate a hypoxic microenvironment. Tumor hypoxia causes resistance to radiotherapy and chemotherapy, and malignant progression Hypoxia-inducible factor-1 (HIF-1) is a master transcriptional regulator for adaptation to hypoxia by inducing more than 100 genes, which are closely associated with malignant phenotype. Thus, HIF-1-active cells are hallmark of malignant tumors. We have been developing fusion protein probes specific to HIF-1-active microenvironment for imaging and targeting malignant tumors. We recently constructed a fusion protein POH, which consisted of Protein Transduction Domain (PTD), Oxygen-dependent Degradation Domain (ODD) and HaloTag. The PTD was a membrane-permeable peptide, which efficiently delivered fusion proteins into cells. The ODD was responsible for the oxygen-dependent regulation of the probe, which stabilized in a hypoxic environment and degraded immediately under normoxic conditions. In addition, HaloTag was used to covalently conjugate with its specific ligand labeled with near-infrared fluorescence (NIRF) dye. POH-NIRF was examined for its target-specificity and in vivo dynamic status by in vivo and ex vivo fluorescence imaging with IVIS-SPECTRUM. To visualize the targets in vivo, we used bioluminescence imaging of tumor cells, which stably retained a HIF-1-dependent luciferase reporter gene. POH-NIRF probes successfully imaged HIF-1-active regions defined by bioluminescence imaging in subcutaneously implanted human xenograft tumors and orthotopic pancreatic cancers 9 to 24 hrs after POH-NIRF injection. Furthermore, immunohistochemical analysis of tumor sections from the mice 6h after POH-NIRF injection revealed the regions imaged with POH-NIFR was overlapped with HIF-1α-positive regions, while the intracellular localization of POH-NIRF was in cytoplasm. Overall results demonstrated that POH-NIRF was a specific probe for HIF-1-active/hypoxic cells and suggested that a PTD-ODD probe would become a unique imaging probe for tumor malignancy.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5230.

Abstract 5240: Influence of cell permeable property of fluorescent dye on the POH in vivo imaging probe specific to HIF-active cancer cells

Tumor hypoxia plays a central role in malignant progression and is resistant to both radiotherapy and chemotherapy. Hypoxia-inducible factor (HIF) is a master transcriptional regulator for adaptation to hypoxia by inducing adaptive changes in gene expression for regulation of angiogenesis, proliferation, and metastasis in cancers. Protein stability of the alpha-subunit of HIF (HIFα) is strictly regulated by the oxygen sensor HIF prolyl hydroxylases (HPHDs). While HPHDs are inactive in hypoxic cells, they hydroxylate the Oxygen-Dependent Degradation (ODD) domain of HIFα in well-oxygenized cells and the hydroxylated HIFα is rapidly degraded through the ubiquitin-proteasome system.

We recently developed PTD-ODD-HaloTag (POH) probes, which penetrated cell membrane by the role of PTD and specifically stabilized in HIF-active cells as HIFα. To evaluate the usefulness of the POH for an in vivo imaging probe, POH protein was covalently bound to HaloTag ligand (HL) labeled with AlexaFluora750 (AF750) or IR800, which have excitation and emission wavelengths in the near infrared (NIR) spectral range (700-800 nm) where non-specific background fluorescence is considerably reduced. The resultant POH-HL-AF750 (POH-A) and POH-HL-IR800 (POH-I) were then examined their target specificity by using cultured cancer cell lines in terms of the cell membrane permeability and the stability in HIF-active cells. When the cells were treated with POH-A or POH-I significantly higher levels of the POH protein and fluorescence intensity were detected in cells cultured under hypoxic or hypoxia-mimic conditions, where HPHDs were suppressed, than normoxic conditions. These findings revealed that both POH-A and POH-I probe were efficiently transduced into cells at the similar extent and specifically stabilized in HIF-active cells. Although POH-A and POH-I showed similar cell membrane permeability, HL-AF750 alone penetrated cell membrane about 16 times less than HL-IR800. Furthermore, POH-I-treated cells showed shorter fluorescence retention time than POH-A-treated cells, indicating that POH-I and/or its pieces diffused away from the cell faster than POH-A. When POH-A and POH-I were applied for in vivo optical imaging of HIF-active hypoxic cells in a subcutaneous xenograft model, POH-I showed significantly higher fluorescent intensity ratio in tumor versus background (T/B) than POH-A and the distribution in the liver and gastrointestinal tract were different between mice administrated with POH-A and POH-I, indicating that the characteristics of NIRF ligand influenced the clearance efficiency and excretion pathway. Overall results demonstrate that POH is a specific probe to HIF-active cells and that high cell permeability of imaging materials conjugated to POH such as fluorescent dyes and isotope-labeled chemicals would improve its in vivo imaging.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5240.

Persisting mild hypothermia suppresses hypoxia-inducible factor-1alpha protein synthesis and hypoxia-inducible factor-1-mediated gene expression

The transcription factor hypoxia-inducible factor-1 (HIF-1) plays an essential role in regulating gene expression in response to hypoxia-ischemia. Ischemia causes the tissue not only to be hypoxic but also to be hypothermic because of the hypoperfusion under certain circumstances. On the other hand, the induced hypothermia is one of the most common therapeutic modalities to extend tolerance to hypoxia. Although hypoxia elicits a variety of cellular and systemic responses at different organizational levels in the body, little is known about how hypoxia-induced responses are affected by low temperature. We examined the influence of mild hypothermic conditions (28-32 degrees C) on HIF-1 in both in vitro and in vivo settings. In vitro experiments adopting cultured cells elucidated that hypoxia-induced HIF-1 activation was resistant to 4-h exposure to the low temperature. In contrast, exposure to the low temperature as long as 24 h suppressed HIF-1 activation and the subsequent upregulation of HIF-1 target genes such as VEGF or GLUT-1. HIF-1alpha protein stability in the cell was not affected by hypothermic treatment. Furthermore, intracellular ATP content was reduced under 1% O(2) conditions but was not largely affected by hypothermic treatment. The evidence indicates that reduction of oxygen consumption is not largely involved in suppression of HIF-1. In addition, we demonstrated that HIF-1 DNA-binding activity and HIF-1-dependent gene expressions induced under 10% O(2) atmosphere in mouse brain were not influenced by treatment under 3-h hypothermic temperature but were inhibited under 5-h treatment. On the other hand, we indicated that warming ischemic legs of mice for 24 h preserved HIF-1 activity. In this report we describe for the first time that persisting low temperature significantly reduced HIF-1alpha neosynthesis under hypoxic conditions, leading to a decrease in gene expression for adaptation to hypoxia in both in vitro and in vivo settings.