Tumor Pericytes Research Articles

Abstract B074: Aberrant pericytes in PDAC: effects on endothelial-pericyte adhesion, vascular integrity, and tumor microenvironment

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in men and women in the U.S., with a 5-year survival rate of 13%. Within the PDAC tumor microenvironment (TME), morphologically aberrant leaky vessels are responsible for hypoxia and impaired immune response, which likely reduces the efficacy of cancer therapies. We and others showed that pericyte (PC) coverage significantly correlates with vascular integrity, function, and intratumor hypoxia. Therefore, understanding the contribution of abnormal PC to the TME evolution is a critical step toward PDAC treatment options. Consequently, we hypothesize that correcting such undesirable phenotype via vascular normalization will enhance treatment efficacy. Our study revealed that tumor-associated pericytes across all PDAC tumor tissues exhibited ectopic alpha-smooth muscle actin (αSMA) cytoskeletal protein expression up to 10 times higher than normal pericytes, which was significantly correlated with vascular leakiness and hypoxia. Our previous publication showed that PDAC-derived extracellular vesicles are potent inducers of αSMA expression in pericytes characterized by biomechanical abnormalities. To evaluate the vascular functional defect, we performed a tube formation assay showing abnormal pericytes contribute to abnormal vasculatures in vitro. Our investigation aims to uncover the cause of the abnormal pericyte phenotype that disrupts the physical adhesion between pericytes and endothelial cells (EC), resulting in compromised vasculature. Our findings reveal consistently upregulated monocarboxylate transporters in vascular cells. To enhance EC-pericyte adhesion, we investigated lactate metabolic communication, which is tightly linked due to the proximity of ECs and pericytes. We have shown that in PDAC, MCT1 lactate exporters are upregulated in EC. Conversely, MCT12 lactate importers are highly expressed in pericytes. The high amount of lactate produced by ECs decreases the pH in the basement membrane. So, we knocked down MCT1 transporters in ECs to increase basement pH, leading to improved PC-EC attachment and pericyte homeostasis. Finally, we performed single-cell RNA sequencing to determine the pathological signature of tumor pericytes and identify potential target molecules for vascular normalization. In conclusion, our study indicates that tumor-associated pericytes undergo phenotype switching and disturbed metabolic communication under the influence of pancreatic cancer cells. These aberrant pericytes might contribute to non-optimal vascular integrity and function. Single-cell RNA sequencing helped understand the molecular signature of the PDAC pericyte, providing a powerful tool to develop novel targeting strategies for vascular normalization. Future work includes exploring the vascular normalization approach by suppressing pericyte phenotype switching to enhance vascular function and chemo- and immunotherapeutic efficacy. Citation Format: Vikneshwari Natarajan, Sangdeuk Ha, Jiha Kim. Aberrant pericytes in PDAC: effects on endothelial-pericyte adhesion, vascular integrity, and tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research; 2024 Sep 15-18; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(17 Suppl_2):Abstract nr B074.

Nanomodulators targeting endothelial WNT and pericytes to reversibly open the blood–tumor barrier for boosted brain tumor therapy

The blood–brain barrier (BBB)/blood–tumor barrier (BTB) impedes brain entry of most brain-targeted drugs, whether they are water-soluble or hydrophobic. Endothelial WNT signaling and neoplastic pericytes maintain BTB low permeability by regulating tight junctions. Here, we proposed nitazoxanide (NTZ) and ibrutinib (IBR) co-loaded ICAM-1-targeting nanoparticles (NI@I-NPs) to disrupt the BTB in a time-dependent, reversible, and size-selective manner by targeting specific ICAM-1, inactivating WNT signaling and depleting pericytes in tumor-associated blood vessels in breast cancer brain metastases. At the optimal NTZ/IBR mass ratio (1:2), BTB opening reached the optimum effect at 48–72 h without any sign of intracranial edema and cognitive impairment. The combination of NI@I-NPs and chemotherapeutic drugs (doxorubicin and etoposide) extended the median survival of mice with breast cancer brain metastases. Targeting BTB endothelial WNT signaling and tumor pericytes via NI@I-NPs could open the BTB to improve chemotherapeutic efficiency against brain metastases.

Abstract LB309: Influence of pathological pericytes on PDAC tumor progression and tumor microenvironment

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the third leading cause of cancer death in men and women in the U.S., with a 5-year survival rate of 12 %. This poor prognosis is partly due to the aggressive nature of the disease, lack of early detection methods, its complex and dense tumor microenvironment (TME), and lack of effective treatment options. Within the PDAC TME, morphologically aberrant leaky vessels are responsible for hypoxia and impaired immune response, which likely reduces the efficacy of cancer therapies. We and others showed that pericyte coverage significantly correlates with vascular integrity/function and intratumoral hypoxia. Therefore, understanding perivascular heterogeneity and the unique contribution of each phenotype to the TME evolution is a critical step toward personalized treatment options for PDAC. Consequently, we hypothesize that correcting such undesirable phenotype via vascular normalization will alleviate the harsh TME and enhance the treatment efficacy. Our study revealed that tumor-associated pericytes across all PDAC tumor tissues exhibited ectopic αSMA expression up to 10 times higher than normal pericytes. This aberrant pericyte phenotype correlated with vascular leakiness, hypoxia, and vessel leakiness. Our attempt to elucidate the underlying mechanism of pericyte phenotype switching using an in-vitro culture system shows that pancreatic cancer cell-derived extracellular vesicles are a potent inducer of αSMA expression in pericytes present mechanical abnormalities and immune-suppressive features. To further determine the pathological signature of tumor pericytes and identify potential target molecules toward vascular normalization, we performed single-cell RNA sequencing (scRNA-seq). Pericytes were isolated from WT pancreas and KPC tumors at 15-20 weeks to obtain desired viable single-cell population suitable for 10x library preparation and Illumina sequencing.We isolated and barcode at least 5000 cells using the 10X genomics system. Sequencing libraries were prepared using the Chromium Single Cell 3ʹ reagent kit v3. They were sequenced until a sequencing depth of 100,000 reads per cell was achieved, and the data was analyzed using Cell Ranger and various other analytical tools (e.g., Seuret, Conos, ScMerge, singleR). We generated custom scripts from the single-cell data to answer the relevant questions. Sequences were demultiplexed based on barcodes and assigned unique molecular identifiers (UMIs). We visualized clusters using graphing methods, such as t-SNE plots and UMAP clustering. This approach helped identify groups of cells with unique and differential transcriptional landscapes and group them into cellular subtypes based on their gene expression profiles. In conclusion, our study indicates that tumor-associated pericytes undergo phenotype switching under the influence of pancreatic cancer cells, and these aberrant pericytes might contribute to non-optimal vascular integrity and function. Single-cell RNA sequencing helped understand the molecular signature of the pericyte subpopulation, providing a powerful tool to develop novel targeting strategies for vascular normalization. Future work includes exploring the vascular normalization approach by suppressing pericyte phenotype switching to enhance vascular function and chemo and immunotherapeutic efficacy. Citation Format: Vikneshwari Natarajan, Sangdeuk Ha, Jiha Kim. Influence of pathological pericytes on PDAC tumor progression and tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB309.

TNFSF15 facilitates the differentiation of CD11b+ myeloid cells into vascular pericytes in tumors.

Immature vasculature lacking pericyte coverage substantially contributes to tumor growth, drug resistance, and cancer cell dissemination. We previously demonstrated that tumor necrosis factor superfamily 15 (TNFSF15) is a cytokine with important roles in modulating hematopoiesis and vascular homeostasis. The main purpose of this study was to explore whether TNFSF15 might promote freshly isolated myeloid cells to differentiate into CD11b+ cells and further into pericytes. A model of Lewis lung cancer was established in mice with red fluorescent bone marrow. After TNFSF15 treatment, CD11b+ myeloid cells and vascular pericytes in the tumors, and the co-localization of pericytes and vascular endothelial cells, were assessed. Additionally, CD11b+ cells were isolated from wild-type mice and treated with TNFSF15 to determine the effects on the differentiation of these cells. We observed elevated percentages of bone marrow-derived CD11b+ myeloid cells and vascular pericytes in TNFSF15-treated tumors, and the latter cells co-localized with vascular endothelial cells. TNFSF15 protected against CD11b+ cell apoptosis and facilitated the differentiation of these cells into pericytes by down-regulating Wnt3a-VEGFR1 and up-regulating CD49e-FN signaling pathways. TNFSF15 facilitates the production of CD11b+ cells in the bone marrow and promotes the differentiation of these cells into pericytes, which may stabilize the tumor neovasculature.

Differential pericyte marker expression in craniofacial benign and malignant vascular tumors.

Vascular anomalies and tumors are common in the head, neck, and craniofacial areas and are associated with abnormalities in the angiomatous architecture. However, the etiology and molecular basis for the pathogenesis of most vascular lesions are still unknown. Pericytes are mural cells that surround endothelial cells. Besides angiogenesis and other physiological functions, pericytes play an important role in vascularized tissue repair and as resident mesenchymal stem/progenitor cells. Perivascular cells demonstrate a distinct immunohistochemical profile, including expression of alpha-smooth muscle actin (α-SMA), CD146, CD105, and PDGFRβ, without endothelial differentiation (absence of CD31 and CD34 immunoreactivity). These pericyte markers have been shown to be expressed in soft tissue hemangiomas. However, they have not been fully examined in intraosseous hemangiomas. In this study, we compared mesenchymal stem cell (MSC)expression of CD146 and α-SMA markers inpericytes from hemangiomas from different tissues and malignant vascular tumors. The results demonstrated an increased expression of pericyte markers in perivascular cells of benign hemangiomas, especially intraosseous hemangiomas and a significantly reduced expression of pericyte markers in malignant angiosarcomas. The evidence provides insight into the function of pericytes in vascular tumors and suggests their role in vascular tumor disease types.

Perivascular localized cells commit erythropoiesis in PDGF-B-expressing solid tumors.

Tumors possess incessant growth features, and expansion of their masses demands sufficient oxygen supply by red blood cells (RBCs). In adult mammals, the bone marrow (BM) is the main organ regulating hematopoiesis with dedicated manners. Other than BM, extramedullary hematopoiesis is discovered in various pathophysiological settings. However, whether tumors can contribute to hematopoiesis is completely unknown. Accumulating evidence shows that, in the tumor microenvironment (TME), perivascular localized cells retain progenitor cell properties and can differentiate into other cells. Here, we sought to better understand whether and how perivascular localized pericytes in tumors manipulate hematopoiesis. To test if vascular cells can differentiate into RBCs, genome-wide expression profiling was performed using mouse-derived pericytes. Genetic tracing of perivascular localized cells employing NG2-CreERT2:R26R-tdTomato mouse strain was used to validate the findings in vivo. Fluorescence-activated cell sorting (FACS), single-cell sequencing, and colony formation assays were applied for biological studies. The production of erythroid differentiation-specific cytokine, erythropoietin (EPO), in TME was checked using quantitative polymerase chain reaction (qPCR), enzyme-linked immunosorbent assay (ELISA, magnetic-activated cell sorting and immunohistochemistry. To investigate BM function in tumor erythropoiesis, BM transplantation mouse models were employed. Genome-wide expression profiling showed that in response to platelet-derived growth factor subunit B (PDGF-B), neural/glial antigen 2 (NG2)+ perivascular localized cells exhibited hematopoietic stem and progenitor-like features and underwent differentiation towards the erythroid lineage. PDGF-B simultaneously targeted cancer-associated fibroblasts to produce high levels of EPO, a crucial hormone that necessitates erythropoiesis. FACS analysis using genetic tracing of NG2+ cells in tumors defined the perivascular localized cell-derived subpopulation of hematopoietic cells. Single-cell sequencing and colony formation assays validated the fact that, upon PDGF-B stimulation, NG2+ cells isolated from tumors acted as erythroblast progenitor cells, which were distinctive from the canonical BM hematopoietic stem cells. Our data provide a new concept of hematopoiesis within tumor tissues and novel mechanistic insights into perivascular localized cell-derived erythroid cells within TME. Targeting tumor hematopoiesis is a novel therapeutic concept for treating various cancers that may have profound impacts on cancer therapy.

Novel TCF21high pericyte subpopulation promotes colorectal cancer metastasis by remodelling perivascular matrix

ObjectiveHaematogenous dissemination is a prevalent route of colorectal cancer (CRC) metastasis. However, as the gatekeeper of vessels, the role of tumour pericytes (TPCs) in haematogenous metastasis remains largely unknown. Here,...

Abstract LB053: PDAC derived exosomes manipulate tumor pericyte phenotype

Abstract Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in men and women in the U.S., with a 5-year survival rate of 10%. This poor prognosis is partly due to the aggressive nature of the disease, lack of early detection methods, its complex and dense tumor microenvironment (TME), and lack of effective treatment options. Within the PDAC TME, morphologically aberrant leaky vessels are responsible for hypoxia and impaired immune response, which likely reduces the efficacy of cancer therapies. We and others showed that pericyte coverage significantly correlates with vascular integrity/function and intratumoral hypoxia. Therefore, understanding perivascular heterogeneity and the unique contribution of each phenotype to the TME evolution is a critical step towards personalized treatment options for PDAC. Our study revealed that tumor-associated pericytes across all PDAC tumor tissues exhibited ectopic αSMA expression up to 10X higher compared to the normal pericytes. This aberrant pericyte phenotype was correlated with vascular leakiness and hypoxia, whereas the Des+ mature pericyte phenotype was inversely correlated with vessel leakiness. Our attempt to elucidate the underlying mechanism of pericyte phenotype switching using in vitro culture system shows that pancreatic cancer cell-derived extracellular vesicles (PC-Exo) is a potent inducer of αSMA expression in pericyte. PC-Exo was also sufficient enough to induce αSMA expression in normal pericytes within the pancreas when injected into the WT mice. In addition to the changes in pericyte markers, PC-Exo stimulated pericytes exhibited immunomodulatory phenotype with significantly higher expression of HLA-DRA, CD274, CD80, E-selectin, and P-selectin. Considering αSMA is a cytoskeletal protein that can influence cellular stiffness, migration, and downstream signaling, we also examined the biomechanical properties of pericytes with altered phenotype. The results show a significant increase in pericyte stiffness and cellular height of aSMA+ pericyte. These pericytes also have elongated morphology and cytoskeletal reorganization visualized by αSMA and phalloidin immunostaining. A recent study showed that acquired αSMA expression converts capillary pericytes into contractile vascular smooth muscle-like cells. Blood vessels are constricted and collapsed within the PDAC TME, which may be partly caused by an abundance of αSMA+ pericytes. In conclusion, our study indicates that tumor-associated pericytes undergo phenotype switching under the influence of pancreatic cancer cells, and these aberrant pericytes might contribute to non-optimal vascular integrity/function. Together, our study indicates that tumor conditioned αSMA+ pericytes present mechanical abnormalities and immune-suppressive features. Future work includes exploring the vascular normalization approach by suppressing pericyte phenotype switching to enhance vascular function and chemo- and immunotherapeutic efficacy. Citation Format: Vikneshwari Natarajan, Alexander Delgado, Reed Jacobson, Lina Alhalhooly, Yongki Choi, Sangdeuk Ha, Jiha Kim. PDAC derived exosomes manipulate tumor pericyte phenotype [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB053.

Acquired αSMA Expression in Pericytes Coincides with Aberrant Vascular Structure and Function in Pancreatic Ductal Adenocarcinoma

Simple SummaryThe pancreatic cancer field suffers from a lack of effective treatment options in part due to the severely compromised tumor vasculature that leads to hypoxia and an immunosuppressive environment. Our study aimed to identify and characterize pathological pericyte phenotypes that contribute to the defective tumor vasculature. We found that a large population of PDAC pericytes present ectopic α-smooth muscle actin (αSMA) expression, and this subtype was induced by cancer cell-derived exosomes. We also showed that the PDAC exosome-induced αSMA+ pericyte exhibits aberrant biomechanical properties and an acquired immunomodulatory phenotype. Considering a lack of efficient anti-angiogenic approaches in PDAC, identifying a unique molecular phenotype or the target molecule of a pathological pericyte will be an entry point toward a vascular normalization approach.The subpopulations of tumor pericytes undergo pathological phenotype switching, affecting their normal function in upholding structural stability and cross-communication with other cells. In the case of pancreatic ductal adenocarcinoma (PDAC), a significant portion of blood vessels are covered by an α-smooth muscle actin (αSMA)-expressing pericyte, which is normally absent from capillary pericytes. The DesminlowαSMAhigh phenotype was significantly correlated with intratumoral hypoxia and vascular leakiness. Using an in vitro co-culture system, we demonstrated that cancer cell-derived exosomes could induce ectopic αSMA expression in pericytes. Exosome-treated αSMA+ pericytes presented altered pericyte markers and an acquired immune-modulatory feature. αSMA+ pericytes were also linked to morphological and biomechanical changes in the pericyte. The PDAC exosome was sufficient to induce αSMA expression by normal pericytes of the healthy pancreas in vivo, and the vessels with αSMA+ pericytes were leaky. This study demonstrated that tumor pericyte heterogeneity could be dictated by cancer cells, and a subpopulation of these pericytes confers a pathological feature.

Hexokinase 2-driven glycolysis in pericytes activates their contractility leading to tumor blood vessel abnormalities

Defective pericyte-endothelial cell interaction in tumors leads to a chaotic, poorly organized and dysfunctional vasculature. However, the underlying mechanism behind this is poorly studied. Herein, we develop a method that combines magnetic beads and flow cytometry cell sorting to isolate pericytes from tumors and normal adjacent tissues from patients with non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC). Pericytes from tumors show defective blood vessel supporting functions when comparing to those obtained from normal tissues. Mechanistically, combined proteomics and metabolic flux analysis reveals elevated hexokinase 2(HK2)-driven glycolysis in tumor pericytes, which up-regulates their ROCK2-MLC2 mediated contractility leading to impaired blood vessel supporting function. Clinically, high percentage of HK2 positive pericytes in blood vessels correlates with poor patient overall survival in NSCLC and HCC. Administration of a HK2 inhibitor induces pericyte-MLC2 driven tumor vasculature remodeling leading to enhanced drug delivery and efficacy against tumor growth. Overall, these data suggest that glycolysis in tumor pericytes regulates their blood vessel supporting role.

Upregulated functional gene expression programmes in tumour pericytes mark progression in patients with low-grade glioma.

Pericytes conceivably play important roles in the tumour microenvironment of glioblastoma multiforme (GBM) by allowing for an aberrant vasculature and acting as a component in the perivascular niche that supports glioma stem‐like cells. However, a lack of specific markers has hampered in‐depth elucidation of the functional contribution of pericytes to GBM. This study provides a comprehensive computational biology approach to annotate pericyte marker genes in the GBM vasculature through integration of data from single‐cell RNA‐sequencing studies of both mouse and human tissue, as well as bulk tumour and healthy tissue gene expression data from patients with GBM. We identified distinct vascular‐ and immune‐related gene expression programmes in tumour pericytes that we assessed for association with GBM characteristics and patient survival. Most compellingly, pericyte gene signatures that were upregulated in tumours compared with normal brain tissue were indicative of progression of low‐grade gliomas into high‐grade glioma, suggested by a markedly shorter overall survival. Our results underline the functional importance of tumour pericytes in low‐grade glioma and may serve as a starting point for efforts for precision targeting of pericytes.

RGS5-TGFβ-Smad2/3 axis switches pro- to anti-apoptotic signaling in tumor-residing pericytes, assisting tumor growth.

Regulator-of-G-protein-signaling-5 (RGS5), a pro-apoptotic/anti-proliferative protein, is a signature molecule of tumor-associated pericytes, highly expressed in several cancers, and is associated with tumor growth and poor prognosis. Surprisingly, despite the negative influence of intrinsic RGS5 expression on pericyte survival, RGS5highpericytes accumulate in progressively growing tumors. However, responsible factor(s) and altered-pathway(s) are yet to report. RGS5 binds with Gαi/q and promotes pericyte apoptosis in vitro, subsequently blocking GPCR-downstream PI3K-AKT signaling leading to Bcl2 downregulation and promotion of PUMA-p53-Bax-mediated mitochondrial damage. However, within tumor microenvironment (TME), TGFβ appeared to limit the cytocidal action of RGS5 in tumor-residing RGS5highpericytes. We observed that in the presence of high RGS5 concentrations, TGFβ-TGFβR interactions in the tumor-associated pericytes lead to the promotion of pSmad2-RGS5 binding and nuclear trafficking of RGS5, which coordinately suppressed RGS5-Gαi/q and pSmad2/3-Smad4 pairing. The RGS5-TGFβ-pSmad2 axis thus mitigates both RGS5- and TGFβ-dependent cellular apoptosis, resulting in sustained pericyte survival/expansion within the TME by rescuing PI3K-AKT signaling and preventing mitochondrial damage and caspase activation. This study reports a novel mechanism by which TGFβ fortifies and promotes survival of tumor pericytes by switching pro- to anti-apoptotic RGS5 signaling in TME. Understanding this altered RGS5 signaling might prove beneficial in designing future cancer therapy.

Anti-tumor effect of local injectable hydrogel-loaded endostatin alone and in combination with radiotherapy for lung cancer

Endostatin (ES) can effectively inhibit neovascularization in most solid tumors and has the potential to make oxygen delivery more efficient and increase the efficacy of radiotherapy (RT). With a short half-life, ES is mainly administered systemically, which leads to low intake in tumor tissue and often toxic systemic side effects. In this study, we used hyaluronic acid-tyramine as a carrier to synthesize an ES-loaded hydrogel drug (ES/HA-Tyr) that can be injected locally. ES/HA-Tyr has a longer half-life and fewer systemic toxic side effects, and it exerts a better anti-angiogenic effect and anti-tumor effect with RT. In vitro, ES/HA-Tyr showed sustained release in the release assay and a stronger ability to inhibit the proliferation of human umbilical vascular endothelial cells (HUVECs) in the MTT assay; it exhibited a more potent effect against HUVEC invasion and a stronger anti-angiogenic effect on HUVECs in tube formation. In vivo, ES/HA-Tyr increased local drug concentration, decreased blood drug concentration, and caused less systemic toxicity. Further, ES/HA-Tyr effectively reduced tumor microvessel density, increased tumor pericyte coverage, decreased tumor hypoxia, and increased RT response. ES/HA-Tyr + RT also had increased anti-tumor and anti-angiogenic effects in Lewis lung cancer (LLC) xenograft models. In conclusion, ES/HA-Tyr showed sustained release, lower systemic toxicity, and better anti-tumor effects than ES. In addition, ES/HA-Tyr + RT enhanced anti-angiogenic effects, reduced tumor hypoxia, and increased the efficacy of RT in LLC-bearing mice.

Experimental study of resveratrol targeting pericytes against glioma

Objective To investigate the effects of resveratrol (RES) on the angiogenesis of glioma cells. Methods U87 cells were used to establish a human orthotopic transplantation model of human glioma nude mice. They were randomly divided into RES drug treatment group and sodium carboxymethyl cellulose (CMC) solvent control group, 18 cases in each group. To observe the survival status of tumor-bearing nude mice, and to map the survival curve, using cell surface molecule CD34 (CD34), α-smooth muscle actin (α-SMA) Tumor microvascular endothelial cells and pericytes were labeled, and glioma microvessel density (MVD) and microvascular pericyte cell density (MPND) were measured, and orthotopic transplantation was observed by transmission electron microscopy. Ultrastructural changes of peripheral cells in glioma microvessels. Results The survival time of the RES group was significantly longer than that of the vehicle control group [(71.67±20.35), (53.41±11.62) d, P<0.05]. The MPND of the RES group was higher than that of the control group (16.12±1.60, 14.40±0.95, P<0.05). The MVD of the control group was higher than that of the treatment group (34.00±2.70, 25.43±1.54, P<0.05). The results of transmission electron microscopy showed that the body density (Vv) of the control group was higher than that of the treatment group (37.70±3.03, 22.00±1.68, P<0.05), and the control group had higher specific membrane surface (δm) than the treatment group (43.75±1.19, 40.10±2.26, P<0.05), the specific surface area (δ) of the treatment group was higher than that of the control group, (2.41±0.50, 1.20±0.60, P<0.05). Conclusion RES can increase the coverage of microvascular pericytes and disturb the perivascular cells of the tumor. Cell interactions inhibit angiogenesis in gliomas and produce anti-glioma effects. Key words: Resveratrol; Glioma; Angiogenesis; Pericytes; Ultrastructure

Pericytes in Sarcomas and Other Mesenchymal Tumors.

Tumors of mesenchymal origin are a diverse group, with >130 distinct entities currently recognized by the World Health Organization. A subset of mesenchymal tumors grow or invade in a perivascular fashion, and their potential relationship to pericytes is a matter of ongoing interest. In fact, multiple intersections exist between pericytes and tumors of mesenchymal origin. First, pericytes are the likely cell of origin for a group of mesenchymal tumors with a common perivascular growth pattern. These primarily benign tumors grow in a perivascular fashion and diffusely express canonical pericyte markers such as CD146, smooth muscle actin (SMA), platelet-derived growth factor receptor beta (PDGFR-β), and RGS5. These benign tumors include glomus tumor, myopericytoma, angioleiomyoma, and myofibroma. Second and as suggested by animal models, pericytes may give rise to malignant sarcomas. This is not a suggestion that all sarcomas within a certain subtype arise from pericytes, but that genetic modifications within a pericyte cell type may give rise to sarcomas. Third, mesenchymal tumors that are likely not a pericyte derivative co-opt pericyte markers in certain contexts. These include the PEComa family of tumors and liposarcoma. Fourth and finally, as "guardians" that enwrap the microvasculature, nonneoplastic pericytes may be important in sarcoma disease progression.

Characteristics of pericytes in diethylstilbestrol (DES)-induced pituitary prolactinoma in rats.

Prolactinomas are the most common tumor of the human pituitary. They result in excessive prolactin secretion and important changes in the vasculature. Pericytes are perivascular cells associated with capillaries and have crucial roles in physiological and pathological neovascularization. We previously reported that pericytes produce type I and III collagens in the anterior pituitary of adult rats. In addition, pituitary pericytes contained well-developed cell organelles and actively synthesized collagens during early postnatal development. However, the characteristics of pericytes in pituitary tumors are unclear. In this study, we used diethylstilbestrol (DES)-treated rats as an animal model of prolactinoma. Using five common pericyte markers, more pericytes were observed in rats treated with DES for 3 months (prolactinoma) compared to the control. Transmission electron microscopy revealed that attached and semidetached pericytes exhibited active cell organelles. Moreover, we identified pericyte migration between capillaries. Although the fine structure of pituitary pericytes was active in prolactinoma, expressions of type I and III collagen mRNAs were greatly diminished. In sum, the characteristics and functions of pericytes were altered in pituitary tumors. This study is the first to clarify fine structural changes of pericytes in rat prolactinomas and improves our understanding of the function of pericytes under pathological conditions.

Periostin is Secreted by Glioblastoma CD90-positive Stromal Cells and Acts as a Pericyte Chemoattractant

Glioblastoma (GBM) stroma is composed of multiple cell types including vascular elements, immune cells and mesenchymal stromal cells (MSCs). Periostin (POSTN) is a secreted extracellular matrix protein which plays a crucial role in the progression of this aggressive and highly vascularized tumor. However, the cellular distribution of gliomaderived POSTN and whether POSTN can act as a chemoattractant for tumor vasculogenic cells is not known. The aim of the present study was to identify the specific cellular distribution of POSTN within GBM and to explore the possibility of POSTN acting as an attractant for tumor pericytes. Here we show that POSTN expression by large is restricted to the stromal compartment of GL261 mouse GBM. Within the stroma, POSTN is mainly localized to CD90+, most likely mesenchymal stromal cells (MSCs), and to pericytes recruited into the tumor. High POSTN protein levels were found to be produced by CD90+ MSCs acutely isolated from human GBM. Both mouse and human CD90+ MSCs co-expressed POSTN and Integrin β1, permitting autocrine interaction between ligand and receptor. Pericytes expressing Integrin β1 and CD90+ perivascular cells expressing POSTN are adjacently localized within the mouse GL261 stroma. A large fraction of human brain pericytes were found to express Integrin β1 and showed Integrin β1- dependent migration in response to POSTN. In summary, our findings tie the expression and action of POSTN to the stromal compartment of GBM and support a role for POSTN in GBM angioproliferation.

Galectin-1 Inhibitor OTX008 Induces Tumor Vessel Normalization and Tumor Growth Inhibition in Human Head and Neck Squamous Cell Carcinoma Models.

Galectin-1 is a hypoxia-regulated protein and a prognostic marker in head and neck squamous cell carcinomas (HNSCC). Here we assessed the ability of non-peptidic galectin-1 inhibitor OTX008 to improve tumor oxygenation levels via tumor vessel normalization as well as tumor growth inhibition in two human HNSCC tumor models, the human laryngeal squamous carcinoma SQ20B and the human epithelial type 2 HEp-2. Tumor-bearing mice were treated with OTX008, Anginex, or Avastin and oxygen levels were determined by fiber-optics and molecular marker pimonidazole binding. Immuno-fluorescence was used to determine vessel normalization status. Continued OTX008 treatment caused a transient reoxygenation in SQ20B tumors peaking on day 14, while a steady increase in tumor oxygenation was observed over 21 days in the HEp-2 model. A >50% decrease in immunohistochemical staining for tumor hypoxia verified the oxygenation data measured using a partial pressure of oxygen (pO2) probe. Additionally, OTX008 induced tumor vessel normalization as tumor pericyte coverage increased by approximately 40% without inducing any toxicity. Moreover, OTX008 inhibited tumor growth as effectively as Anginex and Avastin, except in the HEp-2 model where Avastin was found to suspend tumor growth. Galectin-1 inhibitor OTX008 transiently increased overall tumor oxygenation via vessel normalization to various degrees in both HNSCC models. These findings suggest that targeting galectin-1—e.g., by OTX008—may be an effective approach to treat cancer patients as stand-alone therapy or in combination with other standards of care.

Pericyte-targeting prodrug overcomes tumor resistance to vascular disrupting agents.

Blood vessels in the tumor periphery have high pericyte coverage and are resistant to vascular disrupting agents (VDAs). VDA treatment resistance leads to a viable peripheral tumor rim that contributes to treatment failure and disease recurrence. Here, we provide evidence to support a hypothesis that shifting the target of VDAs from tumor vessel endothelial cells to pericytes disrupts tumor peripheral vessels and the viable rim, circumventing VDA treatment resistance. Through chemical engineering, we developed Z-GP-DAVLBH (from the tubulin-binding VDA desacetylvinblastine monohydrazide [DAVLBH]) as a prodrug that can be selectively activated by fibroblast activation protein α (FAPα) in tumor pericytes. Z-GP-DAVLBH selectively destroys the cytoskeleton of FAPα-expressing tumor pericytes, disrupting blood vessels both within the core and around the periphery of tumors. As a result, Z-GP-DAVLBH treatment eradicated the otherwise VDA-resistant tumor rim and led to complete regression of tumors in multiple lines of xenografts without producing the drug-related toxicity that is associated with similar doses of DAVLBH. This study demonstrates that targeting tumor pericytes with an FAPα-activated VDA prodrug represents a potential vascular disruption strategy in overcoming tumor resistance to VDA treatments.

Endosialin-Expressing Pericytes Promote Metastatic Dissemination.

Metastasis is a multistep process that is critically dependent on the interaction of metastasizing tumor cells with cells in the local microenvironment. Within this tumor stroma, vessel-associated pericytes and myofibroblasts share a number of traits, including the upregulated expression of the transmembrane receptor endosialin (CD248). Comparative experiments in wild-type and endosialin-deficient mice revealed that stromal endosialin does not affect primary tumor growth but strongly promotes spontaneous metastasis. Mechanistically, endosialin-expressing pericytes in the primary tumor facilitate distant site metastasis by promoting tumor cell intravasation in a cell contact-dependent manner, resulting in elevated numbers of circulating tumor cells. Corresponding to these preclinical experiments, in independent cohorts of primary human breast cancers, upregulated endosialin expression significantly correlates with increased metastasis and poorer patient survival. Together, the data demonstrate a critical role for endosialin-expressing primary tumor pericytes in mediating metastatic dissemination and identify endosialin as a promising therapeutic target in breast cancer. Cancer Res; 76(18); 5313-25. ©2016 AACR.