A dual-luciferase bioluminescence system for the assessment of cellular therapies

Bioluminescence imaging is a well-established platform for evaluating engineered cell therapies in preclinical studies. However, despite the discovery of new luciferases and substrates, optimal combinations to simultaneously monitor two cell populations remain limited. This makes the functional assessment of cellular therapies cumbersome and expensive, especially in preclinical in vivo models. In this study, we explored the potential of using a green bioluminescence-emitting click beetle luciferase, CBG99, and a red bioluminescence-emitting firefly luciferase mutant, Akaluc, together to simultaneously monitor two cell populations. Using various chimeric antigen receptor T cells and tumor pairings, we demonstrate that these luciferases are suitable for real-time tracking of two cell types using 2D and 3D cultures in vitro and experimental models in vivo. Our data show the broad compatibility of this dual-luciferase (duo-luc) system with multiple bioluminescence detection equipment ranging from benchtop spectrophotometers to live animal imaging systems. Although this study focused on investigating complex CAR T cells and tumor cell interactions, this duo-luc system has potential utility for the simultaneous monitoring of any two cellular components-for example, to unravel the impact of a specific genetic variant on clonal dominance in a mixed population of tumor cells.

Uncovering receptor-ligand interactions using a high-avidity CRISPR activation screening platform

The majority of clinically approved drugs target proteins that are secreted or cell surface bound. However, further advances in this area have been hindered by the challenging nature of receptor deorphanization, as there are still many secreted and cell-bound proteins with unknown binding partners. Here, we developed an advanced screening platform that combines CRISPR-CAS9 guide-mediated gene activation (CRISPRa) and high-avidity bead-based selection. The CRISPRa platform incorporates serial enrichment and flow cytometry-based monitoring, resulting in substantially improved screening sensitivity for well-known yet weak interactions of the checkpoint inhibitor family. Our approach has successfully revealed that siglec-4 exerts regulatory control over T cell activation through a low affinity trans-interaction with the costimulatory receptor 4-1BB. Our highly efficient screening platform holds great promise for identifying extracellular interactions of uncharacterized receptor-ligand partners, which is essential to develop next-generation therapeutics, including additional immune checkpoint inhibitors.

Engineering CD276/B7-H3-targeted antibody-drug conjugates with enhanced cancer-eradicating capability

CD276/B7-H3 represents a promising target for cancer therapy based on widespread overexpression in both cancer cells and tumor-associated stroma. In previous preclinical studies, CD276 antibody-drug conjugates (ADCs) exploiting a talirine-type pyrrolobenzodiazepine (PBD) payload showed potent activity against various solid tumors but with a narrow therapeutic index and dosing regimen higher than that tolerated in clinical trials using other antibody-talirine conjugates. Here, we describe the development of a modified talirine PBD-based fully human CD276 ADC, called m276-SL-PBD, that is cross-species (human/mouse) reactive and can eradicate large 500-1,000-mm3 triple-negative breast cancer xenografts at doses 10- to 40-fold lower than the maximum tolerated dose. By combining CD276 targeting with judicious genetic and chemical ADC engineering, improved ADC purification, and payload sensitivity screening, these studies demonstrate that the therapeutic index of ADCs can be substantially increased, providing an advanced ADC development platform for potent and selective targeting of multiple solid tumor types.

Camel nanobody-based B7-H3 CAR-T cells show high efficacy against large solid tumours

Rational design of chimeric antigen receptor T (CAR-T) cells based on the recognition of antigenic epitopes capable of evoking the most potent CAR activation is an important objective in optimizing immune therapy. In solid tumors, the B7-H3 transmembrane protein is an emerging target that harbours two distinct epitope motifs, IgC and IgV, in its ectodomain. Here, we generate dromedary camel nanobodies targeting B7-H3 and demonstrate that CAR-T cells, based on the nanobodies recognizing the IgC but not IgV domain, had potent antitumour activity against large tumors in female mice. These CAR-T cells are characterized by highly activated T cell signaling and significant tumor infiltration. Single-cell transcriptome RNA sequencing coupled with functional T-cell proteomics analysis uncovers the top-upregulated genes that might be critical for the persistence of polyfunctional CAR-T cells in mice. Our results highlight the importance of the specific target antigen epitope in governing optimal CAR-T activity and provide a nanobody-based B7-H3 CAR-T product for use in solid tumor therapy.

Immune checkpoint B7-H3 is a therapeutic vulnerability in prostate cancer harboring PTEN and TP53 deficiencies

Checkpoint immunotherapy has yielded meaningful responses across many cancers but has shown modest efficacy in advanced prostate cancer. B7 homolog 3 protein (B7-H3/CD276) is an immune checkpoint molecule and has emerged as a promising therapeutic target. However, much remains to be understood regarding B7-H3's role in cancer progression, predictive biomarkers for B7-H3-targeted therapy, and combinatorial strategies. Our multi-omics analyses identified B7-H3 as one of the most abundant immune checkpoints in prostate tumors containing PTEN and TP53 genetic inactivation. Here, we sought in vivo genetic evidence for, and mechanistic understanding of, the role of B7-H3 in PTEN/TP53-deficient prostate cancer. We found that loss of PTEN and TP53 induced B7-H3 expression by activating transcriptional factor Sp1. Prostate-specific deletion of Cd276 resulted in delayed tumor progression and reversed the suppression of tumor-infiltrating T cells and NK cells in Pten/Trp53 genetically engineered mouse models. Furthermore, we tested the efficacy of the B7-H3 inhibitor in preclinical models of castration-resistant prostate cancer (CRPC). We demonstrated that enriched regulatory T cells and elevated programmed cell death ligand 1 (PD-L1) in myeloid cells hinder the therapeutic efficacy of B7-H3 inhibition in prostate tumors. Last, we showed that B7-H3 inhibition combined with blockade of PD-L1 or cytotoxic T lymphocyte-associated protein 4 (CTLA-4) achieved durable antitumor effects and had curative potential in a PTEN/TP53-deficient CRPC model. Given that B7-H3-targeted therapies have been evaluated in early clinical trials, our studies provide insights into the potential of biomarker-driven combinatorial immunotherapy targeting B7-H3 in prostate cancer, among other malignancies.

Cancer cell survival depends on collagen uptake into tumor-associated stroma

Collagen I, the most abundant protein in humans, is ubiquitous in solid tumors where it provides a rich source of exploitable metabolic fuel for cancer cells. While tumor cells were unable to exploit collagen directly, here we show they can usurp metabolic byproducts of collagen-consuming tumor-associated stroma. Using genetically engineered mouse models, we discovered that solid tumor growth depends upon collagen binding and uptake mediated by the TEM8/ANTXR1 cell surface protein in tumor-associated stroma. Tumor-associated stromal cells processed collagen into glutamine, which was then released and internalized by cancer cells. Under chronic nutrient starvation, a condition driven by the high metabolic demand of tumors, cancer cells exploited glutamine to survive, an effect that could be reversed by blocking collagen uptake with TEM8 neutralizing antibodies. These studies reveal that cancer cells exploit collagen-consuming stromal cells for survival, exposing an important vulnerability across solid tumors with implications for developing improved anticancer therapy.

Abstract 552: FGFR4 and CD276 dualtargeting CAR-T cells for treating rhabdomyosarcoma and other solid tumors

Background: Chimeric antigen receptor T-cell therapies (CAR-T) have shown success in treating refractory and relapsed leukemia and lymphoma, while they perform poorly in solid tumors due to heterogenous expression of tumor-associated antigens (TAAs), limited T cell persistence and propensity for exhaustion. The receptor tyrosine kinase FGFR4 and immune checkpoint molecule CD276 are highly and heterogeneously expressed in some solid tumors, including Rhabdomyosarcoma (RMS), a most common soft tissue sarcoma of childhood, and human hepatocellular carcinoma (HCC). However, their expression is usually low in normal human tissues. These features make FGFR4 and CD276 promising therapeutic targets for CAR-T therapy for RMS and HCC. We have developed a FGFR4 targeting CAR construct (3A11-BBz) with a CD8 hinge (H) and a transmembrane domain (TM) infused with a 4-1BB intracellular domain (ICD). 3A11-BBz CAR can efficiently eliminate low RMS disease burden in metastatic models, but less effectively for bulky disease in RMS intramuscular (I.M.) xenograft models. Testing of a CD276 targeting CAR T-cells showed significant shrinking of tumors in RMS I.M. xenograft models.

Methods: To improve the CAR-T cells efficacy, we first modified the H/TM and ICD of 3A11-BBz CAR to CD28 (3A11-CD28z). To overcome tumor heterogeneity, we also created Bicistronic CARs (BiCisCARs) combining the complete FGFR4 and CD276 CAR into a single construct allowing co-expression of both constructs on the same T cells. We then tested the efficacy of these CARs in-vitro and in-vivo using intramuscular FP-RMS xenograft (RH30) or HCC intraperitoneal models.

Results and Conclusions: We found either FGFR4 targeting CARs or dual targeting BiCisCARs, showed similar in-vitro cytotoxicity against RMS cells and HCC cells. However, CARs with CD28 ICD released more IL-2 than those with 4-1BB ICD when co-cultured with target cells. In RMS I.M. xenograft model, 3A11-CD28z CAR-T cells shrank and eliminated the tumor in 5/8 mice whereas 3A11-BBz only suppressed tumor growth. Furthermore, 3A11-CD28z BiCisCAR eradicated tumor cells in 8/8 mice, whereas 3A11-BBz BiCisCAR showed very poor efficacy. Moreover, there are more 3A11-CD28z BiCisCAR T-cells persisting in blood and spleen than the other bicistronic or single CAR-T cells, suggesting this BiCisCAR-T cells have prolonged persistence. Therefore, we have developed a potent BiCisCAR dual targeting both FGFR4 and CD276 that overcomes RMS heterogeneity and effectively eliminates tumors in-vivo, which will be developed as a future therapeutic CAR for clinical trials.

Citation Format: Meijie Tian, Adam Cheuk, David Milewski, Jun S. Wei, Hsien-Chao Chou, Yong Yean Kim, Young K. Song, Brad St. Croix, Mitchell Ho, Javed Khan. FGFR4 and CD276 dualtargeting CAR-T cells for treating rhabdomyosarcoma and other solid tumors [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 552.

Orphan G-Protein Coupled Receptor GPRC5B Is Critical for Lymphatic Development

Numerous studies have focused on the molecular signaling pathways that govern the development and growth of lymphatics in the hopes of elucidating promising druggable targets. G protein-coupled receptors (GPCRs) are currently the largest family of membrane receptors targeted by FDA-approved drugs, but there remain many unexplored receptors, including orphan GPCRs with no known biological ligand or physiological function. Thus, we sought to illuminate the cadre of GPCRs expressed at high levels in lymphatic endothelial cells and identified four orphan receptors: GPRC5B, AGDRF5/GPR116, FZD8 and GPR61. Compared to blood endothelial cells, GPRC5B is the most abundant GPCR expressed in cultured human lymphatic endothelial cells (LECs), and in situ RNAscope shows high mRNA levels in lymphatics of mice. Using genetic engineering approaches in both zebrafish and mice, we characterized the function of GPRC5B in lymphatic development. Morphant gprc5b zebrafish exhibited failure of thoracic duct formation, and Gprc5b^-/- mice suffered from embryonic hydrops fetalis and hemorrhage associated with subcutaneous edema and blood-filled lymphatic vessels. Compared to Gprc5^+/+ littermate controls, Gprc5b^-/- embryos exhibited attenuated developmental lymphangiogenesis. During the postnatal period, ~30% of Gprc5b^-/- mice were growth-restricted or died prior to weaning, with associated attenuation of postnatal cardiac lymphatic growth. In cultured human primary LECs, expression of GPRC5B is required to maintain cell proliferation and viability. Collectively, we identify a novel role for the lymphatic-enriched orphan GPRC5B receptor in lymphangiogenesis of fish, mice and human cells. Elucidating the roles of orphan GPCRs in lymphatics provides new avenues for discovery of druggable targets to treat lymphatic-related conditions such as lymphedema and cancer.

Cyanine Masking: A Strategy to Test Functional Group Effects on Antibody Conjugate Targeting

Conjugates of small molecules and antibodies are broadly employed diagnostic and therapeutic agents. Appending a small molecule to an antibody often significantly impacts the properties of the resulting conjugate. Here, we detail a systematic study investigating the effect of various functional groups on the properties of antibody-fluorophore conjugates. This was done through the preparation and analysis of a series of masked heptamethine cyanines (CyMasks)-bearing amides with varied functional groups. These were designed to exhibit a broad range of physical properties, and include hydrophobic (-NMe2), pegylated (NH-PEG-8 or NH-PEG-24), cationic (NH-(CH2)2NMe3+), anionic (NH-(CH2)2SO3-), and zwitterionic (N-(CH2)2NMe3+)-(CH2)3SO3-) variants. The CyMask series was appended to monoclonal antibodies (mAbs) and analyzed for the effects on tumor targeting, clearance, and non-specific organ uptake. Among the series, zwitterionic and pegylated dye conjugates had the highest tumor-to-background ratio (TBR) and a low liver-to-background ratio. By contrast, the cationic and zwitterionic probes had high tumor signal and high TBR, although the latter also exhibited an elevated liver-to-background ratio (LBR). Overall, these studies provide a strategy to test the functional group effects and suggest that zwitterionic substituents possess an optimal combination of high tumor signal, TBR, and low LBR. These results suggest an appealing strategy to mask hydrophobic payloads, with the potential to improve the properties of bioconjugates in vivo.

Disruption of anthrax toxin receptor 1 in pigs leads to a rare disease phenotype and protection from senecavirus A infection

Senecavirus A (SVA) is a cause of vesicular disease in pigs, and infection rates are rising within the swine industry. Recently, anthrax toxin receptor 1 (ANTXR1) was revealed as the receptor for SVA in human cells. Herein, the role of ANTXR1 as a receptor for SVA in pigs was investigated by CRISPR/Cas9 genome editing. Strikingly, ANTXR1 knockout (KO) pigs exhibited features consistent with the rare disease, GAPO syndrome, in humans. Fibroblasts from wild type (WT) pigs supported replication of SVA; whereas, fibroblasts from KO pigs were resistant to infection. During an SVA challenge, clinical symptoms, including vesicular lesions, and circulating viremia were present in infected WT pigs but were absent in KO pigs. Additional ANTXR1-edited piglets were generated that were homozygous for an in-frame (IF) mutation. While IF pigs presented a GAPO phenotype similar to the KO pigs, fibroblasts showed mild infection, and circulating SVA nucleic acid was decreased in IF compared to WT pigs. Thus, this new ANTXR1 mutation resulted in decreased permissiveness of SVA in pigs. Overall, genetic disruption of ANTXR1 in pigs provides a unique model for GAPO syndrome and prevents circulating SVA infection and clinical symptoms, confirming that ANTXR1 acts as a receptor for the virus.

Targeted Fluorogenic Cyanine Carbamates Enable In Vivo Analysis of Antibody-Drug Conjugate Linker Chemistry

Antibody-drug conjugates (ADCs) are a rapidly emerging therapeutic platform. The chemical linker between the antibody and the drug payload plays an essential role in the efficacy and tolerability of these agents. New methods that quantitatively assess the cleavage efficiency in complex tissue settings could provide valuable insights into the ADC design process. Here we report the development of a near-infrared (NIR) optical imaging approach that measures the site and extent of linker cleavage in mouse models. This approach is enabled by a superior variant of our recently devised cyanine carbamate (CyBam) platform. We identify a novel tertiary amine-containing norcyanine, the product of CyBam cleavage, that exhibits a dramatically increased cellular signal due to an improved cellular permeability and lysosomal accumulation. The resulting cyanine lysosome-targeting carbamates (CyLBams) are ∼50× brighter in cells, and we find this strategy is essential for high-contrast in vivo targeted imaging. Finally, we compare a panel of several common ADC linkers across two antibodies and tumor models. These studies indicate that cathepsin-cleavable linkers provide dramatically higher tumor activation relative to hindered or nonhindered disulfides, an observation that is only apparent with in vivo imaging. This strategy enables quantitative comparisons of cleavable linker chemistries in complex tissue settings with implications across the drug delivery landscape.

Abstract 1498: Nanobody-based CAR T cells targeting B7-H3 in pancreatic cancer

Pancreatic cancer is a common cause of cancer-related mortality worldwide with a poor 5-year survival rate. Adoptive transfer of T cells engineered with chimeric antigen receptors (CAR T cells) have shown promising potency in hematological malignancies, but it is more challenging to apply CAR T cells in the treatment of solid tumors. One of the major barriers is the lack of appropriate therapeutic targets. B7-H3 (CD276) is an emerging and promising pan-cancer target that is overexpressed in multiple solid tumors including pancreatic ductal adenocarcinoma (PDAC) and neuroblastoma (NB) but limited in normal tissues. Interestingly, it is highly expressed in not only tumor cells but also tumor-associated myeloid cells in the tumor microenvironment. In this study, we isolated a panel of novel B7-H3 specific nanobodies from our camel VHH single domain phage libraries. These nanobodies bind to human B7-H3-expressing tumor cell lines and cross-react with B7-H3 of different species. Notably, three nanobody-based CAR T cells (B12, C4 and G8) demonstrate potent cytolytic effects on B7-H3 positive PDAC and NB cell lines in vitro. In particular, CAR T cells have been tested in a metastatic PDAC model and a NB model in mice, showing that C4 and B12 nanobody-based CAR T cells have potent antitumor efficacy without evident side effects. Therefore, we conclude that our new B7-H3 targeted nanobody-based CAR T cells, in particular C4 and B12 derived CAR T cells, are promising for treating solid tumors such as pancreatic cancer and other deadly solid tumors.

Citation Format: Dan Li, RuiXue Wang, Tianyuzhou Liang, Brad St. Croix, Mitchell Ho. Nanobody-based CAR T cells targeting B7-H3 in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1498.

CAR T cells targeting tumor-associated exons of glypican 2 regress neuroblastoma in mice

Targeting solid tumors must overcome several major obstacles, in particular, the identification of elusive tumor-specific antigens. Here, we devise a strategy to help identify tumor-specific epitopes. Glypican 2 (GPC2) is overexpressed in neuroblastoma. Using RNA sequencing (RNA-seq) analysis, we show that exon 3 and exons 7-10 of GPC2 are expressed in cancer but are minimally expressed in normal tissues. Accordingly, we discover a monoclonal antibody (CT3) that binds exons 3 and 10 and visualize the complex structure of CT3 and GPC2 by electron microscopy. The potential of this approach is exemplified by designing CT3-derived chimeric antigen receptor (CAR) T cells that regress neuroblastoma in mice. Genomic sequencing of T cells recovered from mice reveals the CAR integration sites that may contribute to CAR T cell proliferation and persistence. These studies demonstrate how RNA-seq data can be exploited to help identify tumor-associated exons that can be targeted by CAR T cell therapies.

The B7-H3-Targeting Antibody-Drug Conjugate m276-SL-PBD Is Potently Effective Against Pediatric Cancer Preclinical Solid Tumor Models

PURPOSE

Patients with relapsed pediatric solid malignancies have few therapeutic options, and many of these patients die of their disease. B7-H3 is an immune checkpoint protein encoded by the CD276 gene that is overexpressed in many pediatric cancers. Here, we investigate the activity of the B7-H3-targeting antibody-drug conjugate (ADC) m276-SL-PBD in pediatric solid malignancy patient-derived (PDX) and cell line-derived xenograft (CDX) models.

EXPERIMENTAL DESIGN

B7-H3 expression was quantified by RNA sequencing and by IHC on pediatric PDX microarrays. We tested the safety and efficacy of m276-SL-PBD in two stages. Randomized trials of m276-SL-PBD of 0.5 mg/kg on days 1, 8, and 15 compared with vehicle were performed in PDX or CDX models of Ewing sarcoma (N = 3), rhabdomyosarcoma (N = 4), Wilms tumors (N = 2), osteosarcoma (N = 5), and neuroblastoma (N = 12). We then performed a single mouse trial in 47 PDX or CDX models using a single 0.5 m/kg dose of m276-SL-PBD.

RESULTS

The vast majority of PDX and CDX samples studied showed intense membranous B7-H3 expression (median H-score 177, SD 52). In the randomized trials, m276-SL-PBD showed a 92.3% response rate, with 61.5% of models showing a maintained complete response (MCR). These data were confirmed in the single mouse trial with an overall response rate of 91.5% and MCR rate of 64.4%. Treatment-related mortality rate was 5.5% with late weight loss observed in a subset of models dosed once a week for 3 weeks.

CONCLUSIONS

m276-SL-PBD has significant antitumor activity across a broad panel of pediatric solid tumor PDX models.

Abstract A13: Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma

Neuroblastoma (NB) is the most common extracranial solid cancer in children. Although multimodal therapies with differentiating agents and immunotherapy with anti-GD2 antibody and GM-CSF have shown promising results, it remains deadly in approximately 50% of patients with high-risk disease. Chimeric antigen receptor T-cell therapies (CAR-T) have been found to be effective in treating refractory and relapsed leukemia and lymphoma, and two of them have been recently approved by the FDA. However, current CARs frequently lose efficacy due to T-cell exhaustion, and CARs against solid tumor antigens often lack enough specificity due to a low incidence of somatic mutations resulting in a paucity of tumor neoantigens. There have not been effective CAR-T therapies against other solid cancers to date, although many clinical trials are under way. Therefore, we attempted to develop a high-throughput way of identifying optimal CART cell binders that show activation and expansion in the presence of targets but lack of exhaustion. We previously identified two cell surface cancer-associated antigens, GPC2 (Glypican-2) and CD276 (B7-H3), both highly expressed in NB tumor cells but expressed at low or undetectable levels in normal organs. 14 established binders as well as novel binders targeting these two antigens were cloned into CAR lentiviral constructs and then were separately transduced into T cells to develop 14 CAR-T cells using a 2nd-generation design. All 14 CAR-T cells were pooled and cocultured with CD276/GPC2-expressing NB cancer cells (target cells) for 24 hr. To identify the effective GPC2 or CD276-specific targeting CAR-T cells, we utilized a combined proteomics and transcriptomics method for every single CAR-T cell to quantify RNA and protein at the same. Cocultured CAR-T cells were examined for their activation, exhaustion, cytotoxicity state and distinguished different cell types by staining with CITE-seq (Cellular Indexing of Transcriptomes and Epitopes by Sequencing) antibodies, and then molecularly barcoded using 10X Genomics platform for single-cell RNA-sequencing (scRNA-seq). The data are currently being analyzed and will be presented. Using this method, we will be able to identify which of the CARs are enriched and have an activated T-cell signature, and lack exhaustion marks as determined by the CITE-seq and RNAseq analyses. Finally, top candidate binders for each antigen will be developed into “AND” or “OR” CARs and will be tested in in vitro and in vivo models of NB. Thus, we will develop a high-throughput way to identify high-affinity functional binders against tumor cell surface antigens. This study also will provide novel immunogenomics methods of CARs optimization for development of highly effective immunotherapies against NB and other cancers.

Citation Format: Meijie Tian, Adam Tai-Chi Cheuk, Jeetendra Kumar, Young K. Song, Sivasish Sindiri, Nan Li, Christopher M. Dower, Mitchell Ho, Brad St. Croix, Javed Khan. Immunogenomic approaches to optimize immunotherapeutic targeting of neuroblastoma [abstract]. In: Proceedings of the AACR Special Conference on the Advances in Pediatric Cancer Research; 2019 Sep 17-20; Montreal, QC, Canada. Philadelphia (PA): AACR; Cancer Res 2020;80(14 Suppl):Abstract nr A13.

Novel metabolic role for BDNF in pancreatic β-cell insulin secretion

BDNF signaling in hypothalamic circuitries regulates mammalian food intake. However, whether BDNF exerts metabolic effects on peripheral organs is currently unknown. Here, we show that the BDNF receptor TrkB.T1 is expressed by pancreatic β-cells where it regulates insulin release. Mice lacking TrkB.T1 show impaired glucose tolerance and insulin secretion. β-cell BDNF-TrkB.T1 signaling triggers calcium release from intracellular stores, increasing glucose-induced insulin secretion. Additionally, BDNF is secreted by skeletal muscle and muscle-specific BDNF knockout phenocopies the β-cell TrkB.T1 deletion metabolic impairments. The finding that BDNF is also secreted by differentiated human muscle cells and induces insulin secretion in human islets via TrkB.T1 identifies a new regulatory function of BDNF on metabolism that is independent of CNS activity. Our data suggest that muscle-derived BDNF may be a key factor mediating increased glucose metabolism in response to exercise, with implications for the treatment of diabetes and related metabolic diseases.

Glucose metabolism is regulated by hypothalamic brain functions and factors produced by peripheral tissues. Here, the authors show that the regulator of food intake Brain-derived neurotrophic factor is also produced and secreted by muscle and stimulates pancreas insulin release.

Antxr1, Which is a Target of Runx2, Regulates Chondrocyte Proliferation and Apoptosis

Antxr1/Tem8 is highly expressed in tumor endothelial cells and is a receptor for anthrax toxin. Mutation of Antxr1 causes GAPO syndrome, which is characterized by growth retardation, alopecia, pseudo-anodontia, and optic atrophy. However, the mechanism underlying the growth retardation remains to be clarified. Runx2 is essential for osteoblast differentiation and chondrocyte maturation and regulates chondrocyte proliferation through Ihh induction. In the search of Runx2 target genes in chondrocytes, we found that Antxr1 expression is upregulated by Runx2. Antxr1 was highly expressed in cartilaginous tissues and was directly regulated by Runx2. In skeletal development, the process of endochondral ossification proceeded similarly in wild-type and Antxr1-/- mice. However, the limbs of Antxr1-/- mice were shorter than those of wild-type mice from embryonic day 16.5 due to the reduced chondrocyte proliferation. Chondrocyte-specific Antxr1 transgenic mice exhibited shortened limbs, although the process of endochondral ossification proceeded as in wild-type mice. BrdU-uptake and apoptosis were both increased in chondrocytes, and the apoptosis-high regions were mineralized. These findings indicated that Antxr1, of which the expression is regulated by Runx2, plays an important role in chondrocyte proliferation and that overexpression of Antxr1 causes chondrocyte apoptosis accompanied by matrix mineralization.

Isolation of rabbit single domain antibodies to B7-H3 via protein immunization and phage display

Single domain antibodies have certain advantages including their small size, high stability and excellent tissue penetration, making them attractive drug candidates. Rabbit antibodies can recognize diverse epitopes, including those that are poorly immunogenic in mice and humans. In the present study, we established a method to isolate rabbit VH single domain antibodies for potential cancer therapy. We immunized rabbits with recombinant human B7-H3 (CD276) protein, made a phage-displayed rabbit VH single domain library with a diversity of 7 × 10⁹, and isolated two binders (A1 and B1; also called RFA1 and RFB1) from phage panning. Both rabbit VH single domains exhibited antigen-dependent binding to B7-H3-positive tumor cell lines but not B7-H3 knockout tumor cell lines. Our study shows that protein immunization followed by phage display screening can be used to isolate rabbit single domain antibodies. The two single domain antibodies reported here may have potential applications in cancer immunotherapy.

Abstract C003: Initial testing of m276-PBD CD276 antibody-drug conjugate in preclinical models of pediatric cancers by the Pediatric Preclinical Testing Consortium (PPTC)

Purpose: CD276 (B7-H3) is an immunoregulatory molecule that is reported to be widely expressed in pediatric embryonal tumors, pediatric sarcomas, and tumor infiltrating blood vessels. CD276 protein is expressed at low levels on several normal tissues, including cerebral cortex, liver and germinal lymph node. m276 is a fully-human IgG1 that binds with similar affinity to both mouse CD276 (24 nM kD) and human CD276 (29 nM kD) (Seaman et al., Cancer Cell, 2017). To generate an antibody-drug conjugate, m276 was site-specifically conjugated to the DNA damaging agent pyrrolobenzodiazepine (PBD) via a cleavable valine-alanine linker, providing m276-PBD with a Drug-to-Antibody Ratio (DAR) of 2. Here we examined the antitumor activity of m276-PBD against preclinical xenograft models of pediatric solid tumors. Experimental Procedures: Expression of CD276 across PPTC xenograft models (>200) representing leukemias, brain tumors and solid tumors was determined by RNA seq, and additionally in neuroblastoma models by IHC. Xenograft experiments were undertaken in heterotopic models using standard methods of the PPTC. Response criteria were tumor regression (PR, CR, maintained CR [at 6 weeks]) and Event-Free Survival (EFS). m276-PBD was administered by intraperitoneal injection at a dose of 0.5 mg/kg, once weekly x 3 consecutive weeks. Results: CD276 expression was high in most solid tumors (median 41 FPKM) with highest expression in osteosarcoma. Neuroblastoma, rhabdomyosarcoma, Wilms tumor and embryonal brain tumor models had similar levels of expression, whereas ALL models showed low expression. In vivo efficacy studies are ongoing, but data to date are available for 5 osteosarcoma, 4 rhabdomyosarcoma, 2 Ewing sarcoma and 2 Wilms tumors. Maintained Complete Response (MCR) at 6 weeks was attained in 2/5 osteosarcoma, 3/4 rhabdomyosarcoma and 1/2 Ewing sarcoma. CR was achieved in 1/2 Wilms tumor, 1/2 rhabdomyosarcoma, and 2/5 osteosarcoma models. Body weight loss (<3%) was noted in only one study. Conclusions: Expression of CD276 was high in most PPTC solid tumor models. mCD276-PBD was highly active against most models tested inducing long-lasting CR’s. There was no toxicity, suggesting that this agent has an effective therapeutic window in these models. Mature results (100 days observation) and additional results for neuroblastoma models will be presented.

Citation Format: Raushan Kurmasheva, E. Anders Kolb, Malcolm A. Smith, Beverly A. Teicher, Stephen W. Erickson, John M. Maris, Yael P. Mosse, Kateryna Krytska, David Groff, Matthew Tang, Yifei Wang, Brad St. Croix, Richard Gorlick, Peter J. Houghton. Initial testing of m276-PBD CD276 antibody-drug conjugate in preclinical models of pediatric cancers by the Pediatric Preclinical Testing Consortium (PPTC) [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr C003. doi:10.1158/1535-7163.TARG-19-C003

Seneca Valley Virus Exploits TEM8, a Collagen Receptor Implicated in Tumor Growth

Recent studies reveal that Seneca Valley Virus (SVV) exploits tumor endothelial marker 8 (TEM8) for cellular entry, the same surface receptor pirated by bacterial-derived anthrax toxin. This observation is particularly significant as SVV is a known oncolytic virus which selectively infects and kills tumor cells, particularly those of neuroendocrine origin. TEM8 is a transmembrane glycoprotein that is preferentially upregulated in some tumor cell and tumor-associated stromal cell populations. Both TEM8 and SVV have been evaluated for targeting of tumors of multiple origins, but the connection between the two was previously unknown. Here, we review currently understood interactions between TEM8 and SVV, anthrax protective antigen (PA), and collagen VI, a native binding partner of TEM8, with an emphasis on potential therapeutic directions moving forward.

Abstract A25: TEM8 specific CAR T cells induce regression of patient-derived xenograft and metastatic models of triple-negative breast cancer

Lacking marked expression of human epidermal growth factor receptor 2 (HER2), estrogen receptor (ER), and progesterone receptor (PR), triple-negative breast cancer (TNBC) is a breast cancer subtype in desperate need of targeted therapy options. Tumor endothelial marker 8 (TEM8), initially identified as a tumor endothelium marker in colon cancer, has been shown to be upregulated in TNBC. To confirm this, we stained primary TNBC tissues for TEM8; in all cases TEM8 was expressed with no expression in normal breast tissue. TEM8 is expressed by TNBC cell lines as indicated by flow cytometry and Western blot. We thus engineered chimeric antigen receptor (CAR) T cells to specifically target TEM8 in TNBC. TEM8 CAR T cells distinctly recognized TEM8, secreted immunostimulatory cytokines, and killed TEM8-positive TNBC cells in vitro. In vivo, the adoptive transfer of TEM8 CAR T cells induced regression against orthotopic patient-derived xenograft (PDX) models, including the aggressive claudin-low TNBC PDX, WHIM12. Systemic administration of TEM8 CAR T cells also induced regression against a lung metastasis TNBC model. In all models, treatment with TEM8 CAR T cells resulted in a survival advantage in mice compared to controls. Hence, TEM8 may serve as an attractive targeted immunotherapy of TNBC.

Citation Format: Tiara Byrd, Kristen Fousek, Antonella Pignata, Christopher Szot, Heba Samaha, Lacey Dobrolecki, Htoo Zarni Oo, Poul Sorensen, Matthew Ellis, Michael Lewis, Meenakshi Hegde, Bradley Fletcher, Brad St. Croix, Nabil Ahmed. TEM8 specific CAR T cells induce regression of patient-derived xenograft and metastatic models of triple-negative breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A25.

Tumor stroma-targeted antibody-drug conjugate triggers localized anticancer drug release

Although nonmalignant stromal cells facilitate tumor growth and can occupy up to 90% of a solid tumor mass, better strategies to exploit these cells for improved cancer therapy are needed. Here, we describe a potent MMAE-linked antibody-drug conjugate (ADC) targeting tumor endothelial marker 8 (TEM8, also known as ANTXR1), a highly conserved transmembrane receptor broadly overexpressed on cancer-associated fibroblasts, endothelium, and pericytes. Anti-TEM8 ADC elicited potent anticancer activity through an unexpected killing mechanism we term DAaRTS (drug activation and release through stroma), whereby the tumor microenvironment localizes active drug at the tumor site. Following capture of ADC prodrug from the circulation, tumor-associated stromal cells release active MMAE free drug, killing nearby proliferating tumor cells in a target-independent manner. In preclinical studies, ADC treatment was well tolerated and induced regression and often eradication of multiple solid tumor types, blocked metastatic growth, and prolonged overall survival. By exploiting TEM8+ tumor stroma for targeted drug activation, these studies reveal a drug delivery strategy with potential to augment therapies against multiple cancer types.

TEM8/ANTXR1-Specific CAR T Cells as a Targeted Therapy for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive disease lacking targeted therapy. In this study, we developed a CAR T cell-based immunotherapeutic strategy to target TEM8, a marker initially defined on endothelial cells in colon tumors that was discovered recently to be upregulated in TNBC. CAR T cells were developed that upon specific recognition of TEM8 secreted immunostimulatory cytokines and killed tumor endothelial cells as well as TEM8-positive TNBC cells. Notably, the TEM8 CAR T cells targeted breast cancer stem-like cells, offsetting the formation of mammospheres relative to nontransduced T cells. Adoptive transfer of TEM8 CAR T cells induced regression of established, localized patient-derived xenograft tumors, as well as lung metastatic TNBC cell line-derived xenograft tumors, by both killing TEM8⁺ TNBC tumor cells and targeting the tumor endothelium to block tumor neovascularization. Our findings offer a preclinical proof of concept for immunotherapeutic targeting of TEM8 as a strategy to treat TNBC.Significance: These findings offer a preclinical proof of concept for immunotherapeutic targeting of an endothelial antigen that is overexpressed in triple-negative breast cancer and the associated tumor vasculature. Cancer Res; 78(2); 489-500. ©2017 AACR.

Wnt7a induces a unique phenotype of monocyte-derived macrophages with lower phagocytic capacity and differential expression of pro- and anti-inflammatory cytokines

The variation of macrophage functions suggests the involvement of multiple signalling pathways in fine tuning their differentiation. Macrophages that originate from monocytes in the blood migrate to tissue in response to homeostatic or 'danger' signals and undergo substantial morphological and functional modifications to meet the needs of the dominant signals in the microenvironment. Wnts are secreted glycoproteins that play a significant role in organ and cell differentiation, yet their impact on monocyte differentiation is not clear. In this study, we assessed the role of Wnt1 and Wnt7a on the differentiation of monocytes and the subsequent phenotype and function of monocyte-derived macrophages (MDMs). We show that Wnt7a decreased the expression of CD14, CD11b, CD163 and CD206, whereas Wnt1 had no effect. The Wnt7a effect on CD11b was also observed in the brain and spleen of Wnt7a^-/- adult brain mouse tissue and in embryonic Wnt7a^-/- tissue. Wnt7a reduced the phagocytic capacity of M-MDMs, decreased interleukin-10 (IL-10) and IL-12 secretion and increased IL-6 secretion. Collectively, these findings demonstrate that Wnt7a generates an MDM phenotype with both pro-inflammatory and alternative MDM cytokine profiles and reduced phagocytic capacity. As such, Wnt7a can have a significant impact on macrophage responses in health and disease.

Eradication of Tumors through Simultaneous Ablation of CD276/B7-H3-Positive Tumor Cells and Tumor Vasculature

Targeting the tumor vasculature with antibody-drug conjugates (ADCs) is a promising anti-cancer strategy that in order to be realized must overcome several obstacles, including identification of suitable targets and optimal warheads. Here, we demonstrate that the cell-surface protein CD276/B7-H3 is broadly overexpressed by multiple tumor types on both cancer cells and tumor-infiltrating blood vessels, making it a potentially ideal dual-compartment therapeutic target. In preclinical studies CD276 ADCs armed with a conventional MMAE warhead destroyed CD276-positive cancer cells, but were ineffective against tumor vasculature. In contrast, pyrrolobenzodiazepine-conjugated CD276 ADCs killed both cancer cells and tumor vasculature, eradicating large established tumors and metastases, and improving long-term overall survival. CD276-targeted dual-compartment ablation could aid in the development of highly selective broad-acting anti-cancer therapies.

Abstract 2312: TEM8/ANTXR1 specific T cells co-target tumor stem cells and tumor vasculature in triple-negative breast cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with no approved targeted therapies. Tumor endothelial marker 8 (TEM8), initially identified as a marker of tumor endothelial cells in colorectal cancer and other solid tumors has recently been shown to be upregulated in TNBC and breast cancer stem cells (BCSCs). We investigated whether TEM8 specific chimeric antigen receptor (CAR) T cells recognize and kill both tumor endothelial cells as well as TNBC tumor cells. TEM8 specific CAR molecules were generated using single chain variable fragment derived from the monoclonal antibody, L2. L2 CAR T cells selectively recognized TEM8, secreted immunostimulatory cytokines and effectively killed both TEM8 positive TNBC and tumor endothelial cell lines. Moreover, L2 CAR T cells targeted breast cancer stem cells significantly reducing the number of mammospheres relative to non-transduced T cells. In vivo, adoptive transfer of L2 CAR T cells induced regression of established vascularized TNBC xenografts. Hence, TEM8 may serve as an attractive target for immunotherapy of TNBC.

Citation Format: Tiara Byrd, Kristen Fousek, Antonella Pignata, Christopher Szot, Kevin Bielamowicz, Steven Seaman, Daniel Landi, Nino Rainusso, Poul Sorensen, Joachim Koch, Winfried Wels, Bradley Fletcher, Meenakshi Hegde, Brad St Croix, Nabil Ahmed. TEM8/ANTXR1 specific T cells co-target tumor stem cells and tumor vasculature in triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2312.

COX-2 inhibition potentiates antiangiogenic cancer therapy and prevents metastasis in preclinical models

Antiangiogenic agents that block vascular endothelial growth factor (VEGF) signaling are important components of current cancer treatment modalities but are limited by alternative ill-defined angiogenesis mechanisms that allow persistent tumor vascularization in the face of continued VEGF pathway blockade. We identified prostaglandin E2 (PGE2) as a soluble tumor-derived angiogenic factor associated with VEGF-independent angiogenesis. PGE2 production in preclinical breast and colon cancer models was tightly controlled by cyclooxygenase-2 (COX-2) expression, and COX-2 inhibition augmented VEGF pathway blockade to suppress angiogenesis and tumor growth, prevent metastasis, and increase overall survival. These results demonstrate the importance of the COX-2/PGE2 pathway in mediating resistance to VEGF pathway blockade and could aid in the rapid development of more efficacious anticancer therapies.

GPR124 functions as a WNT7-specific coactivator of canonical β-catenin signaling

G protein-coupled receptor 124 (GPR124) is an orphan receptor in the adhesion family of GPCRs, and previous global or endothelial-specific disruption of Gpr124 in mice led to defective CNS angiogenesis and blood-brain barriergenesis. Similar developmental defects were observed following dual deletion of Wnt7a/Wnt7b or deletion of β-catenin in endothelial cells, suggesting a possible relationship between GPR124 and canonical WNT signaling. Here, we show using in vitro reporter assays, mutation analysis, and genetic interaction studies in vivo that GPR124 functions as a WNT7A/WNT7B-specific costimulator of β-catenin signaling in brain endothelium. WNT7-stimulated β-catenin signaling was dependent upon GPR124's intracellular PDZ binding motif and a set of leucine-rich repeats in its extracellular domain. This study reveals a vital role for GPR124 in potentiation of WNT7-induced canonical β-catenin signaling with important implications for understanding and manipulating CNS-specific angiogenesis and blood-brain barrier-genesis.

Improving VEGF-targeted therapies through inhibition of COX-2/PGE2 signaling

Antiangiogenic agents targeting the vascular endothelial growth factor A (VEGFA) pathway play an important role in current cancer treatment modalities but are limited by alternative angiogenesis mechanisms. Recent studies suggest that enhanced signaling through a COX-2/PGE₂ axis contributes to VEGF-independent tumor angiogenesis. Thus, COX-2/PGE₂ inhibition may potentiate VEGF therapies.

Immuno-PET imaging of tumor endothelial marker 8 (TEM8)

Tumor endothelial marker 8 (TEM8) is a cell surface receptor that is highly expressed in a variety of human tumors and promotes tumor angiogenesis and cell growth. Antibodies targeting TEM8 block tumor angiogenesis in a manner distinct from the VEGF receptor pathway. Development of a TEM8 imaging agent could aid in patient selection for specific antiangiogenic therapies and for response monitoring. In these studies, L2, a therapeutic anti-TEM8 monoclonal IgG antibody (L2mAb), was labeled with ⁸⁹Zr and evaluated in vitro and in vivo in TEM8 expressing cells and mouse xenografts (NCI-H460, DLD-1) as a potential TEM8 immuno-PET imaging agent. ⁸⁹Zr-df–L2mAb was synthesized using a desferioxamine–L2mAb conjugate (df–L2mAb); ¹²⁵I-L2mAb was labeled directly. In vitro binding studies were performed using human derived cell lines with high, moderate, and low/undetectable TEM8 expression. ⁸⁹Zr-df–L2mAb in vitro autoradiography studies and CD31 IHC staining were performed with cryosections from human tumor xenografts (NCI-H460, DLD-1, MKN-45, U87-MG, T-47D, and A-431). Confirmatory TEM8 Western blots were performed with the same tumor types and cells. ⁸⁹Zr-df–L2mAb biodistribution and PET imaging studies were performed in NCI-H460 and DLD-1 xenografts in nude mice. ¹²⁵I-L2mAb and ⁸⁹Zr-df–L2mAb exhibited specific and high affinity binding to TEM8 that was consistent with TEM8 expression levels. In NCI-H460 and DLD-1 mouse xenografts nontarget tissue uptake of ⁸⁹Zr-df–L2mAb was similar; the liver and spleen exhibited the highest uptake at all time points. ⁸⁹Zr-L2mAb was highly retained in NCI-H460 tumors with <10% losses from day 1 to day 3 with the highest tumor to muscle ratios (T:M) occurring at day 3. DLD-1 tumors exhibited similar pharmacokinetics, but tumor uptake and T:M ratios were reduced ∼2-fold in comparison to NCI-H460 at all time points. NCI-H460 and DLD-1 tumors were easily visualized in PET imaging studies despite low in vitro TEM8 expression in DLD-1 cells indicating that in vivo expression might be higher in DLD-1 tumors. From in vitro autoradiography studies ⁸⁹Zr-df–L2mAb specific binding was found in 6 tumor types (U87-MG, NCI-H460, T-47D MKN-45, A-431, and DLD-1) which highly correlated to vessel density (CD31 IHC). Westerns blots confirmed the presence of TEM8 in the 6 tumor types but found undetectable TEM8 levels in DLD-1 and MKN-45 cells. This data would indicate that TEM8 is associated with the tumor vasculature rather than the tumor tissue, thus explaining the increased TEM8 expression in DLD-1 tumors compared to DLD-1 cell cultures. ⁸⁹Zr-df–L2mAb specifically targeted TEM8 in vitro and in vivo although the in vitro expression was not necessarily predictive of in vivo expression which seemed to be associated with the tumor vasculature. In mouse models, ⁸⁹Zr-df–L2mAb tumor uptakes and T:M ratios were sufficient for visualization during PET imaging. These results would suggest that a TEM8 targeted PET imaging agent, such as ⁸⁹Zr-df–L2mAb, may have potential clinical, diagnostic, and prognostic applications by providing a quantitative measure of tumor angiogenesis and patient selection for future TEM8 directed therapies.

A human single-domain antibody elicits potent antitumor activity by targeting an epitope in mesothelin close to the cancer cell surface

Monoclonal antibodies against mesothelin are being evaluated for the treatment of mesothelioma and multiple forms of cancers, and show great promise for clinical development for solid cancers. Antibodies against mesothelin have been shown to act via immunotoxin-based inhibition of tumor growth and induction of antibody-dependent cell-mediated cytotoxicity (ADCC). However, complement-dependent cytotoxicity (CDC), considered an important additional mechanism of therapeutic antibodies against tumors, is inactive for such antibodies. Here, we used phage display antibody engineering technology and synthetic peptide screening to identify SD1, a human single-domain antibody to mesothelin. SD1 recognizes a conformational epitope at the C-terminal end (residues 539-588) of mesothelin close to the cell surface. To investigate SD1 as a potential therapeutic agent, we generated a recombinant human Fc (SD1-hFc) fusion protein. Interestingly, the SD1-hFc protein exhibits strong CDC activity, in addition to ADCC, against mesothelin-expressing tumor cells. Furthermore, it causes growth inhibition of human tumor xenografts in nude mice as a single agent. SD1 is the first human single-domain antibody targeting mesothelin-expressing tumors, shows potential as a cancer therapeutic candidate, and may improve current antibody therapy targeting mesothelin-expressing tumors.

Selective blockade of tumor angiogenesis

Blocking tumor angiogenesis is an important goal of cancer therapy, but clinically approved anti-angiogenic agents suffer from limited efficacy and adverse side effects, fueling the need to identify alternative angiogenesis regulators. Tumor endothelial marker 8 (TEM8) is a highly conserved cell surface receptor overexpressed on human tumor vasculature. Genetic disruption of Tem8 in mice revealed that TEM8 is important for promoting tumor angiogenesis and tumor growth but dispensable for normal development and wound healing. The induction of TEM8 in cultured endothelial cells by nutrient or growth factor deprivation suggests that TEM8 may be part of a survival response pathway that is activated by tumor microenvironmental stress. In preclinical studies, antibodies targeted against the extracellular domain of TEM8 inhibited tumor angiogenesis and blocked the growth of multiple human tumor xenografts. Anti-TEM8 antibodies augmented the activity of other anti-angiogenic agents, vascular targeting agents and conventional chemotherapeutic agents and displayed no detectable toxicity. Thus, anti-TEM8 antibodies provide a promising new tool for selective blockade of neovascularization associated with cancer and possibly other angiogenesis-dependent diseases.

Vascular endothelial growth factor receptor 2 inhibition in-vivo affects tumor vasculature in a tumor type-dependent way and downregulates vascular endothelial growth factor receptor 2 protein without a prominent role for miR-296

The precise molecular effects that antiangiogenic drugs exert on tumor vasculature remain to be poorly understood. We therefore set out to investigate the molecular and architectural changes that occur in the vasculature of two different tumor types that both respond to vascular endothelial growth factor receptor 2 (VEGFR2) inhibitor therapy. Mice bearing Lewis lung carcinoma (LLC) or B16.F10 melanoma were treated with vandetanib (ZD6474), a VEGFR2/epidermal growth factor receptor (EGFR)/REarranged during Transfection (RET) kinase inhibitor, resulting in a significant 80% reduction in tumor outgrowth. Although in LLC the vascular density was not affected by vandetanib treatment, it was significantly decreased in B16.F10. In LLC, vandetanib treatment induced a shift in vascular gene expression toward stabilization, as demonstrated by upregulation of Tie2 and N-cadherin and downregulation of Ang2 and integrin β3. In contrast, only eNOS and P-selectin responded to vandetanib treatment in B16.F10 vasculature. Strikingly, vandetanib reduced protein expression of VEGFR2 in both models, whereas mRNA remained unaffected. Analysis of miR-296 expression allowed us to exclude a role for the recently proposed microRNA-296 in VEGFR2 posttranslational control in LLC and B16.F10 in vivo. Our data demonstrate that VEGFR2/EGFR inhibition through vandetanib slows down both LLC and B16.F10 tumor growth. Yet, the underlying molecular changes in the vasculature that orchestrate the antitumor effect differ between tumor types. Importantly, in both models, vandetanib treatment induced loss of its pharmacological target, which was not directly related to miR-296 expression. Validation of our observations in tumor biopsies from VEGFR2 inhibitor-treated patients will be essential to unravel the effects of VEGFR2 inhibitor therapy on tumor vasculature in relation to therapeutic efficacy.

TEM8/ANTXR1 blockade inhibits pathological angiogenesis and potentiates tumoricidal responses against multiple cancer types

Current antiangiogenic agents used to treat cancer only partially inhibit neovascularization and cause normal tissue toxicities, fueling the need to identify therapeutic agents that are more selective for pathological angiogenesis. Tumor endothelial marker 8 (TEM8), also known as anthrax toxin receptor 1 (ANTXR1), is a highly conserved cell-surface protein overexpressed on tumor-infiltrating vasculature. Here we show that genetic disruption of Tem8 results in impaired growth of human tumor xenografts of diverse origin including melanoma, breast, colon, and lung cancer. Furthermore, antibodies developed against the TEM8 extracellular domain blocked anthrax intoxication, inhibited tumor-induced angiogenesis, displayed broad antitumor activity, and augmented the activity of clinically approved anticancer agents without added toxicity. Thus, TEM8 targeting may allow selective inhibition of pathological angiogenesis.

The cell surface structure of tumor endothelial marker 8 (TEM8) is regulated by the actin cytoskeleton

Tumor endothelial marker 8 (TEM8) is an integrin-like cell surface protein upregulated on tumor blood vessels and a potential vascular target for cancer therapy. Here, we found that the ability of an anti-TEM8 antibody, clone SB5, to recognize the extracellular domain of TEM8 on the cell surface depends on other host-cell factors. By taking advantage of SB5's ability to distinguish different forms of cell surface TEM8, we identified alpha-smooth muscle actin and transgelin, an actin binding protein, as intracellular factors able to alter TEM8 cell surface structure. Overexpression of either of these proteins in cells converted TEM8 from an SB5-exposed to an SB5-masked form and protected cells from SB5-saporin immunotoxins. Because the predominant form of TEM8 on the cell surface is not recognized by SB5, we also developed a new monoclonal antibody, called AF334, which is able to recognize both the SB5-exposed and the SB5-masked forms of TEM8. AF334-saporin selectively killed TEM8-positive cells independent of TEM8 cell surface structure. These studies reveal that TEM8 exists in different forms at the cell surface, a structure dependent on interactions with components of the actin cytoskeleton, and should aid in the rational design of the most effective diagnostic and therapeutic anti-TEM8 monoclonal antibodies.

Age-related properties of the tumour vasculature in renal cell carcinoma

OBJECTIVE

To assess whether ageing processes influence angiogenesis in renal cell carcinoma (RCC) we carried out a pilot study of vascular properties in a series of archival primary kidney tumours in patients of different ages.

PATIENTS AND METHODS

A cohort of patients with RCC was identified restrospectively, with an age range of 35-84 years. Paraffin-embedded, formalin-fixed sections of surgical tumour specimens were stained for endothelial (CD31, von Willebrand factor [vWF]), pericyte (alpha smooth muscle actin [SMA]) and leucocytic (CD45) markers, as well as for proliferative (Ki67) and angiogenic activity (tumour endothelial markers [TEMs], delta-like 4 [Dll4], Dll1, endothelial nitric oxide synthase [eNOS]). Vascular properties were compared between patients above and below 65 years of age.

RESULTS

Microvascular density (MVD) within capillary hot spots was generally higher in patients with non-metastatic clear-cell RCC (ccRCC; n = 21) than in those with metastatic RCC (mRCC; n= 9). Patients with ccRCC who were more than 65 years old showed significantly higher MVD than their younger (< 65 years) counterparts. There were dividing (Ki67-positive) endothelial and mural cells in both small (< 20 µm) capillary and large (> 20 µm), pre-capillary vessels, suggesting the involvement of both angiogenic and remodelling/arteriogenic processes. Tumour endothelial markers (TEM1, TEM7, TEM8), Notch ligands (Dll1, Dll4), and other molecular characteristics (eNOS) were analysed. Age-related differences were observed in the frequency of pre-capillary vessels expressing Dll1, which was significantly higher in tumours of younger patients (< 65 years), while eNOS was more prevalent among capillaries associated with ccRCC in older patients (>6 5 years).

CONCLUSIONS

The results of the present study suggest that age influences the structural and molecular properties of the tumour vasculature in ccRCC. We postulate that vascular ageing could also be relevant in the context of anti-angiogenic therapy.

Host-derived tumor endothelial marker 8 promotes the growth of melanoma

Tumor endothelial marker 8 (TEM8) was initially identified as a gene overexpressed in the vasculature of human tumors and was subsequently identified as an anthrax toxin receptor. To assess the functional role of TEM8, we disrupted the TEM8 gene in mice by targeted homologous recombination. TEM8(-/-) mice were viable and reached adulthood without defects in physiologic angiogenesis. However, histopathologic analysis revealed an excess of extracellular matrix in several tissues, including the ovaries, uterus, skin, and periodontal ligament of the incisors, the latter resulting in dental dysplasia. When challenged with B16 melanoma, tumor growth was delayed in TEM8(-/-) mice, whereas the growth of other tumors, such as Lewis lung carcinoma, was unaltered. These studies show that host-derived TEM8 promotes the growth of certain tumors and suggest that TEM8 antagonists may have utility in the development of new anticancer therapies.

Hypoxia-inducible factor-1 target genes as indicators of tumor vessel response to vascular endothelial growth factor inhibition

Antiangiogenic therapy improves survival in patients with advanced stage cancers. Currently, there are no reliable predictors or markers for tumor vessel response to antiangiogenic therapy. To model effective antiangiogenic therapy, we disrupted the VEGF gene in three representative cancer cell lines. HCT116 xenografts had low proportions of endothelial tubes covered by pericytes that stained with alpha-smooth muscle actin (SMA) antibody. Upon disruption of VEGF, HCT116(VEGF-/-) xenografts had significantly decreased tumor microvessel perfusion compared with their parental counterparts. Furthermore, HCT116(VEGF-/-) xenografts mounted a tumor-reactive response to hypoxia, characterized by the induction of hypoxia-inducible factor-1 (HIF-1) target genes. One highly induced protein was DPP4, a measurable serum protein that has well-described roles in cancer progression. In contrast, LS174T and MKN45 tumor xenografts had high proportion of endothelial tubes that were covered by SMA+ pericytes. Upon disruption of VEGF, LS174T(VEGF-/-) and MKN45(VEGF-/-) xenografts maintained tumor microvessel perfusion. As such, there were no changes in intratumoral hypoxia or HIF-1 alpha induction. Together, these data show that the extent of tumor vessel response to angiogenic inhibition could be correlated with (a) the preexisting coverage of tumor endothelial tubes with SMA+ pericytes and (b) differential tumor induction of HIF-1 target genes. The data further show that DPP4 is a novel marker of HIF-1 induction. Altogether, these preclinical findings suggest novel clinical trials for predicting and monitoring tumor vessel responses to antiangiogenic therapy.

Serial analysis of gene expression (SAGE): experimental method and data analysis

Serial analysis of gene expression (SAGE) involves the generation of short fragments of DNA, or tags, from a defined point in the sequence of all cDNAs in the sample analyzed. This short tag, because of its presence in a defined point in the sequence, is typically sufficient to uniquely identify every transcript in the sample. SAGE allows one to generate a comprehensive profile of gene expression in any sample desired from as little as 100,000 cells or 1 microg of total RNA. SAGE generates absolute, rather than relative, measurements of RNA abundance levels, and this fact allows an investigator to readily and reliably compare data to those produced by other laboratories, making the SAGE data set increasingly useful as more data is generated and shared. Software tools have also been specifically adapted for SAGE tags to allow cluster analysis of both public and user-generated data.

Atherosclerosis and vascular aging as modifiers of tumor progression, angiogenesis, and responsiveness to therapy

It is rarely considered that age-related common vascular co-morbidities may affect therapeutic outcomes of antiangiogenic therapy in cancer. Indeed, the accepted model of human disease consists of 4- to 8-week-old (young) tumor-bearing, but otherwise healthy, experimental mice, yet human cancers are diagnosed and treated in later decades of life when atherosclerosis and vascular diseases are highly prevalent. Here we present evidence that tumor growth and angiogenesis are profoundly altered in mice affected by natural aging and with genetically induced atherosclerosis (in ApoE(-/-) mice). Thus, transplantable tumors (Lewis lung carcinoma and B16F1) grew at higher rates in young (4 to 8 weeks old) ApoE(+/+) and ApoE(-/-) nonatherosclerotic syngeneic recipients than in their old (12 to 18 months old) or atherosclerotic (old/ApoE(-/-)) counterparts. These age-related changes were paralleled by reduced tumor vascularity, lower expression of tumor endothelial marker 1, increased acute tumor hypoxia, depletion of circulating CD45(-)/VEGFR(+) cells, and impaired endothelial sprouting ex vivo. Exposure of tumor-bearing mice to metronomic therapy with cyclophosphamide exerted antimitotic effects on tumors in young hosts, but this effect was reduced in atherosclerotic mice. Collectively, our results suggest that vascular aging and disease may affect tumor progression, angiogenesis, and responses to therapy.

Genes that distinguish physiological and pathological angiogenesis

To unravel the normal vasculature transcriptome and determine how it is altered by neighboring malignant cells, we compared gene expression patterns of endothelial cells derived from the blood vessels of eight normal resting tissues, five tumors, and regenerating liver. Organ-specific endothelial genes were readily identified, including 27 from brain. We also identified 25 transcripts overexpressed in tumor versus normal endothelium, including 13 that were not found in the angiogenic endothelium of regenerating liver. Most of the shared angiogenesis genes have expected roles in cell-cycle control, but those specific for tumor endothelium were primarily cell surface molecules of uncertain function. These studies reveal striking differences between physiological and pathological angiogenesis potentially important for the development of tumor-specific, vascular-targeted therapies.

Large-scale identification of novel transcripts in the human genome

Although the sequencing of the human genome has been completed, the number and identity of genes contained within it remains to be fully determined. We used LongSAGE to analyze 660,357 human transcripts from human brain mRNA and identified expression of 17,409 known genes and >15,000 different transcripts that were not annotated in genome databases. Analysis of a subset of these unannotated transcripts suggests that 85% were differentially expressed in various tissue types and that fewer than 20% would have been detected by ab initio gene predictions. These studies suggest that the human genome contains on the order of twice as many transcribed regions as are currently annotated and that experimental approaches will be required to fully elucidate the novel genes corresponding to these transcripts.