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BackgroundCD47 is a cell surface protein expressed on tumors that binds SIRPα on macrophages and dendritic cells resulting in a ”don’t eat me” signal that allows tumors to evade phagocytosis. The highly differentiated monoclonal antibody, AO-176 directly targets CD47 and blocks this signal. AO-176 is currently being tested in phase 1 clinical trials in solid tumors and multiple myeloma. The purpose of this study was to assess in vivo efficacy of AO-176 in solid tumor models as a single agent and in combination with multiple classes of therapeutics including chemotherapeutics, monoclonal antibodies and T-cell checkpoint inhibitors.MethodsCD47 expression levels on solid tumor types were assessed by immunohistochemistry using a tumor tissue microarray. Cell-based binding was performed using flow cytometry under acidic and physiologic pH conditions to characterize the functional activity of AO-176 in the two pH environments representing tumor and normal physiologic environments. In vivo studies were performed using models of solid cancers.ResultsAll 12 solid tumor indications assessed were positive for cell membrane localized CD47 (3.3–98.6 H-scores). Cell-based binding of AO-176 to solid cancer cell lines was significantly greater (1.6–25-fold decrease in EC50, 11–39% increase in Bmax) in acidic conditions as compared to a neutral pH environment, demonstrating improved binding in the lower pH environments associated with solid tumors. AO-176 treatment in solid tumor xenograft models resulted in potent anti-tumor activity as a monotherapy (40–58% TGI) and in combination with paclitaxel in an ovarian model (99% TGI), cisplatin in an ovarian model (84% TGI), cisplatin in a gastric model (76% TGI), and an anti-VEGFR-2 in a gastric model (86% TGI). In vivo efficacy of CD47 blockade alone (~33% TGI) and in combination with anti-PD-1 (74% TGI) and anti-PD-L1 (80% TGI) T-cell checkpoint inhibitors was observed in a syngeneic model of colon cancer using a surrogate anti-CD47 blocking antibody.ConclusionsAO-176 is a differentiated anti-CD47 agent that in addition to blocking the don’t eat me signal, directly kills cancer cells, shows lower binding to normal cells such as RBCs and demonstrates increased binding activity in acidic conditions as found in the microenvironment of solid tumors. AO-176 also elicits potent anti-tumor activity in xenograft and syngeneic models as a single agent and in combination with chemotherapies, monoclonal antibodies and T-cell checkpoint inhibitors. AO-176 is currently in clinical trials as a single agent and in combination in patients with select solid cancers (NCT03834948) and in multiple myeloma (NCT04445701).

Background Overexpression of CD47 by tumor cells exploits an immune checkpoint preventing tumor recognition and destruction by innate immune cells. Binding of tumor CD47 to SIRPα on macrophages and dendritic cells triggers a ‘don’t eat me’ signal that inhibits phagocytosis and allows escape from innate immune surveillance. Blockade of the CD47/SIRPα axis, however, enables immune recognition and phagocytic clearance of tumor cells. We have developed a clinical stage CD47 targeting antibody AO-176 that is highly differentiated among agents in this class. AO-176 not only blocks the CD47/SIRPα interaction and induces phagocytosis of tumor cells, but it also has a direct killing mechanism (via PCDIII) and induction of immunogenic cell death, leveraged by preferential binding to tumor versus normal cell CD47. Methods CD47 and β1 integrin expression and localization were evaluated using a combination of flow cytometry, western blotting, confocal microscopy and immunohistochemistry. Results Previously, we described that the preferential binding of AO-176 to tumor versus normal cells was due to its interaction with CD47 molecules that were pre-complexed to β1 integrin. This finding was particularly important and suggestive of why AO-176 does not bind red blood cells since they do not express β1 integrin. We have extended these findings to show that β1 integrin as well as CD47 are also expressed at lower levels in normal versus tumor cells, and that solid and hematologic tumor cells overexpress both CD47 and β1 integrin which correlate with poor prognosis in cancer. In addition, we show that AO-176 is able to bind and occupy CD47/β1 integrin complexes to a greater extent at acidic versus physiologic pH such as would be found in tumor microenvironments, an observation that also contributes to the enhanced targeting of AO-176 to tumor cells. Taken together, these findings add further insight into the preferential binding of AO-176 to tumor versus normal cells. Conclusions The context dependent binding of AO-176 to CD47, when complexed to β1 integrin, is unique among CD47 axis targeting agents and together with its direct killing mechanism of action offers a potentially better safety profile and opportunity for a therapeutic advantage. AO-176 is currently being evaluated in Phase 1 clinical trials for the treatment of patients with select solid tumors (NCT03834948) and multiple myeloma (NCT04445701). Trial Registration NCT03834948, NCT04445701.

Objective— Comprehensive understanding of the mechanisms regulating angiogenesis might provide new strategies for angiogenic therapies for treating diverse physiological and pathological ischemic conditions. The E-twenty six (ETS) factor Ets variant 2 (ETV2; aka Ets-related protein 71) is essential for the formation of hematopoietic and vascular systems. Despite its indispensable function in vessel development, ETV2 role in adult angiogenesis has not yet been addressed. We have therefore investigated the role of ETV2 in vascular regeneration. Approach and Results— We used endothelial Etv2 conditional knockout mice and ischemic injury models to assess the role of ETV2 in vascular regeneration. Although Etv2 expression was not detectable under steady-state conditions, its expression was readily observed in endothelial cells after injury. Mice lacking endothelial Etv2 displayed impaired neovascularization in response to eye injury, wounding, or hindlimb ischemic injury. Lentiviral Etv2 expression in ischemic hindlimbs led to improved recovery of blood perfusion with enhanced vessel formation. After injury, fetal liver kinase 1 ( Flk1 ), aka VEGFR2, expression and neovascularization were significantly upregulated by Etv2 , whereas Flk1 expression and vascular endothelial growth factor response were significantly blunted in Etv2 -deficient endothelial cells. Conversely, enforced Etv2 expression enhanced vascular endothelial growth factor–mediated endothelial sprouting from embryoid bodies. Lentiviral Flk1 expression rescued angiogenesis defects in endothelial Etv2 conditional knockout mice after hindlimb ischemic injury. Furthermore, Etv2 +/− ; Flk1 +/− double heterozygous mice displayed a more severe hindlimb ischemic injury response compared with Etv2 +/ − or Flk1 +/ − heterozygous mice, revealing an epistatic interaction between ETV2 and FLK1 in vascular regeneration. Conclusions— Our study demonstrates a novel obligatory role for the ETV2 in postnatal vascular repair and regeneration.

Human hepatocellular carcinoma (HCC) has a high rate of tumor recurrence and metastasis, resulting in shortened survival times. The efficacy of current systemic therapies for HCC is limited. In this study, we used xenograft tumor models to investigate the use of antibodies that block CD47 and inhibit HCC tumor growth. Immunostaining of tumor tissue and HCC cell lines demonstrated CD47 over-expression in HCC as compared to normal hepatocytes. Macrophage phagocytosis of HCC cells was increased after treatment with CD47 antibodies (CD47mAbs) that block CD47 binding to SIRPα. Further, CD47 blockade inhibited tumor growth in both heterotopic and orthotopic models of HCC, and promoted the migration of macrophages into the tumor mass. Our results demonstrate that targeting CD47 by specific antibodies has potential immunotherapeutic efficacy in human HCC.

Despite their divergent developmental ancestry, plasma cells and gastric zymogenic (chief) cells share a common function: high-capacity secretion of protein. Here we show that both cell lineages share increased expression of a cassette of 269 genes, most of which regulate endoplasmic reticulum (ER) and Golgi function, and they both induce expression of the transcription factors X-box binding protein 1 ( Xbp1) and Mist1 during terminal differentiation. XBP1 is known to augment plasma cell function by establishing rough ER, and MIST1 regulates secretory vesicle trafficking in zymogenic cells. We examined morphology and function of plasma cells in wild-type and Mist1−/−mice and found subtle differences in ER structure but no overall defect in plasma cell function, suggesting that Mist1 may function redundantly in plasma cells. We next reasoned that MIST1 might be useful as a novel and reliable marker of plasma cells. We found that MIST1 specifically labeled normal plasma cells in mouse and human tissues, and, moreover, its expression was also characteristic of plasma cell differentiation in a cohort of 12 human plasma cell neoplasms. Overall, our results show that MIST1 is enriched upon plasma cell differentiation as a part of a genetic program facilitating secretory cell function and also that MIST1 is a novel marker of normal and neoplastic plasma cells in mouse and human tissues.

The cellular composition and morphology of the stomach epithelium have been described in detail; however, the molecular mechanisms that regulate the differentiation of the various cell lineages as well as the function of mature gastric cells are far less clear. Recently, dissection of the molecular anatomy of the stomach has been boosted by the advent of functional genomics, which allows investigators to determine patterns of gene expression across virtually the entire cellular transcriptome. In this review, we discuss the impact of functional genomic studies on the understanding of gastric epithelial physiology. We show how functional genomic studies have uncovered genes that are useful as new cell lineage-specific markers of differentiation and provide new insights into cell physiology. For example, vascular endothelial growth factor B (Vegfb) has been identified as a parietal cell-specific marker that may allow parietal cells to regulate the mucosal vascular network. We also discuss how functional genomics has identified aberrantly expressed genes in disease states. Human epididymis 4 (HE4), for example, was recently identified as a metaplasia-induced gene product in mice based on microarray analysis. Finally, we will examine how analysis of higher-order patterns of gene expression can go beyond simply identifying individual genes to show how cells work as integrated systems. Specifically, we show how application of a Gene Ontology (GO) analysis of gene expression patterns from multiple tissues identifies the gastric parietal cell as an outlier, unlike other differentiated cell lineages in the stomach or elsewhere in the body.

A biodegradable positron-emitting dendritic nanoprobe targeted at α v β 3 integrin, a biological marker known to modulate angiogenesis, was developed for the noninvasive imaging of angiogenesis. The nanoprobe has a modular multivalent core-shell architecture consisting of a biodegradable heterobifunctional dendritic core chemoselectively functionalized with heterobifunctional polyethylene oxide (PEO) chains that form a protective shell, which imparts biological stealth and dictates the pharmacokinetics. Each of the 8 branches of the dendritic core was functionalized for labeling with radiohalogens. Placement of radioactive moieties at the core was designed to prevent in vivo dehalogenation, a potential problem for radiohalogens in imaging and therapy. Targeting peptides of cyclic arginine–glycine–aspartic acid (RGD) motifs were installed at the terminal ends of the PEO chains to enhance their accessibility to α v β 3 integrin receptors. This nanoscale design enabled a 50-fold enhancement of the binding affinity to α v β 3 integrin receptors with respect to the monovalent RGD peptide alone, from 10.40 nM to 0.18 nM IC 50 . Cell-based assays of the 125 I-labeled dendritic nanoprobes using α v β 3 -positive cells showed a 6-fold increase in α v β 3 receptor-mediated endocytosis of the targeted nanoprobe compared with the nontargeted nanoprobe, whereas α v β 3 -negative cells showed no enhancement of cell uptake over time. In vivo biodistribution studies of 76 Br-labeled dendritic nanoprobes showed excellent bioavailability for the targeted and nontargeted nanoprobes. In vivo studies in a murine hindlimb ischemia model for angiogenesis revealed high specific accumulation of 76 Br-labeled dendritic nanoprobes targeted at α v β 3 integrins in angiogenic muscles, allowing highly selective imaging of this critically important process.