Lesley G. Ellies

Activatable cell penetrating peptides linked to nanoparticles as dual probes for in vivo fluorescence and MR imaging of proteases

High-resolution imaging of molecules intrinsically involved in malignancy and metastasis would be of great value for clinical detection and staging of tumors. We now report in vivo visualization of matrix metalloproteinase activities by MRI and fluorescence of dendrimeric nanoparticles coated with activatable cell penetrating peptides (ACPPs), labeled with Cy5, gadolinium, or both. Uptake of such nanoparticles in tumors is 4- to 15-fold higher than for unconjugated ACPPs. With fluorescent molecules, we are able to detect residual tumor and metastases as small as 200 μm, which can be resected under fluorescence guidance and analyzed histopathologically with fluorescence microscopy. We show that uptake via this mechanism is comparable to that of other near infrared protease sensors, with the added advantage that the approach is translatable to MRI. Once activated, the Gd-labeled nanoparticles deposit high levels (30–50 μM) of Gd in tumor parenchyma with even higher amounts deposited in regions of infiltrative tumor, resulting in useful T1 contrast lasting several days after injection. These results should improve MRI-guided clinical staging, presurgical planning, and intraoperative fluorescence-guided surgery. The approach may be generalizable to deliver radiation-sensitizing and chemotherapeutic agents.

Surgery with molecular fluorescence imaging using activatable cell-penetrating peptides decreases residual cancer and improves survival

The completeness of tumor removal during surgery is dependent on the surgeon’s ability to differentiate tumor from normal tissue using subjective criteria that are not easily quantifiable. A way to objectively assess tumor margins during surgery in patients would be of great value. We have developed a method to visualize tumors during surgery using activatable cell-penetrating peptides (ACPPs), in which the fluorescently labeled, polycationic cell-penetrating peptide (CPP) is coupled via a cleavable linker to a neutralizing peptide. Upon exposure to proteases characteristic of tumor tissue, the linker is cleaved, dissociating the inhibitory peptide and allowing the CPP to bind to and enter tumor cells. In mice, xenografts stably transfected with green fluorescent protein show colocalization with the Cy5-labeled ACPPs. In the same mouse models, Cy5-labeled free ACPPs and ACPPs conjugated to dendrimers (ACPPDs) delineate the margin between tumor and adjacent tissue, resulting in improved precision of tumor resection. Surgery guided by ACPPD resulted in fewer residual cancer cells left in the animal after surgery as measured by Alu PCR. A single injection of ACPPD dually labeled with Cy5 and gadolinium chelates enabled preoperative whole-body tumor detection by MRI, intraoperative guidance by real-time fluorescence, intraoperative histological analysis of margin status by fluorescence, and postoperative MRI tumor quantification. Animals whose tumors were resected with ACPPD guidance had better long-term tumor-free survival and overall survival than animals whose tumors were resected with traditional bright-field illumination only.

Core 2 Oligosaccharide Biosynthesis Distinguishes between Selectin Ligands Essential for Leukocyte Homing and Inflammation

Mammalian serine/threonine-linked oligosaccharides (O-glycans) are commonly synthesized with the Golgi enzyme core 2 beta-1,6-N-acetylglucosaminyltransferase (C2 GlcNAcT). Core 2 O-glycans have been hypothesized to be essential for mucin production and selectin ligand biosynthesis. We report that mice lacking C2 GlcNAcT exhibit a restricted phenotype with neutrophilia and a partial deficiency of selectin ligands. Loss of core 2 oligosaccharides reduces neutrophil rolling on substrata bearing E-, L-, and P-selectins and neutrophil recruitment to sites of inflammation. However, the diminished presence of L-selectin ligands on lymph node high endothelial venules does not affect lymphocyte homing. These studies indicate that core 2 oligosaccharide biosynthesis segregates the physiologic roles of selectins and reveal a function for the C2 GlcNAcT in myeloid homeostasis and inflammation.

Novel Sulfated Lymphocyte Homing Receptors and Their Control by a Core1 Extension β1,3-N-Acetylglucosaminyltransferase

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to addressins expressed in the high endothelial venules (HEV) of secondary lymphoid organs. Peripheral node addressin recognized by the MECA-79 antibody is apparently part of the L-selectin ligand, but its chemical nature has been undefined. We now identify a sulfated extended core1 mucin-type O-glycan, Gal beta 1-->4(sulfo-->6)GlcNAc beta 1-->3Gal beta 1-->3GalNAc, as the MECA-79 epitope. Molecular cloning of a HEV-expressed core1-beta 1,3-N-acetylglucosaminyltransferase (Core1-beta 3GlcNAcT) enabled the construction of the 6-sulfo sialyl Lewis x on extended core1 O-glycans, recapitulating the potent L-selectin-mediated, shear-dependent adhesion observed with novel L-selectin ligands derived from core2 beta1,6-N-acetylglucosaminyltransferase-I null mice. These results identify Core1-beta 3GlcNAcT and its cognate extended core1 O-glycans as essential participants in the expression of the MECA-79-positive, HEV-specific L-selectin ligands required for lymphocyte homing.

In vivo characterization of activatable cell penetrating peptides for targeting protease activity in cancer

Activatable cell penetrating peptides (ACPPs) are novel in vivo targeting agents comprised of a polycationic cell penetrating peptide (CPP) connected via a cleavable linker to a neutralizing polyanion (). Adsorption and uptake into cells are inhibited until the linker is proteolyzed. An ACPP cleavable by matrix metalloproteinase-2 (MMP-2) in vitro was the first one demonstrated to work in a tumor model in vivo, but only HT-1080 xenografts and resected human squamous cell carcinomas were tested. Generality to other cancer types, in vivo selectivity of ACPPs for MMPs, and spatial resolution require further characterization. We now show that ACPPs can target many xenograft tumor models from different cancer sites, as well as a thoroughly studied transgenic model of spontaneous breast cancer (mouse mammary tumor virus promoter driving polyoma middle T antigen, MMTV-PyMT). Pharmacological inhibitors and genetic knockouts indicate that current ACPPs are selective for MMP-2 and MMP-9 in the above in vivo models. In accord with the known local distribution of MMP activity, accumulation is strongest at the tumor-stromal interface in primary tumors and associated metastases, indicating better spatial resolution (<50 mum) than other currently available MMP-cleavable probes. We also find that background uptake of ACPPs into normal tissues such as cartilage can be decreased by appending inert macromolecules of 30-50 KDa to the polyanionic inhibitory domain. Our results validate an approach that should generally deliver imaging agents and chemotherapeutics to sites of invasion, tumor-promoting inflammation, and metastasis.

Receptor tyrosine kinases and TLR/IL1Rs unexpectedly activate myeloid cell PI3Kγ, a single convergent point promoting tumor inflammation and progression

Tumor inflammation promotes angiogenesis, immunosuppression, and tumor growth, but the mechanisms controlling inflammatory cell recruitment to tumors are not well understood. We found that a range of chemoattractants activating G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs) and Toll-like/IL-1 receptors (TLR/IL1Rs) unexpectedly initiate tumor inflammation by activating the PI3-kinase isoform p110γ in Gr1+CD11b+ myeloid cells. Whereas GPCRs activate p110γ in a Ras/p101-dependent manner, RTKs and TLR/IL1Rs directly activate p110γ in a Ras/p87-dependent manner. Once activated, p110γ promotes inside-out activation of a single integrin, α4β1, causing myeloid cell invasion into tumors. Pharmacological or genetic blockade of p110γ suppressed inflammation, growth, and metastasis of implanted and spontaneous tumors, revealing an important therapeutic target in oncology.

Sialyltransferase ST3Gal-IV operates as a dominant modifier of hemostasis by concealing asialoglycoprotein receptor ligands

A number of poorly characterized genetic modifiers contribute to the extensive variability of von Willebrand disease, the most prevalent bleeding disorder in humans. We find that a genetic lesion inactivating the murine ST3Gal-IV sialyltransferase causes a bleeding disorder associated with an autosomal dominant reduction in plasma von Willebrand factor (VWF) and an autosomal recessive thrombocytopenia. Although both ST3Gal-IV and ST6Gal-I sialyltransferases mask galactose linkages implicated as asialoglycoprotein receptor ligands, only ST3Gal-IV deficiency promotes asialoglycoprotein clearance mechanisms with a reduction in plasma levels of VWF and platelets. Exposed galactose on VWF was also found in a subpopulation of humans with abnormally low VWF levels. Oligosaccharide branch-specific sialylation by the ST3Gal-IV sialyltransferase is required to sustain the physiologic half-life of murine hemostatic components and may be an important modifier of plasma VWF level in humans.

Epidermal Sensing of Oxygen Is Essential for Systemic Hypoxic Response

Skin plays an essential role, mediated in part by its remarkable vascular plasticity, in adaptation to environmental stimuli. Certain vertebrates, such as amphibians, respond to hypoxia in part through the skin; but it is unknown whether this tissue can influence mammalian systemic adaptation to low oxygen levels. We have found that epidermal deletion of the hypoxia-responsive transcription factor HIF-1alpha inhibits renal erythropoietin (EPO) synthesis in response to hypoxia. Conversely, mice with an epidermal deletion of the von Hippel-Lindau (VHL) factor, a negative regulator of HIF, have increased EPO synthesis and polycythemia. We show that nitric oxide release induced by the HIF pathway acts on cutaneous vascular flow to increase systemic erythropoietin expression. These results demonstrate that in mice the skin is a critical mediator of systemic responses to environmental oxygen.

Integrin α4β1 Signaling Is Required for Lymphangiogenesis and Tumor Metastasis

Recent studies have shown that lymphangiogenesis or the growth of lymphatic vessels at the periphery of tumors promotes tumor metastasis to lymph nodes. We show here that the fibronectin-binding integrin alpha4beta1 and its ligand fibronectin are novel functional markers of proliferative lymphatic endothelium. Tumors and lymphangiogenic growth factors, such as vascular endothelial growth factor-C (VEGF-C) and VEGF-A, induce lymphatic vessel expression of integrin alpha4beta1. Integrin alpha4beta1 then promotes growth factor and tumor-induced lymphangiogenesis, as genetic loss of integrin alpha4beta1 expression in Tie2Cre+ alpha4(loxp/loxp) mice or genetic loss of alpha4 signaling in alpha4Y991A knock-in mice blocks growth factor and tumor-induced lymphangiogenesis, as well as tumor metastasis to lymph nodes. In addition, antagonists of integrin alpha4beta1 suppress lymphangiogenesis and tumor metastasis. Our studies show that integrin alpha4beta1 and the signals it transduces regulate the adhesion, migration, invasion, and survival of proliferating lymphatic endothelial cells. As suppression of alpha4beta1 expression, signal transduction, or function in tumor lymphatic endothelium not only inhibits tumor lymphangiogenesis but also prevents metastatic disease, these results show that integrin alpha4beta1-mediated tumor lymphangiogenesis promotes metastasis and is a useful target for the suppression of metastatic disease.

Protease-Activated Receptor (PAR) 2, but not PAR1, Signaling Promotes the Development of Mammary Adenocarcinoma in Polyoma Middle T Mice

The G protein-coupled protease-activated receptors (PAR) are key signaling components for proteases in vascular biology and tumor progression. To address the contributions of PAR1 and PAR2 to breast cancer development, we established cohorts of mouse mammary tumor virus-polyoma middle T (PyMT) PAR1(-/-) and PAR2(-/-) mice, considering that the PyMT model recapitulates aspects of human disease. Appearance of palpable tumors, tumor expansion, and metastasis was indistinguishable between wild-type and PAR1(-/-) mice. PAR1(-/-) breast cancer cells were no longer responsive to thrombin in vitro, excluding compensatory up-regulation of alternative thrombin receptors and indicating that thrombin-PAR1 signaling is dispensable in breast tumor microenvironments. In contrast, palpable tumors and multifocal disease developed slower in PAR2(-/-) mice, and as a consequence of delayed tumor onset, metastasis was reduced. Analysis of early tumors showed persistence of adenomas with delayed appearance of vascularized adenocarcinomas in PAR2(-/-) mice. Furthermore, CXCL1 production by early PAR2(-/-) tumors was reduced. These results are consistent with previous xenograft data that implicated breast cancer PAR2 signaling in the induction of proangiogenic growth factors and chemokines. This study establishes that protease signaling contributes to mammary tumor development and that PAR2, rather than the thrombin receptor PAR1, plays a crucial role in the angiogenic switch.