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TWEAK (TNF-like weak inducer of apoptosis) is a TNF superfamily member implicated in several mechanisms. Although fibroblast growth factor inducible 14 (Fn14)/TweakR has been reported as its receptor, an as yet unrecognized surface molecule(s) might modulate TWEAK function(s). Thus, we set out to identify TWEAK-binding proteins by screening a combinatorial peptide library. Cyclic peptides containing a consensus motif (WXDDG) bound to TWEAK specifically. These peptides were similar to CD163, a scavenger receptor cysteine-rich domain family member, restricted to the monocyte/macrophage lineage and responsible for the uptake of circulating haptoglobin-hemoglobin (Hp-Hb) complexes. Sequence profile analysis suggested that TWEAK mimicked the CD163 natural ligand (Hp-Hb). Consistently, we show dose-dependent TWEAK binding to CD163 and blockade by an anti-CD163 Ab. In a competition assay, both soluble CD163 and Fn14/TweakR were able to compete off TWEAK binding to coated Fn14/TweakR or CD163, respectively. Flow-cytometry and immunofluorescence assays showed that human monocytes (Fn14/TweakR negative and CD163 positive) bind TWEAK, thus blocking the recognition of CD163 and reducing the activation mediated by a specific mAb in these cells. We demonstrate that monocytes can sequester TWEAK from supernatants, thus preventing tumor cell apoptosis; this effect was reverted by preincubation with the peptide mimicking CD163 or with a mAb anti-CD163, indicating specificity. Finally, we show that recombinant human TWEAK binding to CD163-transfected Chinese hamster ovary cells is inhibited by the presence of either unlabeled TWEAK or the Hp-Hb complex. Together, these data are consistent with the hypothesis that CD163 either acts as a TWEAK scavenger in pathological conditions or serves as an alternate receptor for TWEAK in cells lacking Fn14/TweakR.

Purpose: Tumor hypoxia underlies treatment failure and yields a more aggressive, invasive, and metastatic cancer phenotype. TH-302 is a 2-nitroimidazole triggered hypoxia-activated prodrug of the cytotoxin bromo-isophosphoramide mustard (Br-IPM). The purpose of this study is to characterize the antitumor activity of TH-302 and investigate its selective targeting of the hypoxic cells in human tumor xenograft models.Experimental Design: Antitumor efficacy was assessed by tumor growth kinetics or by clonogenic survival of isolated cells after tumor excision. Hypoxic fractions (HF) were determined by immunohistochemistry and morphometrics of pimonidazole staining. Tumor hypoxia levels were manipulated by exposing animals to different oxygen concentration breathing conditions. The localization and kinetics of TH-302 induced DNA damage was determined by gH2AX immunohistochemistry.Results: TH-302 antitumor activity was dose-dependent and correlated with total drug exposure. Correlation was found between antitumor activity and tumor HF across 11 xenograft models. Tumorbearing animals breathing 95% O 2 exhibited attenuated TH-302 efficacy, with whereas those breathing 10% O 2 exhibited enhanced TH-302 efficacy, both compared with air (21% O 2 ) breathing. TH-302 treatment resulted in a reduction in the volume of the HF 48 hours after dosing and a corresponding increase in the necrotic fraction. TH-302 induced DNA damage as measured by gH2AX was initially only present in the hypoxic regions and then radiated to the entire tumor in a time-dependent manner, consistent with TH-302 having a "bystander effect."Conclusions: The results show that TH-302 has broad antitumor activity and selectively targets hypoxic tumor tissues. Clin Cancer Res; 18(3); 758-70. Ó2011 AACR.

Hypoxia is associated with increased metastatic potential and poor prognosis in solid tumors. In this study, we demonstrated in the murine 5T33MM model that multiple myeloma (MM) cells localize in an extensively hypoxic niche compared with the naive bone marrow. Next, we investigated whether hypoxia could be used as a treatment target for MM by evaluating the effects of a new hypoxiaactivated prodrug TH-302 in vitro and in vivo. In severely hypoxic conditions, TH-302 induces G 0 /G 1 cell-cycle arrest by down-regulating cyclinD1/2/3, CDK4/6, p21 cip-1 , p27 kip-1 , and pRb expression, and triggers apoptosis in MM cells by upregulating the cleaved proapoptotic caspase-3, -8, and -9 and poly ADP-ribose polymerase while having no significant effects under normoxic conditions. In vivo treatment of 5T33MM mice induces apoptosis of the MM cells within the bone marrow microenvironment and decreases paraprotein secretion. Our data support that hypoxia-activated treatment with TH-302 provides a potential new treatment option for MM. (Blood. 2010;116(9):1524-1527) IntroductionMultiple myeloma (MM) is an incurable clonal B-cell malignancy characterized by the accumulation of neoplastic plasma cells in the bone marrow (BM). 1 Studies have shown that the intimate reciprocal relationship between tumor cells and the cellular and noncellular microenvironment plays a pivotal role in MM growth and survival. 2,3 Hypoxia, one of the important microenvironmental factors, is well known to be highly associated with increased angiogenesis and metastatic potential as well as poor prognosis in solid tumors. More recently, hypoxia has been demonstrated to be crucial for normal marrow hematopoiesis. [4][5][6] However, the role of hypoxia in the etiology, pathogenesis, and possible treatment of hematologic malignancies, such as MM, is still unknown.Given very low oxygen levels, as found in tumors, are rarely observed in normal tissues, the presence of hypoxic tumor cells is therefore regarded not only as an adverse prognostic factor but also as a potential target for tumor-specific treatment. Currently, several hypoxia-targeted therapeutics are under development. 7-12 TH-302 is a new hypoxia-activated prodrug that is being evaluated in phase 1/2 clinical trials for the treatment of solid tumors as a monotherapy and in combination with 4 chemotherapeutic agents (gemcitabine, pemetrexed, doxorubicin, and docetaxel). TH-302 is a 2-nitroimidazole prodrug of the cytotoxin bromo-isophosphoramide mustard, with a favorable physicochemical, metabolic, and pharmacokinetic profile and exhibits hypoxiaselective cytotoxicity across a broad spectrum of human cancer cell lines in vitro and in vivo efficacy in a large panel of human tumor xenografts. 13,14 The doses used in the clinical studies are in the same range as the doses demonstrating efficacy in both in vitro and in vivo preclinical models.In this study, we investigated the hypoxic nature of MM by staining the BM of naive and 5T33MM mice with the exogenous hypoxia marker pimonidazole and endogenou...

In vivo phage display is a technology used to reveal organ-specific vascular ligand-receptor systems in animal models and, recently, in patients, and to validate them as potential therapy targets. Here, we devised an efficient approach to simultaneously screen phage display libraries for peptides homing to any number of tissues without the need for an individual subject for each target tissue. We tested this approach in mice by selecting homing peptides for six different organs in a single screen and prioritizing them by using software compiled for statistical validation of peptide biodistribution specificity. We identified a number of motif-containing biological candidates for ligands binding to organ-selective receptors based on similarity of the selected peptide motifs to mouse proteins. To demonstrate that this methodology can lead to targetable ligand-receptor systems, we validated one of the pancreas-homing peptides as a mimic peptide of natural prolactin receptor ligands. This new comprehensive strategy for screening phage libraries in vivo provides an advantage over the conventional approach because multiple organs internally control for organ selectivity of each other in the successive rounds of selection. It may prove particularly relevant for patient studies, allowing efficient high-throughput selection of targeting ligands for multiple organs in a single screen.

BackgroundCombinatorial phage display has been used in the last 20 years in the identification of protein-ligands and protein-protein interactions, uncovering relevant molecular recognition events. Rate-limiting steps of combinatorial phage display library selection are (i) the counting of transducing units and (ii) the sequencing of the encoded displayed ligands. Here, we adapted emerging genomic technologies to minimize such challenges.Methodology/Principal FindingsWe gained efficiency by applying in tandem real-time PCR for rapid quantification to enable bacteria-free phage display library screening, and added phage DNA next-generation sequencing for large-scale ligand analysis, reporting a fully integrated set of high-throughput quantitative and analytical tools. The approach is far less labor-intensive and allows rigorous quantification; for medical applications, including selections in patients, it also represents an advance for quantitative distribution analysis and ligand identification of hundreds of thousands of targeted particles from patient-derived biopsy or autopsy in a longer timeframe post library administration. Additional advantages over current methods include increased sensitivity, less variability, enhanced linearity, scalability, and accuracy at much lower cost. Sequences obtained by qPhage plus pyrosequencing were similar to a dataset produced from conventional Sanger-sequenced transducing-units (TU), with no biases due to GC content, codon usage, and amino acid or peptide frequency. These tools allow phage display selection and ligand analysis at >1,000-fold faster rate, and reduce costs ∼250-fold for generating 106 ligand sequences.Conclusions/SignificanceOur analyses demonstrates that whereas this approach correlates with the traditional colony-counting, it is also capable of a much larger sampling, allowing a faster, less expensive, more accurate and consistent analysis of phage enrichment. Overall, qPhage plus pyrosequencing is superior to TU-counting plus Sanger sequencing and is proposed as the method of choice over a broad range of phage display applications in vitro, in cells, and in vivo.

Purpose Subregional hypoxia is a common feature of tumors and is recognized as a limiting factor for the success of radiotherapy and chemotherapy. TH-302, a hypoxia-activated prodrug selectively targeting hypoxic regions of solid tumors, delivers a cytotoxic warhead to the tumor, while maintaining relatively low systemic toxicity. The antitumor activity, different dosing sequences, and dosing regimens of TH-302 in combination with commonly used conventional chemotherapeutics were investigated in human tumor xenograft models. Methods Seven chemotherapeutic drugs (docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide) were tested in combination with TH-302 in eleven human xenograft models, including non-small cell lung cancer (NSCLC), colon cancer, prostate cancer, fibrosarcoma, melanoma, and pancreatic cancer. Results The antitumor activity of docetaxel, cisplatin, pemetrexed, irinotecan, doxorubicin, gemcitabine, and temozolomide was increased when combined with TH-302 in nine out of eleven models tested. Administration of TH-302 2–8 h prior to the other chemotherapeutics yielded superior efficacy versus other sequences tested. Simultaneous administration of TH-302 and chemotherapeutics increased toxicity versus schedules with dosing separations. In a dosing optimization study, TH-302 administered daily at 50 mg/kg intraperitoneally for 5 days per week in the H460 NSCLC model showed the optimal response with minimal toxicity. Conclusions TH-302 enhances the activity of a wide range of conventional anti-neoplastic agents in a broad panel of in vivo xenograft models. These data highlight in vivo effects of schedule and order of drug administration in regimen efficacy and toxicity and have relevance to the design of human regimens incorporating TH-302.

Aminopeptidase N (APN, CD13; EC 3.4.11.2) is a transmembrane metalloprotease with several functions, depending on the cell type and tissue environment. In tumor vasculature, APN is overexpressed in the endothelium and promotes angiogenesis. However, there have been no reports of in vivo inactivation of the APN gene to validate these findings. Here we evaluated, by targeted disruption of the APN gene, whether APN participates in blood vessel formation and function under normal conditions. Surprisingly, APN-null mice developed with no gross or histological abnormalities. Standard neurological, cardiovascular, metabolic, locomotor, and hematological studies revealed no alterations. Nonetheless, in oxygen-induced retinopathy experiments, APN-deficient mice had a marked and dose-dependent deficiency of the expected retinal neovascularization. Moreover, gelfoams embedded with growth factors failed to induce functional blood vessel formation in APNnull mice. These findings establish that APN-null mice develop normally without physiological alterations and can undergo physiological angiogenesis but show a severely impaired angiogenic response under pathological conditions. Finally, in addition to vascular biology research, APN-null mice may be useful reagents in other medical fields such as malignant, cardiovascular, immunological, or infectious diseases.CD13 ͉ knockout mice ͉ retinopathy ͉ vasculogenesis T he aminopeptidases are a large family of proteolytic enzymes that affect protein maturation, degradation, and regulation (1, 2). Aminopeptidase N (APN) is a membrane-bound zincdependent metalloprotease originally identified as a surface marker in myeloid cells (3,4). APN is widely distributed in many cell types, and its role in hydrolyzing unsubstituted N-terminal residues with neutral side chains varies in different locations. In the epithelium of the renal proximal tubule, APN cleaves its only known natural substrate, angiotensin (ang) III, to ang IV; in synaptic membranes, APN metabolizes enkephalins and endorphins; in the heart, it is an integral component of cardiac remodeling postmyocardial infarction (5-10); and in the respiratory system, APN is the cell surface receptor for certain human coronaviruses and potentially for the severe acute respiratory syndrome (SARS) virus (11-13). Additionally, APN functions in signal transduction, cell cycle control, and differentiation (14, 15).We have developed an in vivo system by using ligand peptides displayed on the surface of phage to study organ-and tumorspecific vascular homing; this methodology enables the identification of vascular markers (16,17). We have isolated phage displaying an asparagine-glycine-arginine (NGR)-containing peptide in a tumor-homing selection and have shown that these phage bind selectively to angiogenic blood vessels. When coupled to a cytotoxic drug (18) or fused to a proapoptotic peptide (19) or to tumor necrosis factor (20), NGR-targeted compounds were more effective and less toxic than the respective controls. The cell surface receptor fo...