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Supplemental Figure 1. Cell surface expression of IL-11R in AML patient derived samples and hematopoietic cells from healthy bone marrow as analyzed by flow cytometry.

Supplemental Table 1. Features of synthesized analogs of BMTP-11 for drug-lead optimization.

Purpose: The IL11 receptor (IL11R) is an established molecular target in primary tumors of bone, such as osteosarcoma, and in secondary bone metastases from solid tumors, such as prostate cancer. However, its potential role in management of hematopoietic malignancies has not yet been determined. Here, we evaluated the IL11R as a candidate therapeutic target in human leukemia and lymphoma.Experimental Design and Results: First, we show that the IL11R protein is expressed in a variety of human leukemia– and lymphoma–derived cell lines and in a large panel of bone marrow samples from leukemia and lymphoma patients, whereas expression is absent from nonmalignant control bone marrow. Moreover, a targeted peptidomimetic prototype (termed BMTP-11), specifically bound to leukemia and lymphoma cell membranes, induced ligand–receptor internalization mediated by the IL11R, and resulted in a specific dose-dependent cell death induction in these cells. Finally, a pilot drug lead-optimization program yielded a new myristoylated BMTP-11 analogue with an apparent improved antileukemia cell profile.Conclusions: These results indicate (i) that the IL11R is a suitable cell surface target for ligand-directed applications in human leukemia and lymphoma and (ii) that BMTP-11 and its derivatives have translational potential against this group of malignant diseases. Clin Cancer Res; 21(13); 3041–51. ©2015 AACR.

Supplemental Figure 3. Drug activity of BMTP-11 and BMTP#4 on a panel of established leukemia and lymphoma cell lines.

Supplemental Figure Legends

Supplemental Figure 2. Cell membrane and cytoplasmic expression of IL-11R.

Integrins are large heterodimeric type 1 membrane proteins expressed in all nucleated mammalian cells. Eighteenα-chains and eightβ-chains can combine to form 24 different integrins. They are cell adhesion proteins, which bind to a large variety of cellular and extracellular ligands. Integrins are required for cell migration, hemostasis, translocation of cells out from the blood stream and further movement into tissues, but also for the immune response and tissue morphogenesis. Importantly, integrins are not usually active as such, but need activation to become adhesive. Integrins are activated by outside-in activation through integrin ligand binding, or by inside-out activation through intracellular signaling. An important question is how integrin activity is regulated, and this topic has recently drawn much attention. Changes in integrin affinity for ligand binding are due to allosteric structural alterations, but equally important are avidity changes due to integrin clustering in the plane of the plasma membrane. Recent studies have partially solved how integrin cell surface structures change during activation. The integrin cytoplasmic domains are relatively short, but by interacting with a variety of cytoplasmic proteins in a regulated manner, the integrins acquire a number of properties important not only for cell adhesion and movement, but also for cellular signaling. Recent work has shown that specific integrin phosphorylations play pivotal roles in the regulation of integrin activity. Our purpose in this review is to integrate the present knowledge to enable an understanding of how cell adhesion is dynamically regulated.

Translation of drug candidates into clinical settings requires demonstration of preclinical efficacy and formal toxicology analysis for filling an Investigational New Drug (IND) application with the US Food and Drug Administration (FDA). Here, we investigate the membrane-associated glucose response protein 78 (GRP78) as a therapeutic target in leukemia and lymphoma. We evaluated the efficacy of the GRP78-targeted proapoptotic drug bone metastasis targeting peptidomimetic 78 (BMTP-78), a member of the D (KLAKLAK)2-containing class of agents. BMTP-78 was validated in cells from patients with acute myeloid leukemia and in a panel of human leukemia and lymphoma cell lines, where it induced dose-dependent cytotoxicity in all samples tested. Based on the in vitro efficacy of BMTP-78, we performed formal good laboratory practice toxicology studies in both rodents (mice and rats) and nonhuman primates (cynomolgus and rhesus monkeys). These analyses represent required steps towards an IND application of BMTP-78 for theranostic first-in-human clinical trials.

BACKGROUND The authors developed an ex vivo methodology to perform drug library screening against human leukemia. METHODS The strategy for this screening relied on human blood or bone marrow cultures under hypoxia; under these conditions, leukemia cells deplete oxygen faster than normal cells, causing a hemoglobin oxygenation shift. Several advantages were observed: 1) partial recapitulation of the leukemia microenvironment, 2) use of native hemoglobin oxygenation as a real-time sensor/reporter, 3) cost-effectiveness, 4) species specificity, and 5) a format that enables high-throughput screening. RESULTS For a proof of concept, a chemical library (size, approximately 20,000 compounds) was screened against human leukemia cells. Seventy compounds were identified (“hit” rate, 0.35%; Z-factor = 0.71) that had activity, and 20 compounds were examined to identify 18 true-positive compounds (90%). Finally, the results demonstrated that carbonohydraxonic diamide group-containing compounds are potent antileukemia agents that induce cell death in leukemia cells and in patient-derived samples. CONCLUSIONS The current results indicated that this unique functional assay can identify novel drug candidates and can help with the development of future applications in personalized drug selection for patients with leukemia. Cancer 2014;120:589–602. © 2013 American Cancer Society.

Processes that promote cancer progression such as angiogenesis require a functional interplay between malignant and nonmalignant cells in the tumor microenvironment. The metalloprotease aminopeptidase N (APN; CD13) is often overexpressed in tumor cells and has been implicated in angiogenesis and cancer progression. Our previous studies of APN-null mice revealed impaired neoangiogenesis in model systems without cancer cells and suggested the hypothesis that APN expressed by nonmalignant cells might promote tumor growth. We tested this hypothesis by comparing the effects of APN deficiency in allografted malignant (tumor) and nonmalignant (host) cells on tumor growth and metastasis in APN-null mice. In two independent tumor graft models, APN activity in both the tumors and the host cells cooperate to promote tumor vascularization and growth. Loss of APN expression by the host and/or the malignant cells also impaired lung metastasis in experimental mouse models. Thus, cooperation in APN expression by both cancer cells and nonmalignant stromal cells within the tumor microenvironment promotes angiogenesis, tumor growth, and metastasis.

Targeted drug delivery offers an opportunity for the development of safer and more effective therapies for the treatment of cancer. In this study, we sought to identify short, cell-internalizing peptide ligands that could serve as directive agents for specific drug delivery in hematologic malignancies. By screening of human leukemia cells with a combinatorial phage display peptide library, we isolated a peptide motif, sequence Phe-Phe/Tyr-Any-Leu-Arg-Ser (FF/YXLRS), which bound to different leukemia cell lines and to patient-derived bone marrow samples. The motif was internalized through a receptor-mediated pathway, and we next identified the corresponding receptor as the transmembrane glycoprotein neuropilin-1 (NRP-1). Moreover, we observed a potent anti-leukemia cell effect when the targeting motif was synthesized in tandem to the pro-apoptotic sequence D(KLAKLAK)2. Finally, our results confirmed increased expression of NRP-1 in representative human leukemia and lymphoma cell lines and in a panel of bone marrow specimens obtained from patients with acute lymphoblastic leukemia or acute myelogenous leukemia compared with normal bone marrow. These results indicate that NRP-1 could potentially be used as a target for ligand-directed therapy in human leukemias and lymphomas and that the prototype CGFYWLRSC-GG-D(KLAKLAK)2 is a promising drug candidate in this setting.

Leukocytes migrate from the blood into areas of inflammation by interacting with various adhesion molecules on endothelial cells. Vascular adhesion protein-1 (VAP-1) is a glycoprotein expressed on inflamed endothelium where it plays a dual role: it is both an enzyme that oxidizes primary amines and an adhesin that is involved in leukocyte trafficking to sites of inflammation. Although VAP-1 was identified more than 15 years ago, the counterreceptor(s) for VAP-1 on leukocytes has remained unknown. Here we have identified Siglec-10 as a leukocyte ligand for VAP-1 using phage display screenings. The binding between Siglec-10 and VAP-1 was verified by different adhesion assays, and this interaction was also consistent with molecular modeling. Moreover, the interaction between Siglec-10 and VAP-1 led to increased hydrogen peroxide production, indicating that Siglec-10 serves as a substrate for VAP-1. Thus, the Siglec-10–VAP-1 interaction seems to mediate lymphocyte adhesion to endothelium and has the potential to modify the inflammatory microenvironment via the enzymatic end products.

Matrix metalloproteinases (MMPs), and especially membrane type-1 matrix metalloproteinase (MT1-MMP, MMP-14), play a role in cancer progression and can have a prognostic value. Various synthetic broad-spectrum MMP inhibitors have been developed but have had little success in cancer patient treatment owing to side effects. Until recently, selective targeting of specific MMPs has not been possible due to lack of specific inhibitors. Here we have developed a selective MT1-MMP peptide-inhibitor GACFSIAHECGA, which did not affect the activities of many other MMPs including MMP-1, -2, -3, -7, -8, -9, -10, -11, -12, -13, -15, -17 or -20. In a fluorescent peptide cleavage assay it displayed an IC(50) value of 150 microM. The peptide effectively inhibited the migration and invasion of cancer cell lines in vitro. Furthermore, in vivo the peptide reduced the growth of tongue carcinoma xenografts and prolonged the survival of mice. Overall these results suggest that selective MT1-MMP inhibitors may have utility as anticancer agents.

Acute myelogenous leukemias (AMLs) are characterized by medullary and extramedullary invasion. We hypothesized that a supramolecular complex, the leukemia-cell invadosome, which contains certain integrins, matrix metalloproteinases (MMPs), and other as-yet unidentified proteins, is essential for tissue invasion and may be central to the phenotypic diversity observed in the clinic. Here we show that the specific binding of MMP-9 to leukocyte surface β2 integrin is required for pericellular proteolysis and migration of AML-derived cells. An efficient antileukemia effect was obtained by the hexapeptide HFDDDE, a motif of the MMP-9 catalytic domain that mediates integrin binding: HFDDDE prevented proMMP-9 binding, transmigration through a human endothelial cell layer, and extracellular matrix degradation. Notably, the functional protein anchorage between β2 integrin and proMMP-9 described in this study does not involve the enzymatic active sites targeted by known MMP inhibitors. Taken together, our results provide a biochemical working definition for the human leukemia invadosome. Disruption of specific protein complexes within this supramolecular target complex may yield a new class of anti-AML drugs with anti-invasion (rather than or in addition to cytotoxic) attributes.

Mammalian cell membranes provide an interface between the intracellular and extracellular compartments. It is currently thought that cytoplasmic signaling adapter proteins play no functional role within the extracellular tumor environment. Here, by selecting combinatorial random peptide libraries in tumor-bearing mice, we uncovered a direct, specific, and functional interaction between CRKL, an adapter protein [with Src homology 2 (SH2)- and SH3-containing domains], and the plexin-semaphorin-integrin domain of β 1 integrin in the extracellular milieu. Through assays in vitro, in cellulo, and in vivo, we show that this unconventional and as yet unrecognized protein–protein interaction between a regulatory integrin domain (rather than a ligand-binding one) and an intracellular adapter (acting outside of the cells) triggers an alternative integrin-mediated cascade for cell growth and survival. Based on these data, here we propose that a secreted form of the SH3/SH2 adaptor protein CRKL may act as a growth-promoting factor driving tumorigenesis and may lead to the development of cancer therapeutics targeting secreted CRKL.

Ligand-directed delivery of agents to leukemia and lymphoma cells has the potential to yield new mechanistic disease insights and targeted therapies. Here we set out to target the macropinocytotic pathway with a combinatorial approach. From the screening of acute T-lymphoblastic leukemia Molt-4 cells with a random phage-display peptide library, we isolated a phage displaying the sequence CAYHRLRRC. This peptide contains a lymph node-homing motif (Cys-Ala-Tyr) and a cell-penetrating motif (Arg-Leu-Arg-Arg). Binding of this ligand-directed phage to a large panel of leukemia/lymphoma cells and to patient-derived samples was much higher than to non-leukemia control cells. CAYHRLRRC phage internalization into Molt-4 cells is both energy- and temperature-dependent. Flow cytometry with fluorescein-labeled peptide and endocytosis blocking with specific inhibitors revealed that CAYHRLRRC is indeed taken up through macropinocytosis in Molt-4 and K562 human leukemia cells. Unexpectedly, the cell surface receptor for the CAYHRLRRC peptide is not a heparan sulfate proteoglycan as it would be predicted for other cell-penetrating peptides. Confirming this interpretation, a CAYHRLRRC-directed peptidomimetic-induced cell death in all the leukemia and lymphoma cells was evaluated, whereas a control transactivator of transcription protein (tat)-directed proapoptotic peptidomimetic was non-selective. In summary, the targeting peptide CAYHRLRRC is selectively internalized through macropinocytosis in leukemia and lymphoma cells and has potential as a drug lead for ligand-directed anti-leukemia therapies.

Matrix metalloproteinases (MMP-2 and MMP-9, or gelatinases) are involved in tongue SCC invasion, metastasis and angiogenesis. We have recently shown that a novel and selective hydrophobic cyclic CTTHWGFTLC (CTT1) peptide is inhibitor for MMP-2 and MMP-9 (Koivunen et al., Nat Biotechnol 1999; 17:768–74). In this study, we demonstrate that both the new hydrophilic derivate GRENYHGCTTHWGFTLC (CTT2) peptide and the CTT1 peptide inhibited specifically the human tongue squamous cell carcinoma (HSC-3) cell-derived gelatinolytic activity and in vitro invasion and migration of these cells (p ≤ 0.049). In situ zymography revealed that both peptides also inhibited clearly almost all of the gelatinolytic activity present in the human tongue SCC tissue sections, indicating that MMP-2 and MMP-9 are the major gelatinases detected in the tongue carcinomas. However, CTT2 did not inhibit the type I collagen degradation by human collagenases (MMP-1, MMP-8 and MMP-13). Furthermore, CTT2 reduced the blood vessel density (p ≤ 0.043) and clearly improved the survival of the mice bearing human tongue carcinoma xenografts (p ≤ 0.012). Overall, we suggest that CTT1 and CTT2 peptides being selective gelatinase inhibitors with significant anti-tumor properties could be useful to diminish the invasion and angiogenesis of human tongue carcinomas characterized by enhanced gelatinolytic activity in tumors. © 2005 Wiley-Liss, Inc.

The matrix metalloproteinases(MMP)-2 and -9, also known as the gelatinases have been long recognized as major contributors to the proteolytic degradation of extracellular matrix during tumor invasion. In the recent years, a plethora of non-matrix proteins have also been identified as gelatinase substrates thus significantly broadening our understanding of these enzymes as proteolytic executors and regulators in various physiological and pathological states including embryonic growth and development, angiogenesis and tumor progression, inflammation, infective diseases, degenerative diseases of the brain and vascular diseases. Although the effect of broad-spectrum inhibitors of MMPs in the treatment of cancer has been disappointing in clinical trials, novel mechanisms of gelatinase inhibition have been now identified. Inhibition of the association of the gelatinases with cell-surface integrins appears to offer highly specific means to target these enzymes without inhibiting their catalytic activity in multiple cell types including endothelial cells, tumor cells and leukocytes. Here, we review the multiple functions of the gelatinases in cancer, and especially their role in the tumor cell migration and invasion.

Migration of invasive cells appears to be dependent on matrix metalloproteinases (MMPs) anchored on the cell surface through integrins. We have previously demonstrated an interaction between the integrin alpha-subunit I domain and the catalytic domain of MMP-9. We now show that there is also an interaction between the integrin beta subunit and MMP-9. Using phage display, we have developed MMP-9 inhibitors that bind either to the MMP-9 catalytic domain, the collagen binding domain, or the C-terminal hemopexin-like domain. The C-terminal domain-binding peptide mimics an activation epitope in the stalk of the integrin beta chain and inhibits the association of MMP-9 C-terminal domain with alpha(V)beta(5) integrin. Unlike other MMP-9 binding peptides, it does not directly inhibit catalytic activity of MMP-9, but still prevents proenzyme activation and cell migration in vitro and tumor xenograft growth in vivo. We also find an association between MMP-9 and urokinase-plasminogen activator receptor and find that urokinase-plasminogen activator receptor is cleaved by MMP-9. Collectively, we have defined molecular details for several interactions mediated by the different MMP-9 domains.

We have recently demonstrated that promatrix metalloproteinases (proMMPs), particularly proMMP-9, are potent ligands of the leukocyte β2 integrins. We studied here the complex formation between proMMP-9 and αMβ2, the major MMP and integrin of neutrophils. On resting neutrophils, the proMMP-9/αMβ2 complex was primarily detected in intracellular granules, but after cellular activation it became localized to the cell surface, as demonstrated by immunoprecipitation and double immunofluorescence. Further indication of the complex formation was that neutrophils and αMβ2-transfected L cells, but not the wild-type L cells or leukocyte adhesion deficiency cells, bound to immobilized proMMP-9 or its recombinant catalytic domain in a β2 integrin-dependent manner. Peptides that bound to the αM integrin-I domain and inhibited its complex formation with proMMP-9 prevented neutrophil migration in a transendothelial assay in vitro and in a thioglycolate-elicited peritonitis in vivo. These results suggest that the translocating proMMP-9/αMβ2 complex may be part of the cell surface machinery guiding neutrophil migration.

In situ zymography provides a tool to localize proteolytic activity in tissues in vivo. However, it has been difficult to discriminate between the proteases responsible for the detected activity. We used a selective tissue-permeable gelatinase inhibitor, the CTTHWGFTLC-peptide (CTT) in inflamed human gingiva. The CTT-peptide was evidenced to home, target to, and selectively inhibit the areas of gelatinolytic activity in inflamed human gingiva expressing MMP-2 and -9. Gelatinolytic activity, MMP-9 immunoreactivity, and mRNA expression as well as CD-45-positive inflammatory cells colocalized well in the inflamed human gingival connective tissue. Gelatinolytic activity corresponding to MMP-2 colocalized with laminin-5 gamma2-chain immunoreactivity and was detected in the close vicinity of the sulcular basement membrane region. Furthermore, the CTT-peptide inhibited beta-caseinolysis by human MMP-2 and MMP-9 as well as laminin-5 gamma2-chain degradation by MMP-2 in vitro. Thus, the CTT-peptide may prove to be a useful tool (i) to discriminate between gelatinolytic proteases detected by in situ zymography and (ii) to preventMMP-2-dependent induction of epithelial cell migration and gelatinase-dependent tissue destruction in inflammatory and malignant diseases.

Proteolysis mediated by matrix metalloproteinases (MMPs) and serine proteinases is associated with cancer invasion and metastasis. Activation of latent proMMPs, and especially the proforms of the type IV collagen degrading gelatinases A and B (proMMP-2 and proMMP-9), is thought to be a critical step in this process. We have recently found that human tumour-associated trypsin-2 is a potent activator of proMMP-9 and it also activates proMMP-2 in vitro. Trypsinogen, MMP-2, and MMP-9 are expressed in ovarian cancer. To elucidate the function of trypsin in vivo, we studied whether high concentrations of trypsinogen-1, trypsinogen-2, their α1-proteinase inhibitor (API) complexes, and tumour-associated trypsin inhibitor (TATI) are associated with proMMP-2 and proMMP-9 activation in ovarian tumour cyst fluids. Zymography and immunofluorometric analysis of 61 cyst fluids showed a significant association between high trypsin concentrations and the activation of MMP-9 (P= 0.003–0.05). In contrast, the trypsin concentrations were inversely associated with the activation of MMP-2 (P= 0.01–0.02). Immunohistochemical analysis of ovarian tumour tissue demonstrated expression of trypsinogen-2 and TATI in the secretory epithelium. MMP-2 was detected both in stromal and epithelial cells whereas MMP-9 was detected in neutrophils and macrophage-like cells in stromal and epithelial areas. These results suggest that trypsin may play a role in the regulation of the MMP-dependent proteolysis associated with invasion and metastasis of ovarian cancer. © 2001 Cancer Research Campaign www.bjcancer.com

Purpose: The IL11 receptor (IL11R) is an established molecular target in primary tumors of bone, such as osteosarcoma, and in secondary bone metastases from solid tumors, such as prostate cancer. However, its potential role in management of hematopoietic malignancies has not yet been determined. Here, we evaluated the IL11R as a candidate therapeutic target in human leukemia and lymphoma. Experimental Design and Results: First, we show that the IL11R protein is expressed in a variety of human leukemia– and lymphoma–derived cell lines and in a large panel of bone marrow samples from leukemia and lymphoma patients, whereas expression is absent from nonmalignant control bone marrow. Moreover, a targeted peptidomimetic prototype (termed BMTP-11), specifically bound to leukemia and lymphoma cell membranes, induced ligand–receptor internalization mediated by the IL11R, and resulted in a specific dose-dependent cell death induction in these cells. Finally, a pilot drug lead-optimization program yielded a new myristoylated BMTP-11 analogue with an apparent improved antileukemia cell profile. Conclusions: These results indicate (i) that the IL11R is a suitable cell surface target for ligand-directed applications in human leukemia and lymphoma and (ii) that BMTP-11 and its derivatives have translational potential against this group of malignant diseases. Clin Cancer Res; 21(13); 3041–51. ©2015 AACR.

Abstract —Matrix metalloproteinase (MMP)-2 has been historically associated with the process of vascular remodeling through the cleavage of extracellular matrix proteins. However, we recently found that MMP-2 also cleaves the endothelium-derived peptide big endothelin-1, ET-1[1–38] and yields the novel vasoconstrictor ET-1[1–32]. We therefore investigated the effects of MMP-2 inhibitors as potential vasodilators. MMP inhibition with ortho-phenanthroline (0.3 to 30 μmol/L) induced vasorelaxation of isolated rat mesenteric arteries (maximum of relaxation=74.5±27.6% at 30 μmol/L). However, phosphoramidon (0.3 to 30 μmol/L), which inhibits some metalloenzymes, but not MMP-2, did not dilate the arteries. Selective inhibition of endogenous MMP-2 with the novel tissue-permeable cyclic peptide CTTHWGFTLC (CTT, 10 μmol/L) also caused vasorelaxation (by 85±6%), whereas STTHWGFTLS (10 μmol/L), an inactive CTT analogue, did not dilate the arteries. Interestingly, the vasorelaxation that results from MMP-2 inhibition was endothelium-independent. Thus, we examined whether MMP-2 acted on peptides derived from the smooth muscle or the perivascular nerves. Recombinant human MMP-2 cleaved calcitonin gene-related peptide (CGRP) specifically at the Gly 14 -Leu 15 peptide bond and reduced the vasodilatory potency of CGRP by 20-fold. Inhibition of MMP-2 increased the amount of intact CGRP in arteries and enhanced vasorelaxation induced by anandamide, which stimulates CGRP release. Vasorelaxation in response to MMP-2 inhibition was abolished by CGRP[8–37], a selective CGRP receptor antagonist, and by capsaicin, which depletes arterial perivascular nerves of CGRP. We conclude that vascular MMP-2 cleaves endogenous CGRP and promotes vasoconstriction. These data suggest a novel mechanism of regulating the vasoactive and, possibly, the neurohormonal actions of CGRP and establish MMP-2 as a modulator of vascular function.

Prostate-specific antigen (PSA) is a serine protease with highly prostate-specific expression. Measurement of PSA in serum is widely used for diagnosis and monitoring of prostate cancer. PSA dissolves the seminal gel forming after ejaculation. It has been suggested to mediate invasion and metastasis of prostate cancer but also to exert antiangiogenic activity. We have identified peptides specific for PSA by screening cyclic phage display peptide libraries. PSA-binding peptides were isolated from four different libraries and produced as a fusion protein with glutathione S-transferase (GST). The phage and fusion proteins were shown to bind to PSA specifically as indicated by lack of binding to other serine proteinases. A peptide with four cysteines showed the highest affinity for PSA. Zn2+, an inhibitor of PSA activity, increased the affinity of the peptides to PSA. The binding specificity was characterized by cross-inhibition using monoclonal anti-PSA antibodies of known epitope specificities. The peptides bound to the same region as mAbs specific for free PSA indicating that they bind close to the active site of the enzyme. The peptides enhanced the enzyme activity of PSA against a chromogenic substrate. These results show that peptides binding to PSA and modulating its enzyme activity can be developed by phage display technique. The peptides have the potential to be used for identification of PSA variants and for imaging and targeting of prostatic tumors.

Phage display libraries offer a strategy to isolate peptide ligands to target proteins and to define potential interaction sites between proteins. Recent studies have indicated a novel utility for phage display in that bacteriophage engineered to express peptide ligands to specific cell surface receptors are internalized by mammalian cells. Thus, reporter genes such as green fluorescent protein and lacZ harbored in the phage genome can be delivered to mammalian cells using targeting peptides displayed on the surface of phage. There is also the possibility to generate novel types of peptide libraries expressed intracellularly using a phage capable of inducing expression of its coding genes in human cells.

Many types of human tumor express trypsinogen-2, which may be a significant factor in the activation of pro-MMPs and the invasiveness of tumors. Prevention of trypsinogen-2 expression in cancer cells might be of benefit in cancer therapy. We describe here chemicals capable of down-regulating the expression of trypsinogen-2. Doxycycline (DOXY) and chemically modified tetracyclines (CMTs), previously known as inhibitors of the matrix metalloproteinase (MMP)-dependent proteinase cascade, down-regulated the mRNA and protein expression of trypsinogen-2 by COLO-205 human colon adenocarcinoma cells at therapeutically attainable concentrations (0. 1 to 1.0 microM). DOXY specifically inhibited the activation of pro-MMP-9 and cell migration induced by enteropeptidase, a specific activator of trypsinogen. Pro-MMP-9 activation and cell migration were also inhibited by tumor-associated trypsin inhibitor (TATI), which is a highly specific inhibitor of trypsin. CMT-3 as well as CMT-5 also inhibited cell migration, but an effect on the enteropeptidase-enhanced activation of pro-MMP-9 was not observed. Our results indicate that CMTs, DOXY and TATI inhibit cancer cell migration by down-regulating trypsinogen-2 expression or activity. Inhibition of trypsinogen-2 expression may represent a mechanism contributing to the ability of CMTs to suppress the pericellular proteolytic activity of some tumors.

Prostate-specific antigen (PSA) is a serine proteinase produced mainly by epithelial cells of the prostate. Measurement of PSA in serum is widely used for diagnosis and monitoring of prostate cancer. The major problem of the PSA determination in early diagnosis is the high false positive rate due to benign prostatic hyperplasia, but the clinical accuracy can be improved by determining the proportions of various molecular forms of PSA. The main biological function of PSA is liquefaction of the seminal gel formed after ejaculation, but PSA has also been suggested to regulate invasiveness and metastatic potential of prostatic tumors. Thus, agents binding to and affecting the function of PSA have the potential to be used for diagnosis and therapy of prostate cancer. We have developed peptides specific for PSA by using cyclic phage display peptide libraries. After deducing the amino acid sequence of the peptides by sequencing the relevant part of phage genome, the peptides were expressed as glutathione-S-transferase (GST) fusion proteins or produced by chemical synthesis. The peptides were shown to bind to PSA specifically as indicated by lack of binding to other related serine proteinases. The binding of the peptides with PSA was strongly inhibited by monoclonal antibodies specific for free PSA and they did not bind to PSA-inhibitor complexes indicating that they bind close to the active site of the enzyme. Most of the peptides enhanced the enzyme activity of PSA against a chromogenic substrate. The affinity of the peptides could be increased by including Zn2+ in the reaction mixture. These results show that peptides that bind to PSA and modulate its enzyme activity can be developed by phage display techniques. These peptides have the potential to be used for targeting of prostatic tumors and diagnostics of prostate cancer.

In immunopathological conditions, clinical diagnosis is commonly made on the basis of patient symptoms, measurement of blood leukocyte levels or proinflammatory biomarkers, non-specific radiological findings and, regarding infection, microbiological analysis. Nevertheless, frequently the exact spatial location of inflammation or even infection cannot be reliably identified, despite the use of up-to-date clinical, laboratory and imaging techniques. For this reason, new tools are warranted for use in advanced diagnosis and therapy targeting in patients. The peptide CPCFLLGCC (LLG), known to bind activated β2-integrins in vitro, was fused with green fluorescent protein (GFP) to test the ability of LLG fusions to target and bind activated leukocytes in vivo. A murine skin scratch inflammation model was chosen for the convenient non-surgical detection of GFP. The murine skin lesion inflammation model demonstrated in vivo targeting of LLG-GFP to sites of inflammation. Targeting by LLG-GFP fusion construct depends on the ability of the LLG-moiety to bind activated leukocytes. Control construct unable to bind β2-integrins appeared biologically inert. The data support the possibility of using this fluorescently labeled peptide as a tool for both the detection of and targeting to inflammatory sites characterized by robust leukocyte activation.

The concentrations of trypsinogen-1 and -2 in serum samples from patients who have undergone pancreatectomy were measured by highly sensitive and specific time-resolved immunofluorometric assays. The isoenzyme pattern was determined by ion-exchange chromatography and determination of immunoreactivity in the fractions. All samples contained trypsinogen-2, the mean level being one fifth of that in healthy controls. Trypsinogen-1 was detected in one of nine samples. In addition to the main trypsinogen isoenzymes, we observed in normal serum two trypsinogen isoenzymes previously found in mucinous ovarian cyst fluid. Our results suggest that trypsinogen is not exclusively expressed by the pancreas and certain tumors but that it also may be produced by normal extrapancreatic tissues. This should be considered when an assay of trypsinogen in serum is used for clinical purposes.

We have isolated selective ligands to the cell surface receptors of fibronectin (alpha 5 beta 1 integrin), vitronectin (alpha v beta 3 and alpha v beta 5 integrins) and fibrinogen (alpha IIb beta 3 integrin) from phage libraries expressing cyclic peptides. A mixture of libraries was used that express a series of peptides flanked by a cysteine residue on each side (CX5C, CX6C, CX7C) or only on one side (CX9) of the insert. A majority of the integrin-binding sequences derived from the CX9 library contained another cysteine, indicating preferential selection of conformationally constrained cyclic peptides. Each of the four integrins studied primarily selected RGD-containing phage sequences but favored different ring sizes and different flanking residues around the RGD motif. A cyclic peptide ACRGDGWCG was synthesized based on a phage sequence that bound particularly avidly to the alpha 5 beta 1 integrin. This peptide inhibited cell attachment to fibronectin at about 5-fold lower concentrations than the most potent cyclic peptides described earlier. The most interesting structure appeared to contain two disulphide bonds. One such peptide, ACDCRGDCFCG, was synthetized and shown to be at least 20-fold more potent inhibitor of alpha v beta 5- and alpha v beta 3-mediated cell attachment to vitronectin than similar peptides with a single disulphide bond and 200-fold more potent than commonly used linear RGD peptides. These results emphasize the importance of conformational restriction as a means of improving the potency of integrin-binding peptides and point to a new way of designing effective peptides by resticting the peptide conformation with more than one cyclizing bond.

Phage display screening allows the study of functional protein–protein interactions at the cell surface, but investigating intracellular organelles remains a challenge. Here we introduce internalizing-phage libraries to identify clones that enter mammalian cells through a receptor-independent mechanism and target-specific organelles as a tool to select ligand peptides and identify their intracellular receptors. We demonstrate that penetratin, an antennapedia-derived peptide, can be displayed on the phage envelope and mediate receptor-independent uptake of internalizing phage into cells. We also show that an internalizing-phage construct displaying an established mitochondria-specific localization signal targets mitochondria, and that an internalizing-phage random peptide library selects for peptide motifs that localize to different intracellular compartments. As a proof-of-concept, we demonstrate that one such peptide, if chemically fused to penetratin, is internalized receptor-independently, localizes to mitochondria, and promotes cell death. This combinatorial platform technology has potential applications in cell biology and drug development., Phage display screening can unravel protein–protein interactions, but its application has been mainly restricted to the cell surface. Here, a phage-based reagent is introduced that allows the targeting of combinatorial peptides to cell organelles, providing a tool for the discovery of intracellular ligand-receptors.

Our previous studies showed that the alpha 5 beta 1 integrin selects cysteine pair-containing RGD peptides from a phage display library based on a random hexapeptide. We have therefore searched for more selective peptides for this integrin using a larger phage display library, where heptapeptides are flanked by cysteine residues, thus making the inserts potentially cyclic. Most of the phage sequences that bound to alpha 5 beta 1 (69 of 125) contained the RGD motif. Some of the heptapeptides contained an NGR motif. As the NGR sequence occurs in the cell-binding region of the fibronectin molecule, this sequence could contribute to the specific recognition of fibronectin by alpha 5 beta 1. Selection for high affinity peptides for alpha 5 beta 1 surprisingly yielded a sequence RRETAWA that does not bear obvious resemblance to known integrin ligand sequences. The synthetic cyclic peptide GACRRETAWACGA (*CRRETAWAC*) was a potent inhibitor of alpha 5 beta 1-mediated cell attachment to fibronectin. This peptide is nearly specific for the alpha 5 beta 1 integrin, because much higher concentrations were needed to inhibit the alpha v beta 1 integrin, and there was no effect on alpha v beta 3- and alpha v beta 5-mediated cell attachment to vitronectin. The peptide also did not bind to the alpha IIb beta 3 integrin. *CRRETAWAC* appears to interact with the same or an overlapping binding site in alpha 5 beta 1 as RGD, because cell attachment to *CRRETAWAC* coated on plastic was divalent cation dependent and could be blocked by an RGD-containing peptide. These results reveal a novel binding specificity in the alpha 5 beta 1 integrin.

Molecules differentially expressed in blood vessels among organs or between damaged and normal tissues, are attractive therapy targets; however, their identification within the human vasculature is challenging. Here we screened a peptide library in cancer patients to uncover ligand-receptors common or specific to certain vascular beds. Surveying ∼2.35 × 10 6 motifs recovered from biopsies yielded a nonrandom distribution, indicating that systemic tissue targeting is feasible. High-throughput analysis by similarity search, protein arrays, and affinity chromatography revealed four native ligand-receptors, three of which were previously unrecognized. Two are shared among multiple tissues (integrin α4/annexin A4 and cathepsin B/apolipoprotein E3) and the other two have a restricted and specific distribution in normal tissue (prohibitin/annexin A2 in white adipose tissue) or cancer (RAGE/leukocyte proteinase-3 in bone metastases). These findings provide vascular molecular markers for biotechnology and medical applications.

Human trypsin isoenzymes share extensive sequence similarity, but certain differences in their activity and susceptibility to inhibitors have been observed. Using phage display technology, we identified seven different peptides that bind to and inhibit the activity of trypsin-3, a minor trypsin isoform expressed in pancreas and brain. All of the peptides contain at least two of the amino acids tryptophan, alanine and arginine, whereas proline was found closer to the N-terminus in all but one peptide. All peptides contain two or more cysteines, suggesting a cyclic structure. However, we were able to make synthetic linear variants of these peptides without losing bioactivity. Alanine replacement experiments for one of the peptides suggest that the IPXXWFR motif is important for activity. By molecular modeling the same amino acids were found to interact with trypsin-3. The peptides also inhibit trypsin-1, but only weakly, if at all, trypsin-2 and -C. As trypsin is a highly active enzyme which can activate protease-activated receptors and enzymes that participate in proteolytic cascades involved in tumor invasion and metastasis, these peptides might be useful lead molecules for the development of drugs for diseases associated with increased trypsin activity.

Previous studies have indicated that cyst fluid of ovarian tumors contains 2 trypsinogen isoenzymes, called tumor-associated trypsinogen-I (TAT-I) and trypsinogen-2 (TAT-2), the levels of which correlate with the degree of malignancy of the tumors. In addition, these cyst fluids contain large amounts of tumor-associated trypsin inhibitor (TATI), which is also expressed in many other human tumors. In the present study we examined the production of TAT-I, TAT-2 and TATI in 9 established tumor-cell lines. TAT-2 was produced by 5 cell lines. Its concentration in the conditioned medium of COLO 205 colon adenocarcinoma cells, K-562 erythroleukemia cells and fibrosarcoma cell lines HT 1080, 8387 and A 9733 was 460 micrograms/l, 9.8 micrograms/l, 21 micrograms/l, 8.8 micrograms/l and 0.24 micrograms/l, respectively. TAT-I was detectable in the conditioned medium of COLO 205 and HT 1080 cells at concentrations of 64 micrograms/l and 0.5 micrograms/l, respectively. TATI was detected only in the media of COLO 205 cells at a concentration of 23 micrograms/l. TAT-2 zymogen was purified from the conditioned medium of COLO 205 and HT 1080 cells by immunoaffinity chromatography. According to its aminoterminal amino acid sequence, a molecular mass of 28 kDa by SDS-PAGE, elution pattern in ion-exchange chromatography and ability to be activated by enteropeptidase, the zymogen is identical to that previously isolated from cyst fluid of ovarian tumors. In addition, we found that TAT-2 secretion could be down-regulated by dexamethasone in HT 1080 cells but not in COLO 205 cells. The abundant production of TAT-2 isoenzyme in different cancer cell lines suggests that it could contribute to the increased proteolytic activity of many human tumors.

Tumor-associated trypsin inhibitor (TATI) is a 6,000 Daltons peptide, which is synthesized by several tumors and cell lines. TATI is identical to pancreatic secretory trypsin inhibitor (PSTI). This peptide is also produced by the mucosa of the gastrointestinal tract, where it is thought to protect the mucosal cells from proteolytic breakdown. Elevated serum and urine levels of TATI occur in connection with many types of cancer, especially mucinous ovarian cancer. Elevated levels may also occur in nonmalignant diseases, e.g. in pancreatitis, severe infections and tissue destruction. Thus TATI may behave as an acute phase reactant. Tumors producing TATI often express tumor-associated trypsinogen. Elevation of TATI in cancer and pancreatic disease is therefore associated with expression of trypsin, but such a connection has not been demonstrated in inflammatory disease. TATI can inhibit trypsin-mediated degradation of extracellular matrix by tumor cells. Therefore its role may be to control the activation of tumor-associated trypsinogen. TATI has also been shown to possess growth factor activity in vitro, but it is not known whether this is a physiological function.

Leukocyte motility is known to be dependent on both β2-integrins and matrix metalloproteinases MMP-2/-9 or gelatinases, which mediate leukocyte adhesion and the proteolysis needed for invasion, respectively. Gelatinases not only play an important role in cell migration, tissue remodeling, and angiogenesis during development, but are also involved in the progression and invasiveness of many cancers, including leukemias. The concept that MMPs associate with integrins, as well as their importance in some physiologic and pathologic conditions, has been advanced previously but has not been examined on leukocytes. This review will examine mainly the function of the MMP-integrin complexes in normal leukocyte migration and the effect of integrin and broad-spectrum MMP inhibitors in tumor progression.

Human kallikrein 2 (hK2) is a serine protease produced by the secretory epithelial cells in the prostate. Because hK2 activates several factors participating in proteolytic cascades that may mediate metastasis of prostate cancer, modulation of the activity of hK2 is a potential way of preventing tumor growth and metastasis. Furthermore, specific ligands for hK2 are potentially useful for targeting and imaging of prostate cancer and for assay development. We have used enzymatically active recombinant hK2 captured by a monoclonal antibody exposing the active site of the enzyme to screen phage display peptide libraries. Using libraries expressing 10 or 11 amino acids long linear peptides, we identified six different peptides binding to hK2. Three of these were shown to be specific and efficient inhibitors of the enzymatic activity of hK2 toward a peptide substrate. Furthermore, the peptides inhibited the activation of the proform of prostate-specific antigen by hK2. Amino acid substitution analyses revealed that motifs of six amino acids were required for the inhibitory activity. These peptides are potentially useful for treatment and targeting of prostate cancer.

Tumors express MMP-2 and MMP-9 gelatinases, which are involved in the formation of tumor vasculature. This suggests that a tumor and its surrounding neovasculature can be visualized by a sensitive gelatinase recognition method. We have studied tumor radioimaging using a gelatinase inhibitory peptide CTTHWGFTLC (CTT), which in a mouse model targets the tumor site following an intravenous injection. We determined a solution NMR structure of CTT and its retro-inversion peptide, and prepared 125I and 99mTc-labelled CTT peptide derivatives. Radiolabelled CTT inhibited gelatinases in vitro, and homed to a tumor xenograft in mice. In normal mice, CTT was instead rapidly cleared from the circulation mainly through the kidney and, after 24 h, no significant radioactivity was accumulated in healthy tissues. Gamma camera imaging of a primary tumor in live mice was obtained with double-labelled liposomes, which were coated with 99mTc-CTT and encapsulated with 125I albumin. CTT also targeted liposomes to the lungs of tumor-bearing mice, which may indicate the existence of non-visible lung micrometastases. Our studies suggest that selective gelatinase-targeting compounds could be useful in the early detection and imaging of primary tumors and metastases.

Modern molecular targeting provides new opportunities for imaging, diagnosis and treatment of diseases. Small molecular weight peptides have the potential for enhancing targeting of compounds, and they may also have therapeutic effects by themselves. The limiting step for successful molecular targeting is the development of efficient peptide delivery systems. This review will focus on peptides developed by phage display and combinatorial chemistry for the delivery of pharmaceuticals, radioactive compounds and gene expression vectors. Target cell-specific delivery can be improved by peptides that penetrate the cell membrane or alternatively induce receptor-mediated endocytosis. In addition, peptides that contain endosomal escape signals or nuclear localization motifs may help trafficking of therapeutics to appropriate locations inside the cell. Small molecule radiolabelled peptides are the preferred agents for targeting and for diagnostic imaging of various organs as they are easily synthesized, effectively penetrate tissues, and are rapidly cleared from the circulation. Such peptides have been tested in animals and humans in the fields of cancer, cardiology, neurology, inflammation/infection, atherosclerosis and thrombosis.

The alpha M beta 2 integrin of leukocytes can bind a variety of ligands. We screened phage display libraries to isolate peptides that bind to the alpha M I domain, the principal ligand binding site of the integrin. Only one peptide motif, (D/E)(D/E)(G/L)W, was obtained with this approach despite the known ligand binding promiscuity of the I domain. Interestingly, such negatively charged sequences are present in many known beta 2 integrin ligands and also in the catalytic domain of matrix metalloproteinases (MMPs). We show that purified beta 2 integrins bind to pro-MMP-2 and pro-MMP-9 gelatinases and that that the negatively charged sequence of the MMP catalytic domain is an active beta 2 integrin-binding site. Furthermore, a synthetic DDGW-containing phage display peptide inhibited the ability of beta 2 integrin to bind progelatinases but did not inhibit the binding of cell adhesion-mediating substrates such as intercellular adhesion molecule-1, fibrinogen, or an LLG-containing peptide. Immunoprecipitation and cell surface labeling demonstrated complexes of pro-MMP-9 with both the alpha M beta 2 and alpha L beta 2 integrins in leukocytes, and pro-MMP-9 colocalized with alpha M beta 2 in cell surface protrusions. The DDGW peptide and the gelatinase-specific inhibitor peptide CTTHWGFTLC blocked beta 2 integrin-dependent leukocyte migration in a transwell assay. These results suggest that leukocytes may move in a progelatinase-beta 2 integrin complex-dependent manner.

Screening of phage display libraries allows rapid identification of peptides binding to a target. However, functional analysis of the phage sequences and their reproduction as soluble and stable peptides are often the most time-consuming part in the screening. We have used here intein-based peptide biosynthesis to produce a phage-display derived gelatinase inhibitory peptide CTTHWGFTLC and to identify the critical residues for gelatinase inhibitory activity by performing alanine-scanning mutagenesis. By biosynthetic incorporation of 5-fluorotryptophan, we obtained an inhibitor of MMP-2 and MMP-9 gelatinases that showed a 6-fold enhancement in serum stability in comparison to the wild-type peptide. The new peptide also had an improved ability to inhibit tumor cell migration. These studies indicate the utility of intein methodology for synthesis and design of peptides obtained by phage display.

The molecular diversity of receptors in human blood vessels remains largely unexplored. We developed a selection method in which peptides that home to specific vascular beds are identified after administration of a peptide library. Here we report the first in vivo screening of a peptide library in a patient. We surveyed 47,160 motifs that localized to different organs. This large-scale screening indicates that the tissue distribution of circulating peptides is nonrandom. High-throughput analysis of the motifs revealed similarities to ligands for differentially expressed cell-surface proteins, and a candidate ligand-receptor pair was validated. These data represent a step toward the construction of a molecular map of human vasculature and may have broad implications for the development of targeted therapies.

Several lines of evidence suggest that tumor growth, angiogenesis, and metastasis are dependent on matrix metalloproteinase (MMP) activity. However, the lack of inhibitors specific for the type IV collagenase/gelatinase family of MMPs has thus far prevented the selective targeting of MMP-2 (gelatinase A) and MMP-9 (gelatinase B) for therapeutic intervention in cancer. Here, we describe the isolation of specific gelatinase inhibitors from phage display peptide libraries. We show that cyclic peptides containing the sequence HWGF are potent and selective inhibitors of MMP-2 and MMP-9 but not of several other MMP family members. Our prototype synthetic peptide, CTTHWGFTLC, inhibits the migration of human endothelial cells and tumor cells. Moreover, it prevents tumor growth and invasion in animal models and improves survival of mice bearing human tumors. Finally, we show that CTTHWGFTLC-displaying phage specifically target angiogenic blood vessels in vivo. Selective gelatinase inhibitors may prove useful in tumor targeting and anticancer therapies.

Vascular beds are known to differ in structure and metabolic function, but less is known about their molecular diversity. We have studied organ-specific molecular differences of the endothelium in various tissues by using in vivo screening of peptide libraries expressed on the surface of a bacteriophage. We report here that targeting of a large number of tissues with this method yielded, in each case, phage that homed selectively to the targeted organ. Different peptide motifs were recovered from each of these tissues. The enrichment in homing to the target organs relative to an unselected phage was 3-35-fold. Peptide sequences that conferred selective phage homing to the vasculature of lung, skin, and pancreas were characterized in detail. Immunohistochemistry showed that the phage localized in the blood vessels of their target organ. When tested, the phage homing was blocked in the presence of the cognate peptide. By targeting several tissues and by showing that specific homing could be achieved in each case, we provide evidence that organ- and tissue-specific molecular heterogeneity of the vasculature is a general, perhaps even universal, phenomenon. Our results also show that these molecular differences can serve as molecular addresses.

Echovirus 22 (EV22) is a picornavirus forming a distinct molecular cluster together with echovirus 23. EV22 has an Arg-Gly-Asp (RGD) peptide motif in its capsid protein VP1; similar motifs are known to mediate many cell-cell and microbe-host interactions. To identify peptide sequences that specifically bind to EV22 and potentially play a role in receptor recognition, we have used here peptide libraries displayed in filamentous phage. We isolated an EV22-binding motif CLRSG(R/F)GC. The synthetic CLRSGRGC peptide was able to inhibit EV22 infection. The infection was also inhibited by an RGD-containing peptide representing the C terminus of the EV22 capsid protein VP1 and CWDDGWLC (an RGD-binding peptide; Pasqualini, R., Koivunen, E., and Ruoslahti, E. (1995) J. Cell Biol. 130, 1189-1196). As the EV22-recognizing sequence LRSG is found in the integrin beta1 chain and the entire LRSGRG hexapeptide occurs in the matrix metalloproteinase 9 (MMP-9), we carried out blocking experiments with anti-integrin and anti-MMP-9 antibodies. EV22 infection could be blocked in cell cultures with anti-alphav, -beta1, and, to a lesser extent, with anti-MMP-9 antibodies. These results imply that EV22 recognizes preferentially alphavbeta1-integrin as a cellular receptor and MMP-9 may also play a role in the cell-surface interactions of the virus.

Phage displaying an Arg-Gly-Asp (RGD)-containing peptide with a high affinity for alpha v integrins homed to tumors when injected intravenously into tumor-bearing mice. A substantially higher amount of alpha v-directed RGD phage than control phage was recovered from malignant melanomas and breast carcinoma. Antibodies detected the alpha v-directed RGD phage in tumor blood vessels, but not in several normal tissues. These results show that the alpha v integrins present in tumor blood vessels can bind circulating ligands and that RGD peptides selective for these integrins may be suitable tools in tumor targeting for diagnostic and therapeutic purposes.