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PDF - 53KB, Demonstration of benign immunogenicity profile of PRS-110 in ex vivo PBMC model

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Activation of the MET oncogenic pathway has been implicated in the development of aggressive cancers that are difficult to treat with current chemotherapies. This has led to an increased interest in developing novel therapies that target the MET pathway. However, most existing drug modalities are confounded by their inability to specifically target and/or antagonize this pathway. Anticalins, a novel class of monovalent small biologics, are hypothesized to be “fit for purpose” for developing highly specific and potent antagonists of cancer pathways. Here, we describe a monovalent full MET antagonist, PRS-110, displaying efficacy in both ligand-dependent and ligand-independent cancer models. PRS-110 specifically binds to MET with high affinity and blocks hepatocyte growth factor (HGF) interaction. Phosphorylation assays show that PRS-110 efficiently inhibits HGF-mediated signaling of MET receptor and has no agonistic activity. Confocal microscopy shows that PRS-110 results in the trafficking of MET to late endosomal/lysosomal compartments in the absence of HGF. In vivo administration of PRS-110 resulted in significant, dose-dependent tumor growth inhibition in ligand-dependent (U87-MG) and ligand-independent (Caki-1) xenograft models. Analysis of MET protein levels on xenograft biopsy samples show a significant reduction in total MET following therapy with PRS-110 supporting its ligand-independent mechanism of action. Taken together, these data indicate that the MET inhibitor PRS-110 has potentially broad anticancer activity that warrants evaluation in patients. Mol Cancer Ther; 12(11); 2459–71. ©2013 AACR.

PDF - 31KB, Characterisation of cell line panel for MET and HGF expression

PDF - 136KB, Demonstration of PRS-110 dependent MET trafficking in HT29 cells

Figure S1: PRS-343 specificity for 4-1BB within TNF receptor superfamily. Seven recombinant human TNF receptor superfamily proteins were purchased from Sino Biological (4-1BB: 10041-H08H, RANK: 16078-H08H, GITR: 13643-H08H, Ox40: 10481-H08H) or R&D Systems (CD30: 6126-CD, TNF-RII: 1089-R2, TNF-RI: 636-R1) and used for determination of PRS-343 selectivity for 4-1BB. Proteins were coated to an ELISA plate, PRS-343 was added in a dilution series and detected via HRP-labeled anti-human IgG Fc antibody. Within the set of tested TNF receptor family proteins, PRS-343 binds exclusively to 4-1BB. Figure S2: Characterization of multiple bispecific formats of a 4-1BB targeting Anticalin protein recombinantly fused to an anti-HER2 antibody (A). ELISA based binding properties of all formats were compared to parental building blocks (C) while the ability to activate T-cells (IL2 induction) was assessed in a co-culture assay. Figure S3: Cytokine release assay with PRS-343. PBMC were isolated from the blood of twelve healthy donors and incubated for 72 hours with PRS-343 either air dried, in soluble form, or wet coated. Four concentrations of PRS-343 in a volume of 50 µl were tested in each setting as indicated in the figure. The anti-CD3 monoclonal antibody OKT3 at three different concentrations served as the positive control, and an IgG4 isotype antibody was the negative control. Supernatant levels of ten cytokines (IL-1β, IL-2, IL-4, IL-6, IL-8, IL-10, IL-12p70, GM-CSF, IFN-γ and TNF-α) were analyzed. The figure shows the average response for the ten donors that displayed a significant response to OKT3, and for a selection of the most relevant cytokines. Figure S4: Dose-dependent 4-1BB activation of a 4-1BB over-expressing Jurkat Nf-kB reporter cell line induced by PRS-343 with ON preincubation of the drug in the presence of NCI-N87 (HER2 high), MKN45 (HER2 low) and HepG2 (HER2 null) cell lines, or without tumor cells. Briefly, cancer cells were seeded onto tissue culture plates with PRS-343 (at 10, 1, 0.1 and 0,01 nM) and incubated ON. All plates were then washed twice with PBS. 4-1BB over-expressing Jurkat Nf-kB reporter (at 3:1 ratio) were added to each well. Following a 6 hours incubation, Bio-Glow luciferase reagent was added to each well and luminescence was measured. Figure S5: Fold increase changes of a panel of cytokines induced by human T-cells co-stimulated by PRS-343 in the presence of SKBR-3 (HER2 high) or MCF-7 (HER2 low). Figure S6: h-4-1BB expression in T-cells during co-culture assay. Using a similar set up as described in M&M, purified Pan T-cells (from healthy donors) and SK-BR3 high Her2 expressing cells were co-incubated in the presence of coated anti-CD3 antibody. After 24, 48 and 72 hours of co-incubation, Pan T-cells were collected and 4-1BB expression on CD3 positive cells was assessed by flow cytometry. (A) shows the % of 4-1BB positive T-cells for two donors and (B) shows histogram of h-4-1BB expression on CD3 positive T-cells from two donors (red 24 hours; blue 48 hours; brown 72 hours). Table S1: Relative HER2 cell surface expression on a panel of cell lines. Expression was experimentally determined using a specific anti-HER2-antibody binding capacity (sABC [HER2]) and quantitative indirect immunofluorescence in flow cytometry (QIFIKIT). HER2 surface levels are also provided relative to the level on SKBR3 cells which were chosen as a reference cell line.

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Purpose:4-1BB (CD137) is a key costimulatory immunoreceptor and promising therapeutic target in cancer. To overcome limitations of current 4-1BB–targeting antibodies, we have developed PRS-343, a 4-1BB/HER2 bispecific molecule. PRS-343 is designed to facilitate T-cell costimulation by tumor-localized, HER2-dependent 4-1BB clustering and activation.Experimental Design:PRS-343 was generated by the genetic fusion of 4-1BB–specific Anticalin proteins to a variant of trastuzumab with an engineered IgG4 isotype. Its activity was characterized using a panel of in vitro assays and humanized mouse models. The safety was assessed using ex vivo human cell assays and a toxicity study in cynomolgus monkeys.Results:PRS-343 targets 4-1BB and HER2 with high affinity and binds both targets simultaneously. 4-1BB–expressing T cells are efficiently costimulated when incubated with PRS-343 in the presence of cancer cells expressing HER2, as evidenced by increased production of proinflammatory cytokines (IL2, GM-CSF, TNFα, and IFNγ). In a humanized mouse model engrafted with HER2-positive SK-OV-3 tumor cells and human peripheral blood mononuclear cells, PRS-343 leads to tumor growth inhibition and a dose-dependent increase of tumor-infiltrating lymphocytes. In IND-enabling studies, PRS-343 was found to be well tolerated, with no overt toxicity and no relevant drug-related toxicologic findings.Conclusions:PRS-343 facilitates tumor-localized targeting of T cells by bispecific engagement of HER2 and 4-1BB. This approach has the potential to provide a more localized activation of the immune system with higher efficacy and reduced peripheral toxicity compared with current monospecific approaches. The reported data led to initiation of a phase I clinical trial with this first-in-class molecule.See related commentary by Su et al., p. 5732

T2 endotype asthma is driven by IL-4 and IL-13 signaling via IL-4Ra, which is highly expressed on airway epithelium, airway smooth muscle and immunocytes in the respiratory mucosa, suggesting potential advantages of an inhalable antagonist. Lipocalin 1 (Lcn1), a 16kD protein abundant in human periciliary fluid, has a robust drug-like structure well-suited to protein engineering, but has never been used to make an inhaled "Anticalin" protein therapeutic.To re-engineer Lcn1 into an inhalable IL-4Ra antagonist and assess its pharmacodynamic/kinetic profile.Lcn1 was systematically modified by directed protein mutagenesis yielding a high affinity, slowly dissociating, long-acting full antagonist of IL-4Ra designated 'PRS-060' with properties analogous to dupilumab, competitively antagonizing IL-4Ra dependent cell proliferation, mucus induction and eotaxin expression in vitro. As PRS-060 displayed exquisite specificity for human IL-4Ra, with no cross-reactivity to rodents or higher primates, we created a new triple-humanized mouse model substituting hIL-4Ra, hIL-4, and hIL-13 at their correct syntenic murine loci to model clinical dosing.Inhaled PRS-060 strongly suppressed acute allergic inflammation indices in triple humanized mice with a duration of action longer than its bulk clearance suggesting it may act locally in the lung.Lcn1 can be re-engineered into the Anticalin antagonist PRS-060, exemplifying a new class of inhaled topical, long-acting therapeutic with potential to treat T2 endotype asthma.

Purpose: 4-1BB (CD137) is a key costimulatory immunoreceptor and promising therapeutic target in cancer. To overcome limitations of current 4-1BB–targeting antibodies, we have developed PRS-343, a 4-1BB/HER2 bispecific molecule. PRS-343 is designed to facilitate T-cell costimulation by tumor-localized, HER2-dependent 4-1BB clustering and activation. Experimental Design: PRS-343 was generated by the genetic fusion of 4-1BB–specific Anticalin proteins to a variant of trastuzumab with an engineered IgG4 isotype. Its activity was characterized using a panel of in vitro assays and humanized mouse models. The safety was assessed using ex vivo human cell assays and a toxicity study in cynomolgus monkeys. Results: PRS-343 targets 4-1BB and HER2 with high affinity and binds both targets simultaneously. 4-1BB–expressing T cells are efficiently costimulated when incubated with PRS-343 in the presence of cancer cells expressing HER2, as evidenced by increased production of proinflammatory cytokines (IL2, GM-CSF, TNFα, and IFNγ). In a humanized mouse model engrafted with HER2-positive SK-OV-3 tumor cells and human peripheral blood mononuclear cells, PRS-343 leads to tumor growth inhibition and a dose-dependent increase of tumor-infiltrating lymphocytes. In IND-enabling studies, PRS-343 was found to be well tolerated, with no overt toxicity and no relevant drug-related toxicologic findings. Conclusions: PRS-343 facilitates tumor-localized targeting of T cells by bispecific engagement of HER2 and 4-1BB. This approach has the potential to provide a more localized activation of the immune system with higher efficacy and reduced peripheral toxicity compared with current monospecific approaches. The reported data led to initiation of a phase I clinical trial with this first-in-class molecule. See related commentary by Su et al., p. 5732

Introduction: AZD1402 is an Anticalin protein in clinical development that has the potential to offer an inhaled treatment for asthma patients suffering from T2-driven disease through selective blockade of IL-4Rα. Aims and objective: To characterise the effect of AZD1402 on IL-4Rα signalling in human whole blood (WB) and establish a method to evaluate the functional impact of systemic exposure to AZD1402 following inhaled dosing. Methods: WB from healthy subjects was stimulated with IL-4 in the presence or absence of AZD1402. Phosphorylation of signalling components and released soluble biomarkers were quantified using FACS and multiplex ELISA, respectively. Results: Stimulation of human WB with IL-4 resulted in increased levels of phosphorylated STAT6 (pSTAT6) and in the release of eotaxin-3, TARC, and MDC. AZD1402, when added to WB samples (n=12), inhibited pSTAT6 in a concentration-dependent manner and with similar potency to the anti-IL-4Rα monoclonal antibody dupilumab (IC50 values 1.3 and 0.6 nM, respectively). Inhibition of the release of the soluble cytokines eotaxin-3, TARC, and MDC by AZD1402, at equivalent potencies to dupilumab, was observed (IC50 values of 1.9 nM, 1.2 nM, and 2.6 nM, respectively). The low level of variation observed render this method suitable to detect the presence of systemic (pharmacologically active) levels of AZD1402 following inhaled dosing. Conclusions: AZD1402, potently inhibits IL-4Rα signalling in human WB with IC50 values comparable to those of dupilumab. pSTAT6 responses in WB are used in the NCT03384290 Phase I trial to assess systemic exposure.

Antagonising the IL-4 receptor α (IL-4Rα) interferes with downstream IL-4/IL-13 signalling and clinically has beneficial effects in moderate to severe asthma. Anticalin® proteins are based on human lipocalins and can be engineered to bind specific ligands with high potency and selectivity. AZD1402/PRS-060, is an inhaled Anticalin protein targeting the IL-4Rα, being developed as a treatment for asthma. Potency was established using cell based assays (TF1 cell pSTAT6 activation and goblet cell differentiation). Pharmacodynamic and asthma models were developed in mice expressing human IL-4Rα, IL-4 and IL-13. AZD1402/PRS-060 was identified as a potent (KD 23 pM) and selective antagonist of IL-4Rα. AZD1402/PRS-060 and pitrakinra (hIL-4 mutein) inhibited IL-4 and IL-13 induced pSTAT6 stimulation of TF1 cells (IC50 0.1 and 8.6 nM, respectively). AZD1402/PRS-060 and dupilumab (IL-4Rα mAb) inhibited IL-4 and IL-13 induced proliferation of TF1 cells with similar potency (IC50 0.9 and 0.3 nM). In an Air Liquid Interface goblet cell differentiation assay induced by IL-13 stimulation, AZD1402/PRS-060 inhibited goblet cell metaplasia to a similar extent as AMG317 (IL-4Rα mAb) and pitrakinra. In vivo, 2 µg of AZD1402/PRS-060 (IT) inhibited IL-13 induced eotaxin expression over 24-hours. In the OVA model, inflammatory cell infiltration was reduced by 78% and TARC (CCL17) was reduced by 98% 48 h post challenge. AZD1402/PRS-060, potently inhibits IL-4 and IL-13 signalling in vitro and in vivo and based on these data and the proven benefit of targeting this receptor, AZD1402/PRS-060 has progressed into human clinical trials.

Since it was recently reported that an antibody for proprotein convertase subtilisin/kexin type 9 (PCSK9) reduces the risk of cardiovascular events in a clinical context, PCSK9 inhibition is thought to be an attractive therapy for dyslipidemia. In the present study, we created a novel small biologic alternative to PCSK9 antibodies called DS-9001a, comprising an albumin binding domain fused to an artificial lipocalin mutein (ABD-fused Anticalin protein), which can be produced by a microbial production system. DS-9001a strongly interfered with PCSK9 binding to low-density-lipoprotein receptor (LDL-R) and PCSK9-mediated degradation of LDL-R. In cynomolgus monkeys, single DS-9001a administration significantly reduced the serum LDL-C level up to 21 days (62.4% reduction at the maximum). Moreover, DS-9001a reduced plasma non-high-density-lipoprotein cholesterol and oxidized LDL levels, and their further reductions were observed when atorvastatin and DS-9001a were administered in combination in human cholesteryl ester transfer protein/ApoB double transgenic mice. Additionally, their reductions on the combination of atorvastatin and DS-9001a were more pronounced than those on the combination of atorvastatin and anacetrapib. Besides its favorable pharmacologic profile, DS-9001a has a lower molecular weight (about 22 kDa), yielding a high stoichiometric drug concentration that might result in a smaller administration volume than that in existing antibody therapy. Since bacterial production systems are viewed as more suited to mass production at low cost, DS-9001a may provide a new therapeutic option to treat patients with dyslipidemia. In addition, considering the growing demand for antibody-like drugs, ABD-fused Anticalin proteins could represent a promising new class of small biologic molecules.

The oncofetal isoform of the extracellular matrix protein fibronectin (Fn), which carries the extra-domain B (ED-B) and is exclusively expressed in neovasculature, has gained interest for tumor diagnosis and therapy using engineered antibody fragments. We have employed the human lipocalin 2 (Lcn2) as a small and robust non-immunoglobulin scaffold to select ED-B-specific Anticalins from a new advanced random library using bacterial phage display and ELISA screening against appropriately engineered Fn fragments. As a result, we have isolated and biochemically characterized four different Anticalins that all show low nanomolar affinities for ED-B, right in the range between the monomeric and dimeric forms of the single-chain variable antibody fragment L19 that has been widely applied in this area before. All Anticalins can be readily expressed in Escherichia coli as soluble and strictly monomeric proteins, and they show specific staining of ED-B-positive tumor cells in immunofluorescence microscopy while BIAcore affinity analyses indicate recognition of distinct ED-B epitopes. The crystal structure for one Anticalin, N7A, in complex with the Fn7B8 fragment, was solved at 2.6Å resolution and reveals binding to the gfcc' sheet and cc' loop on ED-B. This is the second example of a protein-specific Lcn2-based Anticalin, which illustrates the remarkable plasticity of the calyx-like ligand pocket of lipocalins with their four structurally hypervariable loops supported by a highly conserved β-barrel. The ED-B-specific Anticalins resulting from this study should provide useful reagents in research and biomedical drug development, both for in vivo imaging and for directed cancer therapy.

We demonstrate that small engineered single-chain binding proteins based on the lipocalin scaffold, so-called Anticalins, can be functionally displayed on the Gram-negative bacterial cell envelope. To this end, the beta-domains of five different bacterial autotransporters (the IgA protease from Neisseria gonorrhoeae, the esterase EstA from Pseudomonas aeruginosa, the YpjA autotransporter from E. coli K12, the AIDA-I adhesin from enteropathogenic E. coli O127:H27 strain 2787 and the protease EspP from enterohemorrhagic E. coli O157:H7 strain EDL933) were compared with respect to display level, functional variance, and bacterial cell viability. Use of the EspP autotransporter led to a system with high genetic stability for the display of fully functional Anticalins in high density on the cell surface of E. coli as shown by quantitative flow cytofluorimetry. This system was applied to engineer an immunostimulatory Anticalin that binds and blocks the extracellular region of human CTLA-4 to achieve a slower dissociation rate. A combinatorial library of the original Anticalin was generated by error-prone PCR, subjected to E. coli cell surface display, and applied to repeated cycles of cell sorting after incubation with the fluorescently labelled target protein under competition with the unlabelled extracellular domain of CTLA-4. The resulting Anticalin variants, which were expressed and purified as soluble proteins, showed more than eightfold decelerated target dissociation, as revealed by real time surface plasmon resonance analysis. Hence, the EspP autotransporter-mediated E. coli surface display in combination with high-throughput fluorescence-activated cell sorting (FACS) provides an efficient strategy to select for Anticalins, and possibly other small protein scaffolds, with improved binding properties, which is particularly useful for in vitro affinity maturation but may also serve for the selection of novel target specificity from naive libraries.

Based on bifunctional diketopiperazines as templates and m-aminomethyl-phenylalanine as arginine mimetic, we have synthesized a new class of structurally related dibasic tryptase inhibitors with systematically increasing spacer length. These compounds were used to scan the distance between the active sites of two neighboring subunits of the beta-tryptase tetramer. The K(i)-values obtained are a function of the distance between the terminal amino groups and indicate optimal binding of inhibitors with 29-31 bonds between the amino groups. These experimental data are in full agreement with predictions derived from a novel modeling program that allows the docking of bivalent ligands.

Background: Human β-tryptase is a mast cell specific trypsin-like serine protease that is thought to play a key role in the pathogenesis of diverse allergic and inflammatory disorders like asthma and psoriasis. The recently resolved crystal structure revealed that the enzymatically active tetramer consists of four quasi-identical monomers. The spatial display of the four identical active sites represents an ideal basis for the rational design of bivalent inhibitors. Results: Based on modeling experiments homobivalent inhibitors were constructed using (i) 6 A ,6 D -dideoxy-6 A ,6 D -diamino-β-cyclodextrin as a rigid template to bridge the space between the two pairs of identical active sites and (ii) 3-(aminomethyl)benzene as a headgroup to occupy the arginine/lysine specific S1 subsites. A comparative analysis of the inhibitory potencies of synthetic constructs that differ in size and type of the spacer between headgroup and template revealed that the construct contained two 3-(aminomethyl)benzenesulfonyl-glycine groups linked to the 6 A ,6 D -diamino groups of β-cyclodextrin as an almost ideal bivalent inhibitor with a cooperativity factor of 1.9 vs. the ideal value of 2. The bivalent binding mode is supported by the inhibitor/tetramer ratio of 2:1 required for inactivation of tryptase and by X-ray analysis of the inhibitor/tryptase complex. Conclusion : The results obtained with the rigid cyclodextrin template underlined the importance of a minimal loss of conformational entropy in bivalent binding, but also showed the limitations imposed by such rigid core molecules in terms of optimal occupancy of binding sites and thus of enthalpic strains in bidentate binding modes. The main advantage of bivalent inhibitors is their high selectivity for the target enzyme that can be achieved utilizing the principle of multivalency.

Tryptases, the predominant proteins of human mast cells, have been implicated as pathogenetic mediators of allergic and inflammatory conditions, most notably asthma. Until recently, the fascinating properties that distinguish tryptases among the serine proteinases, particularly their activity as a heparin-stabilized tetramer, resistance to most proteinaceous inhibitors, and preference for peptidergic over macromolecular substrates presented a riddle. This review solves this riddle with the help of the crystal structure of the human beta(2)-tryptase tetramer, but also indicates controversies between the unique quaternary architecture and some experimental data.

Granzymes are granule-stored lymphocyte serine proteases that are implicated in T- and natural killer cell-mediated cytotoxic defense reactions after target cell recognition. A fifth human granzyme (granzyme 3, lymphocyte tryptase-2), renamed as granzyme K (gene name GZMK), has recently been cloned from lymphocyte tissue. For its further characterization we successfully generated catalytically active enzyme in milligram quantities per liter of Escherichia coli culture. The natural proform of granzyme K with the amino-terminal propeptide Met-Glu was expressed as inclusion bodies and converted to its active enzyme by cathepsin C after refolding of precursor molecules. Recombinant granzyme K cleaves synthetic thiobenzyl ester substrates after Lys and Arg with k(cat)/K(m) values of 3.7 x 10(4) and 4.4 x 10(4) M(-1) s(-1), respectively. Granzyme K activity was shown to be inhibited by the synthetic compounds Phe-Pro-Arg-chloromethyl ketone, phenylmethylsulfonyl fluoride, PefablocSC, and benzamidine, by the Kunitz-type inhibitor aprotinin and by human blood plasma. The plasma-derived inter-alpha-trypsin inhibitor complex, its bikunin subunit, and the second carboxyl-terminal Kunitz-type domain of bikunin were identified as genuine physiologic inhibitors with K(i) values of 64, 50, and 22 nM, respectively. Inter-alpha-trypsin inhibitor and free bikunin have the potential to neutralize extracellular granzyme K activity after T cell degranulation and may thus control unspecific damage of bystander cells at sites of inflammatory reactions.

The x-ray crystal structure of recombinant leech-derived tryptase inhibitor (rLDTI) has been solved to a resolution of 1.9 A in complex with porcine trypsin. The nonclassical Kazal-type inhibitor exhibits the same overall architecture as that observed in solution and in rhodniin. The complex reveals structural aspects of the mast cell proteinase tryptase. The conformation of the binding region of rLDTI suggests that tryptase has a restricted active site cleft. The basic amino terminus of rLDTI, apparently flexible from previous NMR measurements, approaches the 148-loop of trypsin. This loop has an acidic equivalent in tryptase, suggesting that the basic amino terminus could make favorable electrostatic interactions with the tryptase molecule. A series of rLDTI variants constructed to probe this hypothesis confirmed that the amino-terminal Lys-Lys sequence plays a role in inhibition of human lung tryptase but not of trypsin or chymotrypsin. The location of such an acidic surface patch is in accordance with the known low molecular weight inhibitors of tryptase.

Activation of the MET oncogenic pathway has been implicated in the development of aggressive cancers that are difficult to treat with current chemotherapies. This has led to an increased interest in developing novel therapies that target the MET pathway. However, most existing drug modalities are confounded by their inability to specifically target and/or antagonize this pathway. Anticalins, a novel class of monovalent small biologics, are hypothesized to be “fit for purpose” for developing highly specific and potent antagonists of cancer pathways. Here, we describe a monovalent full MET antagonist, PRS-110, displaying efficacy in both ligand-dependent and ligand-independent cancer models. PRS-110 specifically binds to MET with high affinity and blocks hepatocyte growth factor (HGF) interaction. Phosphorylation assays show that PRS-110 efficiently inhibits HGF-mediated signaling of MET receptor and has no agonistic activity. Confocal microscopy shows that PRS-110 results in the trafficking of MET to late endosomal/lysosomal compartments in the absence of HGF. In vivo administration of PRS-110 resulted in significant, dose-dependent tumor growth inhibition in ligand-dependent (U87-MG) and ligand-independent (Caki-1) xenograft models. Analysis of MET protein levels on xenograft biopsy samples show a significant reduction in total MET following therapy with PRS-110 supporting its ligand-independent mechanism of action. Taken together, these data indicate that the MET inhibitor PRS-110 has potentially broad anticancer activity that warrants evaluation in patients. Mol Cancer Ther; 12(11); 2459–71. ©2013 AACR . This article is featured in Highlights of This Issue, [p. 2283][1] [1]: /lookup/volpage/12/2283?iss=11

Background: CD137 (4-1BB) is a key costimulatory immunoreceptor and a member of the TNF-receptor (TNFR) superfamily. While multiple lines of evidence show that CD137 is a highly promising therapeutic target in cancer, current mAb-based approaches are not designed to achieve a tumor-target driven activation and may display toxicity and a limited therapeutic window due to peripheral T cell and NK cell activation. To overcome this limitation, we generated PRS-343, a CD137/HER2 bispecific that is designed to promote CD137 clustering by bridging CD137-positive T cells with HER2-positive tumor cells, thereby providing a potent costimulatory signal to tumor antigen-specific T cells. Methods: Anticalin® proteins are 18 kD protein therapeutics derived from human lipocalins. We utilized phage display to generate an Anticalin protein binding to CD137 with high affinity and specificity. PRS-343 was obtained by genetic fusion of the CD137-specific Anticalin protein to a variant of the HER2-targeting monoclonal antibody trastuzumab with an engineered IgG4 backbone. We have shown previously that the bispecific fusion PRS-343 targets CD137 and HER2 in a bispecific manner and efficiently activates T cells ex vivo in the presence of HER2-positive cells. Here, in vivo proof of concept data is presented utilizing a humanized mouse model in immunocompromised mice and the SK-OV-3 cell line as a HER2-positive xenograft. When tumors had reached a predefined size, mice received human PBMC via an intravenous route and weekly intraperitoneal injections of PRS-343 for three weeks. An IgG4 isotype antibody served as the negative control, while a CD137-targeting benchmark antibody and trastuzumab with an engineered IgG4 backbone (“tras-IgG4”) served as controls for monospecific targeting of CD137 and HER2, respectively. Results: PRS-343 activity was investigated at four different weekly doses of PRS-343 (4μg, 20μg, 100μg and 200μg). We found that PRS-343 dose-dependently led to strong tumor growth inhibition compared to treatment with the isotype control, and that the tumor response was accompanied by a significantly higher tumor infiltration with human lymphocytes (hCD45+). Interestingly, the anti-CD137 benchmark neither displayed tumor growth inhibition nor enhanced lymphocyte infiltration into tumors compared to isotype. The tras-IgG4 control was also devoid of lymphocyte infiltration into the tumor, but displayed a tumor growth inhibition comparable to PRS-343. Taken together, these data show that PRS-343 provided dual activity by both increasing the frequency of tumor-infiltrating lymphocytes by bispecific targeting of CD137 and HER2 as well as mediating direct tumor growth inhibition by the direct, monospecific targeting of HER2. Notably, the tumor growth inhibition provided by targeting HER2 did not require any antibody directed cellular cytotoxicity (ADCC) as both PRS-343 and the tras-IgG4 control lack the ability to interact with Fc-gamma receptors on NK cells that ADCC would require. The animal model also allowed investigating the potential safety of PRS-343: While the anti-CD137 benchmark accelerated the onset of graft-versus-host-disease and led to stronger expansion of CD8+ T cells in the peripheral blood compared to the isotype control group, both of these effects were absent for PRS-343. The data therefore support the envisaged mode of action of selective, tumor-localized costimulatory T cell activation, as well as the concept that such an approach may lead to higher efficacy and reduced systemic toxicity compared to conventional anti-CD137 mAbs. Conclusion: We report potent costimulatory T-cell engagement of the immunoreceptor CD137 in a HER2-dependent manner, utilizing the CD137/HER2 bispecific PRS-343. In a humanized mouse model, PRS-343 displays dual activity based on monospecific HER2-targeting and bispecific, tumor-localized costimulation of CD137. Compared to known CD137-targeting antibodies in clinical development, this approach has the potential to provide a more localized activation of the immune system with higher efficacy and reduced peripheral toxicity. The direct, monospecific HER2-targeting activity may provide an additional therapeutic benefit and work in synergy with local CD137 costimulation. The positive functional ex vivo and in vivo data of PRS-343 as well as the excellent developability profile support investigation of its anti-cancer activity in clinical trials. Citation Format: Marlon J. Hinner, Rachida-Siham Bel Aiba, Corinna Schlosser, Thomas Jaquin, Andrea Allersdorfer, Sven Berger, Alexander Wiedenmann, Gabriele Matschiner, Julia Schüler, Ulrich Moebius, Christine Rothe, Shane A. Olwill. Costimulatory T-cell engagement by PRS-343, a CD137 (4-1BB)/HER2 bispecific, leads to tumor growth inhibition and TIL expansion in humanized mouse model [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B016.

Background. CD137 (4-1BB) is a key costimulatory immunoreceptor and a member of the TNF-receptor (TNFR) superfamily. While multiple lines of evidence show that CD137 is a highly promising therapeutic target in cancer, current mAb-based approaches are not designed to achieve a tumor-target driven activation and may display toxicity and a limited therapeutic window due to peripheral T cell and NK cell activation. To overcome this limitation, we generated PRS-343, a HER2/CD137 bispecific that is designed to promote CD137 clustering by bridging CD137-positive T cells with HER2-positive tumor cells, thereby providing a potent costimulatory signal to tumor antigen-specific T cells. Methods. Anticalin® proteins are 18 kD protein therapeutics derived from human lipocalins. We utilized phage display to generate an Anticalin protein binding to CD137 with high affinity and specificity. PRS-343 was obtained by genetic fusion of the CD137-specific Anticalin protein to a variant of the HER2-targeting monoclonal antibody trastuzumab with an engineered IgG4 backbone. Results. The bispecific fusion PRS-343 targets CD137 and HER2 with nearly identical affinities compared to the parental building blocks, and is capable of binding both targets simultaneously. We show ex vivo that T cells are efficiently activated when incubated with PRS-343 and HER2-positive cells, and that the activation is HER2-dependent. The in vivo activity of PRS-343 was investigated utilizing a humanized mouse model with a tumor cell-line-derived, HER2-positive xenograft. When tumors had reached a predefined size, mice received human PBMC via an intravenous route and weekly intraperitoneal injections of PRS-343 or controls for three weeks. We found that PRS-343 led to strong tumor growth inhibition and a significantly better response compared to either isotype control or anti-CD137 benchmark mAbs. The data, which include phenotyping of peripheral and intra-tumoral lymphocytes, support the envisaged mode of action of tumor-localized costimulatory T cell activation. Conclusion. We report potent costimulatory T-cell engagement of the immunoreceptor CD137 in a HER2-dependent manner, utilizing the HER2/CD137 bispecific PRS-343. Compared to known CD137-targeting antibodies in clinical development, this approach has the potential to provide a more localized activation of the immune system with higher efficacy and reduced peripheral toxicity. The positive functional ex vivo and in vivo data of PRS-343 as well as the excellent developability profile support investigation of its anti-cancer activity in clinical trials. Citation Format: Marlon J. Hinner, Rachida-Siham Bel Aiba, Corinna Schlosser, Alexander Wiedenmann, Andrea Allersdorfer, Gabriele Matschiner, Sven Berger, Ulrich Moebius, Christine Rothe, Shane A. Olwill. Costimulatory T-cell engagement by the HER2/CD137 bispecific PRS-343 leads to strong antitumor effect in humanized mouse model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 556.

Background: CD137 is a potent costimulatory immunoreceptor and a member of the TNF-receptor (TNFR) superfamily. The receptor, also known as 4-1BB, is mainly expressed on activated CD4+ and CD8+ T cells, activated B cells, and natural killer (NK) cells. While multiple lines of evidence show that CD137 is a highly promising therapeutic target, current approaches are not designed to achieve a tumor-target driven activation, which may reduce the available therapeutic window via peripheral T cell activation and toxicity. To overcome this limitation, we applied Anticalin® technology to generate a bispecific protein therapeutic binding to CD137 and a differentially expressed tumor target, HER2. Methods: Anticalin® proteins are 18 kD protein therapeutics derived from human lipocalins which enable straight-forward multimeric drug targeting across several formats. We utilized phage display to generate an Anticalin protein binding to CD137 with high affinity and specificity. The CD137-specific Anticalin protein was genetically fused to a Trastuzumab variant, yielding four different constructs covering a range of distances between the binding sites of the T cell-target and the tumor cell target. To minimize Fc-receptor interaction of the resulting bispecific and concomitant potential toxicity towards CD137-positive cells, the backbone of Trastuzumab was switched from IgG1 to an engineered IgG4 isotype. Results: All four bispecific constructs bound the targets CD137 and HER2 with a nearly identical affinity compared to the parental building blocks, and both targets could be simultaneously bound. Compared to non-engineered Trastuzumab, binding to human receptors FcγRI and FcγRIII was significantly reduced, while binding to the neonatal Fc receptor (FcRn) was retained. Functional activity was demonstrated in human T cell activation assays, and shown to be tumor target (HER2) dependent. Conclusion: We report the first bispecific therapeutic protein that targets the potent costimulatory immunoreceptor CD137 in a tumor-target dependent manner, utilizing HER2 as the tumor target. Compared to currently existing CD137-targeting antibodies, this approach has the potential to provide a more localized activation of the immune system with reduced peripheral toxicity. Bispecific T cell engagers based on CD137 and HER2 may have utility in HER2-positive cancers where there is a significant unmet medical need, such as bladder, ovarian and gastric cancer. Citation Format: Marlon J. Hinner, Rachida-Siham Bel Aiba, Alexander Wiedenmann, Corinna Schlosser, Andrea Allersdorfer, Gabriele Matschiner, Christine Rothe, Ulrich Moebius, Shane A. Olwill. Costimulatory T-cell engagement via a novel bispecific anti-CD137 /anti-HER2 protein based on Anticalin® technology. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B023.

CD137 is a potent costimulatory immunoreceptor and a member of the TNF-receptor (TNFR) superfamily. The receptor, also known as 4-1BB, is mainly expressed on activated CD4+ and CD8+ T cells, activated B cells, and natural killer (NK) cells. While multiple lines of evidence show that CD137 is a highly promising therapeutic target, current approaches using monospecific antibodies may display a limited therapeutic window due to peripheral T cell and NK cell activation, leading to unwanted toxicity. To overcome this limitation, we have generated a bispecific protein therapeutic designed to achieve a tumor-target driven activation of immune cells via binding to CD137 and to a differentially expressed tumor target, HER2. Anticalin® proteins are 18 kD protein therapeutics derived from human lipocalins. Using phage display technology a CD137-specific Anticalin was identified. The Anticalin was recombinantly fused to a trastuzumab variant at either the C or N terminus of the antibody´s heavy or light chain, yielding four different constructs covering a range of distances between the binding sites of the T cell-target and the tumor cell target. To minimize Fcγ-receptor interaction of the resulting bispecific and concomitant potential toxicity towards CD137-positive cells, the backbone of trastuzumab was switched from IgG1 to an engineered IgG4 isotype. Using ELISA or cell-based assays it was shown that all bispecific constructs bound their targets CD137 and HER2 with similar affinity compared to the parental building blocks, and both targets could be simultaneously bound. Binding to human receptors FcγRI and FcγRIII was significantly reduced in the bispecific constructs compared to non-engineered trastuzumab, while binding to the neonatal Fc receptor (FcRn) was retained. All constructs were shown to have excellent drug-like properties including thermal stability and plasma stability. HER2-dependent agonistic engagement of CD137 was demonstrated in ex-vivo T-cell activation assays utilizing HER2-positive human cell lines. The functional activity of the bispecific constructs was found to be dependent on their geometry. In conclusion, we report the first bispecific therapeutic protein that targets the potent costimulatory immunoreceptor CD137 in a tumor-target dependent manner, utilizing HER2 as the tumor target. Compared to currently existing CD137-targeting antibodies, this approach has the potential to provide a more controlled activation of the immune system in the tumor microenvironment with reduced peripheral toxicity. Bispecific T-cell engagers based on CD137 and HER2 have potential utility in HER2-positive cancers where there is a significant unmet medical need. Citation Format: Marlon J. Hinner, Rachida-Siham Bel Aiba, Alexander Wiedenmann, Corinna Schlosser, Andrea Allersdorfer, Gabriele Matschiner, Christine Rothe, Ulrich Moebius, Holbrook E. Kohrt, Shane A. Olwill. Costimulatory T-cell engagement via a novel bispecific anti-CD137 /anti-HER2 protein. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C205.

Human β-tryptase is a mast cell specific serine protease [1,2] with a unique tetrameric architecture, as recently revealed by X-ray crystallography [3,4]. The enzyme consists of four quasi equivalent subunits (A, B, C., and D) each with trypsin-like activity. Therefore, β-tryptase represents an array of four negatively charged S1 pockets with an defined spatial arrangement. In detail, the distance between the specificity pockets of subunits A/D and B/C within the tetramer is 33 A, respectively, whereas the distances between the S1 subsites of subunits A/C and B/D as well as A/B and C/D comprise 45 A. Thus, this protease should act as a molecular ruler capable of recognizing dibasic inhibitors of appropriate length. To prove the concept of a molecular ruler, we have synthesized an array of structurally related dibasic compounds by systematically increasing the distance between the positively charged head groups to address, in particular, the subunit pairs A/D and B/C, respectively.

Human tryptase, a mast-cell-specific serine proteinase that may be involved in causing asthma and other allergic and inflammatory disorders, is unique in two respects: it is enzymatically active only as a heparin-stabilized tetramer, and it is resistant to all known endogenous proteinase inhibitors. The 3-A crystal structure of human beta-tryptase in a complex with 4-amidinophenyl pyruvic acid shows four quasi-equivalent monomers arranged in a square flat ring of pseudo 222 symmetry. Each monomer contacts its neighbours at two different interfaces through six loop segments. These loops are located around the active site of beta-tryptase and differ considerably in length and conformation from loops of other trypsin-like proteinases. The four active centres of the tetramer are directed towards an oval central pore, restricting access for macromolecular substrates and enzyme inhibitors. Heparin chains might stabilize the complex by binding to an elongated patch of positively charged residues spanning two adjacent monomers. The nature of this unique tetrameric architecture explains many of tryptase's biochemical properties and provides a basis for the rational design of monofunctional and bifunctional tryptase inhibitors.

Background: Activation of the c-Met oncogenic pathway has been implicated in the development of aggressive cancers which are difficult to treat with current chemotherapies. Dimerization of c-Met receptor upon binding of Hepatocyte Growth Factor (HGF) leads to the stimulation of proliferative, migratory and survival pathways implicated in tumor development. Moreover it has recently been discovered that patients who become resistant / nonresponsive to therapies such as EGFR or VEGF inhibitors often show an enhanced c-Met expression. This has led to an increased interest in developing novel therapies that target the c-Met pathway. However, most existing drug modalities are confounded by their inability to specifically target and/or antagonize this pathway. Anticalins, a novel class of small biologics, are hypothesized to be ‘fit for purpose’ for developing highly specific and potent antagonists of cancer pathways. A monovalent Anticalin c-Met antagonist displaying efficacy in both ligand-dependent and independent cancer models has been developed. Methods/Results: Here we describe the in vitro and in vivo characterisation of the Anticalin c-Met antagonist PRS-110. In protein-based binding assays PRS-110 specifically binds to c-Met with high affinity and blocks HGF interaction (IC50 3.4 ± 0.7 nM). HUVEC cell proliferation assays demonstrated that PRS-110 efficiently antagonizes HGF-mediated growth. As a monovalent antagonist PRS-110 does not induce the c-Met pathway in the absence of ligand by receptor dimerization - an unwanted activation that can occur with bivalent antibodies. In mice, rats and non-human primates, PEGylated PRS-110 displayed favourable plasma elimination half-life profiles of 41 hours, 61 hours and 72 hours (T½α) respectively, with no signs of macrotoxicity. In vivo administration of PRS-110 resulted in significant, dose-dependent tumor growth inhibition in multiple xenograft models representative of ligand-dependent and ligand-independent c-Met activation. Analysis of c-Met protein levels on xenograft biopsy samples demonstrated a significant reduction in total c-Met (p Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3875. doi:1538-7445.AM2012-3875

Abstract 687 Rationale: Anticalins® have been developed as a new class of therapeutic proteins based on human lipocalins. We reasoned that given the diversity of compounds that these molecules naturally bind, it should be possible to engineer and identify Anticalins with specificity for small, biologically active compounds, including constrained peptides. To test this hypothesis, we asked whether it would be possible to identify an engineered lipocalin that could specifically block hepcidin, a 25 amino acid hepatic hormone. The central role of hepcidin in regulating iron homeostasis through its interaction with the only known cellular iron exporter ferroportin is supported by human genetics and preclinical data and suggests that sub-population of patients with anemia, exhibiting elevated serum levels of hepcidin, may be responsive to therapies directed at blocking hepcidin. Hepcidin-specific antagonistic Anticalins with different pharmacokinetic properties were generated to develop Anticalin drug candidates with different PK/PD relationships as different clearance rates of the Anticalin-hepcidin complex may be desirable when used as a therapeutic approach in different patient populations. Methods: State of the art phage display technology and high throughput screening were used to isolate a human lipocalin-derived Anticalin to specifically bind and antagonize hepcidin. Randomization of Anticalin binding loops and affinity-based phage display selection were used for affinity maturation and optimization of drug-like properties. Anticalins (MW ∼21 kDa) were produced in E.coli and subjected to site-directed PEGylation with different size PEG molecules. Affinity constants for hepcidin from different species were determined using ELISA-based assays and surface plasmon resonance. We then examined the ability of these Anticalin drug candidates to neutralize human hepcidin activities in cellular and in vivo assays. In addition, PK properties were determined in different animal species to predict PK properties in humans by allometric scaling. Results and Discussion: By using 2 different assay formats the lead candidate displayed high affinity (sub-nM) against human hepcidin and the extension of its plasma half-life by site directed PEGylation did not impact target binding. For example, in an SPR kinetic assay where the PEGylated Anticalin was immobilized and human hepcidin used as analyte, a dissociation constant of Kd = 50±3 pM (n=3) was determined for an Anticalin conjugated with a 40 kDa branched PEG molecule. A stable cell line expressing ferroportin fused to green fluorescent protein was established to determine blockade of hepcidin in vitro by measuring hepcidin-induced ferroportin (FPN) internalization and degradation. Hepcidin bioactivity was completely inhibited by the PEGylated Anticalin at concentrations at or above ∼40 nM (n=6), thus demonstrating the ability of the Anticalin to neutralize hepcidin's principal biological activity on the iron exporter FPN. Furthermore, the ability of PRS-080 to neutralize short-term hypoferremic effects was evaluated in mice after stimulation via a single intraperitoneal injection of 1 mg/kg synthetic human hepcidin. The PEGylated version of PRS-080, administered intravenously several hours prior to hepcidin injection, completely prevented the hypoferremic response at a dose of 95 mg/kg and showed partial prevention at 30 mg/kg (59%) and 9.5 mg/kg (23%). Tunable PK properties were demonstrated with an additional set of PEGylated molecules, tested in rats at a dose of 10 mg/kg, and exhibited terminal half-lives of 9.2, 14.2, 20.4, and 40 hours for Anticalins conjugated with 12, 20, 30 kDa linear and 40 kDa branched PEG, respectively. Conclusions: Our data describe the discovery and characterization of a hepcidin-antagonistic Anticalin for the treatment of anemia. PRS-080 displays numerous differentiating features posited to be relevant for the proposed therapeutic concept of inhibiting hepcidin-mediated hypoferremic effects, including: binding of its relatively small target with high affinity and specificity (pocket binding), favourable safety and tolerability (human scaffold, lack of immune effector cell interactions), tunable half-life and low production costs (bacterial expression). Anticalins provide a powerful novel therapeutic approach to develop antagonists against hepcidin and bioactive peptides in general. Disclosures: Hohlbaum: Pieris AG: Employment, Patents & Royalties. Trentman:Pieris AG: Employment, Patents & Royalties. Gille:Pieris AG: Employment, Patents & Royalties. Allersdorfer:Pieris AG: Employment. Belaiba:Pieris AG: Employment. Huelsmeyer:Pieris AG: Employment, Patents & Royalties. Christian:Pieris AG: Employment, Patents & Royalties. Sandal:Pieris AG: Employment. Matschiner:Pieris AG: Employment, Patents & Royalties. Jensen:Pieris AG: Employment, Patents & Royalties. Skerra:Pieris AG: Consultancy, Patents & Royalties, Research Funding. Audoly:Pieris AG: Employment.