Anti-Extra Domain B Splice Variant of Fibronectin Antibody-Drug Conjugate Eliminates Tumors with Enhanced Efficacy When Combined with Checkpoint Blockade.

Extra domain B splice variant of fibronectin (EDB+FN) is an extracellular matrix protein (ECM) deposited by tumor-associated fibroblasts, and is associated with tumor growth, angiogenesis, and invasion. We hypothesized that EDB+FN is a safe and abundant target for therapeutic intervention with an antibody-drug conjugate (ADC). We describe the generation, pharmacology, mechanism of action, and safety profile of an ADC specific for EDB+FN (EDB-ADC). EDB+FN is broadly expressed in the stroma of pancreatic, non-small cell lung (NSCLC), breast, ovarian, head and neck cancers, whereas restricted in normal tissues. In patient-derived xenograft (PDX), cell-line xenograft (CLX), and mouse syngeneic tumor models, EDB-ADC, conjugated to auristatin Aur0101 through site-specific technology, demonstrated potent antitumor growth inhibition. Increased phospho-histone H3, a pharmacodynamic biomarker of response, was observed in tumor cells distal to the target site of tumor ECM after EDB-ADC treatment. EDB-ADC potentiated infiltration of immune cells, including CD3+ T lymphocytes into the tumor, providing rationale for the combination of EDB-ADC with immune checkpoint therapy. EDB-ADC and anti-PD-L1 combination in a syngeneic breast tumor model led to enhanced antitumor activity with sustained tumor regressions. In nonclinical safety studies in nonhuman primates, EDB-ADC had a well-tolerated safety profile without signs of either on-target toxicity or the off-target effects typically observed with ADCs that are conjugated through conventional conjugation methods. These data highlight the potential for EDB-ADC to specifically target the tumor microenvironment, provide robust therapeutic benefits against multiple tumor types, and enhance activity antitumor in combination with checkpoint blockade.

In vitro affinity optimization of an anti-BDNF monoclonal antibody translates to improved potency in targeting chronic pain states in vivo.

The role of brain-derived neurotrophic factor (BDNF) signaling in chronic pain has been well documented. Given the important central role of BDNF in long term plasticity and memory, we sought to engineer a high affinity, peripherally-restricted monoclonal antibody against BDNF to modulate pain. BDNF shares 100% sequence homology across human and rodents; thus, we selected chickens as an alternative immune host for initial antibody generation. Here, we describe the affinity optimization of complementarity-determining region-grafted, chicken-derived R3bH01, an anti-BDNF antibody specifically blocking the TrkB receptor interaction. Antibody optimization led to the identification of B30, which has a > 300-fold improvement in affinity based on BIAcore, an 800-fold improvement in potency in a cell-based pERK assay and demonstrates exquisite selectivity over related neurotrophins. Affinity improvements measured in vitro translated to in vivo pharmacological activity, with B30 demonstrating a 30-fold improvement in potency over parental R3bH01 in a peripheral nerve injury model. We further demonstrate that peripheral BDNF plays a role in maintaining the plasticity of sensory neurons following nerve damage, with B30 reversing neuron hyperexcitability associated with heat and mechanical stimuli in a dose-dependent fashion. In summary, our data demonstrate that effective sequestration of BDNF via a high affinity neutralizing antibody has potential utility in modulating the pathophysiological mechanisms that drive chronic pain states.

Novel Anti-TM4SF1 Antibody-Drug Conjugates with Activity against Tumor Cells and Tumor Vasculature.

Antibody-drug conjugates (ADC) represent a promising therapeutic modality for managing cancer. Here, we report a novel humanized ADC that targets the tetraspanin-like protein TM4SF1. TM4SF1 is highly expressed on the plasma membranes of many human cancer cells and also on the endothelial cells lining tumor blood vessels. TM4SF1 is internalized upon interaction with antibodies. We hypothesized that an ADC against TM4SF1 would inhibit cancer growth directly by killing cancer cells and indirectly by attacking the tumor vasculature. We generated a humanized anti-human TM4SF1 monoclonal antibody, v1.10, and armed it with an auristatin cytotoxic agent LP2 (chemical name mc-3377). v1.10-LP2 selectively killed cultured human tumor cell lines and human endothelial cells that express TM4SF1. Acting as a single agent, v1.10-LP2 induced complete regression of several TM4SF1-expressing tumor xenografts in nude mice, including non-small cell lung cancer and pancreas, prostate, and colon cancers. As v1.10 did not react with mouse TM4SF1, it could not target the mouse tumor vasculature. Therefore, we generated a surrogate anti-mouse TM4SF1 antibody, 2A7A, and conjugated it to LP2. At 3 mpk, 2A7A-LP2 regressed several tumor xenografts without noticeable toxicity. Combination therapy with v1.10-LP2 and 2A7A-LP2 together was more effective than either ADC alone. These data provide proof-of-concept that TM4SF1-targeting ADCs have potential as anticancer agents with dual action against tumor cells and the tumor vasculature. Such agents could offer exceptional therapeutic value and warrant further investigation. Mol Cancer Ther; 14(8); 1868-76. ©2015 AACR.

Development and application of a biomarker assay for determining the pharmacodynamic activity of an antagonist candidate biotherapeutic antibody to IL21R in whole blood.

BACKGROUND: In preparation for potential clinical development of Ab-01, an antagonistic antibody directed against the IL21R, studies were undertaken to address translational medicine needs that fall into four categories: 1) development of a pharmacodynamic biomarker assay suitable for use in the clinic, 2) demonstration that Ab-01 has the desired biological activity in vitro and in vivo in cynomolgus monkeys, the preferred safety study species, 3) pre-clinical in vivo proof-of-concept that the assay can be used to detect Ab-01 pharmacodynamic (PD) activity in treated subjects, and 4) comprehensive assessment of the agonistic potential of Ab-01 when cross-linked. This report and a recently published companion report address the first three of these needs. The fourth has been addressed in a separate study. METHODS: Genes that change RNA expression upon ex vivo rhIL21 stimulation of whole blood were identified in human and cynomolgus monkey. The inhibitory effects of exogenously added Ab-01 were measured ex vivo in human and monkey, and the in vivo inhibitory effects of Ab-01 treatment were measured in monkey. RESULTS: Stimulation of whole human blood for 2 hours with rhIL21 induced robust increases in RNA expression of 6 genes. This response was blocked by Ab-01, indicating that the assay is suitable for measuring Ab-01 activity in blood. rhIL21 induced expression of a similar set of genes in cynomolgus monkey blood. This response was blocked with Ab-01, thus demonstrating that Ab-01 has the desired activity in the species, and that safety studies done in cynomolgus monkeys are relevant. Proof -of-concept for using this assay system to detect PD activity in vivo was generated by measuring the response in monkey blood to ex vivo rhIL21 stimulation before and 5 minutes following in vivo Ab-01 administration. CONCLUSIONS: A robust PD biomarker assay suitable for clinical use has been developed in human whole blood. The successful adaptation of the assay to cynomolgus monkeys has enabled the demonstration of Ab-01 activity both in vitro and in vivo in monkey, thus validating the use of this species in safety studies and establishing proof-of-concept for using this PD assay system to aid in dose selection in clinical studies.

A homogeneous scintillation proximity format for monitoring the activity of recombinant human long-chain-fatty-acyl-CoA synthetase 5.

Fatty acyl coenzyme A (CoA) synthetases are a group of enzymes responsible for the activation of fatty acids through ligated high-energy CoA thioester bonds. Ultimately these fatty acyl-CoA conjugates are routed toward either anabolic or catabolic pathways. Long-chain-fatty-acid-CoA ligase 5 (LACS 5) utilizes a wide range of saturated fatty acids with a substrate preference for C16-C18 unsaturated fatty acids. This enzyme represents a new class of potential drug targets, and, hence, our efforts were focused upon developing a robust assay for utilization in a high throughput screen. Toward that end, we describe a radiometric homogeneous measurement of the enzymatic reaction by employing ionic capture of the reaction product onto YSi scintillation proximity assay (SPA) beads. We present kinetic and inhibition data for LACS 5 using this SPA format. Our results show that the assay method is both robust and well suited for this class of lipid-metabolizing enzymes.

Enzymatic characterization of the pancreatic islet-specific glucose-6-phosphatase-related protein (IGRP).

Glucose is the main physiological stimulus for insulin biosynthesis and secretion by pancreatic beta-cells. Glucose-6-phosphatase (G-6-Pase) catalyzes the dephosphorylation of glucose-6-phosphate to glucose, an opposite process to glucose utilization. G-6-Pase activity in pancreatic islets could therefore be an important factor in the control of glucose metabolism and, consequently, of glucose-dependent insulin secretion. While G-6-Pase activity has been shown to be present in pancreatic islets, the gene responsible for this activity has not been conclusively identified. A homolog of liver glucose-6-phosphatase (LG-6-Pase) specifically expressed in islets was described earlier; however, the authors could not demonstrate enzymatic activity for this protein. Here we present evidence that the previously identified islet-specific glucose-6-phosphatase-related protein (IGRP) is indeed the major islet glucose-6-phosphatase. IGRP overexpressed in insect cells possesses enzymatic activity comparable to the previously described G-6-Pase activity in islets. The K(m) and V(max) values determined using glucose-6-phosphate as the substrate were 0.45 mm and 32 nmol/mg/min by malachite green assay, and 0.29 mm and 77 nmol/mg/min by glucose oxidase/peroxidase coupling assay, respectively. High-throughput screening of a small molecule library led to the identification of an active compound that specifically inhibits IGRP enzymatic activity. Interestingly, this inhibitor did not affect LG-6-Pase activity, while conversely LG-6-Pase inhibitors did not affect IGRP activity. These data demonstrate that IGRP is likely the authentic islet-specific glucose-6-phosphatase catalytic subunit, and selective inhibitors to this molecule can be obtained. IGRP inhibitors may be an attractive new approach for the treatment of insulin secretion defects in type 2 diabetes.

Development of a high-throughput assay for two inositol-specific phospholipase Cs using a scintillation proximity format.

Inositol-specific PLCs comprise a family of enzymes that utilize phosphoinositide substrates, e.g., PIP(2), to generate intracellular second messengers for the regulation of cellular responses. In the past, monitoring this reaction has been difficult due to the need for radiolabeled substrates, separation of the reaction products by organic-phase extraction, and finally radiometric measurements of the segregated products. In this report, we have studied the enzymatic characteristics of two novel PLCs that were derived from functional genomic analyses using a phospholipid-modified solid scintillating support. This method allows for the hydrophobic capture of the [(3)H]phosphoinositide substrate on a well defined scintillation surface and the homogenous measurement of the enzymatic hydrolysis of the substrate by proximity effects. Our results show that the assay format is robust and well suited for this class of lipid-metabolizing enzymes.

Characterization of the kinase domain of the ephrin-B3 receptor tyrosine kinase using a scintillation proximity assay.

We have characterized a recombinantly expressed N-terminally tagged GST fusion of the tyrosine kinase domain of human EphB3. The EphB3 kinase domain was shown to phosphorylate a group of synthetic tyrosine-containing peptides derived from a proprietary biotinylated kinase-biased peptide substrate library. In addition, the enzyme activity was stimulated by the divalent cation, manganese, and inhibited by addition of magnesium. The most active tyrosine-containing peptide, a biotinylated 49-mer, displayed saturation kinetics with an apparent K(m) of approximately 0.4 microM. The apparent K(m) for ATP was determined to be approximately 3 microM. The kinetics of the reaction was linear from concentrations of enzyme of 0.5 to 2 nM, and at or below the K(m) concentrations of the two substrates for at least 2 h at room temperature. Moreover, the tryrosine kinase inhibitor, PP2, produced an IC(50) of roughly 0.8 microM. In addition, the enzyme tolerated the solvent DMSO and was stable to multiple freeze/thaw cycles. Stability of the enzyme at 4 degrees C storage was seen out to 6 h with an approximately 50% reduction of activity by 24 h. Formatting the assay in a 384-well microtiter plate produced good uniformity of signal at 100% inhibition, 50% inhibition, and no inhibition. The coefficient of variance was at or below 10% with a signal-to-background ratio of approximately 24 and a z value of 0.72. Collectively, these results showed the ability to configure a robust HTS for a truncated recombinantly expressed family member of the Ephrin tyrosine kinases.