VISTA checkpoint inhibition by pH-selective antibody SNS-101 with optimized safety and pharmacokinetic profiles enhances PD-1 response

VISTA, an inhibitory myeloid-T-cell checkpoint, holds promise as a target for cancer immunotherapy. However, its effective targeting has been impeded by issues such as rapid clearance and cytokine release syndrome observed with previous VISTA antibodies. Here we demonstrate that SNS-101, a newly developed pH-selective VISTA antibody, addresses these challenges. Structural and biochemical analyses confirmed the pH-selectivity and unique epitope targeted by SNS-101. These properties confer favorable pharmacokinetic and safety profiles on SNS-101. In syngeneic tumor models utilizing human VISTA knock-in mice, SNS-101 shows in vivo efficacy when combined with a PD-1 inhibitor, modulates cytokine and chemokine signaling, and alters the tumor microenvironment. In summary, SNS-101, currently in Phase I clinical trials, emerges as a promising therapeutic biologic for a wide range of patients whose cancer is refractory to current immunotherapy regimens.

Myeloid and dendritic cells enhance therapeutics-induced cytokine release syndrome features in humanized BRGSF-HIS preclinical model

Objectives

Despite their efficacy, some immunotherapies have been shown to induce immune-related adverse events, including the potentially life-threatening cytokine release syndrome (CRS), calling for reliable and translational preclinical models to predict potential safety issues and investigate their rescue. Here, we tested the reliability of humanized BRGSF mice for the assessment of therapeutics-induced CRS features in preclinical settings.

Methods

BRGSF mice reconstituted with human umbilical cord blood CD34+ cells (BRGSF-CBC) were injected with anti-CD3 antibody (OKT3), anti-CD3/CD19 bispecific T-cell engager Blinatumomab, or VISTA-targeting antibody. Human myeloid and dendritic cells' contribution was investigated in hFlt3L-boosted BRGSF-CBC mice. OKT3 treatment was also tested in human PBMC-reconstituted BRGSF mice (BRGSF-PBMC). Cytokine release, immune cell distribution, and clinical signs were followed.

Results

OKT3 injection in BRGSF-CBC mice induced hallmark features of CRS, specifically inflammatory cytokines release, modifications of immune cell distribution and activation, body weight loss, and temperature drop. hFlt3L-boosted BRGSF-CBC mice displayed enhanced CRS features, revealing a significant role of myeloid and dendritic cells in this process. Clinical CRS-managing treatment Infliximab efficiently attenuated OKT3-induced toxicity. Comparison of OKT3 treatment's effect on BRGSF-CBC and BRGSF-PBMC mice showed broadened CRS features in BRGSF-CBC mice. CRS-associated features were also observed in hFlt3L-boosted BRGSF-CBC mice upon treatment with other T-cell or myeloid-targeting compounds.

Conclusions

These data show that BRGSF-CBC mice represent a relevant model for the preclinical assessment of CRS and CRS-managing therapies. They also confirm a significant role of myeloid and dendritic cells in CRS development and exhibit the versatility of this model for therapeutics-induced safety assessment.

SNS-101, a highly selective monoclonal antibody against the active form of VISTA, demonstrates significantly reduced cytokine release

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Background: Active cancer immunotherapeutics frequently give rise to immune-mediated adverse events (AEs), including cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). On-target, off-tumor activation of myeloid lineage cells (e.g. monocytes) has been implicated as a factor in the generation of these immune-mediated AEs. VISTA (V-domain Ig suppressor of T-cell activation) is an immune checkpoint, which is highly expressed on myeloid cells, and binds PSGL-1 on T-cells, but only when ‘activated’ by protonation at low pH (̃pH 6). Inhibition of the VISTA:PSGL-1 interaction in the acidic tumor microenvironment has been shown to be efficacious in multiple syngeneic murine tumor models. However, antibodies binding to VISTA at physiological pH 7.4 have significant potential to induce dose-limiting toxicities such as CRS and/or ICANS and be prematurely eliminated from circulation through targeted-mediated drug disposition (TMDD), reducing the likelihood of reaching efficacious drug occupancy levels. Among several non-pH-selective antibodies in clinical development, JNJ-61610588 (now CI-8993) induced dose-limiting on-target CRS at subtherapeutic dose levels and exhibited TMDD. To mitigate potential CRS and prevent TMDD, we developed SNS-101, a highly selective monoclonal IgG1 antibody for “active” VISTA, which inhibits the critical interaction with PSGL-1. Methods: Using flow cytometry at physiological pH, we compared SNS-101 with clinical stage non-pH-selective anti-VISTA antibodies and examined binding to VISTA-positive cell populations in human PBMCs as well as in human CD34+ cord blood cells reconstituted BRGSF-HIS mice (humanized BRGSF-HIS mice), which develop both human lymphoid and myeloid compartments. Furthermore, we performed in vitro and in vivo CRS studies in a HUVEC/PBMC co-culture system and humanized BRGSF-HIS mice, respectively. Results: Under physiological pH, non-pH-selective antibodies bound to monocytes, neutrophils and NK cells whereas SNS-101 did not exhibit any significant interactions. CRS assays indicate that the magnitude of induced cytokine levels was significantly higher with non-pH-selective antibodies compared to SNS-101. Conclusions: We assessed the binding profile of SNS-101 vs. non-pH-selective VISTA antibodies. Our results demonstrate that SNS-101 does not bind to VISTA-positive cells in circulating blood. In addition, in vitro and in vivo CRS studies suggest that SNS-101 has a lower risk of inducing CRS compared to non-pH selective anti-VISTA antibodies, alleviating liabilities previously associated with anti-VISTA antibodies. IND-enabling studies, including pharmacokinetic and toxicology studies, are ongoing.

228 Antagonistic pH-selective VISTA antibody SNS-101 potentiates anti-PD-1/PD-L1-induced anti-tumor immunity

Background

Immunotherapies, especially immune checkpoint inhibitors, have become a cornerstone of cancer treatment. Remarkable clinical responses have been observed blocking the programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) axis across a spectrum of indications. However, innate and/or acquired resistance to anti-PD-1 blockade remains a major challenge. V-domain Ig suppressor of T-cell activation (VISTA) is a B7-family member, which promotes T-cell and myeloid quiescence and represents a promising target, particularly in combination with anti-PD-1/PD-L1 treatment. Recently, the interaction of VISTA with its receptor PSGL-1 was demonstrated to be significantly enhanced by the acidic tumor microenvironment (TME). As VISTA is highly expressed on myeloid cells, including those in the blood, antibodies binding VISTA at physiological pH 7.4 could result in rapid elimination from circulation through targeted-mediated drug disposition, making efficacious drug occupancy levels difficult to reach and potentially narrowing the therapeutic window. An antibody engineered to selectively bind and block VISTA at low pH in the TME may therefore be an ideal drug candidate.

Methods

In this study, fully human anti-VISTA antibodies were generated through pH-selective enrichment strategies of a yeast-based display library comprising highly diverse synthetic immune repertoires. The ‘parental’ antibodies have been extensively characterized using in vitro flow-cytometry, surface-plasmon resonance (SPR) and PSGL-1/VISTA inhibition assays in primary human CD4 and CD8 T-cells at pH 6.0 and pH 7.4. Eight parental antibodies were identified and tested for combinatorial efficacy with anti-PD-1 in vivo in human VISTA knock-in mice inoculated with syngeneic MC-38 tumors. These antibodies underwent further optimization for enhanced binding affinity at pH 6.0 and decreased binding at pH 7.4. ‘Progeny’ antibody ranking was based on the same in vitro and in vivo characterization as parental antibodies.

Results

Eighty four parental antibodies were initially discovered. Flow-cytometry and SPR analysis revealed candidates displaying pH-dependent binding to endogenously expressed native VISTA on cells, and a PSGL-1/VISTA inhibition assay at pH 6.0 was run to identify and rank potent interface blockers. Eight candidate antibodies were tested in an in vivo intervention study in combination with anti-murine PD-1 demonstrating varied combinatorial efficacy with a subset leading to superior tumor rejection. Characterization of optimized progeny antibodies led to identification of anti-VISTA antibody SNS-101.

Conclusions

Enrichment of highly diverse antibody libraries led to the identification of a pH-selective inhibitory anti-VISTA antibody SNS-101, which exerts excellent combinability with anti-PD-1 leading to superior anti-tumor activity in a mouse model.

Optimization of a nicotine degrading enzyme for potential use in treatment of nicotine addiction

BACKGROUND

Smoking and tobacco use continue to be the largest preventable causes of death globally. A novel therapeutic approach has recently been proposed: administration of an enzyme that degrades nicotine, the main addictive component of tobacco, minimizing brain exposure and reducing its reinforcing effects. Pre-clinical proof of concept has been previously established through dosing the amine oxidase NicA2 from Pseudomonas putida in rat nicotine self-administration models of addiction.

RESULTS

This paper describes efforts towards optimizing NicA2 for potential therapeutic use: enhancing potency, improving its pharmacokinetic profile, and attenuating immunogenicity. Libraries randomizing residues located in all 22 active site positions of NicA2 were screened. 58 single mutations with 2- to 19-fold enhanced catalytic activity compared to wt at 10 μM nicotine were identified. A novel nicotine biosensor assay allowed efficient screening of the many primary hits for activity at nicotine concentrations typically found in smokers. 10 mutants with improved activity in rat serum at or below 250 nM were identified. These catalytic improvements translated to increased potency in vivo in the form of further lowering of nicotine blood levels and nicotine accumulation in the brains of Sprague-Dawley rats. Examination of the X-ray crystal structure suggests that these mutants may accelerate the rate limiting re-oxidation of the flavin adenine dinucleotide cofactor by enhancing molecular oxygen's access. PEGylation of NicA2 led to prolonged serum half-life and lowered immunogenicity observed in a human HLA DR4 transgenic mouse model, without impacting nicotine degrading activity.

CONCLUSIONS

Systematic mutational analysis of the active site of the nicotine-degrading enzyme NicA2 has yielded 10 variants that increase the catalytic activity and its effects on nicotine distribution in vivo at nicotine plasma concentrations found in smokers. In addition, PEGylation substantially increases circulating half-life and reduces the enzyme's immunogenic potential. Taken together, these results provide a viable path towards generation of a drug candidate suitable for human therapeutic use in treating nicotine addiction.

The nicotine-degrading enzyme NicA2 reduces nicotine levels in blood, nicotine distribution to brain, and nicotine discrimination and reinforcement in rats

BACKGROUND

The bacterial nicotine-degrading enzyme NicA2 isolated from P. putida was studied to assess its potential use in the treatment of tobacco dependence.

RESULTS

Rats were pretreated with varying i.v. doses of NicA2, followed by i.v. administration of nicotine at 0.03 mg/kg. NicA2 had a rapid onset of action reducing blood and brain nicotine concentrations in a dose-related manner, with a rapid onset of action. A 5 mg/kg NicA2 dose reduced the nicotine concentration in blood by > 90% at 1 min after the nicotine dose, compared to controls. Brain nicotine concentrations were reduced by 55% at 1 min and 92% at 5 min post nicotine dose. To evaluate enzyme effects at a nicotine dosing rate equivalent to heavy smoking, rats pretreated with NicA2 at 10 mg/kg were administered 5 doses of nicotine 0.03 mg/kg i.v. over 40 min. Nicotine levels in blood were below the assay detection limit 3 min after either the first or fifth nicotine dose, and nicotine levels in brain were reduced by 82 and 84%, respectively, compared to controls. A 20 mg/kg NicA2 dose attenuated nicotine discrimination and produced extinction of nicotine self-administration (NSA) in most rats, or a compensatory increase in other rats, when administered prior to each daily NSA session. In rats showing compensation, increasing the NicA2 dose to 70 mg/kg resulted in extinction of NSA. An enzyme construct with a longer duration of action, via fusion with an albumin-binding domain, similarly reduced NSA in a 23 h nicotine access model at a dose of 70 mg/kg.

CONCLUSIONS

These data extend knowledge of NicA2's effects on nicotine distribution to brain and its ability to attenuate addiction-relevant behaviors in rats and support its further investigation as a treatment for tobacco use disorder.

Aberrant antibody affinity selection in SHIP-deficient B cells

The strength of the Ag receptor signal influences development and negative selection of B cells, and it might also affect B-cell survival and selection in the GC. Here, we have used mice with B-cell-specific deletion of the 5'-inositol phosphatase SHIP as a model to study affinity selection in cells that are hyperresponsive to Ag and cytokine receptor stimulation. In the absence of SHIP, B cells have lower thresholds for Ag- and interferon (IFN)-induced activation, resulting in augmented negative selection in the BM and enhanced B-cell maturation in the periphery. Despite a tendency to spontaneously downregulate surface IgM expression, SHIP deficiency does not alter anergy induction in response to soluble hen-egg lysozyme Ag in the MDA4 transgenic model. SHIP-deficient B cells spontaneously produce isotype-switched antibodies; however, they are poor responders in immunization and infection models. While SHIP-deficient B cells form GCs and undergo mutation, they are not properly selected for high-affinity antibodies. These results illustrate the importance of negative regulation of B-cell responses, as lower thresholds for B-cell activation promote survival of low affinity and deleterious receptors to the detriment of optimal Ab affinity maturation.

Preparation, characterization, and immunogenicity in mice of a recombinant influenza H5 hemagglutinin vaccine against the avian H5N1 A/Vietnam/1203/2004 influenza virus

Production of influenza vaccines requires a minimum of 6 months after the circulating strain is isolated and the use of infectious viruses. The hemagglutinin (protective antigen) of circulating influenza viruses mutates rapidly requiring reformulation of the vaccines. Our goal is to eliminate the risk of working with infectious virus and reduce significantly the production time. A cDNA fragment encoding the influenza virus A/Vietnam/1203/2004 (H5N1) HA gene was prepared using RT-PCR with viral RNA as a template. Recombinant HA (rHA) protein was produced in Escherichia coli and purified from isolated inclusion bodies by urea solubilization and Ni(+)-ion column chromatography. Vaccine candidates were prepared by treating the rHA with formalin, adsorption onto alum or with both. Mice were injected subcutaneously with candidate vaccines two or three times 2 weeks apart. Sera were collected 1 week after the last injection and antibody measured by ELISA and hemagglutination inhibition (HI). The highest antibody response (GM 449EU) was elicited by three injections of 15microg alum-adsorbed rHA. Dosages of 5microg of rHA formulated with formalin and alum, and 5microg alum-adsorbed rHA elicited IgG anti-HA of GM 212 and 177EU, respectively. HI titers, >or=40 were obtained in >or=80% of mice with three doses of all formulations. We developed a method to produce rHA in a time-frame suitable for annual and pandemic influenza vaccination. Using this method, rHA vaccine can be produced in 3-4 weeks and when formulated with alum, induces HA antibody levels in young outbred mice consistent with the FDA guidelines for vaccines against epidemic and pandemic influenza.

Human JIK, a novel member of the STE20 kinase family that inhibits JNK and is negatively regulated by epidermal growth factor

Mammalian members related to Saccharomyces cerevisiae serine/threonine kinase STE20 can be divided into two subfamilies based on their structure and function. The PAK subfamily is characterized by an N-terminal p21-binding domain (also known as CRIB domain), a C-terminal kinase domain, and is regulated by the small GTP-binding proteins Rac1 and Cdc42Hs. The second group is represented by the GCK-like members, which contain an N-terminal catalytic domain and lack the p21-binding domain. Some of them have been demonstrated to induce c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) cascade, while others have been shown to be activated by a subset of stress conditions or apoptotic agents, although little is known about their specific function. Here, we have identified a novel human STE20-related serine/threonine kinase, belonging to the GCK-like subfamily. This kinase does not induce the JNK/SAPK pathway, but, instead, inhibits the basal activity of JNK/SAPK, and diminishes its activation in response to human epidermal growth factor (EGF). Therefore, we designated this molecule JIK for JNK/SAPK-inhibitory kinase. The inhibition of JNK/SAPK signaling pathway by JIK was found to occur between the EGF receptor and the small GTP-binding proteins Rac1 and Cdc42Hs. In contrast, JIK does not activate nor does it inhibit ERK2, ERK6, p38, or ERK5. Furthermore, JIK kinase activity is not modulated by any exogenous stimuli, but, interestingly, it is dramatically decreased upon EGF receptor activation. Thus, JIK might represent the first member of the STE20 kinase family whose activity can be negatively regulated by tyrosine kinase receptors, and whose downstream targets inhibit, rather than enhance, JNK/SAPK activation.

Isolation and characterization of e3B1, an eps8 binding protein that regulates cell growth

Eps8, a substrate of receptor tyrosine kinases, is an SH3 domain containing protein that plays an important role in mitogenic signaling. To determine the cellular function of eps8, we used the SH3 domain of eps8 to screen a human fibroblast M426 expression library and identified, a full-length cDNA clone of 3.2 kb. We designated this clone e3B1 for eps8 SH3 domain binding protein 1. Northern analysis revealed that expression of e3B1 mRNA was ubiquitous in human tissues. The e3B1 gene encodes a SH3 domain containing protein. We show that anti-e3B1 antibodies detect three cytosolic protein species of 65, 68 and 72 kDa in cell lysate isolated from asynchronously growing NIH3T3 cells. E3B1 binds to the SH3 domain of eps8 and Abl in vitro. We also demonstrated that e3B1 associates with eps8 in vivo. Phosphatase digestion and phosphoamino acid analysis revealed that p65e3B1 is a phosphoserine containing protein and p72e3B1 and p68e3B1 are hyperserine-phosphorylated form of p65e3B1. We further determined that the p65e3B1 was the most abundant in serum-starved NIH/EGFR cells. Time course studies initiated by the addition of epidermal growth factor (EGF) revealed that the p72e3B1 started to accumulate at 4 h, peaked at 8 h and remained high until 24 h. Finally, we demonstrate that NIH/EGFR fibroblasts overexpressing e3B1 grow more slowly relative to matched controls.

Direct binding of eps8 to the juxtamembrane domain of EGFR is phosphotyrosine- and SH2-independent

Several signal transducers bind through their SH2 domains to phosphotyrosine-containing motifs present in receptor tyrosine kinases (RTKs). However, the juxtamembrane regions of the epidermal growth factor receptor (EGFR) and of the related erbB-2 protein, while important in mitogenic signaling, lack demonstrable tyrosine phosphorylation sites, suggesting that other modalities of receptor-transducer interactions exist. A candidate for investigating this type of association is p97eps8, a recently described substrate for RTKs. p97eps8 is phosphorylated by several RTKs, associates with EGFR in vivo and, upon overexpression, enhances the transduction of EGFR-mediated mitogenic signals. Here we report that eps8 binds directly to the juxtamembrane region of EGFR through a domain that does not bear resemblance to SH2 domains and by a mechanism that does not require the presence of phosphotyrosine residues. Thus, the physical association between EGFR and eps8 represents a novel interaction between RTKs and their substrates.