Abstract 3244: Improved Fc-mediated effector functions by an anti-CTLA-4 multivalent Fc agent

Numerous therapeutic monoclonal antibodies (mAbs) rely on antibody-dependent cell cytotoxicity (ADCC), antibody-dependent cell phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC) Fc effector functions to deplete target cells and achieve clinical efficacy. It has been previously shown that adding multiple Fc domains to Abs or afucosylating the Fc domain increases Fc effector functions. We have leveraged a proprietary Fc multimerization technology (SIF; selective immunomodulator of Fc receptors) to identify potential novel products designed to improve the immune system’s elimination of tumor and other pathogenic cells. These agents utilize the valency effect of Fc multimerization to increase the binding to Fc receptors and complement, enhancing immune-mediated cytotoxicity mechanisms. CTLA-4 is a clinically validated immune checkpoint inhibitor exemplified by the human IgG1 therapeutic mAb ipilimumab. CTLA-4 is induced upon activation on T cells and constitutively expressed on T regulatory cells (Tregs). Based on data from mouse models of cancer and clinical studies, the proposed mechanisms of action of anti-CTLA-4 mAbs, including ipilimumab, are to block the interaction of CTLA-4 with its ligands CD80 and CD86 resulting in T cell activation and to induce Fc-mediated ADCC of CTLA-4+ cells, mainly intratumoral Tregs. Therefore, we have produced an anti-CTLA-4 multivalent IgG1 Fc agent termed anti-CTLA-4 SIFbody with the purpose of enhancing binding to Fc gamma receptors (FcγRs) and complement and increasing Fc-mediated elimination of intratumoral Tregs. Data from avidity binding to low affinity FcγRs showed more than 100-fold increase with anti-CTLA-4 SIFbody as compared to ipilimumab. In in vitro functional assays using CTLA-4 transfected target cells and primary human effector cells, anti-CTLA-4 SIFbody showed more than 10-fold increase in potency in ADCC and more than 5-fold increase in ADCP as compared to ipilimumab. Anti-CTLA-4 SIFbody induced 80% cell lysis by CDC, whereas ipilimumab failed to show any activity. More importantly, we generated in vitro expanded Tregs with suppressive function and showed that anti-CTLA-4 SIFbody induced significant enhanced ADCC on these cells as compared to ipilimumab and to an afucosylated anti-CTLA-4 mAb. ADCP was also significantly increased on Tregs. Unexpectedly, Tregs were resistant to anti-CTLA-4 SIFbody induced CDC. Notably, the blocking activity of the SIFbody F(ab)s was not altered by the multivalent Fc structure as shown by similar CTLA-4/CD80 and CD86 blockade and induction of IL-2 production upon antigen stimulation of PBMC. In conclusion, these data demonstrate that our Fc multimerization technology applied to an anti-CTLA-4 mAb significantly improves Fc-dependent immune-mediated cytotoxicity and suggest that anti-CTLA-4 SIFbody may represent an optimized novel product to deplete intratumoral Tregs and enhance anti-tumor activity.

Citation Format: Laura Rutitzky, Daniel F. Ortiz, Jonathan C. Lansing, Julia Brown, Joseph Paquette, Kevin Garofalo, Josephine D'Alessandro, Naveen Bhatnagar, Maurice Hains, Abhinav Gupta, Stan Lee, Radouane Zouaoui, Jason Wang, John Schaeck, Salvatore Marchese, Robin Meccariello, Nathaniel Washburn, Kimberly Holte, Carlos J. Bosques, Anthony M. Manning. Improved Fc-mediated effector functions by an anti-CTLA-4 multivalent Fc agent [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3244.

Abstract 561: Discovery of a potential best-in-class anti-CD38 therapeutic utilizing Fc multimerization

CD38 targeting antibodies are at different phases of clinical development, with daratumumab already approved as monotherapy and in combination with standards of care in multiple myeloma (MM). Anti-CD38 monoclonal antibodies (mAbs) induce tumor cell depletion in part by Fc-dependent effector mechanisms such as antibody dependent cellular cytotoxicity (ADCC), antibody dependent cellular phagocytosis (ADCP), and complement dependent cytotoxicity (CDC). However, not all MM patients achieve minimal residual disease (MRD)-negativity and similar clinical response. In addition, some patients on daratumumab develop resistance due to reduced cell surface CD38 and high levels of complement inhibitors (CD55 and CD59). We have leveraged Fc multimerization technology (Ortiz et al Sci Transl Med. 2016; 8: 365) to generate an optimized platform (SIF; selective immunomodulator of Fc receptors) that utilizes the valency effect of Fc multimerization to enhance binding to the Fcγ receptors and complement. We combined the Fab-region of CD38 targeting mAb to SIF platform to generate an anti-CD38 SIFbody to enhance immune and complement mediated cytotoxicity against tumor cells. In several human tumor cell line-based cytotoxic assays using primary human effector cells (NK cells and macrophages) and complement, the anti-CD38 SIFbody demonstrates up to 10-fold increase in efficacy and ≥16-fold increase in potency compared to daratumumab and the surrogate therapeutic anti-CD38 mAb (TAK-079). In isolated whole human blood incubated with tumor cells, the anti-CD38 SIFbody demonstrated 40-100 fold increase in potency and 2-3 fold increase in efficacy. In bone marrow cells isolated from MM patients with >80% plasma cells anti-CD38 SIFbody showed better potency and a 3-5 fold increased efficacy (with 100% plasma cell elimination) than daratumumab, suggesting the SIFbody may be more suitable molecule for achieving greater MRD-negativity rates in MM patients. Daratumumab fails to induce CDC against tumor cell lines with low CD38 and high CD55 and CD59, however the SIFbody achieves 100% efficacy in such settings, suggesting this molecule may be effective in patients who are developing resistance to treatment. In single dose pharmacodynamic and tolerability studies in cynomolgus monkeys SIFbody demonstrated up to 5-fold increase in B cell depletion from peripheral blood compared to TAK-079 across all dose ranges (0.3, 1, & 3 mg/kg) tested without any adverse events. Therefore, by leveraging our Fc multimerization technology we have generated a differentiated potential best-in-class anti-CD38 therapeutic.

Citation Format: Amit Choudhury, Daniel F. Ortiz, Shannon Argueta, Kevin Garofalo, Jonathan C. Lansing, Utsav Jetley, Danice Wilkins, Carlos Bosques, Edward Cochran, Naveen Bhatnagar, Jay Duffner, Abhinav Gupta, Stan Lee, Karunya Srinivasan, Viraj Parge, Radouane Zouaoui, Jason Wang, Anthony M. Manning. Discovery of a potential best-in-class anti-CD38 therapeutic utilizing Fc multimerization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 561.

Elucidating the interplay between IgG-Fc valency and FcγR activation for the design of immune complex inhibitors

Autoantibody immune complex (IC) activation of Fcγ receptors (FcγRs) is a common pathogenic hallmark of multiple autoimmune diseases. Given that the IC structural features that elicit FcγR activation are poorly understood and the FcγR system is highly complex, few therapeutics can directly block these processes without inadvertently activating the FcγR system. To address these issues, the structure activity relationships of an engineered panel of multivalent Fc constructs were evaluated using sensitive FcγR binding and signaling cellular assays. These studies identified an Fc valency with avid binding to FcγRs but without activation of immune cell effector functions. These observations directed the design of a potent trivalent immunoglobulin G-Fc molecule that broadly inhibited IC-driven processes in a variety of immune cells expressing FcγRs. The Fc trimer, Fc3Y, was highly efficacious in three different animal models of autoimmune diseases. This recombinant molecule may represent an effective therapeutic candidate for FcγR-mediated autoimmune diseases.

Development of Glatopa® (Glatiramer Acetate): The First FDA-Approved Generic Disease-Modifying Therapy for Relapsing Forms of Multiple Sclerosis

The multiple sclerosis (MS) treatment landscape in the United States has changed dramatically over the past decade. While many disease-modifying therapies (DMTs) have been approved by the US Food and Drug Administration (FDA) for the treatment of relapsing forms of MS, DMT costs continue to rise. The availability of generics and biosimilars in the MS-treatment landscape is unlikely to have a major impact on clinical benefit. However, their availability will provide alternative treatment options and potentially lower costs through competition, thus increasing the affordability of and access to these drugs. In April 2015, the first generic version of the complex drug glatiramer acetate (Glatopa® 20 mg/mL) injection was approved in the United States as a fully substitutable generic for all approved indications of the 20 mg/mL branded glatiramer acetate (Copaxone®) dosage form. Despite glatiramer acetate's complex nature-being a chemically synthesized (ie, nonbiologic) mixture of peptides-the approval occurred without conducting any clinical trials. Rather, extensive structural and functional characterization was performed to demonstrate therapeutic equivalence to the innovator drug. The approval of Glatopa signifies an important milestone in the US MS-treatment landscape, with the hope that the introduction of generic DMTs and eventually biosimilar DMTs will lead to future improvements in the affordability and access of these much-needed treatments for MS.

Development of Glatopa® (Glatiramer Acetate): The First FDA-Approved Generic Disease-Modifying Therapy for Relapsing Forms of Multiple Sclerosis

The multiple sclerosis (MS) treatment landscape in the United States has changed dramatically over the past decade. While many disease-modifying therapies (DMTs) have been approved by the US Food and Drug Administration (FDA) for the treatment of relapsing forms of MS, DMT costs continue to rise. The availability of generics and biosimilars in the MS-treatment landscape is unlikely to have a major impact on clinical benefit. However, their availability will provide alternative treatment options and potentially lower costs through competition, thus increasing the affordability of and access to these drugs. In April 2015, the first generic version of the complex drug glatiramer acetate (Glatopa® 20 mg/mL) injection was approved in the United States as a fully substitutable generic for all approved indications of the 20 mg/mL branded glatiramer acetate (Copaxone®) dosage form. Despite glatiramer acetate's complex nature-being a chemically synthesized (ie, nonbiologic) mixture of peptides-the approval occurred without conducting any clinical trials. Rather, extensive structural and functional characterization was performed to demonstrate therapeutic equivalence to the innovator drug. The approval of Glatopa signifies an important milestone in the US MS-treatment landscape, with the hope that the introduction of generic DMTs and eventually biosimilar DMTs will lead to future improvements in the affordability and access of these much-needed treatments for MS.

High-resolution physicochemical characterization of different intravenous immunoglobulin products

Intravenous immunoglobulin (IVIg) is a complex mixture drug comprising diverse immunoglobulins and non-IgG proteins purified from the plasma of thousands of healthy donors. Approved IVIg products on the market differ regarding source of plasma, isolation process, and formulation. These products are used widely, and often interchangeably, for the treatment of immunodeficiency and autoimmune and inflammatory diseases, but their mechanisms of action in different indications are not well understood. A primary limitation to understanding the therapeutic relevance of specific components within IVIg has been the limited resolution of analytics historically implemented to characterize its complex mixture. In this study, high-resolution analytics were applied to better understand the composition of IVIg and product variations. We characterized three approved IVIg products: Gammagard®, Privigen®, and Octagam®. Differences in the distribution of molecular weight species, IgG sequence variants, isoforms, glycoforms, and the repertoire of previously reported antibody specificities were identified. We also compared the effect of aging on these products to identify changes in size distribution and posttranslational modifications. This type of characterization may provide insights into the specific factors and components of IVIg that may influence its activity and ultimately lead to optimization of IVIg products for use in autoimmune diseases.

Fast and accurate fitting of relaxation dispersion data using the flexible software package GLOVE

Relaxation dispersion spectroscopy is one of the most widely used techniques for the analysis of protein dynamics. To obtain a detailed understanding of the protein function from the view point of dynamics, it is essential to fit relaxation dispersion data accurately. The grid search method is commonly used for relaxation dispersion curve fits, but it does not always find the global minimum that provides the best-fit parameter set. Also, the fitting quality does not always improve with increase of the grid size although the computational time becomes longer. This is because relaxation dispersion curve fitting suffers from a local minimum problem, which is a general problem in non-linear least squares curve fitting. Therefore, in order to fit relaxation dispersion data rapidly and accurately, we developed a new fitting program called GLOVE that minimizes global and local parameters alternately, and incorporates a Monte-Carlo minimization method that enables fitting parameters to pass through local minima with low computational cost. GLOVE also implements a random search method, which sets up initial parameter values randomly within user-defined ranges. We demonstrate here that the combined use of the three methods can find the global minimum more rapidly and more accurately than grid search alone.

Contaminated heparin associated with adverse clinical events and activation of the contact system

BACKGROUND

There is an urgent need to determine whether oversulfated chondroitin sulfate (OSCS), a compound contaminating heparin supplies worldwide, is the cause of the severe anaphylactoid reactions that have occurred after intravenous heparin administration in the United States and Germany.

METHODS

Heparin procured from the Food and Drug Administration, consisting of suspect lots of heparin associated with the clinical events as well as control lots of heparin, were screened in a blinded fashion both for the presence of OSCS and for any biologic activity that could potentially link the contaminant to the observed clinical adverse events. In vitro assays for the activation of the contact system and the complement cascade were performed. In addition, the ability of OSCS to recapitulate key clinical manifestations in vivo was tested in swine.

RESULTS

The OSCS found in contaminated lots of unfractionated heparin, as well as a synthetically generated OSCS reference standard, directly activated the kinin-kallikrein pathway in human plasma, which can lead to the generation of bradykinin, a potent vasoactive mediator. In addition, OSCS induced generation of C3a and C5a, potent anaphylatoxins derived from complement proteins. Activation of these two pathways was unexpectedly linked and dependent on fluid-phase activation of factor XII. Screening of plasma samples from various species indicated that swine and humans are sensitive to the effects of OSCS in a similar manner. OSCS-containing heparin and synthetically derived OSCS induced hypotension associated with kallikrein activation when administered by intravenous infusion in swine.

CONCLUSIONS

Our results provide a scientific rationale for a potential biologic link between the presence of OSCS in suspect lots of heparin and the observed clinical adverse events. An assay to assess the amidolytic activity of kallikrein can supplement analytic tests to protect the heparin supply chain by screening for OSCS and other highly sulfated polysaccharide contaminants of heparin that can activate the contact system.

Oversulfated chondroitin sulfate is a contaminant in heparin associated with adverse clinical events

Recently, certain lots of heparin have been associated with an acute, rapid onset of serious side effects indicative of an allergic-type reaction. To identify potential causes for this sudden rise in side effects, we examined lots of heparin that correlated with adverse events using orthogonal high-resolution analytical techniques. Through detailed structural analysis, the contaminant was found to contain a disaccharide repeat unit of glucuronic acid linked beta1-->3 to a beta-N-acetylgalactosamine. The disaccharide unit has an unusual sulfation pattern and is sulfated at the 2-O and 3-O positions of the glucuronic acid as well as at the 4-O and 6-O positions of the galactosamine. Given the nature of this contaminant, traditional screening tests cannot differentiate between affected and unaffected lots. Our analysis suggests effective screening methods that can be used to determine whether or not heparin lots contain the contaminant reported here.

Defining the role of active-site loop fluctuations in dihydrofolate reductase catalysis

Dynamic processes are implicit in the catalytic function of all enzymes. To obtain insights into the relationship between the dynamics and thermodynamics of protein fluctuations and catalysis, we have measured millisecond time scale motions in the enzyme dihydrofolate reductase using NMR relaxation methods. Studies of a ternary complex formed from the substrate analog folate and oxidized NADP+ cofactor revealed conformational exchange between a ground state, in which the active site loops adopt a closed conformation, and a weakly populated (4.2% at 30 degrees C) excited state with the loops in the occluded conformation. Fluctuations between these states, which involve motions of the nicotinamide ring of the cofactor into and out of the active site, occur on a time scale that is directly relevant to the structural transitions involved in progression through the catalytic cycle.

High-Frequency Dynamic Nuclear Polarization in MAS Spectra of Membrane and Soluble Proteins

One of the principal promises of solid-state NMR (SSNMR) magic angle spinning (MAS) experiments has been the possibility of determining the structures of molecules in states that are not accessible via X-ray or solution NMR experiments-e.g., membrane or amyloid proteins. However, the low sensitivity of SSNMR often restricts structural studies to small-model compounds and precludes many higher-dimensional solid-state MAS experiments on such systems. To address the sensitivity problem, we have developed experiments that utilize dynamic nuclear polarization (DNP) to enhance sensitivity. In this communication, we report the successful application of MAS DNP to samples of cryoprotected soluble and membrane proteins. In particular, we have observed DNP signal enhancements of up to 50 in 15N MAS spectra of bacteriorhodopsin (bR) and alpha-lytic protease (alpha-LP). The spectra were recorded at approximately 90 K where MAS is experimentally straightforward, and the results suggest that the described protocol will be widely applicable.

Solid-state NMR investigation of the buried X-proline peptide bonds of bacteriorhodopsin

The role of proline residues in the photocycle of bacteriorhodopsin (bR) is addressed using solid-state NMR. (13)C and (15)N chemical shifts from X-Pro peptide bonds in bR are assigned from REDOR difference spectra of pairwise labeled samples, and correlations of chemical shifts with structure are explored in a series of X-Pro model compounds. Results for the three membrane-embedded X-Pro bonds of bR indicate only slight changes in the transition from the resting state of the protein to either the early or late M state of the protonmotive photocycle. These results suggest that the buried prolines serve a principally structural role in bR.

Magnetic resonance studies of the bacteriorhodopsin pump cycle

Active transport requires the alternation of substrate uptake and release with a switch in the access of the substrate binding site to the two sides of the membrane. Both the transfer and switch aspects of the photocycle have been subjects of magnetic resonance studies in bacteriorhodopsin. The results for ion transfer indicate that the Schiff base of the chromophore is hydrogen bonded before, during, and after its deprotonation. This suggests that the initial complex counterion of the Schiff base decomposes in such a way that the Schiff base carries its immediate hydrogen-bonding partner with it as it rotates during the first half of the photocycle. If so, bacteriorhodopsin acts as an inward-directed hydroxide pump rather than as an outward-directed proton pump. The studies of the access switch explore both protein-based and chromophore-based mechanisms. Combined with evidence from functional studies of mutants and other forms of spectroscopy, the results suggest that maintaining access to the extracellular side of the protein after photoisomerization involves twisting of the chromophore and that the decisive switch in access to the cytoplasmic side results from relaxation of the chromophore when the constraints on the Schiff base are released by decomposition of the complex counterion.

Chromophore distortions in the bacteriorhodopsin photocycle: evolution of the H-C14-C15-H dihedral angle measured by solid-state NMR

In recent years, structural information about bacteriorhodopsin has grown substantially with the publication of several crystal structures. However, precise measurements of the chromophore conformation in the various photocycle states are still lacking. This information is critical because twists about the chromophore backbone chain can influence the Schiff base nitrogen position, orientation, and proton affinity. Here, we focus on the C14-C15 bond, using solid-state nuclear magnetic resonance spectroscopy to measure the H-C14-C15-H dihedral angle. In the resting state (bR(568)), we obtain an angle of 164 +/- 4 degrees, indicating a 16 degrees distortion from a planar all-trans chromophore. The dihedral angle is found to decrease to 147 +/- 10 degrees in the early M intermediate (M(o)) and to 150 +/- 4 degrees in the late M intermediate (M(n)). These results demonstrate changes in the chromophore conformation undetected by recent X-ray diffraction studies.

Early and late M intermediates in the bacteriorhodopsin photocycle: a solid-state NMR study

To enforce vectorial proton transport in bacteriorhodopsin (bR), it is necessary that there be a change in molecular structure between deprotonation and reprotonation of the chromophore-i.e., there must be at least two different M intermediates in the functional photocycle. We present here the first detection of multiple M intermediates in native wild-type bacteriorhodopsin by solid-state NMR. Illumination of light-adapted [zeta-15N-Lys]-bR at low temperatures shifts the 15N signal of the retinal Schiff base (SB) downfield by about 150 ppm, indicating a deprotonated chromophore. In 0.3 M Gdn-HCl at pH 10.0, two different M states are obtained, depending on the temperature during illumination. The M state routinely prepared at the lower temperature, Mo, decays to the newly observed M state, Mn, and the N intermediate, as the temperature is increased. Both relax to bR568 at 0 degreesC. A unique reaction sequence is derived: bR568-->Mo-->(Mn+N)-->bR568. Mo and Mn have similar chemical shifts at [12-13C]ret, [14-13C]ret, and [epsilon-13C]Lys216, indicating that Mn, like Mo, has a 13-cis and C=N anti chromophore. However, a small splitting in the [14-13C]ret signal of Mo reveals that it has at least two substates. The 7 ppm greater shielding of the SB nitrogen in Mn compared to Mo suggests an increase in basicity and/or hydrogen bonding. Probing the peptide backbone of the protein, via [1-13C]Val labeling, reveals a substantial structural change between Mo and Mn including the relaxation of perturbations at some sites and the development of new perturbations at other sites. The combination of the change in the protein structure and the increase in the pKa of the SB suggests that the demonstrated Mo-->Mn transition may function as the "reprotonation switch" required for vectorial proton transport.