Preclinical Evaluation of IMGC936, a Next-Generation Maytansinoid-based Antibody-drug Conjugate Targeting ADAM9-expressing Tumors.

ADAM metallopeptidase domain 9 (ADAM9) is a member of the ADAM family of multifunctional, multidomain type 1 transmembrane proteins. ADAM9 is overexpressed in many cancers, including non-small cell lung, pancreatic, gastric, breast, ovarian, and colorectal cancer, but exhibits limited expression in normal tissues. A target-unbiased discovery platform based on intact tumor and progenitor cell immunizations, followed by an IHC screen, led to the identification of anti-ADAM9 antibodies with selective tumor-versus-normal tissue binding. Subsequent analysis revealed anti-ADAM9 antibodies were efficiently internalized and processed by tumor cells making ADAM9 an attractive target for antibody-drug conjugate (ADC) development. Here, we describe the preclinical evaluation of IMGC936, a novel ADC targeted against ADAM9. IMGC936 is comprised of a high-affinity humanized antibody site-specifically conjugated to DM21-C, a next-generation linker-payload that combines a maytansinoid microtubule-disrupting payload with a stable tripeptide linker, at a drug antibody ratio of approximately 2.0. In addition, the YTE mutation (M252Y/S254T/T256E) was introduced into the CH2 domain of the antibody Fc to maximize in vivo plasma half-life and exposure. IMGC936 exhibited cytotoxicity toward ADAM9-positive human tumor cell lines, as well as bystander killing, potent antitumor activity in human cell line-derived xenograft and patient-derived xenograft tumor models, and an acceptable safety profile in cynomolgus monkeys with favorable pharmacokinetic properties. Our preclinical data provide a strong scientific rationale for the further development of IMGC936 as a therapeutic candidate for the treatment of ADAM9-positive cancers. A first-in-human study of IMGC936 in patients with advanced solid tumors has been initiated (NCT04622774).

Preclinical Development of MGC018, a Duocarmycin-based Antibody-drug Conjugate Targeting B7-H3 for Solid Cancer.

B7-H3, also referred to as CD276, is a member of the B7 family of immune regulatory proteins. B7-H3 is overexpressed on many solid cancers, including prostate cancer, renal cell carcinoma, melanoma, squamous cell carcinoma of the head and neck, non-small cell lung cancer, and breast cancer. Overexpression of B7-H3 is associated with disease severity, risk of recurrence and reduced survival. In this article, we report the preclinical development of MGC018, an antibody-drug conjugate targeted against B7-H3. MGC018 is comprised of the cleavable linker-duocarmycin payload, valine-citrulline-seco duocarmycin hydroxybenzamide azaindole (vc-seco-DUBA), conjugated to an anti-B7-H3 humanized IgG1/kappa mAb through reduced interchain disulfides, with an average drug-to-antibody ratio of approximately 2.7. MGC018 exhibited cytotoxicity toward B7-H3-positive human tumor cell lines, and exhibited bystander killing of target-negative tumor cells when cocultured with B7-H3-positive tumor cells. MGC018 displayed potent antitumor activity in preclinical tumor models of breast, ovarian, and lung cancer, as well as melanoma. In addition, antitumor activity was observed toward patient-derived xenograft models of breast, prostate, and head and neck cancer displaying heterogeneous expression of B7-H3. Importantly, MGC018 exhibited a favorable pharmacokinetic and safety profile in cynomolgus monkeys following repeat-dose administration. The antitumor activity observed preclinically with MGC018, together with the positive safety profile, provides evidence of a potentially favorable therapeutic index and supports the continued development of MGC018 for the treatment of solid cancers. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/11/2235/F1.large.jpg.

Multispecific, Multivalent Antibody-Based Molecules Engineered on the DART® and TRIDENTTM Platforms.

Multispecific antibodies bind two or more different antigens and enable new therapeutic applications that cannot be replicated with conventional monoclonal antibodies, such as bridging different cells or bringing soluble proteins in close proximity. The DART and TRIDENT platforms enable the engineering of such antibodies. A DART molecule combines two independent antigen-binding sites in a stabilized, diabody-like structure. A DART molecule can be expressed with or without an Fc domain and thus can be tailored to have a long or short half-life in vivo and to induce or ablate effector function. Linking two DART units or a DART unit and a Fab domain (the latter structure is called TRIDENT format) via an Fc domain creates a monospecific, bispecific, trispecific, or tetraspecific molecule with up to tetravalent targeting of antigens. This article focuses on the design of DART and TRIDENT molecules that target two or three different antigens. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Design and generation of expression plasmids encoding DART and TRIDENT molecules Basic Protocol 2: Expression of DART and TRIDENT molecules by transient transfection of CHO cells Basic Protocol 3: Purification of DART and TRIDENT molecules from CHO cell supernatants.

Development of MGD007, a gpA33 x CD3-Bispecific DART Protein for T-Cell Immunotherapy of Metastatic Colorectal Cancer.

We have developed MGD007 (anti-glycoprotein A33 x anti-CD3), a DART protein designed to redirect T cells to target gpA33 expressing colon cancer. The gpA33 target was selected on the basis of an antibody-based screen to identify cancer antigens universally expressed in both primary and metastatic colorectal cancer specimens, including putative cancer stem cell populations. MGD007 displays the anticipated-bispecific binding properties and mediates potent lysis of gpA33-positive cancer cell lines, including models of colorectal cancer stem cells, through recruitment of T cells. Xenograft studies showed tumor growth inhibition at doses as low as 4 µg/kg. Both CD8 and CD4 T cells mediated lysis of gpA33-expressing tumor cells, with activity accompanied by increases in granzyme and perforin. Notably, suppressive T-cell populations could also be leveraged to mediate lysis of gpA33-expressing tumor cells. Concomitant with CTL activity, both T-cell activation and expansion are observed in a gpA33-dependent manner. No cytokine activation was observed with human PBMC alone, consistent with the absence of gpA33 expression on peripheral blood cell populations. Following prolonged exposure to MGD007 and gpA33 positive tumor cells, T cells express PD-1 and LAG-3 and acquire a memory phenotype but retain ability to support potent cell killing. In cynomolgus monkeys, 4 weekly doses of 100 µg/kg were well tolerated, with prolonged PK consistent with that of an Fc-containing molecule. Taken together, MGD007 displays potent activity against colorectal cancer cells consistent with a mechanism of action endowed in its design and support further investigation of MGD007 as a potential novel therapeutic treatment for colorectal cancer. Mol Cancer Ther; 17(8); 1761-72. ©2018 AACR.

A CD3xCD123 bispecific DART for redirecting host T cells to myelogenous leukemia: preclinical activity and safety in nonhuman primates.

Current therapies for acute myeloid leukemia (AML) are largely ineffective, and AML patients may benefit from targeted immunotherapy approaches. MGD006 is a bispecific CD3xCD123 dual-affinity re-targeting (DART) molecule that binds T lymphocytes and cells expressing CD123, an antigen up-regulated in several hematological malignancies including AML. MGD006 mediates blast killing in AML samples, together with concomitant activation and expansion of residual T cells. MGD006 is designed to be rapidly cleared, and therefore requires continuous delivery. In a mouse model of continuous administration, MGD006 eliminated engrafted KG-1a cells (an AML-M0 line) in human PBMC (peripheral blood mononuclear cell)-reconstituted NSG/ß2m(-/-) mice at doses as low as 0.5 µg/kg per day for ~7 days. MGD006 binds to human and cynomolgus monkey antigens with similar affinities and redirects T cells from either species to kill CD123-expressing target cells. MGD006 was well tolerated in monkeys continuously infused with 0.1 µg/kg per day escalated weekly to up to 1 µg/kg per day during a 4-week period. Depletion of circulating CD123-positive cells was observed as early as 72 hours after treatment initiation and persisted throughout the infusion period. Cytokine release, observed after the first infusion, was reduced after subsequent administrations, even when the dose was escalated. T cells from animals with prolonged in vivo exposure exhibited unperturbed target cell lysis ex vivo, indicating no exhaustion. A transient decrease in red cell mass was observed, with no neutropenia or thrombocytopenia. These studies support clinical testing of MGD006 in hematological malignancies, including AML.

Development of an Fc-enhanced anti-B7-H3 monoclonal antibody with potent antitumor activity.

PURPOSE: The goal of this research was to harness a monoclonal antibody (mAb) discovery platform to identify cell-surface antigens highly expressed on cancer and develop, through Fc optimization, potent mAb therapies toward these tumor-specific antigens. EXPERIMENTAL DESIGN: Fifty independent mAbs targeting the cell-surface immunoregulatory B7-H3 protein were obtained through independent intact cell-based immunizations using human tissue progenitor cells, cancer cell lines, or cell lines displaying cancer stem cell properties. Binding studies revealed this natively reactive B7-H3 mAb panel to bind a range of independent B7-H3 epitopes. Immunohistochemical analyses showed that a subset displayed strong reactivity to a broad range of human cancers while exhibiting limited binding to normal human tissues. A B7-H3 mAb displaying exquisite tumor/normal differential binding was selected for humanization and incorporation of an Fc domain modified to enhance effector-mediated antitumor function via increased affinity for the activating receptor CD16A and decreased binding to the inhibitory receptor CD32B. RESULTS: MGA271, the resulting engineered anti-B7-H3 mAb, mediates potent antibody-dependent cellular cytotoxicity against a broad range of tumor cell types. Furthermore, in human CD16A-bearing transgenic mice, MGA271 exhibited potent antitumor activity in B7-H3-expressing xenograft models of renal cell and bladder carcinoma. Toxicology studies carried out in cynomolgus monkeys revealed no significant test article-related safety findings. CONCLUSIONS: This data supports evaluation of MGA271 clinical utility in B7-H3-expressing cancer, while validating a combination of a nontarget biased approach of intact cell immunizations and immunohistochemistry to identify novel cancer antigens with Fc-based mAb engineering to enable potent antitumor activity.

Anti-tumor activity and toxicokinetics analysis of MGAH22, an anti-HER2 monoclonal antibody with enhanced Fcγ receptor binding properties.

INTRODUCTION: Response to trastuzumab in metastatic breast cancer correlates with expression of the high binding variant (158V) of the activating Fcγ receptor IIIA (CD16A). We engineered MGAH22, a chimeric anti-HER2 monoclonal antibody with specificity and affinity similar to trastuzumab, with an Fc domain engineered for increased binding to both alleles of human CD16A. METHODS: MGAH22 was compared to an identical anti-HER2 mAb except for a wild type Fc domain. Antibody-dependent cell cytotoxicity (ADCC) assays were performed with HER2-expressing cancer cells as targets and human PBMC or purified NK cells as effectors. Xenograft studies were conducted in mice with wild type murine FcγRs; in mice lacking murine CD16; or in mice lacking murine CD16 but transgenic for human CD16A-158F, the low-binding variant. The latter model reproduces the differential binding between wild type and the Fc-optimized mAb for human CD16A. The JIMT-1 human breast tumor line, derived from a patient that progressed on trastuzumab therapy, was used in these studies. Single and repeat dose toxicology studies with MGAH22 administered intravenously at high dose were conducted in cynomolgus monkeys. RESULTS: The optimized Fc domain confers enhanced ADCC against all HER2-positive tumor cells tested, including cells resistant to trastuzumab's anti-proliferative activity or expressing low HER2 levels. The greatest improvement occurs with effector cells isolated from donors homozygous or heterozygous for CD16A-158F, the low-binding allele. MGAH22 demonstrates increased activity against HER2-expressing tumors in mice transgenic for human CD16A-158F. In single and repeat-dose toxicology studies in cynomolgus monkeys, a species with a HER2 expression pattern comparable to that in humans and Fcγ receptors that exhibit enhanced binding to the optimized Fc domain, MGAH22 was well tolerated at all doses tested (15-150 mg/kg) and exhibited pharmacokinetic parameters similar to that of other anti-HER2 antibodies. Induction of cytokine release by MGAH22 in vivo or in vitro was similar to that induced by the corresponding wild type mAb or trastuzumab. CONCLUSIONS: The data support the clinical development of MGAH22, which may have utility in patients with low HER2 expressing tumors or carrying the CD16A low-binding allele.

Application of dual affinity retargeting molecules to achieve optimal redirected T-cell killing of B-cell lymphoma.

We describe the application of a novel, bispecific antibody platform termed dual affinity retargeting (DART) to eradicate B-cell lymphoma through coengagement of the B cell-specific antigen CD19 and the TCR/CD3 complex on effector T cells. Comparison with a single-chain, bispecific antibody bearing identical CD19 and CD3 antibody Fv sequences revealed DART molecules to be more potent in directing B-cell lysis. The enhanced activity with the CD19xCD3 DART molecules was observed on all CD19-expressing target B cells evaluated using resting and prestimulated human PBMCs or purified effector T-cell populations. Characterization of a CD19xTCR bispecific DART molecule revealed equivalent potency with the CD19xCD3 DART molecule, demonstrating flexibility of the DART structure to support T-cell/B-cell associations for redirected T cell-killing applications. The enhanced level of killing mediated by DART molecules was not accompanied by any increase in nonspecific T-cell activation or lysis of CD19(-) cells. Cell-association studies indicated that the DART architecture is well suited for maintaining cell-to-cell contact, apparently contributing to the high level of target cell killing. Finally, the ability of the CD19xTCR DART to inhibit B-cell lymphoma in NOD/SCID mice when coadministered with human PBMCs supports further evaluation of DART molecules for the treatment of B-cell malignancies.

Therapeutic control of B cell activation via recruitment of Fcgamma receptor IIb (CD32B) inhibitory function with a novel bispecific antibody scaffold.

OBJECTIVE: To exploit the physiologic Fcgamma receptor IIb (CD32B) inhibitory coupling mechanism to control B cell activation by constructing a novel bispecific diabody scaffold, termed a dual-affinity retargeting (DART) molecule, for therapeutic applications. METHODS: DART molecules were constructed by pairing an Fv region from a monoclonal antibody (mAb) directed against CD32B with an Fv region from a mAb directed against CD79B, the beta-chain of the invariant signal-transducing dimer of the B cell receptor complex. DART molecules were characterized physicochemically and for their ability to simultaneously bind the target receptors in vitro and in intact cells. The ability of the DART molecules to negatively control B cell activation was determined by calcium mobilization, by tyrosine phosphorylation of signaling molecules, and by proliferation and Ig secretion assays. A DART molecule specific for the mouse ortholog of CD32B and CD79B was also constructed and tested for its ability to inhibit B cell proliferation in vitro and to control disease severity in a collagen-induced arthritis (CIA) model. RESULTS: DART molecules were able to specifically bind and coligate their target molecules on the surface of B cells and demonstrated a preferential simultaneous binding to both receptors on the same cell. DART molecules triggered the CD32B-mediated inhibitory signaling pathway in activated B cells, which translated into inhibition of B cell proliferation and Ig secretion. A DART molecule directed against the mouse orthologs was effective in inhibiting the development of CIA in DBA/1 mice. CONCLUSION: This innovative bispecific antibody scaffold that simultaneously engages activating and inhibitory receptors enables novel therapeutic approaches for the treatment of rheumatoid arthritis and potentially other autoimmune and inflammatory diseases in humans.

Effector cell recruitment with novel Fv-based dual-affinity re-targeting protein leads to potent tumor cytolysis and in vivo B-cell depletion.

Bispecific antibodies capable of redirecting the lytic potential of immune effector cells to kill tumor targets have long been recognized as a potentially potent biological therapeutic intervention. Unfortunately, efforts to produce such molecules have been limited owing to inefficient production and poor stability properties. Here, we describe a novel Fv-derived strategy based on a covalently linked bispecific diabody structure that we term dual-affinity re-targeting (DART). As a model system, we linked an Fv specific for human CD16 (FcgammaRIII) on effector cells to an Fv specific for mouse or human CD32B (FcgammaRIIB), a normal B-cell and tumor target antigen. DART proteins were produced at high levels in mammalian cells, retained the binding activity of the respective parental Fv domains as well as bispecific binding, and showed extended storage and serum stability. Functionally, the DART molecules demonstrated extremely potent, dose-dependent cytotoxicity in retargeting human PBMC against B-lymphoma cell lines as well as in mediating autologous B-cell depletion in culture. In vivo studies in mice demonstrated effective B-cell depletion that was dependent on the transgenic expression of both CD16A on the effector cells and CD32B on the B-cell targets. Furthermore, DART proteins showed potent in vivo protective activity in a human Burkitt's lymphoma cell xenograft model. Thus, DART represents a biologically potent format that provides a versatile platform for generating bispecific antibody fragments for redirected killing and, with the selection of appropriate binding partners, applications outside of tumor cell cytotoxicity.

Transfection of cultured eukaryotic cells using cationic lipid reagents.

The development of high-efficiency methods for the introduction of functional genetic material into eukaryotic cells using cationic lipids has accelerated biological research in the studies of gene expression, control of cell growth, and cell lineage. Transfection mediated by cationic lipids is commonly used in industrial protein production as well as in some clinical gene therapy protocols. This unit describes how to perform transfection of adherent and suspension cells, insect cells, and RNA transfection using cationic lipid reagents.

Optimization of tetracycline-responsive recombinant protein production and effect on cell growth and ER stress in mammalian cells.

The inducible T-REx system and other inducible expression systems have been developed in order to control the expression levels of recombinant protein in mammalian cells. In order to study the effects of heterologous protein expression on mammalian host behavior, the gene for recombinant Human transferrin (hTf) was integrated into HEK-293 cells and expressed under the control of the T-REx inducible technology (293-TetR-Hyg-hTf) or using a constitutive promoter (293-CMV-hTf). A number of inducible clones with variable expression levels were identified for the T-REx system with levels of hTf for the high expressing clones nearly double those obtained using the constitutive cytomegalovirus (CMV) promoter. The level of transferrin produced was found to increase proportionately with tetracycline concentration between 0 and 1 mug/mL with no significant increases in transferrin production above 1 mug/mL. As a result, the optimal induction time and tetracycline concentrations were determined to be the day of plating and 1 mug/mL, respectively. Interestingly, the cells induced to express transferrin, 293-TetR-Hyg-hTf, exhibited lower viable cell densities and percent viabilities than the uninduced cultures for multiple clonal isolates. In addition, the induction of transferrin expression was found to cause an increase in the expression of the ER-stress gene, BiP, that was not observed in the uninduced cells. However, both uninduced and induced cell lines containing the hTf gene exhibited longer survival in culture than the control cells, possibly as a result of the positive effects of hTf on cell survival. Taken together, these results suggest that the high level expression of complex proteins in mammalian cells can limit the viable cell densities of cells in culture as a result of cellular stresses caused by generating proteins that may be difficult to fold or are otherwise toxic to cells. The application of inducible systems such as the T-REx technology will allow us to optimize protein production while limiting the negative effects that result from these cellular stresses.

Advanced transfection with Lipofectamine 2000 reagent: primary neurons, siRNA, and high-throughput applications.

Lipofectamine 2000 is a cationic liposome based reagent that provides high transfection efficiency and high levels of transgene expression in a range of mammalian cell types in vitro using a simple protocol. Optimum transfection efficiency and subsequent cell viability depend on a number of experimental variables such as cell density, liposome and DNA concentrations, liposome-DNA complexing time, and the presence or absence of media components such as antibiotics and serum. The importance of these factors in Lipofectamine 2000 mediated transfection will be discussed together with some specific applications: transfection of primary neurons, high throughput transfection, and delivery of small interfering RNAs.

Transfection of cultured eukaryotic cells using cationic lipid reagents.

The development of high-efficiency methods for the introduction of functional genetic material into eukaryotic cells using cationic lipids has accelerated biological research in the studies of gene expression, control of cell growth, and cell lineage. Transfection mediated by cationic lipids is commonly used in industrial protein production as well as in some clinical gene therapy protocols. Replacing our previous unit on this topic, this new version describes how to perform transfection of adherent and suspension cells, insect cells, and RNA transfection using the cationic lipid system.