Optimizing the design and geometry of T cell engaging bispecific antibodies targeting CEA in colorectal cancer

Metastatic colorectal cancer (mCRC) remains a leading cause of cancer-related deaths, with a 5-year survival rate of only 15%. T cell engaging bispecific antibodies (TCBs) represent a class of biopharmaceuticals that redirect cytotoxic T cells towards tumor cells, thereby turning immunologically "cold" tumors "hot." The carcinoembryonic antigen (CEA) is an attractive tumor-associated antigen (TAA) that is overexpressed in over 98% of CRC patients. In this study, we report the comparison of four different TCB formats employing the antibodies F4 (targeting human CEA) and 2C11 (targeting mouse CD3ε). These formats include both antibody fragment- and IgG-based constructs, with either one or two binding specificities of the respective antibodies. The 2+1 arrangement, using an anti-CEA single-chain diabody (scDbCEA) fused to an anti-CD3 single-chain variable fragment (scFvCD3), emerged as the most potent design, showing tumor killing at subnanomolar concentrations across three different CEA+ cell lines. The in vitro activity was three times greater in C57BL/6 mouse colon adenocarcinoma cells (MC38) expressing high levels of CEA compared to those expressing low levels, highlighting the impact of CEA antigen density in this assay. The optimal TCB candidate was tested in two different immunocompetent mouse models of colorectal cancer and showed tumor growth retardation. Ex vivo analysis of tumor infiltrates showed an increase in CD4+ and CD8+ T cells upon TCB treatment. This study suggests that bivalent tumor targeting, monovalent T cell targeting, and a short spatial separation are promising characteristics for CEA targeting TCBs.

A novel strategy to generate immunocytokines with activity-on-demand using small molecule inhibitors

Cytokine-based therapeutics have been shown to mediate objective responses in certain tumor entities but suffer from insufficient selectivity, causing limiting toxicity which prevents dose escalation to therapeutically active regimens. The antibody-based delivery of cytokines significantly increases the therapeutic index of the corresponding payload but still suffers from side effects associated with peak concentrations of the product in blood upon intravenous administration. Here we devise a general strategy (named "Intra-Cork") to mask systemic cytokine activity without impacting anti-cancer efficacy. Our technology features the use of antibody-cytokine fusions, capable of selective localization at the neoplastic site, in combination with pathway-selective inhibitors of the cytokine signaling, which rapidly clear from the body. This strategy, exemplified with a tumor-targeted IL12 in combination with a JAK2 inhibitor, allowed to abrogate cytokine-driven toxicity without affecting therapeutic activity in a preclinical model of cancer. This approach is readily applicable in clinical practice.

Ex vivo mass spectrometry-based biodistribution analysis of an antibody-Resiquimod conjugate bearing a protease-cleavable and acid-labile linker

Immune-stimulating antibody conjugates (ISACs) equipped with imidazoquinoline (IMD) payloads can stimulate endogenous immune cells to kill cancer cells, ultimately inducing long-lasting anticancer effects. A novel ISAC was designed, featuring the IMD Resiquimod (R848), a tumor-targeting antibody specific for Carbonic Anhydrase IX (CAIX) and the protease-cleavable Val-Cit-PABC linker. In vitro stability analysis showed not only R848 release in the presence of the protease Cathepsin B but also under acidic conditions. The ex vivo mass spectrometry-based biodistribution data confirmed the low stability of the linker-drug connection while highlighting the selective accumulation of the IgG in tumors and its long circulatory half-life.

Generation of a novel fully human non-superagonistic anti-CD28 antibody with efficient and safe T-cell co-stimulation properties

Antibody-based therapeutics represent an important class of biopharmaceuticals in cancer immunotherapy. CD3 bispecific T-cell engagers activate cytotoxic T-cells and have shown remarkable clinical outcomes against several hematological malignancies. The absence of a costimulatory signal through CD28 typically leads to insufficient T-cell activation and early exhaustion. The combination of CD3 and CD28 targeting products offers an attractive strategy to boost T-cell activity. However, the development of CD28-targeting therapies ceased after TeGenero's Phase 1 trial in 2006 evaluating a superagonistic anti-CD28 antibody (TGN1412) resulted in severe life-threatening side effects. Here, we describe the generation of a novel fully human anti-CD28 antibody termed "E1P2" using phage display technology. E1P2 bound to human and mouse CD28 as shown by flow cytometry on primary human and mouse T-cells. Epitope mapping revealed a conformational binding epitope for E1P2 close to the apex of CD28, similar to its natural ligand and unlike the lateral epitope of TGN1412. E1P2, in contrast to TGN1412, showed no signs of in vitro superagonistic properties on human peripheral blood mononuclear cells (PBMCs) using different healthy donors. Importantly, an in vivo safety study in humanized NSG mice using E1P2, in direct comparison and contrast to TGN1412, did not cause cytokine release syndrome. In an in vitro activity assay using human PBMCs, the combination of E1P2 with CD3 bispecific antibodies enhanced tumor cell killing and T-cell proliferation. Collectively, these data demonstrate the therapeutic potential of E1P2 to improve the activity of T-cell receptor/CD3 activating constructs in targeted immunotherapeutic approaches against cancer or infectious diseases.

Generation and in vivo characterization of a novel high-affinity human antibody targeting carcinoembryonic antigen

There are no effective treatment options for most patients with metastatic colorectal cancer (mCRC). mCRC remains a leading cause of tumor-related death, with a five-year survival rate of only 15%, highlighting the urgent need for novel pharmacological products. Current standard drugs are based on cytotoxic chemotherapy, VEGF inhibitors, EGFR antibodies, and multikinase inhibitors. The antibody-based delivery of pro-inflammatory cytokines provides a promising and differentiated strategy to improve the treatment outcome for mCRC patients. Here, we describe the generation of a novel fully human monoclonal antibody (termed F4) targeting the carcinoembryonic antigen (CEA), a tumor-associated antigen overexpressed in colorectal cancer and other malignancies. The F4 antibody was selected by antibody phage display technology after two rounds of affinity maturation. F4 in single-chain variable fragment format bound to CEA in surface plasmon resonance with an affinity of 7.7 nM. Flow cytometry and immunofluorescence on human cancer specimens confirmed binding to CEA-expressing cells. F4 selectively accumulated in CEA-positive tumors, as evidenced by two orthogonal in vivo biodistribution studies. Encouraged by these results, we genetically fused murine interleukin (IL) 12 to F4 in the single-chain diabody format. F4-IL12 exhibited potent antitumor activity in two murine models of colon cancer. Treatment with F4-IL12 led to an increased density of tumor-infiltrating lymphocytes and an upregulation of interferon γ expression by tumor-homing lymphocytes. These data suggest that the F4 antibody is an attractive delivery vehicle for targeted cancer therapy.

Selection of a PD-1 blocking antibody from a novel fully human phage display library

Programmed cell death protein 1 (PD-1) is an immunoregulatory target which is recognized by different monoclonal antibodies, approved for the therapy of multiple types of cancer. Different anti-PD-1 antibodies display different therapeutic properties and there is a pharmaceutical interest to generate and characterize novel anti-PD-1 antibodies. We screened multiple human antibody phage display libraries to target novel epitopes on the PD-1 surface and we discovered a unique and previously undescribed binding specificity (termed D12) from a new antibody library (termed AMG). The library featured antibody fragments in single-chain fragment variable (scFv) format, based on the IGHV3-23*03 (VH ) and IGKV1-39*01 (Vκ) genes. The D12 antibody was characterized by surface plasmon resonance (SPR), cross-reacted with the Cynomolgus monkey antigen and bound to primary human T cells, as shown by flow cytometry. The antibody blocked the PD-1/PD-L1 interaction in vitro with an EC50 value which was comparable to the one of nivolumab, a clinically approved antibody. The fine details of the interaction between D12 and PD-1 were elucidated by x-ray crystallography of the complex at a 3.5 Å resolution, revealing an unprecedented conformational change at the N-terminus of PD-1 following D12 binding, as well as partial overlap with the binding site for the cognate PD-L1 and PD-L2 ligands which prevents their binding. The results of the study suggest that the expansion of antibody library repertoires may facilitate the discovery of novel binding specificities with unique properties that hold promises for the modulation of PD-1 activity in vitro and in vivo.

Immunotherapy with Immunocytokines and PD-1 Blockade Enhances the Anticancer Activity of Small Molecule-Drug Conjugates Targeting Carbonic Anhydrase IX

Small molecule-drug conjugates (SMDCs) represent an alternative to conventional antitumor chemotherapeutic agents, with the potential to improve the therapeutic window of cytotoxic payloads through active delivery at the site of the disease. In this article, we describe novel combination therapies consisting of anti-carbonic anhydrase IX SMDCs combined with different immunomodulatory products. The therapeutic effect of the SMDCs was potentiated by combination with PD-1 blockade and with tumor-homing antibody-cytokine fusions in mouse models of renal cell carcinoma and colorectal cancer. The combination with L19-IL12, a fusion protein specific to the alternatively spliced EDB domain of fibronectin containing the murine IL12 moiety, was also active against large established tumors. Analysis of the microscopic structures of healthy organs performed 3 months after tumor eradication confirmed absence of pathologic abnormalities in the healthy kidney, liver, lung, stomach, and intestine. Our findings may be of clinical significance as they provide motivation for the development of combinations based on SMDCs and immunotherapy for the treatment of renal cell carcinoma and hypoxic tumors.