Abstract 5625: In vitro and in vivo pharmacology of MEDI-565 (MT111), a novel CEA/CD3-bispecific single-chain BiTE antibody in development for the treatment of gastrointestinal adenocarcinomas

Abstract

MEDI-565 (MT111) is a novel bispecific single-chain antibody of the BiTE (Bispecific T cell engager) class that transiently links carcinoembryonic antigen (CEA) on cancer cells with human CD3 on T cells. MEDI-565 specifically binds to human CEA with an affinity of 8.5 nM but not to any other member of the CEACAM family. In targeted expression studies on cryopreserved and formalin-fixed paraffin-embedded sections, MEDI-565 demonstrated membrane-localized binding specifically to epithelial cells in human cancerous tissues. The highest prevalence of MEDI-565 binding (∼90%) was in adenocarcinomas of gastrointestinal origin. In in vitro killing assays, MEDI-565 recruited T cells via the CD3 antigen (affinity of 310 nM) in a process that required concomitant binding to CEA positive tumor cells for T cell activation. As a consequence, T cells expanded, increased cell surface expression of the activation markers CD69 and CD25, and released perforin and granzymes. The release of cytotoxic granule content led to a Ca2+-dependent activation of pro-caspases and subsequent apoptosis of CEA-expressing tumor cells. Efficient target cell lysis by MEDI-565 was predominantly mediated by CD8+ T cells and occurred within a wide range of effector-to-target ratios (80:1 to 5:1) for T cells derived from various human donors. BiTE mediated killing was not affected by the presence of soluble CEA (≤5 µg/mL). The in vivo activity of MEDI-565 was investigated in subcutaneous xenograft models using immunocompromised SCID mice inoculated with mixtures of human T cells and human cancer cell lines. The antibody was eliminated from the serum with a half-life of a few hours following a single intravenous (IV) or subcutaneous (SC) injection. Despite a relatively short serum half-life, daily IV or SC bolus treatments over 5 days provided sufficient levels of exposure to inhibit the growth of CEA-positive tumors in a dose-dependent manner. Inhibition of growth was observed for tumors of different tissue origins and was dependent on the presence of human T cells and CEA expression by tumor cells. There were no MEDI-565-related in-life observations following treatment. These studies demonstrated that MEDI-565 has potent and selective anti-cancer activity in vitro and in vivo and provides evidence that MEDI-565 may be an effective monotherapy to treat CEA-expressing malignancies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5625.

The CEA/CD3-Bispecific Antibody MEDI-565 (MT111) Binds a Nonlinear Epitope in the Full-Length but Not a Short Splice Variant of CEA

“…Consistent with the MEDI-565 binding data, CHO SV CEA did not trigger the activation of T cells from healthy donors in the presence of MEDI-565, as measured by the up-regulation of the IL-2Ra chain/CD25 protein on either CD8 or CD4 T cells ( Figure 6C and D). This T cell activation marker has been shown previously to correlate temporally with the release of cytokines from T cells activated by MEDI-565 [18] and other BiTE antibodies [23,25]. Likewise MEDI-565 also did not mediate the lysis of target cells expressing the splice variant ( Figure 6B).…”

“…Co-expression of the CEA splice variant with full-length CEA on the same cells did not significantly affect the apparent binding affinity of MEDI-565 to full-length CEA (CHO FL CEA, apparent K D = 5.060.15 nM; CHO FL+SV CEA, apparent K D = 5.663.0 nM; p = 0.86). These results were expected since homophilic interactions between fulllength CEA proteins also do not appear to prevent the binding of MEDI-565 [17,18] or other CEA-specific BiTE antibodies [16].…”

“…As a novel CEA-directed therapy, we have developed a CEA-targeting bispecific single-chain antibody of the bispecific T-cell engager (BiTE) class termed MEDI-565 (also known as MT111) [16] , [17] , [18] . BiTE antibodies are a unique subclass of bispecific antibodies that contain one single chain variable fragment (scFv) with specificity for a tumor associated antigen molecularly fused to another scFv with specificity for CD3 on T cells [19] .…”

“…BiTE antibodies activate both CD4+ and CD8+ T cell subsets [23] , [25] , [26] , [27] , [28] ; both subsets of T cells contribute to tumor cell killing at relatively low effector T cell:target tumor cell (E:T) ratios [22] , [29] . Cytokine secretion and the upregulation of cell surface IL-2 receptor by T cells (measured experimentally using antibodies recognizing the IL-2Rα chain/CD25) occur simultaneously and accompany tumor cell killing [18] , [22] , [25] . Both potentiate further T cell activation and proliferation, facilitating the subsequent engagement and killing of additional tumor cells bound by a BiTE antibody.…”

“…MEDI-565 itself is composed of a humanized single-chain antibody recognizing human CEA connected by a short flexible linker to a de-immunized single-chain antibody specific for CD3, and shares the characteristics of the BiTE antibody class as described above [16] , [17] , [18] . It specifically binds to CEA and not to other CEACAM family members [16] .…”