Abstract Number: OC 06.2
Meeting: ISTH 2020 Congress
Background: Tissue Factor (TF) protein isoforms – full-length (flTF) and alternatively spliced (asTF) – are often overexpressed in cancer. Previously, we have shown that a rabbit monoclonal antibody specific for human asTF, termed RabMab1, disrupts binding of asTF to beta-integrins and suppresses proliferation of breast and pancreatic cancer cells expressing endogenous flTF and asTF.
Aims: 1) Humanize RabMab1 and evaluate its systemic pharmacokinetics. 2) Evaluate biological effects of humanized RabMab1 in an orthotopic murine model of pancreatic ductal adenocarcinoma (PDAC).
Methods: Variable regions of RabMab1 heavy and light chains were used to generate chimeric RabMab1 (c-RabMab1). Substitutions of species-specific residues were then carried out to produce fully humanized RabMab1 (h-RabMab1). Pharmacokinetics were assessed via intravenous injections of c-RabMab1 and h-RabMab1 in mice. For anti-tumor efficacy studies, 1×106 Pt45.P1 cells (a high grade, flTF+/asTF+ human PDAC cell line) were orthotopically implanted into nude mice. Treatment with 18 mg/kg h-RabMab1 (n=9), 18 mg/kg hIgG1 isotype control (n=7), or vehicle (n=5) began 10 days post-tumor cell implantation and continued for 44 days. Upon sacrifice, tumor volume was measured and tissue assessed by western blotting, immunohistochemistry, and RNA-seq.
Results: The elimination half-life of h-RabMab1 (908 hrs) was markedly longer when compared to that of c-RabMab1 (280 hrs). Tumors in mice treated with h-RabMab1 were 60% smaller than tumors in either control group. Immunohistochemistry revealed significantly lower levels of CD31, CD206, and Ki67 in the h-RabMab1 group. RNA-seq analysis (https://toppgene.cchmc.org) revealed upregulation of various molecular function linked pathways with the expression levels of IL-18, somatostatin, and TGFbeta2 significantly higher in the h-RabMab1 group; expression of the mesenchymal marker vimentin was suppressed in the h-RabMab1 group (all validated by qRT-PCR).
Conclusions: Our first-in-class anti-asTF antibody is effective at stemming PDAC growth when administered intravenously to mice with pre-formed tumors. These findings pave the way for future clinical development of h-RabMab1.
To cite this abstract in AMA style:Lewis C, Karve A, Matiash K, Stone T, Desai P, Bogdanov V. Preclinical in Vivo Characterization of a First-In-Class, Fully Humanized Antibody Targeting Alternatively Spliced Tissue Factor [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/preclinical-in-vivo-characterization-of-a-first-in-class-fully-humanized-antibody-targeting-alternatively-spliced-tissue-factor/. Accessed September 27, 2023.
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