SC134 specifically binds FucGM1, a SCLC selective target. Glycolipid binding specificity by hybridoma-derived SC134. A, ELISA analysis of FucGM1-binding specificity of SC134. FucGM1 binding is observed, in contrast to lack of binding to closely related gangliosides. Positive control antibody reactivity for the respective gangliosides is shown in Supplementary Fig. S1A. B, Immuno-TLC analysis of SC134 showing reactivity toward DMS79 lipid extract as well as purified FucGM1, combined with lack of GM1 reactivity. C, SC134-binding efficiency for FucGM1 on ELISA. D, SC134 cell surface–binding efficiency on a range of SCLC cell lines. h134 characterization: (E) FucGM1 lipid binding compared with GM1 by ch134 and h134 on ELISA. F, SCLC cell line binding by h134. MFI assessed by flow cytometry. FucGM1 distribution in SCLC tumor tissues: (G) IHC FucGM1 expression analysis using h134 (huIgG1) of frozen patient-derived xenograft SCLC tissues. H, FucGM1 expression by DMS79 in culture. I, FucGM1 expression by DMS79 after growing in NSG mice. J, Restricted FucGM1 expression in frozen normal healthy human tissues, immunostained with h134 (J). The pituitary (a), skin (b), and thymus (c) were the only positive tissues from the 30 normal healthy tissues analyzed. The full arrays are shown in Supplementary Fig. S1D. ch134, chimeric (human IgG1) SC134; MFI, median fluorescence intensity; TLC, thin-layer chromatography.
ARTICLE ABSTRACT
Small cell lung cancer (SCLC) is an aggressive disease with limited treatment options. Fucosyl-GM1 (FucGM1) is a glycolipid overexpressed in the majority of SCLC tumors but virtually absent from normal healthy tissues. In this study, we validate a FucGM1-targeting T cell–redirecting bispecific (TCB) antibody for the treatment of SCLC. More than 80% of patient-derived xenograft tissues of SCLC expressed FucGM1, whereas only three normal human tissues: pituitary, thymus, and skin expressed low and focal FucGM1. A FucGM1-targeting TCB (SC134-TCB), based on the Fc-silenced humanized SC134 antibody, exhibited nanomolar efficiency in FucGM1 glycolipid and SCLC cell surface binding. SC134-TCB showed potent ex vivo killing of SCLC cell lines with donor-dependent EC50 ranging from 7.2 pmol/L up to 211.0 pmol/L, effectively activating T cells, with picomolar efficiency, coinciding with target-dependent cytokine production such as IFNγ, IL2, and TNFα and robust proliferation of both CD4 and CD8 T cells. The ex vivo SC134-TCB tumor controlling activity translated into an effective in vivo anti-DMS79 tumor therapy, resulting in 100% tumor-free survival in a human peripheral blood mononuclear cell admixed setting and 40% overall survival (55% tumor growth inhibition) with systemically administered human peripheral blood mononuclear cells. Combination treatment with atezolizumab further enhanced survival and tumor growth inhibition (up to 73%). A 10-fold SC134-TCB dose reduction maintained the strong in vivo antitumor impact, translating into 70% overall survival (P < 0.0001). Whole-blood incubation with SC134-TCB, as well as healthy human primary cells analysis, revealed no target-independent cytokine production. SC134-TCB presents an attractive candidate to deliver an effective immunotherapy treatment option for patients with SCLC.
