Abstract 2418: Low dose antibody against GM2 ganglioside results in accelerated tumor growth
Authors: Wu Xiaohong , Ragupathi Govind , Hong Feng , Livingston Philip 
Published: February 2011

Abstract
A variety of monoclonal antibodies have demonstrated prolongation of disease free and overall survival in preclinical studies and in the clinic when the tumors were known to be strongly positive for the target antigen. This includes monoclonal antibodies against gangliosides GD2, GD3 and GM2. On the other hand, randomized trials with the antibody inducing GM2-KLH vaccine in melanoma patients have demonstrated either no benefit (Kirkwood, JCO 19(9): 2370, 2001) or a decrease in overall survival (Eggermont, JCO 26 (abstract 9004), 2008). The predominant antibodies induced by the GM2-KLH conjugate vaccine are anti-GM2 IgM antibodies. While GM2 is present on essentially all melanomas, it is expressed at only low levels in the great majority of these cases. We hypothesized therefore that 1) induction of high titers of antibodies against GM2 results in only a low level of cell surface binding antibodies against GM2 because of the low level GM2 expression, and 2) that this results in low level inflammation and angiogenesis, and tumor cell activation, as has been described for sub-lytic levels of cell surface complement activation in other settings.
To address these hypotheses, we explored the impact of a range of doses of PGNX, an anti-GM2 IgM monoclonal antibody, on growth of the luciferase transduced neuroblastoma cell line CHLA-136luc in vitro and in vivo. We incubated 10,000 CHLA-136luc cells with different amounts of PGNX (0.01, 0.05, 2 and 5µg) and 5 µl human complement in 0.1ml medium overnight and measured cell growth using the Wst-1 assay. Increased cell growth was seen at PGNX doses of 0.01 and 0.05 µg (P&lt;0.05 vs. control). The 5µg PGNX dose decreased cell growth (P&lt;0.05 vs. control) and this was confirmed by the Calcein-AM dye release cytotoxicity assay which showed 50% complement mediated lysis. SCID mice were injected intravenously with 0.5 million CHLA-136-luc neuroblastoma cells and treated with 1µg, 5µg or 50µg of PGNX intraperitoneally on days 1 and 14 after tumor challenge. The 50µg dose resulted in strikingly delayed tumor growth, prolonged survival and apparent cure in 10%-40% of mice. This protection from tumor challenge was inhibited by depletion of complement (treatment with cobra venom factor) and depletion of polymorphonucleocytes (treatment with mAb RB), but not by NK cell depletion (mAb NK1.1). Treatment with 5µg or 1µg of PGNX had the opposite effect. The 5µg dose resulted in accelerated tumor growth when measured prior to day 40, but survival was not significantly impacted. At the 1µg PGNX dose, tumor growth was more dramatically accelerated and survival was significantly diminished compared to the no treatment control groups.
Supported by a grants from the NIH PO1 CA 052477 and from The Breast Cancer Research Foundation.
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 2418.