Abstract 5286: Enhancing role of tumor cell gangliosides in tumor angiogenesis

Abstract

Abstract Tumor gangliosides, synthesized and shed by many tumors, have a critical role in enhancing tumor formation and progression. Among possible mechanisms of this pro-tumorigenic activity of tumor gangliosides is enhancement of tumor angiogenesis, although directly probing this possibility in vivo has been difficult. Here we tested this hypothesis by exploring the influence of tumor gangliosides on tumor angiogenesis in a unique syngeneic genetic constitutive ganglioside-depleted tumor cell model developed by oncogenic transformation of murine embryonic fibroblasts lacking the key ganglioside synthetic genes, GM3 synthase and GM2 synthase (Oncogene 29:3297-306, 2010). This resulted in complete, selective, and constitutive ganglioside depletion (DKO tumor cells), without reduction in cell proliferation rate. Syngeneic C57BL/6 mice were injected with 104 to106 DKO cells, or with ganglioside-rich wild type (WT) control tumor cells. DKO tumors had remarkably impaired tumor incidence and progression, supporting a role of gangliosides in tumor growth. We also observed striking avascularity of the ganglioside-depleted DKO tumors and therefore probed their state of angiogenesis. By H and E staining, the DKO tumors had many fewer developed vessels (6% of total vessels, vs. 51% in WT tumors, p<0.0001). These results were confirmed by CD31 immunostaining, which also revealed that the DKO tumors lacked well formed, large, and mature vessels (5%, vs. 35% in WT tumors, p<0.0001). There was no significant difference between WT and DKO tumors in total vessel number (nascent to fully formed). Impeded angiogenesis was noted for DKO tumors at all stages of their development (size and time from inoculation), even though VEGF production and secretion of the WT and DKO tumor cells were equal. The pivotal role of the tumor gangliosides was confirmed by addition of 100 picomoles of purified WT tumor cell gangliosides to the DKO tumor cell inoculum, resulting in significant enhancement of both angiogenesis (doubling of the proportion of large vessels on day 14), and of tumor volume (from 10 mm3 to 230 mm3 on day 19). This enhancing role of shed tumor cell gangliosides is consistent with our previous in vitro findings (Cancer Research 66:10408-14, 2006) that membrane ganglioside enrichment by the addition of exogenous gangliosides lowered the threshold for vascular endothelial cell angiogenic signaling and enhanced vascular endothelial cell proliferation and migration In summary, our findings clearly implicate gangliosides shed by tumor cells into the tumor microenvironment in enhancing tumor formation and accelerating the process of tumor angiogenesis, probably by enhancing or amplifying growth-factor-induced signaling (Supported by NIH grants R01 CA42361 and R01 CA61010). Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5286. doi:1538-7445.AM2012-5286