Glycosphingolipids (GSLs) are neoplastic and normal/cancer stem cell markers and GSL/
cholesterol-containing membrane rafts are increased in
cancer cell plasma membranes. We define a novel means by which
cancer cells can restrict
tumor-associated GSL immunoreactivity. The GSL-
cholesterol complex reorients GSL
carbohydrate to a membrane parallel, rather than perpendicular conformation, largely unavailable for antibody recognition. Methyl-β-
cyclodextrin cholesterol extraction of all primary human
tumor frozen sections tested (ovarian, testicular,
neuroblastoma, prostate, breast, colon,
pheochromocytoma and
ganglioneuroma), unmasked previously "invisible" membrane GSLs for immunodetection. In ovarian
carcinoma, globotriaosyl
ceramide (Gb3), the GSL receptor for the
antineoplastic Escherichia coli-derived
verotoxin, was increased throughout the
tumor. In colon
carcinoma, Gb3 detection was vastly increased within the neovasculature and perivascular stroma. In
tumors considered Gb3 negative (
neuroblastoma, Leydig
testicular tumor and
pheochromocytoma), neovascular Gb3 was unmasked.
Tumor-associated GSL
stage-specific embryonic antigen (SSEA)-1,
SSEA-3,
SSEA-4 and globoH were unmasked according to
tumor:
SSEA-1 in prostate/colon;
SSEA-3 in prostate;
SSEA-4 in
pheochromocytoma/some colon
tumors; globoH in prostate/some colon
tumors. In colon, anti-SSEA-1 was
tumor cell specific. Within the GSL-
cholesterol complex,
filipin-
cholesterol binding was also reduced. These results may relate to the ill-defined benefit of
statins on
cancer prognosis, for example, prostate
carcinoma. We found novel anti-
tumor GSL
antibodies circulating in 3/5
statin-treated, but not untreated,
prostate cancer patients. Lowering
tumor membrane
cholesterol may permit immune recognition of otherwise unavailable
tumor-associated GSL
carbohydrate, for more effective immunosurveillance and active/passive immunotherapy. Our results show standard immunodetection of
tumor GSLs significantly under assesses
tumor membrane GSL content, impinging on the current use of such
antigens as
cancer vaccines.