Preferential Lectin Binding of Cancer Cells upon Sialic Acid Treatment Under Nutrient Deprivation

Abstract

The terminal monosaccharide of glycoconjugates on a eukaryotic cell surface is typically a sialic acid (Neu5Ac). Increased sialylation usually indicates progression and poor prognosis of most carcinomas. Here, we utilize two human mammary epithelial cell lines, HB4A (breast normal cells) and T47D (breast cancer cells) as a model system to demonstrate differential surface glycans when treated with sialic acid under nutrient deprivation. Under a starved condition, sialic acid treatment of both cells resulted in increased activities of α2→3/6 sialyltransferases as demonstrated by solid phase assay using lectin binding. However, a very strong MAL-I (Maackia amurensis agglutinin I) staining on the membrane of sialic acid treated T47D cells was observed, indicating an increase of Neu5Acα2→3Gal on the cell surface. To our knowledge, this is a first report showing the utility of lectins, particularly MAL-I, as a means to discriminate between normal and cancer cells after sialic acid treatment under nutrient deprivation. This method is sensitive and allows selectively detection of glycan sialylation on a cancer cell surface.

Harnessing cancer cell metabolism for theranostic applications using metabolic glycoengineering of sialic acid in breast cancer as a pioneering example

“…In cancer, the neo-expression of the requisite sialyltransferase enables the production of these (or other) TACAs and is considered to be a key event in oncogenic progression. An example of this phenomenon is provided by our recent characterization of breast cancer cells where rapid increases in sialyltransferase expression was observed during recovery from nutrient deprivation [75, 76]. …”

“…Up to very recently, these studies have been conducted under nutrient-rich conditions where only modest changes in overall levels of cell surface sialic acids were typically observed, although in some cases certain TACAs such as PSA increased by 300% or more [169]. By comparison, the impact of supplementation in nutrient-deprived breast cancer cells – where a distinguishing feature was dramatically-reduced cell surface sialylation – was considerably more dramatic insofar surface sialylation was rapidly rescued by supplying the cells with exogenous sialic acid [75]. …”

“…We have already characterized the restoration of surface sialylation in nutrient-deprived breast cancer cells upon exogenous supplementation at a rudimentary biochemical level [75, 76, 101, 170]. These studies discounted the possibility that Neu5Ac was routed for energy production by showing that ATP levels did not increase upon supplementation but instead dramatically decreased in certain cell lines.…”

“…For example, because cell surface glycans offer a surprisingly comprehensive snapshot into the internal metabolic status of a cell and by cataloging these changes under various states of nutrient availability [101, 103, 182–186], TACA profiles that indicate the “energetics” status of cancer cell could be used to assess the stage of cancer and then to suggest a treatment strategy. In particular, we focus on nutrient-deprived breast cancer cells that efficiently take up sialic acids used to restore cell surface display of this sugar [75, 76, 101]. …”

“…In particular, azide- or alkyne-containing monosaccharide analogues provide attractive opportunities for using bioorthogonal chemical reactions to remodel the cell surface [213]. These strategies – which rely on the facile incorporation of “non-human” sialic acids into cell surface glycans – are supported conceptually by our recent publications [75, 76, 101, 170] that provide provocative indications that MGE strategies could be exceptionally valuable for treating cancer because nutrient deprivation enables cancer cells to rapidly and robustly incorporation exogenously-supplied sialic acids thereby providing a therapeutic window to minimize harm to healthy cells.…”