Tumor attenuation by combined heparan sulfate and polyamine depletion

Abstract

Cells depend on polyamines for growth and their depletion represents a strategy for the treatment of cancer. Polyamines assemble de novo through a pathway sensitive to the inhibitor, ␣-difluoromethylornithine (DFMO). However, the presence of cellsurface heparan sulfate proteoglycans may provide a salvage pathway for uptake of circulating polyamines, thereby sparing cells from the cytostatic effect of DFMO. Here we show that genetic or pharmacologic manipulation of proteoglycan synthesis in the presence of DFMO inhibits cell proliferation in vitro and in vivo. In cell culture, mutant cells lacking heparan sulfate were more sensitive to the growth inhibitory effects of DFMO than wild-type cells or mutant cells transfected with the cDNA for the missing biosynthetic enzyme. Moreover, extracellular polyamines did not restore growth of mutant cells, but completely reversed the inhibitory effect of DFMO in wild-type cells. In a mouse model of experimental metastasis, DFMO provided in the water supply also dramatically diminished seeding and growth of tumor foci in the lungs by heparan sulfate-deficient mutant cells compared with the controls. Wild-type cells also formed tumors less efficiently in mice fed both DFMO and a xylose-based inhibitor of heparan sulfate proteoglycan assembly. The effect seemed to be specific for heparan sulfate, because a different xyloside known to affect only chondroitin sulfate did not inhibit tumor growth. Hence, combined inhibition of heparan sulfate assembly and polyamine synthesis may represent an additional strategy for cancer therapy.metastasis ͉ proteoglycans ͉ spermine ͉ chemotherapy ͉ xylosides

Glypican-1 Is a Vehicle for Polyamine Uptake in Mammalian Cells

“…As most mammalian cells express glypican-type HSPG at the cell surface, extracellular polyamines should be efficiently absorbed by the sulfated HS side chains of glypicans (12)(13)(14). The results of this study support the proposal that recycling glypicans serve as membrane carriers for polyamines during import and delivery in cells with inadequate endogenous synthesis of polyamines (Fig.…”

“…Uptake by T24 CellsInvolvement of HSPG in polyamine uptake is indirectly supported by the previous findings that (a) HS binds the polyamine spermine very strongly; (b) HS competitively inhibits spermine uptake; and (c) HSPG-deficient cells have a low spermine uptake (12)(13)(14). Involvement of glypican-type HSPG is suggested by the observations that (d) polyamine deprivation increases the GlcNH 3 ϩ content in Gpc-1 HS chains (15); (e) HS chains in Gpc-1 are cleaved at these GlcNH 3 ϩ units by NO in conjunction with spermine uptake (22); and (f) NO depletion inhibits spermine uptake in DFMO-treated T24 cells (15).…”

“…Subsequently, we showed that exogenous HS competitively inhibits polyamine uptake and that PG-deficient or sulfate-depleted cells have a diminished uptake (13,14). PG-deficient cells are also more sensitive to growth inhibition by DFMO both in vitro and in vivo (14). We have also shown that polyamine-depleted cells synthesize glypican HS chains with an increased spermine affinity (15).…”

“…the affinity of HS for spermine is 10-fold higher than that of DNA (12), which is regarded as a major natural polyamine-binding polyanion (1,7,8). Subsequently, we showed that exogenous HS competitively inhibits polyamine uptake and that PG-deficient or sulfate-depleted cells have a diminished uptake (13,14). PG-deficient cells are also more sensitive to growth inhibition by DFMO both in vitro and in vivo (14).…”

“…Polyamines could then exit endosomes via transporters of the same type as those previously cloned in bacteria (9). Hence, such transporters may be best studied in mutant cells that express very little cell-surface HSPG and therefore cannot sequester polyamines and make them inaccessible to a putative transporter (13,14).…”