Heparan sulfate is an attachment factor for foamy virus entry.

The cellular receptor of foamy viruses (FVs) is unknown. The broad spectrum of permissive cells suggests that the cellular receptor is a molecular structure with almost ubiquitous prevalence. Here, we investigated the ability of heparan sulfate (HS), a glycosaminoglycan (GAG) present on the extracellular matrix of many cells, to bind FV particles and to permit prototype FV (PFV) and feline FV (FFV) entry. Permissivity of different cell lines for FV entry correlated with the amount of heparan sulfate present on the cell surface. The resulting 50% cell culture infectious doses (CCID(50)s) were distributed over a range of 4 logs, which means that the most susceptible cell line tested (HT1080) was more than 10,000 times more susceptible for PFV infection than the least susceptible cell line (CRL-2242). HS surface expression varied over a range of 2 logs. HS expression and FV susceptibility were positively correlated (P < 0.001). Enzymatic digestion of heparan sulfate on HT1080 cells diminished permissivity for PFV entry by a factor of at least 500. Using fast protein liquid chromatography (FPLC), we demonstrated binding of FV vector particles to a gel filtration column packed with heparin, a molecule structurally related to heparan sulfate, allowing for the purification of infectious particles. Both PFV and FFV infection were inhibited by soluble heparin. Our results show that FVs bind to HS and that this interaction is a pivotal step for viral entry, suggesting that HS is a cellular attachment factor for FVs.

Structure-activity relationships of flavonoid-induced cytotoxicity on human leukemia cells.

The aim of this study was to identify structure elements in flavonoids that are associated with enhanced cytotoxic activity. We determined the cytotoxicity (EC(50)) of 23 different flavonoids, including O-methylated and glucuronidated metabolites, on the human leukemia cell line Jurkat E6-1 by analyzing cell death triggered after 24 and 48 h. By comparing the cytotoxicity of selected molecules that differ in only one structure element, we identified several structure-function relationships associated with enhanced cytotoxicity, including the presence of a 2-3 double bond, the presence of a 4-carbonyl group and ortho- compared to meta-hydroxylation in the B ring. Molecules with a 3-hydroxyl group exhibited significantly lower cytotoxicity than their non-hydroxylated counterparts. O-Methylation and glucuronidation were associated with a significant increase in cytotoxicity, suggesting that metabolites found in vivo are more active than unmodified flavonoids. We identified the solubility maximum of the tested flavonoids in culture medium and found a negative correlation between maximum solubility and cytotoxicity. The results of our study may help to identify novel flavonoid structures with optimized cytotoxic activity to be tested for anti-cancer treatment.