Heparin (H),
heparan sulfate (HS), and related
glycosaminoglycans can inhibit
cancer cell invasion, possibly due to their ability to interact with vascular
growth factors, adhesion molecules,
endoglycosidases, and signaling
proteins, in addition to the well-known effects on the clotting system. We evaluated the antitumor activity of a series of semisynthetic sulfaminoheparosan
sulfates (SAHSs) with different degree and distribution of
sulfates, obtained by chemical modifications of the E. coli K5 polysaccharide, namely type A, B, and C compounds. B16-BL6
melanoma cells (10 5 cells/mouse) were injected intravenously (i.v.) in a lateral tail vein of C57BL6 mice at a dose of 0.5 mg/ mouse together with test compounds.
Tumor lung nodules were significantly reduced as compared with controls only by H (95.5 +/- 1.0% inhibition), SAHS-2 (84.2 +/- 5.0% inhibition), and SAHS-4 (91.1 +/- 4.2% inhibition), among compounds tested. SAHS-2 and SAHS-4 are type B compounds, with a
sulfate/carboxylate ratio similar to that of H. A typical mammalian HS showed only 54.8% inhibition. Supersulfated
low-molecular-weight heparin and
heparan sulfate (ssLMWH and ssLMWHS) showed an activity similar to that of unfractionated compounds. H and SAHS-4 inhibited dose dependently B16-BL6 lung colonies, with IC-50 values of 0.05 and 0.1 mg/mouse, respectively. The relationship with ex vivo
anticoagulant potency was evaluated by activated partial thromboplastin time (aPTT) on mouse plasma at different time intervals after i.v. injection (0.1 to 0.5 mg/mouse) of the compound. H showed a dose-dependent
anticoagulant activity lasting up to 2 hours, whereas SAHS-4 showed a potent
anticoagulant effect only at a dose of 0.5 mg/mouse. Accordingly, H but not SAHS-4 consistently inhibited B16-BL6 lung colonies when given 1 hour before
tumor cells. SAHS-4 derivatives, with different size and/or affinity depleted of AT binding sites, showed an inhibitory effect on B16-BL6
melanoma similar to that of SAHS-4, suggesting that the greater antitumor effect of H was not due to AT-mediated inhibition of blood clotting. Interactions with other blood inhibitors, such as
heparin cofactor II or
tissue factor pathway inhibitory
protein cannot be ruled out. The better effect of H may be due to persistence in the circulation and/or ability to inhibit
tumor neoangiogenesis.