Inhibition of tumor cell arrest in lungs by antimetastatic chitin heparinoid

We have investigated the effect of sulfated chitin derivatives on the intravascular events in the metastatic cascade. 6-O-Sulfated carboxymethyl chitin (SCM-chitin III), as well as heparin, significantly inhibited the arrest of B16-BL6 cells in lungs after co-injection with radiolabeled tumor cells, but carboxymethylated chitin (CM-chitin) had no effect. Heparin showed a potent inhibitory effect on tumor cell-elicited platelet aggregation and on blood coagulation, which can subsequently enhance the survival, arrest and invasiveness of tumor cells, whereas SCM-chitin III showed much weaker properties. In contrast, SCM-chitin III was found to inhibit the adhesion of tumor cells to subendothelial matrix, while heparin did not. SCM-chitin III was still active in inhibiting experimental lung metastasis even in mice which had been pretreated with anti-asialo GM1 serum or carrageenan to eliminate NK cells or macrophages. Thus, these results suggest that SCM-chitin-mediated inhibition of tumor metastases is distinct from that by heparin and may be due to interference with tumor cell arrest in the capillaries and consequently to the inhibition of tumor cell adhesion to subendothelial matrix.