Polissacarídeos sulfatados de invertebrados marinhos e progressão tumoral: efeitos na interação tumor-endotélio, angiogênese e radiorresistência

Abstract

The initial steps of metastatic process involve cell adhesion molecules of the selectin family, followed by engagement of different integrin subfamilies. Transendothelial migration across the vessel barrier and the establishment of firm adhesion to the subendothelial matrix are additional steps to be concluded by metastatic tumor cells in order to succefully colonize a secondary tissue site. Cell surface heparan sulfate proteoglycans act as co-receptors for growth factors and cell adhesion molecules. Sulfated polyssaccharides such as heparin and its derivatives act both as potent inhibitors of selectins, and modulators of the biological activity of growth factors and its receptors. In the present work, was investigated the effects of sulfated polyssaccharides isolated from sea urchins (L. variegatus, S. franciscanus, S.pallidus, A. lixula and S. droebachiensis) in different aspects of cancer cell biology, with particular emphasis on FucSulfI, the sulfated fucan from L. variegatus. In Part I, the direct effect of FucSulfI on tumor cell lines was investigated. Among the various fucans tested, FucSulfI exibited the highest inhibitory effect on the adhesion of the prostate cancer cells DU-145 and PC-3, on both TNF-α-activated endotelial layers and extracelular matrix. FucSulf I was able to strongly inhibit tumor cell adhesion to P-selectin. FucSulfI inhibited transendothelial migration of both cell lines and also the MV3 human melanoma cell line. The sulfated fucan was able to significantly inhibit the proliferation of prostate, breast adenocarcinoma, and melanoma cell lines. The treatment of prostate cancer cells with FucSulfI for 48 hours downregulated the expression of neuropilin-1 and FAK, both involved in cell proliferation signaling pathways. Melanoma growth in vivo was also inhibited by FucSulf I.. In Part II, we focused on the effect of FucSulfI in angiogenic endotelial differentiation. This fucan decreased endotelial cell adhesion to fibronectin and gelatin, through direct binding to endotelial cell surface. Was observed that FucSulfI inhibited VEGF-dependent tubulogenesis in vitro, and decreased VEGFR2 phosphorylation, the main receptor tyrosine kinase mediating VEGF effects on endotelial cells. Additionally, soluble VEGF was able to bind to immobilized FucSulfI, suggesting that the mechanism of inhibition of VEGFR2 is probably related to the depletion and/or sequestration of VEGF away from its receptors on cell surface. In view of the significant effects of FucSulfI on cell adhesion, in Part III possible applications of this fucan in the field of tumor radioresistance were explored. It is known that the composition of extracellular matrix interferes with cellular resistance to cell-damaging agents such as drugs or ionising radiation. Was investigated the effect of FucSulfI in cell adhesion and radioresistance of MV3 melanoma cells. Results showed that the fucan inhibits tumor adhesion to fibronectin and activation of FAK. The treatment of MV3 cells with FucSulfI inhibited colony formation by 30%. When cells were submitted to radiation (2Gy) after the treatment with FucSulfI, colony formation was decreased by 80%. In conclusion, based on the data presented in this work, sulfated fucans emerge as promising molecules, displaying a large array of significant anti-tumoral and anti-endothelial activities that could potentially lead to their proposal as new drug candidates for cancer control.