Evaluation of MCP anticancer activity using molecular imaging

Abstract

MCP is a polysaccharide found abundantly in the plant's primary wall and shows activity in several areas of the food industry and nutrition, serving in food production, improving intestinal flow, reducing cholesterol, and being an important nutritional compound. MCP can also act as an anti-tumorigenic molecule in several types of tumors, in addition to avoiding chemoresistance, modulating the immune system, and preventing renal disease caused by radiotherapy and chemotherapy in cancer treatments. This study was divided into three main parts. In the first part, a review was carried out to study the biological activity of MCP and its contribution to cancer therapy, demonstrating treatment doses, types of MCP used, and experimental design, providing a critical view of the exposed data and its relationship with galectin-3 and other theories regarding its mechanisms. In the second part, we radiolabeled MCP with 99mTc and verified the biodistribution and pharmacokinetics of MCP-99mTc orally and intravenously (IV) administrated. First, the structure and monosaccharide composition of MCP were studied, and it was demonstrated that there is a diversity of monosaccharides and molecular weights within the MCP structure and that MCP30 and MCP3 fractions are rich in galactose. Next, we studied the inhibition and binding affinity of MCP for galectin-3 and demonstrated that MCP partially binds Gal-3 and that MCP3 shows an inhibition capacity at a concentration of 25 mg/ml. We radiolabeled MCP with 99mTc and verified its stability in saline in different pH, plasma, and in vivo. MCP-99mTc has a low gastrointestinal absorption (5.27x10-6 % total radioactivity counts) and gastrointestinal elimination when administered via oral and renal and hepatobiliary elimination when administered via IV. Finally, the blood compartment distribution assay showed that MCP-99mTc has a high affinity for plasma proteins and blood cells in C57BL/6 Lgals3 +/+ mice, and this affinity was partially lost when galectin-3 was deleted in C57BL/6 Lgals3 -/- mice. The pharmacokinetic assay showed that MCP-99mTc elimination speed was greater in the C57BL/6 Lgals3-/- mice than in the C57BL/6 Lgals3 +/+, indicating that a lack of galectin-3 increases MCP elimination. In the third part, we analyzed the behavior of MCP-99mTc in animals with SKOV-3 and MKN45 tumors using molecular imaging. First, we demonstrated that cell binding and internalization of MCP were only partially influenced by Galectin-3 expression in vitro using SKOV-3 scrambled and SKOV-3 shRNAGal3 cells (knockdown of Gal-3 expression). Next, we showed that MCP (20 mg/kg) exhibited anticancer activity in a SKOV-3 cell tumor xenograft model, reducing tumor growth by 48.5% and tumor weight by 50% when administered intravenously; however, oral administration of MCP (200 mg/kg) did not show an anticancer effect. Subsequently, we demonstrated that MCP-99mTc reached the tumor and bound to regions of necrosis in the SKOV-3 cell tumor xenograft model when administered intravenously. Finally, we demonstrated that IV administration of MCP (10 mg/kg) in mice with SKOV-3 tumors (lower expression of Gal-3) and MKN45 tumors (greater expression of Gal-3) reduced tumor growth by 58.7% and 35.4%, respectively, and reduced the tumor weight by 51.7% and 30.7 %, respectively. Furthermore, in both tumor xenografts, MCP-99mTc reached the tumor at the same proportion. These results demonstrate that MCP-99mTc radiolabeling is an important tool for studying the anticancer activity of MCP. We also showed that the data do not corroborate the hypothesis of the direct pharmacological effect of MCP exclusively targeting Gal-3, thus contributing to the knowledge of MCP anticancer activity.