Cancers utilize glycans to evade the immune system via the Sialic acid (Sia)-Siglec (Sialic-acid-binding immunoglobulin-like lectins) pathway. Specifically, atypical structural forms of sialic acid bind to inhibitory Siglec receptors on Natural Killer (NK) cells resulting in the suppression of immune cell mediated cytotoxicity. The mechanism of action that governs the Sia-Siglec pathway in cancers is not understood. Specifically, how deviations from the typical form of Sia mechanistically contribute. Here we focused on modulating 9-O and 7,9-O-acetylation of Neu5Ac, via CRISPR-Cas9 gene editing, a functional group that is absent from Sias on many types of cancer cells. The two genes that are responsible for regulating the level of acetylation on Neu5Ac, are Sialic acid acetylesterase (SIAE) and Sialic acid acetyltransferase (CASD1). These genes modulated Siglec binding in colon, lung, and a non-cancerous kidney cell line. In the absence of SIAE, Neu5Ac is acetylated, engagement of cancer associated Siglecs is reduced while binding was increased when the ability to acetylate was removed via CASD1 knock out. In the absence of SIAE NK mediated cytotoxicity increased in both colon and lung cancer cells. In addition to modulating Siglec binding, SIAE expression modulates the level of Sias in a cell, and the α2–6-linkage of Sias - which is specifically upregulated and associated with cancers. Uncovering how functional group alterations on Neu5Ac contribute mechanistically to both Siglec receptor binding, the Sia-Siglec immune evasion pathway, and the production of cancer associated glycosidic linkages -offers a promising avenue for targeted cancer immune therapies in the future.

The high cost of treatment of cancer coupled with the emergence of drug resistance makes it imperative for new drug interventions to curb its occurrence. Hence, the objective of this research was to determine the phytochemical, total phenolic content, antioxidant and antiproliferative effect of Codiaeum variegatum crude extracts and fractions. The MTT cell viability and DPPH assays among others were used to determine the selected properties of the plants. The presence of general glycosides, tannins, alkaloids, flavonoids and sterols was observed in its stem bark and leaf. Triterpenoids were present in the leaf only while saponins were observed in the stem bark only. Strong antioxidant activities were observed in both stem bark and leaf with EC50 values of 0.053±0.004 mg/mL and 1.396±0.073 mg/mL respectively. Both crude extracts showed antiproliferative activity towards all cancer cell lines with the stem bark exhibiting the strongest cytotoxicity. However, both showed strong cytotoxicity towards normal cells as well. The mechanism of cell death was determined to be apoptosis. Further testing of fractions from the stem bark crude extract revealed an increase in cytotoxicity of its chloroform fraction against Jurkat cells with an IC50 of 44.71±0.44 µg/mL. These results establish the antiproliferative nature of this plant.

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