Cytotoxic Activity of Eburnane-type Indole Alkaloids Isolated from Kopsia terengganensis against HT-29 Human Colon Cancer Cell

The genus Kopsia from the Apocynaceae family bears a large group of indole alkaloids which possessed active biological activities. The focus of this study was to elucidate the isolated alkaloids and investigate their biological activity. Six indole alkaloids from the eburnane-type; eburnamine (1), isoeburnamine (2), eburnaminol (3), larutensine (4), eburnamenine (5), eburnamonine (6), and one from aspidospermane-type; quebrachamine (7) were isolated from the bark of Kopsia terengganensis. These alkaloids were characterized using various chromatographic techniques and spectroscopic methods and were compared with the literature. Later, alkaloids 1–4 were subjected to cytotoxic activity using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay against HT-29 colorectal adenocarcinoma. The observed result showed that only compound 3 was able to suppress the growth of cancer cells in a dose-dependent manner with the half-maximal inhibitory concentration (IC₅₀) of 75.8± 3.06 µM. It also shows a good cytotoxic activity compared to cisplatin with IC₅₀ value of >100 µM as a control drug. This illustrated that further exploration on the eburnane-type alkaloid should be taken on other cancer cell lines since it has shown a profound result on human colon cancer.