Comparative Evaluation of the Cytotoxic Effects of Selected New Improved and Traditional Red and White Sri Lankan Rice (Oryza sativa L.) Varieties on Human Colorectal Cancer (Caco-2) Cells

Sri Lankan rice, the country's staple food, is known to possess various functional properties. Despite its richness in health-promoting properties, limited studies have evaluated its anticancer activity. This study evaluated cytotoxicity of freeze dried 70% ethanolic bran extracts of 15 new improved and 11 traditional red and white Sri Lankan rice varieties (RVs) against human colorectal cancer cell line (Caco-2) using sulforhodamine-B cytotoxicity assay (n=4). Initially, all extracts were screened at 250 and 500 µg/mL at 24, 48, and 72 h incubation time periods (ITPs). Extracts showing notable cytotoxicity were further evaluated at 31.25, 62.5, 125, 250 and 500 µg/mL. The results showed significant differences (P < 0.05) in cytotoxic effects among the tested RVs across the screened concentrations at the investigated ITPs. Overall, red RVs exhibited significantly greater cytotoxicity than white varieties (P < 0.05), irrespective of whether they were traditional or new improved RVs. The EC₅₀ values of red RVs ranged from 182.14 ± 2.10 to 2019.00 ± 23.31, 1.58 ± 0.01 to 615.20 ± 4.45, and 1.12 ± 0.01 to 15.92 ± 0.22 µg/mL at 24, 48, and 72 h, ITPs respectively. Among the red RVs, Goda Heeneti exhibited the highest cytotoxicity against Caco-2 cells at all ITPs. The EC₅₀ values of Goda Heeneti at studied ITPs were 182.14 ± 2.10, 1.58 ± 0.01, and 1.12 ± 0.01 µg/mL, respectively. These findings suggest that Sri Lankan red rice bran especially bran of Goda Heeneti variety may serve as a promising nutraceutical source for cancer management. Further studies are warranted to identify the active compounds, elucidate the underlying mechanisms, and evaluate the efficacy through in vivo studies.