Delta- and Gamma-Tocotrienols Inhibit the Proliferation of HCC2998 Human Colorectal Carcinoma Cells via Modulation of Histone Modification Pathways Involved in DNA Damage Response

Colorectal cancer (CRC) remains a significant global health burden, necessitating the exploration of novel therapeutic strategies. Tocotrienols (T3s), particularly gamma (γ)- and delta (δ)-T3 isoforms, exhibit promising anticancer properties. This study investigates the antiproliferative effects of γT3 and δT3 on HCC2998 human colorectal carcinoma cells, elucidating their underlying molecular mechanisms through cell viability assays and comprehensive gene expression profiling. The half-maximal inhibitory concentrations (IC₅₀) for γT3 were determined to be 12.59 ± 0.35 µg/mL (24 h), 11.63 ± 0.05 µg/mL (48 h), and 10.92 ± 0.06 µg/mL (72 h). For δT3, the IC₅₀ values were lower: 9.66 ± 0.17 µg/mL (24 h), 9.33 ± 0.00 µg/mL (48 h), and 9.69 ± 0.05 µg/mL (72 h). Microarray analysis revealed that histone modification pathways were most significantly affected, profoundly influencing the DNA damage response (DDR). Specifically, treatment with γT3 and δT3 led to the upregulation of the ATM tumor suppressor gene and downregulation of key DDR-related genes, including BID, BRCA1, CCNE2, CDC25A, CDC25C, CDK2, E2F1, H2AFX, PMAIP1, RAD51, and SMC1A. These findings indicate that γT3 and δT3 inhibit HCC2998 cell proliferation by activating the DDR pathway, highlighting their potential as therapeutic agents to overcome cell cycle arrest resistance in CRC. This study provides critical insights into the molecular actions of γT3 and δT3, supporting their further investigation as promising candidates for CRC intervention.