According to a study from South Korea, "Our previous studies indicated that dietary CLA inhibits colon tumor cell proliferation in vitro and in vivo. To identify mechanisms by which CLA regulates growth arrest, the HT-29 human colon carcinoma cell line was treated with various physiological concentrations of CLA and analyzed by flow cytometry."

"We detected a dose-dependent increase in the percentage of cells arrested in G after CLA treatment that was accompanied by induction of the cyclin dependent kinase (CDK) inhibitor p21(CIP/WAF). CLA addition also led to increased p21 expression in HCT116 and SW480 cells, indicating that p21 induction is a general consequence of CLA treatment in colon cancer cells," explained D.Y. Lim and colleagues, Hallym University.

"Since both HT-29 and SW480 cells have mutant p53, our data indicate that p53 is not essential for induction of p21. In addition to an increase in p21 levels, HT-29 cell growth arrest was also accompanied by moderate decreases in Cyclin A, D1, E, and proliferating cell nuclear antigen (PCNA) levels."

"Following CLA treatment, p21 associated with and inhibited CDK4 and CDK2, and this correlated with reduced phosphorylation of retinoblastoma proteins. Increased association of p21 with PCNA was also detected. Dietary CLA inhibits cell cycle progression by inducing p21, which negatively regulates the growth promoting activities of CDK/cyclins and PCNA."

The researchers concluded, "These studies indicate that physiological concentrations of CLA inhibit growth of colon cancer cells with either wild-type or mutant p53, and may have therapeutic benefits in vivo."

Lim and colleagues published the results of their research in the Journal of Cellular Physiology (“Inhibition of Colon Cancer Cell Proliferation by the Dietary Compound Conjugated Linoleic Acid is Mediated by the CDK Inhibitor p21(CIP1/WAF1).” J Cell Physiol, 2005;205(1):107-113).

For additional information, contact J.H.Y. Park, Hallym University, Division Life Science, 1 Okchon Dong, Chunchon 200702, South Korea.