The power of natural phenolic compounds: caffeic acid is able to enhance the retinoid-induced differentiation of tumor cells

Background The induced differentiation of tumor cells represents a very important strategy in modern antineoplastic therapy. Retinoids are the most frequently used group of cell differentiation inducers; however, their toxicity and intrinsic or acquired resistance to retinoids substantially limit their use in clinical protocols. Therefore, special attention has been paid to the combined treatment of cancer cells with retinoids and other compounds that may modulate (enhance or prolong) their antineoplastic effects. For example, combinations of retinoids and bile acids or inhibitors of the lipoxygenases and cyclooxygenases were reported as effective. Our research was focused on the caffeic acid (CA), a widely distributed plant phenolic compound, which is an inhibitor of 5-lipoxygenase.