ALTERATIONS OF CHOLESTERYL ESTER METABOLISM CHARACTERISTIC FOR CANCER

Earlier as well as recent evidence obtained in our laboratory is revie wed indicating that specific changes in cholesteryl ester metabolism a re related to tumor growth. Some properties of cholesteryl 14-methylhe xadecanoate, an unknown lipid discovered and identified in our laborat ory are described and its fundamental role as an essential cofactor in protein synthesis is emphasized. Increased quantities of this ester a re present in tissues of tumor-bearing animals and the elevation of it s level in serum is proportional to the tumor growth. Evidence has bee n presented that it may be a useful and reliable marker of malignant t umors in humans. This compound is synthesized in liver cells by enzyme s that were recently purified to homogeneity from rat liver. The activ ity of these enzymes is significantly enhanced in tumor-bearing rats i n a close proportion to the tumor growth. Activity of these preparatio ns from normal rat liver may be greatly enhanced by the addition in vi tro of serum from cancer patients. Since the enzymes are of lecithin-c holesterol acyl transferase type, apparently cancer serum contains som e peculiar molecular species of these phospholipids. Because these lip ids may be specific products of tumor cells, attempts are now in progr ess in this laboratory to identify them and the possibility is studied for their utilization as specific tumor markers.