A New Proteolipid Apparently Associated with Cancer 1

Abstract

In the course of studies of the lipid composition of human serum lipoproteins (1, 2) we observed a new lipid in thin-layer chromatograms (TLC) (3) of lipid extracts from high-density lipoproteins (HDL) from cancer patients. Similar extracts from HDL of normal subjects did not reveal this lipid. We since found that lipids extracted from transplanted animal tumors also contain a similar lipid.

This preliminary communication describes the general chemistry of this lipid, its distribution in rat tissues, its presence in sera from cancer patients, and implications of these observations.

Nature of new lipid. The new lipid was isolated from lipid extracts of Walker carcinosarcoma 256 (W256) by silicic acid column chromatography with stepwise gradient elution (chloroform-methanol mixtures). The isolated lipid had the same R _f in several TLC systems (see below) as did the new lipid in the sera HDL of cancer patients. Complete drying of the isolated new lipid from W256 in vacuo (with N₂ bubbling) caused partial decomposition. Decomposition products, identified by TLC (3, 4), included phosphorus and nonphosphorus containing lipids. It was inferred that the new lipid is a complex unstable under certain conditions. In addition to complete drying, contact with sodium oxalate and treatment with ultrasonic vibration also cause decomposition of this complex. Further chemical studies of the complex revealed that protein (or polypeptide) was also present. The amount of protein determined by the Lowry et al. (5) procedure and the Hess and Lewin (6) modification was 7-8%, and by gas-liquid chromatography analysis of the amino acids (7) in the hydrolyzate of this complex was ∼6-8%. The protein-lipid complex behaves as a lipid being extractable from tissues along with other lipids by chloroform:methanol, 2:1 (v/v), 20 ml of solvent to 1 g of wet tissue.