DETECTION OF SERUM FACTORS ENHANCING CELL MUTABILITY FROM LUNG-CANCERPATIENTS BY APPLICATION OF HYPERMUTABLE HUMAN RS CELLS

A search for serum factors that modulate the mutability of human cells has been attempted in the peripheral blood of lung cancer patients. F actors were separated by dye-ligand chromatography and first identifie d as those exhibiting the ability to enhance the frequency of drug-res istance mutations in human RSa cells. The frequency was assessed by es timation of the cloning efficiency of mutant cells resistant to ouabai n-mediated cell killing (Oua(R)) after irradiation with far-ultraviole t light (UV, mainly 254-nm wavelength), Pre-culture of cells with medi um containing the factors prior to UV irradiation led to about a 19- t o 37-fold increase in the OuaR mutation frequency compared with that o f cells irradiated but not treated with the factors, The enhancing act ivity was detected in the serum of all 7 lung cancer patients, althoug h the serum itself, which had not been treated with chromatography, ha d little or no enhancing activity in all patients. No enhancing activi ty was detected in serum preparations from healthy donors. The enhanci ng activity of lung cancer serum factors on UV-induced mutagenicity wa s next confirmed by detecting an enhancement of K-ras codon 12 base su bstitution mutations in human RSb cells, as analyzed by polymerase cha in reaction (PCR) and differential dot-blot hybridization. Our results , together with previous findings; on suppression of mutagen-induced m utagenicity by human interferons, suggest the existence of extracellul ar factors that modulate the mutability of human cells. (C) 1998 Wiley -Liss, Inc.