Deoxyuridine triphosphatase (dUTPase) expression and sensitivity to the thymidylate synthase (TS) inhibitor ZD9331

Uracil DNA misincorporation and misrepair of DNA have been recognized as im portant events accompanying thymidylate synthase (TS) inhibition, dUTPase c atalyses the hydrolysis of dUTP to dUMP, thereby maintaining low intracellu lar dUTP, We have addressed the relationship between dUTPase expression and cellular sensitivity to TS inhibition in four human lung tumour cell lines . Sensitivity (5-day MTT assay) to the growth inhibitory effects of the non -polyglutamatable, specific quinazoline TS inhibitor ZD9331, Varied up to 2 0-fold (IC50 3-70 nM). TS protein expression correlated with TS activity (r (2) = 0.88, P = 0.05), Intracellular concentrations of drug following expos ure to ZD9331. (1 mu M, 24 h) varied by similar to 2-fold and dTTP pools de creased by > 80% in ail cell lines. No clear associations across the cell l ines between intracellular drug concentrations, TS activity/expression, or TTP depletion could be made. dUTPase activity varied 17-fold and correlated with dUTPase protein expression (r(2) = 0.94, P = 0.03). There was a strik ing variation in the amount of dUTP formed following exposure to ZD9331 (be tween 1.3 and 57 pmole 10(-6) cells) and was in general inversely associate d with dUTPase activity. A large expansion in the dUTP pool was associated with increased sensitivity to a 24-h exposure to ZD9331 in A549 cells that have low dUTPase activity/expression. dUTPase expression and activity were elevated (approximately 3-fold) in two Variants of a human lymphoblastoid c ell line with acquired resistance to TS inhibitors, further suggesting an i mportant role for this enzyme in TS inhibited cells. (C) 2000 Cancer Resear ch Campaign.