Urine levels of N-[9-(beta-D-ribofuranosyl)purin-6-ylcarbamoyl]-L-threonine, N6-(delta 2-isopentenyl)adenosine, and 2'-O-methylguanosine as determined by radioimmunoassay for normal subjects and cancer patients

Abstract

Radioimmunoassays (RIA) are presented for the evaluation of the levels of the following three modified nucleosides in human urine: 2'-O-methylguanosine (Gm), N6-(delta 2-isopentenyl)adenosine (i6A), and N-[9-(beta-D-ribofuranosyl)purin-6-ylcarbamoyl]-L-threonine (t6A). Competitive inhibition of the RIA was provided by 2 to 10 microliters of untreated urine and the sensitivity of each RIA was in the pmol range. Partial fractionation of urine indicated that the majority of inhibitory activity was in the fraction coeluting with a nucleoside standard. The amounts of nucleosides in 24-hr urine samples from eight normal subjects were 2.2 +/- 0.9 mg (S.D.) for t6A; 0.17 +/- 0.09 mg for Gm; and 0.050 +/- 0.019 mg for i6A. The levels of t6A, i6A, and Gm were also determined by RIA of urine samples of patients with lymphomas or solid tumors. Levels of t6A were significantly elevated for patients with lung cancer (p less than 0.001), non-Hodgkin's lymphoma (p less than 0.05), and other solid tumors (p less than 0.02) but not for patients with Hodgkin's disease. The RIA data on the other two nucleosides, i6A and Gm, showed no similarly significant variations. Increased levels of t6A in the cancerous state were substantiated by isolating the t6A fraction from the urine of normal subjects of patients with lung cancer and quantitating the amount by use of UV adsorption. These preliminary results indicate that RIA for t6A might be clinically useful by providing a complementary approach to the assessment of the levels of modified nucleosides by gas-liquid or high-performance-liquid chromatography.