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.