Synthesis and tumor uptake of 5-halo-1-(2'-fluoro-2'-deoxy-beta-D-ribofuranosyl)[2-14C]uracils.
Mercer JR, Knaus EE, Wiebe LI.
A synthesis of 5-chloro- and 5-fluoro-1-(2'-fluoro-2'-deoxy-beta-D-ribofuranosyl)uracil (4a and 4b) and their 2-14C analogues has been developed. The tissue distribution of these radiolabeled compounds in BDF1 mice bearing Lewis lung tumors has been investigated. Compounds 4a and 4b undergo rapid blood clearance and urinary excretion. Selective retention of radioactivity was observed in tumor tissue, spleen, and intestine and with compound 4b also in the bone. Maximum tumor to blood ratios of 4.2 for the 5-chloro compound 4a and 10.3 for the 5-fluoro compound 4b were observed at 4h. These compounds were resistant to phosphorylytic cleavage and dehalogenation as indicated by the metabolic products observed in the urine and the absence of radioactivity in the liver. The interaction of 4b with the mouse erythrocyte transporter system was compared with physiological nucleosides in respect to ability to effect zero-trans influx of thymidine. The results show a competitive inhibition between 4b and the natural nucleoside. Evidence is presented for the direct metabolic defluorination of 5-fluorouracil to form uracil.