Urinary excretion of modified nucleosides as biological marker of RNA turnover in patients with cancer and AIDS.

Using boronate gel affinity chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC), a method for the simultaneous determination of 12 urinary modified nucleosides has been developed. The RP-HPLC fractions were identified by gas chromatography/mass spectrometry analysis. The HPLC quantitation of urinary nucleoside levels before and after surgery of cancer patients suggested that urinary 5'-deoxy-5'-methylthioadenosine and N-[(9-beta-D-ribofuranosyl-9H-purine-6-yl) carbamoyl]-L-threonine (t6A) levels were helpful in monitoring therapeutic effects in cancer patients. From the fact that molar ratios of urinary N2,N2-dimethylguanosine (m2 2G)pseudouridine (psi) and t6A/psi in cancer patients were lower than those of normal or post-surgical cancer patients, the increase of rRNA content in cancer tissues growing rapidly was estimated using the stoichiometric relationship between the ratio of the number of residues of their modified nucleoside in RNAs and the proportion of rRNA to total RNAs in average tissues of whole body. Furthermore, from the estimation of RNA turnover using urinary nucleoside levels, it was found that the half-lives of rRNA rather than tRNA of patients with cancer and those of both RNAs in the case of acquired immunodeficiency syndrome (AIDS) were extremely short compared with those of the normal. Thus, we discovered that the selected urinary modified nucleosides were very useful as a biological marker of whole-body RNA turnover in patients with cancer and AIDS.