EFFECT OF HYDROXYUREA AND NORMAL PLASMA ON DNA-SYNTHESIS IN LYMPHOCYTES FROM FANCONI-ANEMIA PATIENTS

Fanconi anemia (FA) is characterized at the cellular level by a high f requency of spontaneous chromosomal aberrations; crosslinking agents c ause an abnormal increase in the frequency of chromosomal damage, and semiconservative DNA synthesis is severely inhibited. Deoxyribonucleot ides are needed in both semiconservative and repair DNA synthesis. To investigate the involvement of deoxyribonucleotide pools in the inhibi tion of DNA synthesis in FA, we evaluated the effect on FA lymphocytes of hydroxyurea (HU), an inhibitor of ribonucleotide reductase which i s known to alter the intracellular levels of deoxyribonucleotides. To achieve this goal, lymphocyte cultures of 4 FA patients and 4 normal i ndividuals were used. Cultures were treated with HU and/or mitomycin C and normal human plasma. All cultures were processed to detect the nu mber of DNA synthesizing nuclei by autoradiography. Scoring of 2000 nu clei for each kind of culture every 6 h in the last 24 h of incubation showed that, in long incubation periods, DNA synthesis in FA is large ly inhibited by HU and this hypersensitivity may be partially decrease d by addition of normal human plasma. It is known that recovery from d amage induced by HU involves several enzymes such as flavin oxido-redu ctase, superoxide dismutase and catalase which are involved in the pro duction or scavenging of O-2 radicals; FA cells are deficient in the d etoxification of oxygen and this could explain the response of FA cell s to HU.