The involvement of chromatin condensation in camptothecin-induced chromosome breaks in G(0) human lymphocytes

In the present study we evaluated campthotecin (CPT)-induced chromosomal da mage in human lymphocytes in the G(0) phase of the cell cycle as revealed b y the premature chromosome condensation technique. The results obtained her e indicate that CPT was able to induce chromosome fragments in the G(0) pha se of the cell cycle of human lymphocytes as detected in prematurely conden sed chromosomes. This result appears to be rather surprising, since the DNA lesions produced by CPT (e.g. 'protein concealed' DNA single-strand breaks ) should not produce any damage in G(0). A possible explanation for this re sult could come from much evidence to suggest that chromatin condensation p rocesses are significantly involved in the conversion of DNA lesions into c hromosome breaks in prematurely condensed chromosomes. The unexpected clast ogenic behaviour of CPT can be explained taking into account the chromosome condensation induced by mitosis promoting factors when human lymphocytes a re fused in G(0), thus converting the 'protein concealed' DNA single-strand breaks induced by CPT into chromosome breaks. The same perspective should be taken into consideration for breaks induced by CPT under normal physiolo gical conditions in the G(2) phase of the cell cycle.