Benedetto Nicoletti

Incidence of chromosome abnormalities and clinical significance of karyotype in de novo acute myeloid leukemia

Cytogenetic studies with high-resolution banding were performed on specimens from 132 consecutive patients with de novo acute myeloid leukemia (AML). All patients were treated according to therapeutic protocols in the same institution. Clonal abnormalities were detected in 97 of the 124 patients in whom an adequate number of mitoses was obtained (78.2%). Neither sex, FAB classification, WBC, or the extent of bone marrow infiltrate affected the rate of chromosomal aberrations, whereas patients younger than 40 years had a greater proportion of normal karyotypes (p = 0.047). Two different chromosomal classifications were evaluated: the presence of normal and abnormal metaphases (NN-AN-AA classification), and a classification in cytogenetic categories, the latter being based on the frequency of cytogenetic abnormalities. Both classifications were found to correlate significantly with the clinical outcome. They also showed independent prognostic significance when age, sex, and FAB morphology were considered in a multivariate analysis. Two abnormalities were closely associated with specific clinical-pathologic subsets of AML. All the 15 patients with t(15;17) had acute promyelocytic leukemia; this translocation was not found in any other subset of AML. Eight of the nine patients presenting rearrangements at 11q23 belonged to a FAB subset with monocytic differentiation (M4 and M5). Our data suggest that cytogenetic findings should influence the therapeutic approach to AML. In particular, young patients with karyotypes associated with poor responses may be considered for more eradicating treatments, including allogenic bone marrow transplantation.

Cytogenetic study in lymphocytes from children exposed to ionizing radiation after the Chernobyl accident

The present study concerns the monitoring of children from the Byelorussian, Ukrainian and Russian republics exposed to the fall-out of the Chernobyl accident. Cytogenetic analyses have been performed on 41 children coming from different areas and exhibiting varying amounts of 137Cs internal contamination, as evaluated by whole-body counter (WBC) analysis. On a total of 28,670 metaphases scored, radiation-induced chromosome damage is still present, although at a very low frequency. Due to the very low fraction of dicentrics, because of the time elapsed from the accident and the relatively low doses of exposure, radiobiological dosimetry is not possible for these children. However, considering that the WBC data indicate that the children are still exposed to 137Cs contamination, the observed occurrence of stable chromosome rearrangements and breaks may represent the persisting effect of continuous low doses of radiation. The present study also indicates that the parallel use of internal contamination dosimetry and cytogenetics could be usefully employed to monitor individual exposure to radiation and to define further management measures.

Population cytogenetics of aphidicolin-induced fragile sites

SummaryChromosome fragile sites are inducible by aphidicolin in cultured human lymphocytes. To assess the frequency and distribution of these common fragile sites in the general population, a cytogenetic survey was performed on 126 subjects, 59 males and 67 females, whose age ranged from 1 day to 72 years. Common fragile sites, induced by aphidicolin, were widespread and showed a remarkably different sensitivity among individuals; age influenced the overall frequency of fragile sites. Moreover, both age and sex seemed to modulate the expression of specific fragile sites. In our population, the most common fragile sites were: 3p14, 16q23, Xp22, 6q26, 1p31, 4q31, 1p22, 7q22, 2q33, 3q27, 2q31, 7q32, 14q24, 10q22, 5q31, 2q37, 6p21.

Increased chromosome fragility in lymphocytes of short normal children treated with recombinant human growth hormone

A few years ago it was reported that some growth-hormone-deficient children had developed leukemia following therapy with human growth hormone. This raised concern that this therapy may stimulate tumor development. Since it is known that the tendency to develop cancer is closely related to chromosome breakage, we decided to investigate whether recombinant human growth hormone (rhGH) therapy can increase chromosome fragility. Ten short normal children were studied during their first year of treatment. Lymphocytes were collected at 0, 6 and 12 months of rhGH therapy, and we assessed the rate of spontaneous chromosome aberrations, the frequency of sister chromatid exchanges, the proliferative rate indices, the expression of common fragile sites induced by aphidicolin, and the sensitivity towards the radiomimetic action of bleomycin. At 6 months of therapy, there was a significant increase in bleomycin-induced chromosome aberrations, which remained unchanged after 1 year of treatment. An increase in spontaneous chromosome rearrangements at 6 and 12 months of therapy was also observed. These findings are further supported by data obtained from the analysis of 16 short normal children already on rhGH therapy.

STRUCTURAL CHROMOSOMAL REARRANGEMENTS IN HPAII-TREATED HUMAN LYMPHOCYTES

Restriction endonucleases have been shown to induce chromosome damage in a variety of cultured cells. We recently reported the coincidence between MspI-induced breakage and the location of common fragile sites. We have extended our study to HpaII, which induced a 4.5-fold increase in total breakage compared to controls. It appeared that a major contribution was given by stable chromosome rearrangements, which were present at a 14-fold increased frequency in comparison to the spontaneous levels. Moreover, several chromosome bands were involved in rearrangements in different cultures from different donors. Notably, HpaII-induced breakage occurred in the same bands where breakpoints of constitutional and neoplastic rearrangements are located.

Hypersensitivity of lymphoblastoid lines derived from ataxia telangiectasia patients to the induction of chromosomal aberrations by etoposide (VP-16)

Mammalian DNA topoisomerase II represents the cellular target of many antitumor drugs, such as epipodophyllotoxin VP-16 (etoposide). The mechanism by which VP-16 exerts its cytotoxic and antineoplastic actions has not yet been firmly established, although the unique correlation between sensitivity to ionizing radiation and to topoisomerase II inhibitors suggest the involvement of DNA double-strand breaks. In the present study we analyzed the chromosomal sensitivity of lymphoblastoid cell lines derived from ataxia telangiectasia (AT) patients to low concentrations of the drug. Our results indicate that AT derived cells are hypersensitive to the clastogenic activity of VP-16 either when the drug is present for the whole duration of the cell cycle or specifically in the G2 phase, confirming that the induction of DNA double strand breaks, to which AT cells seem typically sensitive, could have an important role in the biological activity of VP-16.

Characteristic chromosomal fragility of human embryonic cells exposed in vitro to aphidicolin

The frequency and distribution of aphidicolin (APC)-induced common fragile sites (cfs) were analyzed in human embryonic cells of different origins. Embryonic lung fibroblasts (MRC-5), amniocytes (AMNIO) and embryonic retina cells (HERO790) are as sensitive to the APC-induced clastogenic effect as peripheral lymphocytes, whereas embryonic kidney cells (HEK) seem more resistant to the induction of chromosomal gaps and breaks by the drug. Analysis of the distribution of fragile sites confirmed that the expression of specific APC-induced cfs varies in different cells and that the embryonic cell strains show a greater similarity among themselves than to lymphocytes. In addition, HEK, MRC-5, HERO790 and AMNIO cells show specific APC induction of the cfs at the 1p31.2 chromosomal band, which seems to be a distinctive feature of the embryonic stage of cells.