CHROMOSOME POLYPLOIDIZATION IN HUMAN LEUKOCYTES INDUCED BY RADIATION

Abstract

A great quantity of literature has accumulated on the effects of radiation and radiomimetic agents upon cells. Much of this work has been performed on mammalian cells both in vivo and in tissue cultures. Some of these damaging effects can be seen in dividing cells. After the development of a technique for tissue culture of human peripheral blood, we were able to demonstrate abnormal patterns and chromosomal polyploidy in cultures from patients who had been treated with A-8103 (a piperazine derivative with antitumor activity) , l nitrogen mustard, 6-mercaptopurine, and A-649 (another antitumor agent).2 During treatment and for some time after treatment in these patients, structural changes could be seen in the chromosomes as either chromatid or chromosome deletions and chromosomal breakage. Abnormally shaped chromosomes were also seen, particularly ring forms and dicentrics. Although aneuploidy was observed, the major numerical variation consisted of metaphases showing polyploidy with random distribution of chromosomes and diplochromosomes. When normal human leukocytes were tested in vitro with the chemotherapeutic agents already mentioned, as well as with streptonigrin and cycl~phosphamide,~ similar results were obtained. From these studies we postulated that two different types of damage were induced in the cells by the chemicals. One type of damage is apparent in the hereditary material, and it can be characterized by the structural chromosomal changes. The second type of damage is interpreted as damage to the mitotic apparatus of the cells, as evidenced by the induction of polyploidy. Simultaneously, initial studies from patients treated with x-rays and cobalt-60 demonstrated that the same type of chromosomal anomalies were present in their peripheral leukocytes as those induced with chemotherapeutic agents. Generally, these were structural variations and chromosome polyploidization. Certainly, chromosomal changes have been described in association with x r a d i a t i ~ n ~ , ~ and 1311 therapye,' and, rarely, following diagnostic x-radiation. However, in most of these reports, the occurrence of polyploidy was overlooked, and when polyploidy was mentioned, it was not characterized. Since both structural damage as well as polyploidy lead to genetic transformation or to somatic cell death, we thought it of paramount interest to determine whether or not induction of chromosomal polyploidy by radiation was a constant feature in human somatic cells. Such effects may have a bearing on both the induction as well as the treatment of cancer. For the present study, we determined not only polyploidy, but also the amount of aneuploidy, chromosomal breakage, ring forms, translocations, dicentrics, and tricentrics as well as other rearrangements appearing in patients exposed to radiation therapy. In addition, normal human leukocytes were exposed to x-rays in cultures, and information of induced damage was obtained.