Specific chromosome instability induced by heavy ions: a step towards transformation of human fibroblasts?

Cultures of human skin fibroblasts were exposed to heavy ions: neon (E = 10.74 MeV/u) and argon (E = 10.52 MeV/u) at fluences of 10(6), 2 x 10(6) and 4 x 10(6) and lead (E = 9.5 MeV/u) at a fluence of 2 x 10(6) particles/cm2. Cultures were further prolonged for up to 25 passages and karyotyping was performed at various times. Radiation-induced chromosome anomalies progressively decreased, became quite rare at passages 5-7 and increased at later passages. Around passages 20-25, most anomalies occurring were dicentrics, involving telomeric regions of 13p and q arms principally and to a lesser degree those of 1p, 16p and 16q arms. These non-random rearrangements paralleled the appearance of clones with unbalanced karyotypes. In particular, two independent proliferating clones were characterized by a monosomy 13. It is concluded that most chromosome lesions directly induced by heavy ions are hardly compatible with cell survival and thus disappear after a few cell generations. However, surviving cells acquire a de novo chromosome instability leading to the formation of clones with unbalanced karyotypes at late passages.