Etoposide induces heritable chromosomal aberrations and aneuploidy during male meiosis in the mouse

Abstract

Etoposide, a topoisomerase II inhibitor widely used in cancer therapy, is suspected of inducing secondary tumors and affecting the genetic constitution of germ cells. A better understanding of the potential heritable risk of etoposide is needed to provide sound genetic counseling to cancer patients treated with this drug in their reproductive years. We used a mouse model to investigate the effects of clinical doses of etoposide on the induction of chromosomal abnormalities in spermatocytes and their transmission to zygotes by using a combination of chromosome painting and 4 ,6-diamidino-2-phenylindole staining. High frequencies of chromosomal aberrations were detected in spermatocytes within 64 h after treatment when over 30% of the metaphases analyzed had structural aberrations (P < 0.01). Significant increases in the percentages of zygotic metaphases with structural aberrations were found only for matings that sampled treated pachytene (28-fold, P < 0.0001) and preleptotene spermatocytes (13-fold, P < 0.001). Etoposide induced mostly acentric fragments and deletions, types of aberrations expected to result in embryonic lethality, because they represent loss of genetic material. Chromosomal exchanges were rare. Etoposide treatment of pachytene cells induced aneuploidy in both spermatocytes (18-fold, P < 0.01) and zygotes (8-fold, P < 0.05). We know of no other report of an agent for which paternal exposure leads to an increased incidence of aneuploidy in the offspring. Thus, we found that therapeutic doses of etoposide affect primarily meiotic germ cells, producing unstable structural aberrations and aneuploidy, effects that are transmitted to the progeny. This finding suggests that individuals who undergo chemotherapy with etoposide may be at a higher risk for abnormal reproductive outcomes especially within the 2 months after chemotherapy.

Chromosome analysis of mouse one-cell androgenones derived from a sperm nucleus exposed to topoisomerase II inhibitors at pre- and post-fertilization stages

“…Although the molecular mechanisms underlying the clastogenicity of merbarone 15 remain to be fully elucidated, the dysfunction of ooplasmic topo II by this agent may cause the torsional stress of DNA to accumulate in remodeled sperm chromatin, thereby generating DNA strand breaks. In the present results, expanding chromatin of androgenones at 2−4 h after ICSI was extremely sensitive to merbarone, as compared to that of other groups.…”

“…On the other hand, there is no available information on the cytogenetic effects of topo II inhibitors on sperm nuclei at pre-or post-fertilization stages, except that mouse testicular sperm nuclei did not suffer chromosome damage by etoposide [11,15]. Sperm nuclei exhibit chromatin dynamics with fertilization as a turning point [19−21].…”

Acidic pH induces topoisomerase II-mediated DNA damage

“…On the other hand, VP-16 is known to induce deletions and DNA rearrangements (47). Based on our current results, acidic pH, being a TOP2 poison, is likely to be a rearrangement mutagen.…”

Relative Susceptibilities of Male Germ Cells to Genetic Defects Induced by Cancer Chemotherapies

“…The animal breeding tests show that most mutagens are effective in differentiating germ cells (Table 2), namely spermatocytes and spermatids [43]. Genetic damage to spermatids is a special case, because genetically damaged spermatids are known to develop into mature sperm that are fully capable of fertilizing eggs despite the presence of DNA damage [2,32]. Taken together, the available data from animal breeding and human sperm studies suggest that it may be ill advised to cryopreserve sperm within the first few weeks after the start of chemotherapy, even though sperm counts and motility are still high.…”

“…We improved the classic cytogenetic analysis of mouse zygotes by combining DAPI staining with chromosome-specific painting probes (PAINT) for the simultaneous detection of numerical as well as stable and unstable chromosomal aberrations [31]. The PAINT/DAPI procedure was recently used to demonstrate that therapeutic doses of etoposide affected primarily male meiotic germ cells producing unstable structural aberrations and aneuploidy, effects that were transmitted to the $ASQ308714 9 printed: 7/13/04 progeny [32]. This was the first report of an agent for which paternal exposure led to an increased incidence of aneuploidy in the offspring.…”