Purpose: We determined whether inhibitor of caspase-3 activated deoxyribonuclease (ICAD) enhances resistance to apoptotic stimuli or inhibits DNA fragmentation by inactivating caspase-3 activated deoxyribonuclease.
Materials and methods: The liposome mediated gene transfer method was used to introduce ICAD complementary DNA into ACHN cells and the expression of ICAD protein per clone was evaluated by Western blot analysis. Effects of cisplatin treatment on growth inhibition and apoptosis in the ACHN sublines were assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, DNA fragmentation assay and Western blot analysis of poly(ADP-ribose) polymerase protein. The limiting dilution assay was also performed to examine the effect of cisplatin treatment under anchorage independent conditions. Furthermore, nude mice bearing the ACHN sublines were given intraperitoneal injection of 5 mg./kg. cisplatin 1 and 2 weeks after the implantation of tumor cells and changes in tumor volume was measured.
Results: ICAD transfected ACHN cells inhibited DNA degradation after cisplatin treatment but not control vector only transfected ACHN cells, whereas a similar degree of apoptotic cell death induced by cisplatin in ICAD and control vector only transfected ACHN cells was observed on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and Western blot analysis of poly(ADP-ribose) polymerase protein. However, the limiting dilution assay revealed that ICAD transfected ACHN cells had high resistance to pretreatment with cisplatin compared with control vector only transfected ACHN cells. Moreover, although there was no significant difference in the in vivo growth of ACHN sublines, cisplatin treatment induced the elimination of control vector only transfected ACHN cell tumors. In contrast, most ICAD transfected ACHN cell tumors continued to grow after cisplatin treatment.
Conclusions: These findings suggest that when ICAD is over expressed in tumor cells, it renders them highly resistant to therapy induced apoptosis, resulting in enhanced tumor progression.