E1A sensitizes HER2/neu-overexpressing Ewing's sarcoma cells to topoisomerase II-targeting anticancer drugs

Overexpression of the HER2/neu oncogene is associated with tumori-genicity and drug resistance in many types of cancer. Three different human Ewing's sarcoma cell lines (TC71, RD, and A4573) were found to express high levels of the HER2/neu protein. Transduction of TC71 cells with the E1A gene using an adenoviral vector (Ad-E1A) down-regulated HER2/neu overexpression in th ose cells and increased cytostasis. E1A-induced apoptosis was demonstrated by both flow cytometric analysis and Western blot analysis using a poly(ADP -ribose) polymerase antibody. After transduction of the E1A gene into these cells, the sensitivity of these cells to VP-16 (etoposide) was enhanced 18 -fold and to Adriamycin 5-fold. However, no change was seen in cisplatin se nsitivity. E1A also significantly increased topoisomerase II alpha protein expression, indicating that the upregulation of topoisomerase II alpha may be one of the mechanisms by which E1A enhanced the sensitivity to topoisome rase II-targeting anticancer drugs, such as VP-16 and Adriamycin, but not c isplatin. In summary, these studies demonstrated that Ad-E1A can down-regul ate HER2/neu overexpression and up-regulate topoisomerase II alpha expressi on in human Ewing's sarcoma cells, increasing their apoptosis rate and enha ncing their sensitivity to VP-16 and Adriamycin.