DR-01 * NOVEL PEDIATRIC EPENDYMOMA MODELS SHOW HIGH CHEMOTHERAPY-RESISTANCE AND HYPERACTIVATION OF ABC-TRANSPORTERS

Abstract

Malignant ependymoma is one of the most frequent CNS-tumors in childhood characterized by a poor outcome owing to low effects of chemotherapy accompanied by high rates of recurrence. However, the underlying mechanisms are still poorly understood. Aim of this study is to investigate the role of ABC-transporters - a well-known resistance mechanism of cancer cells - in primary and recurrent ependymomas. In a collaborative approach primary adherent and neurospheroid cell cultures of four tumors were established of which two developed stable cell lines. The impact of ABC-transporters on chemotherapy-resistance of pediatric ependymoma cells was then analyzed by cytotoxicity assays, Western blot, Microarray and FACS. All tested cells were highly resistant against etoposide and vincristine, both well-known substrates of ABC-transporters. In contrast, treatment with either cisplatin or temozolomide was more effective. With respect to primary versus recurrent as well as supratentorial versus infratentorial tumors no significant difference in chemosensitivity was observed. The analysis of ABC-transporter expression revealed that ABCG2 was highly expressed throughout the cell panel at both protein and RNA level. Moreover, ependymoma cells exhibited the same ABCG2 activity as A549 cells, a well described ABC-transporter resistance model. In contrast to ABCG2, expression of ABCB1 and ABCC1 differed among the tested cells. Combination of chemotherapeutics with the ABC-transporter inhibitors imatinib, erlotinib, cyclosporine A and verapamil had only minor effects on cytotoxic response of ependymoma cells. Interestingly, a synergistic effect of etoposide and vincristine with erlotinib was seen. Taken together primary as well as recurrent ependymomas are highly resistant against classical chemotherapeutics. Furthermore, we could show that ependymoma cells express highly active ABC-transporters. This fact might also have an impact on chemotherapy-resistance towards the therapeutic regimens currently applied in ependymoma therapy. The cellular mechanisms underlying these results will be investigated in further studies.