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Background: Cerebral metastases are common intracranial lesions and have enormous prognostic impact. In many cases, brain metastases seem to be insensitive to chemotherapeutic treatment and are often source of recurrence. To date, the reasons for this are not entirely known. Dormant tumor cells are a population of non-apoptotic, low proliferating cells, which have the ability to be reactivated and can be the source of recurrence. Another mechanism of tumor cell survival are immunological escape mechanisms, involving the Natural Killer Group 2, member D (nkg2d) receptor-ligand system. In a previous study we were able to show that human brain metastases of pulmonary and breast cancer harbor a significant amount of dormant tumor cells, which often coexpress NKG2D ligands. We now wanted to investigate, whether chemotherapeutic treatment has an effect on expression of dormancy markers and nkg2d ligands. Materials and Methods: The murine breast cancer cell line E0771 and the murine pulmonary cancer cell line LLC were treated with ascending doses of cisplatin and cyclophosphamid, two chemotherapeutics which are also used in humans, for 2 to 10 days in comparison to negative controls. We performed a cytotoxicity assay. Expression of the dormancy-associated markers pdgf, fgf2, hif1alpha, epha5, h2bk and igfbp5 and the nkg2d ligands mult1, h60a, h60b, h60c and raet1b were analyzed by qrtPCR and immunocytochemistry (IHC). Results: Cytotoxicity assay revealed, that cells from both lines died significantly after treatment with Cisplatin in comparison to control conditions. Whereas cyclophosphamide had no effect on dormancy marker and nkg2dl expression, treatment with cisplatin led to a significant upregulation of many nkg2dl and dormancy marker expression in LLC and E0771 in a dose and time dependent manner. Results were confirmed via IHC.Conclusions: Although chemotherapy with cisplatin leads to death of many cells in culture, the surviving cells show a high expression of dormancy markers and of certain nkg2d ligands. Not only acquisition of dormancy but also nkg2d ligand expression might play an important role in chemoresistance of brain metastases. Markers from both groups could therefore be effective therapeutic targets.

P10.05 NKG2DL expression and dormancy in cerebral metastases: impact of chemotherapeutic treatment