Methotrexate resistant cell lines for the study of gestational trophoblastic neoplasia

The term gestational trophoblastic disease (GTD) describes a range of pathologies derived from the villous trophoblasts of the placenta. These include benign entities such as partial and complete hydatidiform mole as well as invasive cancers such as gestational choriocarcinoma, placental site trophoblastic tumors, and epithelioid trophoblastic tumors. Collectively, the malignant forms of GTD are known as gestational trophoblastic neoplasia (GTN). The risk of GTN following a complete molar pregnancy ranges between 8-25%. Low risk patients are expected to have a high likelihood of response to single agent chemotherapy with methotrexate or actinomycin D, but the incidence of resistance to single agent chemotherapy among low risk patients remains 25-50%. We used gene expression microarrays to compare methotrexate sensitive trophoblastic cell lines to sublines that were conditioned to become methotrexate resistant. Two trophoblastic cell lines, CRL-1584 (3A-Sub E) and JEG-3 were purchased from American Type Culture collection (ATCC) (Manassas, VA). CRL-1584 (3A-Sub E) was originally derived from human term primary placental cells and then immortalized using SV40 virus. JEG-3 is a clonal human choriocarcinoma. The cell lines were serially passaged in complete medium supplemented with each cell line’s respective IC50 concentration of methotrexate until the cell lines were able to proliferate normally. Subsequently, the concentration of methotrexate was increased by one half-log concentration. The process was repeated iteratively until the cells became senescent. At each log concentration of methotrexate resistance, cell line stocks were frozen to establish a separate subline of each cell line. Based on their relative level of resistance to methotrexate, these were designated JEG-3-R7, JEG-3-R6, and JEG-3-R5 (for 10-7 M through 10-5 M methotrexate resistance). Over the same time period (approximately 11 months), we were able to induce only one order of magnitude of resistance in the normal placenta cell line; that line was designated NP-R7. In parallel, the parent cell lines were passaged in normal medium to control for any physiologic changes induced by prolonged culture in vitro.