The effects of risedronate on bone metastasis of two malignant rat mammary carcinoma cell lines, mta and mtb-01
Boyd, Kelli Lynn
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The goals of this study were to 1) demonstrate that the MTA rat mammary adenocarcinoma cell line is nonresponsive to treatment with the bisphosphonate risedronate and 2) compare the in vitro cellular responses of the MTA (nonresponder) and a related rat mammary adenocarcinoma cell line, MTB-01 (responder) to risedronate in order to identify factors responsible for the MTA cell line's response to bisphosphonate treatment.|To establish the MTA cell line as nonresponsive to risedronate treatment, Berlin- Druckery rats received an intracardiac injection of 105 MTA cells. Risedronate was administered daily to test animals beginning on the day of tumor cell inoculation. Control animals received MTA cells and daily saline injections. Animals were euthanized on day 14 and metastatic bone lesions were enumerated and area measurements were taken microscopically from femurs and vertebrae. There was no statistically significant difference in the size or number of metastatic foci in treated verses untreated groups.|The second set of experiments focused on identification of cellular characteristics of the MTA cell line that may account for the lack of response to risedronate. To accomplish this objective, the effects of risedronate on MTA cells (nonresponder) and MTB-01 cells (responder) were compared utilizing in vitro assays measuring apoptosis, adhesion, and matrix metalloproteinase (MMP) production. Apoptosis was measured by cell morphology at the light microscopic level, DNA fragmentation, TUNEL staining, MiCK assay, Annexin-V binding, and transmission electron microscopy. Gelatin zymography was used to identify MMP-2 or MMP-9 protease production. When compared to MTA cells, MTB-01 cells were susceptible to risedronateinduced apoptosis, had decreased ability to bind to risedronate-treated bone, and did not produce MMP-2 or MMP-9 proteases. MTA cells were less susceptible to risedronateinduced apoptosis and produced MMP-2. Additionally, adhesion of MTA cells to bone matrix was not diminished by risedronate treatment. Our results suggest that the nonresponsive nature of the MTA cell line may be due to MMP-2 production (possibly allowing ongoing destruction of risedronate-treated bone), continued adhesion to risedronate-treated bone matrix, and decreased susceptibility to risedronate-induced apoptosis.