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Methotrexate, Paclitaxel, and Doxorubicin Radiosensitize HER2-Amplified Human Breast Cancer Cells to the Auger Electron-Emitting Radiotherapeutic Agent 111In-NLS-Trastuzumab

D. L. Costantini, D. F. Villani, K. A. Vallis, R. M. Reilly
2010 Journal of Nuclear Medicine  
Our goal in this study was to elucidate the mechanisms by which methotrexate radiosensitizes HER2-positive human breast cancer cells to the Auger electron emitter 111 In-trastuzumab modified with nuclear-localization sequence peptides ( 111 In-NLS-trastuzumab) and to compare these mechanisms with the potential sensitizing effects of paclitaxel and doxorubicin when combined with this radiopharmaceutical. Methods: Experiments were performed in MDA-MB-231 human breast cancer cells, their
more » ... ls, their HER2-transfected subclones (231-H2N), and 2 trastuzumabresistant variants (trastuzumab-resistant-1 and -2 [TrR1 and TrR2]). Effects of coexposure of these cells to 111 In-NLS-trastuzumab and low-dose, radiosensitizing methotrexate, paclitaxel, or doxorubicin were assessed by clonogenic cell-survival assay. Quantification of residual DNA damage was measured by the gH2AX-immunofluorescence assay, and cell cycle distribution was measured by fluorescence-activated cell sorting analysis. The radiation-enhancement ratio was calculated as the ratio of the surviving fraction (SF) of cells treated with 111 In-NLStrastuzumab alone to that of cells treated concurrently with 111 In-NLS-trastuzumab and methotrexate, paclitaxel, or doxorubicin. Results: A reduction in the SF in HER2-positive 231-H2N (55.7% 6 1.3%) and TrR1 (62.6% 6 6.5%) cells was demonstrated after exposure to 111 In-NLS-trastuzumab (;0.2 MBq/mg, 100 nmol/L) but not in MDA-MB-231 or TrR2 cells expressing low levels of HER2 (SF . 90%, P . 0.05). Coadministration of methotrexate, paclitaxel, or doxorubicin enhanced the cytotoxicity of 111 In-NLS-trastuzumab toward 231-H2N and TrR1 cells but not toward MDA-MB-231 or TrR2 cells. The radiationenhancement ratios for methotrexate, paclitaxel, and doxorubicin for 231-H2N or TrR1 cells were 2.0-2.2, 1.6-1.8, and 2.7-2.8, respectively. Methotrexate or doxorubicin combined with 111 In-NLS-trastuzumab, compared to treatment with 111 In-NLStrastuzumab alone, significantly increased residual gH2AX foci in 231-H2N and TrR1 cells but not in MDA-MB-231 or TrR2 cells or in any cell line treated concurrently with paclitaxel and 111 In-NLS-trastuzumab. Cells exposed to low-dose methotrexate accumulated in the G 1 /S phase of the cell cycle, whereas low-dose paclitaxel or doxorubicin caused cells to arrest in the G 2 /M phase. Conclusion: Low-dose methotrexate, paclitaxel, or doxorubicin potently sensitized HER2-overexpressing human breast cancer cells, with and without acquired trastuzumab-resistance, to the Auger electron emissions from 111 In-NLS-trastuzumab through cell cycle distribution changes and in part through the inhibitory effects of these agents on DNA damage repair.
doi:10.2967/jnumed.109.069716 pmid:20150272 fatcat:lbislbq44nhpfio5gcvuhbrxim