Abstract 863: Inhibition of breast cancer metastaticprogression by a novel uPAR targeted monoclonal antibody, ATN-658, correlateswith the uPAR expression.

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Abstract The urokinase plasminogen activator receptor (uPAR) has been implicated in the progression of metastatic disease in a number of different solid tumor types including breast cancer. We have developed a therapeutic monoclonal antibody, ATN-658, that targets uPAR in a novel manner. ATN-658 does not inhibit the binding of uPA to uPAR but appears to have pleiotropic effects on other uPAR interactions including those with various integrins. In the present study, we utilized 231LM2-4H2N, a novel highly metastatic variant of the triple negative breast cancer cell line cell line, MDA-MB-231, to evaluate the effect of ATN-658 on metastasis. This variant has been transfected to also express HER2 and metastases in this model are resistant to targeted treatments such as trastuzumab and sunitinib. Orthotopic 231LM2-4H2N xenograft tumor spontaneously metastasizes to lung and liver and forms large macroscopic metastases that lead to death. We transfected 231LM2-4H2N cells with dTomato and Luc2 to allow for real time assessment of metastatic progression using IVIS imaging. Primary orthotopic tumors were staged to 500 mm3, at which time they were resected and the mice followed using bioluminescence to detect metastases, which typically appear in the lungs within 2-3 weeks post-resection. Mice were randomized once lung metastases were visible and treatment was initiated using vehicle control, lapatanib (30 mg/kg QD), ATN-658 (10 mg/kg Q3D) or the combination of lapatanib and ATN-658. Growth of metastases was estimated using average radiance measurements. ATN-658 inhibited metastatic progression by ∼90% and doubled median survival compared to the vehicle control in this study. Lapatanib had no effect on the size of the metastases or survival and the combination of ATN-658+lapatanib inhibited metastatic progression and survival to the same extent as ATN-658 monotherapy. The activation of ERK was significantly inhibited by ATN-658 in vivo although this alone was insufficient to inhibit tumor growth since lapatanib also inhibited ERK to the same extent suggesting the other effects were being mediated by ATN-658. The effect of ATN-658 monotherapy on metastatic tumor growth was much greater in the 231LM2-4H2N model than in the parental MDA-MB-231 model. In order to probe the reason for this difference in effect, we analyzed the expression of uPAR in the various MDA-MB-231 variants. uPAR expression was significantly upregulated in HER2-transfected MDA-MB-231 breast cancer cells suggesting that the level of uPAR expression may dictate the degree of response to ATN-658. If this hypothesis can be validated, this would provide a patient enrichment strategy for the humanized version of ATN-658, huATN-658, which is getting ready to go into the clinic. Citation Format: Irawati Kandela, Andrey Ugolkov, Giulio Francia, Shafaat Rabbani, Robert S. Kerbel, Andrew P. Mazar. Inhibition of breast cancer metastaticprogression by a novel uPAR targeted monoclonal antibody, ATN-658, correlateswith the uPAR expression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 863. doi:10.1158/1538-7445.AM2013-863