[243] Etanercept as a New Agent for the Treatment of ErbB-2 Overexpressing Breast Tumors.

Martin A Rivas, Mercedes Tkach, Esteban Maronna, Ricardo Sanchez Marull, Wendy Beguelin, Cecilia J Proietti, Maria Celeste Diaz Flaque, Eduardo H Charreau, Patricia V Elizalde, Roxana Schillaci, Isabel Frahm. Instituto de Biología y Medicina Experimental-CONICET, Buenos Aires, Argentina; Sanatorio Mater Dei, Buenos Aires, Argentina

Background: ErbB2 overexpressing breast cancer is associated with high aggressiveness and elevated metastatic potential. Patients with this diagnosis usually undergo treatment with the monoclonal antibody Herceptin. However, about 70% of patients develop primary or secondary resistance to Herceptin. We previously demonstrated that tumor necrosis factor alpha (TNF) induces proliferation of the BT-474 and SKBR-3 human breast cancer cell lines, through the transactivation of ErbB2. Moreover, we observed that TNF induces proliferation of these cell lines even in the presence of Herceptin.
Design: In the present study we evaluated the expression of TNF in the Herceptin-resistant JIMT-1 human breast cancer cell line and the effectiveness of in vivo blockage of TNF with Etanercept, a TNF receptor 2-FcIgG fusion protein, on JIMT-1 tumor growth.
Results: JIMT-1 cell line was grown in RPMI medium in the presence of 10%, 1% and 0.1% fetal calf serum and TNF expression was detected by Western blot. We observed that in all culture conditions JIMT-1 synthesize the pro-TNF protein of 26 kDa. As JIMT-1 is a cell line that overexpress ErbB-2 and show in vivo and in vitro resistance to Herceptin inhibitory effect, and taking into account that TNF is able to transactivate ErbB-2 and to promote growth of breast cancer cells, we asked whether TNF played a role in JIMT-1 growth in vivo. With that purpose we injected 3x106 JIMT-1 cells in NIH nude mice and when the tumors reached approximately 20mm3 (at day 9), we separated animals at random and started the treatment with Etanercept 5 mg/kg though ip injection twice a week or with human IgG as control (8 animals/group). Tumor growth was monitored along 24 days. We observed at day 35th that Etanarcept treatment inhibited 46% JIMT-1 tumor growth respect to IgG-treated animals (P<0.001). Histopathological analysis showed solid papilar, file tumor and G3, GN3 in both experimental groups. However IgG-injected animals showed tumors with no necrosis or fibrosis, while Etanercept-treated tumors exhibited 30-20% necrosis and 10% fibrosis. Moreover mitotic count per HPF was 7 and between 4-6 in IgG and Etanercept group respectively.
Conclusions: As TNF has been shown to be present in the tumor microenvironment of a significant proportion of human infiltrating breast cancers, our findings would have clinical implication and propose Etanercept as a new agent to overcome clinically observed Herceptin resistance.
Category: Breast

Tuesday, March 1, 2011 1:00 PM

Poster Session IV # 11, Tuesday Afternoon


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