HER2 positive (HER2+) is a breast cancer (BC) subtype characterized by HER2 overexpression/amplification that affects nearly 15% of BC patients and correlates with poor prognosis. These patients receive trastuzumab (T), an anti-HER2 monoclonal antibody, but resistance events (40-60%) hamper its clinical benefit. Previously we have demonstrated that TNFα (TNF) induced mucin 4 (MUC4) expression and turned T-sensitive cell lines and tumors into resistant ones.

Nowadays, new anti-HER2 therapies are being used in the clinical setting, such as lapatinib (a dual inhibitor of EGFR and HER2), and antibodies like T-DM1 (combines TZ with the anti-microtubule agent

emtansine), and pertuzumab (P) that impeds HER2 dimerization.

The aim of this work was to study the role of TNF in resistance to the new HER2-targeted therapies.

We used BT-474-C (control cells) and BT-474-T2, engineered in our lab to stably overexpress TNF, and were proven to be sensitive and resistant to T, respectively.

We performed dose-response curves for T-DM1, they show that inhibits proliferation of BT-474- C cells at 0.01 μg/ml. On the other hand, BT-474-T2 cells were resistant in the same experimental conditions and they exhibited reduced T-DM1 binding with respect to BT-474-C. BT-474-C cells were sensitive to low concentrations of T-DM1 with 0.51 nmol/L, but in BT-474-T2 cells T-DM1 was ~10 times less potent than control cells (IC 50 3.34 nmol/L). When we abrogated MUC4 expression, BT-474-T2 cells were sensitized to T-DM1, showing that TNF-induced MUC4 expression is responsible for T-DM1 resistance in this cell line.

We assessed the effect of lapatinib performing a dose-response curve. Results shown a similar IC50 for BT-474 C and T2 cells (0.26 μM and 0.28 μM, respectively).

When we studied P effect, we observed that the combination of T+P was more effective inhibiting proliferation in BT-474-C cells than T alone, despite these results binding of the antibody showed no change between the cell lines. In BT-474-T2 cells proliferation was slightly inhibited by the combined treatment. In vivo experiments showed that BT-474-C tumors were sensitive to T and the combination of T+P, but BT-474-T2 tumors did not respond to any of these treatments.

These results suggest that TNF plays an important role in multiresistance to HER2-targeted therapies, specifically T-DM1 and P, but not in lapatinib resistance. We propose TNF as an attractive target and we suggest that HER2+ patients resistant to T could be eligible for a combination of HER2-targeted therapies and a TNF-blocking treatment to overcome resistance.

Citation Format: María F. Mercogliano, Mara De Martino, Sofia Bruni, Leandro Venturutti, Martín Rivas, Matías Amasino, Cecilia J. Proietti, Patricia V. Elizalde, Roxana Schillaci. TNFα induces multiresistance to HER2-targeted TNFα induces multiresistance to HER2-targeted therapies in HER2-positive breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1195. doi:10.1158/1538-7445.AM2017-1195