Breast cancer is the most common cancer in women and the second leading cause of cancer-related deaths in females. Overexpression of HER-2 occurs in 20-30% of breast cancer patients and is associated with increased aggressiveness and significantly shortened disease-free and overall survival rates. Trastuzumab is the most commonly used adjuvant therapy for HER-2 positive breast cancer; however, therapeutic resistance often develops, likely due to tumor heterogeneity and a failure of effective immune response. Therefore, the overall survival rate of patients with HER-2 positive, metastatic breast cancer remains modest. In this study, we describe a novel targeted therapy for HER-2 positive breast cancer, which induces tumor cell apoptosis and activates immune surveillance against the tumor.

Poly Inosine Poly Cytosine (pIC) is a known activator of apoptotic and inflammatory processes. We recently showed that targeted delivery of pIC into EGFR-overexpressing tumors induced tumor cell killing and the expression of pro-inflammatory cytokines both in vitro and in vivo. In the current study, we report on a novel chemical vector composed of linear polyethylenimine, polyethyleneglycol and a high affinity targeting moiety, HER-2 Affibody, (PPHAffibody), which selectively delivers pIC to HER-2 overexpressing breast cancer cells. We demonstrated that targeted delivery of pIC selectively induced apoptosis in HER-2 overexpressing cells, while cells with little to no HER-2 expression remained unaffected. Importantly, survival of trastuzumab resistant breast cancer significantly decreased upon pIC/PPHAffibody treatment. Confocal microscopy confirmed the selectivity of pIC/PPHAffibody binding and internalization into HER-2 overexpressing cells. To test the effect of pIC/PPHAffibody on immune cell recruitment and activation, ELISA and chemotaxis assays were utilized. Treatment of HER-2 overexpressing breast cancer cells with pIC/PPHAffibody induced the secretion of pro-inflammatory cytokines, such as IP-10 and RANTES, and promoted the chemotaxis of peripheral blood mononuclear cells (PBMC). In co-culture of HER-2 overexpressing tumor cells and PBMCs, pIC/PPHAffibody led to even more profound tumor cell killing than in the absence of PBMCs, indicating that the targeted pIC delivery indeed activates immune cells against the tumor. The in vivo efficacy of pIC/PPHAffibody treatment is currently under investigation. Furthermore, we will test whether pIC/PPHA synergizes with trastuzumab, both in vitro and in vivo.

The data in this study indicate that targeted delivery of pIC restores immune surveillance and selectively induces breast cancer cell apoptosis, overcoming trastuzumab resistance. Thus, pIC/PPHA is a promising new addition to the available therapies for metastatic breast cancer patients.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B243.

Citation Format: Maya Zigler, Salim Joubran, Alexei Shir, Noofar Edinger, Shoshana Klein, Alexander Levitzki. Targeting HER-2 positive breast cancer by inducing apoptosis and immune cell activation, overcoming trastuzumab resistance. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B243.