Investigating the Role of Btk/Her2 Signaling as a Therapeutic Target for Restoration of T Cell Function and Reversal of Trastuzumab Resistance in Her2+ Breast Cancer

The human epidermal growth factor receptor 2 (HER2) is estimated to be aberrantly expressed in up to 25% of invasive breast cancers (iBC). Although selective inhibition of HER2 with FDA-approved Trastuzumab (herceptin) is broadly considered effective for treatment of HER2-overexpressing iBCs, approximately 50% of patients are non-respondent. This indicates that additional/alternative signaling pathways exist and there is a clinical urgency for identifying agents which can target these targets. The activation of Bruton’s tyrosine kinase (BTK) was initially identified to be involved in the initiation of myeloid malignancies. However, mounting evidence implicates BTK’s role in the pathogenesis of solid tumors, including glioblastoma, ovarian and lung cancer; Btk overexpression has been suggested to confer growth and/or survival advantage to cancerous cells. However, to the best of our knowledge, the use of selective BTK inhibitors such as Acalabrutinib as pharmacologic modulator of T cell activity and drug sensitivity in Trastuzumab-resistant BC remains unexplored. Here, our preliminary data demonstrates that BTK is critical for HER2 signaling where it promotes cancer stem cell (CSCs)-like phenotype, modulates T cell activity and is associated with Trustuzumab resistance in HER2-overexpressing cells. Conversely, silencing Btk leads to attenuated mammosphere formation, induced a T-cell inflamed microenvironment, and enhanced sensitivity to Trastuzumab. These results suggest the critical role of BTK in the pathogenesis, anticancer immunity and therapy response of Trastuzumab-resistant HER2-overexpressing BC cells. Herein, to evaluate the potential of targeting BTK for treating HER2+ Trastuzumab-resistant breast cancer, we propose a 3-year project addressing the following specific aims: Aim 1: To investigate the role BTK signaling in HER2 positivity, CSCs phenotype, T-cell exclusion or exhaustion and Trastuzumab resistance in HER2+ BC cells. Aim 2: To determine the molecular mechanism underlying BTK/HER2 signaling-induced T cell exclusion, cancer stemness, and therapy resistance in HER2+ BC cells. Aim 3: To evaluate the translational feasibility of Trastuzumab and Acalabrutinib (second generation BTK inhibitor) combinatorial therapy to enhance anticancer immunity and boost therapeutic efficacy against therapy resistance in HER2+ BC, ex vivo and in vivo. The results collected from this study will provide supports for targeting BTK/HER2 signaling axis in therapy-resistant HER2+ BC and design future clinical trials.