Abstract 296: Trastuzumab sensitizes HER2+ breast cancer to increase efficacy of chemotherapy in vitro and in vivo
Authors: Shah Alay , Jarrett Angela , Syed Anum , Yankeelov Thomas , Sorace Anna 
Published: August 2019

Purpose: Optimization of drug synergy has potential to improve efficacy of combination treatments. Breast cancer that overexpresses the human epidermal growth factor receptor (HER2) has a higher chance of metastasis and recurrence compared to HER2- patients. Standard-of-care treatment typically includes chemotherapy (i.e., paclitaxel, doxorubicin) followed by or in combination with targeted antibody treatments (i.e., trastuzumab, pertuzumab). The purpose of this study is to investigate, the timing, order, and dosage of standard-of-care combination therapies and how they affect the overall efficacy of treatment in HER2+ breast cancer in vitro and in vivo.

Experimental Procedure: BT474, HER2+ breast cancer cells were longitudinally evaluated with time resolved microscopy to measure changes in cell confluence (Incucyte). Cells were treated with combinations of trastuzumab (10-50 ug/ml) and paclitaxel (10-150 nmol/L) with alternating sequencing and timing (24, 48 hrs) of the therapies (N=8 replicates per combination). Cellular confluence was measured over 4 days and normalized percent changes were calculated. BT474 tumor-bearing mice (N=42) were treated singularly or in combination with alternating sequencing of trastuzumab (10 mg/kg) and doxorubicin (1.5 mg/kg). Tumors were evaluated for changes in tumor size and survival. An unpaired t-test was used for statistical comparisons for in vitro and in vivo studies. Assessment of cellular and tumor microenvironment influences on drug synergy are ongoing.

Results: Experimental outcomes indicate that alternating order and dose play a crucial role in the anticancer efficacy and synergistic drug effects. Trastuzumab (25 ug/ml) dosing prior to paclitaxel (50 nmol) significantly decreased cell confluence compared to the same total therapeutic dose where paclitaxel was introduced first in vitro (p &lt; 0.001). Similarly, trastuzumab dosing in vivo prior to a one dose of chemotherapy achieves the same tumor response as a two doses of chemotherapy administered simultaneously with trastuzumab (p &lt; 0.001).

Discussion and Conclusions: Sequencing of targeted and chemotherapies altered treatment response both in vivo and in vitro, resulting in differences in overall cancer cell death. In vitro longitudinal imaging can provide numerous combinations of treatments can be tested to ultimately find optimal treatments to test in vivo. Recent evidence also shows that targeted anti-HER2 therapy can alter vascularity, oxygenation, and immune cell infiltration in HER2+ breast cancer tumors; therefore, further investigations in the temporal effects of the tumor microenvironment are warranted. Improved temporal windows of anticancer effects for standard-of-care combination therapies could improve breast cancer treatment regimens and potentially minimize toxic side effects.

Funding was provided by CPRIT RR160005 and ACS-RSG-18-006-01-CCE.

Citation Format: Alay Shah, Angela Jarrett, Anum Syed, Thomas Yankeelov, Anna Sorace. Trastuzumab sensitizes HER2+ breast cancer to increase efficacy of chemotherapy in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 296.