Abstract P4-02-02: Increased tumor perfusion following treatment with trastuzumab as measured by contrast-enhanced ultrasound

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Abstract Introduction: The primary purpose of this study is to determine if the order of dosing in standard-of-care (SOC) combination therapy for HER2+ breast cancer has an effect on the perfusion characteristics within the tumor. Improving the intratumoral delivery of cytotoxic systemic therapy is a significant challenge in advancing cancer treatment. Knowledge of the vascular changes following SOC treatments could enable optimizing their order and timing, potentially leading to significantly improved response. Currently, one SOC regimen for HER2+ breast cancer treatment is doxorubicin administered for 3-4 cycles prior to trastuzumab. Our goal is to quantitatively map the changes in perfusion in response to different combinations of trastuzumab plus doxorubicin treatment through imaging in a murine model of HER2+ breast cancer. Experimental Design: BT474 breast cancer cells (1×107) were subcutaneously implanted into mice (n = 12) and randomly assigned into three treatment groups: two doses of trastuzumab (10 mg/kg) followed by doxorubicin (1.5 mg/kg), doxorubicin prior to trastuzumab (same total drug dosage as group 1), and saline. After tumors reached ~225 mm3, animals were imaged with contrast-enhanced ultrasound (CEUS) (VisualSonics Vevo 770, Definity microbubbles) before treatment (day 0), and on days 1, 3, 4, and 7. Treatment occurred on days 0, 3 and 4. Percent change (from baseline, day 0 scans) of the CEUS signal intensity quantified from the functional vasculature (surrogate for vessel perfusion) following contrast injection were measured for each animal for each day. Tumors were extracted on day 7, and sectioned, paraffin-embedded, and stained with CD31, alpha-SMA and H&E. Results: Tumors treated with trastuzumab initially exhibited a significant increase in CEUS signal intensity (from the functional vasculature) on day 1 compared to tumors initially treated with doxorubicin (p < 0.01). Additionally, compared to the control tumors, tumors treated with trastuzumab prior to doxorubicin revealed a significant increase in perfusion (change in signal intensity of functional vasculature) of contrast agent on days 3 (p = 0.01), 4 (p = 0.001) and day 7 (p < 0.01). There were no significant differences in the doxorubicin treated first group and the controls on any of the days (p > 0.25). Qualitative differences were noted between control and treated groups for alpha-SMA, no apparent differences were noted in microvessel density. Conclusion: Trastuzumab significantly improves a tumor's vascular perfusion in this HER2+ breast cancer model. Doxorubicin dosing prior to treatment with trastuzumab may potentially be hindering the intratumoral delivery of the subsequently delivered, targeted therapy. Improving the tumor's functional vasculature by altering the order of dosing of these combination therapies by giving trastuzumab prior to cytotoxic therapy has potential to enhance both the delivery and the effectiveness of these combination therapies. These data indicate a potential pathway to optimize therapeutic efficacy for individual HER2+ breast cancer patients. Citation Format: Sorace AG, Barnes SL, Quarles CC, McIntyre JO, Yankeelov TE. Increased tumor perfusion following treatment with trastuzumab as measured by contrast-enhanced ultrasound [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-02-02.