Trastuzumab improves tumor perfusion and vascular delivery of cytotoxic therapy in a murine model of HER2+ breast cancer: preliminary results

Abstract

To employ in vivo imaging and histological techniques to identify and quantify vascular changes early in the course of treatment with trastuzumab in a murine model of HER2+ breast cancer. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantitatively characterize vessel perfusion/permeability (via the parameter Ktrans) and the extravascular extracellular volume fraction (ve) in the BT474 mouse model of HER2+ breast cancer (N = 20) at baseline, day one, and day four following trastuzumab treatment (10 mg/kg). Additional cohorts of mice were used to quantify proliferation (Ki67), microvessel density (CD31), pericyte coverage (α-SMA) by immunohistochemistry (N = 44), and to quantify human VEGF-A expression (N = 29) throughout the course of therapy. Longitudinal assessment of combination doxorubicin ± trastuzumab (N = 42) tested the hypothesis that prior treatment with trastuzumab will increase the efficacy of subsequent doxorubicin therapy. Compared to control tumors, trastuzumab-treated tumors exhibited a significant increase in Ktrans (P = 0.035) on day four, indicating increased perfusion and/or vessel permeability and a simultaneous significant increase in ve (P = 0.01), indicating increased cell death. Immunohistochemical and ELISA analyses revealed that by day four the trastuzumab-treated tumors had a significant increase in vessel maturation index (i.e., the ratio of α-SMA to CD31 staining) compared to controls (P < 0.001) and a significant decrease in VEGF-A (P = 0.03). Additionally, trastuzumab dosing prior to doxorubicin improved the overall effectiveness of the therapies (P < 0.001). This study identifies and validates improved perfusion characteristics following trastuzumab therapy, resulting in an improvement in trastuzumab-doxorubicin combination therapy in a murine model of HER2+ breast cancer. This data suggests properties of vessel maturation. In particular, the use of DCE-MRI, a clinically available imaging method, following treatment with trastuzumab may provide an opportunity to optimize the scheduling and improve delivery of subsequent cytotoxic therapy.

DCE‐ and DW‐MRI as early imaging biomarkers of treatment response in a preclinical model of triple negative breast cancer

“…Specifically, in the idea that anti‐angiogenic mechanisms serve to prune the leaky, underdeveloped vasculature associated with tumor angiogenesis, thus increasing the maturity of the vasculature and (potentially) increasing the observed delivery, which could then materialize as an increase in K trans . This relationship between vascular maturation and an increase in K trans has been shown previously in HER2+ tumors with other non‐vascular disrupting agents . Consistent with our analysis, Sun et al revealed a decrease in CD‐31 following Abraxane treatment at 25 mg/kg with an increase in α‐SMA in treated groups.…”

The effects of intravoxel contrast agent diffusion on the analysis of DCE‐MRI data in realistic tissue domains

“…An example of the error commonly encountered when performing a DCE‐MRI experiment, using a temporal resolution of 1.6 s and Gd‐DTPA, is depicted in Figure . The large error in K trans is particularly of note because of its common application in diagnosing and evaluating response in cancer . Therefore, an accurate estimate of perfusion is necessary to provide accurate predictions of tumor growth and response to therapeutics.…”

Quantitative [18F]FMISO PET Imaging Shows Reduction of Hypoxia Following Trastuzumab in a Murine Model of HER2+ Breast Cancer

“…The observed increase in tumor oxygenation (through reduction in hypoxia) initiated by treatment with trastuzumab has the potential to enhance the effectiveness of cytotoxic radiation therapy, without increasing dose or toxic side effects. Previous research has shown that trastuzumab increases the vascular delivery of a secondary agent during this same timeframe [13]. Increasing vascular delivery and reducing hypoxia presents an opportunity to decrease metastatic potential of the tumor, while improving the treatment efficiency.…”

“…Additionally, as a secondary mechanism of action, trastuzumab suppresses angiogenesis by induction of antiangiogenic factors and inhibition of proangiogenic factors. This alteration in tumor vasculature has been shown through increased vascular maturation [13], decreased release of vascular endothelial growth factor (VEGF) [13-14], and a reduction of vessel diameter and leakiness [14]. Importantly, trastuzumab-induced vascular maturation has been shown to improve perfusion and intratumoral delivery of systemic agents [13].…”

“…This alteration in tumor vasculature has been shown through increased vascular maturation [13], decreased release of vascular endothelial growth factor (VEGF) [13-14], and a reduction of vessel diameter and leakiness [14]. Importantly, trastuzumab-induced vascular maturation has been shown to improve perfusion and intratumoral delivery of systemic agents [13]. Similarly, improved hemodynamic efficiency has the potential to decrease hypoxia and enhance the effectiveness of these therapies.…”