Volumetric contrast-enhanced ultrasound imaging to assess early response to apoptosis-inducing anti-death receptor 5 antibody therapy in a breast cancer animal model

Abstract

Objectives: The objective of this study was to determine whether volumetric contrast-enhanced ultrasound (US) imaging could detect early tumor response to anti-death receptor 5 antibody (TRA-8) therapy alone or in combination with chemotherapy in a preclinical triple-negative breast cancer animal model.

Methods: Animal experiments had Institutional Animal Care and Use Committee approval. Thirty breast tumor-bearing mice were administered Abraxane (paclitaxel; Celgene Corporation, Summit, NJ), TRA-8, TRA-8 + Abraxane, or saline as a controlon days 0, 3, 7, 10, 14, and 17. Volumetric contrast-enhanced US imaging was performedon days 0, 1, 3, and 7 before dosing. Changes in parametric maps of tumor perfusion were compared with the tumor volume and immunohistologic findings.

Results: Therapeutic efficacy was detected within 7 days after drug administration using parametric volumetric contrast-enhanced US imaging. Decreased tumor perfusion was observed in both the TRA-8-alone- and TRA-8 + Abraxane-dosed animals compared to control tumors (P = .17; P = .001, respectively). The reduction in perfusion observed in the TRA-8 + Abraxane group was matched with a corresponding regression in tumor size over the same period. Survival curves illustrate that the combination of TRA-8 + Abraxane improves drug efficacy compared to the same drugs administered alone. Immunohistologic analysis revealed increased levels of apoptotic activity in the TRA-8-dosed tumors, confirming enhanced antitumor effects.

Conclusions: Preliminary results are encouraging, and volumetric contrast-enhanced US-based tumor perfusion imaging may prove clinically feasible for detecting and monitoring the early antitumor effects in response to combination TRA-8 + Abraxane therapy.

Figure 1

Illustration of a surgically placed subcutaneous vascular access port in the animal model with respect to implanted flank tumors.

Figure 2

Time line of both longitudinal volumetric contrast-enhanced US imaging and the treatment schedule. After tumor cell implantation, baseline US scans were performed prior to treatment. Animals were euthanized throughout the study in accordance with established criteria for allowable tumor size. At day 21 after baseline, all remaining animals were euthanized. Tumors were excised from every animal and processed for immunohistologic analysis.

Figure 3

Description of the real-time volumetric contrast-enhanced US system, which was developed using a portable research scanner (A) and a 4-dimensional probe (B). After collection of multidimensional volumetric data (C), custom software (D) analyzed time-intensity curve information voxel by voxel to derive the maximum intensity value of microbubble circulation (I_MAX) representing a surrogate measurement of tumor perfusion.

Figure 4

Spatial sequence of perfusion maps (maximum-intensity projection values) constituting a volumetric scan of tumor vascularity following microbubble infusion. The color bar denotes low and high maximum-intensity projection values. Note the predominance of blood flow on the tumor periphery versus the hypovascular tumor core.

Figure 5

Summary of volumetric contrast-enhanced US-based tumor perfusion measurements derived from spherical regions of interest incorporating intratumoral vascularity. Longitudinal changes in maximum-intensity projection measurements are reported as percent change from baseline estimates.

Figure 6

Description of the longitudinal changes in tumor volume in response to drug treatment throughout the study duration. Note that the error bars on the last control data point are too small to be visible.

Figure 7

Longitudinal analysis of the survival probability for each treatment group.

Figure 8

Representative images and summary of immunohistologic results from excised tumor samples depicting intratumoral apoptosis (A) and microvessel density (B) levels for each treatment group. Arrows in Aand B indicate apoptotic cells and tumor microvessels, respectively.