Abstract 3239: Time-resolved functional perfusion-based analysis of peptide vs. antibody tumor penetration by photoacoustics
Authors: Bull Christopher , Bennet Gavin , Fletcha Athena , Harrison Hellen , Baldassare Leonardo , Hamilton Bruce 
Published: August 2015

Abstract
Introduction: Bicycle Therapeutics is developing bicyclic peptide binders, targeting MT1-MMP (a matrix metalloproteinase involved in tumor metastasis) to deliver toxic agents specifically to tumor cells. Due to their high affinity, small size, enhanced tumor penetration, fully synthetic nature and rapid clearance bicyclic peptide drug conjugates (BDCs) may overcome some of the limitations of the antibody drug conjugate (ADC) format. Photoacoustic imaging is an emerging technology that combines the most compelling features of optical imaging and ultrasound, providing both high optical contrast and high ultrasound resolution at depth. Photoacoustic imaging's unique properties make it superior to other modalities in generating information-rich structural and functional images in multiple critical disease areas, including applications within cancer, cardiovascular disease, and inflammation. Here, a fluorescent-labeled Bicycle peptide (Alexa680), and a corresponding antibody (Alexa750), both bind to the same domain (hemopexin) on MMP14, to measure tumor penetration simultaneously. Both bind to the same domain (hemopexin) on MMP14 with similar (low/subnanomolar) affinities. Functional perfusion was measured by Indocyanine Green (ICG) dynamic imaging. By utilizing photoacoustics, we were able to discriminate regions of high and low perfusion in the tumor and measure the amount of each labeled material.
Methods: Female Nude mice were implanted with human fibrosarcoma cell line (HT-1080) subcutaneously. HT-1080 is known to express large amounts of MMP14. While anesthesized with isofluorane, a tail vein catheter was introduced and the animal placed into a photoacoustic 3D imager (Nexus 128, Endra Inc. Ann Arbor, MI). The fluore-labeled Bicycle Peptide and Antibody were injected and a 30-minute dynamic scan was acquired for both labels simultaneously. This was followed by a 3-minute ICG scan.
Results: Using the ICG scan, regions of high and low perfusion were determined and used to quantify compound penetration. The Bicycle peptide was shown to accumulate into highly perfused regions over the antibody. In the lower perfused regions the bicycle peptide was also shown to amass at higher amounts over the antibody in regions of high vascular perfusion.
Conclusion: Using photoacoustics we were able to show regions of low perfusion were accessible by the Bicycle peptide, to a greater extent than the antibody. Relatively low perfusion in localized tumor refund can limit therapeutic effect. The delivery of a therapeutic using a peptide with high tumor affinity and penetration under poor vascular perfusion would overcome such limitations.
Citation Format: Christopher Bull, Gavin Bennet, Athena Fletcha, Hellen Harrison, Leonardo Baldassare, Bruce Hamilton. Time-resolved functional perfusion-based analysis of peptide vs. antibody tumor penetration by photoacoustics. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3239. doi:10.1158/1538-7445.AM2015-3239