Elastography can map the local inverse relationship between shear modulus and drug delivery within the pancreatic ductal adenocarcinoma microenvironment

Purpose: High tissue pressure prevents chemotherapeutics from reaching the core of pancreatic tumors. Therefore, targeted therapies have been developed to reduce this pressure. While point probes have shown the effectiveness of these pressure-reducing therapies via single location estimates, ultrasound elastography is now widely available as an imaging technique to provide real-time spatial maps of shear modulus (tissue stiffness). However, the relationship between shear modulus and the underlying tumor microenvironmental causes has not been investigated. In this work, elastography was used to investigate how shear modulus influences drug delivery in situ, and how it correlates with collagen density, hyaluronic acid content, and patent vessel density, features of the tumor microenvironment known to influence tissue pressure. Experimental Design: Intravenous injection of verteporfin, an approved human fluorescent drug, was used in two pancreatic cancer xenograft models (AsPC1 (n=25) and BxPC­3 (n=25)). Results: Fluorescence intensity was higher in AsPC-1 tumors than in BxPC-3 tumors (p < 0.0001). Comparing drug uptake images and shear wave elastographic images with histological images revealed that: (1) drug delivery and shear modulus were inversely related, (2) shear modulus increased linearly with increasing collagen density, and (3) shear modulus was marginally correlated with the local assessment of hyaluronic acid content. Conclusions:These results demonstrate that elastography could guide targeted therapy and/or identify patients with highly elevated tissue pressure.

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