Basic Study
Copyright ©The Author(s) 2020. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Mar 7, 2020; 26(9): 904-917
Published online Mar 7, 2020. doi: 10.3748/wjg.v26.i9.904
Magnetic resonance imaging biomarkers for pulsed focused ultrasound treatment of pancreatic ductal adenocarcinoma
Ezekiel Maloney, Yak-Nam Wang, Ravneet Vohra, Helena Son, Stella Whang, Tatiana Khokhlova, Joshua Park, Kayla Gravelle, Stephanie Totten, Joo Ha Hwang, Donghoon Lee
Ezekiel Maloney, Ravneet Vohra, Joshua Park, Donghoon Lee, Department of Radiology, University of Washington, Seattle, WA 98195, United States
Yak-Nam Wang, Applied Physics Laboratory, University of Washington, Seattle, WA 98195, United States
Helena Son, Stella Whang, Tatiana Khokhlova, Kayla Gravelle, Stephanie Totten, Division of Gastroenterology, University of Washington, Seattle 98195, WA, United States
Joo Ha Hwang, Division of Gastroenterology & Hepatology, Stanford University School of Medicine, Redwood City, CA 94063, United States
Author contributions: Maloney E, Wang YN, Vorha R, Son H, Whang S, Khokhlova T, Park J, Gravelle K, and Lee D performed the majority of experiments; Maloney E, Wang YN, Vorha R, and Park J performed the majority of data analysis; Maloney E, Wang YN, and Lee D performed the majority of data interpretation; S Totten assisted Wang YN, S Whang, H Son and K Gravelle in treatment and care of the involved animals, as well as tissue processing/testing; Lee D and Hwang JH designed and coordinated the research; Maloney E wrote the initial draft of the manuscript; Maloney E and Wang YN created the figures; all authors contributed to manuscript content over multiple subsequent rounds of internal editing and revision prior to submission; all authors agreed upon the final content of the manuscript.
Supported by National Institutes of Health, National Cancer Institute, No. R01 CA188654 and No. R01 CA154451.
Institutional animal care and use committee statement: All animal experiments were conducted in accordance with policies of the NIH Guide for the Care and Use of Laboratory Animals and the Institutional Animal Care and Use Committee (IACUC) of the University of Washington. Specific protocols used in this study were approved by the University of Washington IACUC (approved protocols are: “4210-01: MR Methods for Small Animal Imaging” and “4242-05: Enhanced chemotherapeutic drug delivery by High Intensity Focused Ultrasound”).
Conflict-of-interest statement: All other authors have nothing to disclose.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Corresponding author: Donghoon Lee, PhD, Research Professor, Department of Radiology, University of Washington, SLU C256, 850 Republican Street, Seattle, WA 98109, United States.
Received: November 17, 2019
Peer-review started: November 17, 2019
First decision: December 23, 2019
Revised: January 12, 2020
Accepted: February 15, 2020
Article in press: February 15, 2020
Published online: March 7, 2020
Research background

The robust fibroinflammatory stroma characteristic of pancreatic ductal adenocarcinoma (PDA) impedes effective drug delivery. Pulsed focused ultrasound (pFUS) can disrupt this stroma and has improved survival in an early clinical trial. Non-invasive methods to characterize pFUS treatment effects are desirable for advancement of this promising treatment modality in larger clinical trials.

Research motivation

In this study, our objective was to identify non-invasive MRI methods that can be used to assess pFUS treatment effects for PDA, based on data derived from three murine models of PDA, including a genetic model. These methods have translational relevance to future, larger clinical trials that might help to advance pFUS therapy as a valuable supplement to traditional treatment modalities for patients with PDA.

Research objectives

Our primary objective was to identify promising, non-invasive pre-clinical imaging methods to characterize acute pFUS treatment effects for in vivo models of PDA. Robust pre-clinical data such as this builds critical foundation to facilitate efficient clinical trials. Knowledge of reliable methods to characterize the acute phase of treatment also helps to inform selection of methods to characterize long-term treatment follow up assessments in future studies.

Research methods

We utilized quantitative MRI methods at 14 tesla in three mouse models of PDA (subcutaneous, orthotopic and transgenic - KrasLSL-G12D/+, Trp53LSL-R172H/+, Cre or “KPC”) to assess immediate tumor response to pFUS treatment (VIFU 2000 Alpinion Medical Systems; 475 W peak electric power, 1 millisecond pulse duration, 1 Hz, duty cycle 0.1%) vs sham therapy, and correlated our results with histochemical data. These pFUS treatment parameters were previously shown to enhance tumor permeability to chemotherapeutics. T1 and T2 relaxation maps, high (126, 180, 234, 340, 549) vs low (7, 47, 81) b-value apparent diffusion coefficient (ADC) maps, magnetization transfer ratio (MTR) maps, and chemical exchange saturation transfer (CEST) maps for the amide proton spectrum (3.5 parts per million or “ppm”) and the glycosaminoglycan spectrum (0.5-1.5 ppm) were generated and analyzed pre-treatment, and immediately post-treatment, using ImageJ. Animals were sacrificed immediately following post-treatment imaging. The whole-tumor was selected as the region of interest for data analysis and subsequent statistical analysis. T-tests and Pearson correlation were used for statistical inference.

Research results

Mean high-b value ADC measurements increased significantly with pFUS treatment for all models. Mean glycosaminoglycan CEST and T2 measurements decreased significantly post-treatment for the KPC group. Mean MTR and amide CEST values increased significantly for the KPC group. Hyaluronic acid focal intensities in the treated regions were significantly lower following pFUS treatment for all animal models. The MRI changes observed acutely following pFUS therapy likely reflect: (1) Sequelae of variable degrees of microcapillary hemorrhage (T1, MTR and amide CEST); (2) Lower PDA glycosaminoglycan content and associated water content (glycosaminoglycan CEST, T2 and hyaluronic acid focal intensity); and (3) Improved tumor diffusivity (ADC) post pFUS treatment.

Research conclusions

T2, glycosaminoglycan CEST, and ADC maps proved to be reliable means of quantifying pFUS treatment effects in murine models of PDA, and may provide reliable, non-invasive quantitation of acute pFUS treatment effects for patients with PDA in future clinical trials.

Research perspectives

We have identified specific MRI methods as reliable non-invasive means of quantitating acute pFUS treatment effects for murine models of PDA. Future studies of long-term post-treatment disease burden may also benefit from employing the methods we describe. Clinical trials of pFUS therapy for PDA will be more easily accomplished if similar non-invasive methods of tracking immediate treatment endpoints can replace potentially morbid biopsies of this highly sensitive anatomic area. pFUS therapy may also be more efficacious for certain subpopulations of patients with PDA, and the methods we describe may help to non-invasively select enriched patient populations that will derive the greatest benefit from pFUS treatments in future studies.