Abstract 1955: A preclinical ultrasound platform for widefield 3D imaging of rodent tumors

Background: Preclinical ultrasound (US) and contrast-enhanced ultrasound (CEUS) imaging have long been used in oncology to noninvasively measure tumor volume and vascularity. While the value of preclinical US has been repeatedly demonstrated, these modalities are not without several key limitations that make them unattractive to cancer researchers, including: high user-variability, low throughput, and limited imaging field-of-view (FOV). Herein, we present a novel robotic preclinical US/CEUS system that addresses these limitations and demonstrates its use in evaluating tumors in 3D in a rodent model.

Methods: The imaging system was designed to allow seamless whole-body 3D imaging, which requires rodents to be imaged without physical contact between the US transducer and the animal. To achieve this, a custom dual-element transducer was mounted on a robotic carriage, submerged in a hydrocarbon fluid, and the reservoir sealed with an acoustically transmissive top platform. Eight NOD/scid/gamma (NSG) female mice were injected subcutaneously in the flank with 8×109 786-O human clear-cell renal cell carcinoma (ccRCC) cells. Weekly imaging commenced after tumors reached a size of 150 mm3 and continued until tumors reached a maximum size of 1 cm3 (∼4-5 weeks). An additional six nude athymic female mice were injected subcutaneously in the flank with 7 × 105 SVR angiosarcoma cells to perform an inter-operator variability study. Imaging consisted of 3D B-mode (conventional ultrasound) of the whole abdomen (< 1 min), as well as contrast-enhanced acoustic angiography (< 10 min) to measure blood vessel density (BVD). Tumors were manually segmented in 3D (< 2 min) and inter-operator and inter-reader reliability was assessed with Krippendorff’s alpha.

Results: Wide-field US images reconstructed from 3D volumetric data showed superior FOV over conventional US. Several anatomical landmarks could be identified within each image surrounding the tumor, including the liver, small intestines, bladder, and inguinal lymph nodes. Tumor boundaries were clearly delineated in both B-mode and BVD images, with BVD images showing heterogeneous microvessel density at later timepoints suggesting tumor necrosis. Excellent agreement was measured for both inter-reader and inter-operator experiments, with alpha coefficients of 0.914 (95% CI: 0.824-0.948) and 0.959 (0.911-0.981), respectively.

Conclusion: We have demonstrated a novel preclinical US imaging system that can accurately and consistently evaluate tumors in rodent models. The system leverages cost-effective robotic technology, and a new scanning paradigm that allows for easy and reproducible data acquisition to enable wide-field, 3D, multi-parametric ultrasound imaging.

Note: This abstract was not presented at the meeting.

Citation Format: Tomasz Czernuszewicz, Virginie Papadopoulou, Juan D. Rojas, Rajalekha Rajamahendiran, Jonathan Perdomo, James Butler, Max Harlacher, Graeme O'Connell, Dzenan Zukic, Paul A. Dayton, Stephen Aylward, Ryan C. Gessner. A preclinical ultrasound platform for widefield 3D imaging of rodent tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1955.

Abstract 1958: Early treatment response detected in a murine clear cell renal cell carcinoma model in response to combination therapy with antiangiogenic and notch inhibition therapy using a non-invasive imaging tool

Background: Functional and molecular changes often precede gross anatomical changes in cancer, so early assessment of a tumor’s functional and molecular response to therapy can help reduce a patient’s exposure to the side effects of ineffective chemotherapeutics or other treatment strategies. Clear-cell renal cell carcinoma (ccRCC) is an aggressive and hyper-vascular form of renal cancer that is often treated with anti-angiogenic and Notch Inhibition therapies, which target the vasculature feeding the disease. The purpose of this work is to show that ultrasound microvascular imaging can provide indications of response to antiangiogenic and Notch Inhibition therapies prior to measurable changes in tumor size.

Methods: Mice bearing 786-O ccRCC xenograft tumors were treated with SU (Sunitnib malate, Selleckchem, TX), an antiangiogenic drug, and a combination of SU and the Notch inhibitor GSI (Gamma secretase inhibitor, PF-03084014, Pfizer, New York, NY) therapies (n=8). A 3D ultrasound system (SonoVol Inc., Research Triangle Park, NC), in addition to microbubble ultrasound contrast agents, was used to obtain a measurement of microvascular density over time and assess the response of the tumors to the therapies. CD31 immunohistochemistry was performed to serve as a gold standard for comparison against imaging results. Statistical tests included: Spearman correlation to compare imaging and histology; Kruskal-Wallis analysis with Tukey multiple comparison post-test to determine if the vessel density or tumor volume were significantly different between the treatment groups; and receiver operating characteristic (ROC) curve analysis to determine sensitivity/specificity for separating treated/untreated groups.

Results: Data indicated that ultrasound-derived microvascular density can detect response to antiangiogenic and Notch inhibition therapies a week prior to changes in tumor volume. Furthermore, the imaging measurements of vasculature are strongly correlated with physiological characteristics of the tumors as measured by histology (p=0.75). Moreover, data demonstrated that ultrasound measurements of vascular density can determine response to therapy and classify between-treatment groups 1 week after the start of treatment with a high sensitivity and specificity of 94% and 86%, respectively.

Conclusion: This work shows vascular density measurements that are strongly correlated with histology can be obtained using ultrasound, and that imaging-derived vessel density metrics may be a better tool for assessing the response of ccRCC to antiangiogenic and Notch inhibition therapies than anatomical size measurements.

Note: This abstract was not presented at the meeting.

Citation Format: Juan D. Rojas, Virginie Papadopoulou, Tomasz Czernuszewicz, Rajalekha Rajamahendiran, Anna Chytil, Yun-Chen Chiang, Diana Chong, Victoria L. Bautch, Wendy K. Rathmell, Stephen Aylward, Ryan Gessner, Paul Dayton. Early treatment response detected in a murine clear cell renal cell carcinoma model in response to combination therapy with antiangiogenic and notch inhibition therapy using a non-invasive imaging tool [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1958.

Premutation allele pool in myotonic dystrophy type 2

BACKGROUND

The myotonic dystrophies (DM1, DM2) are the most common adult muscle diseases and are characterized by multisystem involvement. DM1 has been described in diverse populations, whereas DM2 seems to occur primarily in European Caucasians. Both are caused by the expression of expanded microsatellite repeats. In DM1, there is a reservoir of premutation alleles; however, there have been no reported premutation alleles for DM2. The (CCTG)(DM2) expansion is part of a complex polymorphic repeat tract of the form (TG)(n)(TCTG)(n)(CCTG)(n)(NCTG)(n)(CCTG)(n). Expansions are as large as 40 kb, with the expanded (CCTG)(n) motif uninterrupted. Reported normal alleles have up to (CCTG)(26) with one or more interruptions.

METHODS

To identify and characterize potential DM2 premutation alleles, we cloned and sequenced 43 alleles from 23 individuals. Uninterrupted alleles were identified, and their instability was confirmed by small-pool PCR. We determined the genotype of a nearby single nucleotide polymorphism (rs1871922) known to be in linkage disequilibrium with the DM2 mutation.

RESULTS

We identified three classes of large non-DM2 repeat alleles: 1) up to (CCTG)(24) with two interruptions, 2) up to (CCTG)(32) with up to four interruptions, and 3) uninterrupted (CCTG)(22-33). Large non-DM2 alleles were more common in African Americans than in European Caucasians. Uninterrupted alleles were significantly more unstable than interrupted alleles (p = 10(-4) to 10(-7)). Genotypes at rs1871922 were consistent with the hypothesis that all large alleles occur on the same haplotype as the DM2 expansion.

CONCLUSIONS

We conclude that unstable uninterrupted (CCTG)(22-33) alleles represent a premutation allele pool for DM2 full mutations.