Dynamic contrast-enhanced MR microscopy identifies regions of therapeutic response in a preclinical model of colorectal adenocarcinoma

Co-Clinical Imaging Resource Program (CIRP): Bridging the Translational Divide to Advance Precision Medicine

The National Institutes of Health’s (National Cancer Institute) precision medicine initiative emphasizes the biological and molecular bases for cancer prevention and treatment. Importantly, it addresses the need for consistency in preclinical and clinical research. To overcome the translational gap in cancer treatment and prevention, the cancer research community has been transitioning toward using animal models that more fatefully recapitulate human tumor biology. There is a growing need to develop best practices in translational research, including imaging research, to better inform therapeutic choices and decision-making. Therefore, the National Cancer Institute has recently launched the Co-Clinical Imaging Research Resource Program (CIRP). Its overarching mission is to advance the practice of precision medicine by establishing consensus-based best practices for co-clinical imaging research by developing optimized state-of-the-art translational quantitative imaging methodologies to enable disease detection, risk stratification, and assessment/prediction of response to therapy. In this communication, we discuss our involvement in the CIRP, detailing key considerations including animal model selection, co-clinical study design, need for standardization of co-clinical instruments, and harmonization of preclinical and clinical quantitative imaging pipelines. An underlying emphasis in the program is to develop best practices toward reproducible, repeatable, and precise quantitative imaging biomarkers for use in translational cancer imaging and therapy. We will conclude with our thoughts on informatics needs to enable collaborative and open science research to advance precision medicine.

Does perfusion computed tomography correlate to pathology in colorectal liver metastases?

Introduction

Targeted therapy against tumor angiogenesis is widely used in clinical practice for patients with colorectal liver metastases (CRLM). Possible predictive biomarkers for tumor angiogenesis, such as, microvessel density (MVD), hypoxia and cell proliferation, can be determined using immunohistochemical staining. However, patients ineligible for surgical treatment need to undergo invasive diagnostic interventions in order to determine these biomarkers. CT perfusion (CTP) is an emerging functional imaging technique, which can non-invasively determine vascular properties of solid tumors. The purpose of this study was to evaluate CTP with histological biomarkers in CRLM.

Material and methods

Patients with CRLM underwent CTP one day before liver surgery. CTP analysis was performed on the entire volume of the largest metastases in each patient. Dual-input maximum slope analysis was used and data concerning arterial flow (AF), portal flow (PF) and perfusion index (PI) were recorded. Immunohistochemical staining with CD34, M75/CA-IX and MIB-1 was performed on the rim in the midsection of the tumor to determine respectively MVD, hypoxia and cell proliferation.

Results

Twenty CRLM in 20 patients were studied. Mean size of the largest CRLM was 37 mm (95% CI 21–54 mm). Mean AF and PF were respectively 64 ml/min/100ml (95% CI 48–79) and 30 ml/min/100ml (95% CI 22–38). Mean PI was 68% (95% CI 62–73). No significant correlation was found between tumor growth patterns and CTP (p = 0.95). MVD did not significantly correlate to AF (r = 0.05; p = 0.84), PF (r = 0.17; p = 0.47) and PI (r = -0.12; p = 0.63). Cell proliferation also did not significantly correlate to AF (r = 0.07; p = 0.78), PF (r = -0.01; p = 0.95) and PI (r = 0.15; p = 0.52). Hypoxia did not significantly correlate to AF (r = -0.05; p = 0.83), however, significantly to PF (r = 0.51; p = 0.02) and a trend to negative correlation with PF (r = -0.43; p = 0.06). However, after controlling the false discovery rate, no significant correlation between CTP and used immunohistochemical biomarkers was found.

Conclusion

In conclusion, this feasibility study found a trend to negative correlation between PI and hypoxia, CTP might therefore possibly evaluate this prognostic marker in CRLM non-invasively. However, CTP is not an appropriate technique for the assessment of microvessels or cell proliferation in CRLM.

Dynamic contrast-enhanced MR microscopy identifies regions of therapeutic response in a preclinical model of colorectal adenocarcinoma

PURPOSE

A typical dynamic contrast-enhanced (DCE)-MRI study often compares the derived pharmacokinetic parameters on manually selected tumor regions or over the entire tumor volume. These measurements include domains where the interpretation of the biomarkers may be unclear (such as in necrotic areas). Here, the authors describe a technique for increasing the sensitivity and specificity of DCE-MRI by identifying tumor regions with a variable response to therapy.

METHODS

Two cohorts (n = 8/group) of nu/nu mice with LS-174T implanted in the mammary fat pad were imaged at five time points over four weeks. The treatment/control group received bevacizumab/saline at a dose of 5 mg/kg or 5 ml/kg twice weekly; imaging experiments were performed weekly. MR images were acquired at an isotropic resolution of 156 μm(3)(2.4 nl) and with a sampling rate of 9.9 s. The histogram of the time-to-peak (TTP) was used to identify two (fast- and slow-enhancing) regions based on a threshold of TTP = 1000 s. The regions were correlated with histology, and the effect of therapy was locally examined.

RESULTS

Tumors in the treatment group had a significantly longer doubling time. The regions defined by thresholding the TTP histogram identified two distinct domains correlating significantly with tumor permeability and microvessel density. In the fast-enhancing region, the mean permeability constant (K(trans)) was significantly lower in the treatment group at day 9; in the slow-enhancing region, K(trans) was not different between the control and treatment groups. At day 9, the relative volume of the fast-enhancing region was significantly lower in the treatment group, while that of the slow-enhancing region was significantly higher.

CONCLUSIONS

Two regions with distinct kinetic parameters were identified based on the histogram of TTP. The effect of bevacizumab, as measured by a decrease in K(trans), was confined to one of these regions. High spatiotemporal resolution MR studies may contribute unique insights into the response of the tumor microenvironment to therapy.