Investigating the Impact of a Primary Tumor on Metastasis and Dormancy Using MRI: New Insights into the Mechanism of Concomitant Tumor Resistance

Does Primary Tumor Resection Induce Accelerated Metastasis in Breast Cancer? A Review

INTRODUCTION

Over a century of cumulative experimental results and clinical data have suggested that surgical procedures of primary tumors promote tumor progression and metastasis in breast cancer and other cancer patients, suggesting a potential interplay linking primary tumors and distant lesions that lead to metastasis development triggered by primary tumor removal. Such evidence may generate a departure in terms of our attitude toward the surgery. However, the reliability and prognostic benefits of tumor surgery, especially for chemotherapy-resistant patients, are indisputable. Thus, it is important to explore the mechanism underlying this surgery-induced cancer progression to guide individual clinical treatment and improve tumor control.

MATERIALS AND METHODS

We conducted a comprehensive review in PubMed in October 2021 to determine the article outline. Non-English and repetitive articles were excluded. The year, topic, key findings, and opinions of each article were gathered.

RESULTS

This review not only comprehensively summarizes the potential mechanisms of primary tumors interacting with the growth of metastases but also discusses whether and how surgical resection of primary lesions can trigger tumor metastasis and development. At the same time, this article also provides our understanding of clinical findings and future directions on this topic. In addition, the combination of surgery and some potentially beneficial therapeutic interventions for postoperative tumor metastasis control was also mentioned.

CONCLUSIONS

There are viewpoints supporting an acceleration of metastasis after surgery for breast cancer and fundamental research on relevant therapies, although controversial. Further attention should be focused on the gap between current preclinical data and the complicated clinical therapeutic combination during surgery in metastatic breast cancer patients.

Safe harbor-targeted CRISPR-Cas9 homology-independent targeted integration for multimodality reporter gene-based cell tracking

Imaging reporter genes provides longitudinal information on the biodistribution, growth, and survival of engineered cells in vivo. A translational bottleneck to using reporter genes is the necessity to engineer cells with randomly integrating vectors. Here, we built homology-independent targeted integration (HITI) CRISPR-Cas9 minicircle donors for precise safe harbor-targeted knock-in of fluorescence, bioluminescence, and MRI (Oatp1a1) reporter genes. Our results showed greater knock-in efficiency using HITI vectors compared to homology-directed repair vectors. HITI clones demonstrated functional fluorescence and bioluminescence reporter activity as well as significant Oatp1a1-mediated uptake of the clinically approved MRI agent gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid. Contrast-enhanced MRI improved the conspicuity of both subcutaneous and metastatic Oatp1a1-expressing tumors before they became palpable or even readily visible on precontrast images. Our work demonstrates the first CRISPR-Cas9 HITI system for knock-in of large DNA donor constructs at a safe harbor locus, enabling multimodal longitudinal in vivo imaging of cells.

Comparing the fate of brain metastatic breast cancer cells in different immune compromised mice with cellular magnetic resonance imaging

Metastasis is the leading cause of mortality in breast cancer patients, with brain metastases becoming increasingly prevalent. Studying this disease is challenging due to the limited experimental models and methods available. Here, we used iron-based cellular MRI to track the fate of a mammary carcinoma cell line (MDA-MB-231-BR) in vivo to characterize the growth of brain metastases in the nude and severely immune-compromised NOD/SCID/ILIIrg-/- (NSG) mouse. Nude and NSG mice received injections of iron-labeled MDA-MB-231-BR cells. Images were acquired with a 3T MR system and assessed for signal voids and metastases. The percentage of signal voids and the number and volume of metastases were quantified. Ex vivo imaging of the liver, histology, and immunofluorescence labeling was performed. Brain metastases grew more rapidly in NSG mice. At day 21 post cell injection, the average number of brain tumors in NSG mice was approximately four times greater than in nude mice. The persistence of iron-labeled cells, visualized as signal voids by MRI, was also examined. The percentage of voids decreased significantly over time for both nude and NSG mice. Body images revealed that the NSG mice also had metastases in the liver, lungs, and lymph nodes while tumors were only detected in the brains of nude mice. This work demonstrates the advantages of using the highly immune-compromised NSG mouse to study breast cancer metastasis, treatments aimed at inhibiting metastasis and outgrowth of breast cancer metastases in multiple organs, and the role that imaging can play toward credentialing these models that cannot be done with other in vitro or histopathologic methods alone.

Multimodality cellular and molecular imaging of concomitant tumour enhancement in a syngeneic mouse model of breast cancer metastasis

The mechanisms that influence metastatic growth rates are poorly understood. One mechanism of interest known as concomitant tumour resistance (CTR) can be defined as the inhibition of metastasis by existing tumour mass. Conversely, the presence of a primary tumour has also been shown to increase metastatic outgrowth, termed concomitant tumour enhancement (CTE). The majority of studies evaluating CTR/CTE in preclinical models have relied on endpoint histological evaluation of tumour burden. The goal of this research was to use conventional magnetic resonance imaging (MRI), cellular MRI, and bioluminescence imaging to study the impact of a primary tumour on the development of brain metastases in a syngeneic mouse model. Here, we report that the presence of a 4T1 primary tumour significantly enhances total brain tumour burden in Balb/C mice. Using in vivo BLI/MRI we could determine this was not related to differences in initial arrest or clearance of viable cells in the brain, which suggests that the presence of a primary tumour can increase the proliferative growth of brain metastases in this model. The continued application of our longitudinal cellular and molecular imaging tools will yield a better understanding of the mechanism(s) by which this physiological inhibition (CTR) and/or enhancement (CTE) occurs.

MRI surveillance of cancer cell fate in a brain metastasis model after early radiotherapy

PURPOSE

Incidence of brain metastasis attributed to breast cancer is increasing and prognosis is poor. It is thought that disseminated dormant cancer cells persist in metastatic organs and may evade treatments, thereby facilitating a mechanism for recurrence. Radiotherapy is used to treat brain metastases clinically, but assessment has been limited to macroscopic tumor volumes detectable by clinical imaging. Here, we use cellular MRI to understand the concurrent responses of metastases and nonproliferative or slowly cycling cancer cells to radiotherapy.

METHODS

MRI cell tracking was used to investigate the impact of early cranial irradiation on the fate of individual iron-labeled cancer cells and outgrowth of breast cancer brain metastases in the human MDA-MB-231-BR-HER2 cell model.

RESULTS

Early whole-brain radiotherapy significantly reduced the outgrowth of metastases from individual disseminated cancer cells in treated animals compared to controls. However, the numbers of nonproliferative iron-retaining cancer cells in the brain were not significantly different.

CONCLUSIONS

Radiotherapy, when given early in cancer progression, is effective in preventing the outgrowth of solitary cancer cells to brain metastases. Future studies of the nonproliferative cancer cells' clonogenic potentials are warranted, given that their persistent presence suggests that they may have evaded treatment. Magn Reson Med 78:1506-1512, 2017. © 2016 International Society for Magnetic Resonance in Medicine.