Cellular MRI Reveals Altered Brain Arrest of Genetically Engineered Metastatic Breast Cancer Cells

Abstract

Purpose The combined use of anatomical magnetic resonance imaging (MRI), cellular MRI, and bioluminescence imaging (BLI) allows for sensitive and improved monitoring of brain metastasis in preclinical cancer models. By using these complementary technologies, we can acquire measurements of viable single cell arrest in the brain after systemic administration, the clearance and/or retention of these cells thereafter, the growth into overt tumours, and quantification of tumour volume and relative cancer cell viability over time. While BLI is very useful in measuring cell viability, some considerations have been reported using cells engineered with luciferase such as increased tumour volume variation, changes in pattern of metastatic disease, and inhibition of in vivo tumour growth. Procedures Here, we apply cellular and anatomical MRI to evaluate in vivo growth differences between iron oxide labeled naïve (4T1BR5) and luciferase-expressing (4T1BR5-FLuc-GFP) murine brain-seeking breast cancer cells. Balb/C mice received an intracardiac injection of 20,000 cells and were imaged with MRI on days 0 and 14. Mice that received 4T1BR5-FLuc-GFP cells were also imaged with BLI on days 0 and 14. Results The number of signal voids in the brain (representing iron-labeled cancer cells) on day 0 was significantly higher in mice receiving 4T1BR5 cells compared to mice receiving 4T1BR5-FLuc-GFP cells (p < 0.0001). Mice that received 4T1BR5 cells also had significantly higher total brain tumour burden and number of brain metastases than mice that received 4T1BR5-FLuc-GFP cells (p < 0.0001). Conclusions By employing highly sensitive cellular MRI tools, we demonstrate that engineered cells did not form tumours as well as their naïve counterparts, which appear to primarily be due to a reduction in cell arrest. These results indicate that engineering cancer cells with reporter genes may alter their tropism towards particular organs and highlight another important consideration for research groups that use reporter gene imaging to track metastatic cancer cell fate in vivo.

Engineering “self-homing” circulating tumour cells as novel cancer theranostics

“…Therapeutics that have natural tumour tropism or are designed to target lesions offer potential benefits of improved therapeutic effectiveness due to high intratumoural concentration of therapeutic payloads, as well as increased safety due to minimization of off-target cytotoxicity in normal tissues [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][27][28][29][30][31][32]. The incorporation of imaging probes (e.g., radiolabels, iron oxides, etc.)…”

“…The incorporation of imaging probes (e.g., radiolabels, iron oxides, etc.) into these targeted agents has been used to allow one to track their whole-body biodistribution to on-tumour and off-tumour sites [28][29][30]32]. An agent that is very effective at naturally localizing to metastases with little off-target accumulation could theoretically also be used as an effective agent for the early diagnosis and treatment of metastatic disease.…”

“…In recent years, numerous classes of tumour-targeting agents have been developed including small molecules [40], antibodies [41][42][43], nanoparticles [44,45], viral [46][47][48] and non-viral gene vectors [49][50][51], and cell-based vectors [4- 19,[27][28][29][30][31][32]. Traditionally, the development of cellbased therapies has focused on the use of stem-cells including tissue-specific stem cells, pluripotent stem cells or mesenchymal stem cells [5,6,[8][9][10][11][12][13][14].…”

“…In the last two decades, several groups have exploited self-homing CTCs as "self-targeted" delivery vehicles for ex vivo loaded anti-cancer therapeutic cargo [27][28][29][30][31][32]. Cargo has included oncolytic viruses such as the H-1 parvovirus and vesicular stomatitis virus (VSV), prodrug converting enzyme genes including herpes simplex virus thymidine kinase (HSV-TK) and cytosine deaminase (CD), transgenes that target the tumour microenvironment such as tumour necrosis factor (TNF), and the secretory version of TNF-related apoptosis-inducing ligand (S-TRAIL).…”

“…Cargo has included oncolytic viruses such as the H-1 parvovirus and vesicular stomatitis virus (VSV), prodrug converting enzyme genes including herpes simplex virus thymidine kinase (HSV-TK) and cytosine deaminase (CD), transgenes that target the tumour microenvironment such as tumour necrosis factor (TNF), and the secretory version of TNF-related apoptosis-inducing ligand (S-TRAIL). Additionally, a few groups have co-engineered the therapeutic CTCs and/or their viral cargo with optical or positron emission tomography (PET) imaging reporter genes to enable the fate of the cells/cargo to be monitored with molecular-genetic imaging [28][29][30]32]. Importantly, while the ability to target, visualize, and treat singular pre-established subcutaneous tumours as well as orthotopic or metastatic lesions in a singular organ (e.g., lungs [28] or brain [32]) has been demonstrated, to the best of our knowledge, the ability of self-homing CTCs to migrate into and be used to visualize and treat spontaneous multi-organ metastatic disease is largely unknown.…”