Trapping Cancer Cells in Their Tracks: Implant Captures Metastatic Tumor Cells

Lonnie D. Shea, PhD

Lonnie D. Shea, PhD

A novel trap and detection system in preclinical trials may leverage advances in the detection of circulating tumor cells (CTCs) to find and stop metastatic cancer cells from spreading, according to a paper inNature Communications.

The study investigators developed a biomaterial implant to recruit and capture metastatic cells and combined it with an imaging system using inverse spectroscopic optical coherence tomography (ISCOT) for label-free detection of cancer cells to form a system to detect early metastases.¹

Researchers used mouse models implanted with tumor cell lines and microporous scaffolds, made of an FDA-approved material called poly (lactide-c0-glycolide) (PLG).¹

Scaffolds Trap Tumor Cells

The researchers used an orthotopic model of human breast cancer to investigate whether or not the scaffolds could capture metastatic cells. The NOD/SCID-IL2Rγ-1- (NSG) mice were implanted (in the right mammary fat pad) with a highly metastatic cell line, which expressed tdTomato and luciferase. One week later, the scaffolds (measuring 5 mm in diameter and 2 mm in height) were implanted in the peritoneal fat pads. This site was chosen because the cell line is not known to spread to this location. It also allowed for vascularization of the scaffolds. The scaffolds were removed after 1 month and a histological and imaging analysis revealed the presence of tumor cells. They were not present in the peritoneal fad pads that had no scaffold. Metastatic tumor cells were attracted to the local environment created by the scaffolds. Using controls, they found that implantation of the scaffolds and mock surgery had no impact on tumor growth. They also discovered fibronectin, which has a role in creating a metastatic site, was present in the scaffolds as early as 7 days after tumor cells were implanted.¹

Scaffolds Reduce Colonization of Metastatic Sites

Examining metastatic sites such as the lung and liver confirmed that the presence of scaffolds reduced the tumor burden in the lung by 88% ± 7% (standard error of mean) versus mice that had mock surgery. Indeed, the relative abundance of tumor cells in the lungs of scaffold mice versus mock surgery was 1:5400 versus 1:645, respectively. The histology revealed a lower number of lesions per section in the lungs of scaffold mice versus mock surgery, at 1.7 ± 0.5 versus 5.5 ± 1.7 respectively. When analyzed by flow cytometry, the colonization of the liver was significantly lower in the mice with scaffolds versus mock surgery (P>.01, Fisher’s exact test). In this case, 8 of 8 mice with mock surgery had liver tumor cells versus 2 of 8 mice with scaffolds.¹

The team discovered that if they analyzed for tumor cells in the lung, liver, and scaffolds at an earlier time point of 14 days, tumor cells were present in scaffolds implanted both intraperitoneally and subcutaneously, but, most importantly, not in the lung or liver. Thus, the scaffolds afford the opportunity to detect metastatic tumor cells before colonization of metastatic sites.¹

Immune Cells Involved in Tumor Cell Recruitment

The authors refer to the body of work that has established the important part played by immune cell types in creating the metastatic niche. They used an immune competent mouse model (BALB/c), also implanted with a breast cancer cell line, in addition to the NSG model to demonstrate that the scaffold would still attract tumor cells in the midst of an intact immune system. Using flow cytometry to analyze the immune environment of the scaffolds and the lung (common site of breast cancer metastasis), pre- and post- implantation, they found an increase in Gr1^hiCD11b⁺cells in the lungs and scaffolds of both mouse strains. The number of these cells increased from day zero through day 28, highlighting similarities of the immune environment within tumors and the scaffolds.¹

Further experiments in which Gr1^hiCD11b⁺cells were seeded onto scaffolds which were then implanted, found this increased the number of tumor cells present in the scaffolds. The authors state this shows the immune environment mediates metastatic recruitment, and using this technique, it was possible to modulate the immune environment within the scaffold. The Gr1^hiCD11b⁺cells attracted tumor cells to the scaffold.¹

Noninvasive Method to Detect Scaffold Tumor Cell Colonization

In addition to using labeled tumor cells, the team successfully used an imaging system called inverse spectroscopic optical coherence tomography (ISCOT) to detect label free tumor cells in situ in subcutaneously implanted scaffolds. At 14 days post implant, the technique successfully detected evidence of metastatic cells in the scaffolds (early metastatic disease), versus scaffolds in tumor free mice.¹

Future

Discussing the implications, the authors highlight the therapeutic value of an implant that not only detects CTCs early on, but also potentially reduces tumor burden. Current technology detects CTCs in blood samples, and is therefore diagnostic only.¹

The tumor cells can also be recovered from the scaffolds and analyzed for metastatic biomarkers and facilitate development of therapies targeting aspects of metastatic cancer cell biology. The scaffold can be “seeded” with cells, or proteins to modulate the immune environment within the scaffold.¹

Study leader Lonnie D. Shea, PhD, professor and William and Valerie Hall Chair, biomedical engineering, and professor chemical engineering at the University of Michigan said, “We need to see if metastatic cells will show up in the implant in humans like they did in mice, and also if it is a safe procedure and that we can use the same imaging to detect cancer cells.”²

References

1. Azarin SM, Yi J, Gower RM, et al. In vivo capture and label-free detection of early metastatic cells. Nat Commun. 2015;6:8094.doi:10.1038/ncomms9094.

2. BBC News. Implant 'traps' spreading cancer cells.http://www.bbc.com/news/health-34191325. Accessed September 11, 2015.