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Imaging primary mouse sarcomas after radiation therapy using cathepsin-activatable fluorescent imaging agents
Kyle C Cuneo1, Jeffrey K Mito, Melodi P Javid
1Department of Radiation Oncology, Duke University School of Medicine, Durham, North Carolina 27710, USA.
Purpose:
Cathepsin-activated fluorescent probes can detect tumors in mice and in canine patients. We previously showed that these probes can detect microscopic residual sarcoma in the tumor bed of mice during gross total resection. Many patients with soft tissue sarcoma (STS) and other tumors undergo radiation therapy (RT) before surgery. This study assesses the effect of RT on the ability of cathepsin-activated probes to differentiate between normal and cancerous tissue.
Methods And Materials:
A genetically engineered mouse model of STS was used to generate primary hind limb sarcomas that were treated with hypofractionated RT. Mice were injected intravenously with cathepsin-activated fluorescent probes, and various tissues, including the tumor, were imaged using a hand-held imaging device. Resected tumor and normal muscle samples were harvested to assess cathepsin expression by Western blot. Uptake of activated probe was analyzed by flow cytometry and confocal microscopy. Parallel in vitro studies using mouse sarcoma cells were performed.
Results:
RT of primary STS in mice and mouse sarcoma cell lines caused no change in probe activation or cathepsin protease expression. Increasing radiation dose resulted in an upward trend in probe activation. Flow cytometry and immunofluorescence showed that a substantial proportion of probe-labeled cells were CD11b-positive tumor-associated immune cells.
Conclusions:
In this primary murine model of STS, RT did not affect the ability of cathepsin-activated probes to differentiate between tumor and normal muscle. Cathepsin-activated probes labeled tumor cells and tumor-associated macrophages. Our results suggest that it would be feasible to include patients who have received preoperative RT in clinical studies evaluating cathepsin-activated imaging probes.
Insights
Radiation therapy (RT) does not impact cathepsin-activated fluorescent probes
Area of Science:
- Oncology
- Medical Imaging
- Biochemistry
Background:
- Cathepsin-activated fluorescent probes detect tumors.
- These probes can identify microscopic residual soft tissue sarcoma (STS) after surgery.
- Preoperative radiation therapy (RT) is common for STS patients.
Purpose of the Study:
- To assess the effect of RT on cathepsin-activated probes' ability to differentiate between cancerous and normal tissue.
- To evaluate probe performance in a murine soft tissue sarcoma model treated with RT.
Main Methods:
- A murine STS model was treated with hypofractionated RT.
- Mice received intravenous cathepsin-activated fluorescent probes.
- Tumor and tissue imaging, Western blot, flow cytometry, and confocal microscopy were used.
Main Results:
- RT did not alter probe activation or cathepsin protease expression.
- Higher radiation doses showed a trend toward increased probe activation.
- Probe-labeled cells included CD11b-positive tumor-associated immune cells.
Conclusions:
- RT does not hinder cathepsin-activated probes' tumor-differentiating capability in STS models.
- Probes label both STS cells and tumor-associated macrophages.
- Patients receiving preoperative RT may be candidates for probe-based imaging studies.
