Longitudinal live animal micro-CT allows for quantitative analysis of tumor-induced bone destruction.

ABSTRACT

The majority of breast cancer and prostate cancer patients with metastatic disease will go on to develop bone metastases, which contribute largely to the patient's morbidity and mortality. Numerous small animal models of cancer metastasis to bone have been developed to study tumor-induced bone destruction, but the advancement of imaging modalities utilized for these models has lagged significantly behind clinical imaging. Therefore, there is a significant need for improvements to live small animal imaging, particularly when obtaining high-resolution images for longitudinal quantitative analyses. Recently, live animal micro-computed tomography (µCT) has gained popularity due to its ability to obtain high-resolution 3-dimensional images. However, the utility of µCT in bone metastasis models has been limited to end-point analyses due to off-target radiation effects on tumor cells. We hypothesized that live animal in vivo µCT can be utilized to perform reproducible and quantitative longitudinal analyses of bone volume in tumor-bearing mice, particularly in a drug treatment model of breast cancer metastasis to bone. To test this hypothesis, we utilized the MDA-MB-231 osteolytic breast cancer model in which the tumor cells are inoculated directly into the tibia of athymic nude mice and imaged mice weekly by Faxitron (radiography), Imtek µCT (in vivo), and Maestro (GFP-imaging). Exvivo µCT and histology were performed at end point for validation. After establishing a high-resolution scanning protocol for the Imtek CT, we determined whether clear, measurable differences in bone volume were detectable in mice undergoing bisphosphonate drug treatments. We found that in vivo µCT could be used to obtain quantifiable and longitudinal images of the progression of bone destruction over time without altering tumor cell growth. In addition, we found that we could detect lesions as early as week 1 and that this approach could be used to monitor the effect of drug treatment on bone. Taken together, these data indicate that in vivo µCT is an effective and reproducible method for longitudinal monitoring of tumor-associated bone destruction in mouse models of tumor-induced bone disease.