Impact of radiofrequency ablation (RFA) on bone quality in a murine model of bone metastases

Abstract

Thermal therapies such as radiofrequency ablation (RFA) are gaining widespread clinical adoption in the local treatment of skeletal metastases. RFA has been shown to successfully destroy tumor cells, yet the impact of RFA on the quality of the surrounding bone has not been well characterized. RFA treatment was performed on femora of rats with bone metastases (osteolytic and osteoblastic) and healthy age matched rats. Histopathology, second harmonic generation imaging and backscatter electron imaging were used to characterize changes in the structure, organic and mineral components of the bone after RFA. RFA treatment was shown to be effective in targeting tumor cells and promoting subsequent new bone formation without impacting the surrounding bone negatively. Mineralization profiles of metastatic models were significantly improved post-RFA treatment with respect to mineral content and homogeneity, suggesting a positive impact of RFA treatment on the quality of cancer involved bone. Evaluating the impact of RFA on bone quality is important in directing the growth of this minimally invasive therapeutic approach with respect to fracture risk assessment, patient selection, and multimodal treatment planning.

Fig 1. Experimental design and workflow.

Micro computer tomography (μCT); radiofrequency ablation treatment (RF Tx); radiofrequency ablation (RFA); hematoxylin and eosin (H&E); human epithelium growth factor receptor (hEGFr); polarization-in, polarization-out (PIPO) second harmonic generation (SHG); backscatter electron (BSE).

Fig 2. Backscatter electron images of rat femur.

Representative sagittal cross-sectional BSE acquisitions. Regions of osteoblast proliferation, indicative of new bone formation, is seen post RFA (yellow arrows). Green arrows indicate probe insertion channels. a-c) Femora from healthy controls. d-f) Femora from ZR-75-1 cell injected rats: Osteoblastic-induced new bone formation is visualized identified inside the dashed rectangle box. g-i) Femora from HeLa cell injected rats: Osteolytic lesions in trabecular bone tissue demonstrate tumor involvement (i.e. dashed rectangular overlay).

Fig 3. Histopathology of healthy bone tissue.

Histology section of the femur of healthy control rats and rats with osteoblastic lesions: a) Mid-sagittal section of a distal femur in a healthy control rat stained with haematoxylin and eosin (BM: bone marrow; TR: trabeculae) b) Mid-sagittal section of a distal femur 4-week post RFA. Fibrous tissue (F) has formed within the treated region with the newly formed bone (NB) visible on the border of the treated area. c) Tumor cells (T; ZR-75-1) in the mid-sagittal section of a distal femur inducing osteoblastic bone formation (BM: bone marrow; TR: trabeculae; OB: osteoblastic bone formation) d) Mid-sagittal section of a distal femur 4 weeks post RFA. Tumor cells are necrotic (N) and fibrous tissue (F) has formed within the treated area.

Fig 4. Histopathology of metastatic bone tissue.

Histology section of the femur with osteolytic metastases: a) Tumor cells (T; HeLa) in the mid-sagittal section of a distal femur (BM: bone marrow; TR: trabeculae; OC: osteoclast; BV: blood vessel) b) Mid-sagittal section of a distal femur 1-week post RFA. Tumor cells are necrotic (N); osteocytes (OC) are dead within the trabeculae of the treated area surrounded by RFA-induced fibrous tissue (F) formation. c) Tumor cells (T) are staining positive for the hEGFr antibody in the mid-sagittal section of a distal femur (BM: bone marrow; TR: trabeculae; OC: osteoclast; BV: blood vessel) d) Mid-sagittal section of a distal femur 1 week post RFA. Tumor cells are necrotic (N), no longer stain positively and fibrous tissue (F) is formed within the treated area.

Fig 5. Mineralization profile of bone tissue.

RFA-induced bone mineral density distribution (BMDD) changes in healthy femora and femora with metastatic lesions calculated from BSE images. The mineralization profile (a) Calcium Width (CaWidth) b) Calcium Mean (CaMean) and c) Calcium Peak (CaPeak)) of healthy and bone with metastatic lesions is modified post treatment. * Represents a significant difference between indicated groups (p < 0.05).