Background: Breast cancer (BC) produces bone resorptive cytokines and growth factors which accelerate the
development of osteoclasts (OCs), leading to osteolytic bone metastases. In the Long-term Odanacatib Fracture Trial
(LOFT), the skeletal-metastasized breast cancer subjects who received odanacatib (ODN) had a delayed tumour
progression and skeletal tumour burden as a result of anti-resorptive effects through inhibition of cathepsin K (CTSK). In
this study, we explored the effect of ODN, a CTSK inhibitor, on the paracrine pro-osteoclast activity of breast cancer
Methods: Immunohistochemistry study was performed to demonstrate CTSK and PTHrP expression in the samples of
primary breast carcinoma. Expression of CTSK mRNA and protein was confirmed by the reverse transcription PCR and
western blotting analysis in two human breast cancer cell lines MDA-MB-231 and MCF-7 BC cell lines. Cells were
incubated with sub-lethal amounts of ODN, and their conditioned supernatants were assessed for their capacity to
differentiate PBMCs of healthy donors into osteoclast and its interference on bone resorbing activities. We also measured
the mRNA levels of major pro-osteoclast (pro-OC) factors in ODN-treated breast cancer cells and their secreted levels by
semi-quantitative reverse transcription PCR and protein expression by immunoblotting.
Results: Different staining intensity was observed in samples containing PTHrP and CTSK in various histological grades
of breast carcinoma. Significant positive relationship was found between CTSK expression and histological grade of BC
and presence or absence of distant metastasis.The present study results also indicate that ODN has no effects on OCs
number , however; ODN decreases the mRNA expression of secreted pro-OC factors such as PTHrP, CXCR-4, and TNFα. Immuno blot indicates that ODN treatment decreased the protein expression of CTSK, IL-6, and IL-1β, and thus
lowered protein levels paralleled the defective phosphorylation of NF-κB. Moreover, there was a significant reduction in
the level of growth factors such as IGF-1, PDGF and TGFβ expression at transcriptional level after ODN treatment as
compared to control.
Conclusion: ODN has shown to prevent osteolytic metastasis by interacting with the NF-κB pathway; inhibiting bone
resorptive cytokines, and growth factors. This effect can also be take into account the delayed development of metastatic
bone disease found in the long-term odanacatib fracture trial (LOFT) study.