Metastatic Bone Disease and Osteoclast Regulation

Metastatic bone disease arises when malignant cells colonise the bone microenvironment, disrupting the balanced activities of bone‐resorbing osteoclasts and bone‐forming osteoblasts. Tumour cells secrete factors such as parathyroid hormone‐related protein (PTHrP), transforming growth factor beta (TGF-β) and interleukins that enhance osteoclast differentiation and activity via the RANK/RANKL axis. The ensuing osteolysis liberates growth factors from the bone matrix, creating a vicious cycle that fuels tumour proliferation and further bone destruction. Osteoclasts mature from mononuclear precursors under the control of macrophage colony‐stimulating factor (M-CSF) and receptor activator of nuclear factor-κB ligand (RANKL), with downstream activation of NFATc1 driving gene programmes for resorption. Regulators such as sclerostin, Wnt signalling components and mechanotransductive cues from osteocytes modulate this process. Recent advances have uncovered biphasic roles for nutrient‐sensing kinases, novel osteocyte-cancer cell crosstalk mechanisms, and osteoblast-derived secretomes that reprogram the metastatic niche. Targeting these pathways offers potential strategies to interrupt the tumour–bone interaction, alleviate skeletal morbidity and improve patient outcomes.

Research from Nature Portfolio

Genetic and pharmacological interrogation of mTORC1 in osteoclast precursors has revealed a dosage-dependent, biphasic regulation of osteoclastogenesis. Loss- and gain-of-function models demonstrated that mTORC1 activity must be precisely tuned: early deletion impairs precursor proliferation whereas late inactivation augments differentiation via calcineurin-mediated dephosphorylation of mTORC1 and enhanced NFATc1 activation. Clinically relevant doses of rapamycin were shown to exacerbate resorption by shifting this balance, illuminating a calcineurin–mTORC1–NFATc1 phosphorylation cascade as a target for fine-tuning osteoclast activity.

Investigations into sclerostin, a Wnt antagonist primarily produced by osteocytes, have uncovered its overexpression in breast cancer metastases. Neutralising antibodies against sclerostin reduced tumour cell migration, invasion and osteolytic lesion formation in xenograft models. These findings position sclerostin inhibition as a dual approach to curb metastatic spread and mitigate bone destruction.

Metastatic Bone Disease and Osteoclast Regulation publication trend

The graph below shows the total number of articles in metastatic bone disease and osteoclast regulation across all publications each year (not limited to Nature Index journals).

Technical terms

Osteoclast: A multinucleated cell derived from monocyte/macrophage precursors specialised in bone resorption.

Osteoblast: A bone‐forming cell responsible for matrix synthesis and mineralisation.

RANKL: Receptor activator of nuclear factor-κB ligand, a cytokine essential for osteoclast differentiation and activation.

NFATc1: Nuclear factor of activated T cells c1, a master transcription factor driving osteoclast‐specific gene expression.

Sclerostin: A glycoprotein secreted by osteocytes that antagonises Wnt signalling and inhibits bone formation.

Primary cilium: A solitary, microtubule‐based cellular projection that mediates mechanosensory and signalling pathways in bone cells.

mTORC1: Mammalian target of rapamycin complex 1, a nutrient-sensing kinase complex that regulates cell growth and metabolism.

Wnt signalling: A pathway involving secreted glycoproteins that regulate cell fate, proliferation and bone homeostasis.

References

1. A Novel Primary Cilium‐Mediated Mechanism Through which Osteocytes Regulate Metastatic Behavior of Both Breast and Prostate Cancer Cells. Advanced Science (2023).
2. mTORC1 impedes osteoclast differentiation via calcineurin and NFATc1. Communications Biology (2018).
3. Sclerostin induced tumor growth, bone metastasis and osteolysis in breast cancer. Scientific Reports (2017).
4. Suppression of breast cancer-associated bone loss with osteoblast proteomes via Hsp90ab1/moesin-mediated inhibition of TGFβ/FN1/CD44 signaling. Theranostics (2022).
5. Skeletal loading regulates breast cancer-associated osteolysis in a loading intensity-dependent fashion. Bone Research (2020).