Drug description:

Zoledronic acid is a bisphosphonate used to treat malignancy associated hypercalcemia, multiple myeloma, and bone metastasis from solid tumors.

Mechanism of action:

Bisphosphonates are taken into the bone where they bind to hydroxyapatite. Bone resorption by osteoclasts causes local acidification, releasing the bisphosphonate, which is taken into the osteoclast by fluid-phase endocytosis.
Endocytic vesicles become acidified, releasing bisphosphonates into the cytosol of osteoclasts where they act.

Osteoclasts mediate resorption of bone.When osteoclasts bind to bone they form podosomes, ring structures of F-actin. Etidronic acid also inhibits V-ATPases in the osteoclast, though the exact subunits are unknown, preventing F-actin from forming podosomes. Disruption of the podosomes causes osteoclasts to detach from bones, preventing bone resorption.

Nitrogen containing bisphosphonates such as zoledronate are known to induce apoptosis of hematopoietic tumor cells by inhibiting the components of the mevalonate pathway farnesyl diphosphate synthase, farnesyl diphosphate, and geranylgeranyl diphosphate. These components are essential for post-translational prenylation of GTP-binding proteins like Rap1. The lack of prenylation of these proteins interferes with their function, and in the case of Rap1, leads to apoptosis.10,9 zoledronate also activated caspases which further contribute to apoptosis.

Source: https://go.drugbank.com/drugs/DB00399