Imatinib mesylate does not increase bone volume in vivo.

Area of Science:

• Pharmacology
• Bone Biology
• Oncology

Background:

• Imatinib mesylate is a tyrosine kinase inhibitor used for specific cancers.
• In vitro studies suggest imatinib affects bone metabolism.
• Clinical observations show stable or increased bone mass in patients on imatinib.

Purpose of the Study:

• To investigate the direct skeletal effects of imatinib in healthy animals.
• To determine if imatinib influences bone volume and turnover independently of disease recovery or weight gain.

Main Methods:

• Mature female rats were treated with vehicle, low-dose (40 mg/kg), or high-dose (70 mg/kg) imatinib for 5 weeks.
• Evaluated bone volume, bone turnover markers (serum osteocalcin), and bone histomorphometry.
• Assessed biochemical and histomorphometric indices of bone resorption.

Main Results:

• Imatinib significantly reduced trabecular bone volume/tissue volume in a dose-dependent manner (P=0.05 for high dose).
• Osteoblast surface and serum osteocalcin levels were significantly decreased by imatinib treatment (P<0.01 for low dose).
• No significant effects on bone resorption were observed.

Conclusions:

• In healthy rats, imatinib treatment does not increase bone mass.
• The drug appears to reduce bone formation markers and bone volume.
• Observed bone density increases in patients may be indirect effects, not directly caused by imatinib.