Noninvasive Imaging of Osteoclasts in Parathyroid Hormone–Induced Osteolysis Using a ⁶⁴Cu-Labeled RGD Peptide

Uptake of ⁶⁴Cu-CB-TE2A-c(RGDyK) by osteoclasts and macrophages. BMMs were harvested from mice and grown in culture. (A) Cells treated with only M-CSF remained TRAP(−) mononuclear macrophages. (C) Cells cultured in presence of MCSF plus RANKL differentiated into large, TRAP(+) osteoclasts (red stain). (B) Cell uptake was determined 2 h after addition of ⁶⁴Cu-CB-TE2A-c(RGDyK) (4 nM) plus c(RGDyK) (0–4,000 nM) to medium of cells grown in 6-well plates. Each data point represents average of triplicate measurements. (D) Integrin expression was evaluated by Western blot against β₃. Lanes: 1 = α_vβ₃ standard, 10 ng; 2 = empty; 3 = osteoclast lysate, 20 μg; 4 = macrophage lysate, 20 μg.

PTH induces osteoclasts resulting in increased uptake of ⁶⁴Cu-CB-TE2A-c(RGDyK) at calvarium. TRAP-stained sections of calvarium of control mice (A) and PTH-treated mice (D) confirm osteoclast induction after PTH treatment. Osteoclasts stain red. (B) Biodistribution (1 h after injection) was performed on control mice (n = 8), PTH-treated mice (n = 8), and PTH-plus-block mice injected with 740 kBq (20 μCi) (10.5–12 ng) of ⁶⁴Cu-CB-TE2A-c(RGDyK). Note that n = 7 for PTH femur because of contamination of 1 sample by urine. (C) Uptake of ⁶⁴Cu-CB-TE2A-c(RGDyK) (biodistribution 1 h after injection: control, n = 7; PTH, n = 7) was plotted against ratio of osteoclast surface area to total surface area.