Abstract
35 Background: The ToGA study established HER2 is a target in the treatment of gastric cancer. Trastuzumab pharmacokinetics and organ distribution is varied in each patient and is heavily affected by the extent of tumor load (Oude Munnink, JCO 2010). 89Zr-trastuzumab HER2 PET can be used to image that variability and may aid in detection and staging of HER2-positive tumors. We are implementing 89Zr-radiolabeled trastuzumab PET in vivo for imaging of HER2-positive gastric cancer and for future non-invasive assessment of HER2 inhibition with a dual irreversible HER1/HER2 inhibitor, BIBW-2992. Methods: 89Zr (t1/2 = 3.17 days) was prepared via the 89Y(p,n)89Zr transmutation with high radiochemical yields (1.52±0.11 mCi/μAh) and purity (>99.99%). Trastuzumab was functionalized with the tris-hydroxamate chelate, desferrioxamine B (DFO) and radiolabeled with [89Zr]Zr-oxalate at room temperature. 89Zr-trastuzumab PET experiments in athymic nu/nu mice bearing sub-cutaneous NCI-N87 (HER2+) and/or SNU1 (HER2-) tumors were conducted. NCI-N87 gastric cancer cells were treated with BIBW-2992. Results: 89Zr-trastuzumab radiolabeling proceeded in high radiochemical yield and specific-activity of 2.82±0.05 mCi/mg. In vitro assays demonstrated >99% radiochemical purity with an immunoreactive fraction of 0.87±7. In vivo biodistribution experiments revealed high and specific uptake in HER2-positive tumors after 72 h (85.2±11.1% ID/g) with retention of activity for over 120 h. No uptake was seen in HER2-negative gastric cancer xenografts. In vitro, BIBW-2992 demonstrates dose dependent growth inhibition in the HER2+ gastric cancer cell line. Conclusions: 89Zr-trastuzumab provides quantitative and highly-specific delineation of HER2-positive gastric cancer. In vivo studies of BIBW2-2992 in gastric cancer with 89Zr-trastuzumab HER2 PET response assessment are underway. A Phase I study of 89Zr-trastuzumab PETin HER2-positive patients is to open at MSKCC imminently. No significant financial relationships to disclose.
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