Comparison of Indium-lll-DTPA-IgG and Tc-99m-MIBI Accumulation in VX-2 Cancer
Although Indium-111-DTPA-IgG (In-lll-DTPA-IgG) was originally developed as an imaging agent for inflammation/infection, it is known to accumulate in some malignant tumors. Whether such accumulation is related to an inflammatory response to the tumor or to some other mechanism remains to be determined. To address this issue, the accumulation of In-lll-DTPA-IgG and Tc-99m-MIBI, which has been recently reported as a tumor-seeking agent, was compared in rabbit VX-2 cancer. In-lll-DTPA-IgG and Tc-99m-MIBI were injected into the femoral region of six VX-2 tumor-bearing rabbits 11, 18, and 21 days after implantation of the tumor. On Tc-99m-MIBI scintigraphy, necrosis was visualized as a defect, whereas In -111 - DTPA - IgG accumulated in necrotic regions. The In-lll-DTPA-IgG or Tc-99m-MIBI tumor to muscle ratios increased as the tumors grew. In-lll-DTPA-IgG demonstrated a higher tumor to muscle ratio than Tc - 99m - MIBI. In addition, the accumulation of In-lll-DTPA-IgG was much higher in necrotic regions than in the viable tumor. These results suggest that the higher tumor uptake of In -111 - DTPA - IgG might be mainly accounted for by accumulation in the necrosis and inflammation, whereas Tc-99m-MIBI accumulates in viable tumor cells alone.