Monitoring antiproliferative responses to kinase inhibitor therapy in mice with 3'-deoxy-3'-18F-fluorothymidine PET.

The aim of this study was to evaluate, whether PET with (18)F-FDG and 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) may be used to monitor noninvasively the antiproliferative effects of tyrosine kinase inhibitors. Using a high-resolution small animal scanner, we measured the effect of the ErbB-selective kinase inhibitor PKI-166 on the (18)F-FDG and (18)F-FLT uptake of ErbB1-overexpressing A431 xenograft tumors. Treatment with PKI-166 markedly lowered tumor (18)F-FLT uptake within 48 h of drug exposure; within 1 wk (18)F-FLT uptake decreased by 79%. (18)F-FLT uptake by the xenografts significantly correlated with the tumor proliferation index as determined by proliferating cell nuclear antigen staining (r = 0.71). Changes in (18)F-FLT uptake did not reflect inhibition of ErbB kinase activity itself but, rather, the effects of kinase inhibition on tumor cell proliferation. Tumor (18)F-FDG uptake generally paralleled the changes seen for (18)F-FLT. However, the baseline signal was significantly lower than that for (18)F-FLT. These results indicate that (18)F-FLT PET provides noninvasive, quantitative, and repeatable measurements of tumor cell proliferation during treatment with ErbB kinase inhibitors and provide a rationale for the use this technology in clinical trials of kinase inhibitors.