These observations led to the development and utilization of the indirect method to ensure that such effects were not confounding the Vv results. The overall similarity in distributions of radioactivity between the two images was consistent with the lack of significant anti-VEGF effect on measured Vv values. Slight splenic uptake of 99mTc observed in SPECT-CT images was observed, as expected, due the spleen��s physiological role in sequestration of RBCs. Furthermore, anti-VEGF administration had no statistically significant effect on measured Vi values. Because calculation of Vi requires knowledge of both vascular and extracellular spaces, statistical analysis of raw %ID/g 111In-DTPA data was performed separately and showed no significant differences between dose groups. Comparing the PBPK modeling results using literature and measured parameter KU-0059436 values demonstrates the importance of obtaining accurate values for physiological parameters. While the change in blood AUC is modest, the impact of using measured physiological values is potentially high when simulating concentration-time curves within certain organs, with changes in liver and intestine AUCs of approximately 50%. Variability in AUC0�C7 for liver is of particular significance when modeling antibody biodistribution because of its role as a clearance organ. Although closer agreement between model predicted and experimental AUC0�C7 values was obtained using literature Vv, Vi, and Q values in liver, kidneys, and lungs, the use of experimentally determined parameter values gave superior results in blood, muscle, and spleen. Both methods demonstrated roughly comparable performance in predicting AUC0�C7 values in heart. The excellent agreement between model predicted and experimental values in muscle is of particular significance given the inclusion of an FcRn submodel in the muscle subcompartment of the PBPK model. This nonlinear twocompartment submodel accounts for linear transfer of antibody from organ vascular space to endosomes via nonspecific bulk fluid uptake by endothelial cells, recycling of FcRn-bound antibody back into plasma, and degradation of non-FcRn-bound antibody. Difficulty in harvesting lungs without pooling of excess blood during sacrifice may have influenced the calculated parameter values for this tissue. In addition, clearance of physiological probes may limit the validity of measurements. This effect was avoided for the vascular volume measurement by use of an indirect RBC labeling protocol to avoid contamination by non-RBC-associated 99mTc; however, 111In-DTPA and 86Rb are also subject to renal clearance and, in the case of 111In-DTPA, possible transchelation of radiometal into metalloproteins may Dasatinib encourage hepatic accumulation. Due to the aforementioned complications, utilization of nominal values for lungs, liver, and kidney may be superior to the use of measured values. The origin of values reported in the literature should be carefully considered, as many are in fact assumed nominal values.