Figure 1. Schematic of the SEAP/Mn-TPPP4 reporter approach.
The secreted alkaline phosphatase reporter enzyme (SEAP, red) is produced by genetically modified cells and acts on the MRI contrast agent Mn-TPPP4 (structure shown), cleaving up to four phosphates and inducing precipitation of the products, which have low solubility compared with Mn-TPPP4. Accumulation of dephosphorylated contrast agents leads to local increases in T1-weighted MRI contrast in the vicinity of cells expressing SEAP.