Several new uPAR-directed therapies have recently been designed based on this new information. be a marker for malignancy stem cells. Several new uPAR-directed therapies have recently been developed based on this new information. A monoclonal antibody has been developed that disrupts the interactions of uPAR with signaling partners and is poised to enter the medical center. In addition, nanoscale drug delivery vehicles targeted to the uPA system using monoclonal antibodies, without disrupting the normal functioning of the system, are also in development. This review will spotlight some of these new discoveries and the new uPA system-based therapeutic approaches that have arisen from them. and localized to OV-MZ-6 tumors in xenograft models 53. A recent study used a uPA GFD mimetic peptide that binds to human uPAR with high affinity conjugated to DOTA loaded with 64Cu to image experimental colon cancer tumors in mice 54. In addition to the detection of these experimental tumors, demonstrating the proof of concept for this approach, this imaging technique was able to correlate uPAR expression levels Eltrombopag Olamine with response to 5-FU and showed that higher uPAR expression rendered the tumors less sensitive to 5-FU. This is the first study that suggests that there may be a threshold effect for uPAR expression in tumor growth and progression and that the level of uPAR expression may mediate drug effect. This will be important to explore further with uPAR targeted therapy in order to understand whether a similar threshold will be required for response to uPAR targeted therapy comparable to what has been observed with other cell-surface tumor targets such as c-MET and HER2 55. Several groups have also focused on using the amino terminal fragment of uPA (ATF, which contains the GFD) to deliver novel therapeutic payloads. The ATF binds to uPAR with an affinity that is similar to full size uPA 56 and provides a scaffold for the conjugation of payloads. Several ATF-toxin fusions have been reported. For example, a fusion protein (ATF-PE) comprised of the ATF and the Pseudomonas exotoxin (PE) retained the binding affinity of wild-type ATF and was cytotoxic to a number of cell lines with IC50 values as low as 0.3 pM 57. ATF-PE required internalization for its cytotoxic activity but this internalization was not mediated by uPAR alone. Experiments using radiolabeled ATF and ATF-PE exhibited a ~2 fold greater internalization of ATF-PE, compared to ATF alone. In addition, adding unlabeled ATF as a competitor to the radiolabeled ATF-PE blocked internalization of ATF-PE, which demonstrates that ATF played an important role in the Eltrombopag Olamine toxicity of ATF-PE. It is likely that this PE moiety itself was responsible for the enhanced internalization of ATF-PE, possibly through interactions with other lipoprotein receptors (e.g. the 2-macroglobulin receptor) 58. In our hands, free ATF is generally not endocytosed via uPAR and trafficked Eltrombopag Olamine to the lysosome although other mechanisms of internalization, as explained above, may be possible. An ATF-diphteria toxin (DTAT) fusion protein has also been described. Much like ATF-PE, DTAT retained the binding activity of wild type ATF and was cytotoxic to U87 glioma cells with an IC50 similar to the Kwhere treatment with DTAT significantly delayed tumor growth, more than doubling the time it required for Rabbit polyclonal to AADACL3 tumors to achieve 2000 mm3 ,60. DTAT also exhibited activity in a model of metastatic NSCLC.