Aims: The urokinase Plasminogen Activator Receptors (uPAR) over-expressed on tumor cells and
their invasive microenvironment are clinically significant molecular targets for cancer research. uPARexpressing
cancerous lesions can be suitably identified and their progression can be monitored with radiolabeled
uPAR targeted imaging probes. Hence this study aimed at preparing and evaluating two 68Ga-labeled AE105
peptide conjugates, 68Ga-NODAGA-AE105 and 68Ga-HBED-CC-AE105 as uPAR PET-probes.
Method:
The peptide conjugates, HBED-CC-AE105-NH2 and NODAGA-AE105-NH2 were manually synthesized
by standard Fmoc solid phase strategy and subsequently radiolabeled with 68Ga eluted from a commercial
68Ge/68Ga generator. In vitro cell studies for the two radiotracers were performed with uPAR positive U87MG
cells. Biodistribution studies were carried out in mouse xenografts with the subcutaneously induced U87MG
tumor.
Results:
The two radiotracers, 68Ga-NODAGA-AE105 and 68Ga-HBED-CC-AE105 that were prepared in >95%
radiochemical yield and >96% radiochemical purity, exhibited excellent in vitro stability. In vivo evaluation
studies revealed higher uptake of 68Ga-HBED-CC-AE105 in U87MG tumor as compared to 68Ga-NODAGAAE105;
however, increased lipophilicity of 68Ga-HBED-CC-AE105 resulted in slower clearance from blood and
other non-target organs. The uPAR specificity of the two radiotracers was ascertained by significant (p<0.05)
reduction in the tumor uptake with a co-injected blocking dose of unlabeled AE-105 peptide.
Conclusion:
Amongst the two radiotracers studied, the neutral 68Ga-NODAGA-AE105 with more hydrophilic
chelator exhibited faster clearance from non-target organs. The conjugation of HBED-CC chelator (less hydrophilic)
resulted in negatively charged 68Ga-HBED-CC-AE105 which was observed to have high retention in
blood that decreased target to non-target ratios.