1. Orthogonally protected artificial amino acid as tripod ligand for automated peptide synthesis and labeling with [(99m)Tc(OH(2))(3)(CO)(3)](+)
Yunjun Shen, Margret Schottelius, Karel Zelenka, Mariarosaria De Simone, Karolin Pohle, Horst Kessler, Hans-Jürgen Wester, Paul Schmutz, Roger Alberto Bioconjug Chem. 2013 Jan 16;24(1):26-35. doi: 10.1021/bc3003327. Epub 2012 Dec 26.
1,2-Diamino-propionic acid (Dap) is a very strong chelator for the [(99m)Tc(CO)(3)](+) core, yielding small and hydrophilic complexes. We prepared the lysine based Dap derivative l-Lys(Dap) in which the ε-NH(2) group was replaced by the tripod through conjugation to its α-carbon. The synthetic strategy produced an orthogonally protected bifunctional chelator (BFC). The -NH(2) group of the α-amino acid portion is Fmoc- and the -NH(2) of Dap are Boc-protected. Fmoc-l-Lys(Dap(Boc)) was either conjugated to the N- and C-terminus of bombesin BBN(7-14) or integrated into the sequence using solid-phase peptide synthesis (SPPS). We also replaced the native lysine in a cyclic RGD peptide with l-Lys(Dap). For all peptides, quantitative labeling with the [(99m)Tc(CO)(3)](+) core at a 10 μM concentration in PBS buffer (pH = 7.4) was achieved. For comparison, the rhenium homologues were prepared from [Re(OH(2))(3)(CO)(3)](+) and Lys(Dap)-BBN(7-14) or cyclo-(RGDyK(Dap)), respectively. Determination of integrin receptor binding showed low to medium nanomolar affinities for various receptor subtypes. The IC(50) of cyclo-(RGDyK(Dap[Re(CO)(3)])) for α(v)β(3) is 7.1 nM as compared to 3.1 nM for nonligated RGD derivative. Biodistribution studies in M21 melanoma bearing nude mice showed reasonable α(v)β(3)-integrin specific tumor uptake. Altogether, orthogonally protected l-Lys(Dap) represents a highly versatile building block for integration in any peptide sequence. Lys(Dap)-precursors allow high-yield (99m)Tc-labeling with [(99m)Tc(OH(2))(3)(CO)(3)](+), forming small and hydrophilic complexes, which in turn leads to peptide radiopharmaceuticals with excellent in vivo characteristics.
2. 68Ga-labeled HBED-CC Variant of uPAR Targeting Peptide AE105 Compared with 68Ga-NODAGA-AE105
Kusum Vats, Rohit Sharma, Haladhar D Sarma, Drishty Satpati, Ashutosh Dash Anticancer Agents Med Chem. 2018;18(9):1289-1294. doi: 10.2174/1871520618666180316152618.
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.
3. HIV-1 protease inhibitors containing an N-hydroxyamino acid core structure
M Marastoni, M Bazzaro, S Salvadori, F Bortolotti, R Tomatis Bioorg Med Chem. 2001 Apr;9(4):939-45. doi: 10.1016/s0968-0896(00)00308-4.
Two series of peptidomimetics containing an N-hydroxyamino acid core structure were prepared by mixed solution solid-phase synthesis and tested for inhibitory activity against the human immunodeficiency virus (HIV-1) protease (Pr) and the virus in cell culture. In general, N-hydroxy Gly containing pseudopeptides displayed modest HIV Pr inhibition (IC50 > or = 930 nM). In the N-hydroxy Phe derivatives, Fmoc-Phe-psi[CO-N(OH)]-Phe-Pro-NHtBu was the best inhibitor of the series (IC50 = 144nM) showing satisfactory inhibition of HIV replication in cell culture (ED50 = 98 nM) and remarkable stability against cell culture and plasma enzymes.
