Radiolabeled divalent peptidomimetic vitronectin receptor antagonists as potential tumor radiotherapeutic and imaging agents.

The integrin receptor alphavbeta3 is overexpressed on the endothelial cells of growing tumors and on some tumor cells themselves. A radiolabeled alphavbeta3 antagonists belonging to the quinolin-4-one class of peptidomimetics (TA138) was previously shown to exhibit high affinity for integrin alphavbeta3 and high selectivity versus other integrin receptors. 111In-TA138 exhibited high tumor uptake in the c-neu Oncomouse mammary adenocarcinoma model and produced excellent scintigraphic images. This study describes the synthesis of eight divalent versions of TA138 and their evaluation as potential tumor radiotherapeutic agents. The two main variables in this study were the length of the spacer bridging the biotargeting moieties and the total negative charge of the molecules imparted by the cysteic acid pharmacokinetic modifiers. Receptor affinity was evaluated in a panel of integrin receptor affinity assays, and biodistribution studies using the 111In-labeled derivatives were carried out in the c-neu Oncomouse model. All divalent agents maintained the high receptor affinity and selectivity of TA138, and six of the eight 111In derivatives exhibited blood clearance that was faster than 111In-TA138 at 24 h postinjection (PI). All divalent agents exhibited tumor uptake and retention at 24 h PI that was higher than 111In-TA138. Tumor/organ ratios were improved for most of the divalent agents at 24 h PI in critical nontarget organs marrow, kidney, and liver, with the agents having intermediate-length spacers (29-43 A) showing the largest improvement. As an example, 111In-15 showed tumor uptake of 14.3% ID/g at 24 h PI and tumor/organ ratios as follows: marrow, 3.24; kidney, 7.29; liver, 8.51. A comparison of therapeutic indices for 90Y-TA138 and 177Lu-15 indicate an improved therapeutic index for the divalent agent. The implications for radiotherapeutic applications and the mechanism of this multivalent effect are discussed.

Structure-activity relationships of 111In- and 99mTc-labeled quinolin-4-one peptidomimetics as ligands for the vitronectin receptor: potential tumor imaging agents.

The integrin receptor alpha(v)beta(3) is overexpressed on the endothelial cells of growing tumors and on some tumor cells themselves. Radiolabeled alpha(v)beta(3) antagonists have demonstrated potential application as tumor imaging agents and as radiotherapeutic agents. This report describes the total synthesis of eight new HYNIC and DOTA conjugates of receptor alpha(v)beta(3) antagonists belonging to the quinolin-4-one class of peptidomimetics, and their radiolabeling with (99m)Tc (for HYNIC) and (111)In (for DOTA). Tethering of the radionuclide-chelator complexes was achieved at two different sites on the quinolin-4-one molecule. All such derivatives maintained high affinity for receptor alpha(v)beta(3) and high selectivity versus receptors alpha(IIb)beta(3), alpha(v)beta(5), alpha(5)beta(1). Biodistribution of the radiolabeled compounds was evaluated in the c-neu Oncomouse mammary adenocarcinoma model. DOTA conjugate (111)In-TA138 presented the best biodistribution profile. Tumor uptake at 2 h postinjection was 9.39% of injected dose/g of tissue (%ID/g). Activity levels in selected organs was as follows: blood, 0.54% ID/g; liver, 1.94% ID/g; kidney, 2.33% ID/g; lung, 2.74% ID/g; bone, 1.56% ID/g. A complete biodistribution analysis of (111)In-TA138 and the other radiolabeled compounds of this study are presented and discussed. A scintigraphic imaging study with (111)In-TA138 showed a clear delineation of the tumors and rapid clearance of activity from nontarget tissues.

Technetium Complexes of a Hydrazinonicotinamide-Conjugated Cyclic Peptide and 2-Hydrazinopyridine: Synthesis and Characterization.

Ternary ligand technetium complexes of a hydrazinonicotinamide-conjugated cyclic peptide (HYNICtide: cyclo(D-Val-NMeArg-Gly-Asp-Mamb(5-(6-(6-hydrazinonicotinamido)hexanamide)))) and 2-hydrazinopyridine (HYPY) were prepared and characterized by various spectroscopic methods. The HPLC concordance experiments for (99m)Tc and (99)Tc analogues show clearly that the same complexes are prepared on the no-carrier-added ((99m)Tc) and the carrier-added ((99)Tc) levels. Using a chirality experiment, it was demonstrated that the presence of two radiometric peaks in the HPLC chromatograms of RP444, RP445, and RP446 is due to the resolution of diastereomers, which result from the presence of chiral cyclic peptide and the formation of two enantiomers of the technetium chelate. In a ligand challenge experiment, we found that the high solution stability of these ternary ligand [(99m)Tc]HYNICtide complexes is due to their kinetic inertness. The 1:1:1:1 composition for Tc:HYNICtide:L:tricine (L = TPPTS, TPPDS, and TPPMS) in these ternary ligand [(99)Tc]HYNICtide complexes is confirmed by (1)H NMR and FAB mass spectral data and is completely consistent with that determined on the tracer ((99m)Tc) level. In addition, the IC(50) values of RP444, RP445, and RP446 and the two isomeric forms of RP444 were determined using a platelet IIb/IIIa binding assay. Both isomeric forms of RP444 were found to have the same binding affinity (IC(50) = 13 +/- 2 nM). Complexes [(99)Tc(HYPY)(PPh(3))(2)Cl(2)] and [(99)Tc(HYPY)(PPh(3))(tricine)] were isolated from the reaction of HYPY with [n-Bu(4)N][TcOCl(4)(-)] in the presence of excess tricine and triphenylphosphine. [(99)Tc(HYPY)(PPh(3))(tricine)] serves as a model for ternary ligand [(99m)Tc]HYNICtide complexes. Both complexes have been characterized by HPLC, spectroscopic (IR, NMR, and FAB-MS) methods, and elemental analysis. The HPLC concordance for complexes [(99m)Tc(HYPY)(PPh(3))(tricine)] and [(99)Tc(HYPY)(PPh(3))(tricine)] shows that the two complexes are identical. The NMR ((1)H and (13)C) data suggests that the complex [(99)Tc(HYPY)(PPh(3))(tricine)] have an octahedral coordination geometry with a monodentate diazenido HYPY, a tetradentate tricine, and a monodentate triphenylphosphine coligand.