Christy S. John

Sigma receptors are expressed in human non-small cell lung carcinoma

N-(2-piperidinoethyl)4-iodobenzamide), IPAB, was used to characterize sigma receptors in non-small cell lung cancer (NSCLC) cell lines. 125IPAB bound with high affinity to large cell carcinoma (NCI-H1299), adenocarcinoma (NCI-H838), and lung carcinoid (NCI-H727) cell lines. Specific IPAB binding was inhibited with high affinity by haloperidol (Ki = 0.6 nM), IPAB (Ki = 14 nM) and 1,3-ditolyl guanidine (DTG) (Ki = 40 nM). Relative to other receptor ligands, IPAB was not readily internalized at 37 degrees C. IPAB had little effect on the growth of NSCLC cells. Scintigraphic imaging studies using 131IPAB in nude mice bearing NCI-H838 xenografts visualized the tumor at 24 or 30 hours after injection. These results suggest that sigma receptors which are present on NSCLC cells may be used as external markers for imaging tumors in vivo.

Synthesis and evaluation of [18F] labeled benzamides: High affinity sigma receptor ligands for PET imaging☆

We have synthesized and characterized four new fluorinated halobenzamides as sigma receptor ligands for use with positron emission tomography (PET). All the compounds were found to have high sigma-1 affinities (Ki = 0.38-0.98 nM), and the 4-fluoro-substituted benzamides were found to be more potent sigma-2 ligands (Ki = 3.77-4.02 nM) than their corresponding 2-fluoro analogs (Ki = 20.3-22.8 nM). The [18F] radiochemical syntheses of two of the analogs gave overall yields between 3-10% (EOS), radiochemical purities > 99%, and specific activities between 800-1200 Ci/mmol (29.6-44.4 TBq/mmol). Rat biodistribution and blocking experiments were performed with 2-[18F](N-fluorobenzylpiperidin-4yl)-4-iodobenzamide, the analog with the best Ki value for sigma-1 sites (0.38 nM). Results of these experiments demonstrate specific uptake of the compound in tissues believed to contain sigma receptors, such as lungs, kidneys, heart, brain, and spleen and indicate its potential as a candidate for use in PET imaging of tissues containing these receptors.

(Arg15, Arg21) VIP: evaluation of biological activity and localization to breast cancer tumors.

VIP analogs, which contain a single lysine amino acid, were synthesized and evaluated using breast cancer cells. (Arg15, Arg20) VIP, (Argl5, Arg21) VIP, and (Arg20, Arg21) VIP inhibited 125I-VIP binding to T47D cells with high affinity (IC50 values of 1.2, 1.0, and 0.8 nM, respectively). The VIP analogs elevated cAMP in T47D cells with ED50 values ranging from 0.1-1 nM. Because (Arg15, Arg21) VIP was the most potent at elevating cAMP, it was characterized further. (Arg15, Arg21) VIP transiently increased c-fos gene expression in breast cancer cells. N-Succinimidyl-4-18F (fluoromethly) benzoate was prepared in one chemical step from N-succinimidyl-4-(4-nitrobenzenesulfonyl)oxomethyl)benzoate by adding 18F in acetone at room temperature. This prosthetic group was then reacted with (Arg15, Arg21) VIP ((RR) VIP). (18F-RR) VIP bound with high affinity to T47D cells and was rapidly internalized. (18F-RR) VIP was injected intravenously into nude mice bearing breast cancer xenografts and after 4 h, the density of (18F-RR) VIP was elevated in the tumors relative to normal organs. These data suggest that VIP receptors may be used to localize breast cancer tumors.

N,N′-Ethylene-di-l-Cysteine (EC) complexes of Ga(III) and In(III): Molecular modeling, thermodynamic stability and in vivo studies

There are several reports in the literature on the evaluation of chelates containing two nitrogens and two sulfurs (N2S2) as four coordinate ligands (in solution) for gallium and indium radiopharmaceuticals. No thermodynamic stability constants of these ligands were reported, and the stability of these complexes in vivo has been questioned. L,L-Ethylenedicysteine (EC) is a N2S2 ligand that also contains two carboxylic acid moieties for complexation of Ga(III) and In(III) in a hexacoordinate environment. The stability constants of Ga- and In-EC have been determined by potentiometric methods. The stability of In-EC was found to be greater than that of Ga-EC, with stability constants (log Ks) of 33.0 and 31.5, respectively. A molecular mechanics evaluation of the Ga- and In-EC complexes support the thermodynamic results. 67Ga- and 111In-labeled complexes of EC were prepared and analyzed by thin layer chromatography and electrophoresis. Both complexes were evaluated in biodistribution studies in normal Sprague-Dawley rats. 111In-EC cleared rapidly through the hepatobiliary system, whereas 67Ga-EC remained in the liver at 1 h post-injection. Although 67Ga-EC was retained in the liver, suggesting instability of the complex in vivo. 67Ga-EC was stable in rat plasma in vivo at 2 h post-injection. Because of the high thermodynamic and in vivo stability of In-EC, derivatives of EC may have applications as bifunctional chelates for 111In-labeled proteins and peptides. More lipophilic analogues of 68Ga-EC may also have potential as myocardial PET imaging agents.

Synthesis, In Vitro Binding, and Tissue Distribution of Radioiodinated 2-[125I]N-(N-Benzylpiperidin-4-yl)-2-Iodo Benzamide, 2-[125I]BP: A Potential σ Receptor Marker for Human Prostate Tumors

The preclinical evaluation of a sigma receptor-specific radiopharmaceutical that binds to human prostate tumor cells with a high affinity is described. We have synthesized and radioiodinated 2-[125I]-N-(N-benzylpiperidin-4-yl)-2-iodobenzamide (2-[125I]BP) that possesses high affinity for both sigma-1 and sigma-2 receptor subtypes that are expressed on a variety of tumor cells. 2-IBP was synthesized, purified and characterized by routine spectroscopic and analytical methods. Radioiodination was accomplished using an oxidative iododestannylation reaction in the presence of chloramine T in high yields (76%-93%) with a very high-specific activity (1700-1900 Ci/mmol). The in vitro competition binding studies of 2-[125I]BP with various sigma receptor ligands in LnCAP human prostate tumor cells showed a dose-dependent saturable binding. The inhibition constants (Ki, nM) for binding of 2-[125I]BP to human prostate tumor cells for 4-IBP, haloperidol and 2-IBP were 4.09, 6.34 and 1.6 nM, respectively. The clearance of 2-[125I]BP, in Sprague-Dawley rats, was rapid from the blood pool, other normal tissues and the total body. Tissue distribution studies in nude mice bearing human prostate tumor (DU-145) also showed a fast clearance from normal organs. The tumor had the highest percentage of injected dose per gram (%ID/g) of all tissues at 4 h as well as 24 h (2.0 +/- 0.05 and 0.147 +/- 0.038 ID/g, respectively) postinjection. The in vivo receptor binding specificity was demonstrated using haloperidol (a known high-affinity sigma receptor ligand). A significant decrease (> 50%, p = 0.001) was observed in tumor concentration when haloperidol was used as a blocking agent. The high affinity of 2-[125I]BP for sgma receptor-binding sites, its fast in vivo clearance from normal organs and its high uptake and retention in tumor implies that 2-[123I]BP or 2-[131I]BP may be a promising tracer for noninvasive imaging of human prostate tumors.

Synthesis, in vitro validation and in vivo pharmacokinetics of [125I]N-[2-(4-Iodophenyl)Ethyl]-N-Methyl-2-(1-Piperidinyl) ethylamine: A high-affinity ligand for imaging sigma receptor positive tumors☆

N-[2-(4-iodophenyl)ethyl]-N-methyl-2-(1-piperidinyl)ethylamine, IPEMP, and the corresponding bromo derivative, BrPEMP, have been synthesized and characterized. Both BrPEMP and IPEMP were evaluated for sigma-1 and sigma-2 subtype receptor affinities and found to possess very high affinities for both receptor subtypes. The precursor for radioiodination n-tributylstannylphenylethylpiperidinylethylamine was prepared from its bromo derivative by palladium-catalyzed stannylation reaction. Radioiodinated 4-[125I]PEMP was readily prepared in high yields and high specific activity by oxidative iododestannylation reaction using chloramine-T as oxidizing agent. Sites labeled by 4-[125I]PEMP in guinea pig brain membranes showed high affinity for BD1008, haloperidol, and (+)-pentazocine (Ki = 5.06 +/- 0.40, 32.6 +/- 2.75, and 48.1 +/- 8.60 nM, respectively), which is consistent with sigma receptor pharmacology. Competition binding studies of 4-[125I]PEMP in melanoma (A375) and MCF-7 breast cancer cells showed a high affinity, dose-dependent inhibition of binding with known sigma ligand N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl) ethylamine, BD1008 (Ki = 5, 11 nM, respectively), supporting the labeling of sigma sites in these cells. Haloperidol, however showed a weaker (Ki = 100-200 nM) affinity for the sites labeled by 4-[125I]PEMP in these cells. Biodistribution studies of 4-[125I]PEMP in rats showed a fast clearance of this radiopharmaceutical from blood, liver, lung, and other organs. A co-injection of 4-IPEMP with 4-[125I]PEMP resulted in 37%, 69%, and 35% decrease in activity in liver, kidney, and brain (organs possessing sigma receptors), respectively at 1-h postinjection. These results suggest that 4-[125I]PEMP is a promising radiopharmaceutical for pursuing further studies in animal models with tumors.

An improved synthesis of [125I]N-(diethylaminoethyl)-4-iodobenzamide: a potential ligand for imaging malignant melanoma.

To improve the radiolabeling yield and the specific activity of [125I]N-(2-diethylaminoethyl)-4-iodobenzamide (DAB), the aryltributyltin precursor was synthesized from the N-(2-diethylaminoethyl)-4-bromobenzamide derivative by palladium catalyzed stannylation using bis(tributyltin). The radiolabeled product, [125I]DAB, was obtained by an iododestannylation reaction in high radiochemical yields (85-94%, radiochemical purity, > 98%) using chloramine-T as an oxidizing agent. The specific activity was greater than 1600 Ci/mmol. The biodistribution studies in nude mice implanted with human malignant melanoma xenograft showed a good tumor uptake (6.14% ID/g at 1 h, 2.81% ID/g at 6 h and 0.42% ID/g at 24 h) of [125I]DAB. Unfortunately, a high uptake in the non-target organs, such as liver and lung, was found. At 1 h post-injection the activity level in liver and lung was 11.76 and 7.58% ID/g, respectively. A slow clearance of activity from liver and lung was observed at 6 h (3.43 and 0.49% ID/g). These results demonstrate that iodinated IDAB is a potential radiopharmaceutical for the management of patients with malignant melanoma.

Technetium complexes of pentadentate amine-phenol ligands

Abstract We have synthesized five new pentadentate amine-phenol ligands as part of a study to develop bifunctional chelating agents for labeling antibodies with 99m Tc. These ligands were prepared by condensing various triamine ligands with salicylaldehyde and reducing the Schiff bases obtained to get the amine-phenol ligands. Radiochemical studies of 99m Tc and 99 Tc complexes were performed with the precursor imine-phenols and the amine-phenol ligands. Technetium complexes were prepared at total technetium concentrations of 0.1–100μM at ligand concentrations of 100 μM. Complexation yields and radiochemical purities were estimated by Chromatographie techniques, paper electrophoresis and by solvent extraction into CHCl 3 . Complexation was achieved with both imine- and amine-phenol ligands. The amine-phenol complexes were found to be stable over a period of 24 h. The lipophilicities and stability of the amine-phenol complexes were higher than those of the imine-phenol complexes. Biodistribution studies with two of the amine-phenol complexes were carried out in Sprague-Dawley rats. A large portion of the injected activity was taken up by the liver and the clearance rate of the chelates from blood was slow.