Substituted halogenated arylsulfonamides: a new class of sigma receptor binding tumor imaging agents

Photoinduced EnT-mediated sulfonamidylimination of alkenes and (hetero)arenes with iminophenylacetic acid oxime esters

A photoinduced EnT-mediated generation of sulfonamidyl radicals has been accomplished using rationally designed iminophenylacetic acid oxime ester reagents under metal-free conditions. This approach offers a mild, regio- and diastereoselective synthesis of N-sulfonyl diamines via diamination of alkenes and (hetero)arenes.

Radioiodination and preclinical evaluation of 4-benzyl-1-(3-[125I]-iodobenzylsulfonyl)piperidine as a breast tumor imaging tracer in mouse

OBJECTIVE

4-Benzyl-1-(3-iodobenzylsulfonyl)piperidine, 4-B-IBSP, has shown high-binding affinity to both sigma (σ) receptors in our previous work. In current study, radiolabeling and preclinical evaluation of 4-benzyl-1-(3-[¹²⁵I]-iodobenzylsulfonyl)piperidine, 4-B-[¹²⁵I]IBSP, in human ductal breast carcinoma (T47D) cells and in breast adenocarcinoma-bearing BALB/c mice are described.

METHODS

Radioiodination of this new σ ligand was performed by a palladium-catalyzed stannylation approach followed by oxidative iododestannylation reaction using Iodo-Gen. Competition-binding assays for binding of 4-B-[¹²⁵I]IBSP to guinea pig brain membranes and to T47D cells were performed with known σ ligands. The selectivity and binding characteristics (B _max and K _d) were analyzed. In vitro stability and in vivo blood metabolism studies were also evaluated. Moreover, biodistribution studies were performed in normal and into the tumor-bearing mice at interval time points post-injection (p.i.). Both in vitro and in vivo blockade experiments were done in the presence of the σ receptors blocking agents.

RESULTS

Radioiodinated ligand was obtained in high yield and high specific activity. The σ inhibition constants (K _i, nM) for 4-(3-iodobenzyl)-1-(benzylsulfonyl)piperazine (4-IBBSPz), (+)-pentazocine, haloperidol, DTG, and 4-B-IBSP were 1.37 ± 0.19, 3.90 ± 0.77, 2.69 ± 0.33, 30.62 ± 2.01, and 0.61 ± 0.05, respectively. 4-B-[¹²⁵I]IBSP bound to σ receptor sites preferably to very high-affinity binding sites on T47D cells. The radioligand showed acceptable in vitro and in vivo stabilities in the blood pool. However, in vivo biodistribution studies in normal Swiss albino mice revealed fast clearance of 4-B-[¹²⁵I]IBSP from blood and the other normal organs. Biodistribution experiments of 4-B-[¹²⁵I]IBSP in breast adenocarcinoma tumor-bearing BALB/c mice showed a relatively high tumor uptake at 30 min p.i. (4.13 ± 0.95) that reaches to 1.57 ± 0.24 even after 240 min p.i. A pre-injection of 4-B-IBSP and haloperidol with 4-B-[¹²⁵I]IBSP resulted in 36-57% decrease in activity in the tumor, liver, and brain at 60 min p.i.

CONCLUSIONS

The high affinity of 4-B-[¹²⁵I]IBSP to σ receptor-binding sites, its relatively high uptake, and preferential retention in the tumor as well as an increasing trend observed in the tumor to blood and in the tumor to muscle ratios suggests that an iodine-123 labeled counterpart, 4-B-[¹²³I]IBSP, would be a promising σ radioligand for pursuing further studies to assess its potential for breast tumors imaging with SPECT.

Synthesis of bridged piperazines with sigma receptor affinity

Bridged piperazines 4 were designed as conformationally restricted piperazine sigma receptor ligands. The chiral pool synthesis started from (S)-glutamate, which was transformed in five reaction steps into the piperazinediones 5 bearing a propionic acid ester side chain. A two-step Dieckmann analogous cyclization provided the bicyclic ketones 7 as key intermediates. The alcohols 8 were prepared by LiAlH4 reduction of the ketones 7. NaBH4 reduction, Williamson ether synthesis and LiAlH4 reduction led to the methyl and benzyl ethers 12 and 13. High sigma1 affinity is attained when one large substituent is introduced either at N-8 or O-2. The most potent sigma1 ligand in this series of compounds is the methyl ether 12b with the N-butyl substituent (K(i)=13.2 nM, selectivity sigma2:sigma1 = 16). Moreover, the N-methyl derivatives 13a (sigma2: K(i)=30.4 nM) and 12a (sigma2 preference) represent promising starting points for the development of potent and selective sigma2 ligands.

Synthesis of novel σ-receptor ligands from methyl α-d-mannopyranoside

For the first time a monosaccharide (methyl alpha-D-mannopyranoside) has been used as starting material for the synthesis of novel sigma-receptor ligands. The hept-3-ulopyranoside dimethyl ketals 14 and 15 were obtained from the nitrile 7 via two synthetic routes. After selective hydrolysis of the ketone dimethyl acetal, various amino substituents were introduced into position 3. High sigma(1)-receptor affinity and selectivity was attained with equatorially arranged amino substituents in position 3 and a dichlorophenylacetamide moiety in position 7. The anomeric mixture of dimethylamines 26alpha/beta displayed the highest sigma(1)-receptor affinity (K(i)=21nM) within this small series of test compounds.

Chiral, nonracemic (piperazin-2-yl)methanol derivatives with sigma-receptor affinity

Starting with the proteinogenic amino acid (S)-serine a series of chiral nonracemic (piperazin-2-yl)methanols 3 with various N-4 substituents is described. The key step in the synthesis of 3 is the reaction of the chloroacetamide 5 with various primary amines to yield the diastereomeric bicyclic piperazinediones cis-6 and trans-6. The scope and limitation of this transformation is thoroughly investigated. The alpha1- and sigma2-receptor affinities of the piperazines 3 are determined in receptor binding studies with guinea pig brain and rat liver membrane preparations using [3H]-labeled (+)-pentazocine and ditolylguanidine, respectively. It was found, that an additional phenyl residue in the N-4 substituent is favorable to high sigma1-receptor affinity. In this series the p-methoxybenzyl substituted piperazine 3d reveals the highest sigma1-receptor affinity (Ki=12.4 nM) with selectivity toward sigma2-, NMDA-, kappa-opioid, and mu-opioid receptors.

Receptor Imaging in Oncology by Means of Nuclear Medicine: Current Status

To date, our understanding of the role of receptors and their cognate ligands in cancer is being successfully translated into the design and development of an arsenal of new, less toxic, and more specific anticancer drugs. Because most of these novel drugs are cytostatic, objective response as measured by morphologic imaging modalities (eg, computed tomography or magnetic resonance imaging) cannot be used as a surrogate marker for drug development or for clinical decision making. Positron emission tomography (PET) can be used to image and quantify the in vivo distribution of positron-emitting radioisotopes such as oxygen-15, carbon-11, and fluorine-18 that can be substituted or added into biologically relevant and specific receptor radioligands. Similarly, single-photon emission computed tomography (SPECT) can be used to image and quantify the in vivo distribution of receptor targeting compounds labeled with indium-111, technetium-99m, and iodine-123. By virtue of their whole-body imaging capacity and the absence of errors of sampling and tissue manipulation as well as preparation, both techniques have the potential to address locoregional receptor status noninvasively and repetitively. This article reviews available data on the in vivo evaluation of receptor systems by means of PET or SPECT for identifying and monitoring patients with sufficient receptor overexpression for tailored therapeutic interventions, and also for depicting tumor tissue and determining the currently largely unknown heterogeneity in receptor expression among different tumor lesions within and between patients.

Synthesis, structural characterization and in vitro antitumor activity of novel 6-chloro-1,1-dioxo-1,4,2-benzodithiazie derivatives

A series of nonconventional aminium N-(6-chloro-7-R-1,1-dioxo-1,4,2-benzodithiazin-3-yl)arylsulfonamidates 7-15 have been synthesized by the reactions of 6-chloro-7-R-3-methylthio-1,4,2-benzodithiazine 1,1-dioxides with 4-dimethylaminopyridine or Et(3)N and some arylsulfonamides. The free N-(6-chloro-7-methyl-1,1-dioxo-1,4,2-benzodithiazin-3-yl)benzenesulfonamides 16-18 were obtained by treatment of their aminium salts with H(2)SO(4) in boiling acetic acid. The in vitro antitumor activity of the compounds 9, 11-14 and 16-18 has been tested in the antitumor screening of the National Cancer Institute (NCI), and relationships between structure and antitumor activity are discussed. 4-Dimethylaminopyridinium 4-chloro-N-(6-chloro-7-methyl-1,1-dioxo-1,4,2-benzodithiazin-3-yl)benzenesulfonamidate 9 is the prominent of the compounds due to its remarkable activity (log GI(50)<-8.00, log TGI=-5.50) and selectivity for the leukemia SR cell line. For that reason experimental and theoretical analysis of the geometric and electronic properties of 9 was carried out.

Synthesis of photoactivable inhibitors of osteoclast vacuolar ATPase

Amides of (2Z,4E)-5-[(5,6-dichloroindol-2-yl)]-2-methoxy-N-[3-[4-[3-(carboxymethoxy)phenyl)] piperazin-1-yl]propyl]-2,4-pentadienamide (1) and of 5-(5,6-dichloro-2-indolyl)-2-methoxy-2,4-pentadienoic acid (2) are strong inhibitors of the vacuolar ATPase located on the plasma membrane of osteoclasts. In order to understand which V-ATPase subunit is involved in the interaction with these novel inhibitors, analogues containing a photoactivable group and an iodine atom were designed. A series of alcohols or amines containing the photoactivable trifluoroaziridinophenyl or benzophenone moiety and an iodine atom were linked to the above acids via an ester or amide group. These compounds could be thereafter used as a radioactive photoprobe to label the protein. Whereas the compounds containing the photoactivable groups maintained good inhibitory activity, the introduction of the bulky iodine atom was generally detrimental, decreasing potency significantly. Better results were obtained by linking 3-(4-aminopiperidinomethyl)-3'-iodobenzophenone to 3-ethoxy-4-(2-(5,6-dichlorobenzimidazolyl))benzoic acid to give the corresponding amide 27, that inhibited vacuolar ATP-ase with a IC(50)=140 nM. The feasibility of introducing a radioactive 125I atom was ascertained by exchanging the iodine with a tributylstannyl group, that was again substituted by iodine.

Cytotoxicity of conventional and atypical antipsychotic drugs in relation to glucose metabolism

The goal of these studies was to analyze the cytotoxicity of both the conventional and atypical antipsychotic drugs in relation to their effects on glucose metabolism. The drugs were evaluated for their effects on the viability of PC12 cells, which are an established model of neuronal cells in culture. In general, the conventional drugs, such as chlorpromazine, fluphenazine and pimozide, were more toxic than the atypical drugs, including clozapine, quetiapine and risperidone. Olanzapine was unique in that it stimulated cell proliferation in this system. There was a good correlation between the cytotoxicity of a drug and its ability to block glucose transport, although there were some exceptions to this trend. Conventional antipsychotics also affected the expression of glucose transporter proteins in whole cell extracts and at the cell surface. Overall, the data support the notion that many of the antipsychotic drugs associated with the development of movement disorders in patients are cytotoxic for cultured cells.

Spiro[1,2,4-benzotriazine-3(4H),4'-(1'-substituted)piperidines] and related compounds as ligands for sigma receptors

As analogues of some conformationally restricted spiropiperidine derivatives which are endowed with high affinity for sigma1 receptor, a set of 16 spiro[1,2,4-benzotriazine-3(4H),4'-(1'-substituted)piperidines] and congeneric compounds was prepared and tested for affinity to sigma1 receptor subtype. All N-arylalkyl substituted derivatives exhibited high affinity for the relevant receptor, with Ki in the low nanomolar range. Affinity for sigma2 subtype (assayed only for a few representative compounds) was from one to three order of magnitude lower. Spiro[1,2,4-benzotriazine-3(4H),4'-(1'-benzyl)piperidine] (2), with a ratio Ki sigma2/Ki sigma1 = 7000 should represent the most selective sigma1 ligand so far described.

Conformationally constrained ethylenediamines: synthesis and receptor binding of 6,8-diazabicyclo[3.2.2]nonanes

The synthesis and receptor affinity of 6,8-diazabicyclo[3.2.2]nonanes representing conformationally constrained ethylenediamines are described. The Dieckmann analogous cyclization of the (piperazin-2-yl)propionate 9 provided the bicyclononane 10 only, when the first cyclization product was trapped with chlorotrimethylsilane. 10 was stereoselectively transformed into the bicyclic amines 19a,b and amides 22a,b, which were investigated in competition experiments with radioligands for their sigma(1)-, sigma(2)-, kappa-, and mu-receptor affinities. The (2R)-configured dimethylamine 19a showed promising sigma(1)-receptor affinity (K(i)=23.8 nM) and selectivity, whereas the (2S)-configured (dichlorophenyl)acetamide 22b displayed a sigma-receptor binding profile (sigma(1): K(i)=184 nM; sigma(2): K(i)=263 nM) very similar to the binding profile of the atypical antipsychotic BMY-14802 (26).

Is a nitrogen atom an important pharmacophoric element in sigma ligand binding?

A lingering question in sigma receptor ligand development is whether a nitrogen atom serves as an important pharmacophoric element in binding affinity. To address this question, we have synthesized several phenylalkylpiperidines and phenylalkylpiperazines and demonstrated that removal of the N atom from a typical phenylalkylpiperidine led to little or no binding to sigma receptors. In addition, where two N atoms occur in a compound, such as with phenylalkylpiperazines, the N atom on the longer alkyl chain appears to be more important. Thus, based on this study, the N atom is an important pharmacophoric element in the binding of phenylalkylpiperidines and phenylalkylpiperazines to sigma receptors.