Characterization and evaluation of two novel fluorescent sigma-2 receptor ligands as proliferation probes (original) (raw)
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Development of molecular probes for imaging sigma-2 receptors in vitro and in vivo
Central nervous system agents in medicinal chemistry, 2009
The sigma-2 (sigma(2)) receptor is proving to be an important protein in the field of cancer biology. The observations that sigma(2) receptors have a 10-fold higher density in proliferating tumor cells than in quiescent tumor cells, and that sigma(2) receptor agonists are capable of killing tumor cells via apoptotic and non-apoptotic mechanisms, indicate that this receptor is an important molecular target for the development of radiotracers for imaging tumors using techniques such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) and for the development of cancer chemotherapeutic agents. In spite of recent promising results towards achieving these goals, research in this field has been hampered by the fact that the molecular identity of the protein sequence of the sigma(2) receptor is currently not known. Consequently, most of what is known about this protein has been obtained using either radiolabeled or fluorescent probes for this recepto...
Cancer Research, 2007
Sigma-2 receptor agonists have been shown to induce cell death via caspase-dependent and caspase-independent pathways. Unfortunately, there is little information regarding the molecular function of sigma-2 receptors that can explain these results. In this study, two fluorescent probes, SW107 and K05-138, were used to study the subcellular localization of sigma-2 receptors by two-photon and confocal microscopy. The results indicate that sigma-2 receptors colocalize with fluorescent markers of mitochondria, lysosomes, endoplasmic reticulum, and the plasma membrane in both EMT-6 mouse and MDA-MB-435 human breast cancer cells. The fluorescent probe, K05-138, was internalized rapidly, reaching a plateau of fluorescent intensity at 5 min. The internalization of K05-138 was reduced f40% by phenylarsine oxide, an inhibitor of endocytosis. These data suggest that sigma-2 ligands are internalized, in part, by an endocytotic pathway. The localization of sigma-2 receptors in several organelles known to have a role in both caspase-dependent and caspaseindependent pathways of cell death supports the conclusions of previous studies suggesting that sigma-2 receptor ligands should be evaluated as potential cancer chemotherapeutic agents.
Development of sigma-1 (σ 1 ) receptor fluorescent ligands as versatile tools to study σ 1 receptors
European Journal of Medicinal Chemistry, 2016
Despite their controversial physiology, sigma-1 (1) receptors are intriguing targets for the development of therapeutic agents for central nervous system diseases. With the aim of providing versatile pharmacological tools to study 1 receptors, we developed three 1 fluorescent tracers by functionalizing three well characterized 1 ligands with a fluorescent tag. A good compromise between 1 binding affinity and fluorescent properties was reached, and the 1 specific targeting of the novel tracers was demonstrated by different techniques: photolabeling, confocal microscopy and flow cytometry. These novel ligands were also successfully used in competition binding studies by flow cytometry, showing their utility in nonradioactive binding assays as an alternative strategy to the more classical radioligand binding assays. To the best of our knowledge these novel tracers are the first 1 fluorescent ligands to be developed, and represent promising tools to strengthen 1 receptors related studies.
Sigma-2 Receptor as Potential Indicator of Stem Cell Differentiation
Molecular Imaging and Biology, 2012
Purpose-The sigma-2 (σ 2 ) receptor is a potential biomarker of proliferative status of solid tumors. Specific synthetic probes using N-substituted-9-azabicyclo[3.3.1]nonan-3α-yl carbamate analogs have been designed and implemented for experimental cancer diagnosis and therapy.
Journal of Medicinal Chemistry, 2011
Fluorescent derivatives of σ 2 high affinity ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1yl)propyl]piperazine 1 (PB28) were synthesized. NBD or dansyl fluorescent tags were connected through a 5-or 6-atom linker in two diverse positions of 1 structure. Good σ 2 affinities were obtained when the fluorescent tag was linked to 5-methoxytetralin nucleus replacing the methyl function. NBD-bearing compound 16 displayed high σ 2 affinity (K i = 10.8 nM) and optimal fluorescent properties. Its uptake in pancreatic tumor cells was evaluated by flow cytometry, showing that it partially occurs through endocytosis. In proliferating cells, the uptake was higher supporting that σ 2 receptors are markers of cell proliferation and that the higher the proliferation is, the stronger the antiproliferative effect of σ 2 agonists is. Colocalization of 16 with subcellular organelles was studied by confocal microscopy: the greatest was in endoplasmic reticulum and lysosomes. Fluorescent σ 2 ligands show their potential in clarifying the mechanisms of action of σ 2 receptors.
Identification of the PGRMC1 protein complex as the putative sigma-2 receptor binding site
Nature Communications, 2011
The sigma-2 receptor, whose gene remains to be cloned, has been validated as a biomarker for tumour cell proliferation. Here we report the use of a novel photoaffinity probe, WC-21, to identify the sigma-2 receptor-binding site. WC-21, a sigma-2 ligand containing both a photoactive azide moiety and a fluorescein isothiocyanate group, irreversibly labels sigma-2 receptors in rat liver; the membrane-bound protein was identified as PGRMC1 (progesterone receptor membrane component 1). Immunocytochemistry reveals that both PGRMC1 and SW120, a fluorescent sigma-2 receptor ligand, colocalize with molecular markers of the endoplasmic reticulum and mitochondria in HeLa cells. Overexpression and knockdown of the PGRMC1 protein results in an increase and a decrease in binding of a sigma-2 selective radioligand, respectively. The identification of the putative sigma-2 receptor-binding site as PGRMC1 should stimulate the development of unique imaging agents and cancer therapeutics that target the sigma-2 receptor/PGRMC1 complex.
Sigma 2 receptors as potential biomarkers of proliferation in breast cancer
Cancer research, 1997
sigma 1 and sigma 2 receptors have been shown to exist in a number of rodent and human tumor cell lines. Although their expression is heterogeneous and their function is unknown, sigma receptors have been proposed as potential targets for diagnostic tumor-imaging agents. In this study, the density of sigma 2 receptors in proliferative (P) and quiescent (Q) cells of the mouse mammary adenocarcinoma, line 66, was examined. Scatchard analyses of sigma 2 receptors were performed on membrane preparations of 66 P cells from 3-day cultures and 66 Q cells from 7-, 10-, and 12-day cultures. The Scatchard studies revealed that 66 P cells had approximately 10 times more sigma 2 receptors/cell than the 66 Q cells from 10-day cultures. Although > 97% of the cells were quiescent after 7 days in culture, the maximum differential in the sigma 2 expression between 66 P and 66 Q cells was not attained until these cells had been in culture for 10 days. These data suggest that ligands labeled with p...
Sigma Receptor (σR) Ligands with Antiproliferative and Anticancer Activity
Sigma receptor (σR) ligands have proven to be useful as cancer diagnostics and anticancer therapeutics and their ligands have been developed as molecular probes in oncology. Moreover, various σR ligands generate cancer cell death in vitro and in vivo. These σR ligands have exhibited promising results against numerous human and rodent cancers and are investigated under preclinical and clinical study trials, indicating a new category of drugs in cancer therapy.
Imaging Sigma Receptors: Applications in Drug Development
Current Pharmaceutical Design, 2007
Sigma receptors have been implicated in a myriad of cellular functions, biological processes and diseases. While the precise biological functions of sigma receptors have not been elucidated, recent work has shed some light on to these enigmatic systems. Sigma receptors have recently been a target of drug development related to psychiatric and neurological disorders. Sigma ligands have also been shown to modulate endothelial cell proliferation and can control angiogenesis which makes them a promising target for oncology applications. Other areas currently being investigated include treatment of gastrointestinal, cardiovascular, endocrine and immune system disorders. Of interest is that the human sigma-1 receptor gene contains a steroid binding component, and several gonadal steroids, including progesterone, testosterone and dehydroepiandrosterone (DHEA), interact with sigma-1 receptors. Of the steroids examined thus far, progesterone binds with the highest affinity to human sigma-1 receptors, with a reported affinity (Ki) as high as 30 nM while the other steroids exhibit lower affinity. For this and other reasons, sigma-1 receptors have been proposed as a link between the central nervous system and the endocrine and reproductive systems. Taken together, the above information highlights an important yet largely unexplored but promising area of research to examine the biological function and therapeutic potential of sigma receptors. This review provides an overview of the current knowledge of these sites with a focus on specific areas where in vivo sigma receptor imaging is currently being investigated.