SR31747A is a sigma receptor ligand exhibiting antitumoural activity both in vitro and in vivo

Recent Advances in the Development of Sigma Receptor Ligands as Cytotoxic Agents: A Medicinal Chemistry Perspective

Since their discovery as distinct receptor proteins, the specific physiopathological role of sigma receptors (σRs) has been deeply investigated. It has been reported that these proteins, classified into two subtypes indicated as σ₁ and σ₂, might play a pivotal role in cancer growth, cell proliferation, and tumor aggressiveness. As a result, the development of selective σR ligands with potential antitumor properties attracted significant attention as an emerging theme in cancer research. This perspective deals with the recent advances of σR ligands as novel cytotoxic agents, covering articles published between 2010 and 2020. An up-to-date description of the medicinal chemistry of selective σ₁R and σ₂R ligands with antiproliferative and cytotoxic activities has been provided, including major pharmacophore models and comprehensive structure–activity relationships for each main class of σR ligands.

Genetic co-expression networks contribute to creating predictive model and exploring novel biomarkers for the prognosis of breast cancer

Genetic co-expression network (GCN) analysis augments the understanding of breast cancer (BC). We aimed to propose GCN-based modeling for BC relapse-free survival (RFS) prediction and to discover novel biomarkers. We used GCN and Cox proportional hazard regression to create various prediction models using mRNA microarray of 920 tumors and conduct external validation using independent data of 1056 tumors. GCNs of 34 identified candidate genes were plotted in various sizes. Compared to the reference model, the genetic predictors selected from bigger GCNs composed better prediction models. The prediction accuracy and AUC of 3 ~ 15-year RFS are 71.0-81.4% and 74.6-78% respectively (rfm, ACC 63.2-65.5%, AUC 61.9-74.9%). The hazard ratios of risk scores of developing relapse ranged from 1.89 ~ 3.32 (p < 10^-8) over all models under the control of the node status. External validation showed the consistent finding. We found top 12 co-expressed genes are relative new or novel biomarkers that have not been explored in BC prognosis or other cancers until this decade. GCN-based modeling creates better prediction models and facilitates novel genes exploration on BC prognosis.

Role of Sigma-1 Receptor in Calcium Modulation: Possible Involvement in Cancer

Ca2+ signaling plays a pivotal role in the control of cellular homeostasis and aberrant regulation of Ca2+ fluxes have a strong impact on cellular functioning. As a consequence of this ubiquitous role, Ca2+ signaling dysregulation is involved in the pathophysiology of multiple diseases including cancer. Indeed, multiple studies have highlighted the role of Ca2+ fluxes in all the steps of cancer progression. In particular, the transfer of Ca2+ at the ER-mitochondrial contact sites, also known as mitochondrial associated membranes (MAMs), has been shown to be crucial for cancer cell survival. One of the proteins enriched at this site is the sigma-1 receptor (S1R), a protein that has been described as a Ca2+-sensitive chaperone that exerts a protective function in cells in various ways, including the modulation of Ca2+ signaling. Interestingly, S1R is overexpressed in many types of cancer even though the exact mechanisms by which it promotes cell survival are not fully elucidated. This review summarizes the findings describing the roles of S1R in the control of Ca2+ signaling and its involvement in cancer progression.

Similarities between the Yin/Yang Doctrine and Hormesis in Toxicology and Pharmacology

Hormesis is a generalizable dose-response relationship characterized by low-dose stimulation and high-dose inhibition. Despite debate over this biphasic dose-response curve, hormesis is challenging central beliefs in the evaluation of chemicals or drugs and has influenced biological model selection, concentration range, study design, and hypothesis testing. We integrate the traditional Chinese philosophy - Yin/Yang doctrine - into the representation of the Western hormetic dose-response relationship and review the Yin/Yang historical philosophy contained in the hormesis concept, aiming to promote general acceptance and wider applications of hormesis. We suggest that the Yin/Yang doctrine embodies the hormetic dose-response, including the relationship between the opposing components, curve shape, and time-dependence, and may afford insights that clarify the hormetic dose-response relationship in toxicology and pharmacology.

Small-Molecule Modulators of Sigma1 and Sigma2/TMEM97 in the Context of Cancer: Foundational Concepts and Emerging Themes

There are two known subtypes of the so-called sigma receptors, Sigma1 and Sigma2. Sigma1 (encoded by the SIGMAR1 gene and also known as Sigma-1 receptor, S1R) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein that allosterically modulates the activity of its associated proteins. Sigma2, recently identified as transmembrane protein 97 (TMEM97), is an integral membrane protein implicated in cellular cholesterol homeostasis. A number of publications over the past two decades have suggested a role for both sigma proteins in tumor biology. Although there is currently no clinically used anti-cancer drug that targets Sigma1 or Sigma2/TMEM97, a growing body of evidence supports the potential of small-molecule compounds with affinity for these proteins, putative sigma ligands, as therapeutic agents to treat cancer. In preclinical models, these compounds have been reported to inhibit cancer cell proliferation, survival, adhesion, and migration; furthermore, they have been demonstrated to suppress tumor growth, to alleviate cancer-associated pain, and to exert immunomodulatory properties. Here, we will address the known knowns and the known unknowns of Sigma1 and Sigma2/TMEM97 ligand actions in the context of cancer. This review will highlight key discoveries and published evidence in support of a role for sigma proteins in cancer and will discuss several fundamental questions regarding the physiological roles of sigma proteins in cancer and sigma ligand mechanism of action.

Sigma1 Pharmacology in the Context of Cancer

Sigma1 (also known as sigma-1 receptor, Sig1R, σ1 receptor) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein. The majority of publications on the subject have focused on the neuropharmacology of Sigma1. However, a number of publications have also suggested a role for Sigma1 in cancer. Although there is currently no clinically used anti-cancer drug that targets Sigma1, a growing body of evidence supports the potential of Sigma1 ligands as therapeutic agents to treat cancer. In preclinical models, compounds with affinity for Sigma1 have been reported to inhibit cancer cell proliferation and survival, cell adhesion and migration, tumor growth, to alleviate cancer-associated pain, and to have immunomodulatory properties. This review will highlight that although the literature supports a role for Sigma1 in cancer, several fundamental questions regarding drug mechanism of action and the physiological relevance of aberrant SIGMAR1 transcript and Sigma1 protein expression in certain cancers remain unanswered or only partially answered. However, emerging lines of evidence suggest that Sigma1 is a component of the cancer cell support machinery, that it facilitates protein interaction networks, that it allosterically modulates the activity of its associated proteins, and that Sigma1 is a selectively multifunctional drug target.

Preparation and evaluation of an astatine-211-labeled sigma receptor ligand for alpha radionuclide therapy

INTRODUCTION

Sigma receptors are overexpressed in a variety of human tumors, making them potential targets for radionuclide receptor therapy. We have previously synthesized and evaluated (131)I-labeled (+)-2-[4-(4-iodophenyl)piperidino]cyclohexanol [(+)-[(131)I]pIV], which has a high affinity for sigma receptors. Therefore, (+)-[(131)I]pIV significantly inhibited tumor cell proliferation in tumor-bearing mice. In the present study, we report the synthesis and the in vitro and in vivo characterization of (+)-[(211)At]pAtV, an (211)At-labeled sigma receptor ligand, that has potential use in alpha-radionuclide receptor therapy.

METHODS

The radiolabeled sigma receptor ligand (+)-[(211)At]pAtV was prepared using a standard halogenation reaction generating a 91% radiochemical yield with 98% purity after HPLC purification. The partition coefficient of (+)-[(211)At]pAtV was measured. Cellular uptake experiments and in vivo biodistribution experiments were performed using a mixed solution of (+)-[(211)At]pAtV and (+)-[(125)I]pIV; the human prostate cancer cell line DU-145, which expresses high levels of the sigma receptors, and DU-145 tumor-bearing mice.

RESULTS

The lipophilicity of (+)-[(211)At]pAtV was similar to that of (+)-[(125)I]pIV. DU-145 cellular uptake and the biodistribution patterns in DU-145 tumor-bearing mice at 1h post-injection were also similar between (+)-[(211)At]pAtV and (+)-[(125)I]pIV. Namely, (+)-[(211)At]pAtV demonstrated high uptake and retention in tumor via binding to sigma receptors.

CONCLUSION

These results indicate that (+)-[(211)At]pAtV could function as an new agent for alpha-radionuclide receptor therapy.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

Sequential cytoprotective responses to Sigma1 ligand-induced endoplasmic reticulum stress

The Sigma1 receptor (Sigma1) is an endoplasmic reticulum (ER) integral membrane protein that is highly expressed in a number of cancer cell lines. Small molecule compounds targeting Sigma1 (Sigma1 ligands) inhibit cancer cell proliferation and induce apoptotic cell death in vitro and inhibit tumor growth in xenograft experiments. However, the cellular pathways activated by Sigma1 protein-ligand interaction are not well defined. Here, we find that treatment with some Sigma1 ligands induces ER stress and activates the unfolded protein response (UPR) in a dose- and time-responsive manner in a range of adenocarcinoma cell lines. Autophagy is engaged after extended treatment with Sigma1 ligands, which suggests that protracted UPR results in autophagy as a secondary response. Inhibition of UPR by RNAi-mediated knockdown of inositol-requiring enzyme 1α and activating transcription factor 4 abrogates autophagosome formation, as does knockdown of essential autophagy gene products Beclin1 and autophagy protein 5. Knockdown of Sigma1 also suppresses IPAG [1-(4-iodophenyl)-3-(2-adamantyl) guanidine] induced UPR marker and autophagosome levels, indicating that this response is indeed Sigma1-mediated. We find that UPR activation precedes autophagosome formation and autophagy precedes apoptosis in Sigma1 ligand-treated cells. These processes are reversible, and washout of IPAG before cell death results in a return of autophagosomes and UPR markers toward basal levels. However, inhibition of Sigma1 ligand-induced UPR or autophagy accelerates apoptotic cell death. Together, these data suggest that UPR and autophagy are engaged as primary and secondary cytoprotective responses, respectively, to Sigma1 ligand-induced disruption of cancer cell protein homeostasis.

1-Cyclohexyl-4-(4-arylcyclohexyl)piperazines: Mixed σ and human Δ(8)-Δ(7) sterol isomerase ligands with antiproliferative and P-glycoprotein inhibitory activity

Many new chemotherapeutic agents are under preclinical investigation and, despite efforts to more selectively target cancer cells, limitations such as toxicity and inherent resistance are often encountered. Therefore, alternative strategies are needed to treat cancer and overcome such limitations. We describe novel cyclohexylpiperazine derivatives, designed as mixed affinity ligands for sigma (σ) receptors and human Δ₈-Δ₇ sterol isomerase (HSI) ligands, which also exhibit P-glycoprotein (P-gp) inhibitory activity, with the aim of exploiting the antiproliferative effects mediated by σ and HSI sites while overcoming P-gp-mediated resistance. All of the compounds displayed high affinities for σ receptors and HSI sites, P-gp inhibitory activity, and σ₂ receptor agonist antiproliferative activity. Antiproliferative activity was also tested in PC-3 cells to establish σ₁ and HSI contribution. Compound cis-11, which displayed the best antiproliferative and P-gp inhibitory activities, was co-administered with 0.1 μM doxorubicin in MDCK-MDR1 cells. Compound cis-11 caused 70 % and 90 % cell death when co-administered at 30 μM and 50 μm, respectively. When administered alone, cis-11 resulted in 50 % cell death, demonstrating its single agent antitumor properties in a tumor cell line overexpressing P-gp.

The sigma-1 receptor chaperone as an inter-organelle signaling modulator

Inter-organelle signaling plays important roles in many physiological functions. Endoplasmic reticulum (ER)-mitochondrion signaling affects intramitochondrial calcium (Ca(2+)) homeostasis and cellular bioenergetics. ER-nucleus signaling attenuates ER stress. ER-plasma membrane signaling regulates cytosolic Ca(2+) homeostasis and ER-mitochondrion-plasma membrane signaling regulates hippocampal dendritic spine formation. Here, we propose that the sigma-1 receptor (Sig-1R), an ER chaperone protein, acts as an inter-organelle signaling modulator. Sig-1Rs normally reside at the ER-mitochondrion contact called the MAM (mitochondrion-associated ER membrane), where Sig-1Rs regulate ER-mitochondrion signaling and ER-nucleus crosstalk. When cells are stimulated by ligands or undergo prolonged stress, Sig-1Rs translocate from the MAM to the ER reticular network and plasmalemma/plasma membrane to regulate a variety of functional proteins, including ion channels, receptors and kinases. Thus, the Sig-1R serves as an inter-organelle signaling modulator locally at the MAM and remotely at the plasmalemma/plasma membrane. Many pharmacological/physiological effects of Sig-1Rs might relate to this unique action of Sig-1Rs.

Identification of candidate epigenetic biomarkers for ovarian cancer detection

Ovarian cancer ranks the most lethal among gynecologic neoplasms in women. To develop potential biomarkers for diagnosis, we have identified five novel genes (CYP39A1, GTF2A1, FOXD4L4, EBP, and HAAO) that are hypermethylated in ovarian tumors, compared with the non-malignant normal ovarian surface epithelia, using the quantitative methylation-specific polymerase chain reactions. Interestingly enough, multivariate Cox regression analysis has identified hypermethylation of CYP39A1 correlated with an increase rate of relapsing (P=0.032, hazard ratio >1). Concordant hypermethylation in at least three loci was observed in 50 out of 55 (91%) of ovarian tumors examined. The test sensitivity and specificity were assessed to be 96 and 67% for CYP39A1; 95 and 88% for GTF2A1; 93 and 67% for FOXD4L4; 81 and 67% for EBP; 89 and 82% for HAAO, respectively. Our data have identified, for the first time, GTF2A1 alone, or GTF2A1 plus HAAO are excellent candidate biomarkers for detecting this disease. Moreover, the known functions of these gene products further implicate dysregulated transcriptional control, cholesterol metabolism, or synthesis of quinolinic acids, may play important roles in attributing to ovarian neoplasm. Molecular therapies, by reversing the aberrant epigenomes using inhibitory agents or by abrogating the upstream signaling pathways that convey the epigenomic perturbations, may be developed into promising treatment regimens.

Novel 4-(4-aryl)cyclohexyl-1-(2-pyridyl)piperazines as Delta(8)-Delta(7) sterol isomerase (emopamil binding protein) selective ligands with antiproliferative activity

To find Delta(8)-Delta(7) sterol isomerase (EBP) selective ligands, various arylpiperazines previously studied and structurally related to some sigma receptors ligands were preliminarily screened. Consequently, a novel series of 2- or 2,6-disubstituted (CH(3), CH(3)O, Cl, F) cis- and trans-4-(4-aryl)cyclohexyl-1-(2-pyridyl)piperazines was developed. Radioreceptor binding assays evidenced cis-19, cis-30 and cis-33 as new ligands with nanomolar affinity toward EBP site and a good selectivity relative to EBP-related sigma receptors. The most selective 2,6-dimethoxy derivative (cis-33) demonstrated the highest potency (EC(50) = 12.9 microM) and efficacy (70%) in inhibiting proliferation of human prostate cancer PC-3 cell line. Among the reference compounds, sigma(2) agonist 36 (PB28) reached the maximum efficacy (100%), suggesting the contribution of the sigma(2) receptor to the antiproliferative activity. This novel class of EBP inhibitors represents a valuable tool for investigating the last steps of cholesterol biosynthesis and related pathologies, as well as a starting point for developing new anticancer drugs.

Cancer biology and hormesis: comments on Calabrese (2005)

Large numbers of chemicals of a variety of types exhibit apparent hormetic effects on cultured human cancer cells, causing stimulation of cell growth or related changes at low doses, followed by inhibition at higher doses. Many of the studies listed are not fully convincing, due to lack of appropriate controls or sufficient number of doses. However, the proposed hormetic response seems firmly established in a subset of these experiments. Significance with regard to in vivo cancer growth has not been pursued and must be a priority for the future. For several examples where in vivo titers are known, such as, resveratrol, suramin, and tamoxifen, comparison of the dose and concentration ranges confirms that hormesis could be an issue in vivo. Further investigations are warranted, especially for therapeutic drugs, phytochemicals, and environmental toxicants.

Cancer biology and hormesis: human tumor cell lines commonly display hormetic (biphasic) dose responses

This article assesses the nature of the dose-response relationship of human tumor cell lines with a wide range of agents including antineoplastics, toxic substances (i.e., environmental pollutants), nonneoplastic drugs, endogenous agonists, and phyto-compounds. Hormetic-like biphasic dose responses were commonly reported and demonstrated in 136 tumor cell lines from over 30 tissue types for over 120 different agents. Quantitative features of these hormetic dose responses were similar, regardless of tumor cell line or agent tested. That is, the magnitude of the responses was generally modest, with maximum stimulatory responses typically not greater than twice the control, while the width of the stimulatory concentration range was usually less than 100-fold. Particular attention was directed to possible molecular mechanisms of the biphasic nature of the dose response, as well as clinical implications in which a low concentration of chemotherapeutic agent may stimulate tumor cell proliferation. Finally, these findings further support the conclusion that hormetic dose responses are broadly generalizable, being independent of biological model, endpoint measured, and stressor agent, and represent a basic feature of biological responsiveness to chemical and physical stressors.

Expression of sigma 1 receptor in human breast cancer

The sigma 1 receptor (S1R) represents a unique drug-binding site that is distinct from any other receptors. We examined S1R expression in human breast cancer and assessed the activity of S1R ligands in breast cancer cell lines. One-hundred nine breast specimens from normal breast, benign breast disease and cancer were examined with immunohistochemistry or RT-PCR and six different cell lines were also evaluated. S1R mRNA overexpression was detected in 64% of breast cancers compared to normal breast tissue. Immunohistochemistry showed positive epithelial cell staining in 60% of invasive and 41% of in situ cancers, 75% of ductal hyperplasia and in 33% of normal breast. The pattern of expression was more diffuse in invasive breast carcinoma compared to other conditions (p = 0.02). S1R expression was neither a prognostic nor a predictive factor for efficacy of adjuvant chemotherapy but the study only included 58 cancer patients and therefore the statistical power is limited. MDA-MB-361, MDA-MB-435, BT20 and MCF7 cells all expressed S1R protein by Western blot. The non-specific S1R ligands haloperidol, reduced haloperidol and progesterone produced a dose-dependent inhibition of the growth at high (>10 microM) concentrations. Reduced haloperidol also showed additive cytotoxic effects when combined with doxorubicin, vinorelbine , paclitaxel and docetaxel in vitro. The S1R-specific ligand, SKF 10047 demonstrated the least growth inhibitory activity and showed no interaction with chemotherapy. These results demonstrate that some normal and most neoplastic breast epithelial cells and cell lines commonly express S1R. High concentrations of haloperidol inhibit the growth of these cells and potentiate the effect of chemotherapy in vitro.

Inhibition of tumor cell proliferation by sigma ligands is associated with K+ Channel inhibition and p27kip1 accumulation

Previous studies have shown that sigma receptors are overexpressed in tumor cells. However, the role of sigma receptors remains enigmatic. Recently, we and others have demonstrated that sigma-1 receptor modulates K+ channels in pituitary. In the present report, patch-clamp and Western blot assays were used in small cell lung cancer (SCLC, NCI-H209, and NCI-H146) and leukemic (Jurkat) cell lines to investigate the effects of sigma ligands on voltage-gated K+ channels and cell proliferation. The sigma ligands (+)-pentazocine, igmesine, and 1,3-di(2-tolyl)guanidine (DTG) all reversibly inhibited voltage-activated K+ currents in both cell lines. The potency of sigma ligand-induced inhibition (10 microM) was igmesine = (+)-pentazocine > DTG, pointing to the involvement of sigma-1 receptors. Addition of the K+ channel blockers tetraethylammonium (TEA) and 4-aminopyridin or one of cited sigma ligands in the culture media reversibly inhibited Jurkat cell growth. Interestingly, K+ channel blockers and sigma ligands caused an accumulation of the cyclin-dependent kinase inhibitor p27kip1 and a decrease in cyclin A expression in Jurkat and SCLC cells, whereas no effect could be detected on p21cip1. Moreover, sigma ligands and TEA had no effect on caspase 3 activity. Accordingly, incubation of cells with sigma ligands did not provoke DNA laddering. These data demonstrate that sigma ligands and voltage-dependent channel blockers inhibit cell growth through a cell cycle arrest in the G1 phase but not via an apoptotic mechanism. Altogether, these results indicate that the sigma-1 receptor-induced inhibition of the cell cycle is, at least in part, the consequence of the inhibition of K+ channels.

Small molecule antagonists of the sigma-1 receptor cause selective release of the death program in tumor and self-reliant cells and inhibit tumor growth in vitro and in vivo

The acquisition of resistance to apoptosis, the cell's intrinsic suicide program, is essential for cancers to arise and progress and is a major reason behind treatment failures. We show in this article that small molecule antagonists of the sigma-1 receptor inhibit tumor cell survival to reveal caspase-dependent apoptosis. sigma antagonist-mediated caspase activation and cell death are substantially attenuated by the prototypic sigma-1 agonists (+)-SKF10,047 and (+)-pentazocine. Although several normal cell types such as fibroblasts, epithelial cells, and even sigma receptor-rich neurons are resistant to the apoptotic effects of sigma antagonists, cells that can promote autocrine survival such as lens epithelial and microvascular endothelial cells are as susceptible as tumor cells. Cellular susceptibility appears to correlate with differences in sigma receptor coupling rather than levels of expression. In susceptible cells only, sigma antagonists evoke a rapid rise in cytosolic calcium that is inhibited by sigma-1 agonists. In at least some tumor cells, sigma antagonists cause calcium-dependent activation of phospholipase C and concomitant calcium-independent inhibition of phosphatidylinositol 3'-kinase pathway signaling. Systemic administration of sigma antagonists significantly inhibits the growth of evolving and established hormone-sensitive and hormone-insensitive mammary carcinoma xenografts, orthotopic prostate tumors, and p53-null lung carcinoma xenografts in immunocompromised mice in the absence of side effects. Release of a sigma receptor-mediated brake on apoptosis may offer a new approach to cancer treatment.

Evaluation of [18F]fluorinated sigma receptor ligands in the conscious monkey brain

PET-imaging of the sigma receptors is very helpful to understand processes, e.g., several central nervous system (CNS)-diseases in which the sigma receptors are involved. The [(18)F]fluoroethylated analogs of SA4503 and SA5845 ([(18)F]FE-SA4503 and [(18)F]FE-SA5845) were evaluated in conscious monkeys to estimate its suitability for human application for PET. Conscious monkeys (Macaca Mulatta) were either scanned with [(18)F]FE-SA4503 or [(18)F]FE-SA5845 (n = 3 for both groups, 220-802 MBq). After a dynamic study of 120 min, radioactivity was displaced by intravenous (i.v.) injection of haloperidol (1 mg/kg). One month later the same set of three monkeys were scanned with [(18)F]FE-SA4503 for 120 min and "cold" SA4503 (1 mg/kg) was infused to displace the radioactivity, and the other three monkeys were pretreated with haloperidol (1 mg/kg) before the 120-min PET-scan with [(18)F]FE-SA5845. Cortical areas (cingulate, frontal, occipital, parietal, temporal), striatum, and thalamus showed high radioactivity uptake. Infusion of haloperidol displaced the radioactivity levels of the two radioligands. The same effect was found for [(18)F]FE-SA4503 after SA4503 displacement. Pretreatment with haloperidol blocked the [(18)F]FE-SA5845 binding to give PET-images with low and uniform uptake in the brain. The findings demonstrated the reversible binding of the two radioligands. Metabolite analysis showed that 14% and 23% parent compound of [(18)F]FE-SA5845 and [(18)F]FE-SA4503, respectively, at 120 min postinjection was present in plasma. Kinetic analysis showed that the binding potential of [(18)F]FE-SA5845 was higher in all brain regions than that of [(18)F]FE-SA4503 (4.75-8.79 vs. 1.65-4.04). The highest binding potential was found in the hippocampus, followed by the cortical regions, thalamus, cerebellar hemisphere, striatum and vermis. Both [(18)F]FE-SA compounds bound specifically to cerebral sigma receptors of the monkey and have potential for mapping sigma receptors in the human brain.

Transcriptomic classification of antitumor agents: application to the analysis of the antitumoral effect of SR31747A

SR31747A is a sigma ligand that exhibits a potent antitumoral activity on various human tumor cell lines both in vitro and in vivo. To understand its mode of action, we used DNA microarray technology combined with a new bioinformatic approach to identify genes that are modulated by SR31747A in different human breast or prostate cancer cell lines. The SR31747A transcriptional signature was also compared with that of seven different representative anticancer drugs commonly used in the clinic. To this aim, we performed a two-dimensional hierarchical clustering analysis of drugs and genes which showed that 1) standard molecules with similar mechanism of action clustered together and 2) SR31747A does not belong to any previously characterized class of standard anticancer drugs. Moreover, we showed that 3) SR31747A mainly exerted its antiproliferative effect by inhibiting the expression of genes playing a key role in DNA replication and cell cycle progression. Finally, contrasting with other drugs, we obtained evidence that 4) SR31747A strongly inhibited the expression of three key enzymes of the nucleotide synthesis pathway (i.e., dihydrofolate reductase, thymidylate synthase, and thymidine kinase) with the latter shown both at the mRNA and protein levels. These results, obtained through a novel molecular approach to characterize and compare anticancer agents, showed that SR31747A exhibits an original mechanism of action, very likely through unexpected targets whose modulations may account for its antitumoral effect.