Arylpiperazine agonists of the serotonin 5-HT1A receptor preferentially activate cAMP signaling versus recruitment of β-arrestin-2

G protein-coupled receptors (GPCRs) mediate biological signal transduction through complex molecular pathways. Therapeutic effects of GPCR-directed drugs are typically accompanied by unwanted side effects, owing in part to the parallel engagement of multiple signaling mechanisms. The discovery of drugs that are ‘functionally selective’ towards therapeutic effects, based on their selective control of cellular responses through a given GPCR, is thus a major goal in pharmacology today. In the present study, we show that several arylpiperazine ligands of the serotonin 5-HT1A receptor (5-HT1AR) preferentially activate 3',5'-cyclic adenosine monophosphate (cAMP) signaling versus b-arrestin-2 recruitment. The pharmacology of these compounds is thus qualitatively different from the endogenous agonist serotonin, indicating functional selectivity of 5-HT1AR-mediated response pathways. Preliminary evidence suggests that phosphorylation of extracellular signal-regulated kinases 1/2 (ERK1/2) downstream of 5-HT1AR is a substrate of functionally selective signaling by partial agonists. We propose that the compounds described in the present study are useful starting points for the development of signaling pathway-selective drugs targeting 5-HT1AR

Sigma-2 receptor agonist derivatives of 1-Cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (PB28) induce cell death via mitochondrial superoxide production and caspase activation in pancreatic cancer

Abstract Background Despite considerable efforts by scientific research, pancreatic cancer is the fourth leading cause of cancer related mortalities. Sigma-2 receptors, which are overexpressed in several tumors, represent promising targets for triggering selective pancreatic cancer cells death. Methods We selected five differently structured high-affinity sigma-2 ligands (PB28, PB183, PB221, F281 and PB282) to study how they affect the viability of diverse pancreatic cancer cells (human cell lines BxPC3, AsPC1, Mia PaCa-2, and Panc1 and mouse Panc-02, KCKO and KP-02) and how this is reflected in vivo in a tumor model. Results Important cytotoxicity was shown by the compounds in the aggressive Panc02 cells, where cytotoxic activity was caspase-3 independent for four of the five compounds. However, both cytotoxicity and caspase-3 activation involved generation of Reactive Oxygen Species (ROS), which could be partially reverted by the lipid antioxidant \u3b1-tocopherol, but not by the hydrophilic N-acetylcysteine (NAC) indicating crucial differences in the intracellular sites exposed to oxidative stress induced by sigma-2 receptor ligands. Importantly, all the compounds strongly increased the production of mitochondrial superoxide radicals except for PB282. Despite a poor match between in vitro and the in vivo efficacy, daily treatment of C57BL/6 mice bearing Panc02 tumors resulted in promising effects with PB28 and PB282 which were similar compared to the current standard-of-care chemotherapeutic gemcitabine without showing signs of systemic toxicities. Conclusions Overall, this study identified differential sensitivities of pancreatic cancer cells to structurally diverse sigma-2 receptor ligands. Of note, we identified the mitochondrial superoxide pathway as a previously unrecognized sigma-2 receptor-activated process, which encourages further studies on sigma-2 ligand-mediated cancer cell death for the targeted treatment of pancreatic tumors

Why PB28 Could Be a Covid 2019 Game Changer?

PB28, a cyclohexylpiperazine derivative, could be a potential strategy for Covid 19 because in a recent study it has been found more active than hydroxychloroquine without interaction with cardiac proteins. PB28 has been designed, developed, and biologically evaluated in the past decade in our research group. A possible mechanism to explain its surprising anti-COVID-19 activity is suggested

Knowledge-Based Design of Long-Chain Arylpiperazine Derivatives Targeting Multiple Serotonin Receptors as Potential Candidates for Treatment of Autism Spectrum Disorder.

Autism spectrum disorder (ASD) includes a group of neurodevelopmental disorders characterized by core symptoms such as impaired social interaction and communication, repetitive and stereotyped behaviors, and restricted interests. To date, there are no effective treatments for these core symptoms. Several studies have shown that the brain serotonin (5-HT) neurotransmission system is altered in both ASD patients and animal models of the disease. Multiple pieces of evidence suggest that targeting 5-HT receptors may treat the core symptoms of ASD and associated intellectual disabilities. In fact, stimulation of the 5-HT1A receptor reduces repetitive and restricted behaviors; blockade of the 5-HT2A receptor reduces both learning deficits and repetitive behavior, and activation of the 5-HT7 receptor improves cognitive performances and reduces repetitive behavior. On such a basis, we have designed novel arylpiperazine derivatives pursuing unprecedently reported activity profiles: dual 5-HT7/5-HT1A receptor agonist properties and mixed 5-HT7 agonist/5-HT1A agonist/5-HT2A antagonist properties. Seventeen new compounds were synthesized and tested in radioligand binding assay at the target receptors. We have identified the dual 5-HT1AR/5-HT7R agonists 8c and 29 and the mixed 5-HT1AR agonist/5-HT7R agonist/5-HT2AR antagonist 20b. These compounds are metabolically stable in vitro and have suitable central nervous system druglike properties

Design, Synthesis, and Characterization of a Fluoroprobe for Live Human Islet Cell Imaging of Serotonin 5-HT1A Receptor

Mounting evidence suggests that the serotonin system serves in signal transmission to regulate insulin secretion in pancreatic islets of Langerhans. Among the 5-HT receptor subtype found in pancreatic islets, serotonin receptor 1 A (5-HT1A) demonstrates a unique ability to inhibit β-cell insulin secretion. We report the design, synthesis, and characterization of two novel fluorescent probes for the 5-HT1A receptor. The compounds were prepared by conjugating the scaffold of the 5-HT1A receptor agonist 8-OH-DPAT with two fluorophores suitable for live-cell imaging. Compound 5a {5-(dimethylamino)-N-[5-[(8-hydroxy-1,2,3,4-tetrahydronaphthalen-2-yl)(propyl)amino]pentyl]naphtalen-1-sulfonammide} showed high affinity for the 5-HT1A receptor (Ki=1.8 nM). Fluoroprobe 5a was able to label the 5-HT1A receptor in pancreatic islet cell cultures in a selective manner, as the fluorescence emission was significantly attenuated by co-administration of the 5-HT1A receptor antagonist WAY-100635. Thus, fluoroprobe 5a showed useful properties to further characterize this unique receptor‘s role

Sigma-2 receptor: Past, present and perspectives on multiple therapeutic exploitations

Identification of sigma-2 receptor (sig-2R) has been controversial. Nevertheless, interest in sig-2R is high for its overexpression in tumors and potentials in oncology. Additionally, sig-2R antagonists inhibit Aβ binding at neurons, blocking the cognitive impairments of Alzheimer's disease. The most representative classes of sig-2R ligands are herein treated with focus on compounds that served to study sig-2R biology and to produce sig-2R: fluorescent ligands; multifunctional anticancer agents; and targeting nanoparticles. Although fluorescent ligands serve as 'green' pharmacological tools, sig-2R-multifunctional conjugates and sig-2R-targeted nanoparticles show how sig-2R targeting increases the activity of anticancer drugs in tumors with reduced toxicity. Altogether, this review draws a picture of the multiple approaches of sig-2R ligands in cancer therapy and as Alzheimer's disease modifying disease agents

Collateral Sensitivity of sigma-2 Receptor ligands: Potentials in the Treatment of Multidrug Resistant Tumors

  Tumors remain one of the main causes of human illnesses and death with MultiDrug Resistance (MDR) being the most severe limitation to the success of chemotherapy. MDR is mainly due to the overexpression of drug efflux transporters, such as P-glycoprotein (P-gp), but attempts to inhibit P-gp have not been clinically successful so far. Lately, some agents were found to be more effective against P-gp overexpressing cells, showing a property termed “collateral sensitivity” (CS). The molecular bases of CS are poorly understood and hypersensitivity to reactive oxygen species (ROS) is one of the hypotheses that accounts for it. We recently identified a few sigma-2 (s2) receptors ligands endowed with CS, likely because of their interaction with P-gp. In fact, a number of CS agents are P-gp substrates: they are actively effluxed by P-gp, and it is believed that they activate a futile ATP cycle, increase oxidative phosphorylation leading to higher ROS production and oxidative stress. Therefore, we verified ROS involvement to study the CS properties of s2 receptors ligands/P-gp substrates (F408 and siramesine) whose activity was measured in three parental and Pg-p-overexpressing cell line pairs. We also demonstrated the major consumption of ATP induced by these compounds in P-gp overexpressing vs the parental cells. We analyzed the effects of siramesine and F408 on mitochondrial respiratory chain (source of ROS and intracellular ATP). Siramesine and F408 decreased both the electron flux rate and the ATP levels, with MDR cells undergoing a much more pronounced decrease than parent cells. Therefore, we demonstrated depletion of mitochondrial ATP supply by siramesine and F408 as the mechanism by which these s2 ligands likely induce CS. In conclusion, CS and s2 ligands-mediated actions warrant further investigation as a way to face MDR

Rigid versus flexible anilines or anilides confirm the bicyclic ring as the hydrophobic portion for optimal σ2 receptor binding and provide novel tools for the development of future σ2 receptor PET radiotracer

Despite their uncertain identification, s2 receptors are promising targets for the development of diagnostics and therapeutics for tumor diseases. Among the s2 ligands developed, the class of the flexible benzamides furnished an optimal pharmacophore for s2 receptor high affinity ligands. A recent investigation suggested that flexible benzamides bind s2 receptors in a bicyclic-like conformation due to an intramolecular H-bond, with 3,4-dihydroisoquinolinone derivatives reaching excellent s2 affinity and selectivity. Herein, the bicyclic-preferred conformation for s2 binding was confirmed through the development of 3,4- dihydroquinolin-(1H)2-one isomeric derivatives, 1,2,3,4-tetrahydroquinolines and the corresponding flexible anilides and anilines, all linked to the 6,7-dimethoxytetrahydroisoquinoline as a basic moiety. 3,4- Dihydroisoquinolin-(1H)2-one (10a) and 1,2,3,4-tetrahydroisoquinoline (11b) emerged for high s2 affinity combined to an excellent s2 versus s1 selectivity. In particular, compound 11b with its low nanomolar s2 affinity and impressive 2807-fold s2 versus s1 selectivity largely exceeded the biological profile of the best 3,4-dihydroisoquinolin-(2H)1-one reference compounds (1). Because of the absence of a cytotoxic effect, the modest interaction with the P-gp, an appropriate lipophilicity and the presence of easily radiolabeling functions, 11b deserves further investigation for the imaging of s2 receptors via PET in tumor