Multifunctional thiosemicarbazones and deconstructed analogues as a strategy to study the involvement of metal chelation, Sigma-2 (σ2) receptor and P-gp protein in the cytotoxic action: In vitro and in vivo activity in pancreatic tumors

Exploration of morpholine-thiophene hybrid thiosemicarbazones for the treatment of ureolytic bacterial infections via targeting urease enzyme: Synthesis, biochemical screening and computational analysis

An important component of the pathogenicity of potentially pathogenic bacteria in humans is the urease enzyme. In order to avoid the detrimental impact of ureolytic bacterial infections, the inhibition of urease enzyme appears to be an appealing approach. Therefore, in the current study, morpholine-thiophene hybrid thiosemicarbazone derivatives (5a-i) were designed, synthesized and characterized through FTIR, 1H NMR, 13C NMR spectroscopy and mass spectrometry. A range of substituents including electron-rich, electron-deficient and inductively electron-withdrawing groups on the thiophene ring was successfully tolerated. The synthesized derivatives were evaluated in vitro for their potential to inhibit urease enzyme using the indophenol method. The majority of compounds were noticeably more potent than the conventional inhibitor, thiourea. The lead inhibitor, 2-(1-(5-chlorothiophen-2-yl)ethylidene)-N-(2-morpholinoethyl)hydrazinecarbothioamide (5g) inhibited the urease in an uncompetitive manner with an IC50 value of 3.80 ± 1.9 µM. The findings of the docking studies demonstrated that compound 5g has a strong affinity for the urease active site. Significant docking scores and efficient binding free energies were displayed by the lead inhibitor. Finally, the ADME properties of lead inhibitor (5g) suggested the druglikeness behavior with zero violation.

Exploring the potential of P-glycoprotein inhibitors in the targeted delivery of anti-cancer drugs: A comprehensive review

Due to the high prevalence of cancer, progress in the management of cancer is the need of the hour. Most cancer patients develop chemotherapeutic drug resistance, and many remain insidious due to overexpression of Multidrug Resistance Protein 1 (MDR1), also known as Permeability-glycoprotein (P-gp) or ABCB1 transporter (ATP-binding cassette subfamily B member 1). P-gp, a transmembrane protein that protects vital organs from outside chemicals, expels medications from malignant cells. The blood-brain barrier (BBB), gastrointestinal tract (GIT), kidneys, liver, pancreas, and cancer cells overexpress P-gp on their apical surfaces, making treatment inefficient and resistant. Compounds that compete with anticancer medicines for transportation or directly inhibit P-gp may overcome biological barriers. Developing nanotechnology-based formulations may help overcome P-gp-mediated efflux and improve bioavailability and cell chemotherapeutic agent accumulation. Nanocarriers transport pharmaceuticals via receptor-mediated endocytosis, unlike passive diffusion, which bypasses ABCB1. Anticancer drugs and P-gp inhibitors in nanocarriers may synergistically increase drug accumulation and chemotherapeutic agent toxicity. The projection of desirable binding and effect may be procured initially by molecular docking of the inhibitor with P-gp, enabling the reduction of preliminary trials in formulation development. Here, P-gp-mediated efflux and several possible outcomes to overcome the problems associated with currently prevalent cancer treatments are highlighted.

Schiff bases and their metal complexes to target and overcome (multidrug) resistance in cancer

Overcoming multidrug resistance (MDR) is one of the major challenges in cancer therapy. In this respect, Schiff base-related compounds (bearing a R1R2CNR3 bond) gained high interest during the past decades. Schiff bases are considered privileged ligands for various reasons, including the easiness of their preparation and the possibility to form complexes with almost all transition metal ions. Schiff bases and their metal complexes exhibit many types of biological activities and are used for the treatment and diagnosis of various diseases. Until now, 13 Schiff bases have been investigated in clinical trials for cancer treatment and hypoxia imaging. This review represents the first collection of Schiff bases and their complexes which demonstrated MDR-reversal activity. The areas of drug resistance covered in this article involve: 1) Modulation of ABC transporter function, 2) Targeting lysosomal ABCB1 overexpression, 3) Circumvention of ABC transporter-mediated drug efflux by alternative routes of drug uptake, 4) Selective activity against MDR cancer models (collateral sensitivity), 5) Targeting GSH-detoxifying systems, 6) Overcoming apoptosis resistance by inducing necrosis and paraptosis, 7) Reactivation of mutated p53, 8) Restoration of sensitivity to DNA-damaging anticancer therapy, and 9) Overcoming drug resistance through modulation of the immune system. Through this approach, we would like to draw attention to Schiff bases and their metal complexes representing highly interesting anticancer drug candidates with the ability to overcome MDR.

Design, synthesis, and bioactivity evaluation of novel indole-selenide derivatives as P-glycoprotein inhibitors against multi-drug resistance in MCF-7/ADR cell

The inhibition of P-glycoprotein (P-gp) has emerged as an intriguing strategy for circumventing multidrug resistance (MDR) in anticancer chemotherapy. In this study, we have designed and synthesized 30 indole-selenides as a new class of P-gp inhibitors based on the scaffold hopping strategy. Among them, the preferred compound H27 showed slightly stronger reversal activity (reversal fold: 271.7 vs 261.6) but weaker cytotoxicity (inhibition ratio: 33.7% vs 45.1%) than the third-generation P-gp inhibitor tariquidar on the tested MCF-7/ADR cells. Rh123 accumulation experiments and Western blot analysis demonstrated that H27 displayed excellent MDR reversal activity by dose-dependently inhibiting the efflux function of P-gp rather than its expression. Besides, UIC-2 reactivity shift assay revealed that H27 could bind to P-gp directly and induced a conformation change of P-gp. Moreover, docking study revealed that H27 matched well in the active pockets of P-gp by forming some key H-bonding interactions, arene-H interactions and hydrophobic contacts. These results suggested that H27 is worth to be a starting point for the development of novel Se-containing P-gp inhibitors for clinic use.

Thiazole, Isatin and Phthalimide Derivatives Tested in vivo against Cancer Models: A Literature Review of the Last Six Years

BACKGROUND

Cancer is a disease characterized by the abnormal multiplication of cells and is the second leading cause of death in the world. The search for new effective and safe anticancer compounds is ongoing due to factors such as low selectivity, high toxicity, and multidrug resistance. Thus, heterocyclic compounds derived from isatin, thiazole and phthalimide that have achieved promising in vitro anticancer activity have been tested in vivo and in clinical trials.

OBJECTIVE

This review focused on the compilation of promising data from thiazole, isatin, and phthalimide derivatives, reported in the literature between 2015 and 2022, with in vivo anticancer activity and clinical trials.

METHODS

A bibliographic search was carried out in the PUBMED, MEDLINE, ELSEVIER, and CAPES PERIODIC databases, selecting relevant works for each pharmacophoric group with in vivo antitumor activity in the last 6 years.

RESULTS

In our study, 68 articles that fit the scope were selected and critically analyzed. These articles were organized considering the type of antitumor activity and their year of publication. Some compounds reported here demonstrated potent antitumor activity against several tumor types.

CONCLUSION

This review allowed us to highlight works that reported promising structures for the treatment of various cancer types and also demonstrated that the privileged structures thiazole, isatin and phthalimide are important in the design of new syntheses and molecular optimization of compounds with antitumor activity.

Cytotoxic pathways activated by multifunctional thiosemicarbazones targeting sigma-2 receptors in breast and lung carcinoma cells

BACKGROUND

Multifunctional thiosemicarbazones (TSCs) able to bind sigma receptors and chelate metals are considered as a promising avenue for the treatment of pancreatic cancer due to the encouraging results obtained on in vitro and in vivo models. Here, we assessed the biochemical mechanism of these TSCs also on lung (A549) and breast (MCF7) cancer cells.

METHODS

The density of sigma-2 receptors in normal (BEAS-2B and MCF10A) and in lung and breast (A549 and MCF7) cancer cells was evaluated by flow cytometry. In these cells, cytotoxicity (MTT assay) and activation of ER- and mitochondria-dependent cell death pathways (by spectrofluorimetric assays to measure Caspases 3/7/9; qRT-PCR detection of GRP78, ATF6, IRE1, PERK; MitoSOX, DCFDA-AM and JC-1 staining), induced by the TSCs FA4, MLP44, PS3 and ACThio1, were evaluated.

RESULTS

FA4 and PS3 exerted more potent cytotoxicity than MLP44 and ACThio1 in all cancer cell lines, where the density of sigma-2 receptors was higher than in normal cells. Remarkably, FA4 promoted ER- and mitochondria-dependent cell death pathways in both cell models, whereas the other TSCs had variable, cell-dependent effects on the activation of the two proapoptotic pathways.

CONCLUSIONS

Our data suggest that FA4 is a promising compound that deserves to be further studied for lung and breast cancer treatment. However, the other multifunctional TSCs also hold promise for the development of therapies towards a personalized medicine approach. Indeed, the presence of the sigma-2 receptor-targeting moiety would lead to a more specific tumor delivery embracing the characteristics of individual tumor types.

Sigma-2 Receptor Ligand Binding Modulates Association between TSPO and TMEM97

Sigma-2 receptor (S2R) is a S2R ligand-binding site historically associated with reportedly 21.5 kDa proteins that have been linked to several diseases, such as cancer, Alzheimer’s disease, and schizophrenia. The S2R is highly expressed in various tumors, where it correlates with the proliferative status of the malignant cells. Recently, S2R was reported to be the transmembrane protein TMEM97. Prior to that, we had been investigating the translocator protein (TSPO) as a potential 21.5 kDa S2R candidate protein with reported heme and sterol associations. Here, we investigate the contributions of TMEM97 and TSPO to S2R activity in MCF7 breast adenocarcinoma and MIA PaCa-2 (MP) pancreatic carcinoma cells. Additionally, the role of the reported S2R-interacting partner PGRMC1 was also elucidated. Proximity ligation assays and co-immunoprecipitation show a functional association between S2R and TSPO. Moreover, a close physical colocalization of TMEM97 and TSPO was found in MP cells. In MCF7 cells, co-immunoprecipitation only occurred with TMEM97 but not with PGRMC1, which was further confirmed by confocal microscopy experiments. Treatment with the TMEM97 ligand 20-(S)-hydroxycholesterol reduced co-immunoprecipitation of both TMEM97 and PGRMC1 in immune pellets of immunoprecipitated TSPO in MP cells. To the best of our knowledge, this is the first suggestion of a (functional) interaction between TSPO and TMEM97 that can be affected by S2R ligands.

Development of Fluorescent 4-[4-(3H-Spiro[isobenzofuran-1,4'-piperidin]-1'-yl)butyl]indolyl Derivatives as High-Affinity Probes to Enable the Study of σ Receptors via Fluorescence-Based Techniques

Sigma (σ) receptor subtypes, σ₁ and σ₂, are targets of wide pharmaceutical interest. The σ₂ receptor holds promise for the development of diagnostics and therapeutics against cancer and Alzheimer's disease. Nevertheless, little is known about the mechanisms activated by the σ₂ receptor. To contribute to the exploitation of its therapeutic potential, we developed novel specific fluorescent ligands. Indole derivatives bearing the N-butyl-3H-spiro[isobenzofuran-1,4'-piperidine] portion were functionalized with fluorescent tags. Nanomolar-affinity fluorescent σ ligands, spanning from green to red to near-infrared emission, were obtained. Compounds 19 (σ pan affinity) and 29 (σ₂ selective), which displayed the best compromise between pharmacodynamic and photophysical properties, were investigated in flow cytometry, confocal, and live cell microscopy, demonstrating their specificity for the σ₂ receptor. To the best of our knowledge, these are the first red-emitting fluorescent σ₂ ligands, validated as powerful tools for the study of σ₂ receptors via fluorescence-based techniques.

Characterization of Sigma-2 Receptor-Specific Binding Sites Using [3H]DTG and [125I]RHM-4

The sigma-2 receptor/transmembrane protein 97 (σ2R/TMRM97) is a promising biomarker of tumor proliferation and a target for cancer therapy. [³H]DTG has been used to evaluate σ2R/TMEM97 binding affinity in compound development studies. However, [³H]DTG has equal and moderate binding affinities to both sigma 1 receptor (σ1R) and σ2R/TMEM97. Furthermore, co-administration with the σ1R masking compound (+)-pentazocine may cause bias in σ2R/TMEM97 binding affinity screening experiments. We have developed a radioiodinated ligand, [¹²⁵I]RHM-4, which has high affinity and selectivity for σ2R/TMEM97 versus σ1R. In this study, a head-to-head comparison between [³H]DTG and [¹²⁵I]RHM-4 on the binding affinity and their effectiveness in σ2R/TMEM97 compound screening studies was performed. The goal of these studies was to determine if this radioiodinated ligand is a suitable replacement for [³H]DTG for screening new σ2R/TMEM97 compounds. Furthermore, to delineate the binding properties of [¹²⁵I]RHM-4 to the σ2R/TMEM97, the structure of RHM-4 was split into two fragments. This resulted in the identification of two binding regions in the σ2R, the "DTG" binding site, which is responsible for binding to the σ2R/TMEM97, and the secondary binding site, which is responsible for high affinity and selectivity for the σ2R/TMEM97 versus the σ1R. The results of this study indicate that [¹²⁵I]RHM-4 is an improved radioligand for in vitro binding studies of the σ2R/TMEM97 versus [³H]DTG.

Novel Sigma-2 receptor ligand A011 overcomes MDR in adriamycin-resistant human breast cancer cells by modulating ABCB1 and ABCG2 transporter function

Multidrug resistance (MDR) is thought to be one of the main reasons for the failure of chemotherapy in cancers. ATP-binding cassette subfamily B member 1 (ABCB1) or P-glycoprotein (P-gp) and ATP-binding cassette subfamily G member 2 (ABCG2) play indispensable roles in cancer cell MDR. Sigma-2 (σ2) receptor is considered to be a cancer biomarker and a potential therapeutic target due to its high expression in various proliferative tumors. Recently, σ2 receptor ligands have been shown to have promising cytotoxic effects against cancer cells and to modulate the activity of P-glycoprotein (ABCB1) in vitro experiments, but their specific effects and mechanisms remain to be elucidated. We found that A011, a σ2 receptor ligand with the structure of 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, showed promising cytotoxicity against breast cancer MCF-7 and adriamycin-resistant MCF-7 (MCF-7/ADR), induced apoptosis, and reversed adriamycin (ADR) and paclitaxel resistance in MCF-7/ADR cells. Furthermore, we demonstrated that A011 increased the accumulation of rhodamine 123 and mitoxantrone in MCF-7/ADR cells. A011 significantly decreased the ATPase activity of the ABCB1 and down-regulated ABCG2 protein expression. In addition, A011, administered alone or in combination with ADR, significantly inhibited tumor growth in the MCF-7/ADR tumor-bearing nude mouse model. A011 may be a potential therapeutic agent for the treatment of tumor resistance.

New Pharmacological Strategies against Pancreatic Adenocarcinoma: The Multifunctional Thiosemicarbazone FA4

A new sigma-2 (σ2) receptor ligand (FA4) was efficiently synthesized and evaluated for cytotoxic, proapoptotic, and antimigratory activity on pancreatic ductal adenocarcinoma (PDAC) primary cell cultures, which restrained the aggressive and chemoresistant behavior of PDAC. This compound showed relevant antiproliferative activity with half maximal inhibitory concentration (IC50) values ranging from 0.701 to 0.825 μM. The cytotoxic activity was associated with induction of apoptosis, resulting in apoptotic indexes higher than those observed after exposure to a clinically relevant concentration of the gemcitabine, the first-line drug used against PDAC. Interestingly, FA4 was also able to significantly inhibit the migration rate of both PDAC-1 and PDAC-2 cells in the scratch wound-healing assay. In conclusion, our results support further studies to improve the library of thiosemicarbazones targeting the σ-2 receptor for a deeper understanding of the relationship between the biological activity of these compounds and the development of more efficient anticancer compounds against PDAC.

Multifunctional thiosemicarbazones targeting sigma receptors: in vitro and in vivo antitumor activities in pancreatic cancer models

PURPOSE

Association of the metal chelating portion of thiosemicarbazone with the cytotoxic activity of sigma-2 receptors appears a promising strategy for the treatment of pancreatic tumors. Here, we developed a novel sigma-2 receptor targeting thiosemicarbazone (FA4) that incorporates a moiety associated with lysosome destabilization and ROS increase in order to design more efficient antitumor agents.

METHODS

The density of sigma receptors in pancreatic cancer cells was evaluated by flow cytometry. In these cells, cytotoxicity (MTT assay) and activation of ER- and mitochondria-dependent cell death pathways (mRNA expression of GRP78, ATF6, IRE1, PERK; ROS levels by MitoSOX and DCFDA-AM; JC-1 staining) induced by the thiosemicarbazones FA4, MLP44, PS3 and ACthio-1, were evaluated. The expression of autophagic proteins (ATG5, ATG7, ATG12, beclin, p62 and LC3-I) was also studied. In addition, the in vivo effect of FA4 in xenograft models with and without gemcitabine challenge was investigated.

RESULTS

We found that FA4 exerted a more potent cytotoxicity than previously studied thiosemicarbazones (MLP44, PS3 and ACthio-1), which were found to display variable effects on the ER or the mitochondria-dependent pro-apoptotic axis. By contrast, FA4 activated pro-apoptotic pathways and decreased autophagy, except in MiaPaCa2 cells, in which autophagic proteins were expressed at lower levels and remained unmodified by FA4. FA4 treatment of PANC-1 xenografted mouse models, poorly responsive to conventional chemotherapy, significantly reduced tumor volumes and increased intratumor apoptosis compared to gemcitabine, with no signs of toxicity.

CONCLUSIONS

Our data indicate that FA4 exhibits encouraging activity in pancreatic cancer cells unresponsive to gemcitabine. These results warrant further investigation in patient-derived pancreatic cancers, and hold promise for the development of therapies that can more efficiently target the specific characteristics of individual tumor types.

Design, Synthesis, Cytotoxic Screening and Molecular Docking Studies of Novel Hybrid Thiosemicarbazone Derivatives as Anticancer Agents

Thiosemicarbazones have been the focus of scientists owing to their broad clinical anticancer range. Herein, A Series of new thiosemicarbazone derivatives 5-9 were synthesized and confirmed through the use of different spectroscopic techniques along with elemental analysis. The in vitro cytotoxic activity of compounds 5-9 against MCF-7 and A549 cell lines and normal breast cells were assessed. Several compounds were found to be active. The most active compound 7 caused MCF-7 cell cycle arrest at G1/ S phases; and induced apoptosis at the pre-G1 phase. The apoptosis-inducing activity of compound 7 was proofed by the elevation of caspase 3/7 activity and also by up-regulation of the expression of Bax and p53 proteins together with the down-regulation of the expression of the Bcl-2 protein. It also had a strong inhibitory effect topoisomerase IIβ enzyme. Molecular Docking study revealed that the synthesized compounds had good docking scores compared to the standard drug Etoposide towards the topoisomerase IIβ protein (3QX3). Overall, these findings confirmed that the new thiosemicarbazone derivatives could aid in the development of promising cancer drug candidates.

Current development of sigma-2 receptor radioligands as potential tumor imaging agents

Sigma receptors are transmembrane proteins with two different subtypes: σ₁ and σ₂. Because of its overexpression in tumors, the σ₂ receptor (σ₂R) is a well-known biomarker for cancer cells. A large number of small-molecule ligands for the σ₂Rs have been identified and tested for imaging the proliferative status of tumors using single photon emission computed tomography (SPECT) and positron emission tomography (PET). These small molecules include derivatives of bicyclic amines, indoles, cyclohexylpiperazines and tetrahydroisoquinolines. This review discusses various aspects of small molecule ligands, such as chemical composition, labeling strategy, affinity for σ₂Rs, and in vitro/in vivo investigations. The recent studies described here could be useful for the development of σ₂R radioligands as potential tumor imaging agents.

Chemical and Biological Evaluation of Thiosemicarbazone-Bearing Heterocyclic Metal Complexes

Thiosemicarbazones (TSCNs) constitute a broad family of compounds (R₁R₂C=N-NH-C(S)- NR₃R₄), particularly attractive because many of them display some biological activity against a wide range of microorganisms and cancer cells. Their activity can be related to their electronic and structural properties, which offer a rich set of donor atoms for metal coordination and a high electronic delocalization providing different binding modes for biomolecules. Heterocycles such as pyrrole, imidazole and triazole are present in biological molecules such as Vitamine B12 and amino acids and could potentially target multiple biological processes. Considering this, we have explored the chemistry and biological properties of thiosemicarbazones series and their complexes bearing heterocycles such as pyrrole, imidazole, thiazole and triazole. We focus at the chemistry and cytotoxicity of those derivatives to find out the structure activity relationships, and particularly we analyzed those examples with the TSCN units in which the mechanism of action information has been profoundly studied and pathways determined, to promote future studies for heterocycle derivatives.

σ2 Receptor and Its Role in Cancer with Focus on a MultiTarget Directed Ligand (MTDL) Approach

Sigma-2 (σ2) is an endoplasmic receptor identified as the Endoplasmic Reticulum (ER) transmembrane protein TMEM97. Despite its controversial identity, which was only recently solved, this protein has gained scientific interest because of its role in the proliferative status of cells; many tumor cells from different organs overexpress the σ2 receptor, and many σ2 ligands display cytotoxic actions in (resistant) cancer cells. These properties have shed light on the σ2 receptor as a potential druggable target to be bound/activated for the diagnosis or therapy of tumors. Additionally, diverse groups have shown how the σ2 receptor can be exploited for the targeted delivery of the anticancer drugs to tumors. As the cancer disease is a multifactorial pathology with multiple cell populations, a polypharmacological approach is very often needed. Instead of the simultaneous administration of different classes of drugs, the use of one molecule that interacts with diverse pharmacological targets, namely MultiTarget Directed Ligand (MTDL), is a promising and currently pursued strategy, that may overcome the pharmacokinetic problems associated with the administration of multiple molecules. This review aims to point out the progress regarding the σ2 ligands in the oncology field, with a focus on MTDLs directed towards σ2 receptors as promising weapons against (resistant) cancer diseases.

Multi-Target Directed Ligands (MTDLs) Binding the σ1 Receptor as Promising Therapeutics: State of the Art and Perspectives

The sigma-1 (σ1) receptor is a 'pluripotent chaperone' protein mainly expressed at the mitochondria-endoplasmic reticulum membrane interfaces where it interacts with several client proteins. This feature renders the σ1 receptor an ideal target for the development of multifunctional ligands, whose benefits are now recognized because several pathologies are multifactorial. Indeed, the current therapeutic regimens are based on the administration of different classes of drugs in order to counteract the diverse unbalanced physiological pathways associated with the pathology. Thus, the multi-targeted directed ligand (MTDL) approach, with one molecule that exerts poly-pharmacological actions, may be a winning strategy that overcomes the pharmacokinetic issues linked to the administration of diverse drugs. This review aims to point out the progress in the development of MTDLs directed toward σ1 receptors for the treatment of central nervous system (CNS) and cancer diseases, with a focus on the perspectives that are proper for this strategy. The evidence that some drugs in clinical use unintentionally bind the σ1 protein (as off-target) provides a proof of concept of the potential of this strategy, and it strongly supports the promise that the σ1 receptor holds as a target to be hit in the context of MTDLs for the therapy of multifactorial pathologies.

Sigma ligands as potent inhibitors of Aβ and AβOs in neurons and promising therapeutic agents of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease and characterized by dementia, memory decline, loss of learning and cognitive disorder. The main pathological features of AD are the deposition of amyloid plaques and the formation of neurofibrillary tangles (NFTs) in the brain. The current anti-AD drugs have shown unsatisfactory therapeutic results. Due to the complications and unclear pathogenesis, AD is still irreversible and incurable. Among several hypotheses proposed by the academic community, the amyloid cascade is widely recognized by scholars and supported by a large amount of evidences. However, controversy over pathogenic factors has also been ongoing. Increasing evidence has shown that amyloid-β (Aβ) and especially amyloid-β oligomers (AβOs) are highly neurotoxic and pathogenic agents that damage neurons, mediate various receptors in the downstream pathways, and ultimately lead to learning and cognitive dysfunction. However, efforts in developing inhibitors of Aβ or amyloid-β precursor protein (APP) have all failed to yield good clinical results. More recently, it has been demonstrated that sigma receptors, including sigma-1 and sigma-2 subtypes, may play critical roles in the regulation of binding and metabolism of AβOs in neuron cells and the pathophysiology of AD. Thus, sigma receptor ligands are being recognized as promising therapeutic agents for treating or ameliorating AD. This article will review the pathophysiology of AD and highlight the sigma ligands that display the capability of preventing or even reversing Aβ- and AβOs-induced neurotoxicity and blocking the signal transduction caused by AβOs.

Anticancer Compounds Based on Isatin-Derivatives: Strategies to Ameliorate Selectivity and Efficiency

In this review we compare and discuss results of compounds already reported as anticancer agents based on isatin-derivatives, metalated as well as non-metallated. Isatin compounds can be obtained from plants, marine animals, and is also found in human fluids as a metabolite of amino acids. Its derivatives include imines, hydrazones, thiosemicarbazones, among others, already focused on numerous anticancer studies. Some of them have entered in pre-clinical and clinical tests as antiangiogenic compounds or inhibitors of crucial proteins. As free ligands or coordinated to metal ions, such isatin derivatives showed promising antiproliferative properties against different cancer cells, targeting different biomolecules or organelles. Binding to metal ions usually improves its biological properties, indicating a modulation by the metal and by the ligand in a synergistic process. They also reveal diverse mechanisms of action, being able of binding DNA, generating reactive species that cause oxidative damage, and inhibiting selected proteins. Strategies used to improve the efficiency and selectivity of these compounds comprise structural modification of the ligands, metalation with different ions, syntheses of mononuclear and dinuclear species, and use of inserted or anchored compounds in selected drug delivery systems.

PB28, the Sigma-1 and Sigma-2 Receptors Modulator With Potent Anti-SARS-CoV-2 Activity: A Review About Its Pharmacological Properties and Structure Affinity Relationships

These unprecedented times have forced the scientific community to gather to face the COVID-19 pandemic. Efforts in diverse directions have been made. A multi-university team has focused on the identification of the host (human) proteins interacting with SARS-CoV-2 viral proteins, with the aim of hampering these interactions that may cause severe COVID-19 symptoms. Sigma-1 and sigma-2 receptors surprisingly belong to the “druggable” host proteins found, with the pan-sigma receptor modulator PB28 displaying the most potent anti–SARS-CoV-2 activity in in vitro assays. Being 20-fold more active than hydroxychloroquine, without cardiac side effects, PB28 is a promising antiviral candidate worthy of further investigation. Our research group developed PB28 in 1996 and have thoroughly characterized its biological properties since then. Structure–affinity relationship (SAfiR) studies at the sigma receptor subtypes were also undertaken with PB28 as the lead compound. We herein report our knowledge of PB28 to share information that may help to gain insight into the antiviral action of this compound and sigma receptors, while providing structural hints that may speed up the translation into therapeutics of this class of ligands.

Proceedings from the Fourth International Symposium on σ-2 Receptors: Role in Health and Disease

The σ-2 receptor (S2R) complex has been implicated in CNS disorders ranging from anxiety and depression to neurodegenerative disorders such as Alzheimer's disease (AD). The proteins comprising the S2R complex impact processes including autophagy, cholesterol synthesis, progesterone signaling, lipid membrane-bound protein trafficking, and receptor stabilization at the cell surface. While there has been much progress in understanding the role of S2R in cellular processes and its potential therapeutic value, a great deal remains unknown. The International Symposium on Sigma-2 Receptors is held in conjunction with the annual Society for Neuroscience (SfN) conference to promote collaboration and advance the field of S2R research. This review summarizes updates presented at the Fourth International Symposium on Sigma-2 Receptors: Role in Health and Disease, a Satellite Symposium held at the 2019 SfN conference. Interdisciplinary members of the S2R research community presented both previously published and preliminary results from ongoing studies of the role of S2R in cellular metabolism, the anatomic and cellular expression patterns of S2R, the relationship between S2R and amyloid β (Aβ) in AD, the role of S2R complex protein PGRMC1 in health and disease, and the efforts to design new S2R ligands for the purposes of research and drug development. The proceedings from this symposium are reported here as an update on the field of S2R research, as well as to highlight the value of the symposia that occur yearly in conjunction with the SfN conference.

Synthesis and Pharmacological Evaluation of σ2 Receptor Ligands Based on a 3-Alkoxyisoxazole Scaffold: Potential Antitumor Effects against Osteosarcoma

Since its initial discovery as the basis for nicotinic acetylcholine receptor ligands, the 3-alkoxyisoxazole scaffold has been shown to be a versatile platform for the development of potent σ1 and σ2 receptor ligands. Herein we report a further SAR exploration of the 3-alkoxyisoxazole scaffold with the aim of obtaining potent σ2 receptor ligands. Various substitutions on the benzene ring and at the basic amino regions resulted in a total of 21 compounds that were tested for their binding affinities for the σ2 receptor. In particular, compound 51 [(2S)-1-(4-ammoniobutyl)-2-(((5-((3,4-dichlorophenoxy)methyl)isoxazol-3-yl)oxy)methyl)pyrrolidin-1-ium chloride] was identified as one of the most potent σ2 ligands within the series, with a K_i value of 7.9 nM. It demonstrated potent antiproliferative effects on both osteosarcoma cell lines 143B and MOS-J (IC₅₀ values of 0.89 and 0.71 μM, respectively), relative to siramesine (IC₅₀ values of 1.81 and 2.01 μM). Moreover, compound 51 inhibited clonal formation of osteosarcoma 143B cells at 1 μM, corresponding to half the dose required of siramesine for similar effects. The general cytotoxicity profile of compound 51 was assessed in a number of normal cell lines, including HaCaT, HAF, and LO2 cells. Furthermore, FACS analysis showed that compound 51 likely inhibits osteosarcoma cell growth by disruption of the cell cycle and promotion of apoptosis.

Design, synthesis and biological evaluation of novel thiosemicarbazone-indole derivatives targeting prostate cancer cells

To discover novel anticancer agents with potent and low toxicity, we designed and synthesized a range of new thiosemicarbazone-indole analogues based on lead compound 4 we reported previously. Most compounds displayed moderate to high anticancer activities against five tested tumor cells (PC3, EC109, DU-145, MGC803, MCF-7). Specifically, the represented compound 16f possessed strong antiproliferative potency and high selectivity toward PC3 cells with the IC₅₀ value of 0.054 μM, compared with normal WPMY-1 cells with the IC₅₀ value of 19.470 μM. Preliminary mechanism research indicated that compound 16f could significantly suppress prostate cancer cells (PC3, DU-145) growth and colony formation in a dose-dependent manner. Besides, derivative 16f induced G1/S cycle arrest and apoptosis, which may be related to ROS accumulation due to the activation of MAPK signaling pathway. Furthermore, molecule 16f could effectively inhibit tumor growth through a xenograft model bearing PC3 cells and had no evident toxicity in vivo. Overall, based on the biological activity evaluation, analogue 16f can be viewed as a potential lead compound for further development of novel anti-prostate cancer drug.

MRP1-Collateral Sensitizers as a Novel Therapeutic Approach in Resistant Cancer Therapy: An In Vitro and In Vivo Study in Lung Resistant Tumor

Multidrug resistance (MDR) is the main obstacle to current chemotherapy and it is mainly due to the overexpression of some efflux transporters such as MRP1. One of the most studied strategies to overcome MDR has been the inhibition of MDR pumps through small molecules, but its translation into the clinic unfortunately failed. Recently, a phenomenon called collateral sensitivity (CS) emerged as a new strategy to hamper MDR acting as a synthetic lethality, where the genetic changes developed upon the acquisition of resistance towards a specific agent are followed by the development of hypersensitivity towards a second agent. Among our library of sigma ligands acting as MDR modulators, we identified three compounds, F397, F400, and F421, acting as CS-promoting agents. We deepened their CS mechanisms in the "pure" model of MRP1-expressing cells (MDCK-MRP1) and in MRP1-expressing/drug resistant non-small cell lung cancer cells (A549/DX). The in vitro results demonstrated that (i) the three ligands are highly cytotoxic for MRP1-expressing cells; (ii) their effect is MRP1-mediated; (iii) they increase the cytotoxicity induced by cis-Pt, the therapeutic agent commonly used in the treatment of lung tumors; and (iv) their effect is ROS-mediated. Moreover, a preclinical in vivo study performed in lung tumor xenografts confirms the in vitro findings, making the three CS-promoting agents candidates for a novel therapeutic approach in lung resistant tumors.

3-benzazecine-based cyclic allene derivatives as highly potent P-glycoprotein inhibitors overcoming doxorubicin multidrug resistance

Aim: Enamino 3-benzazecine compounds, incorporating the C6-C8 allene system, were synthesized and evaluated in vitro as inhibitors of P-glycoprotein (P-gp) and/or multidrug resistance-associated protein 1 (MRP1), two efflux pumps mainly connected with multidrug resistance (MDR) in cancer cells. Results & methodology: Most of the synthesized compounds were selective P-gp inhibitors in Calcein-AM uptake assay. Structure–activity relationships (SARs) pointed out that CO2Me derivatives are more potent than acetyl derivatives, and 10,11-dimethoxy compounds are five to tenfold more potent inhibitors than the respective unsubstituted compounds, and that the P-gp inhibition potency is mainly related to volume parameters. Conclusion: Nanomolar P-gp inhibitors, such as 23 (IC50 = 4.2 nM), restored the antiproliferative activity of doxorubicin in multidrug-resistant cells. The observed activities showed that 3-benzazecine-based compounds may be promising MDR reversers.

Sigma-2 receptor/TMEM97 agonist PB221 as an alternative drug for brain tumor

Background

There are limited effective drugs that can reach the brain to target brain tumors, in particular glioblastoma, which is one of the most difficult cancers to be cured from. Because the overexpression of the sigma-2 receptor is frequently reported in glioma clinical samples and associated with poor prognosis and malignancy, we herein studied the anti-tumor effect of the sigma-2 receptor agonist PB221 (4-cyclohexyl-1-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperidine) on an anaplastic astrocytoma tumor model based on previous encouraging results in pancreatic cancer and neuroblastoma SK-N-SH cells.

Methods

The expression of the sigma-2 receptor, transmembrane protein 97 (TMEM97), in ALTS1C1 and UN-KC6141 cell lines was measured by RT-PCR and quantitative RT-PCR. The binding of sigma-2 receptor fluorescent ligands PB385 (6-[5-[3-(4-cyclohexylpiperazin-1-yl)propyl]-5,6,7,8-tetrahydronaphthalen-5-yloxy]-N-(7-nitro-2,1,3-benzoxadiazol-4-yl)hexanamine) and NO1 (2-{6-[2-(3-(6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H)-yl)propyl)-3,4-dihydroisoquinolin-1(2H)-one-5-yloxy]hexyl}-5-(dimethylamino)isoindoline-1,3-dione) was examined by flow cytometry and the fluorescent plate reader. The antitumor activity of PB221 was initially examined in the murine brain tumor cell line ALTS1C1 and then in the murine pancreatic cell line UN-KC6141. The potential therapeutic efficacy of PB221 for murine brain tumors was examined by in vitro migration and invasion assays and in vivo ectopic and orthotopic ALTS1C1 tumor models.

Results: The IC₅₀ of PB221 for ALTS1C1 and UN-KC6141 cell lines was 10.61 ± 0.96 and 13.13 ± 1.15 μM, respectively. A low dose of PB221 (1 μM) significantly repressed the migration and invasion of ALTS1C1 cells, and a high dose of PB221 (20 μM) resulted in the apoptotic cell death of ALTS1C1 cells. These effects were reduced by the lipid antioxidant α-tocopherol, but not by the hydrophilic N-acetylcysteine, suggesting mitochondrial oxidative stress is involved. The in vivo study revealed that PB221 effectively retarded tumor growth to 36% of the control tumor volume in the ectopic intramuscular tumor model and increased the overall survival time by 20% (from 26 to 31 days) in the orthotopic intracerebral tumor model.

Conclusions

This study demonstrates that the sigma-2 receptor agonist PB221 has the potential to be an alternative chemotherapeutic drug for brain tumors with comparable side effects as the current standard-of-care drug, temozolomide.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5700-7) contains supplementary material, which is available to authorized users.

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.

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A number of aza-heterocyclic compounds, which share the 5,6-dihydropyrrolo[2,1-a]isoquinoline (DHPIQ) scaffold with members of the lamellarin alkaloid family, were synthesized and evaluated for their ability to reverse in vitro multidrug resistance in cancer cells through inhibition of P-glycoprotein (P-gp) and/or multidrug-resistance-associated protein 1. Most of the investigated DHPIQ compounds proved to be selective P-gp modulators, and the most potent modulator, 8,9-diethoxy-1-(3,4-diethoxyphenyl)-3-(furan-2-yl)-5,6-dihydropyrrolo[2,1-a]isoquinoline-2-carbaldehyde, attained sub-micromolar inhibitory potency (IC₅₀ : 0.19 μm). Schiff bases prepared by the condensation of some 1-aryl-DHPIQ aldehydes with p-aminophenol also proved to be of some interest, and one of them, 4-((1-(4-fluorophenyl)-5,6-dihydro-8,9-dimethoxypyrrolo[2,1-a]isoquinolin-2-yl)methyleneamino)phenol, had an IC₅₀ value of 1.01 μm. In drug combination assays in multidrug-resistant cells, some DHPIQ compounds, at nontoxic concentrations, significantly increased the cytotoxicity of doxorubicin in a concentration-dependent manner. Studies of structure-activity relationships and investigation of the chemical stability of Schiff bases provided physicochemical information useful for molecular optimization of lamellarin-like cytotoxic drugs active toward chemoresistant tumors as well as nontoxic reversers of P-gp-mediated multidrug resistance in tumor cells.