Natural Products Discovered in a High-Throughput Screen Identified as Inhibitors of RGS17 and as Cytostatic and Cytotoxic Agents for Lung and Prostate Cancer Cell Lines

The roles of RGS proteins in cardiometabolic disease

G protein-coupled receptors (GPCRs) are the most prominent receptors on the surface of the cell and play a central role in the regulation of cardiac and metabolic functions. GPCRs transmit extracellular stimuli to the interior of the cells by activating one or more heterotrimeric G proteins. The duration and intensity of G protein-mediated signalling are tightly controlled by a large array of intracellular mediators, including the regulator of G protein signalling (RGS) proteins. RGS proteins selectively promote the GTPase activity of a subset of Gα subunits, thus serving as negative regulators in a pathway-dependent manner. In the current review, we summarise the involvement of RGS proteins in cardiometabolic function with a focus on their tissue distribution, mechanisms of action and dysregulation under various disease conditions. We also discuss the potential therapeutic applications for targeting RGS proteins in treating cardiometabolic conditions and current progress in developing RGS modulators. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Celastrol-loaded polymeric mixed micelles shows improved antitumor efficacy in 4 T1 bearing xenograft mouse model through spatial targeting

In this study, we have proposed a novel approach that combines hyaluronic acid (HA), folic acid (FA), and celastrol (CLS) within a polymeric micelle system (CLS-HF/MLs), offering a dual-action strategy against breast cancer. Polymeric mixed micelles were prepared through the thin-film hydration method, and comprehensive quality control parameters were established, encompassing particle size, polydispersity index, zeta potential, surface morphology, encapsulation efficiency, drug content, in vitro drug release, and storage stability assessment. The average particle size of CLS-HF/MLs micelles was found to be 120 nm and their drug loading and encapsulation efficiencies were 15.9 % and 89.52 %, respectively. The in vitro release data showed that the CLS-HF/MLs targeted mixed micelles displayed a prolonged release profile compared to the free drug. Additionally, the stability of the developed polymeric mixed micelles was maintained for up to 8 weeks of storage in terms of particle size and drug content. Furthermore, both flow cytometry and confocal laser scanning microscopy studies indicated a significant enhancement in the cellular uptake efficiency and cytotoxicity of CLS-HF/MLs mixed micelles against MCF-7 cell line. In terms of pharmacokinetic analysis, the half-life and AUC values of CLS-HF/MLs mixed micelles were found to be approximately 4.71- and 7.36-folds higher than the values of free drug (CLS), respectively. The CLS-HF/MLs micelles exhibited remarkable antitumor efficacy (almost complete ablation of the 4 T1-cell bearing tumor xenografts mouse model) due to the dual receptor (CD44 and folate) targeting effects with minimal side effects. When considering the cumulative findings of our present research, it becomes evident that mixed micelles designed for chemotherapy offer a promising and potentially effective therapeutic avenue for the treatment of breast cancer.

Function and regulation of RGS family members in solid tumours: a comprehensive review

G protein-coupled receptors (GPCRs) play a key role in regulating the homeostasis of the internal environment and are closely associated with tumour progression as major mediators of cellular signalling. As a diverse and multifunctional group of proteins, the G protein signalling regulator (RGS) family was proven to be involved in the cellular transduction of GPCRs. Growing evidence has revealed dysregulation of RGS proteins as a common phenomenon and highlighted the key roles of these proteins in human cancers. Furthermore, their differential expression may be a potential biomarker for tumour diagnosis, treatment and prognosis. Most importantly, there are few systematic reviews on the functional/mechanistic characteristics and clinical application of RGS family members at present. In this review, we focus on the G-protein signalling regulator (RGS) family, which includes more than 20 family members. We analysed the classification, basic structure, and major functions of the RGS family members. Moreover, we summarize the expression changes of each RGS family member in various human cancers and their important roles in regulating cancer cell proliferation, stem cell maintenance, tumorigenesis and cancer metastasis. On this basis, we outline the molecular signalling pathways in which some RGS family members are involved in tumour progression. Finally, their potential application in the precise diagnosis, prognosis and treatment of different types of cancers and the main possible problems for clinical application at present are discussed. Our review provides a comprehensive understanding of the role and potential mechanisms of RGS in regulating tumour progression. Video Abstract.

RGS proteins and their roles in cancer: friend or foe?

As negative modulators of G-protein-coupled receptors (GPCRs) signaling, regulators of G protein signaling (RGS) proteins facilitate various downstream cellular signalings through regulating kinds of heterotrimeric G proteins by stimulating the guanosine triphosphatase (GTPase) activity of G-protein α (Gα) subunits. The expression of RGS proteins is dynamically and precisely mediated by several different mechanisms including epigenetic regulation, transcriptional regulation -and post-translational regulation. Emerging evidence has shown that RGS proteins act as important mediators in controlling essential cellular processes including cell proliferation, survival -and death via regulating downstream cellular signaling activities, indicating that RGS proteins are fundamentally involved in sustaining normal physiological functions and dysregulation of RGS proteins (such as aberrant expression of RGS proteins) is closely associated with pathologies of many diseases such as cancer. In this review, we summarize the molecular mechanisms governing the expression of RGS proteins, and further discuss the relationship of RGS proteins and cancer.

Phytochemicals in Inhibition of Prostate Cancer: Evidence from Molecular Mechanisms Studies

Prostate cancer is one of the leading causes of death for men worldwide. The development of resistance, toxicity, and side effects of conventional therapies have made prostate cancer treatment become more intensive and aggressive. Many phytochemicals isolated from plants have shown to be tumor cytotoxic. In vitro laboratory studies have revealed that natural compounds can affect cancer cell proliferation by modulating many crucial cellular signaling pathways frequently dysregulated in prostate cancer. A multitude of natural compounds have been found to induce cell cycle arrest, promote apoptosis, inhibit cancer cell growth, and suppress angiogenesis. In addition, combinatorial use of natural compounds with hormone and/or chemotherapeutic drugs seems to be a promising strategy to enhance the therapeutic effect in a less toxic manner, as suggested by pre-clinical studies. In this context, we systematically reviewed the currently available literature of naturally occurring compounds isolated from vegetables, fruits, teas, and herbs, with their relevant mechanisms of action in prostate cancer. As there is increasing data on how phytochemicals interfere with diverse molecular pathways in prostate cancer, this review discusses and emphasizes the implicated molecular pathways of cell proliferation, cell cycle control, apoptosis, and autophagy as important processes that control tumor angiogenesis, invasion, and metastasis. In conclusion, the elucidation of the natural compounds' chemical structure-based anti-cancer mechanisms will facilitate drug development and the optimization of drug combinations. Phytochemicals, as anti-cancer agents in the treatment of prostate cancer, can have significant health benefits for humans.

Molecular Basis of Prostate Cancer and Natural Products as Potential Chemotherapeutic and Chemopreventive Agents

Prostate cancer is the second most common malignant cancer in males. It involves a complex process driven by diverse molecular pathways that closely related to the survival, apoptosis, metabolic and metastatic characteristics of aggressive cancer. Prostate cancer can be categorized into androgen dependent prostate cancer and castration-resistant prostate cancer and cure remains elusive due to the developed resistance of the disease. Natural compounds represent an extraordinary resource of structural scaffolds with high diversity that can offer promising chemical agents for making prostate cancer less devastating and curable. Herein, those natural compounds of different origins and structures with potential cytotoxicity and/or in vivo anti-tumor activities against prostate cancer are critically reviewed and summarized according to the cellular signaling pathways they interfere. Moreover, the anti-prostate cancer efficacy of many nutrients, medicinal plant extracts and Chinese medical formulations were presented, and the future prospects for the application of these compounds and extracts were discussed. Although the failure of conventional chemotherapy as well as involved serious side effects makes natural products ideal candidates for the treatment of prostate cancer, more investigations of preclinical and even clinical studies are necessary to make use of these medical substances reasonably. Therefore, the elucidation of structure-activity relationship and precise mechanism of action, identification of novel potential molecular targets, and optimization of drug combination are essential in natural medicine research and development.

Screening of metabolic modulators identifies new strategies to target metabolic reprogramming in melanoma

The prognosis of metastatic melanoma remains poor due to de novo or acquired resistance to immune and targeted therapies. Previous studies have shown that melanoma cells have perturbed metabolism and that cellular metabolic pathways represent potential therapeutic targets. To support the discovery of new drug candidates for melanoma, we examined 180 metabolic modulators, including phytochemicals and anti-diabetic compounds, for their growth-inhibitory activities against melanoma cells, alone and in combination with the BRAF inhibitor vemurafenib. Two positive hits from this screen, 4-methylumbelliferone (4-MU) and ursolic acid (UA), were subjected to validation and further characterization. Metabolic analysis showed that 4-MU affected cellular metabolism through inhibition of glycolysis and enhanced the effect of vemurafenib to reduce the growth of melanoma cells. In contrast, UA reduced mitochondrial respiration, accompanied by an increase in the glycolytic rate. This metabolic switch potentiated the growth-inhibitory effect of the pyruvate dehydrogenase kinase inhibitor dichloroacetate. Both drug combinations led to increased production of reactive oxygen species, suggesting the involvement of oxidative stress in the cellular response. These results support the potential use of metabolic modulators for combination therapies in cancer and may encourage preclinical validation and clinical testing of such treatment strategies in patients with metastatic melanoma.

Fragment-Based Nuclear Magnetic Resonance Screen against a Regulator of G Protein Signaling Identifies a Binding "Hot Spot"

Regulator of G protein signaling (RGS) proteins have attracted attention as a result of their primary role in directing the specificity as well as the temporal and spatial aspects of G protein-coupled receptor signaling. In addition, alterations in RGS protein expression have been observed in a number of disease states, including certain cancers. In this area, RGS17 is of particular interest. It has been demonstrated that, while RGS17 is expressed primarily in the central nervous system, it has been found to be inappropriately expressed in lung, prostate, breast, cervical, and hepatocellular carcinomas. Overexpression of RGS17 leads to dysfunction in inhibitory G protein signaling and an overproduction of the intracellular second messenger cAMP, which in turn alters the transcription patterns of proteins known to promote various cancer types. Suppressing RGS17 expression with RNA interference (RNAi) has been found to decrease tumorigenesis and sufficiently prevents cancer cell migration, leading to the hypothesis that pharmacological blocking of RGS17 function could be useful in anticancer therapies. We have identified small-molecule fragments capable of binding the RGS homology (RH) domain of RGS17 by using a nuclear magnetic resonance fragment-based screening approach. By chemical shift mapping of the two-dimensional ¹⁵ N,¹ H heteronuclear single quantum coherence (HSQC) spectra of the backbone-assigned ¹⁵ N-labeled RGS17-RH, we determined the fragment binding sites to be distant from the Gα interface. Thus, our study identifies a putative fragment binding site on RGS17 that was previously unknown.

Biosynthesis, total synthesis, structural modifications, bioactivity, and mechanism of action of the quinone-methide triterpenoid celastrol

Celastrol, a quinone-methide triterpenoid, was extracted from Tripterygium wilfordii Hook. F. in 1936 for the first time. Almost 70 years later, it is considered one of the molecules most likely to be developed into modern drugs, as it exhibits notable bioactivity, including anticancer and anti-inflammatory activity, and exerts antiobesity effects. In addition, the molecular mechanisms underlying its bioactivity are being widely studied, which offers new avenues for its development as a pharmaceutical reagent. Owing to its potential therapeutic effects and unique chemical structure, celastrol has attracted considerable interest in the fields of organic, biosynthesis, and medicinal chemistry. As several steps in the biosynthesis of celastrol have been revealed, the mechanisms of key enzymes catalyzing the formation and postmodifications of the celastrol scaffold have been gradually elucidated, which lays a good foundation for the future heterogeneous biosynthesis of celastrol. Chemical synthesis is also an effective approach to obtain celastrol. The total synthesis of celastrol was realized for the first time in 2015, which established a new strategy to obtain celastroid natural products. However, owing to the toxic effects and suboptimal pharmacological properties of celastrol, its clinical applications remain limited. To search for drug-like derivatives, several structurally modified compounds were synthesized and tested. This review focuses primarily on the latest research progress in the biosynthesis, total synthesis, structural modifications, bioactivity, and mechanism of action of celastrol. We anticipate that this paper will facilitate a more comprehensive understanding of this promising compound and provide constructive references for future research in this field.

Emerging Roles for Regulator of G Protein Signaling 2 in (Patho)physiology

Since their discovery in the mid-1990s, regulator of G protein signaling (RGS) proteins have emerged as key regulators of signaling through G protein-coupled receptors. Among the over 20 known RGS proteins, RGS2 has received increasing interest as a potential therapeutic drug target with broad clinical implications. RGS2 is a member of the R4 subfamily of RGS proteins and is unique in that it is selective for Gα _q Despite only having an RGS domain, responsible for the canonical GTPase activating protein activity, RGS2 can regulate additional processes, such as protein synthesis and adenylate cyclase activity, through protein-protein interactions. Here we provide an update of the current knowledge of RGS2 function as it relates to molecular mechanisms of regulation as well as its potential role in regulating a number of physiologic systems and pathologies, including cardiovascular disease and central nervous system disorders, as well as various forms of cancer. SIGNIFICANCE STATEMENT: Regulator of G protein signaling (RGS) proteins represent an exciting class of novel drug targets. RGS2, in particular, could have broad clinical importance. As more details are emerging on the regulation of RGS2 in various physiological systems, the potential utility of this small protein in therapeutic development is increasing.

Preparation of high drug-loading celastrol nanosuspensions and their anti-breast cancer activities in vitro and in vivo

As one of the main components of Tripterygium wilfordii Hook F, celastrol (CSL) has significant antitumor activity, but its clinical application has been limited by its poor solubility, low oral bioavailability and systemic toxicity. In this study, celastrol nanosuspensions (CSL-NSps) were prepared using an antisolvent precipitation method with poloxamer 188 (P-188) as a stabilizer at a high CSL/P-188 feeding ratio of 8:1. The resultant CSL was spherical in shape with an average particle size of 147.9 nm, a polydispersity index (PDI) of 0.12 and zeta potential of -19.2 mV. The encapsulation efficiency and drug loading content were 98.18% and 86.83%, respectively, and the X-ray diffraction (XRD) pattern showed that CSL existed in an amorphous state in the nanosuspensions. CSL-NSps were quite stable in various physiological media and plasma and were both suitable for oral and intravenous administration. Nanosuspensions greatly enhanced the in vitro dissolution, and the cumulative drug release reached approximately 69.20% within 48 h. In vivo, CSL-NSps (3 mg/kg, i.g.) displayed a significantly enhanced tumor inhibition rate (TIR) in comparison with that of CSL suspension when administered orally (TIR, 50.39%, vs. 41.16%, p < 0.05),  similar to that of PTX injection (8 mg/kg, i.v. TIR, 50.88%). CSL-NSps showed even better therapeutic efficacy than PTX injection (TIR, 64.18%, p < 0.01) when intravenously injected. This has demonstrated that, with the help of nanosuspensions, CSL is likely to be an effective and promising antitumor agent in clinic practice for the treatment of breast cancer.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Selective and sensitive determination of celastrol in traditional Chinese medicine based on molecularly imprinted polymers modified Mn-doped ZnS quantum dots optosensing materials

In this work, we proposed a facile strategy to prepare molecularly imprinted polymers (MIPs) modified Mn-doped ZnS quantum dots (QDs) as optosensing materials via sol-gel polymerization for specific recognition of celastrol (Cel) in traditional Chinese medicine (TCM). Firstly, L-Cysteine (L-Cys) modified Mn-doped ZnS QDs (L-Cys@Mn-ZnS) was used as imprinting substrate. The amino and carboxyl groups on the surface of Mn-ZnS QDs can provide more binding sites for imprinting polymerization. Then, the fluorescent MIPs was synthesized in the presence of L-Cys@Mn-ZnS QDs, template celastrol, 3-aminopropyl triethoxysilane (APTES) and ammonium hydroxide in the ethanol-water (9/1, v/v) solution. The morphology and structure of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The resulting MIPs functionalized Mn-doped ZnS QDs (denoted as MIPs@L-Cys@Mn-ZnS QDs) had higher imprinting factor of 14.19 and significant selectivity. The MIPs@L-Cys@Mn-ZnS QDs as fluorescent probe exhibited sensitive response to Cel in the linear range from 0.1 μM to 3.5 μM and the limit of detection was estimated to be 35.2 nM. The probe was also applied for the detection of Cel in traditional Chinese medicine with recovery ranged from 88.0%-105.0%. The results confirmed that MIPs@L-Cys@Mn-ZnS QDs could efficiently and specifically capture Cel from actual complex traditional Chinese medicine samples.

Regulator of G-protein signaling (RGS) proteins as drug targets: Progress and future potentials

G protein-coupled receptors (GPCRs) play critical roles in regulating processes such as cellular homeostasis, responses to stimuli, and cell signaling. Accordingly, GPCRs have long served as extraordinarily successful drug targets. It is therefore not surprising that the discovery in the mid-1990s of a family of proteins that regulate processes downstream of GPCRs generated great excitement in the field. This finding enhanced the understanding of these critical signaling pathways and provided potentially new targets for pharmacological intervention. These regulators of G-protein signaling (RGS) proteins were viewed by many as nodes downstream of GPCRs that could be targeted with small molecules to tune signaling processes. In this review, we provide a brief overview of the discovery of RGS proteins and of the gradual and continuing discovery of their roles in disease states, focusing particularly on cancer and neurological disorders. We also discuss high-throughput screening efforts that have led to the discovery first of peptide-based and then of small-molecule inhibitors targeting a subset of the RGS proteins. We explore the unique mechanisms of RGS inhibition these chemical tools have revealed and highlight the most up-to-date studies using these tools in animal experiments. Finally, we discuss the future opportunities in the field, as there are clearly more avenues left to be explored and potentials to be realized.

Sanguinarine caused larval lethality and growth inhibition by suppressing energy metabolism in silkworms, Bombyx mori

Sanguinarine (Sang) is a natural alkaloid and distributed in several plants of Papaveraceae. The antitumor, antioxidant, antimicrobial and anti-inflammatory effects of Sang were extensively reported, but its speciality and mechanism against Lepidoptera insects were still unknown. In this study, detailed toxicological parameters of Sang against silkworms, Bombyx mori (B. mori), were determined by a toxicological test. Then, a nuclear magnetic resonance-based (NMR) metabolomics method was adopted to analyze the changes in hemolymph metabolites of silkworms after feeding Sang. The growth of fourth-instar larvae was significantly ceased by the oral administration of 0.05-0.3% Sang and vast deaths appeared in 0.3% Sang group on Day 4 and Day 5. The quantitative analysis of metabolites indicated that trehalose and citrate levels in hemolymph were increased after 24 h of feeding 0.3% Sang, whereas the concentrations of pyruvate, succinate, malate and fumarate were decreased. In addition, the enzymatic determination and reverse transcription quantitative PCR (RT-qPCR) showed that the trehalase (THL) activity and the transcriptional level of one gene coding THL were uniformly weakened by 0.3% Sang. One of the important mechanisms of Sang against silkworms might be interpreted as follows. Sang impaired trehalose hydrolysis, reduced THL activity and transcription, and led to the inhibition of energy metabolism, consequent antigrowth and high lethality in larvae of B. mori. Our findings offered new insights into the insecticidal effect of Sang from the perspective of energy metabolism and provided the basis for the application of Sang in the control of Lepidoptera pests.

High-resolution structure of RGS17 suggests a role for Ca2+ in promoting the GTPase-activating protein activity by RZ subfamily members

Regulator of G protein signaling (RGS) proteins are negative regulators of G protein-coupled receptor (GPCR) signaling through their ability to act as GTPase-activating proteins (GAPs) for activated Gα subunits. Members of the RZ subfamily of RGS proteins bind to activated Gα_o, Gα_z, and Gα_i1-3 proteins in the nervous system and thereby inhibit downstream pathways, including those involved in Ca²⁺-dependent signaling. In contrast to other RGS proteins, little is known about RZ subfamily structure and regulation. Herein, we present the 1.5-Å crystal structure of RGS17, the most complete and highest-resolution structure of an RZ subfamily member to date. RGS17 cocrystallized with Ca²⁺ bound to conserved positions on the predicted Gα-binding surface of the protein. Using NMR chemical shift perturbations, we confirmed that Ca²⁺ binds in solution to the same site. Furthermore, RGS17 had greater than 55-fold higher affinity for Ca²⁺ than for Mg²⁺ Finally, we found that Ca²⁺ promotes interactions between RGS17 and activated Gα and decreases the K_m for GTP hydrolysis, potentially by altering the binding mechanism between these proteins. Taken together, these findings suggest that Ca²⁺ positively regulates RGS17, which may represent a general mechanism by which increased Ca²⁺ concentration promotes the GAP activity of the RZ subfamily, leading to RZ-mediated inhibition of Ca²⁺ signaling.

MicroRNA-199 suppresses cell proliferation, migration and invasion by downregulating RGS17 in hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common primary tumor of the liver, has a poor prognosis and shows rapid progression. MicroRNAs (miRNAs) play important roles in carcinogenesis and tumor progression. Regulators of G-protein signaling (RGS) are critical for defining G-protein-dependent signal fidelity. RGS17 plays an important role in the regulation of cancer cell proliferation, migration and invasion. Here, we showed that miR-199 was downregulated in a hepatocarcinoma cell line. Overexpression of miR-199 significantly suppressed HCC cell proliferation, migration, and invasion in vitro. RGS17 overexpression promoted HCC cell proliferation, migration, and invasion, and reversed the miR-199 mediated inhibition of proliferation, migration, and invasion. Dual-fluorescence reporter experiments confirmed that miR-199 downregulated RGS17 by direct interaction with the 3'-UTR of RGS17 mRNA. In vivo studies showed that miR-199 overexpression significantly inhibited the growth of tumors. Taken together, the results suggested that miR-199 inhibited tumor growth and metastasis by targeting RGS17.

Molecular Determinants of Sensitivity or Resistance of Cancer Cells Toward Sanguinarine

For decades, natural products represented a significant source of diverse and unique bioactive lead compounds in drug discovery field. In Clinical oncology, complete tumors remission is hampered by the development of drug-resistance. Therefore, development of cytotoxic agents that may overcome drug resistance is urgently needed. Here, the natural benzophenanthridine alkaloid sanguinarine has been studied for its cytotoxic activity against multidrug resistance (MDR) cancer cells. We investigated the role of the ATP-binding cassette (ABC) transporters BCRP/ABCG2, P-glycoprotein/ABCB1 and its close relative ABCB5 in drug resistance. Further drug resistance mechanisms analyzed in this study were the tumor suppressor TP53 and the epidermal growth factor receptor (EGFR). Multidrug resistant cells overexpressing BCRP, ABCB5 and mutated ΔEGFR were not cross-resistant toward sanguinarine. Interestingly, P-gp overexpressing cells were hypersensitive to sanguinarine. Doxorubicin uptake assay carried by flow cytometry revealed that sanguinarine is a potent inhibitor of the P-gp transporter. Moreover, immunoblotting analysis proved that P-gp was downregulated in a dose dependent manner after treating P-gp overexpressing cells with sanguinarine. It was surmised that The inhibition of NFκB activity might explain the collateral sensitivity in CEM/ADR5000 cells. The COMPARE and hierarchical cluster analyses of transcriptome-wide expression profiles of tumor cell lines of the National Cancer Institute identified genes involved in various cellular processes (immune response, inflammation signaling, cell migration and microtubule formation) significantly correlated with log₁₀IC₅₀ values for sanguinarine. In conclusion, sanguinarine may have therapeutic potential for treating multidrug resistant tumors.

Screen Targeting Lung and Prostate Cancer Oncogene Identifies Novel Inhibitors of RGS17 and Problematic Chemical Substructures

Regulator of G protein signaling (RGS) proteins temporally regulate heterotrimeric G protein signaling cascades elicited by G protein-coupled receptor activation and thus are essential for cell homeostasis. The dysregulation of RGS protein expression has been linked to several pathologies, spurring discovery efforts to identify small-molecule inhibitors of these proteins. Presented here are the results of a high-throughput screening (HTS) campaign targeting RGS17, an RGS protein reported to be inappropriately upregulated in several cancers. A screen of over 60,000 small molecules led to the identification of five hit compounds that inhibit the RGS17-Gα_o protein-protein interaction. Chemical and biochemical characterization demonstrated that three of these hits inhibited the interaction through the decomposition of parent compound into reactive products under normal chemical library storage/usage conditions. Compound substructures susceptible to decomposition are reported and the decomposition process characterized, adding to the armamentarium of tools available to the screening field, allowing for the conservation of resources in follow-up efforts and more efficient identification of potentially decomposed compounds. Finally, analogues of one hit compound were tested, and the results establish the first ever structure-activity relationship (SAR) profile for a small-molecule inhibitor of RGS17.