Analogs of tetrahydroisoquinoline natural products that inhibit cell migration and target galectin-3 outside of its carbohydrate-binding site

Visible-Light-Driven α-Substituted Amines Enabled by In Situ Formation of Amine Substrate Aggregates

A visible-light-driven, photocatalyst-free, air-promoted, α-substituted reaction of amines with varying nucleophiles is described. The amine substrate aggregates formed in situ through physical π-π stacking by H2O regulation in organic solvent can absorb visible light and then generate iminium ion intermediates, which undergo nucleophilic substitution reactions with varying nucleophiles to afford α-substituted amines. This reaction features catalyst-free, good functional group tolerance, simple operation procedure, and green reaction conditions.

Visible-light promoted photoredox catalysis in flow: addition of biologically important α‑amino radicals to michael acceptors

Visible light promoted photoredox catalyzed formation of α-amino radicals from cyclic tertiary amine compounds and their subsequent addition to Michael acceptors performed in flow conditions allowed access to a wide range of functionalized N-aryl-substituted tetrahydroisoquinolines (THIQs) and N-aryl-substituted tetrahydro-β-carbolines (THBCs). Visible light in conjunction with Ru(bpy)3Cl2 photocatalyst allowed the formation and high reactivities of α-amino radicals in flow conditions at room temperature. These reactions gave valuable products with high efficiencies; some previously unavailable reaction pathways photo or thermal reaction conditions; i.e. direct synthesis of 1-substituted (THBCs) via α-amino radical path were successfully realized in flow. The use of custom-made FEP tube microreactor proved to be the key to succesfull α-amino-radical formation and overall reaction performance in flow. Three types of light transparent custom-made microfluidic devices were tested, among them glass/silicon and FEP type reactor showed very good results in the conversion of tested compounds. Plausible reaction mechanism is proposed in accordance with known principles of photo activation of tertiary amines. Visible light promoted C(sp3)-H functionalization of N-aryl-protected tetrahydroisoquinolines and N-aryl-protected tetrahydro-β-carbolines in microflow conditions via a-amino radical pathway with various coupling partners in excellent yields and efficiencies.

Glycomimetics for the inhibition and modulation of lectins

Carbohydrates are essential mediators of many processes in health and disease. They regulate self-/non-self- discrimination, are key elements of cellular communication, cancer, infection and inflammation, and determine protein folding, function and life-times. Moreover, they are integral to the cellular envelope for microorganisms and participate in biofilm formation. These diverse functions of carbohydrates are mediated by carbohydrate-binding proteins, lectins, and the more the knowledge about the biology of these proteins is advancing, the more interfering with carbohydrate recognition becomes a viable option for the development of novel therapeutics. In this respect, small molecules mimicking this recognition process become more and more available either as tools for fostering our basic understanding of glycobiology or as therapeutics. In this review, we outline the general design principles of glycomimetic inhibitors (Section 2). This section is then followed by highlighting three approaches to interfere with lectin function, i.e. with carbohydrate-derived glycomimetics (Section 3.1), novel glycomimetic scaffolds (Section 3.2) and allosteric modulators (Section 3.3). We summarize recent advances in design and application of glycomimetics for various classes of lectins of mammalian, viral and bacterial origin. Besides highlighting design principles in general, we showcase defined cases in which glycomimetics have been advanced to clinical trials or marketed. Additionally, emerging applications of glycomimetics for targeted protein degradation and targeted delivery purposes are reviewed in Section 4.

Inhibition of galectins in cancer: Biological challenges for their clinical application

Galectins play relevant roles in tumor development, progression and metastasis. Accordingly, galectins are certainly enticing targets for medical intervention in cancer. To date, however, clinical trials based on galectin inhibitors reported inconclusive results. This review summarizes the galectin inhibitors currently being evaluated and discusses some of the biological challenges that need to be addressed to improve these strategies for the benefit of cancer patients.

Chimeric galectin-3 and collagens: Biomarkers and potential therapeutic targets in fibroproliferative diseases

Fibrosis, stiffening and scarring of an organ/tissue due to genetic abnormalities, environmental factors, infection, and/or injury, is responsible for > 40% of all deaths in the industrialized world, and to date, there is no cure for it despite extensive research and numerous clinical trials. Several biomarkers have been identified, but no effective therapeutic targets are available. Human galectin-3 is a chimeric gene product formed by the fusion of the internal domain of the collagen alpha gene [N-terminal domain (ND)] at the 5'-end of galectin-1 [C-terminal domain (CRD)] that appeared during evolution together with vertebrates. Due to the overlapping structural similarities between collagen and galectin-3 and their shared susceptibility to cleavage by matrix metalloproteases to generate circulating collagen-like peptides, this review will discuss present knowledge on the role of collagen and galectin-3 as biomarkers of fibrosis. We will also highlight the need for transformative approaches targeting both the ND and CRD domains of galectin-3, since glycoconjugate binding by the CRD is triggered by ND-mediated oligomerization and the therapies targeted only at the CRD have so far achieved limited success.

Non-carbohydrate strategies to inhibit lectin proteins with special emphasis on galectins

Lectins are a family of glycan-binding proteins, many of which have been established as key targets for therapeutic intervention. They play a central role in many physiological and cellular processes. With the advances in protein crystallography, NMR spectroscopy and computational power over the past couple of decades, the carbohydrate-receptor interactions are now well understood and characterized. Nevertheless, designing efficient carbohydrate inhibitors is a laborious endeavour. They are known to have weak affinities, unsuitable pharmacokinetic properties and highly cumbersome/complex synthetic routes. To circumvent these issues many non-carbohydrate strategies have been reported. Galectins are a sub-family of lectin proteins which have been recognized as crucial targets for a wide variety of diseases. Many candidates targeting galectins are currently in advanced stages of clinical trials. There have been a few reports of non-carbohydrate inhibitors targeting galectins which comprise of peptide-based inhibitors and a recent flourish of heterocyclic inhibitors. In this review, we have briefly highlighted the strategies like fragment-based drug-design and high-throughput screens utilized to identify non-carbohydrate based antagonists for proteins wherein the presence of a sugar was believed to be essential. Additionally, we have described the literature pertaining to non-carbohydrate inhibitors of galectins and how previous reports on rational substitution of a sugar motif could aid in design of heterocyclics that inhibit lectins/galectins. We have concluded with remarks on challenges, gap in our understanding and future perspectives concerned with rational design of non-carbohydrate molecules targeting lectins/galectins.

Visible light promoted photoredox C(sp3)-H bond functionalization of tetrahydroisoquinolines in flow

A merger of organocatalysis and visible light photoredox catalysis performed in flow allowed access to a wide range of functionalized N-aryl-substituted tetrahydroisoquinolines (THIQs) in a formal C-H oxidation/Mannich reaction. Strecker type functionalization and copper-catalyzed alkynylation of several N-aryl-substituted THIQs were also successfully performed in flow, giving valuable products with high efficiencies. The use of custom-made porous polymeric type microreactors proved to be crucial regarding the C-H oxidation step and overall reaction performance.

Design and Synthesis of Tetrahydroisoquinoline Derivatives as Anti-Angiogenesis and Anti-Cancer Agents

AIM

The aim of our research work is the synthesis of tetrahydroisoquinoline derivatives as anti-Angiogenesis and anti-cancer agents.

BACKGROUND

Cancer is the second leading cause of deaths in the United States. The current recovery rate from the advanced treatment for the cancer is excessively low. Therefore, the identification of novel, potent, and less toxic anticancer agents remains a top priority.

OBJECTIVE

To evaluate anti-angiogenesis and anticancer activities of THIQs on different colorectal cancer cell lines (CRC) viz., Colo320, DLD-1, HCT116, SNU-C1, SW480, and GSK3b in pre-treated viability HCT116. and to carry out molecular docking studies of THIQs.

METHODS

Twenty synthesized THIQs were screened in the Eli Lilly's Open Innovation Drug Discovery Program and selected twelve compounds for in vitro primary screening in the KRas (Kirsten rat sarcoma)-Wnt SL (Synthetic Lethal) in the basal viability of different colon cancer cell lines. Docking studies of the active THIQs were also performed in our laboratory, targeting the active sites of KRas and VEGF receptors.

RESULTS

Compound GM-3-18 was found to possess significant activities for KRas inhibition, with IC50 values in the range of 0.9 μM to 10.7 μM, for all colon cancer cell lines. Compound GM-3-121 showed potent anti-angiogenesis activity with IC50 = 1.72 μM. Molecular docking studies showed that the carbonyl oxygen atoms of GM-3-18 and GM-3-121 showed hydrogen bonding interactions with the hydrogen of - OH groups of THR 74 (A).

CONCLUSION

The results indicated that all the compounds showed moderate to high activity for KRas inhibition. The THIQs bearing the chloro group at the 4-position of the phenyl ring (GM-3-18) exhibited significant KRas inhibition against all colon cancer cell lines.

Radixin modulates the function of outer hair cell stereocilia

The stereocilia of the inner ear sensory cells contain the actin-binding protein radixin, encoded by RDX. Radixin is important for hearing but remains functionally obscure. To determine how radixin influences hearing sensitivity, we used a custom rapid imaging technique to visualize stereocilia motion while measuring electrical potential amplitudes during acoustic stimulation. Radixin inhibition decreased sound-evoked electrical potentials. Other functional measures, including electrically induced sensory cell motility and sound-evoked stereocilia deflections, showed a minor amplitude increase. These unique functional alterations demonstrate radixin as necessary for conversion of sound into electrical signals at acoustic rates. We identified patients with RDX variants with normal hearing at birth who showed rapidly deteriorating hearing during the first months of life. This may be overlooked by newborn hearing screening and explained by multiple disturbances in postnatal sensory cells. We conclude radixin is necessary for ensuring normal conversion of sound to electrical signals in the inner ear.

Sonal Prasad et al. identify several mutations in the radixin (RDX) gene that are associated with early-life hearing loss. Using a guinea pig model, they propose that radixin helps convert sound into electrical signals in the mature inner ear.

Multilevel structure-activity profiling reveals multiple green tea compound families that each modulate ubiquitin-activating enzyme and ubiquitination by a distinct mechanism

We developed and implemented a reconstituted system to screen for modulators of the ubiquitination of proliferating cell nuclear antigen, a process that activates pathways of DNA damage tolerance and drug resistance. We identified the primary putatively health-beneficial green tea polyphenol epigallocatechin gallate (EGCG) and certain related small molecules as potent inhibitors of ubiquitination. EGCG directly and reversibly targets the ubiquitin-activating enzyme Uba1, blocking formation of the Uba1~ubiquitin thioester conjugate and thus ubiquitination and in the cell. Structure–activity relationship profiles across multiple biochemical and cellular assays for a battery of EGCG analogues revealed distinct chemical and mechanism-of-action clusters of molecules, with catechin gallates, alkyl gallates, and myricetin potently inhibiting ubiquitination. This study defines a number of related though distinct first-in-class inhibitors of ubiquitination, each series with its own unique activity pattern and mechanistic signature.

Dehydrogenative C(sp3)–H bond functionalization of tetrahydroisoquinolines mediated by organic oxidants under mild conditions

DDQ and IBX are effective SET oxidants of N-aryl-protected and unprotected THIQs. Mannich and Strecker type functionalizations ensued in an overall CDC reaction.

Crystal structure of ethyl 4-(3,4-dimethylphenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate, C23H29NO3

C23H29NO3, orthorhombic, Pbcn (no. 60), a = 18.781(7) Å, b = 15.749(6) Å, c = 14.081(5) Å, V = 4165(3) Å3, Z = 8, R gt(F) = 0.0614, wR ref(F 2) = 0.1874, T = 296(2) K.

Crystal structure of ethyl 2-amino-4-(2,6-dichlorophenyl)-7-methyl-5-oxo-4H,5H-pyrano [4,3-b]pyran-3-carboxylate, C18H15Cl2NO5

C18H15Cl2NO5, monoclinic, P21/c (no. 14), a = 7.423(5) Å, b = 27.798(3) Å, c = 9.550(2) Å, β = 117.62(4)°, V = 1746.0(14) Å3, Z = 4, R gt(F) = 0.0395, wR ref(F 2) = 0.1030, T = 293(2) K.

Crystal structure of methyl 4-(3-cyanophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydro-quinoline-3-carboxylate, C21H22N2O3

C21H22N2O3, orthorhombic, Pbcn (no. 60), a = 15.093(2) Å, b = 13.896(2) Å, c = 17.501(2) Å, V = 3670.5(8) Å3, Z = 8, R gt(F) = 0.0446, wR ref(F 2) = 0.1208, T = 293(2) K.

Crystal structure of ethyl 2-amino-4-(3,4-dimethylphenyl)-5-oxo-4H,5H-pyrano[3,2-c] chromene-3-carboxylate, C23H21NO5

C23H21NO5, monoclinic, P21/c (no. 14), a = 15.829(11) Å, b = 8.294(6) Å, c = 14.718(10) Å, β = 93.339(12)°, V = 1929(2) Å3, Z = 4, R gt(F) = 0.073, wR ref(F 2) = 0.206, T = 296(2) K.

Plasma galectin-3 levels are associated with the risk of incident chronic kidney disease

Galectin-3 has been proposed as a novel biomarker of heart failure and cardiac fibrosis, and may also be associated with fibrosis of other organs such as the kidney. To determine this, we prospectively analyzed data from 9,148 Atherosclerosis Risk in Communities (ARIC) Study participants with measured plasma galectin-3 levels (baseline, visit 4, 1996-98) and without prevalent chronic kidney disease (CKD) or heart failure. We identified 1,983 incident CKD cases through December 31, 2013 over a median follow-up of 16 years. At baseline, galectin-3 was cross-sectionally associated with estimated glomerular filtration rate and urine albumin-to-creatinine ratio; both significant. The results were adjusted for age, sex, race-center, education, physical activity, smoking status, body mass index, systolic blood pressure, anti-hypertensive medication use, history of cardiovascular disease, diabetes, fasting blood glucose, and rs4644 (a single nucleotide polymorphism of galactin-3). There was a significant, graded, and positive association between galectin-3 and incident CKD (quartile 4 vs. 1 hazard ratio: 2.22 [95% confidence interval: 1.89, 2.60]). The association was attenuated but remained significant after adjustment for estimated glomerular filtration rate, urine albumin-to-creatinine ratio, troponin T, and N-terminal pro-brain natriuretic peptide (quartile 4 vs. 1 hazard ratio: 1.75 [95% confidence interval: 1.49, 2.06]), and was stronger among those with hypertension at baseline (significant interaction). Thus, in this community-based population, higher plasma galectin-3 levels were associated with an elevated risk of developing incident CKD, particularly among those with hypertension.

Crystal structure of 4-(4-hydroxy-3-methoxy-phenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydro-quinoline-3-carboxylic acid methyl ester, C21H25NO5

C21H25NO5, monoclinic, P21/n (no. 14) a = 10.4501(19) Å, b = 15.750(3) Å, c = 12.043(2) Å, β = 102.625(3)°, V = 1934.3(6) Å3, Z = 4, R gt(F) = 0.0406, wR ref(F 2) = 0.1177, T = 296(2) K.

Real-time, label-free characterization of oligosaccharide-binding proteins using carbohydrate microarrays and an ellipsometry-based biosensor

Carbohydrates present on cell surfaces mediate cell behavior through interactions with other biomolecules. Due to their structural complexity, diversity, and heterogeneity, it is difficult to fully characterize a variety of carbohydrates and their binding partners. As a result, novel technologies for glycomics applications have been developed, including carbohydrate microarrays and label-free detection methods. In this paper, we report using the combination of oligosaccharide microarrays and the label-free oblique-incidence reflectivity difference (OI-RD) microscopy for real-time characterization of oligosaccharide binding proteins. Aminated human milk oligosaccharides were immobilized on epoxy-coated glass substrates as microarrays for reactions with Family 1 of solute binding proteins from Bifidobacterium longum subsp. infantis (B. infantis). Binding affinities of these protein-oligosaccharide interactions showed preferences of Family 1 of solute binding proteins to host glycans, which helps in characterizing the complex process of human milk oligosaccharides foraging by B. infantis.

Galectin 3 regulates HCC cell invasion by RhoA and MLCK activation

Hepatocellular carcinoma (HCC) carries a poor prognosis with no effective treatment available other than liver transplantation for selected patients. Vascular invasion of HCC is one of the most important negative predictor of survival. As the regulation of invasion of HCC cells is not well understood, our aim was to study the mechanisms by which galectin 3, a β-galactosidase-binding lectin mediates HCC cell migration. HCC was induced by N-diethylnitrosamine in wild-type and galectin 3(-/-) mice, and tumor formation, histology, and tumor cell invasion were assessed. The galectin 3(-/-) mice developed significantly smaller tumor burden with a less invasive phenotype than the wild-type animals. Galectin 3 was upregulated in the wild-type HCC tumor tissue, but not in the surrounding parenchyma. Galectin 3 expression in HCC was induced by NF-κB transactivation as determined by chromatin immunoprecipitation assays. In vitro studies assessed the pro-migratory effects of galectin 3. The migration of hepatoma cells was significantly decreased after transfection by the galectin 3 siRNA and also after using the Rho kinase inhibitor Y-27632. The reorganization of the actin cytoskeleton, RhoA GTPase activity and the phosphorylation of MLC2 (myosin light chain 2) were decreased in the galectin 3 siRNA-transfected cells. In addition, in vitro and in vivo evidence showed that galectin 3 deficiency reduced hepatoma cell proliferation and increased their apoptosis rate. In conclusion, galectin 3 is an important lectin that is induced in HCC cells, and promotes hepatoma cell motility and invasion by an autocrine pathway. Targeting galectin 3 therefore could be an important novel treatment strategy to halt disease progression.

Cardiac glycoside activities link Na(+)/K(+) ATPase ion-transport to breast cancer cell migration via correlative SAR

The cardiac glycosides ouabain and digitoxin, established Na⁺/K⁺ ATPase inhibitors, were found to inhibit MDA-MB-231 breast cancer cell migration through an unbiased chemical genetics screen for cell motility. The Na⁺/K⁺ ATPase acts both as an ion-transporter and as a receptor for cardiac glycosides. To delineate which function is related to breast cancer cell migration, structure–activity relationship (SAR) profiles of cardiac glycosides were established at the cellular (cell migration inhibition), molecular (Na⁺/K⁺ ATPase inhibition), and atomic (computational docking) levels. The SAR of cardiac glycosides and their analogs revealed a similar profile, a decrease in potency when the parent cardiac glycoside structure was modified, for each activity investigated. Since assays were done at the cellular, molecular, and atomic levels, correlation of SAR profiles across these multiple assays established links between cellular activity and specific protein–small molecule interactions. The observed antimigratory effects in breast cancer cells are directly related to the inhibition of Na⁺/K⁺ transport. Specifically, the orientation of cardiac glycosides at the putative cation permeation path formed by transmembrane helices αM1–M6 correlates with the Na⁺ pump activity and cell migration. Other Na⁺/K⁺ ATPase inhibitors that are structurally distinct from cardiac glycosides also exhibit antimigratory activity, corroborating the conclusion that the antiport function of Na⁺/K⁺ ATPase and not the receptor function is important for supporting the motility of MDA-MB-231 breast cancer cells. Correlative SAR can establish new relationships between specific biochemical functions and higher-level cellular processes, particularly for proteins with multiple functions and small molecules with unknown or various modes of action.

Rapid Microwave-Assisted Synthesis of N-Aryl 1,2,3,4-Tetrahydroisoquinolines

N-aryl 1,2,3,4-tetrahydroisoquinolines were prepared rapidly in good yields by the microwave-assisted Pd-catalysed coupling of (hetero)aryl iodides or bromides with 1,2,3,4-tetrahydroisoquinoline. Reactions were typically complete within 5 min for aryl iodides and within 30 min for pyridyl bromides.

Recent advances toward the development of inhibitors to attenuate tumor metastasis via the interruption of lectin-ligand interactions

Aberrant glycosylation is a well-recognized phenomenon that occurs on the surface of tumor cells, and the overexpression of a number of ligands (such as TF, sialyl Tn, and sialyl Lewis X) has been correlated to a worse prognosis for the patient. These unique carbohydrate structures play an integral role in cell-cell communication and have also been associated with more metastatic cancer phenotypes, which can result from binding to lectins present on cell surfaces. The most well studied metastasis-associated lectins are the galectins and selectins, which have been correlated to adhesion, neoangiogenesis, and immune-cell evasion processes. In order to slow the rate of metastatic lesion formation, a number of approaches have been successfully developed which involve interfering with the tumor lectin-substrate binding event. Through the generation of inhibitors, or by attenuating lectin and/or carbohydrate expression, promising results have been observed both in vitro and in vivo. This article briefly summarizes the involvement of lectins in the metastatic process and also describes different approaches used to prevent these undesirable carbohydrate-lectin binding events, which should ultimately lead to improvement in current cancer therapies.

In-vitro Antiproliferative Activity of New Tetrahydroisoquinolines (THIQs) on Ishikawa Cells and their 3D Pharmacophore Models

The antiproliferative activities of new substituted tetrahydroisoquinolines (THIQs) are described. Their cytotoxicities against Ishikawa human endometrial cell line were determined after 72 h drug expose employing Celtiter-Glo assay at concentrations ranging from 0.01 to 100,000 nM. The antiproliferative activities of the compounds understudy were compared to tamoxifen (TAM). In-vitro results indicated that most of the compounds showed better activity than TAM. The most active compounds obtained in this study were 1, 2, 3 and 22 whose IC₅₀ values are 1.41, 0.91, 0.74 and 0.36 μM respectively. This study helped us to evaluate the risk of developing endometrial cancer in the design of non-steroid estrogen receptor modulators with no agonistic effects on uterus. In-silico pharmacophore hypotheses were generated using GALAHAD and PHASE and the best models with a probable bioactive conformation(s) for these compounds were proposed. These conformations and the alignments of the molecular structures give us an insight in designing compounds with better biological activity.

Target identification of bioactive compounds

To fully understand the regulation of cellular events, functional analysis of each protein involved in the regulatory systems is required. Among a variety of methods to uncover protein function, chemical genetics is a remarkable approach in which small molecular compounds are used as probes to elucidate protein functions within signaling pathways. However, identifying the target of small molecular bioactive compounds isolated by cell-based assays represents a crucial hurdle that must be overcome before chemical genetic studies can commence. A variety of methods and technologies for identifying target proteins have been reported. This review therefore aims to describe approaches for identifying these molecular targets.

A synthetic route to highly substituted 1,2,3,4-tetrahydroisoquinolines via Yb(OTf)3 -catalyzed diastereoselective ring opening of bridged oxazolidines: asymmetric synthesis of 2-azapodophyllotoxin

We herein report a robust and efficient synthetic route to highly functionalized enantiopure 1,2,3,4-tetrahydroisoquinolines (THIQs) from Garner aldehyde. We utilized the inherent chirality of Garner aldehyde through 1,2- and 1,3-/1,4-asymmetric inductions iteratively to obtain 1,2,3,4-tetrasubstitued THIQs using rigid and isolable bridged oxazolidines without any external chiral sources. All possible stereoisomers of bridged oxazoliodines were efficiently synthesized from L- and D-Garner aldehydes and transformed into fully functionalized THIQs via diastereoselective ring opening with various nucleophiles in the presence of Yb(OTf)(3). This methodology furnished four out of eight possible diastereomers of 1,2,3,4-tetrasubstituted THIQs despite the electronic nature of substituents on the aryl rings. Finally, the enantioselective synthesis of 2-azapodophyllotoxin was achieved with an overall yield of 35.4% (eight steps) from D-Garner aldehyde using this synthetic route.

G protein-coupled receptor kinase 2 activates radixin, regulating membrane protrusion and motility in epithelial cells

Ezrin/radixin/moesin (ERM) proteins are membrane-cytoskeleton linkers that also have roles in signal transduction. Here we show that G protein-coupled receptor kinase 2 (GRK2) regulates membrane protrusion and cell migration during wound closure in Madin-Darby canine kidney (MDCK) epithelial cell monolayers at least partly through activating phosphorylation of radixin on a conserved, regulatory C-terminal Thr residue. GRK2 phosphorylated radixin exclusively on Thr 564 in vitro. Expression of a phosphomimetic (Thr-564-to-Asp) mutant of radixin resulted in increased Rac1 activity, membrane protrusion and cell motility in MDCK cells, suggesting that radixin functions "upstream" of Rac1, presumably as a scaffolding protein. Phosphorylation of ERM proteins was highest during the most active phase of epithelial cell sheet migration over the course of wound closure. In view of these results, we explored the mode of action of quinocarmycin/quinocarcin analog DX-52-1, an inhibitor of cell migration and radixin function with considerable selectivity for radixin over the other ERM proteins, finding that its mechanism of inhibition of radixin does not appear to involve binding and antagonism at the site of regulatory phosphorylation.