Targeting S100B with Peptides Encoding Intrinsic Aggregation-Prone Sequence Segments.

S100 proteins assume a diversity of oligomeric states including large order self-assemblies, with an impact on protein structure and function. Previous work has uncovered that S100 proteins, including S100B, are prone to undergo ß-aggregation under destabilizing conditions. This propensity is encoded in aggregation-prone regions (APR) mainly located in segments at the homodimer interface, and which are therefore mostly shielded from the solvent and from deleterious interactions, under native conditions. As in other systems, this characteristic may be used to develop peptides with pharmacological potential that selectively induce the aggregation of S100B through homotypic interactions with its APRs, resulting in functional inhibition through a loss of function. Here we report initial studies towards this goal. We applied the TANGO algorithm to identify specific APR segments in S100B helix IV and used this information to design and synthesize S100B-derived APR peptides. We then combined fluorescence spectroscopy, transmission electron microscopy, biolayer interferometry, and aggregation kinetics and determined that the synthetic peptides have strong aggregation propensity, interact with S100B, and may promote co-aggregation reactions. In this framework, we discuss the considerable potential of such APR-derived peptides to act pharmacologically over S100B in numerous physiological and pathological conditions, for instance as modifiers of the S100B interactome or as promoters of S100B inactivation by selective aggregation.

Specificity of Molecular Fragments Binding to S100B versus S100A1 as Identified by NMR and Site Identification by Ligand Competitive Saturation (SILCS).

S100B, a biomarker of malignant melanoma, interacts with the p53 protein and diminishes its tumor suppressor function, which makes this S100 family member a promising therapeutic target for treating malignant melanoma. However, it is a challenge to design inhibitors that are specific for S100B in melanoma versus other S100-family members that are important for normal cellular activities. For example, S100A1 is most similar in sequence and structure to S100B, and this S100 protein is important for normal skeletal and cardiac muscle function. Therefore, a combination of NMR and computer aided drug design (CADD) was used to initiate the design of specific S100B inhibitors. Fragment-based screening by NMR, also termed "SAR by NMR," is a well-established method, and was used to examine spectral perturbations in 2D [1H, 15N]-HSQC spectra of Ca2+-bound S100B and Ca2+-bound S100A1, side-by-side, and under identical conditions for comparison. Of the 1000 compounds screened, two were found to be specific for binding Ca2+-bound S100A1 and four were found to be specific for Ca2+-bound S100B, respectively. The NMR spectral perturbations observed in these six data sets were then used to model how each of these small molecule fragments showed specificity for one S100 versus the other using a CADD approach termed Site Identification by Ligand Competitive Saturation (SILCS). In summary, the combination of NMR and computational approaches provided insight into how S100A1 versus S100B bind small molecules specifically, which will enable improved drug design efforts to inhibit elevated S100B in melanoma. Such a fragment-based approach can be used generally to initiate the design of specific inhibitors for other highly homologous drug targets.

Interfering with S100B-effector protein interactions for cancer therapy.

S100 calcium-binding protein B (S100B) is overexpressed in various malignant tumors, where it regulates cancer cell proliferation and metabolism by physical interactions with other molecules. Interfering with S100B-effector protein interactions is a potential strategy to treat malignant tumors. Although some S100B inhibitors have been discovered by virtual screening (VS), most target the S100B-p53 interaction. Hence, there is scope for the discovery of other S100B-effector protein interaction modulators for malignant tumors. In this review, we provide an overview of S100B-effector protein interaction inhibitor discovery using VS and discuss promising S100B-effector protein interaction targets that permit in silico analysis for drug discovery.

The effects of vitamin-rich carbohydrate pretreatment on the surgical stress response and S-100ß after splenectomy in elderly rats.

BACKGROUND: Preoperative oral carbohydrates has been suggested to attenuate insulin resistance and decrease postoperative complications. In this study, a vitamin-rich carbohydrate beverage was administered before surgery in an animal model to investigate its effects on the surgical stress response and S-100ß levels. METHODS: Thirty aged male Sprague-Dawley rats were randomly assigned to three groups: control group (n = 6), fasting group (n = 12), and carbohydrate-treated group (CHO group, n = 12). Rats in the control group were not given any treatment. Rats in the fasting group received splenectomy after 12 h of fasting. In the CHO group, rats were given 5 ml of vitamin-rich carbohydrate by gavage 2 h before surgery. Fasting plasma glucose, insulin, insulin resistance (HOMA-IR index, IRI), the S-100ß protein level, and the inflammatory mediators IL-1ß, IL-6 and TNF-α were assessed after surgery (postoperative day (POD) 1 and 3). RESULTS: Postoperative insulin resistance was significantly greater in the fasting group than in the control and CHO group. The median plasma S-100ß level was significantly higher in the fasting group than in the control and CHO groups on POD 1. The median plasma IL-1ß level was significantly lower in the CHO group than in the fasting group on POD 1; however, no other differences in the concentrations of immunological biomarkers of stress were found between the fasting group and the CHO group. CONCLUSIONS: Vitamin-rich carbohydrate pretreatment attenuated the metabolic aspect of the surgical stress response and decreased the level of plasma S-100ß, which may decrease the risk of postoperative complications in elderly rats.

S100B suppression alters polarization of infiltrating myeloid-derived cells in gliomas and inhibits tumor growth.

S100B, a member of the multigene family of Ca2+-binding proteins, is overexpressed by most malignant gliomas but its biological role in gliomagenesis is unclear. Recently, we demonstrated that low concentrations of S100B attenuated microglia activation through the induction of STAT3. Furthermore, S100B downregulation in a murine glioma model inhibited macrophage trafficking and tumor growth. Based on these observations, we hypothesized that S100B inhibitors may have antiglioma properties through modulation of tumor microenvironment. To discover novel S100B inhibitors, we developed a high-throughput screening cell-based S100B promoter-driven luciferase reporter assay. Initial screening of 768 compounds in the NIH library identified 36 hits with >85% S100B inhibitory activity. Duloxetine (Dul, an SNRI) was selected for the initial proof-of-concept studies. At low concentrations (1-5 µM) Dul inhibited S100B and CCL2 production in mouse GL261 glioma cells, but had minimal cytotoxic activity in vitro. In vivo, however, Dul (30 mg/kg/14 days) inhibited S100B production, altered the polarization and trafficking of tumor-associated myeloid-derived cells, and inhibited the growth of intracranial GL261 gliomas. Dul therapeutic efficacy, however, was not observed in the K-Luc glioma model that expresses low levels of S100B. These findings affirm the role of S100B in gliomagenesis and justify the development of more potent S100B inhibitors for glioma therapy.

Identifying S100B as a Biomarker and a Therapeutic Target For Brain Injury and Multiple Diseases.

The calcium binding protein S100B has attracted great attention as a biomarker for a variety of diseases. S100B is mainly expressed in glial cells and functions through intracellular and extracellular signaling pathways. The biological roles of S100B have been closely associated with its concentrations and its physiological states. The released S100B can bind to the receptor of advanced glycation end products and induce the initiation of multiple cell signaling transductions. The regulation of S100B bioactivities has been suggested through phosphoinositide 3 kinase/Akt, p53, mitogen-activated protein kinases, transcriptional factors including nuclear factor-kappaB, and cyclic adenosine monophosphate. The levels of S100B in the blood may function to predict the progress or the prognosis of many kinds of diseases, such as cerebrovascular diseases, neurodegenerative diseases, motor neuron diseases, traumatic brain injury, schizophrenia, depression, diabetes mellitus, myocardial infarction, cancer, and infectious diseases. Given that the activity of S100B has been implicated in the pathological process of these diseases, S100B should not be simply regarded as a biomarker, it may also function as therapeutic target for these diseases. Further elucidation of the roles of S100B may formulate innovative therapeutic strategies for multiple diseases.

Small Molecule Inhibitors of Ca(2+)-S100B Reveal Two Protein Conformations.

The drug pentamidine inhibits calcium-dependent complex formation with p53 ((Ca)S100B·p53) in malignant melanoma (MM) and restores p53 tumor suppressor activity in vivo. However, off-target effects associated with this drug were problematic in MM patients. Structure-activity relationship (SAR) studies were therefore completed here with 23 pentamidine analogues, and X-ray structures of (Ca)S100B·inhibitor complexes revealed that the C-terminus of S100B adopts two different conformations, with location of Phe87 and Phe88 being the distinguishing feature and termed the "FF-gate". For symmetric pentamidine analogues ((Ca)S100B·5a, (Ca)S100B·6b) a channel between sites 1 and 2 on S100B was occluded by residue Phe88, but for an asymmetric pentamidine analogue ((Ca)S100B·17), this same channel was open. The (Ca)S100B·17 structure illustrates, for the first time, a pentamidine analog capable of binding the "open" form of the "FF-gate" and provides a means to block all three "hot spots" on (Ca)S100B, which will impact next generation (Ca)S100B·p53 inhibitor design.

S100B Inhibitor Pentamidine Attenuates Reactive Gliosis and Reduces Neuronal Loss in a Mouse Model of Alzheimer's Disease.

Among the different signaling molecules released during reactive gliosis occurring in Alzheimer's disease (AD), the astrocyte-derived S100B protein plays a key role in neuroinflammation, one of the hallmarks of the disease. The use of pharmacological tools targeting S100B may be crucial to embank its effects and some of the pathological features of AD. The antiprotozoal drug pentamidine is a good candidate since it directly blocks S100B activity by inhibiting its interaction with the tumor suppressor p53. We used a mouse model of amyloid beta- (Aß-) induced AD, which is characterized by reactive gliosis and neuroinflammation in the brain, and we evaluated the effect of pentamidine on the main S100B-mediated events. Pentamidine caused the reduction of glial fibrillary acidic protein, S100B, and RAGE protein expression, which are signs of reactive gliosis, and induced p53 expression in astrocytes. Pentamidine also reduced the expression of proinflammatory mediators and markers, thus reducing neuroinflammation in AD brain. In parallel, we observed a significant neuroprotection exerted by pentamidine on CA1 pyramidal neurons. We demonstrated that pentamidine inhibits Aß-induced gliosis and neuroinflammation in an animal model of AD, thus playing a role in slowing down the course of the disease.

Covalent small molecule inhibitors of Ca(2+)-bound S100B.

Elevated levels of the tumor marker S100B are observed in malignant melanoma, and this EF-hand-containing protein was shown to directly bind wild-type (wt) p53 in a Ca(2+)-dependent manner, dissociate the p53 tetramer, and inhibit its tumor suppression functions. Likewise, inhibiting S100B with small interfering RNA (siRNA(S100B)) is sufficient to restore wild-type p53 levels and its downstream gene products and induce the arrest of cell growth and UV-dependent apoptosis in malignant melanoma. Therefore, it is a goal to develop S100B inhibitors (SBiXs) that inhibit the S100B-p53 complex and restore active p53 in this deadly cancer. Using a structure-activity relationship by nuclear magnetic resonance approach (SAR by NMR), three persistent binding pockets are found on S100B, termed sites 1-3. While inhibitors that simultaneously bind sites 2 and 3 are in place, no molecules that simultaneously bind all three persistent sites are available. For this purpose, Cys84 was used in this study as a potential means to bridge sites 1 and 2 because it is located in a small crevice between these two deeper pockets on the protein. Using a fluorescence polarization competition assay, several Cys84-modified S100B complexes were identified and examined further. For five such SBiX-S100B complexes, crystallographic structures confirmed their covalent binding to Cys84 near site 2 and thus present straightforward chemical biology strategies for bridging sites 1 and 3. Importantly, one such compound, SC1982, showed an S100B-dependent death response in assays with WM115 malignant melanoma cells, so it will be particularly useful for the design of SBiX molecules with improved affinity and specificity.

The role of S100B in the interaction between adipocytes and macrophages.

OBJECTIVE: The S100 calcium binding protein B (S100B) implicated in brain inflammation acts via the receptor of advanced glycation end products (RAGE) and is also secreted from adipocytes. We investigated the role of S100B in the interaction between adipocytes and macrophages using a cell-culture model. DESIGN AND METHODS: RAW264.7 macrophages (RAW) were stimulated by recombinant S100B to observe alterations in TNF-α and M1 markers; 3T3-L1 adipocytes (L1) were stimulated by TNF-α to examine S100B secretion. RAW and L1 were then mutually stimulated with conditioned media of each other, or co-cultured. The effects of S100B silencing or a RAGE-neutralizing antibody were also investigated. RESULTS: S100B upregulated TNF-α and M1 markers in RAW, and TNF-α augmented S100B secretion from L1. L1 conditioned media stimulated TNF-α secretion from RAW, and RAW conditioned media increased S100B secretion from L1. The co-culture of RAW and L1 increased TNF-α, S100B, and the expression of M1 markers and the MCP-1 receptor CCR2. The silencing of S100B or RAGE neutralization significantly ameliorated TNF-α hypersecretion from RAW that were stimulated with L1 conditioned media. CONCLUSIONS: Thus, S100B as an adipokine may play a role in the interaction between adipocytes and macrophages to establish a vicious paracrine loop.

Lipoic acid protects C6 cells against ammonia exposure through Na⁺-K⁺-Cl⁻ co-transporter and PKC pathway.

Astrocytes play an essential role in the central nervous system (CNS) homeostasis. They providing metabolic support and protecting against oxidative stress and glutamatergic excitotoxicity. Glutamate uptake, an electrogenic function, is driven by cation gradients and the Na⁺-K⁺-Cl⁻ co-transporter (NKCC1) carries these ions into and out of the cell. Elevated concentrations of ammonia in the brain lead to cerebral dysfunction. Ammonia toxicity can be mediated by an excitotoxic mechanism, oxidative stress and ion discharged. Astrocytes also convert excess ammonia and glutamate into glutamine, via glutamine synthetase (GS). Lipoic acid (LA) is a modulator of the cellular redox status potentially beneficial in neurodegenerative diseases. In this study, we investigated the effect of LA on glial parameters, in C6 cells exposed to ammonia. Ammonia increased S100B secretion and decreased glutamate uptake, GS activity and glutathione (GSH) content. LA was able to prevent these effects. LA exerts its protective effect on glutamate uptake and S100B secretion via mechanisms dependent of NKCC1 and PKC. These findings show that LA is able to modulate glial function impairments by ammonia in vitro, indicating a potential therapeutic agent to improve glutamatergic metabolism and oxidative stress against hyperammonemia.

S100B promotes glioma growth through chemoattraction of myeloid-derived macrophages.

PURPOSE: S100B is member of a multigenic family of Ca(2+)-binding proteins, which is overexpressed by gliomas. Recently, we showed that low concentrations of S100B attenuated microglia activation through the induction of Stat3. We hypothesized that overexpression of S100B in gliomas could promote tumor growth by modulating the activity of tumor-associated macrophages (TAM). EXPERIMENTAL DESIGN: We stably transfected GL261 glioma cell lines with constructs that overexpressed (S100B(high)) or underexpressed (S100B(low)) S100B and compared their growth characteristics to intracranial wild-type (S100B(wt)) tumors. RESULTS: Downregulation of S100B in gliomas had no impact on cell division in vitro but abrogated tumor growth in vivo. Interestingly, compared to S100B(low) tumors, S100B(wt) and S100B(high) intracranial gliomas exhibited higher infiltration of TAMs, stronger inflammatory cytokine expression, and increased vascularity. To identify the potential mechanisms involved, the expression of the S100B receptor, receptor for advanced glycation end products (RAGE), was evaluated in gliomas. Although S100B expression induced RAGE in vivo, RAGE ablation in mice did not significantly inhibit TAM infiltration into gliomas, suggesting that other pathways were involved in this process. To evaluate other mechanisms responsible for TAM chemoattraction, we then examined chemokine pathways and found that C-C motif ligand 2 (CCL2) was upregulated in S100B(high) tumors. Furthermore, analysis of The Cancer Genome Atlas's glioma data bank showed a positive correlation between S100B and CCL2 expression in human proneural and neural glioma subtypes, supporting our finding. CONCLUSIONS: These observations suggest that S100B promotes glioma growth by TAM chemoattraction through upregulation of CCL2 and introduces the potential utility of S100B inhibitors for glioma therapy.

Tetrandrine ameliorates cognitive impairment via inhibiting astrocyte-derived S100B activation in a rat model of chronic cerebral hypoperfusion.

OBJECTIVES: To investigate the effects of tetrandrine (Tet) on cognitive impairment induced by chronic cerebral hypoperfusion and its potential anti-inflammatory mechanism by modulating the expression of S100B, interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS). METHODS: Chronic cerebral hypoperfusion was induced by ligation of the bilateral common carotid arteries for 8 weeks. Rats were treated with Tet (10 mg/kg or 30 mg/kg) intraperitoneally every 3 days for 4 weeks. Cognitive function of rats was evaluated by the Morris water maze. Hematoxylin eosin (H & E) and Nissl staining were used to observe neuronal damage in the hippocampal CA1 region. Immunofluorescence, quantitative real-time polymerase chain reaction (QT-PCR), and western blot were performed to measure S100B, IL-1 beta, TNF-alpha, and iNOS levels in the CA1 region of chronic cerebral hypoperfusion rats. RESULTS: The Tet-treated group significantly decreased the escape latency of chronic cerebral hypoperfusion rats in finding the hidden platform (P <0.05). Compared with the 2-VO (two-vessel occlusion) group, more neurons with regular morphology and/or Nissl bodies in the hippocampus were observed in the Tet-treated group, suggesting attenuated neuronal damage and degeneration. Additionally, S100B, IL-1 beta, TNF-alpha, and iNOS levels were significantly (P <0.05) decreased in the CA1 region of the chronic cerebral hypoperfusion affected rats treated with Tet. CONCLUSION: Our results found that Tet could improve cognitive impairment in the chronic cerebral hypoperfusion rats. Tetrandrine may be a novel and promising candidate for future treatment and/or prevention of chronic cerebral hypoperfusion via inhibiting S100B activation and decreasing the expression of IL-1 beta, TNF-alpha, and iNOS in the hippocampal CA1 region.