Power of Dopamine: Multifunctional Compound Assisted Conversion of the Most Risk Factor into Therapeutics of Alzheimer's Disease.

In Alzheimer's disease (AD), reactive oxygen species (ROS) plays a crucial role, which is produced from molecular oxygen with extracellular deposited amyloid-ß (Aß) aggregates through the reduction of a Cu2+ ion. In the presence of a small amount of redox-active Cu2+ ion, ROS is produced by the Aß-Cu2+ complex as Aß peptide alone is unable to generate excess ROS. Therefore, Cu2+ ion chelators are considered promising therapeutics against AD. Here, we have designed and synthesized a series of Schiff base derivatives (SB) based on 2-hydroxy aromatic aldehyde derivatives and dopamine. These SB compounds contain one copper chelating core, which captures the Cu2+ ions from the Aß-Cu2+ complex. Thereby, it inhibits copper-induced amyloid aggregation as well as amyloid self-aggregation. It also inhibits copper-catalyzed ROS production through sequestering of Cu2+ ions. The uniqueness of our designed ligands has the dual property of dopamine, which not only acts as a ROS scavenger but also chelates the copper ion. The crystallographic analysis proves the power of the dopamine unit. Therefore, dual exploration of dopamine core can be considered as potential therapeutics for future AD treatment.

Short Peptoid Evolved from the Key Hydrophobic Stretch of Amyloid-ß42 Peptide Serves as a Potent Therapeutic Lead of Alzheimer's Disease.

Amyloid-ß 42(Aß42), an enzymatically cleaved (1-42 amino acid long) toxic peptide remnant, has long been reported to play the key role in Alzheimer's disease (AD). Aß42 also plays the key role in the onset of other AD-related factors including hyperphosphorylation of tau protein that forms intracellular neurofibrillary tangles, imbalances in the function of the neurotransmitter acetylcholine, and even generation of reactive oxygen species (ROS), disrupting the cytoskeleton and homeostasis of the cell. To address these issues, researchers have tried to construct several strategies to target multiple aspects of the disease but failed to produce any clinically successful therapeutic molecules. In this article, we report a new peptoid called RA-1 that was designed and constructed from the hydrophobic stretch of the Aß42 peptide, 16KLVFFA21. This hydrophobic stretch is primarily responsible for the Aß42 peptide aggregation. Experimental study showed that the RA-1 peptoid is stable under proteolytic conditions, can stabilize the microtubule, and can inhibit the formation of toxic Aß42 aggregates by attenuating hydrophobic interactions between Aß42 monomers. Furthermore, results from various intracellular assays showed that RA-1 inhibits Aß42 fibril formation caused by the imbalance in AchE activity, reduces the production of cytotoxic reactive oxygen species (ROS), and promotes neurite outgrowth even in the toxic environment. Remarkably, we have also demonstrated that our peptoid has significant ability to improve the cognitive ability and memory impairment in in vivo rats exposed to AlCl3 and d-galactose (d-gal) dementia model. These findings are also validated with histological studies. Overall, our newly developed peptoid emerges as a multimodal potent therapeutic lead molecule against AD.

Design and Development of Benzothiazole-Based Fluorescent Probes for Selective Detection of Aß Aggregates in Alzheimer's Disease.

The formation and accumulation of amyloid beta (Aß) peptide are considered the crucial events that are responsible for the progression of Alzheimer's disease (AD). Herein, we have designed and synthesized a series of fluorescent probes by using electron acceptor-donor end groups interacting with a π-conjugating system for the detection of Aß aggregates. The chemical structure of these probes denoted as RMs, having a conjugated π-system (C═C), showed a maximum emission in PBS (>600 nm), which is the best range for a fluorescent imaging probe. Among all these probes, RM-28 showed an excellent fluorescence property with an emission maximum of >598 nm upon binding to Aß aggregates. RM-28 also showed high sensitivity (7.5-fold) and high affinities toward Aß aggregates (Kd = 175.69 ± 4.8 nM; Ka = 0.5 × 107 M-1). It can cross the blood-brain barrier of mice efficiently. The affinity of RM-28 toward Aß aggregates was observed in 3xTg-AD brain sections of the hippocampus and cortex region using a fluorescent imaging technique, as well as an in vitro fluorescence-based binding assay with Aß aggregates. Moreover, RM-28 is highly specific to Aß aggregates and does not bind with intracellular proteins like bovine serum albumin (BSA) and α-synuclein (α-Syn) aggregates. The results indicate that the probe RM-28 emerges as an efficient and veritable highly specific fluorescent probe for the detection of Aß aggregates in both in vitro and in vivo model systems.

Human Serum Albumin-Inspired Glycopeptide-Based Multifunctional Inhibitor of Amyloid-ß Toxicity.

In Alzheimer's disease (AD), insoluble Aß42 peptide fragments self-aggregate and form oligomers and fibrils in the brain, causing neurotoxicity. Further, the presence of redox-active metal ions such as Cu2+ enhances the aggregation process through chelation with these Aß42 aggregates as well as generation of Aß42-mediated reactive oxygen species (ROS). Herein, we have adopted a bioinspired strategy to design and develop a multifunctional glycopeptide hybrid molecule (Glupep), which can serve as a potential AD therapeutic. This molecule consists of a natural metal-chelating tetrapeptide motif of human serum albumin (HSA), a ß-sheet breaker peptide, and a sugar moiety for better bioavailability. We performed different biophysical and docking experiments, which revealed that Glupep not only associates with Aß42 but also prevents its self-aggregation to form toxic oligomers and fibrils. Moreover, Glupep was also shown to sequester out Cu2+ from the Aß-Cu2+ complex, reducing the ROS formation and toxicity. Besides, this study also revealed that Glupep could protect PC12-derived neurons from Aß-Cu2+-mediated toxicity by reducing intracellular ROS generation and stabilizing the mitochondrial membrane potential. All these exciting features show Glupep to be a potent inhibitor of Aß42-mediated multifaceted toxicity and a prospective therapeutic lead for AD.

Rhodamine-Based Metal Chelator: A Potent Inhibitor of Metal-Catalyzed Amyloid Toxicity.

Alzheimer's disease (AD) exhibits a multitude of syndromes which add up to its complex nature. In AD, amyloid plaques are deposited along with abnormal accumulation of transition-metal ions. These transition-metal ions are redox-active and help to induce the formation of various polymorphic forms of amyloid-ß. Amyloid oligomeric and fibrillar aggregates are the main cause for neuronal toxicity. Another reason for neuronal toxicity arises from generation of reactive oxygen species (ROS) catalyzed by redox-active metal ions through Fenton's reaction. In this direction, an Aß inhibitor possessing the metal chelation property will be the most promising approach against multifaceted AD. Herein, a rhodamine-B-based compound (Rh-BT) has been designed and synthesized. Rhodamine was attached with benzothiazole as a recognition unit for amyloid-ß aggregates. The molecule can effectively capture redox metal ions from the Aß-Cu2+ complex as well as inhibit Aß self-assembly such as toxic oligomeric and fibrillar aggregates. Various biophysical assays show that Rh-BT interacts with the Aß peptide, is capable of decreasing metal-induced ROS generation, and inhibits Aß-Cu2+-induced cytotoxicity. All these results support the multifunctional nature of Rh-BT, which has an Aß-specific recognition unit. In addition to the above properties, Rh-BT also exhibits good serum stability in vivo and blood-brain barrier permeability. Therefore, Rh-BT can be considered as a potent multifunctional therapeutic for the treatment of AD.

Potential Neuroprotective Peptide Emerged from Dual Neurotherapeutic Targets: A Fusion Approach for the Development of Anti-Alzheimer's Lead.

Amyloid-beta (Aß) peptide misfolds into fibrillary aggregates (ß-sheet) and is deposited as amyloid plaques in the cellular environment, which severely damages intraneuronal connections leading to Alzheimer's disease (AD) pathogenesis. Furthermore, neurons are rich in tubulin/microtubules, and the intracellular network of microtubules also gets disrupted by the accumulation of Aß fiber in the brain. Hence, development of new potent molecules, which can simultaneously inhibit Aß fibrillations and stabilize microtubules, is particularly needed for the efficient therapeutic application in AD. To address these issues, here we introduced an innovative fusion strategy to design and develop next generation anti-AD therapeutic leads. This unexplored fusion strategy entails design and development of a potent nonapeptide by taking into account both the hydrophobic core (17-21) of Aß peptide and the taxol binding region of ß-tubulin. In vitro results suggest that this newly designed peptide interacts at the taxol binding region of ß-tubulin with a moderate binding affinity and promotes microtubule polymerization. It has the ability to bind at the hydrophobic core (17-21) of Aß, responsible for its aggregation, and prevent amyloid fibril as well as plaque formation. In addition, it interacts at the CAS site (catalytic anionic site) of acetylcholinesterase (AChE) and significantly inhibits AChE induced Aß fibrillation, stimulates neurite branching, and provides stability to intracellular microtubules and extensive protection of neurons against nerve growth factor (NGF) deprived neuron toxicity. Moreover, this newly designed peptide shows good stability in serum obtained from humans and efficiently permeates the blood-brain barrier (BBB) without showing any toxicity toward differentiated PC12 neurons as well as primary rat cortical neurons. This excellent feature of protecting the neurons by stabilizing the microtubules without showing any toxicity toward neurons will make this peptide a potent therapeutic agent of AD in the near future.

Tripodal molecular propellers perturb microtubule dynamics: indole acts as a blade and plays a crucial role in anticancer activity.

An indole-rich tripodal microtubule inhibitor is designed, which binds at the DCVJ site of tubulin and inhibits its polymerization. It causes apoptotic death of cancer cells without affecting normal cells and inhibits the growth of tumors. Finally, STD-NMR and TR-NOESY experiments reveal that the indole appendages play a crucial role in interacting with tubulin.

Discovery of Neuroregenerative Peptoid from Amphibian Neuropeptide That Inhibits Amyloid-ß Toxicity and Crosses Blood-Brain Barrier.

Development of potential therapeutics for Alzheimer's disease (AD) requires a multifaceted strategy considering the high levels of complexity of the human brain and its mode of function. Here, we adopted an advanced strategy targeting two key pathological hallmarks of AD: senile plaques and neurofibrillary tangles. We derived a lead short tetrapeptide, Ser-Leu-Lys-Pro (SLKP), from a dodeca-neuropeptide of amphibian (frog) brain. Results suggested that the SLKP peptide had a superior effect compared to the dodecapeptide in neuroprotection. This result encouraged us to adopt peptidomimetic approach to synthesize an SLKP peptoid. Remarkably, we found that the SLKP peptoid is more potent than its peptide analogue, which significantly inhibits Aß fibrillization, moderately binds with tubulin, and promotes tubulin polymerization as well as stabilization of microtubule networks. Further, we found that SLKP peptoid is stable in serum, shows significant neuroprotection against Aß mediated toxicity, promotes significant neurite outgrowth, maintains healthy morphology of rat primary cortical neurons and crosses the blood-brain barrier (BBB). To the best of our knowledge, our SLKP peptoid is the first and shortest peptoid to show significant neuroprotection and neuroregeneration against Aß toxicity, as well as to cross the BBB offering a potential lead for AD therapeutics.

Neuro-Regenerative Choline-Functionalized Injectable Graphene Oxide Hydrogel Repairs Focal Brain Injury.

Brain damage is associated with spatial imbalance of cholinergic system, which makes severe impact in recovery of damaged neurons of brain. Therefore, maintenance of cholinergic system is extremely important. Here, we fabricated an injectable hydrogel with acetylcholine-functionalized graphene oxide and poly(acrylic acid). Results revealed that this hydrogel is non-cytotoxic, promotes neurite outgrowth, stabilizes microtubule networks, and enhances the expression of some key neural markers in rat cortical primary neurons. Further, this hydrogel exhibits significant potential in neuro-regeneration and also promotes fast recovery of the sham injured mice brain. Moreover, we found significant enhancement of reactive astrocytes in the hippocampal dentate gyrus region of the sham injured brain, indicating its excellent potential in neural repair of the damaged brain. Finally, above results clearly indicate that this neuro-regenerative hydrogel is highly capable of maintaining the cholinergic balance through local release of acetylcholine in the injured brain, which is crucial for brain repair.

Power of Tyrosine Assembly in Microtubule Stabilization and Neuroprotection Fueled by Phenol Appendages.

Microtubules play a crucial role in maintenance of structure, function, axonal extensions, cargo transport, and polarity of neurons. During neurodegenerative diseases, microtubule structure and function get severely damaged due to destabilization of its major structural proteins. Therefore, design and development of molecules that stabilize these microtubule networks have always been an important strategy for development of potential neurotherapeutic candidates. Toward this venture, we designed and developed a tyrosine rich trisubstituted triazine molecule (TY3) that stabilizes microtubules through close interaction with the taxol binding site. Detailed structural investigations revealed that the phenolic protons are the key interacting partners of tubulin. Interestingly, we found that this molecule is noncytotoxic in PC12 derived neurons, stabilizes microtubules against nocodazole induced depolymerization, and increases expression of acetylated tubulin (Ac-K40), an important marker of tubulin stability. Further, results show that TY3 significantly induces neurite sprouting as compared to the untreated control as well as the two other analogues (TS3 and TF3). It also possesses anti-Aß fibrillation properties as confirmed by ThT assay, which leads to its neuroprotective effect against amyloidogenic induced toxicity caused through nerve growth factor (NGF) deprivation in PC12 derived neurons. Remarkably, our results reveal that it reduces the expression of TrkA (pY490) associated with NGF deprived amyloidogenesis, which further proves that it is a potent amyloid ß inhibitor. Moreover, it promoted the health of the rat primary cortical neurons through higher expression of key neuronal markers such as MAP2 and Tuj1. Finally, we observed that it has good serum stability and has the ability to cross the blood-brain barrier (BBB). Overall, our work indicates the importance of phenolic -OH in promoting neuroprotection and its importance could be implemented in the development of future neurotherapeutics.

Matrix metalloproteinase targeted peptide vesicles for delivering anticancer drugs.

A matrix metalloproteinase (MMP) targeted tetrapeptide vesicle has been designed and developed, which strongly binds at a MMP9 enzymatic site. Interestingly, it has a propensity to encapsulate and deliver the doxorubicin drug specifically to the cancer cell, induces superior apoptotic death, and inhibits the metastatic cancer cell migration and growth of multicellular 3D spheroids.

Genesis of Neuroprotective Peptoid from Aß30-34 Inhibits Aß Aggregation and AChE Activity.

Aß peptide and hyper-phosphorylated microtubule associated protein (Tau) aggregation causes severe damage to both the neuron membrane and key signal processing microfilament (microtubule) in Alzheimer's disease (AD) brains. To date, the key challenge is to develop nontoxic, proteolytically stable amyloid inhibitors, which can simultaneously target multiple pathways involved in AD. Various attempts have been made in this direction; however, clinical outcomes of those attempts have been reported to be poor. Thus, we choose development of peptoid (N-substituted glycine oligomers)-based leads as potential AD therapeutics, which are easy to synthesize, found to be proteolytically stable, and exhibit excellent bioavailability. In this paper, we have designed and synthesized a new short peptoid for amyloid inhibition from 30-34 hydrophobic pocket of amyloid beta (Aß) peptide. The peptoid selectively binds with 17-21 hydrophobic region of Aß and inhibits Aß fibril formation. Various in vitro assays suggested that our AI peptoid binds with tubulin/microtubule and promotes its polymerization and stability. This peptoid also inhibits AChE-induced Aß fibril formation and provides significant neuroprotection against toxicity generated by nerve growth factor (NGF) deprived neurons derived from rat adrenal pheochromocytoma (PC12) cell line. Moreover, this peptoid shows serum stability and is noncytotoxic to primary rat cortical neurons.

Peptide-Based Acetylcholinesterase Inhibitor Crosses the Blood-Brain Barrier and Promotes Neuroprotection.

Design and development of acetylcholinesterase (AChE) inhibitor has tremendous implications in the treatment of Alzheimer's disease (AD). Here, we have adopted a computational approach for the design of a peptide based AChE inhibitor from its active site. We identified an octapeptide, which interacts with the catalytic anionic site (CAS) of AChE enzyme and inhibits its activity. Interestingly, this peptide also inhibits amyloid aggregation through its interaction at the 17-21 region of amyloid-beta (Aß) and stabilizes microtubules by interacting with tubulin as well. Eventually, in the PC12 derived neurons, it shows noncytotoxicity, promotes neurite out-growth, stabilizes intracellular microtubules, and confers significant neuroprotection even upon withdrawal of nerve growth factor (NGF). Further, results reveal that this peptide possesses good serum stability, crosses the blood-brain barrier (BBB), and maintains the healthy architecture of the primary cortical neurons. This work shows discovery of an excellent peptide-based AChE inhibitor with additional potential as a microtubule stabilizer, which will pave the way for the development of potential anti-AD therapeutics in the near future.

Crafting of Neuroprotective Octapeptide from Taxol-Binding Pocket of ß-Tubulin.

Microtubules play a crucial role in maintaining the shape and function of neurons. During progression of Alzheimer's disease (AD), severe destabilization of microtubules occurs, which leads to the permanent disruption of signal transduction processes and memory loss. Thus, microtubule stabilization is one of the key requirements for the treatment of AD. Taxol, a microtubule stabilizing anticancer drug, has been considered as a potential anti-AD drug but was never tested in AD patients, likely because of its' toxic nature and poor brain exposure. However, other microtubule-targeting agents such as epothilone D (BMS-241027) and TPI-287 (abeotaxane) and NAP peptide (davunetide) have entered in AD clinical programs. Therefore, the taxol binding pocket of tubulin could be a potential site for designing of mild and noncytotoxic microtubule stabilizing molecules. Here, we adopted an innovative strategy for the development of a peptide based microtubule stabilizer, considering the taxol binding pocket of ß-tubulin, by using alanine scanning mutagenesis technique. This approach lead us to a potential octapeptide, which strongly binds to the taxol pocket of ß-tubulin, serves as an excellent microtubule stabilizer, increases the expression of acetylated tubulin, and acts as an Aß aggregation inhibitor and neuroprotective agent. Further, results revealed that this peptide is nontoxic against both PC12 derived neurons and primary cortical neurons. We believe that our strategy and discovery of peptide-based microtubule stabilizer will open the door for the development of potential anti-AD therapeutics in near future.

α-Cyclodextrin Interacts Close to Vinblastine Site of Tubulin and Delivers Curcumin Preferentially to the Tubulin Surface of Cancer Cell.

Tubulin is the key cytoskeleton component, which plays a crucial role in eukaryotic cell division. Many anticancer drugs have been developed targeting the tubulin surface. Recently, it has been shown that few polyhydroxy carbohydrates perturb tubulin polymerization. Cyclodextrin (CD), a polyhydroxy carbohydrate, has been extensively used as the delivery vehicle for delivery of hydrophobic drugs to the cancer cell. However, interaction of CD with intracellular components has not been addressed before. In this Article, we have shown for the first time that α-CD interacts with tubulin close to the vinblastine site using molecular docking and Förster resonance energy transfer (FRET) experiment. In addition, we have shown that α-CD binds with intracellular tubulin/microtubule. It delivers a high amount of curcumin onto the cancer cell, which causes severe disruption of intracellular microtubules. Finally, we have shown that the inclusion complex of α-CD and curcumin (CCC) preferentially enters into the human lung cancer cell (A549) as compared to the normal lung fibroblast cell (WI38), causes apoptotic death, activates tumor suppressor protein (p53) and cyclin-dependent kinase inhibitor 1 (p21), and inhibits 3D spheroid growth of cancer cell.

A short GC rich DNA derived from microbial origin targets tubulin/microtubules and induces apoptotic death of cancer cells.

A short GC rich DNA derived from microbial origin interacts with tubulin/microtubules activates p53 over expression and induces apoptotic death of human breast cancer (MCF-7) cells.