Ratiometric Fluorescent Probe Promotes Trans-differentiation of Human Mesenchymal Stem Cells to Neurons.

Development of multifunctional theranostics is challenging and crucial for deciphering complex biological phenomena and subsequently treating critical disease. In particular, development of theranostics for traumatic brain injury (TBI) and understanding its repair mechanism are challenging and highly complex areas of research. Recently, there have been interesting pieces of research work demonstrated that a small molecule-based neuroregenerative approach using stem cells has potential for future therapeutic lead development for TBI. However, these works demonstrated the application of a mixture of multiple molecules as a "chemical cocktail", which may have serious toxic effects in the differentiated cells. Therefore, development of a single-molecule-based potential differentiating agent for human mesenchymal stem cells (hMSCs) into functional neurons is vital for the upcoming neuro-regenerative therapeutics. This lead could be further extraploted for the design of theranostics for TBI. In this study, we have developed a multifunctional single-molecule-based fluorescent probe, which can image the transdifferentiated neurons as well as promote the differentiation process. We demonstrated a promising class of fluorescent probes (CP-4) that can be employed to convert hMSCs into neurons in the presence of fibroblast growth factor (FGF). This fluorescent probe was used in cellular imaging as its fluorescence intensity remained unaltered for up to 7 days of trans-differentiation. We envision that this imaging probe can have an important application in the study of neuropathological and neurodegenerative studies.

Controlling Amyloid Beta Peptide Aggregation and Toxicity by Protease-Stable Ligands.

Polymerization of soluble amyloid beta (Aß) peptide into protease-stable insoluble fibrillary aggregates is a critical step in the pathogenesis of Alzheimer's disease (AD). The N-terminal (NT) hydrophobic central domain fragment 16KLVFF20 plays an important role in the formation and stabilization of ß-sheets by self-recognition of the parent Aß peptide, followed by aggregation of Aß in the AD brain. Here, we analyze the effect of the NT region inducing ß-sheet formation in the Aß peptide by a single amino acid mutation in the native Aß peptide fragment. We designed 14 hydrophobic peptides (NT-01 to NT-14) by a single mutation at 18Val by using hydrophobic residues leucine and proline in the natural Aß peptide fragment (KLVFFAE) and analyzed its effect on the formation of Aß aggregates. Among all these peptides, NT-02, NT-03, and NT-13 significantly affected the Aß aggregate formation. When the NT peptides were coincubated with the Aß peptide, a significant reduction in ß-sheet formation and increment in random coil content of Aß was seen, confirmed by circular dichroism spectroscopy and Fourier transform infrared spectroscopy, followed by the reduction of fibril formation measured by the thioflavin-T (ThT) binding assay. The aggregation inhibition was monitored by Congo red and ThT staining and electron microscopic examination. Moreover, the NT peptides protect the PC-12 differentiated neurons from Aß-induced toxicity and apoptosis in vitro. Thus, manipulation of the Aß secondary structure with protease-stable ligands that promote the random coil conformation may provide a tool to control the Aß aggregates observed in AD patients.

High-Affinity Fluorescent Probes for the Detection of Soluble and Insoluble Aß Deposits in Alzheimer's Disease.

The overproduction and deposition of the amyloid-ß (Aß) aggregates are accountable for the genesis and development of the neurologic disorder Alzheimer's disease (AD). Effective medications and detection agents for AD are still deficient. General challenges for the diagnosis of Aß aggregates in the AD brain are (i) crossing the blood-brain barrier (BBB) and (ii) selectivity to Aß species with (iii) emission maxima in the 500-750 nm region. Thioflavin-T (ThT) is the most used fluorescent probe for imaging Aß fibril aggregates. However, because of the poor BBB crossing (log P = -0.14) and short emission wavelength (482 nm) after binding with Aß fibrils, ThT can be limited to in vitro use only. Herein, we have developed Aß deposit-recognizing fluorescent probes (ARs) with a D-π-A architecture and a longer emission wavelength after binding with Aß species. Among the newly designed probes, AR-14 showed an admirable fluorescence emission (>600 nm) change after binding with soluble Aß oligomers (2.3-fold) and insoluble Aß fibril aggregates (4.5-fold) with high affinities Kd = 24.25 ± 4.10 nM; Ka = (4.123 ± 0.69) × 107 M-1 for fibrils; Kd = 32.58 ± 4.89 nM; and Ka = (3.069 ± 0.46) × 107 M-1 for oligomers with high quantum yield, molecular weight of <500 Da, reasonable log P = 1.77, stability in serum, and nontoxicity, and it can cross the BBB efficiently. The binding affinity of AR-14 toward Aß species is proved by fluorescence binding studies and fluorescent staining of 18-month-old triple-transgenic (3xTg) mouse brain sections. In summary, the fluorescent probe AR-14 is efficient and has an admirable quality for the detection of soluble and insoluble Aß deposits in vitro and in vivo.

Vanillin Benzothiazole Derivative Reduces Cellular Reactive Oxygen Species and Detects Amyloid Fibrillar Aggregates in Alzheimer's Disease Brain.

The misfolding of amyloid beta (Aß) peptides into Aß fibrillary aggregates is a major hallmark of Alzheimer's disease (AD), which responsible for the excess production of hydrogen peroxide (H2O2), a prominent reactive oxygen species (ROS) from the molecular oxygen (O2) by the reduction of the Aß-Cu(I) complex. The excessive production of H2O2 causes oxidative stress and inflammation in the AD brain. Here, we have designed and developed a dual functionalized molecule VBD by using π-conjugation (C═C) in the backbone structure. In the presence of H2O2, the VBD can turn into fluorescent probe VBD-1 by cleaving of the selective boronate ester group. The fluorescent probe VBD-1 can undergo intramolecular charge transfer transition (ICT) by a π-conjugative system, and as a result, its emission increases from the yellow (532 nm) to red (590 nm) region. The fluorescence intensity of VBD-1 increases by 3.5-fold upon binding with Aß fibrillary aggregates with a high affinity (Kd = 143 ± 12 nM). Finally, the VBD reduces the cellular toxic H2O2 as proven by the CCA assay and DCFDA assay and the binding affinity of VBD-1 was confirmed by using in vitro histological staining in 8- and 18-month-old triple transgenic AD (3xTg-AD) mice brain slices.

Evolution of Potential Antimitotic Stapled Peptides from Multiple Helical Peptide Stretches of the Tubulin Heterodimer Interface: Helix-Mimicking Stapled Peptide Tubulin Inhibitors.

Protein-protein interactions play a crucial role in microtubule dynamics. Microtubules are considered as a key target for the design and development of anticancer therapeutics, where inhibition of tubulin-tubulin interactions plays a crucial role. Here, we focused on a few key helical stretches at the interface of α,ß-tubulin heterodimers and developed a structural mimic of these helical peptides, which can serve as potent inhibitors of microtubule polymerization. To induce helicity, we have made stapled analogues of these sequences. Thereafter, we modified the lead sequences of the antimitotic stapled peptides with halo derivatives. It is observed that halo-substituted stapled peptides follow an interesting trend for the electronegativity of halogen atoms in interaction patterns with tubulin and a correlation in the toxicity profile. Remarkably, we found that para-fluorophenylalanine-modified stapled peptide is the most potent inhibitors, which perturbs microtubule dynamics, induces apoptotic death, and inhibits the growth of melanoma.

Designed hybrid anticancer nuclear-localized peptide inhibits aggressive cancer cell proliferation.

Cell proliferation is a crucial step that might promote cancer if deregulated. Therefore, this vital segment is critically controlled by a complicated cell-cycle process in normal cells that is regulated by some regulatory proteins. It has been observed that p16 protein, playing a crucial role in cell-cycle progression/regulation, remains inactivated in different cancer cells. This inactivity of p16 protein leads to the enhancement of cancer cell proliferation by allowing uncontrolled cancer cell division. Hence, the activity of p16 protein needs to be restored using new viral vectors, small molecules as well as peptides to control/suppress this type of abnormal cell proliferation. In this work, we have taken an interesting approach to increase the efficiency and bio-availability of p16 peptide (functional part of p16 protein) to be an aggressive anti-leukemia therapeutic agent by conjugating a nuclear-localized signal (NLS) sequence and a short peptide (AVPI) with it. Moreover, this newly designed NLS attached hybrid peptide greatly affects XIAP expressing but p16 lower expressing human chronic myelogenous leukemia (CML) cell proliferation by targeting both nuclear (CDK4/cyclin D) and cellular factors (XIAP) and promoting the caspase-3 dependent apoptosis pathway.

Discovery of imidazole-based GSK-3ß inhibitors for transdifferentiation of human mesenchymal stem cells to neurons: A potential single-molecule neurotherapeutic foresight.

The transdifferentiation of human mesenchymal stem cells (hMSC) to functional neurons is crucial for the development of future neuro-regenerative therapeutics. Currently, transdifferentiation of hMSCs to neurons requires a "chemical cocktail" along with neural growth factors. The role of the individual molecules present in a "chemical cocktail" is poorly understood and may cause unwanted toxicity or adverse effects. Toward, this goal, we have showcased the discovery of an imidazole-based "single-molecule" transdifferentiation initiator SG-145C. This discovery was achieved via screening of a small molecule library through extensive in silico studies to shortlist the best-fitting molecules. This discovery evolved through a careful selection to target Glycogen synthase kinase-3ß (GSK-3ß), which is one of the important proteins responsible for neurogenesis. Rigorous computational experiments, as well as extensive biological assays, confirmed that SG-145C has significant potential to transdifferentiate hMSCs to neurons. Interestingly, our results suggest that SG-145C can inhibit the proteasomal degradation of phosphorylated ß-catenin, in turn promoting transdifferentiation of hMSCs into neurons via the Wnt pathway.

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.