Supramolecular Structures Generated via Self-Assembly of a Cell Penetrating Tetrapeptide Facilitate Intracellular Delivery of a Pro-apoptotic Chemotherapeutic Drug

Development of drug carriers, which can chaperone xenobiotics directly to their site of action, is an essential step for the advancement of precision medicine. Cationic nanoparticles can be used as a drug delivery platform for various agents including chemotherapeutics, oligonucleotides, and antibodies. Self-assembly of short peptides facilitates the formation of well-defined nanostructures suitable for drug delivery, and varying the polarity of the self-assembly medium changes the nature of noncovalent interactions in such a way as to generate numerous unique nanostructures. Here, we have synthesized an ultrashort cell-penetrating tetrapeptide (sequence Lys-Val-Ala-Val), with Lys as a cationic amino acid, and studied the self-assembly property of the BOC-protected (L1) and -deprotected (L2) analogues. Spherical assemblies obtained from L1/L2 in a 1:1 aqueous ethanol system have the ability to encapsulate small molecules and successfully enter into cells, thus representing them as potential candidates for intracellular drug delivery. To verify the efficacy of these peptides in the facilitation of drug efficacy, we generated encapsulated versions of the chemotherapeutic drug doxorubicin (Dox). L1- and L2-encapsulated Dox (Dox-L1 and Dox-L2), similar to the unencapsulated drug, induced upregulation of regulator of G protein signaling 6 (RGS6) and Gβ5, the critical mediators of ATM/p53-dependent apoptosis in Dox-treated cancer cells. Further, Dox-L1/L2 damaged DNA, triggered oxidative stress and mitochondrial dysfunction, compromised cell viability, and induced apoptosis. The ability of Dox-L1 to mediate cell death could be ameliorated via knockdown of either RGS6 or Gβ5, comparable to the results obtained with the unencapsulated drug. These data provide an important proof of principle, identifying L1/L2 as drug delivery matrices.

Scaffolds Formed via the Non-Equilibrium Supramolecular Assembly of the Synergistic ECM Peptides RGD and PHSRN Demonstrate Improved Cell Attachment in 3D

Self-assembling peptides (SAPs) are a relatively new class of low molecular weight gelators which immobilize their solvent through the spontaneous formation of (fibrillar) nanoarchitectures. As peptides are derived from proteins, these hydrogels are ideal for use as biocompatible scaffolds for regenerative medicine. Importantly, due to the propensity of peptide sequences to act as signals in nature, they are easily functionalized to be cell instructive via the inclusion of bioactive epitopes. In nature, the fibronectin peptide sequence, arginine-glycine-aspartic acid (RGD) synergistically promotes the integrin α₅β₁ mediated cell adhesion with another epitope, proline-histidine-serine-arginine-asparagine (PHSRN); however most functionalization strategies focus on RGD alone. Here, for the first time, we discuss the biomimetic inclusion of both these sequences within a self-assembled minimalistic peptide hydrogel. Here, based on our work with Fmoc-FRGDF (N-flourenylmethyloxycarbonyl phenylalanine-arginine-glycine-aspartic acid-phenylalanine), we show it is possible to present two epitopes simultaneously via the assembly of the epitopes by the coassembly of two SAPs, and compare this to the effectiveness of the signals in a single peptide; Fmoc-FRGDF: Fmoc-PHSRN (N-flourenylmethyloxycarbonyl-proline-histidine-serine-arginine-asparagine) and Fmoc-FRGDFPHSRN (N-flourenylmethyloxycarbonyl-phenylalanine-arginine-glycine-asparticacid-phenylalanine-proline-histidine-serine-arginine-asparagine). We show both produced self-supporting hydrogel underpinned by entangled nanofibrils, however, the stiffness of coassembled hydrogel was over two orders of magnitude higher than either Fmoc-FRGDF or Fmoc-FRGDFPHSRN alone. In-vitro three-dimensional cell culture of human mammary fibroblasts on the hydrogel mixed peptide showed dramatically improved adhesion, spreading and proliferation over Fmoc-FRGDF. However, the long peptide did not provide effective cell attachment. The results demonstrated the selective synergy effect of PHSRN with RGD is an effective way to augment the robustness and functionality of self-assembled bioscaffolds.

N-terminal diproline and charge group effects on the stabilization of helical conformation in alanine-based short peptides: CD studies with water and methanol as solvent

Protein folding problem remains a formidable challenge as main chain, side chain and solvent interactions remain entangled and have been difficult to resolve. Alanine-based short peptides are promising models to dissect protein folding initiation and propagation structurally as well as energetically. The effect of N-terminal diproline and charged side chains is assessed on the stabilization of helical conformation in alanine-based short peptides using circular dichroism (CD) with water and methanol as solvent. A1 (Ac-Pro-Pro-Ala-Lys-Ala-Lys-Ala-Lys-Ala-NH₂ ) is designed to assess the effect of N-terminal homochiral diproline and lysine side chains to induce helical conformation. A2 (Ac-Pro-Pro-Glu-Glu-Ala-Ala-Lys-Lys-Ala-NH₂ ) and A3 (Ac-dPro-Pro-Glu-Glu-Ala-Ala-Lys-Lys-Ala-NH₂ ) with N-terminal homochiral and heterochiral diproline, respectively, are designed to assess the effect of Glu...Lys (i, i + 4) salt bridge interactions on the stabilization of helical conformation. The CD spectra of A1, A2 and A3 in water manifest different amplitudes of the observed polyproline II (PPII) signals, which indicate different conformational distributions of the polypeptide structure. The strong effect of solvent substitution from water to methanol is observed for the peptides, and CD spectra in methanol evidence A2 and A3 as helical folds. Temperature-dependent CD spectra of A1 and A2 in water depict an isodichroic point reflecting coexistence of two conformations, PPII and β-strand conformation, which is consistent with the previous studies. The results illuminate the effect of N-terminal diproline and charged side chains in dictating the preferences for extended-β, semi-extended PPII and helical conformation in alanine-based short peptides. The results of the present study will enhance our understanding on stabilization of helical conformation in short peptides and hence aid in the design of novel peptides with helical structures. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Binding studies of creatinine and urea on iron-nanoparticle

Kidney diseases are complicated and can be fatal. Dialysis and transplantation are the only survival solutions to the patients suffering from kidney failures. Both hemodialysis and peritoneal dialysis are risky, due to the possibility of infection and these are expensive and time consuming. The development of simple and reliable technique for the clearance of creatinine and urea from the body is an important part of biotechnology. We have synthesized an iron nanoparticle (INP) and studied its binding with creatinine and urea. The DLS, TEM, AFM, FT-IR and Powder-XRD studies demonstrate strong binding of creatinine and urea to the nanoparticles. This finding may be helpful if it is used in the dialysis technologies. The proposed method may substantially decrease dialysis time and improve its quality in terms of urea and creatinine clearances.

Potent anticancer activity of cystine-based dipeptides and their interaction with serum albumins

BACKGROUND

Cancer is a severe threat to the human society. In the scientific community worldwide cancer remains a big challenge as there are no remedies as of now. Cancer is quite complicated as it involves multiple signalling pathways and it may be caused by genetic disorders. Various natural products and synthetic molecules have been designed to prevent cell proliferation. Peptide-based anticancer drugs, however, are not explored properly. Though peptides have their inherent proteolytic instability, they could act as anticancer agents.

RESULTS

In this present communication a suitably protected cystine based dipeptide and its deprotected form have been synthesized. Potent anticancer activities were confirmed by MTT assay (a laboratory test and a standard colorimetric assay, which measures changes in colour, for measuring cellular proliferation and phase contrast images. The IC50 value, a measure of the effectiveness of a compound in inhibiting biological or biochemical function, of these compounds ranges in the sub-micromolar level. The binding interactions with serum albumins (HSA and BSA) were performed with all these molecules and all of them show very strong binding at sub-micromolar concentration.

CONCLUSIONS

This study suggested that the cystine-based dipeptides were potential anticancer agents. These peptides also showed very good binding with major carrier proteins of blood, the serum albumins. We are currently working on determining the detailed mechanism of anticancer activity of these molecules.