Co-operative membrane disruption between cell-penetrating peptide and cargo: implications for the therapeutic use of the Bcl-2 converter peptide D-NuBCP-9-r8

Delivery of Oleanolic Acid with Improved Antifibrosis Efficacy by a Cell Penetrating Peptide P10

Oleanolic acid (OA), a common pentacyclic triterpenoid found in plants, has several therapeutic uses, including the treatment of hepatopathy disorders. However, due to OA's weak permeability and limited bioavailability, its therapeutic advantages are limited. Here, we showed that a short peptide known as p10 not only binds to OA but also rapidly enhances OA delivery into cultured hepatic stellate cells (HSCs), lowers their synthesis of fibrogenic proteins, and further reduces the HSC migration capacity. Our findings show that noncovalently conjugating short peptides to OA improves its pharmacological efficacy and permeability.

Design, Synthesis and Evaluation of New Bioactive Oxadiazole Derivatives as Anticancer Agents Targeting Bcl-2

A series of 2-(1H-indol-3-yl)-5-substituted-1,3,4-oxadiazoles, 4a-m, were designed, synthesized and tested in vitro as potential pro-apoptotic Bcl-2 inhibitory anticancer agents based on our previously reported hit compounds. Synthesis of the target 1,3,4-oxadiazoles was readily accomplished through a cyclization reaction of indole carboxylic acid hydrazide 2 with substituted carboxylic acid derivatives 3a-m in the presence of phosphorus oxychloride. New compounds 4a-m showed a range of IC₅₀ values concentrated in the low micromolar range selectively in Bcl-2 positive human cancer cell lines. The most potent candidate 4-trifluoromethyl substituted analogue 4j showed selective IC₅₀ values of 0.52-0.88 μM against Bcl-2 expressing cell lines with no inhibitory effects in the Bcl-2 negative cell line. Moreover, 4j showed binding that was two-fold more potent than the positive control gossypol in the Bcl-2 ELISA binding affinity assay. Molecular modeling studies helped to further rationalize anti-apoptotic Bcl-2 binding and identified compound 4j as a candidate with drug-like properties for further investigation as a selective Bcl-2 inhibitory anticancer agent.

EJP18 peptide derived from the juxtamembrane domain of epidermal growth factor receptor represents a novel membrane-active cell-penetrating peptide

Membrane-active peptides have been extensively studied to probe protein–membrane interactions, to act as antimicrobial agents and cell-penetrating peptides (CPPs) for the delivery of therapeutic agents to cells. Hundreds of membrane-active sequences acting as CPPs have now been described including bioportides that serve as single entity modifiers of cell physiology at the intracellular level. Translation of promising CPPs in pre-clinical studies have, however, been disappointing as only few identified delivery systems have progressed to clinical trials. To search for novel membrane-active peptides a sequence from the EGFR juxtamembrane region was identified (named EJP18), synthesised, and examined in its L- and D-form for its ability to mediate the delivery of a small fluorophore and whole proteins to cancer cell lines. Initial studies identified the peptide as being highly membrane-active causing extensive and rapid plasma membrane reorganisation, blebbing, and toxicity. At lower, non-toxic concentrations the peptides outperformed the well-characterised CPP octaarginine in cellular delivery capacity for a fluorophore or proteins that were associated with the peptide covalently or via ionic interactions. EJP18 thus represents a novel membrane-active peptide that may be used as a naturally derived model for biophysical protein–membrane interactions or for delivery of cargo into cells for therapeutic or diagnostic applications.

New Quinoline-Based Heterocycles as Anticancer Agents Targeting Bcl-2

The Bcl-2 protein has been studied as an anticancer drug target in recent years, due to its gatekeeper role in resisting programmed cancer cell death (apoptosis), and the design of BH3 domain mimetics has led to the clinical approval of Venetoclax (ABT-199) for the treatment of chronic lymphocytic leukaemia. In this work we extend our previous studies on the discovery of indole-based heterocycles as Bcl-2 inhibitors, to the identification of quinolin-4-yl based oxadiazole and triazole analogues. Target compounds were readily synthesized via a common aryl-substituted quinolin-4-carbonyl-N-arylhydrazine-1-carbothioamide (5a–b) intermediate, through simple variation of the basic cyclisation conditions. Some of the quinoline-based oxadiazole analogues (e.g. compound 6i) were found to exhibit sub-micromolar anti-proliferative activity in Bcl-2-expressing cancer cell lines, and sub-micromolar IC₅₀ activity within a Bcl2-Bim peptide ELISA assay. The Bcl-2 targeted anticancer activity of 6i was further rationalised via computational molecular modelling, offering possibilities to extend this work into the design of further potent and selective Bcl-2 inhibitory heteroaromatics with therapeutic potential.

A Cell-Surface-Specific Ratiometric Fluorescent Probe for Extracellular pH Sensing with Solid-State Fluorophore

Extracellular acidity is correlated with the development of various pathological states and bulk pH measurements could not report surface acidity. In this study, we have developed a ratiometric fluorescent probe that aggregates upon interaction with cells, allowing persistent labeling of cells and in situ measurement of cell surface pH. The ternary nanoplatform is constructed by a convenient noncovalent combination of bovine serum albumin protected gold nanoclusters (BSA-AuNCs), fluorescein isothiocyanate (FITC) labeled cationic peptides (CPs), and FITC-free CPs. The red fluorescent AuNCs serve as reference fluorophore, while FITC labeled peptides act as specific recognition element for H⁺ and FITC unlabeled peptides are used for delivery. The probe displays a sensitive fluorescence ratiometric response for pH in the range of 5.0-9.5 with calculated p K_a of 7.2. Further studies have demonstrated that this nanosensor also has properties of high selectivity, reversibility to pH fluctuations, as well as low cytotoxicity. The new surface pH-measurement tool was validated in mapping extracellular pH and monitoring acidification regarding cell metabolism, demonstrating its potential for bioimaging and biosensing.

Investigation of Intracellular Delivery of NuBCP-9 by Conjugation with Oligoarginines Peptides in MDA-MB-231 Cells

Oligoarginines (Rn) are becoming promising tools for the intracellular delivery of biologically active molecules. NuBCP-9, a peptide that induces apoptosis in B-cell lymphoma 2 (Bcl-2)-expressing cancer cells, has been reported to promote the uptake and non-specific cytotoxicity of R8, also called octaarginine. However, it is unknown whether a similar synergistic effect can be seen with other Rn. In this study, we conjugated NuBCP-9 with various Rn (n=8, 10, 12, 14) to investigate and compare their cellular uptake characteristics. In addition, their non-specific cytotoxicity and apoptosis-inducing abilities were evaluated. We found that NuBCP-9 conjugated with Rn enhanced cellular uptake mainly through clathrin-mediated endocytosis and macropinocytosis, and that the uptake pathways were not different from those used by unconjugated Rn. However, the cytotoxicity study showed that NuBCP-9-R12 and NuBCP-9-R14 conjugates enhanced non-specific cytotoxicity. We found that NuBCP-9-R10 conjugate had the highest uptake efficiency and induced correspondingly high levels of apoptosis, while resulting in a tolerable degree of non-specific toxicity.

Concomitant Delivery of Paclitaxel and NuBCP-9 peptide for synergistic enhancement of cancer therapy

Paclitaxel (PTX) is a microtubule inhibitor administered as an albumin-bound nanoformulation for the treatment of breast cancer. However, the effectiveness of PTX is limited by resistance mechanisms mediated in part by upregulation of the anti-apoptotic BCL-2 and P-glycoprotein (P-gp). Present investigation was designed to study the synergistic potential of NuBCP-9 and PTX loaded polymeric nanoparticles to minimize the dose and improve the efficacy and safety. PTX and NuBCP-9 loaded polylactic acid-polyethylene glycol-polypropylene glycol-polyethylene glycol [PLA-(PEG-PPG-PEG)] nanoparticles were prepared by double emulsion solvent evaporation method. PTX and NuBCP-9 loaded NPs displayed an average size of 90 nm with spherical morphology. PTX and NuBCP-9 dual loaded NPs reducedIC50 by ~40-fold and acted synergistically. Treatment of the syngeneic EAT mice with PTX-NuBCP-9/NPs resulted in improved efficacy than that alone treated mice. Overall, the concomitant delivery PTX and NuBCP-9 loaded NPs showed superior activity than that of PTX and NuBCP-9 alone treated mice.

Stereochemistry as a determining factor for the effect of a cell-penetrating peptide on cellular viability and epithelial integrity

Cell-penetrating peptides (CPPs) comprise efficient peptide-based delivery vectors. Owing to the inherent poor enzymatic stability of peptides, CPPs displaying partial or full replacement of l-amino acids with the corresponding d-amino acids might possess advantages as delivery vectors. Thus, the present study aims to elucidate the membrane- and metabolism-associated effects of l-Penetratin (l-PEN) and its corresponding all-d analog (d-PEN). These effects were investigated when exerted on hepatocellular (HepG2) or intestinal (Caco-2 and IEC-6) cell culture models. The head-to-head comparison of these enantiomeric CPPs included evaluation of their effects on cell viability and morphology, epithelial membrane integrity, and cellular ultrastructure. In all investigated cell models, a rapid decrease in cell viability, pronounced membrane perturbation and an altered ultrastructure were detected upon exposure to d-PEN. At equimolar concentrations, these observations were less pronounced or even absent for cells exposed to l-PEN. Both CPPs remained stable for at least 2 h during exposure to proliferating cells (cultured for 24 h), although d-PEN exhibited a longer half-life when compared with that of l-PEN when exposed to well-differentiated cell monolayers (cultured for 18-20 days). Thus, the stereochemistry of the CPP penetratin significantly influences its effects on cell viability and epithelial integrity when profiled against a panel of mammalian cells.

Intracellular delivery of peptide drugs using viral nanoparticles of bacteriophage P22: covalent loading and cleavable release

Viral nanoparticles of bacteriophage P22 are utilized for the intracellular delivery of peptides through covalent loading and cleavable release.

Synthesis and evaluation of 5-(1H-indol-3-yl)-N-aryl-1,3,4-oxadiazol-2-amines as Bcl-2 inhibitory anticancer agents

A series of 5-(1H-indol-3-yl)-N-aryl-1,3,4-oxadiazol-2-amines 8a-j has been designed, synthesized and tested in vitro as potential pro-apoptotic Bcl-2-inhibitory anticancer agents based on our previous lead compound 8a. Synthesis of the target compounds was readily accomplished through a cyclisation reaction between indole-3-carboxylic acid hydrazide (5) and substituted isothiocyanates 6a-j, followed by oxidative cyclodesulfurization of the corresponding thiosemicarbazide 7a-j using 1,3-dibromo-5,5-dimethylhydantoin. Active compounds of the series 8a-j were found to have sub-micromolar IC₅₀ values selectively in Bcl-2 expressing human cancer cell lines; notably the 2-nitrophenyl analogue 8a was found to exhibit potent activity, and compounds 8a and 8e possessed comparable Bcl-2 binding affinity (ELISA assay) to the established natural product-based Bcl-2 inhibitor, gossypol. Molecular modeling studies helped to further rationalise anti-apoptotic Bcl-2 binding, and identified compounds 8a and 8e as candidates for further development as Bcl-2 inhibitory anticancer agents.

Intracellular delivery of peptide cargos using iron oxide based nanoparticles: studies on antitumor efficacy of a BCL-2 converting peptide, NuBCP-9

Delivering peptides into cells targeting the undruggable oncoproteins is an emerging area in cancer therapeutics. Here we report a novel nanoparticle-based delivery system that can transport therapeutic cargos to the intracellular sites without the need for a cell transduction or penetration domain (CPP). In the present study, we have used iron oxide nanoparticles to deliver an oncopeptide, NuBCP-9, targeting the BCL-2 BH3 domain. Citric acid/2-bromo 2-methylpropanoic acid (CA/BMPA)-capped SPIONs were used to immobilize and deliver the NuBCP-9 peptide to the cancer cells without any noticeable off-target effects. Our results have demonstrated that NuBCP-9-SPIONs efficiently penetrate into cancer cells and bind to its intracellular target protein BCL-2. Moreover, significant inhibition of proliferation and substantial induction of cell death were observed when cancer cells were treated with NuBCP-9-SPIONs at different time intervals. Importantly, the IC50 values for killing of breast cancer cells with NuBCP-9-SPIONs were much lower compared to cells treated with the NuBCP-9 peptide linked with a CPP (Arg-8; NuBCP-9-R8). Molecular and biochemical analyses further supported that NuBCP-9-SPIONs killed breast cancer cells by apoptosis-mediated mechanisms. Furthermore, our data demonstrated that administration of NuBCP-9-SPIONs to mice bearing Ehrlich ascites tumors (EAT) was associated with loss of tumorigenicity and extensive apoptosis in tumor tissues. Taken together, these findings show that a non-CPP-tagged peptide can be successfully delivered to undruggable intracellular oncotargets using SPIONs.

Distal phenylalanine modification for enhancing cellular delivery of fluorophores, proteins and quantum dots by cell penetrating peptides

For cell penetrating peptides (CPPs) to fulfil their promise as effective delivery vectors we need a better understanding of their mechanisms of cell binding and uptake. This is especially the case when they are linked to different types of cargo. Here we describe new studies based on our previous findings suggesting that, for peptide-CPP chimeras, distal hydrophobic residues upstream of the CPP sequence can have profound effects on the way they interact with cells. We studied peptides bearing an N-terminal Glycine or Phenylalanine linked via a neutral and flexible bridging group, SGSGSGSG, to three well-studied CPPs: octaarginine, penetratin and TP10. Using a combination of flow cytometry, live-cell imaging and image analysis we examined the effects of this single amino acid change on binding and uptake of Alexa488-fluorophore, bovine serum albumin and quantum dot cargoes. The influence of the glycine-phenylalanine switch for fluorophore delivery was most dramatic in TP10, increasing cellular uptake by 4.4 and 9.9 fold in non-adherent and adherent cells, respectively. Only penetratin showed effective uptake of bovine serum albumin with the phenylalanine variant showing an increase of 1.6 fold over the glycine variant. The uptake of quantum dots was most efficiently demonstrated by octaarginine, with the glycine variant increasing uptake 4.8 fold and the phenylalanine variant increasing uptake 9.5 fold over quantum dots alone. Overall the data demonstrate that hydrophobicity distal to the CPP could be utilised to enhance their capacity to bind to the cell membrane and deliver a range of macromolecules to the insides of cells.

Novel polymeric nanoparticles for intracellular delivery of peptide Cargos: antitumor efficacy of the BCL-2 conversion peptide NuBCP-9

The preclinical development of peptidyl drugs for cancer treatment is hampered by their poor pharmacologic properties and cell penetrative capabilities in vivo. In this study, we report a nanoparticle-based formulation that overcomes these limitations, illustrating their utility in studies of the anticancer peptide NuBCP-9, which converts BCL-2 from a cell protector to a cell killer. NuBCP-9 was encapsulated in polymeric nanoparticles composed of a polyethylene glycol (PEG)-modified polylactic acid (PLA) diblock copolymer (NuBCP-9/PLA-PEG) or PEG-polypropylene glycol-PEG-modified PLA-tetrablock copolymer (NuBCP-9/PLA-PEG-PPG-PEG). We found that peptide encapsulation was enhanced by increasing the PEG chain length in the block copolymers. NuBCP-9 release from the nanoparticles was controlled by both PEG chain length and the PLA molecular weight, permitting time-release over sustained periods. Treatment of human cancer cells with these nanoparticles in vitro triggered apoptosis by NuBCP-9-mediated mechanism, with a potency similar to NuBCP-9 linked to a cell-penetrating poly-Arg peptide. Strikingly, in vivo administration of NuBCP-9/nanoparticles triggered complete regressions in the Ehrlich syngeneic mouse model of solid tumor. Our results illustrate an effective method for sustained delivery of anticancer peptides, highlighting the superior qualities of the novel PLA-PEG-PPG-PEG tetrablock copolymer formulation as a tool to target intracellular proteins.

LXXLL peptide converts transportan 10 to a potent inducer of apoptosis in breast cancer cells

Degenerate expression of transcription coregulator proteins is observed in most human cancers. Therefore, in targeted anti-cancer therapy development, intervention at the level of cancer-specific transcription is of high interest. The steroid receptor coactivator-1 (SRC-1) is highly expressed in breast, endometrial, and prostate cancer. It is present in various transcription complexes, including those containing nuclear hormone receptors. We examined the effects of a peptide that contains the LXXLL-motif of the human SRC-1 nuclear receptor box 1 linked to the cell-penetrating transportan 10 (TP10), hereafter referred to as TP10-SRC1_LXXLL, on proliferation and estrogen-mediated transcription of breast cancer cells in vitro. Our data show that TP10-SRC1_LXXLL induced dose-dependent cell death of breast cancer cells, and that this effect was not affected by estrogen receptor (ER) status. Surprisingly TP10-SRC1_LXXLL severely reduced the viability and proliferation of hormone-unresponsive breast cancer MDA-MB-231 cells. In addition, the regulation of the endogenous ERα direct target gene pS2 was not affected by TP10-SRC1_LXXLL in estrogen-stimulated MCF-7 cells. Dermal fibroblasts were similarly affected by treatment with higher concentrations of TP10-SRC1_LXXLL and this effect was significantly delayed. These results suggest that the TP10-SRC1_LXXLL peptide may be an effective drug candidate in the treatment of cancers with minimal therapeutic options, for example ER-negative tumors.