Synthesis and antiproliferative activities of doxorubicin thiol conjugates and doxorubicin-SS-cyclic peptide

Discovery of novel penetrating peptides able to target human leukemia and lymphoma for enhanced PROTAC delivery

Proteolysis targeting chimeras (PROTAC) are bifunctional chimeric molecules capable of directly degrading binding proteins through the ubiquitin-proteasome pathway. PROTACs have demonstrated significant potential in overcoming drug resistance and targeting previously untreatable targets. However, several limitations still need to be addressed, including their high molecular weight resulting in poor membrane permeability and bioavailability. In this study, we proposed that cancer-targeted penetrating peptides could enhance the cell permeability of PROTACs. We developed 26 novel targeted penetrating peptides for leukemia and lymphoma cells, among which C9C-f(3Bta) and Cyclo-C9C-R exhibited superior membrane permeability, targetability, and stability. By combining C9C-f(3Bta) and Cyclo-C9C-R with IMA-PROTAC, we effectively enhanced the anti-proliferative activity of IMA-PROTAC, facilitated degradation of Bcr-Abl protein in K562 cells, and reduced downstream STAT5 phosphorylation. Furthermore, the combined application promoted cell apoptosis while blocking G1 phase progression. HPLC-MRM-MS revealed that the combination of C9C-f(3Bta) or Cyclo-C9C-R with IMA-PROTAC significantly enhanced intracellular IMA-PROTAC content. In summary, our proof-of-concept study validated the hypothesis that combining PROTACs with targeted penetrating peptides can improve protein degradation efficiency as well as anti-proliferative capabilities.

Doxorubicin conjugates: a practical approach for its cardiotoxicity alleviation

INTRODUCTION

Doxorubicin (DOX) emerges as a cornerstone in the arsenal of potent chemotherapeutic agents. Yet, the clinical deployment of DOX is tarnished by its proclivity to induce severe cardiotoxic effects, culminating in heart failure and other consequential morbidities. In response, a panoply of strategies has undergone rigorous exploration over recent decades, all aimed at attenuating DOX's cardiotoxic impact. The advent of encapsulating DOX within lipidic or polymeric nanocarriers has yielded a dual triumph, augmenting DOX's therapeutic efficacy while mitigating its deleterious side effects.

AREAS COVERED

Recent strides have spotlighted the emergence of DOX conjugates as particularly auspicious avenues for ameliorating DOX-induced cardiotoxicity. These conjugates entail the fusion of DOX through physical or chemical bonds with diminutive natural or synthetic moieties, polymers, biomolecules, and nanoparticles. This spectrum encompasses interventions that impinge upon DOX's cardiotoxic mechanism, modulate cellular uptake and localization, confer antioxidative properties, or refine cellular targeting.

EXPERT OPINION

The endorsement of DOX conjugates as a compelling stratagem to mitigate DOX-induced cardiotoxicity resounds from this exegesis, amplifying safety margins and the therapeutic profile of this venerated chemotherapeutic agent. Within this ambit, DOX conjugates stand as a beacon of promise in the perpetual pursuit of refining chemotherapy-induced cardiac compromise.

Cell plasticity modulation by flavonoids in resistant breast carcinoma targeting the nuclear factor kappa B signaling

Cancer cell plasticity plays a crucial role in tumor initiation, progression, and metastasis and is implicated in the multiple cancer defense mechanisms associated with therapy resistance and therapy evasion. Cancer resistance represents one of the significant obstacles in the clinical management of cancer. Some reversal chemosensitizing agents have been developed to resolve this serious clinical problem, but they have not yet been proven applicable in oncological practice. Activated nuclear factor kappa B (NF-κB) is a frequently observed biomarker in chemoresistant breast cancer (BC). Therefore, it denotes an attractive cellular target to mitigate cancer resistance. We summarize that flavonoids represent an essential class of phytochemicals that act as significant regulators of NF-κB signaling and negatively affect the fundamental cellular processes contributing to acquired cell plasticity and drug resistance. In this regard, flavokawain A, icariin, alpinetin, genistein, wogonin, apigenin, oroxylin A, xanthohumol, EGCG, hesperidin, naringenin, orientin, luteolin, delphinidin, fisetin, norwogonin, curcumin, cardamonin, methyl gallate and catechin-3-O-gallate, ampelopsin, puerarin, hyperoside, baicalein, paratocarpin E, and kaempferol and also synthetic flavonoids such as LFG-500 and 5,3'-dihydroxy-3,6,7,8,4'-pentamethoxyflavone have been reported to specifically interfere with the NF-κB pathway with complex signaling consequences in BC cells and could be potentially crucial in re-sensitizing unresponsive BC cases. The targeting NF-κB by above-mentioned flavonoids includes the modification of tumor microenvironment and epithelial-mesenchymal transition, growth factor receptor regulations, and modulations of specific pathways such as PI3K/AKT, MAP kinase/ERK, and Janus kinase/signal transduction in BC cells. Besides that, NF-κB signaling in BC cells modulated by flavonoids has also involved the regulation of ATP-binding cassette transporters, apoptosis, autophagy, cell cycle, and changes in the activity of cancer stem cells, oncogenes, or controlling of gene repair. The evaluation of conventional therapies in combination with plasticity-regulating/sensitizing agents offers new opportunities to make significant progress towards a complete cure for cancer.

Cell-Penetrating Peptides: A Powerful Tool for Targeted Drug Delivery

The cellular membrane hinders the effective delivery of therapeutics to targeted sites. Cellpenetrating peptide (CPP) is one of the best options for rapidly internalizing across the cellular membrane. CPPs have recently attracted lots of attention because of their excellent transduction efficiency and low cytotoxicity. The CPP-cargo complex is an effective and efficient method of delivering several chemotherapeutic agents used to treat various diseases. Additionally, CPP has become another strategy to overcome some of the current therapeutic agents' limitations. However, no CPP complex is approved by the US FDA because of its limitations and issues. In this review, we mainly discuss the cellpenetrating peptide as the delivery vehicle, the cellular uptake mechanism of CPPs, their design, and some strategies to synthesize the CPP complex via some linkers such as disulfide bond, oxime, etc. Here, we also discuss the recent status of CPPs in the market.

Peptides as carriers of active ingredients: A review

Bioactive compounds are highly valuable in the fields of food and medicine, but their application is limited due to easy deterioration after oral or skin administration. In recent years, the use of peptides as delivery systems for bioactive compounds has been intensively researched because of their special physicochemical characteristics. Peptides can be assembled using various preparation methods and can form several composite materials such as hydrogels, micelles, emulsions and particles. The composite material properties are determined by peptides, bioactive compounds and the construction methods employed. Herein, this paper provides a comprehensive review of the peptides used for active ingredients delivery, fabrication methods for creating delivery systems, structures, targeting characteristics, functional activities and mechanism of delivery systems, as well as their absorption and metabolism, which provided theoretical basis and reference for further research and development of functional composites.

Recent Advances of Cell-Penetrating Peptides and Their Application as Vectors for Delivery of Peptide and Protein-Based Cargo Molecules

Peptides and proteins, two important classes of biomacromolecules, play important roles in the biopharmaceuticals field. As compared with traditional drugs based on small molecules, peptide- and protein-based drugs offer several advantages, although most cannot traverse the cell membrane, a natural barrier that prevents biomacromolecules from directly entering cells. However, drug delivery via cell-penetrating peptides (CPPs) is increasingly replacing traditional approaches that mediate biomacromolecular cellular uptake, due to CPPs' superior safety and efficiency as drug delivery vehicles. In this review, we describe the discovery of CPPs, recent developments in CPP design, and recent advances in CPP applications for enhanced cellular delivery of peptide- and protein-based drugs. First, we discuss the discovery of natural CPPs in snake, bee, and spider venom. Second, we describe several synthetic types of CPPs, such as cyclic CPPs, glycosylated CPPs, and D-form CPPs. Finally, we summarize and discuss cell membrane permeability characteristics and therapeutic applications of different CPPs when used as vehicles to deliver peptides and proteins to cells, as assessed using various preclinical disease models. Ultimately, this review provides an overview of recent advances in CPP development with relevance to applications related to the therapeutic delivery of biomacromolecular drugs to alleviate diverse diseases.

Peptide cargo administration: current state and applications

Effective delivery of drug molecules to the target site is a challenging task. In the last decade, several innovations in the drug delivery system (DDS) have tremendously improved the therapeutic efficacy of drug molecules. Among various DDS, cell-penetrating peptides (CPPs) based DDS have gathered notable attention owing to their safety, efficacy, selectivity, specificity, and ease of synthesis. CPPs are emerging as an efficient and effective pharmaceutical nanocarriers-based platforms for successful management of various important human health disorders. Failure of several current chemotherapeutic strategies is attributed to low solubility, reduced bioavailability, and off-target delivery of several anti-cancer drugs. Similarly, development of therapeutics for vision-threatening disorders is challenged by the anatomical as well as physiological complexity of the eye. Such therapeutic challenges in cancer and ocular disease management can be overcome by developing cell-penetrating peptide (CPP) based peptide drug conjugates (PDCs). CPPs can be used to deliver various types of cargo molecules including nucleic acids, small molecules, and peptides/proteinaceous agents. In this review, we have briefly introduced CPPs and the linker strategies employed for the development of PDCs. Furthermore, recent studies employing CPP-based PDCs for cancer and ocular disease management have been discussed in detail highlighting their significance over conventional DDS. Later sections of the review are focused on the current status of clinical trials and future implications of CPP-based PDCs in vaccine development. KEY POINTS: • Cell-penetrating peptides (CPPs) can deliver a variety of cargo macromolecules via covalent and non-covalent conjugation. • CPP-based peptide drug conjugates (PDCs) can overcome drawbacks of conventional drug delivery methods such as biocompatibility, solubility, stability, and specificity. • Various PDCs are in clinical trial phase for cancer and ocular therapeutics.

Amphiphilic Cell-Penetrating Peptides Containing Arginine and Hydrophobic Residues as Protein Delivery Agents

The entry of proteins through the cell membrane is challenging, thus limiting their use as potential therapeutics. Seven cell-penetrating peptides, designed in our laboratory, were evaluated for the delivery of proteins. Fmoc solid-phase peptide synthesis was utilized for the synthesis of seven cyclic or hybrid cyclic-linear amphiphilic peptides composed of hydrophobic (tryptophan (W) or 3,3-diphenylalanine (Dip) and positively-charged arginine (R) residues, such as [WR]₄, [WR]₉, [WWRR]₄, [WWRR]₅, [(RW)₅K](RW)₅, [R₅K]W₇, and [DipR]₅. Confocal microscopy was used to screen the peptides as a protein delivery system of model cargo proteins, green and red fluorescein proteins (GFP and RFP). Based on the confocal microscopy results, [WR]₉ and [DipR]₅ were found to be more efficient among all the peptides and were selected for further studies. [WR]₉ (1-10 µM) + protein (GFP and RFP) physical mixture did not show high cytotoxicity (>90% viability) in triple-negative breast cancer cells (MDA-MB-231) after 24 h, while [DipR]₅ (1-10 µM) physical mixture with GFP exhibited more than 81% cell viability. Confocal microscopy images revealed internalization of GFP and RFP in MDA-MB-231 cells using [WR]₉ (2-10 μM) and [DipR]₅ (1-10 µM). Fluorescence-activated cell sorting (FACS) analysis indicated that the cellular uptake of GFP was concentration-dependent in the presence of [WR]₉ in MDA-MB-231 cells after 3 h of incubation at 37 °C. The concentration-dependent uptake of GFP and RFP was also observed in the presence of [DipR₅] in SK-OV-3 and MDA-MB-231 cells after 3 h of incubation at 37 °C. FACS analysis indicated that the cellular uptake of GFP in the presence of [WR]₉ was partially decreased by methyl-β-cyclodextrin and nystatin as endocytosis inhibitors after 3 h of incubation in MDA-MB-231 cells, whereas nystatin and chlorpromazine as endocytosis inhibitors slightly reduced the uptake of GFP in the presence of [DipR]₅ after 3 h of incubation in MDA-MB-231. [WR]₉ was able to deliver therapeutically relevant proteins (Histone H2A) at different concentrations. These results provide insight into the use of amphiphilic cyclic peptides in the delivery of protein-related therapeutics.

The Recent Advance of Cell-Penetrating and Tumor-Targeting Peptides as Drug Delivery Systems Based on Tumor Microenvironment

Cancer has become the primary reason for industrial countries death. Although first-line treatments have achieved remarkable results in inhibiting tumors, they could have serious side effects because of insufficient selectivity. Therefore, specific localization of tumor cells is currently the main desire for cancer treatment. In recent years, cell-penetrating peptides (CPPs), as a kind of promising delivery vehicle, have attracted much attention because they mediate the high-efficiency import of large quantities of cargos in vivo and vitro. Unfortunately, the poor targeting of CPPs is still a barrier to their clinical application. In order to solve this problem, researchers use the various characteristics of tumor microenvironment and multiple receptors to improve the specificity toward tumors. This review focuses on the characteristics of the tumor microenvironment, and introduces the development of strategies and peptides based on these characteristics as drug delivery system in the tumor-targeted therapy.

Stable colonization of Akkermansia muciniphila educates host intestinal microecology and immunity to battle against inflammatory intestinal diseases

Gut microbial preparations are widely used in treating intestinal diseases but show mixed success. In this study, we found that the therapeutic efficacy of A. muciniphila for dextran sodium sulfate (DSS)-induced colitis as well as intestinal radiation toxicity was ~50%, and mice experiencing a positive prognosis harbored a high frequency of A. muciniphila in the gastrointestinal (GI) tract. Stable GI colonization of A. muciniphila elicited more profound shifts in the gut microbial community structure of hosts. Coexisting with A. muciniphila facilitated proliferation and reprogrammed the gene expression profile of Lactobacillus murinus, a classic probiotic that overtly responded to A. muciniphila addition in a time-dependent manner. Then, a magnetic-drove, mannose-loaded nanophase material was designed and linked to the surface of A. muciniphila. The modified A. muciniphila exhibited enhancements in inflammation targeting and intestinal colonization under an external magnetic field, elevating the positive-response rate and therapeutic efficacy against intestinal diseases. However, the unlinked cocktail containing A. muciniphila and the delivery system only induced negligible improvement of therapeutic efficacy. Importantly, heat-inactivated A. muciniphila lost therapeutic effects on DSS-induced colitis and was even retained in the GI tract for a long time. Further investigations revealed that the modified A. muciniphila was able to drive M2 macrophage polarization by upregulating the protein level of IL-4 at inflammatory loci. Together, our findings demonstrate that stable colonization of live A. muciniphila at lesion sites is essential for its anti-inflammatory function.

Cyclic and Linear Peptides Containing Alternate WW and RR Residues as Molecular Cargo Delivery Tools

Cell-impermeable and negatively charged compounds' cellular uptake across the cell membranes remains challenging. Herein, the synthesis of four linear [(WWRR)₂, (WWRR)₃, (WWRR)₄, and (WWRR)₅] and four cyclic ([WWRR]₂, [WWRR]₃, [WWRR]₄, and [WWRR]₅) peptides containing alternate two tryptophan (WW) and two arginine (RR) residues and their biological evaluation as molecular transporters are reported. The peptides did not show any significant cytotoxicity in different cell lines (MDA-MB-23, SK-OV-3, and HEK 293) at a concentration of 5 μM and after 3 h of incubation time. The uptake of fluorescence-labeled cargo molecules (F'-GpYEEI, F'-siRNA, and F'-3TC) in the presence of the peptides was monitored in different cell lines (SK-OV-3 and MDA-MB-231) with fluorescence-activated cell sorting. Among all the peptides, [WWRR]₅ (C4) showed the highest cellular uptake of cargo molecules, indicating it can act as effective molecular transporter. Confocal microscopy in MDA-MB-231 cells showed the cellular uptake of F'-GpYEEI in the presence of C4 and the intracellular localization of fluorescence-labeled C4 (F'-C4) in the cytosol. The F'-C4 cellular uptake was found to be concentration- and time-dependent, as shown by flow cytometry in MDA-MB-231 cells. Confocal microscopy and flow cytometry of F'-C4 in MDA-MB-231 cells were examined alone and in the presence of different endocytosis inhibitors (chlorpromazine, methyl-β-cyclodextrin, chloroquine, and nystatin). The data showed that the cellular uptake of F'-C4 in the presence of chlorpromazine, chloroquine, and methyl-β-cyclodextrin was reduced but not completely eliminated, indicating that both energy-independent and energy-dependent pathways contributed to the cellular uptake of F'-C4. Similar results were obtained using the confocal microscopy of C4 and F'-GpYEEI in the presence of endocytosis inhibitors (chlorpromazine, methyl-β-cyclodextrin, chloroquine, and nystatin). These data indicate that C4 has the potential to be used as a cell-penetrating peptide and cargo transporter.

Development of stimulus-sensitive electrospun membranes based on novel biodegradable segmented polyurethane as triggered delivery system for doxorubicin

In this work, redox-sensitive polyurethane urea (PUU) based electrospun membranes have been exploited to chemically tether a pH-sensitive doxorubicin derivative achieved by linking a lipoyl hydrazide to the drug via a hydrazone linkage. First, the lipoyl-hydrazone-doxorubicin derivative labelled as LA-Hy-Doxo has been synthesized and characterized. Then, the molecule has been tethered, via a thiol-disulfide exchange reaction, to the redox-sensitive PUU (PolyCEGS) electrospun membrane. The redox-sensitive PolyCEGS PUU has been produced by using PCL-PEG-PCL polyol and glutathione-tetramethyl ester (GSSG-OMe)₄ as a chain extender. The LA-Hy-Doxo tethered electrospun membrane has showed a dually controlled release triggered by acidic and reducing conditions, producing a significant cytotoxic effect in human breast cancer cell lines (MCF-7) which has validated the system for the post-surgical treatment of solid tumors to contrast recurrence.

Amphiphilic Cell-Penetrating Peptides Containing Natural and Unnatural Amino Acids as Drug Delivery Agents

A series of cyclic peptides, [(DipR)(WR)₄], [(DipR)₂(WR)₃], [(DipR)₃(WR)₂], [(DipR)₄(WR)], and [DipR]₅, and their linear counterparts containing arginine (R) as positively charged residues and tryptophan (W) or diphenylalanine (Dip) as hydrophobic residues, were synthesized and evaluated for their molecular transporter efficiency. The in vitro cytotoxicity of the synthesized peptides was determined in human epithelial ovary adenocarcinoma cells (SK-OV-3), human lymphoblast peripheral blood cells (CCRF-CEM), human embryonic epithelial kidney healthy cells (HEK-293), human epithelial mammary gland adenocarcinoma cells (MDA-MB-468), pig epithelial kidney normal cells (LLC-PK1), and human epithelial fibroblast uterine sarcoma cells (MES-SA). A concentration of 5–10 µM and 3 h incubation were selected in uptake studies. The cellular uptake of a fluorescent-labeled phosphopeptide, stavudine, lamivudine, emtricitabine, and siRNA was determined in the presence of peptides via flow cytometry. Among the peptides, [DipR]₅ (10 µM) was found to be the most efficient transporter and significantly improved the uptake of F’-GpYEEI, i.e., by approximately 130-fold after 3 h incubation in CCRF-CEM cells. Confocal microscopy further confirmed the improved delivery of fluorescent-labeled [DipR]₅ (F’-[K(DipR)₅]) alone and F’-GpYEEI in the presence of [DipR]₅ in MDA-MB-231 cells. The uptake of fluorescent-labeled siRNA (F’-siRNA) in the presence of [DipR]₅ with N/P ratios of 10 and 20 was found to be 30- and 50-fold higher, respectively, compared with the cells exposed to F’-siRNA alone. The presence of endocytosis inhibitors, i.e., nystatin, chlorpromazine, chloroquine, and methyl β-cyclodextrin, did not completely inhibit the cellular uptake of F’-[K(DipR)₅] alone or F’-GpYEEI in the presence of [DipR]₅, suggesting that a combination of mechanisms contributes to uptake. Circular dichroism was utilized to determine the secondary structure, while transmission electron microscopy was used to evaluate the particle sizes and morphology of the peptides. The data suggest the remarkable membrane transporter property of [DipR]₅ for improving the delivery of various small molecules and cell-impermeable negatively charged molecules (e.g., siRNA and phosphopeptide).

Design and application of hybrid cyclic-linear peptide-doxorubicin conjugates as a strategy to overcome doxorubicin resistance and toxicity

Doxorubicin (Dox) is used for breast cancer, leukemia, and lymphoma treatment as an effective chemotherapeutic agent. However, Dox use is restricted due to inherent and acquired resistance and an 8-fold increase in the risk of potentially fatal cardiotoxicity. Hybrid cyclic-linear peptide [R₅K]W₇A and linear peptide R₅KW₇A were conjugated with Dox through a glutarate linker to afford [R₅K]W₇A-Dox and R₅KW₇A-Dox conjugates to generate Dox derivatives. Alternatively, [R₅K]W₇C was conjugated with Dox via a disulfide linker to generate [R₅K]W₇C-S-S-Dox conjugate, where S-S is a disulfide bond. Comparative antiproliferative assays between conjugates [R₅K]W₇A-Dox, [R₅K]W₇C-S-S-Dox, linear R₅KW₇A-Dox, the corresponding physical mixtures of the peptides, and Dox were performed in normal and cancer cells. [R₅K]W₇A-Dox conjugate was 2-fold more efficient than R₅KW₇A-Dox, and [R₅K]W₇C-S-S-Dox conjugates in inhibiting the cell proliferation of human leukemia cells (CCRF-CEM). Therefore, hybrid cyclic-linear [R₅K]W₇A-Dox conjugate was selected for further studies and inhibited the cell viability of CCRF-CEM (84%), ovarian adenocarcinoma (SK-OV-3, 39%), and gastric carcinoma (AGS, 73%) at a concentration of 5 μM after 72 h of incubation, which was comparable to Dox (5 μM) efficacy (CCRF-CEM (85%), SK-OV-3 (33%), and AGS (87%)). While [R₅K]W₇A-Dox had a significant effect on the viability of cancer cells, it exhibited minimal cytotoxicity to normal kidney (LLC-PK1, 5-7%) and heart cells (H9C2, <9%) at concentrations of 5-10 μM (compared to free Dox at 5 μM that reduced the viability of kidney and heart cells by 85% and 44%, respectively). The fluorescence microscopy images were consistent with the cytotoxicity studies, indicating minimal uptake of the cyclic-linear [R₅K]W₇A-Dox (5 μM) in H9C2 cells. In comparison, Dox (5 μM) showed significant uptake, reduced cell viability, and changed the morphology of the cells after 24 h. [R₅K]W₇A-Dox showed 16-fold and 9.5-fold higher activity against Dox-resistant cells MDA231R and MES-SA/MX2 (lethal dose for 50% cell death or LC₅₀ of 2.3 and 4.3 μM, respectively) compared to free Dox (LC₅₀ of 36-41 μM, respectively). These data, along with the results obtained from the cell viability tests, indicate comparable efficiency of [R₅K]W₇A-Dox to free Dox in leukemia, ovarian, and gastric cancer cells, significantly reduced toxicity in normal kidney LLC-PK1 and heart H9C2 cells, and significantly higher efficiency in Dox-resistant cells. A number of endocytosis inhibitors did not affect the cellular uptake of [R₅K]W₇A-Dox.

Delivery of Various Cargos into Cancer Cells and Tissues via Cell-Penetrating Peptides: A Review of the Last Decade

Cell-penetrating peptides (CPPs), also known as protein transduction domains, are a class of diverse amino acid sequences with the ability to cross cellular membranes. CPPs can deliver several bioactive cargos, including proteins, peptides, nucleic acids and chemotherapeutics, into cells. Ever since their discovery, synthetic and natural CPPs have been utilized in therapeutics delivery, gene editing and cell imaging in fundamental research and clinical experiments. Over the years, CPPs have gained significant attention due to their low cytotoxicity and high transduction efficacy. In the last decade, multiple investigations demonstrated the potential of CPPs as carriers for the delivery of therapeutics to treat various types of cancer. Besides their remarkable efficacy owing to fast and efficient delivery, a crucial benefit of CPP-based cancer treatments is delivering anticancer agents selectively, rather than mediating toxicities toward normal tissues. To obtain a higher therapeutic index and to improve cell and tissue selectivity, CPP-cargo constructions can also be complexed with other agents such as nanocarriers and liposomes to obtain encouraging outcomes. This review summarizes various types of CPPs conjugated to anticancer cargos. Furthermore, we present a brief history of CPP utilization as delivery systems for anticancer agents in the last decade and evaluate several reports on the applications of CPPs in basic research and preclinical studies.

Facile one-pot synthesis of amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug for tumor selective drug delivery

More precise drug release is expected by conjugating the drug structural units in the polyprodrugs with dynamic covalent bonds responding to different stimuli. Here, amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug was designed via a facile one-pot method with drug content of 78.6% (1.22 mmol/g) and relatively molecular weight of 2.08 × 10⁴, by condensation polymerization of acid-sensitive dimer of doxorubicin (D-DOX_ADH) with 2-iminothiolane, in presence of PEGylated D-DOX_ADH as end capping reagent for the PEGylation. Polyprodrug nanoparticles were easily obtained with mean hydrodynamic diameter of 177.6 ± 8.9 nm via self-assembly, which showed excellent acid/hypoxia co-triggered degradation and drug release performance. The ideal tumor selective cytotoxicity and enhanced antitumor efficacy were revealed with the in vitro cellular experiments. Such features make the proposed amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug a promising candidate for tumor chemotherapy.

Applications of amphipathic and cationic cyclic cell-penetrating peptides: Significant therapeutic delivery tool

A new class of peptides, cyclic cell-penetrating peptides (CPPs), has great potential for delivering a vast variety of therapeutics intracellularly for treating diverse ailments. CPPs have been used previously; however, their further use is limited due to instability, toxicity, endosomal degradation, and insufficient cellular penetration. Cyclic CPPs are being investigated in delivering therapeutics to treat various ailments, including multi-drug resistant microbial infections, HIV, and cancer. They can act as a carrier for a variety of cargos and target intracellularly. Approximately 40 cyclic peptides-based therapeutics are available in the market, and annually one cyclic peptide-based drug enters the market. Numerous research and review articles have been published in the last decade about linear and cyclic peptides separately. This review is the first to provide a comprehensive deliberation about cationic and amphipathic cyclic CPPs. Herein, we highlights their structures, significant advantages, translocation mechanisms, and delivery application in the area of biomedical sciences.

Recent Advances and Trends in Chemical CPP-Drug Conjugation Techniques

This review summarizes recent developments in conjugation techniques for the synthesis of cell-penetrating peptide (CPP)–drug conjugates targeting cancer cells. We will focus on small organic molecules as well as metal complexes that were used as cytostatic payloads. Moreover, two principle ways of coupling chemistry will be discussed direct conjugation as well as the use of bifunctional linkers. While direct conjugation of the drug to the CPP is still popular, the use of bifunctional linkers seems to gain increasing attention as it offers more advantages related to the linker chemistry. Thus, three main categories of linkers will be highlighted, forming either disulfide acid-sensitive or stimuli-sensitive bonds. All techniques will be thoroughly discussed by their pros and cons with the aim to help the reader in the choice of the optimal conjugation technique that might be used for the synthesis of a given CPP–drug conjugate

A Global Review on Short Peptides: Frontiers and Perspectives

Peptides are fragments of proteins that carry out biological functions. They act as signaling entities via all domains of life and interfere with protein-protein interactions, which are indispensable in bio-processes. Short peptides include fundamental molecular information for a prelude to the symphony of life. They have aroused considerable interest due to their unique features and great promise in innovative bio-therapies. This work focusing on the current state-of-the-art short peptide-based therapeutical developments is the first global review written by researchers from all continents, as a celebration of 100 years of peptide therapeutics since the commencement of insulin therapy in the 1920s. Peptide "drugs" initially played only the role of hormone analogs to balance disorders. Nowadays, they achieve numerous biomedical tasks, can cross membranes, or reach intracellular targets. The role of peptides in bio-processes can hardly be mimicked by other chemical substances. The article is divided into independent sections, which are related to either the progress in short peptide-based theranostics or the problems posing challenge to bio-medicine. In particular, the SWOT analysis of short peptides, their relevance in therapies of diverse diseases, improvements in (bio)synthesis platforms, advanced nano-supramolecular technologies, aptamers, altered peptide ligands and in silico methodologies to overcome peptide limitations, modern smart bio-functional materials, vaccines, and drug/gene-targeted delivery systems are discussed.

Tumor-Cell-Surface Adherable Peptide-Drug Conjugate Prodrug Nanoparticles Inhibit Tumor Metastasis and Augment Treatment Efficacy

Cancer metastasis is the main cause of chemotherapeutic failure. Inhibiting the activity of matrix metalloproteinases (MMPs) is a common strategy for reducing metastasis. However, broad-spectrum MMP-inhibitors (MMPI) may cause undesired side effects. Here, we screened a selective MMP2 inhibitor (CCKIGLFRWR) and linked it with doxorubicin (DOX) to produce an amphiphilic peptide-drug conjugate (PDC). Then novel core-shell nanoparticles were self-assembled from PDC core and modified polylysine (MPL) shell. When the particles were passively targeted to the tumor site, the PDC core was exposed for charge switch of the MPL shell, aggregated for its transformation behavior, and specially adhered to the cell membrane. The disulfide bond between the MMPI peptide and DOX was broken via a low concentration of glutathione-mediated reduction in tumor microenvironment. DOX could effectively enter the tumor cells. Meanwhile, the MMPI peptide could selectively inhibit the activity of the MMP2 and effectively inhibit tumor metastasis.

Synthesis of Gold Nanoparticle: Peptide-Drug Conjugates for Targeted Drug Delivery

Peptide-drug conjugates (PDCs) are being developed for the targeted delivery of drugs to cancer cells. Several approaches are being followed to enhance their stability in biological solutions. Here we describe an effective method to easily couple PDCs to polyethylene-coated gold nanoparticles. We also outline analytical methods to validate the coupling and assays to measure the stability and cytotoxic efficacy of the conjugates.

Understanding Cell Penetration of Cyclic Peptides

Approximately 75% of all disease-relevant human proteins, including those involved in intracellular protein-protein interactions (PPIs), are undruggable with the current drug modalities (i.e., small molecules and biologics). Macrocyclic peptides provide a potential solution to these undruggable targets because their larger sizes (relative to conventional small molecules) endow them the capability of binding to flat PPI interfaces with antibody-like affinity and specificity. Powerful combinatorial library technologies have been developed to routinely identify cyclic peptides as potent, specific inhibitors against proteins including PPI targets. However, with the exception of a very small set of sequences, the vast majority of cyclic peptides are impermeable to the cell membrane, preventing their application against intracellular targets. This Review examines common structural features that render most cyclic peptides membrane impermeable, as well as the unique features that allow the minority of sequences to enter the cell interior by passive diffusion, endocytosis/endosomal escape, or other mechanisms. We also present the current state of knowledge about the molecular mechanisms of cell penetration, the various strategies for designing cell-permeable, biologically active cyclic peptides against intracellular targets, and the assay methods available to quantify their cell-permeability.

Novel therapeutic interventions in cancer treatment using protein and peptide-based targeted smart systems

Cancer, being the most prevalent and resistant disease afflicting any gender, age or social status, is the ultimate challenge for the scientific community. The new generation therapeutics for cancer management has shifted the approach to personalized/precision medicine, making use of patient- and tumor-specific markers for specifying the targeted therapies for each patient. Peptides targeting these cancer-specific signatures hold enormous potential for cancer therapy and diagnosis. The rapid advancements in the combinatorial peptide libraries served as an impetus to the development of multifunctional peptide-based materials for targeted cancer therapy. The present review outlines benefits and shortcomings of peptides as cancer therapeutics and the potential of peptide modified nanomedicines for targeted delivery of anticancer agents.

Cyclic Cell-Penetrating Peptides as Efficient Intracellular Drug Delivery Tools

Cyclic cell-penetrating peptides are relatively a newer class of peptides that have a huge potential for the intracellular delivery of therapeutic agents aimed at treating challenging ailments like multidrug-resistant bacterial diseases, cancer, and HIV infection. Cell-penetrating peptides (CPPs) have been extensively explored as intracellular delivery vehicles; however, they have some inherent limitations like poor stability, endosomal entrapment, toxicity, and suboptimal cell penetration. Owing to their favorable properties that avoid these limitations, cyclic CPPs can provide a good alternative to linear CPPs. Several Reviews have been published in the past decade that cover CPPs and cyclic peptides independently. To the best of our knowledge, this is one of the first Reviews that covers cyclic CPPs comprehensively in the light of studies published so far. In this Review, we have detailed examples of cyclic CPPs, their structures, and cyclization strategies followed by a detailed account of their advantages over their linear counterparts. A hot area in cyclic CPPs is the exploration of cell-penetration mechanisms; this Review highlights this topic in detail. Finally, we will review the applications of cyclic CPPs, followed by conclusions and future prospects.

Synthesis and Antiproliferative Activities of Conjugates of Paclitaxel and Camptothecin with a Cyclic Cell-Penetrating Peptide

Cell-penetrating peptide [WR]₅ has been previously shown to be an efficient molecular transporter for various hydrophilic and hydrophobic molecules. The peptide was synthesized using Fmoc/tBu solid-phase chemistry, and one arginine was replaced with one lysine to enable the conjugation with the anticancer drugs. Paclitaxel (PTX) was functionalized with an esterification reaction at the C2' hydroxyl group of PTX with glutaric anhydride and conjugated with the cyclic peptide [W(WR)₄K(βAla)] in DMF to obtain the peptide-drug conjugate PTX1. Furthermore, camptothecin (CPT) was modified at the C(20)-hydroxyl group through the reaction with triphosgene. Then, it was conjugated with two functionalized cyclic peptides through a formyl linker affording two different conjugates, namely CPT1 and CPT2. All the conjugates showed better water solubility as compared to the parent drug. The cytotoxicity assay of the drugs and their conjugates with the peptides were evaluated in the human breast cancer MCF-7 cell line. PTX inhibited cell proliferation by 39% while the PTX-peptide conjugate inhibited the proliferation by ~18% after 72 h incubation. On the other hand, CPT, CPT1, and CPT2 reduced the cell proliferation by 68%, 39%, and 62%, respectively, in the MCF-7 cell lines at 5 µM concentration after 72 h incubation.

Recent Advances in Cell Penetrating Peptide-Based Anticancer Therapies

Cell-penetrating-peptides (CPPs) are small amino-acid sequences characterized by their ability to cross cellular membranes. They can transport various bioactive cargos inside cells including nucleic acids, large proteins, and other chemical compounds. Since 1988, natural and synthetic CPPs have been developed for applications ranging from fundamental to applied biology (cell imaging, gene editing, therapeutics delivery). In recent years, a great number of studies reported the potential of CPPs as carriers for the treatment of various diseases. Apart from a good efficacy due to a rapid and potent delivery, a crucial advantage of CPP-based therapies is the peptides low toxicity compared to most drug carriers. On the other hand, they are quite unstable and lack specificity. Higher specificity can be obtained using a cell-specific CPP to transport the therapeutic agent or using a non-specific CPP to transport a cargo with a targeted activity. CPP-cargo complexes can also be conjugated to another moiety that brings cell- or tissue-specificity. Studies based on all these approaches are showing promising results. Here, we focus on recent advances in the potential usage of CPPs in the context of cancer therapy, with a particular interest in CPP-mediated delivery of anti-tumoral proteins.

Environmentally friendly synthesis of unsymmetrical dialkyl disulfides by reacting organic halides with thiourea and sodium thiosulfate in an aqueous medium

The developed synthetic procedure is economical and environmentally friendly. It also avoids using toxic organic solvents, and an oxidant or a reductant.