Peptide Conjugates with Small Molecules Designed to Enhance Efficacy and Safety

Engineering peptide drug therapeutics through chemical conjugation and implication in clinics

The development of peptide drugs has made tremendous progress in the past few decades because of the advancements in modification chemistry and analytical technologies. The novel-designed peptide drugs have been modified through various biochemical methods with improved diagnostic, therapeutic, and drug-delivery strategies. Researchers found it a helping hand to overcome the inherent limitations of peptides and bring continued advancements in their applications. Furthermore, the emergence of peptide-drug conjugates (PDCs)-utilizes target-oriented peptide moieties as a vehicle for cytotoxic payloads via conjugation with cleavable chemical agents, resulting in the key foundation of the new era of targeted peptide drugs. This review summarizes the various classifications of peptide drugs, suitable chemical modification strategies to improve the ADME (adsorption, distribution, metabolism, and excretion) features of peptide drugs, and recent (2015-early 2024) progress/achievements in peptide-based drug delivery systems as well as their fruitful implication in preclinical and clinical studies. Furthermore, we also summarized the brief description of other types of PDCs, including peptide-MOF conjugates and peptide-UCNP conjugates. The principal aim is to provide scattered and diversified knowledge in one place and to help researchers understand the pinching knots in the science of PDC development and progress toward a bright future of novel peptide drugs.

Biological Activities of Soy Protein Hydrolysate Conjugated with Mannose and Allulose

The non-enzymatic conjugation of peptides through the Maillard reaction has gained attention as an effective method to enhance biological functions. This study focuses on two conjugate mixtures: crude soy protein hydrolysate (SPH) conjugated with mannose (SPHM) and crude soy protein hydrolysate conjugated with allulose (SPHA). These two mixtures were products of the Maillard reaction, also known as non-enzymatic glycation. In vitro experiments were conducted to evaluate the antioxidant, anti-pancreatic lipase, inhibition of Bovine Serum Albumin (BSA) denaturation, and anti-angiotensin converting enzyme (ACE) activities of these conjugated mixtures. The results indicate that conjugated mixtures significantly enhance the antioxidant potential demonstrated via the DPPH and FRAP assays. SPHA exhibits superior DPPH scavenging activity (280.87 ± 16.39 µg Trolox/mL) and FRAP value (38.91 ± 0.02 mg Trolox/mL). Additionally, both conjugate mixtures, at a concentration of 10 mg/mL, enhance the BSA denaturation properties, with SPHM showing slightly higher effectiveness compared to SPHA (19.78 ± 2.26% and 5.95 ± 3.89%, respectively). SPHA also shows an improvement in pancreatic lipase inhibition (29.43 ± 1.94%) when compared to the SPHM (23.34 ± 3.75%). Furthermore, both the conjugated mixtures and rare sugars exhibit ACE inhibitory properties on their own, effectively reducing ACE activity. Notably, the ACE inhibitory effects of the individual compounds and their conjugate mixtures (SPHM and SPHA) are comparable to those of positive control (Enalapril). In conclusion, SPHM and SPHA demonstrate a variety of bioactive properties, suggesting their potential use in functional foods or as ingredients in supplementary products.

Potency of a small molecule that targets the molluscum contagiosum virus processivity factor increases when conjugated to a tripeptide

We recently developed compound FC-7269 for targeting the Molluscum contagiosum virus processivity factor (mD4) and demonstrated its ability to inhibit viral processive DNA synthesis in vitro and cellular infection of an mD4-dependent virus (Antiviral Res 211, 2023,105520). However, despite a thorough medicinal chemistry campaign we were unable to generate a potent second analog as a requisite for drug development. We overcame this impasse, by conjugating a short hydrophobic trivaline peptide to FC-7269 to produce FC-TriVal-7269 which significantly increased antiviral potency and reduced cellular toxicity.

Targeted delivery of HSP90 inhibitors for efficient therapy of CD44-positive acute myeloid leukemia and solid tumor-colon cancer

Heat shock protein 90 (HSP90) is overexpressed in numerous cancers, promotes the maturation of numerous oncoproteins and facilitates cancer cell growth. Certain HSP90 inhibitors have entered clinical trials. Although less than satisfactory clinical effects or insurmountable toxicity have compelled these trials to be terminated or postponed, these results of preclinical and clinical studies demonstrated that the prospects of targeting therapeutic strategies involving HSP90 inhibitors deserve enough attention. Nanoparticulate-based drug delivery systems have been generally supposed as one of the most promising formulations especially for targeting strategies. However, so far, no active targeting nano-formulations have succeeded in clinical translation, mainly due to complicated preparation, complex formulations leading to difficult industrialization, incomplete biocompatibility or nontoxicity. In this study, HSP90 and CD44-targeted A6 peptide functionalized biomimetic nanoparticles (A6-NP) was designed and various degrees of A6-modification on nanoparticles were fabricated to evaluate targeting ability and anticancer efficiency. With no excipients, the hydrophobic HSP90 inhibitor G2111 and A6-conjugated human serum albumin could self-assemble into nanoparticles with a uniform particle size of approximately 200 nm, easy fabrication, well biocompatibility and avoidance of hepatotoxicity. Besides, G2111 encapsulated in A6-NP was only released less than 5% in 12 h, which may avoid off-target cell toxicity before entering into cancer cells. A6 peptide modification could significantly enhance uptake within a short time. Moreover, A6-NP continues to exert the broad anticancer spectrum of Hsp90 inhibitors and displays remarkable targeting ability and anticancer efficacy both in hematological malignancies and solid tumors (with colon tumors as the model cancer) both in vitro and in vivo. Overall, A6-NP, as a simple, biomimetic and active dual-targeting (CD44 and HSP90) nanomedicine, displays high potential for clinical translation.

Peptide-Mediated Nanocarriers for Targeted Drug Delivery: Developments and Strategies

Effective drug delivery is essential for cancer treatment. Drug delivery systems, which can be tailored to targeted transport and integrated tumor therapy, are vital in improving the efficiency of cancer treatment. Peptides play a significant role in various biological and physiological functions and offer high design flexibility, excellent biocompatibility, adjustable morphology, and biodegradability, making them promising candidates for drug delivery. This paper reviews peptide-mediated drug delivery systems, focusing on self-assembled peptides and peptide-drug conjugates. It discusses the mechanisms and structural control of self-assembled peptides, the varieties and roles of peptide-drug conjugates, and strategies to augment peptide stability. The review concludes by addressing challenges and future directions.

Tripeptides conjugated with thiosemicarbazones: new inhibitors of tyrosinase for cosmeceutical use

The development of skin-care products is recently growing. Cosmetic formulas containing active ingredients with proven efficacy, namely cosmeceuticals, are based on various compounds, including peptides. Different whitening agents featuring anti-tyrosinase activity have been applied in the cosmeceutical field. Despite their availability, their applicability is often limited due to several drawbacks including toxicity, lack of stability, and other factors. In this work, we present the inhibitory effect on diphenolase activity of thiosemicarbazone (TSC)-peptide conjugates. Tripeptides FFY, FWY, and FYY were conjugated with three TSCs bearing one or two aromatic rings via amide bond formation in a solid phase. Compounds were then examined as tyrosinase and melanogenesis inhibitors in murine melanoma B16F0 cell line, followed by the cytotoxicity assays of these cells. In silico investigations explained the differences in the activity, observed among tested compounds. Mushroom tyrosinase was inhibited by TSC1-conjugates at micromolar level, with IC₅₀ lower than this for kojic acid, a widely used reference compound. Up to now, this is the first report regarding thiosemicarbazones conjugated with tripeptides, synthesised for the purpose of tyrosinase inhibition.

Design, synthesis and bioactivity investigation of peptide-camptothecin conjugates as anticancer agents with a potential to overcome drug resistance

Camptothecin (CPT) is a natural plant alkaloid from Camptotheca that exhibits a potent anticancer activity. However, its continued utilization is hindered by drawbacks such as low water solubility and restricted tumor selectivity. Cationic anticancer peptides (CAPs) are generally soluble in water, and exhibit favorable selectivity against malignant cells. In previous study, we have reported a CAP termed KM8-Aib present conspicuous selective anticancer effect. Thus, it is postulated conjugating KM8-Aib with CPT might be a plausible approach to improve the defects of CPT. A series of peptide-CPT conjugates were synthesized and subjected to biological evaluation. Among these compounds, Kb-CC07 displayed the highest selective activity against a set of cancer cell lines including drug-resistant cells, showing the IC50 values in the 0.11-1.01 μM range which is 1.9-22.6 times better than that of CPT, and a wide therapeutic index of 124.5 (vs 5.3 for CPT). The water solubility of Kb-CC07 was also improved by ∼ 100 fold compared with CPT. Further investigation unraveled that Kb-CC07 could effectively penetrate across plasma membranes and delivered more CPT molecules into cancer cells, overcoming the drug-resistance result from efflux drug transporters on tumor surface. In vivo experiments supported that Kb-CC07 has excellent in vivo antiproliferative activity against drug-resistant tumors over CPT (tumor growth inhibition of 98.2% and 37.5% for Kb-CC07 and CPT, respectively, at 5 μmol·kg-1), and prompts CPT accumulation in tumor tissue rather than normal organs, thus producing limited toxicities. To sum up, coupling therapeutic agents to CAPs would be a potential strategy to conquer the shortcomings of anticancer drugs. Additionally, Kb-CC07 is suggested to be a promising anticancer candidate deserving further investigation.

Site-specific bioorthogonal protein labelling by tetrazine ligation using endogenous β-amino acid dienophiles

The tetrazine ligation is an inverse electron-demand Diels-Alder reaction widely used for bioorthogonal modifications due to its versatility, site specificity and fast reaction kinetics. A major limitation has been the incorporation of dienophiles in biomolecules and organisms, which relies on externally added reagents. Available methods require the incorporation of tetrazine-reactive groups by enzyme-mediated ligations or unnatural amino acid incorporation. Here we report a tetrazine ligation strategy, termed TyrEx (tyramine excision) cycloaddition, permitting autonomous dienophile generation in bacteria. It utilizes a unique aminopyruvate unit introduced by post-translational protein splicing at a short tag. Tetrazine conjugation occurs rapidly with a rate constant of 0.625 (15) M-1 s-1 and was applied to produce a radiolabel chelator-modified Her2-binding Affibody and intracellular, fluorescently labelled cell division protein FtsZ. We anticipate the labelling strategy to be useful for intracellular studies of proteins, as a stable conjugation method for protein therapeutics, as well as other applications.

Improving the stability of thiol-maleimide bioconjugates via the formation of a thiazine structure

Linker stability is critically important for the efficacy and safety of peptide and protein conjugates used for biological applications. One common conjugation strategy, thiol-maleimide coupling, generates a succinimidyl thioether linker with limited stability under physiological conditions. We have shown in previous work that when a peptide with an N-terminal cysteine is conjugated to a maleimide reagent, a thiazine structure is formed via a chemical rearrangement. Our preliminary work indicated that the thiazine linker has favorable stability. Here, we report the evaluation of a thiazine linker as an alternative to the widely used succinimidyl thioether linker for thiol-maleimide bioconjugation. The stability of the thiazine conjugate in comparison to the thioether conjugate was assessed across a broad pH range. Additionally, the propensity for retro-Michael reaction and cross-reactivity with other thiols was evaluated by treating conjugates in the presence of glutathione. The studies indicated that the thiazine linker degrades markedly slower than the thioether conjugate. In addition, the thiazine linker is over 20 times less susceptible to glutathione adduct formation. The NMR study of the thiazine structure confirmed that the formation of the thiazine linker is a stereoselective process that yields a single diastereomer. In summary, we propose the use of the thiazine linker obtained by conjugation of maleimide-containing reagents with peptides or proteins presenting an N-terminal cysteine as a novel approach for bioconjugation. The advantages of this approach are the formation of a linker with a well-defined stereochemical configuration, increased stability at physiological pH, and a strongly reduced propensity for thiol exchange.

Development of New Leishmanicidal Compounds via Bioconjugation of Antimicrobial Peptides and Antileishmanial Guanidines

Leishmaniasis refers to a collection of diseases caused by protozoa from the Leishmania genus. These diseases, along with other parasitic afflictions, pose a significant public health issue, particularly given the escalating number of at-risk patients. This group includes immunocompromised individuals and those residing in impoverished conditions. The treatment of leishmaniasis is crucial, particularly in light of the mortality rate associated with nontreatment, which stands at 20-30,000 deaths per year globally. However, the therapeutic options currently available are limited, often ineffective, and potentially toxic. Consequently, the pursuit of new therapeutic alternatives is warranted. This study aims to design, synthesize, and evaluate the leishmanicidal activity of antimicrobial peptides functionalized with guanidine compounds and identify those with enhanced potency and selectivity against the parasite. Accordingly, three bioconjugates were obtained by using the solid-phase peptide synthesis protocol. Each proved to be more potent against intracellular amastigotes than their respective peptide or guanidine compounds alone and demonstrated higher selectivity to the parasites than to the host cells. Thus, the conjugation strategy employed with these compounds effectively contributes to the development of new molecules with leishmanicidal activity.

Synthesis and Evaluation of a Monomethyl Auristatin E─Integrin αvβ6 Binding Peptide-Drug Conjugate for Tumor Targeted Drug Delivery

Many anticancer drugs exhibit high systemic off-target toxicities causing severe side effects. Peptide-drug conjugates (PDCs) that target tumor-specific receptors such as integrin αvβ6 are emerging as powerful tools to overcome these challenges. The development of an integrin αvβ6-selective PDC was achieved by combining the therapeutic efficacy of the cytotoxic drug monomethyl auristatin E with the selectivity of the αvβ6-binding peptide (αvβ6-BP) and with the ability of positron emission tomography (PET) imaging by copper-64. The [64Cu]PDC-1 was produced efficiently and in high purity. The PDC exhibited high human serum stability, integrin αvβ6-selective internalization, cell binding, and cytotoxicity. Integrin αvβ6-selective tumor accumulation of the [64Cu]PDC-1 was visualized with PET-imaging and corroborated by biodistribution, and [64Cu]PDC-1 showed promising in vivo pharmacokinetics. The [natCu]PDC-1 treatment resulted in prolonged survival of mice bearing αvβ6 (+) tumors (median survival: 77 days, vs αvβ6 (-) tumor group 49 days, and all other control groups 37 days).

Beyond canonical PROTAC: biological targeted protein degradation (bioTPD)

Targeted protein degradation (TPD) is an emerging therapeutic strategy with the potential to modulate disease-associated proteins that have previously been considered undruggable, by employing the host destruction machinery. The exploration and discovery of cellular degradation pathways, including but not limited to proteasomes and lysosome pathways as well as their degraders, is an area of active research. Since the concept of proteolysis-targeting chimeras (PROTACs) was introduced in 2001, the paradigm of TPD has been greatly expanded and moved from academia to industry for clinical translation, with small-molecule TPD being particularly represented. As an indispensable part of TPD, biological TPD (bioTPD) technologies including peptide-, fusion protein-, antibody-, nucleic acid-based bioTPD and others have also emerged and undergone significant advancement in recent years, demonstrating unique and promising activities beyond those of conventional small-molecule TPD. In this review, we provide an overview of recent advances in bioTPD technologies, summarize their compositional features and potential applications, and briefly discuss their drawbacks. Moreover, we present some strategies to improve the delivery efficacy of bioTPD, addressing their challenges in further clinical development.

Antiviral Evaluation of New Synthetic Bioconjugates Based on GA-Hecate: A New Class of Antivirals Targeting Different Steps of Zika Virus Replication

Re-emerging arboviruses represent a serious health problem due to their rapid vector-mediated spread, mainly in urban tropical areas. The 2013-2015 Zika virus (ZIKV) outbreak in South and Central America has been associated with cases of microcephaly in newborns and Guillain-Barret syndrome. We previously showed that the conjugate gallic acid-Hecate (GA-FALALKALKKALKKLKKALKKAL-CONH2)-is an efficient inhibitor of the hepatitis C virus. Here, we show that the Hecate peptide is degraded in human blood serum into three major metabolites. These metabolites conjugated with gallic acid were synthesized and their effect on ZIKV replication in cultured cells was evaluated. The GA-metabolite 5 (GA-FALALKALKKALKKL-COOH) was the most efficient in inhibiting two ZIKV strains of African and Asian lineage at the stage of both virus entry (virucidal and protective) and replication (post-entry). We also demonstrate that GA-metabolite 5 does not affect cell growth after 7 days of continuous treatment. Thus, this study identifies a new synthetic antiviral compound targeting different steps of ZIKV replication in vitro and with the potential for broad reactivity against other flaviviruses. Our work highlights a promising strategy for the development of new antivirals based on peptide metabolism and bioconjugation.

Targeting Peptides: The New Generation of Targeted Drug Delivery Systems

Peptides can act as targeting molecules, analogously to oligonucleotide aptamers and antibodies. They are particularly efficient in terms of production and stability in physiological environments; in recent years, they have been increasingly studied as targeting agents for several diseases, from tumors to central nervous system disorders, also thanks to the ability of some of them to cross the blood-brain barrier. In this review, we will describe the techniques employed for their experimental and in silico design, as well as their possible applications. We will also discuss advancements in their formulation and chemical modifications that make them even more stable and effective. Finally, we will discuss how their use could effectively help to overcome various physiological problems and improve existing treatments.

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.

Advancements, challenges and future perspectives on peptide-based drugs: Focus on antimicrobial peptides

Among other health related issues, the rising concerns on drug resistance led to look for alternative pharmaceutical drugs that are effective both against infectious and noninfectious diseases. Antimicrobial peptides (AMPs) emerged as potential therapeutic molecule with wide range of applications. With their limitations, AMPs have gained reputable attentions in research as well as in the pharmaceutical industry. This review highlighted the historical background, research trends, technological advancements, challenges, and future perspectives in the development and applications of peptide drugs. Some vital questions related with the need for pharmaceutical production, factors for the slow and steady journey, the importance of oral bioavailability, and the drug resistance possibilities of AMPs were raised and addressed accordingly. Therefore, the current study is believed to provide a profound understanding in the past and current scenarios and future directions on the therapeutic impacts of peptide drugs.

Antiviral Peptide-Based Conjugates: State of the Art and Future Perspectives

Infectious diseases caused by microbial pathogens (bacteria, virus, fungi, parasites) claim millions of deaths per year worldwide and have become a serious challenge to global human health in our century. Viral infections are particularly notable in this regard, not only because humankind is facing some of the deadliest viral pandemics in recent history, but also because the arsenal of drugs to combat the high levels of mutation, and hence the antigenic variability of (mostly RNA) viruses, is disturbingly scarce. Therefore, the search for new antivirals able to successfully fight infection with minimal or no adverse effects on the host is a pressing task. Traditionally, antiviral therapies have relied on relatively small-sized drugs acting as proteases, polymerases, integrase inhibitors, etc. In recent decades, novel approaches involving targeted delivery such as that achieved by peptide-drug conjugates (PDCs) have gained attention as alternative (pro)drugs for tackling viral diseases. Antiviral PDC therapeutics typically involve one or more small drug molecules conjugated to a cell-penetrating peptide (CPP) carrier either directly or through a linker. Such integration of two bioactive elements into a single molecular entity is primarily aimed at achieving improved bioavailability in conditions where conventional drugs are challenged, but may also turn up novel unexpected functionalities and applications. Advances in peptide medicinal chemistry have eased the way to antiviral PDCs, but challenges remain on the way to therapeutic success. In this paper, we review current antiviral CPP-drug conjugates (antiviral PDCs), with emphasis on the types of CPP and antiviral cargo. We integrate the conjugate and the chemical approaches most often applied to combine both entities. Additionally, we comment on various obstacles faced in the design of antiviral PDCs and on the future outlooks for this class of antiviral therapeutics.

Coenzyme self-sufficiency system-recent advances in microbial production of high-value chemical phenyllactic acid

Phenyllactic acid (PLA), a natural antimicrobial substance, has many potential applications in the food, animal feed, pharmaceutical and cosmetic industries. However, its production is limited by the complex reaction steps involved in its chemical synthesis. Through advances in metabolic engineering and synthetic biology strategies, enzymatic or whole-cell catalysis was developed as an alternative method for PLA production. Herein, we review recent developments in metabolic engineering and synthetic biology strategies that promote the microbial production of high-value PLA. Specially, the advantages and disadvantages of the using of the three kinds of substrates, which includes phenylpyruvate, phenylalanine and glucose as starting materials by natural or engineered microbes is summarized. Notably, the bio-conversion of PLA often requires the consumption of expensive coenzyme NADH. To overcome the issues of NADH regeneration, efficiently internal cofactor regeneration systems constructed by co-expressing different enzyme combinations composed of lactate dehydrogenase with others for enhancing the PLA production, as well as their possible improvements, are discussed. In particular, the construction of fusion proteins with different linkers can achieve higher PLA yield and more efficient cofactor regeneration than that of multi-enzyme co-expression. Overall, this review provides a comprehensive overview of PLA biosynthesis pathways and strategies for increasing PLA yield through biotechnology, providing future directions for the large-scale commercial production of PLA and the expansion of downstream applications.

Peptides as Pharmacological Carriers to the Brain: Promises, Shortcomings and Challenges

Central nervous system (CNS) diseases are among the most difficult to treat, mainly because the vast majority of the drugs fail to cross the blood-brain barrier (BBB) or to reach the brain at concentrations adequate to exert a pharmacological activity. The obstacle posed by the BBB has led to the in-depth study of strategies allowing the brain delivery of CNS-active drugs. Among the most promising strategies is the use of peptides addressed to the BBB. Peptides are versatile molecules that can be used to decorate nanoparticles or can be conjugated to drugs, with either a stable link or as pro-drugs. They have been used to deliver to the brain both small molecules and proteins, with applications in diverse therapeutic areas such as brain cancers, neurodegenerative diseases and imaging. Peptides can be generally classified as receptor-targeted, recognizing membrane proteins expressed by the BBB microvessels (e.g., Angiopep2, CDX, and iRGD), "cell-penetrating peptides" (CPPs; e.g. TAT_47-57, SynB1/3, and Penetratin), undergoing transcytosis through unspecific mechanisms, or those exploiting a mixed approach. The advantages of peptides have been extensively pointed out, but so far few studies have focused on the potential negative aspects. Indeed, despite having a generally good safety profile, some peptide conjugates may display toxicological characteristics distinct from those of the peptide itself, causing for instance antigenicity, cardiovascular alterations or hemolysis. Other shortcomings are the often brief lifetime in vivo, caused by the presence of peptidases, the vulnerability to endosomal/lysosomal degradation, and the frequently still insufficient attainable increase of brain drug levels, which remain below the therapeutically useful concentrations. The aim of this review is to analyze not only the successful and promising aspects of the use of peptides in brain targeting but also the problems posed by this strategy for drug delivery.

Peptide-Based Low Molecular Weight Photosensitive Supramolecular Gelators

Over the last couple of decades, stimuli-responsive supramolecular gels comprising synthetic short peptides as building blocks have been explored for various biological and material applications. Though a wide range of stimuli has been tested depending on the structure of the peptides, light as a stimulus has attracted extensive attention due to its non-invasive, non-contaminant, and remotely controllable nature, precise spatial and temporal resolution, and wavelength tunability. The integration of molecular photo-switch and low-molecular-weight synthetic peptides may thus provide access to supramolecular self-assembled systems, notably supramolecular gels, which may be used to create dynamic, light-responsive "smart" materials with a variety of structures and functions. This short review summarizes the recent advancement in the area of light-sensitive peptide gelation. At first, a glimpse of commonly used molecular photo-switches is given, followed by a detailed description of their incorporation into peptide sequences to design light-responsive peptide gels and the mechanism of their action. Finally, the challenges and future perspectives for developing next-generation photo-responsive gels and materials are outlined.

Non-small molecule PROTACs (NSM-PROTACs): Protein degradation kaleidoscope

The proteolysis targeting chimeras (PROTACs) technology has been rapidly developed since its birth in 2001, attracting rapidly growing attention of scientific institutes and pharmaceutical companies. At present, a variety of small molecule PROTACs have entered the clinical trial. However, as small molecule PROTACs flourish, non-small molecule PROTACs (NSM-PROTACs) such as peptide PROTACs, nucleic acid PROTACs and antibody PROTACs have also advanced considerably over recent years, exhibiting the unique characters beyond the small molecule PROTACs. Here, we briefly introduce the types of NSM-PROTACs, describe the advantages of NSM-PROTACs, and summarize the development of NSM-PROTACs so far in detail. We hope this article could not only provide useful insights into NSM-PROTACs, but also expand the research interest of NSM-PROTACs.

Peptide-Based Bioconjugates and Therapeutics for Targeted Anticancer Therapy

With rapidly growing knowledge in bioinformatics related to peptides and proteins, amino acid-based drug-design strategies have recently gained importance in pharmaceutics. In the past, peptide-based biomedicines were not widely used due to the associated severe physiological problems, such as low selectivity and rapid degradation in biological systems. However, various interesting peptide-based therapeutics combined with drug-delivery systems have recently emerged. Many of these candidates have been developed for anticancer therapy that requires precisely targeted effects and low toxicity. These research trends have become more diverse and complex owing to nanomedicine and antibody–drug conjugates (ADC), showing excellent therapeutic efficacy. Various newly developed peptide–drug conjugates (PDC), peptide-based nanoparticles, and prodrugs could represent a promising therapeutic strategy for patients. In this review, we provide valuable insights into rational drug design and development for future pharmaceutics.

Integrated Design of a Membrane-Lytic Peptide-Based Intravenous Nanotherapeutic Suppresses Triple-Negative Breast Cancer

Membrane-lytic peptides offer broad synthetic flexibilities and design potential to the arsenal of anticancer therapeutics, which can be limited by cytotoxicity to noncancerous cells and induction of drug resistance via stress-induced mutagenesis. Despite continued research efforts on membrane-perforating peptides for antimicrobial applications, success in anticancer peptide therapeutics remains elusive given the muted distinction between cancerous and normal cell membranes and the challenge of peptide degradation and neutralization upon intravenous delivery. Using triple-negative breast cancer as a model, the authors report the development of a new class of anticancer peptides. Through function-conserving mutations, the authors achieved cancer cell selective membrane perforation, with leads exhibiting a 200-fold selectivity over non-cancerogenic cells and superior cytotoxicity over doxorubicin against breast cancer tumorspheres. Upon continuous exposure to the anticancer peptides at growth-arresting concentrations, cancer cells do not exhibit resistance phenotype, frequently observed under chemotherapeutic treatment. The authors further demonstrate efficient encapsulation of the anticancer peptides in 20 nm polymeric nanocarriers, which possess high tolerability and lead to effective tumor growth inhibition in a mouse model of MDA-MB-231 triple-negative breast cancer. This work demonstrates a multidisciplinary approach for enabling translationally relevant membrane-lytic peptides in oncology, opening up a vast chemical repertoire to the arms race against cancer.

The development of peptide-drug conjugates (PDCs) strategies for paclitaxel

INTRODUCTION

Paclitaxel is a powerful and effective anti-tumor drug with wide clinical application. However, there are still some limitations, including poor water solubility, low specificity, and susceptibility to drug resistance. The peptide-drug conjugates (PDCs) represent a rising class of therapeutic drugs, which combines small-molecule chemotherapeutic drugs with highly flexible peptides through a cleavable or non-cleavable linker. When this strategy is applied, the therapeutic effects of paclitaxel can be improved.

AREAS COVERED

In this review, we discuss the application of the PDCs strategy in paclitaxel, including two parts: the tumor targeting peptide-paclitaxel conjugates and the cell penetrating peptide-paclitaxel conjugates.

EXPERT OPINION

Combining drugs with multifunctional peptides covalently is an effective strategy for delivering paclitaxel to tumors. Depending on different functional peptides, conjugates can increase the water solubility of paclitaxel, tumor permeability of paclitaxel, the accumulation of paclitaxel in tumor tissues, and enhance the antitumor effect of paclitaxel. In addition, due to the change of cell entry mechanism, partial conjugates can restore the therapeutic activity of paclitaxel against resistant tumors. Notably, in order to better translate into the clinical field in the future, more research should be conducted to ensure the safety and effectiveness of peptide-paclitaxel conjugates.

The Use of Bioactive Compounds in Hyperglycemia- and Amyloid Fibrils-Induced Toxicity in Type 2 Diabetes and Alzheimer’s Disease

It has become increasingly apparent that defective insulin signaling may increase the risk for developing Alzheimer’s disease (AD), influence neurodegeneration through promotion of amyloid formation or by increasing inflammatory responses to intraneuronal β-amyloid. Recent work has demonstrated that hyperglycemia is linked to cognitive decline, with elevated levels of glucose causing oxidative stress in vulnerable tissues such as the brain. The ability of β-amyloid peptide to form β-sheet-rich aggregates and induce apoptosis has made amyloid fibrils a leading target for the development of novel pharmacotherapies used in managing and treatment of neuropathological conditions such as AD-related cognitive decline. Additionally, deposits of β-sheets folded amylin, a glucose homeostasis regulator, are also present in diabetic patients. Thus, therapeutic compounds capable of reducing intracellular protein aggregation in models of neurodegenerative disorders may prove useful in ameliorating type 2 diabetes mellitus symptoms. Furthermore, both diabetes and neurodegenerative conditions, such as AD, are characterized by chronic inflammatory responses accompanied by the presence of dysregulated inflammatory biomarkers. This review presents current evidence describing the role of various small bioactive molecules known to ameliorate amyloidosis and subsequent effects in prevention and development of diabetes and AD. It also highlights the potential efficacy of peptide–drug conjugates capable of targeting intracellular targets.

Synthesis and preliminary evaluation of octreotate conjugates of bioactive synthetic amatoxins for targeting somatostatin receptor (sstr2) expressing cells

Targeted cancer therapy represents a paradigm-shifting approach that aims to deliver a toxic payload selectively to target-expressing cells thereby sparing normal tissues the off-target effects associated with traditional chemotherapeutics. Since most targeted constructs rely on standard microtubule inhibitors or DNA-reactive molecules as payloads, new toxins that inhibit other intracellular targets are needed to realize the full potential of targeted therapy. Among these new payloads, α-amanitin has gained attraction as a payload in targeted therapy. Here, we conjugate two synthetic amanitins at different sites to demonstrate their utility as payloads in peptide drug conjugates (PDCs). As an exemplary targeting agent, we chose octreotate, a well-studied somatostatin receptor (sstr2) peptide agonist for the conjugation to synthetic amatoxins via three tailor-built linkers. The linker chemistry permitted the evaluation of one non-cleavable and two cleavable self-immolative conjugates. The immolating linkers were chosen to take advantage of either the reducing potential of the intracellular environment or the high levels of lysosomal proteases in tumor cells to trigger toxin release. Cell-based assays on target-positive Ar42J cells revealed target-specific reduction in viability with up to 1000-fold enhancement in bioactivity compared to the untargeted amatoxins. Altogether, this preliminary study enabled the development of a highly modular synthetic platform for the construction of amanitin-based conjugates that can be readily extended to various targeting moieties.

In Silico Studies of Tumor Targeted Peptide-Conjugated Natural Products for Targeting Over-Expressed Receptors in Breast Cancer Cells Using Molecular Docking, Molecular Dynamics and MMGBSA Calculations

In this work, in silico studies were carried out for the design of diterpene and polyphenol-peptide conjugates to potentially target over-expressed breast tumor cell receptors. Four point mutations were induced into the known tumor-targeting peptide sequence YHWYGYTPQN at positions 1, 2, 8 and 10, resulting in four mutated peptides. Each peptide was separately conjugated with either chlorogenate, carnosate, gallate, or rosmarinate given their known anti-tumor activities, creating dual targeting compounds. Molecular docking studies were conducted with the epidermal growth factor receptor (EGFR), to which the original peptide sequence is known to bind, as well as the estrogen receptor (ERα) and peroxisome proliferator-activated receptor (PPARα) using both Autodock Vina and FireDock. Based on docking results, peptide conjugates and peptides were selected and subjected to molecular dynamics simulations. MMGBSA calculations were used to further probe the binding energies. ADME studies revealed that the compounds were not CYP substrates, though most were Pgp substrates. Additionally, most of the peptides and conjugates showed MDCK permeability. Our results indicated that several of the peptide conjugates enhanced binding interactions with the receptors and resulted in stable receptor-ligand complexes; Furthermore, they may successfully target ERα and PPARα in addition to EGFR and may be further explored for synthesis and biological studies for therapeutic applications.

Using Unnatural Protein Fusions to Engineer a Coenzyme Self-Sufficiency System for D-Phenyllactic Acid Biosynthesis in Escherichia coli

The biosynthetic production of D-penyllactic acid (D-PLA) is often affected by insufficient supply and regeneration of cofactors, leading to high production cost, and difficulty in industrialization. In this study, a D-lactate dehydrogenase (D-LDH) and glycerol dehydrogenase (GlyDH) co-expression system was constructed to achieve coenzyme NADH self-sufficiency and sustainable production of D-PLA. Using glycerol and sodium phenylpyruvate (PPA) as co-substrate, the E. coli BL21 (DE3) harboring a plasmid to co-express LfD-LDH and BmGlyDH produced 3.95 g/L D-PLA with a yield of 0.78 g/g PPA, similar to previous studies. Then, flexible linkers were used to construct fusion proteins composing of D-LDH and GlyDH. Under the optimal conditions, 5.87 g/L D-PLA was produced by expressing LfD-LDH-l3-BmGlyDH with a yield of 0.97 g/g PPA, which was 59.3% increased compared to expression of LfD-LDH. In a scaled-up reaction, a productivity of 5.83 g/L/h was reached. In this study, improving the bio-catalytic efficiency by artificial redox self-equilibrium system with a bifunctional fusion protein could reduce the bio-production cost of D-PLA, making this bio-production of D-PLA a more promising industrial technology.

Recent approaches and success of liposome-based nanodrug carriers for the treatment of brain tumor

Brain tumors are nothing but a collection of neoplasms originated either from areas within the brain or from systemic metastasized tumors of other organs that have spread to the brain. It is a leading cause of death worldwide. The presence of the blood-brain barrier (BBB), blood-brain tumor barrier (BBTB), and some other factors may limit the entry of many potential therapeutics into the brain tissues in tumor area at the therapeutic concentration required for satisfying effectiveness. Liposomes are taking an active role in delivering many drugs through the BBB into the tumor due to their nanosize and their physiological compatibility. Further, this colloidal carrier can encapsulate both lipophilic and hydrophilic drugs due to its unique structure. The surface of the liposomes can be modified with various ligands that are very specific to the numerous receptors overexpressed onto the BBB as well as onto the diseased tumor surface site (i.e., BBTB) to deliver selective drugs into the tumor site. Moreover, the enhanced permeability and retention (EPR) effect can be an added advantage for nanosize liposomes to concentrate into the tumor microenvironment through relatively leaky vasculature of solid tumor in the brain where no restriction of penetration applies compared to normal BBB. Here in this review, we have tried to compilethe recent advancement along with the associated challenges of liposomes containing different anticancer chemotherapeutics across the BBB/BBTB for the treatment of gliomas that will be very helpful for the readers for better understanding of different trends of brain tumor targeted liposomes-based drug delivery and for pursuing fruitful research on the similar research domain.

Progress and Future Directions with Peptide-Drug Conjugates for Targeted Cancer Therapy

We review drug conjugates combining a tumor-selective moiety with a cytotoxic agent as cancer treatments. Currently, antibody-drug conjugates (ADCs) are the most common drug conjugates used clinically as cancer treatments. While providing both efficacy and favorable tolerability, ADCs have limitations due to their size and complexity. Peptides as tumor-targeting carriers in peptide-drug conjugates (PDCs) offer a number of benefits. Melphalan flufenamide (melflufen) is a highly lipophilic PDC that takes a novel approach by utilizing increased aminopeptidase activity to selectively increase the release and concentration of cytotoxic alkylating agents inside tumor cells. The only other PDC approved currently for clinical use is ¹⁷⁷Lu-dotatate, a targeted form of radiotherapy combining a somatostatin analog with a radionuclide. It is approved as a treatment for gastroenteropancreatic neuroendocrine tumors. Results with other PDCs combining synthetic analogs of natural peptide ligands with cytotoxic agents have been mixed. The field of drug conjugates as drug delivery systems for the treatment of cancer continues to advance with the application of new technologies. Melflufen provides a paradigm for rational PDC design, with a targeted mechanism of action and the potential for deepening responses to treatment, maintaining remissions, and eradicating therapy-resistant stem cells.

The Synthesis of Conjugated Peptides Containing Triazole and Quinolone-3-Carboxamide Moieties Designed as Anticancer Agents

Background

Cancer is a major health concern in human populations worldwide, and due to its causes being multi-factorial, it is not easily curable. Many attempts have been made to tackle this disease in hopes of finding effective anticancer agents which are not harmful to healthy tissues. Peptides with several medicinal activities have been shown to be good candidates as anticancer agents to replace common classic anticancer drugs. Peptides in conjugation with either biologically active heterocyclic compounds or anticancer drugs may result in new molecules compiling the biological benefits of both individual compounds within a unit structure.

Objective

In this study some triazole-peptide conjugates as well as ciprofloxacin-peptide conjugates were designed, synthesized, and their anticancer activities evaluated. A normal skin cell line, NIH3, was also employed to determine the safety profiles of these conjugates.

Materials and Methods

Two peptides; YIGSR and LSGNK were synthesized by the solid phase peptide synthesis (SPPS) method using Wang resin. Cell viability was examined by employing the MTT assay. To determine the cytotoxicity of the triazole and ciprofloxacin conjugates, two human cancer cell lines were employed; HepG2 (human liver cancer cell line) and LNCaP (human prostatic carcinoma cell line). A human skin fibroblast cell line was also included for comparison.

Results

MTT results showed that all the compounds could inhibit the viability of cancerous cells in a concentration- dependent manner.

Conclusions

The results showed that these peptide conjugates are toxic against the aforementioned cancerous cells and thus may raise a hope for finding new anticancer agents made by such strategy in the near future.

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.

New contrast agents for photoacoustic imaging and theranostics: Recent 5-year overview on phthalocyanine/naphthalocyanine-based nanoparticles

The phthalocyanine (Pc) and naphthalocyanine (Nc) nanoagents have drawn much attention as contrast agents for photoacoustic (PA) imaging due to their large extinction coefficients and long absorption wavelengths in the near-infrared region. Many investigations have been conducted to enhance Pc/Ncs' photophysical properties and address their poor solubility in an aqueous solution. Many diverse strategies have been adopted, including centric metal chelation, structure modification, and peripheral substitution. This review highlights recent advances on Pc/Nc-based PA agents and their extended use for multiplexed biomedical imaging, multimodal diagnostic imaging, and image-guided phototherapy.

TH1902, a new docetaxel-peptide conjugate for the treatment of sortilin-positive triple-negative breast cancer

Triple‐negative breast cancer (TNBC) is a heterogeneous subgroup of cancers which lacks the expression and/or amplification of targetable biomarkers (ie, estrogen receptor, progestrogen receptor, and human epidermal growth factor receptor 2), and is often associated with the worse disease‐specific outcomes than other breast cancer subtypes. Here, we report that high expression of the sortilin (SORT1) receptor correlates with the decreased survival in TNBC patients, and more importantly in those bearing lymph node metastases. By exploiting SORT1 function in ligand internalization, a new anticancer treatment strategy was designed to target SORT1‐positive TNBC‐derived cells both in vitro and in two in vivo tumor xenografts models. A peptide (TH19P01), which requires SORT1 for internalization and to which many anticancer drugs could be conjugated, was developed. In vitro, while the TH19P01 peptide itself did not exert any antiproliferative or apoptotic effects, the docetaxel‐TH19P01 conjugate (TH1902) exerted potent antiproliferative and antimigratory activities when tested on TNBC‐derived MDA‐MB‐231 cells. TH1902 triggered faster and more potent apoptotic cell death than did unconjugated docetaxel. The apoptotic and antimigratory effects of TH1902 were both reversed by two SORT1 ligands, neurotensin and progranulin, and on siRNA‐mediated silencing of SORT1. TH1902 also altered microtubule polymerization and triggered the downregulation of the anti‐apoptotic Bcl‐xL biomarker. In vivo, both i.p. and i.v. administrations of TH1902 led to greater tumor regression in two MDA‐MB‐231 and HCC‐70 murine xenograft models than did docetaxel, without inducing neutropenia. Altogether, the data demonstrates the high in vivo efficacy and safety of TH1902 against TNBC through a SORT1 receptor‐mediated mechanism. This property allows for selective treatment of SORT1‐positive TNBC and makes TH1902 a promising avenue for personalized therapy with the potential of improving the therapeutic window of cytotoxic anticancer drugs such as docetaxel.

Antimicrobial peptides as potential therapeutics for breast cancer

Breast cancer is the most common and deadliest cancer in women worldwide. Although notable advances have been achieved in the treatment of breast cancer, the overall survival rate of metastatic breast cancer patients is still considerably low due to the development of resistance to breast cancer chemotherapeutic agents and the non-optimal specificity of the current generation of cancer medications. Hence, there is a growing interest in the search for alternative therapeutics with novel anticancer mechanisms. Recently, antimicrobial peptides (AMPs) have gained much attention due to their cost-effectiveness, high specificity of action, and robust efficacy. However, there are no clinical data available about their efficacy. This warrants the increasing need for clinical trials to be conducted to assess the efficacy of this new class of drugs. Here, we will focus on the recent progress in the use of AMPs for breast cancer therapy and will highlight their modes of action. Finally, we will discuss the combination of AMP-based therapeutics with other breast cancer therapy strategies, including nanotherapy and chemotherapy, which may provide a potential avenue for overcoming drug resistance.

Design, Synthesis, and Utility of Defined Molecular Scaffolds

A growing theme in chemistry is the joining of multiple organic molecular building blocks to create functional molecules. Diverse derivatizable structures—here termed “scaffolds” comprised of “hubs”—provide the foundation for systematic covalent organization of a rich variety of building blocks. This review encompasses 30 tri- or tetra-armed molecular hubs (e.g., triazine, lysine, arenes, dyes) that are used directly or in combination to give linear, cyclic, or branched scaffolds. Each scaffold is categorized by graph theory into one of 31 trees to express the molecular connectivity and overall architecture. Rational chemistry with exacting numbers of derivatizable sites is emphasized. The incorporation of water-solubilization motifs, robust or self-immolative linkers, enzymatically cleavable groups and functional appendages affords immense (and often late-stage) diversification of the scaffolds. Altogether, 107 target molecules are reviewed along with 19 syntheses to illustrate the distinctive chemistries for creating and derivatizing scaffolds. The review covers the history of the field up through 2020, briefly touching on statistically derivatized carriers employed in immunology as counterpoints to the rationally assembled and derivatized scaffolds here, although most citations are from the past two decades. The scaffolds are used widely in fields ranging from pure chemistry to artificial photosynthesis and biomedical sciences.

Precise engineering of Gemcitabine prodrug cocktails into single polymeric nanoparticles delivery for metastatic thyroid cancer cells

GLOBOCAN estimates 36 types of cancers in 185 countries based on the incidence, mortality, and prevalence in the year 2019. Nowadays, chemotherapy is the most widely used cancer treatment among immune, radio, hormone, and gene therapies. Here, we describe a very simple yet cost-effective approach that synergistically combines drug reconstitution, supramolecular nano-assembly, and tumor-specific targeting to address the multiple challenges posed by the delivery of the chemotherapeutic Gemcitabine (GEM) drug. The GEM prodrugs were gifted to impulsively self-assemble into excellent steady nanoparticles size on covalent conjugation of linoleic acid hydrophobic through amide group with ∼100 nm. Newly synthesized GEM-NPs morphology was confirmed by various electron microscopic techniques. After successful synthesis, we have evaluated the anticancer property of GEM and GEM-NPs against B-CPAP (papillary thyroid carcinoma) and FTC-133 (human follicular thyroid carcinoma) cancer cell lines. Further studies such as AO-EB (acridine orange-ethidium bromide), nuclear staining and flow cytometry analyses on cell death mechanism signified that the cytotoxicity was associated with apoptosis in thyroid cancer cells. GEM-NPs show excellent biocompatibility compared to GEM. The present study explained that GEM-NPs as a safe and hopeful strategy for chemotherapeutics of thyroid cancer therapy and deserve for further clinical evaluations.

Penetrating the Blood-Brain Barrier with New Peptide-Porphyrin Conjugates Having anti-HIV Activity

Passing through the blood-brain barrier (BBB) to treat neurological conditions is one of the main hurdles in modern medicine. Many drugs with promising in vitro profiles become ineffective in vivo due to BBB restrictive permeability. In particular, this includes drugs such as antiviral porphyrins, with the ability to fight brain-resident viruses causing diseases such as HIV-associated neurocognitive disorders (HAND). In the last two decades, BBB shuttles, particularly peptide-based ones, have shown promise in carrying various payloads across the BBB. Thus, peptide–drug conjugates (PDCs) formed by covalent attachment of a BBB peptide shuttle and an antiviral drug may become key therapeutic tools in treating neurological disorders of viral origin. In this study, we have used various approaches (guanidinium, phosphonium, and carbodiimide-based couplings) for on-resin synthesis of new peptide–porphyrin conjugates (PPCs) with BBB-crossing and potential antiviral activity. After careful fine-tuning of the synthetic chemistry, DIC/oxyma has emerged as a preferred method, by which 14 different PPCs have been made and satisfactorily characterized. The PPCs are prepared by coupling a porphyrin carboxyl group to an amino group (either N-terminal or a Lys side chain) of the peptide shuttle and show effective in vitro BBB translocation ability, low cytotoxicity toward mouse brain endothelial cells, and low hemolytic activity. Three of the PPCs, MP-P5, P4-MP, and P4-L-MP, effectively inhibiting HIV infectivity in vitro, stand out as most promising. Their efficacy against other brain-targeting viruses (Dengue, Zika, and SARS-CoV-2) is currently under evaluation, with preliminary results confirming that PPCs are a promising strategy to treat viral brain infections.

Straightforward Functionalization of Sulfur-Containing Peptides via 5- and 6-endo-dig Cyclization Reactions

We present a simple and convenient method for the generation of sulfenyl electrophiles from peptides containing S–S or S–H bonds by employing N-chlorosuccinimide. The corresponding sulfenyl electrophiles are further utilized in 5- and 6-endo-dig cyclization reactions yielding indolizinium salts, indoles, benzo[b]furans, polyaromatic hydrocarbons (PAHs) and isocoumarins, as well as quinolinones bearing a glutathione moiety. PAH derivatives can be used as selective fluorescent dyes for the visualization of lipid droplets in living cells.

A chameleonic macrocyclic peptide with drug delivery applications

Head-to-tail cyclized peptides are intriguing natural products with unusual properties. The PawS-Derived Peptides (PDPs) are ribosomally synthesized as part of precursors for seed storage albumins in species of the daisy family, and are post-translationally excised and cyclized during proteolytic processing. Here we report a PDP twice the typical size and with two disulfide bonds, identified from seeds of Zinnia elegans. In water, synthetic PDP-23 forms a unique dimeric structure in which two monomers containing two β-hairpins cross-clasp and enclose a hydrophobic core, creating a square prism. This dimer can be split by addition of micelles or organic solvent and in monomeric form PDP-23 adopts open or closed V-shapes, exposing different levels of hydrophobicity dependent on conditions. This chameleonic character is unusual for disulfide-rich peptides and engenders PDP-23 with potential for cell delivery and accessing novel targets. We demonstrate this by conjugating a rhodamine dye to PDP-23, creating a stable, cell-penetrating inhibitor of the P-glycoprotein drug efflux pump.

DYRK1A Inhibitors as Potential Therapeutics for β-Cell Regeneration for Diabetes

According to the World Health Organization (WHO), 422 million people are suffering from diabetes worldwide. Current diabetes therapies are focused on optimizing blood glucose control to prevent long-term diabetes complications. Unfortunately, current therapies have failed to achieve glycemic targets in the majority of people with diabetes. In this context, regeneration of functional insulin-producing human β-cells in people with diabetes through the use of DYRK1A inhibitor drugs has recently received special attention. Several small molecule DYRK1A inhibitors have been identified that induce human β-cell proliferation in vitro and in vivo. Furthermore, DYRK1A inhibitors have also been shown to synergize β-cell proliferation with other classes of drugs, such as TGFβ inhibitors and GLP-1 receptor agonists. In this perspective, we review the status of DYRK1A as a therapeutic target for β-cell proliferation and provide perspectives on technical and scientific challenges for future translational development.

Potential therapeutic applications of AKAP disrupting peptides

The 3'-5'-cyclic adenosine monophosphate (cAMP)/PKA pathway represents a major target for pharmacological intervention in multiple disease conditions. Although the last decade saw the concept of highly compartmentalized cAMP/PKA signaling consolidating, current means for the manipulation of this pathway still do not allow to specifically intervene on discrete cAMP/PKA microdomains. Since compartmentalization is crucial for action specificity, identifying new tools that allow local modulation of cAMP/PKA responses is an urgent need. Among key players of cAMP/PKA signaling compartmentalization, a major role is played by A-kinase anchoring proteins (AKAPs) that, by definition, anchor PKA, its substrates and its regulators within multiprotein complexes in well-confined subcellular compartments. Different tools have been conceived to interfere with AKAP-based protein-protein interactions (PPIs), and these primarily include peptides and peptidomimetics that disrupt AKAP-directed multiprotein complexes. While these molecules have been extensively used to understand the molecular mechanisms behind AKAP function in pathophysiological processes, less attention has been devoted to their potential application for therapy. In this review, we will discuss how AKAP-based PPIs can be pharmacologically targeted by synthetic peptides and peptidomimetics.

Peptide-Chitosan Engineered Scaffolds for Biomedical Applications

Peptides are signaling epitopes that control many vital biological events. Increased specificity, synthetic feasibility with concomitant lack of toxicity, and immunogenicity make this emerging class of biomolecules suitable for different applications including therapeutics, diagnostics, and biomedical engineering. Further, chitosan, a naturally occurring linear polymer composed of d-glucosamine and N-acetyl-d-glucosamine units, possesses anti-microbial, muco-adhesive, and hemostatic properties along with excellent biocompatibility. As a result, chitosan finds application in drug/gene delivery, tissue engineering, and bioimaging. Despite these applications, chitosan demonstrates limited cell adhesion and lacks biosignaling. Therefore, peptide-chitosan hybrids have emerged as a new class of biomaterial with improved biosignaling properties and cell adhesion properties. As a result, recent studies encompass increased application of peptide-chitosan hybrids as composites or conjugates in drug delivery, cell therapy, and tissue engineering and as anti-microbial material. This review discusses the recent investigations involving chitosan-peptide materials and uncovers various aspects of these interesting hybrid materials for biomedical applications.

ConjuPepDB: a database of peptide-drug conjugates

Peptide–drug conjugates are organic molecules composed of (i) a small drug molecule, (ii) a peptide and (iii) a linker. The drug molecule is mandatory for the biological action, however, its efficacy can be enhanced by targeted delivery, which often also reduces unwanted side effects. For site-specificity the peptide part is mainly responsible. The linker attaches chemically the drug to the peptide, but it could also be biodegradable which ensures controlled liberation of the small drug. Despite the importance of the field, there is no public comprehensive database on these species. Herein we describe ConjuPepBD, a freely available, fully annotated and manually curated database of peptide drug conjugates. ConjuPepDB contains basic information about the entries, e.g. CAS number. Furthermore, it also implies their biomedical application and the type of chemical conjugation employed. It covers more than 1600 conjugates from ∼230 publications. The web-interface is user-friendly, intuitive, and useable on several devices, e.g. phones, tablets, PCs. The webpage allows the user to search for content using numerous criteria, chemical structure and a help page is also provided. Besides giving quick insight for newcomers, ConjuPepDB is hoped to be also helpful for researchers from various related fields. The database is accessible at: https://conjupepdb.ttk.hu/.

Current strategies for the discovery and bioconjugation of smaller, targetable drug conjugates tailored for solid tumor therapy

Introduction: Antibody-Drug Conjugates (ADCs) have undergone a recent resurgence with 5 product approvals over the last 2 years but for those close to the field, it's been repeated cycles of setbacks and new innovations. A new wave of innovation is in the type of format used to deliver the cytotoxic payloads, with smaller bio-molecules being designed to have more optimal penetration and elimination properties tailored for solid tumors.Areas covered: In this review, the authors cover many of the recently described smaller-format drug conjugates (including formats such as diabodies, Fabs, scFvs, domain antibodies) with an emphasis on the types of conjugation technologies used to attach the chemical linker-payload.Expert opinion: Smaller formats are highly influenced by the structure of the linker-payload, arguably more-so than larger ADCs, so careful consideration is needed where solublising and pharmacokinetic modulation is required. High-quality conjugates are being developed with in vivo tumor efficacy and tolerability properties competitive with ADCs and with a few formats already in clinical development, we expect the pipeline to expand and to reach the market.

A Facile Procedure for One-Pot Stable Conjugation of Two Proglucagon Cysteine-Containing Peptide Analogs

Optimization of peptides for therapeutic purposes often includes chemical conjugation or modification with substituents that serve to broaden pharmacology or improve pharmacokinetics. We report a convenient and rapid procedure for one-pot, site-specific conjugation of two cysteine-containing peptides that utilizes a bivalent linker comprising maleimide and iodoacetyl functional groups. Following maleimide-mediated peptide conjugation the linker was converted from an unstable thiosuccinimide to a stable thioether bond suitable for biological study by mild aqueous hydrolysis. The procedure is exemplified by peptide-peptide, peptide-small molecule, and peptide-fatty acid conjugations. The method provides a facile approach to search for enhanced biological outcomes through additive and sustained peptide pharmacology unencumbered by the prospect of chemical rearrangement in the course of biological study.

Small molecule drug conjugates (SMDCs): an emerging strategy for anticancer drug design and discovery

Mechanisms of how SMDCs work. Small molecule drugs are conjugated with the targeted ligand using pH sensitive linkers which allow the drug molecule to get released at lower lysosomal pH. It helps to accumulate the chemotherapeutic agents to be localized in the tumor environment upon cleaving of the pH-labile bonds.

Peptide-Drug Conjugates with Different Linkers for Cancer Therapy

Drug conjugates are chemotherapeutic or cytotoxic agents covalently linked to targeting ligands such as an antibody or a peptide via a linker. While antibody-drug conjugates (ADCs) are now clinically established for cancer therapy, peptide-drug conjugates (PDCs) are gaining recognition as a new modality for targeted drug delivery with improved efficacy and reduced side effects for cancer treatment. The linker in a drug conjugate plays a key role in the circulation time of the conjugate and release of the drug for full activity at the target site. Herein, we highlight the main linker chemistries utilized in the design of PDCs and discuss representative examples of PDCs with different linker chemistries with the related outcome in cell and animal studies.