Source and exploration of the peptides used to construct peptide-drug conjugates

Recent Advances in Augmenting the Therapeutic Efficacy of Peptide-Drug Conjugates

There is an urgent need for the development of safe and effective modalities for the treatment of diseases owing to drug resistance, undesired side effects, and poor clinical outcomes. Combining cell-targeting and efficient cell-killing properties, peptide-drug conjugates (PDCs) have demonstrated superior efficacy compared with peptides and payloads alone. However, innovative molecular designs of PDCs are essential for further improving targeting precision, protease resistance and stability, cell permeability, and overall treatment efficacy. Several strategies have been developed to address these challenges, such as multivalency approaches, bispecific targeting, and long-acting PDCs. Other novel strategies, including overcoming biological barriers, conjugating novel functional payloads, and targeting macropinocytosis, have also shown promise. This perspective compiles the most recent strategies for enhancing PDC treatment efficacy, highlights key advancements in PDC, and provides insights on future directions for the development of novel PDCs.

Conformation-sensitive targeting of CD18 depletes M2-like tumor-associated macrophages resulting in inhibition of solid tumor progression

BACKGROUND

Tumor-associated macrophages (TAMs) primarily exist in the M2-like phenotype in the tumor microenvironment (TME). M2-TAMs contribute to tumor progression by establishing an immunosuppressive environment. However, TAM targeting is hindered, mainly owing to a lack of specific biomarkers for M2-TAMs. Previously, we demonstrated that a novel peptide drug conjugate (TB511) consisting of a TAM-binding peptide and the apoptosis-promoting peptide targets M2-TAMs. This was achieved through M2-TAM targeting, although the target mechanism of action remained elusive. Herein, we elucidate the anticancer efficacy of TB511 by identifying new target proteins that preferentially bind to M2-TAMs and clarifying the apoptosis-inducing mechanism in these cells.

METHODS

We investigated the target proteins and binding site of TB511 using LC-MS/MS analyses, surface plasmon resonance and peptide-protein interaction 3D modeling. Activated CD18 expression in M2 TAMs was assessed using Quantibrite PE beads in PBMCs. The anticancer efficacy of TB511 was tested using colorectal cancer (CRC) and non-small cell lung cancer (NSCLC) mouse model. The immunotherapeutic effect of TB511 was investigated through spatial transcriptomics in human pancreatic ductal adenocarcinoma (PDAC) model.

RESULTS

Activated CD18 was highly expressed in human tumor tissues and was significantly higher in M2 TAMs than in other immune cells. TB511 showed high binding affinity to CD18 among the cell membrane proteins of M2 macrophages and appeared to bind to the cysteine-rich domain in the activated form. Moreover, TB511 specifically induced apoptosis in M2 TAMs, but its targeting ability to M2 macrophages was inhibited in CD18 blockade or knockout model. In mouse or humanized mouse models of solid tumors such as CRC, NSCLC, and PDAC, TB511 suppressed tumor growth by targeting M2-TAMs via CD18 and enhancing the presence of CD8+ T cells in the TME.

CONCLUSIONS

Collectively, our findings suggest that activated CD18 holds promise as a novel target protein for cancer therapy, and TB511 shows potential as a therapeutic agent for tumor treatment.

Pure drug nanomedicines - where we are?

Pure drug nanomedicines (PDNs) encompass active pharmaceutical ingredients (APIs), including macromolecules, biological compounds, and functional components. They overcome research barriers and conversion thresholds associated with nanocarriers, offering advantages such as high drug loading capacity, synergistic treatment effects, and environmentally friendly production methods. This review provides a comprehensive overview of the latest advancements in PDNs, focusing on their essential components, design theories, and manufacturing techniques. The physicochemical properties and in vivo behaviors of PDNs are thoroughly analyzed to gain an in-depth understanding of their systematic characteristics. The review introduces currently approved PDN products and further explores the opportunities and challenges in expanding their depth and breadth of application. Drug nanocrystals, drug-drug cocrystals (DDCs), antibody-drug conjugates (ADCs), and nanobodies represent the successful commercialization and widespread utilization of PDNs across various disease domains. Self-assembled pure drug nanoparticles (SAPDNPs), a next-generation product, still require extensive translational research. Challenges persist in transitioning from laboratory-scale production to mass manufacturing and overcoming the conversion threshold from laboratory findings to clinical applications.

Guanidines Conjugated with Cell-Penetrating Peptides: A New Approach for the Development of Antileishmanial Molecules

Leishmaniasis is a neglected tropical disease caused by a protozoan of the genus Leishmania, which has visceral and cutaneous forms. The symptoms of leishmaniasis include high fever and weakness, and the cutaneous infection also causes lesions under the skin. The drugs used to treat leishmaniasis have become less effective due to the resistance mechanisms of the protozoa. In addition, the current compounds have low selectivity for the pathogen, leading to various side effects, which results in lower adherence to treatment. Various strategies were developed to solve this problem. The bioconjugation between natural compounds with antimicrobial activity and cell-penetrating peptides could alleviate the resistance and toxicity of current treatments. This work aims to conjugate the cell penetration peptide TAT to the guanidine GVL1. The GVL1-TAT bioconjugate exhibited leishmanicidal activity against Leishmania amazonensis and Leishmania infantum with a high selectivity index. In addition, the bioconjugate was more active against the intracellular enzyme CPP than the individual compounds. This target is very important for the viability and virulence of the parasite within the host cell. Docking studies confirmed the higher interaction of the conjugate with CPP and suggested that other proteins, such as trypanothione reductase, could be targeted. Thus, the data indicated that guanidines conjugated with cell-penetrating peptides could be a good approach for developing antileishmanial molecules.

A novel immunomodulating peptide with potential to complement oligodeoxynucleotide-mediated adjuvanticity in vaccination strategies

The identification of adjuvants to improve vaccination efficacy is a major unmet need. One approach is to augment the functionality of dendritic cells (DCs) by using Toll-like receptor-9 (TLR9) agonists such as cytosine-phosphate-guanine oligodeoxynucleotides (CpG ODNs) as adjuvants. Another approach is adjuvant selection based on production of bioactive interleukin-12 (IL-12). We report a D-peptide isomer, designated D-15800, that induces monocyte differentiation to the DC phenotype in vitro and more effectively stimulates IL-12p70 production upon T cell receptor (TCR) activation than the L-isomer. In the absence of TCR activation and either IL-12p70 or interleukin-2 production, only D-15800 activates CD4+ T and natural killer cells. In the presence of CpG ODN, D-15800 synergistically enhances production of interferon-alpha (IFN-α). Taken together with its biostability in human serum and depot retention upon injection, co-delivery of D-15800 with TLR9 agonists could serve to improve vaccine efficacy.

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.

PBMC-engrafted humanized mice models for evaluating immune-related and anticancer drug delivery systems

Immune-related drug delivery systems (DDSs) in humanized mouse models are at the forefront of cancer research and serve as bridges between preclinical studies and clinical applications. These systems offer unique platforms for exploring new therapies and understanding their interactions with human cells and the immune system. Here, we focus on a DDS and a peripheral blood mononuclear cell (PBMC)-engrafted humanized mouse model that we recently developed, and consider some of the key components, challenges, and applications to advance these systems towards better cancer treatment on the basis of a better understanding of the immune response. Our DDS is unique and has a dual function, an anticancer effect and a capacity to fine-tune the immune reaction. The PBL-NOG-hIL-4-Tg mouse system is superior to other available humanized mouse systems for the development of such multifunctional DDSs because it supports the rapid reconstruction of an individual donor's immunity and avoids the onset of graft-versus-host disease.

Recent Advances in Targeted Cancer Therapy: Are PDCs the Next Generation of ADCs?

Antibody-drug conjugates (ADCs) comprise antibodies, cytotoxic payloads, and linkers, which can integrate the advantages of antibodies and small molecule drugs to achieve targeted cancer treatment. However, ADCs also have some shortcomings, such as non-negligible drug resistance, a low therapeutic index, and payload-related toxicity. Many studies have focused on changing the composition of ADCs, and some have even further extended the concept and types of targeted conjugated drugs by replacing the targeted antibodies in ADCs with peptides, revolutionarily introducing peptide-drug conjugates (PDCs). This Perspective summarizes the current research status of ADCs and PDCs and highlights the structural innovations of ADC components. In particular, PDCs are regarded as the next generation of potential targeted drugs after ADCs, and the current challenges of PDCs are analyzed. Our aim is to offer fresh insights for the efficient design and expedited development of innovative targeted conjugated drugs.

A novel peptide-drug conjugate for glioma-targeted drug delivery

The existence of the blood-brain barrier (BBB) and blood-brain tumor barrier (BBTB) greatly limits the application of chemotherapy in glioma. To address this challenge, an optimal drug delivery system must efficiently cross the BBB/BBTB and specifically deliver therapeutic drugs into glioma cells while minimizing systemic toxicity. Here we demonstrated that glucose-regulated protein 78 (GRP78) and dopamine receptor D2 were highly expressed in patient-derived glioma tissues, and dopamine receptors were highly expressed on the BBB. Subsequently, we synthesized a novel "Y"-shaped peptide and compared the effects of different linkers on the receptor affinity and targeting ability of the peptide. A peptide-drug conjugate (pHA-AOHX-VAP-doxorubicin conjugate, pHA-AOHX-VAP-DOX) with a better affinity for glioma cells and higher solubility was derived for glioma treatment. pHA-AOHX-VAP-DOX could cross both BBB and BBTB via dopamine receptor and GRP78 receptor, and finally target glioma cells, significantly prolonging the survival time of nude mice bearing intracranial glioma. Furthermore, pHA-AOHX-VAP-DOX significantly reduced the toxicity of DOX and increased the maximum tolerated dose (MTD). Collectively, this work paves a new avenue for overcoming multiple barriers and effectively delivering chemotherapeutic agents to glioma cells while providing key evidence to identify potential receptors for glioma-targeted drug delivery.

Peptide-Drug Conjugates: Design, Chemistry, and Drug Delivery System as a Novel Cancer Theranostic

The emergence of peptide-drug conjugates (PDCs) that utilize target-oriented peptide moieties as carriers of cytotoxic payloads, interconnected with various cleavable/noncleavable linkers, resulted in the key-foundation of the new era of targeted therapeutics. They are capable of retaining the integrity of conjugates in the blood circulatory system as well as releasing the drugs at the tumor microenvironment. Other valuable advantages are specificity and selectivity toward targeted-receptors, higher penetration ability, and drug-loading capacity, making them a suitable candidate to play their vital role as promising carrier agents. In this review, we summarized the types of cell-targeting (CTPs) and cell-penetrating peptides (CPPs) that have broad applications in the advancement of targeted drug-delivery systems (DDS). Moreover, the techniques to overcome the limitations of peptide-chemistry for their extensive implementation to construct the PDCs. Besides this, the diversified breakthrough of linker chemistry, and ample knowledge of various cytotoxic payloads used in PDCs in recent years, as well as the mechanism of action of PDCs was critically discussed. 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, also their progression toward a bright future for PDCs as novel theranostics in clinical practice.

Design of pH-responsive antimicrobial peptide melittin analog-camptothecin conjugates for tumor therapy

Melittin, a classical antimicrobial peptide, is a highly potent antitumor agent. However, its significant toxicity seriously hampers its application in tumor therapy. In this study, we developed novel melittin analogs with pH-responsive, cell-penetrating and membrane-lytic activities by replacing arginine and lysine with histidine. After conjugation with camptothecin (CPT), CPT-AAM-1 and CPT-AAM-2 were capable of killing tumor cells by releasing CPT at low concentrations and disrupting cell membranes at high concentrations under acidic conditions. Notably, we found that the C-terminus of the melittin analogs was more suitable for drug conjugation than the N-terminus. CPT-AAM-1 significantly suppressed melanoma growth in vivo with relatively low toxicity. Collectively, the present study demonstrates that the development of antitumor drugs based on pH-responsive antimicrobial peptide-drug conjugates is a promising strategy.

Diverse drug delivery systems for the enhancement of cancer immunotherapy: an overview

Despite the clear benefits demonstrated by immunotherapy, there is still an inevitable off-target effect resulting in serious adverse immune reactions. In recent years, the research and development of Drug Delivery System (DDS) has received increased prominence. In decades of development, DDS has demonstrated the ability to deliver drugs in a precisely targeted manner to mitigate side effects and has the advantages of flexible control of drug release, improved pharmacokinetics, and drug distribution. Therefore, we consider that combining cancer immunotherapy with DDS can enhance the anti-tumor ability. In this paper, we provide an overview of the latest drug delivery strategies in cancer immunotherapy and briefly introduce the characteristics of DDS based on nano-carriers (liposomes, polymer nano-micelles, mesoporous silica, extracellular vesicles, etc.) and coupling technology (ADCs, PDCs and targeted protein degradation). Our aim is to show readers a variety of drug delivery platforms under different immune mechanisms, and analyze their advantages and limitations, to provide more superior and accurate targeting strategies for cancer immunotherapy.

4-Iodine N-Methylpyridinium-Mediated Peptide Synthesis

Through systematic optimization of halopyridinium compounds, we established a peptide coupling protocol utilizing 4-iodine N-methylpyridinium (4IMP) for solid-phase peptide synthesis (SPPS). The 4IMP coupling reagent is easily prepared, bench stable, and cost-effective. Employing 4IMP in the SPPS process has showcased remarkable chemoselectivity and efficiency, effectively eliminating racemization and epimerization. This achievement has been substantiated through the successful synthesis of a range of peptides via the direct utilization of commercially available amino acid substrates for SPPS.

Antibody-drug conjugates: Recent advances in payloads

Antibody‒drug conjugates (ADCs), which combine the advantages of monoclonal antibodies with precise targeting and payloads with efficient killing, show great clinical therapeutic value. The ADCs' payloads play a key role in determining the efficacy of ADC drugs and thus have attracted great attention in the field. An ideal ADC payload should possess sufficient toxicity, low immunogenicity, high stability, and modifiable functional groups. Common ADC payloads include tubulin inhibitors and DNA damaging agents, with tubulin inhibitors accounting for more than half of the ADC drugs in clinical development. However, due to clinical limitations of traditional ADC payloads, such as inadequate efficacy and the development of acquired drug resistance, novel highly efficient payloads with diverse targets and reduced side effects are being developed. This perspective summarizes the recent research advances of traditional and novel ADC payloads with main focuses on the structure-activity relationship studies, co-crystal structures, and designing strategies, and further discusses the future research directions of ADC payloads. This review also aims to provide valuable references and future directions for the development of novel ADC payloads that will have high efficacy, low toxicity, adequate stability, and abilities to overcome drug resistance.

Research advances in peptide‒drug conjugates

Peptide‒drug conjugates (PDCs) are drug delivery systems consisting of a drug covalently coupled to a multifunctional peptide via a cleavable linker. As an emerging prodrug strategy, PDCs not only preserve the function and bioactivity of the peptides but also release the drugs responsively with the cleavable property of the linkers. Given the ability to significantly improve the circulation stability and targeting of drugs in vivo and reduce the toxic side effects of drugs, PDCs have already been extensively applied in drug delivery. Herein, we review the types and mechanisms of peptides, linkers and drugs used to construct PDCs, and summarize the clinical applications and challenges of PDC drugs.

DEDTI versus IEDTI: efficient and predictive models of drug-target interactions

Drug repurposing is an active area of research that aims to decrease the cost and time of drug development. Most of those efforts are primarily concerned with the prediction of drug-target interactions. Many evaluation models, from matrix factorization to more cutting-edge deep neural networks, have come to the scene to identify such relations. Some predictive models are devoted to the prediction's quality, and others are devoted to the efficiency of the predictive models, e.g., embedding generation. In this work, we propose new representations of drugs and targets useful for more prediction and analysis. Using these representations, we propose two inductive, deep network models of IEDTI and DEDTI for drug-target interaction prediction. Both of them use the accumulation of new representations. The IEDTI takes advantage of triplet and maps the input accumulated similarity features into meaningful embedding corresponding vectors. Then, it applies a deep predictive model to each drug-target pair to evaluate their interaction. The DEDTI directly uses the accumulated similarity feature vectors of drugs and targets and applies a predictive model on each pair to identify their interactions. We have done a comprehensive simulation on the DTINet dataset as well as gold standard datasets, and the results show that DEDTI outperforms IEDTI and the state-of-the-art models. In addition, we conduct a docking study on new predicted interactions between two drug-target pairs, and the results confirm acceptable drug-target binding affinity between both predicted pairs.

A Novel Homodimer Peptide-Drug Conjugate Improves the Efficacy of HER2-Positive Breast Cancer Therapy

Tumor-targeting peptide-drug conjugates (PDCs) have become a focus of research in recent years. However, due to the instability of peptides and their short in vivo effective half-life, they have limited clinical application. Herein, we propose a new DOX PDC based on a homodimer HER-2-targeting peptide and acid-sensitive hydrazone bond, which could enhance the anti-tumor effect of DOX and reduce systemic toxicities. The PDC could accurately deliver DOX into HER2-positive SKBR-3 cells, with it showing 2.9 times higher cellular uptake than free DOX and enhanced cytotoxicity with respect to IC₅₀ of 140 nM (vs. 410 nM for free DOX). In vitro assays showed that the PDC had high cellular internalization efficiency and cytotoxicity. In vivo anti-tumor experiments indicated that the PDC could significantly inhibit the growth of HER2-positive breast cancer xenografts in mice and reduce the side effects of DOX. In summary, we constructed a novel PDC molecule targeting HER2-positive tumors, which may overcome some deficiencies of DOX in breast cancer therapy.

A designed cyclic peptide based on Trastuzumab used to construct peptide-drug conjugates for its HER2-targeting ability

Human epidermal growth factor receptor 2 (HER2) has been recognized as an important therapeutic target for its overexpression in many cancers. Trastuzumab is a monoclonal antibody targeting HER2, which has been approved by FDA to treat HER2-positive cancer. In this research, cyclic peptide Cyclo-GCGPep1 was designed based on the binding mode between antibody and HER2 protein in silico, which has been confirmed possessing good affinity with HER2. Cyclo-GCGPep1 was also used to construct peptide-drug conjugates with Camptothecin. Biological evaluations demonstrated that Conjugate 1 has a good antiproliferative activity on SK-BR-3 and NCI-N87 cells. Conjugate 1 retained the pro-apoptotic and Topo I inhibitory ability of Camptothecin. Meanwhile, it has good targeting ability towards HER2-positive cells with the help of Cyclo-GCGPep1. It also has better permeability in the tumor spheroid model than Camptothecin. In summary, the design of cyclic peptide derived from antibody is of significance for the discovery of targeting peptides and Conjugate 1 is expected as a good therapeutic agent for HER2-positive cancers.