New p32/gC1qR Ligands for Targeted Tumor Drug Delivery

Peptide-Hitchhiking for the Development of Nanosystems in Glioblastoma

Glioblastoma (GBM) remains the epitome of aggressiveness and lethality in the spectrum of brain tumors, primarily due to the blood-brain barrier (BBB) that hinders effective treatment delivery, tumor heterogeneity, and the presence of treatment-resistant stem cells that contribute to tumor recurrence. Nanoparticles (NPs) have been used to overcome these obstacles by attaching targeting ligands to enhance therapeutic efficacy. Among these ligands, peptides stand out due to their ease of synthesis and high selectivity. This article aims to review single and multiligand strategies critically. In addition, it highlights other strategies that integrate the effects of external stimuli, biomimetic approaches, and chemical approaches as nanocatalytic medicine, revealing their significant potential in treating GBM with peptide-functionalized NPs. Alternative routes of parenteral administration, specifically nose-to-brain delivery and local treatment within the resected tumor cavity, are also discussed. Finally, an overview of the significant obstacles and potential strategies to overcome them are discussed to provide a perspective on this promising field of GBM therapy.

Brain-targeted drug delivery - nanovesicles directed to specific brain cells by brain-targeting ligands

Neurodegenerative diseases are characterized by extensive loss of function or death of brain cells, hampering the life quality of patients. Brain-targeted drug delivery is challenging, with a low success rate this far. Therefore, the application of targeting ligands in drug vehicles, such as lipid-based and polymeric nanoparticles, holds the promise to overcome the blood-brain barrier (BBB) and direct therapies to the brain, in addition to protect their cargo from degradation and metabolization. In this review, we discuss the barriers to brain delivery and the different types of brain-targeting ligands currently in use in brain-targeted nanoparticles, such as peptides, proteins, aptamers, small molecules, and antibodies. Moreover, we present a detailed review of the different targeting ligands used to direct nanoparticles to specific brain cells, like neurons (C4-3 aptamer, neurotensin, Tet-1, RVG, and IKRG peptides), astrocytes (Aquaporin-4, D4, and Bradykinin B2 antibodies), oligodendrocytes (NG-2 antibody and the biotinylated DNA aptamer conjugated to a streptavidin core Myaptavin-3064), microglia (CD11b antibody), neural stem cells (QTRFLLH, VPTQSSG, and NFL-TBS.40-63 peptides), and to endothelial cells of the BBB (transferrin and insulin proteins, and choline). Reports demonstrated enhanced brain-targeted delivery with improved transport to the specific cell type targeted with the conjugation of these ligands to nanoparticles. Hence, this strategy allows the implementation of high-precision medicine, with reduced side effects or unwanted therapy clearance from the body. Nevertheless, the accumulation of some of these nanoparticles in peripheral organs has been reported indicating that there are still factors to be improved to achieve higher levels of brain targeting. This review is a collection of studies exploring targeting ligands for the delivery of nanoparticles to the brain and we highlight the advantages and limitations of this type of approach in precision therapies.

GSH-Responsive Polymeric Micelles for Remodeling the Tumor Microenvironment to Improve Chemotherapy and Inhibit Metastasis in Breast Cancer

The tumor microenvironment (TME) of breast cancer is hypoxic, which can promote tumor progression, including invasion and metastasis, and limit the efficacy of anti-tumor treatment. Nitric oxide (NO) can dilate blood vessels, effectively alleviate hypoxia, and regulate the TME, which has the potential to improve the anti-tumor therapeutic efficacy. Here, chitosan (CO) and octadecylamine (ODA) were linked by the disulfide bond, and the LinTT1 peptide was linked onto CO-SS-ODA for targeting tumor cells and endothelial cells in tumors. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) was connected to CO. Doxorubicin (DOX) was encapsulated, and GSH hierarchically responsive polymer micelles (TSCO-SS-ODA/DOX) were constructed for the treatment of breast cancer. The micelles had differently responsive drug release in different GSH concentrations. In endothelial cells, the micelles rapidly responded to release NO. In tumor cells, the disulfide bond rapidly broke and released DOX to effectively kill tumor cells. The disulfide bond was not sensitive to GSH concentration in endothelial cells, which had less release of DOX. The killing effect of the micelles to endothelial cells was much lower than that to tumor cells. The cell selective drug release of the drug delivery systems enabled safe and effective treatment of drugs. TSCO-SS-ODA/DOX, which had the excellent ability to target tumors, can alleviate tumor hypoxia, decrease the infiltration of M2 macrophages in tumors, increase the infiltration of M1 macrophages in tumors, and remodel the TME. Notably, TSCO-SS-ODA/DOX can significantly inhibit the growth of the primary tumor and effectively inhibit tumor metastasis. The drug delivery system provided a potential solution for effectively treating breast cancer.

Facile and green fabrication of tumor- and mitochondria-targeted AIEgen-protein nanoparticles for imaging-guided photodynamic cancer therapy

In recent years, aggregation-induced emission (AIE)-active materials have been emerging as a promising means for bioimaging and phototherapy. However, the majority of AIE luminogens (AIEgens) need to be encapsulated into versatile nanocomposites to improve their biocompatibility and tumor targeting. Herein, we prepared a tumor- and mitochondria-targeted protein nanocage by the fusion of human H-chain ferritin (HFtn) with a tumor homing and penetrating peptide LinTT1 using genetic engineering technology. The LinTT1-HFtn could serve as a nanocarrier to encapsulate AIEgens via a simple pH-driven disassembly/reassembly process, thereby fabricating the dual-targeting AIEgen-protein nanoparticles (NPs). The as designed NPs exhibited an improved hepatoblastoma-homing property and tumor penetrating ability, which is favorable for tumor-targeted fluorescence imaging. The NPs also presented a mitochondria-targeting ability, and efficiently generated reactive oxygen species (ROS) upon visible light irradiation, making them valuable for inducing efficient mitochondrial dysfunction and intrinsic apoptosis in cancer cells. In vivo experiments demonstrated that the NPs could provide the accurate tumor imaging and dramatic tumor growth inhibition with minimal side effects. Taken together, this study presents a facile and green approach for fabrication of tumor- and mitochondria-targeted AIEgen-protein NPs, which can serve as a promising strategy for imaging-guided photodynamic cancer therapy. STATEMENT OF SIGNIFICANCE: AIE luminogens (AIEgens) show strong fluorescence and enhanced ROS generation in the aggregate state, which would facilitate the image-guided photodynamic therapy [12-14]. However, the major obstacles that hinder biological applications are their lack of hydrophilicity and selective targeting [15]. To address this issue, this study presents a facile and green approach for the fabrication of tumor‑ and mitochondria‑targeted AIEgen-protein nanoparticles via a simple disassembly/reassembly of the LinTT1 peptide-functionalized ferritin nanocage without any harmful chemicals or chemical modification. The targeting peptide-functionalized nanocage not only restricts the intramolecular motion of AIEgens leading to enhanced fluorescence and ROS production, but also confers good targeting to AIEgens.

Role of gC1qR as a modulator of endothelial cell permeability and contributor to post-stroke inflammation and edema formation

Ischemic stroke is a leading cause of death and disability worldwide. A serious risk of acute ischemic stroke (AIS) arises after the stroke event, due to inflammation and edema formation. Inflammation and edema in the brain are mediated by bradykinin, the formation of which is dependent upon a multi-ligand receptor protein called gC1qR. There are currently no preventive treatments for the secondary damage of AIS produced by inflammation and edema. This review aims to summarize recent research regarding the role of gC1qR in bradykinin formation, its role in inflammation and edema following ischemic injury, and potential therapeutic approaches to preventing post-stroke inflammation and edema formation.

In Silico and In Vivo Studies of a Tumor-Penetrating and Interfering Peptide with Antitumoral Effect on Xenograft Models of Breast Cancer

The combination of a tumor-penetrating peptide (TPP) with a peptide able to interfere with a given protein-protein interaction (IP) is a promising strategy with potential clinical application. Little is known about the impact of fusing a TPP with an IP, both in terms of internalization and functional effect. Here, we analyze these aspects in the context of breast cancer, targeting PP2A/SET interaction, using both in silico and in vivo approaches. Our results support the fact that state-of-the-art deep learning approaches developed for protein-peptide interaction modeling can reliably identify good candidate poses for the IP-TPP in interaction with the Neuropilin-1 receptor. The association of the IP with the TPP does not seem to affect the ability of the TPP to bind to Neuropilin-1. Molecular simulation results suggest that peptide IP-GG-LinTT1 in a cleaved form interacts with Neuropilin-1 in a more stable manner and has a more helical secondary structure than the cleaved IP-GG-iRGD. Surprisingly, in silico investigations also suggest that the non-cleaved TPPs can bind the Neuropilin-1 in a stable manner. The in vivo results using xenografts models show that both bifunctional peptides resulting from the combination of the IP and either LinTT1 or iRGD are effective against tumoral growth. The peptide iRGD-IP shows the highest stability to serum proteases degradation while having the same antitumoral effect as Lin TT1-IP, which is more sensitive to proteases degradation. Our results support the development of the TPP-IP strategy as therapeutic peptides against cancer.

Use of phage display biopanning as a tool to design CAR-T cells against glioma stem cells

Background

Glioblastoma (GBM) is both the most common and aggressive type of primary brain tumor, associated with high mortality rates and resistance to conventional therapy. Despite recent advancements in knowledge and molecular profiling, recurrence of GBM is nearly inevitable. This recurrence has been attributed to the presence of glioma stem cells (GSCs), a small fraction of cells resistant to standard-of-care treatments and capable of self-renewal and tumor initiation. Therefore, targeting these cancer stem cells will allow for the development of more effective therapeutic strategies against GBM. We have previously identified several 7-amino acid length peptides which specifically target GSCs through in vitro and in vivo phage display biopanning.

Methods and results

We have combined two of these peptides to create a dual peptide construct (EV), and demonstrated its ability to bind GSCs in vitro and target intracranial GBM in mouse models. A peptide pull-down performed with peptide EV followed by mass spectrometry determined N-cadherin as the binding partner of the peptide, which was validated by enzyme-linked immunosorbent assay and surface plasmon resonance. To develop cytotoxic cellular products aimed at specifically targeting GSCs, chimeric antigen receptors (CARs) were engineered containing the peptide EV in place of the single-chain variable fragment (scFv) as the antigen-binding domain. EV CAR-transduced T cells demonstrated specific reactivity towards GSCs by production of interferon-gamma when exposed to GSCs, in addition to the induction of GSC-specific apoptosis as illustrated by Annexin-V staining.

Conclusion

These results exemplify the use of phage display biopanning for the isolation of GSC-targeting peptides, and their potential application in the development of novel cytotoxic therapies for GBM.

gC1qR: A New Target for Cancer Immunotherapy

Although breakthroughs in cancer treatment have been achieved, immunotherapy yields only modest benefits in most patients. There is still a gap in clarifying the immune evasiveness and immune-resistance mechanisms. Identifying other candidate targets for cancer immunotherapy is therefore a clear unmet clinical need. The complement system, a pillar of innate immunity, has recently entered the limelight due to its immunoregulatory functions in the tumor microenvironment (TME). In particular, gC1qR, a receptor for globular heads of C1q, serves as a promising new target and has attracted more attention. gC1qR, also named P32/C1qBP/HABP1, is a multifunctional protein that is overexpressed in various cancers and holds prognostic value. It regulates the tumorigenic, progression and metastatic properties of tumor cells through several downstream signaling pathways, including the Wnt/β-catenin, PKC-NF-κB and Akt/PKB pathways. A few preclinical experiments conducted through gC1qR interventions, such as monoclonal antibody, chimeric antigen receptor T-cell (CAR-T) therapy, and tumor vaccination, have shown encouraging results in anticancer activity. The efficacy may rely on the regulatory role on the TME, induction of tumor cells apoptosis and antiangiogenic activity. Nevertheless, the current understanding of the relationship between cancer immunotherapy and gC1qR remains elusive and often contradictory, posing both opportunities and challenges for therapeutic translation in the clinic. In this review, we focus on the current understanding of gC1qR function in cancer immunology and highlight the vital roles in regulating the TME. We also examines the rationale behind targeting gC1qR and discusses the potential for translating into clinical practice.

C1QBP regulates mitochondrial plasticity to impact tumor progression and antitumor immune response

Mitochondrial plasticity including mitochondrial dynamics, metabolic flexibility, and mitochondrial quality control, impact tumor cells’ progression and determine immune cells’ fate. Complement C1q binding protein (C1QBP) plays an indispensable role through regulating mitochondrial morphology, metabolism, and autophagy. C1QBP promotes mitochondrial plasticity to impact tumor metastasis and their therapeutic response. At the same time, C1QBP is involved in regulating immune cells’ maturation, differentiation, and effector function through the enhancement of mitochondrial function. In this regard, manipulation of C1QBP has been shown to adjust the competitive balance between tumor cells and immune cells. In the course of evolution, mitochondrial plasticity has endowed numerous advantages against the relentless microenvironment of tumors. In this current review, we summarize the current knowledge of the mechanism of C1QBP regulation of cancer and immunity. We explain this process in vision of potentially new anticancer therapies.

Metabolic Labeling-Based Chemoproteomics Establishes Choline Metabolites as Protein Function Modulators

Choline is an essential nutrient for mammalian cells. Our understanding of the cellular functions of choline and its metabolites, independent of their roles as choline lipid metabolism intermediates, remains limited. In addition to fundamental cellular physiology, this knowledge has implications for cancer biology because elevated choline metabolite levels are a hallmark of cancer. Here, we establish a mammalian choline metabolite-interacting proteome by utilizing a photocrosslinkable choline probe. To design this probe, we performed metabolic labeling experiments with structurally diverse choline analogues that resulted in the serendipitous discovery of a choline lipid headgroup remodeling mechanism involving sequential dealkylation and methylation steps. We demonstrate that phosphocholine inhibits the binding of one of the proteins identified, the attractive anticancer target p32, to its endogenous ligands and to the promising p32-targeting anticancer agent, Lyp-1. Our results reveal that choline metabolites play vital roles in cellular physiology by serving as modulators of protein function.

Nanomedicine Penetration to Tumor: Challenges, and Advanced Strategies to Tackle This Issue

Nanomedicine has been under investigation for several years to improve the efficiency of chemotherapeutics, having minimal pharmacological effects clinically. Ineffective tumor penetration is mediated by tumor environments, including limited vascular system, rising cancer cells, higher interstitial pressure, and extra-cellular matrix, among other things. Thus far, numerous methods to increase nanomedicine access to tumors have been described, including the manipulation of tumor micro-environments and the improvement of nanomedicine characteristics; however, such outdated approaches still have shortcomings. Multi-functional convertible nanocarriers have recently been developed as an innovative nanomedicine generation with excellent tumor infiltration abilities, such as tumor-penetrating peptide-mediated transcellular transport. The developments and limitations of nanomedicines, as well as expectations for better outcomes of tumor penetration, are discussed in this review.

Core vs. surface labelling of mesoporous silica nanoparticles: advancing the understanding of nanoparticle fate and design of labelling strategies

Despite great interest in the use of silica mesoporous nanoparticles (MSNs) in drug delivery little is known on their biological fate. Positron emission tomography (PET) studies of radiolabelled MSNs face a major difficulty due to the degradation of the MSNs during circulation as it is difficult to assign activity values to either the MSNs or their degradation products. Here, a PET study is conducted using two strategies of labelling. MSNs are either radiolabelled in the core by complexation with silanols from the MSNs with ⁸⁹Zr, or on the MSN coating through attachment of ¹³¹I radiolabelled Lin-TT1 (AKRGARSTA), a homing peptide for targeting cancer tissue. Results from the biodistribution of MSNs with the two labels are compared, obtaining meanful information on the fate of MSNs. While MSNs accumulate in liver and spleen, MSN degradation products ⁸⁹Zr or silicate bearing the radioisotope, are found in the bones and probably in lungs. A partial detachment of the peptide from the surface of the MSN is also observed. This work highlights the importance of choosing an appropriate labelling strategy for nanoparticles since core or surface labelling may result in different particle biodistribution if the labelled component degrades or the label detaches.

Strategies to improve the EPR effect: A mechanistic perspective and clinical translation

Many efforts have been made to achieve targeted delivery of anticancer drugs to enhance their efficacy and to reduce their adverse effects. These efforts include the development of nanomedicines as they can selectively penetrate through tumor blood vessels through the enhanced permeability and retention (EPR) effect. The EPR effect was first proposed by Maeda and co-workers in 1986, and since then various types of nanoparticles have been developed to take advantage of the phenomenon with regards to drug delivery. However, the EPR effect has been found to be highly variable and thus unreliable due to the complex tumor microenvironment. Various physical and pharmacological strategies have been explored to overcome this challenge. Here, we review key advances and emerging concepts of such EPR-enhancing strategies. Furthermore, we analyze 723 clinical trials of nanoparticles with EPR enhancers and discuss their clinical translation.

Preclinical Validation of Tumor-Penetrating and Interfering Peptides against Chronic Lymphocytic Leukemia

Chronic lymphocytic leukemia (CLL) is the most common form of leukemia in adults. The disease is characterized by the accumulation of tumoral B cells resulting from a defect of apoptosis. We have in vitro and in vivo preclinically validated a tumor-penetrating peptide (named TT1) coupled to an interfering peptide (IP) that dissociates the interaction between the serine/threonine protein phosphatase 2A (PP2A) from its physiological inhibitor, the oncoprotein SET. This TT1-IP peptide has an antitumoral effect on CLL, as shown by the increased survival of mice bearing xenograft models of CLL, compared to control mice. The peptide did not show toxicity, as indicated by the mouse body weight and the biochemical parameters, such as renal and hepatic enzymes. In addition, the peptide-induced apoptosis in vitro of primary tumoral B cells isolated from CLL patients but not of those isolated from healthy patients. Finally, the peptide had approximately 5 h half-life in human serum and showed pharmacokinetic parameters compatible with clinical development as a therapeutic peptide against CLL.

PL1 Peptide Engages Acidic Surfaces on Tumor-Associated Fibronectin and Tenascin Isoforms to Trigger Cellular Uptake

Tumor extracellular matrix (ECM) is a high-capacity target for the precision delivery of affinity ligand-guided drugs and imaging agents. Recently, we developed a PL1 peptide (sequence: PPRRGLIKLKTS) for systemic targeting of malignant ECM. Here, we map the dynamics of PL1 binding to its receptors Fibronectin Extra Domain B (FN-EDB) and Tenascin C C-isoform (TNC-C) by computational modeling and cell-free binding studies on mutated receptor proteins, and study cellular binding and internalization of PL1 nanoparticles in cultured cells. Molecular dynamics simulation and docking analysis suggested that the engagement of PL1 peptide with both receptors is primarily driven by electrostatic interactions. Substituting acidic amino acid residues with neutral amino acids at predicted PL1 binding sites in FN-EDB (D52N-D49N-D12N) and TNC-C (D39N-D45N) resulted in the loss of binding of PL1 nanoparticles. Remarkably, PL1-functionalized nanoparticles (NPs) were not only deposited on the target ECM but bound the cells and initiated a robust cellular uptake via a pathway resembling macropinocytosis. Our studies establish the mode of engagement of the PL1 peptide with its receptors and suggest applications for intracellular delivery of nanoscale payloads. The outcomes of this work can be used for the development of PL1-derived peptides with improved stability, affinity, and specificity for precision targeting of the tumor ECM and malignant cells.

p32 promotes melanoma progression and metastasis by targeting EMT markers, Akt/PKB pathway, and tumor microenvironment

Melanoma originates from melanin-producing cells called melanocytes. Melanoma poses a great risk because of its rapid ability to spread and invade new organs. Cellular metastasis involves alteration in the gene expression profile and their transformation from epithelial to mesenchymal state. Despite of several advances, metastatic melanoma being a key cause of therapy failure and mortality remains poorly understood. p32 has been found to be involved in various physiological and pathophysiological conditions. However, the role of p32 in melanoma progression and metastasis remains underexplored. Here, we identify the role of p32 in the malignancy of both murine and human melanoma. p32 knockdown leads to reduced cell proliferation, migration, and invasion in murine and human melanoma cells. Furthermore, p32 promotes in vitro tumorigenesis, inducing oncogenes and EMT markers. Mechanistically, we show p32 regulates tumorigenic and metastatic properties through the Akt/PKB signaling pathway in both murine and human melanoma. Furthermore, p32 silencing attenuates melanoma tumor progression and lung metastasis in vivo, modulating the tumor microenvironment by inhibiting the angiogenesis, infiltration of macrophages, and leukocytes in mice. Taken together, our findings identify that p32 drives melanoma progression, metastasis, and regulates the tumor microenvironment. p32 can be a target of a novel therapeutic approach in the regulation of melanoma progression and metastasis.

Bi-Functional Peptides as a New Therapeutic Tool for Hepatocellular Carcinoma

Background: The interfering peptides that block protein–protein interactions have been receiving increasing attention as potential therapeutic tools. Methods: We measured the internalization and biological effect of four bi-functional tumor-penetrating and interfering peptides into primary hepatocytes isolated from three non-malignant and 11 hepatocellular carcinomas. Results: These peptides are internalized in malignant hepatocytes but not in non-malignant cells. Furthermore, the degree of peptide internalization correlated with receptor expression level and tumor aggressiveness levels. Importantly, penetration of the peptides iRGD-IP, LinTT1-IP, TT1-IP, and RPARPAR-IP induced apoptosis of the malignant hepatocytes without effect on non-malignant cells. Conclusion: Receptor expression levels correlated with the level of peptide internalization and aggressiveness of the tumor. This study highlights the potential to exploit the expression of tumor-penetrating peptide receptors as a predictive marker of liver tumor aggressiveness. These bi-functional peptides could be developed for personalized tumor treatment.

Cationic Liposomes as Vectors for Nucleic Acid and Hydrophobic Drug Therapeutics

Cationic liposomes (CLs) are effective carriers of a variety of therapeutics. Their applications as vectors of nucleic acids (NAs), from long DNA and mRNA to short interfering RNA (siRNA), have been pursued for decades to realize the promise of gene therapy, with approvals of the siRNA therapeutic patisiran and two mRNA vaccines against COVID-19 as recent milestones. The long-term goal of developing optimized CL-based NA carriers for a broad range of medical applications requires a comprehensive understanding of the structure of these vectors and their interactions with cell membranes and components that lead to the release and activity of the NAs within the cell. Structure-activity relationships of lipids for CL-based NA and drug delivery must take into account that these lipids act not individually but as components of an assembly of many molecules. This review summarizes our current understanding of how the choice of the constituting lipids governs the structure of their CL-NA self-assemblies, which constitute distinct liquid crystalline phases, and the relation of these structures to their efficacy for delivery. In addition, we review progress toward CL-NA nanoparticles for targeted NA delivery in vivo and close with an outlook on CL-based carriers of hydrophobic drugs, which may eventually lead to combination therapies with NAs and drugs for cancer and other diseases.

Novel Anthracycline Utorubicin for Cancer Therapy

Novel anticancer compounds and their precision delivery systems are actively developed to create potent and well-tolerated anticancer therapeutics. Here, we report the synthesis of a novel anthracycline, Utorubicin (UTO), and its preclinical development as an anticancer payload for nanocarriers. Free UTO was significantly more toxic to cultured tumor cell lines than the clinically used anthracycline, doxorubicin. Nanoformulated UTO, encapsulated in polymeric nanovesicles (polymersomes, PS), reduced the viability of cultured malignant cells and this effect was potentiated by functionalization with a tumor-penetrating peptide (TPP). Systemic peptide-guided PS showed preferential accumulation in triple-negative breast tumor xenografts implanted in mice. At the same systemic UTO dose, the highest UTO accumulation in tumor tissue was seen for the TPP-targeted PS, followed by nontargeted PS, and free doxorubicin. Our study suggests potential applications for UTO in the treatment of malignant diseases and encourages further preclinical and clinical studies on UTO as a nanocarrier payload for precision cancer therapy.

Novel Anthracycline Utorubicin for Cancer Therapy

Novel anticancer compounds and their precision delivery systems are actively developed to create potent and well-tolerated anticancer therapeutics. Here, we report the synthesis of a novel anthracycline, Utorubicin (UTO), and its preclinical development as an anticancer payload for nanocarriers. Free UTO was significantly more toxic to cultured tumor cell lines than the clinically used anthracycline, doxorubicin. Nanoformulated UTO, encapsulated in polymeric nanovesicles (polymersomes, PS), reduced the viability of cultured malignant cells and this effect was potentiated by functionalization with a tumor-penetrating peptide (TPP). Systemic peptide-guided PS showed preferential accumulation in triple-negative breast tumor xenografts implanted in mice. At the same systemic UTO dose, the highest UTO accumulation in tumor tissue was seen for the TPP-targeted PS, followed by nontargeted PS, and free doxorubicin. Our study suggests potential applications for UTO in the treatment of malignant diseases and encourages further preclinical and clinical studies on UTO as a nanocarrier payload for precision cancer therapy.

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

Peptide-drug conjugates (PDCs) are a class of novel molecules widely designed and synthesized for delivering payload drugs. The peptide part plays a vital role in the whole molecule, because they determine the ability of the molecules to penetrate the membrane and target to the specific targets. Here, we introduce the source of different kinds of cell-penetrating peptides (CPPs) and cell-targeting peptides (CTPs) that have been used or could be used in constructing PDCs as well as their latest application in delivering drugs. What's more, the approaches of developing CPPs and CTPs and the techniques to discover novel peptides are focused on and summarized in the review. This review aims to help relevant researchers fast understand the research status of peptides in PDCs and carry forward the process of novel peptides discovery.

Identification of a Glypican-3 Binding Peptide From a Phage-Displayed Peptide Library for PET Imaging of Hepatocellular Carcinoma

Tumor-targeting peptides functioned as molecular probes are essential for multi-modality imaging and molecular-targeting therapy in caner theronostics. Here, we performed a phage-displayed bio-panning to identify a specific binding peptide targeting Glypican-3 (GPC-3), a promising biomarker in hepatocellular carcinoma (HCC). After screening in the cyclic peptide library, a candidate peptide named F3, was isolated and showed specific binding to HCC cell lines. In a bio-distribution study, higher accumulation of F3 peptide was observed in HepG-2 tumors compared to PC-3 tumors in xenograft models. After labeling with radioactive ⁶⁸Ga, the F3 peptide tracer enabled the specific detection of tumors in HCC tumor models with PET imaging. More importantly, the expression of GPC-3 in human tissue samples may be distinguished by an F3 fluorescent peptide probe indicating its potential for clinical application. This cyclic peptide targeting GPC-3 has been validated, and may be an alternative to serve as an imaging probe or a targeting domain in the drug conjugate.

Acetalated dextran based nano- and microparticles: synthesis, fabrication, and therapeutic applications

Acetalated dextran (Ac-DEX) is a pH-responsive dextran derivative polymer. Prepared by a simple acetalation reaction, Ac-DEX has tunable acid-triggered release profile. Despite its relatively short research history, Ac-DEX has shown great potential in various therapeutic applications. Furthermore, the recent functionalization of Ac-DEX makes versatile derivatives with additional properties. Herein, we summarize the cutting-edge development of Ac-DEX and related polymers. Specifically, we focus on the chemical synthesis, nano- and micro-particle fabrication techniques, the controlled-release mechanisms, and the rational design Ac-DEX-based of drug delivery systems in various biomedical applications. Finally, we briefly discuss the challenges and future perspectives in the field.

The role of peptide-based therapeutics in oncotherapy

Cancer is the second leading cause of death worldwide, and the search for specialised therapy options has been a challenge for decades. The emergence of active targeted therapies provides the opportunity to treat cancerous tissues without harming healthy ones due to peculiar physiological changes. Herein, peptides and peptide analogs have been gaining a lot of attention over the last decade, especially for the on-site delivery of therapeutics to target tissues in order to achieve efficient and reliable cancer treatment. Combining peptides with highly efficient drug delivery platforms could potentially eliminate off-target adverse effects encountered during active targeting of conventional chemotherapeutics. Small size, ease of production and characterisation, low immunogenicity and satisfactory binding affinity of peptides offer some advantages over other complex targeting moiety, no wonder the market of peptide-based drugs continues to expand expeditiously. It is estimated that the global peptide drug market will be worth around USD 48.04 billion by 2025, with a compound annual growth rate of 9.4%. In this review, the current state of art of peptide-based therapeutics with special interest on tumour targeting peptides has been discussed. Moreover, various active targeting strategies such as the use functionalised peptides or peptide analogs are also elaborated.

Peptide-Based Strategies for Targeted Tumor Treatment and Imaging

Cancer is one of the leading causes of death worldwide. The development of cancer-specific diagnostic agents and anticancer toxins would improve patient survival. The current and standard types of medical care for cancer patients, including surgery, radiotherapy, and chemotherapy, are not able to treat all cancers. A new treatment strategy utilizing tumor targeting peptides to selectively deliver drugs or applicable active agents to solid tumors is becoming a promising approach. In this review, we discuss the different tumor-homing peptides discovered through combinatorial library screening, as well as native active peptides. The different structure–function relationship data that have been used to improve the peptide’s activity and conjugation strategies are highlighted.

Homing Peptides for Cancer Therapy

Tumor-homing peptides are widely used for improving tumor selectivity of anticancer drugs and imaging agents. The goal is to increase tumor uptake and reduce accumulation at nontarget sites. Here, we describe current approaches for tumor-homing peptide identification and validation, and provide comprehensive overview of classes of tumor-homing peptides undergoing preclinical and clinical development. We focus on unique mechanistic features and applications of a recently discovered class of tumor-homing peptides, tumor-penetrating C-end Rule (CendR) peptides, that can be used for tissue penetrative targeting of extravascular tumor tissue. Finally, we discuss unanswered questions and future directions in the field of development of peptide-guided smart drugs and imaging agents.

Ligand-Targeted Delivery of Photosensitizers for Cancer Treatment

Photodynamic therapy (PDT) is a promising cancer treatment which involves a photosensitizer (PS), light at a specific wavelength for PS activation and oxygen, which combine to elicit cell death. While the illumination required to activate a PS imparts a certain amount of selectivity to PDT treatments, poor tumor accumulation and cell internalization are still inherent properties of most intravenously administered PSs. As a result, common consequences of PDT include skin photosensitivity. To overcome the mentioned issues, PSs may be tailored to specifically target overexpressed biomarkers of tumors. This active targeting can be achieved by direct conjugation of the PS to a ligand with enhanced affinity for a target overexpressed on cancer cells and/or other cells of the tumor microenvironment. Alternatively, PSs may be incorporated into ligand-targeted nanocarriers, which may also encompass multi-functionalities, including diagnosis and therapy. In this review, we highlight the major advances in active targeting of PSs, either by means of ligand-derived bioconjugates or by exploiting ligand-targeting nanocarriers.

Anti gC1qR/p32/HABP1 Antibody Therapy Decreases Tumor Growth in an Orthotopic Murine Xenotransplant Model of Triple Negative Breast Cancer

gC1qR is highly expressed in breast cancer and plays a role in cancer cell proliferation. This study explored therapy with gC1qR monoclonal antibody 60.11, directed against the C1q binding domain of gC1qR, in a murine orthotopic xenotransplant model of triple negative breast cancer. MDA231 breast cancer cells were injected into the mammary fat pad of athymic nu/nu female mice. Mice were segregated into three groups (n = 5, each) and treated with the vehicle (group 1) or gC1qR antibody 60.11 (100 mg/kg) twice weekly, starting at day 3 post-implantation (group 2) or when the tumor volume reached 100 mm³ (group 3). At study termination (d = 35), the average tumor volume in the control group measured 895 ± 143 mm³, compared to 401 ± 48 mm³ and 701 ± 100 mm³ in groups 2 and 3, respectively (p < 0.05). Immunohistochemical staining of excised tumors revealed increased apoptosis (caspase 3 and TUNEL staining) in 60.11-treated mice compared to controls, and decreased angiogenesis (CD31 staining). Slightly decreased white blood cell counts were noted in 60.11-treated mice. Otherwise, no overt toxicities were observed. These data are the first to demonstrate an in vivo anti-tumor effect of 60.11 therapy in a mouse model of triple negative breast cancer.

gC1qR/HABP1/p32 Is a Potential New Therapeutic Target Against Mesothelioma

Mesothelioma is an aggressive cancer of the serous membranes with poor prognosis despite combination therapy consisting of surgery, radiotherapy, and platinum-based chemotherapy. Targeted therapies, including immunotherapies, have reported limited success, suggesting the need for additional therapeutic targets. This study investigates a potential new therapeutic target, gC1qR/HABP1/p32 (gC1qR), which is overexpressed in all morphologic subtypes of mesothelioma. gC1qR is a complement receptor that is associated with several cellular functions, including cell proliferation and angiogenesis. In vitro and in vivo experiments were conducted to test the hypothesis that targeting gC1qR with a specific gC1qR monoclonal antibody 60.11 reduces mesothelioma tumor growth, using the biphasic mesothelioma cell line MSTO-211H (MSTO). In vitro studies demonstrate cell surface and extracellular gC1qR expression by MSTO cells, and a modest 25.3 ± 1.8% (n = 4) reduction in cell proliferation by the gC1qR blocking 60.11 antibody. This inhibition was specific for targeting the C1q binding domain of gC1qR at aa 76–93, as a separate monoclonal antibody 74.5.2, directed against amino acids 204–218, had no discernable effect. In vivo studies, using a murine orthotopic xenotransplant model, demonstrated an even greater reduction in MSTO tumor growth (50% inhibition) in mice treated with the 60.11 antibody compared to controls. Immunohistochemical studies of resected tumors revealed increased cellular apoptosis by caspase 3 and TUNEL staining, in 60.11 treated tumors compared to controls, as well as impaired angiogenesis by decreased CD31 staining. Taken together, these data identify gC1qR as a potential new therapeutic target against mesothelioma with both antiproliferative and antiangiogenic properties.

Tumor-Targeting Peptides: The Functional Screen of Glioblastoma Homing Peptides to the Target Protein FABP3 (MDGI)

We recently identified the glioblastoma homing peptide CooP (CGLSGLGVA) using in vivo phage display screen. The mammary-derived growth inhibitor (MDGI/FABP3) was identified as its interacting partner. Here, we present an alanine scan of A-CooP to investigate the contribution of each amino acid residue to the binding to FABP3 by microscale thermophoresis (MST) and surface plasmon resonance (SPR). We also tested the binding affinity of the A-CooP-K, KA-CooP, and retro-inverso A-CooP analogues to the recombinant FABP3. According to the MST analysis, A-CooP showed micromolar (K_D = 2.18 µM) affinity to FABP3. Alanine replacement of most of the amino acids did not affect peptide affinity to FABP3. The A-CooP-K variant showed superior binding affinity, while A-[Ala⁵]CooP and A-[Ala⁷]CooP, both replacing a glycine residue with alanine, showed negligible binding to FABP3. These results were corroborated in vitro and in vivo using glioblastoma models. Both A-CooP-K and A-CooP showed excellent binding in vitro and homing in vivo, while A-[Ala⁵]CooP and control peptides failed to bind the cells or home to the intracranial glioblastoma xenografts. These results provide insight into the FABP3–A-CooP interaction that may be important for future applications of drug conjugate design and development.

Targeting Pro-Tumoral Macrophages in Early Primary and Metastatic Breast Tumors with the CD206-Binding mUNO Peptide

M2-like tumor-associated macrophages (M2 TAMs) play important roles in the resistance of tumors to immunotherapies. Selective depletion or reprogramming of M2 TAMs may sensitize the nonresponsive tumors for immune-mediated eradication. However, precision delivery of payloads to M2 TAMs, while sparing healthy tissues, has remained an unresolved challenge. Here, we studied the application of a short linear peptide (CSPGAK, "mUNO") for the delivery of molecular and nanoscale cargoes in M2 TAMs in vitro and the relevance of the peptide for in vivo targeting of early-stage primary breast tumors and metastatic lung foci. First, we performed in silico modeling and found that mUNO interacts with mouse CD206 via a binding site between lectin domains CTLD1 and CTLD2, the same site previously demonstrated to be involved in mUNO binding to human CD206. Second, we showed that cultured M2 macrophages take up fluorescein-labeled (FAM) polymersomes conjugated with mUNO using the sulfhydryl group of its N-terminal cysteine. Pulse/chase studies of FAM-mUNO in M2 macrophages suggested that the peptide avoided lysosomal entrapment and escaped from early endosomes. Third, our in vivo studies with FAM-mUNO demonstrated that intraperitoneal administration results in better pharmacokinetics and higher blood bioavailability than can be achieved with intravenous administration. Intraperitoneal FAM-mUNO, but not FAM-control, showed a robust accumulation in M2-skewed macrophages in mouse models of early primary breast tumor and lung metastasis. This targeting was specific, as no uptake was observed in nonmalignant control organs, including the liver, or other cell types in the tumor, including M1 macrophages. Collectively, our studies support the application of the CD206-binding mUNO peptide for delivery of molecular and nanoscale cargoes to M2 macrophages and manifest the relevance of this mode of targeting primary and metastatic breast tumors.

Neuropilin: Handyman and Power Broker in the Tumor Microenvironment

Neuropilin-1 and neuropilin-2 form a small family of transmembrane receptors, which, due to the lack of a cytosolic protein kinase domain, act primarily as co-receptors for various ligands. Performing at the molecular level both the executive and organizing functions of a handyman as well as of a power broker, they are instrumental in controlling the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. In this setting, the various neuropilin ligands and interaction partners on various cells of the tumor microenvironment, such as cancer cells, endothelial cells, cancer-associated fibroblasts, and immune cells, are surveyed. The suitability of various neuropilin-targeting substances and the intervention in neuropilin-mediated interactions is considered as a possible building block of tumor therapy.

Dual-peptide functionalized acetalated dextran-based nanoparticles for sequential targeting of macrophages during myocardial infarction

The advent of nanomedicine has recently started to innovate the treatment of cardiovascular diseases, in particular myocardial infarction. Although current approaches are very promising, there is still an urgent need for advanced targeting strategies. In this work, the exploitation of macrophage recruitment is proposed as a novel and synergistic approach to improve the addressability of the infarcted myocardium achieved by current peptide-based heart targeting strategies. For this purpose, an acetalated dextran-based nanosystem is designed and successfully functionalized with two different peptides, atrial natriuretic peptide (ANP) and linTT1, which target, respectively, cardiac cells and macrophages associated with atherosclerotic plaques. The biocompatibility of the nanocarrier is screened on both macrophage cell lines and primary macrophages, showing high safety, in particular after functionalization of the nanoparticles' surface. Furthermore, the system shows higher association versus uptake ratio towards M2-like macrophages (approximately 2-fold and 6-fold increase in murine and human primary M2-like macrophages, respectively, compared to M1-like). Overall, the results demonstrate that the nanosystem has potential to exploit the "hitchhike" effect on M2-like macrophages and potentially improve, in a dual targeting strategy, the ability of the ANP peptide to target infarcted heart.

LyP-1-fMWNTs enhanced targeted delivery of MBD1siRNA to pancreatic cancer cells

Functionalized multi‐walled carbon nanotubes have been extensively gained popularity in pancreatic cancer gene therapy. LyP‐1, a peptide, has been proved to specifically bind pancreatic cancer cells. The potential therapeutic effect of LyP‐1–conjugated functionalized multi‐walled carbon nanotubes in treating pancreatic cancer is still unknown. In this study, LyP‐1–conjugated functionalized multi‐walled carbon nanotubes were successfully synthesized, characterized and showed satisfactory size distribution and zeta potential. Compared with functionalized multi‐walled carbon nanotubes, cellular uptake of LyP‐1–functionalized multi‐walled carbon nanotubes was shown to be increased. Compound of LyP‐1–functionalized multi‐walled carbon nanotubes and MBD1siRNA showed superior gene transfection efficiency. Moreover, LyP‐1‐fMWNTs/MBD1siRNA complex could significantly decrease the viability and proliferation and promoted apoptosis of pancreatic cancer cells in vitro. Further xenograft assays revealed that the tumour burden in the nude mice injected with LyP‐1–functionalized multi‐walled carbon nanotubes/MBD1siRNA was significantly relieved. The study demonstrated that LyP‐1–functionalized multi‐walled carbon nanotubes/MBD1siRNA could be a promising candidate for tumour active targeting therapy in pancreatic cancer.

Bi-specific tenascin-C and fibronectin targeted peptide for solid tumor delivery

Oncofetal fibronectin (FN-EDB) and tenascin-C C domain (TNC-C) are nearly absent in extracellular matrix of normal adult tissues but upregulated in malignant tissues. Both FN-EDB and TNC-C are developed as targets of antibody-based therapies. Here we used peptide phage biopanning to identify a novel targeting peptide (PL1, sequence: PPRRGLIKLKTS) that interacts with both FN-EDB and TNC-C. Systemic PL1-functionalized model nanoscale payloads [iron oxide nanoworms (NWs) and metallic silver nanoparticles] homed to glioblastoma (GBM) and prostate carcinoma xenografts, and to non-malignant angiogenic neovessels induced by VEGF-overexpression. Antibody blockage experiments demonstrated that PL1 tumor homing involved interactions with both receptor proteins. Treatment of GBM mice with PL1-targeted model therapeutic nanocarrier (NWs loaded with a proapoptotic peptide) resulted in reduced tumor growth and increased survival, whereas treatment with untargeted particles had no effect. PL1 peptide may have applications as an affinity ligand for delivery of diagnostic and therapeutic compounds to microenvironment of solid tumors.

Complement component 1q subcomponent binding protein in the brain of the rat

Complement component 1q subcomponent binding protein (C1qbp) is a multifunctional protein involved in immune response, energy homeostasis of cells as a plasma membrane receptor, and a nuclear, cytoplasmic or mitochondrial protein. Recent reports suggested its neuronal function, too, possibly in axon maintenance, synaptic function, and neuroplasticity. Therefore, we addressed to identify C1qbp in the rat brain using in situ hybridization histochemistry and immunolabelling at light and electron microscopic level. C1qbp has a topographical distribution in the brain established by the same pattern of C1qbp mRNA-expressing and protein-containing neurons with the highest abundance in the cerebral cortex, anterodorsal thalamic nucleus, hypothalamic paraventricular (PVN) and arcuate nuclei, spinal trigeminal nucleus. Double labelling of C1qbp with the neuronal marker NeuN, with the astrocyte marker S100, and the microglia marker Iba1 demonstrated the presence of C1qbp in neurons but not in glial cells in the normal brain, while C1qbp appeared in microglia following their activation induced by focal ischemic lesion. Only restricted neurons expressed C1qbp, for example, in the PVN, magnocellular neurons selectively contained C1qbp. Further double labelling by using the mitochondria marker Idh3a antibody suggested the mitochondrial localization of C1qbp in the brain, confirmed by correlated light and electron microscopy at 3 different brain regions. Post-embedding immunoelectron microscopy also suggested uneven C1qbp content of mitochondria in different brain areas but also heterogeneity within single neurons. These data suggest a specific function of C1qbp in the brain related to mitochondria, such as the regulation of local energy supply in neuronal cells.

Neuropilins in the Context of Tumor Vasculature

Neuropilin-1 and Neuropilin-2 form a small family of plasma membrane spanning receptors originally identified by the binding of semaphorin and vascular endothelial growth factor. Having no cytosolic protein kinase domain, they function predominantly as co-receptors of other receptors for various ligands. As such, they critically modulate the signaling of various receptor tyrosine kinases, integrins, and other molecules involved in the regulation of physiological and pathological angiogenic processes. This review highlights the diverse neuropilin ligands and interacting partners on endothelial cells, which are relevant in the context of the tumor vasculature and the tumor microenvironment. In addition to tumor cells, the latter contains cancer-associated fibroblasts, immune cells, and endothelial cells. Based on the prevalent neuropilin-mediated interactions, the suitability of various neuropilin-targeted substances for influencing tumor angiogenesis as a possible building block of a tumor therapy is discussed.

Peritoneal Carcinomatosis Targeting with Tumor Homing Peptides

Over recent decades multiple therapeutic approaches have been explored for improved management of peritoneally disseminated malignancies—a grim condition known as peritoneal carcinomatosis (PC). Intraperitoneal (IP) administration can be used to achieve elevated local concentration and extended half-life of the drugs in the peritoneal cavity to improve their anticancer efficacy. However, IP-administered chemotherapeutics have a short residence time in the IP space, and are not tumor selective. An increasing body of work suggests that functionalization of drugs and nanoparticles with targeting peptides increases their peritoneal retention and provides a robust and specific tumor binding and penetration that translates into improved therapeutic response. Here we review the progress in affinity targeting of intraperitoneal anticancer compounds, imaging agents and nanoparticles with tumor-homing peptides. We review classes of tumor-homing peptides relevant for PC targeting, payloads for peptide-guided precision delivery, applications for targeted compounds, and the effects of nanoformulation of drugs and imaging agents on affinity-based tumor delivery.

Application of polymersomes engineered to target p32 protein for detection of small breast tumors in mice

Triple negative breast cancer (TNBC) is the deadliest form of breast cancer and its successful treatment critically depends on early diagnosis and therapy. The multi-compartment protein p32 is overexpressed and present at cell surfaces in a variety of tumors, including TNBC, specifically in the malignant cells and endothelial cells, and in macrophages localized in hypoxic areas of the tumor. Herein we used polyethylene glycol-polycaprolactone polymersomes that were affinity targeted with the p32-binding tumor penetrating peptide LinTT1 (AKRGARSTA) for imaging of TNBC lesions. A tyrosine residue was added to the peptide to allow for ¹²⁴I labeling and PET imaging. In a TNBC model in mice, systemic LinTT1-targeted polymersomes accumulated in early tumor lesions more than twice as efficiently as untargeted polymersomes with up to 20% ID/cc at 24 h after administration. The PET-imaging was very sensitive, allowing detection of tumors as small as ∼20 mm³. Confocal imaging of tumor tissue sections revealed a high degree of vascular exit and stromal penetration of LinTT1-targeted polymersomes and co-localization with tumor-associated macrophages. Our studies show that systemic LinTT1-targeted polymersomes can be potentially used for precision-guided tumor imaging and treatment of TNBC.

The role of the globular heads of the C1q receptor in paclitaxel-induced human ovarian cancer cells apoptosis by a mitochondria-dependent pathway

As a mitochondrial membrane protein, globular C1q receptor (gC1qR) can mediate a variety of biological responses. Our study aims to investigate the role of gC1qR in paclitaxel-induced apoptosis of human ovarian cancer cells and to elucidate its potential molecular mechanism. The level of gC1qR was examined using real-time PCR and western blot analyses. Human ovarian cancer cells viability, migration, and proliferation were detected using the water-soluble tetrazolium salt (WST-1) assay, the transwell assay, and H-thymidine incorporation into DNA (H-TdR) assay, respectively. Apoptosis in cells was assessed using flow cytometric analysis. The intracellular reactive oxygen species was estimated by the fluorescence of H2DCFDA and the mitochondrial membrane potential was tested using a JC-1 probe. The expression of the gC1qR gene decreased significantly in human ovarian cancer tissues relative to the surrounding non-neoplastic ovarian tissues. Cells treated with paclitaxel showed increased gC1qR gene expression, cell apoptosis, and mitochondria dysfunction, and the effects on these cells could be abrogated by the addition of gC1qR small-interfering RNA or α-lipoic acid that was used to protect the mitochondria function. In summary, these data support a mechanism that gC1qR-induced mitochondria dysfunction was involved in the paclitaxel-mediated apoptosis of ovarian cancer cells.

Multi-functional, multicompartmental hyaluronan-binding protein 1 (HABP1/p32/gC1qR): implication in cancer progression and metastasis

Cancer is a complex, multi-factorial, multi-stage disease and a global threat to human health. Early detection of nature and stage of cancer is highly crucial for disease management. Recent studies have proved beyond any doubt about the involvement of the ubiquitous, myriad ligand binding, multi-functional human protein, hyaluronan-binding protein 1 (HABP1), which is identical to the splicing factor associated protein (p32) and the receptor of the globular head of the complement component (gC1qR) in tumorigenesis and cancer metastasis. Simultaneously three laboratories have discovered and named this protein separately as mentioned. Subsequently, different scientists have worked on the distinct functions in cellular processes ranging from immunological response, splicing mechanism, sperm-oocyte interactions, cell cycle regulation to cancer and have concentrated in their respective area of interest, referring it as either p32 or gC1qR or HABP1. HABP1 overexpression has been reported in almost all the tissue-specific forms of cancer and correlated with stage and poor prognosis in patients. In order to tackle this deadly disease and for therapeutic intervention, it is imperative to focus on all the regulatory aspects of this protein. Hence, this work is an attempt to combine an assortment of information on this protein to have an overview, which suggests its use as a diagnostic marker for cancer. The knowledge might assist in the designing of drugs for therapeutic intervention of HABP1/p32/gC1qR regulated specific ligand mediated pathways in cancer.

Peptides as drug delivery vehicles across biological barriers

Peptides are small biological molecules that are attractive in drug delivery and materials engineering for applications including therapeutics, molecular building blocks and cell-targeting ligands. Peptides are small but can possess complexity and functionality as larger proteins. Due to their intrinsic properties, peptides are able to overcome the physiological and transport barriers presented by diseases. In this review, we discuss the progress of identifying and using peptides to shuttle across biological barriers and facilitate transport of drugs and drug delivery systems for improved therapy. Here, the focus of this review is on rationally designed, phage display peptides, and even endogenous peptides as carriers to penetrate biological barriers, specifically the blood-brain barrier(BBB), the gastrointestinal tract (GI), and the solid tumor microenvironment (T). We will discuss recent advances of peptides as drug carriers in these biological environments. From these findings, challenges and potential opportunities to iterate and improve peptide-based approaches will be discussed to translate their promise towards the clinic to deliver drugs for therapeutic efficacy.