Rationally designed anti-HER2/neu peptide mimetic disables P185HER2/neu tyrosine kinases in vitro and in vivo

Peptides Targeting HER2-Positive Breast Cancer Cells and Applications in Tumor Imaging and Delivery of Chemotherapeutics

Breast cancer represents the most common cancer type and one of the major leading causes of death in the female worldwide population. Overexpression of HER2, a transmembrane glycoprotein related to the epidermal growth factor receptor, results in a biologically and clinically aggressive breast cancer subtype. It is also the primary driver for tumor detection and progression and, in addition to being an important prognostic factor in women diagnosed with breast cancer, HER2 is a widely known therapeutic target for drug development. The aim of this review is to provide an updated overview of the main approaches for the diagnosis and treatment of HER2-positive breast cancer proposed in the literature over the past decade. We focused on the different targeting strategies involving antibodies and peptides that have been explored with their relative outcomes and current limitations that need to be improved. The review also encompasses a discussion on targeted peptides acting as probes for molecular imaging. By using different types of HER2-targeting strategies, nanotechnology promises to overcome some of the current clinical challenges by developing novel HER2-guided nanosystems suitable as powerful tools in breast cancer imaging, targeting, and therapy.

Integrin α6 Targeted Near Infrared Fluorescent Imaging and Photoacoustic Imaging of Hepatocellular Carcinoma in Mice

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is the fourth most common cause of cancer-related death and ranks sixth in terms of incident cases worldwide. The purpose of this study was to develop an effective and sensitive method to distinguish liver cancer tissues from normal tissues in HCC patients. Integrin α6 is a promising cell surface target for molecular imaging of HCC, where it is overexpressed and is a prognostic biomarker. We previously identified an integrin α6-targeted peptide CRWYDENAC (RWY) that has been used for positron emission tomography (PET) imaging of HCC in mouse models.

METHODS

We labeled the integrin α6-targeted RWY peptide with cyanine 7 (Cy7) to form an optical probe (Cy7-RWY) for near infrared fluorescent (NIRF) and photoacoustic (PA) imaging in HCC. Mice transplanted with subcutaneous HCC-LM3 or orthotopic HCC-H22 cells that overexpressed integrin α6 were intravenously injected with Cy7-RWY and its corresponding Cy7-control. NIRF and PA images of mice were collected from 0 to 48 h after injection.

RESULTS

Both NIRF and PA signals started to accumulate in the tumor 2 h after injection of Cy7-RWY and peaked at 24 h.

CONCLUSIONS

Cy7-RWY is a promising optical probe for NIRF and PA imaging of HCC in mice, and has potential clinical application for HCC detection.

Downsizing antibodies: Towards complementarity-determining region (CDR)-based peptide mimetics

Monoclonal antibodies emerged as an important therapeutic drug class with remarkable specificity and binding affinity. Nonetheless, these heterotetrameric immunoglobulin proteins come with high manufacturing and therapeutic costs which can take extraordinary proportions, besides other limitations such as their limited in cellulo access imposed by their molecular size (ca. 150 kDa). These drawbacks stimulated the development of downsized functional antibody fragments (ca. 15-50 kDa), together with smaller synthetic peptides (ca. 1-3 kDa) derived from the antibodies' crucial complementarity-determining regions (CDR). Despite the general lack of success in the literal translation of CDR loops in peptide mimetics, rational structure-based and computational approaches have shown their potential for obtaining functional CDR-based peptide mimetics. In this review, we describe the efforts made in the development of antibody and nanobody paratope-derived peptide mimetics with particular focus on the used design strategies, in addition to highlighting the challenges associated with their development.

Ferritin Conjugates With Multiple Clickable Amino Acids Encoded by C-Terminal Engineered Pyrrolysyl-tRNA Synthetase

This study reports the application of expanding genetic codes in developing protein cage-based delivery systems. The evolved Methanosarcina mazei pyrrolysyl-tRNA synthetase (PylRS)•tRNA^Pyl pairs derived from directed evolution are examined to probe their recognition for para-substituted phenylalanine analogs. The evolved MmPylRS, AzFRS, harboring a wide range of substrates, is further engineered at the C-terminal region into another variant, AzFRS-MS. AzFRS-MS shows suppression of the elevated sfGFP protein amount up to 10 TAG stop codons when charging p-azido-l-phenylalanine (AzF, 4), which allows the occurrence of click chemistry. Since protein nanocages used as drug delivery systems that encompass multiple drugs through a site-specific loading approach remain largely unexplored, as a proof of concept, the application of AzFRS-MS for the site-specific incorporation of AzF on human heavy chain ferritin (Ftn) is developed. The Ftn-4 conjugate is shown to be able to load multiple fluorescence dyes or a therapeutic agent, doxorubicin (Dox), through the strain-promoted azide-alkyne cycloaddition (SPAAC) click reaction. Aiming to selectively target Her2⁺ breast cancer cells, Ftn-4-DOX conjugates fused with a HER2 receptor recognition peptide, anti-Her2/neu peptide (AHNP), is developed and demonstrated to be able to deliver Dox into the cell and to prolong the drug release. This work presents another application of evolved MmPylRS systems, whose potential in developing a variety of protein conjugates is noteworthy.

Small-Sized Co-Polymers for Targeted Delivery of Multiple Imaging and Therapeutic Agents

Research has increasingly focused on the delivery of high, often excessive amounts of drugs, neglecting negative aspects of the carrier's physical preconditions and biocompatibility. Among them, little attention has been paid to "small but beautiful" design of vehicle and multiple cargo to achieve effortless targeted delivery into deep tissue. The design of small biopolymers for deep tissue targeted delivery of multiple imaging agents and therapeutics (mini-nano carriers) emphasizes linear flexible polymer platforms with a hydrodynamic diameter of 4 nm to 10 nm, geometrically favoring dynamic juxtaposition of ligands to host receptors, and economic drug content. Platforms of biodegradable, non-toxic poly(β-l-malic acid) of this size carrying multiple chemically bound, optionally nature-derived or synthetic affinity peptides and drugs for a variety of purposes are described in this review with specific examples. The size, shape, and multiple attachments to membrane sites accelerate vascular escape and fast blood clearance, as well as the increase in medical treatment and contrasts for tissue imaging. High affinity antibodies routinely considered for targeting, such as the brain through the blood-brain barrier (BBB), are replaced by moderate affinity binding peptides (vectors), which penetrate at high influxes not achievable by antibodies.

Review: Radionuclide Molecular Imaging Targeting HER2 in Breast Cancer with a Focus on Molecular Probes into Clinical Trials and Small Peptides

As the most frequently occurring cancer worldwide, breast cancer (BC) is the leading cause of cancer-related death in women. The overexpression of HER2 (human epidermal growth factor receptor 2) is found in about 15% of BC patients, and it is often associated with a poor prognosis due to the effect on cell proliferation, migration, invasion, and survival. As a result of the heterogeneity of BC, molecular imaging with HER2 probes can non-invasively, in real time, and quantitatively reflect the expression status of HER2 in tumors. This will provide a new approach for patients to choose treatment options and monitor treatment response. Furthermore, radionuclide molecular imaging has the potential of repetitive measurements, and it can help solve the problem of heterogeneous expression and conversion of HER2 status during disease progression or treatment. Different imaging probes of targeting proteins, such as monoclonal antibodies, antibody fragments, nanobodies, and affibodies, are currently in preclinical and clinical development. Moreover, in recent years, HER2-specific peptides have been widely developed for molecular imaging techniques for HER2-positive cancers. This article summarized different types of molecular probes targeting HER2 used in current clinical applications and the developmental trend of some HER2-specific peptides.

Peptide-Conjugated Nano Delivery Systems for Therapy and Diagnosis of Cancer

Peptides are strings of approximately 2-50 amino acids, which have gained huge attention for theranostic applications in cancer research due to their various advantages including better biosafety, customizability, convenient process of synthesis, targeting ability via recognizing biological receptors on cancer cells, and better ability to penetrate cell membranes. The conjugation of peptides to the various nano delivery systems (NDS) has been found to provide an added benefit toward targeted delivery for cancer therapy. Moreover, the simultaneous delivery of peptide-conjugated NDS and nano probes has shown potential for the diagnosis of the malignant progression of cancer. In this review, various barriers hindering the targeting capacity of NDS are addressed, and various approaches for conjugating peptides and NDS have been discussed. Moreover, major peptide-based functionalized NDS targeting cancer-specific receptors have been considered, including the conjugation of peptides with extracellular vesicles, which are biological nanovesicles with promising ability for therapy and the diagnosis of cancer.

Rational Design of Constrained Peptides as Protein Interface Inhibitors

The lack of progress in developing targeted therapeutics directed at protein–protein complexes has been due to the absence of well-defined ligand-binding pockets and the extensive intermolecular contacts at the protein–protein interface. Our laboratory has developed approaches to dissect protein–protein complexes focusing on the superfamilies of erbB and tumor necrosis factor (TNF) receptors by the combined use of structural biology and computational biology to facilitate small molecule development. We present a perspective on the development and application of peptide inhibitors as well as immunoadhesins to cell surface receptors performed in our laboratory.

Isolation of Cowpea Mosaic Virus-Binding Peptides

The plant virus cowpea mosaic virus (CPMV) is a natural nanocarrier that has been developed as a platform technology for the delivery of various payloads including peptide epitopes for vaccines, contrast agents for imaging, and drugs for therapy. Genetic fusion and chemical conjugations are the mainstay approaches to load the active ingredient to the exterior and/or interior of CPMV. However, these methods have limitations; genetic engineering is limited to biologics, and chemical alteration often requires multistep reactions with modification of both CPMV and the active ingredient. Either method can also result in particle instability. Therefore, to provide an alternate path toward CPMV functionalization, we report the isolation of peptides that specifically bind to CPMV, termed CPMV-binding peptides (CBP). We used a commercial M13 phage display 7-mer peptide library to pan for and select peptides that selectively bind to CPMV. Biopanning and characterization of lead candidates resulted in isolation of the motif "GWRVSEF/L" as the CPMV-specific motif with phenylalanine (F) at the seventh position being stronger than leucine (L). Specificity to CPMV was demonstrated, and cross-reactivity toward other plant viruses was not observed. To demonstrate cargo loading, GWRVSEF was tagged with biotin, fluorescein isothiocyanate (FITC), and a human epidermal growth factor receptor 2 (HER2)-specific targeting peptide ligand. Display of the active ingredient was confirmed, and utility of tagged and targeted CPMV in cell binding assays was demonstrated. The CBP functionalization strategy offers a new avenue for CPMV nanoparticle functionalization and should offer a versatile tool to add active ingredients that otherwise may be difficult to conjugate or display.

Disabling the Nuclear Translocalization of RelA/NF-κB by a Small Molecule Inhibits Triple-Negative Breast Cancer Growth

INTRODUCTION

Constitutive activation of NF-κB has been implicated as being contributive to cancer cell growth, drug resistance, and tumor recurrence in many cancers including breast cancer. Activation of NF-κB leads to nuclear translocation of RelA, a critical component of the NF-κB transcription factor complex, which subsequently binds to specific DNA sites and activates a multitude of genes involved in diverse cell functions. Studies show that triple-negative breast cancer (TNBC) cells possess constitutively active NF-κB and concomitantly have higher levels of nuclear localization of RelA than cytoplasmic RelA. This feature is considered to be associated with the response to chemotherapy. However, currently, there is no specific inhibitor to block nuclear translocation of RelA.

METHODS

A structure-based approach was used to develop a small-molecule inhibitor of RelA nuclear translocation. The interaction between this molecule and RelA was verified biophysically through isothermal titration calorimetry and microscale thermophoresis. TNBC cell lines MDA-MB-231 and MDA-MB-468 and a human TNBC xenograft model were used to verify in vitro and in vivo efficacy of the small molecule, respectively.

RESULTS

We found that the small molecule, CRL1101, bound specifically to RelA as indicated by the biophysical assays. Further, CRL1101 blocked RelA nuclear translocation in breast cancer cells in vitro, and markedly reduced breast tumor growth in a triple-negative breast cancer xenograft model.

CONCLUSION

Our study demonstrates that CRL1101 may lead to new NF-κB-targeted therapeutics for TNBC. Further, blocking of nuclear translocation of shuttling transcription factors may be a useful general strategy in cancer drug development.

Peptide Based Imaging Agents for HER2 Imaging in Oncology

Breast cancer continues to be the most lethal cancer type in women and one of the most diagnosed. Understanding Breast cancer receptor status is one of the most vital processes for determining treatment options. One type of breast cancer, human epidermal growth factor receptor 2 (HER2) positive, has approved receptor-based therapies including trastuzumab and pertuzumab that can significantly increase the likelihood of survival. Current methods to determine HER2 status include biopsies with immunohistochemical staining and/or fluorescence in situ hybridization. However, positron emission tomography (PET) imaging techniques using ⁸⁹Zr-trastuzumab or ⁸⁹Zr-pertuzumab are currently in clinical trials for a non-invasive, full body diagnostic approach. Although the antibodies have strong specificity to the HER2 positive lesions, challenges involving long post-injection time for imaging due to the blood circulation of the antibodies and matching of long-live isotopes leading to increased dose to the patient leave opportunities for alternative PET imaging probes. Peptides have been shown to allow for shorter injection-to-imaging time and can be used with shorter lived isotopes. HER2 specific peptides under development will help improve the diagnosis and potentially therapy options for HER2 positive breast cancer. Peptides showing specificity for HER2 could start widespread development of molecular imaging techniques for HER2 positive cancers.

Perspective on Crystallographic Studies of Antibody Structures

In the past 50 years, there has been a great progress made in understanding and deploying antibodies in biology, medicine, and therapy. In this study, a brief overview is presented on how the crystal structures of antibody fragments guided therapeutic strategies emanating from our laboratories along with some historical perspective.

Transformable peptide nanoparticles arrest HER2 signalling and cause cancer cell death in vivo

Human epidermal growth factor receptor 2 (HER2) is overexpressed in >20% of breast cancers. Dimerization of HER2 receptors leads to the activation of downstream signals enabling the proliferation and survival of malignant phenotypes. Owing to the high expression levels of HER2, combination therapies are currently required for the treatment of HER2⁺ breast cancer. Here, we designed non-toxic transformable peptides that self-assemble into micelles under aqueous conditions but, on binding to HER2 on cancer cells, transform into nanofibrils that disrupt HER2 dimerization and subsequent downstream signalling events leading to apoptosis of cancer cells. The phase transformation of peptides enables specific HER2 targeting, and inhibition of HER2 dimerization blocks the expression of proliferation and survival genes in the nucleus. We demonstrate, in mouse xenofraft models, that these transformable peptides can be used as a monotherapy in the treatment of HER2⁺ breast cancer.

Quantitative Study of the Interaction of Multivalent Ligand-Modified Nanoparticles with Breast Cancer Cells with Tunable Receptor Density

Multivalent nanoparticles that target a cell surface receptor that is overexpressed by cancer cells are a promising delivery system for cancer therapy. However, the impact of the receptor density and nanoparticle ligand valency on the cell uptake has not been studied in a system where both variables can be systematically tuned over a wide range. To address this lacuna, we report cell-uptake studies on a genetically engineered breast cancer cell line with tunable ErbB2 expression by a polypeptide micelle with tunable ligand valency. We examined the uptake of ErbB2-targeting micelles at 5 ligand densities and 11 receptor densities. We identified a matching pattern between receptors and ligands in which a receptor-to-ligand density ratio of 0.7-4.5 and a minimum of ∼1.6 bonds are required to initiate receptor-mediated endocytosis. Lower and upper limits of receptor density in the cell-uptake profile suggested a standard by which to categorize breast cancer patients as ErbB2-low, ErbB2-medium, and ErbB2-high, with each group expected to respond differently to multivalent therapeutic nanoparticles. At ErbB2-medium and ErbB2-high levels, increasing the ligand valency to 40-valent ErbB2-targeting peptides for a 20 nm radius nanoparticle accelerated the cell uptake, suggesting that the use of nanoparticles with high ligand valency for drug delivery will greatly benefit patients in these two groups. This study advances our understanding of how to rationally optimize nanotechnology for targeted drug delivery.

Strategic design to create HER2-targeting proteins with target-binding peptides immobilized on a fibronectin type III domain scaffold

Tumor-binding peptides such as human epidermal growth factor receptor 2 (HER2)-binding peptides are attractive therapeutic and diagnostic options for cancer. However, the HER2-binding peptides (HBPs) developed thus far are susceptible to proteolysis and lose their affinity to HER2 in vivo. In this report, a method to create a HER2-binding fluctuation-regulated affinity protein (HBP-FLAP) consisting of a fibronectin type III domain (FN3) scaffold with a structurally immobilized HBP is presented. HBPs were selected by phage-library screening and grafted onto FN3 to create FN3-HBPs, and the HBP-FLAP with the highest affinity (HBP sequence: YCAHNM) was identified after affinity maturation of the grafted HBP. HBP-FLAP containing the YCAHNM peptide showed increased proteolysis-resistance, binding to HER2 with a dissociation constant (K_D) of 58 nM in ELISA and 287 nM in biolayer interferometry and specifically detects HER2-expressing cancer cells. In addition, HBP-FLAP clearly delineated HER2-expressing tumors with a half-life of 6 h after intravenous injection into tumor-bearing mice. FN3-based FLAP is an excellent platform for developing target-binding small proteins for clinical applications.

A HER2-binding protein, HBP-FLAP, developed by peptide immobilization specifically binds to HER2 and has improved resistance to proteases.

Development of the Tumor-Specific Antigen-Derived Synthetic Peptides as Potential Candidates for Targeting Breast and Other Possible Human Carcinomas

The human epidermal growth factor receptor 2 (HER2) represents one of the most studied tumor-associated antigens for cancer immunotherapy. The receptors for HER2 are overexpressed in various human cancers, such as breast and ovarian cancer. The relatively low expression of this antigen on normal tissues makes it a clinically useful molecular target for tumor imaging and targeted therapy. HER2 overexpression is correlated with aggressive tumor behavior and poor clinical outcomes. Thus, HER2 has become an important prognostic and predictive factor, as well as a potential molecular target. Due to the heterogeneity of breast cancer and possible discordance in HER2 status between primary tumors and distant metastases, assessment of HER2 expression by noninvasive imaging is important. Molecular imaging of HER2 expression may provide essential prognostic and predictive information concerning disseminated cancer and aid in the selection of an optimal therapy. Another tumor-specific antigen is MUC1, which is silent on normal tissues, but overexpressed in almost all human epithelial cell cancers, including >90% of human breast, ovarian, pancreatic, colorectal, lung, prostate, and gastric cancers and is a promising tumor antigen with diagnostic as well as the therapeutic potential of cancer. Radiolabeled small peptide ligands are attractive as probes for molecular imaging, as they reach and bind the target receptor efficiently and clear from blood and non-target organs faster than bulky antibodies. In this study, HER2 and MUC1-based peptides were synthesized and preclinically evaluated in an effort to develop peptide-based SPECT radiopharmaceuticals derived from tumor-associated antigens for the detection of breast cancer. Our findings demonstrate that the tumor antigen peptides radiolabeled efficiently with ^99mTc and showed high metabolic stability in human plasma in vitro. The data from breast tumor cell binding confirmed the high affinity (in low nanomolar range) towards respective breast cancer cell lines. In healthy mice, ^99mTc-labeled peptides displayed favorable pharmacokinetics, with high excretion by the renal system. In tumor xenografts nude mice models, good uptake by the SKBR3, MCF7, and T47D tumors were found, with good tumor-to-blood and tumor to muscle ratios. Additionally, tumor lesions can be seen in γ-camera imaging. Our data suggest that based on its ability to detect HER2- and MUC1-positive breast cancer cells in vivo, ^99mTc-HER2 and ^99mTc-MUC1-targeted peptides may be promising tumor imaging probes and warrant further investigation.

High-Performance Concurrent Chemo-Immuno-Radiotherapy for the Treatment of Hematologic Cancer through Selective High-Affinity Ligand Antibody Mimic-Functionalized Doxorubicin-Encapsulated Nanoparticles

Non-Hodgkin lymphoma is one of the most common types of cancer. Relapsed and refractory diseases are still common and remain significant challenges as the majority of these patients eventually succumb to the disease. Herein, we report a translatable concurrent chemo-immuno-radiotherapy (CIRT) strategy that utilizes fully synthetic antibody mimic Selective High-Affinity Ligand (SHAL)-functionalized doxorubicin-encapsulated nanoparticles (Dox NPs) for the treatment of human leukocyte antigen-D related (HLA-DR) antigen-overexpressed tumors. We demonstrated that our tailor-made antibody mimic-functionalized NPs bound selectively to different HLA-DR-overexpressed human lymphoma cells, cross-linked the cell surface HLA-DR, and triggered the internalization of NPs. In addition to the direct cytotoxic effect by Dox, the internalized NPs then released the encapsulated Dox and upregulated the HLA-DR expression of the surviving cells, which further augmented immunogenic cell death (ICD). The released Dox not only promotes ICD but also sensitizes the cancer cells to irradiation by inducing cell cycle arrest and preventing the repair of DNA damage. In vivo biodistribution and toxicity studies confirm that the targeted NPs enhanced tumor uptake and reduced systemic toxicities of Dox. Our comprehensive in vivo anticancer efficacy studies using lymphoma xenograft tumor models show that the antibody-mimic functional NPs effectively inhibit tumor growth and sensitize the cancer cells for concurrent CIRT treatment without incurring significant side effects. With an appropriate treatment schedule, the SHAL-functionalized Dox NPs enhanced the cell killing efficiency of radiotherapy by more than 100% and eradicated more than 80% of the lymphoma tumors.

An Inhibitor of GSK3B and HDACs Kills Pancreatic Cancer Cells and Slows Pancreatic Tumor Growth and Metastasis in Mice

BACKGROUND & AIMS

Growth, progression, and drug resistance of pancreatic ductal adenocarcinomas (PDACs) have been associated with increased levels and activity of glycogen synthase kinase 3 beta (GSK3B) and histone deacetylases (HDACs). We designed and synthesized molecules that simultaneously inhibit the activities of both enzymes. We tested the effects of one of these molecules, Metavert, in pancreatic cancer cells and mice with pancreatic tumors.

METHODS

We tested the ability of Metavert to bind GSK3B and HDACs using surface plasmon resonance. MIA PaCa-2, Bx-PC3, HPAF-II, and HPDE6 cell lines were incubated with different concentrations of Metavert, with or without paclitaxel or gemcitabine, or with other inhibitors of GSK3B and HDACs; cells were analyzed for apoptosis and migration and by immunoblotting, immunofluorescence, and real-time polymerase chain reaction. Krasþ/LSLG12D;Trp53þ/LSLR172H;Pdx-1-Cre (KPC) mice (2 months old) were given injections of Metavert (5 mg/kg, 3 times/week) or vehicle (control). B6.129J mice with tumors grown from UN-KPC961-Luc cells were given injections of Metavert or vehicle. Tumors and metastases were counted and pancreata were analyzed by immunohistochemistry. Glucose metabolism was measured using 13C-glucose tracer and mass spectroscopy and flow cytometry. Cytokine levels in blood samples were measured using multiplexing enzyme-linked immunosorbent assay.

RESULTS

Metavert significantly reduced survival of PDAC cells but not nontransformed cells; the agent reduced markers of the epithelial-to-mesenchymal transition and stem cells in PDAC cell lines. Cells incubated with Metavert in combination with irradiation and paclitaxel or gemcitabine had reduced survival compared with cells incubated with either agent alone; Metavert increased killing of drug-resistant PDAC cells by paclitaxel and gemcitabine. PDAC cells incubated with Metavert acquired normalized glucose metabolism. Administration of Metavert (alone or in combination with gemcitibine) to KPC mice or mice with syngeneic tumors significantly increased their survival times, slowed tumor growth, prevented tumor metastasis, decreased tumor infiltration by tumor-associated macrophages, and decreased blood levels of cytokines.

CONCLUSIONS

In studies of PDAC cells and 2 mouse models of PDAC, we found a dual inhibitor of GSK3B and HDACs (Metavert) to induce cancer cell apoptosis, reduce migration and expression of stem cell markers, and slow growth of tumors and metastases. Metavert had synergistic effects with gemcitabine.

Doxorubicin conjugated with a trastuzumab epitope and an MMP-2 sensitive peptide linker for the treatment of HER2-positive breast cancer

HER2-positive breast cancer correlates with more aggressive tumor growth, a poorer prognosis and reduced overall survival. Currently, trastuzumab (Herceptin), which is an anti-HER2 antibody, is one of the key drugs. There is evidence indicating that conjugation of trastuzumab with chemotherapy drugs, such as doxorubicin (DOX), for multiple targets could be more effective. However, incomplete penetration into tumors has been noted for those conjugates. Compared to an antibody, peptides may represent an attractive alternative. For HER2, a similar potency has been observed for a 12-amino-acid anti-HER2 peptide mimetic YCDGFYACYMDV-NH₂ (AHNP, disulfide-bridged) and full-length trastuzumab. Thus, a peptide, GPLGLAGDDYCDGFYACYMDV-NH₂, which consists of AHNP and an MMP-2 cleavable linker GPLGLAGDD, was first designed, followed by conjugation with DOX via a glycine residue at the N-terminus to form a novel DOX-peptide conjugate MAHNP-DOX. Using HER2-positive human breast cancer cells BT474 and SKBR3 as in vitro model systems and nude mice with BT474 xenografts as an in vivo model, this conjugate was comprehensively characterized, and its efficacy was evaluated and compared with that of free DOX. As a result, MAHNP-DOX demonstrated a much lower in vitro IC₅₀, and its in vivo extent of inhibition in mice was more evident. During this process, enzymatic cleavage of MAHNP-DOX is critical for its activation and cellular uptake. In addition, a synergistic response was observed after the combination of DOX and AHNP. This effect was probably due to the involvement of AHNP in the PI3K–AKT signaling pathway, which can be largely activated by DOX and leads to anti-apoptotic signals.

Polyethylene glycol-conjugated HER2-targeted peptides as a nuclear imaging probe for HER2-overexpressed gastric cancer detection in vivo

BACKGROUND

The human epidermal growth factor receptor 2 (HER2) involved proliferation, angiogenesis, and reduced apoptosis in gastric cancer (GC), which is a common target for tumor therapy. HER2 is usually overexpressed in more than 15% GC patients, developing a reliable diagnostic tool for tumor HER2 detection is important. In this study, we attend to use polyethylene glycol (PEG) linked anti-HER2/neu peptide (AHNP-PEG) as a nuclear imaging agent probe for HER2 detection in GC xenograft animal model.

METHODS

The HER2 expression of human sera and tissues were detected in GC patients and normal subjects. GC cell lines NCI-N87 (high HER2 levels) and MKN45 (low HER2 levels) were treated with AHNP-PEG to assess the cell viability and HER2 binding ability. The NCI-N87 was treated with AHNP-PEG to observe the level and phosphorylation of HER2. The MKN45 and NCI-N87-induced xenograft mice were intravenous injection with fluorescence labeled AHNP-PEG for detecting in vivo fluorescence imaging properties and biodistribution. The AHNP-PEG was conjugated with diethylenetriaminopentaacetic acid (DTPA) for indium-111 labeling (¹¹¹In-DTPA-AHNP-PEG). The stability of was assessed in vitro. The imaging properties and biodistribution of ¹¹¹In-DTPA-AHNP-PEG were observed in NCI-N87-induced xenograft mice.

RESULTS

The serum HER2 (sHER2) levels in GC patients were significantly higher than the normal subjects. The sHER2 levels were correlated with the tumor HER2 levels in different stages of GC patients. The AHNP-PEG inhibited the cell growth and down-regulated HER2 phosphorylation in HER2-overexpressed human GC cells (NCI-N87) via specific HER2 interaction of cell surface. In addition, the GC tumor tissues from HER2-postive xenograft mice presented higher HER2 fluorescence imaging as compared to HER2-negative group. The HER2 levels in the tumor tissues were also higher than other organs in NCI-N87-induced xenograft mice. Finally, we further observed that the ¹¹¹In-DTPA-AHNP-PEG was significantly enhanced in tumor tissues of NCI-N87-induced xenograft mice compared to control.

CONCLUSIONS

These findings suggest that the sHER2 measurement may be as a potential tool for detecting HER2 expressions in GC patients. The radioisotope-labeled AHNP-PEG may be useful to apply in GC patients for HER2 nuclear medicine imaging.

In silico design of small peptides antagonist against leptin receptor for the treatment of obesity and its associated immune-mediated diseases

Excess adiposity in obese inhibits negatively impacts immune function and host defence. Obesity is characterized by a state of low-grade, chronic inflammation in addition to disturbed levels of circulating nutrients and metabolic hormones. The impact of metabolic abnormalities on obesity-related co-morbidities has undergone intense scrutiny over the past decades. Thus, treatment of obesity and its associated immune-mediated diseases is challenging due to impaired function of leptin system. These disorders are managed through antibiotics and by cytokines replacement. However, the effectiveness of cytokines coupled to the complexity of the cytokine network leads to severe side-effects, which can still occur after careful preclinical evaluation. In addition, synthetic immunotherapeutics carry a degree of risk, time-consuming and expensive. Hence, the complexity of existing therapy and adverse effects emphasizes the need for an alternative approach for the management of immune dysfunction associated with obesity. Computer-aided small molecule antibody technology has been successful in the design of novel biologicals for the diagnosis of diseases and therapeutic interventions. In this study, the crystal structure of leptin receptor (LEPR) complex with monoclonal antibody (9F8 Fab) was explored to predict Ag-Ab interactions using bioinformatics tools. The LEPR of complementarity-determining region (CDR) loops were mutated with published positive control residues of Ser, Thr, Tyr, Trp, and Phe to design a set of 678 peptides which were evaluated through Ag-peptide docking, binding free-energies, and interaction energies. Thus, hypothesized novel peptides can be explored as clinically applicable antagonists for the treatment of obesity and associated immune-mediated diseases.

A targeted immunotherapy approach for HER2/neu transformed tumors by coupling an engineered effector domain with interferon-γ

Despite substantial clinical progress with targeted therapies, current antibody-based approaches have limited efficacy at controlling HER2/neu-positive breast cancers, especially in the absence of chemotherapies. Previously, we showed that the combination of IFNγ and anti-HER2/neu antibody synergistically reduces tumor growth in an in vivo implanted mammary tumor model. Here, we report a recombinant approach to produce an anti-HER2/neu scFv and IFNγ fusion protein using an engineered effector domain (EED) scaffold. The new molecule induces in vitro apoptosis in an IFNγ receptor-dependent manner. At a very low dose in the in vivo xenografted tumor models, the new EED-IFNγ fusion protein demonstrates superior activity over the anti-HER2/neu antibody and is even active on tumors that are resistant to anti-HER2/neu antibody therapy. Examination of tumor infiltrated macrophages and lymphocytes reveals that the fusion protein can induce changes in tumor microenvironment to support immune reactivity against tumors. Our studies have defined a targeted immunotherapy approach for the treatment of cancers.

The Weak Link: Optimization of the Ligand-Nanoparticle Interface To Enhance Cancer Cell Targeting by Polymer Micelles

Many promising targeting ligands are hydrophobic peptides, and these ligands often show limited accessibility to receptors, resulting in suboptimal targeting. A systematic study to elucidate the rules for the design of linkers that optimize their presentation on nanoparticles has not been carried out to date. In this study, we recombinantly synthesized an elastin-like polypeptide diblock copolymer (ELP_BC) that self-assembles into monodisperse micelles. AHNP and EC1, two hydrophobic ErbB2-targeted peptide ligands, were incorporated at the C-terminus of the ELP_BC with an intervening peptide linker. We tested more than 20 designs of peptide linkers, where the linker could be precisely engineered at the gene level to systematically investigate the molecular parameters-sequence, length, and charge-of the peptide linker that optimally assist ligands in targeting the ErbB2 receptor on cancer cells. We found that peptide linkers with a minimal length of 12 hydrophilic amino acids and an overall cationic charge-and that impart a zeta potential of the micelle that is close to neutral-were necessary to enhance the uptake of peptide-modified ELP_BC micelles by cancer cells that overexpress the ErbB2 receptor. This work advances our understanding of the optimal presentation of hydrophobic ligands by nanoparticles and suggests design rules for peptide linkers for targeted delivery by polymer micelles, an emerging class of nanoparticle carriers for drugs and imaging agents.

Synthetic antibody mimics for the inhibition of protein-ligand interactions

The rational/structure-based design and/or combinatorial development of molecules capable of selectively binding to a protein, represents a promising strategy for a range of biomedical applications, in particular the inhibition of disease-associated protein-ligand interactions. The design of such protein binding molecules is often based on an antibody against the target protein, or involves the generation of smaller molecules that retain the binding characteristics of the antibody. Alternatively, protein binding molecules can be selected from protein libraries based on small, stably folded protein scaffolds presenting flexible loops, which are randomized in the libraries. In addition to recombinantly synthesized molecules, synthetic antibody paratope mimetic peptides have emerged as promising molecules for the design of antibody mimics.

Prolonged circulation and increased tumor accumulation of liposomal vincristine in a mouse model of rhabdomyosarcoma

AIM

Our goal was to improve vincristine (VCR) based rhabdomyosarcoma (RMS) therapy by encapsulating the drug into liposomes. A targeting strategy was attempted to enhance tumor accumulation.

MATERIALS & METHODS

VCR was loaded in control and peptide-decorated liposomes via an active method. The interaction of an RMS-specific peptide with the presumed target furin and the cellular uptake of both liposomal groups were studied in vitro. Pharmacokinetics and biodistribution of VCR-containing liposomes were assessed in an RMS xenograft mouse model.

RESULTS

Liposomes ensured high VCR concentration in plasma and in the tumor. Peptide-decorated liposomes showed modest uptake in RMS cells.

CONCLUSION

The investigated peptide-modified liposomal formulation may not be optimal for furin-mediated RMS targeting. Nevertheless, VCR-loaded liposomes could serve as a delivery platform for experimental RMS.

Liposomes derivatized with multimeric copies of KCCYSL peptide as targeting agents for HER-2-overexpressing tumor cells

Mixed liposomes, obtained by coaggregation of 1,2-dioleoyl-sn-glycero-3-phosphocholine and of the synthetic monomer containing a gadolinium complex ([C18]₂DTPA[Gd]) have been prepared. Liposomes externally decorated with KCCYSL (P6.1 peptide) sequence in its monomeric, dimeric, and tetrameric forms are studied as target-selective delivery systems toward cancer cells overexpressing human epidermal growth factor receptor-2 (HER-2) receptors. Derivatization of liposomal surface with targeting peptides is achieved using the postmodification method: the alkyne-peptide derivative Pra-KCCYSL reacts, through click chemistry procedures, with a synthetic surfactant modified with 1, 2, or 4 azido moieties previously inserted in liposome formulation. Preliminary in vitro data on MDA-MB-231 and BT-474 cells indicated that liposomes functionalized with P6.1 peptide in its tetrameric form had better binding to and uptake into BT-474 cells compared to liposomes decorated with monomeric or dimeric versions of the P6.1 peptide. BT-474 cells treated with liposomes functionalized with the tetrameric form of P6.1 showed high degree of liposome uptake, which was comparable with the uptake of anti-HER-2 antibodies such as Herceptin. Moreover, magnetic MRI experiments have demonstrated the potential of liposomes to act as MRI contrast agents.

Peptides for tumor-specific drug targeting: state of the art and beyond

This review outlines the most recent advances in peptide-mediated tumor-targeting and gives insight into the direction of the field.

DNA–affibody nanoparticles for inhibiting breast cancer cells overexpressing HER2

A DNA tetrahedron–affibody–drug nanoparticle is a highly efficient tool to deliver doxorubicin (DOX) to HER2 overexpressing cancer cells specifically. It represents a highly efficacious agent for selectively inhibiting cancer cells which overexpress HER2 receptor.

Strategies to Develop Inhibitors of Motif-Mediated Protein-Protein Interactions as Drug Leads

Protein-protein interactions are fundamental for virtually all functions of the cell. A large fraction of these interactions involve short peptide motifs, and there has been increased interest in targeting them using peptide-based therapeutics. Peptides benefit from being specific, relatively safe, and easy to produce. They are also easy to modify using chemical synthesis and molecular biology techniques. However, significant challenges remain regarding the use of peptides as therapeutic agents. Identification of peptide motifs is difficult, and peptides typically display low cell permeability and sensitivity to enzymatic degradation. In this review, we outline the principal high-throughput methodologies for motif discovery and describe current methods for overcoming pharmacokinetic and bioavailability limitations.

Directed Evolution of Scanning Unnatural-Protease-Resistant (SUPR) Peptides for in Vivo Applications

Peptides typically have poor biostabilities, and natural sequences cannot easily be converted into drug-like molecules without extensive medicinal chemistry. We have adapted mRNA display to drive the evolution of highly stable cyclic peptides while preserving target affinity. To do this, we incorporated an unnatural amino acid in an mRNA display library that was subjected to proteolysis prior to selection for function. The resulting "SUPR (scanning unnatural protease resistant) peptide" showed ≈500-fold improvement in serum stability (t1/2 =160 h) and up to 3700-fold improvement in protease resistance versus the parent sequence. We extended this approach by carrying out SUPR peptide selections against Her2-positive cells in culture. The resulting SUPR4 peptide showed low-nanomolar affinity toward Her2, excellent specificity, and selective tumor uptake in vivo. These results argue that this is a general method to design potent and stable peptides for in vivo imaging and therapy.

HER2-positive breast cancer targeting and treatment by a peptide-conjugated mini nanodrug

HER2+ breast cancer is one of the most aggressive forms of breast cancer. The new polymalic acid-based mini nanodrug copolymers are synthesized and specifically characterized to inhibit growth of HER2+ breast cancer. These mini nanodrugs are highly effective and in the clinic may substitute for trastuzumab (the marketed therapeutic antibody) and antibody-targeted nanobioconjugates. Novel mini nanodrugs are designed to have slender shape and small size. HER2+ cells were recognized by the polymer-attached trastuzumab-mimetic 12-mer peptide. Synthesis of the nascent cell-transmembrane HER2/neu receptors by HER2+ cells was inhibited by antisense oligonucleotides that prevented cancer cell proliferation and significantly reduced tumor size by more than 15 times vs. untreated control or PBS-treated group. We emphasize that the shape and size of mini nanodrugs can enhance penetration of multiple bio-barriers to facilitate highly effective treatment. Replacement of trastuzumab by the mimetic peptide favors reduced production costs and technical efforts, and a negligible immune response.

Dual-targeting hybrid nanoparticles for the delivery of SN38 to Her2 and CD44 overexpressed human gastric cancer

Gastric cancer (GC), particularly of the type with high expression of both human epidermal growth factor receptor 2 (Her2) and cluster determinant 44 (CD44), is one of the most malignant human tumors which causes a high mortality rate due to rapid tumor growth and metastasis. To develop effective therapeutic treatments, a dual-targeting hybrid nanoparticle (NP) system was designed and constructed to deliver the SN38 agent specifically to human solid gastric tumors bearing excessive Her2 and CD44. The hybrid NPs consist of a particle core made of the biodegradable polymer PLGA and a lipoid shell prepared by conjugating the AHNP peptides and n-hexadecylamine (HDA) to the carboxyl groups of hyaluronic acid (HA). Upon encapsulation of the SN38 agent in the NPs, the AHNP peptides and HA on the NP surface allow preferential delivery of the drug to gastric cancer cells (e.g., HGC27 cells) by targeting Her2 and CD44. Cellular uptake and in vivo biodistribution experiments verified the active targeting and prolonged in vivo circulation properties of the dual-targeting hybrid NPs, leading to enhanced accumulation of the drug in tumors. Furthermore, the anti-proliferation mechanism studies revealed that the inhibition of the growth and invasive activity of HGC27 cells was not only attributed to the enhanced cellular uptake of dual-targeting NPs, but also benefited from the suppression of CD44 and Her2 expression by HA and AHNP moieties. Finally, intravenous administration of the SN38-loaded dual-targeting hybrid NPs induced significant growth inhibition of HGC27 tumor xenografted in nude mice compared with a clinical antitumor agent, Irinotecan (CPT-11), and the other NP formulations. These results demonstrate that the designed dual-targeting hybrid NPs are promising for targeted anti-cancer drug delivery to treat human gastric tumors over-expressing Her2 and CD44.

Improved drug delivery and therapeutic efficacy of PEgylated liposomal doxorubicin by targeting anti-HER2 peptide in murine breast tumor model

Targeted cancer therapy is a powerful therapeutic strategy to management of cancer. HER2 as an anticancer target has long been studied. Its overexpression plays an important role in the pathogenesis and progressiveness of breast and other cancers. To establish efficient and reliable drug delivery to HER2-overexpressing cells, the authors of this study have developed anti-HER2 (ErbB2) peptide-liposomal formulations of doxorubicin (DOX) by an engineered breast tumor-targeting peptide ligand, AHNP, Anti-HER2/neu peptide, (FCDGFYACYADV) with three glycine amino acids as spacer before its original sequencing. Towards this goal, PEGylated liposome doxorubicin (PLD) bearing different ligand densities of AHNP was prepared and characterized for their size, zeta potential and peptide conjugation. The AHNP functionalization and density effects on breast tumor cell uptake, selective cytotoxicity, prevention of tumor growth and the tissue biodistribution of encapsulated DOX were studied in mice bearing TUBO breast cancer tumor model. The findings demonstrated that increasing the ligand density of AHNP increases cytotoxicity and cell-uptake in SKBR3 and TUBO cells which overexpress HER2 but not in MDA-MB-231with low HER2 expression profile. The anticancer activity was also superior for targeted liposomal DOX with more AHNP densities. Overall, the results showed that optimum AHNP density functionalization of PLD can significantly improve selectivity and the therapeutic index of liposomal DOX in the treatment of HER2 positive breast cancer and merits further investigation.

Anti-HER2/neu peptide-conjugated iron oxide nanoparticles for targeted delivery of paclitaxel to breast cancer cells

Nanoparticles (NPs) for targeted therapy are required to have appropriate size, stability, drug loading and release profiles, and efficient targeting ligands. However, many of the existing NPs such as albumin, liposomes, polymers, gold NPs, etc. encounter size limit, toxicity and stability issues when loaded with drugs, fluorophores, and targeting ligands. Furthermore, antibodies are bulky and this can greatly affect the physicochemical properties of the NPs, whereas many small molecule-based targeting ligands lack specificity. Here, we report the utilization of biocompatible, biodegradable, small (∼30 nm) and stable iron oxide NPs (IONPs) for targeted delivery of paclitaxel (PTX) to HER2/neu positive breast cancer cells using an anti-HER2/neu peptide (AHNP) targeting ligand. We demonstrate the uniform size and high stability of these NPs in biological medium, their effective tumour targeting in live mice, as well as their efficient cellular targeting and selective killing in human HER2/neu-positive breast cancer cells.

Microwave-assisted solid-phase synthesis of side-chain to side-chain lactam-bridge cyclic peptides

Side-chain to side-chain lactam-bridged cyclic peptides have been utilized as therapeutic agents and biochemical tools. Previous synthetic methods of these peptides need special reaction conditions, form side products and take longer reaction times. Herein, an efficient microwave-assisted synthesis of side-chain to side-chain lactam-bridge cyclic peptides SHU9119 and MTII is reported. The synthesis time and efforts are significantly reduced in the present method, without side product formation. The analytical and pharmacological data of the synthesized cyclic peptides are in accordance with the commercially obtained compounds. This new method could be used to synthesize other side-chain to side-chain lactam-bridge peptides and amenable to automation and extensive SAR compound derivatization.

Sacituzumab Govitecan (IMMU-132), an Anti-Trop-2/SN-38 Antibody-Drug Conjugate: Characterization and Efficacy in Pancreatic, Gastric, and Other Cancers

Sacituzumab govitecan (IMMU-132) is an antibody-drug conjugate (ADC) made from a humanized anti-Trop-2 monoclonal antibody (hRS7) conjugated with the active metabolite of irinotecan, SN-38. In addition to its further characterization, as the clinical utility of IMMU-132 expands to an ever-widening range of Trop-2-expressing solid tumor types, its efficacy in new disease models needs to be explored in a nonclinical setting. Unlike most ADCs that use ultratoxic drugs and stable linkers, IMMU-132 uses a moderately toxic drug with a moderately stable carbonate bond between SN-38 and the linker. Flow cytometry and immunohistochemistry disclosed that Trop-2 is expressed in a wide range of tumor types, including gastric, pancreatic, triple-negative breast (TNBC), colonic, prostate, and lung. While cell-binding experiments reveal no significant differences between IMMU-132 and parental hRS7 antibody, surface plasmon resonance analysis using a Trop-2 CM5 chip shows a significant binding advantage for IMMU-132 over hRS7. The conjugate retained binding to the neonatal receptor, but it lost greater than 60% of the antibody-dependent cell-mediated cytotoxicity activity compared to that of hRS7. Exposure of tumor cells to either free SN-38 or IMMU-132 demonstrated the same signaling pathways, with pJNK1/2 and p21(WAF1/Cip1) upregulation followed by cleavage of caspases 9, 7, and 3, ultimately leading to poly-ADP-ribose polymerase cleavage and double-stranded DNA breaks. Pharmacokinetics of the intact ADC in mice reveals a mean residence time (MRT) of 15.4 h, while the carrier hRS7 antibody cleared at a similar rate as that of the unconjugated antibody (MRT ∼ 300 h). IMMU-132 treatment of mice bearing human gastric cancer xenografts (17.5 mg/kg; twice weekly × 4 weeks) resulted in significant antitumor effects compared to that of mice treated with a nonspecific control. Clinically relevant dosing schemes of IMMU-132 administered either every other week, weekly, or twice weekly in mice bearing human pancreatic or gastric cancer xenografts demonstrate similar, significant antitumor effects in both models. Current Phase I/II clinical trials ( ClinicalTrials.gov , NCT01631552) confirm anticancer activity of IMMU-132 in cancers expressing Trop-2, including gastric and pancreatic cancer patients.

Induction of targeted necrosis with HER2-targeted platinum(iv) anticancer prodrugs

It is well-recognized that the failure of many chemotherapeutics arises due to an inability to induce apoptosis. Most cancers acquire a myriad of pro-survival adaptations, and the vast heterogeneity and accumulation of multiple often unrelated anti-apoptotic signaling pathways have been a major stumbling block towards the development of conventional chemotherapeutics, which can overcome drug resistance. We have developed highly potent and selective HER2-targeted Pt(iv) prodrugs bearing anti-HER2/neu peptides that induce targeted necrosis as a novel strategy to circumvent apoptosis-resistance. These Pt(iv)-peptide conjugates exhibit a unique biphasic mode of cytotoxicity comprising rapid killing of cancer cells via necrosis in the first phase followed by an extended and gradual phase of delayed cell death. We demonstrate that these Pt(iv)-peptide prodrugs are more potent than their Pt(ii) congeners in direct cell-killing and exhibit comparable long-term inhibition of proliferative capacity and with greater selectivity against HER2-positive cancer cells.

Chemically synthesized molecules with the targeting and effector functions of antibodies

This article reports the design, synthesis, and evaluation of a novel class of molecules of intermediate size (approximately 7000 Da), which possess both the targeting and effector functions of antibodies. These compounds—called synthetic antibody mimics targeting prostate cancer (SyAM-Ps)—bind simultaneously to prostate-specific membrane antigen and Fc gamma receptor I, thus eliciting highly selective cancer cell phagocytosis. SyAMs have the potential to combine the advantages of both small-molecule and biologic therapies, and may address many drawbacks associated with available treatments for cancer and other diseases.

A fluorescent protein scaffold for presenting structurally constrained peptides provides an effective screening system to identify high affinity target-binding peptides

Peptides that have high affinity for target molecules on the surface of cancer cells are crucial for the development of targeted cancer therapies. However, unstructured peptides often fail to bind their target molecules with high affinity. To efficiently identify high-affinity target-binding peptides, we have constructed a fluorescent protein scaffold, designated gFPS, in which structurally constrained peptides are integrated at residues K131-L137 of superfolder green fluorescent protein. Molecular dynamics simulation supported the suitability of this site for presentation of exogenous peptides with a constrained structure. gFPS can present 4 to 12 exogenous amino acids without a loss of fluorescence. When gFPSs presenting human epidermal growth factor receptor type 2 (HER2)-targeting peptides were added to the culture medium of HER2-expressing cells, we could easily identify the peptides with high HER2-affinity and -specificity based on gFPS fluorescence. In addition, gFPS could be expressed on the yeast cell surface and applied for a high-throughput screening. These results demonstrate that gFPS has the potential to serve as a powerful tool to improve screening of structurally constrained peptides that have a high target affinity, and suggest that it could expedite the one-step identification of clinically applicable cancer cell-binding peptides.

Cyclic peptides as therapeutic agents and biochemical tools

There are many cyclic peptides with diverse biological activities, such as antibacterial activity, immunosuppressive activity, and anti-tumor activity, and so on. Encouraged by natural cyclic peptides with biological activity, efforts have been made to develop cyclic peptides with both genetic and synthetic methods. The genetic methods include phage display, intein-based cyclic peptides, and mRNA display. The synthetic methods involve individual synthesis, parallel synthesis, as well as split-and-pool synthesis. Recent development of cyclic peptide library based on split-and-pool synthesis allows on-bead screening, in-solution screening, and microarray screening of cyclic peptides for biological activity. Cyclic peptides will be useful as receptor agonist/antagonist, RNA binding molecule, enzyme inhibitor and so on, and more cyclic peptides will emerge as therapeutic agents and biochemical tools.