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Unlocking the Power of Peptides: Current Therapeutic Applications and Future Perspectives

Over the past decade, significant strides have been made in the realm of peptide drug development courtesy of ground-breaking advancements in production, modification, and analytic technologies. Both chemical and biological approaches have been employed to create and alter peptides, complemented by innovative design and delivery strategies.

These pioneering methods have effectively addressed the inherent limitations of peptides, propelling this field forward. A vast array of natural and modified peptides acquired are extensively researched by various research and education centers, spanning different therapeutic domains.

Therapeutic Peptides – Background and Overview

Therapeutic peptides represent a distinct category of medicinal substances comprising a sequence of well-structured amino acids, typically possessing molecular weights ranging from 500 to 5000 Da. The exploration of therapeutic peptides commenced with fundamental investigations into natural human hormones, such as insulin, oxytocin, vasopressin, and gonadotropin-releasing hormone (GnRH), and their specific physiological functions within the human organism. Following the successful synthesis of the first therapeutic peptide, insulin, in 1921, significant strides have been taken in this field, thus leading to the global approval of over 80 peptide drugs. Consequently, the advancement of peptide drugs has emerged as a highly prominent subject within the domain of pharmaceutical research.

During the early years of the 1900s, a remarkable series of events unfolded that forever altered the course of medical history. In this transformative era, numerous bioactive peptides possessing life-preserving properties were unearthed, including the illustrious insulin and adrenocorticotrophic hormone. These extraordinary substances, initially extracted from the bounties of nature, captivated the attention of pioneering researchers who diligently investigated their intricate structures and functions. Among these discoveries, the unearthing and subsequent refinement of insulin, boasting an impressive composition comprising 51 amino acids, stands as an awe-inspiring milestone in the domain of pharmaceutical breakthroughs.

From the 1950s to the 1990s, an array of peptide hormones and their receptors, brimming with therapeutic promise, were unearthed and comprehensively examined. Simultaneously, the techniques employed in protein purification and synthesis, as well as structure elucidation and sequencing, experienced remarkable advancements. It propelled the rapid advancement of peptide drugs, ultimately culminating in the global approval of almost 40 such drugs. It is worth highlighting those alongside natural peptides, the development of synthetic counterparts like synthetic oxytocin, synthetic vasopressin, and recombinant human insulin gained traction during this period.

The onset of the 21st century marked a ground-breaking era for the advancement of peptide drug development. Since then, remarkable progress in structural biology, recombinant biologics, and innovative synthetic and analytic technologies has expedited this process. A refined framework for peptide drug development has been established, encompassing various stages such as peptide drug exploration, drug blueprinting, peptide creation, structural adaptation, and activity assessment. To date, a noteworthy tally of 33 non-insulin peptide drugs has received global approval since 2000. Furthermore, these peptide drugs have transcended their previous status as hormone imitators or compositions solely comprised of natural amino acids.

For instance, ziconotide is a neurotoxic peptide used to treat severe chronic pain, whereas teduglutide is a glucagon-like peptide 2 (GLP-2) variation used to treat short bowel syndrome. Enfuvirtide is a 36-amino acid peptide used in combination therapy to treat HIV-1. It mimics HIV proteins.

Peptide drugs have found extensive use by public healthcare institutions across a diverse range of medical fields, including urology, respiratory health, pain management, oncology, metabolism regulation, cardiovascular care, and antimicrobial treatments. At present, over 170 peptides are actively undergoing clinical development at various research and education centers, with numerous others undergoing preclinical studies.

The market for peptide drugs plays a significant role in the pharmaceutical industry, boasting global sales that surpassed $70 billion in 2019. This figure represents a remarkable twofold increase compared to 2013. Notably, among the top 200 highest-selling drugs in 2019, ten of them were non-insulin peptide drugs, as highlighted by Njardarson et al.

Of particular interest is that the three top-selling peptide drugs were all GLP-1 analogs utilized for the treatment of Type 2 diabetes mellitus (T2DM). Trulicity (dulaglutide) ranked at 19 with $4.39 billion in retail sales, Victoza (liraglutide) ranked at 32 with $3.29 billion in sales, and Rybelsus (semaglutide) ranked at 83 with $1.68 billion in sales.

Advantages and Disadvantages of Therapeutic Peptides

Therapeutic peptides are often employed by public healthcare institutions as hormones, growth factors, neurotransmitters, ligands for ion channels, or agents to combat infections. They can attach themselves to receptors on the surface of cells and initiate internal effects with great precision and affinity. In their mode of action, therapeutic peptides share similarities with biologics such as therapeutic proteins and antibodies. Nevertheless, therapeutic peptides exhibit reduced immunogenicity and are more cost-effective when compared to biologics.

Small molecule medications have a long history of use in medicine and come with several benefits, including easy oral administration, affordable manufacture and sale rates, and effective membrane penetration. Comparing small molecules with peptides and biologics (proteins or antibodies), chemically and natively generated small molecules exhibit competitive economic benefits.

Therapeutic peptides, as amino acid-based therapeutics, encounter a couple of inherent drawbacks that impede their development as effective drugs. These drawbacks include their inability to permeate cell membranes and their poor stability within the body.

Peptides face a challenge when crossing the cell membrane due to various factors like their length and amino acid composition. This limitation restricts their usage in targeting intracellular objectives, resulting in the majority of peptides in clinical development focusing on extracellular targets such as G-protein coupled receptors (GPCRs), gonadotropin-releasing hormone (GnRH) receptors, and Glucagon-like peptide 1 (GLP-1) receptor, as discovered by Lau et al. in 2018.

Furthermore, natural peptides lack the stability provided by secondary or tertiary structures. Comprising chains of amino acids connected by amide bonds, these peptides are prone to be hydrolyzed or degraded by enzymes within the body or when exposed to the environment. Consequently, they possess chemical and physical instability, leading to a short half-life and rapid elimination within the body.

These inherent strengths and weaknesses of peptides pose challenges and opportunities in peptide drug development. They serve as avenues for designing and optimizing peptide drugs to overcome these limitations.

Discovery Of Therapeutic Peptides

Natural peptides found in the Human body

The history of peptide drug discovery began by utilizing naturally occurring hormones and peptides with physiological roles that had been well-researched to treat disorders brought on by hormone deficiency, such as the absence of insulin needed by patients with T1DM or T2DM to regulate blood glucose levels. Insulin injections or activating targets involved in insulin secretion, such as the GLP-1 receptor, are used to treat diabetes. The early approaches utilized for the discovery and development of peptide drugs involved seeking natural peptides and hormones or substituting them with animal homologs such as oxytocin, somatostatin, GnRH, 8-Arg-Vasopressin, and insulin. However, the limitations of these natural peptides sparked interest in improving their natural sequences, which gave rise to several natural hormone-mimicking peptide medications.

Peptides Obtained from Natural Products

Many bioactive peptides from bacteria, plants, fungi, and animals have therapeutic characteristics. For example, VEGF-F or svVEG, found in snake venom, is a VEGF analog. They are typically 80-residue or less cyclic peptides rich in disulfides that might cause cytotoxicity by attacking membrane-bound receptors such as ion channels. Snake and scorpion venom peptides have been altered for medicinal purposes.

Protein-Protein Interactions for Peptides Design

Numerous Protein-Protein Interactions (PPIs) involved in the majority of cellular activities and biological functions have been found thanks to advances in structural biology and proteomics. Only 1% of the PPIs in the human body, or more than 14,000 PPIs, have been examined thus far. PPIs are potentially interesting therapeutic targets because they control numerous crucial cellular pathways in human illnesses. As inhibitors or activators of PPIs, peptides have inherent advantages over small compounds and antibodies. As a result, the rational design of peptides—a new peptide drug discovery technique built on the crystal structure of PPIs—has been created. It is thought to be a fruitful method for finding novel peptide medication candidates.

Peptide Drug Delivery Innovations

Peptide modifications make peptides more drug-like by improving their activity and plasma stability. However, because of the ease with which digestive enzymes in the stomach and intestine may hydrolyze peptides, most peptide medications are administered by public healthcare institutions intravenously. To address these issues, recent studies have investigated the delivery methods for peptide drugs.

An approach that shows promise for making it possible to administer peptide medications orally is co-formulation with permeability enhancers. The oral administration of other peptide medications, including octreotide and insulin currently in clinical trials has also been made possible by co-formulation with various permeability enhancers, enzyme inhibitors, and hydrogels. Additional methods like transdermal delivery, implanted pumps, and pulmonary administration.

Developments and application protocol of Therapeutic Peptides

Therapeutic peptides for the management of type 2 diabetesT2DM, which is frequent in middle-aged and older persons, are brought on by an acquired insulin insufficiency. Peptide medications, such as insulin and GLP-1 receptor agonists (GLP-1RAs), have been used to successfully treat T2DM. L-cells in the ileum secrete the endogenous growth hormone GLP-1.

Cardiovascular disease therapy using therapeutic peptides

Cardiovascular disease is currently the world’s top cause of death and morbidity among non-communicable diseases. One of the risk factors for the development of cardiovascular disease is hypertension thought to be brought on by increased sympathetic nervous system and renin-angiotensin-aldosterone system (RAAS) activity, as well as sodium retention.

According to several research and education centers, the tripeptide IRW generated from egg white increased ACE2 expression in spontaneously hypertensive rats to lower blood pressure. These results suggest that food-derived peptides that target RAAS may be used to treat cardiovascular disorders.

Treatment of gastrointestinal disorders using therapeutic peptides

The gut flora in the human body is a sophisticated micro-ecosystem. The dynamic balance between the strong flora (pathogenic bacteria) and the weak flora (dominant flora, physiological flora) is disrupted in a variety of intestinal diseases brought on by foreign bacteria, viruses, and parasites, contaminated food, unfavorable drug reactions, and genetic factors, including enteritis, constipation, intestinal ulcers, and inflammatory bowel disease (IBD). The widespread use of antibiotics may cause the diversity of symbiotic bacteria to decline even further. Because of their selectivity, effectiveness, and low toxicity, peptide medicines have garnered interest in this field.

Treatment of cancer using therapeutic peptides

Cancer treatment options, like surgery and radiotherapy, have been traditionally used. They have limited effectiveness for individuals with stages of the disease. However, recent advancements in immunotherapy and personalized therapy have significantly improved the survival rates of cancer patients.

Targeted therapy uses a “guided missile” strategy to attack tumor cells by taking advantage of the fact that tumor cells depend on signaling pathways or chemicals. Drugs used in immunotherapy do not directly attack tumor cells. Instead, they alter the immune system of the patient and target immunological checkpoints to attack tumor cells.

Five monoclonal antibodies targeting the PD-1/PD-L1 interaction have been approved by the FDA for the treatment of cancer. PD-1/PD-L1 is a well-known immune checkpoint. However, there are certain drawbacks to antibodies, such as their expensive price, poor oral acceptability, and high immunogenicity.

Due to their tiny size, strong affinity, ease of modification, and minimal immunogenicity, peptides have also gained interest in the diagnosis and therapy of tumors. Some altered peptides have also been shown to be stable. For instance, Carvajal and colleagues created stable-helical peptides.

Modified peptide analogs are commonly used to target receptors, in tumor cells, as natural peptides have a lifespan inside the body. Peptides can be utilized in four ways for treating tumors;

They can be coupled with nanomaterials to create tumor therapy.

They can be labeled with radioisotopes, dyes, or other molecules for imaging purposes.

Peptide vaccinations can stimulate the system to prevent diseases.

Peptides themselves can be used as standalone medications to target specific areas.

Conclusion: Due to their distinctive biochemical properties and therapeutic potential, peptides have recently emerged as a distinct class of therapeutic agents. Although peptides perform better than small compounds and big biologics in some ways, they frequently have poor in vivo stability and membrane impermeability because of the inherent constraints of amino acids.

To address these issues, extensive research at I3TK has been done on the development, manufacture, and optimization of peptide medicines. The rapid generation of efficient and selective lead peptides is made possible by a combination of conventional lead peptide discovery techniques with cutting-edge technologies like rational design and phage display.

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