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Transforming Peptides into Therapeutic Drugs

Peptide drugs are synthetic short chains of amino acids that mimic natural hormones to manage complex metabolic, endocrine, and oncological conditions. Peptide drugs target receptors with high specificity, therefor offer exceptional efficacy and minimal off-target toxicity compared to traditional small-molecule drugs.

Examples of peptide drugs

The peptide drug universe is expanding rapidly. Some of the earliest peptide drugs, in the 1950’s – 1960’s are Oxytocin to induce labor, and Vasopressin for septic shock and frequent urination.

TABLE 1: Five representative FDA-approved peptide or peptide-based drugs first approved after 2020, selected to illustrate substantially different molecular mechanisms and clinical applications.

Drug (Brand)	Peptide mechanism / molecular target	Primary clinical indication	Mechanistic distinction
Vosoritide (Voxzogo)	C-type natriuretic peptide (CNP) analog; activates natriuretic peptide receptor-B (NPR-B), increasing cGMP and counteracting FGFR3-mediated inhibition of chondrocyte proliferation	Achondroplasia in children with open growth plates	Promotes endochondral bone growth by modulating the CNP/NPR-B growth-plate pathway
Pegcetacoplan (Empaveli)	C3 complement inhibitor; binds complement component C3 and C3b, blocking both upstream and downstream complement activation	Paroxysmal nocturnal hemoglobinuria (PNH)	Directly suppresses the complement cascade, preventing complement-mediated hemolysis
Tirzepatide (Mounjaro)	Dual GIP/GLP-1 receptor agonist; activates both glucose-dependent insulinotropic polypeptide and GLP-1 receptors	Type 2 diabetes mellitus; subsequently approved for chronic weight management as Zepbound	Combines two incretin pathways to increase glucose-dependent insulin secretion, reduce glucagon, slow gastric emptying, and reduce appetite
Terlipressin (Terlivaz)	Synthetic vasopressin analog, preferentially activating V1a receptors in vascular smooth muscle, producing vasoconstriction	Hepatorenal syndrome with rapid reduction in kidney function (HRS-1) in adults	Produces systemic/splanchnic vasoconstriction, improving effective arterial blood volume and renal perfusion
Lutetium-177 vipivotide tetraxetan (Pluvicto)	PSMA-targeted peptide/radioligand; binds prostate-specific membrane antigen and delivers β-particle radiation directly to PSMA-positive tumor cells	PSMA-positive metastatic castration-resistant prostate cancer	Uses a peptide-based targeting ligand to deliver radiation selectively to cancer cells, rather than primarily modulating a receptor-signaling pathway

A representative example of recent advances in peptide drugs are those that mimic GLP-1 . GLP-1 targeting peptide drugs mimic the natural peptide Glucagon-Like Peptide-1 (GLP-1), a hormone produced in the intestine that stimulates insulation secretion in response to food uptake, which lowers blood sugar, and lowers appetite. For example, Ozempic, Trulicity, and Rybelsus are all GLP-1 receptor agonists used primarily to improve blood-glucose control in adults with type 2 diabetes. They also commonly produce weight loss by reducing appetite, slowing gastric emptying, and increasing satiety.

Extensions beyond the single receptor agonist include Tirzepatide (Mounjaro), which is a dual GLP-1 and GIP receptor agonist, consisting of a modified peptide designed to activate both glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) receptors. Tirzepatide (Mounjaro) reduces appetite, slows gastric emptying and suppresses glucagon which prevents liver from releasing excess glucose that builds up fat in tissues, while GIP mainly enhances insulin secretion and enhances the conversion of glucose into fatty acids for storage, but it can also facilitate the release of fatty acids from adipose tissue when it is needed. GLP-1 also acts directly on the brain’s appetite centers, reducing cravings and promoting a sense of satisfaction after eating. This combination of metabolic and neurological effects explains why GLP-1 receptor agonists are so effective for both diabetes management and weight loss. Other beneficial effects appear to include heart and kidney health and reduced addictive activity.

Unique properties

Peptide drugs dominate specific therapeutic areas due to their unique biochemical properties:

High Target Specificity: Peptides fit into biological receptors like a precise lock and key, dramatically reducing unwanted side effects.

Low Tissue Accumulation: They break down into harmless natural amino acids, eliminating the risk of liver or kidney toxicity caused by chemical accumulation.

High Potency: Peptides often achieve therapeutic effects at nanomolar concentrations, meaning very low doses are required.

Broad Target Range: They can easily target complex, flat protein surfaces that small molecules fail to bind to effectively.

Structural and Delivery Challenges

Despite their high efficacy, native peptides face significant pharmacological limitations.

TABLE 2: Peptide drug limitations and challenges

Challenge	Impact on the Body	Engineering Solution
Short Half-Life	Rapidly chopped up by blood enzymes (proteases) within minutes.	Chemical Modification: Swapping natural L-amino acids for synthetic D-amino acids or modifying peptide backbones to resist enzymatic breakdown.
Rapid Kidney Clearance	Small size causes them to be quickly filtered out of the blood by the kidneys.	Lipidation: Attaching fatty acid chains (like in semaglutide) to bind to blood albumin, safely extending circulation from hours to days.
Poor Oral Bioavailability	Stomach acids digest them completely, preventing them from crossing into the bloodstream.	Permeation Enhancers: Pairing oral peptides (like oral semaglutide) with delivery agents like SNAC to force absorption through the stomach lining.
Poor Cell Membrane Penetration	Their hydrophilic (water-loving) nature prevents them from slipping inside cells.	Macrocyclization: Stapling the peptide into a rigid ring structure to hide polar groups, letting them slip directly through cell walls.

Assays to Measure Purify and Efficacy of Peptide Products

1. Analytical & Chemical Quantification Assays

HPLC (High-Performance Liquid Chromatography) measures the individual components in a chemical or biological mixture, both qualitative identity and quantitative concentration
Mass Spectrometry (LC-MS / MS) confirms structural identity.
ICP-MS (Inductively Coupled Plasma Mass Spectrometry), the gold standard for verifying stoichiometry.

2. Biological & Functional In Vitro Assays

The potency of most peptide drugs can be quantitated by in vitro cell-based assays that mimic in vivo effects. These include, for example, growth promotion or inhibition, activation of specific genes leading to RNA and protein production, and activation of specific signaling pathways.

The Future of Peptide Discovery

The future of peptide drug discovery is expected to be driven by advances in peptide engineering, computational design, and drug-delivery technologies. These innovations will enable the development of more stable, selective, and longer-acting peptides, as well as orally available and tissue-targeted therapies. Generative AI is being used to design synthetic sequences optimized for binding affinity and stability. Additionally, the development of Peptide-Drug Conjugates (PDCs) allows scientists to use peptides as guided missiles, linking them directly to toxic chemotherapy payloads to destroy cancer cells while completely sparing healthy surrounding tissue. As new approaches expand the range of biological targets accessible to peptides, peptide-based medicines are likely to become an increasingly important class of therapeutics across metabolic, oncologic, immunologic, and rare diseases.

Over-the -Counter (OTC) Peptides

A growing number of Americans are taking over-the counter peptides that haven’t undergone the rigorous testing and approval process of the US Food and Drug Association (FDA). Many of these formulations have dubious efficacy and dangerous contaminants and side effects. Their street value is up to $3 billion dollars. US Health Secretary R J Kennedy wants to make it easier to obtain these peptides. Sceptics worry that individual humans are becoming “lab rats” with hospitalizations, nausea, hair loss, rash, and other reported symptoms. The OTC industry should measure the chemistry of peptide drugs, to quantitate their active molecule content and presence of dangerous contaminants, and the efficacy through potency bioassays.

FDA Action

A U.S. Food and Drug Administration (FDA) advisory committee recommended loosening restrictions on certain popular peptides, drugs marketed as offering a range of benefits like anti-aging and muscle recovery and typically administered by injection or intravenously. The peptides were formerly identified by the FDA as posing significant safety risks, and the vote to loosen restrictions has stirred controversy in medical circles. Many of these peptides have only limited human research supporting their safety and effectiveness, even though some are promoted by proponents as treatments for serious medical conditions. Several of these peptides are widely available through a regulatory gray market online or in wellness clinics, with a few appearing on the World Anti-Doping Agency’s prohibited substances list.

Conclusion

Peptide drugs have emerged as an increasingly important therapeutic class, combining the high target specificity of biologics with many of the manufacturing and formulation advantages of smaller molecules. Recent FDA approvals demonstrate their expanding use across metabolic disease, cancer, rare diseases, immunology, and endocrine disorders. Future development will likely focus on improving oral and other non-injectable delivery, extending half-life, increasing stability, reducing dosing frequency, and developing more complex multi-target and targeted peptide therapeutics. Advances in peptide engineering, conjugation, computational design, and drug-delivery technologies are expected to expand the range of previously “undruggable” targets accessible to peptide medicines, making peptides an increasingly important component of the next generation of therapeutics.

References

Gare CL, et al. From lead to market: chemical approaches to transform peptides into therapeutics. Trends Biochem Sci. 2025;50(6):467-480. doi:10.1016/j.tibs.2025.01.009. PMID: 40011178

Zheng B, Wang X, Guo M, Tzeng CM. Therapeutic Peptides: Recent Advances in Discovery, Synthesis, and Clinical Translation. Int J Mol Sci. 2025;26(11):5131. doi:10.3390/ijms26115131. PMID: 40507941.

Dean TT, Jelú-Reyes J, Allen AC, Moore TW. Peptide-Drug Conjugates: An Emerging Direction for the Next Generation of Peptide Therapeutics. J Med Chem. 2024;67(3):1641-1661. doi:10.1021/acs.jmedchem.3c01835. PMID: 38277480.

Image credit: Portions of the figure in this article were generated using ChatGPT (OpenAI) or Google Gemini.

Disclaimer: This blog post is intended solely for educational and scientific informational purposes. Any mention of therapeutic drug names, including FDA-approved medications, is for the purpose of accurate reporting and discussion of biomedical research and does not constitute medical advice, endorsement, or promotion. Readers should not interpret the content as a recommendation for any specific treatment. Always consult a qualified healthcare professional for medical advice or treatment decisions.

About Marin Biologic Laboratories

Our Recent Publication/Meeting Presentation on Gene Therapy

1. Development of VNX-101, an Adeno-Associated Virus with Less Immunogenicity and Efficient Long-Term Expression of a CD19 T-Cell Engager. Molecular Therapy Methods & Clinical Development, published online July 24, 2025.

3. Cell-Based Potency Assay for Anti-CD3-Anti-CD19 Diabody. Journal of Immunological Methods. 2025. 545-114004.

3. Development of a Pharmacokinetic (PK) Mouse Serum GLP ELISA for an Anti–CD19–AntiCD3 Diabody
bioRxiv 2025.03.19.644217; doi: https://doi.org/10.1101/2025.03.19.644217.

4. American Society of Hematology (ASH) Annual Meeting 2024.
Abstract link: Using Gene Therapy to Solve Challenges with CAR-T Cell Immunotherapy: Lead Selection and Preclinical Development of an Adeno-Associated Virus with Reduced Immunogenicity Exhibiting Efficient and Long-Term Expression of an Anti-CD19 T-Cell Engager.

Comprehensive Assay Solutions for In Vitro and Cell Based Potency Assays and Pharmacokinetics Studies- Our Expertise

With 30 years of expertise in cell culture, cell-based assays, and preclinical/clinical PK/PD analysis, we specialize in offering assay services essential for a wide variety of therapeutic drug development programs, preclinical studies, IND/BLA applications, and commercialization. Our comprehensive services include both preclinical non-GLP and GLP assays, as well as non-GMP and GMP assays, providing critical support throughout the entire development pipeline.

Watch the following video and explore our latest presentation on the development and validation of potency and pharmacokinetic (PK) assays for AAV vectors, highlighting innovative methodologies and industry-leading expertise.