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Systematic review of peptide drugs of Retatrutide

**Abstract**

Retatrutide (R&D code: LY3437943) is a new multi-target peptide drug developed by Eli Lilly and Company. It has shown breakthrough potential in the treatment of metabolic diseases by acting on glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1) and glucagon receptors simultaneously. This paper will systematically explain the scientific connotation and clinical value of Retatrutide from the aspects of structural classification, functional characteristics, physicochemical properties, application fields and future development directions.

### **1. Classification and structural characteristics of Retatrutide**

#### 1. **Structural classification: multi-target peptide agonist**

Retatrutide belongs to the "triple receptor agonist" (Triple Agonist), and its molecular design is based on the structural optimization of natural peptide hormones:

- **Amino acid sequence**: The core sequence contains 39 amino acids, and the half-life is extended by chemical modification (such as the introduction of fatty acid side chains).

- **Receptor binding domain**: Contains specific binding sites for GIP, GLP-1 and glucagon receptors, achieving "one drug with multiple targets".

- **Chemical modification**: Modified with C18 diacid chain (Fatty Diacid Chain) to enhance the ability to bind to plasma proteins and reduce renal clearance.

#### 2. **Physical and chemical properties**

- **Molecular weight**: Approximately 4.8 kDa (the specific value varies slightly due to different modifications).

- **Solubility**: Easily soluble in neutral buffer (such as PBS), in a stable colloidal state at physiological pH.

- **Color and morphology**: The freeze-dried powder is white to off-white, and colorless and transparent in solution.

- **Stability**: Requires refrigeration (2-8°C), and is prone to aggregation or degradation at room temperature.

### **2. Functional classification and mechanism of action**

#### 1. **Metabolic regulation function**

- **GIP receptor stimulant**: Enhances insulin secretion and promotes energy storage in fat cells.

- **GLP-1 receptor activation**: suppress appetite, delay gastric emptying, and reduce blood sugar fluctuations.

- **Glucagon receptor regulation**: improve liver gluconeogenesis and balance energy metabolism through indirect mechanisms.

#### 2. **Advantage analysis**

- **Synergistic effect**: Triple agonists have more significant weight loss and blood sugar lowering effects than single-target drugs (such as semaglutide) or dual-target drugs (such as Tirzepatide).

- **Dose flexibility**: Clinical data show that low doses can achieve significant therapeutic effects and reduce gastrointestinal side effects.

- **Long-term effect**: Subcutaneous injection once a week, high patient compliance. -

### **3. Clinical application classification**

#### 1. **Type 2 diabetes (T2DM)**

- **Efficacy data**: Phase III trials showed that HbA1c was reduced by 1.5-2.3%, and some patients achieved normalization of blood sugar.

- **Combination therapy potential**: Combined with SGLT-2 inhibitors or basal insulin, it can reduce the risk of hypoglycemia.

#### 2. **Obesity**

- **Weight loss effect**: Average weight loss after 48 weeks of treatment is 18-22% (2-3% in the placebo group), surpassing existing GLP-1 drugs.

- **Improvement in body fat distribution**: Significantly reduce visceral fat and reduce cardiovascular risk.

#### 3. **Non-alcoholic steatohepatitis (NASH)**

- **Improvement in liver fibrosis**: Reverse liver damage markers (such as ALT and liver fat content) by regulating lipid metabolism and inflammatory pathways.

### **4. Drug development and preparation process**

#### 1. **Synthesis technology**

- **Solid phase synthesis (SPPS)**: Use Fmoc chemistry to gradually build peptide chains. The key steps include:

- Site-specific coupling of fatty acid side chains.

- Cyclization modification to enhance receptor affinity.

- **Purification process**: Reverse phase high performance liquid chromatography (RP-HPLC) ensures purity > 99%, removes impurity peptides and modified byproducts.

#### 2. **Formulation development**

- **Prefilled injection pen**: Sustained release solution containing preservatives (such as phenol), pH 7.4, osmotic pressure matches physiological conditions.

- **Nano delivery system**: The oral dosage form under study is encapsulated by liposomes to improve bioavailability.

### **5. Pharmacology and safety**

#### 1. **Pharmacokinetic properties**

- **Half-life**: About 120 hours, supporting once-weekly dosing.

- **Distribution and metabolism**: Mainly excreted by liver enzymatic hydrolysis and kidney excretion, without significant accumulation risk.

#### 2. **Safety evaluation**

- **Common side effects**: Nausea (15-20%), diarrhea (10%), mostly transient.

- **Special risks**: thyroid C-cell tumors (observed in rodents, human risk is not clear), long-term monitoring is required.

### **6. Future research directions and challenges**

#### 1. **Indication expansion**

- Alzheimer's disease: explore neuroprotective effects by improving the insulin signaling pathway in the brain.

- Polycystic ovary syndrome (PCOS): regulate metabolic and hormonal disorders.

#### 2. **Technical optimization**

- **Oral dosage form development**: overcome the intestinal absorption barrier of peptide drugs.

- **Personalized treatment**: predict efficacy differences based on genetic polymorphisms.

#### 3. **Market and accessibility**

- Cost control: optimize the biosynthesis process to reduce prices.

- Medical insurance policy: promote inclusion in the chronic disease management catalog.

### **Conclusion**

Retatrutide represents the pinnacle of multi-target peptide drug design, and its triple agonist mechanism provides a new treatment paradigm for metabolic diseases. With the deepening of clinical applications and breakthroughs in formulation technology, this drug is expected to reshape the treatment landscape of diabetes, obesity and related complications, while promoting the cross-development of precision medicine and translational research.