With the development and progress of biotechnology, the research and application of polypeptide drugs have made great breakthroughs, and great achievements have been made, reshaping the modern pharmaceutical industry and clinical treatment mechanism in China, which has attracted much attention in the field of drug preparation science. Polypeptide drugs are easy to be modified and optimized, and their characteristics make them of high medicinal value. Polypeptide drugs generally have short half-life and unstable structure and properties, but compared with macromolecular proteins or antibody drugs, polypeptide drugs are more stable and have higher unit activity at room temperature. The size, polarity, hydrophilicity and charge of polypeptide molecules are not as good as the traditional small molecules, so it is difficult for polypeptide drugs to cross the physiological barrier, so they cannot be taken orally. Therefore, it is necessary to have a deep understanding of its development status, but also to solve the difficulties of preparation science, so as to help peers engaged in related research.
Definition and development status of Part1 polypeptides
1.1 Definition of polypeptide drugs
Amino acids are the basic units of proteins, and polypeptides are amino acids that are converted into a compound by peptide bond bonding to form polypeptide drugs. Peptide drugs are often separated and purified by 10 to 100 amino acid molecules. More than 100 amino acids can form proteins. The main difference between peptides and proteins lies in the length of peptide chains. At the same time, the peptides are more stable, because there is no element [1] that affects protein stability. Peptides are bioactive substances affecting various cell functions in organisms, indispensable in life activities, involving cell growth, hormones, nerves and other fields, clinical specific therapeutic effects, and peptide drugs widely exist in biological system signal molecules, transfer molecules and digestive molecules; peptide used in cardiovascular, blood, muscle, bone, so plays an important role in the medical industry, although the development history of polypeptide drugs is short, but its rapid development, has become the focus of attention.
Research and clinical application of polypeptide drugs: At present, most polypeptide drugs have the characteristics of direct oral failure, short biological half-life and long treatment cycle, so their development and application are the current hot spots, and the development prospect is unlimited. In the 1990s, an average of 9.7 peptide drugs entered the clinical development stage each year, increasing to 19.5 from 200 0 to 2010, and the number is still increasing by [2]. At present, polypeptide drugs have been widely used in clinical practice. Due to its high safety and outstanding efficacy, it has been recognized by more and more doctors and patients, and its status in clinical treatment has been continuously improved. Many varieties have also been included in the treatment guidelines and expert consensus of related diseases at home and abroad, becoming an important supporting force for clinical diagnosis and treatment.
Scientific difficulties and coping strategies for Part2 polypeptide drugs
2.1 Difficulties in the science of polypeptide pharmaceutical preparation
The research of peptide drugs in the field of formulation has attracted much attention, and more attention is paid in the field of non-injection drugs. The research mainly focuses on three aspects: nasal administration, pulmonary administration and oral administration. The difficulties of peptide drugs are mainly manifested in poor stability, short half-life in vivo, difficulty to pass through biological membranes, and poor antigenicity.
Frist， Deacylation reaction. The hydrolysis of Asn / Gln residues forms Asp / Glu; the non-enzymatic reaction is affected by the environment and polypeptide structure, which increases the pH value and increases the temperature.
Second, oxidation. Peptide solution is easy to oxidation, one is the oxide in the solution promotes the oxidation of peptides, the second is the spontaneous oxidation of peptides. The most oxidizing ones of the amino acid residues are Trp, Tyr, Cys, and Met. Oxidation will be affected by the temperature, the partial pressure of oxygen, and the buffer solution.
Third, hydrolysis. Peptide bonds are prone to hydrolysis, and peptide bonds with Asp involved in formation are more prone to break, especially Asp-Pro and Asp-Gly peptide bonds.
Fourth, to form the wrong disulfide bond. Because the disulfide bond or exchange with the thiol group, resulting in tertiary structure change and loss of activity.
Fifth, spin elimination. All amino acid residues except Gly are prone to racemic reactions under base catalysis, especially for Asp residues.
Sixth, denaturation, adsorption, aggregation, or precipitation. Denaturation is mostly related to the destruction of tertiary structure and secondary structure. In the denatured state, polypeptides are prone to chemical reactions, and it is difficult to recover their activity. In the process of polypeptide denaturation, intermediates will be formed first, which are visible to the naked eyes in solution due to their low solubility and easy to aggregate.
2.2 Coping strategies for the difficulties of polypeptide pharmaceutical preparation
First, site-point mutagenesis. Replace the residues that cause peptide instability by genetic engineering, or increase the stability of the peptides.
Second, the chemical modification. Peptides are modified varied and are commonly used as PEG. PEG is a water-soluble polymer compound that is non-toxic and degraded in vivo. It binds to peptides and enhances its thermal stability, resists degradation by proteases, reduces antigenicity and extends its half-life in the body. Careful selection of the modification method or controlling the degree of modification can improve and maintain its original biological activity.
Third, additives. The addition of polyols, gelatin, sugars, amino acids and other additives or some special salts can improve the stability of polypeptides. Among them, sugars and polyols can surround more water molecules around proteins at lower concentrations, significantly improving the stability of peptides. In lyophilization, the above substances can replace water and polypeptides to form hydrogen bonds, to achieve the purpose of improving the stability of polypeptide, and is also conducive to improving the vitrification temperature of lyophilized products. To avoid peptide surface adsorption, aggregation and generation of precipitates, surfactant SDS, Teeen etc.
Fourth, freeze-dried. A series of reactions occurring in polypeptides require the participation of water, including hydrolysis, deamidation and other reactions. Water is the mobile phase of the reaction agent, and the reaction without water polypeptides cannot occur. At the same time, the decrease of water content will increase the denaturation temperature of polypeptides, so lyophilization can be applied to improve the stability of polypeptides. This method is highly feasible.
Study and prospect of Part3 polypeptides
3.1 Study on sustained-release formulation of polypeptides
In clinical applications, oral administration is most popular, but oral peptide drugs cause most of the drug to be absorbed because the peptides cannot pass the physiological barrier. Intravenous administration is rapidly eliminated and degraded due to its short half-life in the blood, and it does not achieve the desired therapeutic effect. In order to relieve the pain of patients with a small amount of drugs, sustained release and controlled release techniques are mainly used: first, polymer, such as hyaluronic acid, is added to improve the adhesion of the drug and reduce its diffusion speed; second, the liposome or solid particles are used to release the peptide drug.
Among the above means, solid particle wrapping is the most used, can be used for the preparation of particulate materials are polyperactone, polyamino acid, polylactic acid, polyogenic acid, etc. At present, polyester materials, especially PLGA. The typical curve of protein release by PLGA microparticles is divided into three phases, namely, the starting burst release phase, diffusion controlled release phase, and decomposition controlled release phase [3]. The first phase means that the protein located on or near the surface of the particles can be released quickly within a few hours; the second phase means that the protein can be released through the pore diffusion in the particles to overlap the continuous release; the third phase is mainly to decompose the polymer and then forms the gap to release the wrapped protein continuously. The difficulty in practical application is reducing the initial explosive release and increasing the drug load. The peptide and peptide microparticle dosage forms prepared using this method are LHRH, GH, IFN, EPO, etc. The particulate preparation of LHRH analog leuprolide can control the release of the drug for as long as a month. The product was first launched in France in 1988, and then successively launched in more than 40 countries in Europe and the United States. The drug was introduced in China in 1993.
3.2 Study on non-injection administration route
The main characteristics of polypeptide drugs are large molecular weight, poor lipid solubility and difficulty in passing the physiological barrier of organisms. In order to achieve the best drug effect, it is necessary to use injection form, but frequent injection is very painful. In order to reduce the pain and drug pain of patients, people have conducted research on the non-injection form of polypeptide drugs. According to the relevant domestic literature, the most studied field on this is nasal and pulmonary medication.
Nasal administration: the mucosal area of the nasal cavity is about 200 cm2, the epithelial cell space is large and closely connected with the capillaries, the lymphatic tissue is rich, the blood flow velocity is about 40 mL / min, and the drug conditions are good. Through nasal inhalation, drugs can directly enter the blood system of the whole body, reduce the possibility of degradation by large protein and aerosol particles, promote drug absorption, and achieve good therapeutic effect. At present, there are mainly two ways of spray and nasal drops, and the bioavailability of nasal drops is higher.
Pulmonary administration: the adsorption surface area of human lungs is 140m2, much larger than the nasal cavity, and the lung capillaries are rich, the epithelial cell space is large, and the permeability is stronger in the process of medication. Some animal experiments also show that polypeptide drugs for lung administration, bioavailability is about 20%~50%, but there will also be some polypeptide drugs by lung protein degradation, or in the process of lung tissue combined with aerosol particles lead to degeneration, as to which peptide drugs suitable for lung administration, still need further analysis. In the process of pulmonary administration, the appropriate administration method is very critical, which will have a direct effect on the effect of pulmonary release. Powder agents using specific inhalation device direct to the lungs is the main way of medication, can play the best treatment effect. The ideal powder needs to meet the following conditions: substantial rapid depolymerization at low flow rates and low pressure to the lungs. The administration method of pulmonary powder agent is still under study.
Oral administration: oral administration is not too painful, also more convenient, popular in clinical, but peptide drugs are not easily absorbed by the gastrointestinal tract, so oral has serious limitations, mainly because of inhibiting disease development, reduce the pain of patients need to take a lot of drugs, and peptide drugs because to unstable chemical structure and properties, difficult through the physiological barrier, easy to be a large number of peptide hydroltic enzyme and proteolytic enzyme degradation, at the same time some drugs even after absorption will be eliminated by liver, make peptide drugs is difficult to achieve oral administration. Currently, most studies have focused on improving the ability of polypeptide drugs to cross physiological barriers and resist protein degradation in [4]. In terms of promoting polypeptide drugs through physiological barriers, the use of promoters is the main means. The common promoters include fatty acids, cholate, chelators, etc., while the means to overcome the obstacles of oral absorbers of polypeptides include the application of micromilk preparations, the use of enzyme inhibitors, etc.
Part4 Conclusion
To sum up, polypeptide drugs are suitable for the treatment of many diseases, so they have attracted more attention, and related studies have been put on the agenda. At present, it is necessary to understand the present situation of the development of peptide drugs, more to dig and solve the peptide drugs in preparation, especially the instability of the difficulty, the article puts forward the strategy, hope can provide power for the development of peptide preparations, and make new achievements in research and development, ultimately the benefit of patients!
Source: Pharmaceutical technology and equipment
reference documentation
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