Selank is a synthetic heptapeptide derived from tuftsin, a natural tetrapeptide fragment of immunoglobulin G, extended at its C-terminus with a Pro-Gly-Pro sequence to resist enzymatic breakdown. Laboratory studies use it to examine gene expression, neurotransmitter-system signalling and cytokine regulation in cell culture and rodent models. It is a small, highly basic peptide, so its handling and analysis differ from those of larger sequences. This article summarises its structure, proposed mechanisms, the published research areas and the analytical and storage standards needed for reproducible work. It is written for laboratory researchers and offers no guidance on human use.
What is Selank?
Selank is classified as a synthetic peptide analogue of tuftsin. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro, usually written TKPRPGP. The first four residues, Thr-Lys-Pro-Arg, are the tuftsin sequence, and the C-terminal Pro-Gly-Pro tripeptide is the stabilising extension. The molecular formula is approximately C33H57N11O9 and the molecular weight is about 752 Da for the free peptide. With a lysine and an arginine and no acidic residues, the peptide is strongly basic and highly water-soluble.
Tuftsin has a defined history. It was described in 1970 by Victor Najjar and Kei Nishioka, who found that a tetrapeptide released from the heavy chain of immunoglobulin G by enzymatic cleavage stimulated phagocytosis by white blood cells in vitro, and they named it after Tufts University. Native tuftsin is cleared within minutes by peptidases. Selank was designed to overcome this limitation, and the Pro-Gly-Pro extension was reported to slow degradation, because proline-rich sequences resist many exopeptidases.
The peptide was developed in Russia at the Institute of Molecular Genetics of the Russian Academy of Sciences, by a group associated with Nikolai Myasoedov and colleagues, in the 1990s and 2000s. A formulation has been registered in Russia for specific clinical uses. That product is manufactured and supplied under national pharmaceutical standards, and research-grade material is not equivalent to it. To the author’s understanding, Selank is not authorised as a medicine in the United Kingdom, and this should be checked against current Medicines and Healthcare products Regulatory Agency (MHRA) records. The MHRA has issued warnings about unlicensed products marketed for human use.
A note on naming is useful. Selank is sometimes confused with Semax, another heptapeptide from the same research institute. They are unrelated in sequence and origin, since Semax is an analogue of a fragment of adrenocorticotropic hormone and Selank is an analogue of tuftsin, and results from one cannot be applied to the other. The material is relevant here only as a laboratory research reagent.
Mechanism of action
No single receptor has been conclusively identified for Selank, and this is the most important point to understand about its mechanism. The literature describes several proposed routes, some of which rest on observations from a small number of research groups.
The first proposed route is derived from tuftsin biology. Tuftsin is reported to bind receptors on phagocytic cells, including macrophages and neutrophils, and to influence their activity. Neuropilin-1 has been proposed as a tuftsin receptor, and the analogue’s behaviour at that receptor has not been fully characterised. Reports that Selank affects cytokine expression, including interleukin-6, in rodent models and in cultured immune cells are consistent with an immune-cell mechanism, though the details are not settled.
The second proposed route involves the GABAergic system. Work on gene expression in rat brain tissue reported that the peptide changed the expression of several genes associated with gamma-aminobutyric acid (GABA) signalling, and some studies proposed allosteric modulation of the GABA-A receptor, though direct receptor-binding evidence is limited and the findings are not uniformly replicated.
The third proposed route concerns enkephalin metabolism. Biochemical studies reported that the peptide inhibited enzymes that degrade enkephalins, endogenous opioid peptides, which would raise their local levels. This is an enzyme-inhibition observation in vitro, and its physiological significance is uncertain.
The fourth proposed route is the regulation of neurotrophin expression, including brain-derived neurotrophic factor (BDNF), reported in rodent hippocampus. As with the peptide’s other reported actions, the molecular link between the peptide and the change in expression has not been established.
For laboratory design, the practical consequence is that controls are essential. Scrambled-sequence peptides, the Pro-Gly-Pro tripeptide alone and native tuftsin allow the contributions of the tuftsin portion and the extension to be separated. In cell-based work, “dosage” means molar concentration in the medium, which depends on net peptide content, adsorption to plasticware and protease activity in any serum used.
What the research shows
The literature on Selank is modest in size and concentrated in a few research groups, most of them in Russia. Four areas are summarised below in general terms. Readers should consult the primary papers for methods, concentrations and statistics, because commercial summaries often overstate findings.
The first area is the original tuftsin work. The 1970 papers describing tuftsin and its stimulation of phagocytosis in vitro established the biology on which the analogue was designed, and later studies characterised its binding to phagocytic cells and its rapid degradation. The foundational literature can be located through a PubMed search on tuftsin and phagocytosis stimulation.
The second area is the design and characterisation of the analogue. Papers from the Russian Academy of Sciences groups described tuftsin analogues extended with Pro-Gly-Pro and compared their stability and activity in biochemical and rodent preparations with those of tuftsin. They reported that the extended peptide persisted longer in biological preparations and reported effects in rodent behavioural and biochemical assays. The early literature can be explored through a PubMed search on Selank, the tuftsin analogue Thr-Lys-Pro-Arg-Pro-Gly-Pro.
The third area is gene expression profiling. Studies from Moscow groups used quantitative PCR and transcriptome methods to examine how the peptide altered the expression of genes in rat brain tissue and in immune cells, including genes associated with GABAergic signalling and inflammatory mediators. These are expression measurements in animals, exposures were expressed per kilogram of body weight and varied with route, and the values should be taken from the primary papers. They are hypothesis-generating and say nothing about any effect outside the experimental model.
The fourth area is peptide metabolism. Biochemical studies described how the peptide is broken down in plasma and tissue extracts and identified the C-terminal tripeptide and short fragments as products, which supports the stability logic of the design and the use of the tripeptide as a control.
A recurring limitation runs through this body of work. Most primary studies come from a small number of laboratories, routes and exposures vary widely, the receptor pharmacology is incompletely defined, and the exact material used is not always characterised analytically. Independent replication would strengthen the evidence, and reproducibility depends on knowing exactly what was in the vial.
Research applications
In the laboratory, Selank is used in several contexts. The most common is cell culture and tissue work on gene expression, where the peptide is a test compound in neuronal, glial and immune cell models, with quantitative PCR or RNA sequencing as the readout. Good practice is to include scrambled-sequence, Pro-Gly-Pro and tuftsin controls.
A second context is immunology. Because the peptide derives from a phagocyte-stimulating tetrapeptide, it is used in studies of macrophage and monocyte function, cytokine production and phagocytosis assays in vitro. Endotoxin control is important in these systems, since immune cells respond strongly to trace lipopolysaccharide.
A third context is peptide pharmacology. The peptide is an example of how a short C-terminal extension can stabilise a fragment of a larger protein, and researchers developing other protease-resistant peptides use it as a comparator in plasma stability assays.
A fourth context is animal models, which require institutional ethical review and, in the United Kingdom, authorisation under the Animals (Scientific Procedures) Act 1986. Study design should include vehicle controls, blinded assessment and analytical confirmation of the material administered.
A fifth context is analytical chemistry. A small, basic, proline-rich heptapeptide is a useful test case for liquid chromatography and mass spectrometry methods for polar peptides that retain poorly on standard columns, and reference material of defined identity and purity supports method development and the detection of unlicensed peptide products.
Purity, storage and handling
Selank is short, but its chemistry presents particular points. The sequence contains no aromatic residues, so ultraviolet absorbance occurs only through the peptide bond at 214 to 220 nm, and a second wavelength offers no help. The peptide is polar and basic, so it may elute early on a standard C18 column, and impurities can run close to the main peak, which means a shallow gradient or an alternative method such as hydrophilic interaction chromatography may be needed. The C-terminal Pro-Gly-Pro sequence is prone to forming diketopiperazine by-products, because a dipeptide at the end of a proline-containing chain can cyclise and detach. Reversed-phase high-performance liquid chromatography (HPLC) is the standard purity method, and a main peak of at least 98 per cent is commonly expected. A stated purity is meaningful only if the method and chromatogram are available.
HPLC must be paired with mass spectrometry. The expected protonated ion is at about m/z 752. A species lacking one residue indicates a deletion product, and a species differing by a few daltons may indicate a related impurity. A clean peak at the wrong mass is a clean peak of the wrong compound.
A batch-specific certificate of analysis matters because purity, peptide content and counterion content vary between synthesis runs. It should carry a lot number matching the vial, the HPLC trace or purity value, the observed and theoretical masses, the test date and ideally the salt form, net peptide content and endotoxin result. The counterion deserves special attention for a peptide of only about 752 Da with two basic residues. Trifluoroacetate from HPLC purification can account for a large fraction of the powder’s mass, so the weighed mass is a poor guide to the amount of peptide, and TFA is not biologically neutral in cell assays. Acetate forms are often preferred, and the salt form should be stated. The highly basic peptide is also hygroscopic, so residual water can be substantial.
Because the weighed mass of a small, basic peptide can differ greatly from its peptide content, and because endotoxin cannot be seen on a label, batch-level verification matters more here than with a larger, less hygroscopic sequence. UK laboratories sourcing Selank should expect a batch-specific certificate of analysis that states the mass found, the salt form and net peptide content, with lyophilised storage at -20°C, and the same documentation standard applies when weighing any best peptides supplier uk claim, since a supplier’s analytical record rather than its search ranking shows whether the vial matches its stated specification.
Lyophilised Selank is generally stored at -20°C in a sealed container with desiccant, and many laboratories use -80°C for long-term archives. Because the powder is hygroscopic, vials should reach room temperature before opening so that condensation does not form on the cold powder, and vials should be resealed promptly. After reconstitution, stability falls. Standard practice is to dissolve the peptide in sterile, endotoxin-free water or a suitable buffer, divide the solution into single-use aliquots and freeze them to avoid repeated freeze-thaw cycles. Refrigerated storage at 2 to 8°C is sometimes used for solutions consumed within days, but the acceptable period should be validated for the assay concerned, preferably by re-running HPLC and mass spectrometry on stored solution.
Light sensitivity is not a significant concern for this sequence, which contains no aromatic, sulphur-containing or other photosensitive residues, though amber vials or dark storage remain good practice. The basic residues make the peptide prone to adsorb to glass and some plastics at low concentrations, so low-bind tubes are preferred for dilute working solutions.
Labelling is a final indicator of quality. Clear naming that distinguishes the peptide from Semax and from tuftsin, with sequence, molecular weight, lot number, salt form and an unambiguous research-only statement, suggests a supplier that understands its market. Any wording that implies use in humans is a warning sign and raises regulatory concerns in the United Kingdom.
Frequently asked questions
What is Selank used for in laboratory research?
It is used as a test compound in studies of gene expression and neurotransmitter-system signalling in cultured cells and approved animal models, in immune-cell assays, in comparative studies of protease-resistant peptides and as a reference in analytical methods. It is a research reagent and not an authorised medicine in the United Kingdom.
What is the sequence and molecular weight of Selank?
Selank is a heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, usually written TKPRPGP, and a molecular weight of about 752 Da. It is an analogue of tuftsin with a Pro-Gly-Pro extension. The certificate of analysis should show a mass spectrometry result matching this value.
Is Selank the same as Semax?
No. Both are heptapeptides developed at the same Russian institute, but Selank is a tuftsin analogue with the sequence TKPRPGP, while Semax is an analogue of an ACTH fragment with the sequence MEHFPGP. They differ in structure, mass and reported biology, so results cannot be shared.
How should Selank be stored for research?
Keep lyophilised peptide at -20°C, or -80°C for long-term archiving, in a sealed, dry container, and allow vials to reach room temperature before opening. After reconstitution, aliquot and freeze the solution to avoid repeated freeze-thaw cycles, and use low-bind tubes.
Selank is supplied for in-vitro laboratory research only and is not intended for human or veterinary use.
