Selank: Discovery and Regulatory History

Introduction

Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is the product of a research program rooted in Soviet and post-Soviet neuropharmacology, centered at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow. Its development sits at the intersection of tuftsin immunology and the broader Russian effort to produce peptide-based central nervous system compounds with a pharmacological profile distinct from classical benzodiazepines. That program produced a compound that reached clinical registration in Russia in 2009 — an outcome that reflects approximately two decades of systematic preclinical and clinical work [1,2].

Discovery Period: Tuftsin and the Design Problem

The direct precursor of Selank is tuftsin, a naturally occurring tetrapeptide (Thr-Lys-Pro-Arg) first isolated and characterized by Najjar and Nishioka at Tufts University in 1970 [3]. Tuftsin is generated by proteolytic cleavage from the Fc region of the IgG heavy chain and was originally identified as a phagocytosis-activating peptide with immunostimulatory activity in vitro and in animal models. Its rapid degradation in plasma — with a half-life measured in seconds — constrained its utility as a therapeutic agent and defined the core design problem for derivative compounds.

In the Russian scientific context, behavioral effects of tuftsin and its analogs in animal stress models during the 1980s positioned the molecule as a starting point for both neurobiological and immunological drug design. A modified molecule that survived plasma enzymatic degradation would be positioned to access CNS targets that tuftsin itself could not consistently reach.

Synthesis of Selank at the Institute of Molecular Genetics

The synthesis of Selank was conducted at the Institute of Molecular Genetics by the group of Nikolay Myasoedov and Lyudmila Andreeva, working in the Department of Chemistry of Physiologically Active Compounds. The work was part of a broader program at the Institute developing synthetic regulatory peptide-based drugs — a program that ran in parallel with the development of Semax (a synthetic ACTH 4–10 analog) and other neuropeptide compounds [1].

The design approach was to extend tuftsin's C-terminus with the tripeptide Pro-Gly-Pro. This extension served two purposes: the flanking proline residues created a sequence resistant to cleavage by many endopeptidases and exopeptidases, substantially extending metabolic half-life compared to tuftsin; and the extension introduced neurotropic and neuromodulatory activity not present in tuftsin itself — the pharmacological properties that became central to subsequent characterization of the compound.

The resulting heptapeptide was synthesized by solid-phase methods and characterized chemically before initial pharmacological testing in rodent models. Early preclinical observations in animal stress and behavioral models distinguished Selank from tuftsin and from classical sedating anxiolytics, motivating the pursuit of regulatory development [1,2].

Early Preclinical Research: 1990s and Early 2000s

Initial pharmacological characterization of Selank accumulated in Russian-language literature through the 1990s. The first English-language publications appeared in Neuroscience and Behavioral Physiology in 2003. A paper by Kozlovskii and Danchev reported observations consistent with facilitation of conditioned active avoidance learning in rats with initially poor learning performance following Selank administration [4]. A companion article by Semenova and colleagues compared Selank alongside other tuftsin-family peptides in rodent conflict-stress paradigms, placing the compound within its structural and pharmacological family context [5].

A 2001 publication in Eksperimental'naia i Klinicheskaia Farmakologiia by Semenova and colleagues reported inhibitory effects on enkephalin-degrading enzymes in vitro [6], providing the biochemical hypothesis that subsequently anchored mechanistic interpretation of Selank's behavioral pharmacology. This enkephalinase inhibition finding — demonstrating that the compound could prolong the availability of endogenous opioid peptides in model systems — became the central pillar of the compound's proposed mechanism of action.

Clinical Investigation and Russian Registration: 2008–2009

The principal published comparative clinical trial was reported by Zozulia, Neznamov, and colleagues in 2008 in Zhurnal Nevrologii i Psikhiatrii [2]. The parallel-group trial enrolled 62 subjects with generalized anxiety disorder or neurasthenia and compared Selank administered intranasally against the benzodiazepine medazepam over 14 days, using the Hamilton Anxiety Rating Scale, Zung Self-Rating Anxiety Scale, and Clinical Global Impression as primary outcomes. The authors characterized anxiolytic effects in the Selank group as comparable to medazepam and noted additional antiasthenic effects in the Selank arm not observed in the medazepam group. Immunological assessments published concurrently by Uchakina and colleagues reported T-helper cytokine profile changes and altered serum leu-enkephalin half-life in Selank-treated subjects, providing a clinical-level parallel to the preclinical enkephalinase mechanism [7].

Selank received registration approval from the Russian Federation Ministry of Health in 2009, made available as a 0.15% nasal drop solution for generalized anxiety disorder and neurasthenia — the culmination of approximately two decades of systematic research at the Institute of Molecular Genetics.

Molecular Pharmacology Research: 2010s

Following registration, academic investigation of Selank continued at increasingly granular molecular levels. A 2014 cDNA microarray study by Dolotov and colleagues identified altered expression of membrane-associated and ion-transport genes in rat hippocampus following Selank administration, providing the first broad transcriptomic characterization of the compound's effects on hippocampal gene expression [8].

Studies published in Frontiers in Pharmacology in 2016 and 2017 used quantitative PCR to characterize GABAergic gene expression changes in rat brain tissue and in IMR-32 human neuroblastoma cells [9,10]. In vivo results reported altered expression of multiple GABAergic pathway genes, while the cell-culture system produced no significant changes — a pattern the authors interpreted as evidence that Selank's effects on GABAergic gene expression depend on intact neural circuit context. These studies refined rather than resolved the mechanistic picture and helped identify the circuit-dependency hypothesis as a productive area of further investigation.

A 2012 study in the Journal of Evolutionary Biochemistry and Physiology reported that Selank produced lasting alterations in carboxypeptidase H activity in rat nervous tissue — persisting 24 hours post-administration — extending the enkephalinase mechanism to a broader class of neuropeptide-processing enzymes [11].

Extended Research: 2019–2022

Research published in 2019 and 2022 extended investigation into two pharmacologically adjacent domains. A 2019 study by Laukova and colleagues in the Bulletin of Experimental Biology and Medicine examined Selank's effects on BDNF content and object recognition in rats with chronic ethanol exposure, reporting altered BDNF levels in hippocampus and prefrontal cortex compared to ethanol-alone controls [12]. A 2019 review in Biology Bulletin by Andreeva and Myasoedov synthesized structural and functional pharmacology across Selank and its fragments, proposing the enkephalin system as a central mechanistic hub and identifying the Pro-Gly-Pro C-terminal extension as a pharmacologically active contributor rather than a passive stabilizing sequence [13].

A 2022 study in the Bulletin of Experimental Biology and Medicine by Konstantinopolsky and colleagues examined Selank in a naloxone-precipitated morphine withdrawal model, reporting attenuation of withdrawal signs by approximately 40% compared to untreated controls [14]. The authors noted this finding as consistent with the compound's proposed opioid system interactions and as opening a new direction for research into Selank's pharmacological profile.

Outside Russia, the compound's regulatory status remains that of an unregistered research compound. No IND applications with the FDA or EMA-regulated clinical trials are publicly documented. The active research program within Russian institutions continues to characterize the compound's molecular pharmacology, with the enkephalin-GABAergic-neurotrophin axis remaining the primary mechanistic framework. A comparable trajectory from Soviet-era laboratory to registered Russian pharmaceutical can be observed in the history of Pinealon, another peptide compound from the same institutional milieu. Researchers seeking sourcing and verification standards for Selank as a research material are directed to the Selank sourcing and quality article.

References

1. Myasoedov NF, Grigoriev VV, Gudasheva TA, Semenova TP, Skryabin AB, Ashmarin IP. A new generation of drugs: synthetic peptides based on natural regulatory peptides. Neuropharmacology. 2013. https://www.scirp.org/journal/paperinformation?paperid=40560

2. Zozulia AA, Neznamov GG, Syunyakov TS, Kost NV, Gabaeva MV, Sokolov OIu, Sebentsova EA, Akhromeeva SA, Panchenko LF, Andriushenko AV, Teleshova ES, Shadrina MI, Slominsky PA, Miasoedov NF. Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the therapy of generalized anxiety disorders and neurasthenia. Zhurnal Nevrologii i Psikhiatrii Imeni S.S. Korsakova. 2008;108(4):38–48. PMID: 18454096.

3. Najjar VA, Nishioka K. "Tuftsin": a natural phagocytosis stimulating peptide. Nature. 1970;228(5272):672–673. https://doi.org/10.1038/228672a0

4. Kozlovskii II, Danchev ND. The optimizing action of the synthetic peptide Selank on a conditioned active avoidance reflex in rats. Neuroscience and Behavioral Physiology. 2003;33(7):639–643. https://doi.org/10.1023/A:1024444321191 PMID: 14552529.

5. Semenova TP, Kozlovskaya MM, Zuikov AV, Kozlovskiy II, Myasoedov NF. Selank and short peptides of the tuftsin family in the regulation of adaptive behavior in stress. Neuroscience and Behavioral Physiology. 2003;33(9):853–860. https://doi.org/10.1023/A:1025988519919 PMID: 12154572.

6. Semenova TP, Kozlovskaya MM, Zakharova NM. The inhibitory effect of Selank on enkephalin-degrading enzymes as a possible mechanism of its anxiolytic activity. Eksperimental'naia i Klinicheskaia Farmakologiia. 2001;64(2):3–6. PMID: 11550013. https://pubmed.ncbi.nlm.nih.gov/11550013/

7. Uchakina ON, Uchakin PN, Miasoedov NF, Andreeva LA, Shcherbenko VE, Mezentseva MV, Gabaeva MV, Sokolov OIu, Zozulia AA, Ershov FI. Immunomodulatory effects of selank in patients with anxiety-asthenic disorders. Zhurnal Nevrologii i Psikhiatrii Imeni S.S. Korsakova. 2008;108(5):71–75. PMID: 18577961.

8. Dolotov OV, Sebentsova EA, Sourina MM, Malygina TR, Serebriakova EV, Andreeva LA, Alfeeva LYu, Grivennikov IA, Myasoedov NF. Changes in the transcription profile of the hippocampus in response to administration of the tuftsin analog Selank. Neuroscience and Behavioral Physiology. 2014;44(8):852–861. https://doi.org/10.1007/s11055-014-9992-4 PMID: 24450168.

9. Volkova A, Shadrina M, Kolomin T, Andreeva L, Limborska S, Myasoedov N, Slominsky P. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Frontiers in Pharmacology. 2016;7:31. https://doi.org/10.3389/fphar.2016.00031 PMC4757669.

10. Filatova EV, Kasian AM, Kolomin TA, Rybalkina EY, Alieva AK, Andreeva LA, Limborska SA, Myasoedov NF, Pavlova GV, Slominsky PA, Shadrina MI. GABA, Selank, and olanzapine affect the expression of genes involved in GABAergic neurotransmission in IMR-32 cells. Frontiers in Pharmacology. 2017;8:89. https://doi.org/10.3389/fphar.2017.00089 PMID: 28293190.

11. Narkevich VB, Klodt PM, Kudrin VS, Volkova AB, Kolomin TA, Andreeva LA, Myasoedov NF, Raevsky KS. Effect of selank on the main carboxypeptidases in the rat nervous tissue. Journal of Evolutionary Biochemistry and Physiology. 2012;48(3):302–308. https://doi.org/10.1134/S0022093012030073 PMID: 22827026.

12. Laukova M, Alaluf LG, Serova LI, Arango V, Sabban EL. Selank, peptide analogue of tuftsin, protects against ethanol-induced memory impairment by regulating BDNF content in the hippocampus and prefrontal cortex in rats. Bulletin of Experimental Biology and Medicine. 2019;167(5):641–644. https://doi.org/10.1007/s10517-019-04588-9

13. Andreeva LA, Myasoedov NF. Physiological effects of Selank and its fragments. Biology Bulletin. 2019;46(4):390–400. https://doi.org/10.1134/S1062359019040071

14. Konstantinopolsky MA, Chernyakova IV, Poletaeva II, Zhukova II, Andreeva LA, Myasoedov NF. Selank, a peptide analog of tuftsin, attenuates aversive signs of morphine withdrawal in rats. Bulletin of Experimental Biology and Medicine. 2022;173(5):581–584. https://doi.org/10.1007/s10517-022-05624-x PMID: 36322304.