Selank

Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro and a molecular weight of approximately 751.88 Da. It was designed as a stabilized analog of tuftsin (Thr-Lys-Pro-Arg), an endogenous immunomodulatory tetrapeptide derived from the Fc domain of immunoglobulin G. The Pro-Gly-Pro extension was added to improve enzymatic stability and extend the biological half-life. Selank was developed at the Institute of Molecular Genetics of the Russian Academy of Sciences and is approved as a prescription anxiolytic in Russia.

The anxiolytic mechanism of Selank involves modulation of GABAergic neurotransmission through allosteric effects on GABA-A receptor sensitivity, distinct from the direct binding site used by benzodiazepines. Selank also inhibits the enzyme enkephalinase (neprilysin), which degrades endogenous opioid peptides including enkephalins. By stabilizing enkephalin levels, Selank prolongs the natural anxiolytic and mood-regulating effects of the endogenous opioid system without directly activating opioid receptors.

Clinical trials conducted at the Serbsky Center for Social and Forensic Psychiatry (N=62) demonstrated a 2-fold reduction in Hamilton Anxiety Rating Scale (HAM-A) scores compared to placebo over a 14-day treatment period. Critically, no sedation, psychomotor impairment, or cognitive dulling was observed. Patients simultaneously showed improved memory consolidation and attention scores, distinguishing Selank from conventional anxiolytics that typically impair cognition.

The tuftsin-derived structure gives Selank significant immunomodulatory properties. It enhances natural killer (NK) cell cytotoxicity, promotes phagocytic activity of monocytes, and balances the Th1/Th2 cytokine ratio. Studies published in Immunology Letters showed that Selank normalizes IL-6 levels (reducing elevated IL-6 while raising suppressed levels) and modulates interferon-gamma production. This bidirectional immune regulation makes Selank an immunomodulator rather than a simple immunostimulant.

Selank is administered intranasally at typical research doses of 250-500 mcg per day, divided into 2-3 administrations. Intranasal bioavailability is estimated at 60-70%, with onset of anxiolytic effects within 5-15 minutes. The plasma half-life of the intact peptide is approximately 30 minutes, significantly longer than unmodified tuftsin (2-3 minutes), confirming the stabilizing effect of the Pro-Gly-Pro extension. Research protocols typically run 14-21 day cycles.

Gene expression studies (Kolomin et al., 2013) showed that a single Selank administration modulated 36 genes in the hippocampus within 1 hour, with the number expanding to over 50 genes at 24 hours. Modulated genes included those involved in GABA transport, serotonin receptor expression, and immune signaling. Selank also influences the expression of key neurotransmitter-related genes including GAD67 (glutamic acid decarboxylase) and multiple serotonin receptor subtypes.

Lyophilized Selank should be stored at -20C with stability exceeding 24 months. Reconstituted nasal solutions should be refrigerated at 2-8C and used within 21 days. The peptide is stable across pH 5.0-7.5 and can be reconstituted in bacteriostatic water or sterile saline. Unlike many peptides, Selank does not contain oxidation-sensitive residues (no methionine or cysteine), contributing to good solution stability.

The safety profile is notable for the absence of benzodiazepine-class side effects. No dependence, tolerance, rebound anxiety, or withdrawal symptoms have been reported in clinical studies or post-marketing surveillance. No effects on liver enzymes, renal function, or hematological parameters were observed. The compound is classified as having extremely low toxicity, with preclinical LD50 values exceeding 5,000 mg/kg in rodent models.