Solid‐phase Synthesis of a Peptide Derivative of Thymosin alpha1 and Initial Studies on its ^99mTc‐Radiolabelling

Abstract

A derivative (1) of the immunopotentiating 28-peptide thymosin alpha1 has been especially designed, so that it can be (99m)Tc-radiolabelled, and synthesized following the Fmoc solid-phase peptide synthesis approach. Derivative 1 contains the N-terminal fragment Talpha1[1-14] as a bioactive segment, at the C-terminus of which a (99m)Tc-chelating moiety consisting of N(alpha),N(alpha)-dimethylglycine, serine and cysteine is linked through the N(epsilon)-amino group of a 'bifunctional' lysine residue; the latter is indirectly anchored on the solid-phase peptide synthesis resin through 6-aminocaproic acid (dmGSCK{N(epsilon)-Talpha1[1-14]}Aca). Synthetic derivative 1 was obtained at high overall yield (approximately 35%) and purity (>95%) and shown to be efficiently radiolabelled with (99m)Tc, thus resulting in the first, to our knowledge, so far reported (99m)Tc-radiolabelled derivative of thymosin alpha1, which may be eventually used as a specific molecular tool for the in vitro/in vivo study of the mode of action of the parent bioactive peptide.

Complexes of an Alpha Thymosin Derivative with 185/187Re and 99mTc: Structural Analysis and Initial Biological Evaluation

“…In the present work, the first reported complex (19) of a synthetic derivative of Tα1 with the ReO(V) 3+ core was studied with NMR revealing the structure 185/187 Re‐1 and the existence of two isomers ( 185/187 Re‐1 ‐ syn and 185/187 Re‐1 ‐ anti , ratio, 3:2), depending on the direction of the side chain of Ser2′ with respect to the oxygen of the ReO bond (Figure 2B). The same isomers ( 99m Tc‐1 ‐ syn and 99m Tc‐1 ‐ anti ) and in the same 3:2 ratio were also found to form by HPLC analysis when synthesis was effected at the 99m Tc tracer level.…”

“…The Ta1 [1][2][3][4][5][6][7][8][9][10][11][12][13][14] derivative was efficiently radiolabeled with 99m Tc (yield >95%) (19) and evaluated in mice with experimental inflammation induced with turpentine oil. Previous studies with 99m Tclabeled thymosin fraction 5 (TF5) in rats with experimentally induced inflammation, have shown that the accumulated radioactivity in inflamed tissue (0.07% ID ⁄ g at 4 h postinjection) was 2.3 times higher compared to the control muscle (23).…”

“…Despite the potent immunostimulating activity of Tα1 and ProTα, there have been no clearly identified receptors and their mechanism of action remains elusive. Aiming at the development of a specific molecular probe for the in vitro/in vivo study of the mode of action of alpha thymosins as well as for accelerating research on the exploitation of these peptides in immunotherapy protocols, we have already presented the synthesis of a peptide derivative of Tα1 ( 1 , Figure 1) and its successful radiolabeling with technetium‐99m (19). In the design of 1 a lysine residue (Lys4′) plays the central role: its side chain is joined to the bioactive N‐terminal half of Tα1 (20) consisting of 14 amino acids (Ac ‐ Ser1‐Asp2‐Ala3‐Ala4‐Val5‐Asp6‐Thr7‐Ser8‐Ser9‐Glu10‐Ile11‐Thr12‐Thr13‐Lys14); its N‐terminus is joined to the metal‐chelating moiety N , N ‐dimethyl‐Gly1′‐ l ‐Ser2′‐ l ‐Cys3′; while its C‐terminus is joined to the 6‐aminocaproic acid (Aca) residue that serves to anchor the peptide to the resin during solid‐phase synthesis.…”

Development of a specific IgY-based ELISA for prothymosin alpha, a bioactive polypeptide with diagnostic and therapeutic potential

“…The fragments ProTα[1-28], ProTα[50-88], ProTα[100-105], and ProTα[100-109] (Fig. 1) were in-house synthesized according to the Fmoc/ t Bu solid-phase peptide synthesis strategy and purified with semi-preparative reversed phase HPLC, following protocols previously described by our group [16, 17]. Yield of peptide synthesis was often low, due to “difficult peptide sequences” existing especially in ProTα[50-88] [18].…”

Expression of thymosin α1 concatemer in transgenic tomato (Solanum lycopersicum) fruits

“…Tα1 for clinical use is mainly derived from animal thymus extraction or chemical synthesis [13,14], but the yield of Tα1 from these means cannot meet the increasing requirements for clinical applications. The available amount of calf or swine thymus seriously limits the yield of Tα1, and the quality of thymus‐derived Tα1 varies among different batches or manufacturers.…”