This shoudl explain the difference in natural GLP-1 foundint he gut and GLP-1 analogues
Semaglutide is a human GLP-1 analogue in clinical development for the treatment of T2D. It shares 94% structural homology with native human GLP-1, with three important modifications: amino-acid substitutions at position 8 (alanine to alpha-aminoisobutyric acid) and position 34 (lysine to arginine), and acylation of the lysine in position 26 with a spacer consisting of two 8-amino-3,6-dioxaoctanoic acid (ADO) moieties, a
glutamic acid moiety, and a C-18 fatty di-acid side chain (
Lau et al., 2015). The fatty di-acid side chain and spacer mediate strong binding with albumin, while the amino-acid substitution at position 34 limits the options for acylation to the one remaining lysine in the sequence; the substitution at position 8 reduces the susceptibility of semaglutide to degradation by DPP-4 (
Lau et al., 2015). Together, these modifications prolong the t1/2 of semaglutide; a previous pharmacokinetic (PK) trial with semaglutide showed the geometric means (coefficient of variation in %) of t1/2 was 165 (14.1) h (approximately 1 week). Additionally, the dose dependent increase of the Ctrough values following 4 weeks of treatment with semaglutide 0.25 mg, 0.5 mg and 1.0 mg was 4.4 (31.5), 11.7 (20.2) and 21.2 (19.7) nmol/L, respectively (
Kapitza et al., 2015).
Changes to semaglutide compared with native human GLP-1 are: amino-acid substitutions at position 8 (alanine to alpha-aminoisobutyric acid) and position 34 (lysine to arginine), and acylation of the lysine in position 26 with two ADO moieties followed by a glutamic acid moiety (the ‘spacer’) and a C-18 fatty di-acid side chain (
Lau et al., 2015). ADO, 8-amino-3,6-dioxaoctanoic acid.
2.1.1. Synthetic procedure for the radioactive building block [3H]-NNC0113-0857
The starting material, NNC0113-3747 (6.6 mg, 6.5 μmol), was dissolved in a solution of N-methyl-2-pyrrolidone (NMP) (1.0 mL) and
trifluoroacetic acid (TFA) (5 μL) before 10 wt% Pd/C (6.5 mg) was added. The mixture was subjected to tritium gas (6.9 Ci) and stirred at room temperature. After 4 h, Pd/C was filtered out and the residue co-evaporated (3 × 1.0 mL) with a 1000:1 solution of EtOH/TFA. The residue was dissolved with NMP (1.0 mL) and the radioactive content was determined (180 mCi/mL, 1.6 mL). High-performance liquid chromatography (HPLC) analysis showed that [3H]-NNC0113-0857 had radiochemical purity of 61%.
2.1.2. Synthetic procedure for [3H]-semaglutide
The peptide backbone (20.4 mg, 6.0 μmol), was dissolved in H2O (5.0 mL) and the pH adjusted to 11 via the addition of NEt3. The solution of [3H]-NNC0113-0857 in NMP (180 mCi/mL, 1.6 mL) was slowly added over 15 min. After 2 h, the reaction was quenched and neutralised to pH 7 by addition of 1 M CH3COOH (120 μL). The reaction mixture was purified by HPLC (column: Luna® reversed phase C18; A-eluent [0.1 M Tris-HCl, 0.05 M·H3PO4, H2O]/EtOH 8:2, pH 7.4; B-eluent [0.1 M Tris-HCI, 0.05 M·H3PO4, H2O]/EtOH 55:45, pH 7.4) and yielded a [3H]-semaglutide solution of 98% purity. [3H]-semaglutide was desalted on a C18 Sep-Pak® filter and eluted with H2O/EtOH (3:7) into a solution with a radioactive content of 16.7 mCi/mL. The solution was concentrated to dryness on a rotary evaporator and then reconstituted in the following vehicle/API solution of semaglutide (1.34 mg/mL, 1.0 mg/mL or 0 mg/mL),
propylene glycol (14 mg/mL), Na2HPO4·2H2O (1.42 mg/mL), phenol (5.5 mg/mL), pH 7.4. HPLC analysis of formulated [3H]-semaglutide gave a radiochemical purity of > 98%.
2.1.3. Stability of [3H]-semaglutide
[3H]-semaglutide stability in vehicle was assessed over a 15-day period at 5 °C and 25 °C and confirmed. Radiochemical purity was determined by HPLC. Prestudy stability tests revealed that the tritium tracer showed a satisfactory stability. The amount of tritiated water formed after 15 days’ storage at 25 °C was low (< 0.1%), as was the amount of impurities (~ 2% at 5 °C and ~ 5% at 25 °C).
2.1.4. Stability of semaglutide in human material
Stability of the tracer was also assessed in plasma and urine and showed that the [3H]-semaglutide tracer was stable in human blood, plasma and urine for up to at least 4 h at room temperature and up to at least 48 h at nominal + 4, − 20 and − 70 °C. The stability of the [3H]-semaglutide radiotracer was, therefore, considered to be adequate for conducting metabolism studies.
Semaglutide is a human glucagon-like peptide-1 analogue in clinical development for the treatment of type 2 diabetes. The absorption, metabolism and e…
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