Abstract
Corrination is the conjugation of a corrin ring containing molecule, such as vitamin B12 (B12) or B12 biosynthetic precursor dicyanocobinamide (Cbi), to small molecules, peptides, or proteins with the goal of modifying pharmacology. Recently, a corrinated GLP-1R agonist (GLP-1RA) exendin-4 (Ex4) has been shown in vivo to have reduced penetration into the central nervous system relative to Ex4 alone, producing a glucoregulatory GLP-1RA devoid of anorexia and emesis. The study herein was designed to optimize the lead conjugate for GLP-1R agonism and binding. Two specific conjugation sites were introduced in Ex4, while also utilizing various linkers, so that it was possible to identify Cbi conjugates of Ex4 that exhibit improved binding and agonist activity at the GLP-1R. An optimized conjugate (22), comparable with Ex4, was successfully screened and subsequently assayed for insulin secretion in rat islets and in vivo in shrews for glucoregulatory and emetic behavior, relative to Ex4.
Highlights
The dramatic rise of type 2 diabetes (T2D) and obesity as comorbidities has driven a concomitant rise in new pharmaceutical interventions to treat such disorders, either together or individually.[1−7] One extremely successful family of pharmaceuticals in this field has been that of glucagon-like peptide-1 receptor agonists (GLP-1RAs),[8−13] such as exenatide (i.e., Exendin-4; Ex4), liraglutide,[14−17] and semaglutide.[16−18] Exenatide and liraglutide confer glucoregulation in tandem with a body weight reduction of 5−6% over ∼1 year,[16,17] while semaglutide can produce a weight loss of 10− 12% over the same time period.[16,17]
We have looked to optimize 1 with a focus on agonism and binding at the GLP-1R while expanding to the little explored chemistry pertaining to the synthesis of Cbi conjugates
The weight loss gleaned from GLP1RAs, for example, has proven to be a beneficial “side effect” of T2D treatment due to the high comorbidity of T2D with obesity.[64]
Summary
The dramatic rise of type 2 diabetes (T2D) and obesity as comorbidities has driven a concomitant rise in new pharmaceutical interventions to treat such disorders, either together or individually.[1−7] One extremely successful family of pharmaceuticals in this field has been that of glucagon-like peptide-1 receptor agonists (GLP-1RAs),[8−13] such as exenatide (i.e., Exendin-4; Ex4), liraglutide,[14−17] and semaglutide.[16−18] Exenatide and liraglutide confer glucoregulation in tandem with a body weight reduction of 5−6% over ∼1 year,[16,17] while semaglutide can produce a weight loss of 10− 12% over the same time period.[16,17] The hypophagic effects of all GLP-1RAs are accompanied by nausea and vomiting (emesis) in upward of 25% of patients,[19−25] the result of penetrance and direct action of the GLP-1RA in the central nervous system (CNS), in the nucleus tractus solitarius and area postrema of the hind-brain.[26−29] the development of a GLP-1RA that does not access the CNS would be expected to mitigate the side effects of nausea and emesis and reduce the hypophagic effects. Our recent report explored the conjugation of Cbi with Ex4, to produce Cbi-Ex4 (1),[39] and its effects were tested in vivo in the musk shrew (Suncus murinus), a mammal capable of emesis[41,42] and responsive to GLP-1R targeting therapeutics.[39,43,44] Our data showed that Cbi-Ex4 enhanced the glucoregulatory response following an intraperitoneal glucose tolerance test (IPGTT), without producing hypophagia, anorexia, body weight loss, and, more importantly, without emesis, all characteristics of classical Ex4-based therapies.[39] We hypothesized that these results are due to reduced drug penetrance into the CNS (see Figure 1).[35−39] This proof-ofconcept corrinated Ex4 (1) was, notably less potent an agonist for the GLP-1R than Ex4 alone (200 vs 30 pM, respectively, in the same GLP-1R FRET assay).[39] With that in mind, we set out to optimize 1 in terms of receptor binding and agonism for the purposes of future translation.
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