Design and Engineering of New Glucagon Like Peptide-1 Analogues.
Pamuk Turner, Diren.
Abstract: ABSTRACT Diabetes mellitus (DM) is a chronic disease that manifests
itself with impaired control of blood glucose levels and affects hundreds of millions of
individuals worldwide. Among various types of DM, Type II diabetes is the most prevalent.
In addition to conventional therapies for diabetes, increasing knowledge of the pathology
of the disease has led to new leads for drug targ... read moreets. Recent studies have revealed that
glucagon like peptide (GLP-1), an incretin hormone, has a significant effect in lowering
blood glucose levels without serious side effects. A naturally occurring analog of GLP-1,
Exenedin-4 (Byetta®), is an approved compound for diabetes. It stimulates insulin secretion
in a glucose-dependent manner, and prevents and reverses the destruction of pancreatic
β-cells. We have synthesized new analogs of GLP-1 using two different strategies.
First, we synthesized a lipidated GLP-1 analog with a flexible linker that can anchor
itself in cell membranes. Restriction of GLP-1 to the membrane could increase the effective
concentration of the peptide around the GLP-1 receptor (GLP-1R); resulting in a more
efficient binding and activation of downstream signals. Our results showed that lipidated
construct had the same efficacy as the GLP-1, however it exhibited less potency.
Nevertheless this construct includes a number of sites for optimization, which may allow
for enhanced activity. We have also investigated longer lasting analogues of GLP-1 by
installing unnatural amino acids at the sites that are susceptible to proteolysis. Using
β-amino acid substitutions at the hydrolytic site, we intended to overcome
protease degradation caused by dipeptidyl peptidase-IV (DPP-IV) enzyme. In addition to
using well-known side chains of glutamic acid (Glu) and leucine (Leu), we also introduced a
fluorinated amino acid with a hexafluoroleucine side chain. We describe a novel and
efficient synthesis of β-hexafluoroleucine along with its use in other systems.
Our results indicate that βGLP-1 analogues had similar efficacies as GLP-1, but
showed diminished activities. Protease stability assays for β-Glu and
β-Leu substituted analogs have revealed that they were more stable than GLP-1,
which holds promise for overall insulinotropic effects of these molecules in
vivo. Our strategies for designing longer lasting analogues of GLP-1 have
been successful to create ligands with similar efficacy for GLP-1R, although stimulation of
signal transduction has not been sufficiently achieved. Due to their efficient binding to
the cognate receptor, GLP-1 analogues described in this study may still yet exhibit
improved glucose lowering properties in vivo. Moreover, using
these constructs as models, further modifications can be made to engineer superior GLP-1
Thesis (Ph.D.)--Tufts University, 2011.
Submitted to the Dept. of Chemistry.
Advisor: Krishna Kumar.
Committee: Clay Bennett, Elena Rybak-Akimova, and David Kaplan.
Keywords: Chemistry, and Biochemistry.read less