Week 5 Part 1 Flashcards
What are the advantages of peptidic drugs?
- High selectivity and potency
- Good efficacy, safety and tolerability
- Mechanism of action well understood
- Predictable metabolism?
- Lower risk of drug-drug interaction
- Well-defined synthesis
- Shorter development time
What are the disadvantages of peptidic drugs?
- Short half-life and fast elimination
- Lower stability
- Sensitive to proteolytic degradation
- Usually not orally available
- SC, IM, Intranasal expensive formulation
- Potential immunogenicity
- High cost of synthesis
What is somatostatin?
- A releasing inhibiting factor released from the hypothalamus
- Suppresses growth hormone secretion
- Plays an important role in pancreatic degradation and other gut function
What gives a very hydrophobic surface of the peptide?
Phenylalanine-phenylalanine and then D-tryptophan
Enable to bind to lipoproteins
Increase half life
What are the factors underlying short half-lives of peptides after I.v. Administration?
- Proteolytic degradation by plasma pro teases or tissue/cell bound proteases
- Rapid clearance by glomerular filtration in kidney
- Tissue endocytosis (e.g. liver) followed by proteosome degradation
- Some small peptide have unusually long half-lives due to binding to plasma proteins
What molecules are readily filtered in the kidney with a glomeruli pore size ~8nm?
Molecules less than 5 kDa
What molecules are less rapidly eliminated?
- Larger polypeptides
What globular proteins are retained in the circulation?
Proteins >50-70kDa with diameter of ~90 A
What does octreotide bind to?
- Lipoproteins
What is NT-proET1 sensitive to?
- Lung proteases
2. Cleaved before it gets to the circulation
What has a really long half-life?
CT-proET-1
What cannot you predict of peptides from?
- Rates of metabolism
2. Size
What is endothelin?
- A very potent vasoconstrictor
- Cause blood pressure change if you inject of 0.7 microgram into rats
- Blood pressure change that lasts for 60 minutes
What is the clearance of endothelin?
- Half life of about 20 seconds
2. Not due to metabolism [very rapid half life due to receptor binding]
What do you need to know the relationship of?
- Circulating half life and biological effect
What is ETB receptor?
- Activation triggers short lasting vasodilation
2. expressed through vasculature on the endothelium - cleared very rapidly in the lungs
What is crucial in process of drug development?
- Understanding biology
- Stability
- clearance mechanism
What is dipeptidyl peptidase 4 (DPP4)?
- A membrane bound peptidase found widely in the vasculature
- Plays a critical role in the degradation of some peptides in the circulation
What are the proteolytic activity of peptide degradation?
- Aspartyl proteases
- Cysteine Proteases
- Serine proteases
- Metallopeptidases
What is Aspartyl proteases?
- Frequently cleave dipeptide bonds between hydrophobic residues
What are examples of Aspartyl proteases?
- Renin
- Pepsin
- Cathepsin D + E
- Presenilins
- Beta-secretases (HIV protease)
What are examples of cysteine proteases?
- Variety of cathepsin, calpain, caspases and ubiquitin specific peptidase
What are examples of serine proteases?
- Trypsin
- Chymotrypsin
- Elastase
- Coagulation factors
- Thrombin
- tPA
- uPA
- Plasmin
- Dipeptidyl peptidase 4 (DPP4)
What are examples of metallopeptidases?
- Amino- and carboxy-peptidases
- Ace
- Neprilysin
- Matrix metallopeptidase
- ADAMTs
- ADAM peptidase families
What can you do with multiple peptidase?
Incubation
What do peptides have in the circulation?
- Poor cell penetration
What is the most relevant proteolytic activity?
- Cell surface peptidases
- membrane anchored
- transmembrane - Soluble circulating peptidases
What are the stability ways to investigate the predict routes of peptide metabolism?
- Incubation with whole blood
- Endothelial cells
- Systemic administration
What are the strategy to prevent enzyme degradation?
- Modification of N- and C-termini
- Chemical modification of side chains, side chains substitution
- Backbone modification including use of D-amino acids
- Peptide cyclisation to increase peptidase resistance
What is the strategies for slow clearance?
- Conjugation to polymers
- Linkage/fusion with long-lives proteins
- Albumin tags
What is the most commonly observed modification of peptide (peptide resistance)
- The amide group
What is important in biological activity?
- Amino acid side group
What is important thing of D-amino acids?
- Reducing susceptibility to peptidases
What does D-amino acids change?
- The relative positions of side-chains groups on amino acids
- Cause a conformational change in the peptide backbone
What is the impact of D-amino acid Substitution?
- Reduced accessibility of peptide bonds
- Reduced affinity for specific peptidases (increased stability)
- No change, or an increase or decrease in biological activity depending on the role of specific residues in receptor binding
What is an example of a modified peptide?
- Desmopressin
What are the 2 critical modifications of Desmopressin?
- Arg8 change in L- to D-form
- retains biological activity in the V2 receptor
- eliminates side effect of raising blood pressure on V1 - Removal of N-terminal amino group
- cyclic peptide
- naturally occurring C-terminal amuse
What is Gonadotropin releasing hormone?
- Peptide that is released from hypothalamus into portal circulation between hypothalamus and anterior pituitary
exploiting biological effects on the pituitary
- De-sensitise the pituitary
- no LH/FSH being secreted - Use smaller doses of gonadotropin releasing hormone agonist which stimulates the pituitary
How do you block LH secretion?
- Give very high dose of GnRH which after receptor de-sensitisation and hence lose LH production
What is another area of exploitation when developing peptide medicine?
- Know something about the evolution of that peptide
2. Phylogenetic insights tells you which amino acids are likely to be critical in biological mechanism
In mammals
- GnRH is fully conserved
What was N-terminal Sequence critical for?
- Receptor binding
2. Biological activity
What did research show about glycine?
- If you changed it to D-amino acid, you convert GnRH into super agonist
- Much more potent in their receptor binding and receptor activation
What was the first GnRH agonist to be licensed
Buserelin
What was the simple modification done on Buserelin?
- Substitution of glycine via tertiary butyl-serine in the D-amino acid form
- At C terminal end, glycine has been changed to a amide structure (ethyl-amide)
What is Buserelin?
- A superagonist
- Used since 1984
- 20-170 times more active than GnRH for
Inducing LH and FSH
What are the formulation of Buserelin?
- Nasal spray
- Injection
- Implant
What are the Therapeutic indications of Buserelin?
- Female infertility
- Breast cancer
- Endometrial hyperplasia
- Endometriosis
- Uterine fibroids
- Prostate cancer
What is an example of GnRH antagonist?
- Degarelix
What does the structure of Degarelix retain?
- Structure retains C terminal amino acids/analogies important for receptor binding
- Modification in N terminal to receptor binding but avoid receptor activations
What are the therapeutic use of Degarelix?
- Androgen-deprivation therapy in hormone dependent prostrate cancer
- Administered by s.c. Injection
What are venoms?
- A source of biologically active peptides
2. Lead molecules for drug discovery
What does many snakes contain?
- Small proteins called disintegrins which are antithrombotic
- Strongly inhibits platelet aggregation
What do these small proteins of snake venom contain and what does it inhibit?
- Amino acid sequence RGS (Arg-Gly-Asp)
2. Inhibit fibrinogen binding to GP IIb/IIIa
What do the RGD-containing venom disintegrin also bind to?
- Other integrin such as a51B1 (fibronectin receptor)
- AvB3 (vitronectin receptor)
- Lack specificity for GP IIb/IIIa
What is barbourin?
73 amino acid disintegrin from the venom of southeastern pigmy rattle snake Sistrurus barbiuri which selectively inhibits fibrinogen binding to GP IIb/IIa and does not bind to other integrin through RGD-ligand sites
What does selectivity of barbourin for GP IIb/IIIa due to?
- KGD (Lys-Gly-Asp)
What does activity of barbourin and other disintegrin depend on?
- Tertiary structure resulting from multiple disulphide bridges
What is Barbourin unsuitable for?
- Therapeutic because of size, structural complexity and potential antigenicity
What are GLP-1 receptor agonist?
- Class of drugs increasingly used for treating type 2 diabetes
What did snake venom lead to?
potentiating peptide from Bothrops jararaca led to ACE inhibitors
What is crucial for angiotensin?
Enzyme system that degraded bradykinin
Snake venom
Anticoagulant
Gila monster
GLP1 agonists
Cone snails
conotoxins
What does activity of Barbourin and other disintegrin depend on?
- Tertiary structure resulting from multiple disulphide bridges
Why is barbourin unsuitable as a therapeutic?
- Size
- Strucutral complexity
- Potential antigenicity
What is Eptifibatide?
Short peptide
7 amino acids long
What is Eptifibatide stabilized by?
disulfide bridge
What does H-arginine retain?
Lysine specifity
Retains the other amino acids critical for binding
Why is proline introduced?
Makes the sequence more compact
What is the indications of Eptifibatide?
- Teo reduce the risk of acute cardiac ischemic event in patient with unstable angina
- Receive non surgery medical treatment
- Undergoing percutaneous coronary intervention
What is formulation of Eptifibatide?
Infusion
What are the features of synthetic peptide for Eptifibatide?
- No N-terminal NH2-group
- C-terminal amide
- Cyclic peptide (disulfide bridge)
- Proline constraint on peptide backbone
Why is GLP-1 agonist used?
Modification to improve stability and half life
Money to treat life-style disease
➢ Diabetes market set to reach $60bn globally by 2025 based on 9 major world markets
What are GLP-1 receptor agonist?
A class of drugs increasingly used for treating type 2 diabetes
Features of GLP-1 agonist
➢ Currently 5-marketed drugs in this class, all injection formulations, representing more than $2 billion in 2013 global sales
What is the market size for GLP-1 agonist expected to reach?
Nearly $8 billion by 2020
What does peptide exendin 4 have?
Anti-diabetic effect
But it cause hypoglyemia as it stimulated insulin release
What is Exenatide?
First of GLP-1 agonist to be licensed
What is exenatide?
- GLP-1 agonist medication
- Belonging to the group of incretin mimetics
- Approved in 2005 for treating type 2 diabetes mellitus by subcutaneous injection
What is exenatide a synthetic version of?
- Exendin 4
- A hormone found in the saliva of Gila monster
- 39-amino acid peptide
- Insulin secretagogue with glucoregulatory effect
How is exenatide manufactured by?
Chemical synthesis
What is therapeutic advantage of exenatide ?
Resistant to breakdown by DPP-IV
What is an advantage of Exendin-4?
Resistance to dipeptidyl peptidase 4 degradation
How is Exenatide used?
- Injected s.c. twice daily
or on a weekly basis with a long-acting formulation
What are approved GlP-1 receptor agonist
- Exenatide
- Liraglutide
- Albiglutide
- Dulaglutide
- Lixisenatide
- Semaglutide
What is Liraglutide?
First GLP-1 agonist to be licensed
What is difference of Liraglutide to GLP1?
They had a modified with a palmitic acid (C16) side chain to promote binding to albumin to increase its half-life from a few minutes to 10h
Liraglutide
typical albumin tag- fatty acid side chain that makes it stick to albumin and gives it a longer circulating half life
What is rationale for Liraglutide?
Albumin acts as a carrier for fatty acids
What is average half life for Liraglutide?
10 hours
What does Albiglutide have?
2 copies of GLP-1 at the N terminal of albumin
What is Albiglutide?
- GLP-1 analogue linked to albumin
2. 645 amino acid protein with 17 disulfide bridges
What are 2 copies of modified human GLP-1?
- Amino acid 1-30 and 31-60
What is the synthesis of Albiglutide?
- Bioengineered in yeast
- saccharomyces cerevisiae
- Recombinant DNA technology
After S.c. injection what does Albiglutide reach?
Maximum blood concentration after 3-5 days with steady state achieved 3-5 weeks
What is the half life of Albiglutide?
4-7 days
Allow once- weekly administration
What is Dulaglutide?
GLP-1 agonist consisting of GLP-1 (7-37) covalently linked to an Fc fragment of human IGg4
Used for treating type 2 diabetes with once weekly administration
What is Lixisenatide?
6 lysine C-terminal extension which improves the half life to 2-4 hours
What is Semaglutide?
Has lys swapped for arginine to make it a more simple target for modification of side chain
