What is the description of an ideal drug?
Small molecule featuring high potency, selectivity, few adverse effects, low production costs & administration in a single daily oral dose.
Give an example of a successful GPCR drug target, stating its action, trade name, company, therapeutic effect & world sales.
- Asthma, COPD
- $538 million
Why are GPCRs successful targets for drugs?
- Largest family of related proteins known to exist
- Ligand/drug binding sites accessible at cell surface
- Multiple ways to manipulate GPCR activity
- Amenable to generic high throughput screening methods to identify NCEs
- Still scope for further exploitation
What is the classical pharmacological apprach to drug discovery?
- Behavioural/Pharmacological Effect
- Determine pharmacology of response
- Develop selective agonists/antagonists
- Receptor Purification
- Receptor Cloning & Expression
What is the First-Line Therapy for treatment of HIV/Aids, what is it and how does it work?
Highly Active Anti-Retroviral Therapy (HAART)
- Reverse Transcriptase & Protease Inhibitors
- Block key steps in viral life cycle
- >20 FDA-Approved therapies
In the treatment of HIV/AIDS, why are combination therapy & new drug variants used?
To minimise emergence of drug-resistant HIV Variants.
What properties do new drugs possess in the treatment of HIV/AIDS that older drugs didn't have?
Minimal side effects & novel mechanism.
Until recently, no drug either eradicated or prevented establishment of infection.
What act as HIV co-receptors on macrophages & T-cells?
What property does the membrane protein CD4 possess in terms of HIV-infection?
CD4 was found to be necessary but not sufficient for HIV-1 infection of T-cells, monocytes & macrophages.
Describe the effect of trophic HIV-1 strains.
- T-trophic HIV-1 strains only infected T-cells
- M-Trophic HIV-1 viruses only infected monocytes/macrophages
- Dual trophic HIV-1 strains infected both
- All strains interacted equally effectively with CD4
What were novel GPCRs which acted as HIV co-receptors cloned from and what did their absence/antibody blockade cause?
- Cloned from T-cells and monocytes
- Absence/antibody blockade of GPCRs blocked HIV-1 entry in CD4+ cells
What is CCR5 and CXCR4?
- CCR5 = M-trophic/R5 strain co-receptor
- CXCR4 = T-trophic/X4 strain co-receptor
What are Chemokines?
Polypeptide mediators of directed migration of immune cells: 7-14 kDa
What form of chemokines is biologically active?
What defines the classification of chemokines?
Highly conserved Cys amino acid residues.
What 2 classes of chemokines are there?
CXC Family - The first two NH2-terminal Cys separated by 1 amino acid CXCL1-CXCL16
CC Family - The first two NH2-terminal Cys residues in juxtaposition CCL1-CCL27
Using the examples CCR5 and CXCR4, describe how chemokine and chemokine receptor distribution vary between cell types.
- CCR5 expressed by monocytes, macrophages & T-cells
- CXCR4 expressed predominantly by T-cells
Using the examples CCR5 and CXCR4, describe how one chemokine receptor can interact with one or more chemokines.
- CCR5 binds the CC chemokines MIP1a, MIP1ß & RANTES
- CXCR4 only binds SDF-1
What are the GPCRs CCR5 & CXCR4 on macrophages & T-cells?
Describe the action of CCR5 and CXCR4 as HIV co-receptors.
- CD4 interaction on T-cell/monocyte with HIV protein gp120 allows gp120 to bind co-receptors (CCR5 or CXCR4 chemokine receptors)
- Binding energy from interaction alters conformation of complex & exposes fusion peptide gp41 which leads to membrane fusion & viral entry
- Synthesis of new viral particles precedes their release & destruction of infected cell
Describe the evidence implicating CCR5/CXCR4 as potential ant-HIV drug targets.
- Release of MIP1a, MIP1ß and RANTES from CD8+ T-cells suppresses HIV infection of monocytes & macrophages - these are CCR5 Agonists
- Individual resistance to HIV infection associated with chemokine receptor mutations e.g Homozygous mutation of CCR5 gene with 32 base pair deletion in protein coding region causes no functional receptor protein at cell surface
- No apparent side effect/complications due to CCR5 deletion
Describe how synthetic chemokine agonists can be used as a potential drug strategy.
Agonists induce rapid sequestration & eventual degradation of chemokine receptors away from cell surface.
What are problems of synthetic chemokine agonists?
- Inflammatory side effects (activation of downstream signalling)
- Short biological half-lives
Describe how synthetic chemokine antagonists can be used as a potential drug strategy.
Aimed at blocking gp120 binding sites without promoting downstream signalling/inflammation.
How can targetting tyrosine kinase signalling in solid tumours be achieved?
Through chemotherapy, using tumour cell-targeted drugs.
How does Vemurafenib, a tumour cell-targetted therapeutic drug, function?
Selectively inhibits mutated B-Raf kinase in metastatic melanoma cells.
How does anti-angiogenic therapy target tyrosine kinase signalling in solid tumours?
By using drugs that inhibit growth of vessels that supplty the tumour.
What is the definition of Angiogenesis and what does the process depend on?
Angiogenesis = Synthesis of new blood vessels from pre-existing vasculature
Process depends on endothelial cell migration & proliferation
What are the normal physiological roles of Angiogenesis?
- Wound healing
- Menstruation (uterus lining, maturation of egg during ovulation)
- Pregnancy (placenta)
- Embryonic development
What are the pathophysiological roles of Angiogenesis?
- Tomour growth & metastasis
- Diabetic retinopathy (vasculopathies)
- Rheumatoid arthritis
Describe the 3 steps of angiogenesis & tumour growth.
1. VEGF Production: "Sprouting"
2. Vessel Growth: Development of microvasculature
3. Tumour Growth/Metastasis: Co-opting of existing vasculature
VEGF = Vascular Endothelial Growth Factor
What 2 growth factors have a Tyr kinase domain & so are involved in Tyr kinase signalling?
VEGF (vascular endothelial growth factor)
PDGF (platelet-derived growth factor)
How is VEGF, and so Tyr kinase signalling, important in Angiogenesis?
- Increases endothelial cell migration & proliferation
- VEGF receptors expressed exclusively in endothelial cells
How is PDGF important in Angiogenesis?
- Increases endothelial cell migration & proliferation
- Acts on smooth muscle cells & pericytes to stabilise new vessel growth
In tumours, what causes an increase in VEGF and what negative effect does this have?
- Hypoxia in tumour microenvironment promotes VEGF increase
- Increases tumour vascularisation/growth
How could PDGF & VEGF be useful in fighting tumour development?
Theoretically possible to block enhanced angiogenesis in disease pharmacologically with PDGF and/or VEGF receptor inhibitors.
Describe the uses and action of Sunitunib.
- Approved in 2006 for treatment of renal cell carcinoma & gastrointestinal stromal tumours
- Orally administered small molecule
- Potent ATP-competitive inhibitor of VEGF and PDGF receptor Tyr kinase activity
Why does blocking ATP binding inhibit RTK function?
Ligand binding promotes receptor dimerisation.
Dimerisation-induced conformational change has 2 effects:
- Allows Mg-ATP to bind to each Tyr kinase domain
- Allows one of the ATP-bound tyrosine kinases to phosphorylate tyrosines on the other partner in the dimeric complex - "Transphosphorylation" - causes RTK to become active.
Descibe the uses & actions of Sorafenib.
- Inhibitor of multiple protein kinases
- Used for treatment of renal & inoperable hepatocellular carcinomas
- Orally administered small molecule
- "Targetted Polypharmacology" key to drug's effectiveness
- Potent ATP-competitive inhibitor of VEGF, PDGF & c-Kit receptor Tyr kinase activity
- Also inhibits Raf kinases (required to activate MAP kinase) - Is the first clinically utilised drug to target this pathway
Describe the disease NSCLC (non small cell lung cancer).
- Represents 80% of all lung cancers; most common cancer
- Only 7% survive more that 5 years after diagnosis
- Treatable by surgery in early stages
- Chemotherapy for later stages only marginally effective
Describe the use of human EGF receptor/HER1 in NSCLC.
- Increased understanding of molecular basis of NSCLC revealed importance of human EGF receptor/HER1 signalling
- Over 20 years, several strategies developed to inhibit signalling from mutated/constitutively active HER1
- Rational drug screening using recombinant HER1 Tyr kinase domain to identify small molecule inhibitors of HER1 signalling
- 2 drugs used now - Gefitinib & Erlotinib
Describe the usage of Gefitinib & Erlotinib.
- Gefitinib used from 2003 for metastatic NSCLC in patients who previously received chemotherapy
- Now been superseded by Erlotinib
- Orally administered
- Both drugs are reversible selective inhibitors of HER1 Tyr kinase activity
- Competitively block ATP binding to inhibit downstream signalling
How effective are drugs on patients and why?
On average, drugs only effective in 10-20% of patients.
Certain populations/groups more sensitive to inhibitor treatment than others, due to specific acquired mutation.
Describe why specific acquired mutations determines effectiveness of drug treatment.
- Specific acquired mutations in HER1 Tyr kinase domain found in NSCLC patients responsive to therapy e.g Leu858Arg mutation causes deletion within activation loop
- Mutations increase Tyr kinase HER1 affinity for Gefitinib & Erlotinib
- Occurrence of mutations correlates directly with effectiveness of therapy
By what pharmacological approach are most drugs developed?
Most currently used drugs developed via classical pharmacological approach
[Function → Gene → Medicine]
By what approach is Maraviroc developed and when was Maraviroc developed?
Increasing number of new drugs, like Maraviroc, developed by reverse pharmacological approach.
[Gene → Function → Medicine]
Maraviroc developed after CCR5 identified as HIV co-receptor.