3. Medicines Design Flashcards
Describe stages of Carcinoma of the prostate
- Normal prostatic epithelium
- Low-grade prostactic intraepithelial neoplasia
- High-grade prostactic intraepithelial neoplasia
- Metastatic prostate cancer
- Androgen-independent cancer
Statistics about Prostate (JUST READ)
- 1 in 8 in the UK will get prostate cancer at some point in their lives
- Your risk increases with age (over 50 yrs old)
- Family history and genes
- Black men are more likely to get prostate cancer than other men
What are the options for treatment of Prostate Cancer?
- Watchful waiting
- slow-growing tumours in frail men - Active surveillance
- small tumour confined to prostate - Surgery
- frequently used but major side-effects - Chemotherapy
- hormone-dependent tumours - Chemotherapy
- hormone-independent tumours - High-intensity focussed ultrasound (HIFU)
- de-bulking - External beam radiotherapy
- small tumours confined to prostate - Permanent seed brachytherapy
- tumours confined to prostate
How does Testosterone promote proliferation?
- Testosterone (T) binds to the androgen receptor (AR)
- This causes a conformational change in the AR
- This complex translocates to the nucleus, where it signals for proliferation
Name drugs that bind to androgen receptor
Flutamide
- Bacteriostatic, later found to have anti-androgenic activity. Now little used for prostate cancer. Hepatotoxic
Nilutamide
- Developed from flutamide, Less hepatotoxic
Bicalutamide
- Binding mode to AR known, introduced 1995. Widely used
Enzalutamide
- Approved in 2012. Now supplanting bicalutamide. Rare CNS toxicity
How does Bicalutamide act at androgen receptor
- Bicalutamide (Bic) binds to the androgen receptor (AR) but does not cause conformatonal change
- Testosterone is blocked from binding
- The Bic-AR complex is internalised but cannot translocate to the nucleus
- Bicalutamide has some agonist activity, especially at mutant AR
How does Enzalutamide act at androgen receptor?
- Enzalutamide (Enz) binds to the androgen receptor (AR) but does not cause conformational change
- Testosterone is blocked from binding
- The Enz-AR complex is internalised but cannot translocate to the nucleus
- Enzalutamide has no agonist activity
How does Testosterone bind to androgen receptor?
How does Bicalutamide bind to androgen receptor?
Testosterone binds through…
- H-bonds
- Hydrophobic interactions
Bicalutamide binds through…
- H-bond to Arg752, Asn705
- ‘does not’ H-bond to Thr877
- hydrophobic side-pocket
Describe biosynthesis of testosterone
- Cholesterol
—> Pregnenolone
—> Progesterone by 3beta-HSD (hydroxysteroid dehydrogenase)
—> 17a-OH-Progesterone by 17a-Hydroxylase
—> Androstenedione by 17,20 Lyase
—> Testosterone by 17b-HSD (hydroxysteroid dehydrogenase)
What are the drugs that inhibit CYP17A1?
Ketoconazole
- non-specific inhibitor of CYPs, Antifungal
Abiraterone
- selective inhibitor of CYP17A1
Abiraterone acetate
- prodrug of abiraterone
How does Prosgesterone bind to CYP17A1?
C=O forms H-bond to Asn202
Hydrocarbon part of steroid binds to hydrophobic hydrophobic side-chains
Anti-androgens Summary (JUST READ)
- Many early prostate cancers require testosterone to grow
: Androgen-dependent - Advanced prostate cancers lose this dependence
: Androgen-independent - Androgen-dependent cancers can be treated by blocking the androgen receptor
: Flutamide, Nilutamide, Bicalutamide, Enzalutamide - Binding to AR through H-bonds & hydrophobic interactions and in side-pocket
- Androgen-dependent cancers can be treated by inhibiting the biosynthesis of Testosterone in the testes and in the adrenals
: inhibition of CYP17A1
: Ketoconazole, Abiraterone, Abiraterone acetate - Binding to CYP17A1 through ligation to Fe, H-bonds & hydrophobic interactions; complementarity of shape; prodrug
20 Amino Acids Summary (JUST READ)
Alanine (Ala)
- Small, Non-polar, No H-bonds, Neutral, Chemically unreactive
Arginine (Arg)
- Medium, Polar, H-bond donor, Basic[cation], weak electrophile/nucleophile
Asparagine (Asn)
- Small, Polar, H-bond donor & acceptor, Neutral, Chemically unreactive
Aspartic acid (Asp) - Small, Polar, H-bond acceptor, Acidic[anion], Nucleophile
Cysteine (Cys)
- Small, Non-polar, No H-bonds, Weak acid, Powerful nucleophile, reducing agent, forms radicals readily
- Disulfide bridges in proteins
: the only covalent link in tertiary structure of proteins
Glutamine (Gln)
- Medium, Polar, H-bond donor & acceptor, Neutral, Chemically unreactive
Glutamic acid (Glu) - Medium, Polar, H-bond acceptor, Acidic[anion], Nucleophile
Glycine (Gly)
- Small, Non-polar, No H-bonds, Neutral, Chemically unreactive
Histidine (His)
- Large, Polar, H-bond donor & acceptor, Weak base[cation], Nucleophile
Isoleucine (Ile)
- Medium, Non-polar, No- H-bonds, Neutral, Chemically unreactive
Leucine (Leu)
- Medium, Non-polar, No H-bonds, Neutral, Chemically unreactive
Lysine (Lys)
- Large, Polar, H-bond donor, Basic[cation], Nucleophile
Methionine (Met)
- Medium, Non-polar, No H-bonds, Neutral, Weak nucleophile
Phenylalanine (Phe)
- Large, Non-polar, No H-bonds, Neutral, Chemically unreactive, Aromatic (pi-stacking)
Proline (Pro)
- Medium, Non-polar, No H-bonds, Neutral, Chemically unreactive, Cyclic (secondary amine)
Serine (Ser)
- Small, Polar, H-bond donor & acceptor, Neutral, Nucleophile
Phosphoserine
- Medium, Polar, H-bond acceptor, Acidic, Anion
Threonine (Thr)
- Medium, Polar, H-bond donor & acceptor, Neutral, Nucleophile
Phosphothreonine
- Medium, Polar, H-bond acceptor, Acidic, Anion
Tryptophan (Trp)
- Large, Non-polar, H-bond donor, Neutral, Chemically unreactive, Aromatic
Tyrosine (Tyr)
- Large, Polar, H-bond donor, Weak acid, Nucleophile, Aromatic
Phosphotyrosine
- Medium, Polar, H-bond acceptor, Acidic, Anion
Valine (Val)
- Medium, Non-polar, No H-bonds, Neutral, Chemically unreactive
Describe Antimetabolites
- Antimetabolites kill (cancer) cells by inhibiting a critical cellular process
- Antimetabolites are usually inhibitors of enzymes
- Biosynthesis of DNA is essential to proliferation of tumour cells
: therefore, most antimetabolites are inhibitors of critical enzymes involved in DNA biosynthesis
What are the 4 main groups of antimetabolite drugs?
Folate ‘antagonists’
- e.g Methotrexate, non-classical lipophilic antifolates, pemetrexed, raltitrexed
Pyrimidine ‘antagonists’
- e.g 5-Fluorouracil (5-FU), fluorodeoxyuridine (FdURD), azacytidine
Purine ‘antagonists’
- e.g 6-Mercaptopurine, thioguanine, tiazofurin
Sugar-modified nucleosides
- e.g Cytarabine (Ara-C), fludarabine, gemicitibine
Describe analogues of folate antagonists regarding its action of antimetabolites
Analogue of dihydrofolate
- binds to DHFR (dihydrofolate reductase) at folate-binding site
Very potent competitive inhibitor of DHFR
Too polar for passive diffusion into cells
- taken up through reduced folate carrier (RFC)
Must be polyglutamylated to be retained in cells
Often used in high-dose regimen, with leucovorin (folate) rescue of normal cells
Widely used drug against many cancer types
Describe actions of lipophilic antifolates
- Enter cells by passive diffusion
: don’t need RFC (Reduced Folate Carrier)
What does Azacytidine do?
- Weak inhibitor of TS (Thymidylate Synthase)
- Phosphorylated to form azacytidine triphosphate, then incorporated into RNA
- Mimics C in RNA but unstable and decomposes, causing damage to RNA
- Inhibits DNA methyltransferases (epigenetic effects)
Describe inhibition of biosynthesis of purine nucleosides
- TAD (from Tiazofurin) inhibits by binding at NAD+ binding site
- Thio-IMP (from 6-MP) and Thio-GMP (from 6-TG) inhibit by binding at purine-binding site
Give an examples of Sugar-modified nucleoside
Cytarabien (Ara-C)
- Converted to triphosphate
- Triphosphate inhibits DNA polymerases as analogue of dCTP
- Some incorporation into DNA, making DNA non-functional
Fludarabine
- Converted to triphosphate
- Triphoshate inhibits DNA polymerases as analogue of dATP
Gemcitabine
- Converted very efficiently to triphoshate F2dCTP
- Triphosphate F2dCTP inhibits DNA polymerases as analogue of dCTP
- 100x more potent than Ara-C
REMEMBER
- dCTP is a feedback inhibitor of dCK, so depletion of dCTP actiavtes dCK
- Activation of dCK increases formation of F2dCMP from gemcitabine
What are Microtubules and how is it regarded with cancer therapy?
- responsible for maintaining the structure of the cell and for seperating the sets of chromosomes during mitosis
- interfering with the formation and remodelling of microtubules inhibits mitosis and, therefore, proliferation of cancer cells
Describe structure of Microtubules
- Microtubules are assemblies of tubulin dimers
- Each tubulin dimer has one alpha and one beta subunit
How does Mitotic spindle poison interfere with Microtubules?
- Microtubules are in dynamic equilibrium with individual tubulin dimers
- Mitotic spindle poisons interfere with this dynamic equilibrium
What are Vinca Alkaloids?
- Vinblastine binds to + end of microtubule, capping it and preventing new tubulin dimers from adding
- Vinca alkaloids bind strongly to individual tubulin dimers, causing conformational change and preventing binding to microtubules
- Individual complexes of vinca alkaloid and tubulin dimers condense into paracrystalline aggregates
- Le Chatelier’s Principle applies
: microtubules shrink
Give 3 examples of Vinca Alkaloids
Vincristine (R=CHO)
Vinblastine (R=ME)
Vindesine
What are Taxols? And give 2 examples
- Taxols bind to taxol-binding sites on the inside surface of the microtubule, preventing disassembly
- Inappropriate microtubules remain
- Concentration of free tubulin dimers decreases
- The low concentration of free tubulin dimers means that new microtubules cannot be assembled
Paclitaxel (taxol), Docetaxel (taxotere)
What are Colchicine-like drugs?
- Colchicine binds to cholchicine-binding sites on the b-tubulin, disfavouring assembly of protofilaments
- Colchicine bound at colchicine-binding sites on b-tubulin in microtubules disfavours disassembly of inappropriate microtubules
What is Poly(ADP-ribose) [PAR]
- After DNA and RNA, poly(ADP-ribose) [PAR] is the third nucleic acid in the mammalian cell
- First observed in 1963; structure determined in 1967
- Polyanionic polymer built from ADP-ribose units derived from NAD+
- Usually built onto Glu side-chains in target proteins
- MW varies with PARP isoform
: upto 100KDa for PAR built by PARP-1 - Linear or branched
What is Poly(ADP-ribose)polymerase-1 [PARP-1]?
- Enzyme mainly found in the nuclei of cells
- Abundant in most cells (ca. 2x10^6 molecules cell^-1)
- 116 KDA protein
Describe therapeutic application of inhibition of PARP-1 in..
- Potentiation of radiotherapy and cytotoxic chemotherapy of cancer
- Radiotherapy of cancer causes DNA strand breaks
- Electrophilic cytotoxic drugs (e.g mustards) cause DNA damage
- Inhibitors of topoisomerase II (e.g doxorubicin) cause DNA single-strand breaks by inhibiting the strand re-joining step
- If the tumour cells can repair the DNA before it is required, then cells survive
- Inhibition of PARP-1 inhibits DNA repair
- Inhibition of PARP-1 potentiates radiotherapy and DNA-targeted chemotherapy
Describe therapeutic application of inhibition of PARP-1 in..
- Reduction of organ damage following ischaemia/reperfusion injury
- When the supply of blood to an organ is interrupted, the cells become hypoxic
- Reperfusion with blood causes rapid resupply of O2 to the hypoxic cells
- O2 is an oxidising diradical and damages DNA
- PARP-1 is over-activated
- Cells are depleted of NAD+ (also important in production of energy)
- Cells die
- Organ failure
How does PARP-1 recognise DNA?
- through Zn fingers
- The thiols of three Cys and the imidazole of one His in the DNA-binding domain of PARP-1 bind to a Zn2+, fixing the conformation of the protein
- The NAD+ binding domain is at the C-terminal of the protein
- Inhibitor olaparib binds at the NAD+ binding site
Describe DNA-damaging therapies
Therapy
1. Radiotherapy
: radiation, bleomycin
- Mono-alkylators
: alkylsulfonates, nitrosoureas, temozolomide - Cross-linkers
: N-mustards, mitomycin C, platinum drugs - Topoisomerase inhibitors
: camptothecins, etoposide - Replication inhibitors
: aphidicolin, hydroxyurea
What drug is Olaparib?
- Inhibits PARP-1, PARP-2, PARP-3
- Clinical trials as a single agent started 2005
- Approved for BRCA-mutant ovarian cancer
What drug is Rucaparib?
- Inhibits PARP-1, PARP-2, Tankyrase-1, Tankyrase-2
- Clinical trials started in 2003, in combination with temozolomide
- Approved for BRCA-mutant ovarian cancer
What drug is Veliparib?
- Inhibits PARP-1, PARP-2, not PAPR-3, Tankyrases
- Phase 1-3 clinical trials, in combination and as single agent
- Approval expected in 2018/2019
Describe Epidermal Growth Factor Receptor (EGFR)
Classical tyrosine kinase receptor
- EGF or TGFa binds to the extracellular domain of EGFR
- Ligand-EGFR complex forms an asymmetric dimer
- Signalling cascades trigger proliferation, migration, adheision
Describe EGFR in cancer
- EGFR is implicated in the development and progression of cancer in two main ways
: Overexpression of EGFR
: Activating mutation in extracellular or intracellular domains - Mutations in the extracellular domain can lead to constitutive (EGF-independent) activity of EGFR and are frequently found in flioblastoma
- Mutations in the kinase domain are found in a subset of non small-cell lung cancers (NSCLCs)
- Most common kinase domain mutation is L858R (40% mutations)
- These mutations are driver mutations (i.e they confer a growth advantage on the cells and so drive cancer)
- The particular mutation occuring in an individual tumour is important as it can determine the sensitivity of the tumour to different drugs
- Selecting drugs based on tumour mutation status is an example of personalised medicine in cancer
- Targeted cancer therapy places a huge selective pressure on the target to evolve, and resistance mutations often emerge. Thus we move from first line therapies, which target the initial state, to second line therapies, which target the new mutant etc.