Cancer Bio (Garrett Lecture 1 - Drug discovery) Flashcards
What are some features of normal cell vs cancer cells?
Normal cells:
- Reproduce exactly
- Undergo contact inhibition
- Stick together in correct place
- Become specialized or mature
- Undergo apoptosis if too damaged
Cancer cells:
- Don’t reproduce themselves exactly
- Don’t obey contact inhibition
- Don’t stick together, don’t always remain localised
- Don’t specialize
- Don’t always undergo apoptosis
What in the definition of neoplasia?
New growth of cells
What is the definition of a tumour?
Swelling of a part of the body, usually caused by abnormal cell growth
What are the 2 types of tumour?
Benign
Malignant - malignant neoplasm termed cancer
Define benign and malignant neoplasms by these criteria: Size, borders, differentiation, growth rate, dividing cells, necrosis, invasion, metastasis
Benign:
- Small
- Well defined borders
- Resembles tissue of origin
- Slow growth
- Dividing cells rare
- No necrosis
- No invasion
- No metastasis
Malignant:
- Large
- Ill defined borders
- Variable differentiation
- Rapid growth
- Dividing cells common
- Necrosis
- Invasion
- Metastasis
What is a carcinoma? Give an example
A cancer derived from epithelial cells
e.g skin, bowel
What is a sarcoma? Give an example
Cancers derived from connective tissue
e.g Liposarcoma, derived from adipose tissue
What is a mesothelioma?
Cancers derived from mesothelioma cells
What are the mesothelioma cells? What structures do they form?
Cells that cover outer surface of most internal organs
- Form lining called mesothelium
Mesotheliomas are commonly associated with exposure to what?
Asbestos
What is a melanoma?
Cancers derived from melanocytes in skin
What are leukaemias?
Cancers of blood forming cells, involving bone marrow
What are lymphomas?
Cancers of the lymphatic system
Derived from cells of lymphoid tissue i.e lymph nodes, glands and lymph organs (e.g. spleen, thymus)
What are the 3 steps in ‘The patients journey’ with cancer?
Detection
Diagnosis
Treatment
What are the 2 main types of cancer drugs (systemic therapy)?
1) Cytotoxic drugs
2) Molecular targeted drugs
- small molecules
- biologicals e.g. antibiotics
How were Nitrogen mustard drugs first identified?
- 1919, Krumbharr published that mustard gas caused significant decrease in white blood cell count
What did Gilman and Goodman do in the 1940’s?
Tested nitrgoen mustards as a treatment for blood cancers e.g hogkins lymphoma
What are the characteristics of modern nitrogen mustard drugs? Give some examples
- Operate by interfering with synthesis, structure and function of DNA or mechanisms of cell division leading to DNA damage
- Have small therapeutic window due to normal cell toxicity
- Have side effects
Chlorambucil - CLL, NHL
Melphalan - Ovarian, breast
What are molecular targeted cancer drugs? How do they work?
- Identify genes that are altered in cancer and produce a deregulated protein that is directly responsible for the initiation/progression of cancer
- Develop drugs that bind and block protein activity
- More effective and less toxic to normal cells
How can patients be selected for molecular targeted drugs?
Diagnostic test:
- Identify patients with gene alteration
Give 2 examples of novel small molecule drugs acting on molecular targets
1) Imatinib
- used in CML
- Inhibits BCR-ABL fusion protein
- encoded by Philadelphia chromosome
2) Vemurafenib/PLX4032
- Targets BRAF V600E protein
- Found mutated in approx 50% of melanomas and 8% of solid tumours
How can BCR-ABL and BRAF V600E mutations be diagnosed?
BCR-ABL:
- FISH or PCR for detection of BCR-ABL gene
BRAF V600E:
- PCR based analysis
What is the main problem with molecular targeted drugs?
Drug resistance
What makes a good cancer drug target?
1) Target validation - target knockdown blocks cancer proliferation - target is present in cells
2) Drugability of target - is there somewhere for the drug to bind
3) Opportunity for structure-based approach
4) Practicalities of a screen
5) Availability of assays to detect target activity in the cell
6) Diagnostics
- ability to test whether patient has drug target
Explain how BRAF matches each criteria as a good drug target
1) Therapeutic validation:
BRAF mutated in mutiple cancers and 50% of melanoma
Common mutation = V600E
2) Drugability of target - enzyme kinase, has ATP binding pocket - can design drugs that mimic ATP
3) Opportunity for structure-based approach
- crystal structure observed
4) Practicalities of a screen - RAF protein available for assay
5) Availability of assays to detect target activity in the cell
- ELISA available for detection of pMEK, pERK (BRAF phosphorylates MEK, which in turn phosphorylates ERK)
6) Diagnostics
- Detection of V600E mutation by PCR assay
Who make cancer drugs? Give examples
1) Pharmaceutical companies
- Roche
2) Biotech companies
- Astex pharmaceuticals
3) Academic/charitable organisations
- Cancer research UK
- The institute of cancer research
What type of molecule is BRAF?
Serine/threonine protein kinase
What is Plexxikon?
Structure based drug design company
What do protein kinases do?
Transfer the terminal phosphate of an ATP onto a substrate
- Tyrosine kinases transfer to tyrosines
- Serine/threonine kinases transfer to serine or threonine
What was developed in the early 2000s that helped in the development of a BRAF kinase inhibitor?
- Basic scaffold structures that could inhibit kinases
- Contain 2 nitrogens that can hydrogen bond to the ATP binding doman
What was the problem with the early structures developed in the early 2000s?
None could selectively bind to BRAF or other kinases altered in cancer
What was the initial aim of Plexxikon in designing a BRAF inhibitor?
- Aim was to find a chemical scaffold that binds to a kinase pocket in one orientation
How did they tackle this aim?
Screened 20,000 scaffold-like compounds of a small molecular weight with 5 different kinases
What were the initial findings?
- 100 structures showing bound compounds were seen
- One structure revealed binding of 7-azaindole to ATP binding site of Pim-1, but in multiple orientations
- Identification of a 3 amino phenyl analouge of 7-azaindole that bound in 1 orientation
What did they then do after the discovery of the 3-amino-phenyl analouge of 7-azaindole?
- Built a library of mono and di-substituted analogs of the 7-azaindole core, with substitutions at positions 3,4 and 5
What did they find from these substitutions?
- Screening showned a compound with a difluro-phenylsulfonamide motif
- Bound specifically to oncogenic BRAF and not to wild type or other kinases
Further optimisation led to the discovery of what drug?
PLX4302 (Vemurafenib)
In Late Stage Preclinical Development, what is formulation and toxicology?
Formulation:
- Determining drug delivery
- Formulate drug as tablets, capsules or injections
Toxicology:
- Checking to see if there are any long term side effects
e. g. heart problems, blindness, kidney/liver failure
Breifly explain the purpose of phase 1,2 and 3 clinical drug trials
Phase 1:
- Is the treatment safe
- Any harmful effects
- Dosages
Phase 2:
- Look at how treatment works
Phase 3:
- Treating new treatment against existing treatments
Completion on phase 3 trials submitted for registration with EMA (europe) or FDA (USA)
Who will take part in phase 1 clinical trials? Where will they be?
- Patients who have failed treatment for their particular cancer, willing to volunteer and are fit enough
- In a specialised Phase 1 Unit (Medicines and Health Products Regulatory Authority (MHRA) approved)
When was Vemurafenib approved as a registered drug? What cancers was it approved for?
- August 11th 2011
- FDA approved
- Use in patients metastatic melanoma with the BRAF V600E mutation
What was the median progression free survival for verurafenib compared to current treatment?
5.3 months compared to 1.6 months
What was a major problem in some patients treated with vemurafenib?
Acquired drug resistance
Name some ways that cancer cells can get around BRAF inhibition
RAS signalling pathway alterations:
Normally:
RAS –> BRAF –> MEK
–> ERK –> Proliferation and survival
1) ARAF or CRAF elevation
- Work in place of BRAF
2) Upregulation of alternative signalling pathway e.g PI3K
What is translational research?
Clinical evaluation of a drug and then using this info to change/improve treatment
What is a curret technique for overcoming vemurafenib resitance in melanoma patients?
Personalised medicine by drug combinations:
- Taking tumour and assessing resistance mechanisms
- Designing drug combinations that inhibit resistance mechanisms
e.g patient with upregulated PI3K signalling, giving BRAF and PI3K inhibitors
Sometimes given as a pair from initial treatment
Sometimes BRAF inhibitor used first and second inhibitor introduced later
