Drug development (an overview with real drugs)

18 important questions on Drug development (an overview with real drugs)

What is background information about chronic myelogenous leukaemia?

- Patients are often asymptomatic diagnosized. Although they have an elevated white blood cell amount on a routine laboratory test.
-  In this way CML must be distingquised from a leukomoid reaction that can give the same results in a routine laboratory test.
- Symptoms of CML could be: a large spleen with pain on the left side, malaise (feeling uncomfortable), joint and/or hip pain, low-grade fever, anemia, increased susceptibility to infections, thrombocytopenia with easy bruishing (kneuzingen)

How does the progress of CML go?

During the first 4 to 6 years the disease is stabile. (the chronic phase)
Then the advance phase dawns consisting of 2 phases; the first phase takes 1 year the second phase is the blastic phase and patients often survive 3 to 6 months in this last phase.

So what is the biggest feature of CML?

It is characterized by an haematological stem-cell disorder that is characterized by excessive proliferation of cells of the myeloid lineage.
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What are genetic aspects of CML?

It is associated with chromosome 22 (philadelphia chromosome) It is a result of a reciprocal translocation between chromosome 22 and chromosome 9. It is detected in 95% of patients with CML. After this the chromosome (BCR ABL) posesses dysregulated kinase activity

What are the molecular mechanisms behind CML?

There is a tyrosine kinase that needs ATP to become activated. Normally, this kinase controls the cellular proliferation, differentitation and motility. It is highly regulated.
A dysregulation of this kinase is linked to a variety of human cancers.

What are aspects for CML disease in such a way that it can be studied?

- There is a clear difference between normal cells and leukaemic cells.
- It is easy measurable in vitro biochemical and cellular assays. (ATP meassurements)
-   There are cell lines available with same chromosomal abnormalities.

This together means that is ideal for in vitro and animal studies.

What was the bioavailability of Glivec?

rat: 6- 82%
monkey: 19 - 55%
humans: more than 98%

What are the five difficulties when we try to extrapolate data from in vivo animal models to in vivo human models?

1) The expression level
2) substrate specificity
3) regulation
4) organ specificity
5) toxicity

How was the distribution of Glivec in rats and mice?

Rats:
- placental transfer
- It can also come into the milk
Mice:
- Almost no brain distribution
- Highest levels in kidney, liver and lung

What is the protein binding in rats, humans, mice and monkey's?

rats: 95%
humans: 98%
Mice: 98%
monkey's: 90%

How is the metabolism of glivec?

It's the same metabolism in humans, dogs and rats. It goes via CYP3A4 and the end metabolite is an N-demethylated piperazine derivative. Only 1 CH3 group is splitted. Besides this enzyme also other enzymes play a role in this like CYP1A2, CYP2D6, CYP2C9 and CYP2C19.

In addition human in vitro microsome studies show that Glivec is a competitive inhibitor of cyp3A4/5, CYP2D6 as well as CYP2C9.

What is the NOAEL in rats and monkey's of Glivec?

Rat: 5  mg/kg/day
monkey: 15 mg/kg/day
in a 13 weeks orally toxicity study.

How does the discovery pathway of glivec go?

1) Disease pathology
2) Pharmacological or biochemical target
3) Molecular target
4) Structure elucidation
5) Drug design
6) Screening assay
7) Chemical leads

What were other targets of Gleevec found by in vitro screening?

- c-KIT: this has something to do with gastrointestinal stromal tumors.
- PDGF receptor: it probably has a role in the tumorigenisis and in the fibrosis.

What is drug targeting?

This results in:
- less site effects
- increasing local concentrations at the target site 
- Providing slow local drug release

What are cells frequent cells in the liver?

- hepatocytes
- Kupffercells
- stellate cells: it is involved in liver fibrosis
- endothelial cells

How does liver fibrosis occur?

1) a hepatocyte gets injured
2) This hepatocyte activates endothelial cells, stellate cells and Kupffer cells.
3) Both endothelial cells and Kupffercells also activate Stellate cells.
4) Once a stellate cell is activated it becomes a myofibroblast
5) The collagen production is activated and fibrosis starts
6) In the liver fibrosis can turn into cirrhosis in which stage a patient needs a donor organ.

What are the mechanisms of resistance to Glivec in CML?

- Efflux of Glivec due to for example PgP-associated MDR protein.
- Protein binding of Glivec for example to circulating AGP

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