Introduction to kinase drug discovery -H

Question 1

What is a kinase, what are their targets, and examples

Answer 1

E.g., Serine/threonine kinases, Tyrosine kinases,
Dual specificity kinases (e.g., Ser/Tyr)

They are enzymes that transfer the terminal phosphate of ATP to a target. A PTM that controls conformational shape, and protein-protein interactions.

They target hydroxyl groups on serine, threonine, or tyrosine, with there being consensus sequences identifying the target residue for phosphorylation.

Question 2

RTK activation and downstream signalling overview

Answer 2

E.g., insulin, EGF, NGF, VEGF

Involved in cell proliferation, survival and differentiation - metabolic decisions.

Upon receptor activation, the receptors dimerise and tyrosine kinase of one phosphorylates its partner and vice versa.

Signalling proteins are recruited, with the SH2 domains of the protein recognising the phosphorylation-Tyr residues and surrounding AAs. The pattern of AAs and phospho-Tyr mediates the extent of downstream signalling.

RTKs can activate PLC-gamma pathways, PI3-kinase, and the Ras/MAPkinase cascade

MAP kinase pathway is initiated by Grb2/SOS interaction with the phosphorylated EGFR, which activates the small G-protein Ras. Ras initiates the Raf-MEK-MAPK cascade causing alterations to gene expression favouring cell proliferation.

Question 3

Jak signalling cascade mechanisms and role

Answer 3

Involved in immune cytokine (IL6) signalling.

Activation of the IL6R and its gp130 co-receptors leads to recruitment of JAK to the phospho-Tyr as well as recruitment and subsequent phosphorylation of Stat at the phospho-Tyr.

Phospho-Stat dimerises and enters the nucleus to alter gene transcription to favour pro-inflammatory gene expression.

Question 4

Different ways and mechanisms to target catalytic receptors

Answer 4

Targets the enzyme domain, utilising small molecules.
Issues arise to generate selective drugs, given the highly conserved ATP binding site. Furthermore, inhibitors need to work against high [ATP], so they need to be potent. They also need to be able cell permeable.

Targeting the growth factor in kinases. Can generate ligand antibodies, e.g., bevacuzimab, and anti-VEGF drug.

Can target the RTK EC domain, e.g., cetuximab (anti-EGFR) an antibody. Antagonises EGF binding.

Issues of selectivity, delivery of drug, immunogenicity, and resistance still are present with antibody-based therapeutics.

Question 5

Role of Kinases in cancer

Answer 5

Promote proliferation and cell survival. (EGFR)

Angiogenesis (VEGFR)

Invasion and metastasis (cMet)

Immunosuppressive effects (TAM kinases - MER and Axl)

Question 6

Treatment for chronic myeloid leukaemia (CML) and its mechanisms

Answer 6

Imatinib was developed for this. Imatinib is an Abl tyrosine kinase inhibitor.

CML is unregulated growth of myeloid cells in the bone marrow. It is associated with the philadelphia chromosome, where there is translocation of ABL to chromosome 22 (which contains BCR). This is a tumour associated fusion gene that over expresses the kinase BCR-Abl. This drives cell survival and proliferation.

Question 7

Non-cancer uses of kinase inhibitors

Answer 7

Tofacitinib for IBD/Crohn’s disease. A Jak kinase inhibitor that prevents cytokine mediated inflammation. May also have potential in treating immune diseases.

Fasudil, a Rho kinase inhibitor, has also been found effective for cerebral vasospasm.

neflamapimod, a p38 MAPK inhibitor, may have potential in treating AD.

LRRK2 mutations (a kinase) have also been associated with PD.