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Discovery and Development of Anticancer Drugs

Kinase Inhibitors

Protein kinase B (PKB/Akt) is a signal transduction kinase that is part of an important network for transmitting external growth signals to the cell nucleus. Upregulation of the activity of this kinase is a feature of several tumour types.

In collaboration with other teams at The Institute of Cancer Research, London, and Astex Therapeutics (Cambridge) we applied structure-based design techniques to advance hits from a fragment-based screen to generate potent and selective pyrrolopyrimidine PKB inhibitors with oral efficacy in preclinical models. Intellectual property from this project is licensed to AstraZeneca and a pyrrolopyrimidine PKB inhibitor AZD5363 is in Phase III clinical trials.

PKB figure

Evolution of potent and selective, oral PKB inhibitors by fragment growing.

Several kinase enzymes are important in the control of the cell growth and replication cycle.

These enzymes may drive progression through the cell cycle, or alternatively can act as regulators at specific checkpoints that ensure the integrity of DNA replication through sensing DNA-damage and initiating repair, while halting the cell cycle. Many tumours are deficient in early phase DNA-damage checkpoints, due to mutation or deletion in the p53 pathway, and thus become dependent on the later S and G2/M checkpoints for DNA repair.

This provides an opportunity to selectively target tumour cells to enhance the efficacy of ionising radiation or widely used DNA-damaging cancer chemotherapies. Inhibitors of the checkpoint kinase CHK1 are of particular interest for combination with genotoxic agents.

In collaboration with Professor Michelle Garrett (University of Kent, previously at the ICR) and Sareum (Cambridge) we used structure-based design to optimise the biological activities and pharmaceutical properties of hits identified through fragment-based screening against the cell cycle kinase CHK1, leading to the oral clinical candidate CCT245737. 

The candidate potentiated the efficacy of standard chemotherapy in models of non-small cell lung, pancreatic and colon cancer. In collaboration with colleagues at the ICR (Professor Louis Chesler, Dr Simon Robinson and Professor Sue Eccles) and Newcastle University (Professor Neil Perkins), we showed that our selective CHK1 inhibitor had efficacy as a single agent in models of tumours with high replication stress, including neuroblastoma and lymphoma.

CCT245737 was progressed through preclinical development with support from the Cancer Research Technology Pioneer Fund and Cancer Research UK Centre for Drug Development and is in separate Phase I clinical trials as a monotherapy and in combination with gemcitabine. CCT245737 was licenced to Sierra Oncology for clinical development, and renamed as SRA737.

CHK1 figure

Evolution of the potent and selective, oral CHK1 clinical candidate CCT245737.

The checkpoint kinase CHK2 has a distinct but less well characterised biological role to that of CHK1. Selective inhibitors are valuable as pharmacological tools to explore the biological consequences of CHK2 inhibition in cancer cells. In collaboration with Professor Michelle Garrett (University of Kent, previously at the ICR), we used structure-based and ligand-based approaches to discover selective inhibitors of CHK2, including the tool compound CCT241533.

We showed that selective CHK2 inhibition has a very different outcome to selective CHK1 inhibition. Notably, while CHK2 inhibition did not potentiate the effect of DNA-damaging chemotherapy, it did sensitize cancer cells to the effects of PARP inhibitors that compromise DNA repair.

CHK2 figure

Structure-guided design of a novel selective CHK2 inhibitor.

Targeting Protein Homeostasis 

Quality control of protein folding, trafficking and degradation is vital to the survival of cells. Tumour cells are especially dependent on molecular chaperones and related proteins that regulate protein homeostasis.

These are attractive targets for new anticancer therapies. The recent development of strategies to achieve targeted degradation of specific proteins using small molecules that hijack the ubiquitin-proteasome degradation machinery presents a powerful alternative to classical small molecule inhibitors of protein function.

drug targets in protein homeostasis figure

Cancer drug targets in protein homeostasis.

Inositol Requiring 1 (IRE1) is an integral membrane protein in the endoplasmic reticulum which is critical in controlling the unfolded protein response.

This cellular stress response ensures the correct folding, processing, export or degradation of proteins in the endoplasmic reticulum. IRE1 possesses both kinase and endoribonuclease enzyme activity. In response to unfolded proteins in the endoplasmic reticulum, IRE1 is activated and splices the mRNA for the transcription factor XBP1, leading to translation of spliced, active XBP1 protein.

In collaboration with Professor Faith Davies (University of Arkansas for Medical Sciences, previously at the ICR) and Professor Richard Bayliss (Leeds University) we have discovered how inhibitors of the IRE1 kinase act as allosteric activators or inhibitors of the endoribonuclease function through changes to protein conformation and dimerization.

In collaboration with Janssen Biopharma we have developed potent and selective allosteric IRE1 inhibitors for use as chemical tools to explore the biology of this important signalling protein.

 IanCollins Kinase inhibitor IRE1

Depending on the conformation of the kinase domain that they bind to, small molecule kinase inhibitors IRE1 can either promote dimerization and activate the endoribonuclease function, or inhibit both dimerization and the RNase activity.

 

The HSP70 family of molecular chaperone ATPases are expressed in response to heat shock and other cellular stresses. In complexes with other proteins, the HSP70 proteins protect misfolded or unfolded client proteins from degradation, and refold them to restore client activity. HSP70 isoforms are overexpressed in many cancers.

In collaboration with Dr Rob van Montfort we using structure-based approaches to discover and optimise inhibitors of HSP70. A screen of low molecule weight compounds using surface plasmon resonance identified a quinazoline fragment that binds to HSP70. The optimization of this and other fragment hits into more potent molecules is ongoing, guided by crystal structures of the bound ligands.

The amounts of proteins in the cell are controlled by a balance between their synthesis and their degradation. Many proteins are degraded by the proteasome following the attachment of ubiquitin tags by E3 ubiquitin ligase complexes, which recognise certain sequences in the target proteins. Small molecules can bind to some E3 ligases and change the repertoire of proteins they recognise.

This hijacking of the ubiquitin-proteasome pathway provides a way to select proteins for degradation that would otherwise be unaffected. In collaboration with Dr Raj Chopra (formerly at the ICR) and Monte Rosa Therapeutics, we have explored ways to synthesize and identify new molecules that redirect the E3 ligase CRBN to degrade proteins relevant to specific cancer types.

IanCollins molecular glues

Small ‘molecular glues’ or larger bifunctional molecules can bind to the protein CRBN in the CUL4-CRBN E3 ligase complex, modulating the specificity of the E3 ligase for binding to protein substrates and resulting in the ubiquitination and degradation of new targets.

Kinesin Inhibitors

Dividing cells must equally portion the two copies of replicated DNA between daughter cells through the formation of a bipolar mitotic spindle of microtubules during chromosome separation. Kinesins are a family of ATP-dependent, microtubule-binding motor proteins that play important roles in the formation and mechanics of the mitotic spindle.

Many cancer cells have more than two centrosomes, potentially leading to fatal multi-polar spindle formation, but overcome this through clustering of the extra centrosomes to give a pseudo-biopolar spindle. The kinesin HSET (KIFC1) is required by tumour cells to cluster supernumerary centrosomes.

In collaboration with Dr Spiros Linardopoulos, Professor Andrew Tutt (Breast Cancer Now Centre) and a commercial collaborator, we are investigating the discovery and optimisation of HSET inhibitors as a potential new treatment for centrosome-amplified tumours.