Structure-Activity Relationship study of inhibitors of Eg5 –- a drug target for cancer chemotherapy


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Kristal Kaan1, Johanna Weiss2, Dominik Menger2, Venkatasubramanian Ulaganathan1, Katarzyna Tkocz1, Christian Laggner4, Florence Popowycz3, Benoît Joseph3, Frank Kozielski1
1The Beatson Institute for Cancer Research, Glasgow, United Kingdom,2University Hospital Heidelberg, Heidelberg, Germany,3Institut de Chimie et Biochimie Moléculaires et Supramoléculaires, Villeurbanne, France,4University of Innsbruck, Innsbruck, Austria

Background

The mitotic spindle is a validated target for cancer chemotherapy. Drugs such as taxanes and vinca alkaloids interfere with microtubule dynamics and cause the mitotic spindle to collapse. However, toxicity and resistance are clinical problems associated with these drugs. Thus, alternative approaches to inhibiting the mitotic spindle are currently being pursued. Eg5 – a kinesin involved in the formation of the bipolar spindle in proliferative cells – has received much attention as a drug target for cancer chemotherapy, with seven inhibitors in clinical trials.

Method

We employ an iterative structure-based drug design method to further improve the potency and drug-like properties of the inhibitors. To this end, we synthesised inhibitor analogues and tested their efficacy in-vitro. We also performed a multidrug resistance study in cell lines over-expressing P-glycoprotein (Pgp) to determine which inhibitors may have the potential to overcome susceptibility to this efflux pump. We then performed molecular docking to explain the structure-activity relationship. Finally, we co-crystallised Eg5 with various analogues to understand the protein-ligand interactions.

Results

We report the synthesis of a new series of S-trityl-L-cysteine (STLC) analogues with improved efficacy and show that some of them may have the potential to overcome susceptibility to the Pgp efflux pump. We also solved the structures of Eg5 in complex with STLC and two analogues.

Conclusion

Through in-vitro assays, we observed that STLC analogues with less sterically demanding para-substituents on one of the phenyl rings are generally more potent and exhibit lower multidrug resistance. Additionally, molecular docking showed that the less sterically demanding substituents point towards the core of the protein, while the bulkier substituents generally fit into the solvent-exposed sub-pocket. The structures of the two Eg5-STLC analogue complexes reveal that halogenated para-substituents may increase the potency of the compounds through increased hydrophobic interactions.