Many anticancer drugs have serious side effects in clinical practice. Kinesin inhibitors block kinesin motor proteins required for cancer cell division, and are promising anticancer drug candidates with minimal side effects. However, its relationship with the kinesin protein remains unclear.
Researchers from Japan have overcome this by solving the crystal structure of the complex formed by the non-hydrolyzable protein kinesin CENP-E and the ATP analog AMPPNP, paving the way for the development of cancer therapies with lower toxicity.
Anticancer drugs are essential for cancer treatment, but their toxicity is not always limited to cancer cells, causing harmful side effects. To develop anticancer therapies that have fewer adverse effects on patients, scientists are focusing on molecules that are less toxic to cells. One such group of drugs are kinesin inhibitors.
These inhibitors prevent cancer development by explicitly targeting the motor protein kinesin, which is necessary for cancer cell division. Centromere-associated protein E (CENP-E), a member of the kinesin motor proteins, is a promising target for inhibitor therapy, as it is critical for tumor cell replication.
However, determining the structure of CENP-E is essential to identify inhibitory molecules that can bind to CENP-E and terminate its function.
The binding of an energy molecule—adenosine triphosphate (ATP)—to the CENP-E motor domain changes its structure or configuration. This also occurs when CENP-E binds to inhibitors. So far, very few CENP-E inhibitors have been reported and none approved for clinical use. Therefore, it is important to obtain structural information on the CENP-E motor domains.
To this end, a research team from Tokyo University of Science (TUS) used X-ray crystallography to elucidate the crystal structure of the complex formed by the CENP-E motor domain and the kinesin inhibitor.
Potential cancer drug targets
The study, led by Hideshi Yokoyama of TUS, along with co-authors Asuka Shibuya of TUS, and Naohisa Ogo, Jun-ichi Sawada, and Akira Asai of the University of Shizuoka, was published in FEB letter.
“CENP-E selectively acts on cell division, making it a potential new target for anticancer drugs with fewer side effects,” said Yokoyama.
First, the team expressed the CENP-E motor domain in bacterial cells, after which they purified it and mixed it with adenylyl-imidodiphosphate (AMPPNP)—a non-hydrolyzable ATP analogue. The mixture is crystallized to obtain X-ray data. Using the data, the team derived the structure of the CENP-E motor domain-AMPPNP complex.
Next, they compared the structure with that of CENP-E-bound adenosine diphosphate (CENP-E-MgADP) as well as with the previously known AMPPNP-kinesin motor protein complex. From this comparison, the team speculated that alpha helix 4 in the motor domain is likely responsible for the loose binding of CENP-E to microtubules, which are cell structures essential for cell division.
“Compared to the α4 helices of other kinesins, α4 of CENP-E binds slowly and with less force to microtubules compared to other kinesins, during the ATP hydrolysis cycle,” notes Yokoyama.
The discovery of the complex’s crystal structure is expected to facilitate additional structure-activity relationship studies, which will bring scientists one step closer to developing anticancer drugs targeting CENP-E.
The research team said they were optimistic about the future applicability of their research and were confident that it would be possible to design a drug based on the methods used in this study.
“The ultimate goal is to use the preparation and crystallization methods described in our study for future drug design studies aimed at developing anticancer drugs with fewer side effects,” said Yokoyama.
Along with fewer side effects, both researchers and biotech companies are working towards more focused cancer treatments. In a recent article, the CEO, CMO, and CSO shared their insights with Labiotech regarding what cancer treatment might look like 10 years from now.