Iain Hagan and Wendy Trotter from the Cell Division group at the Cancer Research UK Manchester Institute have developed a new approach to synchronise the cell division cycle of an entire population of human cells in culture. Iain believes the approach – now published in Open Biology – will be a game changer for cell biologists.
By Iain Hagan
Our new paper is my first publication on human cells since I started working on cell division in yeast 36 years ago. I see it as a bit of a mark of the dawn of a new era for our laboratory.
The method that Wendy and I developed exploits the ability of CDK4/6 inhibitor drugs to arrest cell cycle progression at a natural pause point of the cycle: the restriction point. After synchronisation and re-initiation of the cycle, all the cells in the population go through it at the same time and at the same rate. This makes it possible to do biochemical and functional analyses of the changes that happen in cells at specific points of the cycle.
“After synchronisation and re-initiation of the cycle, all the cells in the population go through it at the same time and at the same rate.”
With this method, we can also keep the cells out of the cycle for up to 48 hours and they retain their ability to resume synchronous cell cycling. We can use that time to turn on, turn off or replace any molecule we want to investigate. When we let the cells return to the cycle, we can find out what happened to the molecules or the cells we’ve interfered with.
Many of these molecular manipulations take hours to come into effect. If cells were still dividing, it would be hard to work out whether any changes observed in the cells were a consequence of problems in the previous cycle, or were indeed providing the desired insight into the function of molecules and the behaviour of cells within the actual cycle under study.
Although these types of analyses may sound straightforward, they have been impossible to do with this level of fidelity up to now. The gold standard for cell cycle synchronisation has been the double thymidine block approach, which stops the cell cycle at the phase of DNA replication. This approach was developed in 1962 – the first paper was published five months before I was born – and there has been nothing to rival it since. But this method causes a lot of damage to DNA, and the subsequent cell cycle is far from normal. So, it’s very difficult to study the biochemistry of DNA replication or transcription, or chromatin biology, with a double thymidine block.
By contrast, the approach we’ve developed uses CDK4/6 inhibitors, which are clinically approved to treat breast cancer. Cancer is a disease of cell proliferation, so stopping the cell cycle has a profound impact on disease progression. One of these drugs in particular, abemaciclib, has emerged as an effective therapy for patients with the hard-to-treat triple negative breast cancer. We show in our paper that CDK4/6 inhibitors have no impact upon DNA integrity, so our approach will be a game changer for researchers studying DNA biology.
“The approach we’ve developed uses CDK4/6 inhibitors, which are clinically approved to treat breast cancer.”
I came up with the idea that led to our new approach in 2014 while teaching on the Biological Basis of Cancer Therapy course that is organised by the CRUK Manchester Institute’s postgraduate manager, Julie Edwards. This course is part of the education programme of the Christie NHS Foundation Trust’s School of Oncology and is taught to clinical and medical oncologists and the University of Manchester’s Masters students. I was in the middle of a lecture and telling the students about the power of CDK4/6 inhibitor drugs to stop the cell cycle when I suddenly thought: “This approach is so powerful in yeast. Why is no one using it in human cells?”
I took the idea to colleagues working in human cells. They said it was interesting, but did not pursue it. But in 2016 Wendy joined the lab as a senior scientific officer and brought in expertise in human cell work. I immediately asked her to test the approach – and it worked first time. But then came the fire in 2017 that burned the CRUK Manchester Institute. We spent several months deconstructing our ruined lab and then moved lab twice and this year we had the lockdown. Given that the cell cycle is 24 hours long, these are challenging experiments. But we have now finally published our work.
As the technique is so powerful, however, we have been telling people about it for a while, and Wendy has been sending out detailed instructions to around 20 labs. Some of these labs have already published papers reporting research they did using this approach. For example, Jonathon Pines, who is head of the division of cancer biology at the Institute of Cancer Research (which is part-funded by Cancer Research UK) used it for a paper published in the Journal of Cell Biology. Gislene Pereira of the University of Heidelberg and German Cancer Research Centre has used it for another paper published by the same journal. And Bill Earnshaw of the Wellcome Centre for Cell Biology, University of Edinburgh, says that the method has opened up entirely new avenues in their research programme.
“As the technique is so powerful, we have been telling people about it for a while.”
We took what would be considered by others as a risky choice: telling everyone about our method so we can help push the field forward, but risk ‘being scooped’. However, the potential impact of the method was too great to worry about this.?I do believe it will be very widely adopted.
A drug that was developed to treat cancer, with great effect, can now advance our understanding of cell division to help identify further routes to cancer therapy.
Read Iain and Wendy's paper