Professor Michael P Lisanti of the University of Salford highlights the potential applications of senolytic drugs in treating age-associated conditions.
Professor Michael P Lisanti, Chair in Translational Medicine at the University of Salford, has been an active research scientist for more than 30 years and is an expert in the field of cellular senescence. In 2018 Lisanti, along with his wife and research partner Professor Federica Sotgia, co-authored a paper entitled ‘Azithromycin and Roxithromycin define a new family of “senolytic” drugs that target senescent human fibroblasts’, which identified the FDA-approved antibiotic azithromycin as a senolytic drug: a compound which can be used to treat the symptoms of ageing.
Their research was made possible through generous funding contributions from Lunella Biotech, Inc, a Canadian-based pharmaceutical developer which fosters medical innovation; the Foxpoint Foundation, also based in Canada; and the Healthy Life Foundation, a UK charity which funds research into ageing and age-related conditions. Lisanti speaks to HEQ about his work and the future of senescence studies.
Can you give us a brief introduction to the results of your research into senescence and senolytic drugs?
We started out focusing on cancer, but the relationship between cancer and ageing led us to shift our focus towards senescence, the process by which cells chronologically age and go into cell cycle arrest. Senescence leads to chronic inflammation: the cells secrete a lot of inflammatory mediators, which allows the cells to become almost infectious; so then neighbouring normal cells become senescent – it has a kind of cataclysmic effect. As you age – especially as you approach around 50 – you begin to accumulate more senescent cells, which are thought to be the root cause of ageing; this then leads to various ageing-associated diseases, such as heart disease, diabetes, dementia and cancer, the most life threatening conditions in the Western world.
The goal, therefore, would be to remove the senescent cells. It is possible to use a genetic trick to remove senescent cells from mice: this causes them to live longer by preventing ageing-associated diseases; but it is not possible to use the same genetic trick for humans. We would therefore need a drug that only kills or removes senescent cells; and that could then potentially lead to rejuvenation, thereby extending the patient’s healthy lifespan.
We set up a drug assay using normal, commercially available, human fibroblasts: MRC-5, which comes from the lungs, and BJ-1, which comes from the skin. The idea was to artificially induce ageing, which we did using a compound called BrdU. This compound is a nucleoside: it incorporates into the DNA and that leads to DNA damage; and the DNA damage in turn induces the senescence phenotype. The overarching concept was to create a population of cells artificially that were senescent; and then to compare primary cells that were normal with cells which were senescent, with the goal of identifying drugs which could only selectively kill the senescent cells and not harm the normal cells.
We had previously observed positive results in tests on the metabolic effects of antibiotics, so our drug screening identified two drugs called azithromycin and roxithromycin, which constitute a new family of senolytic drugs. They’re both clinically approved drugs – azithromycin has been around longer; and has a strong safety profile – and we looked at other members of the same drug family such as erythromycin, which is the parent compound, but erythromycin has no senolytic activity. The characteristics we were looking for appeared to be relatively restricted to azithromycin, which in our observation was very efficiently killing the senescent cells. As we reported in the paper, it had an efficacy of approximately 97%, meaning that it was able to facilitate the growth of the normal cells, while concurrently selectively killing the senescent cells.
How did you measure the efficacy of the drugs?
We tested the drug on normal and senescent cells which were otherwise identical. The senescent cells underwent apoptosis – programmed cell death – so that led us to the conclusion that the drug selectively kills the senescent cells, while at the same time the normal cells are able to continue to proliferate. That selective effect of removing exclusively the senescent cells is what we were searching for; because in this instance we would want a drug that could potentially be used in humans and which would only kill senescent cells.
What would be the next steps in proving the credibility of antibiotics removing inflammatory senescent cells and boosting healthy ones?
Obviously, we would have to do clinical trials going forward, but the first step should be to identify the pharmaceutical application. Given that this drug appears to selectively kill and remove the senescent cells, it could be used potentially to prevent ageing-associated disease; and it could therefore potentially extend the human lifespan, especially in terms of reducing diseases and conditions like diabetes, heart disease, dementia and even cancer.
Cystic fibrosis is the most common genetic disease in humans; patients with cystic fibrosis are prone to bacterial lung infections. Researchers started to explore the possibility of using azithromycin preventatively in patients with cystic fibrosis; and they found that, while it didn’t necessarily affect patients’ susceptibility to infection, it did prevent lung fibrosis – where the lungs become stiff and the patient is unable to breathe – and in doing so, extended the patients’ lifespan. These studies were focused on myofibroblasts, which at the time weren’t really seen as senescent; whereas the literature now acknowledges a general consensus that myofibroblasts are indeed senescent cells.
What is the current relationship between ageing-associated diseases and antimicrobial resistance (AMR)?
We haven’t specifically examined anything relating ageing to antimicrobial resistance; but azithromycin is an antibiotic, which is not ideal within the context of AMR. Potentially in the future, once researchers identify what it is about the azithromycin that is causing the senescent cells to die, they could develop future drugs – azithromycin is a stepping stone in this context, but what it shows is proof of principle that a drug can be identified which selectively kills senescent cells. This indicates that senescent cells are clearly biochemically distinct from the normal cells, and that it is possible to find a drug that selectively kills them and that is relatively safe. It provides a starting point for further new drug discovery to identify other drugs which might also be selective.
Could this discovery of senolytic drugs play a positive or negative role when it comes to antimicrobial resistance?
Ideally, we would want a drug which is not an antibiotic; but that means further research will be necessary to find additional drugs or to refine the senolytic activity which we’ve discovered in this drug. We are in the early stages; the point is that it is experimentally feasible and this would then lend itself to doing new clinical trials in the future, because azithromycin is relatively safe and it probably won’t need to be administered over a long period of time to remove senescent cells – you might not need to use it for any longer than you would as an antibiotic.
This research has been supported by the Foxpoint Foundation (Canada), the Healthy Life Foundation (UK), and Lunella Biotech, Inc. (Canada).
About Michael P Lisanti
Professor Michael P Lisanti is Chair of Translational Medicine at the University of Salford School of Science, Engineering & Environment, UK. His current research programme is focused on eradicating cancer stem cells (CSCs); and anti-ageing therapies, in the context of age-associated diseases, such as cancer and dementia.
Lisanti began his education at New York University, US, graduating magna cum laude in chemistry (1985); before completing an MD-PhD in cell biology and genetics at Cornell University Medical College, US (1992). In 1992, he moved to MIT, US, where he worked alongside Nobel laureate David Baltimore and renowned cell biologist Harvey Lodish as a Whitehead Institute fellow (1992-96).
His career has since taken him to the Albert Einstein College of Medicine, US (1997-2006), the Kimmel Cancer Center, US (2006-12), and the University of Manchester, UK (2012-16), where he served as the Muriel Edith Rickman chair of breast oncology, director of the Breakthrough Breast Cancer and the Breast Cancer Now Research Units, and founder and director of the Manchester Centre for Cellular Metabolism.
Lisanti has contributed to 564 publications in peer-reviewed journals and been cited more than 90,000 times. A list of his works can be found at: https://pubmed.ncbi.nlm.nih.gov/?term=lisanti+mp&sort=date
About Federica Sotgia
Professor Federica Sotgia currently serves as chair in cancer biology and ageing at the University of Salford School of Science, Engineering and Environment, UK, where she focuses on, inter alia, the role of the tumour microenvironment in cancer and the metabolic requirements of tumour-initiating cells.
Sotgia graduated magna cum laude with an MS in biological sciences (1996) from the University of Genova, Italy, where she later completed a PhD in medical genetics (2001). She moved to the Albert Einstein College of Medicine, US, in 1998, originally as a visiting student and then postdoctoral fellow, and she was appointed an instructor in 2002.
Sotgia has since worked as an assistant professor at the Kimmel Cancer Center, US (2006-12), a senior lecturer at the University of Manchester, UK (2012-16), and a Professor in biomedical science at the University of Salford (2016-present).
She has contributed to 206 publications in peer-reviewed journals and been cited upwards of 27,000 times.
A list of her works can be found at: https://pubmed.ncbi.nlm.nih.gov/?term=sotgia+f&sort=date
Professor Michael P Lisanti, MD-PhD, FRSA, FRSB
Chair in Translational Medicine
School of Science, Engineering & Environment
University of Salford
+44 (0)1612 950 240
M.P.Lisanti@salford.ac.uk
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