Dissecting the protumourigenic activities of senescent cells in the development and relapse of paediatric diffuse midline glioma
Primary supervisor: JP Martinez-Barbera, UCL
Secondary supervisor: Silvia Marino, Queen Mary University of London
Project
The overarching goal of this project is to reveal the molecular and cellular mechanisms underlying the tumour-promoting activity of senescent cells in tumour development and relapse in paediatric diffuse midline glioma (DMG).
DMG, previously called diffuse intrinsic pontine glioma (DIPG), is an extremely devastating paediatric brain cancer that is usually diagnosed in children 5-7 years old. The prognosis is abysmal with an 95% mortality at 2 years after diagnosis. These tumours do not occur in adults [1]. The only effective treatment is radiotherapy, but this is palliative and the vast majority of tumours relapse 3-6 months post-RT with fatal consequences. We hypothesise that senescent cells present in the tumour and tumour microenvironment (TME), as the consequence of oncogene-induced senescence and/or radiation-induced senescence fuel tumour growth and relapse.
Senescence is a response to cellular stressors such as oncogenic signalling, replicative exhaustion and genotoxic agents. Upon senescence induction, cells enter a stable cell cycle arrest, which is maintained by critical pathways regulating cell cycle progression (e.g. p53/p21 and p16/RB). Senescent cells undergo multiple phenotypic changes in their morphology, chromatin structure, organelles and metabolism. In addition, senescent cells can elicit cell non-autonomous activities through the senescence-associated secretory phenotype (SASP), a complex secretory programme composed of a multitude of cytokines and chemokines (e.g. IL1α, IL1β, IL6), growth factors (e.g. EGF, FGFs, VEGF), and other active chemicals [2].
Prominent SASP activation has been shown to promote proliferation of transformed cells and creates permissive microenvironments that support tumour initiation, progression, malignancy and metastasis [3]. Robust evidence has shown that senescent cells can be protumourigenic and that senescent cell ablation or modulation of the SASP, can reduce tumour burden, increase mouse survival, decrease tumour relapse and alleviate the negative effects of anticancer treatment [4,5].
Our preliminary data show the presence of senescent cells in DMG-H3K27 murine models during tumour development and after RT, both in cells within the tumour and in the tumour microenvironment (TME) (Figures 1). We have also detected expression of senescent markers in human samples of paediatric DMG-H3K27 (Figure 2). Of translational relevance, we have shown that RT induces senescence in human DMG cell lines (Figure 3), which results in a marked sensitivity to Navitoclax, a Bcl-xL, Bcl2 and Bcl-W inhibitor, both in cell lines and in a PDX model of DMG (Figure 4).
Building on these findings, we will address the following research questions: (i) which cell types are senescent during DMG-H3K27 development and post-RT?; (ii) what molecular and cellular mechanisms underlie their tumour-promoting activity?; (iii) can senotherapies improve RT clinical outcomes?
To address these questions and provide preclinical data to support senotherapy-based clinical trials in the patients, the PhD student will:
Aim 1: Reveal the cell types that become senescence, both within the tumour lineage and TME in developing and post-RT relapsed tumours. These cell populations will be molecularly characterised (e.g. scRNA-seq) in mouse tumours. We have the genetic tools to address this question, including DMG models (Manav Pathania, Cambridge; collaborator) and a new p16-FDR mouse model we have generated and characterised that allows the FACS isolation, tracing and ablation of p16INK4a-expressing senescent cells (Haston et al., Cancer Cell 2003, PMID: 37267953) (Figure 5). Mouse data will be compared with human data available to us through our collaborator (Chris Jones, ICR, Sutton).
Aim 2: Uncover the molecular and cellular mechanisms underlying the tumour-promoting activities of senescent cells using our DMG-H3K27 mouse models and the p16-FDR muse line. The student will ablate senescent cells in the developing tumours to characterise the consequences of senescent cell ablation on the cellular composition of the TME. For example, we hypothesise that senescent cells through the SASP may create an immunosuppressive TME, increase vasculogenesis and induce/maintain glioma stem cells. The student will analyse changes in the immune infiltrate and vascular network brought about by senescent cell ablation. Likewise, the effect on the cancer stem cell compartment will be analysed.
Aim 3: Evaluate preclinically the efficacy of combination therapies of radiotherapy and senolytic treatments. Optimisation of these combination therapies will involve mathematical modelling, which will be carried out in collaboration with Dr Jamie Dean (UCL Faculty of Engineering Sciences).
At the end of the PhD the student will have a deep understanding on the biology of DMG and senescence, in addition to have acquired technical skills in cutting-edge research approaches that will help propel their research career.
Candidate background
I am particularly interested in receiving applications from candidates with a background and research interest in a relevant area of biosciences or medical sciences (for example mouse genetics, senescence or tumorigenesis) to work on a research programme focused on the role of senescence in paediatric diffused midline glioma. Senescent cells have been shown to contribute to tumour promotion through their paracrine signals in adult and paediatric tumours, including brain tumours (e.g. PIMD: 29670296; PIMD: 35241831). Building on previous data and in collaboration with strategic partners, the PhD student will explore the interactions between senescent cells and tumour cells as well as the impact of senescent cell ablation on other cells in the tumour microenvironment, including immune cells, endothelial cells and glioma stem cell. The appointee will dissect the role of senescent cells using combined approaches, including cell culture, organoid culture, mouse modelling and molecular data (e.g. single cell RNA-seq). The host lab has proven experience in the generation and analysis of preclinical models and the study of cellular senescence in vivo (e.g. PMID: 24094324;PMID: 21636786;PMID: 31699993; PMID: 29180744; PMID: 29541918; PMID: 33378554).
Potential Research Placements
- Jamie Dean, Department of Medical Physical & Biomedical Engineering, UCL
- Silvia Marino, Blizard Institute, Queen Mary University of London
- Chris Jones, Institute of Cancer Research
References
- Mackay A, Burford A, Carvalho D, et al. Integrated Molecular Meta-Analysis of 1,000 Pediatric High-Grade and Diffuse Intrinsic Pontine Glioma. Cancer Cell. Oct 9 2017;32(4):520-537.e5. doi:10.1016/j.ccell.2017.08.017
- Gorgoulis V, Adams PD, Alimonti A, et al. Cellular Senescence: Defining a Path Forward. Cell. Oct 31 2019;179(4):813-827. doi:10.1016/j.cell.2019.10.005
- Gonzalez-Meljem JM, Apps JR, Fraser HC, Martinez-Barbera JP. Paracrine roles of cellular senescence in promoting tumourigenesis. Br J Cancer. 05 2018;118(10):1283-1288. doi:10.1038/s41416-018-0066-1
- Demaria M, O’Leary MN, Chang J, et al. Cellular Senescence Promotes Adverse Effects of Chemotherapy and Cancer Relapse. Cancer Discov. Feb 2017;7(2):165-176. doi:10.1158/2159-8290.cd-16-0241
- Velarde MC, Demaria M, Campisi J. Senescent cells and their secretory phenotype as targets for cancer therapy. Interdiscip Top Gerontol. 2013;38:17-27. doi:10.1159/000343572