Dissecting the protumourigenic activities of senescent cells in the development and relapse of paediatric diffused midline glioma

Primary supervisor: Juan Pedro Matinez-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 DMG.

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 (manuscript in preparation) 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). We have also detected expression of senescent markers in human samples of paediatric DMG-H3K27. Of translational relevance, we have shown that combination of RT with senolytic treatment reduces tumour burden and increases survival in both genetically modified and patient-derived xenograft models of DMG.

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 -under second review). 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.

Potential Research Placements

1. Manav Pathania, Department of Oncology, University of Cambridge
2. Chris Jones, Institute of Cancer Research
3. Jamie Dean, Department of Medical Physics & Biomedical Engineering

References

1. 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
2. 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
3. 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
4. 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
5. 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