Inflaming the microenvironment of glioblastoma tumors by ADAR1 inhibition: a two-hit approach for the treatment of brain cancer.

Project Information

GlioTarget

Grant agreement ID: 890933

DOI

10.3030/890933

Project closed

EC signature date 3 March 2020

Start date 1 September 2021

End date 31 August 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 191 149,44

EU contribution

€ 191 149,44

Coordinated by

UNIVERSITE DE LAUSANNE
Switzerland

Periodic Reporting for period 1 - GlioTarget (Inflaming the microenvironment of glioblastoma tumors by ADAR1 inhibition: a two-hit approach for the treatment of brain cancer.)

Reporting period: 2021-09-01 to 2023-08-31

Summary of the context and overall objectives of the project

Glioblastomas represent the most frequent and lethal form of primary brain tumours. Tragically, current therapies for glioblastoma patients invariably fail, likely due to: (i) the challenging location of tumours, which precludes complete surgical removal of malignant cells; (ii) their extreme heterogeneity, cancer cells within the same tumour can present distinct genetic profiles and behaviours and respond differently to therapy; (iii) the presence of a highly immunosuppressive tumour microenvironment, i.e. non-cancerous cells which are hijacked by glioblastoma cells to promote cancer progression and therapy resistance.

In this project, I propose to simultaneously target cancer cells and their supporting microenvironment as a novel therapeutic approach for glioblastoma treatment. My hypothesis is that by exploiting an innate immunity checkpoint present in all cancer cells, we would target the entire heterogeneity of glioblastoma tumours, impede cancer-cell proliferation and reprogram the communication between cancer cells and their microenvironment to foster an anti-tumoural immune response. ADAR1 is a central player in regulating this immune checkpoint, helping cells to distinguish molecules originating from viral infection from those produced during normal physiological processes and thus preventing aberrant immune responses. Sensing of these foreign molecules leads to cell growth arrest, to impede viral spread, and production of signals that alerts the immune system to fight the infection. I hypothesise that by inhibiting ADAR1 we would promote a similar effect in glioblastoma tumours. Importantly, data from our lab and others has shown that glioblastoma cells present unique features which make them vulnerable to ADAR1 inhibition, while this has little impact in healthy cells. I will therefore test this hypothesis in preclinical mouse models. If validated, this project could lead to a more effective treatment for patients, by simultaneously attacking cancer cells from the inside and outside, and would be less toxic, as it exploits a vulnerability present within glioblastoma cells.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

We employed genetic and pharmacological approaches to inhibit ADAR1 in preclinical mouse models of glioblastoma and evaluate its therapeutic potential alone and in combination with standard of care therapy and immunotherapies. In brief, this means we either prevented cancer cells from producing ADAR1 by manipulating their genetic code or inhibited its function by using a drug. By working with mouse models bearing distinct genetic alterations, we evaluated whether our strategy could be effective against the substantial genetic heterogeneity observed in human glioblastomas.

We followed tumour progression using magnetic resonance imaging, a powerful technique employed in patients which allows one to image tumours and quantify growth dynamics along time and in response to treatment. To understand how ADAR1 inhibition remodels the tumour microenvironment, we combined a number of different techniques: (i) flow cytometry allowed us to measure the abundance of the different immune cell populations, such as T lymphocytes, macrophages or microglia, present in the tumour; (ii) immunofluorescence analyses provided a detailed picture of how these cells are spatially distributed within the tumour tissue; (iii) fluorescent-activated cell sorting allowed us to individually purify cancer cells and immune cell populations of interest; (iv) RNA sequencing revealed how cancer cells and different immune cells behave by measuring how cells are translating their genetic code to produce specific proteins that accomplish known cellular functions.

Our pre-clinical trials in different mouse models of glioblastoma showed that genetic deletion of Adar1 in early stages of tumor development or in established tumors leads to delayed tumor growth and increased survival, regardless of the genetic background of the tumors. This provides proof of concept that targeting ADAR1 is a promising novel approach to treat this currently incurable disease.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The idea of targeting ADAR1 to fight glioblastoma tumors could translate into more effective treatments for patients in the long term - by simultaneously attacking cancer cells from the inside and outside - and should result in reduced side effects compared to standard of care therapy, as it exploits a vulnerability present in glioblastoma cancer cells and should therefore be more specific and less toxic. We are currently evaluating whether by combining ADAR1 inhibition with standard of care therapy and immunotherapies we can achieve a synergistic effect that leads to a more pronounced tumour regression and/or delayed recurrence and consequently an extended survival as compared to targeting ADAR1 alone. Importantly, we are now testing the efficacy of inhibiting ADAR1 together with standard of care radiotherapy and immunotherapies based on molecules which are already approved for human use (such as pembrolizumab) or currently under clinical trials (such as BLZ945) which would facilitate the translation of our findings into a direct benefit for patients. If our approach is successful, we envision a timescale of 10 years for all three phases of clinical trials to be completed and a potential new drug to be licensed and made available to patients.

Summary of project objectives and work packages.