Investigating BH3-mimetic drugs as radiosensitising agents in solid cancers

Background- Radiotherapy (RT) is an effective and potentially curative treatment used for many solid tumours.

However, some tumours display innate radio-resistance that leads to the survival of subpopulations of cancer cells and subsequent tumour recurrence.

Consequently, there is a need to identify chemotherapeutics that can be used as radiosensitisers to increase treatment efficacy.

B cell lymphoma 2 (BCL-2) homology domain 3 (BH3) mimetics are a class of cancer therapeutics that target specific anti-apoptotic molecules such as BCL-2, BCL-XL and MCL-1 and thus facilitate apoptotic cell death.

Numerous studies indicate that BH3-mimetics have greatest anti-cancer effect when used in combination with other therapies, which induce stresses that prime cells for apoptosis.

We hypothesise that RT primes cancer cells for apoptosis, such that enhanced and selective tumour cell death will be achieved through RT in combination with BH3-mimetics.

Furthermore, we propose that different configurations of pro- versus anti-apoptotic BCL-2 family expression underlies susceptibility to radiosensitisation by BH3 mimetics targeting distinct anti-apoptotic BCL-2 proteins. Understanding these relationships could lead to improved therapeutic options and personalisation of therapy.

Aims- By building a cross-institute network of expertise, we aim to define the potential for drugs targeting anti-apoptotic BCL-2 proteins to be used in combination with radiotherapy across multiple solid cancers. Methods- (1) Bioinformatic analysis of published human cancer and cell line datasets.

Correlations between radiosensitivity (cell lines)/survival (patients) and BCL-2 family expression in gene-wise and gene-set enrichment approaches.

Selection of cell line panel representative of multiple cancer types (breast, prostate, pancreas, lung and brain) with relative radioresistance and representative patterns of BCL-2 family expression. (2) Cell line screen, utilising a range of doses of 4 different BH3-mimetic drugs (ABT199/BCL-2, S63845/MCL-1, A1331852/BCL-XL, ABT737/BCL-2/BCL-XL) in combination with ionising radiation.

High throughput microscopy to identify therapeutic interaction. (3) Validation of key results by clonogenic assay and on-target effects confirmed with gene targeting/additional BH3-mimetic drugs.

Impact on cell death pathways characterised by western blotting. (4) Bioinformatic correlation of radiosensitisation with BCL-2 family expression and other genomic/transcriptomic/proteomic markers in cell line datasets and potential identification of signatures that could allow pre-selection of patients for targeted radiosensitisation with BH3-mimetics.

How results of this research will be used- This study will be used to provide data for one or more larger grant applications, the potential to publish as a technical paper will be explored and this research will provide mechanistic insight towards additional publications.