Imaging replication stress and DNA damage response in cancer

Background: The majority of cancer deaths result from ineffective treatment of metastatic disease. Currently, there is no satisfactory way to identify patients that will not respond to treatment. The identification of cancer patients that are refractory to the standard of care will allow the selection of alternative therapies that have the potential to improve patient response and survival.

One approach we have taken to visualise therapy resistance is through the imaging of the tumour antioxidant response, which acts to prevent treatment-induced oxidative stress. We are currently evaluating the positron emission tomography imaging agent, [18F]FSPG, as a non-invasive marker of the tumour redox microenvironment. Acting as a surrogate for de novo glutathione biosynthesis, [18F]FSPG tumour uptake is altered following oxidising chemotherapy prior to tumour shrinkage [1]. Moreover, we have shown baseline [18F]FSPG tumour uptake is predictive of response to standard chemotherapies [2].

Scientific hypothesis: In highly proliferating tumour cells, a common consequence is the amplification of DNA damage and DNA replication errors. To ensure faithful inheritance of their genomes, mammalian cells have evolved a DNA damage response (DDR) to repair these defects. Inhibition of DDR pathways in tumours with DDR defects has a synthetic lethal effect [3]. Despite the success of these clinically-translated DDR inhibitors [4], there is no method to accurately determine which patients will respond to these therapies. Here, we will evaluate [18F]FSPG PET as a sensitive marker of the tumour redox environment and investigate its relationship to drug-induced replication stress.Using the refined markers identified from scRNA-seq data will perform more in-depth sequencing and further analysis TAM subsets, this data will be used for pathway analysis to reveal molecular targets and ultimately resolve the function of these subsets through functional studies using our genetic tools.

Experimental plan: As part of a multidisciplinary project, encompassing cancer biology, radiochemistry and the imaging sciences, the PhD student will: 1) Compare baseline [18F]FSPG uptake in vivo in lung tumours harbouring NRF2 mutations following treatment with the PARP inhibitor olaparib; 2) assess tumour response with [18F]FSPG to the DDR inhibitor VX-970, administered as a single agent and in combination with platinum in genetically-modified mouse models of lung cancer; 3) Understand the mechanisms that underpin differential [18F]FSPG uptake through the measurement of ROS, GSH utilisation and oxidative DNA damage, and determine whether baseline [18F]FSPG uptake is predictive of response; 4) use peripheral blood exosome and immune-modifying microRNA quantification to assess the unfolded protein response as a companion prognostic marker [5]. Together, this programme of research will provide an early non-invasive marker of DDR treatment efficacy in vivo. Identifying DDR drug resistance will inform patient management and second-line therapy selection, thereby improving patient outcome.