Combining Tumour-Treating Fields with DNA damage response inhibitors for the improved treatment of glioblastoma

Glioblastoma is the most common and deadliest type of primary brain cancer, taking over 2,500 lives
each year in the UK. glioblastoma has a median overall survival of 10-16 months, despite treatment
consisting of maximal surgical resection followed by chemo- and radio-therapy. glioblastoma survival
rates have seen little improvement over the past 40 years and given this devastating prognosis, new
treatment options for the management of glioblastoma are urgently needed. Recently, Tumour
Treating Fields (TTFields) has emerged as a novel fourth modality for the treatment of high-grade
gliomas following its success in clinical trials, where the addition of TTFields to standard care
temozolomide was shown to increase median progression-free survival (6.7 versus 4.0 months) and
overall survival (20.9 vs 16.0 months) of newly-diagnosed glioblastoma patients compared to
temozolomide alone. TTFields are primarily thought to mediate their anti-cancer effects by disrupting
tubulin dimer alignment during mitosis, resulting in abnormal chromosomal segregation and mitotic
cell death. In addition, recent data suggests that TTFields affect a number of other cellular processes
– 1- cell membrane and blood-brain barrier (BBB) permeability, 2- cell migration and invasion, 3- anti�tumour immunity, 4- autophagy, and 5- replication stress and DNA damage repair, the latter of which
will be the focus of this project. TTFields has also been shown to downregulate DNA damage response
(DDR) proteins and delay the repair of radiotherapy- and chemotherapy-induced DNA lesions, an
effect that is thought to be mediated through reduced homologous recombination repair efficiency
and induction of a ‘BRCAness’ phenotype. Such vulnerabilities within DNA damage repair pathways
provides a rational for the use of TTFields in combinational therapeutic approaches that target the
DDR.
We therefore aim to assess whether combining TTFields with DDR inhibitors (PARPi, ATMi, ATRi and
WEE1i) can enhance the efficacy of TTFields in clinically relevant glioblastoma stem-like cultures
(GSCs) using a number of established cell survival assays. Additionally, we aim to investigate the
mechanisms by which combination treatments of DDR inhibitors and TTFields affect the DNA damage
response. In this thesis we show that combining TTFields with radiation and clinically approved PARP
inhibitor therapy leads to significantly increased amounts of DNA damage with concurrent decreased
clonogenic survival in GSCs. Furthermore, we have shown similar impressive potency when TTFields
treatments are combined with BBB-penetrant ATR inhibitors that are currently being assessed in
various global clinical trials for glioblastoma as well as other cancers. Overall, these exciting findings
support further assessment of TTFields and DDRi combinations to underpin future clinical trials
combining TTFields with clinically approved DDRi to improve outcomes for patients with currently
incurable high-grade gliomas.