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Page 298 Cancer Drug Resist 2018;1:266-302 I http://dx.doi.org/10.20517/cdr.2018.18

loci. In the A2780-CP70 and PEO1-PEO4 pairs, DA regions were predominantly less accessible in resis-
tant lines while equal doses of cisplatin induced fewer platinum-adducts in the resistant line, as shown by
inductively-coupled plasma mass spectrometry. Using a novel assay, Pt-ExoSeq, analysis of genome wide
platinum-adduct distribution distinguished sensitive PEO1 from its resistant counterpart PEO4, when
treated with doses inducing equal total damage in both lines. Chromatin conformation changes associated
with resistance influence adduct formation. Thus, we observe reduced adduct formation in PEO4 compared
to PEO1 at significantly less accessible genomic regions, primarily around gene promoters. However, a set
of intergenic regions with increased damage in PEO4 show a larger reduction in accessibility. To confirm
that greater accessibility increases cisplatin-adduct formation, we increased histone acetylation and chro-
matin accessibility using the histone deacetylase inhibitor Vorinostat, before treating with cisplatin. This
led to greatly increased adduct formation. We show for the first time that platinum-adduct distribution and
chromatin accessibility analysed genome-wide, can differentiate platinum sensitive and resistant ovarian
cell lines and suggest a role for chromatin conformation changes in the emergence of drug resistance by al-
tering the distribution of platinum-DNA adducts throughout the genome and hence their cytotoxic effects.

58. Increased ERK phosphorylation as a candidate driver of resistance to the experimental
cancer drug AT13148

1,2
2
1
Nathan D. Breeds , Denis Akan , Mike I. Walton , Michelle D. Garrett 1,2
1 University of Kent, School of Biosciences, Canterbury, UK
2 The Institute of Cancer Research, CRUK Cancer Therapeutics Unit, London, UK

The AGC family of serine/threonine protein kinases comprises a number of drug targets with therapeutic
potential for the treatment of cancer. AT13148 is an ATP competitive AGC kinase inhibitor, currently in
phase 1 clinical trials, with activity against several members of the AGC kinase family, including ROCK
1/2, AKT, and p70S6K. Due to the prevalence of acquired drug resistance in the clinic, elucidating mecha-
nisms of acquired resistance early in the development of an experimental cancer drug may provide op-
portunities to overcome resistance. The aim of this project was therefore to develop preclinical models of
AT13148 resistance and identify potential driver mechanisms prior to clinical emergence. Isogenic AT13148
resistant sub-clones were generated from the A2780 ovarian carcinoma cell line. These displayed increased
ERK 1/2 phosphorylation concurrent with decreased MEK 1/2 phosphorylation, when compared to the pa-
rental A2780 cell line. In addition, two of the resistant sub-clones were sensitised to AT13148 on exposure
to the ERK inhibitor GDC-0994, implicating ERK as a driver of resistance. These sub-clones also exhibited
cross-resistance to MEK inhibitors (PD-0325901 and selumetinib), with ERK phosphorylation shown to be
refractory to PD-0325901. Loss of DUSP 6 expression, an ERK 1/2 phosphatase, was subsequently detected
in these AT13148 resistant sub-clones and is hypothesised as a potential mechanism of increased ERK
phosphorylation and therefore resistance.

59. Identification of candidate genes that may function in oestrogen receptor - breast cancer

2
1
1
1
Stephen Chandler , Francesco Crea , Mark Hirst , Angela Cox , Sushilaben Rigas 1
1 The Open University, Milton Keynes, UK
2 University of Sheffield, Sheffield, UK
Breast cancer is the most common cancer in women worldwide. Most breast cancers are hormone related
involving the oestrogen receptor (ER), progesterone receptor (PR) and/or the human epidermal growth