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Page 292 Cancer Drug Resist 2018;1:266-302 I http://dx.doi.org/10.20517/cdr.2018.18
1 Oncology Bioscience, IMED Biotech Unit, AstraZeneca, Cambridge, UK
2 Oncology Translational sciences, IMED Biotech Unit, AstraZeneca, Cambridge, UK

Schlafen 11 (SLFN11) is a putative DNA/RNA helicase only found in humans and some primates, with bi-
modal distribution in cancer cells. It was initially discovered by bioinformatics analyses of cancer cell da-
tabases as a genomic determinant of response to various DNA damaging agents (DDA). Most importantly,
recent reports indicate that SLFN11 expression in tumours may serve as a predictive biomarker for strati-
fication of cancer patients treated with DDA and DNA damage response inhibitor (DDRi). In the Sanger
panel of cancer cell lines, we independently validated SLFN11 downregulation in ~50% of cells, and that its
expression correlates with response to DDA as well as PARP inhibitors. To further shed light on SLFN11
mechanism of action we knocked out SLFN11 (KO) in prostate cancer cells DU145 via CRISPR-Cas9. Rel-
evant clones were selected and the isogenic pair was profiled for SLFN11 downregulation at protein levels
(by western blotting and immunofluorescence) and were instrumental for the development of an FFPE im-
munohistochemistry (IHC) assay. This was further implemented and validated in xenograft tissue and was
found to be specific. The susceptibility of SLFN11 KO cells to different DDAs and DDRi was verified by cell
viability assays. Downregulation of SLFN11 conferred resistance to treatments with the topoisomerase in-
hibitors ETP and camptothecin (CPT), as well as to various DDRi. Interestingly, combinations of ETP with
some DDRi were found to be more synergistic in SLFN11 KO than in wild type cells, suggesting that these
combinations could be more effective in cells that lack SLFN11. A detailed analysis of these results will be
presented here and indicate that selective DDA-DDRi strategies may re-sensitize cancers that have become
resistant to chemotherapy due to SLFN11 downregulation.

48. Changing faces of FUS: FUS/TLS represses androgen receptor activity in prostate cancer
through disruption of the transcriptional complex

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G. N. Brooke , R. C. Culley , F. M. Fioretti , C. Reader , E. Rees , S. M. Powell , M. Alkheilewi ,
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A. Pine , L. Latonen , T. Visakorpi , L. Gaughan , D. A. Leach , J. Waxman , C. L. Bevan 1
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1 Imperial College, London, UK
2 University of Essex, Colchester, UK
3 University of Tampere, Finland
4 Newcastle University, UK
Prostate cancer growth is dependent upon the androgen receptor, a ligand-dependent transcription fac-
tor which exerts its effects on transcription in concert with cofactor proteins (coactivators and corepres-
sors). We have previously shown that FUS/TLS, a multi-functional protein, is down-regulated in response
to androgen receptor signalling and that it has tumour suppressor properties. To better understand what
FUS regulates to block tumour growth, the transcriptome of the androgen-dependent prostate cancer cell
line LNCaP was investigated in response to FUS over-expression. This analysis identified a high degree
of overlap between FUS-regulated genes and those regulated by the androgen receptor. Further, FUS was
found to predominantly repress androgen receptor activity and this was confirmed using reporter assays.
Mammalian 2-hybrid and trans-repression assays demonstrated that FUS interacts with the androgen re-
ceptor via its RNA recognition motif domain and contains both transrepression and activation domains.
Interestingly, the transrepression domains are HDAC independent and do not contribute to the repressive
action of FUS upon the androgen receptor. Instead, it appears that FUS represses androgen receptor activ-
ity as a result of competition for coactivators. A modified mammalian 2-hybrid assay demonstrated that
the N-terminal activation function of FUS interacts with coactivators such as SRC1, and chromatin immu-
noprecipitation studies demonstrated that FUS inhibits the formation of the active androgen receptor tran-
scriptional complex. In agreement with our previous findings, FUS levels were reduced in prostate cancer,
but interestingly were elevated in the aggressive, castrate resistant stage of the disease. It therefore appears