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Page 290 Cancer Drug Resist 2018;1:266-302 I http://dx.doi.org/10.20517/cdr.2018.18

metabolism. The mTOR signalling pathway is upregulated in ccRCC and is an important therapeutic tar-
get, but some mTOR inhibitors do not work as expected, particularly second generation ATP-competitive
mTOR kinase and dual PI3K/Akt/mTOR drugs. We have uncovered a resistance pathway to mTOR kinase
inhibition which is mediated by DEP-domain containing mTOR-interacting protein (DEPTOR). DEPTOR
is an endogenous inhibitor of mTOR and is critical for mTOR homeostasis and coordinated negative feed-
back control to PI3K/Akt. Here, we show that DEPTOR is strikingly suppressed in ccRCC tumours and
cell lines. We demonstrate that DEPTOR is repressed by both hypoxia-inducible factors, HIF-1 and HIF-2,
which are upregulated in renal cancer. DEPTOR knock-in and CRISPR/Cas9 mediated knock-out experi-
ments show that DEPTOR is growth inhibitory in ccRCC. Furthermore, loss of DEPTOR confers resistance
to second generation mTOR kinase inhibitors through deregulated mTORC1 feedback to PI3K/Akt. Our
work reveals new mechanistic insight into deregulation of mTOR in ccRCC that is mediated by HIF-de-
pendent reprograming of mTOR/DEPTOR networks. Importantly, we have identified a hitherto unknown
mechanism of resistance to mTOR kinase targeted therapy in ccRCC. This work suggests that restoration
of DEPTOR in ccRCC will confer sensitivity to mTOR kinase inhibition.

44. Acquired resistance to the experimental cancer drug capivasertib is associated with
altered cap-dependent protein translation

1,2
1
Jasmine M. Jakubowski , Denis T. Akan , Mike I. Walton , Michelle D. Garrett 1
2
1 School of Biosciences, University of Kent, Canterbury, UK
2 The Institute of Cancer Research, London, UK

The PI3K/AKT/mTOR (PAM) pathway is important for regulating cell growth, proliferation and survival
in the cell and its deregulation is commonly observed in many cancers. For this reason, PAM inhibitors are
undergoing development as a novel form of targeted cancer treatment. Since emergence of drug resistance
is the major problem facing novel targeted therapies, our aim is to identify resistance mechanisms against
the novel ATP-competitive AKT inhibitor capivasertib (AZD5363), which has currently completed Phase
II clinical trials. The A2780 ovarian carcinoma cell line was used as a model to identify resistance mecha-
nisms against capivasertib. A resistant subpopulation (5363R) was generated by dose escalation exposure
to the drug and subcloned. These were investigated against the parental to identify molecular changes. We
found that the A2780-5363R cells exhibit cross-resistance to both ATP-competitive (17.5 fold difference
in GI ) and allosteric AKT inhibition (8.4 fold) and to inhibitors further downstream the PAM pathway.
50
These include the rapalogue everolimus (78.7 fold) and the mTOR kinase inhibitor vistusertib (3.9 fold). As
4EBP1 phosphorylation is understood to be a rapalogue-resistant function of mTORC1 and coupled with a
reduction of 4EBP1 in the resistant cells, 4EBP1 was identified as a potential candidate resistance mecha-
nism. Pull-down of eIF4E showed reduced 4EBP1 and increased eIF4G binding to eIF4E in the 5363R cells,
independent of mTOR inhibition thus suggesting an increase in cap-dependent protein translation. Protein
synthesis analyses are consistent with this finding. These results show that increased protein translation is
a mechanism of acquired resistance to AZD5363.

45. FLIPi: evaluating a novel therapeutic strategy to target advanced prostate cancer

Daniel Turnham , Norman Maitland , Andrea Brancale , Andrew Westwell , Rhiannon French ,
2
1
3
3
1
Richard Clarkson 1
1 European Cancer Stem Cell Research Institute, School of Bioscience, Cardiff University, Cardiff, UK
2 Department of Biology, University of York, York, UK
3 School of Pharmacy, Cardiff University, Cardiff, UK