Introduction/Background*High-grade serous ovarian cancer (HGSOC) is the most lethal form of gynaecological malignancy. Despite initial chemosensitivity the majority of patients develop resistance to platinum chemotherapy and eventually die. Current treatment options for platinum resistant disease remain limited, therefore interest has turned towards the development of targeted therapeutics. The role of the PI3K/AKT/mTOR pathway, found activated in 70% of HGSOC cases, is well described in chemoresistant disease, in particular through activation of AKT in response to platinum treatment by the DNA damage response protein DNA-PK. Increasing numbers of PI3K/AKT/mTOR inhibitors are in development/clinical use for other cancer types. Our laboratory previously demonstrated that inhibition of AKT or DNA-PK re-sensitises clinically-acquired platinum resistant HGSOC cell lines to cisplatin. Here we aim to assess synergy between a panel of commercially available AKT and DNAPK inhibitors with cisplatin, and elucidate their mechanism of action within the PI3K/AKT/mTOR pathway.
Methodology Platinum resistant immortalised HGSOC cell lines (PEO4, PEA2, OVCAR8, Kuramochi) were treated with cisplatin plus/minus AKT or DNA-PK inhibitors and Isobologram assays performed to establish synergy/antagonism between drug treatments. Cells were treated with inhibitors plus/minus cisplatin at different time points, protein lysates collected, and Reverse Phase Protein Array (RPPA) proteomics performed and analysed to establish mechanisms of action of inhibitors on the PI3K/AKT/mTOR pathway.
Result(s)*Following treatment with cisplatin in combination with AKT or DNA-PK inhibitors, different levels of synergy were observed in platinum resistant HGSOC cell lines; strong synergy was noted for AKT inhibitors Afurosertib, Uprosertib, and Triciribine. Proteomic analysis revealed a response signature for AKT or DNAPK inhibition showing activation of AKT at S473 and decrease of downstream targets pS6_235/236 and 240/44, and p70S6K_T389.
Conclusion*In the platinum resistant immortalised HGSOC cell lines tested, AKT inhibitors showed a synergistic effect when used in combination with cisplatin. Proteomic analysis confirmed targeting of the PI3K/AKT/mTOR pathway. With the aim of resensitising a resistant patient to their platinum-based chemotherapy a synergistic effect between the resensitising compound and chemotherapy agent is essential; this data suggests targeting of the PI3K/AKT/mTOR pathway in platinum-resistant HGSOC patients with AKT or DNAPK inhibition is a potentially useful therapeutic strategy.
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