DNA-PK Mediates AKT Activation and Apoptosis Inhibition in Clinically Acquired Platinum Resistance

Abstract

Clinical resistance to chemotherapy is a frequent event in cancer treatment and is closely linked to poor outcome. High-grade serous (HGS) ovarian cancer is characterized by p53 mutation and high levels of genomic instability. Treatment includes platinum-based chemotherapy and initial response rates are high; however, resistance is frequently acquired, at which point treatment options are largely palliative. Recent data indicate that platinum-resistant clones exist within the sensitive primary tumor at presentation, implying resistant cell selection after treatment with platinum chemotherapy. The AKT pathway is central to cell survival and has been implicated in platinum resistance. Here, we show that platinum exposure induces an AKT-dependent, prosurvival, DNA damage response in clinically platinum-resistant but not platinum-sensitive cells. AKT relocates to the nucleus of resistant cells where it is phosphorylated specifically on S473 by DNA-dependent protein kinase (DNA-PK), and this activation inhibits cisplatin-mediated apoptosis. Inhibition of DNA-PK or AKT, but not mTORC2, restores platinum sensitivity in a panel of clinically resistant HGS ovarian cancer cell lines: we also demonstrate these effects in other tumor types. Resensitization is associated with prevention of AKT-mediated BAD phosphorylation. Strikingly, in patient-matched sensitive cells, we do not see enhanced apoptosis on combining cisplatin with AKT or DNA-PK inhibition. Insulin-mediated activation of AKT is unaffected by DNA-PK inhibitor treatment, suggesting that this effect is restricted to DNA damage-mediated activation of AKT and that, clinically, DNA-PK inhibition might prevent platinum-induced AKT activation without interfering with normal glucose homeostasis, an unwanted toxicity of direct AKT inhibitors.

DNA repair of myeloma plasma cells correlates with clinical outcome: the effect of the nonhomologous end-joining inhibitor SCR7

“…Three repair inhibitors were used: two of them modify NHEJ (NU7026 and SCR7) [39][40][41] and IR-1 disrupts HR (supplemental Materials and methods). 42 To investigate the effect of the combination treatment of melphalan with an inhibitor, we first selected the optimal concentrations of the inhibitors that, when administered alone, showed minimal decrease in cell viability.…”

Dose-Finding Quantitative 18F-FDG PET Imaging Study with the Oral Pan-AKT Inhibitor GSK2141795 in Patients with Gynecologic Malignancies

“…In general, GSK2141795 administered at doses of 75 mg or less daily was tolerable and demonstrated some activity in this difficultto-treat group of patients; although based on the preclinical rationale, the hypothesis would be that this modest activity would be synergistic in combination with platinum and other cytotoxics (12). On a genetic level, PIK3CA/PIK3R1 mutations did not obviously segregate with response to GSK2141795 as measured by RECIST or GCIG CA125 criteria; however, RAS/RAF pathway mutations did coincide with lack of response to AKT inhibition (26,27).…”

“…The preclinical rationale for AKT inhibition in platinum-resistant ovarian cancer was based on in vitro data that small-interfering RNA inhibition of AKT in platinum-resistant ovarian cancer cells could dramatically resensitize these cells to platinum chemotherapy (12) and that in in vitro and preclinical molecular imaging studies with 18 F-FDG and 39-deoxy-39-18 F-fluorothymidine PET this could be recapitulated using a pharmacologic AKT inhibitor (11), raising the hope that a similar strategy could succeed in clinical trials. The wider purpose of this study was therefore to investigate whether molecular imaging could be used to determine optimal dosing of GSK2141795 in individuals, which would be needed to resensitize to platinum chemotherapy in resistant patients.…”

Down-regulation of Ras-related Protein Rab 5C-dependent Endocytosis and Glycolysis in Cisplatin-resistant Ovarian Cancer Cell Lines

“…Alternations in other signaling pathways have also been found in drug resistant ovarian cancer (27)(28)(29). For example, DNA-PK phosphorylates RAC-alpha serine/threonine-protein kinase (AKT) and inhibits cisplatin-mediated apoptosis (28); and silencing of HDAC4 increases acetyl-STAT1 levels to prevent platinum-induced STAT1 activation and restore cisplatin sensitivity (29).…”