Apo2L/TRAIL is an endogenous antitumor protein that possesses efficacy-limiting properties such as short serum half-life, stability, cost, and limitations in delivery when used as a recombinant protein therapeutic. TIC10 is a first-in-class small molecule inducer of the human TRAIL gene that improves these unfavorable drug properties to ultimately increase the efficacy and utility of TRAIL. TIC10 upregulates TRAIL gene transcription by activating the pro-apoptotic transcription factor Foxo3a, which is achieved through dual inhibition of Akt and MEK/ERK. We conducted a siRNA screen using a kinase library to identify kinases that affect TIC10 response in cancer cells assayed by cell viability assays to gain mechanistic insight into the molecular mechanisms of TIC10 and potentially identify a combinatorial target to improve the activity of TIC10. Execution and validation of the siRNA screen revealed 4 kinases (DGKD, SGKL, STK23, KSR) that improved the therapeutic response to TIC10 upon siRNA-mediated knockdown at 36 hours, but not 12 hours, post-treatment in HCT116 human colon cancer cells. We next assayed the effect of knocking down these 4 kinases on cancer cell cytotoxic response to recombinant human TRAIL. These studies revealed no effect with kinase knockdowns, suggesting that the mechanisms of sensitization lie upstream of TIC10-mediated TRAIL production. Network analysis of the “hit” kinases and the previously described mechanism of TIC10 revealed rational overlap of signaling pathways and kinetics. Among the 4 identified kinases, KSR1 possessed the most direct connection to the putative mechanism of TIC10 that involves the dual inhibition of Akt and the MAPK pathway. KSR1 is a MAPK scaffold protein that positively regulates the MAPK signaling pathway. Based on these observations, we are testing the hypothesis that inhibiting KSR1 in combination with TIC10 cooperatively inhibits MAPK signaling to increase TRAIL production. Together, these results suggest that KSR1 is a key player in the cytotoxic response to TIC10 and that combining TIC10 and an inhibitor of KSR1 may result in improved therapeutic response.
Citation Format: Joshua E. Allen, Wafik S. El-Deiry. Kinase library siRNA screen identifies KSR1 as a synergistic therapeutic target in combination with TIC10. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2059. doi:10.1158/1538-7445.AM2013-2059
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