Abstract LB-127: Synthetic lethal RNAi screen of the human kinome with cytarabine (AraC) in leukemia cells

Abstract

Abstract Cytarabine is the backbone of therapy for acute myeloid leukemia (AML) patients, yet due to a high incidence of relapse and treatment-related complications novel, less toxic treatment regimens incorporating AraC need to be designed. To increase the therapeutic effect of cytarabine we developed and performed an RNAi synthetic lethal screening assay using siRNA, targeting 572 human kinases in combination with AraC in human myeloid cell lines TF-1 and THP-1. Several genes that enhance the effectiveness of cytarabine were identified. Among the top candidate genes, a trend became apparent in which several key regulators of the cell cycle as well as DNA repair genes where among the strongest sensitizers (CHEK1, PKMYT, CDC2, AURKB and ATR). The effectiveness of targeting these genes in combination with AraC was verified using a highly robust siRNA drug-dose response assay (siDDR) that validated CHEK1 as strong sensitizer, PKMYT as moderate sensitizer, and did not confirm CDC2 or AURKB as sensitizers. Since CHEK1 is emerging as a potential treatment target in combination chemotherapy in solid tumors, we obtained two commercially available CHEK1 inhibitors, PD 407824 and SB 218078 (both Tocris). PD 407824 strongly sensitized to AraC in the range of 2 to 10 fold decrease in several lines (MV 4;11, THP-1, HL60, HEL, ML-2) whereas in a few no sensitization was observed (MDS-L, U937). Calcusyn software was utilized to ensure the effect was more than simply additive in effect. Less effect was observed for SB 218078, which was surprisingly found to be antagonistic in some lines (TF-1, U937, ML-2, HL-60). Both compounds have slightly different target spectrum's that include CHEK1 plus other kinases. Interestingly, the sequence of addition of the compounds dramatically affected the outcome, with the greatest effects seen when CHEK1 inhibitors were added before AraC. In cases where AraC was added first or simultaneously, the effect was less pronounced or was not seen at all. Herein we present the “first-in-class” human kinome synthetic lethal screen in leukemia suspension cells in combination with AraC. In this unbiased functional genomics screen a strong convergence of hits emerged around G2/M cell cycle and DNA repair control. This information can immediately inform clinical drug development, channel resources and serve to direct development of new therapies in acute myeloid leukemias combining AraC with the first clinical available CHEK1 inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-127.