Fig 1: SAMHD1 determines CNDAC sensitivity of primary AML cells. (A) Correlation of SAMHD1 protein levels and CNDAC concentrations that reduce cell viability by 50% (IC50s) in bone-marrow-derived leukaemic blasts derived from 24 therapy-naïve AML patients. Cells were co-immunostained for CD33, CD34, CD45 (surface markers) and intracellular SAMHD1 and the mean fluorescence intensity (MFI) was analysed by flow cytometry. ATP assays were performed in three technical replicates to determine the CNDAC IC50 values. Linear regression analyses were performed using GraphPad Prism. (B) CNDAC IC50 values in bone-marrow-derived leukaemic blasts derived from six therapy-naïve AML patients either treated with VPX virus-like particles (VPX-VLPs, cause SAMHD1 depletion), VPR virus-like particles (VPR-VLPs, negative control), or left untreated. Horizontal lines and error bars indicate means ± SD of three technical replicates. p-values were determined by two-tailed Student’s t-tests (*p < 0.05; **p < 0.01; ***p < 0.001). (C) CNDAC dose-response curves in primary AML cells of one exemplary patient (Patient E) treated with VPX-VLPs, VPR-VLPs or left untreated. IC50 values represent means ± SD of three technical replicates. (D) Representative Western blots indicating SAMHD1 levels in primary AML cells derived from Patient E in response to treatment with VPX-VLPs. (E) CNDAC-triphosphate (CNDAC-TP) levels as determined by LC-MS/MS in primary AML cells derived from Patient E in response to treatment with VPX-VLPs