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within the region encoding the DNA-binding domain, sug- gesting loss of p53’s tumor suppressive function (Figure 1A, Table 1). In the TP53mut samples, the second allele carried a nonsense mutation (TP53mut-1), was absent (loss of 17p, TP53mut-2, -3), or carried the same missense mutation (TP53mut-4) (Table 1). Somatic and germline TP53mut are
A
associated with (low) hypodiploid ALL.15,19-21 One primo- graft sample (TP53mut-3) showed a hypodiploid karyotype with 44 chromosomes (Table 1). In line with disrupted degradation and accumulation of mutant p53 protein, TP53mut cases showed higher p53 protein levels compared to TP53wt leukemias (Figure 1B).
B
CD
EF
Figure 1. TP53-mutated acute lymphoblastic leukemias are DNA-damage resistant but sensitive to APR-246. (A) All TP53mut B-cell precursor (BCP) acute lym- phoblastic leukemia (ALL) primograft and cell lines harbor missense mutations (filled circles) localized in the DNA-binding domain of TP53. The primograft sample TP53mut-1 carries an additional stop mutation (R213X, open circle). See also Table 1. (B) Increased p53 protein expression in TP53mut compared to TP53wt ALL in primograft (left) and cell line (right) leukemia samples. Western blot, anti-p53 antibody (total, clone DO-7) with GAPDH as a loading control. (C-F) Significantly high- er half maximal inhibitory concentrations (IC50) for doxorubicin in TP53mut (red curves) primograft (C) and cell line (D) BCP-ALL, and significantly lower IC50 values for APR-246 in TP53mut primograft (E) and cell line (F) samples, indicating insensitivity to the DNA-damaging agent doxorubicin but sensitivity to APR-246 in TP53mut BCP-ALL. Dose-response curves reflect cell death induction in response to increasing concentrations summarizing one (primografts, 24 h; C, E) or three (cell lines, 48 h; D, F) independent experiments, each performed in triplicate. Comparison of sensitivities of TP53wt and TP53mut leukemias, F-test, ***P<0.001. See also Online Supplementary Table S2.
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