RA and arsenic induce growth inhibition and apoptosis in NPM1 mutated AML cell line. (A) AML cell lines with normal NPM1 (ML-2, KG1a, and THP-1) or mutated NPM1 (OCI-AML3 and IMS-M2) were treated with arsenic (1 μM or 0.1 μM), RA (1 μM or 0.3 µM) or a combination of both. Cell growth (percent of control) was assayed in triplicate wells. The results represent the average of at least 3 independent experiments. (B) Annexin V staining of THP-1 or OCI-AML3 cells treated for 48 hours as described. (C) TUNEL assay of THP-1 or OCI-AML3 cells treated for 48 hours as described. The results are the average of 3 independent experiments. (D) Flow cytometry analysis using CD11b differentiation marker on OCI-AML3 treated for 48 hours. (E) Western blot analysis for p53, P-p53, p21, or actin in THP-1 and OCI-AML3 cells treated for 48 hours as described.