Cyclin-Dependent Kinase 4/antagonists & inhibitors; Heterocyclic Compounds, 3-Ring/administration & dosage; Leukemia, Myeloid, Acute/drug therapy; Naphthyridines/administration & dosage; Protein Kinase Inhibitors/administration & dosage; fms-Like Tyrosine Kinase 3/antagonists & inhibitors; Animals; Apoptosis/drug effects; Cell Cycle/drug effects; Cell Line, Tumor; Cell Proliferation/drug effects; Dose-Response Relationship, Drug; Heterocyclic Compounds, 3-Ring/pharmacokinetics; Heterocyclic Compounds, 3-Ring/therapeutic use; Humans; Leukemia, Myeloid, Acute/genetics; Leukemia, Myeloid, Acute/pathology; Mice; Mice, Nude; Naphthyridines/pharmacokinetics; Naphthyridines/therapeutic use; Neoplasms, Experimental; Niacinamide/analogs & derivatives; Niacinamide/pharmacology; Phenylurea Compounds/pharmacology; Piperazines/pharmacology; Protein Kinase Inhibitors/pharmacokinetics; Pyridines/pharmacology; Signal Transduction/drug effects; Sorafenib; U937 Cells; Xenograft Model Antitumor Assays