nutlin-3a and Chromosome-Deletion

Despite the high complete response rates achieved with fludarabine-based regimens, relapse is inevitable in chronic lymphocytic leukemia (CLL). Relapsed patients often acquire deletions of the short arm of chromosome 17 (del[17p]), which are closely associated with tumor protein 53 (TP53) mutations. Wild-type p53 up-regulates and activates B-cell CLL/lymphoma 2 (BCL-2)-associated X protein (BAX), and it down-regulates and inactivates BCL-2. The small-molecule BCL-2 inhibitor ABT-737 induces apoptosis in a BAX-dependent and BCL-2 homologous antagonist-killer (BAK)-dependent manner. The role of p53 in sensitivity of CLL cells to BCL-2 inhibition has not been extensively investigated.. The authors investigated the association of del(17p) with ABT-737 sensitivity in CLL cells from 50 patients. Stable p53 and BAX knockdown cells were used for mechanistic studies.. CLL cells with del(17p) were less sensitive to ABT-737-induced BAX activation and apoptosis than CLL cells without del(17p) (39% ± 7.3% vs 63.7% ± 2.9% [specific annexin V induction]; P < .01). A positive correlation between the degrees of apoptosis induced by ABT-737 and by the p53-activating binding protein homolog murine double minute (MDM2) antagonist nutlin-3a (correlation coefficient [r] = 0.75; P < .0001) was observed. CLL cells with del(17p) expressed lower levels of BAX than those without del(17p) (0.67 ± 0.12 vs 1.27 ± 0.10 in relative protein expression levels; P < .01). Knockdown of p53 or BAX in leukemia cells resulted in decreased apoptosis induced by ABT-737.. The current data indicated that p53 dysfunction may lead to decreased apoptosis induction by ABT-737.

Topics: Aged; Aged, 80 and over; Apoptosis; bcl-2-Associated X Protein; Biphenyl Compounds; Cells, Cultured; Chromosome Deletion; Chromosomes, Human, Pair 17; Drug Resistance, Neoplasm; Female; Gene Expression Regulation, Neoplastic; Humans; Imidazoles; Leukemia, Lymphocytic, Chronic, B-Cell; Male; Middle Aged; Mutation; Nitrophenols; Pharmacogenetics; Piperazines; Proto-Oncogene Proteins c-bcl-2; Smith-Magenis Syndrome; Sulfonamides; Treatment Outcome; Tumor Suppressor Protein p53

Myeloma cells are sensitive to TRAIL through the two death receptors DR4 and DR5. Because p53 directly modulates expression of death receptors, we investigated here whether p53 can modulate myeloma sensitivity to TRAIL. We found that p53 affects the sensitivity of myeloma cells to the DR5 agonistic human antibody lexatumumab but not the DR4 antibody mapatumumab. TP53 wild-type myeloma cells overexpressed DR5 in correlation with sensitivity to lexatumumab. Both nongenotoxic (nutlin-3a) and genotoxic (melphalan) p53-inducing stresses increased DR5 expression only in TP53 wild-type cells and synergistically increased lexatumumab efficiency yet did not increase DR4 expression, nor sensitivity to mapatumumab. Silencing of p53 strongly decreased DR5 expression and induced resistance to nutlin-3a and lexatumumab but did not modulate DR4 expression or sensitivity to mapatumumab. Increase of lexatumumab efficiency induced by nutlin-3a was related to a p53-dependent increase of DR5 expression. In primary myeloma cells, nutlin-3a increased DR5 expression and lexatumumab efficiency but did not increase mapatumumab efficiency. Taken together, our findings indicate that p53 controls the sensitivity of myeloma through DR5 but not DR4 and suggest that a subset of patients with multiple myeloma may benefit from DR5 therapy.

Topics: Antibodies, Monoclonal; Caspase 8; Cell Death; Cell Line, Tumor; Chromosome Deletion; Chromosomes, Human, Pair 17; Drug Resistance, Neoplasm; Enzyme Activation; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gene Silencing; Humans; Imidazoles; Multiple Myeloma; Piperazines; Receptors, TNF-Related Apoptosis-Inducing Ligand; Stress, Physiological; Tumor Suppressor Protein p53

Haploinsufficiency for ribosomal protein genes has been implicated in the pathophysiology of Diamond-Blackfan anemia (DBA) and the 5q-syndrome, a subtype of myelodysplastic syndrome. The p53 pathway is activated by ribosome dysfunction, but the molecular basis for selective impairment of the erythroid lineage in disorders of ribosome function has not been determined. We found that p53 accumulates selectively in the erythroid lineage in primary human hematopoietic progenitor cells after expression of shRNAs targeting RPS14, the ribosomal protein gene deleted in the 5q-syndrome, or RPS19, the most commonly mutated gene in DBA. Induction of p53 led to lineage-specific accumulation of p21 and consequent cell cycle arrest in erythroid progenitor cells. Pharmacologic inhibition of p53 rescued the erythroid defect, whereas nutlin-3, a compound that activates p53 through inhibition of HDM2, selectively impaired erythropoiesis. In bone marrow biopsies from patients with DBA or del(5q) myelodysplastic syndrome, we found an accumulation of nuclear p53 staining in erythroid progenitor cells that was not present in control samples. Our findings indicate that the erythroid lineage has a low threshold for the induction of p53, providing a basis for the failure of erythropoiesis in the 5q-syndrome, DBA, and perhaps other bone marrow failure syndromes.

Topics: Anemia, Diamond-Blackfan; Anemia, Macrocytic; Animals; Benzothiazoles; Cell Cycle; Cell Lineage; Cell Nucleolus; Chromosome Deletion; Chromosomes, Human, Pair 5; Cyclin-Dependent Kinase Inhibitor p21; Erythroid Precursor Cells; Haploinsufficiency; Hematopoiesis; Humans; Imidazoles; Mice; Mice, Inbred BALB C; Myelodysplastic Syndromes; Piperazines; Protein Binding; Proto-Oncogene Proteins c-mdm2; Ribosomal Proteins; RNA, Small Interfering; Toluene; Tumor Suppressor Protein p53