nitrophenols and Blast-Crisis

The Bcr-Abl tyrosine kinase regulates several Bcl-2 family proteins that confer resistance to apoptosis in chronic myeloid leukemia (CML) cells. Given p53's ability to modulate the expression and activity of Bcl-2 family members, we hypothesized that targeting Bcr-Abl, Bcl-2, and p53 concomitantly could have therapeutic benefits in blast crisis (BC) CML and in quiescent CML CD34+ cells that are insensitive to tyrosine kinase inhibitors (TKI). We examined the effects of the MDM2 inhibitor nutlin3a and its combination with the dual Bcl-2 and Bcl-xL inhibitor ABT-737, and the Bcr-Abl inhibitor nilotinib on BC CML patient samples. We found that in quiescent CD34+ progenitors, p53 expression is significantly lower, and MDM2 is higher, compared to their proliferating counterparts. Treatment with nutlin3a induced apoptosis in bulk and CD34+CD38- cells, and in both proliferating and quiescent CD34+ progenitor CML cells. Nutlin3a synergized with ABT-737 and nilotinib, in part by inducing pro-apoptotic, and suppressing anti-apoptotic, Bcl-2 proteins. Nilotinib inhibited the expression of Bcl-xL and Mcl-1 in BC CML cells. These results demonstrate that p53 activation by MDM2 blockade can sensitize BC CML cells, including quiescent CD34+ cells, to Bcl-2 inhibitor- and TKI-induced apoptosis. This novel strategy could be useful in the therapy of BC CML.

Topics: ADP-ribosyl Cyclase 1; Antigens, CD34; Antineoplastic Agents; Apoptosis; bcl-X Protein; Biphenyl Compounds; Blast Crisis; Cell Proliferation; Enzyme Activation; Fusion Proteins, bcr-abl; Gene Expression Regulation, Leukemic; Humans; Imatinib Mesylate; Imidazoles; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Membrane Glycoproteins; Nitrophenols; Piperazines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-bcl-2; Proto-Oncogene Proteins c-mdm2; Pyrimidines; Sulfonamides; Tumor Cells, Cultured; Tumor Suppressor Protein p53

Despite being highly effective for newly diagnosed chronic myeloid leukemia (CML), imatinib not only is inactive against quiescent CML stem cells, but also has limited activity against blast crisis (BC) CML. The relative activity of Bcr-Abl and the expression levels of antiapoptotic proteins in proliferating and quiescent CD34(+) BC CML progenitor cells and the effects of targeting antiapoptotic proteins in these cells are unknown. Here we report higher levels of p-CrkL in quiescent than in proliferating CD34(+) progenitor cells and comparable expression levels of Bcl-2, Bcl-xL, Mcl-1 and XIAP in the two populations in BC CML. Inhibition of Bcl-2/Bcl-xL by ABT-737 in cells from patients with tyrosine kinase inhibitor (TKI)-resistant BC CML promoted apoptosis in quiescent CD34(+) progenitor cells with an efficacy similar to that in proliferating cells. Combination of ABT-737 with imatinib (which decreases Mcl-1 levels) or triptolide (which decreases Mcl-1 and XIAP) synergistically induced death of both proliferating and quiescent CD34(+) progenitor cells obtained from TKI-resistant BC CML patients. These results suggest that antiapoptotic proteins are critical targets in BC CML and that activation of apoptosis signaling can eliminate both proliferating and quiescent CD34(+) progenitor cells in BC CML, independent of response to TKIs.

Topics: Antigens, CD34; Apoptosis; Benzamides; Biphenyl Compounds; Blast Crisis; Cell Line, Tumor; Diterpenes; Epoxy Compounds; Fusion Proteins, bcr-abl; Hematopoietic Stem Cells; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Nitrophenols; Phenanthrenes; Piperazines; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Proto-Oncogene Proteins c-bcl-2; Pyrimidines; RNA, Messenger; Signal Transduction; Sulfonamides