bafilomycin-a1 and Leukemia--Myelogenous--Chronic--BCR-ABL-Positive

Autophagy that is induced by starvation or cellular stress can enable cancer cell survival by sustaining energy homeostasis and eliminating damaged organelles and proteins. In response to stress, cancer cells have been reported to accumulate the protein p62/SQSTM1 (p62), but its role in the regulation of autophagy is controversial. Here, we report that the plant phytoalexin resveratrol (RSV) triggers autophagy in imatinib-sensitive and imatinib-resistant chronic myelogenous leukemia (CML) cells via JNK-dependent accumulation of p62. JNK inhibition or p62 knockdown prevented RSV-mediated autophagy and antileukemic effects. RSV also stimulated AMPK, thereby inhibiting the mTOR pathway. AMPK knockdown or mTOR overexpression impaired RSV-induced autophagy but not JNK activation. Lastly, p62 expression and autophagy in CD34+ progenitors from patients with CML was induced by RSV, and disrupting autophagy protected CD34+ CML cells from RSV-mediated cell death. We concluded that RSV triggered autophagic cell death in CML cells via both JNK-mediated p62 overexpression and AMPK activation. Our findings show that the JNK and AMPK pathways can cooperate to eliminate CML cells via autophagy.

Topics: Adaptor Proteins, Signal Transducing; Amino Acid Chloromethyl Ketones; AMP-Activated Protein Kinases; Antineoplastic Agents; Antineoplastic Agents, Phytogenic; Autophagy; Benzamides; Blotting, Western; Caspase Inhibitors; Caspases; Cell Survival; Drug Resistance, Neoplasm; Humans; Imatinib Mesylate; JNK Mitogen-Activated Protein Kinases; K562 Cells; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Macrolides; Microscopy, Confocal; Microscopy, Electron; Piperazines; Pyrimidines; Resveratrol; RNA Interference; Sequestosome-1 Protein; Stilbenes; Tumor Cells, Cultured; Vacuolar Proton-Translocating ATPases

Imatinib mesylate (IM), a potent inhibitor of the BCR/ABL tyrosine kinase, has become standard first-line therapy for patients with chronic myeloid leukemia (CML), but the frequency of resistance increases in advancing stages of disease. Elimination of BCR/ABL-dependent intracellular signals triggers apoptosis, but it is unclear whether this activates additional cell survival and/or death pathways. We have shown here that IM induces autophagy in CML blast crisis cell lines, CML primary cells, and p210BCR/ABL-expressing myeloid precursor cells. IM-induced autophagy did not involve c-Abl or Bcl-2 activity but was associated with ER stress and was suppressed by depletion of intracellular Ca2+, suggesting it is mechanistically nonoverlapping with IM-induced apoptosis. We further demonstrated that suppression of autophagy using either pharmacological inhibitors or RNA interference of essential autophagy genes enhanced cell death induced by IM in cell lines and primary CML cells. Critically, the combination of a tyrosine kinase inhibitor (TKI), i.e., IM, nilotinib, or dasatinib, with inhibitors of autophagy resulted in near complete elimination of phenotypically and functionally defined CML stem cells. Together, these findings suggest that autophagy inhibitors may enhance the therapeutic effects of TKIs in the treatment of CML.

Topics: Animals; Antineoplastic Agents; Autophagy; Benzamides; Calcium; Cell Death; Cell Line, Tumor; Chloroquine; Dasatinib; Endoplasmic Reticulum; Fusion Proteins, bcr-abl; Gene Expression; Humans; Imatinib Mesylate; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Macrolides; Mice; Mice, Inbred C3H; Microtubule-Associated Proteins; Neoplastic Stem Cells; Piperazines; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Pyrimidines; RNA Interference; Thiazoles; Transcription Factor CHOP; Xenograft Model Antitumor Assays