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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: OBJECTIVE, METHODS, RESULTS. Meshes: Amino Acid Chloromethyl Ketones, Antineoplastic Combined Chemotherapy Protocols, Apoptosis, Caspase Inhibitors, Caspases, Cell Cycle, Cysteine Proteinase Inhibitors, Drug Interactions, Enzyme Activation, Etoposide, HL-60 Cells, HSP70 Heat-Shock Proteins, Humans, Leukemia, Promyelocytic, Acute, Leupeptins, Microtubules, Nocodazole, Proteasome Inhibitors, Up-Regulation.
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Do proteasome inhibitors abolish cell death downstream of caspase activation during anti-microtubule drug-induced apoptosis in leukemia cells? Context: Anti-microtubule drugs and proteasome inhibitors are currently among the most intensively studied anti-tumor agents, however little is known about their pharmacological interactions at the cellular level. The human promyelocytic leukemia cell line, HL-60, was exposed to nocodazole or etoposide in combination with proteasome or caspase inhibitors. Apoptotic cell death was detected by flow cytometry as sub-G1 population. Caspase and proteasome activities were monitored by the fluorogenic substrates Ac-DEVD-AMC and Suc-LLVY-AMC, respectively, in cell lysate. Heat shock protein 70 (HSP70) expression was determined by Western blotting. Nocodazole, a microtubule inhibitor, induced caspase-dependent apoptosis in the HL-60 cell line. At sub-cytotoxic concentrations, proteasome inhibitors, including MG-132 or clasto-beta-lactone, decreased nocodazole-induced apoptotic DNA fragmentation without affecting the induction of caspase-3 activity. In contrast, MG-132 decreased both DNA fragmentation and caspase activation induced by etoposide, a topoisomerase-II inhibitor. HSP70 had previously been found to inhibit apoptosis independently from caspase activation. In this study, MG-132 up-regulated HSP70 protein expression, both in the presence or absence of nocodazole.
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Proteasome inhibitors decreased anti-microtubule agent-induced apoptotic DNA fragmentation downstream of caspase-3 activation, possibly due to increased HSP70 expression. The results indicate that combination treatment with these novel anti-tumor agents in leukemia requires careful evaluation of their molecular interaction at the level of apoptosis induction. Final Decision: yes