alvocidib and pyrazolanthrone

The efficacy of many chemotherapeutic agents can be attenuated by expression of the anti-apoptotic proteins Bcl-2, Bcl-X(L) and Mcl-1. Flavopiridol and dinaciclib are cyclin-dependent kinase 7 and 9 inhibitors that transcriptionally inhibit expression of Mcl-1. We have investigated the ability of flavopiridol and dinaciclib to sensitize a panel of leukemia cell lines to vinblastine and paclitaxel. Both drugs acutely sensitized most of the leukemia lines to vinblastine, with 100% apoptosis in 4 h. Furthermore, dinaciclib sensitized freshly isolated chronic lymphocytic leukemia cells to vinblastine. This rapid induction of apoptosis was attributed to vinblastine-mediated activation of JNK because (a) flavopiridol and dinaciclib failed to induce apoptosis when combined with non-JNK activating concentrations of vinblastine; (b) JNK inhibitors suppressed JNK activity and prevented apoptosis; (c) flavopiridol did not potentiate apoptosis induced by paclitaxel which does not activate JNK in these cells; and (d) Jurkat cells failed to activate JNK in response to vinblastine and were not sensitive to combinations of vinblastine and flavopiridol or dinaciclib. The rapid induction of apoptosis by this combination in multiple cell systems but not in normal lymphocytes provides justification for performing a clinical trial to assess the efficacy in patients.

Topics: Anthracenes; Antineoplastic Agents, Phytogenic; Apoptosis; Bridged Bicyclo Compounds, Heterocyclic; Cell Cycle; Cell Line, Tumor; Cell Survival; Cyclic N-Oxides; Cyclin-Dependent Kinase 9; Cyclin-Dependent Kinase-Activating Kinase; Cyclin-Dependent Kinases; Dose-Response Relationship, Drug; Drug Synergism; Flavonoids; HL-60 Cells; Humans; Immunoblotting; Indolizines; JNK Mitogen-Activated Protein Kinases; Jurkat Cells; Myeloid Cell Leukemia Sequence 1 Protein; Paclitaxel; Piperidines; Protein Kinase Inhibitors; Proto-Oncogene Proteins c-bcl-2; Pyridinium Compounds; U937 Cells; Vinblastine

Flavopiridol was developed as a drug for cancer therapy due to its ability to inhibit cell cycle progression by targeting cyclin-dependent kinases (CDKs). In this study, we show that flavopiridol may also have a neuroprotective action. We show that at therapeutic dosage (or at micromolar range), flavopiridol almost completely prevents colchicine-induced apoptosis in cerebellar granule neurones. In agreement with this, flavopiridol inhibits both the release of cyt c and the activation of caspase-3 induced in response to colchicine treatment. We demonstrate that in this cellular model for neurotoxicity, neither re-entry in the cell cycle nor activation of stress-activated protein kinases, such as c-Jun N-terminal kinase (JNK) or p38 MAP kinase, is involved. In contrast, we show that colchicine-induced apoptosis correlates with a substantial increase in the expression of cdk5 and Par-4, which is efficiently prevented by flavopiridol. Accordingly, a cdk5 inhibitor such as roscovitine, but not a cdk4 inhibitor such as 3-ATA, was also able to protect neurons from apoptosis as well as prevent accumulation of cdk5 and Par-4 in response to colchicine. Our data suggest a potential therapeutic use of flavopiridol in disorders of the central nervous system in which cytoskeleton alteration mediated by cdk5 activation and Par-4 expression has been demonstrated, such as Alzheimer's disease.

Topics: Amino Acid Chloromethyl Ketones; Animals; Animals, Newborn; Anthracenes; Anti-Bacterial Agents; Apoptosis; Apoptosis Regulatory Proteins; Blotting, Western; Bromodeoxyuridine; Carrier Proteins; Caspase 3; Caspases; CDC2-CDC28 Kinases; Cell Count; Cell Survival; Cells, Cultured; Cerebellum; Chromatin; Colchicine; Cyclin E; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 5; Cyclin-Dependent Kinases; Cytochromes c; Dose-Response Relationship, Drug; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Flavonoids; Flow Cytometry; Immunohistochemistry; Intracellular Signaling Peptides and Proteins; JNK Mitogen-Activated Protein Kinases; Kainic Acid; MAP Kinase Kinase 4; Microtubules; Minocycline; Mitogen-Activated Protein Kinase Kinases; Neurons; Neuroprotective Agents; Piperidines; Purines; Rats; Rats, Sprague-Dawley; Roscovitine; Time Factors; Tubulin