bryostatin-1 and 7-hydroxystaurosporine

Protein kinase C (PKC) is a family of serine-threonine protein kinases that are involved in signal transduction pathways that regulate growth factor response, proliferation, and apoptosis. Its central role in these processes, which are closely involved in tumor initiation, progression, and response to antitumor agents, makes it an attractive therapeutic target in cancer. Despite initial activity seen in melanoma (bryostatin and UCN-01), non-Hodgkin's lymphoma (ISIS 3521, bryostatin, and UCN-01), and ovarian carcinoma (ISIS 3521 and bryostatin) in phase I studies, single-agent activity in those phase II studies reported to date has been limited. Preclinical data highlight a role for PKC in modulation of drug resistance and synergy with conventional cytotoxic drugs. A randomized phase III study of ISIS 3521 in combination with carboplatin and paclitaxel, compared with chemotherapy alone, in advanced non-small-cell lung cancer is underway. This paper reviews the rationale for using PKC inhibitors in cancer therapy, the challenges for clinical trial design, and the recent clinical experience with modulators of PKC activity.

Topics: Alkaloids; Animals; Antineoplastic Agents; Apoptosis; Bryostatins; Clinical Trials as Topic; Drug Resistance, Multiple; Enzyme Activation; Enzyme Inhibitors; Humans; Lactones; Macrolides; Molecular Structure; Oligodeoxyribonucleotides, Antisense; Protein Kinase C; Research Design; Staurosporine; Thionucleotides; Tumor Cells, Cultured

Chronic lymphocytic leukemia (CLL) is the most common adult leukemia for which therapeutic options remain unsatisfying as cure has remained elusive. Recent laboratory discoveries and promising results from completed phase III studies with fludarabine provide reason to reassess therapeutic goals in the treatment of patients with symptomatic CLL. Early enrollment of patients on protocols using combination therapies with fludarabine and new agents such as flavopiridol, IDEC-C2B8, Campath-1H, UCN-01, bryostatin, FR 901228, and melarsoprol will hopefully represent the next advance to improved overall survival and ultimately the cure of CLL.

Topics: Alkaloids; Antineoplastic Agents, Alkylating; Bryostatins; Flavonoids; Humans; Lactones; Leukemia, Lymphocytic, Chronic, B-Cell; Macrolides; Piperidines; Staurosporine; Topoisomerase I Inhibitors

The effects of the PKC activator and down-regulator bryostatin 1 and the PKC and Chk1 inhibitor 7-hydroxystaurosporine (UCN-01) were compared with respect to potentiation of 1-beta-D-arabinofuranosylcytosine (ara-C)-induced apoptosis in human myelomonocytic leukemia cells (U937). Whereas bryostatin 1 and UCN-01 both markedly enhanced ara-C-induced mitochondrial injury (e.g., cytochrome c and Smac/DIABLO release, loss of mitochondrial membrane potential), caspase activation, and apoptosis, ectopic expression of an N-terminal loop-deleted Bcl-2 mutant protein protected cells from ara-C/UCN-01- but not ara-C/bryostatin 1-mediated lethality. Conversely, ectopic expression of CrmA or dominant-negative caspase-8 abrogated potentiation of ara-C-mediated apoptosis by bryostatin 1 but not by UCN-01. Exposure of cells to ara-C and bryostatin 1 (but not UCN-01) resulted in sustained release of tumor necrosis factor (TNF) alpha; moreover, potentiation of ara-C lethality by bryostatin 1 (but not by UCN-01) was reversed by coadministration of TNF soluble receptors or the selective PKC inhibitor bisindolylmaleimide (1 microM). Finally, similar events were observed in the human promyelocytic leukemia cell line HL-60. Together, these findings suggest that potentiation of ara-C lethality in human myeloid leukemia cells by bryostatin 1 but not UCN-01 involves activation of the extrinsic, receptor-mediated apoptotic pathway, and represents a consequence of bryostatin 1-mediated release of TNF-alpha. They also argue that the mechanism by which bryostatin 1 promotes ara-C-induced mitochondrial injury, caspase activation, and apoptosis involves factors other than or in addition to PKC down-regulation or modulation of Bcl-2 phosphorylation status.

Topics: Alkaloids; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Bryostatins; Carrier Proteins; Caspases; Cytarabine; Cytochrome c Group; Drug Synergism; Enzyme Activation; Gene Deletion; HL-60 Cells; Humans; Indoles; Intracellular Signaling Peptides and Proteins; Lactones; Leukemia, Myeloid; Macrolides; Maleimides; Mitochondrial Proteins; Mutation; Phosphorylation; Protein Kinase C; Proto-Oncogene Proteins c-bcl-2; Receptors, Tumor Necrosis Factor; Staurosporine; Tumor Cells, Cultured; Tumor Necrosis Factor-alpha; U937 Cells

The effects of the non-tumor-promoting protein kinase C (PKC) activator bryostatin 1 and the PKC inhibitors staurosporine and UCN-01 were examined with respect to modulation of 1-[beta-D-arabinofuranosyl]cytosine (ara-C)-induced apoptosis in human myeloid leukemia cells (HL-60) overexpressing the antiapoptotic protein Bcl-2. HL-60/Bcl-2 cells displayed a 5-fold increase in Bcl-2 protein compared with empty-vector counter-parts (HL-60/pCEP4) but comparable levels of Bax, Mcl-1, and Bcl-xL. After exposure to an equimolar concentration of ara-C (10 microM for 6 hr), HL-60/Bcl-2 cells were significantly less susceptible to apoptosis, DNA fragmentation, and loss of clonogenicity than HL-60/pCEP4 cells. The protective effect of increased Bcl-2 expression was manifested by a failure of ara-C to induce activation/cleavage of the Yama protease (CPP32; caspase-3) and degradation of one of its substrates, poly(ADP-ribose)polymerase to an 85-kDa cleavage product. When HL-60/Bcl-2 cells were preincubated with bryostatin 1 (10 nM; 24 hr) or coincubated with either staurosporine (50 nM; 6 hr) or UCN-01 (300 nM; 6 hr) after a 1-hr preincubation, exposures that exerted minimal effects alone, ara-C-induced apoptosis and DNA fragmentation were restored to levels equivalent to, or greater than, those observed in empty-vector controls. These events were accompanied by restoration of the ability of ara-C to induce CPP32 cleavage and activation, poly(ADP-ribose) polymerase degradation, and inhibition of colony formation. Western analysis of Bcl-2 protein obtained from overexpressing cells treated with bryostatin 1, staurosporine, or UCN-01 revealed the appearance of a slowly migrating species and a general broadening of the protein band, effects that were insensitive to the protein synthesis inhibitor cycloheximide. Alterations in Bcl-2 protein mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis were reversed by treatment of lysates with alkaline phosphatase or protein phosphatase 2A; actions of the latter were blocked by the specific phosphatase inhibitor okadaic acid. In vivo labeling studies of Bcl-2 protein demonstrated increased incorporation of [32PO4]orthophosphate in drug-treated cells. Last, phosphorylated Bcl-2 failed to display decreased binding to the proapoptotic protein Bax. Collectively, these findings indicate that bryostatin 1, which down-regulates PKC, and staurosporine and UCN-01, which directly inhibit the enzyme, circumvent resistance of B

Topics: Alkaloids; Antimetabolites, Antineoplastic; Antineoplastic Agents; Apoptosis; Blotting, Western; Bryostatins; Cytarabine; DNA, Neoplasm; Down-Regulation; Drug Resistance, Neoplasm; Drug Synergism; Endopeptidases; Enzyme Inhibitors; HL-60 Cells; Humans; Lactones; Macrolides; Phosphorylation; Protein Kinase C; Proto-Oncogene Proteins c-bcl-2; Staurosporine