bryostatin-1 and Carcinoma--Small-Cell

Daphnane-type diterpene gnidimacrin (NSC 252940) shows significant antitumor activity against murine tumors and human tumor cell lines. This compound binds to and directly activates protein kinase C (PKC), arresting the cell cycle at the G(1) phase through inhibition of cdk2 activity in human K562 leukemia cells. In our study, we examined whether cellular PKC is involved in the antiproliferating effect of gnidimacrin. In a 24-hr exposure of K562 cells to high concentrations of bryostatin 1 (0.11-3.3 microM), both expression of PKC alpha and PKC betaII was downregulated, and thereafter these cells became resistant to gnidimacrin in response to the degree of PKC downregulation. In addition, PKC alpha and PKC betaII genes were transfected to gnidimacrin-resistant human hepatoma HLE cells that demonstrated positive expression of PKC alpha and negative expression of PKC betaII. PKC betaII gene-transfected cells became sensitive to gnidimacrin in relation to the degree of PKC betaII expression. The most sensitive clone to show 0.001 microg/mL (1.2 nM) as IC(50) in a continuous 4-day exposure was obtained. While PKC alpha gene-transfected cells exhibited an increase in PKC alpha expression and became sensitive to gnidimacrin, sensitivity was one-hundredth of that in PKC betaIotaIota gene-transfected cells. These results suggest that PKC, in particular PKC betaIotaIota, is necessary in the antitumor effect of gnidimacrin.

Topics: Antineoplastic Agents, Phytogenic; Bryostatins; Carcinoma, Small Cell; CDC2-CDC28 Kinases; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinases; Diterpenes; Drug Resistance, Neoplasm; Enzyme Activation; Enzyme Induction; G1 Phase; Gene Expression Regulation, Leukemic; Gene Expression Regulation, Neoplastic; HL-60 Cells; Humans; Isoenzymes; K562 Cells; Lactones; Lung Neoplasms; Macrolides; Neoplasm Proteins; Protein Kinase C; Protein Kinase C beta; Protein Kinase C-alpha; Protein Serine-Threonine Kinases; Recombinant Fusion Proteins; Transfection; Tumor Cells, Cultured

Protein kinase C (PKC) influences cellular sensitivity to cis-diamminedichloroplatinum(II) (cDDP). We have investigated whether the PKC signal transduction pathway is affected during the development of cellular resistance to cDDP. Activators of PKC, such as phorbol 12,13-dibutyrate (PDBu), enhanced the sensitivity of human small cell lung cancer H69 cells to cDDP by 2-fold but had no effect on the sensitivity of cDDP-resistant H69 cells (H69/CP) to cDDP. The maximum sensitization was achieved with 10 nM PDBu and blocked by down-regulation of PKC with higher concentrations of PDBu (1 microM) or bryostatin 1 (0.1 microM). PKC activity was decreased significantly in H69/CP cells compared to the drug-sensitive variant. A similar reduction in PKC activity was noted in ovarian carcinoma 2008 cells that were resistant to cDDP. A modest decrease in PKC activity was also observed in etoposide-resistant H69 (H69/VP-16) cells but not in Taxol-resistant H69 cells or bleomycin-resistant human head and neck carcinoma A-253 cells. H69 cells expressed conventional PKC alpha and-beta, novel PKC delta, atypical PKC zeta and-iota, and novel/atypical PKC mu. A decrease in cPKC alpha and-beta and an increase in nPKC delta were associated with the cDDP-resistant phenotype. The abundance of aPKC zeta or-iota was unaffected. H69/ VP-16 cells also displayed a reduction in cPKC beta and an increase in nPKC delta. Taxol-resistant H69 cells had no alteration in the expression of any of the PKC isozymes. Thus, a reduction in cPKCs and an increase in nPKC may be associated with cDDP resistance.

Topics: Antineoplastic Agents; Bleomycin; Bryostatins; Carcinoma; Carcinoma, Small Cell; Cisplatin; Drug Resistance, Neoplasm; Enzyme Activation; Etoposide; Female; Head and Neck Neoplasms; Herpes Simplex Virus Protein Vmw65; Humans; Lactones; Lung Neoplasms; Macrolides; Ovarian Neoplasms; Paclitaxel; Phorbol 12,13-Dibutyrate; Protein Kinase C; Signal Transduction; Tumor Cells, Cultured