u-0126 and Carcinoma--Small-Cell

Cisplatin is widely used for the treatment of solid tumors, including small cell lung cancers, but its success is often compromised due to relapse and resistance to further treatment. p70 ribosomal S6 kinase (p70S6K) has been shown to be upregulated in lung cancer cells. In the present study, we investigated whether the p70S6K pathway contributes to cisplatin resistance in human small cell lung cancer H69 cells. The levels of phosphorylated p70S6K and its downstream target S6 but not total p70S6K or S6 were elevated in the H69 cells that acquired resistance to cisplatin (H69/CP) compared to parental H69 cells. Cisplatin treatment resulted in the activation of p70S6K and downregulation of p70S6K was associated with cisplatin-induced PARP cleavage. While the ability of cisplatin to induce apoptosis was attenuated in H69/CP cells, inhibition of p70S6K by rapamycin enhanced cisplatin-induced apoptosis in these cells as evident by the increase in cisplatin-induced poly(ADP-ribose) polymerase (PARP) cleavage. The phosphoinositide 3-kinase (PI3K) inhibitor Ly294002 alone induced PARP cleavage and further augmented cisplatin-induced PARP cleavage. In contrast, inhibition of extracellular signal-regulated kinase (ERK) by U0126 attenuated cisplatin-induced PARP cleavage. Both rapamycin and Ly294002 enhanced cisplatin-induced acti-vation of ERK1/2. Taken together, these results suggest that activation of p70S6K contributes to cisplatin resistance in small cell lung cancer H69 cells, and inhibition/downregulation of p70S6K as well as activation of ERK1/2 could circumvent cisplatin resistance.

Topics: Antineoplastic Agents; Apoptosis; Butadienes; Carcinoma, Small Cell; Cell Line, Tumor; Chromones; Cisplatin; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases; Humans; Lung Neoplasms; Morpholines; Nitriles; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Poly(ADP-ribose) Polymerases; Protein Kinase Inhibitors; Ribosomal Protein S6 Kinases, 70-kDa; Sirolimus

We previously demonstrated the doxorubicin-induced urokinase-type plasminogen activator (uPA) expression in human RC-K8 lymphoma cells and NCI-H69 small cell lung carcinoma cells in which reactive oxygen species might be involved. Western blotting analysis revealed phosphorylation/activation of mitogen-activated protein (MAP) kinases, such as extracellular signal-regulated kinase (ERK) 1/2, p38 MAP kinase and stress-activated protein kinase/c-jun N-terminal protein kinase (SAPK/JNK) in doxorubicin-treated RC-K8 and H69 cells, and, therefore, we attempted to identify the MAP kinases implicated in doxorubicin-induced uPA expression by the use of their specific inhibitors. U0126, SB202190 and JNKI-1, inhibitors for MAPK kinase, (MEK) 1/2, p38 MAP kinase and SAPK/JNK, respectively, specifically and clearly inhibited their corresponding kinases. U0126 and SB202190, but not JNKI-1, almost completely inhibited the doxorubicin-induced uPA expression in both RC-K8 and H69 cells. However, U0126 rather enhanced the doxorubicin-induced activation of caspase-3 and poly ADP-ribose polymerase (PARP), and U0126 itself activated caspase-3 and PARP. Interestingly, JNKI-1 inhibited the doxorubicin-induced activation of caspase-3 and PARP. Therefore, doxorubicin treatment activates the above three kinases, but different MAP kinase signaling is responsible in the doxorubicin-induced caspase activation and expression of uPA. Thus, we could possibly manipulate the direction of doxorubicin-induced MAP kinase activation and the effects of doxorubicin on the tumor cell biology by the use of MAP kinase inhibitors.

Topics: Blotting, Northern; Blotting, Western; Butadienes; Carcinoma, Small Cell; Caspase 3; Caspases; Cell Line, Tumor; Doxorubicin; Enzyme Activation; Enzyme Inhibitors; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Neoplastic; Humans; Imidazoles; Lung Neoplasms; Lymphoma; MAP Kinase Kinase 4; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase 8; Nitriles; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Poly Adenosine Diphosphate Ribose; Pyridines; Urokinase-Type Plasminogen Activator