Statins synergistically potentiate 7-hydroxystaurosporine (UCN-01) lethality in human leukemia and myeloma cells by disrupting Ras farnesylation and activation

Statins inhibit Akt/PKB signaling via P2X7 receptor in pancreatic cancer cells

Cholesterol-lowering statins have been shown to inhibit growth of pancreatic cancer cells in vitro and in vivo. Epidemiological studies also indicate a chemopreventive effect of statins. We have investigated the effect of statins on Akt/protein kinase B signaling. We found that atorvastatin decreased constitutive- and insulin-induced pAkt in Panc-1 and MIA PaCa-2 cells. Statins also inhibited pAkt in combination with gemcitabine- and 5-fluorouracil, and sensitized cells to gemcitabine- and 5-fluorouracil-induced apoptosis and inhibition of cell proliferation. In line with our previous data, it was found that the P2X7-purinergic receptor mediated the effects of statins in Panc-1 and MIA PaCa-2 cells. Thus, experiments employing P2X7 siRNA and inhibitors supported an involvement of P2X7. In Capan-2 cells, which expressed P2X7 in low levels, statins did not reduce pAkt levels nor did statins sensitize them to cytostatic drugs. However, statin inhibited the growth of Capan-2 cells and this correlated to inhibition of NFkappaB and Raf/MEK pathways. As shown previously, these latter effects can be explained by an inhibited protein prenylation. Our data suggest that statins primarily target a functional P2X7-Akt signaling in pancreatic cancer cells. By targeting the P2X7-Akt axis, statins can sensitize pancreatic cancer cells to chemotherapeutic drugs. Our data are also in line with a role for P2X7 in the chemopreventive effect of statins on pancreatic cancer.

Interruption of the Ras/MEK/ERK signaling cascade enhances Chk1 inhibitor-induced DNA damage in vitro and in vivo in human multiple myeloma cells

The role of the Ras/MEK/ERK pathway was examined in relation to DNA damage in human multiple myeloma (MM) cells exposed to Chk1 inhibitors in vitro and in vivo. Exposure of various MM cells to marginally toxic concentrations of the Chk1 inhibitors UCN-01 or Chk1i modestly induced DNA damage, accompanied by Ras and ERK1/2 activation. Interruption of these events by pharmacologic (eg, the farnesyltransferase inhibitor R115777 or the MEK1/2 inhibitor PD184352) or genetic (eg, transfection with dominant-negative Ras or MEK1 shRNA) means induced pronounced DNA damage, reflected by increased gammaH2A.X expression/foci formation and by comet assay. Increased DNA damage preceded extensive apoptosis. Notably, similar phenomena were observed in primary CD138(+) MM cells. Enforced MEK1/2 activation by B-Raf transfection prevented R115777 but not PD184352 from inactivating ERK1/2 and promoting Chk1 inhibitor-induced gammaH2A.X expression. Finally, coadministration of R115777 diminished UCN-01-mediated ERK1/2 activation and markedly potentiated gammaH2A.X expression in a MM xenograft model, associated with a striking increase in tumor cell apoptosis and growth suppression. Such findings suggest that Ras/MEK/ERK activation opposes whereas its inhibition dramatically promotes Chk1 antagonist-mediated DNA damage. Together, these findings identify a novel mechanism by which agents targeting the Ras/MEK/ERK pathway potentiate Chk1 inhibitor lethality in MM.

Transient exposure of carcinoma cells to RAS/MEK inhibitors and UCN-01 causes cell death in vitro and in vivo

The present studies were initiated to determine in greater molecular detail how MEK1/2 inhibitors [PD184352 and AZD6244 (ARRY-142886)] interact with UCN-01 (7-hydroxystaurosporine) to kill mammary carcinoma cells in vitro and radiosensitize mammary tumors in vitro and in vivo and whether farnesyl transferase inhibitors interact with UCN-01 to kill mammary carcinoma cells in vitro and in vivo. Expression of constitutively activated MEK1 EE or molecular suppression of JNK and p38 pathway signaling blocked MEK1/2 inhibitor and UCN-01 lethality, effects dependent on the expression of BAX, BAK, and, to a lesser extent, BIM and BID. In vitro colony formation studies showed that UCN-01 interacted synergistically with the MEK1/2 inhibitors PD184352 or AZD6244 and the farnesyl transferase inhibitors FTI277 and R115,777 to kill human mammary carcinoma cells. Athymic mice carrying approximately 100 mm(3) MDA-MB-231 cell tumors were subjected to a 2-day exposure of either vehicle, R115,777 (100 mg/kg), the MEK1/2 inhibitor PD184352 (25 mg/kg), UCN-01 (0.2 mg/kg), or either of the drugs in combination with UCN-01. Transient exposure of tumors to R115,777, PD184352, or UCN-01 did not significantly alter tumor growth rate or the mean tumor volume in vivo approximately 15 to 30 days after drug administration. In contrast, combined treatment with R115,777 and UCN-01 or with PD184352 and UCN-01 significantly reduced tumor growth. Tumor cells isolated after combined drug exposure exhibited a significantly greater reduction in plating efficiency using ex vivo colony formation assays than tumor cells that were exposed to either drug individually. Irradiation of mammary tumors after drug treatment, but not before or during treatment, significantly enhanced the lethal effects of UCN-01 and MEK1/2 inhibitor treatment. These findings argue that UCN-01 and multiple inhibitors of the RAS-MEK pathway have the potential to suppress mammary tumor growth, and to interact with radiation, in vitro and in vivo.

PI3 kinase/AKT pathway as a therapeutic target in multiple myeloma

The development of novel therapies for multiple myeloma depends on a comprehensive understanding of the events leading to cellular proliferation and survival. Controlling pathways that regulate growth signals is an emerging and complementary approach to myeloma treatment. The PI3K/Akt pathway is a central gatekeeper for crucial cellular functions including adhesion, angiogenesis, migration and development of drug resistance. Established proteins and genes such as mTOR, p53, NF-kappaB and BAD are all regulated through PI3K and Akt activation, making them attractive targets for broad downstream effects. Direct PI3K inhibition has demonstrated impressive tumor inhibition and regression in cell-line and animal models, and multiple agents including SF1126 are currently in clinical trials. Drugs such as perifosine that are specific for Akt are also in development. Combinations of these agents with existing therapies are rational approaches on the path to improving myeloma treatment.

MEK1/2 inhibitors potentiate UCN-01 lethality in human multiple myeloma cells through a Bim-dependent mechanism

The role of Bim in synergistic interactions between UCN-01 and MEK1/2 inhibitors in human multiple myeloma cells was investigated. Exposure of U266 or RPMI8226 cells to UCN-01 resulted in ERK1/2 activation-associated Bim(EL) phosphorylation/down-regulation, events abrogated by MEK1/2 inhibitors. Enforced activation of ERK1/2 by transfection with constitutively active MEK1 diminished the capacity of PD98059 but not PD184352 to block UCN-01-mediated Bim(EL) phosphorylation and to potentiate apoptosis. Cotreatment with MEK1/2 inhibitors increased the association of Bim(EL) with both Bcl-2 and Bcl-x(L) in UCN-01-treated cells, leading to Bax/Bak conformational change and Bax mitochondrial translocation. Down-regulation of Bim(EL) by shRNA substantially diminished UCN-01/MEK inhibitor-mediated Bax/Bak activation and apoptosis. Furthermore, transfection of cells with S65A Bim, a mutant resistant to UCN-01-mediated phosphorylation, significantly sensitized cells to UCN-01 lethality. Conversely, ectopic expression of either Bcl-2 or Bcl-x(L) did not alter UCN-01/MEK1/2 inhibitor-mediated modifications in Bim(EL) phosphorylation but largely prevented cell death. Finally, IL-6 or IGF-1 failed to prevent MEK1/2 inhibitors from blocking UCN-01-induced Bim(EL) phosphorylation/degradation or cell death. Collectively, these findings argue that UCN-01-mediated ERK1/2 activation leads to Bim(EL) phosphorylation/inactivation, resulting in cytoprotection, and that interference with these events by MEK1/2 inhibitors plays a critical role in synergistic induction of apoptosis by these agents.