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1.  Inhibition of MCL-1 enhances lapatinib toxicity and overcomes lapatinib resistance via BAK-dependent autophagy 
Cancer biology & therapy  2009;8(21):2084-2096.
Prior studies demonstrated that resistance to the ERBB1/2 inhibitor Lapatinib in HCT116 cells was mediated by increased MCL-1 expression. We examined whether inhibition of BCL-2 family function could restore Lapatinib toxicity in Lapatinib adapted tumor cells and enhance Lapatinib toxicity in naive cells. The BCL-2 family antagonist Obatoclax (GX15-070), that inhibits BCL-2/BCL-Xl/MCL-1 function, enhanced Lapatinib toxicity in parental HCT116 and Lapatinib adapted HCT116 cells. In breast cancer lines, regardless of elevated ERBB1/2 expression, GX15-070 enhanced Lapatinib toxicity within 3–12 h.The promotion of Lapatinib toxicity neither correlated with cleavage of caspase 3 nor was blocked by inhibition caspases; and was not associated with changes in the activities of ERK1/2, JNK1/2 or p38 MAPK but with reduced AKT, mTOR and S6K1 phosphorylation. The promotion of Lapatinib toxicity by GX15-070 correlated with increased cytosolic levels of apoptosis inducing factor (AIF) and expression of ATG8 (LC3), and the formation of large vesicles that intensely stained for a transfected LC3-GFP construct. Knockdown of the autophagy regulatory proteins ATG5 or Beclin1 suppressed the induction of LC3-GFP vesicularization and significantly reduced cell killing, whereas knock down of MCL-1 and BCL-Xl enhanced the induction of LC3-GFP vesicularization and significantly enhanced cell killing. Knockdown of Beclin1 and AIF abolished cell killing. Collectively, our data demonstrate that Obatoclax mediated inhibition of MCL-1 rapidly enhances Lapatinib toxicity in tumor cells via a toxic form of autophagy and via AIF release from the mitochondrion.
PMCID: PMC3887451  PMID: 19823038
lapatinib; obatoclax; autophagy; cell death; resistance
2.  MDA-7/IL-24–induced cell killing in malignant renal carcinoma cells occurs by a ceramide/CD95/PERK–dependent mechanism 
Molecular cancer therapeutics  2009;8(5):1280-1291.
Melanoma differentiation associated gene-7/interleukin-24 (mda-7/IL-24) is a novel cytokine displaying selective apoptosis-inducing activity in transformed cells without harming normal cells. The present studies focused on clarifying the mechanism(s) by which glutathione S-transferase (GST)-MDA-7 altered cell survival of human renal carcinoma cells in vitro. GST-MDA-7 caused plasma membrane clustering of CD95 and the association of CD95 with procaspase-8. GST-MDA-7 lethality was suppressed by inhibition of caspase-8 or by overexpression of short-form cellular FLICE inhibitory protein, but only weakly by inhibition of cathepsin proteases. GST-MDA-7–induced CD95 clustering (and apoptosis) was blocked by knockdown of acidic sphingomyelinase or, to a greater extent, ceramide synthase-6 expression. GST-MDA-7 killing was, in parallel, dependent on inactivation of extracellular signal–regulated kinase 1/2 and on CD95-induced p38 mitogen-activated protein kinase and c-jun NH2-terminal kinase-1/2 signaling. Knockdown of CD95 expression abolished GST-MDA-7–induced phosphorylation of protein kinase R–like endoplasmic reticulum kinase. GST-MDA-7 lethality was suppressed by knockout or expression of a dominant negative protein kinase R–like endoplasmic reticulum kinase that correlated with reduced c-jun NH2-terminal kinase-1/2 and p38 mitogen-activated protein kinase signaling and maintained extracellular signal–regulated kinase-1/2 phosphorylation. GST-MDA-7 caused vacuolization of LC3 through a mechanism that was largely CD95 dependent and whose formation was suppressed by knockdown of ATG5 expression. Knockdown of ATG5 suppressed GST-MDA-7 toxicity. Our data show that in kidney cancer cells GST-MDA-7 induces ceramide-dependent activation of CD95, which is causal in promoting an endoplasmic reticulum stress response that activates multiple proapoptotic pathways to decrease survival.
doi:10.1158/1535-7163.MCT-09-0073
PMCID: PMC2889018  PMID: 19417161
3.  Inhibition of MCL-1 in breast cancer cells promotes cell death in vitro and in vivo 
Cancer Biology & Therapy  2010;10(9):903-917.
The present studies have examined approaches to suppress MCL-1 function in breast cancer cells, as a means to promote tumor cell death. Treatment of breast cancer cells with CDK inhibitors (flavopiridol; roscovitine) enhanced the lethality of the ERBB1 inhibitor lapatinib in a synergistic fashion. CDK inhibitors interacted with lapatinib to reduce MCL-1 expression and overexpression of MCL-1 or knock down of BAX and BAK suppressed drug combination lethality. Lapatinib-mediated inhibition of ERK1/2 and to a lesser extent AKT facilitated CDK inhibitor-induced suppression of MCL-1 levels. Treatment of cells with the BH3 domain/MCL-1 inhibitor obatoclax enhanced the lethality of lapatinib in a synergistic fashion. Knock out of MCL-1 and BCL-XL enhanced lapatinib toxicity to a similar extent as obatoclax and suppressed the ability of obatoclax to promote lapatinib lethality. Pre-treatment of cells with lapatinib or with obatoclax enhanced basal levels of BAX and BAK activity and further enhanced drug combination toxicity. In vivo tumor growth data in xenograft and syngeneic model systems confirmed our in vitro findings. Treatment of cells with CDK inhibitors enhanced the lethality of obatoclax in a synergistic fashion. Overexpression of MCL-1 or knock down of BAX and BAK suppressed the toxic interaction between CDK inhibitors and obatoclax. Obatoclax and lapatinib treatment or obatoclax and CDK inhibitor treatment or lapatinib and CDK inhibitor treatment radiosensitized breast cancer cells. Lapatinib and obatoclax interacted to suppress mammary tumor growth in vivo. Collectively our data demonstrate that manipulation of MCL-1 protein expression by CDK inhibition or inhibition of MCL-1 sequestering function by Obatoclax renders breast cancer cells more susceptible to BAX/BAK-dependent mitochondrial dysfunction and tumor cell death.
doi:10.4161/cbt.10.9.13273
PMCID: PMC3040858  PMID: 20855960
MCL-1; Lapatinib; Obatoclax; Flavopiridol; Roscovitine; CDK inhibitor; RTK inhibitor; BCL-2 inhibitor; BAK
4.  Vorinostat and sorafenib increase ER stress, autophagy and apoptosis via ceramide-dependent CD95 and PERK activation 
Cancer biology & therapy  2008;7(10):1648-1662.
We recently noted that low doses of sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I trials. The present studies mechanistically extended our initial observations. Low doses of sorafenib and vorinostat, but not the individual agents, caused an acidic sphingomyelinase and fumonisin B1-dependent increase in CD95 surface levels and CD95 association with caspase 8. Knock down of CD95 or FADD expression reduced sorafenib/vorinostat lethality. Signaling by CD95 caused PERK activation that was responsible for both promoting caspase 8 association with CD95 and for increased eIF2α phosphorylation; suppression of eIF2α function abolished drug combination lethality. Cell killing was paralleled by PERK- and eIF2α-dependent lowering of c-FLIP-s protein levels and over-expression of c-FLIP-s maintained cell viability. In a CD95-, FADD- and PERK-dependent fashion, sorafenib and vorinostat increased expression of ATG5 that was responsible for enhanced autophagy. Expression of PDGFRβ and FLT3 were essential for high dose single agent sorafenib treatment to promote autophagy. Suppression of PERK function reduced sorafenib and vorinostat lethality whereas suppression of ATG5 levels elevated sorafenib and vorinostat lethality. Over-expression of c-FLIP-s blocked apoptosis and enhanced drug-induced autophagy. Thus sorafenib and vorinostat promote ceramide-dependent CD95 activation followed by induction of multiple downstream survival regulatory signals: ceramide-CD95-PERK-FADD-pro-caspase 8 (death); ceramide-CD95-PERK-eIF2α -↓c-FLIP-s (death); ceramide-CD95-PERK-ATG5-autophagy (survival).
PMCID: PMC2674577  PMID: 18787411
Vorinostat; Sorafenib; CD95; c-FLIP-s; PDGFRβ; FLT3; autophagy; ceramide; cell death; ASMase
5.  Lapatinib resistance in HCT116 cells is mediated by elevated MCL-1 expression, decreased BAK activation, and not by ERBB receptor mutation 
Molecular pharmacology  2008;74(3):807-822.
We have defined some of the mechanisms by which the kinase inhibitor Lapatinib kills HCT116 cells. Lapatinib inhibited radiation-induced activation of ERBB1/2, ERK1/2 and AKT, and radiosensitized HCT116 cells. Prolonged incubation of HCT116 cells with Lapatinib caused cell killing followed by outgrowth of Lapatinib adapted cells. Adapted cells were resistant to serum-starvation –induced cell killing and were cross resistant to multiple therapeutic drugs. Lapatinib was competent to inhibit basal and EGF-stimulated ERBB1 phosphorylation in adapted cells. Co-expression of dominant negative ERBB1 and dominant negative ERBB2 inhibited basal and EGF-stimulated ERBB1 and ERBB2 phosphorylation in parental cells. However in neither parental nor adapted cells did expression of dominant negative ERBB1 and dominant negative ERBB2 recapitulate the cell death promoting effects of Lapatinib. Adapted cells had increased expression of MCL-1, decreased expression of BAX, and decreased activation of BAX and BAK. Over-expression of BCL-XL protected parental cells from Lapatinib toxicity. Knock down of MCL-1 expression enhanced Lapatinib toxicity in adapted cells that was reverted by knock down of BAK expression. Inhibition of caspase function modestly reduced Lapatinib toxicity in parental cells whereas knock down of AIF expression suppressed Lapatinib toxicity. Thus in HCT116 cells Lapatinib adaptation can be mediated by altered expression of pro- and anti-apoptotic proteins that maintain mitochondrial function.
doi:10.1124/mol.108.047365
PMCID: PMC2574656  PMID: 18544666
Lapatinib; Ras; cell death
6.  Vorinostat and sorafenib synergistically kill tumor cells via FLIP suppression and CD95 activation 
Purpose and Design
Mechanism(s) by which the multi-kinase inhibitor sorafenib and the histone deacetylase inhibitor vorinostat interact to kill hepatic, renal and pancreatic adenocarcinoma cells have been defined.
Results
Low doses of sorafenib and vorinostat interacted in vitro in a synergistic fashion to kill hepatic, renal and pancreatic adenocarcinoma cells in multiple short term viability (24–96h) and in long term colony formation assays. Cell killing was suppressed by inhibition of cathepsin proteases and caspase 8, and to a lesser extent by inhibition of caspase 9. Twenty four hours after exposure, the activities of ERK1/2, AKT and NFκB were only modestly modulated by sorafenib and vorinostat treatment. However, 24h after exposure, sorafenib and vorinostat- treated cells exhibited markedly diminished expression of c-FLIP-s, full length BID, BCL-2, BCLXL, MCL-1, XIAP, increased expression of BIM, and increased activation of BAX, BAK and BAD. Expression of eIF2α S51A blocked sorafenib and vorinostat –induced suppression of c-FLIP-s levels and over-expression of c-FLIP-s abolished lethality. Sorafenib and vorinostat treatment increased surface levels of CD95 and CD95 association with caspase 8. Knock down of CD95 or FADD expression significantly reduced sorafenib / vorinostat -mediated lethality.
Conclusions
These data demonstrate that combined exposure of epithelial tumor cell types to sorafenib and vorinostat diminishes expression of multiple anti-apoptotic proteins, promotes activation of the CD95 extrinsic apoptotic and the lysosomal protease pathways, and that suppression of c-FLIP-s expression represents a critical event in transduction of the pro-apoptotic signals from CD95 to promote mitochondrial dysfunction and death.
doi:10.1158/1078-0432.CCR-08-0469
PMCID: PMC2561272  PMID: 18765530
Vorinostat; Sorafenib; CD95; c-FLIP-s; caspase 8; cathepsin; cell death

Results 1-6 (6)