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Cell and Tumor Biology |
1 Department of Surgery, Beth Israel Deaconess Medical Center and 2 Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts
Requests for reprints: Jirong Bai, Research West 857, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215. Phone: 617-667-0575; Fax: 617-975-5562; E-mail: jbai{at}bidmc.harvard.edu.
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Abstract |
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- and TRAIL-mediated apoptosis by sublethal-dose single and combined antitumor drugs, including geldanamycin, PS-341, Trichostatin A, and doxorubicine. Geldanamyin and PS-341 synergistically block NF
B activation, suppress Akt/PKB pathway, and down-regulate Bcl-XL, Bcl-2, cIAP-1, and cyclin D1 expression. This combined regimen dramatically enhances TRAIL cytotoxic effects and breaks through chemoresistance. Bcl-XL plays a vital role in pancreatic cancer chemoresistance. Geldanamycin, PS-341, and TRAIL triple combination may be a novel therapeutic strategy for pancreatic cancer.
Key Words: Bcl-XL • NF-B • RNAi • pancreatic cancer • chemoresistance
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Introduction |
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RelA/p50, a heterodimeric component of NFB transcription factors (5, 6), is constitutively activated in the majority of pancreatic cancer cell lines and tumors but not in normal pancreatic tissues (7). The activation of NFB deregulates the biological functions of its downstream antiapoptotic factors (8), including Bcl-2 and Bcl-XL (9–12), inhibitors of apoptotic proteins (IAP; refs. 13–15), Fas-associated phosphatase-1 (Fap-1; ref. 16), and cFLIP (8, 13), as well as death receptor decoys (DcR; refs. 17, 18). These factors cooperatively and negatively regulate apoptotic pathways in tumor cells by blocking proapoptotic functions and suppressing activation of caspase cascades. Bcl-XL overexpression is detected in pancreatic cancer tissues (19) and is linked to abnormal NFB signaling (11). However, its role in pancreatic cancer chemoresistance has not been established.
In this study, we hypothesize that down-regulation of a predominantly overexpressed antiapoptotic factor could disable antiapoptotic mechanisms in pancreatic cancer cells. We have asked whether death receptor–based apoptotic pathways remain potent in pancreatic cancer cells. Which antiapoptotic factors are predominantly overexpressed? Do the predominantly overexpressed antiapoptotic factors play a vital role in chemoresistance? What roles may DcRs play in pancreatic cancer cell survival? To answer these questions, we have examined the surface expression of TNF-R1 and TRAIL-R1/2 and Fas in four pancreatic cancer cell lines with diverse biological characteristics and have analyzed their potency in mediating apoptosis. Pancreatic cancer has a much poorer prognosis than any other type of tumor (1). At the molecular level, we have investigated the cellular coexpression of antiapoptotic factors Bcl-2, Bcl-XL, cIAP-1, cIAP-2, Survivin, cFLIP and Fap-1, and DcRs, as well as cell cycle regulators cyclin D1 and p21Cip1 in pancreatic cancer cells and compared the results with those from five other human malignant tumor cell lines to identify if pancreatic cancer cells express some unique factors.
Clinical investigations show that fluorouracil-based standard chemoradiation or gemcitabine chemotherapy protocols do not prolong overall survival rates in patients with pancreatic cancer (3, 20–22). New biological antitumor therapies based on the following drugs are being evaluated today (23, 24). Geldanamycin, a heat shock protein 90 inhibitor, disrupts heat shock protein 90 chaperoning functions and enhances TNF apoptotic effects (25). PS-341 is a specific proteasome inhibitor that blocks NFB activation and suppresses tumor growth (26, 27). Trichostatin A, a histone deacetylase inhibitor, modifies chromatin structure and alters the biological functions of transcription factors involved in oncogenesis (26). But the efficacy of these drugs in pancreatic cancer is unknown. In this study, we have determined the cytotoxic effects of geldanamycin, PS-341, Trichostatin A, and doxorubicine on pancreatic cancer cells in the presence or absence of death receptor ligands. We have analyzed whether these drugs influence NFB activation, Akt/PKB pathway, and the expression of Bcl-2, Bcl-XL and cIAP-1, as well as cell cycle regulators (cyclin D1 and p21Cip1) in pancreatic cancer cells. Ultimately, we have investigated the direct effects of loss of predominant Bcl-XL function on chemoresistance in human pancreatic cancer by developing retroviral-based RNA interference (RNAi) expression vectors and Bcl-XL knockdown pancreatic cancer cell lines. We show for the first time that the genetic depletion of the predominant endogenous Bcl-XL overexpression drives pancreatic cancer cells to death receptor–triggered apoptosis by using various drug treatments.
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Materials and Methods |
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Establishment of Bcl-XL Knockdown Pancreatic Cancer Cells. Plasmid DNA for Bcl-XL knockdown and control retroviral vectors were transfected into a murine retroviral packaging cell line to produce VSV-G pseudotyped retroviral particles as described previously (28, 29). Then pancreatic cancer cells were infected with VSV-G pseudotyped retroviral particles at 50 MOI in the presence of 4 µg/mL polybrene (29). Subsequently, GFP+ cells were isolated by fluorescence-activated cell sorting to establish Bcl-XL knockdown and control cells.
Antibodies, Cytokines, Drugs, and Protein Lysates. Rabbit polyclonal antibodies against the human Bcl-XL, cIAP-1 and cIAP-2 were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Rabbit polyclonal and monoclonal antibodies (mAb) to human caspase-3, caspase-7, and caspase-8 were purchased from BD PharMingen (San Diego, CA). Antibodies to human caspase-9, Akt, Bcl-2, cyclin D1, and p21Cip1 were obtained from Cell Signaling Technology (Beverly, MA). mAb to human ß-actin (AC-15) and human poly(ADP-ribose) polymerase (PARP) were obtained from Sigma (St. Louis, MO) and BIOMOL (Plymouth Meeting, PA), respectively. Recombinant human TRAIL, recombinant human TNF, mAb to cFLIP, and an agonistic anti-human CD95 mAb (clones DX2; ref. 30) were obtained from R&D System (Minneapolis, MN). PS-341 was a gift from Millennium Pharmaceuticals (Cambridge, MA). Trichostatin A was purchased from Alexis Biochemicals (San Diego, CA). Geldanamycin and doxorubicine were purchased from Sigma. Protein samples for normal human pancreas tissues of three adult donors were provided by U.S. Biological (Swampscott, MA).
Immunoblot Analysis. Total cellular extracts were prepared with HEPES lysis buffer [20 mmol/L HEPES (pH 7.9), 0.5 mol/L NaCl, 5 mmol/L EDTA, 1% Triton X-100, 0.1% SDS, 0.5% sodium deoxycholic acid, 1 mmol/L DTT, and 1 mmol/L phenylmethylsulfonyl fluoride]. Equal amounts of protein samples were separated in a reducing condition in a 10% or 12% SDS-PAGE gel and blotted onto a polyvinylidene difluoride filter of Millipore (Billerica, MA). The filter was incubated with a primary antibody followed by staining with a horseradish peroxidase-labeled secondary antibody. Results were developed with a SuperSignal West Pico Chemiluminescent Substrate of Pierce Biotechnology (Rockford, IL) following manufacturer's instruction. The analysis of Fap-1 was carried out in a 6% SDS-PAGE gel.
Apoptosis Assay. Cell sensitivity to treatment of TNF, TRAIL, or agonistic anti-CD95 mAb or drugs was measured by nonradioactive cell proliferation assays [3-4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenyl)-2H-tetrazolium, inner salt (MTS) assays] from Promega (Madison, WI) following the manufacturer's instructions. Vector-transduced and nontransduced pancreatic cancer cells were seeded in 96-well plates overnight. The cells of duplicate wells were treated with diluted cytokines, mAb, or drugs at 37°C for 48 hours. Subsequently, MTS reagent was added to each well. The results were measured four hours later. Readings from control wells of each set of tests (incubated with growth medium alone) served as positive controls, representing 100% cell survival. Based on this, the percentage of cell viability of drug-treated cells was calculated. Statistical significances in cell viability between Bcl-XL knockdown and control cells following drug treatments were evaluated by two-tailed Student's t test. A probability level of <0.05 is considered significant.
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Results |
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All pancreatic cancer cell lines showed no apoptosis upon stimulation by TRAIL (1-100 ng/mL; Fig. 1A) and an agonistic anti-Fas mAb DX2 (0.1-1,000 ng/mL; Fig. 1B), respectively. TNF exposure caused concentration dependent apoptosis (0.5-25 ng/mL) in Mia PaCa-2 culture (Fig. 1C). Higher TNF concentration did not enhance its killing of Mia PaCa-2 cells. TNF showed no toxic effects on AsPC-1, BxPC-3, and Panc-1.
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Pancreatic cancer cells also overexpress DcRs (Fig. 2C). Eight tumor cell lines overexpressed DcR3, a Fas decoy, compared with normal pancreas tissues. DcR2, a TRAIL-R decoy, was only identified in three of four pancreatic cancer cell lines, but not in normal pancreas tissues, Panc-1 and other nonpancreatic tumor cells. DcR1, also a TRAIL-R decoy, was not detected in these cancer cell lines. Compared with human epithelial cancer cell lines, Jurkat cells only expressed low-level Bcl-XL and cleaved Bcl-2 and DcR3 but not other factors. DcR2 overexpression in pancreatic cancer cell lines may be associated with increased resistance to TRAIL induced apoptosis (S2a and S2b).
Genetic Inactivation of Bcl-XL in Pancreatic Cancer Cells. We established three different Bcl-XL RNAi expression vectors (Fig. 3A and B) to determine the role of Bcl-XL in pancreatic cancer chemoresistance. These RNAi vectors were introduced into Panc-1 cells by retroviral infection. Panc-1 cells predominantly overexpress Bcl-XL. Compared with nontransduced and SINeG-Ric- (control vector) transduced cells, Bcl-XL expression was dramatically down-regulated by SINeG-XRi117 transduction (Fig. 3C). SINeG-XRi458 was more effective (Fig. 3C). SINeG-XRi, containing both XRi117 and XRi458 cassettes, completely abolished the Bcl-XL expression (Fig. 3D). Bcl-XL knockdown did not affect the expression of Bcl-2, cIAP-1 and cyclin D1 in these cells (data not shown).
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- and TRAIL-mediated cytotoxicity. Bcl-XL expression in Mia PaCa-2 was not predominant. Bcl-XL knockdown Mia PaCa-2 cells were also established (data not shown). Its effects on Mia PaCa-2 apoptosis will be addressed in the Discussion.
Bcl-XL Depletion Drives Pancreatic Cancer Cells to Apoptosis by Geldanamycin and PS-341 in the Presence of TNF. Bcl-XL depletion dramatically increased the susceptibility of Bcl-XL knockdown cells (SINeG-XRi) to sublethal-dose geldanamycin and PS-341 in the presence of TNF (Fig. 4A and B). In the absence of geldanamycin and PS-341, TNF alone did not significantly reduce the viability of Bcl-XL knockdown, control vector–transduced (SINeG-Ric), and nontransduced Panc-1 cells (Fig. 4A, TNF alone). When cells were exposed to drugs alone (0 µg/mL TNF) for 48 hours, the viability of Bcl-XL knockdown cells declined by 23% for proteasome inhibitor PS-341 (Fig. 4A) and 30% for heat shock protein 90 inhibitor geldanamycin (Fig. 4B) whereas the viability of control cells (Panc-1 and SINeG-Ric transducers) only declined by 7% to 9% (PS-341) and 13% to 14% (geldanamycin) under the same conditions. This suggests that Bcl-XL depletion sensitizes pancreatic cancer cells to geldanamycin and PS-341. In the presence of 1 to 50 ng/mL TNF and sublethal-dose PS-341 (10 nmol/L) or geldanamycin (500 nmol/L), the viability of Bcl-XL knockdown cells decreased by 45% to 64% for PS-341 treatment and 47% to 53% for geldanamycin treatment. However, under the identical conditions, the viability of control cells (Panc-1 and SINeG-Ric transducers) decreased by 15% to 30% (PS-341) and 15% to 22% (geldanamycin), indicating that Bcl-XL depletion significantly decreased pancreatic cancer cell viability by an average of 30% (geldanamycin treatment) or 30% to 34% (PS-341 treatment) over the background of the control cells (P < 0.01) treated with TNF/PS-341 or TNF/geldanamycin.
TNF alone (25 ng/mL) did not activate caspase-3 and caused no cleavage of pro-PARP in both Bcl-XL knockdown and control cells (data not shown). However, combining PS-341 with TNF activated caspase cascades and prompted the effective cleavage of the majority of pro-caspase-3 and degradation of almost the entire pro-PARP in SINeG-Xri-transduced cells (Fig. 4D, lane 2). For Panc-1 cells, the cleavage of pro-caspase-3 was not as effective as that occurred in SINeG-XRi cells treated by TNF/PS-341. Under this condition, about 50% of pro-PARP remained not cleaved in Panc-1 cells.
Geldanamycin combined with TNF displayed similar effects on caspase-3 activation and pro-PARP cleavage during 48-hour treatment (Fig. 4D, lane 4). These were consistent with the results from apoptosis assays described in Fig. 4A and B.
Heat Shock Protein 90 and Proteasome Inhibitors Synergistically Potentiate TNF Killing of Pancreatic Cancer Cells. Combining geldanamycin (500 nmol/L) with PS-341 (10 nmol/L) without TNF slightly improved the cytotoxic effects of geldanamycin and PS-341 on Bcl-XL knockdown but not on control pancreatic cancer cells compared with relevant single drug regimens (Fig. 4C). However, the combination of TNF (1-50 ng/mL) with sublethal-dose geldanamycin/PS-341 dramatically enhanced the tumorcidal effects of geldanamycin/PS-341 and TNF on both Bcl-XL knockdown and control cells. Furthermore, the geldanamycin/PS-341/TNF triple combination significantly decreased control cell viability (Panc-1 and SINeG-Ric–transduced cells) by 45% to 57% (P < 0.01) in comparison with geldanamycin/TNF and PS-341/TNF treatments. The latter two regimens killed only 15% to 22% (Fig. 4B) and 15% to 30% (Fig. 4A) of control cells, respectively. Even a low dose of TNF (1 ng/mL) caused 45% of Panc-1 and 43% of SINeG-Ric–transduced cells to proceed to apoptosis in the presence of geldanamycin/PS-341 combination therapy. As to Bcl-XL- knockdown cells, geldanamycin/PS-341 combination further increased TNF-induced cytotoxicity by an average of 15%, representing 60% to 70% cell death (P < 0.05) compared with control cells under the same conditions (Fig. 4C).
Geldanamycin and PS-341 combinatorial therapy more effectively activated caspase cascades than either drug in the presence of TNF (25 ng/mL) in both Bcl-XL knockdown and control pancreatic cancer cells (Fig. 4D). Combined treatment caused the cleavage of most pro-PARP in control cells and complete degradation of pro-PARP in Bcl-XL knockdown counterparts (Fig. 4D, lane 3).
Predominant Bcl-XL Overexpresssion Blocks both Intrinsic and Extrinsic Apoptosis Pathways. The cleavage of pro-caspase-9 and pro-capsase-8 activates intrinsic and extrinsic apoptosis pathways, respectively. In the presence of 10 nmol/L PS-341 alone, SINeG-Ric– and SINeG-XRi–transduced counterparts showed no cleaved caspase-8 (Fig. 5A, lane 1) and caspase-9 (Fig. 5B, lane 1). Combining PS-341 with TNF did not cause the cleavage of pro-caspase-8 and pro-caspase-9 in SINeG-Ric–transduced cells. However, SINeG-XRi cells produced abundant cleaved caspase-8 (Fig. 5A, lanes 2-3) and caspase-9 products (Fig. 5B, lanes 2-3) under the same conditions. The cleavage of executioner caspase-3 and caspase-7 could be seen in SINeG-XRi cells treated with PS-341 and TNF but not in control cells (Fig. 5C and D). PS-341 and TNF combination caused the degradation of most full-length pro-PARP proteins in SINeG-XRi cells but not in control cells (Fig. 5E). Taken together, these results strongly support that Bcl-XL predominant overexpression protects Panc-1 cells from TNF-mediated killing by blocking both intrinsic and extrinsic apoptotic pathways.
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Geldanamycin/PS-341, Trichostatin A/PS-341 (Fig. 6A and B), and Trichostatin A/geldanamycin (data not shown) combinations with low-dose TRAIL were all effective in initiating apoptosis in pancreatic cancer cells compared with single drug-based treatments. Bcl-XL knockdown cells were much more sensitive to TRAIL-induced apoptosis than control counterparts that overexpress Bcl-XL under identical conditions (Fig. 6A-B). For geldanamycin/PS-341 regimen, TRAIL induced 35%, 59%, and 77% apoptosis for Bcl-XL knockdown cells at 5, 10, and 25 ng/mL TRAIL versus 13%, 26%, and 56% apoptosis for control cells under the same conditions (Fig. 6A). This indicates that Bcl-XL depletion significantly reduced the viability on these cells 
2-fold (P < 0.01) compared with control cells.
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Geldanamycin/PS-341 Combination Is More Effective in Inducing Cytotoxicity than Trichostatin A/Geldanamycin and Trichostatin A/PS-341 in Pancreatic Cancer Cells. In the presence of 5, 10, 25, and 50 ng/mL TRAIL (Fig. 6C), geldanamycin/PS-341 reduced the viability of Panc-1 cells by 18%, 35%, 67%, and 78%, respectively. Trichostatin A/geldanamycin treatment reduced cell viability by 14%, 18%, 31%, and 56% and Trichostatin A/PS-341 by 11%, 18%, 54%, and 77% under the same conditions. It seems that geldanamycin/PS-341 was more effective than Trichostatin A/geldanamycin in killing pancreatic cancer cells in the presence of 10, 25, and 50 ng/mL TRAIL (P < 0.01).
Forty-eight hours after drug treatment, TRAIL-treated (TRAIL alone, 25 ng/mL) and nontreated Bcl-XL knockdown (Fig. 6D, lane 1, SINeG-XRi) and control cells (Fig. 6D, lane 1, Panc-1) did not produce 85-kDa cleaved PARP fragments. In the absence of TRAIL, geldanamycin/PS-341 did not cause PARP cleavage in Panc-1 cells (Fig. 6D, lane 3, Panc-1) but yielded visible 85-kDa fragments in Bcl-XL depleted cells (lane 3, SINeG-XRi). Trichostatin A/PS-341 caused no PARP cleavage in both Bcl-XL knockdown and control counterparts (Fig. 6D, lane 5). Bcl-XL knockdown and control cells treated with geldanamycin/Trichostatin A, however, showed similar levels of cleaved 85-kDa products (Fig. 6D, lane 4). Compared with Panc-1 cells in the presence of TRAIL, PARP proteins were nearly completely degraded in Bcl-XL depleted cells following combinatorial drug treatments. Triple therapy with geldanamycin, PS-341, and TRAIL, caused pro-PARP to disappear altogether in Bcl-XL depleted cells (Fig. 6D, lane 6). For Bcl-XL knockdown cells treated with Trichostatin A/geldanamycin and Trichostatin A/PS-341, little pro-PARP remained following TRAIL stimulation (Fig. 6D, lanes 7 and 8, SINeG-XRi) compared with control Panc-1 cells under the same conditions (Fig. 6D, lanes 7 and 8, Panc-1).
When the extent of PARP cleavage in Panc-1 cells was compared between geldanamycin/PS-341/TRAIL (Fig. 6D, lane 6, Panc-1), Trichostatin A/geldanamycin/TRAIL (lane 7), and Trichostatin A/PS-341/TRAIL (lane 8), the degradation of PARP was significant for geldanamycin/PS-341/TRAIL compared with two other regimens. There were no significant differences between Trichostatin A/PS-341/TRAIL and Trichostatin A/geldanamycin/TRAIL treatments as to PARP cleavage (Fig. 6D, lanes 7 and 8, Panc-1).
NFB-driven reporter gene assays show that geldanamycin and PS-341 combination is much more effective in blocking constitutive (20.9-fold, S3a) and TNF-induced (29-fold, S3b) NFB activation than either drug. Geldanamycin and PS-341 combination nearly completely blocked IB degradation (S3c) and caused Akt/PKB depletion (S3d). In addition, this combination more effectively suppressed the expression of Bcl-XL, Bcl-2, cIAP-1, and cyclin D1 than either drug (S3d). Akt/PKB degradation and the suppression of the antiapoptotic factors were more profound in Bcl-XL knockdown cells (S3d).
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Discussion |
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-induced apoptosis. Such high prevalence of insensitivity to TNF receptor–mediated apoptosis may provide a mechanism for pancreatic cancer cells to escape the immune system. A secondary means of evasion for pancreatic cancer cells is the overexpression of DcRs. All four pancreatic cancer cell lines tested express higher levels of DcR3 than normal pancreas tissues. DcR3 is a Fas decoy that has much higher affinity to FasL than Fas, and blocks Fas-triggered apoptosis (31). DcR3 overexpression coincides with resistance to Fas-triggered apoptosis in pancreatic cancer cell lines; however, its exact role in pancreatic tumorigenesis remains to be established. We have shown that DcR2 is overexpressed in three of four pancreatic cancer cell lines but not in normal pancreas tissues and five other human tumor counterparts. DcR2 negative Panc-1 cells express a lower level of TRAIL receptors than DcR2-positive BxPC-3 and Mia PaCa-2. However, Panc-1 cells are more sensitive to TRAIL-induced apoptosis than BxPC-3 and Mia PaCa-2 in the presence of geldanamycin and PS-341 combinatorial therapy (S1). This suggests that DcR2 overexpression may be associated with the increased resistance of BxPC-3 and Mia PaCa-2 to TRAIL-induced apoptosis.
Our experiments reveal that Bcl-XL or Bcl-2 is predominantly overexpressed in pancreatic cancer cell lines tested. Bcl-XL is not only predominantly overexpressed in pancreatic cancer cells, but also in three other epithelial cancer cell lines: prostate (LNCap), colorectal (SW480), and small bowel (HT29). Previous studies have used overexpression systems with a foreign promoter to define Bcl-XL functions (32, 33). It is not clear, however, such systems can accurately simulate the exact role that endogenous Bcl-XL plays in a naturally occurring tumor. As such, we have used RNA interference to knock down Bcl-XL overexpression, and for the first time, have examined the effects of Bcl-XL depletion on apoptosis in pancreatic cancer cells.
We show that the predominant Bcl-XL overexpression in pancreatic cancer cells effectively blocks the activation of intrinsic and extrinsic apoptosis pathways. RNAi-mediated knockdown of the predominant Bcl-XL significantly enhances antitumor drug–induced caspase activation as well as TNF- or TRAIL-triggered apoptosis. In contrast, RNAi-mediated knockdown of non-predominant Bcl-XL in Mia PaCa-2 cells did not increase the sensitivity of Mia PaCa-2 to the similar treatments used in this study (data not shown). Bcl-XL knockdown shows that a predominantly overexpressed antiapoptotic protein is a critical factor for the survival of pancreatic cancer cells. These findings emphasize that Bcl-XL is a critical antiapoptotic factor that may contribute to chemoresistance in various cancers, including pancreatic cancer, and suggests Bcl-XL as an important molecular target for future drug discovery.
We have found that the majority of pancreatic cancer cell lines are strongly resistant to PS-341, geldanamycin, Trichostatin A, and doxorubicine.3 Chemotherapy regimens based on these drugs at sublethal doses effectively kill leukemia (34), breast, and lung cancer cells in vitro (35, 36) but only have marginal cytotoxic effects on pancreatic cancer cells. Our study reveals that it is necessary to combine a death ligand, such as TNF, with two optimal antitumor drugs to overcome the anti-apoptotic mechanisms in pancreatic cancer cells in vitro. TNF is extremely toxic in vivo, ruling out its usefulness in pancreatic cancer chemotherapy. TRAIL receptors, however, are widely expressed in various types of human tumor cells (37–39), including the pancreatic cancer cell lines tested in this study. Recombinant TRAIL is harmless to many normal human cells and causes no adverse effects on nonhuman primates. It effectively induces apoptosis in a variety of human tumor cell lines and tumor xenografts (38–41). Unfortunately, TRAIL alone does not cause cytotoxicity in pancreatic cancer cells. However, we now show that combining TRAIL with geldanamycin/PS-341, and geldanamycin/Trichostatin A or Trichostatin A/PS-341 effectively kills control pancreatic cancer cells. This killing effect is maximized when Bcl-XL is depleted.
Geldanamycin and PS-341 synergistically enhance TNF- and TRAIL-triggered apoptosis by increasing the activation of caspase cascades through down-regulation of antiapoptotic factors and cell cycle regulators, a phenomenon not previously described. Geldanamycin and PS-341 induce these effects by both blocking NFB activation and disrupting the Akt/PKB signaling pathway as well as cell cycle progression. This study suggests that geldanamycin, PS-341, and TRAIL combination may be a novel therapeutic strategy in the future treatment of pancreatic cancer.
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Acknowledgments |
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The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
We thank Ben Enos and Akikazu Murakami of Dana-Farber Cancer Institute for technical support.
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Footnotes |
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Received 10/ 1/04. Revised 12/ 8/04. Accepted 1/ 4/05.
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