Novel Proteasome Inhibitor PS-341 Inhibits Activation of Nuclear Factor-κB, Cell Survival, Tumor Growth, and Angiogenesis in Squamous Cell Carcinoma (original) (raw)
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Molecular Cancer Therapeutics, 2002
Recent studies have shown that the transcription factor, nuclear factor B (NF-B), regulates critical survival pathways in a variety of different cell types, including human pancreatic cancer cells. The activation of NF-B is controlled by proteasomemediated degradation of its endogenous polypeptide inhibitor, inhibitor of nuclear factor B␣. We investigated the effects of PS-341, a peptide boronate inhibitor of the proteasome in human pancreatic cancer cells in vitro and in vivo. Comparison of PS-341's effects on the growth of eight different human pancreatic cancer cell lines revealed marked heterogeneity in drug responsiveness, ranging from highly resistant (IC 50 > 10 M; Panc-48, HS766T, and Mia-PaCa-2) to extremely sensitive (IC 50 < 40 nM; L3.6pl, Hpaf2, and BxPC3). However, these effects did not correlate with differential inhibition of NF-B activation. Direct quantification of apoptosis revealed that PS-341's effects on cell growth largely correlated with sensitivity to programmed cell death. Evaluation of PS-341's effects on established orthotopic tumor xenografts demonstrated that biweekly intravenous administration of the maximum-tolerated dose of the drug (1 mg/kg) led to significant reductions in the volumes of L3.6pl tumors but not Mia-PaCa-2 tumors. Laser scanning cytometer-mediated quantification of drug-induced apoptosis in the xenografts confirmed that PS-341 induced DNA fragmentation and activation of caspase-3 in L3.6pl tumors but not in Mia-PaCa-2 tumors. However, histological examination of drug-treated tumors revealed extensive central necrosis and reductions in microvessel density and VEGF expression in both tumor types. Taken together, our results demonstrate that PS-341 inhibits the growth of human pancreatic tumors via direct effects on tumor cells and indirect effects on the tumor vasculature.
Journal of Biological Chemistry, 2006
Cisplatin is one of the most common DNA-damaging agents used for treating patients with solid tumors such as squamous cell carcinoma (SCC). Unfortunately, significant levels of resistance in SCC cells emerge rapidly following cisplatin treatment. Here we report that the proteasome inhibitor PS-341, the representative of a new class of chemotherapeutic drugs, was capable of inducing apoptosis in cisplatin-resistant SCC cells via the endoplasmic reticulum stress. PS-341 stimulated the phosphorylation of PERK and the unfolded protein response, resulting in the induction of the transcription factor ATF-4. Importantly, the Bcl-2 homology domain 3-only (BH3-only) protein Noxa was found to be strongly induced in cisplatin-resistant SCC cells by PS-341 but not by cisplatin. The knock-down of Noxa using small interference RNA significantly abolished PS-341-mediated apoptosis in SCC cells. Using eIF2␣ mutant mouse embryonic fibroblasts, we found that functional eIF2␣ played an essential role in PS-341-induced Noxa expression. Taken together, our novel findings reveal a direct link between PS-341-induced endoplasmic reticulum stress and the mitochondria-dependent apoptotic pathway and suggest that PS-341 may be utilized for overcoming cisplatin-resistance in human SCC. . The abbreviations used are: ER, endoplasmic reticulum; BH3, Bcl-2-homology domain; MEF, mouse embryonic fibroblast; SCC, squamous cell carcinoma; UPR, unfolded protein response; eIF2, eukaryotic translation initiation factor 2; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; RT, reverse transcription; siRNA, small interference RNA; GFP, green fluorescent protein; HNSCC, head and neck squamous cell carcinoma; PERK, RNAdependent protein kinase-like ER kinase.
Cancer research, 2001
Inducible activation of nuclear factor-kappaB (NF-kappaB) inhibits the apoptotic response to chemotherapy and irradiation. Activation of NF-kappaB via phosphorylation of an inhibitor protein IkappaB leads to degradation of IkappaB through the ubiquitin-proteasome pathway. We hypothesized that inactivation of proteasome function will inhibit inducible NF-kappaB activation, thereby increasing levels of apoptosis in response to chemotherapy and enhancing antitumor effects. To assess the effects of proteasome inhibition on chemotherapy response, human colorectal cancer cells were pretreated with the dipeptide boronic acid analogue PS-341 (1 microM) prior to exposure to SN-38, the active metabolite of the topoisomerase I inhibitor, CPT-11. Inducible activation of NF-kappaB and growth response were evaluated in vitro and in vivo. Effects on p53, p21, p27 and apoptosis were determined. Pretreatment with PS-341 inhibited activation of NF-kappaB induced by SN-38 and resulted in a significant...
The Proteasome Inhibitor PS-341 in Cancer Therapy
Clinical Cancer Research an Official Journal of the American Association For Cancer Research, 1999
The anticancer activity of the boronic acid dipeptide proteasome inhibitor PS-341 was examined in vitro and in vivo. PS-341 was a potent cytotoxic agent toward MCF-7 human breast carcinoma cells in culture, producing an IC 90 of 0.05 M on 24 h of exposure to the drug. In the EMT-6 tumor cell survival assay, PS-341 was equally cytotoxic administered p.o. or by i.p. injection up to a dose of 2 mg/kg. PS-341 was also toxic to the bone marrow colony-forming unit-granulocyte macrophage. PS-341 increased the tumor cell killing of radiation therapy, cyclophosphamide, and cisplatin in the EMT-6/Parent tumor, but was not able to overcome the in vivo resistance of the EMT-6/CTX and EMT-6/CDDP tumors. In the tumor growth delay assay, PS-341 administered p.o. had antitumor activity against the Lewis lung carcinoma, both primary and metastatic disease. In combination, regimens with 5-fluorouracil, cisplatin, Taxol and adriamycin, PS-341 seemed to produce primarily additive tumor growth delays against the s.c. tumor and was highly effective against disease metastatic to the lungs. The proteasome is an interesting new target for cancer therapy, and the proteasome inhibitor PS-341 warrants continued investigation in cancer therapy.
2001
Inducible activation of nuclear factor-B (NF-B) inhibits the apoptotic response to chemotherapy and irradiation. Activation of NF-B via phosphorylation of an inhibitor protein IB leads to degradation of IB through the ubiquitin-proteasome pathway. We hypothesized that inactivation of proteasome function will inhibit inducible NF-B activation, thereby increasing levels of apoptosis in response to chemotherapy and enhancing antitumor effects. To assess the effects of proteasome inhibition on chemotherapy response, human colorectal cancer cells were pretreated with the dipeptide boronic acid analogue PS-341 (1 M) prior to exposure to SN-38, the active metabolite of the topoisomerase I inhibitor, CPT-11. Inducible activation of NF-B and growth response were evaluated in vitro and in vivo. Effects on p53, p21, p27 and apoptosis were determined.
Oncogene, 2005
The proteasome plays a pivotal role in controlling cell proliferation, apoptosis, and differentiation in a variety of normal and tumor cells. PS-341, a novel boronic acid dipeptide that inhibits 26S proteasome activity, has prominent effects in vitro and in vivo against several solid tumors. We examined its antiproliferation, proapoptotic effects using three human glioblastoma multiforme (GBM) cell lines and five primary GBM explants. PS-341 markedly inhibited proliferation of GBM cell lines and explants in liquid and soft agar culture. These cells developed a G2/M cell cycle arrest with a concomitant decreased percentage of cells in S phase (E2-fold), associated with an increased expression of p21 WAF1 , p27 KIP1 , as well as cyclin B1 and decreased levels of CDK2, CDK4, and E2F4. About 35-40% of the cells became apoptotic when exposed to PS-341 (10 À7 M, 24-48 h) as shown by Annexin V analysis; in concert with these findings, immunobloting showed a C-terminal 85 kDa apoptotic fragment of poly ADP-ribose polymerase (PARP), and a decreased level of Bcl2 and Bcl-xl. PS-341 downregulated the expression of Bcl-2 and Bcl-xl in protein levels at an early time of treatment. These changes occurred irrespective of the p53 mutational status of the cells. PS-341 activated JNK/c-Jun signaling in GBM cells, and the JNK inhibitor SP600125 blocked the JNK signaling to reverse partially the PS-341 growth inhibition. PS-341 (10 À7 M, 24 h) decreased nuclear NF-jB levels as shown by Western blot, and reduced transcriptional activity of NF-jB as measured by reporter assays in these transformed cells. Also, PS-341 enhanced TRAIL (TNF-related apoptosis-inducing ligand) and TNFa (tumor necrosis factor alpha) induced cell death and apoptosis (two-to five-fold) in GBM cells. In summary, PS-341 has profound effects on growth and apoptosis of GBM cells, suggesting that PS-341 may be an effective therapy for patients with gliomas.
Cancer research, 2002
The proteasome is a ubiquitous and essential intracellular enzyme that degrades many proteins regulating cell cycle, apoptosis, transcription, cell adhesion,angiogenesis, and antigen presentation. We have shown recently that the proteasome inhibitor PS-341 inhibits growth, induces apoptosis, and overcomes drug resistance in human myeloma cells in vitro. In this study, we examined the efficacy, toxicity, and in vivo mechanism of action of PS-341 using a human plasmacytoma xenograft mouse model. One hundred immunodeficient (beige-nude-xid) mice were used in two independent experiments. The mice were injected s.c. with 3 x 10(7) RPMI-8226 myeloma cells. When tumors became measurable (9.2 days; range, 6-13 days after tumor injection), mice were assigned to treatment groups receiving PS-341 0.05 mg/kg (n = 13), 0.1 mg/kg (n = 15), 0.5 mg/kg (n = 14), or 1.0 mg/kg (n = 14) twice weekly via tail vein, or to control groups (n = 13) receiving the vehicle only. Significant inhibition of tumor...
Nuclear Factor-κB: A Holy Grail in Cancer Prevention and Therapy
Current Signal Transduction Therapy, 2006
Nuclear factor-B (NF-B) is a transcription factor that is activated in response to various inflammatory stimuli such as cytokines, growth factors, hormones, mitogens, carcinogens, chemotherapeutic agents, viral products, eukaryotic parasites, endotoxin, fatty acids, metals, radiation, hypoxia, and psychological, physical, oxidative, and chemical stresses. In addition, constitutively active NF-B is frequently encountered in a wide variety of tumors, including breast, ovarian, colon, pancreatic, thyroid, prostate, lung, head and neck, bladder, and skin cancers; B-cell lymphoma; Hodgkin's disease; T-cell lymphoma; adult T-cell leukemia; acute lymphoblastic leukemia; multiple myeloma; chronic lymphocytic leukemia; and acute myelogenous leukemia. Furthermore, NF-B activation has been shown to regulate the expression of over 400 genes involved in cellular transformation, proliferation, inflammation, viral replication, antiapoptosis, angiogenesis, invasion and metastasis, oxidative stress, and osteoclastogenesis. Therefore, because of the critical role NF-B plays in the pathogenesis of cancer, specific inhibitors of this factor are being sought. Agents that prevent cancer or inflammation have been found to suppress NF-B activation. Although I B kinase is the major kinase, over 30 different protein kinases have been linked to the activation of NF-B by different stimuli. The development of a drug that can specifically suppress NF-B activation requires a full understanding of the mechanism by which NF-B is activated in response to these various stimuli.