Molecular sequelae of proteasome inhibition in human multiple myeloma cells

Importance of the different proteolytic sites of the proteasome and the efficacy of inhibitors varies with the protein substrate

The relative importance of the different proteolytic sites in mammalian proteasomes in protein degradation has not been studied systematically. Nevertheless, it is widely assumed that inhibition of the chymotrypsin-like site, the primary target of the proteasome inhibitors used in research and cancer therapy, reflects the degree of inhibition of protein breakdown. Here we demonstrate that selective inactivation of the chymotrypsin-like site reduced degradation of model proteins by pure 26 S proteasomes by only 11-50% and decreased only slightly the breakdown of proteins in HeLa cells. Inactivation of the caspase-like site decreased breakdown of model proteins by 12-22% and of the trypsin-like site by 3-35%. The relative contributions of these different sites depended on the protein substrate, and the importance of the trypsin-like sites depended on the substrate's content of basic residues. Simultaneous inhibition of the chymotrypsin-like and the caspase- or trypsin-like sites was needed to reduce degradation by >50%. Thus, 1) all three types of active sites contribute significantly to protein breakdown, 2) their relative importance varies widely with the substrate, 3) assaying the chymotrypsin-like activity overestimates the actual reduction in protein degradation, and 4) inhibition of multiple sites is required to markedly decrease proteolysis.

THE PROTEASOME AND PROTEASOME INHIBITORS IN CANCER THERAPY

The proteasome, a multicatalytic proteinase complex, is responsible for the majority of intracellular protein degradation. Pharmacologic inhibitors of the proteasome possess in vitro and in vivo antitumor activity, and bortezomib, the first such agent to undergo clinical testing, has significant efficacy against multiple myeloma and non-Hodgkin lymphoma (NHL). Preclinical studies demonstrate that proteasome inhibition potentiates the activity of other cancer therapeutics, in part by downregulating chemoresistance pathways. Early clinical studies of bortezomib-based combinations, showing encouraging activity, support this observation. Molecular characterization of resistance to proteasome inhibitors has revealed novel therapeutic targets for sensitizing malignancies to these agents, such as the heat shock pathway. Below, we review the pharmacologic, preclinical, and clinical data that have paved the way for the use of proteasome inhibitors for cancer therapy; outline strategies aimed at enhancing the efficacy of proteasome inhibitors; and review other potential targets in the ubiquitin proteasome pathway for the treatment of cancer.

Proteasome inhibition induces hepatic stellate cell apoptosis

Induction of hepatic stellate cell (HSC) apoptosis attenuates hepatic fibrosis, and, therefore, mechanisms to induce HSC cell death are of therapeutic interest. Proteasome inhibitors induce apoptosis in transformed cells, especially those cells dependent upon nuclear factor kappa B (NF-kappaB) activation. Because stimulated HSCs also trigger NF-kappaB activation, the aim of this study was to determine if proteasome inhibitors induce HSC apoptosis. The immortalized human HSC line, LX-2, and primary rat HSCs were treated with the proteasome inhibitors bortezomib and MG132. Both proteasome inhibitors induced HSC apoptosis. Proteasome inhibition blocked NF-kappaB activation and, more importantly, NF-kappaB inhibition by Bay11-7082-triggered HSC apoptosis. Activated HSC survival is dependent upon the NF-kappaB target gene A1, an anti-apoptotic Bcl-2 family member, as siRNA targeted knockdown of A1-induced HSC apoptosis. In contrast, proteasome inhibition-induced alterations in TRAIL, death receptor 5, and Bim could not be implicated in the apoptotic response. The relevance of these findings was confirmed in the bile-duct-ligated mouse where bortezomib reduced hepatic markers of stellate cell activation and fibrosis. In conclusion, proteasome inhibition is a potential therapeutic strategy for inducing HSC apoptosis and inhibiting liver fibrogenesis.

PS-341 (bortezomib) induces lysosomal cathepsin B release and a caspase-2-dependent mitochondrial permeabilization and apoptosis in human pancreatic cancer cells

PS-341 (bortezomib) is a potent and reversible proteosome inhibitor that functions to degrade intracellular polyubiquitinated proteins. PS-341 induces apoptosis and has shown broad antitumor activity with selectivity for transformed cells. We studied the effect of PS-341 on lysosomal and mitochondrial permeabilization, including the role of caspase-2 activation in apoptosis induction in the BxPC-3 human pancreatic carcinoma cell line. PS-341 induced a dose-dependent apoptosis in association with reactive oxygen species generation and cleavage of caspase-2 to its 33- and 14-kDa fragments. PS-341 disrupted lysosomes with redistribution of cathepsin B to the cytosol, as shown using fluorescence confocal microscopy, that was blocked by the free radical scavenger tiron but not by a caspase-2 inhibitor (benzyloxycarbonyl (Z)-VDVAD-fluoromethyl ketone (FMK)). PS-341-induced caspase-2 activation was attenuated by a selective pharmacological inhibitor of cathepsin B (R-3032), suggesting that cathepsin B release occurs upstream of caspase-2. PS-341-induced mitochondrial depolarization was attenuated by Z-VDVAD-FMK, tiron, and an inhibitor of the mitochondrial permeability transition pore (bongkrekic acid). Regulation of mitochondrial permeability by caspase-2 was confirmed using caspase-2 small interfering RNA. PS-341-induced cytochrome c release and phosphatidylserine externalization were attenuated by Z-VDVAD-FMK and partially by R-3032. PS-341 activated the BH3-only proteins Bik and Bim and down-regulated Bcl-2 and Bcl-xL mRNA and protein expression. Taken together, PS-341 induces lysosomal cathepsin B redistribution upstream of caspase-2. Caspase-2 activation regulates PS-341-induced mitochondrial depolarization and apoptosis, suggesting that caspase-2 can serve as a link between lysosomal and mitochondrial permeabilization.

Targeting the proteasome as a therapeutic strategy against haematological malignancies

The ubiquitin-proteasome pathway is responsible for the vast majority of regulated eukaryotic intracellular proteolysis. Inhibition of the proteasome induces beneficial antitumour effects by blocking cell-cycle progression, inducing apoptosis and suppressing angiogenesis. Bortezomib is the first proteasome inhibitor to reach the clinical arena, where Phase I - III trials verified its activity against relapsed/refractory multiple myeloma. Testing is ongoing to determine bortezomib's role in front-line therapy of this plasma cell dyscrasia, as well as in non-Hodgkin's lymphoma, in which encouraging single-agent activity has been seen. Proteasome inhibition is also a rational strategy to overcome chemoresistance and induce chemosensitisation. Combinations of bortezomib and other agents have enhanced efficacy, and additional studies are probing the activity of several regimens in lymphoid and myeloid malignancies. The current state of knowledge about the activity of bortezomib, both alone and in combination with standard chemotherapeutics, as part of the emerging armamentarium against haematological malignancies is reviewed.

Bortezomib: a valuable new antineoplastic strategy in multiple myeloma

Although the treatment of multiple myeloma has improved over the past decade, the disease remains incurable. Bortezomib, a first-in-class selective proteasome inhibitor, was approved in the United States in 2003 and the European Union in 2004 for the treatment of relapsed and refractory multiple myeloma in patients who have received at least 2 prior therapies and demonstrated disease progression on the last therapy. In vitro, bortezomib induces apoptosis of multiple myeloma cells and inhibits cell adhesion within the bone marrow microenvironment. Preclinical and clinical data have shown that bortezomib enhances sensitivity and reverses resistance to standard therapeutic agents used in multiple myeloma. The efficacy and safety of bortezomib was established in patients with relapsed and/or refractory disease. In a large phase III trial in patients with relapsed multiple myeloma, median time to progression and overall survival were significantly improved with bortezomib compared with high-dose dexamethasone. Importantly, the preliminary results of several phase I and II studies are also showing high antimyeloma activity of bortezomib alone or in combination with dexamethasone or cytotoxic agents such as doxorubicin, melphalan, or thalidomide in patients with newly diagnosed multiple myeloma. Ideally, the introduction of bortezomib will result in a significant improvement in the future management of multiple myeloma.

Bortezomib: proteasome inhibition as an effective anticancer therapy

VELCADER (bortezomib, Millennium Pharmaceuticals, Inc., Cambridge, MA, and Johnson & Johnson Pharmaceutical Research & Development, L.L.C., Raritan, NJ) is a first-in-class proteasome inhibitor developed specifically for use as an antineoplastic agent. Inhibition of the proteasome results in disruption of homeostatic mechanisms within the cell that can lead to cell death. Bortezomib's first indication, for the treatment of relapsed myeloma in patients who have received at least two prior treatments and progressed on their previous treatment, was based in part on the magnitude of activity demonstrated in phase II trials. Bortezomib is currently indicated for patients who have received at least one prior therapy in the United States and European Union, although patients in the European Union must have already undergone bone marrow transplantation or be unsuitable for the procedure. A phase III trial demonstrated the superiority of bortezomib over high-dose dexamethasone in response rate, time to progression, and survival in patients with myeloma who had relapsed after 1-3 prior therapies. Clinical development is ongoing to investigate its activity as monotherapy and in combination regimens for the treatment of non-Hodgkin's lymphoma, solid tumors, and earlier presentations of myeloma.

Mammalian target of rapamycin inhibitors activate the AKT kinase in multiple myeloma cells by up-regulating the insulin-like growth factor receptor/insulin receptor substrate-1/phosphatidylinositol 3-kinase cascade

Mammalian target of rapamycin (mTOR) inhibitors, such as rapamycin and CCI-779, have shown preclinical potential as therapy for multiple myeloma. By inhibiting expression of cell cycle proteins, these agents induce G1 arrest. However, by also inhibiting an mTOR-dependent serine phosphorylation of insulin receptor substrate-1 (IRS-1), they may enhance insulin-like growth factor-I (IGF-I) signaling and downstream phosphatidylinositol 3-kinase (PI3K)/AKT activation. This may be a particular problem in multiple myeloma where IGF-I-induced activation of AKT is an important antiapoptotic cascade. We, therefore, studied AKT activation in multiple myeloma cells treated with mTOR inhibitors. Rapamycin enhanced basal AKT activity, AKT phosphorylation, and PI3K activity in multiple myeloma cells and prolonged activation of AKT induced by exogenous IGF-I. CCI-779, used in a xenograft model, also resulted in multiple myeloma cell AKT activation in vivo. Blockade of IGF-I receptor function prevented rapamycin's activation of AKT. Furthermore, rapamycin prevented serine phosphorylation of IRS-1, enhanced IRS-1 association with IGF-I receptors, and prevented IRS-1 degradation. Although similarly blocking IRS-1 degradation, proteasome inhibitors did not activate AKT. Thus, mTOR inhibitors activate PI3-K/AKT in multiple myeloma cells; activation depends on basal IGF-R signaling; and enhanced IRS-1/IGF-I receptor interactions secondary to inhibited IRS-1 serine phosphorylation may play a role in activation of the cascade. In cotreatment experiments, rapamycin inhibited myeloma cell apoptosis induced by PS-341. These results provide a caveat for future use of mTOR inhibitors in myeloma patients if they are to be combined with apoptosis-inducing agents.

Perifosine, an oral bioactive novel alkylphospholipid, inhibits Akt and induces in vitro and in vivo cytotoxicity in human multiple myeloma cells

Perifosine is a synthetic novel alkylphospholipid, a new class of antitumor agents which targets cell membranes and inhibits Akt activation. Here we show that baseline phosphorylation of Akt in multiple myeloma (MM) cells is completely inhibited by perifosine [octadecyl-(1,1-dimethyl-piperidinio-4-yl)-phosphate] in a time- and dose-dependent fashion, without inhibiting phosphoinositide-dependent protein kinase 1 phosphorylation. Perifosine induces significant cytotoxicity in both MM cell lines and patient MM cells resistant to conventional therapeutic agents. Perifosine does not induce cytotoxicity in peripheral blood mononuclear cells. Neither exogenous interleukin-6 (IL-6) nor insulinlike growth factor 1 (IGF-1) overcomes Perifosine-induced cytotoxicity. Importantly, Perifosine induces apoptosis even of MM cells adherent to bone marrow stromal cells. Perifosine triggers c-Jun N-terminal kinase (JNK) activation, followed by caspase-8/9 and poly (ADP)-ribose polymerase cleavage. Inhibition of JNK abrogates perifosine-induced cytotoxicity, suggesting that JNK plays an essential role in perifosine-induced apoptosis. Interestingly, phosphorylation of extracellular signal-related kinase (ERK) is increased by perifosine; conversely, MEK inhibitor synergistically enhances Perifosine-induced cytotoxicity in MM cells. Furthermore, perifosine augments dexamethasone, doxorubicin, melphalan, and bortezomib-induced MM cell cytotoxicity. Finally, perifosine demonstrates significant antitumor activity in a human plasmacytoma mouse model, associated with down-regulation of Akt phosphorylation in tumor cells. Taken together, our data provide the rationale for clinical trials of perifosine to improve patient outcome in MM.

Chaperoning oncogenes: Hsp90 as a target of geldanamycin

Heat shock protein 90 (Hsp90) is a molecular chaperone required for the stability and function of a number of conditionally activated and/or expressed signaling proteins, as well as multiple mutated, chimeric, and/or over-expressed signaling proteins, that promote cancer cell growth and/or survival. Hsp90 inhibitors, by interacting specifically with a single molecular target, cause the inactivation, destabilization, and eventual degradation of Hsp90 client proteins, and they have shown promising anti-tumor activity in preclinical model systems. One Hsp90 inhibitor, 17-AAG, has completed Phase I clinical trial and several Phase II trials of this agent are in progress. Hsp90 inhibitors are unique in that, although they are directed toward a specific molecular target, they simultaneously inhibit multiple signaling pathways that frequently interact to promote cancer cell survival. Further, by inhibiting nodal points in multiple overlapping survival pathways utilized by cancer cells, a combination of an Hsp90 inhibitor with standard chemotherapeutic agents may dramatically increase the in vivo efficacy of the standard agent. Hsp90 inhibitors may circumvent the characteristic genetic plasticity that has allowed cancer cells to eventually evade the toxic effects of most molecularly targeted agents. The mechanism-based use of Hsp90 inhibitors, both alone and in combination with other drugs, should be effective toward multiple forms of cancer.

Hsp90 inhibitors in the clinic

Specific inhibitors of Hsp90 have recently entered human clinical trials. At the time of writing, trials have been initiated only in metastatic cancer, although a rationale exists for using these agents in a variety of human diseases where protein (mis)folding is involved in the disease pathophysiology. Hsp90 inhibitors offer a unique anti-cancer opportunity because they provide simultaneous combinatorial blockade of multiple oncogenic pathways. The first compound in this class, 17-AAG, has completed phase I trials and phase II trials are in progress. The toxicity has been manageable and evidence of possible clinical activity has been seen in metastatic melanoma, prostate cancer and multiple myeloma. Other inhibitors with improved properties are approaching clinical trials. This chapter presents an update of the current clinical trials using Hsp90 inhibitors, focussing on the areas that will be increasingly relevant in the next 5 years.

The combination of the farnesyl transferase inhibitor lonafarnib and the proteasome inhibitor bortezomib induces synergistic apoptosis in human myeloma cells that is associated with down-regulation of p-AKT

The identification of signaling pathways critical to myeloma growth and progression has yielded an array of novel agents with clinical activity. Multiple myeloma (MM) growth is IL-6 dependent, and IL-6 is secreted in an autocrine/paracrine fashion with signaling via the Ras/Raf/mitogen-activated protein kinase (MAPK) pathway. We hypothesized that combining a Ras pathway inhibitor (lonafarnib, SCH66336) with a proteasome inhibitor (bortezomib, Velcade, PS-341) would enhance myeloma-cell killing. MM cell lines and primary human cells were used to test either single agent bortezomib, lonafarnib, or the combination on MM signaling and apoptosis. Combination therapy induced synergistic tumor-cell death in MM cell lines and primary MM plasma cells. Cell death was rapid and associated with increased caspase 3, 8, and 9 cleavage and concomitant down-regulation of p-AKT. Down-regulation of p-AKT was seen only in combination therapy and not seen with either single agent. Cells transfected with constitutively active p-AKT, wild-type AKT, or Bcl-2 continued to demonstrate synergistic cell death in response to the combination. The order of addition was critically important, supporting bortezomib followed by lonafarnib as the optimal schedule. The combination of a proteasome inhibitor and farnesyl transferase inhibitor demonstrates synergistic myeloma-cell death and warrants further preclinical and clinical studies.

Targeted therapy in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is an incurable malignancy. Recent insights into its biology has allowed the use of novel therapies targeting not only the deregulated intracellular signaling in MM cells but also its interaction with the bone marrow microenvironment that confers drug resistance, growth, and survival advantage to the malignant cells.

METHODS

We review and summarize the recent advances in our knowledge of myeloma biology as well as the mechanism of action and clinical efficacy for novel therapeutic agents in clinical trials.

RESULTS

Several novel therapeutic agents are currently in clinical trials. Thalidomide is already established for both initial and salvage treatment. Bortezomib is being tested alone and in combination with conventional chemotherapy in various settings. Other agents are less effective in producing response but have been able to stabilize disease in patients with relapsed and/or refractory disease, such as arsenic trioxide, farnesyltransferase inhibitors, 2-methoxyestradiol, and vascular endothelial growth factor receptor inhibitors. Insights into drug resistance mechanism have also led to the development of novel agents that sensitize myeloma cells to chemotherapy (Bcl-2 antisense). Gene expression studies have in many instances identified pathways other than the intended target of the drug and have provided insights into the therapeutic mechanisms.

CONCLUSIONS

In the future, patients with MM will have more therapeutic options available than ever before. The challenge will be to identify patient subgroups that will benefit most from the different therapies and then determine how these biologically based therapies could be combined and incorporated into the overall management of patients.

Conventional therapy and approach to management

The treatment of multiple myeloma (MM) has undergone major changes in the last decade. There is now an array of therapeutic options, including autologous stem-cell transplantation, non-myeloablative (mini) allogeneic transplantation, and new drugs such as thalidomide and bortezomib. There is also an awareness that there are subsets of patients with MM who have not gained much from the recent advances, including patients with certain adverse prognostic factors (high-risk MM). In this article, we outline our approach to the diagnosis, risk stratification and treatment of MM with a focus on conventional therapy. We incorporate a risk-based strategy for the treatment of MM that also takes into account the eligibility of the patient to undergo stem-cell transplantation. We also outline the role and current indications for the use of new active agents in this disease.

Novel biological therapies for the treatment of multiple myeloma

The therapeutic management of multiple myeloma (MM) for the last several decades has mainly involved regimens based on use of glucocorticoids and cytotoxic chemotherapeutics. Despite progress in delineating the activity of such regimens, at either conventional or high doses, MM has remained an incurable disease, without substantial improvement in the median overall survival. This has sparked major interest in the development of novel therapies that in part capitalize on recent advances in our understanding of the biology of MM, including the molecular mechanisms by which MM cell-host bone marrow (BM) interactions regulate tumor-cell growth, survival, and drug resistance in the BM milieu. The development of in vitro and in vivo models of MM-stromal interactions has allowed not only for better characterization of these molecular phenomena but also for identification of specific therapeutic strategies to overcome these interactions and achieve an enhanced anti-MM effect, even against MM resistant to conventional therapies. Herein, we review the latest progress in the development of these novel anti-MM therapies, with major focus on therapies which have translated from preclinical evaluation to clinical application, including thalidomide and its more potent immunomodulatory (IMiD) derivatives, the first-in-class proteasome inhibitor bortezomib (formerly known as PS-341), and arsenic trioxide (As2O3).

Altering protein turnover in tumor cells: New opportunities for anti-cancer therapies

The promising effects of the proteasome inhibitor bortezomib (Velcade, PS-341) in the treatment of certain types of cancer have fired up the interest on this multicatalytic proteolytic machinery. A number of recent reviews thoroughly describe various aspects of the ubiquitin-proteasome system and its importance in the control of cell growth and tumorigenesis. Here, we will focus on recent data unveiling a link between the proteasome and some elements of the apoptotic machinery including Bcl-2 members, caspases, IAPs and IAP antagonists. Perturbing their turnover significantly contributes to the apoptotic response and the anti-neoplastic activity of proteasome inhibitors.

Other Compounds and Targets in Non–Small Cell Lung Cancer

It has become increasingly apparent in recent years that a therapeutic plateau has been reached for patients with advanced stage non-small cell lung cancer (NSCLC) treated with conventional cytotoxic agents. As a result, investigators have directed their efforts toward the development of treatments encompassing novel targeted agents. Apoptosis is one of many cellular pathways currently under investigation as a therapeutic target for the treatment of NSCLC. Anti-inflammatory agents, including cyclooxygenase inhibitors, have been shown to inhibit apoptosis and appear promising based on preclinical studies. However, several phase II studies indicate that this therapeutic strategy is unlikely to be successful. In contrast, the proteosome inhibitor bortezomib has shown promise in preliminary studies, and further efforts to elucidate the role this agent may play in the treatment of NSCLC are ongoing. Agonists of the tumor necrosis factor-related, apoptosis-inducing ligand have also entered into early clinical studies in patients with NSCLC. Further studies will be needed to fully clarify how agents targeting the apoptotic pathway can be used in the treatment of NSCLC, but the results of current clinical trials suggest that certain agents may be active.

Bortezomib, a novel proteasome inhibitor, in the treatment of hematologic malignancies

Proteasome inhibition is a novel approach to treating malignancy, and bortezomib is the first proteasome inhibitor in this class to be approved for clinical use. In preclinical studies, bortezomib caused cell cycle arrest and apoptosis in myeloma and lymphoma cell lines as well as in other neoplastic cell types. Phase I clinical trials established an optimal dosing strategy and demonstrated a manageable toxicity profile. Cyclical thrombocytopenia and peripheral neuropathy, which generally abate after cessation of treatment, are the most clinically significant toxicities. Two phase II trials, SUMMIT and CREST, demonstrated impressive activity with bortezomib 1.3 mg/m2 monotherapy in relapsed and refractory myeloma, with an impressive 35% response rate (complete+partial+minimal responses) in SUMMIT and a 50% response rate in CREST, using the rigorous European Group for Blood and Marrow Transplantation criteria. A recently completed phase III trial showed the significant clinical benefits of bortezomib over high-dose dexamethasone in patients with relapsed myeloma. Results of ongoing trials with bortezomib in the first-line treatment of myeloma have been extremely encouraging and have demonstrated the benefit of using bortezomib as part of an induction regimen prior to stem cell transplantation. Importantly, two clinical trials with bortezomib as monotherapy in refractory non-Hodgkin's lymphoma have shown impressive response rates, particularly in aggressive mantle cell lymphoma.

Proteasome inhibitors can alter the signaling pathways and attenuate the P-glycoprotein-mediated multidrug resistance

Numerous signaling pathways were reported to be involved in the resistance for conventional cytotoxic drugs, although one of the main reasons is the overexpression of P-glycoprotein (P-gp) in multidrug resistant cancer cells. The overexpression of P-gp has been associated with the resistance to a wide range of anticancer drugs. Doxorubicin and paclitaxel are substrates of this transporter system and have an important role for the various human malignancies. In the present study, drug-sensitive MCF7 and multidrug resistant MCF7/ADR (characterized by overexpression of P-gp) human breast cancer cell lines were used as an experimental model. We have found that PS341 and MG132, proteasome inhibitors, reduced the degree of the multidrug resistance (MDR) in MCF7/ADR cells. This phenomenon was accompanied by a decrease in the IC50 value of doxorubicin and paclitaxel from 55.9 +/- 3.46 to 0.60 +/- 0.08 microM, and from 17.61 +/- 1.77 to 0.59 +/- 0.12 microM, respectively. The IC50 values of sensitive cells for doxorubicin and paclitaxel were about 0.42 and 0.83 microM, respectively. The effect of PS341 and MG132 on MCF7/ADR cells was associated with a significant decrease in both protein and gene levels of P-gp expression. Moreover, with regard to the expression of possible signal transduction pathways of mitogen-activated protein kinase (MAPK) related to the activation of mdr1, proteasome inhibitors did significantly influence the activation of these proteins. Western blot analysis revealed that 24 hr exposure of multidrug resistant MCF7/ADR cells with proteasome inhibitors did change the levels of DNA binding activity of nuclear factor-kappaB (NF-kappaB), pERK1/2, c-Jun, and p-c-Jun. In conclusion, we could remark that proteasome inhibitors (especially PS341) attenuate the resistance of MCF7/ADR cells for P-gp substrate drugs of doxorubicin and paclitaxel. Several proteins are supposed to be associated with the resensitization of the cells to conventional cytotoxic drugs, although decreased activity of P-gp is at least involved in the proteasome inhibitor-related resensitization. And influence with MAPK pathways, which have been reported to be associated with the regulation of P-gp, might be contributed to the resensitization brought by proteasome inhibitors.

A putative stimulatory role for activator turnover in gene expression

The ubiquitin-proteasome system (UPS) promotes the destruction of target proteins by attaching to them a ubiquitin chain that is recognized by the 26S proteasome. The UPS influences most cellular processes, and its targets include transcriptional activators that are primary determinants of gene expression. Emerging evidence indicates that non-proteolytic functions of the UPS might stimulate transcriptional activity. Here we show that the proteolysis of some transcriptional activators by the UPS can stimulate their function. We focused on the role of UPS-dependent proteolysis in the function of inducible transcriptional activators in yeast, and found that inhibition of the proteasome reduced transcription of the targets of the activators Gcn4, Gal4 and Ino2/4. In addition, mutations in SCF(Cdc4), the ubiquitin ligase for Gcn4 (ref. 5), or mutations in ubiquitin that prevent degradation, also impaired the transcription of Gcn4 targets. These transcriptional defects were manifested despite the enhanced abundance of Gcn4 on cognate promoters. Proteasome inhibition also decreased the association of RNA polymerase II with Gcn4, Gal4 and Ino2/4 targets, as did mutations in SCF(Cdc4) for Gcn4 targets. Expression of a stable phospho-site mutant of Gcn4 (ref. 7) or disruption of the kinases that target Gcn4 for turnover alleviated the sensitivity of Gcn4 activity to defects in the UPS.

A novel orally active proteasome inhibitor induces apoptosis in multiple myeloma cells with mechanisms distinct from Bortezomib

Bortezomib therapy has proven successful for the treatment of relapsed and/or refractory multiple myeloma (MM); however, prolonged treatment is associated with toxicity and development of drug resistance. Here, we show that the novel proteasome inhibitor NPI-0052 induces apoptosis in MM cells resistant to conventional and Bortezomib therapies. NPI-0052 is distinct from Bortezomib in its chemical structure, effects on proteasome activities, mechanisms of action, and toxicity profile against normal cells. Moreover, NPI-0052 is orally bioactive. In animal tumor model studies, NPI-0052 is well tolerated and prolongs survival, with significantly reduced tumor recurrence. Combining NPI-0052 and Bortezomib induces synergistic anti-MM activity. Our study therefore provides the rationale for clinical protocols evaluating NPI-0052, alone and together with Bortezomib, to improve patient outcome in MM.

Unique Gene Expression Profile Based on Pathologic Response in Epithelial Ovarian Cancer

Purpose

We investigated whether tumor tissue obtained at diagnosis expresses a specific gene profile that is predictive of findings at second-look surgery in patients with epithelial ovarian cancer (EOC).

Patients and Methods

Tumor tissue obtained at the time of diagnosis was profiled with oligonucleotide microarrays. Class prediction analysis was performed in a training set of 24 patients who had undergone a second-look procedure. The resultant predictive signature was then tested on an independent validation set comprised of 36 patients.

Results

A 93-gene signature referred to as the Chemotherapy Response Profile (CRP) was identified through its association with pathologic complete response. When applied to a separate validation set, the CRP distinguished between patients with unfavorable versus favorable overall survival (median 41 months v not yet reached, respectively, log-rank P = .007), with a median follow-up of 52 months. The signature maintained independent prognostic value in multivariate analysis, controlling for other known prognostic factors such as age, stage, grade, and debulking status. There was no genetic overlap between the CRP and our previously described Ovarian Cancer Prognostic Profile (OCPP), which demonstrated similar prognostic value. The combination of the CRP and OCPP yielded better prognostic discrimination then either profile alone. Genes present in the CRP include BAX, a proapoptotic protein previously associated with chemotherapy response in ovarian cancer.

Conclusion

Identification of a gene expression profile based on pathologic response in EOC provides independent prognostic information and offers potential insights into the mechanism of drug resistance. Efforts to identify a more tailored profile using selected genes from both the CRP and OCPP are underway.

Growth factors and antiapoptotic signaling pathways in multiple myeloma

Failure of myeloma cells to undergo apoptosis plays an important role in the accumulation of myeloma cells within the bone marrow (BM). Moreover, inhibition of drug-induced apoptosis has been indicated as a major contributor of drug resistance in myeloma. The BM microenvironment promotes survival and blocks the apoptotic effects of various cytotoxic agents through the production of cytokines as well as through direct physical interactions. Several antiapoptotic proteins and antiapoptotic signaling cascades have been identified that contribute to the antiapoptotic phenotype of the myeloma cell. In this review, we discuss mechanisms that result in enhanced survival and drug resistance of myeloma cells. Insight into these mechanisms is essential to make progress in the therapy of myeloma.

Antimyeloma activity of heat shock protein-90 inhibition

We show that multiple myeloma (MM), the second most commonly diagnosed hematologic malignancy, is responsive to hsp90 inhibitors in vitro and in a clinically relevant orthotopic in vivo model, even though this disease does not depend on HER2/neu, bcr/abl, androgen or estrogen receptors, or other hsp90 chaperoning clients which are hallmarks of tumor types traditionally viewed as attractive clinical settings for use of hsp90 inhibitors, such as the geldanamycin analog 17-AAG. This class of agents simultaneously suppresses in MM cells the expression and/or function of multiple levels of insulin-like growth factor receptor (IGF-1R) and interleukin-6 receptor (IL-6R) signaling (eg, IKK/NF-kappaB, PI-3K/Akt, and Raf/MAPK) and downstream effectors (eg, proteasome, telomerase, and HIF-1alpha activities). These pleiotropic proapoptotic effects allow hsp90 inhibitors to abrogate bone marrow stromal cell-derived protection on MM tumor cells, and sensitize them to other anticancer agents, including cytotoxic chemotherapy and the proteasome inhibitor bortezomib. These results indicate that hsp90 can be targeted therapeutically in neoplasias that may not express or depend on molecules previously considered to be the main hsp90 client proteins. This suggests a more general role for hsp90 in chaperoning tumor- or tissue-type-specific constellations of client proteins with critical involvement in proliferative and antiapoptotic cellular responses, and paves the way for more extensive future therapeutic applications of hsp90 inhibition in diverse neoplasias, including MM.

Proteasome inhibitor therapy in multiple myeloma

Multiple myeloma remains incurable despite available therapies, and novel therapies that target both tumor cell and bone marrow microenvironment are urgently needed. Preclinical in vitro and in vivo studies show remarkable anti-multiple myeloma activity of the proteasome inhibitor bortezomib/PS-341 even in multiple myeloma cells refractory to multiple prior therapies, including dexamethasone, melphalan, and thalidomide. Based on these findings, the U.S. Food and Drug Administration recently approved the first proteasome inhibitor bortezomib (Velcade), formerly known as PS-341, for the treatment of relapsed/refractory multiple myeloma. Bortezomib therapy has set an outstanding example of translational research in the field of oncology. Genomics and proteomic studies further provide rationale for combining bortezomib with conventional and novel agents to inhibit multiple myeloma growth, overcome drug resistance, reduce attendant toxicity, and improve patient outcome in multiple myeloma.

Cytokines and signal transduction

Many studies have characterized the role of growth factors in multiple myeloma (MM) pathogenesis and have derived novel therapies to improve patient outcome based upon targeting cytokines and their signaling cascades both in the MM cell and in the bone-marrow (BM) microenvironment. These cytokines include interleukin 6 (IL-6), insulin-like growth factor 1 (IGF-1), vascular endothelial growth factor (VEGF), tumor necrosis factor alpha (TNF-alpha), transforming growth factor beta (TGF-beta), stromal cell-derived factor 1alpha (SDF-1alpha), IL-21, B-cell stimulating factor 3 (BSF-3) and fibroblast growth factor (FGF). These cytokines are secreted from stromal cells (SCs), endothelial cells and/or osteoclasts, and promote MM cell growth, survival and migration, as well as paracrine cytokine secretion and angiogenesis in the BM milieu. Thus inhibition of signaling cascades induced by these cytokine provides rationale for a therapeutic option for MM.

Proteasome inhibitors as therapeutics

The ubiquitin–proteasome pathway is a principle intracellular mechanism for controlled protein degradation and has recently emerged as an attractive target for anticancer therapies, because of the pleiotropic cell-cycle regulators and modulators of apoptosis that are controlled by proteasome function. In this chapter, we review the current state of the field of proteasome inhibitors and their prototypic member, bortezomib, which was recently approved by the U.S. Food and Drug Administration for the treatment of advanced multiple myeloma. Particular emphasis is placed on the pre-clinical research data that became the basis for eventual clinical applications of proteasome inhibitors, an overview of the clinical development of this exciting drug class in multiple myeloma, and a appraisal of possible uses in other haematological malignancies, such non-Hodgkin's lymphomas.

PROTEASOME INHIBITION IN MULTIPLE MYELOMA: Therapeutic Implication

Normal cellular functioning requires processing of proteins regulating cell cycle, growth, and apoptosis. The ubiquitin-proteasome pathway (UBP) modulates intracellular protein degradation. Specifically, the 26S proteasome is a multienzyme protease that degrades misfolded or redundant proteins; conversely, blockade of the proteasomal degradation pathways results in accumulation of unwanted proteins and cell death. Because cancer cells are more highly proliferative than normal cells, their rate of protein translation and degradation is also higher. This notion led to the development of proteasome inhibitors as therapeutics in cancer. The FDA recently approved the first proteasome inhibitor bortezomib (Velcade™), formerly known as PS-341, for the treatment of newly diagnosed and relapsed/refractory multiple myeloma (MM). Ongoing studies are examining other novel proteasome inhibitors, in addition to bortezomib, for the treatment of MM and other cancers.

NF-kappaB as a target for the prevention of graft-versus-host disease: comparative efficacy of bortezomib and PS-1145

NF-kappaB is a transcription factor that controls the expression of a number of genes important for mediating immune and inflammatory responses. In this study, we examined whether bortezomib and PS-1145, each of which inhibits NF-kappaB, could protect mice from lethal graft-versus-host disease (GVHD), which is characterized by immune activation and proinflammatory cytokine production. When administered within the first 2 days after transplantation, bortezomib and PS-1145 both protected mice from fatal GVHD, did not compromise donor engraftment, and effected marked reduction in the levels of serum cytokines that are normally increased during GVHD. Extending the course of bortezomib administration or delaying the initiation of this agent for as few as 3 days after bone marrow transplantation (BMT), however, significantly exacerbated GVHD-dependent mortality because of severe pathological damage in the colon. In contrast, prolonged administration of PS-1145, which, unlike bortezomib, is a selective inhibitor of NF-kappaB, caused no early toxicity and resulted in more complete protection than that observed with an abbreviated PS-1145 treatment schedule. These results confirm a critical role for NF-kappaB in the pathophysiology of GVHD and indicate that targeted inhibition of NF-kappaB may have a superior therapeutic index and may constitute a viable therapeutic approach to reduce GVHD severity.

Preconditioning of primary human endothelial cells with inflammatory mediators alters the "set point" of the cell

Endothelial cells are highly sensitive to changes in the extracellular milieu. Sepsis results in activation of inflammatory and coagulation pathways. We hypothesized that sepsis-associated mediators may alter the response capacity (so-called "set point") of endothelial cells. Human umbilical vein endothelial cells (HUVEC) were preincubated in the presence or absence of tumor necrosis factor (TNF)-alpha, lipopolysaccharide (LPS), hypoxia, hyperthermia, and/or high glucose; treated with or without thrombin for 4 h; and then processed for RNase protection assays of selected activation markers. Priming with TNF-alpha and LPS significantly inhibited thrombin-mediated induction of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, tissue factor, and E-selectin, but not platelet-derived growth factor-A or CD44. In electrophoretic mobility shift assays, thrombin-treated HUVEC demonstrated inducible binding of p65 NF-kappaB, an effect that was significantly blunted by pretreatment of cells with TNF-alpha and LPS. Consistent with these results, TNF-alpha and LPS attenuated the effect of thrombin on IkappaB phosphorylation, total cytoplasmic IkappaB, and nuclear translocation of p65 NF-kappaB. The inhibitory effect of TNF-alpha on thrombin signaling persisted for up to 24 h following removal of the cytokine. Taken together, these data suggest that inflammatory mediators prime endothelial cells to modulate subsequent thrombin response.

Proteasome inhibitors trigger NOXA-mediated apoptosis in melanoma and myeloma cells

Patients with metastatic melanoma or multiple myeloma have a dismal prognosis because these aggressive malignancies resist conventional treatment. A promising new oncologic approach uses molecularly targeted therapeutics that overcomes apoptotic resistance and, at the same time, achieves tumor selectivity. The unexpected selectivity of proteasome inhibition for inducing apoptosis in cancer cells, but not in normal cells, prompted us to define the mechanism of action for this class of drugs, including Food and Drug Administration-approved bortezomib. In this report, five melanoma cell lines and a myeloma cell line are treated with three different proteasome inhibitors (MG-132, lactacystin, and bortezomib), and the mechanism underlying the apoptotic pathway is defined. Following exposure to proteasome inhibitors, effective killing of human melanoma and myeloma cells, but not of normal proliferating melanocytes, was shown to involve p53-independent induction of the BH3-only protein NOXA. Induction of NOXA at the protein level was preceded by enhanced transcription of NOXA mRNA. Engagement of mitochondrial-based apoptotic pathway involved release of cytochrome c, second mitochondria-derived activator of caspases, and apoptosis-inducing factor, accompanied by a proteolytic cascade with processing of caspases 9, 3, and 8 and poly(ADP)-ribose polymerase. Blocking NOXA induction using an antisense (but not control) oligonucleotide reduced the apoptotic response by 30% to 50%, indicating a NOXA-dependent component in the overall killing of melanoma cells. These results provide a novel mechanism for overcoming the apoptotic resistance of tumor cells, and validate agents triggering NOXA induction as potential selective cancer therapeutics for life-threatening malignancies such as melanoma and multiple myeloma.

Identification and Validation of Novel Therapeutic Targets for Multiple Myeloma

In vitro and in vivo models have been developed that have allowed for delineation of mechanisms of multiple myeloma (MM) cell homing to bone marrow (BM); tumor cell adhesion to extracellular matrix proteins and BM stromal cells; and cytokine-mediated growth, survival, drug resistance, and migration within the BM milieu. Delineation of the signaling cascades mediating these sequelae has identified multiple novel therapeutic targets in the tumor cell and its BM microenvironment. Importantly, novel therapies targeting the tumor cell and the BM, as well as those targeting the tumor cell or BM alone, can overcome the growth, survival, conventional drug resistance, and migration of MM cells bound to BM using both in vitro and in vivo severe combined immunodeficiency mouse models of human MM. These studies have translated rapidly from the bench to the bedside in derived clinical trials, and have already led to the United States Food and Drug Administration approval of the novel proteasome inhibitor bortezomib for treatment of relapsed/refractory MM. Novel agents will need to be combined to enhance cytotoxicity, avoid development of drug resistance, and allow for use of lower doses in combination therapies. Genomics, proteomics, and cell signaling studies have helped to identify in vivo mechanisms of sensitivity versus resistance to novel therapies, as well as aiding in the rational application of combination therapies. These studies have therefore provided the framework for a new treatment paradigm targeting the MM cell in its BM milieu to overcome drug resistance and improve patient outcome in MM.

Genomics in multiple myeloma: biology and clinical implications

The advent of new techniques, such as interphase fluorescence in situ hybridization, and, more recently, global array-based gene expression profiling, has accelerated genomic research in myeloma. Distinct biologic subtypes, characterized by unique genetic abnormalities with differing clinical outcomes, have been identified. The identification of these primary genetic defects, and the deregulated oncogenes and pathways in myeloma, has allowed for the development of more targeted therapies. This has led to the discovery of an increased number of active agents in the treatment of myeloma. Genetics also have prognostic importance in myeloma. Recent studies have elucidated a genetic prognostic hierarchy, and have enabled improved definition of the prognostic significance of their interactions. The current challenges are to: improve the dissection of the genetic heterogeneity of the disease; better define progression events; improve the risk stratification of patients; more accurately select patients who will respond well to a particular treatment; and develop more rational combinations of treatment. Genomics will have an important role to play in all of these goals.

Targeted therapy for haematological malignancies: clinical update from the American Society of Hematology, 2004

Recent advances in the treatment and management of haematological malignancies are due in large part to an improved understanding of the basic biology that drives tumour cell growth and survival. This improved understanding has led to the clinical study and approval of a number of different targeted agents across a number of different haematological tumours. This review of clinical data covers some of the exciting clinical advances that were reported at the recent American Society of Hematology meeting in San Diego, USA. This paper focuses on three important areas of biological research that has yielded clinical trials that have affected clinical outcomes. The areas covered include proteasome inhibition and myeloma, tyrosine kinase inhibitors that are directed at the BCR-ABL fusion protein and chronic myeloid leukaemia/acute lymphoblastic leukaemia, and FLT3 inhibitors and acute myeloid leukaemia acute lymphoblastic leukaemia therapy.

Gene signatures of progression and metastasis in renal cell cancer

PURPOSE

To address the progression, metastasis, and clinical heterogeneity of renal cell cancer (RCC).

EXPERIMENTAL DESIGN

Transcriptional profiling with oligonucleotide microarrays (22,283 genes) was done on 49 RCC tumors, 20 non-RCC renal tumors, and 23 normal kidney samples. Samples were clustered based on gene expression profiles and specific gene sets for each renal tumor type were identified. Gene expression was correlated to disease progression and a metastasis gene signature was derived.

RESULTS

Gene signatures were identified for each tumor type with 100% accuracy. Differentially expressed genes during early tumor formation and tumor progression to metastatic RCC were found. Subsets of these genes code for secreted proteins and membrane receptors and are both potential therapeutic or diagnostic targets. A gene pattern ("metastatic signature") derived from primary tumor was very accurate in classifying tumors with and without metastases at the time of surgery. A previously described "global" metastatic signature derived by another group from various non-RCC tumors was validated in RCC.

CONCLUSION

Unlike previous studies, we describe highly accurate and externally validated gene signatures for RCC subtypes and other renal tumors. Interestingly, the gene expression of primary tumors provides us information about the metastatic status in the respective patients and has the potential, if prospectively validated, to enrich the armamentarium of diagnostic tests in RCC. We validated in RCC, for the first time, a previously described metastatic signature and further showed the feasibility of applying a gene signature across different microarray platforms. Transcriptional profiling allows a better appreciation of the molecular and clinical heterogeneity in RCC.

FTY720 Induces Apoptosis in Multiple Myeloma Cells and Overcomes Drug Resistance

The novel immunomodulator FTY720 down-modulates sphingosine-1-phosphate receptor 1 on lymphocytes at low nanomolar concentrations, thereby inhibiting sphingosine-1-phosphate receptor 1-dependent egress of lymphocytes from lymph nodes into efferent lymphatics and blood. At high micromolar concentration, FTY720 has been shown to induce growth inhibition and/or apoptosis in human cancer cells in vitro. In this study, we investigated the biological effects of FTY720 on multiple myeloma cells. We found that FTY720 induces potent cytotoxicity against drug-sensitive and drug-resistant multiple myeloma cell lines as well as freshly isolated tumor cells from multiple myeloma patients who do not respond to conventional agents. FTY720 triggers activation of caspase-8, -9, and -3, followed by poly(ADP-ribose) polymerase cleavage. Interestingly, FTY720 induces alterations in mitochondrial membrane potential (DeltaPsim) and Bax cleavage, followed by translocation of cytochrome c and Smac/Diablo from mitochondria to the cytosol. In combination treatment studies, both dexamethasone and anti-Fas antibodies augment anti-multiple myeloma activity induced by FTY720. Neither interleukin-6 nor insulin-like growth factor-I, which both induce multiple myeloma cell growth and abrogate dexamethasone-induced apoptosis, protect against FTY720-induced growth inhibition. Importantly, growth of multiple myeloma cells adherent to bone marrow stromal cells is also significantly inhibited by FTY720. Finally, it down-regulates interleukin-6-induced phosphorylation of Akt, signal transducers and activators of transcription 3, and p42/44 mitogen-activated protein kinase; insulin-like growth factor-I-triggered Akt phosphorylation; and tumor necrosis factor alpha-induced IkappaBalpha and nuclear factor-kappaB p65 phosphorylation. These results suggest that FTY720 overcomes drug resistance in multiple myeloma cells and provide the rationale for its clinical evaluation to improve patient outcome in multiple myeloma.

Caspase activation and apoptosis in response to proteasome inhibitors

Several studies have indicated that proteasome inhibitors (PIs) are promising anticancer agents. We have discovered that PIs have the unique ability to activate effector caspases through a mitochondrial Bcl-2 inhibitable but caspase-9 independent pathway. Stabilization of released Smac induced by blockade of the proteasome could explain the apoptosome-independent cell death induced by PIs. In fact, Smac/DIABLO critically supports this PIs-dependent caspase activation. By using a new assay, we confirm that at a single cell level both Smac and PIs can activate caspases in the absence of the apoptosome. Moreover, we have observed two PIs-induced kinetics of caspase activation, with caspase-9 being still required for the rapid caspase activation in response to mitochondrial depolarization, but dispensable for the slow DEVDase activation. In summary, our data indicate that PIs can activate downstream caspases at least in part through Smac/DIABLO stabilization.

Control of ASPP2/(53BP2L) protein levels by proteasomal degradation modulates p53 apoptotic function

The p53 pathway is a central mediator of the apoptotic response. ASPP2/(53BP2L) (apoptosis-stimulating protein of p53 2, also known as 53BP2L) enhances apoptosis through selective stimulation of p53 transactivation of proapoptotic target genes. Although the Rb/E2F pathway regulates ASPP2/(53BP2L) transcription, the complex mechanisms controlling ASPP2/(53BP2L) levels and function remain unknown. We now report that proteasomal degradation modulates ASPP2/(53BP2L) protein levels and apoptotic function. Treatment of cells with proteasomal inhibitors, including the clinically utilized proteasomal inhibitor bortezomib, increases ASPP2/(53BP2L) protein but not RNA levels. Likewise, anthracycline-based chemotherapy, which has multiple mechanisms of action, including proteasomal inhibition, increases ASPP2/(53BP2L) protein but not RNA levels. Proteasomal inhibition or anthracycline treatment increases ASPP2/(53BP2L) protein stability and half-life. Furthermore, the central region of the ASPP2/(53BP2L) protein is ubiquitinated as would be expected for a proteasomal substrate. More importantly, small interfering RNA knockdown of ASPP2/(53BP2L) levels attenuated bortezomib-induced apoptosis, and this effect was greater in wild-type p53 cells. Because elevated levels of ASPP2/(53BP2L) are proapoptotic, these results described an important new molecular mechanism that modulates the p53-ASPP2/(53BP2L) apoptotic pathway.

A pilot study of bortezomib in Korean patients with relapsed or refractory myeloma

Recent clinical trials showed that bortezomib, a novel proteasome inhibitor, had therapeutic activity in multiple myeloma. However, there was no data about the feasibility of bortezomib in Korean patients. We performed a pilot study of bortezomib in patients with relapsed or refractory myeloma (1.3 mg/m2 twice weekly for 2 week in a 3-week cycle). Seven patients were enrolled. The median age of patients was 59 yr. All patients previously received VAD (vincristine, doxorubicin and dexamethasone) and thalidomide chemotherapy. Three patients previously received alkylator-containing chemotherapy and 4 patients, autologous stem cell transplantation. Bortezomib monotherapy resulted in 3 partial remissions (43%), 3 no changes (43%) and 1 progressive disease (14%). One patient who had no response to bortezomib monotherapy experienced partial remission after addition of dexamethasone to bortezomib. The most common serious toxicity was thrombocytopenia (grade 3/4, 10 of 20 cycles (50%)) and grade 3 peripheral neuropathy was developed in 2 of 20 cycles (10%). Drug-related adverse event led to discontinuation of bortezomib in 1 patient. There was no treatment related mortality. Overall, bortezomib seems to be effective and feasible. Conduction of larger clinical studies on Korean patients is necessary to characterize clinical efficacy and safety of bortezomib more precisely.

Investigation of antitumor effects of synthetic epothilone analogs in human myeloma models in vitro and in vivo

26-Trifluoro-(E)-9,10-dehydro-12,13-desoxyepothilone B [Fludelone (Flu)] has shown broad antitumor activity in solid tumor models. In the present study, we showed, in vitro, that Flu significantly inhibited multiple myeloma (MM) cell proliferation (with 1-15 nM IC50), whereas normal human bone marrow stromal cells (HS-27A and HS-5 lines) were relatively resistant (10- to 15-fold higher IC50). Cell-cycle analysis demonstrated that Flu caused G2/M phase arrest and induced cell apoptosis. After Flu treatment, caspase-3, -8, and -9 were activated, cytochrome c and second mitochondrial-derived activator of caspase were released to the cytosol, and c-Jun N-terminal kinase was activated, indicating that mitochondria were involved in the apoptosis. Flu toxicity to human hematopoietic stem cells was evaluated by CD34+ cell-apoptosis measurements and hematopoietic-progenitor assays. There was no significant toxicity to noncycling human CD34+ cells. We compared the efficacy of Flu with the epothilone analog 12,13-desoxyepothilone B (dEpoB) in xenograft nonobese diabetic/severe combined immunodeficient mouse models with subcutaneous or disseminated MM. Flu caused tumor disappearance in RPMI 8226 subcutaneous xenografts after only five doses of the drug (20 mg/kg of body weight), with no sign of relapse after 100 d of observation. In a disseminated CAG MM model, mice treated with Flu had a significantly decreased tumor burden, as determined by bioluminescence imaging, and prolonged overall survival vs. mice treated with dEpoB or vehicle control, indicating that Flu may be a promising agent for MM therapy.

Differential Regulation of Noxa in Normal Melanocytes and Melanoma Cells by Proteasome Inhibition: Therapeutic Implications

Melanoma is the most aggressive form of skin cancer and advanced stages are invariably resistant to conventional therapeutic agents. Using bortezomib as a prototypic proteasome inhibitor, we have identified a novel and critical role of the proteasome in the maintenance of the malignant phenotype of melanoma cells that could have direct translational implications. Thus, melanoma cells from early, intermediate, and late stages of the disease could not sustain proteasome inhibition and underwent an effective activation of caspase-dependent and -independent death programs. This effect was tumor cell selective, because under similar conditions, normal melanocytes remained viable. Intriguingly, and despite of interfering with a cellular machinery in charge of controlling the half-life of the vast majority of cellular proteins, bortezomib did not promote a generalized disruption of melanoma-associated survival factors (including NF-kappaB, Bcl-2, Bcl-x(L), XIAP, TRAF-2, or FLIP). Instead, we identified a dramatic induction in vitro and in vivo of the BH3-only protein Noxa in melanoma cells (but not in normal melanocytes) in response to proteasome inhibition. RNA interference validated a critical role of Noxa for the cytotoxic effect of bortezomib. Notably, the proteasome-dependent regulation of Noxa was found to extend to other tumor types, and it could not be recapitulated by standard chemotherapeutic drugs. In summary, our results revealed Noxa as a new biomarker to gauge the efficacy of bortezomib specifically in tumor cells, and provide a new strategy to overcome tumor chemoresistance.

Inhibition of nuclear factor-kappaB and target genes during combined therapy with proteasome inhibitor bortezomib and reirradiation in patients with recurrent head-and-neck squamous cell carcinoma

PURPOSE

To examine the effects the proteasome inhibitor bortezomib (VELCADE) on transcription factor nuclear factor-kappaB (NF-kappaB) and target genes and the feasibility of combination therapy with reirradiation in patients with recurrent head-and-neck squamous cell carcinoma (HNSCC).

METHODS AND MATERIALS

The tolerability and response to bortezomib 0.6 mg/m2 and 0.9 mg/m2 given twice weekly concurrent with daily reirradiation to 50-70 Gy was explored. Blood proteasome inhibition and NF-kappaB-modulated cytokines and factors were measured. Proteasome inhibition, nuclear localization of NF-kappaB phospho-p65, apoptosis, and expression of NF-kappaB-modulated mRNAs were compared in serial biopsies from accessible tumors.

RESULTS

The maximally tolerated dose was exceeded, and study was limited to 7 and 2 patients, respectively, given bortezomib 0.6 mg/m2 and 0.9 mg/m2/dose with reirradiation. Grade 3 hypotension and hyponatremia were dose limiting. Mucositis was Grade 3 or less and was delayed. The mean blood proteasome inhibition at 1, 24, and 48 h after 0.6 mg/m2 was 32%, 16%, and 7% and after 0.9 mg/m2 was 56%, 26%, and 14%, respectively. Differences in proteasome and NF-kappaB activity, apoptosis, and expression of NF-kappaB-modulated cell cycle, apoptosis, and angiogenesis factor mRNAs were detected in 2 patients with minor tumor reductions and in serum NF-kappaB-modulated cytokines in 1 patient with a major tumor reduction.

CONCLUSIONS

In combination with reirradiation, the maximally tolerated dose of bortezomib was exceeded at a dose of 0.6 mg/m2 and the threshold of proteasome inhibition. Although this regimen with reirradiation is not feasible, bortezomib induced detectable differences in NF-kappaB localization, apoptosis, and NF-kappaB-modulated genes and cytokines in tumor and serum in association with tumor reduction, indicating that other schedules of bortezomib combined with primary radiotherapy or reirradiation may merit future investigation.

PS-341–mediated selective targeting of multiple myeloma cells by synergistic increase in ionizing radiation-induced apoptosis

OBJECTIVE

Multiple myeloma remains incurable with current therapy. The proteosome inhibitor, PS-341, has shown objective clinical responses in relapsed refractory myeloma patients. We investigated the potential of enhancing the radiosensitivity of myeloma cells by combining with PS-341; the underlying mechanisms were delineated.

MATERIALS AND METHODS

Clonogenic assays were used to evaluate cell survival after exposure to PS-341, ionizing radiation (IR), or PS-341 followed by IR. Apoptosis was studied by annexin V-propidium iodide staining and caspase activation. Cell-cycle phase distribution of cells was determined. Nuclear factor-kappaB (NF-kappaB) activity was monitored by enzyme-linked immunosorbent assay and Western blotting. The expression of death receptor Fas/APO-1/CD95 was analyzed by flow cytometry. The consequential caspase-8 activation was detected by Western blotting.

RESULTS

In clonogenic assays, sequential exposure to nontoxic doses of PS-341 (10 nM) and IR (6 Gy) resulted in synergistic inhibition of proliferation of myeloma cells by modulating the apoptotic sensitivity of these cells. Biochemically, sublethal dose of IR led to potent induction of NF-kappaB activity, and this response was significantly inhibited by pretreatment with PS-341, or by the NF-kappaB inhibitory peptide SN-50. Enhanced Fas expression was seen in myeloma cells exposed sequentially to PS-341 and IR. Finally, PS-341 sensitized primary myeloma (CD138+ve) cells to IR but had little effect on CD138-ve bone marrow cells from myeloma patients.

CONCLUSION

These data indicate that PS-341 can sensitize myeloma cells to IR by both intrinsic and extrinsic apoptotic pathways. The study indicates improved therapeutic benefits in treatment of multiple myeloma by combining PS-341 with conventional radiotherapy.

Triterpenoid electrophiles (avicins) suppress heat shock protein-70 and x-linked inhibitor of apoptosis proteins in malignant cells by activation of ubiquitin machinery: implications for proapoptotic activity

Avicins are plant-derived triterpenoid stress metabolites that have both proapoptotic and cytoprotective properties. Avicins induce apoptosis in Jurkat T leukemia cells by targeting mitochondria and release of cytochrome c that occurs in a p53-independent manner. However, postmitochondrial antiapoptotic barriers, such as increased expression of heat shock proteins (Hsp) and X-linked inhibitor of apoptosis proteins (XIAP), frequently exist in cancer cells and often account for resistance to chemotherapy and a poor prognosis. In this article, we show the role of avicins in the activation of stress-regulated ubiquitination and degradation of Hsp70 and XIAP. This is the first report showing the regulation of Hsp70 via the ubiquitin/proteasome pathway. We also show the induction of E3alpha ubiquitin ligase in avicin-treated Jurkat T leukemia cells, and its involvement in the degradation of XIAP. Avicin-mediated suppression of Hsp70 and XIAP was further confirmed in other leukemic/lymphoma cell lines and freshly isolated peripheral blood lymphocytes from Sezary syndrome patients. No change in the Hsp70 and XIAP proteins was observed in peripheral blood lymphocytes from normal donors. We propose that the ability of avicins to induce ubiquitination and regulate the degradation of Hsp70 and XIAP in leukemia cells could have important implications in the treatment of drug-resistant neoplasia and inflammatory disorders.

Bortezomib or high-dose dexamethasone for relapsed multiple myeloma

BACKGROUND

This study compared bortezomib with high-dose dexamethasone in patients with relapsed multiple myeloma who had received one to three previous therapies.

METHODS

We randomly assigned 669 patients with relapsed myeloma to receive either an intravenous bolus of bortezomib (1.3 mg per square meter of body-surface area) on days 1, 4, 8, and 11 for eight three-week cycles, followed by treatment on days 1, 8, 15, and 22 for three five-week cycles, or high-dose dexamethasone (40 mg orally) on days 1 through 4, 9 through 12, and 17 through 20 for four five-week cycles, followed by treatment on days 1 through 4 for five four-week cycles. Patients who were assigned to receive dexamethasone were permitted to cross over to receive bortezomib in a companion study after disease progression.

RESULTS

Patients treated with bortezomib had higher response rates, a longer time to progression (the primary end point), and a longer survival than patients treated with dexamethasone. The combined complete and partial response rates were 38 percent for bortezomib and 18 percent for dexamethasone (P<0.001), and the complete response rates were 6 percent and less than 1 percent, respectively (P<0.001). Median times to progression in the bortezomib and dexamethasone groups were 6.22 months (189 days) and 3.49 months (106 days), respectively (hazard ratio, 0.55; P<0.001). The one-year survival rate was 80 percent among patients taking bortezomib and 66 percent among patients taking dexamethasone (P=0.003), and the hazard ratio for overall survival with bortezomib was 0.57 (P=0.001). Grade 3 or 4 adverse events were reported in 75 percent of patients treated with bortezomib and in 60 percent of those treated with dexamethasone.

CONCLUSIONS

Bortezomib is superior to high-dose dexamethasone for the treatment of patients with multiple myeloma who have had a relapse after one to three previous therapies.

Current treatment options for myeloma

In most cases multiple myeloma is an incurable plasma cell malignancy. Despite the use of conventional therapy or high-dose chemotherapy with autologous stem cell transplantation (ASCT), patients continue to relapse at a constant rate. A small minority of patients are cured by allogeneic transplantation. Novel drugs targeting not only the myeloma cell but also its interactions with the malignant microenvironment have recently been used in patients with relapsed/refractory disease. So far, ASCT has been the treatment of choice for eligible myeloma patients. However, many questions regarding the management of myeloma patients remain unanswered. How safe is ASCT in elderly patients? Is there a role for non-myeloablative allogeneic transplantation in multiple myeloma? What is the role of novel agents, such as thalidomide, its analogues and bortezomib, in the treatment of newly diagnosed patients or as maintenance post-ASCT? This review summarises all available data for the current treatment options for myeloma providing a useful algorithm for its management.