Proteasome inhibition as a novel therapeutic target in human cancer

Targeting NF-κB in hematologic malignancies

The transcription factor nuclear factor kappa B (NF-kappaB) can intervene in oncogenesis by virtue of its capacity to regulate the expression of a plethora of genes that modulate apoptosis, and cell survival as well as proliferation, inflammation, tumor metastasis and angiogenesis. Different reports demonstrate the intrinsic activation of NF-kappaB in lymphoid and myeloid malignancies, including preneoplastic conditions such as myelodysplastic syndromes, underscoring its implication in malignant transformation. Targeting intrinsic NF-kappaB activation, as well as its upstream and downstream regulators, may hence constitute an additional approach to the oncologist's armamentarium. Several small inhibitors of the NF-kappaB-activatory kinase IkappaB kinase, of the proteasome, or of the DNA binding of NF-kappaB subunits are under intensive investigation. Currently used cytotoxic agents can induce NF-kappaB activation as an unwarranted side effect, which confers apoptosis suppression and hence resistance to these drugs. Thus, NF-kappaB inhibitory molecules may be clinically useful, either as single therapeutic agents or in combination with classical chemotherapeutic agents, for the treatment of hematological malignancies.

Treatment of mantle cell lymphoma: targeting the microenvironment

Mantle cell lymphoma is a distinct entity among the non-Hodgkin's lymphomas characterized by a specific chromosomal translocation, the t(11;14)(q13;q32), overexpression of cyclin-D1 and frequent disease manifestations at extranodal sites. Mantle cell lymphoma remains difficult to treat and belongs to the lymphomas with the poorest long-term outcome. Recent advances in our understanding of lymphoma biology suggest that both alterations of the lymphoma cells themselves and interactions with the microenvironment are important for the growth and survival of the malignant B-cell clone. This novel approach to therapy is being exploited by evaluating drugs such as bortezomib and thalidomide that target interactions between tumor cells and cells of the microenvironment. Thus, with the use of novel therapeutic interventions, it is hoped that clinicians will be able to improve the outcome of patients with mantle cell lymphoma.

Cul4A targets p27 for degradation and regulates proliferation, cell cycle exit, and differentiation during erythropoiesis

As erythroid progenitors differentiate into precursors and finally mature red blood cells, lineage-specific genes are induced, and proliferation declines until cell cycle exit. Cul4A encodes a core subunit of a ubiquitin ligase that targets proteins for ubiquitin-mediated degradation, and Cul4A-haploinsufficient mice display hematopoietic dysregulation with fewer multipotential and erythroid-committed progenitors. In this study, stress induced by 5-fluorouracil or phenylhydrazine revealed a delay in the recovery of erythroid progenitors, early precursors, and normal hematocrits in Cul4A(+/-) mice. Conversely, overexpression of Cul4A in a growth factor-dependent, proerythroblast cell line increased proliferation and the proportion of cells in S phase. When these proerythroblasts were induced to terminally differentiate, endogenous Cul4A protein expression declined 3.6-fold. Its enforced expression interfered with erythrocyte maturation and cell cycle exit and, instead, promoted proliferation. Furthermore, p27 normally accumulates during erythroid terminal differentiation, but Cul4A-enforced expression destabilized p27 and attenuated its accumulation. Cul4A and p27 proteins coimmunoprecipitate, indicating that a Cul4A ubiquitin ligase targets p27 for degradation. These findings indicate that a Cul4A ubiquitin ligase positively regulates proliferation by targeting p27 for degradation and that Cul4A down-regulation during terminal erythroid differentiation allows p27 to accumulate and signal cell cycle exit.

FUNCTIONAL IMAGING OF TUMOR PROTEOLYSIS

The roles of proteases in cancer are now known to be much broader than simply degradation of extracellular matrix during tumor invasion and metastasis. Furthermore, proteases from tumor-associated cells (e.g., fibroblasts, inflammatory cells, endothelial cells) as well as tumor cells are recognized to contribute to pathways critical to neoplastic progression. Although elevated expression (transcripts and proteins) of proteases, and in some cases protease inhibitors, has been documented in many tumors, techniques to assess functional roles for proteases require that we measure protease activity and inhibition of that activity rather than levels of proteases, activators, and inhibitors. Novel techniques for functional imaging of protease activity, both in vitro and in vivo, are being developed as are imaging probes that will allow us to determine protease activity and in some cases to discriminate among protease activities. These should be useful clinically as surrogate endpoints for therapies that alter protease activities.

Second- and third-line treatments in non-small cell lung cancer

Slow but steady progress has been made in the treatment of advanced non-small cell lung cancer. For first-line therapy, multiple chemotherapy combination therapies can extend survival and improve quality of life. And recently, for the first time ever, a noncytotoxic agent, the antivascular endothelial growth factor antibody bevacizumab, has been shown to improve survival when added to chemotherapy. Striking improvements have also been made in second-line treatment. In August 2004, only one agent was US Food and Drug Administration (FDA) approved in this setting, docetaxel, but by the beginning of 2005, two more were available, pemetrexed and erlotinib. All three of these drugs can significantly benefit patients, with 1-year survival in excess of 30%. Choosing between the three agents can be challenging, and this review focuses on the toxicity differences and predictors of response that can help guide this decision. Docetaxel and pemetrexed, both traditional intravenous cytotoxins, are excellent options for patients who have shown some response to first-line chemotherapy, but at this time, no other means exist to determine likelihood of response. When choosing between the two, pemetrexed causes significantly less neutropenia than does docetaxel, at least on the standard every-3-week regimen. With erlotinib, an oral epidermal growth factor receptor (EGFR) inhibitor, there are factors that can predict for response, including little or no smoking history, and adenocarcinoma histology. Therefore, patients who fit these characteristics are good candidates for second-line erlotinib. However, the relationship between response to erlotinib and improved survival remains unclear, and several laboratory analyses that may help further, such as evaluation of EGFR gene copy number, are still under development. Although erlotinib is the only FDA-approved option currently available for third-line therapy, many patients with good performance status may benefit from third-line therapy and beyond. In addition to the approved second-line options, other single-agent chemotherapies to consider for treatment beyond second-line are gemcitabine, irinotecan, and oral topotecan. Many new drugs, including bevacizumab, ZD6474 (AstraZeneca, Wilmington, DE), sorafenib, cetuximab, paclitaxel poliglumex, epothilones, and others, alone or in combination with traditional agents, are currently undergoing investigation and hold great promise.

Highbrow proteasome in high-throughput technology

Proteasome is a major protease of the ubiquitin-proteasome pathway involved in the regulation of practically all intracellular biochemical processes. The enzyme core is created by a heteromultimer of complex architecture built with multiple subunits arranged into a tube-like structure. The multiple active sites of diverse peptidase specificity are hidden inside the tube. Access to the interior is guarded by a gate formed by the N-termini of specialized subunits and by the attachment of additional multisubunit protein complexes controlling the enzymatic capabilities of the core. Proteasome, due to its Byzantine molecular architecture and equally sophisticated enzymatic mechanism, is by itself a fascinating biophysical object. Recently, the position of the protease advanced from an academically remarkable protein processor to a providential anticancer drug target and futuristic nanomachine. Proteomics studies actively shape our current understanding of the protease and direct the future applications of the proteasome in medicine.

The Immunomodulatory Benzodiazepine Bz-423 Inhibits B-Cell Proliferation by Targeting c-Myc Protein for Rapid and Specific Degradation

Myc proteins regulate cell growth and are oncogenic in many cancers. Although these proteins are validated molecular anticancer targets, new therapies aimed at modulating myc have yet to emerge. A benzodiazepine (Bz-423) that was discovered in efforts to find new drugs for lupus was found recently to have antiproliferative effects on Burkitt's lymphoma cells. We now show that the basis for the antiproliferative effects of Bz-423 is the rapid and specific depletion of c-myc protein, which is coupled to growth-suppressing effects on key regulators of proliferation and cell cycle progression. c-Myc is depleted as a result of signals coupled to Bz-423 binding its molecular target, the oligomycin sensitivity-conferring protein subunit of the mitochondrial F(1)F(o)-ATPase. Bz-423 inhibits F(1)F(o)-ATPase activity, blocking respiratory chain function and generating superoxide, which at growth-inhibiting concentrations triggers proteasomal degradation of c-myc. Bz-423-induced c-myc degradation is independent of glycogen synthase kinase but is substantially blocked by mutation of the phosphosensitive residue threonine 58, which when phosphorylated targets c-myc for ubiquitination and subsequent proteasomal degradation. Collectively, this work describes a new lead compound, with drug-like properties, which regulates c-myc by a novel molecular mechanism that may be therapeutically useful.

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.

Clinical management of recurrent breast cancer: development of multidrug resistance (MDR) and strategies to circumvent it

The multidrug resistance (MDR) phenotype is often associated with recurrent breast cancer. Many cytotoxic agents used to treat breast cancer, such as anthracyclines and taxanes, are susceptible to MDR-mediated loss of sensitivity to these agents. Overexpression of mdr-1/P-glycoprotein (P-gp) is one of the main mechanisms underlying the development of the MDR phenotype. Also involved in the development of the MDR phenotype are other proteins from the ATP-binding cassette family of transporters (eg, MRP, BCRP), as well as alterations of tumor targets and their downstream effector molecules. Additionally, P-gp expression in other anatomic locations (such as the brush border of the gastrointestinal epithelium and blood-brain barrier) may further compromise the success of treatment for patients with breast cancer. Several strategies have been developed to overcome or circumvent MDR, mostly through inhibition or modulation of P-gp. Despite successful proof of concept in the laboratory, to date none of these agents has had a major impact in the clinic.

Severe pulmonary complications in Japanese patients after bortezomib treatment for refractory multiple myeloma

Bortezomib is a novel proteasome inhibitor with significant antimyeloma activity. Its frequent adverse effects are manageable, including gastrointestinal symptoms, peripheral neuropathy, and thrombocytopenia. Severe lung toxicity has not previously been reported. Between June 2004 and September 2005, 13 Japanese patients with multiple myeloma were treated with bortezomib in Toranomon Hospital, Juntendo University School of Medicine, and Jichi Medical School. Four of them developed severe pulmonary complications, and 2 died of respiratory failure without progression of underlying disease. To our knowledge, this is the first report on life-threatening pulmonary adverse effects after bortezomib therapy. Previous clinical studies on bortezomib, mostly in the United States and Europe, have shown low incidences of pulmonary adverse effects. Our study suggests that bortezomib can cause serious lung injury, and that its incidence might vary among different ethnicities. Clinicians need to be alert to the possibility.

Identification of an HLA-A24-restricted cytotoxic T lymphocyte epitope from human papillomavirus type-16 E6: The combined effects of bortezomib and interferon-γ on the presentation of a cryptic epitope

About 50% of cervical cancers are associated with human papillomavirus type 16 (HPV-16), and since the HPV-16 E6 and E7 oncoproteins are constitutively expressed in the tumor cells, they are attractive targets for cytotoxic T lymphocyte (CTL)-mediated immunotherapy. Nevertheless, only a limited number of HPV-16 E6 epitopes have been identified to date. Using reverse immunological methods, we have generated a CTL clone against the HPV-16 E6(49-57) epitope restricted by HLA-A*2402, which is the most common allele in Japan and relatively frequent worldwide, capable of lysing 293T cells transduced with HLA-A*2402 and HPV-16 E6. Although it was unable to recognize the SiHa cervical cancer cell line positive for HPV-16 and HLA-A*2402, the cells became susceptible to lysis when transduced with E6-E7 genes, which was unexpectedly offset by pretreatment with interferon (IFN)-gamma alone. Interestingly, however, combined pretreatment with a proteasome inhibitor, bortezomib and IFN-gamma fully restored CTL-mediated lysis of the original SiHa cells. Furthermore, such intervention of 2 of 4 other cervical cancer cell lines expressing HPV-16 E6 and HLA-A*2402 was found to induce IFN-gamma production by specific CTLs. Tetramer analysis further revealed that induction of E6(49-57)-specific T cells was possible in 5 of 7 patients with HPV-16-positive high grade cervical intraepithelial neoplasia or cervical cancer by in vitro stimulation with E6(49-57) peptide. Thus, these findings together indicate that E6(49-57) is a candidate epitope for immunotherapy and immunological monitoring of such patients.

Influence of proteasome inhibitors on apoptosis

PURPOSE OF REVIEW

Proteasome inhibitors are a novel class of drugs that alter normal cellular control of apoptosis. As such, they are being investigated as novel therapies to alter uncontrolled cellular proliferation and treat cancers. This review explores new information about how the proteasome regulates apoptosis and how proteasome inhibitors can be exploited as anti-tumor drugs.

RECENT FINDINGS

Proteasome inhibitors block the activation of nuclear factor kappa B in a number of cell systems, as well as altering apoptotic regulatory proteins and intracellular signals that influence the fate of the cell. These effects are true for many tumor cell lines. The US Food and Drug Administration-approved proteasome inhibitor bortezomib blocks erroneous cell proliferation and induces apoptosis in many tumor models.

SUMMARY

Proteasome inhibitors have demonstrated promise in vitro, and as a result clinical trials have begun to investigate these agents as therapy for numerous human cancers. Furthermore, newer agents are being designed to inhibit the proteasome system and exert further anti-tumor activity.

Biomarkers of potential prognostic significance in diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is a biologically heterogeneous disease for which the current approach to treatment is only successful for 50% of patients. The prognostic value of various clinical and biological factors in predicting treatment outcome is discussed in this paper. A review of the English literature was performed including original articles and relevant reviews from MEDLINE that addressed the topics of DLBCL biology and potential prognostic factors. The International Prognostic Index is, to date, the most successful clinical model for predicting outcome. In addition, a rapidly expanding list of molecules has been identified by conventional and newer diagnostic methods that may be of significant prognostic value. Gene expression profiling has led to the discovery of new biological subtypes of DLBCL based on patterns of gene expression, and a host of new genes that may play important roles in this disease. Various derangements in apoptosis, cell-cycle regulation, differentiation, and signal transduction have been noted, while the host environment and immune response also appear to modify clinical outcome. Although to our knowledge, the fundamental abnormalities underlying DLBCL remain elusive, progress is being continuously made to further the understanding of the biological heterogeneity of this disease and the use of various clinical and biological variables to predict treatment outcome. The goal is to be able to identify subgroups of patients at high risk of treatment failure and develop more effective treatment based on specific biological defects that may represent new rational therapeutic targets.

The survival kinases Akt and Pim as potential pharmacological targets

The Akt and Pim kinases are cytoplasmic serine/threonine kinases that control programmed cell death by phosphorylating substrates that regulate both apoptosis and cellular metabolism. The PI3K-dependent activation of the Akt kinases and the JAK/STAT-dependent induction of the Pim kinases are examples of partially overlapping survival kinase pathways. Pharmacological manipulation of such kinases could have a major impact on the treatment of a wide variety of human diseases including cancer, inflammatory disorders, and ischemic diseases.

Hypertonic upregulation of betaine transport in renal cells is blocked by a proteasome inhibitor

The renal betaine transporter (BGT1) protects cells in the hypertonic medulla by mediating uptake and accumulation of the osmolyte betaine. Transcription plays an essential role in upregulating BGT1 transport in MDCK cells subjected to hypertonic stress. During hypertonic stress, the abundance of the transcription factor TonEBP increases and it shifts from the cytoplasm to the nucleus where it activates transcription of the BGT1 gene. Little is known about post-transcriptional regulation of BGT1 protein. In the presence of the proteasome inhibitor MG-132, which blocked nuclear translocation of TonEBP, the hypertonic upregulation of BGT1 protein and transport was prevented and cell viability in hypertonic medium was impaired over 24 h. Urea also prevented the hypertonic upregulation of BGT1 protein and transport, but did not interfere with TonEBP translocation and cell viability. Shorter treatments of hypertonic cells with MG-132 avoided viability problems and produced dose-dependent inhibition of translocation and transport. When stably transfected MDCK cells that over-expressed BGT1 were treated for 6 h with hypertonic medium containing 3 microM MG-132, there was 43% inhibition of nuclear translocation, 83% inhibition of BGT1 transport, and no change in viability. While other proteasome functions may be involved, these data are consistent with a critical role for nuclear translocation of TonEBP in upregulation and membrane insertion of BGT1 protein.

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.

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.

Chemical blockage of the proteasome inhibitory function of bortezomib: impact on tumor cell death

The proteasome inhibitor bortezomib is emerging as a potent anti-cancer agent. Still, recent clinical trials have revealed a significant secondary toxicity of bortezomib. Consequently, there is much interest in dissecting the mechanism of action of this compound to rationally improve its therapeutic index. The cytotoxic effect of bortezomib is frequently characterized by interfering with downstream events derived from the accumulation of proteasomal targets. Here we identify the first chemical agent able to act upstream of the proteasome to prevent cell killing by bortezomib. Specifically, we show that the polyhydroxyl compound Tiron can function as a competitive inhibitor of bortezomib. This effect of Tiron was surprising, since it is a classical radical spin trap and was expected to scavenge reactive oxygen species produced as a consequence of bortezomib action. The inhibitory effect of Tiron against bortezomib was selective, since it was not shared by other antioxidants, such as vitamin E, MnTBAP, L-N-acetyl-cysteine, and FK-506. Comparative analyses with nonboronated proteasome inhibitors (i.e. MG132) revealed a specificity of Tiron for bortezomib. We exploited this novel feature of Tiron to define the "point of no return" of proteasome inhibition in melanoma cells and to block cell death in a three-dimensional model of human skin. Cells from T-cell lymphoma, breast carcinoma, and non-small cell lung cancer were also responsive to Tiron, suggesting a broad impact of this agent as a bortezomib blocker. These results may have important implications for the analysis of bortezomib in vivo and for the design of drug mixtures containing proteasome inhibitors.

HSP90 and the chaperoning of cancer

Standing watch over the proteome, molecular chaperones are an ancient and evolutionarily conserved class of proteins that guide the normal folding, intracellular disposition and proteolytic turnover of many of the key regulators of cell growth, differentiation and survival. This essential guardian function is subverted during oncogenesis to allow malignant transformation and to facilitate rapid somatic evolution. Pharmacologically 'bribing' the essential guard duty of the chaperone HSP90 (heat-shock protein of 90 kDa) seems to offer a unique anticancer strategy of considerable promise.

Les inhibiteurs du protéasome

INTRODUCTION

Proteasome is involved in cell cycle and apoptosis regulation. Its deregulation could participate to oncogenesis.

EXEGESIS

Bortezomib is the first proteasome inhibitor to reach clinical development. Its main adverse events are asthenia, thrombocytopenia and cumulative neurotoxicity which can limits long term use. As single agent, bortezomib displays antitumoral effects in refractory multiple myeloma and mantle cell lymphoma but has only modest activity in solid tumors. Preclinical data suggest that bortezomib could enhance antitumor activity of cytotoxics.

CONCLUSION

Proteasome inhibition is a promising therapeutic pathway, especially in lymphoid malignancies.

Multiple myeloma: diagnosis and treatment

Major advances have occurred in our understanding of the biology of multiple myeloma (MM) and in its treatment in the past decade. New diagnostic criteria have been developed, and an international Staging System has replaced the Durle-Salmon Staging System. It is now possible to classify MM as standard risk or high risk on the basis of specific Independent prognostic factors. The role of single and double autologous stem cell transplantation has been clarified by randomized trials. Most importantly, thalidomide, bortezomib, and lenalidomide have emerged as new active agents and are being incorporated rapidly into the treatment of both newly diagnosed and relapsed MM. The current approach to the diagnosis, prognosis, and management of MM is reviewed.

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.

The proteasome inhibitor bortezomib induces apoptosis in mantle-cell lymphoma through generation of ROS and Noxa activation independent of p53 status

Mantle-cell lymphoma (MCL) is a mature B-cell lymphoma with an aggressive course and generally poor prognosis. Conventional chemotherapy has little efficacy. Bortezomib is a novel, reversible, and highly specific proteasome inhibitor that appears as a new hope for MCL treatment. We have analyzed the in vitro sensitivity to bortezomib in 4 MCL cell lines and in primary tumor cells from 10 MCL patients. Bortezomib induced phosphatidylserine exposure, mitochondrial depolarization, ROS generation, Bax and Bak conformational changes, and caspase activation. In addition, ROS scavengers, but not pancaspase inhibitors, blocked all apoptosis hallmarks. Protein and mRNA-expression analysis, revealed marked up-regulation of the BH3-only protein Noxa, between 4 to 6 hours after bortezomib addition, independent of p53 status. However, this up-regulation was faster and higher in cells with functional p53. Noxa RNA interference markedly decreased sensitivity to bortezomib, pointing to this protein as a key mediator between proteasome inhibition and mitochondrial depolarization in MCL cells. Noxa interacts with the antiapoptotic protein Mcl-1 and promotes Bak release from Mcl-1, suggesting that up-regulation of Noxa might counteract Mcl-1 accumulation after bortezomib treatment. These findings should be useful to extend the therapeutic strategies in MCL patients and to improve their prognosis.

Inhibition of astroglial nuclear factor kappaB reduces inflammation and improves functional recovery after spinal cord injury

In the central nervous system (CNS), the transcription factor nuclear factor (NF)-kappaB is a key regulator of inflammation and secondary injury processes. After trauma or disease, the expression of NF-kappaB-dependent genes is highly activated, leading to both protective and detrimental effects on CNS recovery. We demonstrate that selective inactivation of astroglial NF-kappaB in transgenic mice expressing a dominant negative (dn) form of the inhibitor of kappaB alpha under the control of an astrocyte-specific promoter (glial fibrillary acidic protein [GFAP]-dn mice) leads to a dramatic improvement in functional recovery 8 wk after contusive spinal cord injury (SCI). Histologically, GFAP mice exhibit reduced lesion volume and substantially increased white matter preservation. In parallel, they show reduced expression of proinflammatory chemokines and cytokines, such as CXCL10, CCL2, and transforming growth factor-beta2, and of chondroitin sulfate proteoglycans participating in the formation of the glial scar. We conclude that selective inhibition of NF-kappaB signaling in astrocytes results in protective effects after SCI and propose the NF-kappaB pathway as a possible new target for the development of therapeutic strategies for the treatment of SCI.

Proteasome inhibition sensitizes hepatocellular carcinoma cells, but not human hepatocytes, to TRAIL

TRAIL exhibits potent anti-tumor activity on systemic administration in mice. Because of its proven in vivo efficacy, TRAIL may serve as a novel anti-neoplastic drug. However, approximately half of the tumor cell lines tested so far are TRAIL resistant, and potential toxic side effects of certain recombinant forms of TRAIL on human hepatocytes have been described. Pretreatment with the proteasome inhibitor MG132 and PS-341 rendered TRAIL-resistant hepatocellular carcinoma (HCC) cell lines but not primary human hepatocytes sensitive for TRAIL-induced apoptosis. We investigated the different levels of possible MG132-induced interference with resistance to apoptotic signal transduction. Although proteasome inhibition efficiently suppressed nuclear factor-kappaB (NF-kappaB) activity, specific suppression of NF-kappaB by mutIkappaBalpha failed to sensitize TRAIL-resistant cell lines for TRAIL-induced apoptosis. In contrast to the previously reported mechanism of sensitization by 5-fluorouracil (5-FU), cellular FLICE-inhibitory protein (cFLIP)(L) and cFLIP(S) were markedly upregulated in the TRAIL death inducing signaling complex (DISC) by proteasome inhibitor pretreatment. Compared with 5-FU pretreatment, caspase-8 was more efficiently recruited to the DISC in MG132 pretreated cells despite the presence of fewer death receptors and more cFLIP in the DISC. But downregulation of cFLIP by short interference RNA (siRNA) further sensitized the HCC cell lines. In conclusion, these results show that otherwise chemotherapy-resistant tumor cells can be sensitized for TRAIL-induced apoptosis at the DISC level in the presence of high levels of cFLIP, which suggests the existence of an additional factor that modulates the interaction of FADD and the TRAIL death receptors. Of clinical relevance, proteasome inhibitors sensitize HCC cells but not primary human hepatocytes for TRAIL-induced apoptosis.

The concept of synthetic lethality in the context of anticancer therapy

Two genes are synthetic lethal if mutation of either alone is compatible with viability but mutation of both leads to death. So, targeting a gene that is synthetic lethal to a cancer-relevant mutation should kill only cancer cells and spare normal cells. Synthetic lethality therefore provides a conceptual framework for the development of cancer-specific cytotoxic agents. This paradigm has not been exploited in the past because there were no robust methods for systematically identifying synthetic lethal genes. This is changing as a result of the increased availability of chemical and genetic tools for perturbing gene function in somatic cells.

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.

American Society of Clinical Oncology 41st annual meeting

For many years the annual meeting of the American Society of Clinical Oncology (ASCO) has been the premier meeting in clinical oncology, and one that is closely scrutinised by Wall Street and international investors because of the economic significance of cancer therapies to the pharmaceutical and biotechnology industries. The area of biologicals and targeted therapies exploded in the late 1990s after the blockbuster results with the monoclonal antibody rituximab in the treatment of lymphoma. Although historically a somewhat conservative organisation that is still closely tied to classical cytotoxic chemotherapy, ASCO has been able to integrate various areas of biological therapy into its scope of clinical activity. Although ASCO still has 'American' in its title, it is really the 'International' Society of Clinical Oncology, as reflected by the attendance at this year's meeting by approximately 30,000, with approximately two-thirds attending from outside the US. There were 9708 abstracts published in conjunction with the meeting, 86 of which are referenced in this review. There were 10 papers chosen for plenary presentations and many other key papers were presented at other oral abstract sessions and poster discussion session that were organised by tumour type. In addition to key papers submitted by specific tumour type, for this year's meeting there were 103 abstracts published in the session entitled 'Developmental Therapeutics: Immunotherapy', and 218 in the session entitled Developmental Therapeutics: Molecular Targets', for a total of 321 biological therapy abstracts compared with only 125 abstracts for the session entitled 'Developmental Therapeutics: Cytotoxic Therapy'. This meeting review is organised by biotherapy modality rather than tumour type.

Intracellular signal transduction pathway proteins as targets for cancer therapy

Circulating cytokines, hormones, and growth factors control all aspects of cell proliferation, differentiation, angiogenesis, apoptosis, and senescence. These chemical signals are propagated from the cell surface to intracellular processes via sequential kinase signaling, arranged in modules that exhibit redundancy and cross talk. This signal transduction system comprising growth factors, transmembrane receptor proteins, and cytoplasmic secondary messengers is often exploited to optimize tumor growth and metastasis in malignancies. Thus, it represents an attractive target for cancer therapy. This review will summarize current knowledge of selected intracellular signaling networks and their role in cancer therapy. The focus will be on pathways for which inhibitory agents are currently undergoing clinical testing. Original data for inclusion in this review were identified through a MEDLINE search of the literature. All papers from 1966 through March 2005 were identified by the following search terms: "signal transduction," "intracellular signaling," "kinases," "proliferation," "growth factors," and "cancer therapy." All original research and review papers related to the role of intracellular signaling in oncogenesis and therapeutic interventions relating to abnormal cell signaling were identified. This search was supplemented by a manual search of the Proceedings of the Annual Meetings of the American Association for Cancer Research, American Society of Clinical Oncology, and the American Association for Cancer Research (AARC)--European Organisation for Research and Treatment of Cancer (EORTC)--National Cancer Institute (NCI) Symposium on New Anticancer Drugs.

Synthesis and Identification of Small Molecules that Potently Induce Apoptosis in Melanoma Cells through G1 Cell Cycle Arrest

Late-stage malignant melanoma is a cancer that is refractory to current chemotherapeutic treatments. The average survival time for patients with such a diagnosis is 6 months. In general, the vast majority of anticancer drugs operate through induction of cell cycle arrest and cell death in either the DNA synthesis (S) or mitosis (M) phase of the cell cycle. Unfortunately, the same mechanisms that melanocytes possess to protect cells from DNA damage often confer resistance to drugs that derive their toxicity from S or M phase arrest. Described herein is the synthesis of a combinatorial library of potential proapoptotic agents and the subsequent identification of a class of small molecules (triphenylmethylamides, TPMAs) that arrest the growth of melanoma cells in the G1 phase of the cell cycle. Several of these TPMAs are quite potent inducers of apoptotic death in melanoma cell lines (IC(50) approximately 0.5 muM), and importantly, some TPMAs are comparatively nontoxic to normal cells isolated from the bone marrow of healthy donors. Furthermore, the TPMAs were found to dramatically reduce the level of active nuclear factor kappa-B (NFkappaB) in the cell; NFkappaB is known to be constitutively active in melanoma, and this activity is critical for the proliferation of melanoma cells and their evasion of apoptosis. Compounds that reduce the level of NFkappaB and arrest cells in the G1 phase of the cell cycle can provide insights into the biology of melanoma and may be effective antimelanoma agents.