Update on the Proteasome Inhibitor Bortezomibin Hematologic Malignancies

IMMUNOGENETIC AND PHARMACOCHEMICAL CHARACTERIZATION OF THE ABO SYSTEM GLYCOPROTEIN PROPERTIES AS CRITERIA OF INDIVIDUAL SENSITIVITY TO ANTITUMOR AGENT BORTEZOMIB IN THE PLASMA CELL MYELOMA PATIENTS

OBJECTIVE

Experimental study of the effect profile of bortezomib in the plasma cell myeloma (PCM) patients depend- ing on a specific phenotype carrier state and a pharmacochemical characteristics of ABO system glycoproteins.

MATERIALS AND METHODS

The research was conducted on the 104 PCM patients, including the Chornobyl NPP acci- dent survivors (n = 49) and 65 study subjects in the comparison group. Immunogenetic criteria for positive response to the applied treatment protocols were issued according to the duration of remission, absence of infectious com- plications, and evidence of chronic renal failure as a disease complication.

RESULTS

Possibility of glycoproteins A and B participation in the formation of human biological individuality at a level of protein-protein interaction with antineoplastic drug bortezomib, which is widely used in cancer management prac- tice, in particular in the PCM treatment is considered. The glycoprotein B was shown being a selective target for borte- zomib, slowing down the recognition and interaction of antigen B with monoclonal anti-B antibody, while the agglu- tination period lengthens at that by 66 %. Assumption that the formation of bortezomib complex with glycoprotein B provides a background for interaction with the key reaction of proteasome 26S inhibition, which to some extent con- tributes to the drug effect retardation was confirmed through the quantum-chemical calculations. Equilibrium is shift- ed toward the main reaction leading to a higher drug efficacy in patients with blood groups O (I) and A (II).

CONCLUSIONS

Since the complexation occurs predominantly in alkaline medium the administration of drugs with alkaline reaction should be restricted for at least round the clock after administration of bortezomib according to its half-life in plasma in patients with B (III) blood group and chronic renal failure.

Proteasome Inhibitors in Cancer Therapy and their Relation to Redox Regulation

Redox homeostasis is important for the maintenance of cell survival. Under physiological conditions, redox system works in a balance and involves activation of many signaling molecules. Regulation of redox balance via signaling molecules is achieved by different pathways and proteasomal system is a key pathway in this process. Importance of proteasomal system on signaling pathways has been investigated for many years. In this direction, many proteasome targeting molecules have been developed. Some of them are already in the clinic for cancer treatment and some are still under investigation to highlight underlying mechanisms. Although there are many studies done, molecular mechanisms of proteasome inhibitors and related signaling pathways need more detailed explanations. This review aims to discuss redox status and proteasomal system related signaling pathways. In addition, cancer therapies targeting proteasomal system and their effects on redox-related pathways have been summarized.

Bortezomib in antibody-mediated autoimmune diseases (TAVAB): study protocol for a unicentric, non-randomised, non-placebo controlled trial

INTRODUCTION

The clinical characteristics of autoantibody-mediated autoimmune diseases are diverse. Yet, medical treatment and the associated complications are similar, that is, the occurrence of long-term side effects and the problem that a significant proportion of patients are non-responders. Therefore, new therapeutic options are needed. Bortezomib, a proteasome inhibitor, is effective in the treatment of multiple myeloma and data from experimental models and case reports suggest an effect in the treatment of autoantibody-mediated autoimmunity. In our study, we will determine the effect of bortezomib treatment on a shared surrogate parameter for clinical efficacy, namely change in autoantibody levels, which we chose as primary parameter.

METHODS AND ANALYSIS

We designed a phase IIa trial with altogether n=18 treatment-refractory patients suffering from myasthenia gravis, systemic lupus erythematosus and rheumatoid arthritis that will be treated with bortezomib add-on to pre-existing therapy. Primary endpoint is the change in autoantibody levels 6 months after therapy. Secondary endpoints include concomitant medication, disease-specific clinical scores and measures of quality of life and activities of daily living.

ETHICS AND DISSEMINATION

Safety parameters include neurophysiological and clinical signs of peripheral neuropathy as well as potential central nervous system side effects determined by olfactory and neuropsychological testing. The study has been approved by the local ethical committee and first participants have already been enrolled. This proof of concept study will contribute to improve our understanding of plasma cell-specific treatment approaches by assessing its safety and efficacy in reducing serum levels of antibodies known to mediate autoimmune disorders.We plan to publish the final results of our study in a peer reviewed journal and to present our findings at international conferences.

TRIAL REGISTRATION NUMBER

NCT02102594.

Proteomic approach for understanding milder neurotoxicity of Carfilzomib against Bortezomib

The proteasomal system is responsible for the turnover of damaged proteins. Because of its important functions in oncogenesis, inhibiting the proteasomal system is a promising therapeutic approach for cancer treatment. Bortezomib (BTZ) is the first proteasome inhibitor approved by FDA for clinical applications. However neuropathic side effects are dose limiting for BTZ as many other chemotherapeutic agents. Therefore second-generation proteasome inhibitors have been developed including carfilzomib (CFZ). Aim of the present work was investigating the mechanisms of peripheral neuropathy triggered by the proteasome inhibitor BTZ and comparing the pathways affected by BTZ and CFZ, respectively. Neural stem cells, isolated from the cortex of E14 mouse embryos, were treated with BTZ and CFZ and mass spectrometry was used to compare the global protein pool of treated cells. BTZ was shown to cause more severe cytoskeletal damage, which is crucial in neural cell integrity. Excessive protein carbonylation and actin filament destabilization were also detected following BTZ treatment that was lower following CFZ treatment. Our data on cytoskeletal proteins, chaperone system, and protein oxidation may explain the milder neurotoxic effects of CFZ in clinical applications.

Proteasome inhibitors in cancer therapy: Treatment regimen and peripheral neuropathy as a side effect

Proteasomal system plays an important role in protein turnover, which is essential for homeostasis of cells. Besides degradation of oxidized proteins, it is involved in the regulation of many different signaling pathways. These pathways include mainly cell differentiation, proliferation, apoptosis, transcriptional activation and angiogenesis. Thus, proteasomal system is a crucial target for treatment of several diseases including neurodegenerative diseases, cystic fibrosis, atherosclerosis, autoimmune diseases, diabetes and cancer. Over the last fifteen years, proteasome inhibitors have been tested to highlight their mechanisms of action and used in the clinic to treat different types of cancer. Proteasome inhibitors are mainly used in combinational therapy along with classical chemo-radiotherapy. Several studies have proved their significant effects but serious side effects such as peripheral neuropathy, limits their use in required effective doses. Recent studies focus on peripheral neuropathy as the primary side effect of proteasome inhibitors. Therefore, it is important to delineate the underlying mechanisms of peripheral neuropathy and develop new inhibitors according to obtained data. This review will detail the role of proteasome inhibition in cancer therapy and development of peripheral neuropathy as a side effect. Additionally, new approaches to prevent treatment-limiting side effects will be discussed in order to help researchers in developing effective strategies to overcome side effects of proteasome inhibitors.

Discovery of Compound A--a selective activator of the glucocorticoid receptor with anti-inflammatory and anti-cancer activity

Glucocorticoids are among the most effective anti-inflammatory drugs, and are widely used for cancer therapy. Unfortunately, chronic treatment with glucocorticoids results in multiple side effects. Thus, there was an intensive search for selective glucocorticoid receptor (GR) activators (SEGRA), which retain therapeutic potential of glucocorticoids, but with fewer adverse effects. GR regulates gene expression by transactivation (TA), by binding as homodimer to gene promoters, or transrepression (TR), via diverse mechanisms including negative interaction between monomeric GR and other transcription factors. It is well accepted that metabolic and atrophogenic effects of glucocorticoids are mediated by GR TA. Here we summarized the results of extensive international collaboration that led to discovery and characterization of Compound A (CpdA), a unique SEGRA with a proven “dissociating” GR ligand profile, preventing GR dimerization and shifting GR activity towards TR both in vitro and in vivo. We outlined here the unusual story of compound's discovery, and presented a comprehensive overview of CpdA ligand properties, its anti-inflammatory effects in numerous animal models of inflammation and autoimmune diseases, as well as its anti-cancer effects. Finally, we presented mechanistic analysis of CpdA and glucocorticoid effects in skin, muscle, bone, and regulation of glucose and fat metabolism to explain decreased CpdA side effects compared to glucocorticoids. Overall, the results obtained by our and other laboratories underline translational potential of CpdA and its derivatives for treatment of inflammation, autoimmune diseases and cancer.

The combination of bortezomib with enzastaurin or lenalidomide enhances cytotoxicity in follicular and mantle cell lymphoma cell lines

We analyzed the combination of a proteasome inhibitor (bortezomib) with enzastaurin (PKC/AKT-inhibitor) or lenalidomide (immunomodulatory agent) for the inhibition of proliferation and induction of apoptosis in B-cell lymphoma cell lines and primary malignant cells. The effects of bortezomib, enzastaurin or lenalidomide, alone or in combinations, on cell viability and apoptosis were evaluated using the Cell Proliferation Kit and flow cytometry analysis. The interaction between drugs was examined by the Chou-Talalay method. Cell cycle analysis was performed by flow cytometry. The PI3K/AKT, PKC and MAPK/ERK signaling pathways were analyzed using western blot. Bortezomib with either enzastaurin or lenalidomide synergistically induced anti-proliferative and pro-apoptotic effects in B-cell lymphoma cells, even in the presence of the bone marrow microenvironment. The direct cytotoxicity is mediated by signaling events involving the PI3K/AKT, PKC and MAPK/ERK pathways leading to cell death. The significant increase of apoptosis was mediated by an increased ratio of pro-apoptotic proteins (Bax, Bad and Bim) to anti-apoptotic proteins (Bcl-2, Bcl-xL and Mcl-1), triggering the cleavage of caspases -3, -9, -8 and PARP. Further evaluation of the combination of bortezomib with enzastaurin or lenalidomide for the treatment of B-cell lymphoma is warranted, with the goal to improve the quality of life and survival of patients.

Elevated calpain activity in acute myelogenous leukemia correlates with decreased calpastatin expression

Calpains are intracellular cysteine proteases that have crucial roles in many physiological and pathological processes. Elevated calpain activity has been associated with many pathological states. Calpain inhibition can be protective or lethal depending on the context. Previous work has shown that c-myc transformation regulates calpain activity by suppressing calpastatin, the endogenous negative regulator of calpain. Here, we have investigated calpain activity in primary acute myelogenous leukemia (AML) blast cells. Calpain activity was heterogeneous and greatly elevated over a wide range in AML blast cells, with no correlation to FAB classification. Activity was particularly elevated in the CD34+CD38− enriched fraction compared with the CD34+CD38+ fraction. Treatment of the cells with the specific calpain inhibitor, PD150606, induced significant apoptosis in AML blast cells but not in normal equivalent cells. Sensitivity to calpain inhibition correlated with calpain activity and preferentially targeted CD34+CD38− cells. There was no correlation between calpain activity and p-ERK levels, suggesting the ras pathway may not be a major contributor to calpain activity in AML. A significant negative correlation existed between calpain activity and calpastatin, suggesting calpastatin is the major regulator of activity in these cells. Analysis of previously published microarray data from a variety of AML patients demonstrated a significant negative correlation between calpastatin and c-myc expression. Patients who achieved a complete remission had significantly lower calpain activity than those who had no response to treatment. Taken together, these results demonstrate elevated calpain activity in AML, anti-leukemic activity of calpain inhibition and prognostic potential of calpain activity measurement.

Chemical and biological evaluation of dipeptidyl boronic acid proteasome inhibitors for use in prodrugs and pro-soft drugs targeting solid tumors

Bortezomib, a dipeptidyl boronic acid and potent inhibitor of the 26S proteasome, is remarkably effective against multiple myeloma (MM) but not against solid tumors. Dose-limiting adverse effects from "on target" inhibition of the proteasome in normal cells and tissues appear to be a key obstacle. Achieving efficacy against solid tumors therefore is likely to require making the inhibitor more selective for tumor tissue over normal tissues. The simplest strategy that might provide such tissue specificity would be to employ a tumor specific protease to release an inhibitor from a larger, noninhibitory structure. However, such release would necessarily generate an inhibitor with a free N-terminal amino group, raising a key question: Can short peptide boronic acids with N-terminal amino groups have the requisite properties to serve as warheads in prodrugs? Here we show that dipeptides of boroLeu, the smallest plausible candidates for the task, can indeed be sufficiently potent, cell-penetrating, cytotoxic, and stable to degradation by cellular peptidases to serve in this capacity.

Ubiquitin Ligases in Cancer: Ushers for Degradation

The regulated degradation of cellular proteins by the ubiquitin-proteasome system impacts a range of vital cellular processes in both normal and cancerous cells. An ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin ligase (E3) catalyzes the conjugation of the protein ubiquitin to a target protein and, thereby, tags that protein for recognition and destruction by the proteasome. Ubiquitin ligases are particularly interesting because they determine substrate selection. This review examines the role of dysregulated ubiquitin ligase activity in the development and progression of various cancers, and highlights why ubiquitin ligases have emerged as extremely attractive targets for therapeutic intervention in a number of human malignancies.

Phase I study of proteasome inhibitor bortezomib plus CHOP in patients with advanced, aggressive T-cell or NK/T-cell lymphoma

The aim of the study was to determine the maximum tolerated dose (MTD) and safety of the combination of bortezomib and cyclophosphamide, doxorubicin, vincristine, and prednisolone (CHOP) as first-line therapy in advanced, aggressive T-cell lymphoma. Patients received increasing doses of bortezomib on days 1 and 8 (weekly schedule, 1.0, 1.3, and 1.6 mg/m(2)/dose) in addition to 750 mg/m(2) cyclophosphamide, 50 mg/m(2) doxorubicin, 1.4 mg/m(2) vincristine on day 1 and 100 mg/day prednisolone on days 1 to 5, every 3 weeks. Six cycles of therapy administered every 21 days were planned. Thirteen patients, who had stage III/IV chemonaive aggressive T-cell lymphoma, received a total of 55 cycles of treatment. One patient experienced hematologic dose-limiting toxicity (grade 4 neutropenia associated with febrile episode) at the 1.0 mg/m(2)/dose of bortezomib. There was no dose-limiting non-hematologic toxicity. The MTD was not reached at 1.6 mg/m(2) dose level of bortezomib. The overall complete remission rate in all patients was 61.5% (95% confidence interval = 31.6-86.1). Bortezomib can be safely combined with CHOP chemotherapy and constitutes an active regimen in advanced-stage, aggressive T-cell lymphoma patients. The recommended dose for subsequent phase II studies of bortezomib plus CHOP is 1.6 mg/m(2)/dose of bortezomib on days 1 and 8 every 3 weeks as first-line treatment.

Development of rituximab-resistant lymphoma clones with altered cell signaling and cross-resistance to chemotherapy

Immunotherapy with rituximab (chimeric anti-CD20 monoclonal antibody, Rituxan), alone or in conjunction with chemotherapy, has significantly improved the treatment outcome of lymphoma patients. Via an elusive mechanism, a subpopulation of patients becomes unresponsive and/or relapses. To recapitulate various aspects of acquired resistance, rituximab-resistant (RR) clones were established from lymphoma lines and compared with parental cells. Surface CD20 expression was diminished in the clones. The clones neither responded to rituximab-mediated growth reduction or complement-dependent cytotoxicity nor underwent apoptosis in response to cross-linked rituximab. Rituximab failed to chemosensitize the RR clones, which exhibited constitutive hyperactivation of the nuclear factor-kappaB and extracellular signal-regulated kinase 1/2 pathways, leading to overexpression of B-cell lymphoma protein 2 (Bcl-2), Bcl-2-related gene (long alternatively spliced variant of Bcl-x gene), and myeloid cell differentiation 1 and higher drug resistance. Unlike parental cells, rituximab neither inhibited the activity of these pathways nor diminished the expression of resistant factors. Pharmacologic inhibitors of the survival pathways or Bcl-2 family members reduced the activity of these pathways, diminished antiapoptotic protein expression, and chemosensitized the RR clones. These novel in vitro results denote that continuous long-term rituximab exposure culminates in RR clones that do not respond to rituximab-mediated effects, have altered cellular signaling dynamics, and exhibit different genetic and phenotypic properties compared with parental cells. The data also reveal that although RR clones exhibit higher resistance to rituximab and cytotoxic drugs, these clones can be chemosensitized following treatment with pharmacologic inhibitors (e.g., dehydroxymethylepoxyquinomicin, bortezomib, PD098059) that target survival/antiapoptotic pathways. The findings also identify intracellular targets for potential molecular therapeutic intervention to increase treatment efficacy. The significance and potential clinical relevance of the findings are discussed.

Bortezomib plus melphalan and prednisone in elderly untreated patients with multiple myeloma: results of a multicenter phase 1/2 study

Standard first-line treatment for elderly multiple myeloma (MM) patients ineligible for stem cell transplantation is melphalan plus prednisone (MP). However, complete responses (CRs) are rare. Bortezomib is active in patients with relapsed MM, including elderly patients. This phase 1/2 trial in 60 untreated MM patients aged at least 65 years (half older than 75 years) was designed to determine dosing, safety, and efficacy of bortezomib plus MP (VMP). VMP response rate was 89%, including 32% immunofixation-negative CRs, of whom half of the IF– CR patients analyzed achieved immunophenotypic remission (no detectable plasma cells at 10–4 to 10–5 sensitivity). VMP appeared to overcome the poor prognosis conferred by retinoblastoma gene deletion and IgH translocations. Results compare favorably with our historical control data for MP—notably, response rate (89% versus 42%), event-free survival at 16 months (83% versus 51%), and survival at 16 months (90% versus 62%). Side effects were predictable and manageable; principal toxicities were hematologic, gastrointestinal, and peripheral neuropathy and were more evident during early cycles and in patients aged 75 years or more. In conclusion, in elderly patients ineligible for transplantation, the combination of bortezomib plus MP appears significantly superior to MP, producing very high CR rates, including immunophenotypic CRs, even in patients with poor prognostic features.

Proteasome inhibition with bortezomib: a new therapeutic strategy for non-Hodgkin's lymphoma

The incidence of non-Hodgkin's lymphoma (NHL) has markedly increased in the US and other westernized countries in recent years and presents a considerable clinical challenge. NHL is divided into subtypes that follow an aggressive or indolent course. Follicular lymphoma (FL), the most common indolent subtype, and mantle cell lymphoma (MCL), an aggressive subtype that accounts for approximately 5% of cases, are generally incurable. MCL has a relatively poor prognosis, with a median survival of 3-4 years. Despite improving response rates with new agents and regimens, the lack of demonstrated improvement in overall survival in many subtypes supports the development of novel approaches, such as proteasome inhibition. Bortezomib is the first proteasome inhibitor to be evaluated in human studies. It has already been approved as second-line treatment in multiple myeloma and is now under active investigation in NHL. The US FDA has granted bortezomib fast-track designation for relapsed and refractory MCL. In vitro and in vivo studies have demonstrated single-agent activity against various lymphoid tumors, and additive or synergistic effects in combination with other agents, including standard chemotherapy drugs employed in NHL. Phase 2 clinical trials indicate that bortezomib is well tolerated and active in several NHL subtypes, with response rates of 18-60% in FL and 39-56% in MCL. A number of combination trials are currently underway with a range of standard agents. Bortezomib has the potential to play a significant role throughout the NHL treatment algorithm in the future.

An Electrodiagnostic Evaluation of the Effect of Pre-existing Peripheral Nervous System Disorders in Patients Treated with the Novel Proteasome Inhibitor Bortezomib

AIMS

Bortezomib (Velcade), a novel proteasome inhibitor, has shown promise in the treatment of malignancies, including multiple myeloma and non-Hodgkin's lymphoma. Several studies have identified neuropathy as a potentially dose-limiting side effect of treatment with bortezomib. We report the clinical and electrodiagnostic data from four patients who developed signs and symptoms of peripheral neuropathy from treatment with bortezomib.

MATERIALS AND METHODS

Patients were included if they were enrolled in active phase 2 trials of bortezomib for non-Hodgkin's lymphoma or prostate cancer, developed signs and symptoms of peripheral neuropathy, and were referred for electrodiagnostic evaluation.

RESULTS

Four patients, including two with non-Hodgkin's lymphoma and two with prostate cancer, underwent electrodiagnostic testing. Electrodiagnostic evaluation showed pre-existing peripheral nervous system disorders in three out of four patients. Multiple peripheral nervous system disorders were present in two out of four patients.

CONCLUSIONS

Bortezomib can cause a predominately sensory axonal polyneuropathy. Pre-existing peripheral nervous system disorders, such as neuropathy and radiculopathy, are common in patients with cancer, and may pre-dispose to the development of symptomatic neuronal toxicity when treated with bortezomib. Baseline electrodiagnostic evaluation may identify patients with pre-existing peripheral nervous system disorders at risk for additive neuronal toxicity from neurotoxic chemotherapeutic agents.

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.

The ubiquitin–proteasome system and cancer

The ubiquitin proteasome system (UPS) has emerged from obscurity to be seen as a major player in all regulatory processes in the cell. The concentrations of key proteins in diverse regulatory pathways are controlled by post-translational ubiquitination and degradation by the 26 S proteasome. These regulatory cascades include growth-factor-controlled signal-transduction pathways and multiple points in the cell cycle. The cell cycle is orchestrated by a combination of cyclin-dependent kinases, kinase inhibitors and protein phosphorylation, together with the timely and specific degradation of cyclins and kinase inhibitors at critical points in the cell cycle by the UPS. These processes provide the irreversibility needed for movement of the cycle through gap 1 (G1), DNA synthesis (S), gap 2 (G2) and mitosis (M). The molecular events include cell-size control, DNA replication, DNA repair, chromosomal rearrangements and cell division. It is doubtful whether these events could be achieved without the temporally and spatially regulated combination of protein phosphorylation and ubiquitin-dependent degradation of key cell-cycle regulatory proteins. The oncogenic transformation of cells is a multistep process that can be triggered by mutation of genes for proteins involved in regulatory processes from the cell surface to the nucleus. Since the UPS has critical functions at all these levels of control, it is to be expected that UPS activities will be central to cell transformation and cancer progression.

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.

Mantle cell lymphoma

PURPOSE OF REVIEW

Mantle cell lymphoma is the B-cell lymphoma with the worst prognosis. Until now, no standard treatment has resulted in cure. Improvements in understanding of the disease are needed to advance therapeutic efforts.

RECENT FINDINGS

Pathology and immunohistochemistry can identify the subset of patients with the worse prognosis. New data suggest that at least a subset of mantle cell lymphoma cases have undergone some form of antigene selection, and particular types of Ig gene rearrangement seem to give a better prognosis. The cell cycle, the ATM, gene and the nuclear factor kappaB pathways are the main targets of the genetic abnormalities occurring in mantle cell lymphoma: new genomic and expression data have been recently published. Unfortunately, this progress has not yet brought any major improvements in therapeutic approaches, which still remain highly unsatisfactory. Autologous and allogenic bone marrow transplantations appear to be the only current treatments that might improve the outcome of patients with PMCL. New additional treatment modalities are currently under investigation.

SUMMARY

This review summarizes all the most recent data published on the biology and treatment of mantle cell lymphoma.

Cellular and molecular signal transduction pathways modulated by rituximab (rituxan, anti-CD20 mAb) in non-Hodgkin's lymphoma: implications in chemosensitization and therapeutic intervention

The clinical application of rituximab (chimeric mouse anti-human CD20 mAb, Rituxan, IDEC-C2B8), alone and/or combined with chemotherapy, has significantly ameliorated the treatment outcome of patients with relapsed and refractory low-grade or follicular non-Hodgkin's lymphoma (NHL). The exact in vivo mechanisms of action of rituximab are not fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and apoptosis have been suggested. We have proposed that modifications of the cellular signaling pathways by rituximab may be crucial for its clinical response. The B-cell restricted cell surface phosphoprotein CD20 is involved in many cellular signaling events including proliferation, activation, differentiation, and apoptosis upon crosslinking. Monomeric rituximab chemosensitizes drug-resistant NHL cells via selective downregulation of antiapoptotic factors through the type II mitochondrial apoptotic pathway. Several signaling pathways are affected by rituximab which are implicated in the underlying molecular mechanisms of chemosensitization. ARL (acquired immunodeficiency syndrome (AIDS)-related lymphoma) and non-ARL cell lines have been examined as in vitro model systems. In ARL, rituximab diminishes the activity of the p38MAPK signaling pathway resulting in inhibition of the interleukin (IL)-10/IL-10R autocrine/paracrine cytokine autoregulatory loop leading to the inhibition of constitutive STAT-3 activity and subsequent downregulation of Bcl-2 expression leading to chemosensitization. Rituximab upregulates Raf-1 kinase inhibitor protein (RKIP) expression in non-ARL cells. Through physical association with Raf-1 and nuclear factor kappaB (NF-kappa B)-inducing kinase (NIK), RKIP negatively regulates two major survival pathways, namely, the extracellular signal-regulated kinase1/2 (ERK1/2) and the NF-kappa B pathways, respectively. Downmodulation of the ERK1/2 and NF-kappa B pathways inhibits the transcriptional activity of AP-1 and NF-kappa B transcription factors, respectively, both of which lead to the downregulation of Bcl-(xL) (Bcl-2 related gene (long alternatively spliced variant of Bcl-x gene)) transcription and expression and sensitization to drug-induced apoptosis. Bcl-(xL)-overexpressing cells corroborated the pivotal role of Bcl-(xL) in chemosensitization. The specificity of rituximab-mediated signaling and functional effects were corroborated by the use of specific pharmacological inhibitors. Many patients do not respond and/or relapse and the mechanisms of unresponsiveness are unknown. Rituximab-resistant B-NHL clones were generated to investigate the acquired resistance to rituximab-mediated signaling, and chemosensitization. Resistant clones display different phenotypic, genetic and functional properties compared to wild-type cells. This review summarizes the data highlighting a novel role of rituximab as a signal-inducing antibody and as a chemosensitizing agent through negative regulation of major survival pathways. Studies presented herein also reveal several intracellular targets modified by rituximab, which can be exploited for therapeutic and prognostic purposes in the treatment of patients with rituximab- and drug-refractory NHL.