The tumor microenvironment shapes hallmarks of mature B-cell malignancies.

B-cell tumorigenesis results from a host of known and unknown genetic anomalies, including non-random translocations of genes that normally function as determinants of cell proliferation or cell survival to regions juxtaposed to active immunoglobulin heavy chain enhancer elements, chromosomal aneuploidy, somatic mutations that further affect oncogenic signaling and loss of heterozygosity of tumor-suppressor genes. However, it is critical to recognize that even in the setting of a genetic disease, the B-cell/plasma cell tumor microenvironment (TME) contributes significantly to malignant transformation and pathogenesis. Over a decade ago, we proposed the concept of cell adhesion-mediated drug resistance to delineate a form of TME-mediated drug resistance that protects hematopoietic tumor cells from the initial effect of diverse therapies. In the interim, it has been increasingly appreciated that TME also contributes to tumor initiation and progression through sustained growth/proliferation, self-renewal capacity, immune evasion, migration and invasion as well as resistance to cell death in a host of B-cell malignancies, including mantle cell lymphoma, diffuse large B-cell lymphoma, Waldenstroms macroglobulinemia, chronic lymphocytic leukemia and multiple myeloma. Within this review, we propose that TME and the tumor co-evolve as a consequence of bidirectional signaling networks. As such, TME represents an important target and should be considered integral to tumor progression and drug response.

A parallel-arm phase I trial of the humanised anti-IGF-1R antibody dalotuzumab in combination with the AKT inhibitor MK-2206, the mTOR inhibitor ridaforolimus, or the NOTCH inhibitor MK-0752, in patients with advanced solid tumours.

BACKGROUND: Two strategies to interrogate the insulin growth factor 1 receptor (IGF-1R) pathway were investigated: vertical inhibition with dalotuzumab and MK-2206 or ridaforolimus to potentiate PI3K pathway targeting and horizontal cross-talk inhibition with dalotuzumab and MK-0752 to exert effects against cellular proliferation, angiogenesis, and stem cell propagation. METHODS: A phase I, multi-cohort dose escalation study was conducted in patients with advanced solid tumours. Patients received dalotuzumab (10 mg kg(-1)) and escalating doses of MK-2206 (90-200 mg) or escalating doses of dalotuzumab (7.5-10 mg kg(-1)) and MK-0752 (1800 mg) weekly. Upon maximum tolerated dose determination, patients with low-RAS signature, high-IGF1 expression ovarian cancer were randomised to dalotuzumab/MK-2206 versus dalotuzumab/ridaforolimus, whereas patients with high IGF1/low IGF2 expression colorectal cancer received dalotuzumab/MK-0752. RESULTS: A total of 47 patients were enrolled: 29 in part A (18 in the dalotuzumab/MK-2206 arm and 11 in the dalotuzumab/MK-0752 arm) and 18 in part B (6 in each arm). Dose-limiting toxicities (DLTs) for dalotuzumab/MK-2206 included grade 4 neutropenia and grade 3 serum sickness-like reaction, maculopapular rash, and gastrointestinal inflammation. For dalotuzumab/MK-0752, DLTs included grade 3 dehydration, rash, and diarrhoea. Seven patients remained on study for >4 cycles. CONCLUSIONS: Dalotuzumab/MK-2206 and dalotuzumab/MK-0752 combinations were tolerable. Further developments of prospectively validated predictive biomarkers to aid in patient selection for anti-IGF-1R therapies are needed.

Disruption of the MYC-miRNA-EZH2 loop to suppress aggressive B-cell lymphoma survival and clonogenicity.

c-MYC (hereafter MYC) overexpression has been recognized in aggressive B-cell lymphomas and linked to adverse prognosis. MYC activation results in widespread repression of micro-RNA (miRNA) expression and associated with lymphoma aggressive progression. Our recent study identified a MYC-miRNA-EZH2 feed-forward loop linking overexpression of MYC, EZH2 and miRNA repression. Here, using a novel small-molecule BET bromodomain inhibitor, JQ1, and the EZH2 inhibitor, DZNep, we demonstrated that combined treatment of JQ1 and DZNep cooperatively disrupted MYC activation, resulting in a greater restoration of miR-26a expression and synergistically suppressed lymphoma growth and clonogenicity in aggressive lymphoma cells. Furthermore, CHIP assay demonstrated that MYC recruited EZH2 to miR-26a promoter and cooperatively repressed miR-26a expression in aggressive lymphoma cell lines, as well as primary lymphoma cells. Loss- or gain-of-function approaches revealed that miR-26a functioned as a tumor suppressor miRNA and mediated the combinatorial effects of JQ1 and DZNep. These findings represent a novel promising approach for silencing MYC-miRNA-EZH2 amplification loop for combinatorial therapy of aggressive B-cell lymphomas.

Surgery for valvular heart disease: a population-based study in a Brazilian urban center.

BACKGROUND: In middle income countries, the burden of rheumatic heart disease (RHD) remains high, but the prevalence of other heart valve diseases may rise as the population life expectancy increases. Here, we compared population-based data on surgical procedures to assess the relative importance of causes of heart valve disease in Salvador, Brazil. METHODOLOGY/PRINCIPAL FINDINGS: Medical charts of patients who underwent surgery for valvular heart disease from January 2002-December 2005 were reviewed. Incidence of surgery for valvular heart disease was calculated. Logistic regression was used to identify factors associated with in-hospital death following surgery. The most common etiologies for valvular dysfunction in 491 valvular heart surgery patients were RHD (60.3%), degenerative valve disease (15.3%), and endocarditis (4.5%). Mean annual incidence for surgeries due to any valvular heart diseases, RHD, and degenerative valvular disease were 5.02, 3.03, and 0.77 per 100,000 population, respectively. Incidence of surgery due to RHD was highest in young adults; procedures were predominantly paid by the public health sector. In contrast, the incidence of surgery due to degenerative valvular disease was highest among those older than 60 years of age; procedures were mostly paid by the private sector. The overall in-hospital case-fatality ratio was 11.9%. Independent factors associated with death included increase in age (odds ratio: 1.04 per year of age; 95% confidence interval: 1.02-1.06), endocarditis (6.35; 1.92-21.04), multiple valve operative procedures (4.35; 2.12-8.95), and prior heart valve surgery (2.49; 1.05-5.87). CONCLUSIONS/SIGNIFICANCE: RHD remains the main cause for valvular heart surgery in Salvador, which primarily affects young adults without private health insurance. In contrast, surgery due to degenerative valvular disease primarily impacts the elderly with private health insurance. Strategies to reduce the burden of valvular heart disease will need to address the disparate factors that contribute to RHD as well as degenerative valve disease.

Myc represses miR-15a/miR-16-1 expression through recruitment of HDAC3 in mantle cell and other non-Hodgkin B-cell lymphomas.

Our recent study demonstrated miR-15a/16-1 downregulation in mantle cell lymphoma (MCL). Here, we investigated mechanisms of miR-15a/16-1 transcriptional repression and its epigenetic regulation by c-Myc and histone deacetylase (HDAC) in MCL. c-Myc expression was detected in MCL cell lines and in the primary MCL samples, and pri-miR-15a/16-1 mRNAs were significantly upregulated in Mino and Jeko-1 cells with c-Myc knockdown by small interfering RNAs (siRNAs). Our co-immunoprecipitation analysis showed that c-Myc interacted with HDAC3. Moreover, using chromatin immunoprecipitation, we demonstrated that both c-Myc and HDAC3 co-localized to the two promoters of the miR-15a/16-1 cluster gene, DLEU2, and inhibition of HDAC3 increased histone acetylation of the DLEU2 promoters. Luciferase reporter assay confirmed the dependence of Myc-mediated DLEU2 transcriptional repression on HDAC3. Treatment with the pan-HDAC inhibitor, suberoylanilide hydroxamic acid and HDAC3 siRNA resulted in increased miR-15a/16-1 expression. The regulatory mechanism of miR-15a/16-1 was further demonstrated in Burkitt lymphoma and Myc overexpressing cell lines. These findings highlight the role of HDAC3 in Myc-induced miR-15a/16-1 changes and reveal novel mechanisms for c-Myc-driven microRNA suppression and malignant transformation in aggressive B-cell malignancies.

Follicular dendritic cell-induced microRNA-mediated upregulation of PRDM1 and downregulation of BCL-6 in non-Hodgkin's B-cell lymphomas.

B-cell lymphoma 6 (BCL6) and PR domain containing 1 (PRDM1) are considered as master regulators for germinal center (GC) formation and terminal B-cell differentiation. Dysregulation of BCL6 and PRDM1 has been associated with lymphomagenesis. Here, we show for the first time that direct cell-cell contact between follicular dendritic cells (FDC) and B-lymphocytes, by influencing the expression of a set of microRNAs (miRNAs), regulates the expression of BCL6 and PRDM1. We identify that, on cell adhesion to FDC, FDC induces upregulation of PRDM1 expression through downregulation of miR-9 and let-7 families and induces downregulation of BCL-6 through upregulation of miR-30 family in B-lymphocytes and lymphoma cells. We further demonstrate that the miR-30 family directly controls BCL-6 expression and miR-9-1 and let-7a directly control PRDM-1 expression through targeting their 3'UTR, mediating the FDC effect. Our studies define a novel regulatory mechanism in which the FDC, through induction of miRNAs in B-lymphocytes, orchestrates the regulation of transcription factors, promotes germinal center B-cell survival and differentiation. Dysregulation of miRNAs may interfere with B-cell survival and maturation, thus representing a novel molecular mechanism, as well as a potential therapeutic target in B-cell lymphomas.

Lymphoma cell adhesion-induced expression of B cell-activating factor of the TNF family in bone marrow stromal cells protects non-Hodgkin's B lymphoma cells from apoptosis.

This study explores whether lymphoma cell adhesion-induced B cell-activating factor (BAFF) expression in bone marrow stromal cells (BMSCs) protects B lymphoma cells from apoptosis. We first showed protection of lymphoma cells from apoptosis by conditioned medium of a stromal cell-lymphoma cell coculture, either spontaneous or induced by mitoxantrone, implying a role for soluble factor(s) in lymphoma cell survival. Addition of BAFF counteracted mitoxantrone-induced apoptosis and elicited a reduction in spontaneous apoptosis in primary lymphomas, suggesting a role of BAFF in sustaining B-cell survival. Abundant BAFF was detected in the BMSC cell line (HS-5) and primary BMSCs by flow cytometry, RT-PCR and immunoblotting. BAFF levels were 20- to 200-fold higher in BMSCs than in lymphoma cells, and lymphoma cell adhesion to BMSCs augmented BAFF secretion twofold through upregulation of BAFF gene expression. Finally, neutralization of BAFF by TACI-Ig or depletion of BAFF by small hairpin RNA (shRNA) in BMSCs significantly enhanced lymphoma cell response to chemotherapy and overcame stroma-mediated drug resistance, suggesting that lymphoma cells use BMSC-derived BAFF as a survival factor. These findings support the hypothesis that lymphoma cells interact with BMSCs, resulting in stromal niches with high BAFF concentration, and identify BMSC-derived BAFF as a functional determinant for B lymphoma cell survival in the bone marrow environment.

Bone marrow stromal cells prevent apoptosis of lymphoma cells by upregulation of anti-apoptotic proteins associated with activation of NF-kappaB (RelB/p52) in non-Hodgkin's lymphoma cells.

Stromal cells are an essential component of the bone marrow microenvironment that regulate or supports tumor survival. In this study we therefore studied the role of stromal cells in lymphoma cell survival. We demonstrated that adhesion of the B-cell lymphoma cell lines SUDH-4 and 10 to bone marrow stroma inhibited mitoxantrone-induced apoptosis. This adhesion-dependent inhibition of mitoxantrone-induced apoptosis correlated with decreased activation of caspases-8 and 9, and cleavage of caspase 3 and PARP. Electrophoretic mobility shift assays (EMSA) analysis demonstrated significantly increased NF-kappaB binding activity in lymphoma cells adhered to stroma cells compared to lymphoma cells in suspension. This DNA binding activity could be attributed to cell adhesion-mediated proteolysis of the NF-kappaB precursor, p100 (NF-kappaB2). This resulted in the generation of active p52, which translocated to the nucleus in complex with p65 and RelB. Coculture with stromal cells also induced expression of the NF-kappaB-regulated anti-apoptotic molecules, XIAP, cIAP(1) and cIAP(2). Inhibition of NF-kappaB significantly suppressed HS-5-induced protection against apoptosis in lymphoma cell lines as well as in primary lymphoma cells. Thus, bone marrow stroma protects B-cell lymphoma cells against apoptosis, at least in part through activation of NF-kappaB dependent mechanism involving up-regulation of NF-kappaB regulated antiapoptotic proteins. Consequently, this study suggests a new approach to decrease the resistance of lymphoma to chemotherapy.

Beta1 integrin mediated adhesion increases Bim protein degradation and contributes to drug resistance in leukaemia cells.

It has been shown that the tumour microenvironment confers resistance to chemotherapy. Specifically, it was previously reported that adhesion of haematopoietic tumour cells to fibronectin (FN) via beta1 integrins confers a multi-drug resistance phenotype commonly referred to as cell adhesion mediated drug resistance. The present study showed that the pro-apoptotic BCL-2 family member Bim was reduced when leukaemia cells were adherent to FN via beta1 integrins. beta1 integrin-mediated regulation of Bim in K562 cells was demonstrated to be partly a result of increased proteasomal-mediated degradation of Bim protein levels, and proteasome inhibitors prevent Bim degradation. Increased degradation of Bim was not related to activation of the mitogen-activated protein kinase pathway, as adhesion of K562 cells caused a reduction in phospho-extracellular signal-related kinase (ERK)1/2 levels. In addition, pharmacological inhibition of MAP/ERK (MEK) with PD98059 did not increase Bim levels. Reducing Bim levels by short hairpin RNA targeting inhibited imatinib and mitoxantrone-induced cell death. These results showed that beta1 integrin-mediated adhesion regulates Bim degradation and may contribute to the minimal residual disease associated with many haematopoietic malignancies. Together our data indicate that disrupting beta1 integrin-mediated regulation of Bim degradation may increase the efficacy of drugs, including imatinib, used to treat haematopoietic malignancies.

Bone marrow stromal-derived soluble factors and direct cell contact contribute to de novo drug resistance of myeloma cells by distinct mechanisms.

The tumor microenvironment plays a critical role in determining the fate of tumor cells. We have previously reported that adhesion of human myeloma and leukemia cell lines to the extracellular matrix protein, fibronectin, confers a multidrug-resistant phenotype. Mechanisms associated with this cell adhesion-mediated drug resistance are drug-type specific. In the present study, we examined the influence of bone marrow stromal cells (BMSCs) on myeloma cell response to the topoisomerase II inhibitor, mitoxantrone. Apoptosis was inhibited by more than 50% when cells were adhered to BMSCs as compared to myeloma cells maintained in suspension. To investigate the mechanisms contributing to the resistance of myeloma cells in contact with BMSCs, we examined the protective effects of BMSCs under four separate conditions: (1) direct cell contact; (2) BMSCs conditioned medium; (3) medium conditioned by coculturing myeloma cells in direct contact with BMSCs; and (4) medium conditioned by coculturing myeloma cells and BMSCs without direct physical contact. Conditioned medium from BMSCs alone was not sufficient to protect myeloma cells from drug-induced apoptosis; however, soluble factors produced during the myeloma-BMSCs interaction decreased the sensitivity of myeloma cells to mitoxantrone, suggesting a dynamic interaction between myeloma cells and BMSCs. We also found that myeloma cells in direct contact with BMSCs underwent growth arrest, whereas soluble factors produced by myeloma cells-BMSCs coincubation stimulated the proliferation of myeloma cells. These data show that both cell-cell adhesion of BMSCs with myeloma cells and soluble factors induced by this cell-cell interaction are involved in the protection of myeloma cells from mitoxantrone-induced apoptosis; however, the mechanisms contributing to the drug resistance are different.

The farnesyl transferase inhibitor, FTI-277, inhibits growth and induces apoptosis in drug-resistant myeloma tumor cells.

Mutations of the ras gene are among the most commonly identified transforming events in human cancers, including multiple myeloma. Farnesyltransferase inhibitors (FTI) were developed to prevent Ras processing and induce cancer cell death. Several FTIs are in phase II and one is in phase III clinical trials. Preclinically, most of the focus has been on solid tumors, and the effects of FTIs in multiple myeloma have not been investigated. In this study we examined the cytotoxic activity and inhibition of Ras processing in three myeloma cell lines with differing Ras mutation status. H929 cells with activated N-Ras were more sensitive to FTI-277 treatment than 8226 and U266 cells with activated K-Ras or wild-type Ras, respectively. A combination of FTI-277 and a geranylgeranyltransferase I inhibitor (GGTI)-2166 inhibited K-Ras processing and enhanced cell death in 8226 cells. U266 cells and Bcl-x(L) transfectants were equally sensitive to FTI-277 treatment. Similarly, 8226 cells selected for resistance to various chemotherapeutic agents, which resulted in either P-glycoprotein overexpression, altered topoisomerase II activity, or elevated glutathione levels, were equally sensitive to FTI-277. These preclinical studies suggest that prenylation inhibitors may represent new therapeutic agents for the treatment of refractory or drug-resistant multiple myeloma.

Inhibition of JAK kinase activity enhances Fas-mediated apoptosis but reduces cytotoxic activity of topoisomerase II inhibitors in U266 myeloma cells.

Our previous work demonstrated that the Janus kinase (JAK)-Stat3 pathway regulates expression of Bcl-x(L) in the U266 human multiple myeloma cell line and prevents Fas-mediated apoptosis. Inhibition of this pathway by the JAK selective kinase inhibitor AG490 or dominant-negative Stat3 protein results in down-regulation of Bcl-x(L) expression and enhanced sensitivity to Fas-mediated apoptosis. Because Bcl-x(L) has also been implicated in resistance to chemotherapeutic drugs, we investigated whether inhibition of the JAK-Stat3 pathway and subsequent reduction in Bcl-x(L) expression would also enhance cytotoxic drug activity. Contrary to this prediction, pretreatment of U266 myeloma cells with AG490, followed by exposure to topoisomerase II- inhibiting agents, antagonized drug-induced apoptosis. This effect correlated with reduced cyclin D1 expression and cell cycle arrest. The cell cycle arrest following AG490 pretreatment further correlated with reduced mitoxantrone-induced DNA double-strand breaks and reduced cell death, findings consistent with the critical requirement of DNA damage for drug cytotoxicity. These studies demonstrate that inhibition of the JAK-Stat3 pathway can result in paradoxical effects relative to cytotoxic drug response. These paradoxical responses may be explained by the findings that JAK-Stat3 signaling regulates the expression of multiple genes involved in controlling cell proliferation and apoptosis. Thus, understanding the cellular context of inhibiting signal transduction pathways is essential for the design of novel combination therapies for cancer.

Multiple myeloma.

Multiple myeloma (MM) is a malignancy of the plasma cell characterized by migration and localization to the bone marrow where cells then disseminate and facilitate the formation of bone lesions. Unfortunately, while treatment of this disease is effective in palliating the disease, and even prolonging survival, this disease is generally regarded as incurable. Understanding the basic biology of myeloma cells will ultimately lead to more effective treatments by developing target based therapy. In Section I, Dr. Bergsagel discusses the molecular pathogenesis of MM and shares insights regarding specific chromosomal translocations and their role in the genesis and progression of MM. New information regarding FGFR3 as an oncogene as well as how activating mutations may contribute to disease evolution and may be an important target for novel therapeutics of MM is presented. In Section II, Dr. Anderson elaborates on novel therapeutic approaches to MM also targeting fundamental genetic abnormalities in MM cells. Both preclinical and clinical studies of novel agents including PS-341 and IMiDs are highlighted. In Section III, Dr. Harousseau discusses the role of autologous stem cell transplant in MM. He highlights clinical trials addressing the question of conditioning regimens and the impact of tandem transplants. He also addresses the role of allogeneic BMT and the use of attenuated dose conditioning regimens (so called mini-allogeneic transplants) in the treatment of MM. In Section IV, Dr. Dalton provides an overview of the current state of myeloma therapy and summarizes the different and exciting approaches being undertaken to cure this disease.

CD95 antigen mutations in hematopoietic malignancies.

The CD95 receptor, also known as Fas/Apo-1, is a member of the Tumor Necrosis Factor receptor (TNF-R) family of death receptors. Apoptosis mediated by CD95 plays a central role in maintaining homeostasis of the immune system. Dysregulation of the CD95 apoptotic pathway has been proposed as a mechanism of oncogenesis by providing a survival advantage to potentially malignant cells. This extended lifespan could allow the accumulation of further mutations leading to malignant transformation. Several mechanisms of resistance to CD95 mediated apoptosis have been identified, including reduced surface expression of the receptor, overexpression of anti-apoptotic molecules, and loss of function mutations. This review will focus on the potential role of the CD95-CD95 ligand system in the pathogenesis of hematological malignancies, with particular emphasis on recent work from our laboratory examining the expression of CD95 in B cell lymphomas. We demonstrate that CD95 mutations occur at low frequency in NHL tumors, however, surface expression of the CD95 protein varies with the subtype of lymphoma. Loss of surface CD95 is more likely to occur in lymphomas of aggressive histology, and is unrelated to the detection of CD95 mutations.

Reduction in drug-induced DNA double-strand breaks associated with beta1 integrin-mediated adhesion correlates with drug resistance in U937 cells.

We previously showed that adhesion of myeloma cells to fibronectin (FN) by means of beta1 integrins causes resistance to certain cytotoxic drugs. The study described here found that adhesion of U937 human histiocytic lymphoma cells to FN provides a survival advantage with respect to damage induced by the topoisomerase (topo) II inhibitors mitoxantrone, doxorubicin, and etoposide. Apoptosis induced by a topo II inhibitor is thought to be initiated by DNA damage. The neutral comet assay was used to determine whether initial drug-induced DNA damage correlated with cellular-adhesion-mediated drug resistance. Cellular adhesion by means of beta1 integrins resulted in a 40% to 60% reduction in mitoxantrone- and etoposide-induced DNA double-strand breaks. When the mechanisms regulating the initial drug-induced DNA damage were examined, a beta1 integrin-mediated reduction in drug-induced DNA double-strand breaks was found to correlate with reduced topo II activity and decreased salt-extractable nuclear topo IIbeta protein levels. Confocal studies showed changes in the nuclear localization of topo IIbeta; however, alterations in the nuclear-to-cytoplasmic ratio of topo IIbeta in FN-adhered cells were not significantly different. Furthermore, after a high level of salt extraction of nuclear proteins, higher levels of topo IIbeta-associated DNA binding were observed in FN-adhered cells than in cells in suspension. Together, these data suggest that topo IIbeta is more tightly bound to the nucleus of FN-adhered cells. Thus, FN adhesion by means of beta1 integrins appears to protect U937 cells from initial drug-induced DNA damage by reducing topo II activity secondarily to alterations in the nuclear distribution of topo IIbeta.

Cell adhesion-mediated drug resistance (CAM-DR) protects the K562 chronic myelogenous leukemia cell line from apoptosis induced by BCR/ABL inhibition, cytotoxic drugs, and gamma-irradiation.

Integrin-mediated cellular adhesion to extracellular matrix (ECM) components is an important determinant of chemotherapeutic response of human myeloma cells. Here, we demonstrate that when K562 chronic myelogenous leukemia (CML) cells are adhered to fibronectin (FN), they become resistant to apoptosis induced by the BCR/ABL inhibitors AG957 and STI-571, as well as DNA damaging agents and gamma-irradiation. This phenomenon, termed cell adhesion-mediated drug resistance (CAM-DR), was induced by adhesion through the alpha5beta1 (VLA-5) integrin. Phosphotyrosine analysis demonstrates that anti-apoptotic signaling through integrins in K562 cells is independent of the tyrosine kinases activated by BCR/ABL, with the possible exception of an unknown 80 kDa protein. Cytoprotection of FN-adhered CML cells indicates that tumor-ECM interactions may be critical for the emergence of drug-resistant tumor populations and treatment failure in this disease. Antagonists of beta1 integrin-mediated adhesion or corresponding signal transduction elements may sensitize CML cells to chemotherapy and prevent resistance to the novel BCR/ABL kinase inhibitors being used for the treatment of this disease.

Ascorbic acid enhances arsenic trioxide-induced cytotoxicity in multiple myeloma cells.

Multiple myeloma (MM) is a clonal B-cell malignancy characterized by slow-growing plasma cells in the bone marrow (BM). Patients with MM typically respond to initial chemotherapies; however, essentially all progress to a chemoresistant state. Factors that contribute to the chemorefractory phenotype include modulation of free radical scavenging, increased expression of drug efflux pumps, and changes in gene expression that allow escape from apoptotic signaling. Recent data indicate that arsenic trioxide (As(2)O(3)) induces remission of refractory acute promyelocytic leukemia and apoptosis of cell lines overexpressing Bcl-2 family members; therefore, it was hypothesized that chemorefractory MM cells would be sensitive to As(2)O(3). As(2)O(3) induced apoptosis in 4 human MM cell lines: 8226/S, 8226/Dox40, U266, and U266/Bcl-x(L). The addition of interleukin-6 had no effect on cell death. Glutathione (GSH) has been implicated as an inhibitor of As(2)O(3)-induced cell death either through conjugating As(2)O(3) or by sequestering reactive oxygen induced by As(2)O(3). Consistent with this possibility, increasing GSH levels with N-acetylcysteine attenuated As(2)O(3) cytotoxicity. Decreases in GSH have been associated with ascorbic acid (AA) metabolism. Clinically relevant doses of AA decreased GSH levels and potentiated As(2)O(3)-mediated cell death of all 4 MM cell lines. Similar results were obtained in freshly isolated human MM cells. In contrast, normal BM cells displayed little sensitivity to As(2)O(3) alone or in combination with AA. Together, these data suggest that As(2)O(3) and AA may be effective antineoplastic agents in refractory MM and that AA might be a useful adjuvant in GSH-sensitive therapies. (Blood. 2001;98:805-813)

Overexpression of a dominant-negative signal transducer and activator of transcription 3 variant in tumor cells leads to production of soluble factors that induce apoptosis and cell cycle arrest.

Gene therapy of B16 tumors with a dominant-negative signal transducer and activator of transcription (Stat3) variant, designated Stat3beta, results in inhibition of tumor growth and tumor regression. Although only 10-15% of the tumor cells are transfected in vivo, the Stat3beta-induced antitumor effect is associated with massive apoptosis of B16 tumor cells, indicative of a potent bystander effect. Here, we provide evidence that blocking Stat3 signaling in B16 cells results in release of soluble factors that are capable of inducing apoptosis and cell cycle arrest of nontransfected B16 cells. RNase protection assays using multi-template probes specific for key physiological regulators of apoptosis reveal that overexpression of Stat3beta in B16 tumor cells induces the expression of the apoptotic effector, tumor necrosis factor-related apoptosis-inducing ligand. These in vitro results suggest that the observed in vivo bystander effect leading to tumor cell growth inhibition is mediated, at least in part, by soluble factors produced as a result of overexpression of Stat3beta in tumor cells.

Cell adhesion is a key determinant in de novo multidrug resistance (MDR): new targets for the prevention of acquired MDR.

Clinical circumvention of multidrug resistance (MDR) is a Sisyphian task faced in the treatment of many cancers. Identification of several mechanisms of acquired MDR has led to the development of chemosensitizing agents that counter specific mechanisms of MDR. Initial successes in therapy using "chemosensitizers" often culminate in relapse due to the multifactorial nature of acquired MDR. Therefore, it may be important to design therapeutic strategies that focus on mechanisms that allow for cell survival after initial treatments, before the acquisition of MDR. It has been proposed that extracellular effectors such as cytokines, matrix components, and adjacent cells may provide sanctuary to cancer cells by preventing stress-induced cell death. This review focuses on research implicating the cancer cell environment as a particularly important determinant in the emergence of drug resistance. More specifically, we will discuss the role of direct contact between cancer cells and the extracellular matrix or with adjacent cells as extrinsic effectors of de novo MDR. Cell adhesion has been demonstrated to prevent cell death through a number of mechanisms. Identification of cell adhesion-mediated drug resistance as an initial or de novo effector of MDR suggests that therapies targeting interactions between cancer cells and their environment may lead to the sensitization of cancer cells to chemotherapy or radiotherapy before the emergence of acquired mechanisms of MDR.

Mechanisms associated with cell adhesion mediated drug resistance (CAM-DR) in hematopoietic malignancies.

The tumor microenvironment is often overlooked when considering tumor response to chemotherapeutic agents. This environment consists of soluble factors, components of the extracellular matrix as well as cell-cell interactions. Recently, it has become clear that cell-cell and cell-matrix interactions result in cytoskeletal reorganization and the activation of multiple signal transduction pathways that directly influence cell survival, growth and differentiation. Experimental evidence shows that anti-apoptotic pathways initiated by cell adhesion are operative in tumor cells and, furthermore, cause resistance to mechanistically distinct cytotoxics. For hematopoietic tumors, cell adhesion to a single matrix, fibronectin is sufficient to inhibit apoptosis induced by mechanistically distinct cyctotoxics. Adhesion of hematopoietic tumors to this matrix blocks cell cycle progression, and for the human multiple myeloma 8226 cell line adhesion to fibronectin resulted in increased p27kip1 levels, which correlated with cell cycle arrest and drug resistance. A decrease in initial DNA damage induced by topoisomerase II inhibitors has also been observed in adherent hematopoietic tumor cell lines. Further studies investigating the mechanisms of cell adhesion mediated drug resistance may reveal novel targets directed at the reversal of de novo drug resistance.