Resistance to anticancer immunity in cancer patients: potential strategies to reverse resistance.

In the 1990s, the application of immunotherapy approaches to target cancer cells resulted in significant clinical responses in patients with advanced malignancies who were refractory to conventional therapies. While early immunotherapeutics were focused on T cell-mediated cytotoxic activity, subsequent efforts were centered on targeted antibody-mediated anticancer therapy. The initial success with antibody therapy encouraged further studies and, consequently, there are now more than 25 FDA-approved antibodies directed against a range of targets. Although both T cell and antibody therapies continue to result in significant clinical responses with minimal toxicity, a significant subset of patients does not respond to immunotherapy and another subset develops resistance following an initial response. This review is focused on describing examples showing that cancer resistance to immunotherapies indeed occurs. In addition, it reviews the mechanisms being used to overcome the resistance to immunotherapies by targeting the tumor cell directly and/or the tumor microenvironment.

Marizomib, a proteasome inhibitor for all seasons: preclinical profile and a framework for clinical trials.

The proteasome has emerged as an important clinically relevant target for the treatment of hematologic malignancies. Since the Food and Drug Administration approved the first-in-class proteasome inhibitor bortezomib (Velcade) for the treatment of relapsed/refractory multiple myeloma (MM) and mantle cell lymphoma, it has become clear that new inhibitors are needed that have a better therapeutic ratio, can overcome inherent and acquired bortezomib resistance and exhibit broader anti-cancer activities. Marizomib (NPI-0052; salinosporamide A) is a structurally and pharmacologically unique ß-lactone-γ-lactam proteasome inhibitor that may fulfill these unmet needs. The potent and sustained inhibition of all three proteolytic activities of the proteasome by marizomib has inspired extensive preclinical evaluation in a variety of hematologic and solid tumor models, where it is efficacious as a single agent and in combination with biologics, chemotherapeutics and targeted therapeutic agents. Specifically, marizomib has been evaluated in models for multiple myeloma, mantle cell lymphoma, Waldenstrom's macroglobulinemia, chronic and acute lymphocytic leukemia, as well as glioma, colorectal and pancreatic cancer models, and has exhibited synergistic activities in tumor models in combination with bortezomib, the immunomodulatory agent lenalidomide (Revlimid), and various histone deacetylase inhibitors. These and other studies provided the framework for ongoing clinical trials in patients with MM, lymphomas, leukemias and solid tumors, including those who have failed bortezomib treatment, as well as in patients with diagnoses where other proteasome inhibitors have not demonstrated significant efficacy. This review captures the remarkable translational studies and contributions from many collaborators that have advanced marizomib from seabed to bench to bedside.

Overexpression of Yin Yang 1 in the pathogenesis of human hematopoietic malignancies.

The transcription factor Yin Yang (YY) 1 has been reported to be overexpressed in several tumor types and plays a role in both the progression of the disease as well as the maintenance of tumor cell resistance to cell death by cytotoxic drugs. YY1 also has been reported to be a prognostic factor for several cancers and was proposed to be a therapeutic target. The expression, function, and role of YY1 in the pathogenesis of hematologic malignancies are summarized briefly herein. Data are represented for B non-Hodgkin lymphoma, AIDS-related lymphoma, multiple myeloma, and children's acute lymphocytic leukemia.

Inhibition of epithelial to mesenchymal transition in metastatic prostate cancer cells by the novel proteasome inhibitor, NPI-0052: pivotal roles of Snail repression and RKIP induction.

Metastasis is associated with the loss of epithelial features and the acquisition of mesenchymal characteristics and invasive properties by tumor cells, a process known as epithelial to mesenchymal transition (EMT). Snail expression, through nuclear factor (NF)-kappaB activation, is an EMT determinant. The proteasome inhibitor, NPI-0052, induces the metastasis tumor suppressor/immune surveillance cancer gene, Raf kinase inhibitor protein (RKIP), via NF-kappaB inhibition. We hypothesized that NPI-0052 may inhibit Snail expression and, consequently, the metastatic phenotype in DU-145 prostate cancer cells. Cell treatment with NPI-0052 induced E-cadherin and inhibited Snail expression and both tumor cell invasion and migration. Inhibition of Snail inversely correlated with the induction of RKIP. The underlying mechanism of NPI-0052-induced inhibition of the metastatic phenotype was corroborated by: (1) treatment with Snail siRNA in DU-145 inhibited EMT and, in contrast, overexpression of Snail in the nonmetastatic LNCaP cells induced EMT, (2) NPI-0052-induced repression of Snail via inhibition of NF-kappaB was corroborated by the specific NF-kappaB inhibitor DHMEQ and (3) RKIP overexpression mimicked NPI-0052 in the inhibition of Snail and EMT. These findings demonstrate, for the first time, the role of NPI-0052 in the regulation of EMT via inhibition of NF-kappaB and Snail and induction of RKIP.

Enhanced cytotoxicity of an anti-transferrin receptor IgG3-avidin fusion protein in combination with gambogic acid against human malignant hematopoietic cells: functional relevance of iron, the receptor, and reactive oxygen species.

The human transferrin receptor (hTfR) is a target for cancer immunotherapy due to its overexpression on the surface of cancer cells. We previously developed an antibody-avidin fusion protein that targets hTfR (anti-hTfR IgG3-Av) and exhibits intrinsic cytotoxicity against certain malignant cells. Gambogic acid (GA), a drug that also binds hTfR, induces cytotoxicity in several malignant cell lines. We now report that anti-hTfR IgG3-Av and GA induce cytotoxicity in a new broader panel of hematopoietic malignant cell lines. Our results show that the effect of anti-hTfR IgG3-Av is iron-dependent whereas that of GA is iron-independent in all cells tested. In addition, we observed that GA exerts a TfR-independent cytotoxicity. We also found that GA increases the generation of reactive oxygen species that may play a role in the cytotoxicity induced by this drug. Additive cytotoxicity was observed by simultaneous combination treatment with these drugs and synergy by using anti-hTfR IgG3-Av as a chemosensitizing agent. In addition, we found a concentration of GA that is toxic to malignant hematopoietic cells but not to human hematopoietic progenitor cells. Our results suggest that these two compounds may be effective, alone or in combination, for the treatment of human hematopoietic malignancies.

2-Methoxyestradiol (2-ME) reduces the airway inflammation and remodeling in an experimental mouse model.

Patients with asthma experience airway structural changes, termed airway remodeling, in response to persistent inflammation. 2-Methoxyestradiol (2-ME) is an anti-angiogenic agent and downregulates hypoxia-inducible factor 1 (HIF-1) and inhibits HIF-1alpha-induced transcriptional activation of vascular endothelial growth factor (VEGF) expression. We hypothesized that 2-ME may interfere with the development of the clinical manifestations of asthma. We used a chronic murine model of allergic airway inflammation with subepithelial fibrosis in BALB/c mice. Mice were sensitized with ovalbumin (OVA) that was administered intraperitoneally at days 0-5 and challenged intratracheally (IT) with OVA on days 12-22. The mice received 2-ME IT at days 24, 26 and 28 and sacrificed at day 32. The sensitized/challenged mice developed an extensive cell inflammatory response of the airways. 2-ME administration significantly reduced the cellular infiltrate in the perivascular and peribronchial lung tissues, reduced goblet mucous production, reduced airway fibrosis and thickness of smooth muscle and blood vessels, and reduced eosinophil infiltration. Mice treated with 2-ME had a significant decrease of HIF-1 and VEGF expression in the perivascular, peribronchial, and interstitium of lung tissues. Collagen IV expression was also significantly reduced in 2-ME treated mice compared to untreated mice. The 2-ME treatment was associated with a significant decrease of OVA-specific IgE antibodies. These findings provide the first indication that IT administration of 2-ME is effective in preventing and reversing antigen-induced airway remodeling in the OVA allergen inflammatory murine model. The potential role of 2-ME in patients is discussed.

Rituximab-induced inhibition of antiapoptotic cell survival pathways: implications in chemo/immunoresistance, rituximab unresponsiveness, prognostic and novel therapeutic interventions.

Rituximab (chimeric anti-CD20 monoclonal antibody) is the first Food and Drug Administration approved antitumor antibody and is used in the treatment of B-non-Hodgkin's lymphoma (B-NHL). It is used as single monotherapy or in combination with chemotherapy and has improved the treatment outcome of patients with B-NHL. The in vivo mechanisms of rituximab-mediated antitumor effects include antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cell cytotoxicity (CDC), growth-inhibition and apoptosis. A subset of patients does not initially respond to rituximab and several responsive patients develop resistance to further rituximab treatment. The mechanism of rituximab unresponsiveness is not known. Besides the above-postulated mechanisms, rituximab has been shown to trigger the cells via CD-20. Studies performed with B-NHL cell lines as model systems revealed several novel mechanisms of rituximab-mediated effects that are involved in chemo/immunosensitization and the development of resistance to rituximab. Rituximab has been shown to inhibit the p38 mitogen-activated protein kinase, nuclear factor-kappaB (NF-kappaB), extracellular signal-regulated kinase 1/2 (ERK 1/2) and AKT antiapoptotic survival pathways, all of which result in upregulation of phosphatase and tensin homolog deleted on chromosome ten and Raf kinase inhibitor protein and in the downregulation of antiapoptotic gene products (particularly Bcl-2, Bcl-(xL) and Mcl-1), and resulting in chemo/immunosensitization. Further, rituximab treatment inhibits the overexpressed transcription repressor Yin Yang 1 (YY1), which negatively regulates Fas and DR5 expression and its inhibition leads to sensitization to Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis. Rituximab-resistant clones were generated as model to examine the mechanism of in vivo rituximab unresponsiveness. These clones showed reduced expression of CD20 and hyperactivation of the above antiapoptotic signaling pathways and failure of rituximab to trigger the cells leading to inhibition of ADCC, CDC and chemo/immunosensitization. Interference with the hyperactivated pathways with various pharmacological and proteasome inhibitors reversed resistance. Furthermore, the above findings have identified several gene products that can serve as new prognostic/diagnostic biomarkers as well as targets for therapeutic intervention in B-NHL.

Rituximab inhibits the constitutively activated PI3K-Akt pathway in B-NHL cell lines: involvement in chemosensitization to drug-induced apoptosis.

Rituximab (chimeric anti-CD20 monoclonal antibody) is currently being used, alone or in combination with chemotherapy, in the treatment of B-non-Hodgkin's lymphoma (B-NHL). We have reported that rituximab treatment of B-NHL cell lines sensitizes the drug-resistant tumor cells to apoptosis by various chemotherapeutic drugs and chemosensitization was, in large part, owing to the selective inhibition of the anti-apoptotic Bcl-(XL) gene product. The constitutive activation of the Akt pathway in B-NHL results in overexpression and functional activation of Bcl-(xL). Hence, we hypothesized that rituximab-induced inhibition of Bcl-(xL) expression and chemosensitization may result, in part, from its inhibitory activity of the Akt pathway. This hypothesis was tested using the drug-resistant Ramos and Daudi B-NHL cell lines. Time kinetic analysis revealed that treatment with rituximab inhibited phosphorylation of Akt, but not unphosphorylated Akt, and the inhibition was first detected at 6 h post-rituximab treatment. Similar time kinetics revealed rituximab-induced inhibition of p-PDK1, p-Bad, p-IKKalpha/beta and p-Ikappabetaalpha and no inhibition of unphosphorylated proteins. In addition, rituximab treatment resulted in significant increase of Bcl-(xL)-Bad heterodimeric complexes as compared to untreated cells. The role of the Akt pathway in the regulation of resistance was corroborated by the use of the Akt inhibitor, LY294002, and by transfection with siRNA Akt. Treatment of tumor cells with LY294002 or with Akt siRNA, but not control siRNA, resulted in inhibition of Bcl-(xL) expression and sensitization to drug-induced apoptosis. Although rituximab did not inhibit the Akt pathway nor sensitized the rituximab-resistant Ramos RR1 clone, treatment with LY294002 or Akt siRNA sensitized the clone to drug-induced apoptosis. The present findings demonstrate for the first time that rituximab inhibits the constitutively activated Akt pathway in B-NHL cell lines, and this inhibition contributes to sensitization of drug-resistant cells to apoptosis by chemotherapeutic drugs. The findings also identify the Akt pathway as target for therapeutic intervention in the reversal of rituximab and drug-resistant B-NHL.

Interference with nuclear factor kappa B and c-Jun NH2-terminal kinase signaling by TRAF6C small interfering RNA inhibits myeloma cell proliferation and enhances apoptosis.

The tumor necrosis factor receptor (TNFR)-associated factor (TRAF) family of six adaptor proteins (TRAF1-6) links the TNFR superfamily to the nuclear factor kappa B (NF-kappaB) and activator protein-1 (AP-1) transcriptional activators. Unlike other TRAFs, TRAF6 is also involved in Toll-like/interleukin (IL)-1 receptor (TIR) signal transduction. Thus, inhibition of TRAF6 function could interrupt both CD40 (TNFR family) and IL-1 growth signals, pathways critical to myeloma proliferation. To block TRAF6-mediated IL-1 signaling, we constructed small interfering RNA (siRNA) against TRAF6. We found that siRNA targeting the TRAF6 C-terminal (siTRAF6C) receptor interaction domain specifically reduced only TRAF6 protein expression, without affecting TRAF2 or 5 levels, and substantially interfered with IL-1-induced NF-kappaB and c-Jun/AP-1 activation. Inhibition by siTRAF6C was concentration-dependent. SiTRAF6C also significantly reduced myeloma proliferation and enhanced apoptosis in a similar dose-dependent fashion in vitro. More importantly, marked siTRAF6C growth inhibition was detected in vivo when these cells were implanted into the bone marrow of irradiated normal mice. In contrast, introduction of siRNA derived from the TRAF6 Zn-finger domain or an irrelevant siRNA construct failed to alter cell growth or cell death. These studies suggest that TRAF6 may be a new molecular target to block cell signal transduction important for the survival and proliferation of multiple myeloma cells.

Transcription factor YY1: structure, function, and therapeutic implications in cancer biology.

The ubiquitous transcription factor Yin Yang 1 (YY1) is known to have a fundamental role in normal biologic processes such as embryogenesis, differentiation, replication, and cellular proliferation. YY1 exerts its effects on genes involved in these processes via its ability to initiate, activate, or repress transcription depending upon the context in which it binds. Mechanisms of action include direct activation or repression, indirect activation or repression via cofactor recruitment, or activation or repression by disruption of binding sites or conformational DNA changes. YY1 activity is regulated by transcription factors and cytoplasmic proteins that have been shown to abrogate or completely inhibit YY1-mediated activation or repression; however, these mechanisms have not yet been fully elucidated. Since expression and function of YY1 are known to be intimately associated with progression through phases of the cell cycle, the physiologic significance of YY1 activity has recently been applied to models of tumor biology. The majority of the data are consistent with the hypothesis that YY1 overexpression and/or activation is associated with unchecked cellular proliferation, resistance to apoptotic stimuli, tumorigenesis and metastatic potential. Studies involving hematopoetic tumors, epithelial-based tumors, endocrine organ malignancies, hepatocellular carcinoma, and retinoblastoma support this hypothesis. Molecular mechanisms that have been investigated include YY1-mediated downregulation of p53 activity, interference with poly-ADP-ribose polymerase, alteration in c-myc and nuclear factor-kappa B (NF-kappaB) expression, regulation of death genes and gene products, and differential YY1 binding in the presence of inflammatory mediators. Further, recent findings implicate YY1 in the regulation of tumor cell resistance to chemotherapeutics and immune-mediated apoptotic stimuli. Taken together, these findings provide strong support of the hypothesis that YY1, in addition to its regulatory roles in normal biologic processes, may possess the potential to act as an initiator of tumorigenesis and may thus serve as both a diagnostic and prognostic tumor marker; furthermore, it may provide an effective target for antitumor chemotherapy and/or immunotherapy.

Can we develop biomarkers that predict response of cancer patients to immunotherapy?

PRIMARY OBJECTIVE: The primary objective is to delineate the potential utility of cancer biomarkers that correlate and predict response to immunotherapy in cancer patients who are refractory to conventional therapeutics. Unlike significant development of biomarkers that predict response to chemotherapy, very few biomarkers have been developed to predict the response to immunotherapy. MAIN OUTCOMES AND RESULTS: This article describes briefly the importance of characterizing and validating biomarkers for immunotherapy. A few examples have been provided, such as the transcription factor NF-kappaB, the transcription repressor Yin-Yang 1 (YY1), the pro-apoptotic gene product (Smac/DIABLO) and the circulating Fas and Fas ligand. These biomarkers have been determined to be of prognostic significance in different cancers. CONCLUSIONS: Immunotherapy is considered as an alternative therapy in the treatment of cancer patients who are refractory to chemotherapy/radiation/hormonal therapies. Cross-resistance to apoptosis develops between cancer cells that are resistant to conventional therapeutics and immunotherapy. Therefore, it is important to develop biomarkers that will determine patient response to immunotherapy.

Resveratrol and cancer: chemoprevention, apoptosis, and chemo-immunosensitizing activities.

The polyphenolic compound Resveratrol is a naturally occurring phytochemical and can be found in many plant species, including grapes, peanuts and various herbs. Several studies have established that Resveratrol can exert anti-oxidant and anti-inflammatory activities. It also has activity in the regulation of multiple cellular events associated with carcinogenesis. This review describes the general properties of Resveratrol including its relationship to estrogen, its effect on lipid metabolism, its cardiovascular effects, and its role on gene expression. Resveratrol has also been examined in several model systems for its potential effect against cancer. Its anti-cancer effects include its role as a chemopreventive agent, its ability to inhibit cell proliferation, its direct effect in cytotoxicity by induction of apoptosis and on its potential therapeutic effect in pre-clinical studies. In addition, Resveratrol has been shown to exert sensitization effects on cancer cells that will result in a synergistic cytotoxic activity when Resveratrol is used in combination with cytotoxic drugs in drug-resistant tumor cells. Clearly, the studies with Resveratrol provide support for the use of Resveratrol in human cancer chemoprevention and combination with chemotherapeutic drugs or cytotoxic factors in the treatment of drug refractory tumor cells.

Potentiation of the sensitivity of renal cell carcinoma cells to TRAIL-mediated apoptosis by subtoxic concentrations of 5-fluorouracil.

Cytotoxic chemotherapy has shown little antitumour activity against renal cell carcinoma (RCC). Although immunotherapy is relatively effective against RCC, the response rate is approximately 20%. Therefore, there is an urgent need to increase this response rate. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L) is one member of the tumour necrosis factor ligand family that selectively induces apoptosis of cancer cells. Since several cytotoxic anticancer drugs including 5-fluorouracil (5-FU) also mediate apoptosis, we reasoned that combined treatment of cancer cells with TRAIL and drugs might result in synergy and overcome the resistance of the cancer cell. This study has examined whether TRAIL can synergise with 5-FU in both cytotoxic and apoptotic assays against drug-resistant RCC cells. Cytotoxicity was determined by an 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis. Treatment of Caki-1 cells with TRAIL in combination with 5-FU resulted in a synergistic cytotoxic effect. Synergy was also achieved in freshly derived RCC cells from 3 patients. The enhanced cytotoxicity was obtained irrespective of the sequence of the treatment, but the highest cytotoxicity was observed when Caki-1 cells were treated with TRAIL and 5-FU simultaneously. The synergy achieved in cytotoxicity with TRAIL and 5-FU was shown to be due to apoptosis. The mechanisms responsible for the synergistic cytotoxicity and apoptosis were examined. Treatment of Caki-1 cells with 5-FU enhanced the expression of p53 and bax, but had no effect on the expression of bcl-2. Incubation of Caki-1 cells with TRAIL enhanced the intracellular accumulation of 5-FU and 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP). Treatment of Caki-1 cells with TRAIL downregulated the expression of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) modestly, and upregulated the expression of orotate phosphoribosyltransferase (OPRT). However, the expression level of thymidine phosphorylase (TP) was not affected by TRAIL. This study demonstrates that combined treatment of RCC cells with TRAIL and 5-FU overcomes their resistance. The sensitisation obtained with freshly isolated RCC cells required low subtoxic concentrations of 5-FU. These findings support the potential application in vivo of a combination of TRAIL and 5-FU in the treatment of TRAIL/5-FU-resistant RCC.

Adriamycin sensitizes the adriamycin-resistant 8226/Dox40 human multiple myeloma cells to Apo2L/tumor necrosis factor-related apoptosis-inducing ligand-mediated (TRAIL) apoptosis.

The newly discovered member of the tumor necrosis factor superfamily, Apo2L/tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), has been identified as an apoptosis-inducing agent in sensitive tumor cells but not in the majority of normal cells, and hence it is of potential therapeutic application. However, many tumor cells are resistant to Apo2L/TRAIL-mediated apoptosis. Various chemotherapeutic drugs have been shown to sensitize tumor cells to members of the tumor necrosis factor family. However, it is not clear whether sensitization by drugs and sensitivity to drugs are related or distinct events. This study examined whether an Adriamycin-resistant multiple myeloma (MM) cell line (8226/Dox40) can be sensitized by Adriamycin (ADR) to Apo2L/TRAIL-mediated apoptosis. Treatment with the combination of Apo2L/TRAIL and subtoxic concentrations of ADR resulted in synergistic cytotoxicity and apoptosis for both the parental 8226/S and the 8226/Dox40 tumor cells. Adriamycin treatment modestly up-regulated Apo2L/TRAIL-R2 (DR5) and had no effect on the expression of Fas-associated death domain, c-FLIP, Bcl-2, Bcl(xL), Bax, and IAP family members (cIAP-1, cIAP-2, XIAP, and survivin). The protein levels of pro-caspase-8 and pro-caspase-3 were not affected by ADR, whereas pro-caspase-9 and Apaf-1 were up-regulated. Combination treatment with Apo2L/TRAIL and ADR resulted in significant mitochondrial membrane depolarization and activation of caspase-9 and caspase-3 and apoptosis. Because ADR is shown to sensitize ADR-resistant tumor cells to Apo2L/TRAIL, these findings reveal that ADR can still signal ADR-resistant tumor cells, resulting in the modification of the Apo2L/TRAIL-mediated signaling pathway and apoptosis. These in vitro findings suggest the potential application of combination therapy of Apo2L/TRAIL and subtoxic concentrations of sensitizing chemotherapeutic drugs in the clinical treatment of drug-resistant/Apo2L/TRAIL-resistant multiple myeloma.

Inhibitory effects of 17beta-estradiol and progesterone on ovarian carcinoma cell proliferation: a potential role for inducible nitric oxide synthase.

OBJECTIVES: Indirect evidence suggests that estrogen and progesterone are involved in the etiology of ovarian cancer (Oca). Estrogen and progesterone are also thought to modulate nitric oxide (NO) in human ovarian tumor tissue via regulation of inducible nitric oxide synthase (iNOS). Objectives in this study were: (1) to investigate the effects of 17beta-estradiol (E(2)) and progesterone (P(4)) on Oca cell proliferation employing elevated hormone concentrations occurring within the microenvironment of the ovary, and (2) to determine whether E(2) or P(4) affects iNOS expression and NO generation in Oca cells. METHODS: Proliferation assays assessed the effects of E(2) and P(4) on cell growth in three human Oca cell lines (HOC-7, OVCAR-3, SKOV-3). Reverse transcriptase polymerase chain reaction was used to assess mRNA expression and Western blots to determine protein levels. NO generation was determined via the Griess reaction. RESULTS: Elevated E(2), P(4), or E(2) plus P(4) (E + P), significantly inhibited HOC-7 cells and OVCAR-3 cells, but not SKOV-3 cells. E(2) at 10 microM downregulated iNOS expression and significantly reduced NO production in HOC-7 cells, while 10 microM P(4) or 10 microM E + P increased iNOS expression and NO production. Conclusions. Our findings demonstrate that elevated E(2), P(4), or E + P results in significant growth inhibition of Oca cells, and we propose a role for iNOS and NO in how these hormones modulate their activities in Oca cells.

Rituximab inactivates signal transducer and activation of transcription 3 (STAT3) activity in B-non-Hodgkin's lymphoma through inhibition of the interleukin 10 autocrine/paracrine loop and results in down-regulation of Bcl-2 and sensitization to cytotoxic drugs.

Development of the chimeric mouse antihuman CD20 antibody, Rituximab, presented a notable advance in the treatment of patients with non-Hodgkin's lymphoma (NHL). Its use allowed the specific targeting of tumor B cells without the systemic toxicity of traditional therapies. The mechanisms by which Rituximab induces its antitumor activity are not fully understood. We have shown previously that Rituximab down-regulates Bcl-2 expression in some B-NHL cell lymphoma lines through an interleukin 10 (IL-10)-dependent autocrine loop, an effect that renders the resistant cells susceptible to chemotherapeutic drugs. The objective of this study was to delineate the signaling pathway by which Bcl-2 is controlled by Rituximab and IL-10. We hypothesized that the down-regulation of IL-10 by Rituximab decreases activation of the signal transducer and activator of transcription 3 (STAT3) protein, which in turn, is responsible for decreased levels of Bcl-2. We demonstrate by phosphoprotein immunoblotting and gel shift analyses that endogenous IL-10 induces activation of STAT3 in the 2F7 cell line. Furthermore, we show that Rituximab and anti-IL-10 antibody treatment decreases the ability of STAT3 to bind to its DNA binding site. The decrease in STAT3 activation by these treatments correlates with a decrease in Bcl-2 expression. Additionally, piceatannol, an inhibitor of STAT3 activation, down-regulates the expression of Bcl-2. Altogether, these results demonstrate that Bcl-2 expression is under the regulation of the STAT3 signaling pathway, which is regulated by endogenously secreted IL-10. Hence, Rituximab-induced down-regulation of IL-10 expression is responsible for the down-regulation of Bcl-2 and sensitization of NHL cells by therapeutic drugs. Furthermore, these findings support the notion that circulating IL-10 in vivo may control the resistance of NHL to drug-mediated cytotoxicity.

Nitric oxide inhibits the transcription repressor Yin-Yang 1 binding activity at the silencer region of the Fas promoter: a pivotal role for nitric oxide in the up-regulation of Fas gene expression in human tumor cells.

NO has been increasingly implicated in control of the transcriptional machinery and serves as an intracellular second messenger to modify gene expression. We have demonstrated that NO up-regulated Fas receptor expression in ovarian carcinoma cell lines, albeit the mechanism involved is not known. Thus, we hypothesized that NO, directly or indirectly, may modify the transcriptional machinery that is responsible for the increased expression of the Fas gene. We examined the effect of NO on Fas gene expression using a Fas promoter-driven luciferase reporter system. Transient transfection of AD10 cells with pGL-3-FasP demonstrated that the IFN-gamma-dependent NO generation increases the trans-activation of the Fas promoter, and this increase was blocked by the NOS inhibitor (N(G)-monomethyl-L-arginine), but could be restored by the addition of the NO donor S-nitroso-N-acetylpenicillamine. Systematic deletion of the Fas promoter revealed that the functional region responsible for the NO-mediated effect was located at the silencer region, suggesting that NO may be responsible for the disruption of a repressor mechanism. We demonstrate that NO up-regulates the expression of the Fas receptor on AD10 cells via the specific inactivation of the transcription repressor yin-yang 1 DNA binding activity to the silencer region of the Fas promoter. These findings reveal a new mechanism of NO-mediated gene regulation by interfering with a repressor transcription factor at the silencer region of the Fas promoter.

Inhibition of interleukin 10 by rituximab results in down-regulation of bcl-2 and sensitization of B-cell non-Hodgkin's lymphoma to apoptosis.

Treatment of patients with non-Hodgkin's lymphoma (NHL) is frequently hampered by development of chemoresistance. Rituximab is a chimeric mouse antihuman CD20 antibody that offers an alternative; however, its mechanism of action is not clearly understood. Treatment of lymphoma cell lines with Rituximab sensitizes the cells to the cytotoxic and apoptotic effects of therapeutic drugs, e.g., cisplatin, fludarabine, vinblastine, and Adriamycin. This study investigated the mechanism(s) involved in the reversal of drug resistance by Rituximab therapy. NHL cells synthesize and secrete antiapoptotic cytokines implicated in drug resistance, including interleukin (IL)-6, IL-10, and tumor necrosis factor alpha. We hypothesized, therefore, that sensitization by Rituximab may be due in part to modification of cytokine production. In this study, examination of cytokine secretion by NHL 2F7 tumor cells revealed down-regulation of IL-10 by Rituximab treatment. Moreover, cytotoxicity assays using exogenous IL-10 and IL-10-neutralizing antibodies demonstrated that IL-10 serves as an antiapoptotic/protective factor in these tumor cells against cytotoxic drugs. Furthermore, expression in 2F7 cells of the protective factor, Bcl-2, was shown to be dependent on IL-10 levels and down-regulated by Rituximab. Other gene products such as Bax, Bcl-x, Bad, p53, c-myc, and latent membrane protein-1 (LMP) were not affected by Rituximab treatment. Drug sensitization, as well as down-regulation of both IL-10 and Bcl-2, was corroborated in experiments using the NHL cell line 10C9. The Ramos and Daudi NHL cell lines were not sensitizable, nor did their Bcl-2 or IL-10 levels change. These studies demonstrate that one mechanism by which Rituximab sensitizes NHL to chemotherapeutic drugs is mediated through down-regulation of antiapoptotic IL-10 autocrine/paracrine loops and Bcl-2. The clinical relevance of these findings is discussed.