Induction of monoamine oxidase A-mediated oxidative stress and impairment of NRF2-antioxidant defence response by polyphenol-rich fraction of Bergenia ligulata sensitizes prostate cancer cells in vitro and in vivo

Prostate cancer (PCa) is a major cause of mortality and morbidity in men. Available therapies yield limited outcome. We explored anti-PCa activity in a polyphenol-rich fraction of Bergenia ligulata (PFBL), a plant used in Indian traditional and folk medicine for its anti-inflammatory and antineoplastic properties. PFBL constituted of about fifteen different compounds as per LCMS analysis induced apoptotic death in both androgen-dependent LNCaP and androgen-refractory PC3 and DU145 cells with little effect on NKE and WI38 cells. Further investigation revealed that PFBL mediates its function through upregulating ROS production by enhanced catalytic activity of Monoamine oxidase A (MAO-A). Notably, the differential inactivation of NRF2-antioxidant response pathway by PFBL resulted in death in PC3 versus NKE cells involving GSK-3β activity facilitated by AKT inhibition. PFBL efficiently reduced the PC3-tumor xenograft in NOD-SCID mice alone and in synergy with Paclitaxel. Tumor tissues in PFBL-treated mice showed upregulation of similar mechanism of cell death as observed in isolated PC3 cells i.e., elevation of MAO-A catalytic activity, ROS production accompanied by activation of β-TrCP-GSK-3β axis of NRF2 degradation. Blood counts, liver, and splenocyte sensitivity analyses justified the PFBL safety in the healthy mice. To our knowledge this is the first report of an activity that crippled NRF2 activation both in vitro and in vivo in response to MAO-A activation. Results of this study suggest the development of a novel treatment protocol utilizing PFBL to improve therapeutic outcome for patients with aggressive PCa which claims hundreds of thousands of lives each year.

A Toll-like Receptor 5 agonist entolimod mitigates radiation damage through a neutrophil-dependent mechanism

The increased risk of exposure to life-threating nuclear and radiation emergencies warrants the development of FDA-approved medical radiation countermeasures (MRC) as radio mitigators, which can be used after exposure to total body irradiation. Currently, Neupogen and Neulasta are the only FDA-approved radio mitigators but are unfortunately limited by adverse side effects and the need for additional medical supportive care. Bacterial flagellin, the natural agonist of Toll-like receptor (TLR) 5, and apharmacologically optimized derivative entolimod developed by us have powerful activity as a single agent MRC in rodents and non-human primates. Currently entolimod is being developed as a MRC under the FDA’s Animal Efficacy Rule, which guides development of drugs for which efficacy testing in humans would be unethical. The lack of induction of cytokine storm post systemically administered entolimod was demonstrated in rodents, non-human primates, and Phase I clinical trials involving nearly 200 subjects. Entolimod stimulates TLR5 on hepatocytes followed by activation of immunoregulatory signaling pathways, production of pro-inflammatory cytokines, and rapid recruitment of immune cells to the liver. Neutrophils are among the first immune cells that are rapidly recruited to both non-lymphoid and lymphoid tissues post-entolimod. We found that this entolimod-elicited neutrophil response was essential to mitigating radiation damage by promoting the recovery of hematopoietic stem cells in the bone marrow. This work underscores the underappreciated importance of TLR5-elicited neutrophils in promoting there generation of hematopoiesis following total body irradiation.

Entolimod, a clinical-stage TLR5 agonist, activates antitumor T cell immunity against liver and lung metastases through distinct mechanisms

Innate immune modulators can generate an antitumor T cell response. However, significant toxicities associated with systemic administration have significantly limited their clinical use. The natural TLR5 agonist flagellin is unique amonginnate immune modulators because the tissue specificity of TLR5 expression induces a uniquely safe profile of cytokines following systemic TLR5 activation. Entolimod, a pharmacologically optimized flagellin derivative, was initially developed to treat and prevent acute radiation syndrome. Systemic administration of entolimod also showed antitumor effects in multiple preclinical mouse models mimicking clinically occurring liver metastasis. Entolimod suppresses liver metastasis through activation of NF-κB-, AP-1-, and STAT-3-driven immunomodulatory pathways in hepatocytes and a highly coordinated CD4+ T cell independent NK-DC-CD8+ T cell response. Although these studies characterized entolimod as a liver tropic immunotherapy, entolimod also suppresses spontaneous mammary lung metastasis. In contrast to the liver metastatic model, CD4+ T cells are required for the antitumor NK and CD8+ T cell response, indicating that the etiology of the cancer may explain the difference in the therapeutic effects ofTLR5 agonists. These results further strengthen that TLR5 agonists are a safe, effective and broadly applicable immunotherapeutic agent against metastases, which are currently a major cause of cancer-associated mortality. Recent completion of a phase I trial of entolimod in patients with advanced metastatic solid tumors has provided the rationale to test that the efficacy demonstrated in animal cancer models can be translated into immunotherapy of human tumors.

Abstract B090: A Toll-like receptor 5 agonist entolimod as a potential anticancer immunotherapeutic agent

Liver metastases are a major common cause of mortality of patients with different types of cancer due to lack of effective treatment options. Anticancer immunotherapy provides an attractive approach for developing a more effective systemic therapy for patients with metastatic liver cancer. We generated a Toll-like receptor 5 (TLR5) agonistic agent entolimod™ (CBLB502), a pharmacologically optimized derivative of bacterial Salmonella flagellin that is now at advanced stage of clinical development as a medical countermeasure to reduce adverse side effects of radiation therapy. We also found that entolimod, in addition to its radioprotective properties, has anticancer effects against a variety of TLR5-positive tumors and TLR5-negative tumors residing in a TLR5-expressing environment such as the liver in mice. We hypothesized that entolimod can suppress tumor growth in a TLR5-responsive microenvironment such as the liver independently of the TLR5 status of tumor cells. We tested the therapeutic potential of entolimod against TLR5 responsive and non-responsive tumors using mouse triple negative 4T1 breast and CT26 colorectal adenocarcinoma models mimicking clinically occurring development of post-surgery liver metastases in cancer patients. Our results demonstrate that entolimod treatment was efficient in suppressing metastatic growth when injected systemically in both models. Investigating the mechanism of entolimod's antitumor activity we found that several major transcriptional factors, such as NF-κB, STAT-3 and AP-1, are rapidly activated in hepatocytes leading to a short-term neutrophilic infiltration and long-term NK cell accumulation and activation that coordinate CD8+ and CD4+ T cell immunity against liver metastases. This resulted in significant improvement of long-term tumor-free survival and durable, tumor-specific T cell memory. Importantly, unlike other TLR agonists entolimod is safe and does not show signs of septic shock even with systemic administration. Moreover, the results of two phase 1 clinical trials with 150 healthy volunteers and 26 patients with advanced cancers demonstrated good tolerability and safe profile of the response, which supports entolimod's potential as an immunotherapeutic agent. This also suggests that entolimod can be potentially combined with radiation, chemotherapeutic, targeted, and other immunotherapeutic agents to improve the efficacy of anticancer therapy.

Citation Format: Craig Brackett, Bojidar Kojouharov, Sandra Gollnick, Andrei Gudkov, Lyudmila Burdelya. A Toll-like receptor 5 agonist entolimod as a potential anticancer immunotherapeutic agent. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B090.

A Toll-like receptor (TLR) 5 agonist entolimod mediates anti-metastatic activity via NK cell-dependent T cell activation (TUM2P.1029)

Directing innate immunity against cancer is a promising but poorly developed approach to immunotherapy due to the risk of acute inflammation induced by innate immunity activators. In this regard, TLR5 is a unique innate immune receptor with a distinct tissue specificity of expression and induction of a specific cytokine profile upon activation by its agonist bacterial flagellin that is significantly safer than that induced by other TLR agonists. Entolimod is an optimized Salmonella flagellin derivative with demonstrated safety and efficacy in protecting normal cells from stresses such as radiation or chemotherapy, while not protecting or stimulating tumors. We show here that systemic administration of entolimod has potent antitumor effects in mouse syngeneic colon (CT26) and breast (4T1) cancer models, including suppression of liver metastases and development of CD8 T cell memory. In these models, entolimod treatment leads to blood-borne homing of NK cells to the liver followed by activation of CD4 and CD8 T cells. Antibody-mediated depletion and adoptive transfer experiments showed that all three of these cell types are essential for entolimod’s antitumor effects and demonstrate a pivotal role for NK cell-mediated CD8 and CD4 T cell activation and formation of CD8 T cell memory. Therefore, entolimod has strong promise as a safe, effective and broadly applicable immunotherapeutic agent against liver metastases, which are currently a major cause of cancer-associated mortality.

Activation of innate and adaptive immunity by a TLR5 agonist to prevent and suppress liver metastasis (TUM7P.947)

Colorectal cancer (CRC) liver metastases are a major cause of mortality of CRC patients providing incentive to develop systemic therapies to prevent and treat this condition. We are exploring the use of a TLR5 agonist Entolimod™ (CBLB502) for immunotherapy against CRC liver metastases. Entolimod is a pharmacologically optimized Salmonella flagellin derivative that is at advanced stage of clinical development as a medical radiation countermeasure. We found that liver is the major primary Entolimod target organ. Entolimod rapidly triggers a TLR5-elicited response in hepatocytes that activates NF-kB and quickly mobilizes immunity to the liver. This includes short-term neutrophilic infiltrate and long-term NK cell accumulation that coordinate CD8 and CD4 T cell immunity against CRC liver metastases. As a result, Entolimod administration dramatically improved long-term survival in a mouse model that mimicked clinically occurring development of post-surgery liver metastases in CRC patients. Importantly, Entolimod induces durable, tumor-specific T cell memory. Unlike other TLR agonists, systemic administration of Entolimod does not induce septic shock-like syndrome due to lack of production of cytokine storm-inducing cytokines upon TLR5 activation. These safe and long-lasting TLR5-elicited changes within liver provide important groundwork for further clinical development of Entolimod, which is currently in clinical trials as a potential immunotherapy against CRC liver metastases.

Acute TLR5 stimulation with a flagellin-derived agonist induces cytotoxic lymphocyte-mediated tumor immunity (P2064)

Toll-like receptor (TLR) mediated recognition of pathogen associated molecular patterns allows the immune system to rapidly respond to a pathogenic insult. This feature makes TLR agonists attractive agents that can stimulate a favorable immune response. CBLB502 is a pharmacologically optimized TLR5 agonist derived from Salmonella enterica flagellin. In this study, we examined the effect of CBLB502 on tumor immunity using two lymphoma models, both of which do not express TLR5, and thus do not directly respond to CBLB502. Upon challenge with the T cell lymphoma RMAS, CBLB502 treatment after tumor inoculation protects approximately 50% of C57BL/6 mice from death caused by tumor growth. This protective effect is both natural killer (NK) cell and perforin dependent. In addition, CBLB502 stimulates clearance of the B cell lymphoma A20 in BALB/c mice in a CD8+ T cell dependent fashion. ImageStream flow cytometry analyses reveal that CD11b+ and CD11c+ cells, but neither NK nor T cells, directly respond to CBLB502 as determined by nuclear translocation of NFκB. NFκB can regulate a variety of pro-inflammatory cytokines; accordingly, CBLB502 increases serum levels of IL-6, IL-15, TNFα, and IFN-γ. Furthermore, CBLB502 promotes antigen-presenting cell maturation as evidenced by CD86 upregulation. These findings demonstrate that CBLB502 can stimulate a robust antitumor immune response by indirectly activating cytotoxic lymphocytes through TLR5-expressing accessory immune cells.

An agonist of Toll-like receptor 5 sustains hepatic natural killer and dendritic cell recruitment to the liver while eliciting anti-cancer effects against liver metastases (P2110)

Toll-like receptors (TLRs) are key components of innate immunity that act as sensors of conserved microbial patterns. To elucidate the mechanisms behind differences in physiological responses mediated by different TLRs, we compared tissue specificity of NF-κB activation in mice by agonists of three cell-surface TLRs: TLR5 agonist CBLB502, a pharmacologically optimized Salmonella flagellin derivative; TLR4 agonist, LPS; and TLR2/6 agonist CBLB612, a mycoplasma lipopeptide mimic. While the liver was defined as a major primary target organ of all three TLR agonists, the cellular response to each agonist was distinct. Thus, liver hepatocytes directly respond to TLR5 and TLR2/6 but not to TLR4, while Kupffer macrophages respond to TLR2/6 and TLR4 but not to TLR5 agonists. Mobilization of NK and DCs to the liver was transient (<24 h) in response to CBLB612 and LPS and sustained (>120 h) following CBLB502 administration. Differences in the liver innate immune response to these three TLR agonists are likely a reflection of cell type-specific expression and differences in molecular mechanisms triggered by different TLRs. Durable hepatic NK cell response by CBLB502 elicits strong TLR5 agonist-dependent effects against colon and breast cancer liver metastases. These long-lasting, TLR5-mediated changes within the liver provide important groundwork for further clinical development of CBLB502, which is currently in clinical trials as a potential radioprotector and immunotherapeutic agent.

Abstract 4398: Liver is a major primary target for the Toll-like receptor-5 agonist CBLB502 providing radioprotective, antimicrobial and antitumor responses

We have previously shown that activation of Toll-like receptor 5 (TLR5) by bacterial flagellin and by pharmacologically optimized flagellin derivative CBLB502 protects mice and monkeys from lethal radiation injury to the hematopoietic and gastrointestinal systems. Here, we report that the liver is a major primary CBLB502 target organ in mice, with hepatocytes specifically showing rapid and strong NF-kB and STAT3 activation. Livers from CBLB502-treated mice showed up-regulation of numerous downstream genes encoding intracellular and secreted proteins with anti-apoptotic, anti-microbial and immunomodulatory activities. Unlike the TLR4 agonist LPS, the liver response to TLR5 agonists appears to be direct and does not involve high levels of proinflammatory cytokines. Thus, while LPS is toxic, TLR5 agonists have strong clinical potential. The importance of liver for CBLB502 radioprotective activity was confirmed by temporary occlusion of liver blood circulation which completely abrogated the protective effect of CBLB502 on hematopoietic precursor cells in irradiated mice. CBLB502 also protected liver tissue itself, increasing mouse resistance to lethal Salmonella tiphymurium liver infection and to hepatotoxic Fas agonistic antibodies. By testing CBLB502 in combination with radiation treatment of experimental mouse tumors in vivo, we demonstrated that its tissue protection properties are limited to normal tissues with no tumor protection detected in any of numerous mouse tumor models. Moreover, direct antitumor effects of CBLB502 treatment was observed in several tumor models. Comparison of the effect of CBLB502 on in vivo growth of isogenic pairs of tumor cell lines differing in their TLR5 status showed that the antitumor effect of the TLR5 agonist is TLR5 dependent and is associated with tumor infiltration by immunocytes, presumably attracted following activation of TLR5 signaling in the tumor cells. Remarkably, CBLB502 caused an immunotherapeutic effect in TLR5-negative tumors (CT26 colon adenocarcinoma and A20 lymphoma) growing as experimental liver metastases. Based on these results, we project clinical applications of CBLB502 as an anticancer immunotherapeutic drug against liver metastases independently on TLR5 status and TLR5-expressing tumors in other locations as well as supporting care drug to reduce adverse hepatotoxicity from radiation and chemotherapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4398. doi:1538-7445.AM2012-4398

Abstract A63: TLR5 agonist CBLB502 protects mice from Fas-mediated liver damage without protecting tumors

We have previously shown the strong radioprotective properties of the Toll-like receptor 5 (TLR5) agonist flagellin and its derivative CBLB502 in both mouse and non-human primate models (Burdelya et al., 2008, Science 320: 226–230). Because no protection has been observed in any in vitro cell model regardless of the TLR5 status of the cells, we hypothesized that the radioprotective effects of the TLR5 agonist are indirect and mediated by factors produced by primary cells responding to flagellin in the organism. Using a combination of tools, including NF-kB-responsive reporter mice and immunohistochemical determination of tissues responding to CBLB502 by NF-kB activation, we defined liver hepatocytes as the primary pharmacological targets of flagellin. Surgical exclusion of the liver from the blood circulation completely abolished radioprotection of the bone marrow hematopoietic progenitor cells by CBLB502 suggesting that the liver acts as a mediator of at least some of the effects of the TLR5 agonist. Since the induction of NF-kB is known to activate multiple pro-survival mechanisms, we further hypothesized that administration of the TLR5 agonist can result in liver resistance to otherwise toxic conditions. Mice treated with Fas agonistic antibodies were employed as a model of acute hepatotoxicity. Injection of CBLB502 showed a strong preventive effect against Fas-mediated injury rescuing all of the injected mice in contrast to complete lethality in the control groups. The ability of CBLB502 to protect the liver was also demonstrated via reduced levels of liver enzymes in the peripheral blood and caspase activation in liver extracts of mice treated with Fas agonistic antibodies. Using two syngeneic tumor models, colon adenocarcinoma CT26 and lymphoma A20, growing as liver metastases in mice, we found that CBLB502 injections not only prevented liver damage, but also suppressed tumor appearance and growth when injected with or without anti-Fas antibodies. Thus, TLR5 agonist has potential to become a new agent for liver protection and suppression of liver metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A63.

Stat3 activity in melanoma cells affects migration of immune effector cells and nitric oxide-mediated antitumor effects

Infiltration of immune effector cells in tumors is critical for antitumor immune responses. However, what regulates immune cell infiltration of tumors remains to be identified. Stat3 is constitutively activated with high frequency in diverse cancers, promoting tumor cell growth and survival. Blocking Stat3 signaling in tumors in vivo results in tumor growth inhibition that involves killing of nontransfected tumor cells and infiltration of immune effector cells, suggesting that Stat3 activity in tumor cells might affect immune cell recruitment. However, dying tumor cells can also attract immune cells. In this study, we show in isogenic murine melanomas that natural Stat3 activity is associated with tumor growth and reduction of T cell infiltration. Blocking Stat3 signaling in the melanoma cells containing high Stat3 activity results in expression of multiple chemoattractants, leading to increased migration of lymphocytes, NK cells, neutrophils, and macrophages. In addition, blocking Stat3 triggers tumor cells to produce soluble factors capable of activating macrophage production of NO in vitro and in vivo. TNF-alpha and IFN-beta, which are secreted by Stat3-inhibited tumor cells, are able to activate macrophage NO production, whereas neutralizing TNF-alpha in the tumor supernatant from Stat3-blocked tumor cells abrogates nitrite production. Moreover, interrupting Stat3 signaling in tumor cells leads to macrophage-mediated, nitrite-dependent cytostatic activity against nontransduced tumor cells. These results suggest that tumor Stat3 activity affects recruitment of diverse immune effectors and it can be manipulated to activate the effector phase of innate immune responses.

Regulation of the innate and adaptive immune responses by Stat-3 signaling in tumor cells

Although tumor progression involves processes such as tissue invasion that can activate inflammatory responses, the immune system largely ignores or tolerates disseminated cancers. The mechanisms that block initiation of immune responses during cancer development are poorly understood. We report here that constitutive activation of Stat-3, a common oncogenic signaling pathway, suppresses tumor expression of proinflammatory mediators. Blocking Stat-3 in tumor cells increases expression of proinflammatory cytokines and chemokines that activate innate immunity and dendritic cells, leading to tumor-specific T-cell responses. In addition, constitutive Stat-3 activity induces production of pleiotropic factors that inhibit dendritic cell functional maturation. Tumor-derived factors inhibit dendritic cell maturation through Stat-3 activation in progenitor cells. Thus, inhibition of antitumor immunity involves a cascade of Stat-3 activation propagating from tumor to dendritic cells. We propose that tumor Stat-3 activity can mediate immune evasion by blocking both the production and sensing of inflammatory signals by multiple components of the immune system.

Combination therapy with AG-490 and interleukin 12 achieves greater antitumor effects than either agent alone

Constitutive activation of Janus kinases (JAKs) and signal transducers and activators of transcription (STAT) occurs at very high frequency in various hematopoietic malignancies and solid tumors. It has been demonstrated that the tyrosine kinase inhibitor, AG-490, selectively blocks JAK activity and completely eliminates leukemia cells in a severe combined immunodeficient (SCID) mouse model. Because many cytokines, including interleukin (IL)-12, have been shown to signal through JAK/STAT pathways, AG-490 may inhibit cytokine-based cancer therapy. In this study, we evaluated the effects of AG-490 on IL-12 functional signaling and IL-12-mediated antitumor response in vivo. Previous studies have established the critical roles of macrophages and IFN-gamma in mediating IL-12-induced antitumor effects. Our results show that in vivo administration of AG-490 causes tumor cell apoptosis but does not inhibit IL-12-mediated macrophage activation and IFN-gamma production by lymphocytes. Furthermore, our data indicate that combined therapy with AG-490 and IL-12-induces greater antitumor effects than either agent alone in a murine myeloma tumor model. These results suggest that JAK/STAT inhibitors deserve further investigation for use with IL-12 therapy in treating human cancers with elevated JAK/STAT activity.

Anti-CD40 antibody induces antitumor and antimetastatic effects: the role of NK cells

We assessed the effect of the stimulatory anti-CD40 Ab on NK cell activation in vivo and the therapeutic potential of activated NK cells in tumor-bearing mice. Single-dose i.p. injection of the anti-CD40 Ab resulted in production of IL-12 and IFN-gamma in vivo, followed by a dramatic increase in NK cell cytolytic activity in PBLs. NK cell activation by anti-CD40 Ab was also observed in CD40 ligand knockout mice. Because NK cells express CD40 ligand but not CD40, our results suggest that NK activation is mediated by increased cytokine production upon CD40 ligation of APCs. Treatment of tumor-bearing mice with anti-CD40 Ab resulted in substantial antitumor and antimetastatic effects in three tumor models. Depletion of NK cells with anti-asialo GM1 Ab reduced or abrogated the observed antitumor effects in all the tested models. These results indicate that a stimulatory CD40 Ab indirectly activates NK cells, which can produce significant antitumor and antimetastatic effects.

Macrophage and interleukin-1 induced nitric oxide production and cytostasis in hamster tumor cells varying in malignant potential

Nitric oxide has been shown to contribute to cytotoxicity in mouse and rat tumor cells. In these studies we examined the role of nitric oxide in cytostasis in hamster tumor cells varying in their malignant potential. Spontaneously transformed hamster embryonic fibroblasts (STHE cells) with low metastatic activity produced significantly greater amounts of nitric oxide in response to interleukin-1 (IL-1) or lipopolysaccharide (LPS)-activated hamster alveolar macrophages (HAM) than did tumor cell lines with high experimental metastatic activity (HET-SR, HET-SR1, STHE-83/20 cells). HET-SR cells, which exhibit low spontaneous metastastic activity, also produced relatively high levels of nitric oxide in response to IL-1, whereas the response of the spontaneously metastatic lines, HET-SR1 and STHE-83/20 cells, was low. IL-1 and HAM also induced cytostasis in nitric oxide-producing STHE and HET-SR cells. However, the nitric oxide synthase inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), had no effect on this activity. These findings, together with the observation that anti-tumor necrosis factor alpha antibody prevented HAM-mediated cytostasis in all of the tumor cell lines demonstrate that nitric oxide is not involved in hamster macrophage-induced tumor cell growth suppression. In contrast to HAM, rat alveolar macrophages, which produced nitric oxide in response to LPS, exerted similar levels of cytostasis toward all of the hamster tumor cell variants, an action that was blocked by L-NMMA in HET-SR, HET-SR1, and STHE-83/20 cells. Thus production of nitric oxide by hamster tumor cells is inversely correlated with their malignant potential. However, nitric oxide does not appear to be involved in IL-1- or HAM-mediated cytostasis toward hamster tumor cells.