The synthetic oleanane triterpenoid CDDO-2P-Im binds GRP78/BiP to induce unfolded protein response-mediated apoptosis in myeloma

Synthetic oleanane triterpenoids (SOTs) are small molecules with broad anticancer properties. A recently developed SOT, 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]-4(-pyridin-2-yl)-1H-imidazole (CDDO-2P-Im or '2P-Im'), exhibits enhanced activity and improved pharmacokinetics over CDDO-Im, a previous generation SOT. However, the mechanisms leading to these properties are not defined. Here, we show the synergy of 2P-Im and the proteasome inhibitor ixazomib in human multiple myeloma (MM) cells and 2P-Im activity in a murine model of plasmacytoma. RNA sequencing and quantitative reverse transcription PCR revealed the upregulation of the unfolded protein response (UPR) in MM cells upon 2P-lm treatment, implicating the activation of the UPR as a key step in 2P-Im-induced apoptosis. Supporting this hypothesis, the deletion of genes encoding either protein kinase R-like endoplasmic reticulum kinase (PERK) or DNA damage-inducible transcript 3 protein (DDIT3; also known as CHOP) impaired the MM response to 2P-Im, as did treatment with ISRIB, integrated stress response inhibitor, which inhibits UPR signaling downstream of PERK. Finally, both drug affinity responsive target stability and thermal shift assays demonstrated direct binding of 2P-Im to endoplasmic reticulum chaperone BiP (GRP78/BiP), a stress-inducible key signaling molecule of the UPR. These data reveal GRP78/BiP as a novel target of SOTs, and specifically of 2P-Im, and suggest the potential broader utility of this class of small molecules as modulators of the UPR.

Nrf2 protects against radiation-induced oral mucositis via antioxidation and keratin layer thickening

Radiation-induced oral mucositis is one of the most common adverse events in radiation therapy for head and neck cancers, but treatments for oral mucositis are limited to palliative and supportive care. New approaches are required to prevent radiation-induced mucositis and to improve treatments. The Keap1-Nrf2 system regulates cytoprotection against oxidative and electrophilic stresses. Nrf2 also regulates keratin layer thickness in mouse tongues. Therefore, we hypothesized that Nrf2 may protect the tongue epithelium against radiation-induced mucositis via elimination of reactive oxygen species and induction of keratin layer thickening. To test this hypothesis, we prepared a system for γ-ray exposure of restricted areas and irradiated the tongues of model mice with Nrf2 and Keap1 loss-of-function. We discovered that loss of Nrf2 expression indeed sensitized the tongue epithelium to radiation-induced ulcer formation with inflammation. Constitutive Nrf2 activation by genetic Keap1 knockdown alleviated radiation-induced DNA damage by increasing antioxidation. In agreement with the genetic Nrf2 activation model, the Nrf2 inducer CDDO-Im prevented irradiation damage to the tongue epithelium. These results demonstrate that Nrf2 activation has the potential to prevent the development of radiation-induced mucositis and that Nrf2 inducers are an important therapeutic drug for protection of the upper aerodigestive tract from radiation-induced mucositis.

CDDO-imidazolide Targets Multiple Amino Acid Residues on the Nrf2 Adaptor, Keap1

Synthetic triterpenoids including CDDO, its methyl ester (CDDO-Me, bardoxolone methyl), and its imidazolide (CDDO-Im) enhance Nrf2-mediated antioxidant and anti-inflammatory activity in many diseases by reacting with thiols on the adaptor protein, Keap1. Unlike monofunctional CDDO-Me, the bifunctional analog, CDDO-Im, has a second reactive site (imidazolide) and can covalently bind to amino acids other than cysteine on target proteins such as glutathione S-transferase pi (GSTP), serum albumin, or Keap1. Here we show for the first time that bifunctional CDDO-Im (in contrast to CDDO-Me), as low as 50 nM, can covalently transacylate arginine and serine residues in GSTP and cross-link them to adjacent cysteine residues. Moreover, we show that CDDO-Im binds covalently to Keap1 by forming permanent Michael adducts with eight different cysteines, and acyl adducts with lysine and several tyrosine residues. Modeling studies suggest that the Tyr 85 adduct stabilizes the Keap1-Cul3 complex, thereby enhancing the potency of CDDO-Im.

Retinoid X receptor agonist LG100268 modulates the immune microenvironment in preclinical breast cancer models

Despite numerous therapeutic advances in the past decade, breast cancer is expected to cause over 42,000 deaths in the United States in 2019. Breast cancer had been considered an immunologically silent tumor; however recent findings suggest that immune cells play important roles in tumor growth even in the breast. Retinoid X receptors (RXRs) are a subclass of nuclear receptors that act as ligand-dependent transcription factors that regulate a variety of cellular processes including proliferation and differentiation; in addition, they are essential for macrophage biology. Rexinoids are synthetic molecules that bind and activate RXRs. Bexarotene is the only rexinoid approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma. Other more-potent rexinoids have been synthesized, such as LG100268 (LG268). Here, we report that treatment with LG 268, but not bexarotene, decreased infiltration of myeloid-derived suppressor cells and CD206-expressing macrophages, increased the expression of PD-L1 by 50%, and increased the ratio of CD8/CD4, CD25 T cells, which correlates with increased cytotoxic activity of CD8 T cells in tumors of MMTV-Neu mice (a model of HER2-positive breast cancer). In the MMTV-PyMT murine model of triple negative breast cancer, LG268 treatment of established tumors prolonged survival, and in combination with anti-PD-L1 antibodies, significantly (p = 0.05) increased the infiltration of cytotoxic CD8 T cells and apoptosis. Collectively, these data suggest that the use of LG268, a RXR agonist, can improve response to immune checkpoint blockade in HER2+ or triple-negative breast cancer.

Abstract LB-186: The rexinoid LG100268 decreases immunosuppressive immune cells and activates T cells in two preclinical models of breast cancer

Breast cancer (BC) was considered an immunologically silent tumor, however recent findings suggest that immune cells present in the tumor microenvironment play important roles in tumor growth. Retinoid X receptors (RXRs) are a subclass of nuclear receptors that act as ligand-dependent transcription factors that regulate a variety of cellular processes including proliferation and differentiation. Rexinoids are synthetic molecules that bind and activate RXRs. Bexarotene (Targretin®) is the only rexinoid approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma. Other more potent rexinoids have been synthesized, such as LG100268 (LG268) and LG101506. Because recent studies have suggested that RXRs are involved in immune regulation, we studied the effects of LG268 as an immune modulator in a preclinical model of breast cancer. MMTV-Neu mice with tumors approximately 32 mm3 in volume were treated with control diet or LG268 (100 mg/kg diet) for 5 days. Rexinoid treatment significantly (p=0.0047) reduced tumor weight from 3.2% of body weight in the control group to 1.1% in the treated group. Bexarotene (100 mg/kg diet), however, did not reduce tumor weight even after 10 days of treatment. Analysis of the tumor by flow cytometry showed a significant (p=0.0013) reduction in the percentage of myeloid derived suppressor cells (MDSCs) in the treated mice (3.4% vs 1.6%). MDSCs are associated with a lack of immune surveillance against tumor cells, and in BC, are correlated with higher metastatic burden and poor survival. The reduction in MDSCs was accompanied by a 80% reduction in p-STAT1 (p=0.02). The percentage of activated CD4 T cells (CD45, CD3, CD4, CD25) also decreased when mice were treated with LG268 (27.5% vs 13%; p=0.012). Moreover, the ratio of CD8/CD4, CD25 cells was increased in the tumors of treated mice (1.58 vs 3.07; p=0.04), suggesting increased activation of cytotoxic T cells. Higher CD8/CD4, CD25 ratios correlate with better outcomes in patients with several solid tumors. To further elucidate the effects of LG268 on immunosuppressive T cells, CD4 cells were isolated from spleen and stimulated with CD28, IL-2 and TGFβ, skewing the cells towards regulatory T cells. CD4 Treg FOXP3 expressing cells contribute to the immunosuppressive milieu in tumors. Treatment with LG268 at 100 nM reduced the mRNA expression of FOXP3 by 40% (p=0.03) when compared with untreated CD4 T cells. In the MMTV-PyMT model of triple negative BC, LG268 (100 mg/kg diet) significantly (p=0.018) extended survival by an average of 29 days when compared with the controls. Histopathological analysis revealed that tumors treated with LG268 had higher infiltration of CD8 cytotoxic T cells, which correlated with increased cleaved caspase 3. These results show that RXR agonists can be used to modulate immune cell populations present in the tumor microenvironment, and reduce immunosuppressive MDSC cells and CD4 T regulatory cell populations in breast cancer models. We thank the Breast Cancer Research Foundation for support.

Citation Format: Ana Sofia Leal, Sarah Carapellucci, Kayla ZydecK, Michael B. Sporn, Karen T. Liby. The rexinoid LG100268 decreases immunosuppressive immune cells and activates T cells in two preclinical models of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-186.

Testing Novel Pyrimidinyl Rexinoids: A New Paradigm for Evaluating Rexinoids for Cancer Prevention

Rexinoids, selective ligands for retinoid X receptors (RXR), have shown promise in preventing many types of cancer. However, the limited efficacy and undesirable lipidemic side-effects of the only clinically approved rexinoid, bexarotene, drive the search for new and better rexinoids. Here we report the evaluation of novel pyrimidinyl (Py) analogues of two known chemopreventive rexinoids, bexarotene (Bex) and LG100268 (LG268) in a new paradigm. We show that these novel derivatives were more effective agents than bexarotene for preventing lung carcinogenesis induced by a carcinogen. In addition, these new analogues have an improved safety profile. PyBex caused less elevation of plasma triglyceride levels than bexarotene, while PyLG268 reduced plasma cholesterol levels and hepatomegaly compared with LG100268. Notably, this new paradigm mechanistically emphasizes the immunomodulatory and anti-inflammatory activities of rexinoids. We reveal new immunomodulatory actions of the above rexinoids, especially their ability to diminish the percentage of macrophages and myeloid-derived suppressor cells in the lung and to redirect activation of M2 macrophages. The rexinoids also potently inhibit critical inflammatory mediators including IL6, IL1β, CCL9, and nitric oxide synthase (iNOS) induced by lipopolysaccharide. Moreover, in vitro iNOS and SREBP (sterol regulatory element-binding protein) induction assays correlate with in vivo efficacy and toxicity, respectively. Our results not only report novel pyrimidine derivatives of existing rexinoids, but also describe a series of biological screening assays that will guide the synthesis of additional rexinoids. Further progress in rexinoid synthesis, potency, and safety should eventually lead to a clinically acceptable and useful new drug for patients with cancer.

Abstract LB-344: The rexinoid LG100268 modulates immune cell populations in mammary gland tumors of MMTV-neu mice

Despite numerous therapeutic advances in the past decade, breast cancer is expected to cause around 41,000 deaths in 2018. Breast cancer was considered an immunologically silent tumor, however recent findings suggest that immune cells present in the tumor microenvironment play important roles in tumor growth. Retinoid X receptors (RXRs) are a subclass of nuclear receptors that act as ligand-dependent transcription factors that regulate a variety of cellular processes including proliferation and differentiation. Rexinoids are synthetic molecules that bind and activate RXRs. Bexarotene (Targretin®) is the only rexinoid approved by the FDA for the treatment of refractory cutaneous T-cell lymphoma. Other more potent rexinoids have been synthesized, such as LG100268 and LG101506. The rexinoid LG100268 delays the development of mammary tumors in MMTV-Neu mice. Because recent findings suggested an involvement of RXRs in immune regulation, we studied the effects of LG100268 as an immune modulator in preclinical breast cancer. MMTV-Neu mice with tumors approximately 32 mm3 in volume were treated with control diet or LG100268 (100 mg/kg diet) for 5 days. Rexinoid treatment significantly (p<0.05) reduced tumor weight from 3.2% of body weight in the control group to 1.1% in the treated group. Analysis of the tumor by flow cytometry showed a significant (p<0.05) reduction in the percentage of myeloid derived suppressor cells (MDSCs) in the treated mice (3.4% vs 1.6%). MDSCs associate with a lack of immune surveillance against tumor cells, and in breast cancer, are associated with higher metastatic burden and poor survival. The percentage of activated CD4 T cells (CD45, CD3, CD4, CD25) also decreased when mice were treated with LG100268 (27.5% vs 13%; p<0.05). Moreover, the ratio of CD8/CD4, CD25 cells was increased in the tumors of treated mice (1.58 vs 3.07), suggesting more activation of cytotoxic T cells. Higher CD8/CD4, CD25 ratios correlate with better outcomes in patients with several solid tumors. Tumors treated with LG100268 also showed decreased expression of CD31, indicating reduced vascularization. To further elucidate the effects of LG100268 on immunosuppressive T cells, CD4 cells were isolated from spleen and stimulated with CD28, IL-2 and TGFβ, skewing the cells towards regulatory T cells. CD4 Treg FOXP3 expressing cells contribute to the immunosuppressive milieu in tumors. Treatment with LG100268 at 100 nM reduced the mRNA expression of FOXP3 by 45% when compared with untreated CD4 T cells. These results show that RXR agonists can be used to modulate the immune populations present in the tumor microenvironment in breast cancer, and reduce immunosuppressive MDSC cells and CD4 T regulatory cell populations.

We thank the Breast Cancer Research Foundation for supporting this research.

Citation Format: Ana Sofia Leal, Sarah Carapellucci, Kayla Zydeck, Nupur Raychaudhuri, Michael B. Sporn, Karen T. Liby. The rexinoid LG100268 modulates immune cell populations in mammary gland tumors of MMTV-neu mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-344.

Chemoprevention of Preclinical Breast and Lung Cancer with the Bromodomain Inhibitor I-BET 762

Breast cancer and lung cancer remain the top two leading causes of cancer-related deaths in women. Because of limited success in reducing the high mortality of these diseases, new drugs and approaches are desperately needed. Cancer prevention is one such promising strategy that is effective in both preclinical and clinical studies. I-BET 762 is a new bromodomain inhibitor that reversibly targets BET (bromodomain and extraterminal) proteins and impairs their ability to bind to acetylated lysines on histones, thus interrupting downstream transcription. This inhibitor has anti-inflammatory effects and induces growth arrest in many cancers and is currently under clinical trials for treatment of cancer. However, few studies have investigated the chemopreventive effects of bromodomain inhibitors. Here, we found that I-BET 762 significantly delayed tumor development in preclinical breast and lung cancer mouse models. This drug not only induced growth arrest and downregulated c-Myc, pSTAT3, and pERK protein expression in tumor cells in vitro and in vivo but also altered immune populations in different organs. These results demonstrate the promising potential of using I-BET 762 for cancer prevention and suggest the striking effects of I-BET 762 are the result of targeting both tumor cells and the tumor microenvironment. Cancer Prev Res; 11(3); 143-56. ©2017 AACR.

Bromodomain inhibitors, JQ1 and I-BET 762, as potential therapies for pancreatic cancer

Bromodomain inhibitors (JQ1 and I-BET 762) are a new generation of selective, small molecule inhibitors that target BET (bromodomain and extra terminal) proteins. By impairing their ability to bind to acetylated lysines on histones, bromodomain inhibitors interfere with transcriptional initiation and elongation. BET proteins regulate several genes responsible for cell cycle, apoptosis and inflammation. In this study, JQ1 and I-BET 762 decreased c-Myc and p-Erk 1/2 protein levels and inhibited proliferation in pancreatic cancer cells. The tumor microenvironment is known to play an important role in pancreatic cancer, and these drugs suppressed the production of nitric oxide and a variety of inflammatory cytokines, including IL-6, CCL2, and GM-CSF, in both immune and pancreatic cancer cells in vitro. Notably, the bromodomain inhibitors also reduced protein levels of p-Erk 1/2 and p-STAT3 in mouse models of pancreatic cancer. All of these proteins are essential for tumor promotion, progression and metastasis. In conclusion, the bromodomain inhibitors JQ1 and I-BET 762 targeted and suppressed multiple pathways in pancreatic cancer. I-BET 762 and a number of other bromodomain inhibitors are currently being tested in several clinical trials, making them potentially promising drugs for the treatment of pancreatic cancer, an often-fatal disease.

Design, synthesis, and biological activity of second-generation synthetic oleanane triterpenoids

Synthetic manipulation of oleanolic acid affords a novel and biologically active C-24 demethylated CDDO-Me.

Abstract A88: The synthetic triterpenoid CDDO-Imidazolide reduces immune cell infiltration and cytokine secretion in the KC mouse model of pancreatic cancer

Survival rates for pancreatic cancer remain at 7-8%, and as the incidence and deaths are expected to increase, new drugs are needed for the prevention and treatment of this devastating disease. LSL-KrasG12D/+;Pdx-1-Cre (KC) mice replicate the genetics, symptoms and histopathology found in human pancreatic cancer. Immune cells infiltrate into the pancreas of these mice and produce inflammatory cytokines that promote tumor growth. This process can be accelerated with the administration of lipopolysaccharide (LPS) or caerulein so KC mice at 9 weeks of age were injected once a week for 4 weeks with LPS (4mg/kg). One or four weeks after the LPS injections, plasma, pancreas and spleens were collected. KC mice were particularly sensitive to the effects of LPS, as only 48% of the KC mice survived an LPS challenge while 100% of wildtype (WT) mice survived. Survival was increased when KC mice were pre-treated with the triterpenoid CDDO-Imidazolide (CDDO-Im) (71% survival). LPS increased the percentage of CD45+ immune cells in the pancreas and immunosuppressive Gr1+ myeloid derived suppressor cells (MDSC) in the spleen of KC mice. In contrast, CDDO-Im decreased the infiltration of CD45+ cells into the pancreas and the percentage of Gr1+ MDSC in the spleen of KC mice challenged with LPS. Levels of inflammatory cytokine levels also were markedly higher in KC mice vs. WT mice challenged with LPS. Pre-treatment with CDDO-Im decreased the production of IL-6, CCL-2, VEGF, and G-CSF in the KC mice. These cytokines are prognostic markers in pancreatic cancer or play important roles in the progression of this disease. Disrupting inflammation during tumorigenesis with drugs such as CDDO-Im might be useful for preventing pancreatic cancer, especially in high risk populations.

Citation Format: Ana Sofia Leal, Michael B. Sporn, Patricia A. Pioli, Karen T. Liby.{Authors}. The synthetic triterpenoid CDDO-Imidazolide reduces immune cell infiltration and cytokine secretion in the KC mouse model of pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A88.

The triterpenoid CDDO-imidazolide reduces immune cell infiltration and cytokine secretion in the KrasG12D;Pdx1-Cre (KC) mouse model of pancreatic cancer

Because the 5-year survival rate for pancreatic cancer remains under 10%, new drugs are needed for the prevention and treatment of this devastating disease. Patients with chronic pancreatitis have a 12-fold higher risk of developing pancreatic cancer. LSL-Kras^G12D/+;Pdx-1-Cre (KC) mice replicate the genetics, symptoms and histopathology found in human pancreatic cancer. Immune cells infiltrate into the pancreas of these mice and produce inflammatory cytokines that promote tumor growth. KC mice are particularly sensitive to the effects of lipopolysaccharide (LPS), as only 48% of KC mice survived an LPS challenge while 100% of wildtype (WT) mice survived. LPS also increased the percentage of CD45+ immune cells in the pancreas and immunosuppressive Gr1+ myeloid-derived suppressor cell in the spleen of these mice. The triterpenoid CDDO-imidazolide (CDDO-Im) not only reduced the lethal effects of LPS (71% survival) but also decreased the infiltration of CD45+ cells into the pancreas and the percentage of Gr1+ myeloid-derived suppressor cell in the spleen of KC mice 4-8 weeks after the initial LPS challenge. While the levels of inflammatory cytokine levels were markedly higher in KC mice versus WT mice challenged with LPS, CDDO-Im significantly decreased the production of IL-6, CCL-2, vascular endothelial growth factor and G-CSF in the KC mice. All of these cytokines are prognostic markers in pancreatic cancer or play important roles in the progression of this disease. Disrupting the inflammatory process with drugs such as CDDO-Im might be useful for preventing pancreatic cancer, especially in high-risk populations.

Rexinoids for prevention and treatment of cancer: opportunities and challenges

Rexinoids are selective ligands for the nuclear receptors known as RXRs. They do not bind to the receptors for all-trans-retinoic acid (RARs). Many new rexinoids have been synthesized and then assayed for their ability to suppress proliferation of cancer cells, to inhibit activation of inflammatory cells of the tumor microenvironment, and to prevent carcinogenesis in animal models relevant to human disease. Here we review the literature on the effects of 4 such rexinoids: bexarotene, LG100268, LG101506, and NRX194204. These rexinoids also have potent synergistic effects when used in combination with other active pharmacological agents, and practical clinical applications would benefit from these actions.

Abstract 293: Therapeutic effects of the bromodomain inhibitors JQ1 and I-BET 762 on pancreatic cancer

Pancreatic cancer is expected to be the second most deadly cancer by 2030 with very few effective therapeutic options to improve patient survival. Bromodomain inhibitors (JQ1 and I-BET 762) are a new generation of chemotherapeutic drugs that target BET proteins, impairing their ability to bind to acetyl modified lysines and therefore interfering with transcriptional initiation and elongation. BET proteins regulate several genes responsible for cell cycle, apoptosis and inflammation. I-BET 762 is currently in clinical trials for cancer and has the advantage of oral administration.

Kras is one of the most common mutated genes in pancreatic cancer (90%); however its protein is a difficult drug target. p-Erk, responsible for several pathways regulating cell survival, is a downstream effector of Kras that has been shown to be essential for the progression and maintenance of pancreatic cancer. LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre (KPC) and LSL-KrasG12D/+;Pdx-1-Cre (KC) mouse models are commonly used to study pancreatic cancer. KPC mice develop the full spectrum of pancreatic cancer by an average age of 20 weeks. The KC mouse model is commonly used to study pancreatic cancer progression after stimulation with a pancreatic inflammatory agent, such as cerulein.

JQ1 and I-BET 762 reduce the protein levels of p-ERK 1/2 in cells lines derived from a pancreatic tumor or ascites of KPC animals. JQ1 and I-BET 762 are also effective at inhibiting cell growth in human pancreatic cells harboring Kras mutations. When KC mice are injected with LPS to induce inflammation and pancreatitis, p-ERK 1/2 protein levels are significantly increased. This model is being used to test the effects of JQ1 and I-BET 762 after a single LPS injection, in KC mice.

Pancreatic cancer is driven by several cytokines and chemokines, including CCL2 and IL-6, which recruit and regulate the inflammatory cells (macrophages, T cells and MDSC (Myeloid derived suppressor cells) cells) in the tumor. Levels of IL-6 and CCL2 in cell lines developed from KPC mice are reduced when treated with JQ1 and I-BET 762. KC mice stimulated with LPS also have higher levels of CCL2 and IL-6 than mice stimulated with saline.

In conclusion this study showed that the bromodomain inhibitors JQ1 and I-BET 762 had positive effects in suppressing targets of inflammation in pancreatic cancer.

We thank James Bradner for the generous gift of JQ1.

Citation Format: Ana S. Leal, Charlotte R. Williams, Michael B. Sporn, Karen T. Liby. Therapeutic effects of the bromodomain inhibitors JQ1 and I-BET 762 on pancreatic cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 293. doi:10.1158/1538-7445.AM2015-293

Abstract LB-265: Comparison of oleanane triterpenoids and dimethyl fumarate in lung cancer

Lung cancer accounts for the highest number of cancer-related deaths in the United States, highlighting the need for better therapies. Nrf2 is an important therapeutic target as activation of this pathway detoxifies harmful insults and reduces oxidative stress. However, the role of Nrf2 in cancer biology is controversial. Protection against oxidative stress and inflammation can confer a survival advantage to tumor cells, leading to a poor prognosis, and constitutive activation of Nrf2 has been detected in numerous tumors. In our study, we examined the role of two clinically relevant classes of Nrf2 activators, the synthetic triterpenoids (CDDO-Im and CDDO-Me) and dimethyl fumarate (DMF) in mouse macrophages (Raw 264.7) and in VC1 lung cancer cells. Although both triterpenoids and DMF activated Nrf2, CDDO-Im and CDDO-Me were more potent than DMF. Specifically, 25-50 nM CDDO-Im or CDDO-Me increased NQO1 and HO-1 expression 100-fold. Conversely, 10 μM of DMF was necessary to elicit the same effect. Additionally, 100 nM of CDDO-Im significantly (p<0.05) reduced ROS production induced by tert-butyl hydroperoxide by 69%, while 10 μM of DMF reduced ROS production by 44%. Moreover, nitric oxide production was significantly decreased by triterpenoids at nanomolar concentrations while DMF had a similar effect at micromolar concentrations (p<0.05). Using microarray analysis, we examined whether these Nrf2 activators target the same genes. Only 52 of 99 Nrf2 genes were targeted by all three compounds, and each drug targeted a unique subset of Nrf2 genes. Notably, CDDO-Im, CDDO-Me and DMF induced HO-1 expression by 9.1, 5.3 and 1.6 fold respectively. We then utilized Nrf2 knockout fibroblasts to confirm that induction of HO-1 expression was regulated via both Nrf2-dependent and Nrf2-independent pathways. To examine the effect of these Nrf2 activators in vivo, A/J mice were injected with vinyl carbamate to induce lung cancer. Beginning one week after initiation, mice were fed drugs in diet for 15 weeks. CDDO-Me was the most effective drug in this model; it reduced the average number and size of tumors by 32% (2.2 ± 0.3) and 76% (0.09 ± 0.01), respectively, compared to controls (3.2 ± 0.2 and 0.4 ± 0.04; p<0.05). Average tumor burden was also reduced by 83% (0.2 ± 0.03), compared to the controls (1.2 ± 0.1; p<0.05). Additionally, the percentage of high-grade tumors significantly decreased from 52% in the controls to 31% in the CDDO-Me group (p<0.05). Though less potent, CDDO-Im had similar effects as CDDO-Me. In contrast, when mice were fed DMF in diet, the average number of tumors increased by 29% (4.1 ± 0.4) compared to controls (3.2± 0.2; p<0.05). The percentage of high-grade tumors in mice fed DMF diet also increased to 63% vs. 52% in the controls (p<0.05). These data indicate that DMF increased the severity of lung carcinogenesis in these mice. Collectively, our study suggests that although CDDO-Im, CDDO-Me and DMF all activate Nrf2, they target distinct genes, resulting in different effects for the prevention of lung cancer.

Citation Format: Ciric To, Darlene B. Royce, Charlotte R. Williams, Renee Risingsong, Michael B. Sporn, Karen T. Liby. Comparison of oleanane triterpenoids and dimethyl fumarate in lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-265. doi:10.1158/1538-7445.AM2015-LB-265

Novel synthetic pyridyl analogues of CDDO-Imidazolide are useful new tools in cancer prevention

Two new analogues of CDDO-Imidazolide (CDDO-Im), namely 1-[2-Cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]-4(-pyridin-2-yl)-1H-imidazole ("CDDO-2P-Im") and 1-[2-Cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]-4(-pyridin-3-yl)-1H-imidazole ("CDDO-3P-Im") have been synthesized and tested for their potential use as chemopreventive drugs. At nanomolar concentrations, they were equipotent to CDDO-Im for inducing differentiation and apoptosis in U937 leukemia cells. As inflammation and oxidative stress contribute to carcinogenesis, we also assessed their cytoprotective potential. The new compounds suppressed inducible nitric oxide synthase (iNOS) expression in RAW264.7 macrophage-like cells and significantly elevated heme oxygenase-1 (HO-1) and quinone reductase (NQO1) mRNA and protein levels in various mouse tissues in vivo. Most importantly, pharmacokinetic studies performed in vitro in human plasma and in vivo showed that each new analogue was more stable than CDDO-Im. Much higher concentrations of the new derivatives were found in mouse liver, lung, pancreas and kidney after gavage in contrast to CDDO-Im. Because of their better bioavailability and their excellent anti-inflammatory profile in vitro, CDDO-2P-Im and CDDO-3P-Im were tested for prevention in a highly relevant mouse lung cancer model, in which A/J mice develop lung carcinomas after injection of vinyl carbamate, a potent carcinogen. CDDO-2P-Im and CDDO-3P-Im were as effective as CDDO-Im for reducing the size and the severity of the lung tumors.

Dimethyl fumarate and the oleanane triterpenoids, CDDO-imidazolide and CDDO-methyl ester, both activate the Nrf2 pathway but have opposite effects in the A/J model of lung carcinogenesis

Lung cancer accounts for the highest number of cancer-related deaths in the USA, highlighting the need for better prevention and therapy. Activation of the Nrf2 pathway detoxifies harmful insults and reduces oxidative stress, thus preventing carcinogenesis in various preclinical models. However, constitutive activation of the Nrf2 pathway has been detected in numerous cancers, which confers a survival advantage to tumor cells and a poor prognosis. In our study, we compared the effects of two clinically relevant classes of Nrf2 activators, dimethyl fumarate (DMF) and the synthetic oleanane triterpenoids, CDDO-imidazolide (CDDO-Im) and CDDO-methyl ester (CDDO-Me) in RAW 264.7 mouse macrophage-like cells, in VC1 lung cancer cells and in the A/J model of lung cancer. Although the triterpenoids and DMF both activated the Nrf2 pathway, CDDO-Im and CDDO-Me were markedly more potent than DMF. All of these drugs reduced the production of reactive oxygen species and inhibited nitric oxide production in RAW264.7 cells, but the triterpenoids were 100 times more potent than DMF in these assays. Microarray analysis revealed that only 52 of 99 Nrf2-target genes were induced by all three compounds, and each drug regulated a unique subset of Nrf2 genes. These drugs also altered the expression of other genes important in lung cancer independent of Nrf2. Although all three compounds enhanced the phosphorylation of CREB, only DMF increased the phosphorylation of Akt. CDDO-Me, at either 12.5 or 50mg/kg of diet, was the most effective drug in our lung cancer mouse model. Specifically, CDDO-Me significantly reduced the average tumor number, size and burden compared with the control group (P < 0.05). Additionally, 52% of the tumors in the control group were high-grade tumors compared with only 14% in the CDDO-Me group. Though less potent, CDDO-Im had similar activity as CDDO-Me. In contrast, 61-63% of the tumors in the DMF groups (400-1200mg/kg diet) were high-grade tumors compared with 52% for the controls (P < 0.05). Additionally, DMF significantly increased the average number of tumors compared with the controls (P < 0.05). Thus, in contrast to the triterpenoids, which effectively reduced pathogenesis in A/J mice, DMF enhanced the severity of lung carcinogenesis in these mice. Collectively, these results suggest that although CDDO-Im, CDDO-Me and DMF all activate the Nrf2 pathway, they target distinct genes and signaling pathways, resulting in opposite effects for the prevention of experimental lung cancer.

Neuroprotective role of Nrf2 for retinal ganglion cells in ischemia-reperfusion

Retinal ischemia plays a critical role in multiple vision-threatening diseases and leads to death of retinal neurons, particularly ganglion cells. Oxidative stress plays an important role in this ganglion cell loss. Nrf2 (NF-E2-related factor 2) is a major regulator of the antioxidant response, and its role in the retina is increasingly appreciated. We investigated the potential retinal neuroprotective function of Nrf2 after ischemia-reperfusion (I/R) injury. In an experimental model of retinal I/R, Nrf2 knockout mice exhibited much greater loss of neuronal cells in the ganglion cell layer than wild-type mice. Primary retinal ganglion cells isolated from Nrf2 knockout mice exhibited decreased cell viability compared to wild-type retinal ganglion cells, demonstrating the cell-intrinsic protective role of Nrf2. The retinal neuronal cell line 661W exhibited reduced cell viability following siRNA-mediated knockdown of Nrf2 under conditions of oxidative stress, and this was associated with exacerbation of increase in reactive oxygen species. The synthetic triterpenoid CDDO-Im (2-Cyano-3,12-dioxooleana-1,9-dien-28-imidazolide), a potent Nrf2 activator, inhibited reactive oxygen species increase in cultured 661W under oxidative stress conditions and increased neuronal cell survival after I/R injury in wild-type, but not Nrf2 knockout mice. Our findings indicate that Nrf2 exhibits a retinal neuroprotective function in I/R and suggest that pharmacologic activation of Nrf2 could be a therapeutic strategy. Oxidative stress is thought to be an important mediator of retinal ganglion cell death in ischemia-reperfusion injury. We found that the transcription factor NF-E2-related factor 2 (Nrf2), a major regulator of oxidative stress, is an important endogenous neuroprotective molecule in retinal ganglion cells in ischemia-reperfusion, exerting a cell-autonomous protective effect.  The triterpenoid 2-Cyano-3,12-dioxooleana-1,9-dien-28-imidazolide (CDDO-Im) reduces neurodegeneration following ischemia-reperfusion in an Nrf2-dependent fashion. This suggests that Nrf2-activating drugs including triterpenoids could be a therapeutic strategy for retinal neuroprotection.

Abstract LB-245: The EGRF receptor inhibitor Erlotinib, alone or in combination with the rexinoid LG100268, is effective for prevention in mouse models of lung and pancreatic cancer with Kras mutations

Lung cancer and pancreatic cancer are leading causes of cancer deaths, with extremely poor 5 year survival rates for both types of cancer. The epidermal growth factor receptor (EGFR) and its ligands regulate cell growth, and EGFR expression is frequently elevated in lung and pancreatic cancer. Tumors with activating mutations in EGFR are treated clinically with drugs such as erlotinib, a tyrosine kinase EGFR inhibitor. Up to 90% of pancreatic cancers and 35% of lung cancers contain activating mutations in Kras, but tumors with Kras mutations are usually resistant to EGRF inhibitors. Erlotinib is an approved drug for treating pancreatic cancer, but it only extends survival by a few weeks. We have previously shown that the rexinoid LG100268 (268) is effective for prevention of experimental lung and pancreatic cancers with Kras mutations, and a recent clinical trial suggests that the combination of a rexinoid and erlotinib might be useful for treating lung cancer, even in tumors with Kras mutations. In order to test whether this combination of drugs might be useful for prevention of lung cancer, female A/J mice were injected i.p. with vinyl carbamate (16 mg/kg) once a week for two weeks. The carcinogen induces Kras mutations and microscopic adenocarcinomas in the lungs within 4-6 weeks. Starting one week after the last injection of carcinogen, the mice were fed the rexinoid 268 (40 mg/kg diet), erlotinib (150 mg/kg diet) or the combination for 16 weeks. All 3 groups significantly (P &lt; 0.05 for each group vs. control and the combination vs. the individual drugs) reduced the average size of lung tumors by 45-80%, from an average of 3.2 ± 0.6 mm3 in the control group (n = 28) to 1.8 ± 0.4 with erlotinib, 1.1 ± 0.3 with 268 and 0.7 ±0.08 mm3 with the combination (n = 12 per group). The average tumor burden was also significantly reduced 43% by erlotinib, 77% by 268 and 85% by the combination. The total tumor burden per slide was 10.5 ± 1.5 mm3 in the control group but only 2.5 ± 0.5 mm3 in mice fed 268, 6.0 ±1.0 in mice fed erlotinib, and 1.6 ± 0.3 mm3 in mice fed the combination (P &lt; 0.05). The percentage of high grade invasive tumors was also significantly (P &lt; 0.05) reduced from 51% in the control group to 22-34% in mice on a chemopreventive diet. In the LSL-KrasG12D/+;LSL-Trp53R127H/+;Pdx-1-Cre (KPC) mouse model of pancreatic cancer, Kras mutations drive carcinogenesis, and the clinical symptoms and histopathology found in this model replicate the human disease. To test the effectiveness of an EGFR inhibitor in the KPC model, mice were fed erlotinib (150 mg/kg diet), beginning at 4 weeks of age until the mice displayed overt symptoms (cachexia, abdmoninal distension) of pancreatic cancer. Erlotinib significantly (P &lt; 0.05) increased survival compared to the control group (n = 26-27 per group). Average lifespan was extended from an average of 24.7 ± 2.4 weeks in the control group vs. 29.3 ± 2.8 weeks in mice on erlotinib diet, an increase of 4.5 weeks. Ongoing experiments are testing the efficacy of the combination of erlotinib and 268 in the KPC model and studying the mechanism of action of these drugs in Kras-driven models.

Citation Format: Karen T. Liby, Charlotte R. Williams, Renee Risingsong, Michael B. Sporn, Ryan M. Collins, Darlene B. Royce. The EGRF receptor inhibitor Erlotinib, alone or in combination with the rexinoid LG100268, is effective for prevention in mouse models of lung and pancreatic cancer with Kras mutations. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-245. doi:10.1158/1538-7445.AM2014-LB-245

A synthetic triterpenoid CDDO-Im inhibits tumorsphere formation by regulating stem cell signaling pathways in triple-negative breast cancer

Triple-negative breast cancer is associated with poor prognosis because of a high rate of tumor recurrence and metastasis. Previous studies demonstrated that the synthetic triterpenoid, CDDO-Imidazolide (CDDO-Im) induced cell cycle arrest and apoptosis in triple-negative breast cancer. Since a small subpopulation of cancer stem cells has been suggested to be responsible for drug resistance and metastasis of tumors, our present study determined whether the effects of CDDO-Im in triple-negative breast cancer are due to the inhibition of a cancer stem cell subpopulation. CDDO-Im treatment markedly induced cell cycle arrest at G2/M-phase and apoptosis in the triple-negative breast cancer cell lines, SUM159 and MDA-MB-231. Because SUM159 cells were more sensitive to CDDO-Im than MDA-MB-231 cells, the effects of CDDO-Im on the cancer stem cell subpopulation were further investigated in SUM159 cells. SUM159 cells formed tumorspheres in culture, and the cancer stem cell subpopulation, CD24−/EpCAM+ cells, was markedly enriched in SUM159 tumorspheres. The CD24−/EpCAM+ cells in SUM159 tumorspheres were significantly inhibited by CDDO-Im treatment. CDDO-Im also significantly decreased sphere forming efficiency and tumorsphere size in both primary and secondary sphere cultures. PCR array of stem cell signaling genes showed that expression levels of many key molecules in the stem cell signaling pathways, such as Notch, TGF-β/Smad, Hedgehog and Wnt, were significantly down-regulated by CDDO-Im in SUM159 tumorspheres. Protein levels of Notch receptors (c-Notch1, Notch1 and Notch3), TGF-β/Smad (pSmad2/3) and Hedgehog downstream effectors (GLI1) also were markedly reduced by CDDO-Im. In conclusion, the present study demonstrates that the synthetic triterpenoid, CDDO-Im, is a potent anti-cancer agent against triple-negative breast cancer cells by targeting the cancer stem cell subpopulation.

An efficient synthesis of methyl 2-cyano-3,12-dioxoursol-1,9-dien-28-oate (CDDU-methyl ester): analogues, biological activities, and comparison with oleanolic acid derivatives

An efficient synthesis of methyl 2-cyano-3,12-dioxoursol-1,9-dien-28-oate (CDDU-methyl ester) from commercially available ursolic acid, which features an oxidative ozonolysis-mediated C-ring enone formation, and provides the first access to ursolic acid-derived cyano enone analogues with C-ring activation. These new ursolic acid analogues show potent biological activities, with potency of approximately five-fold less than the corresponding oleanolic acid derivatives.

Synthetic triterpenoid induces 15-PGDH expression and suppresses inflammation-driven colon carcinogenesis

Colitis-associated colon cancer (CAC) develops as a result of inflammation-induced epithelial transformation, which occurs in response to inflammatory cytokine-dependent downregulation of 15-hydroxyprostaglandin dehydrogenase (15-PGDH) and subsequent suppression of prostaglandin metabolism. Agents that both enhance 15-PGDH expression and suppress cyclooxygenase-2 (COX-2) production may more effectively prevent CAC. Synthetic triterpenoids are a class of small molecules that suppress COX-2 as well as inflammatory cytokine signaling. Here, we found that administration of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-C28-methyl ester (CDDO-Me) suppresses CAC in mice. In a spontaneous, inflammation-driven intestinal neoplasia model, deletion of Smad4 specifically in T cells led to progressive production of inflammatory cytokines, including TNF-α, IFN-γ, iNOS, IL-6, IL-1β; as well as activation of STAT1 and STAT3; along with suppression of 15-PGDH expression. Oral administration of CDDO-Me to mice with SMAD4-deficient T cells increased survival and suppressed intestinal epithelial neoplasia by decreasing production of inflammatory mediators and increasing expression of 15-PGDH. Induction of 15-PGDH by CDDO-Me was dose dependent in epithelial cells and was abrogated following treatment with TGF-β signaling inhibitors in vitro. Furthermore, CDDO-Me-dependent 15-PGDH induction was not observed in Smad3-/- mice. Similarly, CDDO-Me suppressed azoxymethane plus dextran sodium sulfate-induced carcinogenesis in wild-type animals, highlighting the potential of small molecules of the triterpenoid family as effective agents for the chemoprevention of CAC in humans.

The PARP inhibitors, veliparib and olaparib, are effective chemopreventive agents for delaying mammary tumor development in BRCA1-deficient mice

Poly-ADP ribose polymerase (PARP) inhibitors are effective for the treatment of BRCA-deficient tumors. Women with these mutations have an increased risk of developing breast cancer and would benefit from effective chemoprevention. This study examines whether the PARP inhibitors, veliparib and olaparib, delay mammary gland tumor development in a BRCA1-deficient (BRCA1(Co/Co);MMTV-Cre;p53(+/-)) mouse model. In dose de-escalation studies, mice were fed with control, veliparib (100 mg/kg diet), or olaparib (200, 100, 50, or 25 mg/kg diet) continuously for up to 43 weeks. For intermittent dosing studies, mice cycled through olaparib (200 mg/kg diet) for 2 weeks followed by a 4-week rest period on control diet. To examine biomarkers, mice were fed with olaparib using the intermittent dosing regimen and mammary glands were evaluated by immunohistochemistry. In mice treated with veliparib or olaparib (200 mg/kg diet), the average age of the first detectable tumor was delayed by 2.4 and 6.5 weeks, respectively, compared with controls. Olaparib also increased the average lifespan of mice by 7 weeks. In dose de-escalation studies, lower concentrations of olaparib delayed tumor development but were less effective than the highest dose. When fed intermittently, olaparib delayed the onset of the first palpable tumor by 5.7 weeks and significantly reduced proliferation and induced apoptosis in hyperplastic mammary glands. In summary, veliparib and olaparib are effective for delaying tumor development and extending the lifespan of BRCA1-deficient mice, and intermittent dosing with olaparib was as effective as continuous dosing. These results suggest that the use of PARP inhibitors is a promising chemopreventive option.

Complete protection against aflatoxin B(1)-induced liver cancer with a triterpenoid: DNA adduct dosimetry, molecular signature, and genotoxicity threshold

In experimental animals and humans, aflatoxin B1 (AFB1) is a potent hepatic toxin and carcinogen. The synthetic oleanane triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Im), a powerful activator of Keap1-Nrf2 signaling, protects against AFB1-induced toxicity and preneoplastic lesion formation (GST-P-positive foci). This study assessed and mechanistically characterized the chemoprotective efficacy of CDDO-Im against AFB1-induced hepatocellular carcinoma (HCC). A lifetime cancer bioassay was undertaken in F344 rats dosed with AFB1 (200 μg/kg rat/day) for four weeks and receiving either vehicle or CDDO-Im (three times weekly), one week before and throughout the exposure period. Weekly, 24-hour urine samples were collected for analysis of AFB1 metabolites. In a subset of rats, livers were analyzed for GST-P foci. The comparative response of a toxicogenomic RNA expression signature for AFB1 was examined. CDDO-Im completely protected (0/20) against AFB1-induced liver cancer compared with a 96% incidence (22/23) observed in the AFB1 group. With CDDO-Im treatment, integrated level of urinary AFB1-N(7)-guanine was significantly reduced (66%) and aflatoxin-N-acetylcysteine, a detoxication product, was consistently elevated (300%) after the first AFB1 dose. In AFB1-treated rats, the hepatic burden of GST-P-positive foci increased substantially (0%-13.8%) over the four weeks, but was largely absent with CDDO-Im intervention. The toxicogenomic RNA expression signature characteristic of AFB1 was absent in the AFB1 + CDDO-Im-treated rats. The remarkable efficacy of CDDO-Im as an anticarcinogen is established even in the face of a significant aflatoxin adduct burden. Consequently, the absence of cancer requires a concept of a threshold for DNA damage for cancer development.

Abstract PP01-01: Chemoprevention of Cancer: Past, Present, and Future

We will summarize highlights of new concepts relating to chemoprevention of cancer during a long career of research on this topic. Particular emphasis will be placed on the following topics: carcinogenesis as a chronic disease process, the question of whether asymptomatic people are truly healthy, the use of drugs both singly and in combination for chemoprevention of cancer, tumor cell heterogeneity, the importance of the use of multifunctional drugs for chemoprevention, and the application of drugs developed in cancer studies for diseases other than cancer.

Citation Format: Michael B. Sporn. Chemoprevention of Cancer: Past, Present, and Future. [abstract]. In: Proceedings of the Twelfth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2013 Oct 27-30; National Harbor, MD. Philadelphia (PA): AACR; Can Prev Res 2013;6(11 Suppl): Abstract nr PP01-01.

Oral administration of a gemini vitamin D analog, a synthetic triterpenoid and the combination prevents mammary tumorigenesis driven by ErbB2 overexpression

HER2 (or ErbB2), a member of ErbB receptor tyrosine kinases, is overexpressed in approximately 20% of human breast cancer, and the ErbB2 signaling pathway is a critical therapeutic target for ErbB2-overexpressing breast cancer. We investigated the inhibitory effects of the Gemini vitamin D analog BXL0124, the synthetic triterpenoid CDDO-Im and the combination on the tumorigenesis of ErbB2-overexpressing breast cancer. MMTV-ErbB2/neu transgenic mice were treated with BXL0124, CDDO-Im, or the combination from three months of age until the end of the experiment. Formation and growth of MMTV-ErbB2/neu mammary tumors were monitored every week, and all three treatments delayed the development of mammary tumors without significant toxicity. Decreased activation of ErbB2 as well as other ErbB receptors, ErbB1 and ErbB3, in MMTV-ErbB2/neu mammary tumors was shown by all treatments. Protein levels of downstream targets of the ErbB2 signaling pathway, including activated-Erk1/2, activated-Akt, c-Myc, CycD1, and Bcl2, were repressed by all three treatments, with the combination treatment exhibiting the strongest effects. To investigate therapeutic efficacy, the combination of BXL0124 and CDDO-Im was given to MMTV-ErbB2/neu mice after mammary tumors were established between 23 and 30 weeks of age. Short-term treatment with the combination did not show effects on tumor growth nor the ErbB2 signaling pathway. The present study shows BXL0124, CDDO-Im, and the combination as potential agents for prevention, but not treatment, against the tumorigenesis of ErbB2-overexpressing breast cancer.

Abstract 180: Inhibition of tumorigenesis by a novel Gemini vitamin D analog BXL0124 and a synthetic triterpenoid CDDO-Im in MMTV-HER2/neu transgenic mice

HER2 amplification is one of major genetic alterations in breast cancer, representing about 20% breast cancer cases. Gemini vitamin D analogs and synthetic triterpenoids have been shown to repress the growth of HER2-overexpressing breast cancer cells and inhibit mammary tumorigenesis of MMTV-HER2/neu transgenic mice. In previous leukemia studies, CDDO and its derivatives have been shown to synergize with vitamin D or vitamin D analogs to induce monocytic differentiation, demonstrating the potential combinatory effects for cancer prevention. In the present study, we investigated the anti-cancer activity of a novel Gemini vitamin D analog BXL0124, a potent synthetic triterpenoid CDDO-Im alone and in combination utilizing the MMTV-HER2/neu transgenic mouse model. BXL0124 (0.3 μg/kg body weight), CDDO-Im (3 μmole/kg body weight) or their combination was orally administered to MMTV-HER2/neu transgenic mice three times a week, beginning at 12 weeks of age. The body weight and tumor size of each mouse were measured weekly, and the mice were sacrificed when they were 56 weeks old. BXL0124, CDDO-Im and their combination delayed the development of MMTV-HER2/neu mammary tumors. The tumor multiplicity was decreased by BXL0124 (0.84), CDDO-Im (0.65, p&lt;0.05) and their combination (0.53, p&lt;0.05) compared to control (1.11). The averaged tumor weight was also reduced by BXL0124 (0.63 g), CDDO-Im (0.44g, p&lt;0.05) and their combination (0.43 g, p&lt;0.05) compared to control (0.89 g). In MMTV-HER2/neu mammary tumors, the activation of HER2 and EGFR as well as downstream signaling molecules, including JAK2, Src, Mek1/2 and Erk1/2, were markedly repressed by BXL0124, CDDO-Im and their combination. The protein levels of cyclin D1, c-Myc, PCNA and Bcl2 were decreased, whereas the protein level of p21 was increased by BXL0124, CDDO-Im and their combination. While HER2 was expressed in all tumor area, the activation of HER2 was found predominantly in the front invading edge area of MMTV-HER2/neu mammary tumors. All three treatments markedly decreased the activation of HER2 signaling at the front invading edge area. In conclusion, our study demonstrated that BXL0124, CDDO-Im and their combination may be promising chemopreventive agents targeting the HER2 signaling pathway in HER2-positive breast cancer. (This work was supported in part by the National Institutes of Health National Cancer Institute R01-CA-127645 and the National Institutes of Health National Institute of Environmental Health Science Grant ES005022.)

Citation Format: Jae Young So, Amanda K. Smolarek, Hubert Maehr, Milan Uskokovic, Karen Liby, Michael B. Sporn, Nanjoo Suh. Inhibition of tumorigenesis by a novel Gemini vitamin D analog BXL0124 and a synthetic triterpenoid CDDO-Im in MMTV-HER2/neu transgenic mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 180. doi:10.1158/1538-7445.AM2013-180

Is lycopene an effective agent for preventing prostate cancer?

The role of lycopene, an open-chain carotenoid found in tomatoes and devoid of retinoid activity, as an anticarcinogenic, chemopreventive agent, especially for use in prostate cancer, is still under active investigation. In this issue, Qui and colleagues show that lycopene induces responses in human prostate epithelial cells that are antiproliferative, antioxidative, and anti-inflammatory, as well as downregulating targets in the androgen receptor signaling pathway. In this perspective, we review aspects of the molecular and cellular biology of lycopene that support its use for prevention of prostate cancer. Whether lycopene itself or its metabolites induce most of its benefits is still uncertain. At present, meta-analysis of clinical studies of lycopene for prevention of prostate cancer in men does not yet support the definitive clinical use of this carotenoid in a preventive setting.

Targeting Nrf2-mediated gene transcription by extremely potent synthetic triterpenoids attenuate dopaminergic neurotoxicity in the MPTP mouse model of Parkinson's disease

Although the etiology of Parkinson's disease (PD) remains unclear, ample empirical evidence suggests that oxidative stress is a major player in the development of PD and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity. Nuclear factor E2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that upregulates a battery of antioxidant response element (ARE)-driven antioxidative and cytoprotective genes that defend against oxidative stress.

AIMS

We evaluated whether the strategy of activation of Nrf2 and its downstream network of cytoprotective genes with small molecule synthetic triterpenoids (TP) attenuate MPTP-induced PD in mice.

RESULTS

We show that synthetic TP are thus far the most potent and direct activators of the Nrf2 pathway using a novel Neh2-luciferase reporter. They upregulate several cytoprotective genes, including those involved in glutathione biosynthesis in vitro. Oral administration of TP that were structurally modified to penetrate the brain-induced messenger RNA and protein levels for a battery of Nrf2-dependent cytoprotective genes reduced MPTP-induced oxidative stress and inflammation, and ameliorated dopaminergic neurotoxicity in mice. The neuroprotective effect of these TP against MPTP neurotoxicity was dependent on Nrf2, since treatment with TP in Nrf2 knockout mice failed to block against MPTP neurotoxicity and induce Nrf2-dependent cytoprotective genes.

INNOVATION

Extremely potent synthetic TP that are direct activators of the Nrf2 pathway block dopaminergic neurodegeneration in the MPTP mouse model of PD.

CONCLUSION

Our results indicate that activation of Nrf2/antioxidant response element (ARE) signaling by synthetic TP is directly associated with their neuroprotective effects against MPTP neurotoxicity and suggest that targeting the Nrf2/ARE pathway is a promising approach for therapeutic intervention in PD.

NADPH oxidase and Nrf2 regulate gastric aspiration-induced inflammation and acute lung injury

Recruitment of neutrophils and release of reactive oxygen species are considered to be major pathogenic components driving acute lung injury (ALI). However, NADPH oxidase, the major source of reactive oxygen species in activated phagocytes, can paradoxically limit inflammation and injury. We hypothesized that NADPH oxidase protects against ALI by limiting neutrophilic inflammation and activating Nrf2, a transcriptional factor that induces antioxidative and cytoprotective pathways. Our objective was to delineate the roles of NADPH oxidase and Nrf2 in modulating acute lung inflammation and injury in clinically relevant models of acute gastric aspiration injury, a major cause of ALI. Acid aspiration caused increased ALI (as assessed by bronchoalveolar lavage fluid albumin concentration) in both NADPH oxidase-deficient mice and Nrf2(-/-) mice compared with wild-type mice. NADPH oxidase reduced airway neutrophil accumulation, but Nrf2 decreased ALI without affecting neutrophil recovery. Acid injury resulted in a 120-fold increase in mitochondrial DNA, a proinflammatory and injurious product of cellular necrosis, in cell-free bronchoalveolar lavage fluid. Pharmacologic activation of Nrf2 by the triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9 (11)-dien-28-oyl]imidazole limited aspiration-induced ALI in wild-type mice and reduced endothelial cell injury caused by mitochondrial extract-primed human neutrophils, leading to the conclusion that NADPH oxidase and Nrf2 have coordinated, but distinct, functions in modulating inflammation and injury. These results also point to Nrf2 as a therapeutic target to limit ALI by attenuating neutrophil-induced cellular injury.

ΔNp63α-mediated activation of bone morphogenetic protein signaling governs stem cell activity and plasticity in normal and malignant mammary epithelial cells

Genetic analysis of TP63 indicates that ΔNp63 isoforms are required for preservation of regenerative stasis within diverse epithelial tissues. In squamous carcinomas, TP63 is commonly amplified, and ΔNp63α confers a potent survival advantage. Genome-wide occupancy studies show that ΔNp63 promotes bidirectional target gene regulation by binding more than 5,000 sites throughout the genome; however, the subset of targets mediating discreet activities of TP63 remains unclear. We report that ΔNp63α activates bone morphogenic proteins (BMP) signaling by inducing the expression of BMP7. Immunohistochemical analysis indicates that hyperactivation of BMP signaling is common in human breast cancers, most notably in the basal molecular subtype, as well as in several mouse models of breast cancer. Suppression of BMP signaling in vitro with LDN193189, a small-molecule inhibitor of BMP type I receptor kinases, represses clonogenicity and diminishes the cancer stem cell-enriched ALDH1(+) population. Importantly, LDN193189 blocks reconstitution of mixed ALDH1(+)/ALDH1(-) cultures indicating that BMP signaling may govern aspects of cellular plasticity within tumor hierarchies. These results show that BMP signaling enables reversion of committed populations to a stem-like state, potentially supporting progression and maintenance of tumorigenesis. Treatment of a mouse model of breast cancer with LDN193189 caused reduced expression of markers associated with epithelial-to-mesenchymal transition (EMT). Furthermore, in vivo limiting dilution analysis assays revealed that LDN193189 treatment suppressed tumor-initiating capacity and increased tumor latency. These studies support a model in which ΔNp63α-mediated activation of BMP signaling governs epithelial cell plasticity, EMT, and tumorigenicity during breast cancer initiation and progression.

The combination of the histone deacetylase inhibitor vorinostat and synthetic triterpenoids reduces tumorigenesis in mouse models of cancer

Novel drugs and drug combinations are needed for the chemoprevention and treatment of cancer. We show that the histone deacetylase inhibitor vorinostat [suberoylanilide hydroxamic acid (SAHA)] and the methyl ester or ethyl amide derivatives of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Me and CDDO-Ea, respectively) cooperated to inhibit the de novo synthesis of nitric oxide in RAW 264.7 macrophage-like cells and in primary mouse peritoneal macrophages. Additionally, SAHA enhanced the ability of synthetic triterpenoids to delay formation of estrogen receptor-negative mammary tumors in MMTV-polyoma middle T (PyMT) mice. CDDO-Me (50 mg/kg diet) and SAHA (250 mg/kg diet) each significantly delayed the initial development of tumors by 4 (P < 0.001) and 2 (P < 0.05) weeks, respectively, compared with the control group in the time required to reach 50% tumor incidence. CDDO-Ea (400 mg/kg diet), as a single agent, did not delay tumor development. The combination of either triterpenoid with SAHA was significantly more potent than the individual drugs for delaying tumor development, with a 7 week (P < 0.001) delay before 50% tumor incidence was reached. SAHA, alone and in combination with CDDO-Me, also significantly (P < 0.05) inhibited the infiltration of tumor-associated macrophages into the mammary glands of PyMT mice and levels of the chemokine macrophage colony-stimulating factor in primary PyMT tumor cells. In addition, SAHA and the synthetic triterpenoids cooperated to suppress secreted levels of the pro-angiogenic factor matrix metalloproteinase-9. Similar results were observed in mouse models of pancreatic and lung cancer. At concentrations that were anti-inflammatory, SAHA had no effect on histone acetylation. These studies suggest that both SAHA and triterpenoids effectively delay tumorigenesis, thereby demonstrating a promising, novel drug combination for chemoprevention.

Synthetic oleanane triterpenoids: multifunctional drugs with a broad range of applications for prevention and treatment of chronic disease

We review the rationale for the use of synthetic oleanane triterpenoids (SOs) for prevention and treatment of disease, as well as extensive biological data on this topic resulting from both cell culture and in vivo studies. Emphasis is placed on understanding mechanisms of action. SOs are noncytotoxic drugs with an excellent safety profile. Several hundred SOs have now been synthesized and in vitro have been shown to: 1) suppress inflammation and oxidative stress and therefore be cytoprotective, especially at low nanomolar doses, 2) induce differentiation, and 3) block cell proliferation and induce apoptosis at higher micromolar doses. Animal data on the use of SOs in neurodegenerative diseases and in diseases of the eye, lung, cardiovascular system, liver, gastrointestinal tract, and kidney, as well as in cancer and in metabolic and inflammatory/autoimmune disorders, are reviewed. The importance of the cytoprotective Kelch-like erythroid cell-derived protein with CNC homology-associated protein 1/nuclear factor (erythroid-derived 2)-like 2/antioxidant response element (Keap1/Nrf2/ARE) pathway as a mechanism of action is explained, but interactions with peroxisome proliferator-activated receptor γ (PARPγ), inhibitor of nuclear factor-κB kinase complex (IKK), janus tyrosine kinase/signal transducer and activator of transcription (JAK/STAT), human epidermal growth factor receptor 2 (HER2)/ErbB2/neu, phosphatase and tensin homolog (PTEN), the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway, mammalian target of rapamycin (mTOR), and the thiol proteome are also described. In these interactions, Michael addition of SOs to reactive cysteine residues in specific molecular targets triggers biological activity. Ultimately, SOs are multifunctional drugs that regulate the activity of entire networks. Recent progress in the earliest clinical trials with 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO) methyl ester (bardoxolone methyl) is also summarized.

NRF2 and cancer: the good, the bad and the importance of context

Many studies of chemopreventive drugs have suggested that their beneficial effects on suppression of carcinogenesis and many other chronic diseases are mediated through activation of the transcription factor NFE2-related factor 2 (NRF2). More recently, genetic analyses of human tumours have indicated that NRF2 may conversely be oncogenic and cause resistance to chemotherapy. It is therefore controversial whether the activation, or alternatively the inhibition, of NRF2 is a useful strategy for the prevention or treatment of cancer. This Opinion article aims to rationalize these conflicting perspectives by critiquing the context dependence of NRF2 functions and the experimental methods behind these conflicting data.

Pharmacological induction of heme oxygenase-1 by a triterpenoid protects neurons against ischemic injury

BACKGROUND AND PURPOSE

Heme oxygenase-1 (HO-1) is an inducible Phase 2 enzyme that degrades toxic heme; its role in cerebral ischemia is not fully understood. We hypothesize that chemically induced HO-1 upregulation with the novel triterpenoid CDDO-Im (2-cyano-3,12 dioxooleana-1,9 dien-28-oyl imidazoline), a robust inducer of Phase 2 genes, protects neurons against ischemic injury.

METHODS

Using 3 different models of ischemia, including oxygen-glucose deprivation in neuronal cultures, global ischemia in rats, and focal ischemia in mice, we determined (1) whether CDDO-Im induces HO-1 expression and protects against ischemic injury; and (2) whether HO-1 inhibition disrupts the neuroprotective effect of CDDO-Im.

RESULTS

CDDO-Im treatment (50-300 nmol/L) resulted in 8-fold HO-1 upregulation in cultured neurons and protected against oxygen-glucose deprivation. The protection was abolished when the cultures were transfected with nuclear factor (erythroid-derived 2) like-2-shRNA or coincubated with tin protoporphyrin IX, a specific HO-1 inhibitor. In the rat model of global ischemia, intracerebroventricular infusion of CDDO-Im (0.5-1.5 μg) augmented HO-1 expression in hippocampal neurons and resulted in significant increases in CA1 neuronal survival after global ischemia. To further strengthen the clinical relevance of the CDDO-Im treatment, we tested its effects in the mouse model of temporary focal ischemia (60 minutes). Postischemic intraperitoneal injection of CDDO-Im (10-100 μg) enhanced HO-1 expression and significantly reduced neurological dysfunction and infarct volume. Intracerebroventricular infusion of tin protoporphyrin IX reduced the neuroprotective effect of CDDO-Im against global and focal ischemia.

CONCLUSIONS

CDDO-Im confers neuroprotection against ischemic injury by upregulating HO-1, suggesting that enhance of HO-1 expression may be a legitimate strategy for therapeutic intervention of stroke.

The synthetic triterpenoid CDDO-methyl ester delays estrogen receptor-negative mammary carcinogenesis in polyoma middle T mice

Novel drugs are needed for the prevention and treatment of breast cancer. Synthetic triterpenoids are a promising new class of compounds with activity in a variety of preclinical cancer models. We tested activity of the methyl ester derivative of the synthetic triterpenoid, 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Me), in a relevant model of estrogen receptor-negative breast cancer, the polyoma-middle T (PyMT), in which the oncoprotein drives carcinogenesis. The developing tumors recapitulate key features of the human disease. Mice were fed CDDO-Me (50 mg/kg diet), starting at 4 weeks of age. CDDO-Me significantly increased the age of mice at onset of first tumor (P < 0.001) by an average of 4.3 weeks and overall survival (P < 0.001) by 5.2 weeks. The drug also inhibited the infiltration of tumor-associated macrophages into mammary glands of PyMT mice at 12 weeks of age and reduced levels of the chemokines CXCL12 and CCL2 in primary PyMT mammary tumor cells. Treatment with this multifunctional drug also inhibited secretion of matrix metalloproteinase-9 in primary tumor cells from PyMT mice and decreased proliferation of these cells by inhibiting cyclin D1 and decreasing phosphorylation of epidermal growth factor receptor and STAT3.

Triterpenoid modulation of IL-17 and Nrf-2 expression ameliorates neuroinflammation and promotes remyelination in autoimmune encephalomyelitis

Inflammatory cytokines and endogenous anti-oxidants are variables affecting disease progression in multiple sclerosis (MS). Here we demonstrate the dual capacity of triterpenoids to simultaneously repress production of IL-17 and other pro-inflammatory mediators while exerting neuroprotective effects directly through Nrf2-dependent induction of anti-oxidant genes. Derivatives of the natural triterpene oleanolic acid, namely CDDO-trifluoroethyl-amide (CDDO-TFEA), completely suppressed disease in a murine model of MS, experimental autoimmune encephalomyelitis (EAE), by inhibiting Th1 and Th17 mRNA and cytokine production. Encephalitogenic T cells recovered from treated mice were hypo-responsive to myelin antigen and failed to adoptively transfer the disease. Microarray analyses showed significant suppression of pro-inflammatory transcripts with concomitant induction of anti-inflammatory genes including Ptgds and Hsd11b1. Finally, triterpenoids induced oligodendrocyte maturation in vitro and enhanced myelin repair in an LPC-induced non-inflammatory model of demyelination in vivo. These results demonstrate the unique potential of triterpenoid derivatives for the treatment of neuroinflammatory disorders such as MS.

Abstract A103: The synthetic triterpenoid CDDO-methyl ester targets tumor-associated macrophages to delay carcinogenesis in the PyMT model of estrogen receptor negative breast cancer

Breast cancer is the most common cancer among women in the United States. The incidence rates of breast cancer are no longer significantly declining, and approximately 40,000 women die from the disease each year. Hence, novel drugs are needed for the prevention and treatment of the disease. Synthetic triterpenoids are a promising new class of compounds with chemopreventive activity in a variety of preclinical cancer models. We tested the methyl ester derivative of the synthetic triterpenoid, 2-cyano-3, 12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Me), in a relevant model of ER-negative breast cancer. In this mouse model, the polyoma-middle T (PyMT) oncoprotein drives carcinogenesis in the mammary gland. The developing tumors recapitulate key features of the human disease including significant infiltration of tumor-associated macrophages (TAM). Depletion of TAMs has been previously shown to delay tumor progression. PyMT mice were fed CDDO-Me (50 mg/kg diet), starting at 4 weeks of age. CDDO-Me significantly increased the age of mice at onset of first tumor by an average of 4.3 weeks (P &lt; 0.001) and overall survival by 5.2 weeks (P &lt; 0.001). CDDO-Me significantly (P &lt; 0.05) inhibited the infiltration of TAMs into mammary glands of PyMT mice along with levels of the chemokines CXCL12 and CCL2 in primary PyMT mammary tumor cells. Treatment with CDDO-Me also inhibited secretion of MMP-9 in primary tumor cells from PyMT mice and decreased proliferation of these cells by inhibiting cyclin D1 and decreasing phosphorylation of EGFR and STAT3, key breast cancer biomarkers. Thus, CDDO-Me delayed breast carcinogenesis via inhibition of TAM infiltration and by inhibition of key pathways in breast carcinogenesis. Taken together, these findings implicate CDDO-Me as a promising chemopreventive agent for ER-negative breast cancer via inhibition of TAM infiltration and diverse oncogenic pathways.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):A103.

Abstract B76: Synthetic triterpenoids as candidate drugs for cancer prevention and treatment

Angiogenesis is a limiting step for the switch from a dormant to malignant state in tumor progression. During tumor development tumor cells induce profound changes in the surrounding tissue, leading to the formation of an altered tumor microenvironment that is critical in permitting further tumor growth and tumor progression. Retinoblastoma (Rb) and colorectal cancer (CRC) display the complexity of the microenvironment constituted by different cell types and their extracellular matrix.

Here we assessed the efficacy of two synthetic derivates of triterpenoid CDDO, CDDO-Im and CDDO-Me, on endothelial, retinoblastoma and colon cancer cells in order to evaluate their effect on angiogenesis, cancer progression and metastatic dissemination.

We observed that CDDO-Im and CDDO-Me inhibited endothelial cells proliferation, migration and tube-formation, hampering the nuclear translocation of NF-kB and affecting the MAPK pathway. In vivo, in a matrigel sponge assay CDDO-Im interfered with angiogenesis when administrated into the pellets or by intraperitoneal injection.

To assess whether these compounds could successfully impairs neuroectodermal-derived tumor growth, we performed in vitro experiments on Y79 and Weri-Rb1 retinoblastoma cells. We performed MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] and LDH (Lactate Dehydrogenase) assays to evaluate CDDO-Im effect on retinoblastoma cell viability and an Annexin V and 7-Amino-Actinomycin D staining to test apoptosis. We observed that CDDO-Im treatment induced a reduction of cell viability at nanomolar doses and early and late apoptosis at different time points.

In order to overcome the side effects of standard chemotherapy drugs, such as vincristine sulphate, we evaluated if CDDO-Im could be used to lower chemotherapy doses. When we combined non-cytotoxic doses of CDDO-Im with vincristine sulphate we observed that after 72 hours of co-treatment, CDDO-Im was able to accomplish the same antiproliferative effect obtained using double doses of vincristine alone.

We also tested the in vitro anti-tumour activity of CDDO-Me on human adenocarcinoma HT29 cell line. The triterpenoid was used alone or in combination with 5FU (5 Fluorouracil), the major chemotherapeutic agent used for CRC therapy. We performed an MTT assay to evaluate its effect on cell viability, an apoptosis test and an alkaline comet assay to assess the potential genotoxic damage.

Preliminary results demonstrated that CDDO-Me induced an almost immediate inhibitory effect on HT29 cells, reducing cell viability already after 24 hours of treatment at 1000-fold lower concentration then 5FU. When HT29 were co-treated with both CDDO-Me and 5FU, no additive effects were observed. Respect to 5FU, CDDO-Me did not induce apoptosis even after long-term treatment, as well as genotoxicity, suggesting that it is able to block cell growth without exerting toxic effects.

These data suggest that the two synthetic triterpenoid CDDO-Im and CDDO-Me could be promising compounds for cancer treatment, acting both on cancer cells and on endothelial cells that support tumor-associated angiogenesis. Our results open the possibility to use chemopreventive molecules in combination with current chemotherapic drugs, to improve their efficacy without cytotoxicity.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):B76.

CDDO-methyl ester delays breast cancer development in BRCA1-mutated mice

The breast cancer-associated gene 1 (BRCA1) is the most frequently mutated tumor suppressor gene in familial breast cancers. Mutations in BRCA1 also predispose to other types of cancers, pointing to a fundamental role of this pathway in tumor suppression and emphasizing the need for effective chemoprevention in these high-risk patients. Because the methyl ester of the synthetic triterpenoid 2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oic acid (CDDO-Me) is a potent chemopreventive agent, we tested its efficacy in a highly relevant mouse model of BRCA1-mutated breast cancer. Beginning at 12 weeks of age, Brca1(Co/Co); MMTV-Cre;p53(+/-) mice were fed powdered control diet or diet containing CDDO-Me (50 mg/kg diet). CDDO-Me significantly (P < 0.05) delayed tumor development in the Brca1-mutated mice by an average of 5.2 weeks. We also observed that levels of ErbB2, p-ErbB2, and cyclin D1 increased in a time-dependent manner in the mammary glands in Brca1-deficient mice, and CDDO-Me inhibited the constitutive phosphorylation of ErbB2 in tumor tissues from these mice. In BRCA1-deficient cell lines, the triterpenoids directly interacted with ErbB2, decreased constitutive phosphorylation of ErbB2, inhibited proliferation, and induced G(0)-G(1) arrest. These results suggest that CDDO-Me has the potential to prevent BRCA1-mutated breast cancer.

Tumor-infiltrating myeloid cells induce tumor cell resistance to cytotoxic T cells in mice

Cancer immunotherapeutic approaches induce tumor-specific immune responses, in particular CTL responses, in many patients treated. However, such approaches are clinically beneficial to only a few patients. We set out to investigate one possible explanation for the failure of CTLs to eliminate tumors, specifically, the concept that this failure is not dependent on inhibition of T cell function. In a previous study, we found that in mice, myeloid-derived suppressor cells (MDSCs) are a source of the free radical peroxynitrite (PNT). Here, we show that pre-treatment of mouse and human tumor cells with PNT or with MDSCs inhibits binding of processed peptides to tumor cell-associated MHC, and as a result, tumor cells become resistant to antigen-specific CTLs. This effect was abrogated in MDSCs treated with a PNT inhibitor. In a mouse model of tumor-associated inflammation in which the antitumor effects of antigen-specific CTLs are eradicated by expression of IL-1β in the tumor cells, we determined that therapeutic failure was not caused by more profound suppression of CTLs by IL-1β-expressing tumors than tumors not expressing this proinflammatory cytokine. Rather, therapeutic failure was a result of the presence of PNT. Clinical relevance for these data was suggested by the observation that myeloid cells were the predominant source of PNT in human lung, pancreatic, and breast cancer samples. Our data therefore suggest what we believe to be a novel mechanism of MDSC-mediated tumor cell resistance to CTLs.

Proteomic analysis shows synthetic oleanane triterpenoid binds to mTOR

New multifunctional drugs that target multiple disease-relevant networks offer a novel approach to the prevention and treatment of many diseases. New synthetic oleanane triterpenoids (SO), such as CDDO (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid) and its derivatives, are multifunctional compounds originally developed for the prevention and treatment of inflammation and oxidative stress. However, the protein binding partners and mechanisms of action of these SO are not yet fully understood. Here we characterize the putative target profile of one SO, CDDO-Imidazolide (CDDO-Im), by combining affinity purification with mass spectroscopic proteomic analysis to identify 577 candidate binding proteins in whole cells. This SO pharmaco-interactome consists of a diverse but interconnected set of signaling networks; bioinformatic analysis of the protein interactome identified canonical signaling pathways targeted by the SO, including retinoic acid receptor (RAR), estrogen receptor (ER), insulin receptor (IR), janus kinase/signal transducers and activators of transcription (JAK/STAT), and phosphatase and tensin homolog (PTEN). Pull-down studies then further validated a subset of the putative targets. In addition, we now show for the first time that the mammalian target of rapamycin (mTOR) is a direct target of CDDO-Im. We also show that CDDO-Im blocks insulin-induced activation of this pathway by binding to mTOR and inhibiting its kinase activity. Our basic studies confirm that the SO, CDDO-Im, acts on a protein network to elicit its pharmacological activity.

Nrf2 has a protective role against neuronal and capillary degeneration in retinal ischemia-reperfusion injury

Retinal ischemia-reperfusion (I/R) involves an extensive increase in reactive oxygen species as well as proinflammatory changes that result in significant histopathologic damage, including neuronal and vascular degeneration. Nrf2 has a well-known cytoprotective role in many tissues, but its protective function in the retina is unclear. We investigated the possible role of Nrf2 as a protective mechanism in retinal ischemia-reperfusion injury using Nrf2(-/-) mice. I/R resulted in an increase in retinal levels of superoxide and proinflammatory mediators, as well as leukocyte infiltration of the retina and vitreous, in Nrf2(+/+) mice. These effects were greatly accentuated in Nrf2(-/-) mice. With regard to histopathologic damage, Nrf2(-/-) mice exhibited loss of cells in the ganglion cell layer and markedly accentuated retinal capillary degeneration, as compared to wild-type. Treatment with the Nrf2 activator CDDO-Me increased antioxidant gene expression and normalized I/R-induced superoxide in the retina in wild-type but not Nrf2(-/-) mice. CDDO-Me treatment abrogated retinal capillary degeneration induced by I/R in wild-type but not Nrf2(-/-) mice. These studies indicate that Nrf2 is an important cytoprotective mechanism in the retina in response to ischemia-reperfusion injury and suggest that pharmacologic induction of Nrf2 could be a new therapeutic strategy for retinal ischemia-reperfusion and other retinal diseases.

CDDO-imidazolide induces DNA damage, G2/M arrest and apoptosis in BRCA1-mutated breast cancer cells

Breast cancer-associated gene 1 (BRCA1) protein plays important roles in DNA damage and repair, homologous recombination, cell-cycle regulation, and apoptosis. The synthetic triterpenoid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]imidazole (CDDO-Imidazolide, CDDO-Im) is a promising anticancer and chemopreventive agent with potent antiproliferative and apoptotic activities against a wide variety of cancer types. However, the mechanisms responsible for the selective apoptotic effects of CDDO-Im in cancer cells remain elusive. In the present work, CDDO-Im induced G2/M arrest and apoptosis in BRCA1-mutated mammary tumor cell lines. Prior to the induction of apoptosis, CDDO-Im induced DNA damage and the phosphorylation of H2AX followed by activation of the DNA damage response. Moreover, CDDO-Im also induced the generation of reactive oxygen species (ROS), which is associated with the induction of DNA damage, in both mouse and human tumor cells containing a BRCA1 mutation. The inhibition of ROS generation by uric acid prevented the induction of DNA damage by CDDO-Im. Furthermore, treatment with CDDO-Im did not induce ROS in nonmalignant MCF-10A breast epithelial cells or in E18-14C-27 breast cancer cells with wild-type BRCA1 genes and was not cytotoxic to normal mouse 3T3 fibroblasts, highlighting a selective therapeutic potential of CDDO-Im for BRCA1-associated breast cancer cells. Altogether, our results show that CDDO-Im induces ROS and subsequent DNA damage, thereby facilitating the activation of the DNA damage checkpoint, G2/M arrest, and finally apoptosis in BRCA1-mutated cancer cells. The particular relevance of these findings to the chemoprevention of cancer is discussed. Cancer Prev Res; 4(3); 425-34. ©2011 AACR.

Abstract 2523: Synthetic triterpenoids protect against toxicity and enhance the efficacy of treatment with carboplatin/paclitaxel in experimental lung cancer

Lung cancer remains the leading cause of cancer deaths worldwide, with no real improvement in 5 yr survival rates in over 30 yrs. While prevention offers the most promising approach for reducing mortality, new drugs are clearly needed. We have previously shown that synthetic triterpenoids, including the methyl ester (Me) and ethyl amide (EA) of CDDO (2-cyano-3,12-dioxooleana-1,9-dien-28-oic acid), are effective for prevention and treatment of experimental lung cancer; CDDO-Me is currently in early clinical trials. When used for treatment of lung cancer in A/J mice, the triterpenoids caused growth-arrest rather than tumor regression, so we tested the triterpenoids in combination with carboplatin and paclitaxel, standard chemotherapeutic agents used to treat human lung cancer. Female A/J mice were injected i.p. with vinyl carbamate to induce lung cancer; adenocarcinomas are visible on lung sections as early as 4 wks after initiation. In a pilot study, mice were fed triterpenoids and received 5 injections of carboplatin (50 mg/kg) and paclitaxel (15 mg/kg), one wk apart, beginning eight wks after initiation. This protocol was toxic in the mice treated with carboplatin/paclitaxel alone, as only 38% (3 of 8) mice survived. In contrast, 88% (14 of 16) of the mice survived when treated with triterpenoids in combination with carboplatin/ paclitaxel. In a second study, lung cancer was induced by vinyl carbamate, but treatment was delayed until 12 wks after initiation, and the 5 carboplatin/ paclitaxel injections were given every other wk instead of every wk. Survival improved to 91% in the carboplatin/paclitaxel group (21 of 23 mice) and was 97% (31 of 32 mice) in the groups given triterpenoid in combination with carboplatin/paclitaxel. Although treatment with carboplatin/paclitaxel alone significantly (P &lt; 0.05) reduced total tumor volume by 81% compared to the control group (16.1 mm3 for the controls vs. 3.1 mm3 for the group treated with carboplatin/paclitaxel), treatment with the combination of CDDO-EA (800 mg/kg diet) and carboplatin/paclitaxel reduced tumor volume to 1.1 mm3, a 93% reduction compared to the controls (P &lt; 0.05 vs. control and carboplatin/paclitaxel alone). In VC1 lung cancer cells derived from a tumor from an A/J mouse, CDDO-EA directly interacted with IKK and cyclin D1, blocked the degradation of IKBα in cells treated with TNFα, decreased inhibited proliferation by decreasing cyclin D1 levels and increasing p21, and induced apoptosis. Ongoing studies will determine whether the combination of CDDO-EA and carboplatin/paclitaxel induces apoptosis in these tumors in vivo and will explore the mechanisms of action for the protection of the triterpenoids against carboplatin/paclitaxel toxicity in normal tissues while simultaneously enhancing the therapeutic effect in lung cancer. Supported by NIH grant R01 CA78814 and Reata Pharmaceuticals, Inc.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2523. doi:10.1158/1538-7445.AM2011-2523