Abstract PS18-32: Hyperleptinemia in obese state renders luminal breast cancers refractory to tamoxifen coordinating a crosstalk between Med1, miR205 and Erb B kinases

Background and Aim: Obese state is associated with increased breast cancer growth, metastasis, and poor overall survival. In this study, we seek to decipher the underlying molecular mechanisms by which obesity/hyperleptinemia reduces the efficacy of tamoxifen. Methods: The impact of obesity on tamoxifen was evaluated utilizing clonogenicity, high-fat-diet- induced obese mice and leptin-treated xenograft-models. Mechanistic studies involved immunoblotting, real-time PCR, immunocytochemistry, chromatin immunoprecipitation assay, phosphokinase array and in silico analysis. Results: Obese mice with hyperleptinemia exhibit increased tumor progression and respond poorly to tamoxifen compared to non-obese mice. Exogenous leptin abrogates tamoxifen-mediated growth inhibition and potentiates breast tumor growth even in the presence of tamoxifen. Mechanistically, leptin induces nuclear translocation of phosphorylated-ER and increases the expression of ER-responsive genes while reducing tamoxifen-mediated gene repression by abrogating tamoxifen-induced recruitment of corepressors NCoR, SMRT and Mi2. Further, we found that coactivator Med1 potentially associates with 48 (out of 75) obesity-signature genes. Interestingly, leptin upregulates Med1 expression by decreasing miR-205 and increases its functional activation via phosphorylation that is mediated by activation of Her2 and EGFR. It is important to note that Med1 silencing abrogates the negative effects of leptin on tamoxifen efficacy. Additionally, honokiol or adiponectin treatment effectively inhibits leptin-induced Med1 expression and improve tamoxifen efficacy in hyperleptinemic state.Conclusion: In conclusion, these studies show the molecular mechanisms by which obese/hyperleptinemic state may contribute to poor response to tamoxifen implicating leptin-miR205-Med1 and leptin-Her2-EGFR-Med1 axes and present bioactive compound honokiol and adipocytokine adiponectin as agents that can block leptin’s negative effect on tamoxifen.

Citation Format: Arumugam Nagalingam, Nethaji Muniraj, Sumit Siddharth, Dimiter Avtanski, Sheetal Parida, Pajamurthy Kuppusamy, Neeraj K Saxena, Nethaji Muniraj. Hyperleptinemia in obese state renders luminal breast cancers refractory to tamoxifen coordinating a crosstalk between Med1, miR205 and Erb B kinases [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS18-32.

Induction of STK11-dependent cytoprotective autophagy in breast cancer cells upon honokiol treatment

Cancer cells hijack autophagy pathway to evade anti-cancer therapeutics. Many molecular signaling pathways associated with drug-resistance converge on autophagy induction. Honokiol (HNK), a natural phenolic compound purified from Magnolia grandiflora, has recently been shown to impede breast tumorigenesis and, in the present study, we investigated whether breast cancer cells evoke autophagy to modulate therapeutic efficacy and functional networks of HNK. Indeed, breast cancer cells exhibit increased autophagosomes-accumulation, MAP1LC3B-II/LC3B-II-conversion, expression of ATG proteins as well as elevated fusion of autophagosomes and lysosomes upon HNK treatment. Breast cancer cells treated with HNK demonstrate significant growth inhibition and apoptotic induction, and these biological processes are blunted by macroautophagy/autophagy. Consequently, inhibiting autophagosome formation, abrogating autophagosome-lysosome fusion or genetic-knockout of BECN1 and ATG7 effectively increase HNK-mediated apoptotic induction and growth inhibition. Next, we explored the functional impact of tumor suppressor STK11 in autophagy induction in HNK-treated cells. STK11-silencing abrogates LC3B-II-conversion, and blocks autophagosome/lysosome fusion and lysosomal activity as illustrated by LC3B-Rab7 co-staining and DQ-BSA assay. Our results exemplify the cytoprotective nature of autophagy invoked in HNK-treated breast cancer cells and put forth the notion that a combined strategy of autophagy inhibition with HNK would be more effective. Indeed, HNK and chloroquine (CQ) show synergistic inhibition of breast cancer cells and HNK-CQ combination treatment effectively inhibits breast tumorigenesis and metastatic progression. Tumor-dissociated cells from HNK-CQ treated tumors exhibit abrogated invasion and migration potential. Together, these results implicate that breast cancer cells undergo cytoprotective autophagy to circumvent HNK and a combined treatment with HNK and CQ can be a promising therapeutic strategy for breast cancer.

Withaferin A inhibits lysosomal activity to block autophagic flux and induces apoptosis via energetic impairment in breast cancer cells

Withaferin A (WFA), a steroidal lactone, negatively regulates breast cancer growth however, its mechanisms of action remain largely elusive. We found that WFA blocks autophagy flux and lysosomal proteolytic activity in breast cancer cells. WFA increases accumulation of autophagosomes, LC3B-II conversion, expression of autophagy-related proteins and autophagosome/lysosome fusion. Autolysosomes display the characteristics of acidic compartments in WFA-treated cells; however, the protein degradation activity of lysosomes is inhibited. Blockade of autophagic flux reduces the recycling of cellular fuels leading to insufficient substrates for tricarboxylic acid (TCA) cycle and impaired oxidative phosphorylation. WFA decreases expression and phosphorylation of lactate dehydrogenase, the key enzyme that catalyzes pyruvate-to-lactate conversion, reduces adenosine triphosphate levels and increases AMP-activated protein kinase (AMPK) activation. AMPK inhibition abrogates while AMPK activation potentiates WFA's effect. WFA and 2-deoxy-d-glucose combination elicits synergistic inhibition of breast cancer cells. Genetic knockout of BECN1 and ATG7 fails to rescue cells from WFA treatment; in contrast, addition of methyl pyruvate to supplement TCA cycle protects WFA-treated cells. Together, these results implicate that WFA is a potent lysosomal inhibitor; energetic impairment is required for WFA-induced apoptosis and growth inhibition and combining WFA and 2-DG is a promising therapeutic strategy for breast cancer.

Abstract 4271: Induction of STK11-dependent cytoprotective autophagy in breast cancer cells upon Honokiol treatment

Background and Aim: Honokiol, a natural phenolic compound isolated from an extract of seed cones from Magnolia grandiflora, is widely known for its therapeutic potential as an antioxidant, anti-inflammatory, antithrombosis, and anti-depressant agent. Our recent studies show that honokiol impedes breast carcinogenesis. Cancer cells undergo cytoprotective autophagy and evade chemotherapy therefore many clinical trials are investigating the efficacy of autophagy inhibition in combination with chemotherapy. In the present study, we investigated the involvement of autophagic process in honokiol-mediated functional networks in breast cancer and explored the efficacy of combination regimens involving honokiol and chloroquine.

Methods: Autophagy studies were conducted utilizing immunoblot, RT-PCR, immunofluorescence analyses, confocal imaging and transmission electron microscopy for autophagy markers. Autophagic flux was analyzed using a plasmid tfLC3B and acridine orange staining. The fusion of autophagosome and lysosome was examined by using GFP-LC3/LysoTracker-red. Functional impact of autophagic process was evaluated using genetic knockout (KO) of AGT7 and BECN1 in MCF7 cells as well as combined treatment with autophagy inhibitors (3-MA, Baf-1 and CQ) and honokiol. Alterations in ATP levels were measured by ATPliteTM luminescence assay. In vivo studies using mammary gland implantation of cancer cells in NOD-SCID mice were conducted to evaluate the efficacy of combination regimen of Honokiol and Chloroquine.

Results: We found that Honokiol induces autophagy flux, increases accumulation of autophagosomes and elevates LC3B-II-conversion. Utilizing tandem-mCherry-GFP-LC3B assay and LysoTracker Red-staining, we observed that honokiol increases the autophagosome/lysosome fusion in breast cancer cells. We found that Honokiol induces autophagic response in a STK11-dependent manner as STK11-null breast cancer cells do not exhibit LC3B-II-puncta in response to Honokiol. Next, we explored the functional impact of autophagy in Honokiol mediated breast cancer inhibition and found that inhibiting autophagosome formation, abrogating autophagosome-lysosome fusion or genetic-knockout of BECN1/Beclin1 and ATG7 effectively increases the efficacy of Honokiol. These results clearly showed the cytoprotective nature of Honokiol-mediated autophagy and put forth the notion that a combined strategy of autophagy-inhibition with Honokiol would be more effective. Indeed, our in vivostudies showed that a combined treatment with Honokiol and Chloroquine can effectively inhibit primary tumor growth as well as metastatic progression.

Conclusion: Together, these results implicate that honokiol is a potent inducer of cytoprotective autophagy and a combined treatment of honokiol and chloroquine is a promising therapeutic strategy for breast cancer.

Citation Format: Nethaji Muniraj, Marey Shriver, Arumugam Nagalingam, Sumit Siddharth, Sheetal Parida, Neeraj K Saxena, Dipali Sharma. Induction of STK11-dependent cytoprotective autophagy in breast cancer cells upon Honokiol treatment [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 4271.

Concomitant Inhibition of Cytoprotective Autophagy Augments the Efficacy of Withaferin A in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality, and despite recent advances in early diagnosis and therapeutics, HCC related morbidity and mortality rate continue to rise. Clearly, it is imperative to develop novel effective therapies for HCC to improve long-term survival of HCC patients. We found that Withaferin A (WFA), a bioactive compound derived from Withania somnifera, is an effective agent for HCC inhibition. Interestingly, we observed that in addition to inducing apoptotic cell death, WFA also induces autophagy in HCC cells. Utilizing mRFP-EGFP-LC3B, LC3B-GFP/Lysotracker and LC3B-GFP/Rab7-RFP, we show that WFA induces autophagosomes-lysosomes fusion. WFA-induced autolysosomes exhibit intact protein degradation activity as evident with cathepsin-D activation and DQ-BSA assays. Importantly, we present that inhibiting WFA-induced autophagy either by blocking autophagosome-formation or by elevating lysosomal pH (Chloroquine and Bafilomycin) enhances WFA-induced growth-inhibition and apoptosis, indicating the presence of cytoprotective autophagy. Indeed, WFA and CQ combination shows synergism and higher efficacy in comparison to either monotherapy. Collectively, we reveal that the efficacy of WFA is somewhat diminished by the concomitant induction of cytoprotective autophagy which can be successfully conquered by cotreatment with CQ, and we pave the way for development of a novel combination therapeutic strategy for HCC.

Abstract 1334: Withaferin A induces cytoprotective autophagy in hepatocellular cancer cells and concomitant autophagic inhibition augments the efficacy of Withaferin A in hepatocellular carcinoma

Background and Aim: Hepatocellular carcinoma (HCC) is the fifth most common cancer in the world and the third most common cause of cancer-related deaths. While multiple chemotherapeutic and targeted agents have been developed for other cancers, Sorafenib, an oral multikinase inhibitor, is the only approved agent for the treatment of advanced HCC. Clearly, it is imperative to develop novel effective therapeutic strategies for HCC to improve long-term survival of HCC patients. We found Withaferin A (WFA), a bioactive alkaloid derived from Withania somnifera, as an effective agent for HCC inhibition. Interestingly, we observed that WFA also induces autophagy in HCC cells. Autophagy can be cancer inducing or cancer inhibiting at the functional level. We aim to systemically investigate the anti-HCC efficacy of WFA, investigate the functional impact of autophagy and explore the efficacy of combined regimens of WFA and autophagic inhibitors.

Methods: Using in vitro and in vivo models, we established that WFA inhibits liver tumorigenesis. tfLC3B, LC3B-GFP/Lysotracker and LC3B/Rab7 were used to examine the fusion of autophagosomes with lysosomes. Cathepsin-D activation and DQ-BSA assays were conducted to analyze the protein degradation activity in lysosomes. Multiple cell based assays and Chou-Talalay synergy quantification assays were conducted to analyze the synergistic effect of WFA with autophagic inhibitors. IHC staining was used to study autophagic markers in vivo.

Results: WFA inhibited anchorage dependent cell growth in vitro and reduced the HCC tumor burden in vivo. In addition to inducing apoptotic cell death, WFA induced cleavage of Light Chain 3B (LC3B) and increased the expression of autophagic proteins (ATG5, ATG7 and Beclin1) both in vitro and in vivo. The redistribution of LC3B-GFP from cytosol to autophagosome demonstrated enhanced autophagosome formation in WFA treated cells. The fusion of autophagosome with lysosome was observed in WFA-treated HCC cells indicating autolysosome formation. WFA treated HCC cells exhibited elevated lysosomal degradation activity. Inhibiting autophagy either by blocking autophagosome formation or elevating lysosomal pH (CQ and BAF) enhanced WFA-induced growth inhibition and apoptosis indicating the presence of cytoprotective autophagy. Combination index analysis of WFA and CQ showed synergism and increased efficacy as compared to either monotherapy. These in vitro findings were corroborated with in vivo experiments.

Conclusion: Our results reveal that WFA inhibits hepatocellular carcinoma by apoptotic induction but the efficacy of WFA is somewhat abrogated by the concomitant induction of cytoprotective autophagy. Our preclinical findings present evidence to support WFA and chloroquine as an effective combination treatment regimen for HCC.

Citation Format: Sumit Siddharth, Nethaji Muniraj, Neeraj K. Saxena, Dipali Sharma. Withaferin A induces cytoprotective autophagy in hepatocellular cancer cells and concomitant autophagic inhibition augments the efficacy of Withaferin A in hepatocellular carcinoma [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 1334.

Abstract 1335: Withaferin A induces nonprotective autophagy in a STK11-independent manner and mediates breast cancer inhibition via energetic impairment

Background and Aim: Cancer cells undergo cytoprotective autophagy and evade chemotherapy therefore many clinical trials are investigating the efficacy of autophagy inhibition in combination with chemotherapy. At the functional level, autophagic process can be cytoprotective, cytotoxic, cytostatic or nonprotective. We investigated strategies to convert cellular autophagic response to non-protective autophagy which does not interfere with therapeutic regimens exploiting bioactive molecules.

Methods: Utilizing in vivo xenograft models, we established that Withaferin A (WA), a bioactive molecule from Withania Somnifera inhibits breast tumorigenesis. Autophagy studies were conducted utilizing immunoblot, RT-PCR, and immunofluorescence analyses for autophagy markers, transmission electron microscopy and confocal imaging. The fusion of autophagosome and lysosome was examined by using GFP-LC3/LysoTracker-red and GFP-LC3/mCherryRAB7A. Protein degradation activity of lysosomes and ATP levels were examined by DQ-BSA assay, Cathepsin activity and quantitative ATP assay.

Results: WA inhibited growth and induced apoptosis in breast cancer cells resulting in inhibition of breast carcinogenesis in vivo. Although WA increased tumor suppressor LKB1 which is known to be involved in autophagy, WA-mediated increased cleavage of Light Chain 3 type II (LC3-II) and punctated LC3-II staining was LKB1-independent. The redistribution of EGFP-LC3 from cytosol to autophagosome indicated increased formation of autophagosomes in WA-treated cells. However, WA-induced increased autophagosome-formation was not mediated by increased activation of autophagy by upstream processes but was due to blockade of lysosomal-degradation as evident by higher level of sequestosome 1 (SQSTM1/p62) and decreased turnover of LC3. WA was found to be a potent lysosomal deacidification agent capable of blocking autophagic flux. Accordingly, inhibiting autophagy by blocking formation of autophagosomes or elevating lysosomal pH did not interfere with WA-mediated growth-inhibition. WA blocked autophagic flux decreasing recycling of cellular fuels leading to reduced energy supply. Investigating this alternative mechanism, we discovered that indeed, WA reduced ATP levels and increased phosphorylation of AMP-activated protein kinase (AMPK). Modulating substrates for tricarboxylic acid (TCA) cycle with methyl pyruvate protected WA-treated cells while 2DG potentiated WA-induced cell death.

Conclusion: Our results indicate that WA induces a non-protective autophagy and blocks energy fuels in cancer cells by reducing ATP levels and inhibiting lysosomal acidification hence offering a three-pronged approach to facilitate cancer cell death. WA might be a useful strategic addition to chemotherapy regimens to evade cytoprotective effects of autophagy.

Citation Format: Nethaji Muniraj, Arumugam Nagalingam, Neeraj K. Saxena, Dipali Sharma. Withaferin A induces nonprotective autophagy in a STK11-independent manner and mediates breast cancer inhibition via energetic impairment [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 1335.

Concomitant activation of ETS-like transcription factor-1 and Death Receptor-5 via extracellular signal-regulated kinase in withaferin A-mediated inhibition of hepatocarcinogenesis in mice

Hepatocellular carcinoma (HCC) has the second lowest 5-year survival rate (~16%) of all tumor types partly owing to the lack of effective therapeutic agents. Withaferin A (WA) is a bioactive molecule derived from Withania somnifera and the present study is designed to systemically investigate the anti-HCC efficacy of WA. WA inhibited growth, migration and invasion of HCC cells. Using a phospho-kinase screening array, we discovered that WA increased phosphorylation of ERK and p38 in HCC. Further analyses revealed a key role of ERK leading to increased phosphorylation of p90-ribosomal S6 kinase (RSK) and a concomitant activation of ETS-like transcription factor-1(ELK1) and Death Receptor protein-5 (DR5) in HCC. Importantly, oral administration of WA effectively inhibited HepG2-xenografts and DEN-induced-HCC in C57BL/6 mice. Analyses of WA-treated HepG2-xenografts and DEN-induced-HCC tumors showed elevated levels of ERK, RSK, ELK1 and DR5 along with decreased expression of Ki67. In silico analyses of HCC, utilizing published profiling studies showed an inverse correlation between DR5 and Ki67. These data showed the efficacy of WA as an effective agent for HCC inhibition and provided first in vitro and in vivo evidence supporting the key role of a novel crosstalk between WA, ERK/RSK, ELK1, and DR5 in HCC inhibition.

ADIPOQ/adiponectin induces cytotoxic autophagy in breast cancer cells through STK11/LKB1-mediated activation of the AMPK-ULK1 axis

ADIPOQ/adiponectin, an adipocytokine secreted by adipocytes in the breast tumor microenvironment, negatively regulates cancer cell growth hence increased levels of ADIPOQ/adiponectin are associated with decreased breast cancer growth. However, its mechanisms of action remain largely elusive. We report that ADIPOQ/adiponectin induces a robust accumulation of autophagosomes, increases MAP1LC3B-II/LC3B-II and decreases SQSTM1/p62 in breast cancer cells. ADIPOQ/adiponectin-treated cells and xenografts exhibit increased expression of autophagy-related proteins. LysoTracker Red-staining and tandem-mCherry-GFP-LC3B assay show that fusion of autophagosomes and lysosomes is augmented upon ADIPOQ/adiponectin treatment. ADIPOQ/adiponectin significantly inhibits breast cancer growth and induces apoptosis both in vitro and in vivo, and these events are preceded by macroautophagy/autophagy, which is integral for ADIPOQ/adiponectin-mediated cell death. Accordingly, blunting autophagosome formation, blocking autophagosome-lysosome fusion or genetic-knockout of BECN1/Beclin1 and ATG7 effectively impedes ADIPOQ/adiponectin induced growth-inhibition and apoptosis-induction. Mechanistic studies show that ADIPOQ/adiponectin reduces intracellular ATP levels and increases PRKAA1 phosphorylation leading to ULK1 activation. AMPK-inhibition abrogates ADIPOQ/adiponectin-induced ULK1-activation, LC3B-turnover and SQSTM1/p62-degradation while AMPK-activation potentiates ADIPOQ/adiponectin's effects. Further, ADIPOQ/adiponectin-mediated AMPK-activation and autophagy-induction are regulated by upstream master-kinase STK11/LKB1, which is a key node in antitumor function of ADIPOQ/adiponectin as STK11/LKB1-knockout abrogates ADIPOQ/adiponectin-mediated inhibition of breast tumorigenesis and molecular analyses of tumors corroborate in vitro mechanistic findings. ADIPOQ/adiponectin increases the efficacy of chemotherapeutic agents. Notably, high expression of ADIPOQ receptor ADIPOR2, ADIPOQ/adiponectin and BECN1 significantly correlates with increased overall survival in chemotherapy-treated breast cancer patients. Collectively, these data uncover that ADIPOQ/adiponectin induces autophagic cell death in breast cancer and provide in vitro and in vivo evidence for the integral role of STK11/LKB1-AMPK-ULK1 axis in ADIPOQ/adiponectin-mediated cytotoxic autophagy.

Abstract 3301: A three-pronged attack on cancer cells: Induction of non-protective autophagy, inhibition of lysosomal acidification and promotion of energetic impairment

Background and Aim: Cancer cells undergo cytoprotective autophagy and evade chemotherapy therefore many clinical trials are investigating the efficacy of autophagy inhibition in combination with chemotherapy. At the functional level, autophagic process can be cytoprotective, cytotoxic, cytostatic or nonprotective. We investigated strategies to convert cellular autophagic response to non-protective autophagy which does not interfere with therapeutic regimens exploiting bioactive molecules.

Methods: Utilizing in vivo xenograft models, we established that Withaferin A (WA), a bioactive molecule from Withania Somnifera inhibits breast tumorigenesis. Autophagy studies were conducted utilizing immunoblot, RT-PCR, and immunofluorescence analyses for autophagy markers, transmission electron microscopy and confocal imaging. The fusion of autophagosome and lysosome was examined by using GFP-LC3/LysoTracker-red and GFP-LC3/mCherryRAB7A. Protein degradation activity of lysosomes and ATP levels were examined by DQ-BSA assay, Cathepsin activity and quantitative ATP assay.

Results: WA inhibited growth and induced apoptosis in breast cancer cells resulting in inhibition of breast carcinogenesis in vivo. Although WA increased tumor suppressor LKB1 which is known to be involved in autophagy, WA-mediated increased cleavage of Light Chain 3 type II (LC3-II) and punctated LC3-II staining was LKB1-independent. The redistribution of EGFP-LC3 from cytosol to autophagosome indicated increased formation of autophagosomes in WA-treated cells. However, WA-induced increased autophagosome-formation was not mediated by increased activation of autophagy by upstream processes but was due to blockade of lysosomal-degradation as evident by higher level of sequestosome 1 (SQSTM1/p62) and decreased turnover of LC3. WA was found to be a potent lysosomal deacidification agent capable of blocking autophagic flux. Accordingly, inhibiting autophagy by blocking formation of autophagosomes or elevating lysosomal pH did not interfere with WA-mediated growth-inhibition. WA blocked autophagic flux decreasing recycling of cellular fuels leading to reduced energy supply. Investigating this alternative mechanism, we discovered that indeed, WA reduced ATP levels and increased phosphorylation of AMP-activated protein kinase (AMPK). Modulating substrates for tricarboxylic acid (TCA) cycle with methyl pyruvate protected WA-treated cells while 2DG potentiated WA-induced cell death.

Conclusion: Our results indicate that WA induces a non-protective autophagy and blocks energy fuels in cancer cells by reducing ATP levels and inhibiting lysosomal acidification hence offering a three-pronged approach to facilitate cancer cell death. WA might be a useful strategic addition to chemotherapy regimens to evade cytoprotective effects of autophagy.

Citation Format: Nethaji Muniraj, Arumugam Nagalingam, Panjamurthy Kuppusamy, Neeraj K. Saxena, Dipali Sharma. A three-pronged attack on cancer cells: Induction of non-protective autophagy, inhibition of lysosomal acidification and promotion of energetic impairment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3301. doi:10.1158/1538-7445.AM2017-3301

Abstract 3319: Elevating adipokine adiponectin level can induce cytotoxic autophagy in breast cancer cells and potentiate the efficacy of chemotherapeutic regimens: preclinical studies

Adiponectin, an adipocytokine secreted by adipocytes in the breast tumor microenvironment, negatively regulates cancer cell growth hence increased levels of adiponectin are associated with decreased breast cancer growth. However, its mechanisms of action remain largely elusive. We report that adiponectin induces a robust accumulation of autophagosomes, increases LC3II and decreases p62/SQSTM1 in breast cancer cells. Adiponectin-treated cells and xenografts exhibit increased expression of autophagy-related proteins. Lysotracker-Red-staining and tandem-mCherry-GFP-LC3 assay show that autophagosomes/lysosomes fusion is augmented upon adiponectin treatment. Adiponectin significantly inhibits breast cancer growth and induces apoptosis both in vitro and in vivo, and these events are preceded by autophagy, which is integral for adiponectin-mediated cell death. Accordingly, blunting autophagosomes-formation, blocking autophagosomes-autolysosome fusion or genetic-knockout of BECN1/Beclin1/ATG7 effectively impedes adiponectin induced growth-inhibition and apoptosis-induction. Mechanistic studies show that adiponectin reduces intracellular ATP levels and increases AMPK phosphorylation leading to ATG1 activation. AMPK-inhibition abrogates adiponectin-induced ATG1-activation, LC3II-turnover and p62-degradation while AMPK-activation potentiates adiponectin’s effects. Further, adiponectin-mediated AMPK-activation and autophagy-induction are regulated by upstream master-kinase LKB1, which is a key node in anti-tumor function of adiponectin as LKB1-knockout abrogates adiponectin-mediated inhibition of breast tumorigenesis and molecular analyses of tumors corroborate in vitro mechanistic findings. Adiponectin increases the efficacy of chemotherapeutic agents. Notably, high expression of adiponectin receptor, adiponectin and BECN1 significantly correlates with increased overall survival in chemotherapy-treated breast cancer patients. Collectively, these data uncover that adiponectin induces autophagic cell death in breast cancer and provide in vitroa and in vivo evidence for the integral role of LKB1-AMPK-ATG1 axis in adiponectin-mediated cytotoxic-autophagy.

Citation Format: Seung J Chung, Ganji Purnachandra Nagaraju, Arumugam Nagalingam, Nethaji Muniraj, Panjamurthy Kuppusamy, Alyssa Walker, Juhyung woo, Balázs Győrffy, Edward Gabrielson, Neeraj K. Saxena, Dipali Sharma. Elevating adipokine adiponectin level can induce cytotoxic autophagy in breast cancer cells and potentiate the efficacy of chemotherapeutic regimens: preclinical studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3319. doi:10.1158/1538-7445.AM2017-3319

Activation of tumor suppressor LKB1 by honokiol abrogates cancer stem-like phenotype in breast cancer via inhibition of oncogenic Stat3

Tumor suppressor and upstream master kinase Liver kinase B1 (LKB1) plays a significant role in suppressing cancer growth and metastatic progression. We show that low-LKB1 expression significantly correlates with poor survival outcome in breast cancer. In line with this observation, loss-of-LKB1 rendered breast cancer cells highly migratory and invasive, attaining cancer stem cell-like phenotype. Accordingly, LKB1-null breast cancer cells exhibited an increased ability to form mammospheres and elevated expression of pluripotency-factors (Oct4, Nanog and Sox2), properties also observed in spontaneous tumors in Lkb1^-/- mice. Conversely, LKB1-overexpression in LKB1-null cells abrogated invasion, migration and mammosphere-formation. Honokiol (HNK), a bioactive molecule from Magnolia grandiflora increased LKB1 expression, inhibited individual cell-motility and abrogated the stem-like phenotype of breast cancer cells by reducing the formation of mammosphere, expression of pluripotency-factors and aldehyde dehydrogenase activity. LKB1, and its substrate, AMP-dependent protein kinase (AMPK) are important for HNK-mediated inhibition of pluripotency factors since LKB1-silencing and AMPK-inhibition abrogated, while LKB1-overexpression and AMPK-activation potentiated HNK's effects. Mechanistic studies showed that HNK inhibited Stat3-phosphorylation/activation in an LKB1-dependent manner, preventing its recruitment to canonical binding-sites in the promoters of Nanog, Oct4 and Sox2. Thus, inhibition of the coactivation-function of Stat3 resulted in suppression of expression of pluripotency factors. Further, we showed that HNK inhibited breast tumorigenesis in mice in an LKB1-dependent manner. Molecular analyses of HNK-treated xenografts corroborated our in vitro mechanistic findings. Collectively, these results present the first in vitro and in vivo evidence to support crosstalk between LKB1, Stat3 and pluripotency factors in breast cancer and effective anticancer modulation of this axis with HNK treatment.

Benzyl Isothiocyanate potentiates p53 signaling and antitumor effects against breast cancer through activation of p53-LKB1 and p73-LKB1 axes

Functional reactivation of p53 pathway, although arduous, can potentially provide a broad-based strategy for cancer therapy owing to frequent p53 inactivation in human cancer. Using a phosphoprotein-screening array, we found that Benzyl Isothiocynate, (BITC) increases p53 phosphorylation in breast cancer cells and reveal an important role of ERK and PRAS40/MDM2 in BITC-mediated p53 activation. We show that BITC rescues and activates p53-signaling network and inhibits growth of p53-mutant cells. Mechanistically, BITC induces p73 expression in p53-mutant cells, disrupts the interaction of p73 and mutant-p53, thereby releasing p73 from sequestration and allowing it to be transcriptionally active. Furthermore, BITC-induced p53 and p73 axes converge on tumor-suppressor LKB1 which is transcriptionally upregulated by p53 and p73 in p53-wild-type and p53-mutant cells respectively; and in a feed-forward mechanism, LKB1 tethers with p53 and p73 to get recruited to p53-responsive promoters. Analyses of BITC-treated xenografts using LKB1-null cells corroborate in vitro mechanistic findings and establish LKB1 as the key node whereby BITC potentiates as well as rescues p53-pathway in p53-wild-type as well as p53-mutant cells. These data provide first in vitro and in vivo evidence of the integral role of previously unrecognized crosstalk between BITC, p53/LKB1 and p73/LKB1 axes in breast tumor growth-inhibition.

Designing a broad-spectrum integrative approach for cancer prevention and treatment

Targeted therapies and the consequent adoption of "personalized" oncology have achieved notable successes in some cancers; however, significant problems remain with this approach. Many targeted therapies are highly toxic, costs are extremely high, and most patients experience relapse after a few disease-free months. Relapses arise from genetic heterogeneity in tumors, which harbor therapy-resistant immortalized cells that have adopted alternate and compensatory pathways (i.e., pathways that are not reliant upon the same mechanisms as those which have been targeted). To address these limitations, an international task force of 180 scientists was assembled to explore the concept of a low-toxicity "broad-spectrum" therapeutic approach that could simultaneously target many key pathways and mechanisms. Using cancer hallmark phenotypes and the tumor microenvironment to account for the various aspects of relevant cancer biology, interdisciplinary teams reviewed each hallmark area and nominated a wide range of high-priority targets (74 in total) that could be modified to improve patient outcomes. For these targets, corresponding low-toxicity therapeutic approaches were then suggested, many of which were phytochemicals. Proposed actions on each target and all of the approaches were further reviewed for known effects on other hallmark areas and the tumor microenvironment. Potential contrary or procarcinogenic effects were found for 3.9% of the relationships between targets and hallmarks, and mixed evidence of complementary and contrary relationships was found for 7.1%. Approximately 67% of the relationships revealed potentially complementary effects, and the remainder had no known relationship. Among the approaches, 1.1% had contrary, 2.8% had mixed and 62.1% had complementary relationships. These results suggest that a broad-spectrum approach should be feasible from a safety standpoint. This novel approach has potential to be relatively inexpensive, it should help us address stages and types of cancer that lack conventional treatment, and it may reduce relapse risks. A proposed agenda for future research is offered.

Indolo-pyrido-isoquinolin based alkaloid inhibits growth, invasion and migration of breast cancer cells via activation of p53-miR34a axis

The tumor suppressor p53 plays a critical role in suppressing cancer growth and progression and is an attractive target for the development of new targeted therapies. We synthesized several indolo-pyrido-isoquinolin based alkaloids to activate p53 function and examined their therapeutic efficacy using NCI-60 screening. Here, we provide molecular evidence that one of these compounds, 11-methoxy-2,3,4,13-tetrahydro-1H-indolo[2',3':3,4]pyrido[1,2-b]isoquinolin-6-ylium-bromide (termed P18 or NSC-768219) inhibits growth and clonogenic potential of cancer cells. P18 treatment results in downregulation of mesenchymal markers and concurrent upregulation of epithelial markers as well as inhibition of migration and invasion. Experimental epithelial-mesenchymal-transition (EMT) induced by exposure to TGFβ/TNFα is also completely reversed by P18. Importantly, P18 also inhibits mammosphere-formation along with a reduction in the expression of stemness factors, Oct4, Nanog and Sox2. We show that P18 induces expression, phosphorylation and accumulation of p53 in cancer cells. P18-mediated induction of p53 leads to increased nuclear localization and elevated expression of p53 target genes. Using isogenic cancer cells differing only in p53 status, we show that p53 plays an important role in P18-mediated alteration of mesenchymal and epithelial genes, inhibition of migration and invasion of cancer cells. Furthermore, P18 increases miR-34a expression in p53-dependent manner and miR-34a is integral for P18-mediated inhibition of growth, invasion and mammosphere-formation. miR-34a mimics potentiate P18 efficacy while miR-34a antagomirs antagonize P18. Collectively, these data provide evidence that P18 may represent a promising therapeutic strategy for the inhibition of growth and progression of breast cancer and p53-miR-34a axis is important for P18 function.

Sustained proliferation in cancer: Mechanisms and novel therapeutic targets

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene and quercetin) have been found to inhibit one or more pathways that contribute to proliferation (e.g., hypoxia inducible factor 1, nuclear factor kappa B, phosphoinositide 3 kinase/Akt, insulin-like growth factor receptor 1, Wnt, cell cycle associated proteins, as well as androgen and estrogen receptor signaling). These data, in combination with bioinformatics analyses, will be very important for identifying signaling pathways and molecular targets that may provide early diagnostic markers and/or critical targets for the development of new drugs or drug combinations that block tumor formation and progression.

Honokiol abrogates leptin-induced tumor progression by inhibiting Wnt1-MTA1-β-catenin signaling axis in a microRNA-34a dependent manner

Obesity greatly influences risk, progression and prognosis of breast cancer. As molecular effects of obesity are largely mediated by adipocytokine leptin, finding effective novel strategies to antagonize neoplastic effects of leptin is desirable to disrupt obesity-cancer axis. Present study is designed to test the efficacy of honokiol (HNK), a bioactive polyphenol from Magnolia grandiflora, against oncogenic actions of leptin and systematically elucidate the underlying mechanisms. Our results show that HNK significantly inhibits leptin-induced breast-cancer cell-growth, invasion, migration and leptin-induced breast-tumor-xenograft growth. Using a phospho-kinase screening array, we discover that HNK inhibits phosphorylation and activation of key molecules of leptin-signaling-network. Specifically, HNK inhibits leptin-induced Wnt1-MTA1-β-catenin signaling in vitro and in vivo. Finally, an integral role of miR-34a in HNK-mediated inhibition of Wnt1-MTA1-β-catenin axis was discovered. HNK inhibits Stat3 phosphorylation, abrogates its recruitment to miR-34a promoter and this release of repressor-Stat3 results in miR-34a activation leading to Wnt1-MTA1-β-catenin inhibition. Accordingly, HNK treatment inhibited breast tumor growth in diet-induced-obese mouse model (exhibiting high leptin levels) in a manner associated with activation of miR-34a and inhibition of MTA1-β-catenin. These data provide first in vitro and in vivo evidence for the leptin-antagonist potential of HNK revealing a crosstalk between HNK and miR34a and Wnt1-MTA1-β-catenin axis.

Adipocytokines and hepatic fibrosis

Obesity and metabolic syndrome pose significant risk for the progression of many types of chronic illness, including liver disease. Hormones released from adipocytes, adipocytokines, associated with obesity and metabolic syndrome, have been shown to control hepatic inflammation and fibrosis. Hepatic fibrosis is the final common pathway that can result in cirrhosis, and can ultimately require liver transplantation. Initially, two key adipocytokines, leptin and adiponectin, appeared to control many fundamental aspects of the cell and molecular biology related to hepatic fibrosis and its resolution. Leptin appears to act as a profibrogenic molecule, while adiponectin has strong-antifibrotic properties. In this review, we emphasize pertinent data associated with these and other recently discovered adipocytokines that may drive or halt the fibrogenic response in the liver.

Abstract LB-61: Inhibiting “Dedifferentiation” in breast cancer cells using Honokiol - a plant derived polyphenol

Introduction: Dedifferentiation involves terminally differentiated cells reverting back to less differentiated cells such as precursor cells or stem cells within their own lineage allowing the cells to proliferate again before re-differentiation. Tumorigenesis involves uncontrolled cell proliferation and many host-related factors aid in dedifferentiation of tumor cells into stem cell like phenotypes hence providing a mechanism leading to tumor heterogeneity and aggressiveness. Pluripotency factors Oct4, Nanog and Sox2 have been implicated in dedifferentiation and are highly expressed in tumors. The importance of active constitutive agents in natural products has become increasingly apparent owing to their potential cancer chemopreventive and therapeutic properties. Honokiol (HNK) is a natural phenolic compound isolated from an extract of seed cones from Magnolia grandiflora. Recent studies from our laboratory demonstrated that HNK has suppressing effects on different aspects of cancer progression. The present study was designed to specifically examine the potential of HNK to inhibit pluripotency related transcription factors and reverse the process of dedifferentiation associated with uncontrolled cell proliferation in tumorigenesis.

Results: Here, we provide evidence that HNK inhibits the ability of breast cancer cells to form mammospheres. HNK treatment inhibits dedifferentiation/pluripotency markers Oct4, Nanog, Sox2 in MCF-7, MDA-MB-231, T47D, MDA-MB-468 breast cancer cells. An analysis of underlying signaling mechanism reveal that HNK inhibits phosphorylation of Stat3 and the downregulation of pluripotency factors is mediated via inhibition of Stat3. Stat3 inhibitor, Stattic potentiates the effect of HNK while overexpression of constitutively active Stat3 interferes with HNK-mediated inhibition of Oct4, Nanog and Sox2. It is interesting to note that HNK treatment also increases the expression of upstream kinase and tumor suppressor LKB1. Utilizing LKB1-null cells and gain-of-function strategies, we show that HNK-mediated inhibition of Oct4, Nanog and Sox2 is regulated by tumor suppressor LKB1. The ability of HNK to inhibit mammosphere formation is abrograted in breast cancer cells stably-silenced for LKB1. In vitro and in vivo analyses show novel functional interactions between HNK, Stat3, LKB1 and dedifferentiation/pluripotency markers.

Conclusions: Taken together, these studies provide evidence for a previously unrecognized cross-talk between HNK and dedifferentiation/pluripotency markers Oct4, Nanog, Sox2 via tumor suppressor LKB1-Stat3 axis in inhibiting “dedifferentiation” in breast cancer.

Citation Format: Sonali Sengupta, Michael Y. Bonner, Jack L. Arbiser, Neeraj K. Saxena, Dipali Sharma. Inhibiting “Dedifferentiation” in breast cancer cells using Honokiol - a plant derived polyphenol. [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-61. doi:10.1158/1538-7445.AM2014-LB-61

Abstract LB-187: Novel mechanistic insights into the bioactive compound honokiol-mediated inhibition of epithelial to mesenchymal transition in breast cancer: Therapeutic modulation of miR-34a via tumor suppressor LKB1

Introduction: An emerging hypothesis is that epithelial-mesenchymal-transition (EMT) bestows metastatic potential to epithelial cancer cells enabling them to invade, migrate and subsequently disseminate to form distant metastases resulting in non-curable disease. Pharmacological inhibition of EMT can potentially lead to reversion of aggressive breast cancer cells to a more-differentiated epithelial phenotype by inducing mesenchymal-epithelial transition (MET) to prevent metastasis and diminish distant recurrence. The importance of active constitutive agents in natural products has become increasingly apparent owing to their potential cancer chemopreventive and therapeutic properties. Honokiol (HNK) is a natural phenolic compound isolated from an extract of seed cones from Magnolia grandiflora. Recent studies from our lab demonstrated that HNK has suppressing effects on different aspects of cancer progression. The present study was designed to specifically examine the potential of HNK to inhibit EMT and elucidate the molecular mechanism by which HNK inhibits EMT in breast cancer cells.

Aim: To elucidate the mechanism by which HNK inhibits EMT in breast cancer cells.

Results: Here, we provide molecular evidence that HNK inhibits EMT in breast cancer cells resulting in significant downregulation of mesenchymal marker proteins and concurrent upregulation of epithelial markers. In vitro and in vivo analyses show functional interactions between HNK, STAT3, and EMT-signaling components. Mechanistically, HNK inhibits recruitment of STAT3 on mesenchymal transcription factor ZEB1 promoter resulting in decreased ZEB1 expression and nuclear translocation. We also discover that HNK increases E-cadherin expression via STAT3-mediated release of ZEB1 from E-cadherin promoter. Since ZEB1 is a transcriptional repressor of miR-34a, we next examined the effect of HNK on miR-34a expression. Intriguingly, we found that HNK upregulates the levels of miR-34a in a time- and dose-dependent manner. It is interesting to note that HNK treatment also increases the expression of upstream kinase and tumor suppressor LKB1. Utilizing LKB1-null cells and gain-of-function strategies, we found that HNK-mediated increase in miR-34a is regulated by tumor suppressor LKB1.

Conclusions: Taken together, these studies provide evidence for a previously unrecognized cross-talk between HNK and miR-34a via tumor suppressor LKB1 in inhibiting EMT in breast cancer.

Citation Format: Dimiter B. Avtanski, Michael Y. Bonner, Timothy P. Tiutan, Jack L. Arbiser, Neeraj K. Saxena, Dipali Sharma. Novel mechanistic insights into the bioactive compound honokiol-mediated inhibition of epithelial to mesenchymal transition in breast cancer: Therapeutic modulation of miR-34a via tumor suppressor LKB1. [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-187. doi:10.1158/1538-7445.AM2014-LB-187

Adiponectin modulates focal adhesion disassembly in activated hepatic stellate cells: implication for reversing hepatic fibrosis

Previous evidence indicates that adiponectin possesses antifibrogenic activity in inhibiting liver fibrosis. Therapeutic strategies, however, are limited by adiponectin quaternary structure and effective concentrations in circulation. Here we postulate a novel molecular mechanism, whereby adiponectin targets focal adhesion kinase (FAK) activity and disrupts key features of the fibrogenic response. Adiponectin-null (Ad(-/-)) mice and wild-type littermates were exposed to either saline or carbon tetrachloride (CCl4) for 6 wk. CCl4-gavaged mice were also injected with attenuated adenoviral adiponectin (Ad-Adn) or Ad-LacZ for 2 wk. Hepatic stellate cells (HSCs) were treated with or without adiponectin to elucidate signal transduction mechanisms. In vivo delivery of Ad-Adn markedly attenuates CCl4-induced expression of key integrin proteins and markers of HSC activation: αv, β3, β1, α2(I) collagen, and α-smooth muscle actin. Confocal experiments of liver tissues demonstrated that adiponectin delivery also suppressed vinculin and p-FAK activity in activated HSCs. In vitro, adiponectin induced dephosphorylation of FAK, mediated by a physical association with activated tyrosine phosphatase, Shp2. Conversely, Shp2 knockdown by siRNA significantly attenuated adiponectin-induced FAK deactivation, and expression of TIMP1 and α2(I) collagen was abolished in the presence of adiponectin and si-FAK. Finally, we documented that either adiponectin or the synthetic peptide with adiponectin properties, ADP355, suppressed p-FAK in synthetic matrices with stiffness measurements of 9 and 15 kPa, assessed by immunofluorescent imaging and quantitation. The in vivo and in vitro data presented indicate that disassembly of focal adhesion complexes in HSCs is pivotal for hepatic fibrosis therapy, now that small adiponectin-like peptides are available.

Mechanistic elucidation of the antitumor properties of withaferin a in breast cancer

Withaferin A (WFA) is a steroidal lactone with antitumor effects manifested at multiple levels that are mechanistically obscure. Using a phospho-kinase screening array, we discovered that WFA activated phosphorylation of the S6 kinase RSK (ribosomal S6 kinase) in breast cancer cells. Pursuing this observation, we defined activation of extracellular signal-regulated kinase (ERK)-RSK and ETS-like transcription factor 1 (Elk1)-CHOP (C-EBP homologous protein) kinase pathways in upregulating transcription of the death receptor 5 (DR5). Through this route, WFA acted as an effective DR5 activator capable of potentiating the biologic effects of celecoxib, etoposide, and TRAIL. Accordingly, WFA treatment inhibited breast tumor formation in xenograft and mouse mammary tumor virus (MMTV)-neu mouse models in a manner associated with activation of the ERK/RSK axis, DR5 upregulation, and elevated nuclear accumulation of Elk1 and CHOP. Together, our results offer mechanistic insight into how WFA inhibits breast tumor growth.

Honokiol inhibits epithelial-mesenchymal transition in breast cancer cells by targeting signal transducer and activator of transcription 3/Zeb1/E-cadherin axis

Epithelial-mesenchymal transition (EMT), a critical step in the acquisition of metastatic state, is an attractive target for therapeutic interventions directed against tumor metastasis. Honokiol (HNK) is a natural phenolic compound isolated from an extract of seed cones from Magnolia grandiflora. Recent studies from our lab show that HNK impedes breast carcinogenesis. Here, we provide molecular evidence that HNK inhibits EMT in breast cancer cells resulting in significant downregulation of mesenchymal marker proteins and concurrent upregulation of epithelial markers. Experimental EMT induced by exposure to TGFβ and TNFα in spontaneously immortalized nontumorigenic human mammary epithelial cells is also completely reversed by HNK as evidenced by morphological as well as molecular changes. Investigating the downstream mediator(s) that may direct EMT inhibition by HNK, we found functional interactions between HNK, Stat3, and EMT-signaling components. In vitro and in vivo analyses show that HNK inhibits Stat3 activation in breast cancer cells and tumors. Constitutive activation of Stat3 abrogates HNK-mediated activation of epithelial markers whereas inhibition of Stat3 using small molecule inhibitor, Stattic, potentiates HNK-mediated inhibition of EMT markers, invasion and migration of breast cancer cells. Mechanistically, HNK inhibits recruitment of Stat3 on mesenchymal transcription factor Zeb1 promoter resulting in decreased Zeb1 expression and nuclear translocation. We also discover that HNK increases E-cadherin expression via Stat3-mediated release of Zeb1 from E-cadherin promoter. Collectively, this study reports that HNK effectively inhibits EMT in breast cancer cells and provide evidence for a previously unrecognized cross-talk between HNK and Stat3/Zeb1/E-cadherin axis.

Multifaceted leptin network: the molecular connection between obesity and breast cancer

High plasma levels of leptin, a major adipocytokine produced by adipocytes, are correlated with increased fat mass in obese state. Leptin is emerging as a key candidate molecule linking obesity with breast cancer. Acting via endocrine, paracrine, and autocrine manner, leptin impacts various stages of breast tumorigenesis from initiation and primary tumor growth to metastatic progression. Leptin also modulates the tumor microenvironment mainly through supporting migration of endothelial cells, neo-angiogenesis and sustaining recruitment of macrophage and monocytes. Various studies have shown that hyperactive leptin-signaling network leads to concurrent activation of multiple oncogenic pathways resulting in enhanced proliferation, decreased apoptosis, acquisition of mesenchymal phenotype, potentiated migration and enhanced invasion potential of tumor cells. Furthermore, the capability of leptin to interact with other molecular effectors of obese state including, estrogen, IGF-1, insulin, VEGF and inflammatory cytokines further increases its impact on breast tumor progression in obese state. This article presents an overview of the studies investigating the involvement of leptin in breast cancer.

Abstract 5497: A novel bioactive approach to inhibit leptin-induced epithelial-mesenchymal transition in breast cancer

Introduction: Molecular effects of obesity, a well-established risk factor for breast cancer progression, are mediated by adipocytokine leptin. Recent studies from our lab reveal that leptin induces epithelial-mesenchymal transition (EMT) and tumorsphere formation via concomitant activation of Akt/GSK3β and MTA1/Wnt1 signaling axes leading to β-catenin activation. Given the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of leptin are much desired. We showed previously that honokiol (HNK), a bioactive polyphenol from Magnolia grandiflora, inhibits breast carcinogenesis. The present study provides first evidence for the efficacy of HNK against oncogenic effects of leptin including EMT.

Methods: Efficacy of HNK to inhibit oncogenic effects of leptin was evaluated by using clonogenicity, anchorage-independent growth, matrigel invasion and spheroid-migration assays. RT-PCR, Western blot and immunofluorescence analyses were used to examine the molecular changes associated with EMT as well as underlying molecular pathways. Functional importance of MTA1/Wnt1/β-catenin axis was examined by using overexpression, phospho-deficient constructs and specific inhibitors. Finally, mouse xenografts, immuniohistochemical, RT-PCR and Western blot analysis of tumors was used.

Results: HNK treatment circumvents leptin-induced EMT-associated phenotypic changes. A biochemical hallmark of EMT is loss of expression of epithelial markers with a concurrent increase in mesenchymal marker expression. HNK elicits increased expression of E-cadherin, occludin and cytokeratin-18 (epithelial markers) and decreased expression of vimentin, fibronectin and N-cadherin (mesenchymal markers) in leptin-treated cells providing molecular evidence for reversal of EMT. HNK also inhibits expression and nuclear translocation of transcriptional effectors of EMT: Snail, Slug, Zeb1 and Zeb2. Analysis of underlying molecular mechanisms reveals that HNK effectively inhibits leptin-induced MTA1/Wnt1/β-catenin axis. Furthermore, using nontoxic doses of HNK, we show that HNK treatment effectively inhibits leptin-induced breast tumorigenesis in vivo. Analysis of breast tumors show that HNK treatment reverses leptin-associated signaling (MTA1/Wnt1/β-catenin axis) along with decreased expression of mesenchymal markers and increased expression of epithelial markers.

Conclusions: In this study, we demonstrate for the first time that HNK is able to abolish leptin-induced EMT and provide in vitro and in vivo evidence for the integral role of a previously unrecognized crosstalk between honokiol and MTA1/Wnt1/ β catenin axis. Thus, HNK may be used as a non-toxic and non-endocrine rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.

Citation Format: Dimiter B. Avtanski, Arumugam Nagalingam, Panjamurthy Kuppusamy, Neeraj K. Saxena, Dipali Sharma. A novel bioactive approach to inhibit leptin-induced epithelial-mesenchymal transition in breast cancer. [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 5497. doi:10.1158/1538-7445.AM2013-5497

Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis

A number of factors have been identified that increase the risk of hepatocellular carcinoma (HCC). Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first-line therapy for the treatment of type II diabetes in which it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. Although a number of preclinical studies show the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. In addition, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin-mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC in which increased lipid synthesis is observed. As a whole these studies show that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at-risk patients.

Metformin prevents liver tumorigenesis by inhibiting pathways driving hepatic lipogenesis

A number of factors have been identified that increase the risk of hepatocellular carcinoma (HCC). Recently it has become appreciated that type II diabetes increases the risk of developing HCC. This represents a patient population that can be identified and targeted for cancer prevention. The biguanide metformin is a first-line therapy for the treatment of type II diabetes in which it exerts its effects primarily on the liver. A role of metformin in HCC is suggested by studies linking metformin intake for control of diabetes with a reduced risk of HCC. Although a number of preclinical studies show the anticancer properties of metformin in a number of tissues, no studies have directly examined the effect of metformin on preventing carcinogenesis in the liver, one of its main sites of action. We show in these studies that metformin protected mice against chemically induced liver tumors. Interestingly, metformin did not increase AMPK activation, often shown to be a metformin target. Rather metformin decreased the expression of several lipogenic enzymes and lipogenesis. In addition, restoring lipogenic gene expression by ectopic expression of the lipogenic transcription factor SREBP1c rescues metformin-mediated growth inhibition. This mechanism of action suggests that metformin may also be useful for patients with other disorders associated with HCC in which increased lipid synthesis is observed. As a whole these studies show that metformin prevents HCC and that metformin should be evaluated as a preventive agent for HCC in readily identifiable at-risk patients.

Leptin-induced epithelial-mesenchymal transition in breast cancer cells requires β-catenin activation via Akt/GSK3- and MTA1/Wnt1 protein-dependent pathways

Perturbations in the adipocytokine profile, especially higher levels of leptin, are a major cause of breast tumor progression and metastasis; the underlying mechanisms, however, are not well understood. In particular, it remains elusive whether leptin is involved in epithelial-mesenchymal transition (EMT). Here, we provide molecular evidence that leptin induces breast cancer cells to undergo a transition from epithelial to spindle-like mesenchymal morphology. Investigating the downstream mediator(s) that may direct leptin-induced EMT, we found functional interactions between leptin, metastasis-associated protein 1 (MTA1), and Wnt1 signaling components. Leptin increases accumulation and nuclear translocation of β-catenin leading to increased promoter recruitment. Silencing of β-catenin or treatment with the small molecule inhibitor, ICG-001, inhibits leptin-induced EMT, invasion, and tumorsphere formation. Mechanistically, leptin stimulates phosphorylation of glycogen synthase kinase 3β (GSK3β) via Akt activation resulting in a substantial decrease in the formation of the GSK3β-LKB1-Axin complex that leads to increased accumulation of β-catenin. Leptin treatment also increases Wnt1 expression that contributes to GSK3β phosphorylation. Inhibition of Wnt1 abrogates leptin-stimulated GSK3β phosphorylation. We also discovered that leptin increases the expression of an important modifier of Wnt1 signaling, MTA1, which is integral to leptin-mediated regulation of the Wnt/β-catenin pathway as silencing of MTA1 inhibits leptin-induced Wnt1 expression, GSK3β phosphorylation, and β-catenin activation. Furthermore, analysis of leptin-treated breast tumors shows increased expression of Wnt1, pGSK3β, and vimentin along with higher nuclear accumulation of β-catenin and reduced E-cadherin expression providing in vivo evidence for a previously unrecognized cross-talk between leptin and MTA1/Wnt signaling in epithelial-mesenchymal transition of breast cancer cells.

Honokiol activates AMP-activated protein kinase in breast cancer cells via an LKB1-dependent pathway and inhibits breast carcinogenesis

INTRODUCTION

Honokiol, a small-molecule polyphenol isolated from magnolia species, is widely known for its therapeutic potential as an antiinflammatory, antithrombosis, and antioxidant agent, and more recently, for its protective function in the pathogenesis of carcinogenesis. In the present study, we sought to examine the effectiveness of honokiol in inhibiting migration and invasion of breast cancer cells and to elucidate the underlying molecular mechanisms.

METHODS

Clonogenicity and three-dimensional colony-formation assays were used to examine breast cancer cell growth with honokiol treatment. The effect of honokiol on invasion and migration of breast cancer cells was evaluated by using Matrigel invasion, scratch-migration, spheroid-migration, and electric cell-substrate impedance sensing (ECIS)-based migration assays. Western blot and immunofluorescence analysis were used to examine activation of the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) axis. Isogenic LKB1-knockdown breast cancer cell line pairs were developed. Functional importance of AMPK activation and LKB1 overexpression in the biologic effects of honokiol was examined by using AMPK-null and AMPK-wild type (WT) immortalized mouse embryonic fibroblasts (MEFs) and isogenic LKB1-knockdown cell line pairs. Finally, mouse xenografts, immunohistochemical and Western blot analysis of tumors were used.

RESULTS

Analysis of the underlying molecular mechanisms revealed that honokiol treatment increases AMP-activated protein kinase (AMPK) phosphorylation and activity, as evidenced by increased phosphorylation of the downstream target of AMPK, acetyl-coenzyme A carboxylase (ACC) and inhibition of phosphorylation of p70S6kinase (pS6K) and eukaryotic translation initiation factor 4E binding protein 1 (4EBP1). By using AMPK-null and AMPK-WT (MEFs), we found that AMPK is required for honokiol-mediated modulation of pACC-pS6K. Intriguingly, we discovered that honokiol treatment increased the expression and cytoplasmic translocation of tumor-suppressor LKB1 in breast cancer cells. LKB1 knockdown inhibited honokiol-mediated activation of AMPK and, more important, inhibition of migration and invasion of breast cancer cells. Furthermore, honokiol treatment resulted in inhibition of breast tumorigenesis in vivo. Analysis of tumors showed significant increases in the levels of cytoplasmic LKB1 and phospho-AMPK in honokiol-treated tumors.

CONCLUSIONS

Taken together, these data provide the first in vitro and in vivo evidence of the integral role of the LKB1-AMPK axis in honokiol-mediated inhibition of the invasion and migration of breast cancer cells. In conclusion, honokiol treatment could potentially be a rational therapeutic strategy for breast carcinoma.

Med1 plays a critical role in the development of tamoxifen resistance

Understanding the molecular pathways that contribute to the development of tamoxifen resistance is a critical research priority as acquired tamoxifen resistance is the principal cause of poor prognosis and death of patients with originally good prognosis hormone-responsive breast tumors. In this report, we provide evidence that Med1, an important subunit of mediator coactivator complex, is spontaneously upregulated during acquired tamoxifen-resistance development potentiating agonist activities of tamoxifen. Phosphorylated Med1 and estrogen receptor (ER) are abundant in tamoxifen-resistant breast cancer cells due to persistent activation of extracellular signal-regulated kinases. Mechanistically, phosphorylated Med1 exhibits nuclear accumulation, increased interaction with ER and higher tamoxifen-induced recruitment to ER-responsive promoters, which is abrogated by inhibition of Med1 phosphorylation. Stable knockdown of Med1 in tamoxifen-resistant cells not only reverses tamoxifen resistance in vitro but also in vivo. Finally, higher expression levels of Med1 in the tumor significantly correlated with tamoxifen resistance in ER-positive breast cancer patients on adjuvant tamoxifen monotherapy. In silico analysis of breast cancer, utilizing published profiling studies showed that Med1 is overexpressed in aggressive subsets. These findings provide what we believe is the first evidence for a critical role for Med1 in tamoxifen resistance and identify this coactivator protein as an essential effector of the tamoxifen-induced breast cancer growth.

Glp-1 analog, liraglutide, ameliorates hepatic steatosis and cardiac hypertrophy in C57BL/6J mice fed a Western diet

The aims of this study were designed to determine whether liraglutide, a long-acting glucagon-like peptide, could reverse the adverse effects of a diet high in fat that also contained trans-fat and high-fructose corn syrup (ALIOS diet). Specifically, we examined whether treatment with liraglutide could reduce hepatic insulin resistance and steatosis as well as improve cardiac function. Male C57BL/6J mice were pair fed or fed ad libitum either standard chow or the ALIOS diet. After 8 wk the mice were further subdivided and received daily injections of either liraglutide or saline for 4 wk. Hyperinsulinemic-euglycemic clamp studies were performed after 6 wk, revealing hepatic insulin resistance. Glucose tolerance and insulin resistance tests were performed at 8 and 12 wk prior to and following liraglutide treatment. Liver pathology, cardiac measurements, blood chemistry, and RNA and protein analyses were performed. Clamp studies revealed hepatic insulin resistance after 6 wk of ALIOS diet. Liraglutide reduced visceral adiposity and liver weight (P < 0.001). As expected, liraglutide improved glucose and insulin tolerance. Liraglutide improved hypertension (P < 0.05) and reduced cardiac hypertrophy. Surprisingly, liver from liraglutide-treated mice had significantly higher levels of fatty acid binding protein, acyl-CoA oxidase II, very long-chain acyl-CoA dehydrogenase, and microsomal triglyceride transfer protein. We conclude that liraglutide reduces the harmful effects of an ALIOS diet by improving insulin sensitivity and by reducing lipid accumulation in liver through multiple mechanisms including, transport, and increase β-oxidation.

GLP-1 analogs reduce hepatocyte steatosis and improve survival by enhancing the unfolded protein response and promoting macroautophagy

Background

Nonalcoholic fatty liver disease (NAFLD) is a known outcome of hepatosteatosis. Free fatty acids (FFA) induce the unfolded protein response (UPR) or endoplasmic reticulum (ER) stress that may induce apoptosis. Recent data indicate ER stress to be a major player in the progression of fatty liver to more aggressive lesions. Autophagy on the other hand has been demonstrated to be protective against ER stress- induced cell death. We hypothesized that exendin-4 (GLP-1 analog) treatment of fat loaded hepatocytes can reduce steatosis by autophagy which leads to reduced ER stress-related hepatocyte apoptosis.

Methodology/Principal Findings

Primary human hepatocytes were loaded with saturated, cis- and trans-unsaturated fatty acids (palmitic, oleic and elaidic acid respectively). Steatosis, induced with all three fatty acids, was significantly resolved after exendin-4 treatment. Exendin-4 sustained levels of GRP78 expression in fat-loaded cells when compared to untreated fat-loaded cells alone. In contrast, CHOP (C/EBP homologous protein); the penultimate protein that leads to ER stress-related cell death was significantly decreased by exendin-4 in hepatocytes loaded with fatty acids. Finally, exendin-4 in fat loaded hepatocytes clearly promoted gene products associated with macroautophagy as measured by enhanced production of both Beclin-1 and LC3B-II, markers for autophagy; and visualized by transmission electron microscopy (TEM). Similar observations were made in mouse liver lysates after mice were fed with high fat high fructose diet and treated with a long acting GLP-1 receptor agonist, liraglutide.

Conclusions/Significance

GLP-1 proteins appear to protect hepatocytes from fatty acid-related death by prohibition of a dysfunctional ER stress response; and reduce fatty acid accumulation, by activation of both macro-and chaperone-mediated autophagy. These findings provide a novel role for GLP-1 proteins in halting the progression of more aggressive lesions from underlying steatosis in humans afflicted with NAFLD.

Survivin upregulation, dependent on leptin-EGFR-Notch1 axis, is essential for leptin-induced migration of breast carcinoma cells

Obese breast cancer patients exhibit a higher risk for larger tumor burden and an increased likelyhood of metastasis. The molecular effects of obesity on carcinogenesis are mediated by the autocrine and paracrine effects of the adipocytokine leptin. Leptin participates in the tumor progression and metastasis of human breast. We show that leptin induces clonogenicity and increases the migration potential of breast cancer cells. We found that survivin expression is induced in response to leptin. In this study, we examine the role and leptin-mediated regulation of survivin. Leptin treatment leads to survivin upregulation, due in part to the activation of Notch1 and the release of a transcriptionally active Notch1 intracellular domain (NICD). Chromatin immunoprecipitation analysis shows that NICD gets recruited to the survivin promoter at the CSL (CBF1/RBP-Jk, Su(H), Lag-1) binding site in response to leptin treatment. Inhibition of Notch1 activity inhibits leptin-induced survivin upregulation. Leptin-induced transactivation of epidermal growth factor receptor (EGFR) is involved in leptin-mediated Notch1 and survivin upregulation, demonstrating a novel upstream role of leptin-EGFR-Notch1 axis. We further show that leptin-induced migration of breast cancer cells requires survivin, as overexpression of survivin further increases, whereas silencing survivin abrogates leptin-induced migration. Using a pharmacological approach to inhibit survivin, we show that 3-hydroxy-3-methylglutaryl-coenzyme-A-reductase inhibitors, such as lovastatin, can effectively inhibit leptin-induced survivin expression and migration. Importantly, leptin increased breast tumor growth in nude mice. These data show a novel role for survivin in leptin-induced migration and put forth pharmacological survivin inhibition as a potential novel therapeutic strategy. This conclusion is supported by in vivo data showing the overexpression of leptin and survivin in epithelial cells of high-grade ductal carcinomas in situ and in high-grade invasive carcinomas.

Abstract 860: Benzyl isothiocyanate inhibits oncogenic actions of leptin in human breast cancer cells by suppressing activation of signal transducer and activator of transcription 3

Obesity is a well-established risk factor for breast cancer progression and molecular effects of obesity are mediated by adipocytokine, leptin. Considering the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of this adipocytokine are much desired. We showed previously that benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables (e.g., gardencress), confers significant protection against mammary carcinogenesis in a transgenic mouse model (MMTV-neu). The BITC-mediated prevention of mammary cancer development in MMTV-neu mice correlated with reduced cell proliferation, increased apoptosis, and tumor infiltration of T cells. The present study provides first evidence for efficacy of BITC against oncogenic effects of letpin. BITC-treatment circumvented leptin-induced clonogenicity and anchorage-independent growth of MDA-MB-231 (an estrogen-independent cell line with mutant p53) and MCF-7 human breast cancer cells (an estrogen-responsive cell line with wild-type p53) at pharmacologic doses. Leptin-stimulated migration and invasion of these cells was also inhibited significantly in the presence of BITC. Analysis of the underlying molecular mechanisms revealed that BITC-treatment suppressed leptin-induced phosphorylation of signal transducer and activator of transcription 3 (Stat3) and cyclin D1 transactivation. BITC-treatment efficiently inhibited Stat3 recruitment to the cyclin D1 promoter in a chromatin immunoprecipitation analysis. Furthermore overexpression of constitutively active Stat3 imparted significant protection against BITC-mediated inhibition of cyclin D1 transactivation whereas RNA interference of Stat3 resulted in a significant increase in BITC-mediated inhibition of cyclin D1 transactivation in the presence of leptin. BITC-mediated inhibition of MDA-MB-231 xenograft growth correlated with a decrease in level of phospho-Stat3. These studies indicate that Stat3 plays an important role in BITC-mediated inhibition of leptin-induced cyclin D1 transactivastion. Taken together, these data show that BITC treatment can inhibit the oncogenic actions of leptin via blocking its downstream signaling molecule, Stat3.

In conclusion, BITC could potentially be a rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels. This work was supported in part by the USPHS grants NCI-RO1 CA129347 (to SVS), NIDDK-K01DK076742 and R03DK089130 (to NKS), NCI-R01CA131294 and NCI-R21 CA155686 (to DS).

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 860. doi:10.1158/1538-7445.AM2011-860

Benzyl isothiocyanate inhibits oncogenic actions of leptin in human breast cancer cells by suppressing activation of signal transducer and activator of transcription 3

Molecular effects of obesity, a well-established risk factor for breast cancer progression, are mediated by adipocytokine leptin. Given the important role of leptin in breast cancer growth and metastasis, novel strategies to antagonize biological effects of this adipocytokine are much desired. We showed previously that benzyl isothiocyanate (BITC), a constituent of edible cruciferous vegetables (e.g. garden cress), confers significant protection against mammary carcinogenesis in a transgenic mouse model. The present study provides first evidence for the efficacy of BITC against oncogenic effects of leptin. The BITC treatment circumvented leptin-induced clonogenicity and anchorage-independent growth of MDA-MB-231 and MCF-7 human breast cancer cells. Leptin-stimulated migration and invasion of these cells was also inhibited in the presence of BITC. Analysis of the underlying molecular mechanisms revealed that BITC treatment suppressed leptin-induced Stat3 phosphorylation and cyclin D1 transactivation. The BITC-mediated inhibition of MDA-MB-231 xenograft growth correlated with a modest yet significant decrease in levels of Tyr705 phosphorylated Stat3. The BITC treatment efficiently inhibited Stat3 and SRC1 recruitment to cyclin D1 promoter in a chromatin immunoprecipitation analysis. Furthermore, overexpression of constitutively active Stat3 imparted significant protection against BITC-mediated inhibition of cyclin D1 transactivation, whereas RNA interference of Stat3 resulted in a significant increase in BITC-mediated inhibition of cyclin D1 transactivation in the presence of leptin. These results indicate that Stat3 plays an important role in BITC-mediated inhibition of leptin-induced cyclin D1 transactivation. In conclusion, BITC could potentially be a rational therapeutic strategy for breast carcinoma in obese patients with high leptin levels.

Adiponectin activation of AMPK disrupts leptin-mediated hepatic fibrosis via suppressors of cytokine signaling (SOCS-3)

Adiponectin is an adipocytokine that was recently shown to be anti-fibrogenic in hepatic fibrosis. Leptin, on the other hand, promotes hepatic fibrosis. The purpose of the present study was to elucidate a mechanism (or mechanisms) whereby adiponectin dampens leptin signaling in activated hepatic stellate cells (HSCs), and prevents excess extracellular matrix production. Activated HSCs, between passages 2 and 5, were cultured and exposed to recombinant human adiponectin and recombinant leptin. Immunoblot analysis for SOCS-3, TIMP-1, and the phosphorylated species of Stat3 and adenosine monophosphate-activated protein kinase (AMPK) were conducted. We also examined MMP-1 activity by immunosorbant fluorimetric analysis. In HSCs, adiponectin-induced phosphorylation of AMPK, and subsequently suppressed leptin-mediated Stat3 phosphorylation and SOCS-3 induction. Adiponectin also blocked leptin-stimulated secretion of TIMP-1, and significantly increased MMP-1 activity, in vitro. To extend this study, we treated adiponectin knockout mice (Ad-/-) daily with 5 mg/kg recombinant leptin and/or carbon tetrachloride (2 ml/kg) for 6 weeks. Post-necropsy analysis was performed to examine for inflammation, and histological changes in the Ad-/- and wild-type mice. There was no significant difference in inflammation, or aminotransferases, between mice receiving carbon tetrachloride and leptin versus carbon tetrachloride alone. As anticipated, the combination of leptin and CCl(4) enhanced hepatic fibrosis in both wild-type and Ad-/- mice, as estimated by amount of collagen in injured livers, but wild-type mice had significantly higher levels of SOCS-3 and significantly lower levels of TIMP-1 mRNA and protein than did adiponectin KO mice exposed to both CCl(4) and leptin. We therefore conclude that the protective effects of adiponectin against liver fibrosis require AMPK activation, and may occur through inhibition of the Jak-Stat signal transduction pathway.

Adiponectin modulates C-jun N-terminal kinase and mammalian target of rapamycin and inhibits hepatocellular carcinoma

BACKGROUND & AIMS

Epidemiological studies have shown that obesity is a risk factor for hepatocellular carcinoma (HCC). Lower adiponectin levels are associated with poor prognosis in obese HCC patients, hence it is plausible that adiponectin acts as a negative regulator of HCC. We investigated the effects of adiponectin on HCC development and its molecular mechanisms.

METHODS

Assays with Huh7 and HepG2 HCC cells were used to examine the signal transduction pathways involved in the protective functions of adiponectin in HCC. These studies were followed by in vivo approaches using HCC xenografts and tumor analysis. Results from in vitro and in vivo findings were corroborated using human HCC tissue microarray and analysis of clinicopathological characteristics.

RESULTS

Adiponectin increased apoptosis of HCC cells through activation of caspase-3. Adiponectin increased phosphorylation of c-Jun-N-terminal kinase (JNK) and inhibition of c-Jun-N-terminal kinase-phosphorylation inhibited adiponectin-induced apoptosis and caspase-3 activation. Adiponectin increased phosphorylation of 5'-adenosine monophosphate-activated protein kinase and tumor suppressor tuberous sclerosis complex 2 and inhibited mammalian target of rapamycin phosphorylation. Inhibition of 5'-adenosine monophosphate-activated protein kinase phosphorylation not only inhibited adiponectin-induced c-Jun-N-terminal kinase phosphorylation, but also blocked biological effects of adiponectin. Adiponectin substantially reduced liver tumorigenesis in nude mice. Importantly, analysis of adiponectin expression levels in tissue microarray of human HCC patients revealed an inverse correlation of adiponectin expression with tumor size.

CONCLUSIONS

Adiponectin protects against liver tumorigenesis; its reduced expression is associated with poor prognosis in obese patients with HCC.

Adiponectin antagonizes the oncogenic actions of leptin in hepatocellular carcinogenesis

Obesity is rapidly becoming a pandemic and is associated with increased carcinogenesis. Obese populations have higher circulating levels of leptin in contrast to low concentrations of adiponectin. Hence, it is important to evaluate the dynamic role between adiponectin and leptin in obesity-related carcinogenesis. Recently, we reported the oncogenic role of leptin including its potential to increase tumor invasiveness and migration of hepatocellular carcinoma (HCC) cells. In the present study we investigated whether adiponectin could antagonize the oncogenic actions of leptin in HCC. We employed HCC cell lines HepG2 and Huh7, the nude mice-xenograft model of HCC, and immunohistochemistry data from tissue-microarray to demonstrate the antagonistic role of adiponectin on the oncogenic actions of leptin. Adiponectin treatment inhibited leptin-induced cell proliferation of HCC cells. Using scratch-migration and electric cell-substrate impedance-sensing-based migration assays, we found that adiponectin inhibited leptin-induced migration of HCC cells. Adiponectin treatment effectively blocked leptin-induced invasion of HCC cells in Matrigel invasion assays. Although leptin inhibited apoptosis in HCC cells, we found that adiponectin treatment induced apoptosis even in the presence of leptin. Analysis of the underlying molecular mechanisms revealed that adiponectin treatment reduced leptin-induced Stat3 and Akt phosphorylation. Adiponectin also increased suppressor of cytokine signaling (SOCS3), a physiologic negative regulator of leptin signal transduction. Importantly, adiponectin significantly reduced leptin-induced tumor burden in nude mice. In HCC samples, leptin expression significantly correlated with HCC proliferation as evaluated by Ki-67, whereas adiponectin expression correlated significantly with increased disease-free survival and inversely with tumor size and local recurrence.

CONCLUSION

Collectively, these data demonstrate that adiponectin has the molecular potential to inhibit the oncogenic actions of leptin by blocking downstream effector molecules.

Metastasis suppression by adiponectin: LKB1 rises up to the challenge

Adiponectin is an adipocytokine involved in the pathogenesis of various obesity-related disorders. Also, it has been shown that adiponectin has therapeutic potential for metabolic syndrome, systemic insulin resistance, cardiovascular disease and more recently carcinogenesis. Adiponectin can modulate breast cancer cell growth and proliferation. Anti-metastatic effects of adiponectin have also been elucidated. It has been shown that adiponectin inhibits important metastatic properties such as adhesion, invasion and migration of breast cancer cells. Examination of the underlying molecular mechanisms has shown that adiponectin treatment increases AMP-activated protein kinase (AMPK) phosphorylation and activity. Adiponectin also increases phosphorylation of downstream target of AMPK, Acetyl-CoA Carboxylase (ACC) and decreases phosphorylation of p70S6 kinase (S6K). Importantly, adiponectin treatment increases the expression of tumor suppressor gene, LKB1 in breast cancer cells. LKB1 is required for adiponectin-mediated modulation of AMPK-S6K axis and more importantly, its biological functions including inhibition of adhesion, migration and invasion of breast cancer cells. Although further studies are required to analyze the effect of adiponectin on LKB1-AMPK-S6K axis, these data present a novel mechanism involving specific upregulation of tumor suppressor gene LKB1 by which adiponectin inhibits adhesion, invasion and migration of breast cancer cells. These results highlight a new role for LKB1 in adiponectin action and may have significant implication for development of novel therapeutic options. Cancer research has largely focused on the molecular basis of oncogenic transformation and tumorigenesis for many years. Recent progress in cancer research has put the metastatic process at the center stage because higher metastatic potential of tumor cells is the major cause of mortality from solid tumors. Metastasis is a complex process that involves modulation of various molecular signaling networks. Tumor cells alter the microenvironment, attain greater cellular adhesion along with better ability to invade and migrate to gain access to circulation. These wandering tumor cells defy anoikis, survive in the circulation, exit into new permissive organ site and colonize distant organs. The microenvironment in which the tumor originates plays an important role in tumor initiation, progression and metastasis.

Abstract LB-269: Activation of energy sensor AMP-activated protein kinase by rosiglitazone: A novel means to rescue triple-negative breast cancer cells from metastasis

Background: A recent epidemiological study reported that triple-negative (TN) breast cancers occurred in association with obesity, which itself has been associated with increased risk for breast cancer. Obesity was present in 49.6% of patients with TN cancer but only in 35.8% of those with non-TN cancer. Considering the increasing epidemic of obesity this 13.8% increase is highly significant. Molecular effects of obesity on breast cancer growth and metastasis are mediated by dysregulation of adipocytokines, leptin and adiponectin. Our lab has previously shown that increased leptin signaling increases breast cancer metastasis whereas another adipocytokine, adiponectin inhibits metastatic potential of breast cancer cells. In the present study, we investigated the potential of thiazolidinediones (TZD) as adiponectin-mimetic in breast carcinogenesis and metastasis.

Methods: TN breast carcinoma cell lines, MDA-MB-231 and MDA-MB-468, were used to study the effects on TZDs on TN breast cancer cell viability, anchorage-dependent tumor growth and anchorage-independent growth using the XTT colorimetric assay, clonigenecity assays, and soft-agar assays, respectively. Cell migration (wound-healing) assays were performed to assess the effects of TZDs on cell motility. Reverse-transcription polymerase chain reaction (RT-PCR) and immunoblotting were used to detect mRNA and protein expression levels in TZD treated cells, respectively.

Results: Various Thiazolidinediones (TZD) have been developed including Rosiglitazone (RZG), Troglitazone (TGZ), and Pioglitazone (PZG). We found that rosiglitazone (RZG), a novel class of TZD increases adiponectin levels in TN breast cancer cells. We show that RGZ inhibits cell proliferation, anchorage-dependent and -independent growth of TN breast cancer cells in a dose-dependent manner. The ability of a cancer cell to migrate is an essential prerequisite for metastasis. Importantly, RZG treatment inhibits migration potential of TN breast cancer cells. Further examination of the underlying molecular mechanisms revealed that RGZ treatment increases phosphorylation of energy sensor AMP-activated protein kinase in TN breast cancer cells. Increased phosphorylation of AMPK increases its activity as evident by activation of its downstream target, ACC. Intriguingly, we discovered that RGZ treatment also decreases the activation of p-S6K indicating mTOR inhibition. Using AMPK-WT and AMPK-null fibroblasts, we further show that AMPK is required for RZG-mediated inhibition of metastatic potential of TN breast cancer cells.

Conclusions: Our studies show that inhibition of metastatic properties of TN breast cancer cells by RGZ involves increased adiponectin levels, elevated AMPK (pAMPK) expression and activity. Our study suggests that RGZ can be used as a novel therapeutic agent for the treatment of aggressive, metastatic TN breast tumors that are unresponsive to current therapeutic regiments.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-269.

Abstract LB-224: Leptin-induced breast cancer cell migration requires upregulation of antiapoptotic protein, survivin

Background: Leptin, an adipocytokine secreted by adipose tissue, is responsible for many biological functions including appetite regulation, energy homeostasis, bone formation, and more recently, carcinogenesis. Levels of circulating leptin are typically elevated in obese states and have been associated with increased tumor proliferation, angiogenesis, and increased metastatic behavior. Therefore, obesity has been clearly associated with increased risk of cancer and metastasis. Breast cancer remains as the second leading cause of cancer-related deaths to American women. Many epidemiological studies have shown that obese women are more at risk for developing breast cancer compared to non-obese women. Therefore, it is imperative to understand the contribution of leptin to breast cancer development and progression.

Methods and Results: In this study, we used MCF-7 and MDA-MB-231 breast cancer cell lines to examine the relationship between leptin and survivin, a dual-function protein. Survivin has become an interesting target in cancer research because it is highly expressed in cancerous tissues while being nearly undetectable in normal tissues. We observed that leptin increases mRNA and protein expression of survivin in a time-dependent manner. Earlier studies from our lab demonstrated that leptin increases breast cancer cell migration and invasion and underlying mechanisms involved a bidirectional crosstalk between leptin and IGF1 leading to transactivation of EGFR. Examining the underlying mechanisms, we found that blocking EGFR activation decreased leptin-induced survivin expression indicating the involvement of EGFR. To examine the role of survivin in leptin-induced migration of breast cancer cells, we transfected both cell lines with wild-type or p-silencer-survivin and subjected the cells to scratch and electric cell-substrate impedance sensing (ECIS) migration assays. We found that survivin overexpression increased migration potential of breast cancer cells compared to untransfected cells. In addition, leptin treatment further enhanced migration of breast cancer cells with survivin overexpression. Inhibition of survivin inhibited migration of breast cancer cells alone and even in the presence of leptin. These studies showed the importance of survivin in leptin-induced migration of breast cancer cells. For therapeutic purposes, we treated the breast cancer cells with lovastatin, commonly used as an HMG-CoA reducatase inhibitor. Lovastatin has been previously shown to inhibit survivin expression. We treated cells with lovastatin in a dose-dependent manner and observed a complete inhibition of survivin expression. Combination treatment with leptin did not restore survivin protein expression. Importantly, lovastatin treatment efficiently inhibited migration of breast cancer cells even in the presence of leptin.

Conclusion: In conclusion, we have established a novel role for survivin in leptin-induced migration of breast cancer cells. Targeting survivin using lovastatin may provide new therapeutic targets for the treatment of metastatic breast carcinogenesis in obese patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-224.

Abstract LB-57: Integral role of Med1 in conferring tamoxifen resistance to poor prognosis (luminal-B) estrogen receptor positive breast cancer

Background: Gene expression studies have identified two biologically distinct estrogen receptor (ER)-positive subtypes of breast cancer: luminal A and luminal B. Some luminal B tumors can be identified by their expression of Her2 but the major biological distinction between luminal A and luminal B is their proliferation signature. Upon treatment with adjuvant tamoxifen, luminal A breast tumors show a good prognosis, however the clinical outcome of luminal B breast tumor is poor. The underlying mechanisms for the differential response to adjuvant tamoxifen therapy between luminal A and luminal B breast tumors are probably multifactorial and remain largely unknown. In this study, we examined the molecular mechanisms contributing to the poor prognosis of the luminal B ER-positive breast cancer subtype in response to tamoxifen.

Methods and Results: We developed a physiologically relevant luminal B ER-positive breast cancer (luminal B) model. This cell line model exhibited an elevated growth factor signaling pathway. We showed that tamoxifen treatment inhibited clonogenicity and anchorage-independent growth of luminal A breast cancer cells. Interestingly, acting as a potent agonist, tamoxifen resulted in significantly increased clonogenicity and anchorage-independent growth in luminal B cells. We found that tamoxifen also increased expression of ER-responsive genes in luminal B cells in contrast to luminal A cells where it effectively inhibited ER-transactivation and ER-responsive gene expression. Mediator complex is an essential coactivator complex for the expression of ER-responsive genes. Investigating the underlying mechanisms, we discovered that anchor subunit of mediator coactivator complex, Med1, was overexpressed in luminal B cells. Furthermore, we found hyper-phosphorylation of Med1 and ER in luminal B cells due to persistent activation of ERK. Hyper-phosphorylated Med1 showed increased recruitment to ER-responsive promoters in the presence of tamoxifen in luminal B cells. Stably silencing Med1 in luminal B cells not only inhibited tamoxifen-induced clonogenicity and anchorage-independent growth, it also inhibited tamoxifen-induced ER-transactivation. These data clearly showed the essential role of Med1 in mediating tamoxifen response in luminal B cells.

Conclusions: These data demonstrate a novel role of Med1 in promotion of tamoxifen-induced growth of luminal B breast cancer cells and suggest that inhibiting Med1/or its activation may prove to be beneficial to overcome/reduce poor prognosis of basal B breast tumors. This conclusion is supported by in vivo data showing overexpression of Med1 in luminal B estrogen receptor-positive breast tumors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-57.

Unresolving pericarditis: suspect filariasis in the tropics

Filariasis, a mosquito-borne disease, is wide spread in India. While laboratory diagnosis has been conventionally done by demonstrating microfilaria in peripheral blood smears, occasionally they are reported in various body fluids including pericardial fluid. We report the case of 33-year-old man with severe dyspnoea and chest pain, referred from a private nursing home with a provisional diagnosis of unresolving pericarditis. Pericardial tap revealed massive pericardial effusion with actively motile microfilariae. No microfilariae (Mf) were seen in the peripheral blood. Haemorrhagic effusion resolved completely with DEC. Though relatively uncommon, tropical diseases must always be considered in the etiological diagnosis of pericardial effusion.

Epigenetic Reactivation of Estrogen Receptor: Promising Tools for Restoring Response to Endocrine Therapy

Breast tumors expressing estrogen receptor alpha (ER) respond well to therapeutic strategies using SERMs (selective estrogen receptor modulators) such as tamoxifen. However, about thirty percent of invasive breast cancers are hormone independent because they lack ER expression due to hypermethylation of ER promoter. Treatment of ER-negative breast cancer cells with demethylating agents and histone deacetylase inhibitors leads to expression of ER mRNA and functional protein. Additionally, growth factor signaling pathways have also been implicated in ER silencing in ER-negative tumor phenotype. Recently, important role of components of ubiquitin-proteasome pathway has been shown in mediating downregulation of ER. In this article, we will review various mechanisms underlying the silencing of ER in ER negative tumor phenotype and discuss diverse strategies to combat it. Ongoing studies may provide the mechanistic insight to design therapeutic strategies directed towards epigenetic and non-epigenetic mechanisms in the prevention or treatment of ER-negative breast cancer.

Bidirectional crosstalk between leptin and insulin-like growth factor-I signaling promotes invasion and migration of breast cancer cells via transactivation of epidermal growth factor receptor

Obesity is an independent risk factor for breast cancer, and obese breast cancer patients exhibit a higher risk for larger tumor burden and increased metastasis. Obesity, as associated with metabolic syndrome, results in an increase in circulating insulin-like growth factor (IGF), which acts as a mitogen. In addition, higher plasma level of adipocytokine leptin is associated with obesity. In the present study, we show that cotreatment with leptin and IGF-I significantly increases proliferation as well as invasion and migration of breast cancer cells. We found a novel bidirectional crosstalk between leptin and IGF-I signaling; IGF-I induced phosphorylation of leptin receptor (Ob-Rb) and leptin induced phosphorylation of IGF-I receptor (IGF-IR), whereas cotreatment induced synergistic phosphorylation and association of Ob-Rb and IGF-IR along with activation of downstream effectors, Akt and extracellular signal-regulated kinase. Leptin increased phosphorylation of IGF signaling molecules insulin-receptor substrate (IRS)-1 and IRS-2. Interestingly, we found that leptin and IGF-I cotreatment synergistically transactivated epidermal growth factor receptor (EGFR), depending on the proteolytic release of EGFR ligands, as the broad-spectrum matrix metalloproteinase inhibitor GM6001 could inhibit this effect. Using clinically relevant EGFR inhibitors, erlotinib and lapatinib, we found that inhibition of EGFR activation effectively inhibited leptin- and IGF-I-induced invasion and migration of breast cancer cells. Taken together, these data suggest a novel bidirectional crosstalk between leptin and IGF-I signaling that transactivates EGFR and promotes the metastatic properties as well as invasion and migration of breast cancer cells. Our findings indicate the possibility of using EGFR inhibitors erlotinib and lapatinib to counter the procancerous effects of leptin and IGF-I in breast cancers.

Co-targeting leptin and insulin-like growth factor I signaling: dramatic effects of epidermal growth factor receptor inhibitors on triple negative breast cancer cells

Abstract #3044

Introduction: Obesity is an independent risk factor for breast cancer and obese breast cancer patients exhibit a higher risk for larger tumor burden, increased metastasis and poor response to endocrine therapy. Obesity affects breast carcinogenesis by autocrine and paracrine effects of adipocytokine leptin and IGF-1. We have previously shown that leptin induces growth stimulation of breast cancer cells by recruiting histone acetyltransferases and mediator complex to cyclin D1 promoter via activation of Stat3. In the present study, we found a novel bidirectional crosstalk between IGF-1 and leptin signaling that promotes invasion and migration of triple-negative (ER, PR, HER2 negative) breast cancer cells; MDA-MB-231, MDA-MB-468, MDA-MB-435 and HCC-1806.&#x2028; Methods and Results: IGF-1 induced significant tyrosine phosphorylation of leptin receptor (Ob-Rb) and leptin induced tyrosine phosphorylation of IGF-1 Receptor (IGF-1R). Combined treatment of leptin and IGF-1 induced synergistic activation of both Ob-Rb and IGF-1R along with activation of Akt and ERK. Furthermore, IGF-1 and leptin synergistically transactivated epidermal growth factor receptor (EGFR) and induced proliferation of triple negative breast cancer cells. We also found that tyrosine phosphorylation of EGFR induced by combined treatment of leptin and IGF-1 was significantly inhibited not only by EGFR tyrosine kinase inhibitor, AG1478 but also with a broad-spectrum matrix metalloproteinase inhibitor, GM6001 indicating that leptin and IGF-1 induced EGFR transactivation is dependent on proteolytic release of EGFR ligands. Intriguingly, we also found that combined treatment of leptin and IGF-1 potently induced invasion of triple negative breast cancer cells in Matrigel invasion and quantitative Electric Cell-Substrate Impedance Sensing invasion assays. Inhibition of leptin and IGF-1 mediated EGFR activation using a highly potent, reversible inhibitor of HER1/EGFR tyrosine kinase, erlotinib or dual epidermal growth factor receptor (EGFR)/human EGFR-2 (HER2) kinase inhibitor, lapatinib effectively inhibited leptin and IGF-1 induced invasion. Also, inhibition of EGFR activation using erlotinib and lapatinib reduced leptin- and IGF-1-induced migration of triple negative breast cancer cells.&#x2028; Discussion: Taken together these data indicate a novel bidirectional crosstalk between leptin and IGF-1 signaling that transactivates EGFR and promotes metastatic properties, invasion and migration of triple negative breast carcinoma cells. Our novel findings indicate the possibility of using EGFR inhibitors erlotinib and lapatinib to counter the pro-cancerous effects of leptin and IGF-1 signaling in triple negative breast cancers.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3044.

Adiponectin activates tumor suppressor LKB1 and AMP-activated protein kinase signaling to inhibit malignant properties of breast cancer cells

Abstract #3067

Introduction: The prevalence of obesity in the developed world has reached epidemic proportions in recent years. Obese breast cancer patients exhibit a higher risk for metastasis, larger tumor burden and poorer response to endocrine therapy. Therefore, it is very important to understand the adverse effects of obesity on breast cancer in order to devise appropriate new approaches to their treatment. Obesity is considered an endocrine disorder and serum levels of adiponectin, an adipocytokine proposed to have therapeutic potential, get significantly lowered with obesity. More recently, low serum adiponectin levels were associated with increased risk and more aggressive phenotype (larger tumor size and high histological grade) of breast cancer in women. Recently, anti-proliferative and pro-apoptotic response of adiponectin was shown in breast cancer cells but the molecular mechanisms governing the anti-cancer effects of adiponectin largely remain unknown. In the present study, we found a novel mechanism underlying adiponectin action involving upregulation of tumor suppressor LKB1 and activation of AMPK (AMP-activated protein kinase) signaling to inhibit malignant properties of breast cancer cells.&#x2028; Methods and Results: Adiponectin inhibited malignant properties such as invasion and migration of breast cancer cells in matrigel invasion, scratch migration and quantitative Electric Cell-Substrate Impedance Sensing (ECIS) invasion and migration assays. Interestingly, adiponectin induced phosphorylation of AMPK at Thr 172 in breast cancer cells. Adiponectin treatment also affected downstream targets of mTOR signaling pathway, including decreased phosphorylation of p70S6K showing the involvement of mTOR-S6K axis. Intriguingly, we found that adiponectin increased the expression of tumor suppressor LKB1 in breast cancer cells. Co-immunoprecipitation assays revealed that LKB1 co-immunoprecipitated with tumor suppressor TSC2. Increase in expression of upstream kinase LKB1 might directly regulate adiponectin induced activation of AMPK. We also found that breast cancer cells transfected with wild-type LKB1 plasmids increased phosphorylation of AMPK and decreased phosphorylation of p70S6K showing decrease in mTOR activity. In contrast, breast cancer cells transfected with kinase dead LKB1 decreased phosphorylation of AMPK and increased activation of p70S6K.&#x2028; Discussion: Taken together these data indicate a novel crosstalk between adiponectin and tumor suppressor LKB1 that modulates AMPK-S6K axis and inhibits metastatic properties, invasion and migration of breast cancer cells. The influence of adipocytokine, adiponectin on breast carcinogenesis is just beginning to be elucidated and our study is the first to show the direct involvement of tumor suppressor genes LKB1 and TSC2 in anti-cancer effects of adiponectin.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3067.