Single Live Cell Imaging of Multidrug Resistance Using Silver Ultrasmall Nanoparticles as Biosensing Probes in Triple-Negative Breast Cancer Cells

Silver ultrasmall nanoparticles (Ag UNPs) (size < 5 nm) were used as biosensing probes to analyze the efflux kinetics contributing to multidrug resistance (MDR) in single live triple-negative breast cancer (TNBC) cells by using dark-field optical microscopy to follow their size-dependent localized surface plasmon resonance. TNBC cells lack expression of estrogen (ER-), progesterone (PR-), and human epidermal growth factor 2 (HER2-) receptors and are more likely to acquire resistance to anticancer drugs due to their ability to transport harmful substances outside the cell. The TNBC cells displayed greater nuclear and cytoplasmic efflux, resulting in less toxicity of Ag UNPs in a concentration-independent manner. In contrast, more Ag UNPs and an increase in cytotoxic effects were observed in the receptor-positive breast cancer cells that have receptors for ER+, PR+, and HER2+ and are known to better respond to anticancer therapies. Ag UNPs accumulated in receptor-positive breast cancer cells in a time-and concentration-dependent mode and caused decreased cellular growth, whereas the TNBC cells due to the efflux were able to continue to grow. The TNBC cells demonstrated a marked increase in survival due to their ability to have MDR determined by efflux of Ag UNPs outside the nucleus and the cytoplasm of the cells. Further evaluation of the nuclear efflux kinetics of TNBC cells with Ag UNPs as biosensing probes is critical to gain a better understanding of MDR and potential for enhancement of cancer drug delivery.

Abstract 949: Novel stilbene compounds inhibit triple-negative breast cancer invasive potential

Triple-negative breast cancer (TNBC) is a highly aggressive breast subtype of breast cancer that lacks targeted therapies. We have previously identified several novel stilbene compounds that effectively decreased viability of TNBC. Stilbenes are natural defense compounds produced by plants and have been popularized in recent years due to general observed health benefits. Resveratrol, the most widely studied stilbene, has been revealed to possess significant antioxidant and anti-cancer effects. Many stilbenes are classified as phytoestrogens, but unlike estrogens, stilbenes do not appear to negatively impact normal breast tissue or reproductive organ health. Thus, these compounds represent new alternatives for cancer therapeutic development. The focus of this research was to identify stilbene compounds with anti-migration and/or anti-invasive properties in TNBC cells and to determine the mechanism of these inhibitory effects. Two TNBC cell lines, MDA-MB-157 and BT-549, were treated with stilbene compounds at sub-lethal doses and assessed for effects on migration and invasion using transwell assays. Cell morphology changes were evaluated with results suggestive of reversal of epithelial-to-mesenchymal transition (EMT), a key contributor in the metastatic process and a common characteristic of many TNBC cells. Gene expression analysis confirmed stilbene-induced changes of EMT-related genes. These data indicate that stilbenes, like resveratrol and related analogues, reduce cell motility and invasion through regulation of EMT gene expression in TNBC cells. Development of synthetic analogs of natural compounds remains a viable drug development opportunity for new therapeutics.

Citation Format: Lyndsay V. Rhodes, Kaelyn Julmeus. Novel stilbene compounds inhibit triple-negative breast cancer invasive potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 949.

Application of a small molecule inhibitor screen approach to identify CXCR4 downstream signaling pathways that promote a mesenchymal and fulvestrant-resistant phenotype in breast cancer cells

Chemokine receptor 4 (CXCR4) and its ligand stromal-derived factor 1 (SDF-1) have well-characterized functions in cancer metastasis; however, the specific mechanisms through which CXCR4 promotes a metastatic and drug-resistant phenotype remain widely unknown. The aim of the present study was to demonstrate the application of a phenotypic screening approach using a small molecule inhibitor library to identify potential CXCR4-mediated signaling pathways. The present study demonstrated a new application of the Published Kinase Inhibitor Set (PKIS), a library of small molecule inhibitors from diverse chemotype series with varying levels of selectivity, in a phenotypic medium-throughput screen to identify potential mechanisms to pursue. Crystal violet staining and brightfield microscopy were employed to evaluate relative cell survival and changes to cell morphology in the screens. ‘Hits’ or lead active compounds in the first screen were PKIS inhibitors that reversed mesenchymal morphologies in CXCR4-activated breast cancer cells without the COOH-terminal domain (MCF-7-CXCR4-ΔCTD) and in the phenotypically mesenchymal triple-negative breast cancer cells (MDA-MB-231, BT-549 and MDA-MB-157), used as positive controls. In a following screen, the phenotypic and cell viability screen was used with a positive control that was both morphologically mesenchymal and had acquired fulvestrant resistance. Compounds within the same chemotype series were identified that exhibited biological activity in the screens, the ‘active’ inhibitors, were compared with inactive compounds. Relative kinase activity was obtained using published datasets to discover candidate kinase targets responsible for CXCR4 activity. MAP4K4 and MINK reversed both the mesenchymal and drug-resistant phenotypes, NEK9 and DYRK2 only reversed the mesenchymal morphology, and kinases, including ROS, LCK, HCK and LTK, altered the fulvestrant-resistant phenotype. Oligoarray experiments revealed pathways affected in CXCR4-activated cells, and these pathways were compared with the present screening approach to validate our screening tool. The oligoarray approach identified the integrin-mediated, ephrin B-related, RhoA, RAC1 and ErbB signaling pathways to be upregulated in MCF-7-CXCR4-ΔCTD cells, with ephrin B signaling also identified in the PKIS phenotypic screen. The present screening tool may be used to discover potential mechanisms of targeted signaling pathways in solid cancers.

Resveratrol analogues surprisingly effective against triple‑negative breast cancer, independent of ERα

Resveratrol, a plant‑derived stilbene compound, has exhibited anticancerous properties, including breast cancer. Stilbenes have a molecular structure highly similar to estrogen and have the ability to bind estrogen receptors and regulate activity. Numerous studies have demonstrated the effectiveness of resveratrol in estrogen receptor‑positive (ER‑positive) subtypes of breast cancer, yet the effects in ER‑negative subtypes, including triple‑negative breast cancer (TNBC), have been limited. In the present study, resveratrol and 28 analogues were tested on a panel of ER‑positive and TNBC cell lines to determine effects on cell viability. Several compounds exhibited significant impacts on cell viability and suggested changes in cell morphology, with high potency of select compounds compared to resveratrol observed in a dose‑dependent manner. Due to the lack of estrogen receptors in TNBC and the estrogenic nature of stilbenes, regulation of breast cancer‑associated cellular pathways was assessed for five analogues shown to significantly inhibit cell viability. Top regulated pathways included apoptosis (confirmed by caspase assay) and DNA damage repair. Overall, our results indicated several resveratrol analogues to be active in ER‑negative phenotypes, acting through an ER receptor‑independent manner, supporting further investigation into their mechanism of action and use as potential chemotherapeutics in higher‑risk breast cancer cases.

Drug resistance profiling of a new triple negative breast cancer patient-derived xenograft model

Background

Triple-negative breast cancer (TNBC) represents an aggressive subtype with limited therapeutic options. Experimental preclinical models that recapitulate their tumors of origin can accelerate target identification, thereby potentially improving therapeutic efficacy. Patient-derived xenografts (PDXs), due to their genomic and transcriptomic fidelity to the tumors from which they are derived, are poised to improve the preclinical testing of drug-target combinations in translational models. Despite the previous development of breast and TNBC PDX models, those derived from patients with demonstrated health-disparities are lacking.

Methods

We use an aggressive TNBC PDX model propagated in SCID/Beige mice that was established from an African-American woman, TU-BcX-2 K1, and assess its metastatic potential and drug sensitivities under distinct in vitro conditions. Cellular derivatives of the primary tumor or the PDX were grown in 2D culture conditions or grown in mammospheres 3D culture. Flow cytometry and fluorescence staining was used to quantify cancer stem cell-like populations. qRT-PCR was used to describe the mesenchymal gene signature of the tumor. The sensitivity of TU-BcX-2 K1-derived cells to anti-neoplastic oncology drugs was compared in adherent cells and mammospheres. Drug response was evaluated using a live/dead staining kit and crystal violet staining.

Results

TU-BcX-2 K1 has a low propensity for metastasis, reflects a mesenchymal state, and contains a large burden of cancer stem cells. We show that TU-BcX-2 K1 cells have differential responses to cytotoxic and targeted therapies in 2D compared to 3D culture conditions insofar as several drug classes conferred sensitivity in 2D but not in 3D culture, or cells grown as mammospheres.

Conclusions

Here we introduce a new TNBC PDX model and demonstrate the differences in evaluating drug sensitivity in adherent cells compared to mammosphere, or suspension, culture.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5401-2) contains supplementary material, which is available to authorized users.

Abstract 4410: ZEB2 drives cell motility and metastasis in ER+ breast cancer cells through a novel, E-cadherin independent pathway

Breast cancer is the most commonly diagnosed cancer in women, with the second highest mortality rate. The overwhelming majority of breast cancer deaths are a direct result of distant metastatic spread to vital organs such as lung, bone, and brain. The zinc finger transcription factor ZEB2 has been implicated as a driver of cancer cell motility, tissue invasion and metastasis in a number of diverse malignancies, but its role in breast cancer is not completely understood. We chose to examine the effects of direct overexpression of ZEB2 in the MCF-7 cell line, a luminal and estrogen receptor positive (ER+) derived breast cancer line. MCF-7-ZEB2 cells demonstrated significantly increased migration and invasion as well as an altered morphology in vitro compared to that of vector. Additionally, MCF-7-ZEB2 cells exhibited increased lung metastasis in vivo when implanted in an orthotopic xenograft mouse model. ZEB2 function in metastasis has canonically been attributed to transcriptional repression of the cell junction protein E-Cadherin. Here we establish that in ER+ breast cancer cells, ZEB2 fails to repress E-cadherin and promotes cell motility and metastasis through the induction of an E-cadherin independent signaling cascade. Next generation RNA sequencing analysis of the MCF-7-ZEB2 cells compared to vector revealed alteration of the MAPK signaling cascade, evidenced by enhanced expression of key motility and MAPK associated genes, including PLAU, EGF, ACTA2, and MMP9. Pharmacological inhibition of MAPK pathway completely abrogated ZEB2 induced migration, cell morphology changes and expression of target motility genes, confirming a necessary role for MAPK signaling in ZEB2-driven cell motility in ER+ breast cancer. Together these results indicate that the ZEB2 transcription factor drives motility in breast cancer cells through a novel MAPK dependent pathway, warranting further investigation into the mechanisms involved in ZEB2 action. Elucidating the pathways involved in ZEB2 function which are specific to ER+ breast cancer is an important step in understanding the processes underlying metastasis and has the potential to yield new therapeutic targets.

Citation Format: Hope E. Burks, Lyndsay V. Rhodes, Elizabeth C. Martin, Van T. Hoang, Steven Elliott, Melody Badoo, Theresa Phamduy, Aaron Buechlein, Douglas Rusch, Douglas Chrisey, Erik Flemington, Kenneth Nephew, Bridgette Collins-Burow, Matthew E. Burow. ZEB2 drives cell motility and metastasis in ER+ breast cancer cells through a novel, E-cadherin independent pathway. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4410.

Abstract 1596: Induction of mesenchymal-to-epithelial transition through pan-MEK inhibition in triple-negative breast cancer

Triple-negative breast cancer (TNBC) presents a clinical challenge due to the aggressive nature of the disease and a lack of targeted therapies. Constitutive activation of the MAPK/extracellular signal-regulated kinases (MEK) pathways has been linked to chemoresistance and metastatic progression through distinct mechanisms, including activation of epithelial-to-mesenchymal transition (EMT). Here we proposed to investigate dual inhibition of MEK1/2 and MEK5 as a more efficacious method for intervention to target mesenchymal and highly metastatic breast cancer cells than MEK1/2 or MEK5 alone through the use of a novel pan-MEK inhibitor SC-151. Interestingly, TNBC cells demonstrated a change in cell morphology indicative of mesenchymal-to-epithelial transition (MET) and exhibited a significant decrease in migration potential following pan-MEK inhibition. Additionally, immuno-compromised mice inoculated with MDA-MB-231 cells and treated with SC-151 demonstrated decreased tumor volumes compared to vehicle-treated animals. To parse the roles of MEK1/2 and MEK5 in EMT and tumorigenesis, we used the CRISPR/Cas9 approach to knock out ERK5 expression in the TNBC cell line MDA-MB-231. Similar to biological changes induced by pan-MEK inhibition, loss of ERK5 promoted epithelial characteristics in TNBC cells at the morphological and molecular level and impaired tumor formation in vivo. Treatment of ERK5-ko cells with SC-151 further enhanced these effects in vitro, suggesting that MEK1/2 and MEK5 play distinct roles in maintaining the mesenchymal phenotype. Further analysis revealed that constitutive activation of MEK5 abrogated the effects of SC-151 on the reversal of EMT, highlighting the requirement for MEK5 inhibition in MET induction. Taken together, these findings show that while the MEK5-ERK5 pathway may be sufficient in EMT regulation, MEK1/2 signaling further sustains the mesenchymal state of TNBC cells. Thus, dual MEK inhibition exerts optimal effects in the reversal of EMT. These data present a novel compound and viable therapeutic strategy to target both MEK1/2 and MEK5 in phenotypically mesenchymal and clinically aggressive breast cancer cells, warranting further investigation into mechanisms by which MEK1/2 and MEK5 individually modulate the EMT axis. Additionally, as MEK inhibition has been shown to sensitize resistant cancer cells to targeted therapies, synergistic and sensitizing effects of SC-151 combined with inhibitors of alternative signaling pathways as well as kinases upstream of MEK will be examined.

Citation Format: Van T. Hoang, Steven Elliott, Elizabeth C. Martin, Lyndsay V. Rhodes, Hope E. Burks, Margarite Matossian, Suravi Chakrabarty, Darlene Monlish, Theresa B. Phamduy, Lowry Curley, Muralidharan Anbalagan, Brian G. Rowan, Doug Chrisey, Jane E. Cavanaugh, Patrick T. Flaherty, Bridgette M. Collins-Burow, Matthew E. Burow. Induction of mesenchymal-to-epithelial transition through pan-MEK inhibition in triple-negative breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1596.

Abstract 3318: Exploring the utility of natural and synthetic resveratrol derivatives for bone regrowth following loss due to breast cancer therapies

Many of the most widely used therapies for the treatment of breast cancer have been associated with enhanced rate of bone loss, including chemotherapies and hormone therapies, due to alteration of normal hormone signaling. Bone loss is due to a shift in the balance between osteoblast and osteoclast cells that are derived from a common precursor, mesenchymal stem cells (MSC), found in the bone marrow. Estrogen is an important mediator of both hormone-responsive breast cancers and normal bone development and regeneration, favoring MSC differentiation down the osteoblast lineage. Stilbenes, defense compounds produced by plants including red grapes, peanuts, and blueberries, have been popularized in recent years based on observed health benefits. Resveratrol, the most widely studied stilbene, has been credited with many health benefits including cardiovascular health, anti-cancer and antioxidant effects, and inhibition of obesity and diabetes. Many stilbenes, including resveratrol can be classified as phytoestrogens due to their ability to bind and alter the activity of the estrogen receptor. A series of 28 stilbene compounds, including resveratrol and pterostilbene, were obtained by the U.S. Department of Agriculture and screened for effects on MSC differentiation. MSC were treated with stilbene compounds (both E and Z isoforms) and cultured in either osteogenic or adipogenic differentiation media for 7-21 days. Following differentiation, cells were stained with (1) Alizarin Red S to identify calcium deposits or (2) Oil Red O to identify lipid droplets. Several compounds were found to stimulate osteogenesis while inhibiting adipogenesis and were selected for further study and development. Realtime PCR for known genes associated with osteogenesis (ALPL, RUNX2, OCN, OPN) and adipogenesis (ADIPOQ, GLUT4, LEP, PPARG) were used to confirm differentiation and gain insight into the mechanism of altered differentiation. Unlike estrogen, stilbenes do not appear to negatively impact breast and reproductive organs. Stilbenes thus represent a novel option for inducing a preferential shift of MSCs toward the osteogenic lineage while potentially avoiding the negative health effects of estrogen. Targeting the differentiation of MSC to favor bone formation represents a viable target for the development of novel therapeutics for bone loss following cancer treatment. Further, identifying compounds that stimulate osteogenesis while repressing adipogenesis could benefit other metabolic disorders like obesity associated with increased breast cancer risk.

Citation Format: Evan Robert, Lyndsay V. Rhodes. Exploring the utility of natural and synthetic resveratrol derivatives for bone regrowth following loss due to breast cancer therapies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3318.

Dual regulation by microRNA-200b-3p and microRNA-200b-5p in the inhibition of epithelial-to-mesenchymal transition in triple-negative breast cancer

Epithelial to mesenchymal transition (EMT) involves loss of an epithelial phenotype and activation of a mesenchymal one. Enhanced expression of genes associated with a mesenchymal transition includes ZEB1/2, TWIST, and FOXC1. miRNAs are known regulators of gene expression and altered miRNA expression is known to enhance EMT in breast cancer. Here we demonstrate that the tumor suppressive miRNA family, miR-200, is not expressed in triple negative breast cancer (TNBC) cell lines and that miR-200b-3p over-expression represses EMT, which is evident through decreased migration and increased CDH1 expression. Despite the loss of migratory capacity following re-expression of miR-200b-3p, no subsequent loss of the conventional miR-200 family targets and EMT markers ZEB1/2 was observed. Next generation RNA-sequencing analysis showed that enhanced expression of pri-miR-200b lead to ectopic expression of both miR-200b-3p and miR-200b-5p with multiple isomiRs expressed for each of these miRNAs. Furthermore, miR-200b-5p was expressed in the receptor positive, epithelial breast cancer cell lines but not in the TNBC (mesenchymal) cell lines. In addition, a compensatory mechanism for miR-200b-3p/200b-5p targeting, where both miRNAs target the RHOGDI pathway leading to non-canonical repression of EMT, was demonstrated. Collectively, these data are the first to demonstrate dual targeting by miR-200b-3p and miR-200b-5p and a previously undescribed role for microRNA processing and strand expression in EMT and TNBC, the most aggressive breast cancer subtype.

Glyceollin, a novel regulator of mTOR/p70S6 in estrogen receptor positive breast cancer

An estimated 70% of breast cancer tumors utilize estrogen receptor (ER) signaling to maintain tumorigenesis and targeting of the estrogen receptor is a common method of treatment for these tumor types. However, ER-positive (+) breast cancers often acquire drug resistant or altered ER activity in response to anti-estrogens. Here we demonstrate glyceollin, an activated soy compound, has anti-estrogen effects in breast cancers. We demonstrate through estrogen response element luciferase and phosphorylation-ER mutants that the effects of glyceollin arise from mechanisms distinct from conventional endocrine therapies. We show that glyceollin suppresses estrogen response element activity; however, it does not affect ER-alpha (α) phosphorylation levels. Additionally we show that glyceollin suppresses the phosphorylation of proteins known to crosstalk with ER signaling, specifically we demonstrate an inhibition of ribosomal protein S6 kinase, 70 kDa (p70S6) phosphorylation following glyceollin treatment. Our data suggests a mechanism for glyceollin inhibition of ERα through the induced suppression of p70S6 and demonstrates novel mechanisms for ER inhibition.

Elevated expression of long intergenic non-coding RNA HOTAIR in a basal-like variant of MCF-7 breast cancer cells

Epigenetic regulation of gene expression is critical to phenotypic maintenance and transition of human breast cancer cells. HOX antisense intergenic RNA (HOTAIR) is a long intergenic non-coding RNA that epigenetically represses gene expression via recruitment of enhancer of zeste homolog 2 (EZH2), a histone methyltransferase. Elevated expression of HOTAIR promotes progression of breast cancer. In the current study we examined the expression and function of HOTAIR in MCF-7-TNR cells, a derivative of the luminal-like breast cancer cell line MCF-7 that acquired resistance to TNF-α-induced cell death. The expression of HOTAIR, markers of the luminal-like and basal-like subtypes, and growth were compared between MCF-7 and MCF-7-TNR cells. These variables were further assessed upon inhibition of HOTAIR, EZH2, p38 MAPK, and SRC kinase in MCF-7-TNR cells. When compared with MCF-7 cells, MCF-7-TNR cells exhibited an increase in the expression of HOTAIR, which correlated with characteristics of a luminal-like to basal-like transition as evidenced by dysregulated gene expression and accelerated growth. MCF-7-TNR cells exhibited reduced suppressive histone H3 lysine27 trimethylation on the HOTAIR promoter. Inhibition of HOTAIR and EZH2 attenuated the luminal-like to basal-like transition in terms of gene expression and growth in MCF-7-TNR cells. Inhibition of p38 and SRC diminished HOTAIR expression and the basal-like phenotype in MCF-7-TNR cells. HOTAIR was robustly expressed in the native basal-like breast cancer cells and inhibition of HOTAIR reduced the basal-like gene expression and growth. Our findings suggest HOTAIR-mediated regulation of gene expression and growth associated with the basal-like phenotype of breast cancer cells.

microRNA regulation of mammalian target of rapamycin expression and activity controls estrogen receptor function and RAD001 sensitivity

Background

The AKT/mammalian target of rapamycin (mTOR) signaling pathway is regulated by 17α-estradiol (E2) signaling and mediates E2-induced proliferation and progesterone receptor (PgR) expression in breast cancer.

Methods and results

Here we use deep sequencing analysis of previously published data from The Cancer Genome Atlas to demonstrate that expression of a key component of mTOR signaling, rapamycin-insensitive companion of mTOR (Rictor), positively correlated with an estrogen receptor-α positive (ERα⁺) breast tumor signature. Through increased microRNA-155 (miR-155) expression in the ERα⁺ breast cancer cells we demonstrate repression of Rictor enhanced activation of mTOR complex 1 (mTORC1) signaling with both qPCR and western blot. miR-155-mediated mTOR signaling resulted in deregulated ERα signaling both in cultured cells in vitro and in xenografts in vivo in addition to repressed PgR expression and activity. Furthermore we observed that miR-155 enhanced mTORC1 signaling (observed through western blot for increased phosphorylation on mTOR S2448) and induced inhibition of mTORC2 signaling (evident through repressed Rictor and tuberous sclerosis 1 (TSC1) gene expression). mTORC1 induced deregulation of E2 signaling was confirmed using qPCR and the mTORC1-specific inhibitor RAD001. Co-treatment of MCF7 breast cancer cells stably overexpressing miR-155 with RAD001 and E2 restored E2-induced PgR gene expression. RAD001 treatment of SCID/CB17 mice inhibited E2-induced tumorigenesis of the MCF7 miR-155 overexpressing cell line. Finally we demonstrated a strong positive correlation between Rictor and PgR expression and a negative correlation with Raptor expression in Luminal B breast cancer samples, a breast cancer histological subtype known for having an altered ERα-signaling pathway.

Conclusions

miRNA mediated alterations in mTOR and ERα signaling establishes a new mechanism for altered estrogen responses independent of growth factor stimulation.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-229) contains supplementary material, which is available to authorized users.

Abstract 1571: The tumor suppressor Liver Kinase B1 inhibits triple-negative breast cancer cell metastasis via regulation of AP-1 signaling

The basal sub-type, which shares features with triple-negative breast cancer (TNBC), is among the most lethal breast cancer subtype, characterized by a highly aggressive and metastatic phenotype. Although pathways that may represent targets for novel therapeutic intervention for basal like breast cancer (BLBC) have begun to be elucidated, the ability to define and selectively target the invasive and metastatic phenotype of basal-type/TNBC remains a major challenge facing the breast cancer field.

Liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11), is a known tumor suppressor in many cancers including breast. Low LKB1expression has been observed in breast cancer patients and we report a significant association between loss of LKB1 expression and poor prognosis specifically in the basal sub-type of breast cancer. Induction of LKB1 expression in BLBC cell lines inhibited invasiveness in vitro as well as lung and brain metastatic burden in an orthotopic xenograft tumor model. Further analysis of BLBC cell lines overexpressing LKB1 by next generation sequencing (RNA-seq) revealed striking regulation of metastasis-associated pathways, including cell adhesion, extra cellular matrix remodeling, and epithelial-to-mesenchymal transition (EMT). We further demonstrated marked inhibition of matrix metalloproteinase 1 (MMP-1) expression and activity via regulation AP-1 family member cJun. Additionally, LKB1 overexpression inhibited EMT-associated genes (CDH2, Vimentin, Twist) and induced the epithelial cell marker CDH1, indicating a reversal of the EMT phenotype in a triple-negative breast cancer cell line MDA-MB-231. We have demonstrated a role for LKB1 expression in the regulation of cell invasion and metastasis in addition to tumorigenesis. Taken together these data support future development of therapeutic agents to induce the LKB1 signaling pathway in BLCB/triple-negative breast cancer.

Citation Format: Lyndsay V. Rhodes, Chandra R. Tate, Hope E. Burks, Van T. Hoang, Diari Gilliam, Elizabeth C. Martin, Steven Elliott, David FB Miller, Aaron Buechlein, Douglas Rusch, Haixu Tang, Kenneth P. Nephew, Matthew E. Burow, Bridgette M. Collins-Burow. The tumor suppressor Liver Kinase B1 inhibits triple-negative breast cancer cell metastasis via regulation of AP-1 signaling. [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 1571. doi:10.1158/1538-7445.AM2014-1571

Abstract 1052: Dual role of MEK1/2 and MEK5 in the reversal of epithelial-to-mesenchymal transition

The mitogen-activated protein kinase (MAPK) pathway has well-established roles in cellular processes including proliferation, differentiation, and regulation of cell fate, namely survival and apoptosis. In breast cancer, constitutive activation of the MAPK/extracellular signal-regulated kinases (ERK) pathways have been linked to chemoresistance and metastatic progression through distinct mechanisms including the activation of epithelial-to-mesenchymal transition (EMT). Our previous studies have shown that overexpression of MEK5 promotes EMT markers and induces the progression to a mesenchymal phenotype. Here, we tested the effects of a novel MEK1/2 and MEK5 inhibitor, SC-1-151, and other known MAPK signaling inhibitors (PD184,352 (MEK1/2), AZD6244 (MEK1/2), BIRB796 (p38)) on a panel of mesenchymal and highly metastatic breast cancer cell lines. While the MEK1/2 and p38 inhibitors decreased cell viability across cell lines, only the dual inhibition of MEK1/2 and MEK5 though the use of SC-1-151 demonstrated a change in cell morphology indicative of mesenchymal-to-epithelial transition (MET). Furthermore, the cells exhibited a significant decrease in migration potential following SC-1-151 treatment.

Further analysis of the effects of SC-1-151 in the triple-negative breast cancer cell lines revealed an alteration of the genes associated with EMT, notably a decrease in expression of Fra-1, a transcription factor downstream of MAPK. Immuno-compromised mice inoculated with the MDA-MD-231 cell line and treated with SC-1-151 demonstrated decreased tumor volumes compared to vehicle-treated animals at day 30 post cell injection, implicating the role of MEK inhibition on tumorigenesis. These data demonstrate the need for a better understanding of the dual role of MEK1/2 and MEK5 signaling in breast cancer, and suggest that inhibition of the MEK1/2 and MEK5 signaling pathways leads to a decrease in EMT and cell migration.

Citation Format: Van T. Hoang, Steven Elliott, Elizabeth C. Martin, Lyndsay V. Rhodes, Henry C. Segar, Hope Burks, Suravi Chakrabarty, Darlene Monlish, Theresa B. Phamduy, Doug Chrisey, Jane E. Cavanaugh, Patrick Flaherty, Bridgette M. Collins-Burow, Matthew E. Burow. Dual role of MEK1/2 and MEK5 in the reversal of epithelial-to-mesenchymal transition. [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 1052. doi:10.1158/1538-7445.AM2014-1052

Obesity associated alterations in the biology of adipose stem cells mediate enhanced tumorigenesis by estrogen dependent pathways

Introduction

Obesity has been associated with increased incidence and mortality of breast cancer. While the precise correlation between obesity and breast cancer remains to be determined, recent studies suggest that adipose tissue and adipose stem cells (ASCs) influence breast cancer tumorigenesis and tumor progression.

Methods

Breast cancer cells lines were co-cultured with ASCs (n = 24), categorized based on tissue site of origin and body mass index (BMI), and assessed for enhanced proliferation, alterations in gene expression profile with PCR arrays, and enhanced tumorigenesis in immunocompromised mice. The gene expression profile of ASCs was assess with PCR arrays and qRT-PCR and confirmed with Western blot analysis. Inhibitory studies were conducted by delivering estrogen antagonist ICI182,780, leptin neutralizing antibody, or aromatase inhibitor letrozole and assessing breast cancer cell proliferation. To assess the role of leptin in human breast cancers, Oncomine and Kaplan Meier plot analyses were conducted.

Results

ASCs derived from the abdominal subcutaneous adipose tissue of obese subjects (BMI > 30) enhanced breast cancer cell proliferation in vitro and tumorigenicity in vivo. These findings were correlated with changes in the gene expression profile of breast cancer cells after co-culturing with ASCs, particularly in estrogen receptor-alpha (ESR1) and progesterone receptor (PGR) expression. Analysis of the gene expression profile of the four groups of ASCs revealed obesity induced alterations in several key genes, including leptin (LEP). Blocking estrogen signaling with ICI182,780, leptin neutralizing antibody, or letrozole diminished the impact of ASCs derived from obese subjects. Women diagnosed with estrogen receptor/progesterone receptor positive (ER⁺/PR⁺) breast cancers that also expressed high levels of leptin had poorer prognosis than women with low leptin expression.

Conclusion

ASCs isolated from the abdomen of obese subjects demonstrated increased expression of leptin, through estrogen stimulation, which increased breast cancer cell proliferation. The results from this study demonstrate that abdominal obesity induces significant changes in the biological properties of ASCs and that these alterations enhance ER⁺/PR⁺ breast cancer tumorigenesis through estrogen dependent pathways.

Suppression of triple-negative breast cancer metastasis by pan-DAC inhibitor panobinostat via inhibition of ZEB family of EMT master regulators

Triple-negative breast cancer (TNBC) is a highly aggressive breast cancer subtype that lacks effective targeted therapies. The epithelial-to-mesenchymal transition (EMT) is a key contributor in the metastatic process. We previously showed the pan-deacetylase inhibitor LBH589 induces CDH1 expression in TNBC cells, suggesting regulation of EMT. The purpose of this study was to examine the effects of LBH589 on the metastatic qualities of TNBC cells and the role of EMT in this process. A panel of breast cancer cell lines (MCF-7, MDA-MB-231, and BT-549), drugged with LBH589, was examined for changes in cell morphology, migration, and invasion in vitro. The effect on in vivo metastasis was examined using immunofluorescent staining of lung sections. EMT gene expression profiling was used to determine LBH589-induced changes in TNBC cells. ZEB overexpression studies were conducted to validate requirement of ZEB in LBH589-mediated proliferation and tumorigenesis. Our results indicate a reversal of EMT by LBH589 as demonstrated by altered morphology and altered gene expression in TNBC. LBH589 was shown to be a more potent inhibitor of EMT than other HDAC inhibitors, SAHA and TMP269. Additionally, we found that LBH589 inhibits metastasis of MDA-MB-231 cells in vivo. These effects of LBH589 were mediated in part by inhibition of ZEB, as overexpression of ZEB1 or ZEB2 mitigated the effects of LBH589 on MDA-MB-231 EMT-associated gene expression, migration, invasion, CDH1 expression, and tumorigenesis. These data indicate therapeutic potential of LBH589 in targeting EMT and metastasis of TNBC.

Abstract A016: Electrical impedance assessment of the effect of LBH589 on the cellular behavior and migratory potential of breast cancer cells

We have previously shown histone deacetylase inhibitor, LBH589 (Panobinostat), to increase E-cadherin expression and alter mesenchymal MDA-MB-231 cell morphology to a more epithelial phenotype suggestive of the reversal of EMT (epithelial-to-mesenchymal transition). As EMT has been linked to enhanced cell motility, we examined the effects of LBH589 on breast cancer cells in vitro. Electrical Cell-substrate Impedance Sensing (ECIS) allows for real-time, noninvasive measurement of cell behavior and reproducible wounding by lethal electroporation of the cell monolayer for migration studies.

Method: A 1 uA, 4kHz AC current applied across surface electrodes (250-μm diameter) provided electrical impedance monitoring capability, as MBA-MB-231 or MCF-7 breast cancer cells attached, spread, proliferate on the substrate. Measurements were reported as calculated resistance and capacitance. As cells grow on the substrate, the cell-electrode interaction is such that the current is forced to flow underneath and between cells. At 64 kHz, the capacitance is an indicator of electrode surface coverage. At 1 kHz, the resistance is an indicator of tight-junction formation between adjacent cells. As a monolayer develops, a decrease in capacitance and increase in resistance is observed. Upon visual confirmation of established cell monolayers, cells were treated with the LBH589 and cellular response was measured for 24 hrs. Afterwards, an elevated current (1 mA, 40 kHz, duration &gt;200 ms) was applied to the surface electrode, permanently damaging cell plasma membranes directly above the electrode and creating a defined gap in the monolayer or ‘wound’. Repopulation of the ‘wound’ was then monitored for 24 hrs.

Results: Cells were successfully grown and electrically monitored on the ECIS arrays. Micrographs show that proliferating MCF-7 and MDA-MB-231 cells gradually covered the electrode surface. MCF-7 cells arranged into a ‘cobblestone’ monolayer without gaps between adjacent cells, whereas MDA-MB-231 cells formed a loose monolayer with spaces between neighboring cells. At 22 hrs, the capacitance values for MCF-7 and MDA-MB-231 cells were observed to stabilize at ~1.3 nF and ~7.5 nF, respectively. The corresponding resistance values were ~40,000 Ohm and ~2,100 Ohm, respectively.

LBH589 exposure did not affect MCF-7 morphology, as capacitance or resistance values remained nearly constant at ~1.5 nF and ~40,000 Ohm, respectively. However, LBH589 appears to have a gradual effect on MDA-MB-231 cell monolayers, decreasing the capacitance value to ~3.5 nF and resistance to ~3,400 Ohm. Micrograph images taken after exposure indicate morphological changes in MDA-MB-231 cells from spindle-shaped to a more epithelial phenotypes.

In situ lethal electroporation introduced a ‘wound’ in the monolayer, generating a migration assay with a circular gap 250 μm in diameter. Live/dead staining performed 30 mins after electroporation indicated that cells on the electrode were dead. The corresponding resistance and capacitance values dropped to baseline (cell-free media) levels prior to recovery to control levels (non-electroporated cells). Based on measured resistance, the time to recovery for both LBH589-treated and untreated MCF-7 cells was ~7 hrs (radial migration rate of 17.9 μm/hr). Similarly, the time to recovery for treated MDA-MB-231 cells was ~2 hrs (62.5 μm/hr).

Conclusion: LBH589 appears to have an effect the morphology and the migration of MDA-MB-231, but not MCF-7, cells, as monitored by electrical measurements. ECIS provides a powerful tool to measure real-time functional cellular behavior, as well as a robust and reproducible method for assessing the migration potential of cancer cells. Measurement of dynamic cellular response following drug treatment could lead to more accurate evaluation of drug treatment against cancer.

Citation Format: Theresa B. Phamduy, Lyndsay V. Rhodes, Matthew E. Burow, Douglas B. Chrisey. Electrical impedance assessment of the effect of LBH589 on the cellular behavior and migratory potential of breast cancer cells. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A016.

MEK5/ERK5 signaling suppresses estrogen receptor expression and promotes hormone-independent tumorigenesis

Endocrine resistance and metastatic progression are primary causes of treatment failure in breast cancer. While mitogen activated protein kinases (MAPKs) are known to promote ligand-independent cell growth, the role of the MEK5-ERK5 pathway in the progression of clinical breast carcinoma remains poorly understood. Here, we demonstrated increased ERK5 activation in 30 of 39 (76.9%) clinical tumor samples, as well as across breast cancer cell systems. Overexpression of MEK5 in MCF-7 cells promoted both hormone-dependent and hormone-independent tumorigenesis in vitro and in vivo and conferred endocrine therapy resistance to previously sensitive breast cancer cells. Expression of MEK5 suppressed estrogen receptor (ER)α, but not ER-β protein levels, and abrogated downstream estrogen response element (ERE) transcriptional activity and ER-mediated gene transcription. Global gene expression changes associated with upregulation of MEK5 included increased activation of ER-α independent growth signaling pathways and promotion of epithelial-to-mesenchymal transition (EMT) markers. Taken together, our findings show that the MEK5-ERK5 pathway mediates progression to an ER(-), mesenchymal and endocrine therapy resistant phenotype. Given the need for new clinical therapeutic targets, our results demonstrate the therapeutic potential of targeting the MEK5-ERK5 pathway in breast cancer.

Phytoalexins, miRNAs and breast cancer: a review of phytochemical-mediated miRNA regulation in breast cancer

There is growing interest in the diverse signaling pathways that regulate and affect breast tumorigenesis, including the role of phytochemicals and the emerging role of microRNAs (miRNAs). Recent studies demonstrate that miRNAs regulate fundamental cellular and developmental processes at the transcriptional and translational level under normal and disease conditions. While there is growing evidence to support the role of phytoalexin-mediated miRNA regulation of cancer, few reports address this role in breast cancer. Recent reports by our group and others demonstrate that natural products, including stilbenes, curcumin, and glyceollins, could alter the expression of specific miRNAs, which may lead to increased sensitivity of cancer cells to conventional anti-cancer agents and, therefore, hormone-dependent and hormone-independent tumor growth inhibition. This review will discuss how dietary intake of natural products, by regulating specific miRNAs, contribute to the prevention and treatment of breast cancer.

In vitro and in vivo evaluation of novel anticancer agents in triple negative breast cancer models

Triple negative breast cancer (TNBC) is subtype of breast disease devoid of the estrogen, progesterone, and Her2/neu receptors which are targets for pharmacological intervention. There is a need for novel anti-breast cancer agents that target TNBC. Therefore, novel isochalcone DJ52 was evaluated using the alamar blue dye exclusion assay, the luciferase colony assay, and xenograft models to determine its efficacy and potency. DJ52 significantly decreased proliferation of cells measured by using the alamar blue dye method and produced IC50 values of DJ52, DJ56, and DJ82 at 10-6M, 10-5M, and 10-5M, respectively. In vivo studies were conducted by injecting MDA-MB-231 cells into SCID mice to determine tumor regression was measured over 20 days. DJ52 at 50 mg/kg caused significant decrease in tumor volume (p value <.05) by nearly 50% compared with the control with vehicle alone. These data suggest that DJ52 has merit for further evaluation as a novel anticancer agent.

A new method for stranded whole transcriptome RNA-seq

This report describes an improved protocol to generate stranded, barcoded RNA-seq libraries to capture the whole transcriptome. By optimizing the use of duplex specific nuclease (DSN) to remove ribosomal RNA reads from stranded barcoded libraries, we demonstrate improved efficiency of multiplexed next generation sequencing (NGS). This approach detects expression profiles of all RNA types, including miRNA (microRNA), piRNA (Piwi-interacting RNA), snoRNA (small nucleolar RNA), lincRNA (long non-coding RNA), mtRNA (mitochondrial RNA) and mRNA (messenger RNA) without the use of gel electrophoresis. The improved protocol generates high quality data that can be used to identify differential expression in known and novel coding and non-coding transcripts, splice variants, mitochondrial genes and SNPs (single nucleotide polymorphisms).

Inhibition of p38 mitogen-activated protein kinase alters microRNA expression and reverses epithelial-to-mesenchymal transition

Acquired chemoresistance and epithelial-to-mesenchymal transition (EMT) are hallmarks of cancer progression and of increasing clinical relevance. We investigated the role of miRNA and p38 mitogen-activated protein kinase (MAPK) signaling in the progression of breast cancer to a drug-resistant and mesenchymal phenotype. We demonstrate that acquired death receptor resistance results in increased hormone-independent tumorigenesis compared to hormone-sensitive parental cells. Utilizing global miRNA gene expression profiling, we identified miRNA alterations associated with the development of death receptor resistance and EMT progression. We further investigated the role of p38 MAPK in this process, showing dose-dependent inactivation of p38 by its inhibitor RWJ67657 and decreased downstream ATF and NF-κB signaling. Pharmacological inhibition of p38 also decreased chemoresistant cancer tumor growth in xenograft animal models. Interestingly, inhibition of p38 partially reversed the EMT changes found in this cell system, as illustrated by decreased gene expression of the EMT markers Twist, Snail, Slug and ZEB and protein and mRNA levels of Twist, a known EMT promoter, concomitant with decreased N-cadherin protein. RWJ67657 treatment also altered the expression of several miRNAs known to promote therapeutic resistance, including miR-200, miR-303, miR-302, miR-199 and miR-328. Taken together, our results demonstrate the roles of multiple microRNAs and p38 signaling in the progression of cancer and demonstrate the therapeutic potential of targeting the p38 MAPK pathway for reversing EMT in an advanced tumor phenotype.

Insulin-like growth factor-1 signaling regulates miRNA expression in MCF-7 breast cancer cell line

In breast carcinomas, increased levels of insulin-like growth factor 1 (IGF-1) can act as a mitogen to augment tumorigenesis through the regulation of MAPK and AKT signaling pathways. Signaling through these two pathways allows IGF-1 to employ mechanisms that favor proliferation and cellular survival. Here we demonstrate a subset of previously described tumor suppressor and oncogenic microRNAs (miRNAs) that are under the direct regulation of IGF-1 signaling. Additionally, we show that the selective inhibition of either the MAPK or AKT pathways prior to IGF-1 stimulation prevents the expression of previously described tumor suppressor miRNAs that are family and cluster specific. Here we have defined, for the first time, specific miRNAs under the direct regulation of IGF-1 signaling in the estrogen receptor positive MCF-7 breast cancer cell line and demonstrate kinase signaling as a modulator of expression for a small subset of microRNAs. Taken together, these data give new insights into mechanisms governing IGF-1 signaling in breast cancer.

Preferential star strand biogenesis of pre-miR-24-2 targets PKC-alpha and suppresses cell survival in MCF-7 breast cancer cells

microRNAs (miRNA) are regulators of cellular pathways and alterations of normal miRNA expression levels have been shown to increase tumorigenesis. miR-24 has been demonstrated as having both tumor suppressive and oncogenic properties depending on cell context. Here, we demonstrate a possible role for pre-miR-24-2 as a tumor suppressor in the MCF-7 breast cancer cell line through the preferential processing of mature miR-24-2* over miR-24. Specifically, we show that the ectopic expression of miR-24-2* in MCF-7 breast cancer cells results in a suppression of cellular survival both in vivo and in vitro. Notably, the overexpression of miR-24-2* results in a dampening of cell survival through the targeted suppression of PKCα. In addition, a similar biological change is observed in vivo where MCF-7 cells overexpressing pre-miR-24-2 have decreased tumorigenicity and tumor incidence. Taken together our data demonstrate that when overexpressed biogenesis of the pre-miR-24-2 favors miR-24-2* in the MCF-7 breast cancer cell line and suggests a tumor suppressive role for miR-24-2* observed through the inhibition of PKCα-mediated cellular survival.

Altered death receptor signaling promotes epithelial-to-mesenchymal transition and acquired chemoresistance

Altered death receptor signaling and resistance to subsequent apoptosis is an important clinical resistance mechanism. Here, we investigated the role of death receptor resistance in breast cancer progression. Resistance of the estrogen receptor alpha (ER)-positive, chemosensitive MCF7 breast cancer cell line to tumor necrosis factor (TNF) was associated with loss of ER expression and a multi-drug resistant phenotype. Changes in three major pathways were involved in this transition to a multidrug resistance phenotype: ER, Death Receptor and epithelial to mesenchymal transition (EMT). Resistant cells exhibited altered ER signaling, resulting in decreased ER target gene expression. The death receptor pathway was significantly altered, blocking extrinsic apoptosis and increasing NF-kappaB survival signaling. TNF resistance promoted EMT changes, resulting in a more aggressive phenotype. This first report identifying specific mechanisms underlying acquired resistance to TNF could lead to a better understanding of the progression of breast cancer in response to chemotherapy treatment.

Targeting triple-negative breast cancer cells with the histone deacetylase inhibitor panobinostat

INTRODUCTION

Of the more than one million global cases of breast cancer diagnosed each year, approximately fifteen percent are characterized as triple-negative, lacking the estrogen, progesterone, and Her2/neu receptors. Lack of effective therapies, younger age at onset, and early metastatic spread have contributed to the poor prognoses and outcomes associated with these malignancies. Here, we investigate the ability of the histone deacetylase inhibitor panobinostat (LBH589) to selectively target triple-negative breast cancer (TNBC) cell proliferation and survival in vitro and tumorigenesis in vivo.

METHODS

TNBC cell lines MDA-MB-157, MDA-MB-231, MDA-MB-468, and BT-549 were treated with nanomolar (nM) quantities of panobinostat. Relevant histone acetylation was verified by flow cytometry and immunofluorescent imaging. Assays for trypan blue viability, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) proliferation, and DNA fragmentation were used to evaluate overall cellular toxicity. Changes in cell cycle progression were assessed with propidium iodide flow cytometry. Additionally, qPCR arrays were used to probe MDA-MB-231 cells for panobinostat-induced changes in cancer biomarkers and signaling pathways. Orthotopic MDA-MB-231 and BT-549 mouse xenograft models were used to assess the effects of panobinostat on tumorigenesis. Lastly, flow cytometry, ELISA, and immunohistochemical staining were applied to detect changes in cadherin-1, E-cadherin (CDH1) protein expression and the results paired with confocal microscopy in order to examine changes in cell morphology.

RESULTS

Panobinostat treatment increased histone acetylation, decreased cell proliferation and survival, and blocked cell cycle progression at G2/M with a concurrent decrease in S phase in all TNBC cell lines. Treatment also resulted in apoptosis induction at 24 hours in all lines except the MDA-MB-468 cell line. MDA-MB-231 and BT-549 tumor formation was significantly inhibited by panobinostat (10 mg/kg/day) in mice. Additionally, panobinostat up-regulated CDH1 protein in vitro and in vivo and induced cell morphology changes in MDA-MB-231 cells consistent with reversal of the mesenchymal phenotype.

CONCLUSIONS

This study revealed that panobinostat is overtly toxic to TNBC cells in vitro and decreases tumorigenesis in vivo. Additionally, treatment up-regulated anti-proliferative, tumor suppressor, and epithelial marker genes in MDA-MB-231 cells and initiated a partial reversal of the epithelial-to-mesenchymal transition. Our results demonstrate a potential therapeutic role of panobinostat in targeting aggressive triple-negative breast cancer cell types.

Proteomic analysis of acquired tamoxifen resistance in MCF-7 cells reveals expression signatures associated with enhanced migration

Introduction

Acquired tamoxifen resistance involves complex signaling events that are not yet fully understood. Successful therapeutic intervention to delay the onset of hormone resistance depends critically on mechanistic elucidation of viable molecular targets associated with hormone resistance. This study was undertaken to investigate the global proteomic alterations in a tamoxifen resistant MCF-7 breast cancer cell line obtained by long term treatment of the wild type MCF-7 cell line with 4-hydroxytamoxifen (4-OH Tam).

Methods

We cultured MCF-7 cells with 4-OH Tam over a period of 12 months to obtain the resistant cell line. A gel-free, quantitative proteomic method was used to identify and quantify the proteome of the resistant cell line. Nano-flow high-performance liquid chromatography coupled to high resolution Fourier transform mass spectrometry was used to analyze fractionated peptide mixtures that were isobarically labeled from the resistant and control cell lysates. Real time quantitative PCR and Western blots were used to verify selected proteomic changes. Lentiviral vector transduction was used to generate MCF-7 cells stably expressing S100P. Online pathway analysis was performed to assess proteomic signatures in tamoxifen resistance. Survival analysis was done to evaluate clinical relevance of altered proteomic expressions.

Results

Quantitative proteomic analysis revealed a wide breadth of signaling events during transition to acquired tamoxifen resistance. A total of 629 proteins were found significantly changed with 364 up-regulated and 265 down-regulated. Collectively, these changes demonstrated the suppressed state of estrogen receptor (ER) and ER-regulated genes, activated survival signaling and increased migratory capacity of the resistant cell line. The protein S100P was found to play a critical role in conferring tamoxifen resistance and enhanced cell motility.

Conclusions

Our data demonstrate that the adaptive changes in the proteome of tamoxifen resistant breast cancer cells are characterized by down-regulated ER signaling, activation of alternative survival pathways, and enhanced cell motility through regulation of the actin cytoskeleton dynamics. Evidence also emerged that S100P mediates acquired tamoxifen resistance and migration capacity.

Endocrine disruptor regulation of microRNA expression in breast carcinoma cells

Background

Several environmental agents termed “endocrine disrupting compounds” or EDCs have been reported to bind and activate the estrogen receptor-α (ER). The EDCs DDT and BPA are ubiquitously present in the environment, and DDT and BPA levels in human blood and adipose tissue are detectable in most if not all women and men. ER-mediated biological responses can be regulated at numerous levels, including expression of coding RNAs (mRNAs) and more recently non-coding RNAs (ncRNAs). Of the ncRNAs, microRNAs have emerged as a target of estrogen signaling. Given the important implications of EDC-regulated ER function, we sought to define the effects of BPA and DDT on microRNA regulation and expression levels in estrogen-responsive human breast cancer cells.

Methodology/Principal Findings

To investigate the cellular effects of DDT and BPA, we used the human MCF-7 breast cancer cell line, which is ER (+) and hormone sensitive. Our results show that DDT and BPA potentiate ER transcriptional activity, resulting in an increased expression of receptor target genes, including progesterone receptor, bcl-2, and trefoil factor 1. Interestingly, a differential increase in expression of Jun and Fas by BPA but not DDT or estrogen was observed. In addition to ER responsive mRNAs, we investigated the ability of DDT and BPA to alter the miRNA profiles in MCF-7 cells. While the EDCs and estrogen similarly altered the expression of multiple microRNAs in MCF-7 cells, including miR-21, differential patterns of microRNA expression were induced by DDT and BPA compared to estrogen.

Conclusions/Significance

We have shown, for the first time, that BPA and DDT, two well known EDCs, alter the expression profiles of microRNA in MCF-7 breast cancer cells. A better understanding of the molecular mechanisms of these compounds could provide important insight into the role of EDCs in human disease, including breast cancer.

Glyceollin-elicited soy protein consumption induces distinct transcriptional effects as compared to standard soy protein

Glyceollins are stress-induced compounds in soybeans with bioactive properties distinct from parent soy isoflavones. The goals of this study were to evaluate the effects of dietary glyceollin-enriched and standard soy protein isolates and identify candidate target pathways of glyceollins on transcriptional profiles within mammary gland tissue. Thirty female postmenopausal cynomolgus monkeys were randomized to diets containing one of three protein sources for 3 weeks: (1) control casein/lactalbumin (C/L), (2) standard soy protein containing 194 mg/day isoflavones (SOY), and (3) glyceollin-enriched soy protein containing 189 mg/day isoflavones + 134 mg/day glyceollins (GLY). All diets contained a physiologic dose of estradiol (E2) (1 mg/day). All doses are expressed in human equivalents scaled by caloric intake. Relative to the control C/L diet, the GLY diet resulted in greater numbers of differentially regulated genes, which showed minimal overlap with those of SOY. Effects of GLY related primarily to pathways involved in lipid and carbohydrate metabolism, including peroxisome proliferator-activated receptor (PPAR)-γ and AMP-activated protein kinase (AMPK) signaling, adipocytokine expression, triglyceride synthesis, and lipase activity. Notable genes upregulated by the GLY diet included PPAR-γ, adiponectin, leptin, lipin 1, and lipoprotein lipase. The GLY diet also resulted in lower serum total cholesterol, specifically nonhigh-density lipoprotein cholesterol, and increased serum triglycerides as compared to the C/L diet. No effects of GLY or SOY were seen on serum insulin, adipocytokines, or vascular and bone turnover markers. These preliminary findings suggest that glyceollin-enriched soy protein has divergent effects from standard soy with some specificity for adipocyte activity and nutrient metabolism.

Glyceollins as novel targeted therapeutic for the treatment of triple-negative breast cancer

The purpose of this study was to investigate the effects of glyceollins on the suppression of tumorigenesis in triple-negative breast carcinoma cell lines. We further explored the effects of glyceollins on microRNA and protein expression in MDA-MB-231 cells. Triple-negative (ER-, PgR- and Her2/neu-) breast carcinoma cells were used to test the effects of glyceollins on tumorigenesis in vivo. Following this procedure, unbiased microarray analysis of microRNA expression was performed. Additionally, we examined the changes in the proteome induced by glyceollins in the MDA-MB-231 cells. Tumorigenesis studies revealed a modest suppression of MDA-MB-231 and MDA-MB-468 cell tumor growth in vivo. In response to glyceollins we observed a distinct change in microRNA expression profiles and proteomes of the triple-negative breast carcinoma cell line, MDA-MB-231. Our results demonstrated that the glyceollins, previously described as anti-estrogenic agents, also exert antitumor activity in triple-negative breast carcinoma cell systems. This activity correlates with the glyceollin alteration of microRNA and proteomic expression profiles.

The histone deacetylase inhibitor trichostatin A alters microRNA expression profiles in apoptosis-resistant breast cancer cells

The development of drug resistance represents a major complication in the effective treatment of breast cancer. Epigenetic therapy, through the use of histone deacetylase inhibitors (HDACi) or demethylation agents, is an emerging area of therapeutic targeting in a number of ontological entities, particularly in the setting of aggressive therapy-resistant disease. Using the well-described HDAC inhibitor trichostatin A (TSA) we demonstrate the suppression of in vitro clonogenicity in the previously described apoptosis-resistant MCF-7TN-R breast carcinoma cell line. Additionally, recent work has demonstrated that these agents can alter the expression profile of microRNA signatures in malignant cells. Using an unbiased microRNA microarray analysis, changes in miRNA expression of MCF-7TN-R cells treated with TSA for 24 h were analyzed. We observed significant up-regulation of 22 miRNAs and down-regulation of 10 miRNAs in response to TSA treatment. Our results demonstrate that the HDACi, TSA, exerts anticancer activity in the apoptosis-resistant MCF-7TN-R breast carcinoma cell line. This activity is correlated with TSA alteration of microRNA expression profiles indicative of a less aggressive phenotype.

Pharmacological inhibition of sphingosine kinase isoforms alters estrogen receptor signaling in human breast cancer

Recently, crosstalk between sphingolipid signaling pathways and steroid hormones has been illuminated as a possible therapeutic target. Sphingosine kinase (SK), the key enzyme metabolizing pro-apoptotic ceramide to pro-survival sphingosine-1-phosphate (S1P), is a promising therapeutic target for solid tumor cancers. In this study, we examined the ability of pharmacological inhibition of S1P formation to block estrogen signaling as a targeted breast cancer therapy. We found that the Sphk1/2 selective inhibitor (SK inhibitor (SKI))-II, blocked breast cancer viability, clonogenic survival and proliferation. Furthermore, SKI-II dose-dependently decreased estrogen-stimulated estrogen response element transcriptional activity and diminished mRNA levels of the estrogen receptor (ER)-regulated genes progesterone receptor and steroid derived factor-1. This inhibitor binds the ER directly in the antagonist ligand-binding domain. Taken together, our results suggest that SKIs have the ability to act as novel ER signaling inhibitors in breast carcinoma.

Cytokine receptor CXCR4 mediates estrogen-independent tumorigenesis, metastasis, and resistance to endocrine therapy in human breast cancer

Estrogen independence and progression to a metastatic phenotype are hallmarks of therapeutic resistance and mortality in breast cancer patients. Metastasis has been associated with chemokine signaling through the SDF-1-CXCR4 axis. Thus, the development of estrogen independence and endocrine therapy resistance in breast cancer patients may be driven by SDF-1-CXCR4 signaling. Here we report that CXCR4 overexpression is indeed correlated with worse prognosis and decreased patient survival irrespective of the status of the estrogen receptor (ER). Constitutive activation of CXCR4 in poorly metastatic MCF-7 cells led to enhanced tumor growth and metastases that could be reversed by CXCR4 inhibition. CXCR4 overexpression in MCF-7 cells promoted estrogen independence in vivo, whereas exogenous SDF-1 treatment negated the inhibitory effects of treatment with the anti-estrogen ICI 182,780 on CXCR4-mediated tumor growth. The effects of CXCR4 overexpression were correlated with SDF-1-mediated activation of downstream signaling via ERK1/2 and p38 MAPK (mitogen activated protein kinase) and with an enhancement of ER-mediated gene expression. Together, these results show that enhanced CXCR4 signaling is sufficient to drive ER-positive breast cancers to a metastatic and endocrine therapy-resistant phenotype via increased MAPK signaling. Our findings highlight CXCR4 signaling as a rational therapeutic target for the treatment of ER-positive, estrogen-independent breast carcinomas needing improved clinical management.

Effects of human mesenchymal stem cells on ER-positive human breast carcinoma cells mediated through ER-SDF-1/CXCR4 crosstalk

BACKGROUND

Adult human mesenchymal stem cells (hMSC) have been shown to home to sites of carcinoma and affect biological processes, including tumour growth and metastasis. Previous findings have been conflicting and a clear understanding of the effects of hMSCs on cancer remains to be established. Therefore, we set out to investigate the impact of hMSCs on the oestrogen receptor positive, hormone-dependent breast carcinoma cell line MCF-7.

RESULTS

In this study, we show the effects of hMSCs on cancer cells are mediated through a secreted factor(s) which are enhanced by cancer cell-hMSC contact/communication. In addition to enhanced proliferation when in co-culture with hMSCs, MCF-7 cells were found to have increased migration potential in vitro. Inhibition of ER signalling by the pure anti-oestrogen ICI 182,780 decreased the effect of hMSCs on MCF-7 cell proliferation and migration supporting a role for ER signalling in the hMSC/MCF-7 cell interaction. Additionally, hMSCs have been shown to secrete a wide variety of growth factors and chemokines including stromal cell-derived factor-1 (SDF-1). This coupled with the knowledge that SDF-1 is an ER-mediated gene linked with hormone-independence and metastasis led to the investigation of the SDF-1/CXCR4 signalling axis in hMSC-MCF-7 cell interaction. Experiments revealed an increase in SDF-1 gene expression both in vivo and in vitro when MCF-7 cells were cultured with hMSCs. SDF-1 treatment of MCF-7 cells alone increased proliferation to just below that seen with hMSC co-culture. Additionally, blocking SDF-1 signalling using a CXCR4-specific inhibitor decreased hMSC induced proliferation and migration of MCF-7. However, the combined treatment of ICI and AMD3100 reduced MCF-7 cell proliferation and migration below control levels, indicating targeting both the ER and CXCR4 pathways is effective in decreasing the hMSCs induction of MCF-7 cell proliferation and migration.

CONCLUSIONS

The sum of these data reveals the relationship between tumour microenvironment and tumour growth and progression. Better understanding of the mechanisms involved in this tumour stroma cell interaction may provide novel targets for the development of treatment strategies for oestrogen receptor positive, hormone-independent, and endocrine-resistant breast carcinoma.

Antiestrogenic effects of the novel sphingosine kinase-2 inhibitor ABC294640

Alterations in sphingolipid metabolism have been shown to contribute to the development of endocrine resistance and breast cancer tumor survival. Sphingosine kinase (SK), in particular, is overexpressed in breast cancer and is a promising target for breast cancer drug development. In this study, we used the novel SK inhibitor ABC294640 as a tool to explore the relationship between SK and estrogen (E2) receptor (ER) signaling in breast cancer cells. Treatment with ABC294640 decreased E2-stimulated ERE-luciferase activity in both MCF-7 and ER-transfected HEK293 cells. Furthermore, the inhibitor reduced E2-mediated transcription of the ER-regulated genes progesterone receptor and SDF-1. Competitive receptor-binding assays revealed that ABC294640 binds in the antagonist ligand-binding domain of the ER, acting as a partial antagonist similar to tamoxifen. Finally, treatment with ABC294640 inhibited ER-positive breast cancer tumor formation in vivo. After 15 d of treatment with ABC294640, tumor volume was reduced by 68.4% (P < 0.05; n = 5) compared with control tumors, with no marked weight loss or illness. Taken together, these results provide strong evidence that this novel SK inhibitor, which had not previously been known to interact with E2 signaling pathways, has therapeutic potential in treating ER-positive breast cancer via inhibition of both SK and ER signaling.

Effects of 7-O substitutions on estrogenic and anti-estrogenic activities of daidzein analogues in MCF-7 breast cancer cells

Daidzein (1) is a natural estrogenic isoflavone. We report here that 1 can be transformed into anti-estrogenic ligands by simple alkyl substitutions of the 7-hydroxyl hydrogen. To test the effect of such structural modifications on the hormonal activities of the resulting compounds, a series of daidzein analogues have been designed and synthesized. When MCF-7 cells were treated with the analogues, those resulting from hydrogen substitution by isopropyl (3d), isobutyl (3f), cyclopentyl (3g), and pyrano- (2) inhibited cell proliferation, estrogen-induced transcriptional activity, and estrogen receptor (ER) regulated progesterone receptor (PgR) gene expression. However, methyl (3a) and ethyl (3b) substitutions of the hydroxyl proton only led to moderate reduction of the estrogenic activities. These results demonstrated the structural requirements for the transformation of daidzein from an ER agonist to an antagonist. The most effective analogue, 2, was found to reduce in vivo estrogen stimulated MCF-7 cell tumorigenesis using a xenograft mouse model.

Abstract 4606: An in vitro and in vivo evaluation of novel anticancer agents in a triple negative breast cancer model

Patients diagnosed with triple negative breast cancer, which is the absence of the estrogen (ER), progesterone (PR), and Her2/neu receptor have a poor prognosis and there is a critical need to develop novel antineoplastic agents for this breast cancer sub-type. Therefore, the focus of this project is to identify novel anticancer agents with in vitro and in vivo antiproliferative activity in a triple negative breast cancer model. Previously, our laboratory synthesized a group of novel isochalcones called DJ compounds that demonstrated significant in vitro antiproliferative effects. Cell proliferation of MDA-MB-231 cells was measured using the alamar blue dye method and produced IC50 values of DJ52, DJ56, and DJ82 at 10−6M, 10−5M, and 10−5M, respectively. Binding studies have indicated that these agents do not bind the ER but appear to inhibit a phosphorylation step in the epidermal growth factor (EGFR) receptor pathway. In vivo studies were also conducted by implanting tumors derived from MDA-MB231 cells into SCID mice to determine tumor regression was measured over 20 days. DJ52 at 50mg/kg caused significant decrease (p value &lt;.05) decreased tumor volume by nearly fifty percent compared to the control with vehicle alone. Therefore, these data suggests that DJ52 has merit for further evaluation for potential intervention in patients diagnosed with triple negative breast cancer. Our laboratory continues our efforts to understand the mechanism of action of these agents to potentially provide alternative pharmacological options for these patients for better health outcomes.

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 4606.

Adult human mesenchymal stem cells enhance breast tumorigenesis and promote hormone independence

Adult human mesenchymal stem cells (hMSCs) have been shown to home to sites of breast cancer and integrate into the tumor stroma. We demonstrate here the effect of hMSCs on primary breast tumor growth and the progression of these tumors to hormone independence. Co-injection of bone marrow-derived hMSCs enhances primary tumor growth of the estrogen receptor-positive, hormone-dependent breast carcinoma cell line MCF-7 in the presence or absence of estrogen in SCID/beige mice. We also show hormone-independent growth of MCF-7 cells when co-injected with hMSCs. These effects were found in conjunction with increased immunohistochemical staining of the progesterone receptor in the MCF-7/hMSC tumors as compared to MCF-7 control tumors. This increase in PgR expression indicates a link between MCF-7 cells and MSCs through ER-mediated signaling. Taken together, our data reveal the relationship between tumor microenvironment and tumor growth and the progression to hormone independence. This tumor stroma-cell interaction may provide a novel target for the treatment of estrogen receptor-positive, hormone-independent, and endocrine-resistant breast carcinoma.

Human uterine smooth muscle and leiomyoma cells differ in their rapid 17beta-estradiol signaling: implications for proliferation

Uterine leiomyomas, benign uterine smooth muscle tumors that affect 30% of reproductive-aged women, are a significant health concern. The initiation event for these tumors is unclear, but 17beta-estradiol (E2) is an established promoter of leiomyoma growth. E2 not only alters transcription of E2-regulated genes but also can rapidly activate signaling pathways. The aim of our study is to investigate the role of rapid E2-activated cytoplasmic signaling events in the promotion of leiomyomas. Western blot analysis revealed that E2 rapidly increases levels of phosphorylated protein kinase C alpha (PKC alpha) in both immortalized uterine smooth muscle (UtSM) and leiomyoma (UtLM) cell lines, but increases levels of phosphorylated ERK1/2 only in UtLM cells. Our studies demonstrate a paradoxical effect of molecular and pharmacological inhibition of PKC alpha on ERK1/2 activation and cellular proliferation in UtLM and UtSM cells. PKC alpha inhibition decreases levels of phosphorylated ERK1/2 and proliferation in UtLM cells but raises these levels in UtSM cells. cAMP-PKA signaling is rapidly activated only in UtSM cells with E2 and inhibits ERK1/2 activation and proliferation. We therefore propose a model whereby E2's rapid activation of PKC alpha and cAMP-PKA signaling plays a central role in the maintenance of a low proliferative index in normal uterine smooth muscle via its inhibition of the MAPK cascade and these pathways are altered in leiomyomas to promote MAPK activation and proliferation. These studies demonstrate that rapid E2-signaling pathways contribute to the promotion of leiomyomas.

Hantavirus pulmonary syndrome associated with Monongahela virus, Pennsylvania

The first two recognized cases of rapidly fatal hantavirus pulmonary syndrome in Pennsylvania occurred within an 8-month period in 1997. Illness in the two patients was confirmed by immunohistochemical techniques on autopsy material. Reverse transcription-polymerase chain reaction analysis of tissue from one patient and environmentally associated Peromyscus leucopus (white-footed mouse) identified the Monongahela virus variant. Physicians should be vigilant for such Monongahela virus-associated cases in the eastern United States and Canada, particularly in the Appalachian region.

Nosocomial herpes simplex virus infection associated with oral endotracheal intubation

BACKGROUND

To determine by culture the frequency of herpes simplex virus reactivation complicating oral endotracheal intubation. Additionally, clinical appearance and recognition of patient infection by attendant health care workers were studied. Last, evidence of any occupational acquisition of herpes simplex virus infection was sought.

METHODS

In a prospective, non-randomized study, three serial viral cultures were taken of oro-facial or mucosal sites on the day of oral endotracheal intubation and in the subsequent 3rd and 5th or 7th days from 51 consecutive adults undergoing oral endotracheal intubation in a suburban community hospital. Clinical variables including appearances of lesions and therapeutic interventions were noted during serial assessments by study authors. Employee health records were reviewed for evidence of health care worker occupational herpes simplex virus infection associated with these cases.

RESULTS

Of 51 patients, 4 were culture positive on the day of oral endotracheal intubation. Of the remaining 47 patients, serial cultures during the first week post intubation revealed herpes simplex virus in 25 (53.2%) patients. Of cohort variables studied, a history of prior oral herpes simplex virus was significantly associated with a subsequent positive viral culture for herpes simplex virus (relative risk, 2.29; 95% confidence interval, 1.48 to 3.56). Typical or atypical lesions were visible in only 52% of the herpes simplex virus culture-positive cases. No occupational transmission of herpes simplex virus was detected. Tape-securing practices appeared to contribute to the morbidity of herpes simplex virus eruptions.

CONCLUSIONS

Nosocomial reactivation of herpes simplex virus infection complicated oral endotracheal intubation in our patient population in approximately one half of the patients who were intubated for more than 48 hours during the first week after the procedure. Clinically, the infection was recognizable in only one half of the virus culture-positive cases. Increased awareness of this infection is needed by health care workers, patients, and families. More information is needed on optimal therapy and prevention.

Rapid assessment of human immunodeficiency virus seroprevalence in a community-based hospital

BACKGROUND

To aid in development of patient testing policy, in-service education, and resource planning, it is necessary to have a useful and meaningful tool for determining the population-specific HIV seroprevalence rate for our hospital patients. We were offered by the Centers for Disease Control a newly developed survey tool: "Rapid Assessment of HIV Seroprevalence in Hospital Patients." We subsequently served as one pilot site for this tool.

METHODS

A population-based sample of 1000 patients (500 inpatients, 500 outpatients) was stratified into age and sex groups on the basis of admission statistics from the previous year in a general community hospital system in southeastern Pennsylvania that consists of two clinical campuses: an urban site with 343 beds and a suburban site with 506 beds. The study was conducted as an anonymous, unlinked screening for HIV antibody in 1000 serum samples.

RESULTS

We found our overall seroprevalence rate to be 2.60% (Poisson 95% confidence interval, 1.77% to 3.81%), or 1 in 38 patient specimens. The highest rates for both sexes were found in the age range 25 to 44 years.

CONCLUSIONS

This protocol is a useful survey tool for community hospitals to determine the HIV seroprevalence rate in patient populations, a practical necessity for planning and education. Survey results would aid in implementation of current Centers for Disease Control guidelines for HIV testing of inpatients and outpatients in the acute care hospital setting.

Impact of human immunodeficiency virus on medical and surgical residents

BACKGROUND--Previous surveys of resident physicians on human immunodeficiency virus (HIV) matters have tended to focus on urban programs serving a patient population with an expected high prevalence of HIV infection. The objective of this study was to survey a community hospital residency program in a nonurban area with a perceived low HIV patient seroprevalence. METHODS--A 32-question survey was completed on an anonymous basis by the entire 74 member multidisciplinary resident physician group at a two-campus university-affiliated hospital program in southeastern Pennsylvania in May 1991. RESULTS--Residents perceived their patient population's HIV seroprevalence rate to be low although they believed their personal risk of occupational exposure to blood-borne infection was moderate to high. House staff most often complied with universal precautions for fear of acquiring a blood-borne illness and most often did not comply because of time constraints. Not perceiving the exposure as a health risk was the primary reason for nonreporting of exposures. Occupational exposure rates were alarmingly high, with suturing using a curved needle being the most common exposure method. Most residents were unfamiliar with HIV legislation. A majority of the house staff wanted improved HIV patient management training and life and disability insurance against occupationally acquired HIV. Many other important issues were addressed in this survey. CONCLUSION--Residents even in low seroprevalence environments do fear occupationally acquired HIV. A great need exists for improved training in universal precautions, acquired immunodeficiency syndrome legislation, and HIV patient management as well as for insurance against occupationally acquired HIV.

Isolation of Legionella pneumophila from clinical specimens: salutary effects of lung tissue dilution

Diagnosis of legionnaires' disease is seldom confirmed by isolation of Legionella pneumophila. In 2 cases, isolates were obtained using inoculums of diluted lung tissue suspension, even though no growth ocurred when undiluted suspensions were used. It is speculated that tissue dilution decreases the concentration of antimicrobial agents and antibacterial properties associated with lung host defense mechanisms, which allows improved recovery rates. This technique is recommended when attempting isolation of L. pneumophila from clinical specimens.

Diagnostic specificity of immunoglobulin M (IgM) response in differentiation Legionnaires' disease from psittacosis

Specific IgM and IgG antibody responses to Legionella pneumophila (LDB) and Chlamydia psittaci (PSI) in serum specimens from 22 cases of Legionnaires' Disease (LD) were examined by micro-immunofluorescence (IF) tests to explore the diagnostic significance of the IgM antibody response. Serial samples from 5 patients with LD showed greater than or equal to 4-fold changes in IgG antibody against LDB and PSI. All 5 patients possessed IgM antibodies against LDB but not against PSI. In single convalescent serum samples from 17 additional cases, 16 exhibited IgG and 15 showed IgM antibodies against LDB; all 17 exhibited IgG but not IgM antibodies against PSI. The IgM antibody response appears more specific than the corresponding IgG response in the serodiagnosis of LD, and may be valuable in differentiating LDB infections from those due to PSI.

The Philadelphia epidemic of Legionnaire's disease: clinical, pulmonary, and serologic findings two years later

Clinical, pulmonary, and serologic findings in Legionnaires who attended the 1976 American Legion Convention in Philadelphia were studied 2 years after the Legionnaires' disease epidemic there. All 31 survivors of Legionnaires' disease studied became ill within 2 weeks after the convention, and 18 had not fully recovered 2 years after the epidemic. Twenty-five (28%) of 90 additional Legionnaires exposed at the convention but not diagnosed as having Legionnaires' disease became ill during the same time interval; five of these had symptoms during the next 2 years. Survivors had decreased diffusion capacities measured by the carbon monoxide single-breath method. These differences could not be accounted for by ventilation abnormalities or concurrent illness. Significant levels of IgG or IgM antibodies persisted in 94% of survivors of Legionnaires' disease and in 53% of Legionnaires exposed at the convention, which suggests a high prevalence of subclinical infection. Persistence of IgM antibody raises the question of latency or subclinical infection as part of the natural history of Legionnaires' disease.