Abstract 2590: Nano-exosomes with miRNA: A new therapeutic approach

Access to reliable and effective therapeutics for patients suffering from aggressive triple-negative breast cancer (TNBC) has been clinically challenging to achieve due to lack of targetable mutations and high heterogeneity in the tumor cells. Therapeutic approaches to reduce mortality in the TNBC patient subset requires an innovative and targeted approach to drug delivery, which is presented here in the form of labeled-exosomes. In this study, we have developed a novel method to bioengineer exosomes, where an antibody is covalently bonded to a fatty acid, which is then anchored into the exosomal membrane to create labeled-exosomes. Our data demonstrate that labeled-exosomes can contain up to 700,000-fold higher miRNA concentrations and can deliver miRNA cargo with increased efficiency into MDA-MB-231 TNBC cells. Results further reveal that insertion of a specific antibody-label to the exosomal membrane significantly increases microRNA uptake into MDA-MB-231 cells, and is further enhanced in cells overexpressing that same antibody marker on their surface. The customizable bioengineering of the labeled-exosomes makes it a highly versatile tool to target cells based on surface marker expression and increase miRNA or other therapeutic cargo delivery. Most importantly, the relevancy of this model reaches far beyond its success in just TNBC cells and can also be translated to several different disease models that require specific targeting with an encapsulated miRNA or therapeutic. We believe this is a novel and exciting utilization of exosomes with a high degree of customization based on surface markers on the target cell, as well as microRNA cargo loaded into the exosome to inhibit a specific oncogene.

Citation Format: Sudeepti Kuppa, Balazs Rada, Arthur Roberts, Mandi M. Murph. Nano-exosomes with miRNA: A new therapeutic approach [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 2590.

Diet-regulated behavior: FVB/N mice fed a lean diet exhibit increased nocturnal bouts of aggression between littermates

The hyperactive FVB/N inbred mouse strain is widely used for transgenic research applications, although rarely for behavioral studies. These mice have visual impairments via retinal degeneration, but are considered highly intelligent and rely largely on olfaction. While investigating diet-induced obesity in autotaxin transgenic FVB/N mice, we observed an increase in the necessity for male, but not female, cage separations. Based on the observations, we hypothesized that feeding FVB/N mice a lean diet increases nocturnal bouts of aggression between male littermates. The diets of adult littermates were switched from normal chow to either ad libitum high-fat (45% fat) or lean (10% fat) matched diets for 27 weeks, whereby the mice reached an average of 43 g versus 35 g, respectively. Then, cage separations due to nocturnal bouts of aggression became mandatory, even though littermates peacefully cohabitated for 10-16 weeks previously. Since the data was of an unusual nature, it required uncommon statistical methods to be engendered to evaluate whether and where significance existed. Therefore, utilizing the randomization and population models, we established a methodology and postulated that either testosterone, the autotaxin transgene or diet alteration was the causal factor. Statistical evaluation demonstrated a significant correlation between cage separations and aggressive behavior associated with the lean-diet-fed mice, not autotaxin. Biochemical data did not appear to explain the behavior. In contrast, energy metabolism highlighted differences between the groups of normally hyperactive mice by diet. This characteristic makes FVB/N male mice unsuitable subjects for long-term studies with lean-diet modifications.

Direct identification of microribonucleic acid miR-451 from plasma using liquid chromatography mass spectrometry

In recent years, small endogenous RNAs have come to the forefront of both basic and translational research. For example, many studies have pointed to the potential role of microRNAs (miRNAs) as disease biomarkers. However, precise quantitative methods for the analysis of miRNAs are still lacking. In this study, we report the first mass spectrometry-based quantitation of miR-451, a circulatory microRNA. Using a highly selective sample preparation method with an average recovery of 83.6% and a novel mobile phase chemistry, we were able to reach an LOQ of 0.5 ng/mL. Because of such high sensitivity, we could detect and quantify the endogenous miR-451 from both human and rat plasma. Considering the increased precision of LC-MS compared to other methods, these results usher in a new era of miRNA biomarker discovery and validation.

Abstract A30: Autotaxin-induced miRNA exportation and associated mechanisms contributing to tumorigenesis and immune modulation

Approximately 30% of tumors from patients with serous ovarian carcinoma show a significant overexpression of the extracellular enzyme, autotaxin. This circulating enzyme is responsible for lipid metabolism, specifically the hydrolysis of a phosphatidylcholine head group from lysophosphatidyl choline (LPC) to yield lysophosphatidic acid (LPA), which is abundantly found in malignant ascites fluid. As a consequence, numerous growth factor-like pathways through LPA receptors (LPARs), which are cell surface G protein-coupled receptors that bind lipid agonists such as LPA, are aberrantly initiated in ovarian cancer cells, and miRNA feedback mechanisms, which normally regulate such signaling, are disregarded. The purpose of our study is to further understand how serous ovarian cancer cells disregard counteracting miRNA feedback mechanisms that could otherwise prevent tumorigenesis and tumor progression. Therefore, we hypothesize that ovarian cancer cells can hijack miRNA feedback mechanisms by exporting miRNA to alter the signaling of surrounding cells in the stroma and tumor microenvironment, allowing the cancer cells to thrive. We further hypothesize that miR-30c-2-3p, the key component of the feedback mechanism that regulates oncogenic transcription mediated by lysophosphatidic acid, is exported packaged in exosomes. From there, it is likely that exosomes containing miR-30c-2-3p are engulfed by other surrounding cells of the immune system, possibly contributing to immune modulation or suppression in ovarian cancer. Our data will present evidence to support this hypothesis.

Foremost, we used an in vivo model of disease as one measure of miR-30c-2-3p expression, circulation, and uptake by surrounding cells through comparison of tumor-bearing and non-tumor-bearing transgenic mice with enhanced autotaxin expression. Chiefly, adipocytes vary in their ability to produce autotaxin in vitro, yet these numbers are inconsistent with circulating levels in transgenic mice, suggesting that miR-30c-2-3p is being absorbed by another cell type. Since ovarian cancer is notorious for its multifactorial immune-suppression properties, we investigated the uptake of exosomal miR-30c-2-3p by peripheral blood mononuclear cells (PBMCs), containing monocytes, lymphocytes, and dendritic cells. Coculture of PBMCs and OVCAR-3 cells has demonstrated a significant (p<0.05) increase in extracellular miR-30c-2-3p compared to OVCAR-3 cells alone, suggesting a strong interplay between the immune players and cancer cells. Utilizing OVCAR-3-GFP cells, which stably express palmitoylated GFP on their plasma membrane, in vitro studies can visually observe the transfer of cancer cell-derived exosomes to immune cells, possibly shedding light on an intracellular response related to immune suppression. Further investigation involving the influence of individual immune cell types and cancer cells utilizing OVCAR-3-ATXwt and OVCAR-3-ATXmut cells will also be conducted in search of immune-suppression mechanisms in ovarian cancer. In conclusion, our overall study will provide evidence to show how unappreciated factors like miRNA may play a major role in the molecular mechanisms contributing to tumor progression in serous ovarian cancer.

Citation Format: Sudeepti S. Kuppa, Balazs Rada, Mandi M. Murph. Autotaxin-induced miRNA exportation and associated mechanisms contributing to tumorigenesis and immune modulation. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr A30.

Autotaxin exacerbates tumor progression by enhancing MEK1 and overriding the function of miR-489-3p

Upregulated expression of autotaxin, a secreted phospholipase and phosphodiesterase enzyme, appears in malignant disease. The identification of a circulating miRNA signature should distinguish autotaxin-mediated disease and also elucidate unknown molecular mechanisms that rationalize its malignant potential. Using female transgenic 'AT-ATX' mice, whereby human wild-type autotaxin is expressed in liver under the control of the alpha-1 antitrypsin promoter, transgenic animals express augmented autotaxin in circulation and a percentage develop tumors. Serum collected at necropsy had circulating miRNAs analyzed for statistical significance. The ensuing autotaxin-mediated miRNome differentiated between groups: healthy FVB/N mice versus AT-ATX mice with and without tumors. Intriguingly, miR-489-3p was sharply increased in AT-ATX tumor-bearing mice. Tissue analysis showed a correlation between miR-489-3p expression in tumors and surrounding milieu with autotaxin concentration in circulation. Sequence alignment suggested miR-489-3p targets MEK1, which was confirmed through in vitro studies. Exogenously added miR-489-3p, which decreases MEK1 in normal cells, dramatically increased MEK1 expression in cells stably expressing autotaxin. Taken together, this suggests that autotaxin overrides the normal regulatory function of miR-489-3p to inhibit MEK1 via coordinately increased miR-489-3p appearing in serum.

Assessing the Interplay between the Physicochemical Parameters of Ion-Pairing Reagents and the Analyte Sequence on the Electrospray Desorption Process for Oligonucleotides

Alkylamines are widely used as ion-pairing agents during LC-MS of oligonucleotides. In addition to a better chromatographic separation, they also assist with the desorption of oligonucleotide ions into the gas phase, cause charge state reduction, and decrease cation adduction. However, the choice of such ion-pairing agents has considerable influence on the MS signal intensity of oligonucleotides as they can also cause significant ion suppression. Interestingly, optimal ion-pairing agents should be selected on a case by case basis as their choice is strongly influenced by the sequence of the oligonucleotide under investigation. Despite imposing major practical difficulties to analytical method development, such a highly variable system that responds very strongly to the nuances of the electrospray composition provides an excellent opportunity for a fundamental study of the electrospray ionization process. Our investigations using this system quantitatively revealed the major factors that influenced the ESI ionization efficiency of oligonucleotides. Parameters such as boiling point, proton affinity, partition coefficient, water solubility, and Henry's law constants for the ion-pairing reagents and the hydrophobic thymine content of the oligonucleotides were found to be the most significant contributors. Identification of these parameters also allowed for the development of a statistical predictive algorithm that can assist with the choice of an optimum IP agent for each particular oligonucleotide sequence. We believe that research in the field of oligonucleotide bioanalysis will significantly benefit from this algorithm (included in Supplementary Material) as it advocates for the use of lesser-known but more suitable ion-pair alternatives to TEA for many oligonucleotide sequences. Graphical Abstract ᅟ.

The Role of Fluorinated Alcohols as Mobile Phase Modifiers for LC-MS Analysis of Oligonucleotides

Hexafluoroisopropanol (HFIP) has been widely used as an acidic modifier for mobile phases for liquid chromatography-mass spectrometry (LC-MS) analysis of oligonucleotides ever since the first report of its use for this purpose. This is not surprising, considering the exceptional performance of HFIP compared with carboxylic acids, which cause significant MS signal suppression in electrospray ionization. However, we have found that other fluorinated alcohols can also be utilized for mobile phase preparation and the choice of optimal fluorinated alcohol is determined by the ion-pairing (IP) agent. Although HFIP is a very good choice to be used alongside less hydrophobic IP agents, other fluorinated alcohols such as 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol (HFMIP) can significantly outperform HFIP when used with more hydrophobic IP agents. We also found that more acidic fluorinated alcohols assist with the transfer of oligonucleotides with secondary structure (e.g., folded strands and hairpins) into the gas phase. Graphical Abstract ᅟ.

Lysophosphatidic Acid Mediates Activating Transcription Factor 3 Expression Which Is a Target for Post-Transcriptional Silencing by miR-30c-2-3p

Although microRNAs (miRNAs) are small, non-protein-coding entities, they have important roles in post-transcriptional regulation of most of the human genome. These small entities generate fine-tuning adjustments in the expression of mRNA, which can mildly or massively affect the abundance of proteins. Previously, we found that the expression of miR-30c-2-3p is induced by lysophosphatidic acid and has an important role in the regulation of cell proliferation in ovarian cancer cells. The goal here is to confirm that ATF3 mRNA is a target of miR-30c-2-3p silencing, thereby further establishing the functional role of miR-30c-2-3p. Using a combination of bioinformatics, qRT-PCR, immunoblotting and luciferase assays, we uncovered a regulatory pathway between miR-30c-2-3p and the expression of the transcription factor, ATF3. Lysophosphatidic acids triggers the expression of both miR-30c-2-3p and ATF3, which peak at 1 h and are absent 8 h post stimulation in SKOV-3 and OVCAR-3 serous ovarian cancer cells. The 3´-untranslated region (3´-UTR) of ATF3 was a predicted, putative target for miR-30c-2-3p, which we confirmed as a bona-fide interaction using a luciferase reporter assay. Specific mutations introduced into the predicted site of interaction between miR-30c-2-3p and the 3´-UTR of ATF3 alleviated the suppression of the luciferase signal. Furthermore, the presence of anti-miR-30c-2-3p enhanced ATF3 mRNA and protein after lysophosphatidic acid stimulation. Thus, the data suggest that after the expression of ATF3 and miR-30c-2-3p are elicited by lysophosphatidic acid, subsequently miR-30c-2-3p negatively regulates the expression of ATF3 through post-transcriptional silencing, which prevents further ATF3-related outcomes as a consequence of lysophosphatidic acid signaling.

Suppression of the GTPase-activating protein RGS10 increases Rheb-GTP and mTOR signaling in ovarian cancer cells

The regulator of G protein signaling 10 (RGS10) protein is a GTPase activating protein that accelerates the hydrolysis of GTP and therefore canonically inactivates G proteins, ultimately terminating signaling. Rheb is a small GTPase protein that shuttles between its GDP- and GTP-bound forms to activate mTOR. Since RGS10 suppression augments ovarian cancer cell viability, we sought to elucidate the molecular mechanism. Following RGS10 suppression in serum-free conditions, phosphorylation of mTOR, the eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1), p70S6K and S6 Ribosomal Protein appear. Furthermore, suppressing RGS10 increases activated Rheb, suggesting RGS10 antagonizes mTOR signaling via the small G-protein. The effects of RGS10 suppression are enhanced after stimulating cells with the growth factor, lysophosphatidic acid, and reduced with mTOR inhibitors, temsirolimus and INK-128. Suppression of RGS10 leads to an increase in cell proliferation, even in the presence of etoposide. In summary, the RGS10 suppression increases Rheb-GTP and mTOR signaling in ovarian cancer cells. Our results suggest that RGS10 could serve in a novel, and previously unknown, role by accelerating the hydrolysis of GTP from Rheb in ovarian cancer cells.

Vinyl sulfone analogs of lysophosphatidylcholine irreversibly inhibit autotaxin and prevent angiogenesis in melanoma

Autotaxin (ATX) is an enzyme discovered in the conditioned medium of cultured melanoma cells and identified as a protein that strongly stimulates motility. This unique ectonucleotide pyrophosphatase and phosphodiesterase facilitates the removal of a choline headgroup from lysophosphatidylcholine (LPC) to yield lysophosphatidic acid (LPA), which is a potent lipid stimulator of tumorigenesis. Thus, ATX has received renewed attention because it has a prominent role in malignant progression with significant translational potential. Specifically, we sought to develop active site-targeted irreversible inhibitors as anti-cancer agents. Herein we describe the synthesis and biological activity of an LPC-mimetic electrophilic affinity label that targets the active site of ATX, which has a critical threonine residue that acts as a nucleophile in the lysophospholipase D reaction to liberate choline. We synthesized a set of quaternary ammonium derivative-containing vinyl sulfone analogs of LPC that function as irreversible inhibitors of ATX and inactivate the enzyme. The analogs were tested in cell viability assays using multiple cancer cell lines. The IC50 values ranged from 6.74 to 0.39 μM, consistent with a Ki of 3.50 μM for inhibition of ATX by the C16H33 vinyl sulfone analog CVS-16 (10b). A phenyl vinyl sulfone control compound, PVS-16, lacking the choline-like quaternary ammonium mimicking head group moiety, had little effect on cell viability and did not inhibit ATX. Most importantly, CVS-16 (10b) significantly inhibited melanoma progression in an in vivo tumor model by preventing angiogenesis. Taken together, this suggests that CVS-16 (10b) is a potent and irreversible ATX inhibitor with significant biological activity both in vitro and in vivo.

PKA-type I selective constrained peptide disruptors of AKAP complexes

A-Kinase Anchoring Proteins (AKAPs) coordinate complex signaling events by serving as spatiotemporal modulators of cAMP-dependent protein kinase activity in cells. Although AKAPs organize a plethora of diverse pathways, their cellular roles are often elusive due to the dynamic nature of these signaling complexes. AKAPs can interact with the type I or type II PKA holoenzymes by virtue of high-affinity interactions with the R-subunits. As a means to delineate AKAP-mediated PKA signaling in cells, we sought to develop isoform-selective disruptors of AKAP signaling. Here, we report the development of conformationally constrained peptides named RI-STapled Anchoring Disruptors (RI-STADs) that target the docking/dimerization domain of the type 1 regulatory subunit of PKA. These high-affinity peptides are isoform-selective for the RI isoforms, can outcompete binding by the classical AKAP disruptor Ht31, and can selectively displace RIα, but not RIIα, from binding the dual-specific AKAP149 complex. Importantly, these peptides are cell-permeable and disrupt Type I PKA-mediated phosphorylation events in the context of live cells. Hence, RI-STAD peptides are versatile cellular tools to selectively probe anchored type I PKA signaling events.

Abstract 2672: Vinyl sulfone analogues of lysophosphatidylcholine irreversibly inhibit autotaxin and prevent angiogenesis in melanoma

Autotaxin (ATX) is an enzyme discovered in the conditioned medium of cultured melanoma cells and identified as a protein that strongly stimulates motility. This unique ectonucleotide pyrophosphatase and phosphodiesterase facilitates the removal of a choline headgroup from lysophosphatidylcholine (LPC) to yield lysophosphatidic acid (LPA), which is a potent lipid stimulator of tumorigenesis. Thus, ATX has received renewed attention because it has a prominent role in malignant progression and represents a promising area of research with significant translational potential. Since ATX inhibitors may have broad implications for therapy, we sought to create a novel series of inhibitors for use against cancer, especially melanoma. Herein we report on the synthesis and biological activity of a targeted affinity label for the active site of ATX, which has a critical threonine residue that acts as a nucleophile in the lysophospholipase D reaction to liberate choline. We synthesized a set of vinyl sulfone analogs of ATX that function as irreversible inhibitors of ATX and inactivate the enzyme. We commenced biological testing of this compound with viability assays against multiple cancer cell lines whereby the IC50 values ranged from 6.74 - 0.39 μM, which was consistent with the Ki of the vinyl sulfone (3.50 μM). In addition, this compound was also able to significantly inhibit melanoma cell wound closure and pore migration. Most importantly, the vinyl sulfone significantly inhibited melanoma progression using an in vivo tumor model by preventing angiogenesis. Taken together, this suggests that the vinyl sulfone is a potent and irreversible ATX inhibitor with significant biological activity both in vitro and in vivo.

Note: This abstract was not presented at the meeting.

Citation Format: Mandi M. Murph, Molly Altman, Wei Jia, Duy Nguyen, Jada Fambrough, William J. Hardman, Guowei Jiang, Damian Madan, Jianxing Zhang, Glenn D. Prestwich. Vinyl sulfone analogues of lysophosphatidylcholine irreversibly inhibit autotaxin and prevent angiogenesis in melanoma. [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 2672. doi:10.1158/1538-7445.AM2014-2672

Molecular epigenetics in the management of ovarian cancer: are we investigating a rational clinical promise?

Epigenetics is essentially a phenotypical change in gene expression without any alteration of the DNA sequence; the emergence of epigenetics in cancer research and mainstream oncology is fueling new hope. However, it is not yet known whether this knowledge will translate to improved clinical management of ovarian cancer. In this malignancy, women are still undergoing chemotherapy similar to what was approved in 1978, which to this day represents one of the biggest breakthroughs for treating ovarian cancer. Although liquid tumors are benefiting from epigenetically related therapies, solid tumors like ovarian cancer are not (yet?). Herein, we will review the science of molecular epigenetics, especially DNA methylation, histone modifications and microRNA, but also include transcription factors since they, too, are important in ovarian cancer. Pre-clinical and clinical research on the role of epigenetic modifications is also summarized. Unfortunately, ovarian cancer remains an idiopathic disease, for the most part, and there are many areas of patient management, which could benefit from improved technology. This review will also highlight the evidence suggesting that epigenetics may have pre-clinical utility in pharmacology and clinical applications for prognosis and diagnosis. Finally, drugs currently in clinical trials (i.e., histone deacetylase inhibitors) are discussed along with the promise for epigenetics in the exploitation of chemoresistance. Whether epigenetics will ultimately be the answer to better management in ovarian cancer is currently unknown; but we hope so in the future.

Transcriptional suppression, DNA methylation, and histone deacetylation of the regulator of G-protein signaling 10 (RGS10) gene in ovarian cancer cells

RGS10 regulates ovarian cancer cell growth and survival, and RGS10 expression is suppressed in cell models of ovarian cancer chemoresistance. However, the mechanisms governing RGS10 expression in ovarian cancer are poorly understood. Here we report RGS10 suppression in primary ovarian cancer and CAOV-3 ovarian cancer cells compared to immortalized ovarian surface epithelial (IOSE) cells, and in A2780-AD chemoresistant cells compared to parental A2780 cells. RGS10-1 and RGS10-2 transcripts are expressed in ovarian cancer cells, but only RGS10-1 is suppressed in A2780-AD and CAOV-3 cells, and the RGS10-1 promoter is uniquely enriched in CpG dinucleotides. Pharmacological inhibition of DNA methyl-transferases (DNMTs) increased RGS10 expression, suggesting potential regulation by DNA methylation. Bisulfite sequencing analysis identified a region of the RGS10-1 promoter with significantly enhanced DNA methylation in chemoresistant A2780-AD cells relative to parental A2780 cells. DNA methylation in CAOV-3 and IOSE cells was similar to A2780 cells. More marked differences were observed in histone acetylation of the RGS10-1 promoter. Acetylated histone H3 associated with the RGS10-1 promoter was significantly lower in A2780-AD cells compared to parental cells, with a corresponding increase in histone deacetylase (HDAC) enzyme association. Similarly, acetylated histone levels at the RGS10-1 promoter were markedly lower in CAOV-3 cells compared to IOSE cells, and HDAC1 binding was doubled in CAOV-3 cells. Finally, we show that pharmacological inhibition of DNMT or HDAC enzymes in chemoresistant A2780-AD cells increases RGS10 expression and enhances cisplatin toxicity. These data suggest that histone de-acetylation and DNA methylation correlate with RGS10 suppression and chemoresistance in ovarian cancer. Markers for loss of RGS10 expression may identify cancer cells with unique response to therapeutics.

Abstract 2140: Regulator of G-protein signaling 2 blunts cellular viability mediated by a stabilized lysophosphatidic acid analogue (2S-OMPT) in the presence of chemotherapy in an ovarian cancer cell model of chemoresistance

Lysophosphatidic acid (LPA) enhances growth, survival, viability and proliferation in numerous models. Thus, the receptors for LPA are also implicated in oncogenic signaling and represent a group of “druggable” therapeutic targets in cancer. Regulator of G protein Signaling 2 (RGS2) is a GTPase activating protein (GAP) that deactivates the G alpha subunits of heterotrimeric G proteins, turning off G protein-coupled receptor (GPCR) signaling. In our previous studies examining computational bioinformatics, we demonstrated that reduced RGS gene expression develops with the occurrence of drug resistance in ovarian cancer cell lines. The purpose of our study was to investigate whether the LPA receptors are also involved in mediating viability as a result of enhanced GPCR signaling due to reduced RGS proteins in this chemoresistance model. This is important since RGS proteins can deactivate G alpha subunits of many different GPCRs, and are not specific to merely the LPA receptors. If a “druggable” GPCR is mediating viability in chemoresistance, it is critical to identify which ones are responsible. To test this idea we used the metabolically stabilized LPA analogue L-sn-1-O-oleoyl-2-O-methylglyceryl-3-phosphothionate (2S-OMPT) as a potent non-hydrolyzable agonist for LPA receptors at a concentration (10 µM) sufficient to activate multiple LPA receptors. We hypothesized that if LPA signaling was not involved, then OMPT would override any contribution of RGS2 on modulating the viability response in the presence of chemotherapy. Using a tet-off promoter system, we generated an inducible stable model of RGS2-expressing HeyA8-MDR cells, which we have previously confirmed are resistant to taxanes. After 48 h OMPT pre-treatment, HeyA8-MDR-RGS2-inducible cells were exposed to cisplatin for 24 h and evaluated for viability. IC50 values for cisplatin were lower in the RGS2-induced HeyA8-MDR cells that were not pretreated with OMPT, a demonstration of enhanced sensitivity to cisplatin in the presence of RGS2. All conditions pre-treated with OMPT demonstrated enhanced viability even in the presence of chemotherapy; however, ovarian cancer cells that were pretreated with OMPT and cultured in tet-free medium to induce RGS2 expression showed a significant blunting of viability. This supports the interaction between LPA receptors and RGS2 in the control of drug sensitivity in ovarian cancer chemoresistance and provides a mechanism for our current and previous observations.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2140. doi:1538-7445.AM2012-2140

MicroRNA-30c-2* expressed in ovarian cancer cells suppresses growth factor-induced cellular proliferation and downregulates the oncogene BCL9

MicroRNAs (miRNAs) are small noncoding RNAs that function as master regulators of posttranscriptional gene expression with each miRNA negatively regulating hundreds of genes. Lysophosphatidic acid (LPA) is a mitogenic lipid present within the ovarian tumor microenvironment and induces LPA receptor activation and intracellular signaling cascades like ERK/MAPK, leading to enhanced cellular proliferation. Here, we show that in SKOV-3 and OVCAR-3 cells, LPA stimulation at concentrations ranging from 1 nmol/L to 20 μmol/L for 30 to 60 minutes increases miR-30c-2*, and this effect is mediated through a combination of receptors because knock down of multiple LPA receptors is required for inhibition. The epidermal growth factor and platelet-derived growth factor also increase miR-30c-2* transcript expression, suggesting a broader responsive role for miR-30c-2*. Thus, we investigated the functional role of miR-30c-2* through ectopic expression of synthetic miRNA precursors of mature miRNA or antagomir transfection and observed that microRNA-30c-2* reduces, and the antagomir enhances, cell proliferation and viability in OVCAR-3, cisplatin-insensitive SKOV-3 and chemoresistant HeyA8-MDR cells. Ectopic expression of miR-30c-2* reduces BCL9 mRNA transcript abundance and BCL9 protein. Consistent with this observation, miR-30c-2* ectopic expression also reduced BCL9 luciferase reporter gene expression. In comparison with IOSE cells, all cancer cells examined showed increased BCL9 expression, which is consistent with its role in tumor progression. Taken together, this suggest that growth factor induced proliferation mediates a neutralizing response by significantly increasing miR-30c-2* which reduces BCL9 expression and cell proliferation in SKOV-3 and OVCAR-3 cells, likely as a mechanism to regulate signal transduction downstream.

Regulators of G-Protein signaling RGS10 and RGS17 regulate chemoresistance in ovarian cancer cells

BACKGROUND

A critical therapeutic challenge in epithelial ovarian carcinoma is the development of chemoresistance among tumor cells following exposure to first line chemotherapeutics. The molecular and genetic changes that drive the development of chemoresistance are unknown, and this lack of mechanistic insight is a major obstacle in preventing and predicting the occurrence of refractory disease. We have recently shown that Regulators of G-protein Signaling (RGS) proteins negatively regulate signaling by lysophosphatidic acid (LPA), a growth factor elevated in malignant ascites fluid that triggers oncogenic growth and survival signaling in ovarian cancer cells. The goal of this study was to determine the role of RGS protein expression in ovarian cancer chemoresistance.

RESULTS

In this study, we find that RGS2, RGS5, RGS10 and RGS17 transcripts are expressed at significantly lower levels in cells resistant to chemotherapy compared with parental, chemo-sensitive cells in gene expression datasets of multiple models of chemoresistance. Further, exposure of SKOV-3 cells to cytotoxic chemotherapy causes acute, persistent downregulation of RGS10 and RGS17 transcript expression. Direct inhibition of RGS10 or RGS17 expression using siRNA knock-down significantly reduces chemotherapy-induced cell toxicity. The effects of cisplatin, vincristine, and docetaxel are inhibited following RGS10 and RGS17 knock-down in cell viability assays and phosphatidyl serine externalization assays in SKOV-3 cells and MDR-HeyA8 cells. We further show that AKT activation is higher following RGS10 knock-down and RGS 10 and RGS17 overexpression blocked LPA mediated activation of AKT, suggesting that RGS proteins may blunt AKT survival pathways.

CONCLUSIONS

Taken together, our data suggest that chemotherapy exposure triggers loss of RGS10 and RGS17 expression in ovarian cancer cells, and that loss of expression contributes to the development of chemoresistance, possibly through amplification of endogenous AKT signals. Our results establish RGS10 and RGS17 as novel regulators of cell survival and chemoresistance in ovarian cancer cells and suggest that their reduced expression may be diagnostic of chemoresistance.

Targeting melanoma growth and viability reveals dualistic functionality of the phosphonothionate analogue of carba cyclic phosphatidic acid

BACKGROUND

Although the incidence of melanoma in the U.S. is rising faster than any other cancer, the FDA-approved chemotherapies lack efficacy for advanced disease, which results in poor overall survival. Lysophosphatidic acid (LPA), autotaxin (ATX), the enzyme that produces LPA, and the LPA receptors represent an emerging group of therapeutic targets in cancer, although it is not known which of these is most effective.

RESULTS

Herein we demonstrate that thio-ccPA 18:1, a stabilized phosphonothionate analogue of carba cyclic phosphatidic acid, ATX inhibitor and LPA1/3 receptor antagonist, induced a marked reduction in the viability of B16F10 metastatic melanoma cells compared with PBS-treated control by 80-100%. Exogenous LPA 18:1 or D-sn-1-O-oleoyl-2-O-methylglyceryl-3-phosphothioate did not reverse the effect of thio-ccPA 18:1. The reduction in viability mediated by thio-ccPA 18:1 was also observed in A375 and MeWo melanoma cell lines, suggesting that the effects are generalizable. Interestingly, siRNA to LPA3 (siLPA3) but not other LPA receptors recapitulated the effects of thio-ccPA 18:1 on viability, suggesting that inhibition of the LPA3 receptor is an important dualistic function of the compound. In addition, siLPA3 reduced proliferation, plasma membrane integrity and altered morphology of A375 cells. Another experimental compound designed to antagonize the LPA1/3 receptors significantly reduced viability in MeWo cells, which predominantly express the LPA3 receptor.

CONCLUSIONS

Thus the ability of thio-ccPA 18:1 to inhibit the LPA3 receptor and ATX are key to its molecular mechanism, particularly in melanoma cells that predominantly express the LPA3 receptor. These observations necessitate further exploration and exploitation of these targets in melanoma.

Lysophosphatidic acid-induced transcriptional profile represents serous epithelial ovarian carcinoma and worsened prognosis

Background

Lysophosphatidic acid (LPA) governs a number of physiologic and pathophysiological processes. Malignant ascites fluid is rich in LPA, and LPA receptors are aberrantly expressed by ovarian cancer cells, implicating LPA in the initiation and progression of ovarian cancer. However, there is an absence of systematic data critically analyzing the transcriptional changes induced by LPA in ovarian cancer.

Methodology and Principal Findings

In this study, gene expression profiling was used to examine LPA-mediated transcription by exogenously adding LPA to human epithelial ovarian cancer cells for 24 h to mimic long-term stimulation in the tumor microenvironment. The resultant transcriptional profile comprised a 39-gene signature that closely correlated to serous epithelial ovarian carcinoma. Hierarchical clustering of ovarian cancer patient specimens demonstrated that the signature is associated with worsened prognosis. Patients with LPA-signature-positive ovarian tumors have reduced disease-specific and progression-free survival times. They have a higher frequency of stage IIIc serous carcinoma and a greater proportion is deceased. Among the 39-gene signature, a group of seven genes associated with cell adhesion recapitulated the results. Out of those seven, claudin-1, an adhesion molecule and phenotypic epithelial marker, is the only independent biomarker of serous epithelial ovarian carcinoma. Knockdown of claudin-1 expression in ovarian cancer cells reduces LPA-mediated cellular adhesion, enhances suspended cells and reduces LPA-mediated migration.

Conclusions

The data suggest that transcriptional events mediated by LPA in the tumor microenvironment influence tumor progression through modulation of cell adhesion molecules like claudin-1 and, for the first time, report an LPA-mediated expression signature in ovarian cancer that predicts a worse prognosis.

Lysophosphatidic acid receptors determine tumorigenicity and aggressiveness of ovarian cancer cells

BACKGROUND

Lysophosphatidic acid (LPA) acts through the cell surface G protein-coupled receptors, LPA1, LPA2, or LPA3, to elicit a wide range of cellular responses. It is present at high levels in intraperitoneal effusions of human ovarian cancer increasing cell survival, proliferation, and motility as well as stimulating production of neovascularizing factors. LPA2 and LPA3 and enzymes regulating the production and degradation of LPA are aberrantly expressed by ovarian cancer cells, but the consequences of these expression changes in ovarian cancer cells were unknown.

METHODS

Expression of LPA1, LPA2, or LPA3 was inhibited or increased in ovarian cancer cells using small interfering RNAs (siRNAs) and lentivirus constructs, respectively. We measured the effects of changes in LPA receptor expression on cell proliferation (by crystal violet staining), cell motility and invasion (using Boyden chambers), and cytokines (interleukin 6 [IL-6], interleukin 8 [IL-8], and vascular endothelial growth factor [VEGF]) production by enzyme-linked immunosorbent assay. The role of LPA receptors in tumor growth, ascites formation, and cytokine production was assessed in a mouse xenograft model. All statistical tests were two-sided.

RESULTS

SKOV-3 cells with increased expression of LPA receptors showed increased invasiveness, whereas siRNA knockdown inhibited both migration (P < .001, Student t test) and invasion. Knockdown of the LPA2 or LPA3 receptors inhibited the production of IL-6, IL-8, and VEGF in SKOV-3 and OVCAR-3 cells. SKOV-3 xenografts expressing LPA receptors formed primary tumors of increased size and increased ascites volume. Invasive tumors in the peritoneal cavity occurred in 75% (n = 4) of mice injected with LPA1 expressing SKOV-3 and 80% (n = 5) of mice injected with LPA2 or LPA3 expressing SKOV-3 cells. Metastatic tumors expressing LPA1, LPA2, and LPA3 were identified in the liver, kidney, and pancreas; tumors expressing LPA2 and LPA3 were detected in skeletal muscle; and tumors expressing LPA2 were also found in the cervical lymph node and heart. The percent survival of mice with tumors expressing LPA2 or LPA3 was reduced in comparison with animals with tumors expressing beta-galactosidase.

CONCLUSIONS

Expression of LPA2 or LPA3 during ovarian carcinogenesis contributes to ovarian cancer aggressiveness, suggesting that the targeting of LPA production and action may have potential for the treatment of ovarian cancer.

Lysophosphatidic acid decreases the nuclear localization and cellular abundance of the p53 tumor suppressor in A549 lung carcinoma cells

Lysophosphatidic acid (LPA) is a bioactive lipid that promotes cancer cell proliferation and motility through activation of cell surface G protein-coupled receptors. Here, we provide the first evidence that LPA reduces the cellular abundance of the tumor suppressor p53 in A549 lung carcinoma cells, which express endogenous LPA receptors. The LPA effect depends on increased proteasomal degradation of p53 and it results in a corresponding decrease in p53-mediated transcription. Inhibition of phosphatidylinositol 3-kinase protected cells from the LPA-induced reduction of p53, which implicates this signaling pathway in the mechanism of LPA-induced loss of p53. LPA partially protected A549 cells from actinomycin D induction of both apoptosis and increased p53 abundance. Expression of LPA(1), LPA(2), and LPA(3) receptors in HepG2 hepatoma cells, which normally do not respond to LPA, also decreased p53 expression and p53-dependent transcription. In contrast, neither inactive LPA(1) (R124A) nor another G(i)-coupled receptor, the M(2) muscarinic acetylcholine receptor, reduced p53-dependent transcription in HepG2 cells. These results identify p53 as a target of LPA action and provide a new dimension for understanding how LPA stimulates cancer cell division, protects against apoptosis, and thereby promotes tumor progression.

Agonist-induced endocytosis of lysophosphatidic acid-coupled LPA1/EDG-2 receptors via a dynamin2- and Rab5-dependent pathway

Lysophosphatidic acid (LPA) is a serum-borne phospholipid that exerts a pleiotropic range of effects on cells through activation of three closely related G-protein-coupled receptors termed LPA1/EDG-2, LPA2/EDG-4 and LPA3/EDG-7. Of these receptors, the LPA1 receptor is the most widely expressed. In this study, we investigated the agonist-induced endocytosis of the human LPA1 receptor, bearing an N-terminal FLAG epitope tag, in stably transfected HeLa cells. Treatment with LPA induced the rapid endocytosis of approximately 40% of surface LPA1 within 15 minutes. Internalization was both dose dependent and LPA specific since neither lysophophatidylcholine nor sphingosine-1-phosphate induced LPA1 endocytosis. Removal of agonist following 30 minutes incubation resulted in recycling of LPA1 back to the cell surface. LPA1 internalization was strongly inhibited by dominant-inhibitory mutants of both dynamin2 (K44A) and Rab5a (S34N). In addition, both dynamin2 K44A and Rab5 S34N mildly inhibited LPA1-dependent activation of serum response factor. Finally, our results also indicate that LPA1 exhibits basal, LPA-dependent internalization in the presence of serum-containing medium.

Transfer of M2 muscarinic acetylcholine receptors to clathrin-derived early endosomes following clathrin-independent endocytosis

Upon agonist stimulation, many G protein-coupled receptors such as beta(2)-adrenergic receptors are internalized via beta-arrestin- and clathrin-dependent mechanisms, whereas others, like M(2) muscarinic acetylcholine receptors (mAChRs), are internalized by clathrin- and arrestin-independent mechanisms. To gain further insight into the mechanisms that regulate M(2) mAChR endocytosis, we investigated the post-endocytic trafficking of M(2) mAChRs in HeLa cells and the role of the ADP-ribosylation factor 6 (Arf6) GTPase in regulating M(2) mAChR internalization. Here, we report that M(2) mAChRs are rapidly internalized by a clathrin-independent pathway that is inhibited up to 50% by expression of either GTPase-defective Arf6 Q67L or an upstream Arf6 activator, Galpha(q) Q209L. In contrast, M(2) mAChR internalization was not affected by expression of dominant-negative dynamin 2 K44A, which is a known inhibitor of clathrin-dependent endocytosis. Nevertheless, M(2) mAChRs, which are initially internalized in structures that lack clathrin-dependent endosomal markers, quickly localize to endosomes that contain the clathrin-dependent, early endosomal markers early endosome autoantigen-1, transferrin receptor, and GTPase-defective Rab5 Q79L, which is known to swell early endosomal compartments. These results suggest that M(2) mAChRs initially internalize via an Arf6-associated, clathrin-independent pathway but then quickly merge with the clathrin endocytic pathway at the level of early endosomes.