Abstract 3969: Screening of kinase inhibitors as bioenergetic metabolism modulator using the XF Real-Time ATP Rate Assay

Cancer cells are metabolically reprogrammed through tumor initiation and progression, and there are increasing developments in cancer therapies exploiting the potential metabolic vulnerability. A better understanding of cancer cell metabolic regulation can also contribute to modulating the harsh tumor microenvironment, which strongly affects the efficacy of emerging anti-cancer immunotherapies. As one of the critical contributors to cancer therapy design, there is increasing demand for time-efficient and reliable analytic tools when searching for drugs and genes modulating cancer cell metabolism. The XF Real-Time ATP Rate Assay measures ATP production from glycolysis and mitochondrial respiration simultaneously and provides a quantitative overview of the bioenergetic phenotype of the cells. By using ATP production rate as a universal unit of bioenergetic metabolism, this assay quickly detects metabolic modulations induced by chemical stimuli or genetic modifications. It allows the identification of potential targets for therapy design. In this study, we used the Seahorse XF Pro Analyzer combined with the XF ATP Rate assay to screen 80 kinase inhibitors for the suppressive effects on energy metabolism and/or inducing a metabolic phenotype shift in THP-1 cells, a monocytic leukemia cell line, using PBMC as the control. We identified four mitochondrial and two glycolytic suppressors using the screening and dose-response views available in Seahorse Analytics, a cloud-based data analysis tool for Seahorse XF assays. These compounds showed moderate or no effects on the net ATP production rates but induced a significant shift in the metabolic phenotype of THP-1 cells. Among the selected kinase inhibitors, AG-879 (ErbB2 inhibitor), SU-1498 (VEGFR inhibitor), and U-0126 (MEK1/2 inhibitor) showed the most potent inhibitory effect on mitochondrial energy production in THP-1 cells. Dose-response studies indicated that SU-1498 and U-0126 have higher potency in THP-1 than PBMC, and thus they can be considered good cancer-cell targets for mitochondrial suppressors. In contrast, AG-879 showed a similar or higher inhibitory effect on PBMC even though it is the most potent mitochondrial suppressor among the selected compounds. These results demonstrate that the XF Real-Time ATP Rate Assay can be used as a primary assay for screening and validating drug candidate(s) targeting the bioenergetic metabolism of cancer cells.

Citation Format: Yoonseok Kam, Lisa Winer, Natalia Romero. Screening of kinase inhibitors as bioenergetic metabolism modulator using the XF Real-Time ATP Rate Assay. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3969.

Proton export upregulates aerobic glycolysis

INTRODUCTION

Aggressive cancers commonly ferment glucose to lactic acid at high rates, even in the presence of oxygen. This is known as aerobic glycolysis, or the "Warburg Effect." It is widely assumed that this is a consequence of the upregulation of glycolytic enzymes. Oncogenic drivers can increase the expression of most proteins in the glycolytic pathway, including the terminal step of exporting H⁺ equivalents from the cytoplasm. Proton exporters maintain an alkaline cytoplasmic pH, which can enhance all glycolytic enzyme activities, even in the absence of oncogene-related expression changes. Based on this observation, we hypothesized that increased uptake and fermentative metabolism of glucose could be driven by the expulsion of H⁺ equivalents from the cell.

RESULTS

To test this hypothesis, we stably transfected lowly glycolytic MCF-7, U2-OS, and glycolytic HEK293 cells to express proton-exporting systems: either PMA1 (plasma membrane ATPase 1, a yeast H⁺-ATPase) or CA-IX (carbonic anhydrase 9). The expression of either exporter in vitro enhanced aerobic glycolysis as measured by glucose consumption, lactate production, and extracellular acidification rate. This resulted in an increased intracellular pH, and metabolomic analyses indicated that this was associated with an increased flux of all glycolytic enzymes upstream of pyruvate kinase. These cells also demonstrated increased migratory and invasive phenotypes in vitro, and these were recapitulated in vivo by more aggressive behavior, whereby the acid-producing cells formed higher-grade tumors with higher rates of metastases. Neutralizing tumor acidity with oral buffers reduced the metastatic burden.

CONCLUSIONS

Therefore, cancer cells which increase export of H⁺ equivalents subsequently increase intracellular alkalization, even without oncogenic driver mutations, and this is sufficient to alter cancer metabolism towards an upregulation of aerobic glycolysis, a Warburg phenotype. Overall, we have shown that the traditional understanding of cancer cells favoring glycolysis and the subsequent extracellular acidification is not always linear. Cells which can, independent of metabolism, acidify through proton exporter activity can sufficiently drive their metabolism towards glycolysis providing an important fitness advantage for survival.

Abstract 2323: A bioenergetic functional screening assay workflow to identify, validate, and characterize anti-cancer compounds

As bioenergetic metabolism is recognized as a critical activity supporting cell proliferation, differentiation, and even death, many proposed targets for cancer therapy are functionally linked to cellular bioenergetic metabolism. Here, we introduce an assay workflow for screening and analyzing potential anticancer drugs affecting cellular metabolism using extracellular flux analysis. The Agilent Seahorse XF Real-Time ATP rate assay can be used as a starting point to identify therapeutic compounds that induce a perturbation in metabolic phenotype. It provides a quantitative comparison of basal mitochondrial and glycolytic activities using the universal unit of ATP production rate. Through this initial comparative screening, the effect of different compounds on basal energetic state and pathway-specific metabolic perturbations can be identified providing information that cannot be assessed by intracellular ATP level measurements or cytotoxicity assays. A more comprehensive functional analysis can then be applied to validate the target mode of action through pathway-specific analysis tools such as the XF Cell Mito Stress Test and the XF Glycolytic Rate Assay. In this study, we tested the proposed workflow in three different NSCLC cell lines with different genetic backgrounds using a mock panel of known metabolic modulators including thiosemicarbazones, EGFR inhibitors, KRAS inhibitors, a glutaminase inhibitor, a Glut1 inhibitor, a chemotherapy drug, and a radiotherapy sensitizer candidate. The ATP production rate data from lung cancer cell lines exposed for 1 hour or 24 hours to the compounds, successfully identified the effects of metabolic pathway-specific modulation as well as metabolic phenotypic switching. In addition, dose-response studies using cell lines with different genetic backgrounds demonstrated differential susceptibility to the tested compounds. The workflow was then applied using a broader panel of 72 potential mitochondrial toxicants compounds. The assay could identify potent mitochondrial and glycolytic suppressor compounds effective on A549, a lung cancer cell line. A more comprehensive XF analysis then validated the mode of action for the identified metabolic suppressors. These results demonstrate the benefit of using the XF Real-Time ATP rate assay as an initial assay to uncover novel metabolic targets in early drug discovery research, guiding further research toward functional validation with the appropriate comprehensive XF assays.

Citation Format: Yoonseok Kam, Lisa Winer, Natalia Romero. A bioenergetic functional screening assay workflow to identify, validate, and characterize anti-cancer compounds [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 2323.

A Novel Solution to Better Understand the Link Between T Cell Metabolism and Function

In recent years, metabolism has emerged as a key driver of immune cell function in both healthy and disease settings. Indeed, it has been shown that metabolic reprogramming is a determinant of T cell phenotype and fate. Moreover, reprogramming of the metabolic pathways of T cells can be used as a strategy to improve the antitumor efficacy of adoptive T cell therapies. The Agilent Seahorse XF T cell Metabolic Profiling (XF TCMP) kit is a new solution that, combined with the Seahorse XF analyzer, allows for the simultaneous measurement of basal metabolic demand, metabolic poise and respiratory capacity in T cells. These parameters have been linked with optimal function and improved persistence of T cell therapies. The assay uses an improved uncoupler (BAM15) for more robust measurements of T cell bioenergetic capacity with less optimization than other uncouplers used. The XF TCMP kit was used to evaluate the metabolic phenotype of human T cells expanded in different nutrient conditions. T cells expanded in different cell culture media resulted in populations with different metabolic profiles. These metabolic profiles correlated with different functional markers, supporting the link between metabolism and function. The XF TCMP kit was also used to assess metabolic poise and bioenergetic capacity under nutrient-restriction, allowing us to better understand fuel requirements after expansion. Together, the data show that the XF TCMP kit provides a complete metabolic assessment of T cells in real-time. The assay can be used to develop improved anti-tumor T cell therapies by evaluating strategies that improve the persistence of infused cells or assess how T cells sustain metabolic fitness in nutrient restricted environments to maintain function.

Mitochondrial ATP fuels ABC transporter-mediated drug efflux in cancer chemoresistance

Chemotherapy remains the standard of care for most cancers worldwide, however development of chemoresistance due to the presence of the drug-effluxing ATP binding cassette (ABC) transporters remains a significant problem. The development of safe and effective means to overcome chemoresistance is critical for achieving durable remissions in many cancer patients. We have investigated the energetic demands of ABC transporters in the context of the metabolic adaptations of chemoresistant cancer cells. Here we show that ABC transporters use mitochondrial-derived ATP as a source of energy to efflux drugs out of cancer cells. We further demonstrate that the loss of methylation-controlled J protein (MCJ) (also named DnaJC15), an endogenous negative regulator of mitochondrial respiration, in chemoresistant cancer cells boosts their ability to produce ATP from mitochondria and fuel ABC transporters. We have developed MCJ mimetics that can attenuate mitochondrial respiration and safely overcome chemoresistance in vitro and in vivo. Administration of MCJ mimetics in combination with standard chemotherapeutic drugs could therefore become an alternative strategy for treatment of multiple cancers.

Metabolic analysis of tyrosine-kinase inhibitor effect on T cell activation

Tyrosine kinase inhibitors have been actively investigated as potential therapies for various cancers including blood tumors. However, as T cell activation can also be mediated by various tyrosine kinases, relevant inhibitors are also now being considered as pharmacological modulators of CAR-T cells; an example being dasatinib, which has been found to modulate CAR-T activity through Lck inhibition. T cell activation and subsequent differentiation are tightly associated with cellular metabolism, with T cells showing dynamic changes in two primary metabolic activities of glycolysis and mitochondrial respiration throughout the T cell life cycle. This metabolic response begins with an immediate early increase in glycolytic activity which has been shown to be an essential and signature response to activation. In this study, this fundamental biological process is exploited using the Agilent Seahorse XF technology, illustrating how activation can be measured in real-time in response to anti-CD3/CD28 activator injection, and further, how this parameter can be used to conveniently determine the modulatory effect of kinase inhibitors on T cell activation. Consistent with previous observations that kinase inhibitors can suppress naive T cell activation in vitro, here a similar kinase dependency in re-activation of resting (pre-activated) T cells was observed. Several kinase inhibitors also were able to downregulate the glycolytic rate elevated when applied post-activation. Taken together these data suggest that real-time metabolic analysis is a valuable tool in the characterization of putative T cell modulators, including tyrosine kinase inhibitors, and has the potential to inform the design of specific CAR-T modulators.

Abstract 810: Differential use of lactate for mitochondria respiration by NSCLC cells

Metabolic liabilities in cancer cells provide the opportunity for novel therapeutic approaches. This is especially true as the dogma that all cancer cells are glycolytic is being challenged. Phenotypic screening of cancer cell lines can demonstrate what these liabilities are and suggest approaches for drugs that target these vulnerabilities. As an example, non-small cell lung cancer (NSCLC) is typically driven by oncogenic mutations in either KRAS or EGFR. However, the impact of these mutations on cellular metabolic phenotype is not well-studied. In this study, we observed that the two KRAS-mutated NSCLC cell lines (A549 and H460) primarily relied on glycolysis for ATP production while EGFR-mutated cell lines (H1975 and PC9) were more reliant on mitochondrial respiration to meet energy demands. There is emerging evidence to suggest that lactate is a major fuel for cancer cell energy metabolism especially in the glucose-limited tumor microenvironment. Thus, we next compared the use of lactate with other carbon sources for ATP production in NSCLC cells. We found there was differential usage of lactate for mitochondrial respiration between KRAS and EGFR-mutated NSCLC cells. EGFR-mutated NSCLC cells used lactate and increased mitochondrial respiration when lactate was acutely administrated regardless of glucose availability. In contrast, the use of lactate for the mitochondrial respiration by KRAS-mutated cells was limited. In A549 cells, no significant change in mitochondrial respiration rate was observed at all by acute injection of lactate. Together, these results imply that NSCLC variants have adopted different metabolic phenotypes depending on the oncogenic background and more oxidative phenotype may be correlated to higher lactate use for TCA cycle in production of ATP.

Citation Format: Pamela Swain, Natalia Romero, Yoonseok Kam, Brian P. Dranka. Differential use of lactate for mitochondria respiration by NSCLC cells [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 810.

Abstract 2092: Metabolic approach to EGFR-targeted therapy in non-small cell lung cancer

Mutation of the epidermal growth factor receptor (EGFR) is a major genetic driver of non-small cell lung cancer (NSCLC). While first-line tyrosine-kinase inhibitors (TKIs) have improved patient survival, many patients eventually develop resistance to these drugs. Combination therapies are now being researched to overcome this resistance. Pathways that may synergize with EGFR signaling are of interest since a liability created with one compound may then be exploited by a second. It is well known that glycolysis is controlled by EGFR signaling in cancer cells. However, the interplay of cell metabolism and EGFR inhibitors is not fully understood. Using PC9 cells which have known constitutive EGFR activation, we examined the relative poise of ATP production from mitochondria and glycolysis. In response to any of four different TKIs: afatinib, CO-1686, dacomitinib and erlotinib, a rapid decrease in glycolytic activity was induced. However, the total ATP production rates were not changed significantly as a result of increased mitochondrial ATP production. We next examined the mitochondrial fuel sources which support this increase by selectively blocking individual fuel pathways. In the presence of either a mitochondrial pyruvate carrier or glutaminase inhibitor, total ATP production rate decreased, and cell viability followed. Taken together, these data suggest that a combinational application of EGFR-targeted therapy and mitochondrial-targeted therapy may provide metabolic stress to cancer cells. Further study is required to understand the interplay of the tumor microenvironment and metabolic niches that may be found therein.

Citation Format: Yoonseok Kam, Pamela Swain, Natalia Romero, Brian P. Dranka. Metabolic approach to EGFR-targeted therapy in non-small cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2092.

Differential modulation of T cell activation

Dysregulated T cell responses cause inflammation and autoimmune diseases. These conditions are managed with agents to limit and down-modulate the diverse cellular processes that control T cell activation. Cellular metabolism is a primary regulator of immune cell fate and function. T cell activation is correlated with metabolic shifts, especially in glycolysis, providing increased metabolic flux to support high rates of cellular proliferation. In this study we evaluated the impact of immunosuppressive compounds on the magnitude and kinetics of early anti-CD3/CD28 mediated T cell activation from a metabolic perspective. We employed compounds with divergent inhibitory mechanisms in order to understand the relationship of specific inhibitory pathways and metabolic function. Using an Agilent Seahorse XF Analyzer, T cells were activated in situ and activation was quantified in real time using proton efflux rate (PER) as a measure of glycolysis. Here, we report that anti-CD3/CD28-mediated T cell activation was suppressed when cells were pretreated with 20 μM prednisone. In contrast, activation was increased in the presence of 20 μM cyclosporin A. In non-activated cells, neither compound had a measurable effect on metabolism within 30 min of treatment. These data show a correlation in timing of suppression with the context of the drugs action. Future studies will utilize additional inhibitory pathway modulators to further examine the mechanisms of T cell activation in the context of immunosuppression.

Abstract A67: Bi-phasic metabolic responses to in situ macrophage activation

The cellular metabolism of macrophages is an emerging element regulating inflammatory macrophages which are a critical component of tumor microenvironment. The inflammatory macrophage with highly glycolytic phenotype is also known to elevate the glycolytic activity upon pathogenic stimulation such as lipopolysaccharide (LPS). In this study, the dynamic changes in glycolysis were traced in a real-time manner by measuring proton efflux rates (PERs) and oxygen consumption rates (OCR) after an in-situ activation using Seahorse XFe96 analyzer. The PER of human peripheral blood monocyte (PBMC) derived M1 macrophages was increased within an hour after injection of LPS, which corresponding to cytokine release, tumor necrosis factor α (TNFα) and interleukin 1β (IL-1β). In contrast to PBMC-derived M1 macrophage activation, macrophage cell lines of RAW264.7 and J774.A1 required co-stimulation with interferon γ (IFNγ) for the full activation. Interestingly, the LPS and IFNγ co-stimulation modulates glycolytic rates in a bi-phasic manner which was identified only in long term (> 6 hr) monitoring. A series of long term XF analysis using in situ activation revealed that the immediate early glycolytic response fully relies on LPS stimulation while the secondary elevation in PER depends on IFNγ stimulus, which turns on inducible nitric oxide synthase (iNOS) signaling and in turn suppresses mitochondrial respiration. The TNFα production is closely related to the immediate early glycolytic elevation, but independent from IFNγ-induced second elevation. The IFNγ-dependent second glycolysis increase was totally abolished by iNOS inhibitors whereas the immediate early glycolysis elevation was not affected at all. These data imply a temporal orchestration mechanism of LPS and IFNγ signaling in the metabolic regulation and activation of inflammatory macrophages.

Citation Format: Yoonseok Kam, Pamela M. Swain, Brian P. Dranka. Bi-phasic metabolic responses to in situ macrophage activation [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A67.

Abstract 62: Effect of cancer cell-derived exosome on energy metabolism associated with macrophage activation

Macrophage is a critical microenvironmental component which can control tumor progression, and dynamic changes in cellular metabolism accompany the polarization. As well as other immune cells, the activation of macrophages can be modulated by cancer cells. Cancer-derived exosome is a newly emerging microenvironmental factor enables cancer cells to communicate with macrophages. In this study, examined were the activation-associated bioenergetic changes and the effect of cancer cell-derived exosome on the changes by a) monitoring the early metabolic kinetics and b) profiling bioenergetic phenotype resulted. In vitro activation of RAW264.7 macrophage cell line by injecting lipopolysaccharide (LPS) and interferon γ (IFNγ) in a Seahorse XF analyzer induced an immediate early increase in glycolytic rate. It also showed a delayed down-regulation of mitochondrial respiration, which resulted in a secondary elevation of glycolytic rate. This secondary glycolytic response was only obtained by LPS-IFNγ co-stimulation and mediated by induced nitric oxide synthase (iNOS) signaling. In contrast to the dynamic changes in metabolic phenotype, the total ATP production rate appeared to be stably maintained according to the XF data normalized by cell number. However, macrophage activation significantly increased glycolysis-dependent portion of ATP production. ATPs were generated almost solely by glycolysis after the delayed mitochondrial down-regulation by iNOS. Co-injection of cancer cell-derived exosomes with LPS slightly but significantly accelerated the immediate early glycolytic response as well as the delayed mitochondrial down-regulation. Furthermore, exosomes induced the immediate early glycolytic response even in the absence of LPS. These results imply that presence of cancer cell-derived exosomes may promote macrophage activation and accelerate pro-inflammatory immune response in a tumor microenvironment.

Citation Format: Yoonseok Kam, Brian P. Dranka. Effect of cancer cell-derived exosome on energy metabolism associated with macrophage activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 62.

Abstract 3487: Bioenergetic profiling of cancer cell lines: Quantifying the impact of glycolysis on cell proliferation

Fast proliferating cells require tight regulation to achieve a balance between the use of nutrients for ATP production (through glycolysis and oxidative phosphorylation) and the use of intermediate metabolites to sustain the increased biosynthetic activity. Cancer cells, but also high proliferative non-transformed cells exhibit high glycolytic activity during rapid proliferation even in the presence of normal oxygen concentrations in culture. However, despite the high glycolytic activity, the role of glycolysis is not necessary as a major contributor of ATP but to allow nutrient assimilation into biosynthetic precursors. Using Agilent Seahorse extracellular flux analysis, we have developed a cell-based assay which allows simultaneous measurement of the two-main cellular metabolic pathways to calculate the total rate of cellular ATP production as well as the fractional contribution from each pathway. The assay allows for real time changes in total ATP production rate to be quantified, and also the relative source of that ATP after exposure to drugs or changes in extracellular fuel supply. When we applied this new assay to a panel of 20 cancer and highly proliferative cell lines, we found that even in cell lines considered highly glycolytic, ATP production from glycolysis never represents more than 65% of total energy production and between 30-50% for most of the cell lines analyzed. The correlation between glycolytic ATP contribution to total ATP production and other cell phenotypes such as proliferation rate and motility was also analyzed. The use of this assay will allow for improved characterization of the bioenergetic profile of cancer cell variants, discrimination between normal and cancer cell types, and allow researchers to better understand the role of aerobic glycolysis in cell proliferation.

Citation Format: Natalia Romero, Pamela M. Swain, Yoonseok Kam, George Rogers, Brian P. Dranka. Bioenergetic profiling of cancer cell lines: Quantifying the impact of glycolysis on cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3487.

Hypoxia-induced reactive oxygen species contribute to immune checkpoint molecule expression in T cells undergoing rapid clonal proliferation

In response to antigen and costimulation, T cells undergo a series of metabolic transitions supporting clonal expansion and differentiation. We recently showed how CD28 and 4-1BB intracellular co-stimulatory domains induce glycolytic vs oxidative metabolic programs, respectively, in the context of a chimeric antigen receptor. Understanding how endogenous co-stimulatory pathways, in particular CD28, supports differentiation and memory cell development despite encountering hostile environments characterized by varying oxygen tension and metabolic checkpoints is of clear importance to cellular immunotherapy.

Immune checkpoint molecule (ICM) expression is associated with T cell exhaustion characterized by reduced proliferative capacity and diminished effector function. While studying the role of LCFAO in primary human T cell differentiation, we uncovered that the CPT1a inhibitor, etomoxir (ETO), induces expression of the PD-1, Tim-3, and Lag-3 ICMs. This is mediated by non-specific effects on oxidative metabolism, culminating in reactive oxygen species (ROS) production. The induction of ICM expression by ETO is calcineurin-dependent and reversed by the antioxidant N-acetylcysteine (NAC). We show that Tim-3 is upregulated by T cells in highly hypoxic xenograft tumors independent of TCR signaling. Transition of highly activated T cell cultures from normoxia (21% O2) to hypoxia (1% O2) induces Tim-3, which is reversed by NAC. These results suggest that ICMs, especially Tim-3, are part of a natural regulatory system that responds to oxidative stress and tempers T cell activation and associated metabolism to minimize oxidative damage to T cell clones expanding following antigen receptor activation.

Changes in metabolic phenotype and cellular ATP production during CD4+ T cell activation

Activation of CD4+ T cells is followed by rapid proliferation and differentiation into specific subsets (Treg or Teff). These transitions are accompanied by tight regulated changes in energetic demand and cellular metabolic reprogramming. Using Agilent Seahorse extracellular flux analysis, we have developed a cell-based assay for simultaneous measurement of the two-main cellular ATP-producing pathways, i.e. glycolysis and oxidative phosphorylation. The assay allows for quantification of real time changes in total ATP production rate, and the fractional contribution of the individual pathways to support bioenergetic demands. We found that naïve CD4+ T cells obtain most of its ATP from mitochondrial oxidative phosphorylation. After activation with anti CD3/CD28 conjugated beads, total ATP production rate significantly increases, and that rise is sustained by an increase in glycolytic ATP production, but also in mitochondrial ATP production. When glucose is replaced by galactose in the assay medium, T cell activation is inhibited despite partial compensation of total ATP production through mitochondrial respiration. Time-course of bioenergetic phenotype during T-cell expansion shows a deep increase in ATP production rate up to day 6–7 with glycolysis contributing up to 70% of total ATP production. When glucose is replaced by galactose 72 hr after activation, total ATP production rate was fully compensated by mitochondrial ATP production but still the inhibition of glycolytic activity by galactose reduces cell proliferation. The results obtained highlight the role of glycolytic activity beyond energetic supply and its importance for biosynthetic and redox requirements or cell activation and proliferation.

The CPT1a inhibitor, etomoxir induces severe oxidative stress at commonly used concentrations

Etomoxir (ETO) is a widely used small-molecule inhibitor of fatty acid oxidation (FAO) through its irreversible inhibitory effects on the carnitine palmitoyl-transferase 1a (CPT1a). We used this compound to evaluate the role of fatty acid oxidation in rapidly proliferating T cells following costimulation through the CD28 receptor. We show that ETO has a moderate effect on T cell proliferation with no observable effect on memory differentiation, but a marked effect on oxidative metabolism. We show that this oxidative metabolism is primarily dependent upon glutamine rather than FAO. Using an shRNA approach to reduce CPT1a in T cells, we further demonstrate that the inhibition of oxidative metabolism in T cells by ETO is independent of its effects on FAO at concentrations exceeding 5 μM. Concentrations of ETO above 5 μM induce acute production of ROS with associated evidence of severe oxidative stress in proliferating T cells. In aggregate, these data indicate that ETO lacks specificity for CTP1a above 5 μM, and caution should be used when employing this compound for studies in cells due to its non-specific effects on oxidative metabolism and cellular redox.

Abstract 5432: Characterization of metabolic fuel dependency in multidrug resistant breast cancer cells

Multidrug resistance (MDR) is a common resistant mechanism of cancer cells to cytotoxic drugs in systemic therapy. MDR is characterized by increased expression of ATP-dependent drug exporting pumps which remove cytotoxic compounds from the cytosol. However, the mechanism whereby cancer cells rapidly respond to this increased ATP demand is not fully understood although the glycolytic nature of MDR phenotype has been evidenced repeatedly by previous reports. We thus hypothesized that flexibility and dependency on mitochondrial fuels would be altered in concert with the switch to glycolysis. In order to more accurate analyze glycolytic pathway, we newly developed an assay to improve glycolytic rate measurements by accounting for TCA-dependent CO2 contribution to extracellular acidification and to correlate Seahorse extracellular flux data with lactate production. In a comparison of glycolytic rates between MCF7 breast cancer cell line and its MDR variant MCF7/Dox using this new assay, we confirmed that in MCF7/Dox cells glycolysis rate under basal conditions is significantly increased compared to wild type cells. Furthermore, MCF7Dox presents a significant increase in compensatory glycolysis when mitochondrial ATP production is blocked. This metabolic profile switch is accompanied by a decreased dependency on glutamine to fuel mitochondrial respiration an increased tolerance of the MCF7/Dox cells to glutamine deprivation as compared to the MCF7 wild type. In contrast, dependency on glucose and fatty acids mitochondrial-oxidation was largely unchanged in MDR cells. Additionally, an increase in long chain fatty acid oxidation is observed when glucose and glutamine oxidation is blocked indicating that MDR cells has higher mitochondrial flexibility to compensate for inhibition of alternative fuels utilization although it preferentially uses glucose. Together these data demonstrate that acquisition of multidrug resistance in MCF7 cells fundamentally changes their metabolism from a glutamine-driven, oxidative phosphorylation dependent phenotype to a highly glycolytic and glucose-dependent phenotype. These findings have potential therapeutic relevance in the context of inhibition of specific mitochondrial fuel pathways to prevent therapy resistance.

Citation Format: Yoonseok Kam, Natalia Romero, Pamela Swain, Brian P. Dranka. Characterization of metabolic fuel dependency in multidrug resistant breast cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5432. doi:10.1158/1538-7445.AM2017-5432

Exploiting evolutionary principles to prolong tumor control in preclinical models of breast cancer

Conventional cancer treatment strategies assume that maximum patient benefit is achieved through maximum killing of tumor cells. However, by eliminating the therapy-sensitive population, this strategy accelerates emergence of resistant clones that proliferate unopposed by competitors-an evolutionary phenomenon termed "competitive release." We present an evolution-guided treatment strategy designed to maintain a stable population of chemosensitive cells that limit proliferation of resistant clones by exploiting the fitness cost of the resistant phenotype. We treated MDA-MB-231/luc triple-negative and MCF7 estrogen receptor-positive (ER(+)) breast cancers growing orthotopically in a mouse mammary fat pad with paclitaxel, using algorithms linked to tumor response monitored by magnetic resonance imaging. We found that initial control required more intensive therapy with regular application of drug to deflect the exponential tumor growth curve onto a plateau. Dose-skipping algorithms during this phase were less successful than variable dosing algorithms. However, once initial tumor control was achieved, it was maintained with progressively smaller drug doses. In 60 to 80% of animals, continued decline in tumor size permitted intervals as long as several weeks in which no treatment was necessary. Magnetic resonance images and histological analysis of tumors controlled by adaptive therapy demonstrated increased vascular density and less necrosis, suggesting that vascular normalization resulting from enforced stabilization of tumor volume may contribute to ongoing tumor control with lower drug doses. Our study demonstrates that an evolution-based therapeutic strategy using an available chemotherapeutic drug and conventional clinical imaging can prolong the progression-free survival in different preclinical models of breast cancer.

Evolutionary strategy for systemic therapy of metastatic breast cancer: balancing response with suppression of resistance

Conventional systemic therapy for disseminated breast cancer is based on the general assumption that the greatest patient benefit is achieved by killing the maximum number of tumor cells. While this strategy often achieves a significant reduction in tumor burden, most patients with metastatic breast cancer ultimately die from their disease as therapy fails because tumor cells evolve resistance. We propose that the conventional maximum dose/maximum cell kill cancer therapy, when viewed from an evolutionary vantage, is suboptimal and likely even harmful as it accelerates evolution and growth of the resistant phenotypes that ultimately cause patient death. As an alternative, we are investigating evolutionary therapeutic strategies that shift the treatment goal from killing the maximum number of cancer cells to maximizing patient survival. Here we introduce two novel approaches for systemic therapy for metastatic breast cancer, considering the evolutionary nature of tumor progression; adaptive therapy and double-bind therapy.

Sweat but no gain: inhibiting proliferation of multidrug resistant cancer cells with "ersatzdroges"

ATP-binding cassette (ABC) drug transporters consuming ATPs for drug efflux is a common mechanism by which clinical cancers develop multidrug resistance (MDR). We hypothesized that MDR phenotypes could be suppressed by administration of "ersatzdroges," nonchemotherapy drugs that are, nevertheless, ABC substrates. We reasoned that, through prolonged activation of the ABC pumps, ersatzdroges will force MDR cells to divert limited resources from proliferation and invasion thus delaying disease progression. We evaluated ABC substrates as ersatzdroge by comparing their effects on proliferation and survival of MDR cell lines (MCF-7/Dox and 8226/Dox40) with the effects on the drug-sensitive parental lines (MCF-7 and 8226/s, respectively) in glucose-limited condition. The changes in glucose and energy demands were also examined in vitro and in vivo. MCF-7/Dox showed higher ATP demand and susceptibility to glucose resource limitation. Ersatzdroges significantly decreased proliferation of MCF-7/Dox when the culture media contained physiological glucose concentrations (1.0 g/L) or less, but had no effect on MCF-7. Similar evidence was obtained from 8226/Dox40 and 8226/s comparison. In vivo 18F-FDG-PET imaging demonstrated that glucose uptake was increased by systemic administration of an ersatzdroge in tumors composed of MDR. These results suggest that administration of ersatzdroges, by increasing the metabolic cost of resistance, can suppress proliferation of drug-resistance phenotypes. This provides a novel and relatively simple application model of evolution-based strategy, which can exploit the cost of resistance to delay proliferation of drug-resistant cancer phenotypes. Furthermore, suggested is the potential of ersatzdroges to identify tumors or regions of tumors that express the MDR phenotype.

Evolutionary approaches to prolong progression-free survival in breast cancer

Many cancers adapt to chemotherapeutic agents by upregulating membrane efflux pumps that export drugs from the cytoplasm, but this response comes at an energetic cost. In breast cancer patients, expression of these pumps is low in tumors before therapy but increases after treatment. While the evolution of therapeutic resistance is virtually inevitable, proliferation of resistant clones is not, suggesting strategies of adaptive therapy. Chemoresistant cells must consume excess resources to maintain resistance mechanisms, so adaptive therapy strategies explicitly aim to maintain a stable population of therapy-sensitive cells to suppress growth of resistant phenotypes through intratumoral competition. We used computational models parameterized by in vitro experiments to illustrate the efficacy of such approaches. Here, we show that low doses of verapamil and 2-deoxyglucose, to accentuate the cost of resistance and to decrease energy production, respectively, could suppress the proliferation of drug-resistant clones in vivo. Compared with standard high-dose-density treatment, the novel treatment we developed achieved a 2-fold to 10-fold increase in time to progression in tumor models. Our findings challenge the existing flawed paradigm of maximum dose treatment, a strategy that inevitably produces drug resistance that can be avoided by the adaptive therapy strategies we describe.

Abstract 793: Evolutionary therapy modeling for multidrug resistance: A novel concept of false drug

The emergence of drug resistance is almost inevitably encountered during systematic cancer therapies resulting in treatment failure and tumor progression. The multidrug resistance (MDR), mediated by xenobiotic metabolism, is among the most well-known and well-studied mechanisms for drug resistance. Although MDR emergence is an evolutionary process, cancer therapies rarely incorporate evolutionary dynamics into their design. Here we present a study to develop a cancer treatment strategy targeting the metabolic cost of MDR and its evolutionary consequence. Through a new therapeutic strategy that reduces the fitness and proliferation of resistant cells by forcing them to use excess energy, we expect to stabilize the tumor volume by maintaining a constant population of sensitive cells and suppressing emergence of resistance. P-glycoprotein (PGP) is the best-known multidrug transporter responsible for MDR and lowers the intracellular drug concentration by an active drug export. A doxorubicin-resistant cell line MCF-7/dox showed significant overexpression of PGP pump when compared to MCF-7/wt, the parental drug-sensitive cell line. We focused on the metabolic energy cost due to the overexpression of the pump protein and its activity which requires about 2 ATP for each molecule of drug extruded. We hypothesized that the cost requires diversion of some resources which are, therefore, not available for proliferation thus reducing the evolutionary fitness of resistant cells. As expected, MCF-7/dox showed higher glycolytic activity and higher glucose demand for the growth and survival compared to the parental cell line MCF-7/wt. Due to the increased glucose consumption, MCF-7/dox appeared to be less competitive in a mixed culture with MCF-7/wt when the glucose resource was limited. We were able to increase the glycolytic activity further by applying other PGP substrates including verapamil at a non-cytotoxic dose. From these results, we propose a novel therapy using a “false drug,” which is not cytotoxic but nevertheless exported by PGP. The expenditure of resources required to extrude the false drug without any survival benefit is expected to further reduce the fitness of the MDR phenotype. When the mixed population was treated with verapamil at a non-lethal dosage, the drug-resistant population was significantly decreased further than when verapamil was not present. 2-deoxy glucose (2-DG), a glycolysis inhibitor, showed synergistic effect with verapamil in further reducing the MCF-7/dox population size.

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 793. doi:1538-7445.AM2012-793

Cellular modeling of cancer invasion: integration of in silico and in vitro approaches

Cancer invasion is one of the hallmarks of cancer and a prerequisite for cancer metastasis. However, the invasive process is very complex, depending on multiple correlated intrinsic and environmental factors, and thus is difficult to study experimentally in a fully controlled way. Therefore, there is an increased demand for interdisciplinary integrated approaches combining laboratory experiments with multiscale in silico modeling. In this review, we will summarize current computational techniques applicable to model cancer invasion in silico, with a special focus on a class of individual-cell-based models developed in our laboratories. We also discuss their integration with traditional and novel in vitro experimentation, including new invasion assays whose design was inspired by computational modeling.

Abstract 4916: Systems biology analysis of subpopulation-based heterogeneity for cellular radiosensitivity modeling

Intrinsic cellular radiosensitivity is a key parameter used in radiotherapy modeling. Our previous studies showed that a cellular model based on the in vitro clonogenic assay measuring survival fraction at 2Gy (SF2) accurately predicts tumor response in patients treated with radiotherapy. However, SF2 as determined from a heterogeneous cell population represents its averaged sensitivity, whilst we have shown, using live cell imaging, that cultured tumor cell populations include colonies of varying sizes, cell numbers and growth rates. In order to link this subpopulation-based heterogeneity to the parental cell line radiosensitivity, and to build an integrative predicting model, we designed a novel systems biology approach that combines SF2 clonogenic assay experimentation, high-content screening and image analysis together with a quantitative bio-mathematical study. We integrated a 96-well plate-based SF2 assay with a semi-automated image analysis using CellProfilerTM, and measured morphological parameters including SF2, colony tightness index (colony density), and colony growth rate. We have also developed new algorithms to complement those implemented in CellProfilerTM to identify some highly dispersed colonies. As a preliminary trial, we analyzed five non-small cell lung cancer (NSCLC) cell lines characterized by different levels of radiosensitivity in vitro. We observed several common phenotypic shifts after irradiation, such as reduction in growth rate and cell density. However, the response patterns for each subpopulation was highly heterogenous across cell lines. Interestingly, the variability in morphological response was better correlated to radiosensitivity than the average colony density. In order to further assess subpopulation heterogeneity, we isolated 15 random sub-clones from H460 cells and found significant intrinsic SF2 heterogeneity. In addition to morphology, we examined the intrinsic variability in the expression level of several molecular biomarkers including STAT1, a molecular maker in our prediction model, and CD44, a cancer stem cell marker proposed to be related with radioresistance. Both markers showed significant variability, which was negatively correlated with the colony density. In conclusion, we propose a novel systems-based approach that integrates high content phenotypic information at a single cell level to study tumor-intrinsic heterogeneity and its contribution to clinically-relevant radioresistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4916. doi:10.1158/1538-7445.AM2011-4916

Nest expansion assay: a cancer systems biology approach to in vitro invasion measurements

Background

Traditional in vitro cell invasion assays focus on measuring one cell parameter at a time and are often less than ideal in terms of reproducibility and quantification. Further, many techniques are not suitable for quantifying the advancing margin of collectively migrating cells, arguably the most important area of activity during tumor invasion. We have developed and applied a highly quantitative, standardized, reproducible Nest Expansion Assay (NEA) to measure cancer cell invasion in vitro, which builds upon established wound-healing techniques. This assay involves creating uniform circular "nests" of cells within a monolayer of cells using a stabilized, silicone-tipped drill press, and quantifying the margin expansion into an overlaid extracellular matrix (ECM)-like component using computer-assisted applications.

Findings

The NEA was applied to two human-derived breast cell lines, MCF10A and MCF10A-CA1d, which exhibit opposite degrees of tumorigenicity and invasion in vivo. Assays were performed to incorporate various microenvironmental conditions, in order to test their influence on cell behavior and measures. Two types of computer-driven image analysis were performed using Java's freely available ImageJ software and its FracLac plugin to capture nest expansion and fractal dimension, respectively – which are both taken as indicators of invasiveness. Both analyses confirmed that the NEA is highly reproducible, and that the ECM component is key in defining invasive cell behavior. Interestingly, both analyses also detected significant differences between non-invasive and invasive cell lines, across various microenvironments, and over time.

Conclusion

The spatial nature of the NEA makes its outcome susceptible to the global influence of many cellular parameters at once (e.g., motility, protease secretion, cell-cell adhesion). We propose the NEA as a mid-throughput technique for screening and simultaneous examination of factors contributing to cancer cell invasion, particularly suitable for parameterizing and validating Cancer Systems Biology approaches such as mathematical modeling.

Cadherin-bound beta-catenin feeds into the Wnt pathway upon adherens junctions dissociation: evidence for an intersection between beta-catenin pools

β-catenin is an essential component of two cellular systems: cadherin-based adherens junctions (AJ) and the Wnt signaling pathway. A functional or physical connection between these β-catenin pools has been suggested in previous studies, but not conclusively demonstrated to date. To further examine this intersection, we treated A431 cell colonies with lysophosphatidic acid (LPA), which forces rapid and synchronized dissociation of AJ. A combination of immunostaining, time-lapse microscopy using photoactivatable-GFP-tagged β-catenin, and image analyses indicate that the cadherin-bound pool of β-catenin, internalized together with E-cadherin, accumulates at the perinuclear endocytic recycling compartment (ERC) upon AJ dissociation, and can be translocated into the cell nucleus upon Wnt pathway activation. These results suggest that the ERC may be a site of residence for β-catenin destined to enter the nucleus, and that dissociation of AJ may influence β-catenin levels in the ERC, effectively affecting β-catenin substrate levels available downstream for the Wnt pathway. This intersection provides a mechanism for integrating cell-cell adhesion with Wnt signaling and could be critical in developmental and cancer processes that rely on β-catenin-dependent gene expression.

A novel circular invasion assay mimics in vivo invasive behavior of cancer cell lines and distinguishes single-cell motility in vitro

BACKGROUND

Classical in vitro wound-healing assays and other techniques designed to study cell migration and invasion have been used for many years to elucidate the various mechanisms associated with metastasis. However, many of these methods are limited in their ability to achieve reproducible, quantitative results that translate well in vivo. Such techniques are also commonly unable to elucidate single-cell motility mechanisms, an important factor to be considered when studying dissemination. Therefore, we developed and applied a novel in vitro circular invasion assay (CIA) in order to bridge the translational gap between in vitro and in vivo findings, and to distinguish between different modes of invasion.

METHOD

Our method is a modified version of a standard circular wound-healing assay with an added matrix barrier component (Matrigel), which better mimics those physiological conditions present in vivo. We examined 3 cancer cell lines (MCF-7, SCOV-3, and MDA-MB-231), each with a different established degree of aggressiveness, to test our assay's ability to detect diverse levels of invasiveness. Percent wound closure (or invasion) was measured using time-lapse microscopy and advanced image analysis techniques. We also applied the CIA technique to DLD-1 cells in the presence of lysophosphatidic acid (LPA), a bioactive lipid that was recently shown to stimulate cancer cell colony dispersal into single migratory cells, in order to validate our method's ability to detect collective and individual motility.

RESULTS

CIA method was found to be highly reproducible, with negligible levels of variance measured. It successfully detected the anticipated low, moderate, and high levels of invasion that correspond to in vivo findings for cell lines tested. It also captured that DLD-1 cells exhibit individual migration upon LPA stimulation, and collective behavior in its absence.

CONCLUSION

Given its ability to both determine pseudo-realistic invasive cell behavior in vitro and capture subtle differences in cell motility, we propose that our CIA method may shed some light on the cellular mechanisms underlying cancer invasion and deserves inclusion in further studies. The broad implication of this work is the development of a reproducible, quantifiable, high-resolution method that can be applied to various models, to include an unlimited number of parameters and/or agents that may influence invasion.

Dispersal of epithelial cancer cell colonies by lysophosphatidic acid (LPA)

We describe a model system in which cancer cell colonies disperse into single, highly migratory cells in response to lysophosphatidic acid (LPA). Though LPA is known to stimulate chemotaxis and chemokinesis, a colony dispersal effect has not been reported, to our knowledge. Cancer colony dispersal by LPA is comprised of an ordered sequence of events: (1) stimulation of membrane ruffling and formation of lamellipodia, (2) dissolution of adherens junctions, (3) single cell migration in a mesenchymal-like morphology we term "ginkgo-leaf." The net result is dispersal of carcinoma cells from a compact colony. We analyzed these three steps using live-cell imaging and computer-assisted quantification and measured the following parameters: onset of lamellipodia formation, lamellipodia velocity, colony dispersal, trans-epithelial resistance, migrating cell number and speed. Because hepatocyte growth factor (HGF) was described as an epithelial scatter factor, we compared it to LPA in our system and found that HGF has no epithelial colony dispersal properties and that this effect is strictly related to LPA. Given its striking similarity to tumor cell budding observed in patients, we propose that LPA-colony dispersal may provide a cellular mechanism underlying cancer invasion and as such deserves further studies.

Requirement of phospholipase D1 activity in H-RasV12-induced transformation

The ability of the Ras oncogene to transform normal cells has been well established. One downstream effector of Ras is the lipid hydrolyzing enzyme phospholipase D. Recent evidence has emerged indicating a role for phospholipase D in cell proliferation, membrane trafficking, and migration. To study the potential importance of phospholipase D in the oncogenic ability of Ras, we used Rat-2 fibroblasts with reduced phospholipase D1 activity (Rat-2V25). Here, we show that H-Ras transformation of Rat-2 fibroblasts requires normal phospholipase D1 activity. WT Rat-2 fibroblasts transfected with the H-RasV12 oncogene grew colonies in soft agar and tumors in nude mice. However, Rat-2V25 cells when transfected with the H-RasV12 oncogene did not form colonies in soft agar or produce tumors when xenografted onto nude mice. Interestingly, in the presence of phosphatidic acid, the product of phospholipase D, growth in soft agar and tumor formation was restored. We also observed a dramatic increase in the expression of phospholipase D1 in colorectal tumors when compared with adjacent normal mucosa. Our studies identify phospholipase D1 as a critical downstream mediator of H-Ras-induced tumor formation.

Role of phospholipase D in the activation of protein kinase D by lysophosphatidic acid

Protein kinase D was auto-phosphorylated at Ser916 and trans-phosphorylated at Ser744/Ser748 in Rat-2 fibroblasts treated with lysophosphatidic acid. Both phosphorylations were inhibited by 1-butanol, which blocks phosphatidic acid formation by phospholipase D. The phosphorylations were also reduced in Rat-2 clones with decreased phospholipase D activity. Platelet-derived growth factor-induced protein kinase D phosphorylation showed a similar requirement for phospholipase D, but that induced by 4beta-phorbol 12 myristate 13-acetate did not. Propranolol an inhibitor of diacylglycerol formation from phosphatidic acid blocked the phosphorylation of protein kinase D, whereas dioctanoylglycerol induced it. The temporal pattern of auto-phosphorylation of protein kinase D closely resembled that of phospholipase D activation and preceded the trans-phosphorylation by protein kinase C. These results suggest that protein kinase D is activated by lysophosphatidic acid through sequential phosphorylation and that diacylglycerol produced by PLD via phosphatidic acid is required for the autophosphorylation that occurs prior to protein kinase C-mediated phosphorylation.

Role of phospholipase D1 in the regulation of mTOR activity by lysophosphatidic acid

Mitogens activate protein translation through phosphorylation of p7S6 kinase (p70(S6K)) and eIF4E binding protein 1 (4E-BP1) mediated by the mammalian target of rapamycin (mTOR) or phosphoinositide 3-kinase (PI3K). A recent report (Science 294, 1942, 2001) has implicated phospholipase D (PLD) in mTOR signaling. We studied the role of PLD in the phosphorylation of p70(S6K) and 4E-BP1 induced by lysophosphatidic acid (LPA) and platelet-derived growth factor (PDGF) using fibroblasts deficient in PLD activity and also 1-butanol, which inhibits phosphatidic acid production by PLD. The reduction in PLD activity in both situations impaired the effect of LPA on mTOR signaling but did not inhibit the effect of PDGF. PDGF induced marked phosphorylation of Akt (a PI3K target) but this was not affected by PLD deficiency. LPA caused much less phosphorylation of Akt and this was dependent on PLD activity. Toxin B, which inactivates Rho GTPases, markedly impaired PLD1 activation and phosphorylation of Akt, p70(S6K), and 4E-BP1 induced by LPA but had a minimal or no effect on the actions of PDGF. These results support the hypothesis that LPA activates protein translation through the action of PLD1-generated PA on mTOR and the PI3K/Akt pathway whereas PDGF acts through P13K/Akt independent of PLD1.

Dimerization of phospholipase d isozymes

Two mammalian phospholipase D (PLD) isozymes (PLD1 and PLD2) have been reported. In this study, we differentially tagged these isozymes with enhanced green fluorescent protein (EGFP-rPLD1 and EGFP-rPLD2) or Xpress peptide epitope (Xpress-rPLD1 and Xpress-rPLD2) to examine the association between these isozymes. Overexpressed EGFP-rPLD1 coimmunoprecipitated with Xpress-rPLD1 using anti-Xpress antibody. However, the coimmunoprecipitation was independent of the activity of rPLD1. Xpress-rPLD2 also bound to EGFP-rPLD1 although the binding was less efficient than observed with Xpress-rPLD1. The association between rPLD2 and rPLD1 was confirmed by coimmunoprecipitation of EGFP-rPLD2 with Xpress-rPLD1. EGFP-rPLD2 also bound to Xpress-rPLD2 as shown by coimmunoprecipitation. Immunofluorescence staining of COS-7 cells coexpressing EGFP-rPLDs and Xpress-rPLDs showed that the PLD isozymes colocalized in the perinuclear and plasma membrane regions, suggesting that they could associate in a cellular setting. These results suggest that rPLD1 and rPLD2 can exist as homodimers and can form heterodimers.

Factors affecting prostacyclin receptor agonist efficacy in different cell types

Octimibate and related nonprostanoid prostacyclin mimetics are partial agonists displaying highly tissue-specific responses. Octimibate demonstrated considerably greater efficacy for stimulation of adenylyl cyclase activity in Chinese hamster ovary cells transiently expressing mouse prostacyclin receptors (mIP-CHO cells) when compared to human SK-N-SH neuroblastoma cells, which endogenously express prostacyclin (IP) receptors. Pretreatment of both cell types with pertussis toxin (PTx) failed to influence IP agonist efficacy or potency, indicating a lack of involvement of an agonist-stimulated inhibitory G(i)-coupled pathway. Although stimulation of mIP-CHO cells with the full agonist cicaprost increased both [3H]cyclic AMP and [3H]inositol phosphate ([3H]IP) accumulation (pEC(50) values of 8.35 and 6.82, respectively), IP receptor signalling through G(q) in SK-N-SH cells was absent. Inhibition of protein kinase C (PKC) in mIP-CHO cells increased [3H]IP accumulation but had no effect on [3H]cyclic AMP accumulation. Therefore, the poor coupling of the IP receptor in SK-N-SH cells to G(q) is unlikely to explain the relatively low efficacy of octimibate for stimulating adenylyl cyclase in these cells. Furthermore, protein kinase A (PKA) inhibition appears to enhance IP receptor signalling through both G(s) and G(q) in mIP-CHO cells.

A comparative study of quantitative structure activity relationship methods based on antitumor diarylsulfonylureas

A series of 28 diarylsulfonylureas with antitumor activity was subjected to a three-dimensional quantitative activity relationship (3D-QSAR) study. Three different QSAR methods, comparative molecular field analysis (CoMFA), hologram QSAR (HQSAR) and comparative molecular similarity indices analysis (CoMSIA), were compared in terms of their potential for predictability. All three QSAR-based models had good predictability and yielded q(2) values 0.74, 0.63 and 0.72, respectively. The CoMFA model provided the highest q(2) and r(2) values, which implied the significance of correlation of steric and electrostatic fields with biological activities. The number of components was 3-4 for all three QSAR methods. The quality of HQSAR or CoMSIA was slightly lower than that of CoNFA in terms of q(2) and r(2) values. HQSAR does not require the generation of a three-dimensional structure of molecules and CoMSIA does not require molecular superposition, therefore they are faster than CoMFA in data processing.

Phospholipase D activity is required for actin stress fiber formation in fibroblasts

Phospholipase D (PLD) is a ubiquitously expressed enzyme of ill-defined function. In order to explore its cellular actions, we inactivated the rat PLD1 (rPLD1) isozyme by tagging its C terminus with a V5 epitope (rPLD1-V5). This was stably expressed in Rat-2 fibroblasts to see if it acted as a dominant-negative mutant for PLD activity. Three clones that expressed rPLD1-V5 were selected (Rat2V16, Rat2V25, and Rat2V29). Another clone (Rat2V20) that lost expression of rPLD1-V5 was also obtained. In the three clones expressing rPLD1-V5, PLD activity stimulated by phorbol myristate acetate (PMA) or lysophosphatidic acid (LPA) was reduced by ~50%, while the PLD activity of Rat2V20 cells was normal. Changes in the actin cytoskeleton in response to LPA or PMA were examined in these clones. All three clones expressing rPLD1-V5 failed to form actin stress fibers after treatment with LPA. However, Rat2V20 cells formed stress fibers in response to LPA to the same extent as wild-type Rat-2 cells. In contrast, there was no significant change in membrane ruffling induced by PMA in the cells expressing rPLD1-V5. Since Rho is an activator both of rPLD1 and stress fiber formation, the activation of Rho was monitored in wild-type Rat-2 cells and Rat2V25 cells, but no significant difference was detected. The phosphorylation of vimentin mediated by Rho-kinase was also intact in Rat2V25 cells. Rat2V25 cells also showed normal vinculin-containing focal adhesions. However, the translocation of alpha-actinin to the cytoplasm and to the detergent-insoluble fraction in Rat2V25 cells was reduced. These results indicate that PLD activity is required for LPA-induced rearrangement of the actin cytoskeleton to form stress fibers and that PLD might be involved in the cross-linking of actin filaments mediated by alpha-actinin.

Gating connexin 43 channels reconstituted in lipid vesicles by mitogen-activated protein kinase phosphorylation

The regulation of gap junctional permeability by phosphorylation was examined in a model system in which connexin 43 (Cx43) gap junction hemichannels were reconstituted in lipid vesicles. Cx43 was immunoaffinity-purified from rat brain, and Cx43 channels were reconstituted into unilamellar phospholipid liposomes. The activities of the reconstituted channels were measured by monitoring liposome permeability. Liposomes containing the Cx43 protein were fractionated on the basis of permeability to sucrose using sedimentation in an iso-osmolar density gradient. The gradient allowed separation of the sucrose-permeable and -impermeable liposomes. Liposomes that were permeable to sucrose were also permeable to the communicating dye molecule lucifer yellow. Permeability, and therefore activity of the reconstituted Cx43 channels, were directly dependent on the state of Cx43 phosphorylation. The permeability of liposomes containing Cx43 channels was increased by treatment of liposomes with calf intestinal phosphatase. Moreover, liposomes formed with Cx43 that had been dephosphorylated by calf intestinal phosphatase treatment showed increased permeability to sucrose. The role of phosphorylation in the gating mechanism of Cx43 channels was supported further by the observation that phosphorylation of Cx43 by mitogen-activated protein kinase reversibly reduced the permeability of liposomes containing dephosphorylated Cx43. Our results show a direct correlation between gap junctional permeability and the phosphorylation state of Cx43.

Transfer of second messengers through gap junction connexin 43 channels reconstituted in liposomes

Gap junction channels reconstituted in liposomes provide a pathway for the transfer of second messengers. Gap junction channels were formed in the artificial unilamellar liposomes using immunoaffinity-purified connexin 43 gap junction protein from rat brain. Sucrose-permeable and -impermeable liposomes were separated on the basis of sucrose permeability in the iso-osmolar sucrose density gradient. The liposomes permeable to sucrose were also permeable to a communicating dye molecule, Lucifer yellow. In the present study, we examined the transfer of second messengers through the connexin 43 channels reconstituted in liposomes and first report the direct evidence that the gap junction channels are permeable to second messengers including adenosine 3',5'-cyclic phosphate and inositol 1,4,5-trisphosphate.

Inhibition of the phosphorylation of a myristoylated alanine-rich C kinase substrate by methyl methanesulfonate in cultured NIH 3T3 cells

The effect of methyl methanesulfonate (MMS) on the phosphorylation of an acidic 80-kDa myristoylated alanine-rich C kinase substrate (MARCKS) protein was investigated in NIH 3T3 fibroblasts. An alkylating agent, MMS inhibited protein kinase C activity and the phosphorylation of MARCKS. MMS treatment also lowered the cellular amounts of second messengers of inositol-1,4,5-trisphosphate and diacylglycerol. Data suggest that MMS decreased the phosphorylation of phospholipase C, a protein whose activity is influenced by its phosphorylation state. We present here the first report that MMS intervenes in a signal cascade by inhibiting the phosphorylation of phospholipase C, which in turn leads to the inactivation of protein kinase C and the subsequent inhibition of MARCKS phosphorylation.