Metabolic consequences of treatment with AKT inhibitor perifosine in breast cancer cells

New Advances in Targeted Therapy of HER2-Negative Breast Cancer

Breast cancer has an extremely high incidence in women, and its morbidity and mortality rank first among female tumors. With the increasing development of molecular biology and genomics, molecular targeted therapy has become one of the most active areas in breast cancer treatment research and has also achieved remarkable achievements. However, molecular targeted therapy is mainly aimed at HER2-positive breast cancer and has not yet achieved satisfactory curative effect on HER2-negative breast cancer. This article describes the potential targets that may be used for breast cancer treatment from the aspects of PI3K/AKT signaling pathway, DDR, angiogenesis, the cell cycle, breast cancer stem cells, etc., and explores possible inhibitors for the treatment of HER2-negative breast cancer, such as PI3K inhibitors, AKT inhibitors and m-TOR inhibitors that inhibit the PI3K/AKT signaling pathway, small molecule tyrosine kinase inhibitors that restrain angiogenesis, CDK inhibitors, aurora kinase inhibitors and HDAC inhibitors that block cell cycle, as well as the drugs targeting breast cancer stem cells which have been a hit, aiming to provide a new idea and strategy for the treatment of HER2-negative breast cancer.

ChoK-Full of Potential: Choline Kinase in B Cell and T Cell Malignancies

Aberrant choline metabolism, characterized by an increase in total choline-containing compounds, phosphocholine and phosphatidylcholine (PC), is a metabolic hallmark of carcinogenesis and tumor progression. This aberration arises from alterations in metabolic enzymes that control PC biosynthesis and catabolism. Among these enzymes, choline kinase α (CHKα) exhibits the most frequent alterations and is commonly overexpressed in human cancers. CHKα catalyzes the phosphorylation of choline to generate phosphocholine, the first step in de novo PC biosynthesis. CHKα overexpression is associated with the malignant phenotype, metastatic capability and drug resistance in human cancers, and thus has been recognized as a robust biomarker and therapeutic target of cancer. Of clinical importance, increased choline metabolism and CHKα activity can be detected by non-invasive magnetic resonance spectroscopy (MRS) or positron emission tomography/computed tomography (PET/CT) imaging with radiolabeled choline analogs for diagnosis and treatment monitoring of cancer patients. Both choline-based MRS and PET/CT imaging have also been clinically applied for lymphoid malignancies, including non-Hodgkin lymphoma, multiple myeloma and central nervous system lymphoma. However, information on how choline kinase is dysregulated in lymphoid malignancies is very limited and has just begun to be unraveled. In this review, we provide an overview of the current understanding of choline kinase in B cell and T cell malignancies with the goal of promoting future investigation in this area.

Laminin α5 modulates fibroblast proliferation in epidural fibrosis through the PI3K/AKT/mTOR signaling pathway

Lumbar laminectomy is commonly deemed as the most valid surgery for a series of lumbar illnesses, such as lumbar disc herniation, which could lead to spinal canal stenosis. However, epidural fibrosis is one of the most common complications that limits the application of lumbar laminectomy, which is mainly caused by proliferation of local fibroblasts. Laminins are glycoproteins that consist of α, β and γ chains, which serve a crucial role in biological cell behaviors, such as adhesion, differentiation, migration and proliferation, especially the isoform with the fifth α chain-laminin α5. The PI3K/AKT/mTOR signaling pathway was demonstrated to be associated with various biological functions in cells. The aim of the present study was to explore whether laminin α5 is an important factor in epidural fibrosis by modulating the proliferation of fibroblasts through the activation of PI3K/AKT/mTOR signaling pathway. In the animal model, the results of the hematoxylin-eosin staining, cell counting, Masson's trichrome staining and immunohistochemical staining showed laminin α5 to be positively associated with epidural fibrosis. Furthermore, to verify the assumption that laminin α5 could modulate fibroblast proliferation through the PI3K/AKT/mTOR signal pathway, fibroblasts were transfected with laminin α5-small interfering (si)RNA. The results of western blotting (proliferating cell nuclear antigen and cyclin D1), the Cell Counting Kit-8 and EdU incorporation assays indicated that the proliferative level of fibroblasts decreased, and the expression of phosphorylated (p)-focal adhesion kinase 1, p-AKT and p-mTOR was reduced. Subsequently, laminin α5 was overexpressed and the change in cell proliferation and expression of associated proteins contrasted with that observed in siRNA. The results demonstrated that laminin α5 could interfere the activation of the PI3K/AKT/mTOR signaling pathway. Finally, the inhibition of the PI3K/AKT/mTOR signaling pathway by LY294002 resulted in decreased fibroblast proliferation. In conclusion, laminin α5 could modulate fibroblast proliferation in epidural fibrosis through the PI3K/AKT/mTOR signaling pathway.

Focus on the glycerophosphocholine pathway in choline phospholipid metabolism of cancer

Activated choline metabolism is a hallmark of carcinogenesis and tumor progression, which leads to elevated levels of phosphocholine and glycerophosphocholine in all types of cancer tested so far. Magnetic resonance spectroscopy applications have played a key role in detecting these elevated choline phospholipid metabolites. To date, the majority of cancer-related studies have focused on phosphocholine and the Kennedy pathway, which constitutes the biosynthesis pathway for membrane phosphatidylcholine. Fewer and more recent studies have reported on the importance of glycerophosphocholine in cancer. In this review article, we summarize the recent literature on glycerophosphocholine metabolism with respect to its cancer biology and its detection by magnetic resonance spectroscopy applications.

Toxoplasma gondii excreted-secreted antigens suppress Foxp3 via PI3K-AKT-mTOR signaling pathway

Toxoplasma gondii excreted-secreted antigens (ESA) cause spontaneous abortion or fetal teratogenesis during the pregnancy in mice, especially in the early stage. Those adverse pregnancy outcomes are due to the deficit in regulatory T cells (Tregs). Forkhead box P3 (Foxp3), a critical transcription factor, modulates Tregs differentiation and its function. Besides, phosphatidylinositol 3-kinase-protein kinase B-mammalian target of rapamycin (PI3K-AKT-mTOR) signaling network is implicated in interfering with Foxp3 induction. We previously demonstrated that ESA diminished the number of Tregs and inhibited its function. And ESA suppressed Foxp3 expression via the attenuation of transforming growth factor β RII/Smad2/Smad3/Smad4 pathway. The current study aimed to investigate whether the PI3K-AKT-mTOR signaling network is involved in Foxp3 downregulation induced by ESA. We found that ESA upregulated PI3K, P-AKT, mTOR, and P-mTOR. Knockdown of PI3K cooperated with ESA to restore Foxp3 expression mediated by ESA. This suppressive role of ESA on Foxp3 expression was abrogated by AKT inhibitor. In addition, neutralization of Toll-like receptor 4 could restore the expression of Foxp3, PI3K, and its downstream effectors induced by ESA. Collectively, the findings indicated that ESA inhibited Foxp3 expression via the upregulation of PI3K-AKT-mTOR signaling pathway.

In-cell determination of Lactate Dehydrogenase Activity in a Luminal Breast Cancer Model ⁻ ex vivo Investigation of Excised Xenograft Tumor Slices Using dDNP Hyperpolarized [1-13C]pyruvate

[1-¹³C]pyruvate, the most widely used compound in dissolution-dynamic nuclear polarization (dDNP) magnetic resonance (MR), enables the visualization of lactate dehydrogenase (LDH) activity. This activity had been demonstrated in a wide variety of cancer models, ranging from cultured cells, to xenograft models, to human tumors in situ. Here we quantified the LDH activity in precision cut tumor slices (PCTS) of breast cancer xenografts. The Michigan Cancer Foundation-7 (MCF7) cell-line was chosen as a model for the luminal breast cancer type which is hormone responsive and is highly prevalent. The LDH activity, which was manifested as [1-¹³C]lactate production in the tumor slices, ranged between 3.8 and 6.1 nmole/nmole adenosine tri-phosphate (ATP) in 1 min (average 4.6 ± 1.0) on three different experimental set-ups consisting of arrested vs. continuous perfusion and non-selective and selective RF pulsation schemes and combinations thereof. This rate was converted to an expected LDH activity in a mass ranging between 3.3 and 5.2 µmole/g in 1 min, using the ATP level of these tumors. This indicated the likely utility of this approach in clinical dDNP of the human breast and may be useful as guidance for treatment response assessment in a large number of tumor types and therapies ex vivo.

Drug Effect Prediction by Integrating L1000 Genomic and Proteomic Big Data

The library of integrated Network-Based Cellular Signatures (LINCS) project aims to create a network-based understanding of biology by cataloging changes in gene expression and signal transduction. Gene expression and proteomic data in LINCS L1000 are cataloged for human cancer cells treated with compounds and genetic reagents. For understanding the related cell pathways and facilitating drug discovery, we developed binary linear programming (BLP) to infer cell-specific pathways and identify compounds' effects using L1000 gene expression and phosphoproteomics data. A generic pathway map for the MCF7 breast cancer cell line was built. Within them, BLP extracted the cell-specific pathways, which reliably predicted the compounds' effects. In this way, the potential drug effects are revealed by our models.

Metabolic biomarkers of response to the AKT inhibitor MK-2206 in pre-clinical models of human colorectal and prostate carcinoma

BACKGROUND

AKT is commonly overexpressed in tumours and plays an important role in the metabolic reprogramming of cancer. We have used magnetic resonance spectroscopy (MRS) to assess whether inhibition of AKT signalling would result in metabolic changes that could potentially be used as biomarkers to monitor response to AKT inhibition.

METHODS

Cellular and metabolic effects of the allosteric AKT inhibitor MK-2206 were investigated in HT29 colon and PC3 prostate cancer cells and xenografts using flow cytometry, immunoblotting, immunohistology and MRS.

RESULTS

In vitro treatment with MK-2206 inhibited AKT signalling and resulted in time-dependent alterations in glucose, glutamine and phospholipid metabolism. In vivo, MK-2206 resulted in inhibition of AKT signalling and tumour growth compared with vehicle-treated controls. In vivo MRS analysis of HT29 subcutaneous xenografts showed similar metabolic changes to those seen in vitro including decreases in the tCho/water ratio, tumour bioenergetic metabolites and changes in glutamine and glutathione metabolism. Similar phosphocholine changes compared to in vitro were confirmed in the clinically relevant orthotopic PC3 model.

CONCLUSION

This MRS study suggests that choline metabolites detected in response to AKT inhibition are time and microenvironment-dependent, and may have potential as non-invasive biomarkers for monitoring response to AKT inhibitors in selected cancer types.

Evaluation of the combination of the dual m-TORC1/2 inhibitor vistusertib (AZD2014) and paclitaxel in ovarian cancer models

Activation of the PI3K/mTOR pathway has been shown to be correlated with resistance to chemotherapy in ovarian cancer. We aimed to investigate the effects of combining inhibition of mTORC1 and 2 using the mTOR kinase inhibitor vistusertib (AZD2014) with paclitaxel in in vitro and in vivo ovarian cancer models. The combination of vistusertib and paclitaxel on cell growth was additive in a majority of cell lines in the panel (n = 12) studied. A cisplatin- resistant model (A2780Cis) was studied in vitro and in vivo. We demonstrated inhibition of mTORC1 and mTORC2 by vistusertib and the combination by showing reduction in p-S6 and p-AKT levels, respectively. In the A2780CisR xenograft model compared to control, there was a significant reduction in tumor volumes (p = 0.03) caused by the combination and not paclitaxel or vistusertib alone. In vivo, we observed a significant increase in apoptosis (cleaved PARP measured by immunohistochemistry; p = 0.0003). Decreases in phospholipid and bioenergetic metabolites were studied using magnetic resonance spectroscopy and significant changes in phosphocholine (p = 0.01), and ATP (p = 0.04) were seen in tumors treated with the combination when compared to vehicle-control. Based on this data, a clinical trial evaluating the combination of paclitaxel and vistusertib has been initiated (NCT02193633). Interestingly, treatment of ovarian cancer patients with paclitaxel caused an increase in p-AKT levels in platelet-rich plasma and it was possible to abrogate this increase with the co-treatment with vistusertib in 4/5 patients: we believe this combination will benefit patients with ovarian cancer.

Pediatric and adult glioblastoma radiosensitization induced by PI3K/mTOR inhibition causes early metabolic alterations detected by nuclear magnetic resonance spectroscopy

Poor outcome for patients with glioblastomas is often associated with radioresistance. PI3K/mTOR pathway deregulation has been correlated with radioresistance; therefore, PI3K/mTOR inhibition could render tumors radiosensitive. In this study, we show that NVP-BEZ235, a dual PI3K/mTOR inhibitor, potentiates the effects of irradiation in both adult and pediatric glioblastoma cell lines, resulting in early metabolic changes detected by nuclear magnetic resonance (NMR) spectroscopy. NVP-BEZ235 radiosensitises cells to X ray exposure, inducing cell death through the inhibition of CDC25A and the activation of p21cip1(CDKN1A). Lactate and phosphocholine levels, increased with radiation, are decreased after NVP-BEZ235 and combination treatment, suggesting that inhibiting the PI3K/mTOR pathway reverses radiation induced metabolic changes. Importantly, NVP-BEZ235 potentiates the effects of irradiation in a xenograft model of adult glioblastoma, where we observed a decrease in lactate and phosphocholine levels after seven days of combination treatment. Although tumor size was not affected due to the short length of the treatment, a significant increase in CASP3 mRNA was observed in the combination group. Taken together, our data suggest that NMR metabolites could be used as biomarkers to detect an early response to combination therapy with PI3K/mTOR inhibitors and radiotherapy in adult and pediatric glioblastoma patients.

In vitro nuclear magnetic resonance spectroscopy metabolic biomarkers for the combination of temozolomide with PI3K inhibition in paediatric glioblastoma cells

Recent experimental data showed that the PI3K pathway contributes to resistance to temozolomide (TMZ) in paediatric glioblastoma and that this effect is reversed by combination treatment of TMZ with a PI3K inhibitor. Our aim is to assess whether this combination results in metabolic changes that are detectable by nuclear magnetic resonance (NMR) spectroscopy, potentially providing metabolic biomarkers for PI3K inhibition and TMZ combination treatment. Using two genetically distinct paediatric glioblastoma cell lines, SF188 and KNS42, in vitro 1H-NMR analysis following treatment with the dual pan-Class I PI3K/mTOR inhibitor PI-103 resulted in a decrease in lactate and phosphocholine (PC) levels (P<0.02) relative to control. In contrast, treatment with TMZ caused an increase in glycerolphosphocholine (GPC) levels (P≤0.05). Combination of PI-103 with TMZ showed metabolic effects of both agents including a decrease in the levels of lactate and PC (P<0.02) while an increase in GPC (P<0.05). We also report a decrease in the protein expression levels of HK2, LDHA and CHKA providing likely mechanisms for the depletion of lactate and PC, respectively. Our results show that our in vitro NMR-detected changes in lactate and choline metabolites may have potential as non-invasive biomarkers for monitoring response to combination of PI3K/mTOR inhibitors with TMZ during clinical trials in children with glioblastoma, subject to further in vivo validation.

Probing the PI3K/Akt/mTor pathway using 31P-NMR spectroscopy: routes to glycogen synthase kinase 3

Akt is an intracellular signalling pathway that serves as an essential link between cell surface receptors and cellular processes including proliferation, development and survival. The pathway has many downstream targets including glycogen synthase kinase3 which is a major regulatory kinase for cell cycle transit as well as controlling glycogen synthase activity. The Akt pathway is frequently up-regulated in cancer due to overexpression of receptors such as the epidermal growth factor receptor, or mutation of signalling pathway kinases resulting in inappropriate survival and proliferation. Consequently anticancer drugs have been developed that target this pathway. MDA-MB-468 breast and HCT8 colorectal cancer cells were treated with inhibitors including LY294002, MK2206, rapamycin, AZD8055 targeting key kinases in/associated with Akt pathway and the consistency of changes in ³¹P-NMR-detecatable metabolite content of tumour cells was examined. Treatment with the Akt inhibitor MK2206 reduced phosphocholine levels in MDA-MB-468 cells. Treatment with either the phosphoinositide-3-kinase inhibitor, LY294002 and pan-mTOR inhibitor, AZD8055 but not pan-Akt inhibitor MK2206 increased uridine-5′-diphosphate-hexose cell content which was suppressed by co-treatment with glycogen synthase kinase 3 inhibitor SB216763. This suggests that there is an Akt-independent link between phosphoinositol-3-kinase and glycogen synthase kinase3 and demonstrates the potential of ³¹P-NMR to probe intracellular signalling pathways.

Differentiating inflamed and normal lungs by the apparent reaction rate constants of lactate dehydrogenase probed by hyperpolarized (13)C labeled pyruvate

BACKGROUND

Clinically translatable hyperpolarized (HP) (13)C-NMR can probe in vivo enzymatic reactions, e.g., lactate dehydrogenase (LDH)-catalyzed reaction by injecting HP (13)C-pyruvate into the subject, which is converted to (13)C labeled lactate by the enzyme. Parameters such as (13)C-lactate signals and lactate-to-pyruvate signal ratio are commonly used for analyzing the HP (13)C-NMR data. However, the biochemical/biological meaning of these parameters remains either unclear or dependent on experimental settings. It is preferable to quantify the reaction rate constants with a clearer physical meaning. Here we report the extraction of the kinetic parameters of the LDH reaction from HP (13)C-NMR data and investigate if they can be potential predictors of lung inflammation.

METHODS

Male Sprague-Dawley rats (12 controls, 14 treated) were used. One dose of bleomycin (2.5 U/kg) was administered intratracheally to the treatment group. The lungs were removed, perfused, and observed by the HP-NMR technique, where a HyperSense dynamic nuclear polarization system was used to generate the HP (13)C-pyruvate for injecting into the lungs. A 20 mm (1)H/(13)C dual-tuned coil in a 9.4-T Varian vertical bore NMR spectrometer was employed to acquire the (13)C spectral data every 1 s over a time period of 300 s using a non-selective, 15-degree radiofrequency pulse. The apparent rate constants of the LDH reaction and their ratio were quantified by applying ratiometric fitting analysis to the time series data of (13)C labeled pyruvate and lactate.

RESULTS

The apparent forward rate constant kp =(3.67±3.31)×10(-4) s(-1), reverse rate constant kl =(4.95±2.90)×10(-2) s(-1), rate constant ratio kp /kl =(7.53±5.75)×10(-3) for the control lungs; kp =(11.71±4.35)×10(-4) s(-1), kl =(9.89±3.89)×10(-2) s(-1), and kp /kl =(12.39±4.18)×10(-3) for the inflamed lungs at the 7(th) day post treatment. Wilcoxon rank-sum test showed that the medians of these kinetic parameters of the 7-day cohort were significantly larger than those of the control cohort (P<0.001, P=0.001, and P=0.019, respectively). The rate constants of individual lungs correlated significantly with the histology scores of neutrophils and organizing pneumonia foci but not macrophages. Both kp and kp /kl positively correlated with lactate labeling signals. No correlation was found between kl and lactate labeling signals.

CONCLUSIONS

The results indicate bleomycin-induced lung inflammation significantly increased both the forward and reverse reaction rate constants of LDH and their ratio at day-7 after bleomycin treatment.

Interrogating two schedules of the AKT inhibitor MK-2206 in patients with advanced solid tumors incorporating novel pharmacodynamic and functional imaging biomarkers

PURPOSE

Multiple cancers harbor genetic aberrations that impact AKT signaling. MK-2206 is a potent pan-AKT inhibitor with a maximum tolerated dose (MTD) previously established at 60 mg on alternate days (QOD). Due to a long half-life (60-80 hours), a weekly (QW) MK-2206 schedule was pursued to compare intermittent QW and continuous QOD dosing.

EXPERIMENTAL DESIGN

Patients with advanced cancers were enrolled in a QW dose-escalation phase I study to investigate the safety and pharmacokinetic-pharmacodynamic profiles of tumor and platelet-rich plasma (PRP). The QOD MTD of MK-2206 was also assessed in patients with ovarian and castration-resistant prostate cancers and patients with advanced cancers undergoing multiparametric functional magnetic resonance imaging (MRI) studies, including dynamic contrast-enhanced MRI, diffusion-weighted imaging, magnetic resonance spectroscopy, and intrinsic susceptibility-weighted MRI.

RESULTS

A total of 71 patients were enrolled; 38 patients had 60 mg MK-2206 QOD, whereas 33 received MK-2206 at 90, 135, 150, 200, 250, and 300 mg QW. The QW MK-2206 MTD was established at 200 mg following dose-limiting rash at 250 and 300 mg. QW dosing appeared to be similarly tolerated to QOD, with toxicities including rash, gastrointestinal symptoms, fatigue, and hyperglycemia. Significant AKT pathway blockade was observed with both continuous QOD and intermittent QW dosing of MK-2206 in serially obtained tumor and PRP specimens. The functional imaging studies demonstrated that complex multiparametric MRI protocols may be effectively implemented in a phase I trial.

CONCLUSIONS

Treatment with MK-2206 safely results in significant AKT pathway blockade in QOD and QW schedules. The intermittent dose of 200 mg QW is currently used in phase II MK-2206 monotherapy and combination studies (NCT00670488).

Lactate and choline metabolites detected in vitro by nuclear magnetic resonance spectroscopy are potential metabolic biomarkers for PI3K inhibition in pediatric glioblastoma

The phosphoinositide 3-kinase (PI3K) pathway is believed to be of key importance in pediatric glioblastoma. Novel inhibitors of the PI3K pathway are being developed and are entering clinical trials. Our aim is to identify potential non-invasive biomarkers of PI3K signaling pathway inhibition in pediatric glioblastoma using in vitro nuclear magnetic resonance (NMR) spectroscopy, to aid identification of target inhibition and therapeutic response in early phase clinical trials of PI3K inhibitors in childhood cancer. Treatment of SF188 and KNS42 human pediatric glioblastoma cell lines with the dual pan-Class I PI3K/mTOR inhibitor PI-103, inhibited the PI3K signaling pathway and resulted in a decrease in phosphocholine (PC), total choline (tCho) and lactate levels (p<0.02) as detected by phosphorus (31P)- and proton (1H)-NMR. Similar changes were also detected using the pan-Class I PI3K inhibitor GDC-0941 which lacks significant mTOR activity and is entering Phase II clinical trials. In contrast, the DNA damaging agent temozolomide (TMZ), which is used as current frontline therapy in the treatment of glioblastoma postoperatively (in combination with radiotherapy), increased PC, glycerophosphocholine (GPC) and tCho levels (p<0.04). PI-103-induced NMR changes were associated with alterations in protein expression levels of regulatory enzymes involved in glucose and choline metabolism including GLUT1, HK2, LDHA and CHKA. Our results show that by using NMR we can detect distinct biomarkers following PI3K pathway inhibition compared to treatment with the DNA-damaging anti-cancer agent TMZ. This is the first study reporting that lactate and choline metabolites are potential non-invasive biomarkers for monitoring response to PI3K pathway inhibitors in pediatric glioblastoma.

Integrating genomics and proteomics data to predict drug effects using binary linear programming

The Library of Integrated Network-Based Cellular Signatures (LINCS) project aims to create a network-based understanding of biology by cataloging changes in gene expression and signal transduction that occur when cells are exposed to a variety of perturbations. It is helpful for understanding cell pathways and facilitating drug discovery. Here, we developed a novel approach to infer cell-specific pathways and identify a compound's effects using gene expression and phosphoproteomics data under treatments with different compounds. Gene expression data were employed to infer potential targets of compounds and create a generic pathway map. Binary linear programming (BLP) was then developed to optimize the generic pathway topology based on the mid-stage signaling response of phosphorylation. To demonstrate effectiveness of this approach, we built a generic pathway map for the MCF7 breast cancer cell line and inferred the cell-specific pathways by BLP. The first group of 11 compounds was utilized to optimize the generic pathways, and then 4 compounds were used to identify effects based on the inferred cell-specific pathways. Cross-validation indicated that the cell-specific pathways reliably predicted a compound's effects. Finally, we applied BLP to re-optimize the cell-specific pathways to predict the effects of 4 compounds (trichostatin A, MS-275, staurosporine, and digoxigenin) according to compound-induced topological alterations. Trichostatin A and MS-275 (both HDAC inhibitors) inhibited the downstream pathway of HDAC1 and caused cell growth arrest via activation of p53 and p21; the effects of digoxigenin were totally opposite. Staurosporine blocked the cell cycle via p53 and p21, but also promoted cell growth via activated HDAC1 and its downstream pathway. Our approach was also applied to the PC3 prostate cancer cell line, and the cross-validation analysis showed very good accuracy in predicting effects of 4 compounds. In summary, our computational model can be used to elucidate potential mechanisms of a compound's efficacy.

Silencing of the glycerophosphocholine phosphodiesterase GDPD5 alters the phospholipid metabolite profile in a breast cancer model in vivo as monitored by (31) P MRS

Abnormal choline phospholipid metabolism is an emerging hallmark of cancer, which is implicated in carcinogenesis and tumor progression. The malignant metabolic phenotype is characterized by high levels of phosphocholine (PC) and relatively low levels of glycerophosphocholine (GPC) in aggressive breast cancer cells. Phosphorus ((31) P) MRS is able to non-invasively detect these water-soluble metabolites of choline as well as ethanolamine phospholipid metabolism. Here we have investigated the effects of stably silencing glycerophosphoester diesterase domain containing 5 (GDPD5), which is an enzyme with glycerophosphocholine phosphodiesterase activity, in MDA-MB-231 breast cancer cells and orthotopic tumor xenografts. Tumors in which GDPD5 was stably silenced with GDPD5-specific shRNA contained increased levels of GPC and phosphoethanolamine (PE) compared with control tumors.

MR-detectable metabolic consequences of mitogen-activated protein kinase kinase (MEK) inhibition

Metabolic reprogramming is increasingly being viewed as a hallmark of cancer. Accordingly, metabolic readouts can serve as biomarkers of response to therapy. The goal of this study was to investigate some of the MRS-detectable metabolic consequences of mitogen-activated protein kinase kinase (MEK) inhibition. We investigated PC3 prostate cancer, MCF-7 breast cancer and A375 melanoma cells, and determined that, consistent with previous studies, MRS-detectable levels of phosphocholine decreased significantly in all cell lines (to 63%, 50% and 18% of the control, respectively) following MEK inhibition with U0126. This effect was mediated by a decrease in the expression of choline kinase α, the enzyme that catalyzes the phosphorylation of choline. In contrast, the impact of MEK inhibition on glycolysis was cell line dependent. A375 cells, which express mutant BRAF, demonstrated significant decreases in glucose uptake (to 36% of control) and lactate production (to 42% of control) in line with positron emission tomography data. In contrast, in PC3 and MCF-7 cells, increases in glucose uptake (to 198% and 192% of control, respectively) and lactate production (to 177% and 212% of control, respectively) were observed, in line with a previous hyperpolarized (13) C MRS study. This effect is probably mediated by the activation of the phosphoinositide 3-kinase pathway and AMP-activated protein kinase. Our findings demonstrate the value of translatable non-invasive MRS methods for the provision of information on cellular metabolism as an indication of the activation of potential feedback loops following MEK inhibition.

Nuclear envelope invaginations and cancer

The nuclear envelope (NE) surrounds the nucleus and separates it from the cytoplasm. The NE is not a passive structural component, but rather contributes to various cellular processes such as genome organization, transcription, signaling, and stress responses. Although the NE is mostly a smooth surface, it also forms invaginations that can reach deep into the nucleoplasm and may even traverse the nucleus completely. Cancer cells are generally characterized by irregularities and invaginations of the NE that are of diagnostic and prognostic significance. In the current chapter, we describe the link between nuclear invaginations and irregularities with cancer and explore possible mechanistic roles they might have in tumorigenesis.

MEK1/2 inhibition decreases lactate in BRAF-driven human cancer cells

The RAS/BRAF/MEK/ERK signaling pathway is a central driver in cancer with many BRAF and MEK inhibitors being evaluated in clinical trials. Identifying noninvasive biomarkers of early pharmacodynamic responses is important for development of these targeted drugs. As increased aerobic glycolysis is often observed in cancer, we hypothesized that MEK1/2 (MAP2K1/MAP2K2) inhibitors may reduce lactate levels as detected by magnetic resonance spectroscopy (MRS), as a metabolic biomarker for the pharmacodynamic response. MRS was used to monitor intracellular and extracellular levels of lactate in human cancer cells in vitro and in melanoma tumors ex vivo. In addition, we used (1)H MRS and a fluorescent glucose analog to evaluate the effect of MEK inhibition on glucose uptake. MEK1/2 signaling inhibition reduced extracellular lactate levels in BRAF-dependent cells but not BRAF-independent cells. The reduction in extracellular lactate in BRAF-driven melanoma cells was time-dependent and associated with reduced expression of hexokinase-II driven by c-Myc depletion. Taken together, these results reveal how MEK1/2 inhibition affects cancer cell metabolism in the context of BRAF oncogene addiction. Furthermore, they offer a preclinical proof-of-concept for the use of MRS to measure lactate as a noninvasive metabolic biomarker for pharmacodynamic response to MEK1/2 inhibition in BRAF-driven cancers.

Treatment with the MEK inhibitor U0126 induces decreased hyperpolarized pyruvate to lactate conversion in breast, but not prostate, cancer cells

Alterations in cell metabolism are increasingly being recognized as a hallmark of cancer and are being exploited for the development of diagnostic tools and targeted therapeutics. Recently, ¹³C MRS-detectable hyperpolarized pyruvate to lactate conversion has been validated in models as a noninvasive imaging method for the detection of tumors and treatment response, and has successfully passed phase I clinical trials. To date, response to treatment has been associated with a decrease in hyperpolarized lactate production. In this study, we monitored the effect of treatment with the mitogen-activated protein kinase (MEK) inhibitor U0126 in prostate and breast cancer cells. Following treatment, we observed a 31% decrease in the flux of hyperpolarized ¹³C label in treated MCF-7 breast cancer cells relative to controls. In contrast, and unexpectedly, the flux increased to 167% in treated PC3 prostate cancer cells. To mechanistically explain these observations, we investigated treatment-induced changes in the different factors known to affect the pyruvate to lactate conversion. NADH (nicotinamide adenine dinucleotide, reduced form) levels remained unchanged, whereas lactate dehydrogenase expression and activity, as well as intracellular lactate, increased in both cell lines, providing an explanation for the elevated hyperpolarized lactate observed in PC3 cells. The expression of MCT1, which mediates pyruvate transport, decreased in treated MCF-7, but not PC3, cells. This identifies pyruvate transport as rate limiting in U0126-treated MCF-7 cells and explains the decrease in hyperpolarized lactate observed in these cells following treatment. Our findings highlight the complexity of interactions between MEK and metabolism, and the need for mechanistic validation before hyperpolarized ¹³C MRS can be used to monitor treatment-induced molecular responses.