Role of microtubules in glucose uptake by C6 glioma cells

Metabolic adaptation towards glycolysis supports resistance to neoadjuvant chemotherapy in early triple negative breast cancers

BACKGROUND

Neoadjuvant chemotherapy (NAC) is the standard of care for patients with early-stage triple negative breast cancers (TNBC). However, more than half of TNBC patients do not achieve a pathological complete response (pCR) after NAC, and residual cancer burden (RCB) is associated with dismal long-term prognosis. Understanding the mechanisms underlying differential treatment outcomes is therefore critical to limit RCB and improve NAC efficiency.

METHODS

Human TNBC cell lines and patient-derived organoids were used in combination with real-time metabolic assays to evaluate the effect of NAC (paclitaxel and epirubicin) on tumor cell metabolism, in particular glycolysis. Diagnostic biopsies (pre-NAC) from patients with early TNBC were analyzed by bulk RNA-sequencing to evaluate the predictive value of a glycolysis-related gene signature.

RESULTS

Paclitaxel induced a consistent metabolic switch to glycolysis, correlated with a reduced mitochondrial oxidative metabolism, in TNBC cells. In pre-NAC diagnostic biopsies from TNBC patients, glycolysis was found to be upregulated in non-responders. Furthermore, glycolysis inhibition greatly improved response to NAC in TNBC organoid models.

CONCLUSIONS

Our study pinpoints a metabolic adaptation to glycolysis as a mechanism driving resistance to NAC in TNBC. Our data pave the way for the use of glycolysis-related genes as predictive biomarkers for NAC response, as well as the development of inhibitors to overcome this glycolysis-driven resistance to NAC in human TNBC patients.

Identification of Candidate Biomarker and Drug Targets for Improving Endometrial Cancer Racial Disparities

Racial disparities in incidence and survival exist for many human cancers. Racial disparities are undoubtedly multifactorial and due in part to differences in socioeconomic factors, access to care, and comorbidities. Within the U.S., fundamental causes of health inequalities, including socio-economic factors, insurance status, access to healthcare and screening and treatment biases, are issues that contribute to cancer disparities. Yet even these epidemiologic differences do not fully account for survival disparities, as for nearly every stage, grade and histologic subtype, survival among Black women is significantly lower than their White counterparts. To address this, we sought to investigate the proteomic profiling molecular features of endometrial cancer in order to detect modifiable and targetable elements of endometrial cancer in different racial groups, which could be essential for treatment planning. The majority of proteins identified to be significantly altered among the racial groups and that can be regulated by existing drugs or investigational agents are enzymes that regulate metabolism and protein synthesis. These drugs have the potential to improve the worse outcomes of endometrial cancer patients based on race.

Plant-derived glucose transport inhibitors with potential antitumor activity

Glucose, a key nutrient utilized by human cells to provide cellular energy and a carbon source for biomass synthesis, is internalized in cells via glucose transporters that regulate glucose homeostasis throughout the human body. Glucose transporters have been used as important targets for the discovery of new drugs to treat cancer, diabetes, and heart disease, owing to their abnormal expression during these disease conditions. Thus far, several glucose transport inhibitors have been used in clinical trials, and increasing numbers of natural products have been characterized as potential anticancer agents targeting glucose transport. The present review focuses on natural product glucose transport inhibitors of plant origin, including alkaloids, flavonoids and other phenolic compounds, and isoprenoids, with their potential antitumor properties also discussed.

Cell line studies and analytical measurements of three paclitaxel complex variations

The copper(II) cation, sucrose, and hydroxychloroquine were complexed with the chemotherapy agent paclitaxel and studied for medicinal activity. Data (GI₅₀, LD₅₀) from single dose and five dose National Cancer Institute sixty cell line panels are presented. Analytical measurements of different complexes were made using Nuclear Magnetic Resonance (¹H NMR), Matrix Assisted Laser Desorption Ionization-Time of Flight-Mass Spectrometry (MALDI-TOF-MS) and Fourier Transform-Ion Cyclotron Resonance (FT-ICR). Molecular modeling is utilized to better understand the impact that species could have on physical parameters associated with Lipinski's Rule of Five, such as logP and TPSA. On average, Cu(II) and hydroxychloroquine decreased GI₅₀ values, while sucrose increased GI₅₀ values of paclitaxel.

Quantitative correlation at the molecular level of tumor response to docetaxel by multimodal diffusion-weighted magnetic resonance imaging and [¹⁸F]FDG/[¹⁸F]FLT positron emission tomography

We aimed to quantitatively characterize the treatment effects of docetaxel in the HCT116 xenograft mouse model, applying diffusion-weighted magnetic resonance imaging (MRI) and positron emission tomography (PET) using 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) and 3'-deoxy-3'-[¹⁸F]-fluorothymidine ([¹⁸F]FLT). Mice were imaged at four time points over 8 days. Docetaxel (15 mg/kg) was administered after a baseline scan. Voxel-wise scatterplots of PET and apparent diffusion coefficient (ADC) data of tumor volumes were evaluated with a threshold cluster analysis and compared to histology (GLUT1, GLUT3, Ki67, activated caspase 3a). Compared to the extensive tumor growth observed in the vehicle-treated group (from 0.32 ± 0.21 cm³ to 0.69 ± 0.40 cm³), the administration of docetaxel led to tumor growth stasis (from 0.32 ± 0.20 cm³ to 0.45 ± 0.23 cm³). The [¹⁸F]FDG/ADC cluster analysis and the evaluation of peak histogram values revealed a significant treatment effect matching histology as opposed to [¹⁸F]FLT/ADC. [¹⁸F]FLT uptake and the Ki67 index were not in good agreement. Our voxel-based cluster analysis uncovered treatment effects not seen in the separate inspection of PET and MRI data and may be used as an independent analysis tool. [¹⁸F]FLT/ADC cluster analysis could still point out the treatment effect; however, [¹⁸F]FDG/ADC reflected the histology findings in higher agreement.

Clinical pathological characteristics of breast cancer patients with secondary diabetes after systemic therapy: a retrospective multicenter study

The objective of this study was to investigate the clinical pathological characteristics of breast cancer (BC) patients with secondary diabetes after systemic therapy without preexisting diabetes. A total of 1434 BC patients received systemic therapy and were analyzed retrospectively. Fasting plasma glucose (FPG) levels were monitored prior to the treatments, during the course of systemic therapy, and at the follow-up visits. Cox regression models were used to estimate the associations between the clinical pathological characteristics of BC and the cause-specific hazard of developing secondary diabetes. Among the 1434 BC patients, 151 had preexisting type 2 diabetes. Of the remaining 1283 patients with normal FPG levels prior to the systemic therapy, 59 developed secondary diabetes and 72 displayed secondary impaired fasting glucose (IFG) over a mean follow-up of 41 months. The prevalence of secondary type 2 diabetes in BC patients was 4.6 % (59/1283), which was obviously higher than that of the normal control group (1.4 %, P < 0.001). The percentage of older patients (P < 0.05), menopausal patients (P < 0.001), and obese patients (P < 0.01) tended to be lower in the secondary diabetic group. In addition, these patients with secondary diabetes had later pathological stages (P < 0.01), more lymph node metastasis (P < 0.05), negative estrogen receptor (ER) expression (P < 0.05), and smaller size of tumors (P < 0.05). After adjusting for age and BMI, the risk of developing secondary diabetes and IFG in subjects with later pathological stage BC (hazard ratio (HR) = 1.623; 95 % confidence interval (CI) 1.128–2.335 (P < 0.01)), negative progesterone receptor (PR) expression (HR = 0.530; 95 % CI 0.372–0.755 (P < 0.001)), positive human epidermal growth factor receptor 2 (HER2) expression (HR = 1.822; 95 % CI 1.230–2.700 (P < 0.01)), and more lymph node metastasis (HR = 1.595; 95 % CI 1.128–2.258 (P < 0.01)) was significantly higher. In conclusion, this study shows that an increase in the incidence of diabetes among breast cancer survivors after systemic therapy, especially the patients with later pathological stages, more lymph node metastasis, negative hormone receptor expression, and positive HER2 expression. Our study suggests that greater diabetes screening and prevention strategies among breast cancer patients after systemic treatment are needed in China.

A phase I dose-escalation trial of 2-deoxy-D-glucose alone or combined with docetaxel in patients with advanced solid tumors

PURPOSE

This phase I trial was initiated to evaluate the safety, pharmacokinetics (PK) and maximum tolerated dose (MTD) of the glycolytic inhibitor, 2-deoxy-D-glucose (2DG) in combination with docetaxel, in patients with advanced solid tumors.

METHODS

A modified accelerated titration design was used. 2DG was administered orally once daily for 7 days every other week starting at a dose of 2 mg/kg and docetaxel was administered intravenously at 30 mg/m(2) for 3 of every 4 weeks beginning on day 1 of week 2. Following the completion of dose escalation, cohorts of patients were then treated with 2DG for 21 days or every day of each 4-week cycle for up to 12 cycles.

RESULTS

Thirty-four patients were enrolled: 21 on every other week, 6 on a 21 of 28-day cycle and 7 on the continuous 2DG dosing schedule. There were no dose-limiting toxicities which met the MTD criteria. The most common adverse events were fatigue, sweating, dizziness and nausea mimicking the hypoglycemic symptoms expected from 2DG administration. Therefore, 63 mg/kg was selected as the clinically tolerable dose. The most significant adverse effects noted at 63-88 mg/kg doses were reversible hyperglycemia (100 %), gastrointestinal bleeding (6 %) and reversible grade 3 QTc prolongation (22 %). Eleven patients (32 %) had stable disease, 1 patient (3 %) partial response and 22 patients (66 %) progressive disease as their best response. There was no PK interaction between 2DG and docetaxel.

CONCLUSION

The recommended dose of 2DG in combination with weekly docetaxel is 63 mg/kg/day with tolerable adverse effects.

Syntaxin 1C, a soluble form of syntaxin, attenuates membrane recycling by destabilizing microtubules

Syntaxin 1C (STX1C), produced by alternative splicing of the stx1A gene, is a soluble syntaxin lacking a SNARE domain and a transmembrane domain. It is unclear how soluble syntaxin can control intracellular membrane trafficking. We found that STX1C affected microtubule (MT) dynamics through its tubulin-binding domain (TBD) and regulated recycling of intracellular vesicles carrying glucose transporter-1 (GLUT1). We demonstrated that the amino acid sequence VRSK of the TBD was important for the interaction between STX1C and tubulin and that wild-type STX1C (STX1C-WT), but not the TBD mutant, reduced the V(max) of glucose transport and GLUT1 translocation to the plasma membrane in FRSK cells. Moreover, by time-lapse analysis, we revealed that STX1C-WT suppressed MT stability and vesicle-transport motility in cells expressing GFP-α-tubulin, whereas TBD mutants had no effect. We also identified that GLUT1 was recycled in the 45 minutes after endocytosis and that GLUT1 vesicles moved along with MTs. Finally, we showed, by a recycling assay and FCM analysis, that STX1C-WT delayed the recycling phase of GLUT1 to PM, without affecting the endocytotic process of GLUT1. These data indicate that STX1C delays the GLUT1 recycling phase by suppressing MT stability and vesicle-transport motility through its TBD, providing the first insight into how soluble syntaxin controls membrane trafficking.

Paclitaxel combined with inhibitors of glucose and hydroperoxide metabolism enhances breast cancer cell killing via H2O2-mediated oxidative stress

Cancer cells (relative to normal cells) demonstrate alterations in oxidative metabolism characterized by increased steady-state levels of reactive oxygen species (i.e., hydrogen peroxide, H(2)O(2)) that may be compensated for by increased glucose metabolism, but the therapeutic significance of these observations is unknown. In this study, inhibitors of glucose (i.e., 2-deoxy-d-glucose, 2DG) and hydroperoxide (i.e., l-buthionine-S,R-sulfoximine, BSO) metabolism were utilized in combination with a chemotherapeutic agent, paclitaxel (PTX), thought to induce oxidative stress, to treat breast cancer cells. 2DG + PTX was more toxic than either agent alone in T47D and MDA-MB231 human breast cancer cells, but not in normal human fibroblasts or normal human mammary epithelial cells. Increases in parameters indicative of oxidative stress, including steady-state levels of H(2)O(2), total glutathione, and glutathione disulfide, accompanied the enhanced toxicity of 2DG + PTX in cancer cells. Antioxidants, including N-acetylcysteine and polyethylene glycol-conjugated catalase and superoxide dismutase, inhibited the toxicity of 2DG + PTX and suppressed parameters indicative of oxidative stress in cancer cells, whereas inhibition of glutathione synthesis using BSO further sensitized breast cancer cells to 2DG + PTX. These results show that combining inhibitors of glucose (2DG) and hydroperoxide (BSO) metabolism with PTX selectively (relative to normal cells) enhances breast cancer cell killing via H(2)O(2)-induced metabolic oxidative stress, and suggest that this biochemical rationale may be effectively utilized to treat breast cancers.

Activation of syntaxin 1C, an alternative splice variant of HPC-1/syntaxin 1A, by phorbol 12-myristate 13-acetate (PMA) suppresses glucose transport into astroglioma cells via the glucose transporter-1 (GLUT-1)

Syntaxin 1C is an alternative splice variant lacking the transmembrane domain of HPC-1/syntaxin 1A. We found previously that syntaxin 1C is expressed as a soluble protein in human astroglioma (T98G) cells, and syntaxin 1C expression is enhanced by stimulation with phorbol 12-myristate 13-acetate (PMA). However, the physiological function of syntaxin 1C is not known. In this study, we examined the relationship between syntaxin 1C and glucose transport. First, we discovered that glucose transporter-1 (GLUT-1) was the primary isoform in T98G cells. Second, we demonstrated that glucose uptake in T98G cells was suppressed following an increase in endogenous syntaxin 1C after stimulation with PMA, which did not alter the expression levels of other plasma membrane syntaxins. We further examined glucose uptake and intracellular localization of GLUT-1 in cells that overexpressed exogenous syntaxin 1C; glucose uptake via GLUT-1 was inhibited without affecting sodium-dependent glucose transport. The value of Vmax for the dose-dependent uptake of glucose was reduced in syntaxin 1C-expressing cells, whereas there was no change in Km. Immunofluorescence studies revealed a reduction in the amount of GLUT-1 in the plasma membrane in cells that expressed syntaxin 1C. Based on these results, we postulate that syntaxin 1C regulates glucose transport in astroglioma cells by changing the intracellular trafficking of GLUT-1. This is the first report to indicate that a syntaxin isoform that lacks a transmembrane domain can regulate the intracellular transport of a plasma membrane protein.

Hypertonic activation of the renal betaine/GABA transporter is microtubule dependent

BACKGROUND

Epithelial cells in the renal inner medulla accumulate osmolytes such as betaine to maintain normal cell volume during prolonged extracellular hypertonic stress. Betaine accumulation is the result of activation of transcription of the BGT1 transporter gene followed by increased betaine transport.

METHODS

We studied the possible role of microtubules in this adaptive mechanism using renal cells in culture. RESULTS.: In cultured renal cell lines [Madin-Darby canine kidney (MDCK) and mouse inner medullary collecting duct (mIMCD-3)], up-regulation of BGT1 activity was maximal after 24 to 30 hours in growth medium made hypertonic (510 mOsm/kg) by the addition of sucrose or NaCl. Up-regulation was reversed within 24 to 36 hours after returning cells to isotonic medium. Both cycloheximide (20 micromol/L) and nocodazole (20 micromol/L) blocked the hypertonic up-regulation of BGT1. Nocodazole was partially effective even when added 16 to 20 hours after the switch to hypertonic medium. Recovery from nocodazole action was rapid, and there was full activation of BGT1 transport within three to six hours after nocodazole removal, suggesting rapid trafficking to the cell surface once microtubules repolymerized. Hypertonic activation of BGT1 transport was detected in an isolated membrane fraction and was blocked by cycloheximide but not by nocodazole. Confocal microscopy confirmed the increased abundance of BGT1 proteins in the plasma membrane of hypertonic cells and showed that BGT1 remained intracellular during nocodazole treatment.

CONCLUSIONS

Hypertonic activation of BGT1 in renal cells requires de novo protein synthesis and microtubule-dependent trafficking of additional transporters to the cell surface. The apparent resistance of membrane BGT1 to nocodazole blockade is likely due to the presence in the membrane fraction of an increased intracellular pool of active BGT1 transporters.

The bleb formation of the extracellular pseudopodia; early evidence of microtubule depolymerization by estramustine phosphate in glioma cell; in vitro study

Estramustine phosphate (EMP) is an anti-microtubule agent that depolymerizes microtubules and also causes apoptosis of glioma cells. Both of these pharmacological actions have been previously studied within the same cytotoxic range of EMP concentrations. The purpose of this study was to investigate which of these two phenomena occurred before the other. A preliminary MTT assay was done to distinguish non-cytotoxic (0.005-0.1 microM) and cytotoxic (0.5-10 microM) of EMP for BT4C cells. To investigate apoptotic changes, transmission electron microscopy (TEM), DNA laddering, and in situ endo-labeling (TUNEL) method were employed. A chemotaxis assay was used to assess cell motility. Scanning electron microscopy and TEM immunocytochemistry with an anti-beta tubulin antibody were applied to detect morphological changes of the microtubules. Suppression of cell motility by cytotoxic doses of EMP (0.5-10 microM) group was attributed by the cyto-reductive effect, relating to apoptosis. At 0.01-0.1 microM (non-cytotoxic doses), EMP did not indue apoptosis. At these concentrations, TEM and immunohistochemistry revealed the formation of blebs on the tip of the pseudopodia that contained abnormally depolymerized microtubules, a finding that was not observed at a low temperature or during cell migration. Cell chemotaxis was significantly inhibited by cytostatic EMP doses (0.05 and 0.1 microM). Bleb formation of the pseudopodia might be evidence of the abnormal disassembly of microtubules by cytostatic EMP concentrations, prior to the induction of apoptosis. In glioma cells EMP probably initiates apoptosis by causing the depolymerization of microtubules. Inhibition of cell motility by cytostatic doses of EMP could be beneficial to support other therapies.

Role of microtubules in the regulation of metabolism in isolated cerebral microvessels

We used (13)C-labeled substrates and nuclear magnetic resonance spectroscopy to examine carbohydrate metabolism in vascular smooth muscle of freshly isolated pig cerebral microvessels (PCMV). PCMV utilized [2-(13)C]glucose mainly for glycolysis, producing [2-(13)C]lactate. Simultaneously, PCMV utilized the glycolytic intermediate [1-(13)C]fructose 1,6-bisphosphate (FBP) mainly for gluconeogenesis, producing [1-(13)C]glucose with only minor [3-(13)C]lactate production. The dissimilarity in metabolism of [2-(13)C]FBP derived from [2-(13)C]glucose breakdown and metabolism of exogenous [1-(13)C]FBP demonstrates that carbohydrate metabolism is compartmented in PCMV. Because glycolytic enzymes interact with microtubules, we disrupted microtubules with vinblastine. Vinblastine treatment significantly decreased [2-(13)C]lactate peak intensity (87.8 +/- 3.7% of control). The microtubule-stabilizing agent taxol also reduced [2-(13)C]lactate peak intensity (90.0 +/- 2. 4% of control). Treatment with both agents further decreased [2-(13)C]lactate production (73.3 +/- 4.0% of control). Neither vinblastine, taxol, or the combined drugs affected [1-(13)C]glucose peak intensity (gluconeogenesis) or disrupted the compartmentation of carbohydrate metabolism. The similar effects of taxol and vinblastine, drugs that have opposite effects on microtubule assembly, suggest that they produce their effects on glycolytic rate by competing with glycolytic enzymes for binding, not by affecting the overall assembly state of the microtubule network. Glycolysis, but not gluconeogenesis, may be regulated in part by glycolytic enzyme-microtubule interactions.