Complex N-glycan and metabolic control in tumor cells

Golgi beta1,6N-acetylglucosaminyltransferase V (Mgat5) produces beta1,6GlcNAc-branched complex N-glycans on cell surface glycoproteins that bind to galectins and promote surface residency of glycoproteins, including cytokine receptors. Carcinoma cells from polyomavirus middle T (PyMT) transgenic mice on a Mgat5-/- background have reduced surface levels of epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) receptors and are less sensitive to acute stimulation by cytokines in vitro compared with PyMT Mgat5+/+ tumor cells but are nonetheless tumorigenic when injected into mice. Here, we report that PyMT Mgat5-/- cells are reduced in size, checkpoint impaired, and following serum withdrawal, fail to down-regulate glucose transport, protein synthesis, reactive oxygen species (ROS), and activation of Akt and extracellular signal-regulated kinase. To further characterize Mgat5+/+ and Mgat5-/- tumor cells, a screen of pharmacologically active compounds was done. Mgat5-/- tumor cells were comparatively hypersensitive to the ROS inducer 2,3-dimethoxy-1,4-naphthoquinone, hyposensitive to tyrosine kinase inhibitors, to Golgi disruption by brefeldin A, and to mitotic arrest by colcemid, hydroxyurea, and camptothecin. Finally, regulation of ROS, glucose uptake, and sensitivities to EGF and TGF-beta were rescued by Mgat5 expression or by hexosamine supplementation to complex N-glycan biosynthesis in Mgat5-/- cells. Our results suggest that complex N-glycans sensitize tumor cells to growth factors, and Mgat5 is required to balance responsiveness to growth and arrest cues downstream of metabolic flux.     

Targeting cisplatin-resistant human tumor cells with metabolic inhibitors

Purpose

Although cisplatin is the drug of choice in treating lung cancer patients, relapse and resistance is a common drawback to its clinical effectiveness. Based on cisplatin’s reported ability to interfere with numerous cellular components, including mitochondria, we probed alterations in metabolism in cisplatin-resistant tumor cell lines to reveal targets for overcoming this important form of resistance.

Methods

Cisplatin-resistant lung and ovarian cancer cell lines were used to evaluate the efficacy of metabolic inhibitors for selectively targeting cisplatin-resistant cells under varying oxygen conditions.

Results

Three cisplatin-resistant cancer cell lines expressed lower HKII protein when compared to the respective cisplatin-sensitive cancer cell lines from which they were derived. Under anaerobic and hypoxic conditions, treatment with the glycolytic inhibitors 2-deoxyglucose (2-DG) and 2-fluorodeoxyglucose (2-FDG) correlated with increased cytotoxicity and more pronounced decreases in lactate production in cisplatin-resistant cells, indicating a greater blockage of glycolysis. Knockdown of HKI or HKII with siRNA in the parental lung cancer cell lines led to increased 2-FDG-induced cell death under anaerobic conditions. Under normal oxygen conditions, blockage of either fatty acid oxidation or deprivation of glutamine resulted in cell death in cisplatin-resistant lung cancer cell lines.

Conclusions

Altered hexokinase levels in cisplatin-resistant cancer cell lines leads to increased sensitivity to glycolytic inhibition under anaerobic conditions, whereas under normoxic conditions, blockage of either fatty acid oxidation or deprivation of glutamine leads to cell death. These findings may be clinically applicable when considering cisplatin resistance.     

Effects of tumor metabolic microenvironment on regulatory T cells

Recent studies have shown that on one hand, tumors need to obtain a sufficient energy supply, and on the other hand they must evade the body’s immune surveillance. Because of their metabolic reprogramming characteristics, tumors can modify the physicochemical properties of the microenvironment, which in turn affects the biological characteristics of the cells infiltrating them. Regulatory T cells (Tregs) are a subset of T cells that regulate immune responses in the body. They exist in large quantities in the tumor microenvironment and exert immunosuppressive effects. The main effect of tumor microenvironment on Tregs is to promote their differentiation, proliferation, secretion of immunosuppressive factors, and chemotactic recruitment to play a role in immunosuppression in tumor tissues. This review focuses on cell metabolism reprogramming and the most significant features of the tumor microenvironment relative to the functional effects on Tregs, highlighting our understanding of the mechanisms of tumor immune evasion and providing new directions for tumor immunotherapy.     

代谢重编程介导肿瘤微环境免疫抑制的研究评述

近十年免疫疗法在肿瘤的治疗中取得了突破性进展,导致肿瘤治疗的范式转变。然而大多数患者并不能从中获益,如何提高患者免疫治疗的应答率是亟待解决的热点问题。免疫疗法的成功有赖于机体免疫效应细胞的活化及杀伤效应。然而,在肿瘤微环境严苛的代谢和营养应激下,免疫细胞的功能常处于紊乱状态,导致抗肿瘤免疫应答受损。因此,通过靶向肿瘤代谢重塑免疫微环境,恢复抗肿瘤免疫应答,有望在与免疫疗法的联合应用中取得协同效应。本文着重探讨代谢重编程及其代谢产物如何调节抗肿瘤免疫应答,旨在为肿瘤免疫治疗提供新的思路和方法。     

代谢重编程介导肿瘤微环境免疫抑制的研究评述

近十年免疫疗法在肿瘤的治疗中取得了突破性进展,导致肿瘤治疗的范式转变。然而大多数患者并不能从中获益,如何提高患者免疫治疗的应答率是亟待解决的热点问题。免疫疗法的成功有赖于机体免疫效应细胞的活化及杀伤效应。然而,在肿瘤微环境严苛的代谢和营养应激下,免疫细胞的功能常处于紊乱状态,导致抗肿瘤免疫应答受损。因此,通过靶向肿瘤代谢重塑免疫微环境,恢复抗肿瘤免疫应答,有望在与免疫疗法的联合应用中取得协同效应。本文着重探讨代谢重编程及其代谢产物如何调节抗肿瘤免疫应答,旨在为肿瘤免疫治疗提供新的思路和方法。     

Role of mesenchymal stem cells in osteosarcoma and metabolic reprogramming of tumor cells

The tumor microenvironment plays an important role in cancer progression. Here, we focused on the role of reactive mesenchymal stem cells (MSC) in osteosarcoma (OS), and used human adipose MSC and a panel of OS cell lines (Saos-2, HOS, and 143B) to investigate the mutual effect of normal-cancer cell metabolic programming. Our results showed that MSC are driven by oxidative stress induced by OS cells to undergo Warburg metabolism, with increased lactate production. Therefore, we analyzed the expression of lactate monocarboxylate transporters. By real time PCR and immunofluorescence, in MSC we detected the expression of MCT-4, the transporter for lactate efflux, whereas MCT-1, responsible for lactate uptake, was expressed in OS cells. In agreement, silencing of MCT-1 by siRNA significantly affected the ATP production in OS cancer cells. Thus, cancer cells directly increase their mitochondrial biogenesis using this energy-rich metabolite that is abundantly provided by MSC as an effect of the altered microenvironmental conditions induced by OS cells. We also showed that lactate produced by MSC promotes the migratory ability of OS cells. These data provide novel information to be exploited for cancer therapies targeting the mutual metabolic reprogramming of cancer cells and their stroma.     

The metabolic interactions between tumor cells and tumor-associated stroma (TAS) in prostatic cancer

Tumor-associated stroma (TAS) is not simply a supporting element for cancer cells, but plays an important role in tumor growth, invasion and metastasis. Changes on the level of stromal constituents, such as loss of Caveolin-1 and increased thymidine phosphorylase (TP) expression, have been associated with tumor aggressiveness. The mutual cooperation between stromal fibroblasts and cancer cells is another distinguishing feature, which has recently emerged. In this investigation, both the loss of Caveolin-1 and the increased TP expression in the prostatic TAS was associated with high Gleason score (p = 0.0002 and 0.003, respectively); the two proteins were acting both independently and synergistically. In addition, TP was significantly associated with high stromal Ki-67 (MIB1) proliferation index (p = 0.03). Analysis of the metabolic interactions between stromal and epithelial elements showed that, while prostatic cancer cells express principally (> 91%) lactate dehydrogenase-5 (LDH-5) (anaerobic metabolism), the tumor-associated fibroblasts/myofibroblasts (TAFs) express largely (67.8%) LDH-1 (aerobic metabolism)—the terms TAFs and TAS are used interchangeably. These two isoenzyme pathways act complementary; the LDH-5 pathway converts pyruvate to lactate, whereas the LDH-1 enzyme system utilizes the secreted metabolite lactate to produce pyruvate, essential for continuous energy supply to tumor cells. Monocarboxylate transporter-1 (MCT-1)—the main facilitator of lactate uptake in tumor cells, was expressed exclusively in prostate cancer cells and related directly to LDH-5 overexpression. These findings support and extend our previous studies on energy recycling between the aerobic stroma and the anaerobic cancer cells within the framework of Warburg effect.     

PET-CT在恶性肿瘤治疗后评价中的作用与局限性

PET-CT即正电子发射断层与计算机断层显像,它将PET的功能代谢显像和CT的解剖显像融合在一起,明显提高了单独使用PET或CT诊断疾病的准确性。PET-CT在恶性肿瘤治疗早期可以评估治疗疗效,对下一步临床处理有指导意义;治疗结束后,作为一种随访方法,可用于早期检测肿瘤的复发及转移。但是,PET-CT评价指标众多,目前尚无一个公认的标准,致使其在临床运用中结果不一致。另外,有许多因素能引起PET-CT诊断的假阳性与假阴性限制了PET-CT的临床运用。本文就PET-CT在恶性肿瘤治疗后评价中的作用与局限性做一综述。     

Analysis of some metabolic conditions promoting selective sensitivity of tumor cells to peroxidative stress

Some metabolic parameters enhancing the sensitivity of tumor ceils and their iipoprotein refractive granules (RG) to peroxidative stress were investigated during the growth cycle of ascite tumorsin vivo. The majority of tumor cells only in the stationary growth phase had the increased sensitivity to peroxidative stress, tested by fluorescence intensivity of peroxidation products. The increase of this intensity correlates well with the decrease of tumor proliferation, the functional activity of mitochondria, the cellular level of ATP and extracellular pH. These metabolic conditions are favourable for increasing the neutral lipid accumulation in the stationary tumor cells, their RG and nuclei, as compared to exponentially growing cells. The sensitivity of tumor cells to peroxidation can be also enhanced with the help of exogenous polyunsaturated fatty acid (PUFA). Based on literature and our own data on Ehrlich ascites carcinoma (EAC), a working hypothesis is proposed to explain the enhanced selective sensitivity of tumor cells to PUFA peroxidation products (PP) suppressing the cell growth (especially in the stationary phase of EAC growth).     

The fate of irradiated tumor cells

Radiotherapy remains a key component of modern multimodal anticancer treatment approaches. Although most clinically relevant improvements in radiation oncology are based on optimized radiation technology, it now becomes obvious that biology-based approaches will further boost the efficacy of modern radiation oncology. Of relevance to this is the question of the ultimate fate of an irradiated cell and the mechanistic basis of the induced cell death or inactivation observed. Research bearing on this question is reported in this issue of Oncogene by Wendt et al. (2005), who show that the levels of p21CIP/WAF1 play a key role in determining whether an irradiated tumour cell is arrested in the G2 phase of the cell cycle, rather than apoptosing. The demonstration that caffeine treatment can abrogate this G2 arrest, and that the cells go on to die, has implications for overcoming treatment resistance imposed by radiation-induced upregulation of p21CIP/WAF1.     

糖代谢标记在肿瘤靶向治疗中的应用策略

肿瘤细胞的特异性识别和结合是实现肿瘤靶向治疗的关键,缺乏有效靶标仍然是肿瘤靶向治疗面临的主要问题。糖代谢标记以其可以进行活体标记并且具有密度高、毒性低、干扰小等特点,使其能够为肿瘤靶向治疗提供新的策略。基于糖代谢标记策略,可以对肿瘤细胞进行半抗原、抗原、化疗药物及细胞毒性药物等的标记,从而实现对肿瘤细胞的特异性识别,或激活机体的细胞和体液免疫应答,还可以通过标记免疫细胞增加其对肿瘤细胞的特异性识别和结合。糖代谢标记在肿瘤靶向治疗中具有广阔的应用前景。     

Analysis of some metabolic conditions promoting selective sensitivity of tumor cells to peroxidative stress.

Some metabolic parameters enhancing the sensitivity of tumor cells and their lipoprotein refractive granules (RG) to peroxidative stress were investigated during the growth cycle of ascite tumors in vivo. The majority of tumor cells only in the stationary growth phase had the increased sensitivity to peroxidative stress, tested by fluorescence intensivity of peroxidation products. The increase of this intensity correlates well with the decrease of tumor proliferation, the functional activity of mitochondria, the cellular level of ATP and extracellular pH. These metabolic conditions are favourable for increasing the neutral lipid accumulation in the stationary tumor cells, their RG and nuclei, as compared to exponentially growing cells. The sensitivity of tumor cells to peroxidation can be also enhanced with the help of exogenous polyunsaturated fatty acid (PUFA). Based on literature and our own data on Ehrlich ascites carcinoma (EAC), a working hypothesis is proposed to explain the enhanced selective sensitivity of tumor cells to PUFA peroxidation products (PP) suppressing the cell growth (especially in the stationary phase of EAC growth).     

The lifetime of hypoxic human tumor cells

Purpose: For hypoxic and anoxic cells in solid tumors to be a therapeutic problem, they must live long enough to be therapeutically relevant, or else be rapidly recruited into the proliferating compartment during therapy. We have, therefore, estimated lifetime and recruitment rate of hypoxic human tumor cells in multicell spheroids in vitro, or in xenografted tumors in SCID mice.Materials and Methods: Cell turnover was followed by flow cytometry techniques, using antibodies directed at incorporated halogenated pyrimidines. The disappearance of labeled cells was quantified, and verified to be cell loss rather than label dilution. Repopulation was studied in SiHa tumor xenografts during twice-daily 2.5-Gy radiation exposures.Results: The longevity of hypoxic human tumor cells in spheroids or xenografts exceeded that of rodent cell lines, and cell turnover was slower in xenografts than under static growth as spheroids. Human tumor cells remained viable in the hypoxic regions of xenografts for 4–10 days, compared to 3–5 days in spheroids, and 1–3 days for most rodent cells in spheroids. Repopulation was observed within the first few radiation treatments for the SiHa xenografts and, with accumulated doses of more than 10 Gy, virtually all recovered cells had progressed through at least one S-phase.Conclusion: Our results suggest an important difference in the ability of human vs. rodent tumor cells to withstand hypoxia, and raise questions concerning the increased longevity seen in vivo relative to the steady-state spheroid system.     

肿瘤及肿瘤基质细胞释放的外泌体对肿瘤耐药产生的影响

恶性肿瘤已成为当今严重威胁人类健康的疾病之一,存在早发现难、治愈率低和预后差等三大难点.虽然,化疗是癌症治疗的主要手段,但由此产生的耐药也是当今影响疗效的最棘手问题之一,从而使患者面对无药可用的尴尬境地.外泌体(exosomes)作为细胞间信息传递的重要通讯员,在肿瘤耐药传递方面发挥重要作用.研究发现,肿瘤细胞和肿瘤微环境(tumor microenvironment,TME)中的基质细胞均可分泌携带耐药相关分子(包括蛋白质和miRNAs等)的外泌体,并通过外泌体在TME中相互作用,传递耐药分子,从而增强肿瘤细胞对药物的耐受性;同时肿瘤细胞外泌体还可以介导药物外排,从而影响药效;基质细胞也可与肿瘤细胞相互作用影响肿瘤细胞对药物的敏感性.同时,这些机制的发现也为克服肿瘤耐药提供了新思路,研究表明通过去除或抑制含耐药分子的外泌体,或者通过改变外泌体的成分(减少耐药分子或增加抗耐药分子),可在一定程度上逆转耐药.本文就肿瘤及肿瘤基质细胞释放的外泌体在肿瘤耐药中的作用以及由此而来的耐药逆转的研究进展作一综述.     

The metabolic activation of chrysene by hamster embryo cells

The major deoxyribonudeoside—hydrocarbon adducts presentin hydrolysates of DNA isolated from hamster embryo cells treatedwith chrysene were examined by chromatography on Sephadex LH20and by h.p.l.c. on Zorbax ODS. The results show that both majoradducts have chromatographic properties identical to those ofadducts formed when r-1, t-2-dihydroxy-t-3,4-oxy-1,2,3,4-tetrahydrochrysenereacts with DNA and provide evidence that metabolic activationof chrysene occurs via the formation of this ‘bay-region’diolepoxide.