Ceramide-induced apoptosis of human thyroid cancer cells resistant to apoptosis by irradiation

Radiosensitizing capacity of fenofibrate in glioblastoma cells depends on lipid metabolism

Despite advances in multimodal therapy approaches such as resection, chemotherapy and radiotherapy, the overall survival of patients with grade 4 glioblastoma (GBM) remains extremely poor (average survival time <2 years). Altered lipid metabolism, which increases fatty acid synthesis and thereby contributes to radioresistance in GBM, is a hallmark of cancer. Therefore, we explored the radiosensitizing effect of the clinically approved, lipid-lowering drug fenofibrate (FF) in different GBM cell lines (U87, LN18). Interestingly, FF (50 μM) significantly radiosensitizes U87 cells by inducing DNA double-strand breaks through oxidative stress and impairing mitochondrial membrane integrity, but radioprotects LN18 cells by reducing the production of reactive oxygen species (ROS) and stabilizing the mitochondrial membrane potential. A comparative protein and lipid analysis revealed striking differences in the two GBM cell lines: LN18 cells exhibited a significantly higher membrane expression density of the fatty acid (FA) cluster protein transporter CD36 than U87 cells, a higher expression of glycerol-3-phosphate acyltransferase 4 (GPAT4) which supports the production of large lipid droplets (LDs), and a lower expression of diacylglycerol O-acyltransferase 1 (DGAT1) which regulates the formation of small LDs. Consequently, large LDs are predominantly found in LN18 cells, whereas small LDs are found in U87 cells. After a combined treatment of FF and irradiation, the number of large LDs significantly increased in radioresistant LN18 cells, whereas the number of small LDs decreased in radiosensitive U87 cells. The radioprotective effect of FF in LN18 cells could be associated with the presence of large LDs, which act as a sink for the lipophilic drug FF. To prevent uptake of FF by large LDs and to ameliorate its function as a radiosensitizer, FF was encapsulated in biomimetic cell membrane extracellular lipid vesicles (CmEVs) which alter the intracellular trafficking of the drug. In contrast to the free drug, CmEV-encapsulated FF was predominantly enriched in the lysosomal compartment, causing necrosis by impairing lysosomal membrane integrity. Since the stability of plasma and lysosomal membranes is maintained by the presence of the stress-inducible heat shock protein 70 (Hsp70) which has a strong affinity to tumor-specific glycosphingolipids, necrosis occurs predominantly in LN18 cells having a lower membrane Hsp70 expression density than U87 cells. In summary, our findings indicate that the lipid metabolism of tumor cells can affect the radiosensitizing capacity of FF when encountered either as a free drug or as a drug loaded in biomimetic lipid vesicles.

Monitoring concentration and lipid signature of plasma extracellular vesicles from HR+ metastatic breast cancer patients under CDK4/6 inhibitors treatment

Extracellular vesicles (EVs) are cell-derived small membrane structures that transport various molecules. They have emerged as potential circulating biomarkers for monitoring responses to cancer therapies. This study aimed to comprehensively characterize plasma-carried EVs in hormone receptor-positive (HR+) metastatic breast cancer (MBC) patients treated with first-line CDK4/6 inhibitors (iCDK4/6) combined with endocrine therapy. MBC patients were classified into three groups based on their response to therapy: resistant, intermediate or sensitive. In a prospective cohort, we monitored the concentration of circulating EVs, analyzed their lipid signature and correlated these factors with treatment response. To facilitate the translation of EV research to clinical practice, we established a three-step procedure: (1) EVs were isolated from plasma using semi-automatized size exclusion chromatography (SEC); (2) EV concentration, termed vesiclemia, was determined by drop counting via interferometric light microscopy (ILM); and (3) EV lipid composition was analyzed by mass spectrometry. ILM-based vesiclemia values were highly fluctuating upon iCDK4/6 treatment, while early increase associated with accelerated progression. Of note, vesiclemia remained a steady parameter over a 1-year period in age-matched healthy women. Additionally, analysis of the EV cargo unveiled a distinct sphingolipid profile, characterized by increased levels of ceramides and sphingomyelins in resistant patients within the first 2 months of treatment. Based on 16 sphingolipid species, sensitive and resistant patients were correctly classified with an overall accuracy of 82%. This specific sphingolipid pattern was exclusively discernible within EVs, and not in plasma, highlighting the significance of EVs in the early prediction of individual responses to iCDK4/6 and disease progression. Overall, this study provides insights of the longitudinal characterization of plasma-borne EVs in both a healthy group and HR+ MBC patients under iCDK4/6 therapies. Combined vesiclemia and EV sphingolipid profile emphasize the promising potential of EVs as non-invasive biomarkers for monitoring early treatment response.

The role of lipid metabolism in cancer radioresistance

Radiotherapy is one of the main therapies for cancer. The process leading to radioresistance is still not fully understood. Cancer radiosensitivity is related to the DNA reparation of cancer cells and the tumor microenvironment (TME), which supports cancer cell survival. Factors that affect DNA reparation and the TME can directly or indirectly affect the radiosensitivity of cancer. Recent studies have shown that lipid metabolism in cancer cells, which is involved in the stability of cell membrane structure, energy supply and signal transduction of cancer cells, can also affect the phenotype and function of immune cells and stromal cells in the TME. In this review, we discussed the effects of lipid metabolism on the radiobiological characteristics of cancer cells and the TME. We also summarized recent advances in targeted lipid metabolism as a radiosensitizer and discussed how these scientific findings could be translated into clinical practice to improve the radiosensitivity of cancer.

Emerging Roles of Ceramides in Breast Cancer Biology and Therapy

One of the classic hallmarks of cancer is the imbalance between elevated cell proliferation and reduced cell death. Ceramide, a bioactive sphingolipid that can regulate this balance, has long been implicated in cancer. While the effects of ceramide on cell death and therapeutic efficacy are well established, emerging evidence indicates that ceramide turnover to downstream sphingolipids, such as sphingomyelin, hexosylceramides, sphingosine-1-phosphate, and ceramide-1-phosphate, is equally important in driving pro-tumorigenic phenotypes, such as proliferation, survival, migration, stemness, and therapy resistance. The complex and dynamic sphingolipid network has been extensively studied in several cancers, including breast cancer, to find key sphingolipidomic alterations that can be exploited to develop new therapeutic strategies to improve patient outcomes. Here, we review how the current literature shapes our understanding of how ceramide synthesis and turnover are altered in breast cancer and how these changes offer potential strategies to improve breast cancer therapy.

Acid and Neutral Sphingomyelinase Behavior in Radiation-Induced Liver Pyroptosis and in the Protective/Preventive Role of rMnSOD

Sphingomyelins (SMs) are a class of relevant bioactive molecules that act as key modulators of different cellular processes, such as growth arrest, exosome formation, and the inflammatory response influenced by many environmental conditions, leading to pyroptosis, a form of programmed cell death due to Caspase-1 involvement. To study liver pyroptosis and hepatic SM metabolism via both lysosomal acid SMase (aSMase) and endoplasmic reticulum/nucleus neutral SMase (nSMase) during the exposure of mice to radiation and to ascertain if this process can be modulated by protective molecules, we used an experimental design (previously used by us) to evaluate the effects of both ionizing radiation and a specific protective molecule (rMnSOD) in the brain in collaboration with the Joint Institute for Nuclear Research, Dubna (Russia). As shown by the Caspase-1 immunostaining of the liver sections, the radiation resulted in the loss of the normal cell structure alongside a progressive and dose-dependent increase of the labelling, treatment, and pretreatment with rMnSOD, which had a significant protective effect on the livers. SM metabolic analyses, performed on aSMase and nSMase gene expression, as well as protein content and activity, proved that rMnSOD was able to significantly reduce radiation-induced damage by playing both a protective role via aSMase and a preventive role via nSMase.

Emergence of membrane sphingolipids as a potential therapeutic target

BACKGROUND

Though sphingolipids are ubiquitously present in eukaryotic cells, but until the last decade, they were merely considered as a structural component of the plasma membrane with limited function. However, over the last decade, numerous functions have been ascribed to sphingolipids after the seminal discoveries on the bioactivities of several sphingolipids.

SCOPE OF REVIEW

Sphingolipids are now well-recognized signals for fundamental cellular processes. Here we discussed about the advent of several sphingolipids components as potential therapeutic target for both human and plants.

MAJOR CONCLUSIONS

Sphingolipid contents and/or sphingolipid-metabolizing enzyme expression/activity often get impaired during pathophysiological conditions, and hence manipulation of this signaling pathway may be beneficial in disease diagnosis, and the plasma concentrations can serve as an important prognostic and diagnostic marker for the disease.

GENERAL SIGNIFICANCE

Sphingolipids are emerging as a goldmine for new therapeutic drug targets with promising new applications (cosmeceutical and nutraceutical), thereby opening new avenues for pharmaceuticals and nutraceutical industries.

Radiation and Thyroid Cancer

Radiation-induced damage is a complex network of interlinked signaling pathways, which may result in apoptosis, cell cycle arrest, DNA repair, and cancer. The development of thyroid cancer in response to radiation, from nuclear catastrophes to chemotherapy, has long been an object of study. A basic overview of the ionizing and non-ionizing radiation effects of the sensitivity of the thyroid gland on radiation and cancer development has been provided. In this review, we focus our attention on experiments in cell cultures exposed to ionizing radiation, ultraviolet light, and proton beams. Studies on the involvement of specific genes, proteins, and lipids are also reported. This review also describes how lipids are regulated in response to the radiation-induced damage and how they are involved in thyroid cancer etiology, invasion, and migration and how they can be used as both diagnostic markers and drug targets.

Role of NF-kappaB in thyroid cancer

Thyroid cancer is the most common neoplasia of the endocrine system and accounts for approximately 1% of all newly diagnosed cancer cases. Its incidence has rapidly grown over the past few decades. Although most thyroid carcinomas are of the well-differentiated papillary histology, and respond well to treatment with surgical resection followed by radioactive iodine ablation, tumors with more aggressive phenotype, such as follicular, poorly differentiated, anaplastic, and medullary cancers, lead to almost 1500 patient deaths annually. Therefore, understanding molecular mechanisms that regulate the biology of these carcinomas could be helpful to identify new molecules acting as novel targets for therapeutic intervention. NF-kappaB has been recently shown to play an important role in thyroid cancer for its ability to control the proliferative and the anti-apoptotic signaling pathways of thyroid neoplastic cells. Oncogenic proteins RET/PTC, RAS and BRAF, that are involved in many aspects of thyroid carcinogenesis, can induce NF-kappaB activation in papillary, follicular, and medullary thyroid carcinomas, while constitutive de-regulated NF-kappaB activity has been found in anaplastic thyroid carcinomas. A number of NF-kappaB inhibitors have been demonstrated to induce anti-proliferative effects and/or massive apoptosis, especially in combination with radio- or chemo-therapy. The results obtained suggest that targeting NF-kappaB could be a promising strategy for advanced thyroid cancer treatment.

The BCL-2 protein BAK is required for long-chain ceramide generation during apoptosis

The BCL-2 family members BAK and BAX are required for apoptosis and trigger mitochondrial outer membrane permeabilization (MOMP). Here we identify a MOMP-independent function of BAK as a required factor for long-chain ceramide production in response to pro-apoptotic stress. UV-C irradiation of wild-type (WT) cells increased long-chain ceramides; blocking ceramide generation prevented caspase activation and cell death, demonstrating that long-chain ceramides play a key role in UV-C-induced apoptosis. In contrast, UV-C irradiation did not increase long-chain ceramides in BAK and BAX double knock-out cells. Notably, this was not specific to the cell type (baby mouse kidney cells, hematopoietic) nor the apoptotic stimulus employed (UV-C, cisplatin, and growth factor withdrawal). Importantly, long-chain ceramide generation was dependent on the presence of BAK, but not BAX. However, ceramide generation was independent of the known downstream actions of BAK in apoptosis (MOMP or caspase activation), suggesting a novel role for BAK in apoptosis. Finally, enzymatic assays identified ceramide synthase as the mechanism by which BAK regulates ceramide metabolism. There was no change in CerS expression at the message or protein level, indicating regulation at the post-translational level. Moreover, CerS activity in BAK KO microsomes can be reactivated upon addition of BAK-containing microsomes. The data presented indicate that ceramide-induced apoptosis is dependent upon BAK and identify a novel role for BAK during apoptosis. By establishing a unique role for BAK in long-chain ceramide metabolism, these studies further demonstrate that the seemingly redundant proteins BAK and BAX have distinct mechanisms of action during apoptosis induction.

De novo ceramide synthesis is responsible for the anti-tumor properties of camptothecin and doxorubicin in follicular thyroid carcinoma

Doxorubicin and camptothecin are two cytotoxic chemotherapeutic agents triggering apoptosis in various cancer cells, including thyroid carcinoma cells. Recent studies revealed a critical role of ceramide in chemotherapy and suggested that anti-cancer drugs may kill tumor cells through sphingomyelinase activation. However, in comparison to sphingomyelin hydrolysis, the relative involvement of de novo ceramide synthesis remained poorly explored and highly controversial. Here, we evidenced that both doxorubicin and camptothecin triggered ceramide accumulation in thyroid carcinoma cells. We demonstrated that ceramide increase occurred via the de novo pathway without neither acidic nor neutral sphingomyelinase contribution. Interestingly, de novo ceramide generation was responsible for the drug-induced malignant cell apoptosis through a caspase-3-dependent pathway and a decrease of thrombospondin amount. Furthermore, blocking ceramide metabolism by inhibiting glucosylceramide synthase strengthened the camptothecin and doxorubicin-dependent effects. Altogether, we evidenced that de novo ceramide synthesis mediates the anti-tumor properties of doxorubicin and camptothecin in thyroid carcinoma and suggested that glucosylation of ceramide may contribute to the drug-resistance phenotype in thyroid malignancies.

Nuclear factor-kB in thyroid carcinogenesis and progression: a novel therapeutic target for advanced thyroid cancer

Apoptosis is an essential physiological process of elimination of destined cells during the development and differentiation or after damage from external stresses such as ionizing radiation or chemotherapeutic agents. Disruption of apoptosis is proved to cause various diseases including cancer. Among numerous molecules involved in diverse anti- or pro-apoptotic signaling pathways, NF-kappaB is one of the key factors controlling anti-apoptotic responses. Its anti-apoptotic effect is thought to be mediated through not only transcriptional activation of dependent genes but also by crosstalking with the JNK pathway. Oncogenic proteins such as Ret/PTC, Ras and BRAF can induce NF-kappaB activation making it an important change in thyroid cancer. A number of specific or non-specific NF-kappaB inhibitors have been tried to take over the cascade in in vitro and in vivo experiments. These agents can induce massive apoptosis especially in combination with radio- or chemotherapy. Current results suggest that the inhibition of the NF-kappaB may be a promising strategy for advanced thyroid cancer treatment but further investigations are warranted to develop specific and clinically effective NF-kappaB inhibitors in future.

Selective pharmacologic inhibition of c-Jun NH2-terminal kinase radiosensitizes thyroid anaplastic cancer cell lines via induction of terminal growth arrest

CONTEXT

The high radioresistance of anaplastic thyroid cancer (ATC) and cultured ATC cells stipulates for the means of increasing their radiosensitivity. It has been shown that c-Jun NH(2)-terminal kinase (JNK) activation is one of the manifestations of radiation response in ATC cells.

OBJECTIVE

Assessment of the effect of selective JNK inhibition on ATC cell radiosensitivity and clarification of the associated mechanisms.

RESULTS

The JNK inhibitor markedly suppressed ATC cell growth in a reversible cytostatic manner. The combination treatment with JNK inhibitor plus ionizing radiation induced a significant decrease in clonogenic survival of irradiated cells as compared with either singular treatment. The effect was not due to apoptosis of exposed cells but to a profound senescence-like terminal growth arrest occurring irrespectively of cells' p53 mutational status. Postradiational DNA damage repair was also significantly compromised in the presence of SP600125.

CONCLUSIONS

JNK signaling is an essential component of ATC cell proliferation and survival after radiation therapy. Hence, pharmacological interference with JNK pathway in combination with radiotherapy may be a promising treatment of ATC.

Interleukin-1beta-induced apoptosis through adenylyl cyclase and ERK1/2 inhibition in primary cultured thyroid cells

The programmed cell death plays a crucial role in the regulation of numerous physiological and pathological phenomena. In this study, we show that interleukin-1 beta (IL-1beta) induces an early production of endogenous ceramides via N-sphingomyelinase (N-Smase) as well as an inhibition of adenylyl cyclase activity in pig thyroid cells. This effect is followed by a down-regulation of the extracellular signal-regulated protein kinase (ERK1/2) phosphorylation, an activation of caspase-3, and ends by setting up the programmed cell death. The permeable exogenous C(2)-ceramide reproduces IL-1beta effects on: (i) inhibition of adenylyl cyclase activity, (ii) down-regulation of ERK1/2 phosphorylation, (iii) activation of caspase-3, and (iv) apoptosis in pig thyroid cells. Cell treatment with a PKA inhibitor down-regulates ERK1/2 phosphorylation. Furthermore, inhibition of ERK1/2 signaling pathway by U-0126 enhances caspase-3 activity and sets up programmed cell death. Both IL-1beta and exogenous C(2)-ceramide effects are reproduced by U-0126 so illustrating the implication of ERK1/2 down-regulation in both caspase-3 activation and apoptosis induction. Our study shows for the first time that endogenous ceramides are important second messengers in IL-1beta-induced apoptosis in pig thyroid cells through inhibition of adenylyl cyclase and ERK1/2 activities.

Mitochondrial ceramide and the induction of apoptosis

In most cell types, a key event in apoptosis is the release of proapoptotic intermembrane space proteins from mitochondria to the cytoplasm. In general, it is the release of these intermembrane space proteins that is responsible for the activation of caspases and DNases that are responsible for the execution of apoptosis. The mechanism for the increased permeability of the mitochondrial outer membrane during the induction phase of apoptosis is currently unknown and highly debated. This review will focus on one such proposed mechanism, namely, the formation of ceramide channels in the mitochondrial outer membrane. Ceramides are known to play a major regulatory role in apoptosis by inducing the release of proapoptotic proteins from the mitochondria. As mitochondria are known to contain the enzymes responsible for the synthesis and hydrolysis of ceramide, there exists a mechanism for regulating the level of ceramide in mitochondria. In addition, mitochondrial ceramide levels have been shown to be elevated prior to the induction phase of apoptosis. Ceramide has been shown to form large protein permeable channels in planar phospholipid and mitochondrial outer membranes. Thus, ceramide channels are good candidates for the pathway with which proapoptotic proteins are released from mitochondria during the induction phase of apoptosis.

Overcoming resistance to gamma-rays in squamous carcinoma cells by poly-drug elevation of ceramide levels

Recent strategies to sensitize radioresistant tumours are based on combining gamma-irradiation with inducers of apoptosis. We report that the combination of three inhibitors of sphingolipid metabolism, DL-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol.HCl(DL-PDMP)+imipramine +/- D-erythro-2-(N-myristoylamino)-1-phenyl-1-propanol (D-MAPP), with 10-Gy irradiation triggers both mitotic and apoptotic killing in radioresistant SQ20B squamous carcinoma cells. In these cells, apoptosis is defective due to a lack of ceramide generation upstream, which cannot be explained by sphingomyelinase (neutral and acidic) deficiency or rapid derivation to the sphingolipid pathway. We present evidence of a functional transduction death pathway when ceramide generation is restored, which involves the mitochondrial-mediated pathway coupled to alterations in redox status and to executive caspases activation. The poly-drug treatment restored apoptosis to levels similar to those observed in radiosensitive SCC61 squamous carcinoma cells. Simultaneous exposure to gamma-irradiation and poly-drug treatment acted synergistically in SQ20B cells to produce a marked increase in both mitochondrial dysfunction and caspase cleavage, which led to a 7.8-fold increase in apoptosis within 48 h, relative to irradiated cells. Moreover, the results suggest that the ceramide released by irradiation or poly-drug treatment converges upon common cellular targets. Modulation of endogenous ceramide levels by inhibitors of sphingolipid metabolism may represent a new cellular target for the sensitization of radioresistant tumours to gamma-ray therapy.

Effective cytotoxicity against human leukemias and chemotherapy-resistant leukemia cell lines by N-N-dimethylsphingosine

We evaluated the cytotoxicity of dimethylsphingosine (DMS) against four human leukemia cell lines: two acute (HL60 and a multi-drug resistance MDR-positive derivative HL60-dox) and two blast crisis chronic myelogenous leukemias (JFP1, from a treatment refractory patient and K562), and against blasts isolated from 11 leukemia patients. Cell line viability decreased proportionally to DMS concentration and treatment time (P<0.001). HL60-dox and JFP1 were the most sensitive, indicating DMS efficacy against human leukemia MDR. Importantly, leukemia samples showed a similar sensitivity to DMS as that of the cell lines, firstly demonstrating PKC-independent sphingolipid activity against fresh human tumor specimens. DMS-based chemotherapy may improve leukemia treatment.

Radiation-inducible hSNK gene is transcriptionally regulated by p53 binding homology element in human thyroid cells

We identified a species relevant to polo-like kinase family, a human homologue of mouse serum-inducible kinase, hSNK gene, whose mRNA expression was rapidly increased in cultured human thyroid cells after X-ray irradiation. The cDNA cloning and genomic analysis of the hSNK gene showed the presence of 14 exons spanning over 6 kb of genomic DNA that encodes a 2.9-kb mRNA product. Promoter analysis demonstrated possible existence of a radiation-responsive element in the p53 binding homology element (p53RE) localized to near upstream of basal promoter of the hSNK gene. Nuclear protein extracts from HeLa and various human thyroid carcinoma cell lines bound selectively to p53RE. Anti-p53 or anti-p73 antibodies, however, failed to recognize the p53RE-protein complex formed in the presence of such nuclear extracts. These results suggest that radiation-responsive transcription factor(s) directly participates in the regulation of hSNK gene expression via the binding to p53RE in promoter region.

Transient activation of c-Jun NH2-terminal kinase by growth factors influences survival but not apoptosis of human thyrocytes

Activation of c-Jun NH2-terminal kinase (JNK), a member of the mitogen-activated protein kinase (MAPK) family, is involved in apoptosis or cell proliferation. We have previously demonstrated that ionizing radiation or thyroid-stimulating hormone activated JNK without linking to thyroid cell apoptosis. To clarify the involvement of JNK activation in thyroid cell survival, we investigated the effects of various growth factors on induction of JNK activation in cultured human thyroid cells. JNK activation was observed at 30 minutes after fetal bovine serum (FBS) stimulation and returned to basal level at 240 minutes. Epidermal growth factor (EGF), transforming growth factor-beta (TGF-beta) and hepatocyte growth factor (HGF) also induced JNK activation, but did not trigger apoptotic cell death. Furthermore, we observed high basal activation of JNK in four of five human thyroid cancer cell lines. Overexpression of c-Met, an HGF receptor, was observed in two of the four cell lines with high basal JNK activity. Our results suggest that JNK activation does not induce apoptosis but is associated with survival or transformation of human thyroid cells.

PKC delta mediates ionizing radiation-induced activation of c-Jun NH(2)-terminal kinase through MKK7 in human thyroid cells

The thyroid gland is one of the most sensitive organs in ionizing radiation (IR)-induced carcinogenesis. To determine, therefore, the specific cascade of IR-induced signal transduction in human thyroid cells, we investigated the functional role of protein kinase C (PKC), especially its interlocking activation of c-Jun NH(2)-terminal kinase (JNK) pathway. In the present study, using adenovirus expression vectors for diverse dominant-negative (DN) types of PKC isoforms (alpha, beta2, delta, epsilon and zeta) expressed in primary cultured human thyroid cells, only DN/PKC delta suppressed IR-induced JNK activation. In addition, Rottlerin, a PKC delta specific inhibitor, inhibited IR-induced JNK activation. IR-induced activation of transcription factor AP-1, downstream target of JNK, was also attenuated by DN/PKC delta. To examine the involvement of upstream kinases of JNK, we performed immune-complex kinase assays of mitogen-activated protein kinase kinase 4 (MKK4) and MKK7. IR activated MKK7 but not MKK4, and this activation was inhibited by Rottlerin. Furthermore, IR-induced JNK activation was suppressed by overexpression of kinase-deficient MKK7. Our results indicate that IR selectively activates the cascade of PKC delta-MKK7-JNK-AP-1 in human thyroid cells, suggesting a not apoptotic but radio-resistant role of PKC delta in human thyroid cells following IR.