Antiglioma effects of N6-isopentenyladenosine, an endogenous isoprenoid end product, through the downregulation of epidermal growth factor receptor

tRNA modifications and tRNA-derived small RNAs: new insights of tRNA in human disease

tRNAs are codon decoders that convert the transcriptome into the proteome. The field of tRNA research is excited by the increasing discovery of specific tRNA modifications that are installed at specific, evolutionarily conserved positions by a set of specialized tRNA-modifying enzymes and the biogenesis of tRNA-derived regulatory fragments (tsRNAs) which exhibit copious activities through multiple mechanisms. Dysregulation of tRNA modification usually has pathological consequences, a phenomenon referred to as "tRNA modopathy". Current evidence suggests that certain tRNA-modifying enzymes and tsRNAs may serve as promising diagnostic biomarkers and therapeutic targets, particularly for chemoresistant cancers. In this review, we discuss the latest discoveries that elucidate the molecular mechanisms underlying the functions of clinically relevant tRNA modifications and tsRNAs, with a focus on malignancies. We also discuss the therapeutic potential of tRNA/tsRNA-based therapies, aiming to provide insights for the development of innovative therapeutic strategies. Further efforts to unravel the complexities inherent in tRNA biology hold the promise of yielding better biomarkers for the diagnosis and prognosis of diseases, thereby advancing the development of precision medicine for health improvement.

N6-isopentenyladenosine inhibits aerobic glycolysis in glioblastoma cells by targeting PKM2 expression and activity

Glioblastoma (GBM) is a primary tumor in the central nervous system with poor prognosis. It exhibits elevated glucose uptake and lactate production. This metabolic state of aerobic glycolysis is known as the Warburg effect. N6-isopentenyladenosine (iPA), a natural cytokine modified with an isopentenyl moiety derived from the mevalonate pathway, has well-established anti-tumor activity. It inhibits cell proliferation in glioma cells, inducing cell death by apoptosis and/or necroptosis. In the present study, we found that iPA inhibits aerobic glycolysis in unmodified U87MG cells and in the same cell line engineered to over-express wild-type epidermal growth factor receptor (EGFR) or EGFR variant III (vIII), as well as in a primary GBM4 patient-derived cell line. The detection of glycolysis showed that iPA treatment suppressed ATP and lactate production. We also evaluated the response of iPA treatment in normal human astrocyte primary cells, healthy counterpart cells of the brain. Aerobic glycolysis in treated normal human astrocyte cells did not show significant changes compared to GBM cells. To determine the mechanism of iPA action on aerobic glycolysis, we investigated the expression of certain enzymes involved in this metabolic pathway. We observed that iPA reduced the expression of pyruvate kinase M2 (PKM2), which plays a key role in the regulation of aerobic glycolysis, promoting tumor cell proliferation. The reduction of PKM2 expression is a result of the inhibition of the inhibitor of nuclear factor kappa-B kinase subunit, beta/nuclear factor-kappa B pathway upon iPA treatment. In conclusion, these experimental results show that iPA may inhibit aerobic glycolysis of GBM in stabilized cell lines and primary GBM cells by targeting the expression and activity of PKM2.

N6-Isopentenyladenosine Impairs Mitochondrial Metabolism through Inhibition of EGFR Translocation on Mitochondria in Glioblastoma Cells

Glioblastoma multiforme (GBM) is the most aggressive malignant brain tumor and is poorly susceptible to cytotoxic therapies. Amplification of the epidermal growth factor receptor (EGFR) and deletion of exons 2 to 7, which generates EGFR variant III (vIII), are the most common molecular alterations of GBMs that contribute to the aggressiveness of the disease. Recently, it has been shown that EGFR/EGFRvIII-targeted inhibitors enhance mitochondrial translocation by causing mitochondrial accumulation of these receptors, promoting the tumor drug resistance; moreover, they negatively modulate intrinsic mitochondria-mediated apoptosis by sequestering PUMA, leading to impaired apoptotic response in GBM cells. N6-isopentenyladenosine (i6A or iPA), a cytokinin consisting of an adenosine linked to an isopentenyl group deriving from the mevalonate pathway, has antiproliferative effects on numerous tumor cells, including GBM cells, by inducing cell death in vitro and in vivo. Here, we observed that iPA inhibits the mitochondrial respiration in GBM cells by preventing the translocation of EGFR/EGFRvIII to the mitochondria and allowing PUMA to interact with them by promoting changes in mitochondrial activity, thus playing a critical role in cell death. Our findings clearly demonstrate that iPA interferes with mitochondrial bioenergetic capacity, providing a rationale for an effective strategy for treating GBM.

Extracellular N6 -isopentenyladenosine (i6A) addition induces cotranscriptional i6A incorporation into ribosomal RNAs

N⁶ -isopentenyladenosine (i⁶A), a modified adenosine monomer, is known to induce cell death upon its addition to the culture medium. However, the molecular fate of extracellularly added i⁶A has yet to be identified. Here we show that i⁶A addition to cell culture medium results in i⁶A incorporation into cellular RNA in several cell lines, including the 5-fluorouracil (5-FU)-resistant human oral squamous cell carcinoma cell line FR2-SAS and its parental 5-FU-sensitive cell line SAS. i⁶A was predominantly incorporated into 18S and 28S rRNAs, and i⁶A incorporation into total RNA was mostly suppressed by treating these cell lines with an RNA polymerase I (Pol I) inhibitor. i⁶A was incorporated into RNA even upon inactivation of TRIT1, the only cellular i⁶A-modifying enzyme. These results indicate that upon cellular uptake of i⁶A, it is anabolized to be used for Pol I transcription. Interestingly, at lower i⁶A concentrations, the cytotoxic effect of i⁶A was substantially more pronounced in FR2-SAS cells than in SAS cells. Moreover, in FR2-SAS cells, i⁶A treatment decreased the rate of cellular protein synthesis and increased intracellular protein aggregation, and these effects were more pronounced than in SAS cells. Our work provides insights into the molecular fate of extracellularly applied i⁶A in the context of intracellular nucleic acid anabolism and suggests investigation of i⁶A as a candidate for a chemotherapy agent against 5-FU-resistant cancer cells.

Modified Adenosines Sensitize Glioblastoma Cells to Temozolomide by Affecting DNA Methyltransferases

Glioblastoma (GBM) is the most common and lethal primary malignant brain tumor, and due to its unique features, its management is certainly one of the most challenging ones among all cancers. N6-isopentenyladenosine (IPA) and its analog N6-benzyladenosine (N6-BA) are modified nucleosides endowed with potent antitumor activity on different types of human cancers, including GBM. Corroborating our previous finding, we demonstrated that IPA and N6-BA affect GBM cell line proliferation by modulating the expression of the F-box WD repeat domain-containing-7 (FBXW7), a tumor suppressor with a crucial role in the turnover of many proteins, such as SREBPs and Mcl1, involved in malignant progression and chemoresistance. Luciferase assay revealed that IPA-mediated upregulation of FBXW7 translates in transcriptional inactivation of its oncogenic substrates (Myc, NFkB, or HIF-1α). Moreover, downregulating MGMT expression, IPA strongly enhances the killing effect of temozolomide (TMZ), producing a favorable sensitizing effect starting from a concentration range much lower than TMZ EC50. Through DNA methyltransferase (DNMT) activity assay, analysis of the global DNA methylation, and the histone modification profiles, we demonstrated that the modified adenosines behave similar to 5-AZA-dC, known DNMT inhibitor. Overall, our results provide new perspectives for the first time, suggesting the modified adenosines as epigenetic tools able to improve chemo- and radiotherapy efficacy in glioblastoma and potentially other cancers.

N6-isopentenyladenosine induces cell death through necroptosis in human glioblastoma cells

Targeting necroptosis is considered a promising therapeutic strategy in cancer, including Glioblastoma Multiforme (GBM), one of the most lethal brain tumors. Necroptosis is a mechanism of programmed cell death overcoming the apoptosis resistance mechanism underlying GBM tumorigenesis and malignant progression. N6-isopentenyladenosine (iPA), adenosine modified with isoprenoid derivative, displays antitumor activity in different cancer models. In previous studies, we demonstrated that iPA interferes with EGFR signaling reducing glioma cell viability. Here, we show that iPA induces necroptosis in glioblastoma cell lines and in primary cells established from tumor explants, without affecting the viability of non-cancerous brain cell lines, (Normal Human Astrocyte). The activation of RIP1, RIP3, and MLKL and the upregulation of necrosome formation were increased upon iPA treatment while caspase-3, caspase-8, and PARP were not activated in GBM cells. Co-treatment with specific necroptosis inhibitor necrostatin-1 (Nec-1) or Necrosulfonamide (NSA) prevented cell death caused by iPA treatment while the general caspase inhibitor Z-VAD-fluoromethylketone (z-VAD-fmk) did not elicit any effect, suggesting that this molecule induces caspase-independent necroptosis. These results suggest that iPA treatment can be able to bypass the apoptosis resistance mechanism in glioblastoma thereby offering higher therapeutic efficacy.

Genome-Wide Identification and Characterisation of Cytokinin-O-Glucosyltransferase (CGT) Genes of Rice Specific to Potential Pathogens

Cytokinin glucosyltransferases (CGTs) are key enzymes of plants for regulating the level and function of cytokinins. In a genomic identification of rice CGTs, 41 genes with the plant secondary product glycosyltransferases (PSPG) motif of 44-amino-acid consensus sequence characteristic of plant uridine diphosphate (UDP)-glycosyltransferases (UGTs) were identified. In-silico physicochemical characterisation revealed that, though the CGTs belong to the same subfamily, they display varying molecular weights, ranging from 19.6 kDa to 59.7 kDa. The proteins were primarily acidic (87.8%) and hydrophilic (58.6%) and were observed to be distributed in the plastids (16), plasma membrane (13), mitochondria (5), and cytosol (4). Phylogenetic analysis of the CGTs revealed that their evolutionary relatedness ranged from 70-100%, and they aligned themselves into two major clusters. In a comprehensive analysis of the available transcriptomics data of rice samples representing different growth stages only the CGT, Os04g25440.1 was significantly expressed at the vegetative stage, whereas 16 other genes were highly expressed only at the reproductive growth stage. On the contrary, six genes, LOC_Os07g30610.1, LOC_Os04g25440.1, LOC_Os07g30620.1, LOC_Os04g25490.1, LOC_Os04g37820.1, and LOC_Os04g25800.1, were significantly upregulated in rice plants inoculated with Rhizoctonia solani (RS), Xoo (Xanthomonas oryzae pv. oryzae) and Mor (Magnaporthe oryzae). In a qRT-PCR analysis of rice sheath tissue susceptible to Rhizoctonia solani, Mor, and Xoo pathogens, compared to the sterile distilled water control, at 24 h post-infection only two genes displayed significant upregulation in response to all the three pathogens: LOC_Os07g30620.1 and LOC_Os04g25820.1. On the other hand, the expression of genes LOC_Os07g30610.1, LOC_Os04g25440, LOC_Os04g25490, and LOC_Os04g25800 were observed to be pathogen-specific. These genes were identified as the candidate-responsive CGT genes and could serve as potential susceptibility genes for facilitating pathogen infection.

Towards an Improvement of Anticancer Activity of Benzyl Adenosine Analogs

N6-Isopentenyladenosine (i6A) is a naturally occurring modified nucleoside displaying in vitro and in vivo antiproliferative and pro-apoptotic properties. In our previous studies, including an in silico inverse virtual screening, NMR experiments and in vitro enzymatic assays, we demonstrated that i6A targeted farnesyl pyrophosphate synthase (FPPS), a key enzyme involved in the mevalonate (MVA) pathway and prenylation of downstream proteins, which are aberrant in several cancers. Following our interest in the anticancer effects of FPPS inhibition, we developed a panel of i6A derivatives bearing bulky aromatic moieties in the N6 position of adenosine. With the aim of clarifying molecular action of N6-benzyladenosine analogs on the FPPS enzyme inhibition and cellular toxicity and proliferation, herein we report the evaluation of the N6-benzyladenosine derivatives’ (compounds 2a–m) effects on cell viability and proliferation on HCT116, DLD-1 (human) and MC38 (murine) colorectal cancer cells (CRC). We found that compounds 2, 2a and 2c showed a persistent antiproliferative effect on human CRC lines and compound 2f exerted a significant effect in impairing the prenylation of RAS and Rap-1A proteins, confirming that the antitumor activity of 2f was related to the ability to inhibit FPPS activity.

Silencing IKBKE inhibits the migration and invasion of glioblastoma by promoting Snail1 degradation

PURPOSE

Glioblastoma multiforme (GBM) is one of the most common malignant brain tumors in adults and has high mortality and relapse rates. Over the past few years, great advances have been made in the diagnosis and treatment of GBM, but unfortunately, the five-year overall survival rate of GBM patients is approximately 5.1%. Inhibitor of nuclear factor kappa-B kinase subunit epsilon (IKBKE) is a major oncogenic protein in tumors and can promote evil development of GBM. Snail1, a key inducer of the epithelial-mesenchymal transition (EMT) transcription factor, is subjected to ubiquitination and degradation, but the mechanism by which Snail1 is stabilized in tumors remains unclear. Our study aimed to investigate the mechanism of IKBKE regulating Snail1 in GBM.

METHODS

First, we analyzed the correlation between the expression of IKBKE and the tumor grade and prognosis through public databases and laboratory specimen libraries. Second, immunohistochemistry (IHC) and western blot were used to detect the correlation between IKBKE and Snail expression in glioma samples and cell lines. Western blot and immunofluorescence (IF) experiments were used to detect the quality and distribution of IKBKE and Snail1 proteins. Third, In situ animal model of intracranial glioma to detect the regulatory effect of IKBKE on intracranial tumors.

RESULTS

In this study, Our study reveals a new connection between IKBKE and Snail1, where IKBKE can directly bind to Snail1, translocate Snail1 into the nucleus from the cytoplasm. Downregulation of IKBKE results in Snail1 destabilization and impairs the tumor cell migration and invasion capabilities.

CONCLUSION

Our studies suggest that the IKBKE-Snail1 axis may serve as a potential therapeutic target for GBM treatment.

N6-Isopentenyladenosine Hinders the Vasculogenic Mimicry in Human Glioblastoma Cells through Src-120 Catenin Pathway Modulation and RhoA Activity Inhibition

BACKGROUND

Vasculogenic mimicry (VM) is a functional microcirculation pattern formed by aggressive tumor cells. Thus far, no effective drugs have been developed to target VM. Glioblastoma (GBM) is the most malignant form of brain cancer and is a highly vascularized tumor. Vasculogenic mimicry represents a means whereby GBM can escape anti-angiogenic therapies.

METHODS

Here, using an in vitro tube formation assay on Matrigel, we evaluated the ability of N6-isopentenyladenosine (iPA) to interfere with vasculogenic mimicry (VM). RhoA activity was assessed using a pull-down assay, while the modulation of the adherens junctions proteins was analyzed by Western blot analysis.

RESULTS

We found that iPA at sublethal doses inhibited the formation of capillary-like structures suppressing cell migration and invasion of U87MG, U343MG, and U251MG cells, of patient-derived human GBM cells and GBM stem cells. iPA reduces the vascular endothelial cadherin (VE-cadherin) expression levels in a dose-dependent manner, impairs the vasculogenic mimicry network by modulation of the Src/p120-catenin pathway and inhibition of RhoA-GTPase activity.

CONCLUSIONS

Taken together, our results revealed iPA as a promising novel anti-VM drug in GBM clinical therapeutics.

Imaging Metformin Efficacy as Add-On Therapy in Cells and Mouse Models of Human EGFR Glioblastoma

Glioblastoma (GBM) is a highly aggressive tumor of the brain. Despite the efforts, response to current therapies is poor and 2-years survival rate ranging from 6-12%. Here, we evaluated the preclinical efficacy of Metformin (MET) as add-on therapy to Temozolomide (TMZ) and the ability of [¹⁸F]FLT (activity of thymidine kinase 1 related to cell proliferation) and [¹⁸F]VC701 (translocator protein, TSPO) Positron Emission Tomography (PET) radiotracers to predict tumor response to therapy. Indeed, TSPO is expressed on the outer mitochondrial membrane of activated microglia/macrophages, tumor cells, astrocytes and endothelial cells. TMZ-sensitive (Gli36ΔEGFR-1 and L0627) or -resistant (Gli36ΔEGFR-2) GBM cell lines representative of classical molecular subtype were tested in vitro and in vivo in orthotopic mouse models. Our results indicate that in vitro, MET increased the efficacy of TMZ on TMZ-sensitive and on TMZ-resistant cells by deregulating the balance between pro-survival (bcl2) and pro-apoptotic (bax/bad) Bcl-family members and promoting early apoptosis in both Gli36ΔEGFR-1 and Gli36ΔEGFR-2 cells. In vivo, MET add-on significantly extended the median survival of tumor-bearing mice compared to TMZ-treated ones and reduced the rate of recurrence in the TMZ-sensitive models. PET studies with the cell proliferation radiopharmaceutical [¹⁸F]FLT performed at early time during treatment were able to distinguish responder from non-responder to TMZ but not to predict the duration of the effect. On the contrary, [¹⁸F]VC701 uptake was reduced only in mice treated with MET plus TMZ and levels of uptake negatively correlated with animals’ survival. Overall, our data showed that MET addition improved TMZ efficacy in GBM preclinical models representative of classical molecular subtype increasing survival time and reducing tumor relapsing rate. Finally, results from PET imaging suggest that the reduction of cell proliferation represents a common mechanism of TMZ and combined treatment, whereas only the last was able to reduce TSPO. This reduction was associated with the duration of treatment response. TSPO-ligand may be used as a complementary molecular imaging marker to predict tumor microenvironment related treatment effects.

Keratinocytes Migration Promotion, Proliferation Induction, and Free Radical Injury Prevention by 3-Hydroxytirosol

3-hydroxytyrosol (HT) is the main phenolic compound found in olive oil with known antioxidant, anti-inflammatory, and antimicrobial properties in several dermatological conditions, both when taken in the form of olive oil or pure in cosmeceutical formulations. To date, its direct effect on the wound healing process and the molecular mechanisms involved have not yet been elucidated. Thus, in the present study, we aimed to explore its effects in vitro in epidermal keratinocyte cultures focusing on the molecular mechanism implied. HT was able to induce keratinocyte proliferation in the low micromolar range, increasing the expression of cyclin dependent kinases fundamental for cell cycle progression such as CDK2 and CDK6. Furthermore, it increased cell migration through the activation of tissue remodeling factors such as matrix metalloproteinase-9 (MMP-9) protein. Then, we evaluated whether HT also showed antioxidant activity at this concentration range, protecting from H₂O₂-induced cytotoxicity. The HT prevented the activation of ATM serine/threonine kinase (ATM), Checkpoint kinase 1 (Chk1), Checkpoint kinase 2 (Chk2), and p53, reducing the number of apoptotic cells. Our study highlighted novel pharmacological properties of HT, providing the first evidence of its capability to induce keratinocyte migration and proliferation required for healing processes and re-epithelialization.

Identification of New Genetic Clusters in Glioblastoma Multiforme: EGFR Status and ADD3 Losses Influence Prognosis

Glioblastoma multiforme (GB) is one of the most aggressive tumors. Despite continuous efforts to improve its clinical management, there is still no strategy to avoid a rapid and fatal outcome. EGFR amplification is the most characteristic alteration of these tumors. Although effective therapy against it has not yet been found in GB, it may be central to classifying patients. We investigated somatic-copy number alterations (SCNA) by multiplex ligation-dependent probe amplification in a series of 137 GB, together with the detection of EGFRvIII and FISH analysis for EGFR amplification. Publicly available data from 604 patients were used as a validation cohort. We found statistical associations between EGFR amplification and/or EGFRvIII, and SCNA in CDKN2A, MSH6, MTAP and ADD3. Interestingly, we found that both EGFRvIII and losses on ADD3 were independent markers of bad prognosis (p = 0.028 and 0.014, respectively). Finally, we got an unsupervised hierarchical classification that differentiated three clusters of patients based on their genetic alterations. It offered a landscape of EGFR co-alterations that may improve the comprehension of the mechanisms underlying GB aggressiveness. Our findings can help in defining different genetic profiles, which is necessary to develop new and different approaches in the management of our patients.

S-adenosylmethionine tRNA modification: unexpected/unsuspected implications of former/new players

S-adenosylmethionine supplies methyl groups to many acceptors, including lipids, proteins, RNA, DNA, and a wide range of small molecules. It acts as the precursor in the biosynthesis of metal ion chelating compounds, such as nicotianamine and phytosiderophores, of the polyamines spermidine and spermine and of some plant hormones. Finally, it is the source of catalytic 5′-deoxyadenosyl radicals.

Radical S-adenosylmethionine (SAM) enzymes (RS) represent one of the most abundant groups (more than 100,000) of enzymes, exerting a plethora of biological functions, some of which are still unknown.

In this work, we will focus on two RS: CDK5RAP1 and CDKAL1, both of which are involved in tRNA modifications that result in important tRNA folding and stability and in maintaining high translational fidelity. Based on this crucial role, their impairment can be important in the development of different human diseases.

Ganoderma lucidum Ethanol Extracts Enhance Re-Epithelialization and Prevent Keratinocytes from Free-Radical Injury

Ganoderma lucidum or Reishi is recognized as the most potent adaptogen present in nature, and its anti-inflammatory, antioxidant, immunomodulatory and anticancer activities are well known. Moreover, lately, there has been an increasing interest from pharmaceutical companies in antiaging G. lucidum-extract-based formulations. Nevertheless, the pharmacological mechanisms of such adaptogenic and regenerative actions remain unclear. The present investigation aimed to explore its molecular and cellular effects in vitro in epidermal keratinocyte cultures by applying liquid chromatography coupled to ion trap time-of-flight mass spectrometry (LCMS-IT-TOF) for analysis of ethanol extracts using ganoderic acid-A as a reference compound. The G. lucidum extract showed a keratinocyte proliferation induction accompanied by an increase of cyclic kinase protein expressions, such as CDK2 and CDK6. Furthermore, a noteworthy migration rate increase and activation of tissue remodelling factors, such as matrix metalloproteinases 2 and 9 (MMP-2 and MMP-9), were observed. Finally, the extract showed an antioxidant effect, protecting from H₂O₂-induced cytotoxicity; preventing activation of AKT (protein kinase B), ERK (extracellular signal-regulated kinase), p53 and p21; and reducing the number of apoptotic cells. Our study paves the path for elucidating pharmacological properties of G. lucidum and its potential development as cosmeceutical skin products, providing the first evidence of its capability to accelerate the healing processes enhancing re-epithelialization and to protect cells from free-radical action.

Chemical Deprenylation of N6 -Isopentenyladenosine (i6 A) RNA

N⁶ -isopentenyladenosine (i⁶ A) is an RNA modification found in cytokinins, which regulate plant growth/differentiation, and a subset of tRNAs, where it improves the efficiency and accuracy of translation. The installation and removal of this modification is mediated by prenyltransferases and cytokinin oxidases, and a chemical approach to selective deprenylation of i⁶ A has not been developed. We show that a selected group of oxoammonium cations function as artificial deprenylases to promote highly selective deprenylation of i⁶ A in nucleosides, oligonucleotides, and live cells. Importantly, other epigenetic modifications, amino acid residues, and natural products were not affected. Moreover, a significant phenotype difference in the Arabidopsis thaliana shoot and root development was observed with incubation of the cation. These results establish these small organic molecules as direct chemical regulators/artificial deprenylases of i⁶ A.

3-Hydroxytyrosol Promotes Angiogenesis In Vitro by Stimulating Endothelial Cell Migration

Cardiovascular diseases, followed by strokes, represent the leading cause of mortality worldwide. Despite its success in preventing cardiovascular diseases, the therapeutic potential of 3-Hydroxytyrosol (HT) for treating ischemic diseases is yet to be investigated in detail, especially with regard to ischemic heart disease, which is a major challenge for humans. We assessed that low concentrations (1-5 µM) of HT, generally achieved after the ingestion of olive oil, stimulate endothelial cells migration and angiogenesis in an in vitro model. At early time points (1-6 h), HT induces the expression of different proteins such as proto-oncogene tyrosine-protein kinase Src (Src), rho-associated protein kinase (ROCK) and matrix metalloproteinase-2 (MMP-2) protein influencing cell adhesion, cytoskeletal dynamics and cell migration. We observed that at the same time, HT induces prominent vascular formation in the tube formation assay, accompanied by an increase in the expression of the vascular endothelial growth factor receptor (VEGF-R2) and PI3K-Akt-eNOS protein pathways, which are recognized for their central role in angiogenesis. Therefore, in addition to the proven capability of HT to regulate reactive oxygen species (ROS) levels, through both direct scavenging properties and indirect antioxidant efficacy, our results revealed that HT promotes angiogenesis, arguing in favor of great pharma-nutritional potential in ischemic injuries.

Phytohormones: Multifunctional nutraceuticals against metabolic syndrome and comorbid diseases

Metabolic syndrome is characterized by the co-occurrence of diverse symptoms initiating the development of type 2 diabetes, cardiovascular diseases, and a variety of comorbid diseases. The complex constellation of numerous comorbidities makes it difficult to develop common therapeutic approaches that ameliorate these pathological features simultaneously. The plant hormones abscisic acid, salicylic acid, auxin, and cytokinins, have shown promising anti-inflammatory and pro-metabolic effects that could mitigate several disorders relevant to metabolic syndrome. Intriguingly, besides plants, human cells and gut microbes also endogenously produce these molecules, indicating a role in the complex interplay between inflammatory responses associated with metabolic syndrome, the gut microbiome, and nutrition. Here, we introduce how bioactive phytohormones can be generated endogenously and through the gut microbiome. These molecules subsequently influence immune responses and metabolism. We also elaborate on how phytohormones can beneficially modulate metabolic syndrome comorbidities, and propose them as nutraceuticals.

N6-Isopentenyladenosine Enhances the Radiosensitivity of Glioblastoma Cells by Inhibiting the Homologous Recombination Repair Protein RAD51 Expression

Glioblastoma is among the most common malignant brain tumors and has a dismal prognosis due to the poor response to therapeutic regimens such as ionizing radiation and DNA-alkylating agents. In our study, we investigated the radiosensitizing activity of the N⁶-isopentenyladenosine (iPA), an naturally modified adenosine harboring an isopenenyl moiety, which shows antiproliferative effects on glioblastoma cell lines. We observed that co-treatment with ionizing radiation and iPA at micromolar concentration inhibited colony formation and viability of glioblastoma cell lines but not of non-malignant human cells. The combined treatment significantly attenuated the repair of radiation-induced DNA damage by inhibiting both the expression and irradiation-induced foci formation of RAD51, a key player in the homologous recombination repair process, leading to persistent DNA damage, as reflected by an increase of γ-H2AX foci. The radiosensitizing effect relied also on the inhibition of STAT5a/b activation, which is crucial for RAD51 expression, suggesting that iPA modulates the STAT5a/b-RAD51 axis following exposure to ionizing radiation. Overall, these data suggest that iPA, by acting through RAD51 inhibition at the mechanistic level, could function as a promising radiosensitizing agent and warrants further evaluation in prospective clinical trials.

2-Methylthio Conversion of N6-Isopentenyladenosine in Mitochondrial tRNAs by CDK5RAP1 Promotes the Maintenance of Glioma-Initiating Cells

2-Methylthio-N⁶-isopentenyl modification of adenosine (ms²i⁶A) is an evolutionally conserved modification found in mitochondrial (mt)-tRNAs. Cdk5 regulatory subunit-associated protein 1 (CDK5RAP1) specifically converts N6-isopentenyladenosine (i⁶A) to ms²i⁶A at position A37 of four mt-DNA-encoded tRNAs, and the modification regulates efficient mitochondrial translation and energy metabolism in mammals. Here, we report that the ms² conversion mediated by CDK5RAP1 in mt-tRNAs is required to sustain glioma-initiating cell (GIC)-related traits. CDK5RAP1 maintained the self-renewal capacity, undifferentiated state, and tumorigenic potential of GICs. This regulation was not related to the translational control of mt-proteins. CDK5RAP1 abrogated the antitumor effect of i⁶A by converting i⁶A to ms²i⁶A and protected GICs from excessive autophagy triggered by i⁶A. The elevated activity of CDK5RAP1 contributed to the amelioration of the tumor-suppressive effect of i⁶A and promoted GIC maintenance. This work demonstrates that CDK5RAP1 is crucial for the detoxification of endogenous i⁶A and that GICs readily utilize this mechanism for survival.

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CDK5RAP1 is required to sustain the growth of GICs through ms² modification of i⁶A

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Deficit of CDK5RAP1 inhibits the growth of GIC through i⁶A accumulation

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CDK5RAP1 detoxifies i⁶A by conversion into ms²i⁶A in the mitochondria of GICs

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Mitochondria serve as antidotal machinery against i⁶A in GICs

N6-Isopentenyladenosine Inhibits Colorectal Cancer and Improves Sensitivity to 5-Fluorouracil-Targeting FBXW7 Tumor Suppressor

N6-isopentenyladenosine has been shown to exert potent in vitro antitumor activity on different human cancers, including colorectal cancer. Although some potential biochemical targets have been identified, its precise mechanism of action remains unclear. We found that N6-isopentenyladenosine affects colorectal cancer proliferation in in vitro models carrying different mutational status of FBXW7 and TP53 genes, and in HCT116 xenografts in SCID mice, by increasing the expression of the well-established tumor suppressor FBXW7, a component of the SCF-E3 ubiquitin ligase complex that promotes degradation of various oncoproteins and transcription factors, such as c-Myc, SREBP and Mcl1. Corroborating our previous studies, we identified for the first time the FBXW7/SREBP/FDPS axis as a target of the compound. Pull down of ubiquitinated proteins, immunoprecipitation and luciferase assays, reveal that through the increase of FBXW7/c-Myc binding, N6-isopentenyladenosine induces the ubiquitination of c-Myc, inhibiting its transcriptional activity. Moreover, in FBXW7- and TP53-wild type cells, N6-isopentenyladenosine strongly synergizes with 5-Fluorouracil to inhibit colon cancer growth in vitro. Our results provide novel insights into the molecular mechanism of N6-isopentenyladenosine, revealing its multi-targeting antitumor action, in vitro and in vivo. Restoring of FBXW7 tumor-suppressor represents a valid therapeutic tool, enabling N6-isopentenyladenosine as optimizable compound for patient-personalized therapies in colorectal cancer.

Identification and characterization of the first cytokinin glycosyltransferase from rice

BACKGROUND

Cytokinins are one of the five major hormones families in plants and are important for their normal growth and environmental adaptability. In plants, cytokinins are mostly present as glycosides in plants, and their glycosylation modifications are catalyzed by family 1 glycosyltransferases. Current research on cytokinin glycosylation has focused on the biochemical identification of enzymes and the analysis of metabolites in Arabidopsis. There are few studies that examine how cytokinin glycosylation affects its synthesis and accumulation in plants. It is particularly important to understand these processes in food crops such as rice (Oryza sativa); however, to date, cytokinin glycosyltransferase genes in rice have not been reported.

RESULTS

In this study, we identified eight rice genes that were functionally homologous to an Arabidopsis cytokinin glycosyltransferase gene. These genes were cloned and expressed in a prokaryotic system to obtain their purified proteins. Through enzymatic analysis and liquid chromatography-mass spectrometry, a single rice glycosyltransferase, Os6, was identified that glycosylated cytokinin in vitro. Os6 was overexpressed in Arabidopsis, and the extraction of cytokinin glycosides showed that Os6 is functionally active in planta.

CONCLUSIONS

The identification and characterization of the first cytokinin glycosyltransferase from rice is important for future studies on the cytokinin metabolic pathway in rice. An improved understanding of rice cytokinin glycosyltransferases may facilitate genetic improvements in rice quality.

Cholesterol Metabolism: A Potential Therapeutic Target in Glioblastoma

Glioblastoma is a highly lethal adult brain tumor with no effective treatments. In this review, we discuss the potential to target cholesterol metabolism as a new strategy for treating glioblastomas. Twenty percent of cholesterol in the body is in the brain, yet the brain is unique among organs in that it has no access to dietary cholesterol and must synthesize it de novo. This suggests that therapies targeting cholesterol synthesis in brain tumors might render their effects without compromising cell viability in other organs. We will describe cholesterol synthesis and homeostatic feedback pathways in normal brain and brain tumors, as well as various strategies for targeting these pathways for therapeutic intervention.

The isoprenoid end product N6-isopentenyladenosine reduces inflammatory response through the inhibition of the NFκB and STAT3 pathways in cystic fibrosis cells

Objective

N6-isopentenyladenosine (iPA) is an intermediate of the mevalonate pathway that exhibits various anti-cancer effects. However, studies on its anti-inflammatory activity are scarce and underlying molecular mechanisms are unknown. Therefore, we aimed to investigate the ability of iPA to exert anti-inflammatory effects in the human cystic fibrosis (CF) cell model of exacerbated inflammation.

Materials and methods

TNFα-stimulated CF cells CuFi-1 and its normal counterpart NuLi-1 were pre-treated with increasing concentrations of iPA and cell viability and proliferation were assessed by MTT and BrdU assays. The effect of iPA on IL-8 and RANTES secretion was determined by ELISA, and the activation and expression of signaling molecules and selenoproteins were studied by Western blot. To assess the direct effect of iPA on NFκB activity, luciferase assay was performed on TNFα-stimulated HEK293/T cells transfected with a NFκB reporter plasmid.

Results

We demonstrated for the first time that iPA prevents IL-8 and RANTES release in TNFα-stimulated CF cells and this effect is mediated by increasing the expression of the direct NFκB inhibitor IκBα and decreasing the levels of STAT3. Consistent with this, we showed that iPA inhibited TNFα-mediated NFκB activation in HEK/293T cells. Finally, we also found that iPA improved the levels of glutathione peroxidase 1 and thioredoxin reductase 1 only in CF cells suggesting its ability to maintain sufficient expression of these anti-oxidant selenoproteins.

Conclusions

Our findings indicate that iPA can exert anti-inflammatory activity especially in the cases of excessive inflammatory response as in CF.

Deregulated expression and activity of Farnesyl Diphosphate Synthase (FDPS) in Glioblastoma

Glioblastoma (GBM), the most aggressive brain cancer, is highly dependent on the mevalonate (MVA) pathway for the synthesis of lipid moieties critical for cell proliferation but the function and regulation of key intermediate enzymes like farnesyl-diphosphate synthase (FDPS), up to now, remained unknown. A deregulated expression and activity of FDPS was the central research idea of the present study. FDPS mRNA, protein and enzyme activity were analyzed in a cohort of stage III-IV glioma patients (N = 49) and primary derived cells. FDPS silencing helped to clarify its function in the maintenance of malignant phenotype. Interestingly, compared to tumor-free peripheral (TFB) brain and normal human astrocytes (NHA), FDPS protein expression and enzyme activity were detected at high degree in tumor mass where a correlation with canonical oncogenic signaling pathways such as STAT3, ERK and AKT was also documented. Further, FDPS knockdown in U87 and GBM primary cells but not in NHA, enhanced apoptosis. With the effort to develop a more refined map of the connectivity between signal transduction pathways and metabolic networks in cancer FDPS as a new candidate metabolic oncogene in glioblastoma, might suggest to further target MVA pathway as valid therapeutic tool.

N6-isopentenyladenosine dual targeting of AMPK and Rab7 prenylation inhibits melanoma growth through the impairment of autophagic flux

Targeting the autophagic process is considered a promising therapeutic strategy in cancer since a great number of tumors, including melanoma, show high basal levels of protective autophagy that contributes to tumor progression and chemoresistance. Here, exploiting both in vitro and in vivo approaches, we identified N6-isopentenyladenosine (iPA), an end product of the mevalonate pathway, as a novel autophagy inhibitor with an interesting anti-melanoma activity. iPA, after being phosphorylated by adenosine kinase into 5'-iPA-monophosphate, induces autophagosome accumulation through AMPK activation, measured by increased fluorescent GFP-LC3 puncta and enhanced conversion into the lipidated autophagosome-associated LC3-II. However, at a later stage iPA blocks the autophagic flux monitored by p62 accumulation, Luciferase reporter-based assay for LC3 turnover in living cells and fluorescence of a tandem RFP-GFP-LC3 construct. Impaired autophagic flux is due to the block of autophagosome-lysosome fusion through the defective localization and function of Rab7, whose prenylation is inhibited by iPA, resulting in a net inhibition of autophagy completion that finally leads to melanoma apoptotic cell death. AMPK silencing prevents apoptosis upon iPA treatment, whereas basal autophagosome turnover is still inhibited due to unprenylated Rab7. These results strongly support the advantage of targeting autophagy for therapeutic gain in melanoma and provide the preclinical rational to further investigate the antitumor action of iPA, able to coordinately induce autophagosome accumulation and inhibit the autophagic flux, independently targeting AMPK and Rab7 prenylation. This property may be particularly useful for the selective killing of tumors, like melanoma, that frequently develop chemotherapy resistance due to protective autophagy activation.

Recognition by natural killer cells of N6-isopentenyladenosine-treated human glioma cell lines

Cancer cell stress induced by cytotoxic agents promotes antitumor immune response. Here, we observed that N6-isopentenyladenosine (iPA), an isoprenoid modified adenosine with a well established anticancer activity, was able to induce a significant upregulation of cell surface expression of natural killer (NK) cell activating receptor NK Group 2 member D (NKG2D) ligands on glioma cells in vitro and xenografted in vivo. Specifically suboptimal doses of iPA (0.1 and 1 µM) control the selective upregulation of UL16-binding protein 2 on p53wt-expressing U343MG and that of MICA/B on p53mut-expressing U251MG cells. This event made the glioblastoma cells a potent target for NK cell-mediated recognition through a NKG2D restricted mechanism. p53 siRNA-mediated knock-down and pharmacological inhibition (pifithrin-α), profoundly prevented the iPA action in restoring the immunogenicity of U343MG cells through a mechanism that is dependent upon p53 status of malignancy. Furthermore, accordingly to the preferential recognition of senescent cells by NK cells, we found that iPA treatment was critical for glioma cells entry in premature senescence through the induction of S and G2/M phase arrest. Collectively, our results indicate that behind the well established cytotoxic and antiangiogenic effects, iPA can also display an immune-mediated antitumor activity. The indirect engagement of the innate immune system and its additional activity in primary derived patient's glioma cell model (GBM17 and GBM37), fully increase its translational relevance and led to the exploitation of the isoprenoid pathway for a valid therapeutic intervention in antiglioma research.

The isoprenoid derivative N6 -benzyladenosine CM223 exerts antitumor effects in glioma patient-derived primary cells through the mevalonate pathway

BACKGROUND AND PURPOSE

N⁶ -Isopentenyladenosine (i6A) is a modified nucleoside exerting in vitro and in vivo antiproliferative effects. We previously demonstrated that the actions of i6A correlate with the expression and activity of farnesyl pyrophosphate synthase (FPPS), a key enzyme involved in the mevalonate (MVA) pathway, which is aberrant in brain cancer. To develop new anti-glioma strategies, we tested related compounds exhibiting greater activity than i6A.

EXPERIMENTAL APPROACH

We designed and synthesized i6A derivatives characterized by the introduction of diverse chemical moieties in the N6 position of adenosine and tested for their efficacy in U87 cells and in primary glioma cultures, derived from patients. NMR-based structural analysis, molecular docking calculations and siRNA mediated knockdown were used to clarify the molecular basis of their action, targeting FPPS protein.

KEY RESULTS

CM223, the i6A derivative including a benzyl moiety in N6 position of adenine, showed marked activity in selectively targeting glioma cells, but not normal human astrocytes. This was due to induction of intrinsic pathways of apoptosis and inhibition of proliferation, along with blockade of FPPS-dependent protein prenylation, which counteracted oncogenic signalling mediated by EGF receptors.

CONCLUSION AND IMPLICATIONS

The biological effects together with structural data on interaction of CM223 with FPPS, provided additional evidence for the correlation of the i6A/CM223 antitumor activity with FPPS modulation. Because the MVA pathway is an important promising target, CM223 and its derivatives should be considered interesting active molecules in antiglioma research.