Macro-management of microRNAs in cell cycle progression of tumor cells and its implications in anti-cancer therapy

An Overview of the Role of MicroRNAs on Carcinogenesis: A Focus on Cell Cycle, Angiogenesis and Metastasis

In recent years, the importance of epigenetic markers in the carcinogenesis of different malignant neoplasms has been demonstrated, also demonstrating their utility for understanding metastatic spread and tumor progression in cancer patients. Among the different biomarkers, microRNAs represent a set of non-coding RNAs that regulate gene expression, having been involved in a wide variety of neoplasia acting in different oncogenic pathways. Both the overexpression and downregulation of microRNAs represent a complex interaction with various genes whose ultimate consequence is increased cell proliferation, tumor invasion and interaction with various driver markers. It should be noted that in current clinical practice, even though the combination of different microRNAs has been shown to be useful by different authors at diagnostic and prognostic levels, there are no diagnostic kits that can be used for the initial approach or to assess recurrences of oncological diseases. Previous works have cited microRNAs as having a critical role in several carcinogenic mechanisms, ranging from cell cycle alterations to angiogenesis and mechanisms of distant metastatic dissemination. Indeed, the overexpression or downregulation of specific microRNAs seem to be tightly involved in the modulation of various components related to these processes. For instance, cyclins and cyclin-dependent kinases, transcription factors, signaling molecules and angiogenic/antiangiogenic products, among others, have been recognized as specific targets of microRNAs in different types of cancer. Therefore, the purpose of this article is to describe the main implications of different microRNAs in cell cycle alterations, metastasis and angiogenesis, trying to summarize their involvement in carcinogenesis.

MiREDiBase, a manually curated database of validated and putative editing events in microRNAs

MicroRNAs (miRNAs) are regulatory small non-coding RNAs that function as translational repressors. MiRNAs are involved in most cellular processes, and their expression and function are presided by several factors. Amongst, miRNA editing is an epitranscriptional modification that alters the original nucleotide sequence of selected miRNAs, possibly influencing their biogenesis and target-binding ability. A-to-I and C-to-U RNA editing are recognized as the canonical types, with the A-to-I type being the predominant one. Albeit some bioinformatics resources have been implemented to collect RNA editing data, it still lacks a comprehensive resource explicitly dedicated to miRNA editing. Here, we present MiREDiBase, a manually curated catalog of editing events in miRNAs. The current version includes 3,059 unique validated and putative editing sites from 626 pre-miRNAs in humans and three primates. Editing events in mature human miRNAs are supplied with miRNA-target predictions and enrichment analysis, while minimum free energy structures are inferred for edited pre-miRNAs. MiREDiBase represents a valuable tool for cell biology and biomedical research and will be continuously updated and expanded at https://ncrnaome.osumc.edu/miredibase .

Detecting and Characterizing A-To-I microRNA Editing in Cancer

Adenosine to inosine (A-to-I) editing consists of an RNA modification where single adenosines along the RNA sequence are converted into inosines. Such a biochemical transformation is catalyzed by enzymes belonging to the family of adenosine deaminases acting on RNA (ADARs) and occurs either co- or post-transcriptionally. The employment of powerful, high-throughput detection methods has recently revealed that A-to-I editing widely occurs in non-coding RNAs, including microRNAs (miRNAs). MiRNAs are a class of small regulatory non-coding RNAs (ncRNAs) acting as translation inhibitors, known to exert relevant roles in controlling cell cycle, proliferation, and cancer development. Indeed, a growing number of recent researches have evidenced the importance of miRNA editing in cancer biology by exploiting various detection and validation methods. Herein, we briefly overview early and currently available A-to-I miRNA editing detection and validation methods and discuss the significance of A-to-I miRNA editing in human cancer.

In silico analysis of the association of hsa-miR-16 expression and cell survival in MDA-MB-231 breast cancer cells subjected to photodynamic therapy

BACKGROUND

Breast cancer is the most common malignancy effecting women, and the triple-negative breast cancer (TNBC) subtype is particularly aggressive. This study aimed to evaluate the differential expression pattern of microRNAs (miRNAs) between untreated MDA-MB-231 cells (TNBC cell model) and those that survived photodynamic therapy (PDT) to gain insights into cell survival mechanisms.

METHODS

Two PDT cycles were applied to MDA-MB-231 cells, using δ-aminolevulinic acid (ALA) followed by laser light at 635 nm. RNA was obtained from cells surviving PDT and untreated cells. The miRNAs expression profile was analyzed to detect the differences between the two groups. The potential target network of hsa-miR-16 was examined in silico with the integrative database Ingenuity® Pathway Analysis software.

RESULTS

After the first and second PDT cycles, 17.8% and 49.6% of the MDA-MB-231 cells were viable. Microarray profiling of miRNAs showed decreased hsa-miR-16 expression (p < 0.05) in MDA-MB-231 cells surviving PDT when compared to the control cells. The predicted downstream targets of hsa-miR-16 were: 1) tumor suppressor protein 53; 2) molecules related to the cell cycle, such as cyclin D1, D3, and E1, and checkpoint kinase 1; 3) cell proliferation molecules, including fibroblast growth factor 1, 2 and 7 and fibroblast growth factor receptor 1; and 4) apoptosis-related molecules, consisting of BCL-2, B-cell leukemia/lymphoma 2, caspase 3, and cytochrome c.

CONCLUSIONS

The differential expression of hsa-miR-16 between untreated MDA-MB-231 cells and those surviving PDT has not been previously reported. There was a lower expression of hsa-miR-16 in treated cells, which probably altered its downstream target network. In silico analysis predicted, a network related to the cell cycle, proliferation and apoptosis. These results are congruent with previous descriptions of hsa-miR-16 as a tumor suppressor and suggest that the treated population has increased their capacity to survive.

Gene expression changes in arterial and venous endothelial cells exposed to gestational diabetes mellitus

We investigated the molecular changes in fetoplacental blood vessel endothelial cells in gestational diabetes mellitus (GDM). Raw gene expression profile data of arterial and venous endothelial cells from GDM complicated pregnancies and healthy controls were downloaded and used for bioinformatic analysis. There were two differentially expressed genes (DEGs) in venous endothelial cells and 178 DEGs in arterial endothelial cells induced by GDM. The altered genes were clustered to pathways associated with cell cycle, p53 signaling pathway, and cellular senescence. The disease associated gene-pathway network that was constructed comprised eight down-regulated genes (including FBXO5, CCNB1, and CDK1), one up-regulated gene (CCND2), hsa04068: FoxO signaling pathway and hsa04114: Oocyte mitosis pathway. CCND2 was a significant node in the microRNA (miRNA)-target network, which was regulated by seven miRNAs that included hsa-miR-1299, hsa-miR-1200, and hsa-miR-miR-593-5p. FBXO5 was a significant node regulated by two miRNAs. CCND2 and FBXO5 were also the significant nodes in the transcriptional factors-target network and integrated regulatory network. The cell cycle pathway was significantly altered in arterial endothelial cells during GDM, which was involved with the differential expression of CCND2 and FBXO5.

MicroRNA-217 functions as a tumor suppressor in cervical cancer cells through targeting Rho-associated protein kinase 1

The abnormal expression of microRNAs (miRNAs/miRs) has been widely reported in various tumor types. miR-217 was demonstrated to be aberrantly expressed in a number of tumors, including pancreatic adenocarcinoma and osteosarcoma; however, its specific expression pattern has never been investigated in cervical cancer cells. Compared with normal control, the level of Rho-associated protein kinase 1 (ROCK1) expression was markedly increased in cervical cancer tissues and cells compared with that in non-cancerous tissues and cells. The expression of miR-217 was significantly reduced in cervical cancer tissues and cell lines. Overexpression of miR-217 could suppress colony formation and the cell invasion capacity of SiHa and HeLa cells. Flow cytometry indicated that miR-217 significantly increased cell apoptosis in SiHa and HeLa cells. Dual-luciferase reporter assays demonstrated that ROCK1 was a target gene of miR-217. In addition, overexpression of ROCK1 also led to an increased invasion capacity in SiHa cells, even when miR-217 was inhibited, indicating that the anti-invasive effects of miR-217 were mediated through ROCK1. In summary, the results of the present study indicated that miR-217 functions as a tumor suppressor in cervical cancer cells, primarily by targeting ROCK1.

Ginkgetin induces G2-phase arrest in HCT116 colon cancer cells through the modulation of b‑Myb and miRNA34a expression

Ginkgetin has been reported to display antitumor activity. However, the relevant pathway integrating cell cycle regulation and signaling pathways involved in growth inhibition in CRC cells remains to be identified. In this study, ginkgetin-treated HCT116 CRC cells exhibited significant dose-dependent growth inhibition with a GI50 value of 4.0 µM for 48-h treatment, together with apoptosis, via G2-phase cell cycle arrest. When HCT116 cells were treated with 10 µM ginkgetin for 48 h, the percentage of cells in G2/M phase increased by 2.2-fold (43.25%) versus the untreated control (19.69%). Ginkgetin regulated the expression of genes that are critically involved in G2 phase arrest cells, such as b‑Myb, CDC2 and cyclin B1. Furthermore, we found that the suppression of b‑Myb expression by ginkgetin was rescued ~5.1-fold by treatment with a miR-34a inhibitor (500 nM) and b‑Myb was downregulated by >80% by 100 nM miR‑34a mimic. These data suggest that the miRNA34a/b‑Myb/cyclin B1 cascade plays a critical role in ginkgetin-induced G2 cell cycle arrest, as well as in the inhibition of HCT116 cell proliferation. Moreover, the administration of ginkgetin (10 mg/kg) reduced tumor volumes by 36.5% and tumor weight by 37.6% in the mice xenografted with HCT116 cells relative to their vehicle-treated counterparts. Therefore, ginkgetin is the first compound shown to regulate b‑Myb by modulating miR-34a, and we suggest the use of ginkgetin as an inducer of G2 arrest for the treatment of CRC.

Regulation of multidrug resistance by microRNAs in anti-cancer therapy

Multidrug resistance (MDR) remains a major clinical obstacle to successful cancer treatment. Although diverse mechanisms of MDR have been well elucidated, such as dysregulation of drugs transporters, defects of apoptosis and autophagy machinery, alterations of drug metabolism and drug targets, disrupti on of redox homeostasis, the exact mechanisms of MDR in a specific cancer patient and the cross-talk among these different mechanisms and how they are regulated are poorly understood. MicroRNAs (miRNAs) are a new class of small noncoding RNAs that could control the global activity of the cell by post-transcriptionally regulating a large variety of target genes and proteins expression. Accumulating evidence shows that miRNAs play a key regulatory role in MDR through modulating various drug resistant mechanisms mentioned above, thereby holding much promise for developing novel and more effective individualized therapies for cancer treatment. This review summarizes the various MDR mechanisms and mainly focuses on the role of miRNAs in regulating MDR in cancer treatment.

MicroRNA aberrations: An emerging field for gallbladder cancer management

Gallbladder cancer (GBC) is infrequent but most lethal biliary tract malignancy characterized by an advanced stage diagnosis and poor survival rates attributed to absence of specific symptoms and effective treatment options. These necessitate development of early prognostic/predictive markers and novel therapeutic interventions. MicroRNAs (miRNAs) are small, non-coding RNA molecules that play a key role in tumor biology by functioning like tumor suppressor- or onco- genes and their aberrant expression are associated with the pathogenesis of several neoplasms with overwhelming clinical implications. Since miRNA signature is tissue specific, here, we focused on current data concerning the miRNAs abberations in GBC pathogenesis. In GBC, miRNAs with tumor suppressor activity (miR-135-5p, miR-335, miR-34a, miR-26a, miR-146b-5p, Mir-218-5p, miR-1, miR-145, mir-130a) were found downregulated, while those with oncogenic property (miR-20a, miR-182, mir-155) were upregulated. The expression profile of miRNAs was significantly associated with GBC prognosis and prediction, and forced over-expression/ inhibition of these miRNAs was shown to affect tumor growth and development. Further, differential expression of miRNAs in the blood samples of GBC patients suggest miRNAs as promising noninvasive biomarker. Thus, miRNAs represent potential candidate for GBC management, though many hurdles need to be overcome before miRNAs therapy can be clinically applied to GBC prevention and treatment.

MicroRNA expression and its association with DNA repair in preimplantation embryos

Active DNA repair pathways are crucial for preserving genomic integrity and are likely among the complex mechanisms involved in the normal development of preimplantation embryos. MicroRNAs (miRNA), short non-coding RNAs, are key regulators of gene expression through the post-transcriptional and post-translational modification of mRNA. The association of miRNA expression with infertility or polycystic ovarian syndrome has been widely investigated; however, there are limited data regarding the importance of miRNA regulation in DNA repair during preimplantation embryo development. In this article, we review normal miRNA biogenesis and consequences of aberrant miRNA expression in the regulation of DNA repair in gametes and preimplantation embryos.

MicroRNAs and Cancer Drug Resistance

The discovery of small regulatory noncoding RNAs revolutionized our thinking on gene regulation. The class of microRNAs (miRs), a group of small noncoding RNAs (20-22 nt in length) that bind imperfectly to the 3'-untranslated region of target mRNA, has been insistently implicated in several pathological conditions including cancer. Indeed, major hallmarks of cancer, such as cell differentiation, cell proliferation, cell cycle, cell survival, and cell invasion, has been described as being regulated by miRs. Recent studies have also implicated miRs in cancer drug resistance. Regardless of the several studies done until now, drug resistance still is a burden for cancer therapy and patients' outcome, often resulting in more aggressive tumors that tend to metastasize to distant organs. Hence, with this review, we aim to summarize the miRs that influence molecular pathways that are involved in cancer drug resistance, such as drug metabolism, drug influx/efflux, DNA damage response (DDR), epithelial-to-mesenchymal transition (EMT), and cancer stem cells.

MicroRNA‑34a attenuates the proliferation, invasion and metastasis of gastric cancer cells via downregulation of MET

Proliferation, invasion and metastasis are key features of gastric cancer, contributing to high mortality rates in patients with gastric cancer worldwide. As a direct target of p53, the functions of microRNA (miR)‑34a are important, but controversial, in the progression of gastric cancer. In the present study, the clinical importance of miR‑34a in GC specimens (n=40) were investigated and were confirmed in an independent cohort from The Cancer Genome Atlas (TCGA; n=352). The prognostic value of miR‑34a was analyzed using a Kaplan‑Meier survival curve in the TCGA cohort, in combination with complete follow‑up data (n=157). The level of miR‑34a was detected in the human gastric cancer cell line and normal gastric epithelial cell line. The effect of miR‑34a on proliferation and invasion were evaluated using Cell Counting Kit 8, colony formation and cell invasion assays. The molecular basis of miR‑34a was determined by bioinformatics prediction. The correlation between miR‑34a and MET was assessed using reverse transcription‑quantitative polymerase chain reaction and western blot analyses. The results indicated that miR‑34a was downregulated in the gastric cancer tissues, compared with the normal gastric tissues (P<0.01). miR‑34a was negatively correlated with the depth of invasion and lymph node metastasis of gastric cancer (P<0.01). In the TCGA cohort, the levels of miR‑34a were lower in T3 and T4 tumor stages, compared with the level in the T1 stage, and low levels of miR‑34a predicted significantly longer survival rates in patients with GC (P<0.05). miR‑34a also attenuated the proliferation ability, and inhibited the colony formation and cell invasion abilities of the cells (P<0.01). A negative correlation was observed between miR‑34a and MET in gastric cancer (P<0.01; r=‑0.9526), and >60% of cases exhibited consistent expression of miR‑34a and MET in gastric cancer (P<0.01). In conclusion, miR‑34a was associated with the clinicopathological features of gastric cancer and was a valuable predictor of patient prognosis. miR‑34a acted as a tumor suppressor to inhibit gastric cancer proliferation and invasion via the downregulation of MET.

MicroRNA-126 is down-regulated in human esophageal squamous cell carcinoma and inhibits the proliferation and migration in EC109 cell via PI3K/AKT signaling pathway

MicroRNA-126 (miR-126) was found down-regulated in different types of cancer including esophageal squamous cell carcinoma (ESCC). However, the onco-genetic role of miR-126 in ESCC still remains unknown. In the present study, we found the relative expression of miR-126 in ESCC was significant decreased in ESCC tissues compared to adjacent normal tissues. Overexpression of miR-126 in EC109 cells resulted in significant decrease in cell proliferation, colon formation and migration. PI3K regulatory subunit p85 beta (PIK3R2), a member of PI3K/AKT signaling pathway was found upregulated in ESCC tissues and there is a negative relation between expression of PIK3R2 and miR-126. Restoration of miR-126 in EC109 cells induced a reduction in PIK3R2 protein levels, accompanied with a substantial reduction in phosphorylated AKT levels in EC109 cells, suggesting impairment in PI3K/AKT signaling pathway. The luciferase reporter assay confirmed that PIK3R2 was a direct target of miR-126. Furthermore, we also indicated overexpression of miR-126 suppresses G2/M transition in EC109 cells. Taken together, our study suggests that miR-126 functions as a potential tumor suppressor in ESCC progression via regulating PI3K/AKT signaling pathway partly by targeting PIK3R2, and targeting of miR-126 may provide a novel strategy for the diagnosis and treatment of ESCC.

TGF-beta induced RBL2 expression in renal cancer cells by down-regulating miR-93

PURPOSE

TGF-beta can induce G1 arrest via many mechanisms including up-regulating p21, p27, and Rb. However, as the member of Rb family, whether RBL2 is induced by TGF-beta treatment remains exclusive.

METHODS

The expression of RBL2 and miR-93 after TGF-beta treatment was determined by quantitative real-time PCR and western blot. The growth of renal cancer cells was determined by CCK-8 assays and cell cycle was determined by PI staining. The binding of miR-93 on RBL2 3'-UTR was determined by double luciferase system.

RESULTS

In renal cancer cells, TGF-beta treatment induced expression of RBL2 in a time- and concentration-dependent manner, and RBL2 mediated TGF-beta induced growth inhibition and cell cycle arrest in renal cancer cells. Furthermore, we found that miR-93 directly targeted RBL2 by binding to its 3'-UTR in renal cancer cells. Over-expression of miR-93 significantly reduced the expression of RBL2, whereas knock down of miR-93 up-regulated the expression of RBL2. More importantly, TGF-beta treatment inhibited miR-93 expression, which resulted in up-regulation of RBL2 after TGF-beta treatment.

CONCLUSION

TGF-beta induced RBL2 expression through down-regulating miR-93 in renal cancer cells. The newly identified TGF-beta/miR-93/RBL2 signal pathway reveals a new mechanism of TGF-beta induced growth arrest in renal cancer.

Characterization of microRNA expression in serous ovarian carcinoma

Serous ovarian cancer is a major gynecologic malignancy with a poor 5‑year survival rate. However, little is known regarding the behavior and genetics of ovarian tumorigenesis. MicroRNAs (miRNAs) have been shown to be dysregulated in ovarian carcinomas. To assess the miRNA expression profiles in serous ovarian cancer, we defined the patterns of miRNA expression in 100 formalin‑fixed, paraffin‑embedded ovarian cancer tissues blocks as well as 50 corresponding normal oviduct tissues using miRNA microarray. MiRNA expression profiling showed that 63 miRNAs were downregulated and 43 miRNAs were upregulated in serous ovarian cancer tissues compared with control tissues. The expression of five dysregulated miRNAs was validated using quantitative polymerase chain reaction (RT‑qPCR). GO term and pathway analysis revealed that the biological process of the cell cycle was significantly enriched and the MAPK signaling pathway was highly involved in the progression of ovarian cancer. The results suggested that the aberrant expression of miRNAs is involved in ovarian carcinogenesis and thus these miRNAs may function as diagnostic and prognostic biomarkers.

Friend or foe: the role of microRNA in chemotherapy resistance

Chemotherapy has been widely used in treating cancer patients. Despite the tremendous progress in cancer treatment achieved during the last decades, drug resistance still accounts for most of the tumor relapses in chemotherapy-treated patients. Emerging evidence shows that microRNAs play an important role in regulating the drug sensitivity of tumor cells. However, the mechanism of microRNA-mediated drug resistance is not fully understood. Current data suggest that microRNAs can be categorized as oncogenic or tumor-suppressive based on their functions and targets. In tumor cells undergoing drug treatment, microRNAs can function either by decreasing expression of genes associated with multiple drug resistance or by promoting escape from apoptosis and inducing tumor stem cell development. This review aims to provide an updated understanding of the role of microRNAs in regulating chemotherapy resistance and a discussion of potential therapeutic applications.

Simultaneously expressed miR-424 and miR-381 synergistically suppress the proliferation and survival of renal cancer cells---Cdc2 activity is up-regulated by targeting WEE1

OBJECTIVES

MiRNAs are intrinsic RNAs that interfere with protein translation. Few studies on the synergistic effects of miRNAs have been reported. Both miR-424 and miR-381 have been individually reported to be involved in carcinogenesis. They share a common putative target, WEE1, which is described as an inhibitor of G2/M progression. Here, we studied the synergistic effects of miR-424 and miR-381 on renal cancer cells.

METHODS

The viability of 786-O cells was analyzed after transfection with either a combination of miR-424 and miR-381 or each miRNA alone. We investigated cell cycle progression and apoptosis with flow cytometry. To confirm apoptosis and the abrogation of G2/M arrest, we determined the level of pHH3, which is an indicator of mitosis, and caspase-3/7 activity. The expression levels of WEE1, Cdc25, γH2AX, and Cdc2 were manipulated to investigate the roles of these proteins in the miRNA-induced anti-tumor effects. To verify that WEE1 was a direct target of both miR-424 and miR-381, we performed a dual luciferase reporter assay.

RESULTS

We showed that the combination of these miRNAs synergistically inhibited proliferation, abrogated G2/M arrest, and induced apoptosis. This combination led to Cdc2 activation through WEE1 inhibition. This regulation was more effective when cells were treated with both miRNAs than with either miRNA alone, indicating synergy between these miRNAs. WEE1 was verified to be a direct target of each miRNA according to the luciferase reporter assay.

CONCLUSIONS

These data clearly demonstrate that these two miRNAs might synergistically act as novel modulators of tumorigenesis by down-regulating WEE1 expression in renal cell cancer cells.

MicorRNA 106b ∼ 25 cluster and gastric cancer

Conventional strategies for the early diagnosis and treatment of gastric cancer are not yet satisfactory, and it calls for better diagnosis and treatments based on a deeper understanding of the molecular mechanisms. It has been revealed that the number of verified human microRNA (miRNA) expression contribute to the initiation and progression of cancer. Among them, miR-106b ∼ 25 cluster is of particular interest. The miRNA-106b ∼ 25 cluster is composed of the highly conserved miRNA-106b, miRNA-93 and miRNA-25. The miRNA-106b ∼ 25 polycistron exerted potential proliferative, anti-apoptotic and cell cycle-promoting effects on cancer cells. Over-expression of the miRNA-106b ∼ 25 cluster is known to overcome TGF-beta mediated growth suppression via targeting p21 and Bim. This cluster can additionally target the inhibitory Smad7 protein and increase TGF-beta RI which is sufficient to induce epithelial-to-mesenchymal transition (EMT). MiRNA-93 can promote angiogenesis. The tumor suppressor genes RB and PTEN are the direct targets of miRNA-106b ∼ 25. Especially, miRNA-106b ∼ 25 clusters play an important role in oncogenesis of gastric cancer. Focus on the essential role in tumorgenisis and extremely low expression of miRNA-106b ∼ 25 in normal tissues, it maybe an appropriate target of gastric cancer treatment and a novel biomarkers for detecting gastric cancer.

Metallofullerol nanoparticles with low toxicity inhibit tumor growth by induction of G0/G1 arrest

AIMS

[Gd@C(82)(OH)(22)](n) is a new type of nanoparticle with potent antineoplastic activity and low toxicity compared with traditional drugs. In this study, we explored, for the first time, the effect of [Gd@C(82)(OH)(22)](n) on the cell cycle using human breast cancer MCF-7 and human umbilical vein endothelial ECV304 cell lines by flow cytometry.

METHODS

Cell viability was assessed through CCK-8 assay, and MCF-7 tumor-bearing mice were examined after 2 weeks of treatment with [Gd@C(82)(OH)(22)](n). Cell cycle-related gene expression was detected by microarray and confirmed by real-time PCR and RNAi.

RESULTS

Cell viability studies confirmed that [Gd@C(82)(OH)(22)](n) inhibits breast cancer effectively with very low toxicity. Flow cytometric data and microarray results reveal that [Gd@C(82)(OH)(22)](n) mediates G0/G1 arrest in both cell lines by regulating the expression of several genes, such as cyclin D2, cyclin E and CDK4, among others, in the related cell cycle.

CONCLUSION

Results further demonstrated that [Gd@C(82)(OH)(22)](n) could inhibit tumor growth by inducing tumor cell and vein endothelial cell G0/G1 arrest, which may explain the low toxicity of [Gd@C(82)(OH)(22)](n).