Insights into the involvement of noncoding RNAs in 5-fluorouracil drug resistance

5-Fluorouracil resistance-based immune-related gene signature for COAD prognosis

Background

Drug resistance is the primary obstacle to advanced tumor therapy and the key risk factor for tumor recurrence and death. 5-Fluorouracil (5-FU) chemotherapy is the most common chemotherapy for individuals with colorectal cancer, despite numerous options.

Methods

The Gene Expression Omnibus database was utilized to extract expression profile data of HCT-8 human colorectal cancer wild-type cells and their 5-FU-induced drug resistance cell line. These data were used to identify 5-FU resistance-related differentially expressed genes (5FRRDEGs), which intersected with the colorectal adenocarcinoma (COAD) transcriptome data provided by the Cancer Genome Atlas Program database. A prognostic signature containing five 5FRRDEGs (GOLGA8A, KLC3, TIGD1, NBPF1, and SERPINE1) was established after conducting a Cox regression analysis. We conducted nomogram development, drug sensitivity analysis, tumor immune microenvironment analysis, and mutation analysis to assess the therapeutic value of the prognostic qualities.

Results

We identified 166 5FRRDEGs in patients with COAD. Subsequently, we created a prognostic model consisting of five 5FRRDEGs using Cox regression analysis. The patients with COAD were divided into different risk groups by risk score; the high-risk group demonstrated a worse prognosis than the low-risk group.

Conclusion

In summary, the 5FRRDEG-based prognostic model is an effective tool for targeted therapy and chemotherapy in patients with COAD. It can accurately predict the survival prognosis of these patients as well as to provide the direction for exploring the resistance mechanism underlying COAD.

The Critical Function of microRNAs in Developing Resistance against 5- Fluorouracil in Cancer Cells

Although there have been significant advancements in cancer treatment, resistance and recurrence in patients make it one of the leading causes of death worldwide. 5-fluorouracil (5-FU), an antimetabolite agent, is widely used in treating a broad range of human malignancies. The cytotoxic effects of 5-FU are mediated by the inhibition of thymidylate synthase (TYMS/TS), resulting in the suppression of essential biosynthetic activity, as well as the misincorporation of its metabolites into RNA and DNA. Despite its huge benefits in cancer therapy, the application of 5-FU in the clinic is restricted due to the occurrence of drug resistance. MicroRNAs (miRNAs) are small, non-coding RNAs that act as negative regulators in many gene expression processes. Research has shown that changes in miRNA play a role in cancer progression and drug resistance. This review examines the role of miRNAs in 5-FU drug resistance in cancers.

Recent Advances in Drug Discovery for Triple-Negative Breast Cancer Treatment

Triple-negative breast cancer (TNBC) is one of the most heterogeneous and aggressive breast cancer subtypes with a high risk of death on recurrence. To date, TNBC is very difficult to treat due to the lack of an effective targeted therapy. However, recent advances in the molecular characterization of TNBC are encouraging the development of novel drugs and therapeutic combinations for its therapeutic management. In the present review, we will provide an overview of the currently available standard therapies and new emerging therapeutic strategies against TNBC, highlighting the promises that newly developed small molecules, repositioned drugs, and combination therapies have of improving treatment efficacy against these tumors.

Review of 5-FU resistance mechanisms in colorectal cancer: clinical significance of attenuated on-target effects

The emergence of chemoresistant disease during chemotherapy with 5-Fluorouracil-based (5-FU-based) regimens is an important factor in the mortality of metastatic CRC (mCRC). The causes of 5-FU resistance are multi-factorial, and besides DNA mismatch repair deficiency (MMR-D), there are no widely accepted criteria for determining which CRC patients are not likely to be responsive to 5-FU-based therapy. Thus, there is a need to systematically understand the mechanistic basis for 5-FU treatment failure and an urgent need to develop new approaches for circumventing the major causes of 5-FU resistance. In this manuscript, we review mechanisms of 5-FU resistance with an emphasis on: (1) altered anabolic metabolism limiting the formation of the primary active metabolite Fluorodeoxyuridylate (5-Fluoro-2'-deoxyuridine-5'-O-monophosphate; FdUMP); (2) elevated expression or activity of the primary enzymatic target thymidylate synthase (TS); and (3) dysregulated programmed cell death as important causes of 5-FU resistance. Importantly, these causes of 5-FU resistance can potentially be overcome through the use of next-generation fluoropyrimidine (FP) polymers (e.g., CF10) that display reduced dependence on anabolic metabolism and more potent TS inhibitory activity.

Curcumin as an Enhancer of Therapeutic Efficiency of Chemotherapy Drugs in Breast Cancer

Female breast cancer is the world’s most prevalent cancer in 2020. Chemotherapy still remains a backbone in breast cancer therapy and is crucial in advanced and metastatic breast cancer treatment. The clinical efficiency of chemotherapy regimens is limited due to tumor heterogeneity, chemoresistance, and side effects. Chemotherapeutic drug combinations with natural products hold great promise for enhancing their anticancer efficacy. Curcumin is an ideal chemopreventive and chemotherapy agent owning to its multitargeting function on various regulatory molecules, key signaling pathways, and pharmacological safety. This review aimed to elucidate the potential role of curcumin in enhancing the efficacy of doxorubicin, paclitaxel, 5-fluorouracil, and cisplatin via combinational therapy. Additionally, the molecular mechanisms underlying the chemosensitizing activity of these combinations have been addressed. Overall, based on the promising therapeutic potential of curcumin in combination with conventional chemotherapy drugs, curcumin is of considerable value to develop as an adjunct for combination chemotherapy with current drugs to treat breast cancer. Furthermore, this topic may provide the frameworks for the future research direction of curcumin–chemotherapy combination studies and may benefit in the development of a novel therapeutic strategy to maximize the clinical efficacy of anticancer drugs while minimizing their side effects in the future breast cancer treatment.

Human Satellite III long non-coding RNA imparts survival benefits to cancer cells

Long non-coding RNAs (lncRNAs) are heterogeneous group of transcripts that lack coding potential and have essential roles in gene regulations. Recent days have seen an increasing association of non-coding RNAs with human diseases, especially cancers. One interesting group of non-coding RNAs strongly linked to cancers are heterochromatic repetitive Satellite RNAs. Satellite RNAs are transcribed from pericentromeric heterochromatic region of the human chromosomes. Satellite II RNA, most extensively studied, is upregulated in wide variety of epithelial cancer. Similarly, alpha satellite is over expressed in BRCA1- deficient tumors. Though much is known about alpha satellites and SatII repeats, little is known about Satellite III (SatIII) lncRNAs in human cancers. SatIII repeats, though transcriptionally silent in normal conditions is actively transcribed under condition of stress, mainly heat shock. In the present study, we show that colon and breast cancer cells aberrantly transcribes SatIII, in a Heat shock factor I (HSF1)-independent manner. Our study also reveals that, overexpression of SatIII RNA favours cancer cell survival by overriding chemo drug-induced cell death. Interestingly, knockdown of SatIII sensitizes cells towards chemotherapeutic drugs. This sensitization is possibly mediated by restoration of p53 protein expression that facilitates cell death. Heat shock however helps SatIII to continue with its pro-cell survival function. Our results, therefore suggest SatIII to be an important regulator of human cancers. Induction of SatIII is not only a response to the oncogenic stress but also facilitates cancer progression by a distinct pathway that is different from heat stress pathway. This article is protected by copyright. All rights reserved.

The Role of Non-Coding RNAs in Breast Cancer Drug Resistance

Breast cancer (BC) is one of the commonly occurring malignancies in females worldwide. Despite significant advances in therapeutics, the mortality and morbidity of BC still lead to low survival and poor prognosis due to the drug resistance. There are certain chemotherapeutic, endocrine, and target medicines often used for BC patients, including anthracyclines, taxanes, docetaxel, cisplatin, and fluorouracil. The drug resistance mechanisms of these medicines are complicated and have not been fully elucidated. It was reported that non-coding RNAs (ncRNAs), such as micro RNAs (miRNA), long-chain non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) performed key roles in regulating tumor development and mediating therapy resistance. However, the mechanism of these ncRNAs in BC chemotherapeutic, endocrine, and targeted drug resistance was different. This review aims to reveal the mechanism and potential functions of ncRNAs in BC drug resistance and to highlight the ncRNAs as a novel target for achieving improved treatment outcomes for BC patients.

A novel view on an old drug, 5-fluorouracil: an unexpected RNA modifier with intriguing impact on cancer cell fate

5-Fluorouracil (5-FU) is a chemotherapeutic drug widely used to treat patients with solid tumours, such as colorectal and pancreatic cancers. Colorectal cancer (CRC) is the second leading cause of cancer-related death and half of patients experience tumour recurrence. Used for over 60 years, 5-FU was long thought to exert its cytotoxic effects by altering DNA metabolism. However, 5-FU mode of action is more complex than previously anticipated since 5-FU is an extrinsic source of RNA modifications through its ability to be incorporated into most classes of RNA. In particular, a recent report highlighted that, by its integration into the most abundant RNA, namely ribosomal RNA (rRNA), 5-FU creates fluorinated active ribosomes and induces translational reprogramming. Here, we review the historical knowledge of 5-FU mode of action and discuss progress in the field of 5-FU-induced RNA modifications. The case of rRNA, the essential component of ribosome and translational activity, and the plasticity of which was recently associated with cancer, is highlighted. We propose that translational reprogramming, induced by 5-FU integration in ribosomes, contributes to 5-FU-driven cell plasticity and ultimately to relapse.

A Direct and Sensitive Method for Determination of 5-Fluorouracil in Colorectal Cancer Cells: Evaluating the Effect of Stromal Cell on Drug Resistance of Cancer Cells

Fibroblasts in the stroma play a critical role in tumor evolution. In this study, we assessed the influence of colonic fibroblasts on colon cancer cells treated with 5-fluorouracil (5-FU), and mouse colon cancer cell lines MC38 and colonic fibroblasts NIH3T3 were used in this study. A sensitive and rapid UHPLC-MS/MS method for the quantitation of 5-FU from the cell and their medium has been successfully developed and validated. The cells were lysed with methanol, and the mixture was evaporated and then redissolved to extract intracellular 5-FU. The analysis was performed on UHPLC-MS/MS using an Atlantis T3-C18 column (3 μm, 2. 1 ∗ 100 mm) and gradient elution with acetonitrile and 0.1% formic acid in water. Method validation included the following parameters: the matrix effect range 88.82%-93.64% and the recovery range 93.52%-94.56%. The intraday and interday precision and accuracy were <11% and within ±6%, and the stability, specificity, carry-over, dilution effect, and linearity all conformed to the criteria. The method was applied to detect the concentration of 5-FU inside cells and cell culture medium. The preliminary results present that NIH3T3 could enhance the drug resistance of MC38 to 5-FU with a decreased intracellular concentration of 5-FU in MC38, which showed a positive relationship with NIH3T3 number.

Emerging role of NRF2 in ROS-mediated tumor chemoresistance

Chemoresistance is a central cause for the tumor management failure. Cancer cells disrupt the redox homeostasis through reactive oxygen species (ROS) regulatory mechanisms, leading to tumor progression and chemoresistance. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of neutralizing cellular ROS and restoring redox balance. Understanding the role of NRF2 in ROS-mediated chemoresistance can be helpful in the development of chemotherapy strategies with better efficiency. In this review, we sum up the roles of ROS in the development of chemoresistance to classical chemotherapy agents including cisplatin, 5-fluorouracil, gemcitabine, oxaliplatin, paclitaxel, and doxorubicin, and how to overcome ROS-mediated tumor chemoresistance by targeting NRF2. Finally, we propose that targeting NRF2 might be a promising strategy to resist ROS-driven chemoresistance and acquire better efficacy in cancer treatment.

Potential of miR-21 to Predict Incomplete Response to Chemoradiotherapy in Rectal Adenocarcinoma

Background: Patients with locally advanced rectal adenocarcinoma (LARC) are treated with neoadjuvant chemoradiotherapy (CRT). However, biomarkers for patient selection are lacking, and the association between miRNA expression and treatment response and oncological outcomes is unclear.

Objectives: To investigate miRNAs as predictors of response to neoadjuvant CRT and its association with oncological outcomes.

Methods: This retrospective study analyzed miRNA expression (miR-16, miR-21, miR-135b, miR-145, and miR-335) in pre- and post-chemoradiation rectal adenocarcinoma tissue and non-neoplastic mucosa in 91 patients treated with neoadjuvant CRT (50.4 Gy) and proctectomy. Two groups were defined: a pathological complete responders group (tumor regression grade—TRG 0) and a pathological incomplete responders group (TRG 1, 2, and 3).

Results: miR-21 and miR-135b were upregulated in tumor tissue of incomplete responders comparing with non-neoplastic tissue (p = 0.008 and p < 0.0001, respectively). Multivariate analysis showed significant association between miR-21 in pre-CRT tumor tissue and response, with a 3.67 odds ratio (OR) of incomplete response in patients with higher miR-21 levels (p = 0.04). Although with no significance, patients treated with 5-fluorouracil (5-FU) presented reduced odds of incomplete response compared with those treated with capecitabine (OR = 0.19; 95% confidence interval (CI) 0.03–1.12, p = 0.05). Moreover, significant differences were seen in overall survival (OS) in relation to clinical TNM stage (p = 0.0004), cT (p = 0.0001), presence of distant disease (p = 0.002), mesorectal tumor deposits (p = 0.003), and tumor regression grade (p = 0.04).

Conclusion: miR-21 may predict response to CRT in rectal cancer (RC).

EGCG sensitizes chemotherapeutic-induced cytotoxicity by targeting the ERK pathway in multiple cancer cell lines

Epigallocatechin-3-gallate (EGCG), a major polyphenol component of green tea, presents anticancer efficacy. However, its exact mechanism of action is not known. In this study, we evaluated the effect of EGCG alone or in combination with current chemotherapeutics [gemcitabine, 5-flourouracil (5-FU), and doxorubicin] on pancreatic, colon, and lung cancer cell growth, as well as the mechanisms involved in the combined action. EGCG reduced pancreatic, colon, and lung cancer cell growth in a concentration and time-dependent manner. EGCG strongly induced apoptosis and blocked cell cycle progression. Moreover, EGCG enhanced the growth inhibitory effect of 5-FU and doxorubicin. Of note, EGCG enhanced 5-FU's and doxorubicin's effect on apoptosis, but not on cell cycle. Mechanistically, EGCG reduced ERK phosphorylation concentration-dependently, and sensitized gemcitabine, 5-FU, and doxorubicin to further suppress ERK phosphorylation in multiple cancer cell lines. In conclusion, EGCG presents a strong anticancer effect in pancreatic, colon, and lung cancer cells and is a robust combination partner for multiple chemotherapeutics as evidenced by reducing cancer cell growth, in part, by inhibiting the ERK pathway.

LINC00689 participates in proliferation, chemoresistance and metastasis via miR-31-5p/YAP/β-catenin axis in colorectal cancer

As a kind of high-incidence malignant tumors in the digestive tract, colorectal cancer (CRC) has extremely morbidity and mortality in the population. LncRNAs have been proved to regulate the proliferation, chemoresistance and metastasis of tumors including CRC. LINC00689 and miR-31-5p in CRC were found misregulated in CRC by TCGA analysis. However, the mechanism of LINC00689 and miR-31-5p in regulating CRC remains unknown. The expression levels of LINC00689, miR-31-5p and LATS2 in CRC tissues and cell lines were examined by qRT-PCR assay. Cell proliferation, metastasis (including invasion and migration) were quantified by MTT assay, colony formation and Transwell assay, respectively. Western blotting assay was then performed to verify the levels of YAP/β-catenin and metastasis-related proteins. Dual-luciferase reporter assay and RIP assay were performed to evaluate the interaction between LINC00689 (LATS2) and miR-31-5p. Moreover, the function of LINC00689 and miR-31-5p were confirmed by CRC xenograft in nude mice. LINC00689 was decreased while miR-31-5p was increased in CRC. The overexpression of LINC00689 or the knockdown of miR-31-5p inhibited cell proliferation, chemoresistance and metastasis of CRC cells. Meanwhile, the up-regulated LATS2 suppressed the activity of YAP/β-catenin pathway to repress CRC occurrence. Silencing LATS2 reversed the inhibition effects of overexpression of LINC00689 or knockdown of miR-31-5p on proliferation, chemoresistance and metastasis of CRC cells. LINC00689 indeed acted as a miR-31-5p sponge to inhibit CRC proliferation, chemoresistance and metastasis through up-regulating LATS2 and repressing YAP/β-catenin signaling pathway.

Molecular Insights into miRNA-Driven Resistance to 5-Fluorouracil and Oxaliplatin Chemotherapy: miR-23b Modulates the Epithelial–Mesenchymal Transition of Colorectal Cancer Cells

Although treatment of colorectal cancer with 5-florouracil and oxaliplatin is widely used, it is frequently followed by a relapse. Therefore, there is an urgent need for profound understanding of chemotherapy resistance mechanisms as well as the profiling of predictive markers for individualized treatment. In this study, we identified the changes in 14 miRNAs in 5-fluouracil and 40 miRNAs in oxaliplatin-resistant cell lines by miRNA sequencing. The decrease in miR-224-5p expression in the 5-fluorouracil-resistant cells correlated with drug insensitivity due to its overexpression-induced drug-dependent apoptosis. On the other hand, the miR-23b/27b/24-1 cluster was overexpressed in oxaliplatin-resistant cells. The knockout of miR-23b led to the partial restoration of oxaliplatin susceptibility, showing the essential role of miR-23b in the development of drug resistance by this cluster. Proteomic analysis identified target genes of miR-23b and showed that endothelial-mesenchymal transition (EMT) was implicated in oxaliplatin insensibility. Data revealed that EMT markers, such as vimentin and SNAI2, were expressed moderately higher in the oxaliplatin-resistant cells and their expression increased further in the less drug-resistant cells, which had miR-23b knockout. This establishes that the balance of EMT contributes to the drug resistance, showing the importance of the miR-23b-mediated fine-tuning of EMT in oxaliplatin-resistant cancer cells.

5-fluorouracil and other fluoropyrimidines in colorectal cancer: Past, present and future

5-Fluorouracil (5-FU) is an essential component of systemic chemotherapy for colorectal cancer (CRC) in the palliative and adjuvant settings. Over the past four decades, several modulation strategies including the implementation of 5-FU-based combination regimens and 5-FU pro-drugs have been developed and tested to increase the anti-tumor activity of 5-FU and to overcome the clinical resistance. Despite the encouraging progress in CRC therapy to date, the patients' response rates to therapy continue to remain low and the patients' benefit from 5-FU-based therapy is frequently compromised by the development of chemoresistance. Inter-individual differences in the treatment response in CRC patients may originate in the unique genetic and epigenetic make-up of each individual. The critical element in the current trend of personalized medicine is the proper comprehension of causes and mechanisms contributing to the low or lack of sensitivity of tumor tissue to 5-FU-based therapy. The identification and validation of predictive biomarkers for existing 5-FU-based and new targeted therapies for CRC treatment will likely improve patients' outcomes in the future. Herein we present a comprehensive review summarizing options of CRC treatment and the mechanisms of 5-FU action at the molecular level, including both anabolic and catabolic ways. The main part of this review comprises the currently known molecular mechanisms underlying the chemoresistance in CRC patients. We also focus on various 5-FU pro-drugs developed to increase the amount of circulating 5-FU and to limit toxicity. Finally, we propose future directions of personalized CRC therapy according to the latest published evidence.

The regulatory ZFAS1/miR-150/ST6GAL1 crosstalk modulates sialylation of EGFR via PI3K/Akt pathway in T-cell acute lymphoblastic leukemia

BACKGROUND

Noncoding RNAs, including microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are becoming key parts in the development of multidrug resistance (MDR) in T-cell acute lymphoblastic leukemia (T-ALL). Abnormal expression in sialyated N-glycans have been observed in MDR leukemia. However, the role of sialylation regulated MDR remains poorly understood. The aim of this work is to analyze the alternation of N-glycans in T-ALL MDR.

METHODS

Here, mass spectrometry (MS) is analyzed to screen the N-glycan profiles from ALL cell line CR and adriamycin (ADR)-resistant CR (CR/A) cells. The expression of sialyltransferase (ST) genes in T-ALL cell lines and bone marrow mononuclear cells (BMMCs) of T-ALL patients were analyzed using qRT-PCR. Functionally, T-ALL cell proliferation and MDR are detected through CCK8 assay, colony formation assay, western blot and flow cytometry. RIP assay and Dual-luciferase reporter gene assay confirm the binding association between ZFAS1 and miR-150. Xenograft nude mice models are used to determine the role of ST6GAL1 in vivo.

RESULTS

Elevated expression of α2, 6-sialyltransferase 1 (ST6GAL1) has been detected. The altered level of ST6GAL1 was corresponding to the drug-resistant phenotype of T-ALL cell lines both in vitro and in vivo. ZFAS1/miR-150/ST6GAL1 axis was existed in T-ALL cell lines. MiR-150 was downregulated and inversely correlated to ST6GAL1 expression. ZFAS1 was a direct target of miR-150 and positively modulated ST6GAL1 level by binding miR-150. ZFAS1/miR-150/ST6GAL1 axis functioned to regulate ADR-resistant cell growth and apoptosis. Besides, EGFR was demonstrated to be a substrate of ST6GAL1, and the sialylated EGFR had an impact on the PI3K/Akt pathway.

CONCLUSION

Results suggested that ZFAS1/miR-150/ST6GAL1 axis involves in the progression of T-ALL/MDR further mediates sialylated EGFR via PI3K/Akt pathway. This work might have an application against T-ALL MDR.

The Phenolic compound Kaempferol overcomes 5-fluorouracil resistance in human resistant LS174 colon cancer cells

Resistance to 5-Fluorouracil chemotherapy is a major cause of therapeutic failure in colon cancer cure. Development of combined therapies constitutes an effective strategy to inhibit cancer cells and prevent the emergence of drug resistance. For this purpose, we investigated the anti-tumoral effect of thirteen phenolic compounds, from the Tunisian quince Cydonia oblonga Miller, alone or combined to 5-FU, on the human 5-FU-resistant LS174-R colon cancer cells in comparison to parental cells. Our results showed that only Kaempferol was able to chemo-sensitize 5-FU-resistant LS174-R cells. This phenolic compound combined with 5-FU exerted synergistic inhibitory effect on cell viability. This combination enhanced the apoptosis and induced cell cycle arrest of both chemo-resistant and sensitive cells through impacting the expression levels of different cellular effectors. Kaempferol also blocked the production of reactive oxygen species (ROS) and modulated the expression of JAK/STAT3, MAPK, PI3K/AKT and NF-κB. In silico docking analysis suggested that the potent anti-tumoral effect of Kaempferol, compared to its two analogs (Kaempferol 3-O-glucoside and Kampferol 3-O-rutinoside), can be explained by the absence of glucosyl groups. Overall, our data propose Kaempferol as a potential chemotherapeutic agent to be used alone or in combination with 5-FU to overcome colon cancer drug resistance.

Non-coding RNA in drug resistance of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has been one of the most highly lethal cancers. The acquisition of drug resistance accounts for the majority of poor effects of chemotherapy in HCC. Non-coding RNAs (ncRNAs) including miRNAs, long ncRNAs (lncRNAs), and circular RNA (circRNA) have been well-documented to participate in cancer occurrence and progression. Recently, multiple studies have highlighted the key roles of ncRNAs in chemoresistance of HCC. In addition, accumulating evidence has demonstrated that they can serve as biomarkers in diagnosis, treatment, and prognosis of HCC. In this review, we first overviewed up-to-date findings regarding miRNA and lncRNA in drug resistance of HCC, then summarized specific mechanisms that they modulate chemoresistance of HCC, and finally discussed their potential clinical application in overcoming the obstacle of HCC chemoresistance in the future.

Cantharidin inhibits melanoma cell proliferation via the miR‑21‑mediated PTEN pathway

Cantharidin (CTD) is an active component isolated from the blister beetle that has been demonstrated to exert antitumor effects on multiple types of cancer. The current study aimed to investigate whether the potential inhibitory effects of CTD exist in human melanoma cells and to assess the underlying antitumor mechanisms of CTD. Using the Cell Counting Kit‑8 assay, it was demonstrated that CTD treatment reduced A375 cell proliferation significantly in a dose‑dependent manner. The colony formation assay demonstrated that CTD treatment could decrease the number of A375 cell colonies. Using subcutaneous xenograft tumor models, it was also demonstrated that CTD retarded solid tumor growth significantly. Furthermore, CTD treatment could induce A375 cell apoptosis, as detected by Annexin V‑fluorescein isothiocyanate/propidium iodide staining and western blot analysis. Notably, CTD treatment reduced microRNA (miR)‑21 expression and enhanced phosphatase and tensin homolog (PTEN) protein expression levels in A375 cells. Furthermore, overexpressing miR‑21 in A375 cells with the miR‑21 agomir blocked the antitumor effect of CTD both in vitro and in vivo. Finally, it was demonstrated that the inhibitory effects of CTD on A375 cells may be regulated by attenuating miR‑21‑mediated PTEN suppression. Based on these observations, it was suggested that CTD be used as a novel anti‑proliferation agent of human melanoma via targeting the miR‑21‑PTEN signaling pathway.

The Network of Non-coding RNAs in Cancer Drug Resistance

Non-coding RNAs (ncRNAs) have been implicated in most cellular functions. The disruption of their function through somatic mutations, genomic imprinting, transcriptional and post-transcriptional regulation, plays an ever-increasing role in cancer development. ncRNAs, including notorious microRNAs, have been thus proposed to function as tumor suppressors or oncogenes, often in a context-dependent fashion. In parallel, ncRNAs with altered expression in cancer have been reported to exert a key role in determining drug sensitivity or restoring drug responsiveness in resistant cells. Acquisition of resistance to anti-cancer drugs is a major hindrance to effective chemotherapy and is one of the most important causes of relapse and mortality in cancer patients. For these reasons, non-coding RNAs have become recent focuses as prognostic agents and modifiers of chemo-sensitivity. This review starts with a brief outline of the role of most studied non-coding RNAs in cancer and then highlights the modulation of cancer drug resistance via known ncRNAs based mechanisms. We identified from literature 388 ncRNA-drugs interactions and analyzed them using an unsupervised approach. Essentially, we performed a network analysis of the non-coding RNAs with direct relations with cancer drugs. Within such a machine-learning framework we detected the most representative ncRNAs-drug associations and groups. We finally discussed the higher integration of the drug-ncRNA clusters with the goal of disentangling effectors from downstream effects and further clarify the involvement of ncRNAs in the cellular mechanisms underlying resistance to cancer treatments.

Epigenetics and MicroRNAs in Pharmacogenetics

Germline pharmacogenetics has so far mainly studied common variants in "pharmacogenes," i.e., genes encoding drug metabolizing enzymes and transporters (DMET genes), certain auxiliary and regulatory genes, and drug target genes. Despite remarkable progress in understanding genetically determined differences in pharmacokinetics and pharmacodynamics of drugs, currently known common variants even in important pharmacogenes explain genetic variability only partially. This suggests "missing heritability" that may in part be due to rare variants in the classical pharmacogenes, but current evidence suggests that largely unexplored resources with potential for pharmacogenetics exist, both within already known pharmacogenes and in entirely new areas. In particular, recent studies suggest that epigenetic processes and noncoding RNAs, including mostly microRNAs (miRNAs), represent important and largely unexplored layers of DMET gene regulation that may fill some of the gaps in understanding interindividual variability and lead to new biomarkers. In this chapter we summarize recent advances in the understanding of genetic variability in epigenetic and miRNA-mediated processes with focus on their significance for DMET regulation and pharmacokinetic or pharmacological endpoints.