In Vitro and In Silico Mechanistic Insights into miR-21-5p-Mediated Topoisomerase Drug Resistance in Human Colorectal Cancer Cells.

Although chemotherapy for treating colorectal cancer has had some success, drug resistance and metastasis remain the major causes of death for colorectal cancer patients. MicroRNA-21-5p (hereafter denoted as miR-21) is one of the most abundant miRNAs in human colorectal cancer. A Kaplan-Meier survival analysis found a negative prognostic correlation of miR-21 and metastasis-free survival in colorectal cancer patients (The Cancer Genome Atlas Colon Adenocarcinoma/TCGA-COAD cohort). To explore the role of miR-21 overexpression in drug resistance, a stable miR-21-overexpressing clone in a human DLD-1 colorectal cancer cell line was established. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) cell viability assay found that miR-21 overexpression induced drug resistance to topoisomerase inhibitors (SN-38, doxorubicin, and etoposide/VP-16). Mechanistically, we showed that miR-21 overexpression reduced VP-16-induced apoptosis and concomitantly enhanced pro-survival autophagic flux without the alteration of topoisomerase expression and activity. Bioinformatics analyses suggested that miR-21 overexpression induced genetic reprogramming that mimicked the gene signature of topoisomerase inhibitors and downregulated genes related to the proteasome pathway. Taken together, our results provide a novel insight into the role of miR-21 in the development of drug resistance in colorectal cancer.

Correction: Systematic discovery of drug action mechanisms by an integrated chemical genomics approach: identification of functional disparities between azacytidine and decitabine.

[This corrects the article DOI: 10.18632/oncotarget.8455.].

EZH2 inhibitors transcriptionally upregulate cytotoxic autophagy and cytoprotective unfolded protein response in human colorectal cancer cells.

Enhancer of zeste homolog 2 (EZH2) has been emerged as novel anticancer target. Various EZH2 small-molecule inhibitors have been developed in recent years. A major class of EZH2 inhibitors are S-adenosyl-L-methionine (SAM)-competitive inhibitors, such as EPZ005687, EI1, GSK126, UNC1999 and GSK343. Autophagy, a physiological process of self-digestion, is involved in the turnover of proteins or intracellular organelles. It can serve as cytoprotective or cytotoxic function in cancer. Our previous study has found that UNC1999 and GSK343 are potent autophagy inducers. In this study, the underlying molecular mechanisms were further investigated. Our results showed that UNC1999 and GSK343 transcriptionally upregulated autophagy of human colorectal cancer (CRC) cells through inducing LC3B gene expression. Besides, UNC1999/GSK343-induced autophagy was partially dependent on ATG7 but independent to EZH2 inhibition. Microarray and PCR array analyses identified that UNC1999 and GSK343 also induced endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UNC1999/GSK343-induced ER stress/UPR contributed to the survival of cancer cells, which was opposite to UNC1999/GSK343-induced autophagy that promoted cell death.

Systematic discovery of drug action mechanisms by an integrated chemical genomics approach: identification of functional disparities between azacytidine and decitabine.

Polypharmacology (the ability of a drug to affect more than one molecular target) is considered a basic property of many therapeutic small molecules. Herein, we used a chemical genomics approach to systematically analyze polypharmacology by integrating several analytical tools, including the LINCS (Library of Integrated Cellular Signatures), STITCH (Search Tool for Interactions of Chemicals), and WebGestalt (WEB-based GEne SeT AnaLysis Toolkit). We applied this approach to identify functional disparities between two cytidine nucleoside analogs: azacytidine (AZA) and decitabine (DAC). AZA and DAC are structurally and mechanistically similar DNA-hypomethylating agents. However, their metabolism and destinations in cells are distinct. Due to their differential incorporation into RNA or DNA, functional disparities between AZA and DAC are expected. Indeed, different cytotoxicities of AZA and DAC toward human colorectal cancer cell lines were observed, in which cells were more sensitive to AZA. Based on a polypharmacological analysis, we found that AZA transiently blocked protein synthesis and induced an acute apoptotic response that was antagonized by concurrently induced cytoprotective autophagy. In contrast, DAC caused cell cycle arrest at the G2/M phase associated with p53 induction. Therefore, our study discriminated functional disparities between AZA and DAC, and also demonstrated the value of this chemical genomics approach that can be applied to discover novel drug action mechanisms.

S-Adenosyl-L-methionine-competitive inhibitors of the histone methyltransferase EZH2 induce autophagy and enhance drug sensitivity in cancer cells.

The enhancer of zeste homolog 2 (EZH2) has emerged as a novel anticancer target. Various EZH2 inhibitors have been developed in recent years. Among these, 3-deazaneplanocin A (DZNep) is known to deplete EZH2 protein expression through an indirect pathway. In contrast, GSK343 directly inhibits enzyme activity through an S-adenosyl-L-methionine-competitive pathway. Therefore, we proposed that DZNep and GSK343 may exert differential effects against cancer cells. In this study, we found that GSK343 but not DZNep induced autophagic cell death of cancer cells. Inhibition of EZH2 expression was not required for GSK343-induced autophagy. In addition, GSK343 enhanced the anticancer activity of a multikinase inhibitor, sorafenib, in human hepatocellular carcinoma cells. Our results show that GSK343 is a more potent anticancer agent than DZNep, and for the first time, we show that it acts as an autophagy inducer.

A gene expression signature-based approach reveals the mechanisms of action of the Chinese herbal medicine berberine.

Berberine (BBR), a traditional Chinese herbal medicine, was shown to display anticancer activity. In this study, we attempted to provide a global view of the molecular pathways associated with its anticancer effect through a gene expression-based chemical approach. BBR-induced differentially expressed genes obtained from the Gene Expression Omnibus (GEO) at the National Center for Biotechnology Information (NCBI) were analyzed using the Connectivity Map (CMAP) database to compare similarities of gene expression profiles between BBR and CMAP compounds. Candidate compounds were further analyzed using the Search Tool for Interactions of Chemicals (STITCH) database to explore chemical-protein interactions. Results showed that BBR may inhibit protein synthesis, histone deacetylase (HDAC), or AKT/mammalian target of rapamycin (mTOR) pathways. Further analyses demonstrated that BBR inhibited global protein synthesis and basal AKT activity, and induced endoplasmic reticulum (ER) stress and autophagy, which was associated with activation of AMP-activated protein kinase (AMPK). However, BBR did not alter mTOR or HDAC activities. Interestingly, BBR induced the acetylation of α-tubulin, a substrate of HDAC6. In addition, the combination of BBR and SAHA, a pan-HDAC inhibitor, synergistically inhibited cell proliferation and induced cell cycle arrest. Our results provide novel insights into the mechanisms of action of BBR in cancer therapy.