MicroRNA: A New Player for Cancer Chemoprevention

Sulindac Modulates the Response of Proficient MMR Colorectal Cancer to Anti-PD-L1 Immunotherapy

Immune-checkpoint inhibitor (ICI) therapy has been widely used to treat different human cancers, particularly advanced solid tumors. However, clinical studies have reported that ICI immunotherapy benefits only ∼15% of patients with colorectal cancer, specifically those with tumors characterized by microsatellite instability (MSI), a molecular marker of defective DNA mismatch repair (dMMR). For the majority of patients with colorectal cancer who carry proficient MMR (pMMR), ICIs have shown little clinical benefit. In this study, we examined the efficacy of sulindac to enhance the response of pMMR colorectal cancer to anti-PD-L1 immunotherapy. We utilized a CT26 syngeneic mouse tumor model to compare the inhibitory effects of PD-L1 antibody (Ab), sulindac, and their combination on pMMR colorectal cancer tumor growth. We found that mice treated with combination therapy showed a significant reduction in tumor volume, along with increased infiltration of CD8+ T lymphocytes in the tumor tissues. We also demonstrated that sulindac could downregulate PD-L1 by blocking NF-κB signaling, which in turn led to a decrease in exosomal PD-L1. Notably, PD-L1 Ab can be bound and consumed by exosomal PD-L1 in the blood circulation. Therefore, in combination therapy, sulindac downregulating PD-L1 leads to increased availability of PD-L1 Ab, which potentially improves the overall efficacy of anti-PD-L1 therapy. We also show that low-dose sulindac does not appear to have a systemic inhibitory effect on prostaglandin E2 (PGE2). In conclusion, our findings provide unique insights into the mechanism of action and efficacy for sulindac as an immunomodulatory agent in combination with anti-PD-L1 therapy for the treatment of pMMR colorectal cancer.

Potential tumor‑suppressive role of microRNA‑99a‑3p in sunitinib‑resistant renal cell carcinoma cells through the regulation of RRM2

Sunitinib is the most common primary molecular‑targeted agent for metastatic clear cell renal cell carcinoma (ccRCC); however, intrinsic or acquired sunitinib resistance has become a significant problem in medical practice. The present study focused on microRNA (miR)‑99a‑3p, which was significantly downregulated in clinical sunitinib‑resistant ccRCC tissues in previous screening analyses, and investigated the molecular network associated with it. The expression levels of miR‑99a‑3p and its candidate target genes were evaluated in RCC cells, including previously established sunitinib‑resistant 786‑o (SU‑R‑786‑o) cells, and clinical ccRCC tissues, using reverse transcription‑quantitative polymerase chain reaction. Gain‑of‑function studies demonstrated that miR‑99a‑3p significantly suppressed cell proliferation and colony formation in RCC cells, including the SU‑R‑786‑o cells, by inducing apoptosis. Based on in silico analyses and RNA sequencing data, followed by luciferase reporter assays, ribonucleotide reductase regulatory subunit‑M2 (RRM2) was identified as a direct target of miR‑99a‑3p in the SU‑R‑786‑o cells. Loss‑of‑function studies using small interfering RNA against RRM2 revealed that cell proliferation and colony growth were significantly inhibited via induction of apoptosis, particularly in the SU‑R‑786‑o cells. Furthermore, the RRM2 inhibitor Didox (3,4‑dihydroxybenzohydroxamic acid) exhibited anticancer effects in the SU‑R‑786‑o cells and other RCC cells. To the best of our knowledge, this is the first report demonstrating that miR‑99a‑3p directly regulates RRM2. Identifying novel genes targeted by tumor‑suppressive miR‑99a‑3p in sunitinib‑resistant RCC cells may improve our understanding of intrinsic or acquired resistance and facilitate the development of novel therapeutic strategies.

miR-223 increases gallbladder cancer cell sensitivity to docetaxel by downregulating STMN1

Background

MicroRNAs (miRs) are involved in cancer carcinogenesis, and certain regulatory miRs could provide promising therapeutic methods for refractory malignancies, such as gallbladder cancer (GBC). miR-223 was found to play a pivotal role in enhancing chemotherapeutic effects, therefore evoking interest in the role of miR-223 in GBC.

Results

miR-223 was decreased in GBC tissues and cell lines, and ectopic miR- 223 expression exhibited multiple anti-tumorigenic effects in GBC cells, including decreased proliferation, migration and invasion in vitro. However, treatment with a miR-223 inhibitor increased cell viability. We determined that STMN1 was negatively correlated with and regulated by miR-223 in GBC. miR-223 increased GBC sensitivity to docetaxel in vitro and in vivo, and the induced sensitivity to docetaxel was suppressed by the restoration of STMN1 expression.

Methods

We examined miR-223 expression in GBC tissue and GBC cell lines using qRT-PCR. The effects of modulated miR-223 expression in GBC cells were assayed using Cell Counting Kit-8 (CCK8), flow cytometry, and wound-healing and invasion assays. Susceptibility to docetaxel was evaluated in miR-223/STMN1-modulated GBC cells and xenograft tumor models. The protein expression of relevant genes was examined by Western blotting.

Conclusions

These findings indicated that miR-223 might serve as an onco-suppressor that enhances susceptibility to docetaxel by downregulating STMN1 in GBC, highlighting its promising therapeutic value.

MicroRNA-509-3p inhibits cancer cell proliferation and migration by targeting the mitogen-activated protein kinase kinase kinase 8 oncogene in renal cell carcinoma

microRNAs (miRNAs; miR) are a class of small non-coding RNA molecules, which are involved in the pathogenesis of human diseases through the negative regulation of gene expression. Previous studies have demonstrated that miR-509-3p is a novel miRNA associated with cell proliferation and migration in 786-O renal cell carcinoma (RCC) cells. However, the mechanism of action of miR-509-3p in RCC remains to be elucidated. The present study aimed to examine the functional role and mechanism of miR-509-3p in the development of RCC. The results demonstrated that the expression levels of miR-509-3p were downregulated in the 786-O and ACHN RCC cell lines compared with the normal tissues of 10 patients with RCC, as determined by reverse transcription-quantitative polymerase chain reaction. The mRNA expression levels of mitogen-activated protein kinase kinase kinase 8 (MAP3K8) were upregulated in the RCC cell lines. Functional investigations demonstrated that the overexpression of miR-509-3p inhibited the migration and proliferation of the RCC cells, as determined by wound scratch and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. Luciferase reporter assays revealed that the overexpression of miR-509-3p reduced the transcriptional activity of MAP3K8. Furthermore, the present study demonstrated that the ectopic transfection of miR-509-3p led to a significant reduction in the mRNA and protein expression levels of MAP3K8 in the RCC cells. Finally, knockdown of MAP3K8 inhibited the migration and proliferation of the RCC cells. Therefore, the results of the present study demonstrated that the miR-509-3p RCC suppressor was a significant regulator of the MAP3K8 oncogene, suggesting that it may have a potential therapeutic role in the treatment of RCC.

MicroRNA-451a is associated with cell proliferation, migration and apoptosis in renal cell carcinoma

MicroRNAs (miRNAs) are an important class of small, non‑coding RNA molecules that regulate gene expression at the transcriptional or post‑transcriptional level. They are involved in apoptosis, proliferation and migration and are known to have an important role in many types of cancer. Aberrant expression of miRNA‑451a (miR‑451a) has previously been reported in tumors, however its role in renal cell carcinoma (RCC) is currently unknown. The aim of the present study was to investigate the role of miR‑451a in RCC. The expression of miR‑451a was analyzed in 50 paired RCC and normal tissues by quantitative polymerase chain reaction. Furthermore, the effects of miR‑451a on cell migration, proliferation and apoptosis were evaluated, using migration scratch, MTT and flow cytometric assays. The present study demonstrated that miR‑451a was upregulated in RCC, as compared with paired normal tissues (P<0.05). Downregulation of miR‑451a using a synthesized inhibitor, significantly suppressed cell migration and proliferation, and induced apoptosis of renal cancer cells in vitro, as compared with a negative control (P<0.05). In the present study, it was determined that miR‑451a may have an important role as a tumor enhancer in RCC. These results imply that miR‑451a may be a promising therapeutic target for the treatment of RCC.

Mechanistic Role of MicroRNA in Cancer Chemoprevention by Nonsteroidal Anti-inflammatory Drugs

Over the past several decades, studies have documented the significance of nonsteroidal anti-inflammatory drugs (NSAIDs) on cancer chemoprevention by lowering incidence and slowing down progression of malignant disease, which consequently lead to decline of cancer-related mortality and improvement of disease progression free survival (PFS). Inhibition of cyclooxygenase (COX) has been primarily believed to be the key mechanism responsible for anticancer activity of NSAIDs, while the serious toxicity caused by COX inhibitory effect reduces the enthusiasm to use NSAIDs as chemoprevention agents in the clinic. Recently, more and more studies demonstrate that non-COX inhibitory mechanisms may account for anticancer properties of NSAIDs, at least partially, which potentially support the indication of NSAIDs on cancer chemoprevention. MicroRNAs (miRNAs) are a set of non-coding and small RNA molecules with master regulatory effect on over 30% human genes through the post-transcriptional and translational modulation. Although miRNAs have been reported to be involved in many normal and pathological processes including cell proliferation, apoptosis, differentiation, as well as tumorigenesis, their roles in NSAIDs' properties of cancer chemoprevention have not yet been studied exclusively. Here, we will review the prior studies reporting interactions between miRNAs and COX/non-COX pathways with intent to provide insights into better understanding molecular mechanisms of cancer chemoprevention by NSAIDs.