microRNA-206 impairs c-Myc-driven cancer in a synthetic lethal manner by directly inhibiting MAP3K13

Evolving copy number gains promote tumor expansion and bolster mutational diversification

The timing and fitness effect of somatic copy number alterations (SCNA) in cancer evolution remains poorly understood. Here we present a framework to determine the timing of a clonal SCNA that encompasses multiple gains. This involves calculating the proportion of time from its last gain to the onset of population expansion (lead time) as well as the proportion of time prior to its first gain (initiation time). Our method capitalizes on the observation that a genomic segment, while in a specific copy number (CN) state, accumulates point mutations proportionally to its CN. Analyzing 184 whole genome sequenced samples from 75 patients across five tumor types, we commonly observe late gains following early initiating events, occurring just before the clonal expansion relevant to the sampling. These include gains acquired after genome doubling in more than 60% of cases. Notably, mathematical modeling suggests that late clonal gains may contain final-expansion drivers. Lastly, SCNAs bolster mutational diversification between subpopulations, exacerbating the circle of proliferation and increasing heterogeneity.

A gene mutation-based risk model for prognostic prediction in liver metastases

BACKGROUND

Liver metastasis is the major challenge in the treatment for malignant tumors. Genomic profiling is increasingly used in the diagnosis, treatment and prediction of prognosis in malignancies. In this study, we constructed a gene mutation-based risk model to predict the survival of liver metastases.

METHOD

We identified the gene mutations associated with survival and constructed the risk model in the training cohort including 800 patients with liver metastases from Memorial Sloan-Kettering Cancer Center (MSKCC) dataset. Other 794 patients with liver metastases were collected from 4 cohorts for validation. Furthermore, the analyses of tumor microenvironment (TME) and somatic mutations were performed on 51 patients with breast cancer liver metastases (BCLM) who had both somatic mutation data and RNA-sequencing data.

RESULTS

A gene mutation-based risk model involved 10 genes was constructed to divide patients with liver metastases into the high- and low-risk groups. Patients in the low-risk group had a longer survival time compared to those in the high-risk group, which was observed in both training and validation cohorts. The analyses of TME in BCLM showed that the low-risk group exhibited more immune infiltration than the high-risk group. Furthermore, the mutation signatures of the high-risk group were completely different from those of the low-risk group in patients with BCLM.

CONCLUSIONS

The gene mutation-based risk model constructed in our study exhibited the reliable ability of predicting the prognosis in liver metastases. The difference of TME and somatic mutations among BCLM patients with different risk score can guide the further research and treatment decisions for liver metastases.

Clinical significance of mitogen-activated protein kinase kinase kinases in hepatitis B virus -related hepatocellular carcinoma and underlying mechanism exploration

The purpose of this research was to explore the diagnostic/prognostic significance and prospective molecular mechanisms of mitogen-activated protein kinase kinase kinases (MAP3Ks) in hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC). Diagnostic/prognostic significance of MAP3Ks was screened in the GSE1450 data set and validated in the Guangxi cohort. Various bioinformatics tools were used to explore the biological functions of prognosis-related genes. Subsequently, molecular biology assays were used to verify the biological functions and molecular mechanisms of specific gene. MAP3K9 was observed to be differentially expressed in HCC and adjacent tissues with satisfactory diagnostic value. It was discovered in survival analysis that MAP3K13 and MAP3K15 were associated with overall survival (OS) of patients with HBV-related HCC in the GSE1450 data set and the Guangxi cohort. Nomograms were established based on prognosis-related genes and clinical factors for individualized risk assessment. The assays on HCC cells demonstrated that MAP3K13 regulated the death and proliferation of HCC cells by activating the JNK pathway and inducing the expression of apoptosis-related factors. In conclusion, our results suggested that MAP3K9 might serve as a diagnostic biomarker in HBV-related HCC and MAP3K13 and MAP3K15 might serve as useful prognostic biomarkers. Besides, cytological assays prompted that MAP3K13 might impact the prognosis of HCC by regulating the JNK pathway and inducing apoptosis.

Fast and powerful conditional randomization testing via distillation

We consider the problem of conditional independence testing: given a response $Y$ and covariates $(X,Z)$, we test the null hypothesis that $Y {\perp\!\!\!\perp} X \mid Z$. The conditional randomization test was recently proposed as a way to use distributional information about $X\mid Z$ to exactly and nonasymptotically control Type-I error using any test statistic in any dimensionality without assuming anything about $Y\mid (X,Z)$. This flexibility, in principle, allows one to derive powerful test statistics from complex prediction algorithms while maintaining statistical validity. Yet the direct use of such advanced test statistics in the conditional randomization test is prohibitively computationally expensive, especially with multiple testing, due to the requirement to recompute the test statistic many times on resampled data. We propose the distilled conditional randomization test, a novel approach to using state-of-the-art machine learning algorithms in the conditional randomization test while drastically reducing the number of times those algorithms need to be run, thereby taking advantage of their power and the conditional randomization test’s statistical guarantees without suffering the usual computational expense. In addition to distillation, we propose a number of other tricks, like screening and recycling computations, to further speed up the conditional randomization test without sacrificing its high power and exact validity. Indeed, we show in simulations that all our proposals combined lead to a test that has similar power to most powerful existing conditional randomization test implementations, but requires orders of magnitude less computation, making it a practical tool even for large datasets. We demonstrate these benefits on a breast cancer dataset by identifying biomarkers related to cancer stage.

LINC01287 facilitates proliferation, migration, invasion and EMT of colon cancer cells via miR-4500/MAP3K13 pathway

Background

Accumulated studies indicate that aberrant expression of long noncoding RNAs (lncRNAs) is associated with tumorigenesis and progression of colon cancer. In the present study, long intergenic non-protein coding RNA 1287 (LINC01287) was identified to up-regulate in colon cancer by transcriptome RNA-sequencing, but the exact function remained unclear.

Methods

Transcriptome RNA-sequencing was conducted to identify dysregulated lncRNAs. Expression of LINC01287 was evaluated by real-time quantitative PCR. The downstream targets of LINC01287 and miR-4500 were verified by luciferase reporter assay, pull down assay and western blot. The potential functions of LINC01287 were evaluated by cell viability assay, colony formation assay, soft agar assay, flow cytometry, transwell migration and invasion assay, and tumor xenograft growth in colon cancer cells.

Results

Our results indicated that LINC01287 was up-regulated in colon cancer patients. High LINC01287 expression was associated with advanced TNM stage, lymph node metastasis, distant metastasis and shorter overall survival. Knockdown of LINC01287 inhibited cell growth, colony formation in plates and soft agar, transwell cell migration and invasion, and epithelial-mesenchymal transition (EMT) of colon cancer cells, while LINC01287 overexpression had contrary effects. In addition, LINC01287 mediated MAP3K13 expression by sponging miR-4500, thus promoted NF-κB p65 phosphorylation. Restored MAP3K13 expression or miR-4500 knockdown partially abrogated the effects of silencing LINC01287 in colon cancer cells.

Conclusion

Our findings demonstrated that the LINC01287/miR-4500/MAP3K13 axis promoted progression of colon cancer. Therefore, LINC01287 might be a potential therapeutic target and prognostic marker for colon cancer patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08528-7.

Wallenda-Nmo Axis Regulates Growth via Hippo Signaling

Both Hippo signaling pathways and cell polarity regulation are critical for cell proliferation and the maintenance of tissue homeostasis, despite the well-established connections between cell polarity disruption and Hippo inactivation, the molecular mechanism by which aberrant cell polarity induces Hippo-mediated overgrowth remains underexplored. Here we use Drosophila wing discs as a model and identify the Wnd-Nmo axis as an important molecular link that bridges loss-of-cell polarity-triggered Hippo inactivation and overgrowth. We show that Wallenda (Wnd), a MAPKKK (mitogen-activated protein kinase kinase kinase) family member, is a novel regulator of Hippo pathways in Drosophila and that overexpression of Wnd promotes growth via Nemo (Nmo)- mediated Hippo pathway inactivation. We further demonstrate that both Wnd and Nmo are required for loss-of-cell polarity-induced overgrowth and Hippo inactivation. In summary, our findings provide a novel insight on how cell polarity loss contributes to overgrowth and uncover the Wnd-Nmo axis as an essential additional branch that regulates Hippo pathways in Drosophila.

KMT2D promotes proliferation of gastric cancer cells: evidence from ctDNA sequencing

BACKGROUND

ctDNA sequencing could be used for early cancer screening, prognosis prediction, and medication guidance. However, data of its application in gastric cancer are still lacking. In this study, using ctDNA sequencing, we aimed to screen the mutant genes closely associated with gastric cancer and to explore the impact of these genes on gastric cancer development.

METHODS

ctDNA for high-throughput sequencing was obtained from gastric cancer patients, and the high-frequency mutant gene KMT2D was identified. Immunohistochemical examination was conducted to assess the expression of KMT2D in gastric cancer tissues. KMT2D knockdown was performed to establish the stably transfected gastric cancer cells. Then, CCK8, plate clone formation assay, and Transwell assay were conducted, and a subcutaneous tumor-bearing model was induced in nude mice to investigate the changes in cell proliferation and invasion capability. Transcriptome sequencing was also performed to investigate the differences in cellular gene expression.

RESULTS

Detection of ctDNA found 113 gastric cancer-related mutations, 11 of which are the top 20 high-frequency mutations of gastric cancer recorded by COSMIC (Catalogue of Somatic Mutations in Cancer, COSMIC). They are TP53, ARID1A, CDH1, PIK3CA, KMT2C, KMT2D, APC, SPEN, CTNNB1, SETBP1, and KMT2A. The gene closely related to the clinical characteristics of the patient is KMT2D. The high-frequency mutant gene KMT2D was identified in gastric cancer tissues. The positive rate of KMT2D expression in cancer tissues was 74.3%, which was higher than that in para-carcinoma tissues (56.8%). The knockdown of KMT2D inhibited the proliferation, invasion, and tumor formation capacity of the gastric cancer cells, causing differences in the gene expression profiles, and the expression of different functional gene clusters was up- or downregulated.

CONCLUSION

The findings of this study revealed that KMT2D could be an oncogene capable of promoting gastric cancer proliferation.

Curcumin inhibits migration and invasion of non-small cell lung cancer cells through up-regulation of miR-206 and suppression of PI3K/AKT/mTOR signaling pathway

Curcumin has been proved to inhibit cell proliferation and induce cell apoptosis in non-small cell lung cancer (NSCLC). However, little is known about antimetastatic effects and molecular mechanisms of curcumin in NSCLC. In this study, we investigated the involvement of miR-206 in curcumin's anti-invasion and anti-migration in NSCLC. Cell proliferation was determined by MTT assay. Cell migration and invasion were analyzed by wound healing assay and transwell assay. MiRNA-206 expression was detected by real-time PCR. Western blot was used to detect the protein expression of PI3K/AKT/mTOR signaling pathway. Curcumin significantly inhibited migration and invasion in A549 cells, accompanied by significantly elevated miR-206 expression. Overexpression of miR-206 could inhibit migration and invasion of A549 cells, but it could also significantly decrease the phosphorylation levels of mTOR and AKT. The inhibition of miR-206 promoted cell migration, invasion and increased the phosphorylation level of mTOR and AKT. Furthermore, miR-206 mimics improved the inhibitory effects of curcumin on cell migration, invasion and the phosphorylation level of mTOR and AKT in A549 cells. On the contrary, MiR-206 inhibitors reversed the inhibitory effects of curcumin on cell migration, invasion and the phosphorylation level of mTOR and AKT. In conclusion, curcumin inhibited cell invasion and migration in NSCLC by elevating the expression of miR-206 which further suppressed the activation of the PI3K/AKT/mTOR pathway.

Inhibition of miR-1193 leads to synthetic lethality in glioblastoma multiforme cells deficient of DNA-PKcs

Glioblastoma multiforme (GBM) is the most malignant primary brain tumor and has the highest mortality rate among cancers and high resistance to radiation and cytotoxic chemotherapy. Although some targeted therapies can partially inhibit oncogenic mutation-driven proliferation of GBM cells, therapies harnessing synthetic lethality are ‘coincidental’ treatments with high effectiveness in cancers with gene mutations, such as GBM, which frequently exhibits DNA-PKcs mutation. By implementing a highly efficient high-throughput screening (HTS) platform using an in-house-constructed genome-wide human microRNA inhibitor library, we demonstrated that miR-1193 inhibition sensitized GBM tumor cells with DNA-PKcs deficiency. Furthermore, we found that miR-1193 directly targets YY1AP1, leading to subsequent inhibition of FEN1, an important factor in DNA damage repair. Inhibition of miR-1193 resulted in accumulation of DNA double-strand breaks and thus increased genomic instability. RPA-coated ssDNA structures enhanced ATR checkpoint kinase activity, subsequently activating the CHK1/p53/apoptosis axis. These data provide a preclinical theory for the application of miR-1193 inhibition as a potential synthetic lethal approach targeting GBM cancer cells with DNA-PKcs deficiency.

Multitasking: Dual Leucine Zipper-Bearing Kinases in Neuronal Development and Stress Management

The dual leucine zipper-bearing kinase (DLK) and leucine zipper-bearing kinase (LZK) are evolutionarily conserved MAPKKKs of the mixed-lineage kinase family. Acting upstream of stress-responsive JNK and p38 MAP kinases, DLK and LZK have emerged as central players in neuronal responses to a variety of acute and traumatic injuries. Recent studies also implicate their function in astrocytes, microglia, and other nonneuronal cells, reflecting their expanding roles in the multicellular response to injury and in disease. Of particular note is the potential link of these kinases to neurodegenerative diseases and cancer. It is thus critical to understand the physiological contexts under which these kinases are activated, as well as the signal transduction mechanisms that mediate specific functional outcomes. In this review we first provide a historical overview of the biochemical and functional dissection of these kinases. We then discuss recent findings on regulating their activity to enhance cellular protection following injury and in disease, focusing on but not limited to the nervous system.

MicroRNA-206 regulates cell proliferation by targeting G6PD in skeletal muscle

Skeletal muscle is a major component of body mass and plays a central role in the control of whole-body metabolism in humans and animals. Therefore, elucidation of the underlying mechanisms of skeletal growth and development are expected to lead to the discovery of novel genes and pathways related to muscle disease. miR-206, a skeletal muscle-specific microRNA, plays a crucial role in myogenesis; however, miR-206 is known to function in myogenic differentiation, whether or not it affects muscle cells' proliferation, and the underlying mechanisms are unknown. In this study, we investigated the effect of miR-206 on muscle cell proliferation and differentiation, as well as its effect on myofiber type conversion using mouse C2C12 myoblasts. The results showed that overexpression of miR-206 inhibited cell proliferation and promoted muscle cell differentiation, but it did not affect myofiber type conversion. Intriguingly, we found that overexpression of miR-206 suppressed muscle cell proliferation and induced cell cycle arrest in G₀/G₁ phase by inhibiting the glucose-6-phosphate dehydrogenase (G6PD) gene. Taken together, we demonstrated that the miR-206-G6PD pathway suppresses muscle cell proliferation, and these findings may facilitate the treatment of muscle diseases.-Jiang, A., Dong, C., Li, B., Zhang, Z., Chen, Y., Ning, C., Wu, W., Liu, H. MicroRNA-206 regulates cell proliferation by targeting G6PD in skeletal muscle.

The MAP3K13-TRIM25-FBXW7α axis affects c-Myc protein stability and tumor development

c-Myc (Myc) is a master transcription factor that is often deregulated and highly expressed by at least 50% of cancers. In many cases, Myc protein levels correlate with resistance to therapy and poor prognosis. However, effective direct inhibition of Myc by pharmacologic approaches has remained unachievable. Here, we identify MAP3K13 as a positive regulator of Myc to promote tumor development. Our findings show that MAP3K13 upregulation is predictive of poor outcomes in patients with hepatocellular carcinoma (HCC). Mechanistically, MAP3K13 phosphorylates the E3 ubiquitin ligase TRIM25 at Ser₁₂ to decrease its polyubiquitination and proteasomal degradation. This newly stabilized TRIM25 then directly ubiquitinates Lys₄₁₂ of FBXW7α, a core subunit of the SKP1-Cullin-F-box (SCF) ubiquitin ligase complex involved in Myc ubiquitination, thereby stabilizing Myc. Together, these results reveal a novel regulatory pathway that supervises Myc protein stability via the MAP3K13-TRIM25-FBXW7α signaling axis. In addition, they provide a potential therapeutic target in Myc over-expressing human cancers.

Amplification of Glyceronephosphate O-Acyltransferase and Recruitment of USP30 Stabilize DRP1 to Promote Hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide, and the underlying pathophysiology of HCC is highly complex. In this study, we report that, in a bioinformatic screen of 2,783 genes encoding metabolic enzymes, GNPAT, which encodes the enzyme glyceronephosphate O-acyltransferase, is amplified, upregulated, and highly correlated with poor clinical outcome in human patients with HCC. High GNPAT expression in HCC was due to its amplification and transcriptional activation by the c-Myc/KDM1A complex. GNPAT compensated the oncogenic phenotypes in c-Myc-depleted HCC cells. Mechanistically, GNPAT recruited the enzyme USP30, which deubiquitylated and stabilized dynamin-related protein 1 (DRP1), thereby facilitating regulation of mitochondrial morphology, lipid metabolism, and hepatocarcinogenesis. Inhibition of GNPAT and DRP1 dramatically attenuated lipid metabolism and hepatocarcinogenesis. Furthermore, DRP1 mediated the oncogenic phenotypes driven by GNPAT. Taken together, these results indicate that GNPAT and USP30-mediated stabilization of DRP1 play a critical role in the development of HCC.Significance: This study identifies and establishes the role of the enzyme GNPAT in liver cancer progression, which may serve as a potential therapeutic target for liver cancer. Cancer Res; 78(20); 5808-19. ©2018 AACR.

MYC-related microRNAs signatures in non-Hodgkin B-cell lymphomas and their relationships with core cellular pathways

In order to investigate the role of microRNAs in the pathogenesis of different B-cell lymhoma subtypes, we have applied an array-based assay to a series of 76 mixed non-Hodgkin B-cell lymphomas, including Burkitt's lymphoma (BL), diffuse large B-cell lymphoma, primary mediastinal B-cell lymphoma, mantle cell lymphoma (MCL) and follicular lymphoma. Lymphomas clustered according to histological subtypes, driven by two miRNA clusters (the miR-29 family and the miR-17-92 cluster). Since the two miRNA clusters are known to be MYC-regulated, we investigated whether this would be supported in MYC-driven experimental models, and found that this signature separated BL cell lines and a MYC-translocated MCL cell lines from normal germinal center B-cells and other B-cell populations. Similar results were also reproduced in tissue samples comparing BL and reactive lymph node samples. The same series was then quantitatively analyzed for MYC expression by immunohistochemistry and MYC protein levels were compared with corresponding miRNA signatures. A specific metric was developed to summarize the levels of MYC-related microRNAs and the corresponding protein levels. We found that MYC-related signatures are directly related to MYC protein expression across the whole spectrum of B-cells and B-cell lymphoma, suggesting that the MYC-responsive machinery shows predominantly quantitative, rather than qualitative, modifications in B-cell lymphoma. Novel MYC-related miRNAs were also discovered by this approach. Finally, network analysis found that in BL MYC-related differentially expressed miRNAs could control, either positively or negatively, a limited number of hub proteins, including BCL2, CDK6, MYB, ZEB1, CTNNB1, BAX and XBP1.

MiR-200c is a cMyc-activated miRNA that promotes nasopharyngeal carcinoma by downregulating PTEN

The c-Myc transcription factor regulates a complex transcriptional program that leads to cellular transformation by targeting a large number of protein-encoding genes and non-coding RNAs. In this study, we show that a microRNA, miR-200c, is a novel c-Myc target that promotes cellular transformation and metastasis in nasopharyngeal carcinoma. MiR-200c achieves this oncogenic effect, at least in part, by targeting and inhibiting the tumor suppressor gene PTEN (phosphatase and tensin homolog), which is a key inhibitor of the AKT kinase signaling that promotes tumorigenesis in nasopharyngeal carcinoma. Our study thus identifies cMyc-miR-200c-PTEN-AKT as a functional module that promotes cellular transformation in nasopharyngeal carcinoma.

Pterostilbene down-regulates hTERT at physiological concentrations in breast cancer cells: Potentially through the inhibition of cMyc

Human telomerase reverse transcriptase (hTERT) encodes the catalytic subunit of telomerase, which has been shown to be upregulated in many cancers. Pterostilbene is a naturally occurring stilbenoid and phytoalexin found primarily in blueberries that exhibits antioxidant activity and inhibits the growth of various cancer cell types. Therefore, the aim of this study was to determine whether treatment with pterostilbene, at physiologically achievable concentrations, can inhibit the proliferation of breast cancer cells and down-regulate the expression of hTERT. We found that pterostilbene inhibits the cellular proliferation of MCF-7 and MDA-MB-231 breast cancer cells in both a time- and dose-dependent manner, without significant toxicity to the MCF10A control cells. Pterostilbene was also shown to increase apoptosis in both breast cancer cell lines. Dose-dependent cell cycle arrest in G1 and G2/M phase was observed after treatment with pterostilbene in MCF-7 and MDA-231 cells, respectively. hTERT expression was down-regulated after treatment in both a time- and dose-dependent manner. Pterostilbene also reduced telomerase levels in both cell lines in a dose-dependent manner. Moreover, cMyc, a proposed target of the pterostilbene-mediated inhibition of hTERT, was down-regulated both transcriptionally and posttranscriptionally after treatment. Collectively, these findings highlight a promising use of pterostilbene as a natural, preventive, and therapeutic agent against the development and progression of breast cancer.

MicroRNA-148a deficiency promotes hepatic lipid metabolism and hepatocarcinogenesis in mice

miRNAs are involved in many physiologic and disease processes by virtue of degrading specific mRNAs or inhibiting their translation. miR-148a has been implicated in the control of tumor growth and cholesterol and triglyceride homeostasis using in vitro or in vivo gene expression- and silencing-based approaches. Here miR-148a knockout (KO) mice were used to investigate the intrinsic role of miR-148a in liver physiology and hepatocarcinogenesis in mice. miR-148a downregulation was found to be correlated with poor clinical outcomes in hepatocellular carcinoma (HCC) patients. Under regular chow diet (RCD) or high fat diet (HFD), miR-148a deletion significantly accelerated DEN-induced hepatocarcinogenesis in mice. Mechanistically, miR-148a deletion promotes lipid metabolic disorders in mice. Moreover, restoration of miR-148a reversed these defects. Finally, miR-148a was found to directly inhibit several key regulators of hepatocarcinogenesis and lipid metabolism. These findings reveal crucial roles for miR-148a in the hepatic lipid metabolism and hepatocarcinogenesis. They further identify miR-148a as a potential therapeutic target for certain liver diseases, including cancer.

MicroRNA-30a attenuates mutant KRAS-driven colorectal tumorigenesis via direct suppression of ME1

Frequent KRAS mutations contribute to multiple cancers including ~40% of human colorectal cancers (CRCs). Systematic screening of 1255 microRNAs (miRNAs) identified miR-30a as a synthetic lethal in KRAS-mutant CRC cells. miR-30a was downregulated in CRCs and repressed by P65. miR-30a directly targeted malic enzyme 1 (ME1) and KRAS, and inhibited anchorage-independent growth and in vivo tumorigenesis by KRAS-mutant CRC cells. ME1 was significantly upregulated in KRAS-mutant CRCs. Eliminating ME1 by short hairpin RNA (shRNA) resulted in obviously decreased NADPH production, levels of triglyceride and fatty acid, and an inhibition of tumorigenicity of KRAS-mutant CRCs. miR-30a overexpression and ME1 suppression attenuated AOM/DSS-induced colorectal tumorigenesis. The critical roles of miR-30a and ME1 in the development of KRAS-mutant CRCs indicate therapy potentials for this subtype of cancer.

Synthetic lethality: emerging targets and opportunities in melanoma

Great progress has been made in the treatment of melanoma through use of targeted therapies and immunotherapy. One approach that has not been fully explored is synthetic lethality, which exploits somatically acquired changes, usually driver mutations, to specifically kill tumour cells. We outline the various approaches that may be applied to identify synthetic lethal interactions and define how these interactions may drive drug discovery efforts.

Strategies to Inhibit Myc and Their Clinical Applicability

Myc is an oncogene deregulated in most-perhaps all-human cancers. Each Myc family member, c-, L-, and N-Myc, has been connected to tumor progression and maintenance. Myc is recognized as a "most wanted" target for cancer therapy, but has for many years been considered undruggable, mainly due to its nuclear localization, lack of a defined ligand binding site, and physiological function essential to the maintenance of normal tissues. The challenge of identifying a pharmacophore capable of overcoming these hurdles is reflected in the current absence of a clinically-viable Myc inhibitor. The first attempts to inhibit Myc used antisense technology some three decades ago, followed by small molecule inhibitors discovered through "classical" compound library screens. Notable breakthroughs proving the feasibility of systemic Myc inhibition were made with the Myc dominant negative mutant Omomyc, showing both the great promise in targeting this infamous oncogene for cancer treatment as well as allaying fears about the deleterious side effects that Myc inhibition might have on normal proliferating tissues. During this time many other strategies have appeared in an attempt to drug the undruggable, including direct and indirect targeting, knockdown, protein/protein and DNA interaction inhibitors, and translation and expression regulation. The inhibitors range from traditional small molecules to natural chemicals, to RNA and antisense, to peptides and miniproteins. Here, we briefly describe the many approaches taken so far, with a particular focus on their potential clinical applicability.

MicroRNA-based screens for synthetic lethal interactions with c-Myc

microRNAs (miRs) are small, non-coding RNAs, which play crucial roles in the development and progression of human cancer. Given that miRs are stable, easy to synthetize and readily introduced into cells, they have been viewed as having potential therapeutic benefit in cancer. c-Myc (Myc) is one of the most commonly deregulated oncogenic transcription factors and has important roles in the pathogenesis of cancer, thus making it an important, albeit elusive therapeutic target. Here we review the miRs that have been identified as being both positive and negative targets for Myc and how these participate in the complex phenotypes that arise as a result of Myc-driven transformation. We also discussseveral recent reports of Myc-synthetic lethal interactions with miRs.These highlight the importance and complexity of miRs in Myc-mediated biological functions and the opportunities for Myc-driven human cancer therapies.