Brief inactivation of c-Myc is not sufficient for sustained regression of c-Myc-induced tumours of pancreatic islets and skin epidermis

A Review of Nuclei Detection and Segmentation on Microscopy Images Using Deep Learning With Applications to Unbiased Stereology Counting

The detection and segmentation of stained cells and nuclei are essential prerequisites for subsequent quantitative research for many diseases. Recently, deep learning has shown strong performance in many computer vision problems, including solutions for medical image analysis. Furthermore, accurate stereological quantification of microscopic structures in stained tissue sections plays a critical role in understanding human diseases and developing safe and effective treatments. In this article, we review the most recent deep learning approaches for cell (nuclei) detection and segmentation in cancer and Alzheimer's disease with an emphasis on deep learning approaches combined with unbiased stereology. Major challenges include accurate and reproducible cell detection and segmentation of microscopic images from stained sections. Finally, we discuss potential improvements and future trends in deep learning applied to cell detection and segmentation.

Computer Image Analysis Reveals C-Myc as a Potential Biomarker for Discriminating between Keratoacanthoma and Cutaneous Squamous Cell Carcinoma

The distinction between Keratoacanthoma (KA) and Cutaneous Squamous Cell Carcinoma (cSCC) is critical yet usually challenging to discriminate clinically and histopathologically. One approach to differentiate KA from cSCC is through assessing the immunohistochemical staining patterns of the three indicators, β-catenin, C-Myc, and CyclinD1, which are critical molecules that play important roles in the Wnt/β-catenin signaling pathway. Ki-67, as a proliferation biomarker for human tumor cells, was also assessed as an additional potential marker for differentiating KA from cSCC. In this report, these four indicators were analyzed in 42 KA and 30 cSCC cases with the use of the computer automated image analysis system. Computer automated image analysis is a time-based and cost-effective method of determining IHC staining in KA and cSCC samples. We found that C-Myc staining was predominantly localized in the nuclei of basal cells within KA patients, whereas cSCC staining was predominantly localized in the nuclei of diffuse cells. This C-Myc staining pattern has a sensitivity of 78.6% and a specificity of 66.7% for identifying KA. Moreover, positive rates of distinct expression patterns of C-Myc and Ki-67 may also serve as a means to clinically distinguish KA from cSCC. Taken together, our results suggest that these markers, in particular C-Myc, may be useful in differentiating KA from cSCC.

Modelling the MYC-driven normal-to-tumour switch in breast cancer

The potent MYC oncoprotein is deregulated in many human cancers, including breast carcinoma, and is associated with aggressive disease. To understand the mechanisms and vulnerabilities of MYC-driven breast cancer, we have generated an in vivo model that mimics human disease in response to MYC deregulation. MCF10A cells ectopically expressing a common breast cancer mutation in the phosphoinositide 3 kinase pathway (PIK3CA^H1047R) led to the development of organised acinar structures in mice. Expressing both PIK3CA^H1047R and deregulated MYC led to the development of invasive ductal carcinoma. Therefore, the deregulation of MYC expression in this setting creates a MYC-dependent normal-to-tumour switch that can be measured in vivo. These MYC-driven tumours exhibit classic hallmarks of human breast cancer at both the pathological and molecular level. Moreover, tumour growth is dependent upon sustained deregulated MYC expression, further demonstrating addiction to this potent oncogene and regulator of gene transcription. We therefore provide a MYC-dependent model of breast cancer, which can be used to assay invivo tumour signalling pathways, proliferation and transformation from normal breast acini to invasive breast carcinoma. We anticipate that this novel MYC-driven transformation model will be a useful research tool to better understand the oncogenic function of MYC and for the identification of therapeutic vulnerabilities.

Summary: We present a MYC-driven transformation model of breast cancer that recapitulates the disease in vivo and which can be used to identify MYC-dependent cancer vulnerabilities.

MYC-y mice: from tumour initiation to therapeutic targeting of endogenous MYC

MYC is one of the best-studied oncogenes in terms of mouse models of malignancy. MYC overexpression has been targeted to several tissues using transgenic constructs, and more recently as mouse models have evolved, conditional systems have been developed to allow the regulation of MYC expression or activity in vivo. The ability to target MYC expression to specific tissues and cell lineages, as well as the ability to regulate that expression, has made genetically engineered mouse models (GEMM) a valuable resource for studying the importance of MYC in the process of tumourigenesis. Here we review how these models have been used to address the role of MYC in tumour initiation and maintenance, how subtle changes in levels of MYC can influence tumourigenesis, and finally the ongoing efforts to target endogenous MYC genetically and with novel therapies.

Targeting MYC-Regulated miRNAs to Combat Cancer

The MYC protein controls many cellular processes, including proliferation, cell cycle progression, cell growth, metabolism, angiogenesis, differentiation, cell adhesion, and motility. This is primarily achieved through transcriptional regulation of large gene networks that ultimately results in activation or repression of target genes. Given its broad regulatory scope, the expression of the MYC gene itself needs to be tightly controlled. Deregulation of MYC expression promotes tumorigenesis and, not surprisingly, MYC is frequently activated in many different human cancers. Furthermore, these tumors become highly dependent on sustained MYC expression, while MYC inactivation results in desirable anticancer effects, such as cell death, differentiation, and/or senescence. Thus, MYC has emerged as an attractive target for cancer therapy. In addition to regulating protein-coding genes, MYC also governs the expression of microRNAs, many of which have important regulatory roles in cancer development and progression. Here we will discuss how MYC-regulated miRNAs could be exploited for therapeutic development for cancer.

Reviewing once more the c-myc and Ras collaboration: converging at the cyclin D1-CDK4 complex and challenging basic concepts of cancer biology

The c-myc is a proto-oncogene that manifests aberrant expression at high frequencies in most types of human cancer. C-myc gene amplifications are often observed in various cancers as well. Ample studies have also proved that c-myc has a potent oncogenicity, which can be further enhanced by collaborations with other oncogenes such as Bcl-2 and activated Ras. Studies on the collaborations of c-myc with Ras or other genes in oncogenicity have established several basic concepts and have disclosed their underlying mechanisms of tumor biology, including "immortalization" and "transformation". In many cases, these collaborations may converge at the cyclin D1-CDK4 complex. In the meantime, however, many results from studies on the c-myc, Ras and cyclin D1-CDK4 also challenge these basic concepts of tumor biology and suggest to us that the immortalized status of cells should be emphasized. Stricter criteria and definitions for a malignantly transformed status and a benign status of cells in culture also need to be established to facilitate our study of the mechanisms for tumor formation and to better link up in vitro data with animal results and eventually with human cancer pathology.

The role of supercoiling in transcriptional control of MYC and its importance in molecular therapeutics

MYC is deregulated in most tumour types, but an effective means to selectively target its aberrant expression is not yet available. Supercoiling that is induced by transcription has been demonstrated to have dynamic effects on DNA in the MYC promoter element: it converts duplex DNA to non-duplex DNA structures, even at considerable distances from the transcriptional start site. These non-duplex DNA structures, which control both turning on and off of transcription and the rate of transcription firing, are amenable to small-molecule targeting. This dynamic system provides a unique opportunity for the treatment of tumours in which MYC is an important oncogene.

Cancer micrometastasis and tumour dormancy

Many epithelial cancers carry a poor prognosis even after curative resection of early stage tumours. Tumour progression in these cancer patients has been attributed to the existence and persistence of disseminated tumour cells (DTC) in various body compartments as a sign of minimal residual disease. Bone marrow (BM) has been shown to be a common homing organ and reservoir for DTC. A significant correlation between the presence of DTC in BM and metastatic relapse has been reported in various tumour types. However, only a portion of patients with DTC in BM at primary surgery relapse. Thus far, little is known about the conditions required for the persistence of dormancy or the escape from the dormant phase into the active phase of metastasis formation. Thereby, this peculiar stage of conceivably balanced tumour cell division and death may last for decades in cancer patients. Most likely, the ability of a dormant DTC to "be activated" is a complex process involving (i) somatic aberrations in the tumour cells, (ii) the interaction of the DTC with the new microenvironment at the secondary site, and (iii) hereditary components of the host (i.e., cancer patient). In this review, we will summarize the key findings of research on micrometastatic cancer cells and discuss these findings in the context of the concept of tumour dormancy.

Current status and issues in cancer stem cell study

Cancer stem cells (CSCs) have been positively identified and successfully isolated from some but not all cancers. The studies on CSCs to date suggest that these cells are rare among the tumor cell population, and they are capable of self-renewing and maintaining tumor growth and heterogeneity. Therapies aimed at CSCs have shown some promise, but their further development will require a more thorough understanding of the biology of CSCs and methods for identifying and isolating this cell subpopulation. This review examines what is known to date regarding the similarities and differences between cancer and somatic stem cells: CSC surface marker development and cell isolation (including a model isolation from our lab), the frequency, potential origin, and signal transduction of CSCs, and the current state of CSC-targeting therapeutic strategies.

C-Myc is a critical mediator of the phenotypes of Apc loss in the intestine

The Adenomatous polyposis coli (Apc) gene is mutated in up to 80% of sporadic colorectal cancers. After Apc loss, there is deregulation of the Wnt signaling pathway and transactivation of T-cell factor/leukemia enhancing factor target genes such as C-Myc. This review focuses on recent data highlighting the importance of the C-Myc oncogene and its transcriptional targets in establishing all of the phenotypes caused by the deletion of the Apc tumor suppressor gene within the intestinal epithelium. The importance of investigating Apc and C-Myc gene function in the correct tissue context is also discussed.

Genomic and proteomic analysis reveals a threshold level of MYC required for tumor maintenance

MYC overexpression has been implicated in the pathogenesis of most types of human cancers. MYC is likely to contribute to tumorigenesis by its effects on global gene expression. Previously, we have shown that the loss of MYC overexpression is sufficient to reverse tumorigenesis. Here, we show that there is a precise threshold level of MYC expression required for maintaining the tumor phenotype, whereupon there is a switch from a gene expression program of proliferation to a state of proliferative arrest and apoptosis. Oligonucleotide microarray analysis and quantitative PCR were used to identify changes in expression in 3,921 genes, of which 2,348 were down-regulated and 1,573 were up-regulated. Critical changes in gene expression occurred at or near the MYC threshold, including genes implicated in the regulation of the G(1)-S and G(2)-M cell cycle checkpoints and death receptor/apoptosis signaling. Using two-dimensional protein analysis followed by mass spectrometry, phospho-flow fluorescence-activated cell sorting, and antibody arrays, we also identified changes at the protein level that contributed to MYC-dependent tumor regression. Proteins involved in mRNA translation decreased below threshold levels of MYC. Thus, at the MYC threshold, there is a loss of its ability to maintain tumorigenesis, with associated shifts in gene and protein expression that reestablish cell cycle checkpoints, halt protein translation, and promote apoptosis.

Oncogene cooperation in tumor maintenance and tumor recurrence in mouse mammary tumors induced by Myc and mutant Kras

Most, if not all, cancers are composed of cells in which more than one gene has a cancer-promoting mutation. Although recent evidence has shown the benefits of therapies targeting a single mutant protein, little attention has been given to situations in which experimental tumors are induced by multiple cooperating oncogenes. Using combinations of doxycycline-inducible and constitutive Myc and mutant Kras transgenes expressed in mouse mammary glands, we show that tumors induced by the cooperative actions of two oncogenes remain dependent on the activity of a single oncogene. Deinduction of either oncogene individually, or both oncogenes simultaneously, led to partial or complete tumor regression. Prolonged remission followed deinduction of Kras(G12D) in the context of continued Myc expression, deinduction of a MYC transgene with continued expression of mutant Kras produced modest effects on life extension, whereas simultaneous deinduction of both MYC and Kras(G12D) transgenes further improved survival. Disease relapse after deinduction of both oncogenes was associated with reactivation of both oncogenic transgenes in all recurrent tumors, often in conjunction with secondary somatic mutations in the tetracycline transactivator transgene, MMTV-rtTA, rendering gene expression doxycycline-independent. These results demonstrate that tumor viability is maintained by each gene in a combination of oncogenes and that targeted approaches will also benefit from combination therapies.

MicroRNA let-7a down-regulates MYC and reverts MYC-induced growth in Burkitt lymphoma cells

Regulation of the MYC oncogene remains unclear. Using 10058-F4, a compound that inhibits MYC-MAX transcription factor, MYC protein and gene expression were down-regulated in Namalwa cells, a Burkitt lymphoma. Compound 10058-F4 decreased MYC mRNA (45%), MYC protein (50%), and cell growth (32%). MYC-MAX transcription factor was disrupted 24 h after treatment, resulting in transcriptional inhibition of target genes. Because microRNAs (miRNA) disrupt mRNA translation, let-7a, let-7b, and mir-98 were selected using bioinformatics for targeting MYC. Inhibition of MYC-MAX transcription factor with 10058-F4 increased levels of members of the let-7 family. In inhibited cells at 24 h, let-7a, let-7b, and mir-98 were induced 4.9-, 1.3-, and 2.4-fold, respectively, whereas mir-17-5p decreased 0.23-fold. These results were duplicated using microRNA multianalyte suspension array technology. Regulation of MYC mRNA by let-7a was confirmed by transfections with pre-let-7a. Overexpression of let-7a (190%) decreased Myc mRNA (70%) and protein (75%). Down-regulation of Myc protein and mRNA using siRNA MYC also elevated let-7a miRNA and decreased Myc gene expression. Inverse coordinate regulation of let-7a and mir-17-5p versus Myc mRNA by 10058-F4, pre-let-7a, or siRNA MYC suggested that both miRNAs are Myc-regulated. This supports previous results in lung and colon cancer where decreased levels of the let-7 family resulted in increased tumorigenicity. Here, pre-let-7a transfections led to down-regulation of expression of MYC and its target genes and antiproliferation in lymphoma cells. These findings with let-7a add to the complexity of MYC regulation and suggest that dysregulation of these miRNAs participates in the genesis and maintenance of the lymphoma phenotype in Burkitt lymphoma cells and other MYC-dysregulated cancers.

Histological complexities of pancreatic lesions from transgenic mouse models are consistent with biological and morphological heterogeneity of human pancreatic cancer

Although pancreatic cancer is the fourth leading cause of cancer death, it has received much less attention compared to other malignancies. There are several transgenic animal models available for studies of pancreatic carcinogenesis, but most of them do not recapitulate, histologically, human pancreatic cancer. Here we review some detailed molecular complexity of human pancreatic cancer and their reflection in histomorphological complexities of pancreatic lesions developed in various transgenic mouse models with a special concern for studying the effects of chemotherapeutic and chemopreventive agents. These studies usually require a large number of animals that are at the same age and gender and should be either homozygote or heterozygote but not a mixture of both. Only single-transgene models can meet these special requirements, but many currently available models require a mouse to simultaneously bear several transgene alleles. Thus it is imperative to identify new gene promoters or enhancers that are specific for the ductal cells of the pancreas and are highly active in vivo so as to establish new single-transgene models that yield pancreatic ductal adenocarcinomas for chemotherapeutic and chemopreventive studies.

Conditional transgenic models define how MYC initiates and maintains tumorigenesis

MYC is one of the most commonly overexpressed oncogenes in human cancer. The targeted inactivation of MYC is a possible therapy for neoplasia. Conditional transgenic mouse model systems are tractable methods to precisely dissect how and when the inactivation of MYC might be effective in the treatment for human cancer. From these model systems, several general principles emerge. MYC inactivation stereotypically results in the proliferative arrest, differentiation and/or apoptosis of tumor cells. The specific consequences of MYC inactivation appear to depend both on the type of cancer as well as the constellation of genetic events unique to a given tumor. Tumors can escape from dependence upon MYC by acquiring compensatory genetic events. MYC inactivation can uncover the stem cell properties of tumor cells that differentiate into normal appearing cells. In some cases, these differentiated cells are actually dormant tumor cells that recover their neoplastic properties upon MYC reactivation. In other cases, even brief MYC inactivation is sufficient to induce sustained tumor regression. Insights from conditional transgenic mouse models will be useful in the development of therapies that target MYC for the treatment of cancer.

Identification of small molecules that induce apoptosis in a Myc-dependent manner and inhibit Myc-driven transformation

The Myc transcription factor plays a central role in the regulation of cell cycle progression, apoptosis, angiogenesis, and cellular transformation. Myc is a potent oncoprotein that is deregulated in a wide variety of human tumors and is therefore an attractive target for novel cancer therapies. Using a cellular screening approach, we have identified low-molecular-weight compounds, Myc pathway response agents (MYRAs), that induce apoptosis in a c-Myc-dependent manner and inhibit Myc-driven cellular transformation. MYRA-A inhibits Myc transactivation and interferes with the DNA-binding activity of Myc family proteins but has no effect on the E-box-binding protein USF. In contrast, MYRA-B induces Myc-dependent apoptosis without affecting Myc transactivation or Myc/Max DNA binding. Our data show that cellular screening assays can be a powerful strategy for the identification of candidate substances that modulate the Myc pathway. These compounds can be useful tools for studying Myc function and may also be of therapeutic potential as leads for drug development.

Rehabilitation of cancer through oncogene inactivation

The inactivation of the MYC oncogene alone can reverse tumorigenesis. Upon MYC inactivation, tumors stereotypically reverse, undergoing proliferative arrest, cellular differentiation and/or apoptosis. The precise consequences of MYC inactivation appear to depend upon both genetic and epigenetic parameters. In some types of cancer following MYC inactivation, tumor cells become well differentiated and biologically and histologically normal, inducing sustained tumor regression. However, in some cases, these normal-appearing cells are actually dormant tumor cells and upon MYC reactivation they rapidly recover their tumorigenic properties. Future therapies to treat cancer will need to address the possibility that tumor cells can camouflage a normal phenotype following treatment, resting in a dormant, latently cancerous state.

Repressible transgenic model of NRAS oncogene–driven mast cell disease in the mouse

To create a model in which to study the effects of RAS dysregulation in hematopoietic disease, we developed separate founder lines of transgenic mice, with the tetracycline transactivator (tTA) driven by the Vav hematopoietic promoter in one line and NRASV12 driven by the tetracycline responsive element (TRE2) in the other. When these lines are crossed, doubly transgenic animals uniformly develop a disease similar to human aggressive systemic mastocytosis (ASM) or mast cell leukemia (MCL) when they are between 2 and 4 months of age. Disease is characterized by tissue infiltrates of large, well-differentiated mast cells in the spleen, liver, skin, lung, and thymus. Analysis of bone sections shows small to large foci of similarly well-differentiated mast cells. Results also show that transgene expression and diseases are repressible through the administration of doxycycline in the drinking water of affected animals, indicating that NRASV12 expression is required to initiate and maintain disease in doubly transgenic mice. Our inducible system of transgenes, developed as a model of mutant NRASV12 oncogene–driven myeloid disease, will be useful for studying the role of RAS dysregulation in hematopoietic disease in general and in discrete human diseases, specifically ASM and MCL.

Tumor dormancy and MYC inactivation: pushing cancer to the brink of normalcy

Upon MYC inactivation, tumors variously undergo proliferative arrest, cellular differentiation, and apoptosis and in some cases, apparently permanently revoking tumorigenesis. In liver tumor cells, we recently showed that MYC inactivation uncovers stem cell properties and triggers differentiation, but in this case, their neoplastic properties are restorable by MYC reactivation. Thus, whereas oncogene inactivation can push cancer to the brink of normalcy, some cells retain the latent capacity to turn cancerous again, arguing that they may exist in a state of tumor dormancy.