Gene expression signature of c-MYC-immortalized human fibroblasts reveals loss of growth inhibitory response to TGFβ

Ras-Mediated Activation of NF-κB and DNA Damage Response in Carcinogenesis

Cancer is a multi-step process during which cells acquire mutations that eventually lead to uncontrolled cell growth and division and evasion of programmed cell death. The oncogenes such as Ras and c-Myc may be responsible in all three major stages of cancer i.e., early, intermediate, and late. The NF-κB has been shown to control the expression of genes linked with tumor pathways such as chronic inflammation, tumor cell survival, anti-apoptosis, proliferation, invasion, and angiogenesis. In the last few decades, various biomarker pathways have been identified that play a critical role in carcinogenesis such as Ras, NF-κB and DNA damage.

Efficient and simple approach to in vitro culture of primary epithelial cancer cells

Primary breast and prostate epithelial cancer cells may be efficiently cultured in vitro using simple and easily validatable approach–plates coated with a mixture of extracellular matrix components and tissue-specific primary cell medium.

Primary cancer cells constitute a favourable testing platform for in vitro research in oncology field as they reflect tumour state more accurately than the most commonly employed stable cell lines. Unfortunately, due to limited availability of material and difficulties with protocols validation, primary models are rarely implemented into laboratory practice.

We have compared protocols for primary cultures, differing in media components and plate coatings. In terms of culture establishment, application of Geltrex® coating demonstrated equal efficiency to feeder layer (83% compared with 72% successfully established breast and 80% compared with 80% prostate tumour specimens), yet it was substantially less complicated and easier to validate. Both Geltrex® coating and tissue-specific primary cell medium were permanently required to successfully maintain primary epithelial prostate cancer cells (PEPCs) in culture. In case of primary epithelial breast cancer cells (PEBCs), collagen I coating enabled to obtain comparable number of passages to Geltrex® coating (P=0.438). Commercial primary cell media demonstrated lower efficiency than tissue-specific ones (PEPCs–5 compared with 8 and PEBCs–6 compared with 9 passages). Interestingly, both analysed tumour types were unsusceptible to induction of culture lifespan extension when transduced with SV40LT, BMI-1 or hEST2 genes, commonly applied as potential immortalizing agents.

In conclusion, the approach based on extracellular matrix reconstitution and tissue-specific primary cell media is easy to validate and provides in vitro expansion sufficient for analytical purposes (approximately 8 passages). Therefore, it may facilitate implementation of hardly available experimental models for a variety of analyses.

Mechanisms underlying the cytotoxicity of a novel quinazolinedione-based redox modulator, QD232, in pancreatic cancer cells

BACKGROUND AND PURPOSE

Pancreatic cancer is characterized by alterations in several key signalling proteins, including increased expression and activity of the Src tyrosine kinase and focal adhesion kinase (FAK), which have been linked to its chemoresistance. Sustained Src inhibition reactivates survival pathways regulated by the transcription factor STAT3, also leading to resistance. Therefore, simultaneously targeting Src/FAK and STAT3 signalling could provide an important strategy for treating pancreatic cancer. Recently, we described novel quinazolinediones that increased generation of reactive oxygen species (ROS) and were cytotoxic in pancreatic cancer cells. Here, we have investigated effects of our lead compound, QD232, on Src/FAK and STAT3 signalling.

EXPERIMENTAL APPROACH

The major signalling pathways affected by QD232 in pancreatic cancer cell lines were identified by Kinexus proteomic analysis. Changes in key signalling proteins were confirmed by Western blotting. Cell migration was assessed by Boyden chamber and wound healing assays. Direct inhibition of kinase activity in vitro was assayed with a panel of 92 oncogenic kinases. Safety and efficacy of QD232 were determined in a xenograft mouse model of pancreatic cancer.

KEY RESULTS

QD232 potently inhibited Src/FAK and STAT3 phosphorylation, decreasing pancreatic cancer cell viability and migration. Furthermore, QD232 arrested cell cycle progression and induced apoptosis in these cells at low micromolar concentrations. Effects of QD232 on Src/FAK and STAT3 phosphorylation were blocked by N-acetylcysteine or glutathione.

CONCLUSIONS AND IMPLICATIONS

QD232 is a novel compound with a unique, ROS-dependent mechanism, effective in drug-resistant cancer cell lines. This compound shows potential as therapy for pancreatic cancer.

Synthetic lethal screens as a means to understand and treat MYC-driven cancers

Although therapeutics against MYC could potentially be used against a wide range of human cancers, MYC-targeted therapies have proven difficult to develop. The convergence of breakthroughs in human genomics and in gene silencing using RNA interference (RNAi) have recently allowed functional interrogation of the genome and systematic identification of synthetic lethal interactions with hyperactive MYC. Here, we focus on the pathways that have emerged through RNAi screens and present evidence that a subset of genes showing synthetic lethality with MYC are significantly interconnected and linked to chromatin and transcriptional processes, as well as to DNA repair and cell cycle checkpoints. Other synthetic lethal interactions with MYC point to novel pathways and potentially broaden the repertoire of targeted therapies. The elucidation of MYC synthetic lethal interactions is still in its infancy, and how these interactions may be influenced by tissue-specific programs and by concurrent genetic change will require further investigation. Nevertheless, we predict that these studies may lead the way to novel therapeutic approaches and new insights into the role of MYC in cancer.

Design and discovery of novel quinazolinedione-based redox modulators as therapies for pancreatic cancer

BACKGROUND

Altered cellular bioenergetics and oxidative stress are emerging hallmarks of most cancers including pancreatic cancer. Elevated levels of intrinsic reactive oxygen species (ROS) in tumors make them more susceptible to exogenously induced oxidative stress. Excessive oxidative insults overwhelm their adaptive antioxidant capacity and trigger ROS-mediated cell death. Recently, we have discovered a novel class of quinazolinediones that exert their cytotoxic effects by modulating ROS-mediated signaling.

METHODS

Cytotoxic potential was determined by colorimetric and colony formation assays. An XF24 Extracellular Flux Analyzer, and colorimetric and fluorescent techniques were used to assess the bioenergetics and oxidative stress effects, respectively. Mechanism was determined by Western blots.

RESULTS

Compound 3a (6-[(2-acetylphenyl)amino]quinazoline-5,8-dione) was identified through a medium throughput screen of ~1000 highly diverse in-house compounds and chemotherapeutic agents for their ability to alter cellular bioenergetics. Further structural optimizations led to the discovery of a more potent analog, 3b (6-[(3-acetylphenyl)amino]quinazoline-5,8-dione) that displayed anti-proliferative activities in low micromolar range in both drug-sensitive and drug-resistant cancer cells. Treatment with 3b causes Akt activation resulting in increased cellular oxygen consumption and oxidative stress in pancreatic cancer cells. Moreover, oxidative stress induced by 3b promoted activation of stress kinases (p38/JNK) resulting in cancer cell death. Treatment with antioxidants was able to reduce cell death confirming ROS-mediated cytotoxicity.

CONCLUSION

In conclusion, our novel quinazolinediones are promising lead compounds that selectively induce ROS-mediated cell death in cancer cells and warrant further preclinical studies.

GENERAL SIGNIFICANCE

Since 3b (6-[(3-acetylphenyl)amino]quinazoline-5,8-dione) exerts Akt-dependent ROS-mediated cell death, it might provide potential therapeutic options for chemoresistant and Akt-overexpressing cancers.

Oncoapoptotic signaling and deregulated target genes in cancers: special reference to oral cancer

Cancer is a class of diseases characterized by uncontrolled cell growth. The development of cancer takes place in a multi-step process during which cells acquire a series of mutations that eventually lead to unrestrained cell growth and division, inhibition of cell differentiation, and evasion of cell death. Dysregulation of oncoapoptotic genes, growth factors, receptors and their downstream signaling pathway components represent a central driving force in tumor development. The detailed studies of signal transduction pathways for mechanisms of cell growth and apoptosis have significantly advanced our understanding of human cancers, subsequently leading to more effective treatments. Oral squamous cell carcinoma represents a classic example of multi-stage carcinogenesis. It gradually evolves through transitional precursor lesions from normal epithelium to a full-blown metastatic phenotype. Genetic alterations in many genes encoding crucial proteins, which regulate cell proliferation, differentiation, survival and apoptosis, have been implicated in oral cancer. As like other solid tumors, in oral cancer these genes include the ones coding for cell cycle regulators or oncoproteins (e.g. Ras, Myc, cyclins, CDKs, and CKIs), tumor suppressors (e.g. p53 and pRb), pro-survival proteins (e.g. telomerase, growth factors or their receptors), anti-apoptotic proteins (e.g. Bcl2 family, IAPs, and NF-kB), pro-apoptotic proteins (e.g. Bax and BH-3 family, Fas, TNF-R, and caspases), and the genes encoding key transcription factors or elements for signal transduction leading to cell growth and apoptosis. Here we discuss the current knowledge of oncoapoptotic regulation in human cancers with special reference to oral cancers.

A high-throughput siRNA screening platform to identify MYC-synthetic lethal genes as candidate therapeutic targets

Targeted therapeutics toward specific genes and pathways represent the future of oncological treatments. However, several commonly activated oncogenes, such as MYC, have proven difficult to target by pharmacological agents. To broaden the menu of potentially druggable therapeutic targets, we describe a method to detect genes essential for the survival of MYC overexpressing cells, which we will refer to as MYC-synthetic lethal genes (MYC-SL) (Toyoshima et al., Proc Natl Acad Sci USA 109:9545-9550, 2012). These genes represent candidate targets for drug development to be utilized for MYC-driven cancers as well as probes to further our understanding of the biology of MYC-driven tumorigenesis. The discovery platform includes the following components: (1) an isogenic cell system that enables overexpression of MYC without oncogene-induced senescence (OIS) response (Benanti and Galloway, Mol Cell Biol 24:2842-2852, 2004; Benanti et al., Mol Cancer Res 5:1181-1189, 2007); (2) arrayed siRNA libraries targeting individual genes; (3) automated laboratory equipment for dispensing of cells, siRNAs, and readout assays; and (4) bioinformatics and software for data mining and visualization. This flexible platform can be readily applied to other oncogenes or tumor suppressor genes.