Miniaturization of the Clonogenic Assay Using Confluence Measurement

Biological Activity of Oleanolic Acid Derivatives HIMOXOL and Br-HIMOLID in Breast Cancer Cells Is Mediated by ER and EGFR

Breast cancer is one of the most frequently observed malignancies worldwide and represents a heterogeneous group of cancers. For this reason, it is crucial to properly diagnose every single case so a specific and efficient therapy can be adjusted. One of the most critical diagnostic parameters evaluated in cancer tissue is the status of the estrogen receptor (ER) and epidermal growth factor receptor (EGFR). Interestingly, the expression of the indicated receptors may be used in a personalized therapy approach. Importantly, the promising role of phytochemicals in the modulation of pathways controlled by ER and EGFR was also demonstrated in several types of cancer. One such biologically active compound is oleanolic acid, but due to poor water solubility and cell membrane permeability that limits its use, alternative derivative compounds were developed. These are HIMOXOL and Br-HIMOLID, which were demonstrated to be capable of inducing apoptosis and autophagy or diminishing the migratory and invasive potential of breast cancer cells in vitro. In our study, we revealed that proliferation, cell cycle, apoptosis, autophagy, and also the migratory potential of HIMOXOL and Br-HIMOLID in breast cancer cells are mediated by ER (MCF7) and EGFR (MDA-MB-231) receptors. These observations make the studied compounds interesting in the context of anticancer strategies.

Repurposing Benztropine, Natamycin, and Nitazoxanide Using Drug Combination and Characterization of Gastric Cancer Cell Lines

Gastric cancer (GC) ranked as the fifth most incident cancer in 2020 and the third leading cause of cancer mortality. Surgical prevention and radio/chemotherapy are the main approaches used in GC treatment, and there is an urgent need to explore and discover innovative and effective drugs to better treat this disease. A new strategy arises with the use of repurposed drugs. Drug repurposing coupled with drug combination schemes has been gaining interest in the scientific community. The main objective of this project was to evaluate the therapeutic effects of alternative drugs in GC. For that, three GC cell lines (AGS, MKN28, and MKN45) were used and characterized. Cell viability assays were performed with the reference drug 5-fluororacil (5-FU) and three repurposed drugs: natamycin, nitazoxanide, and benztropine. Nitazoxanide displayed the best results, being active in all GC cells. Further, 5-FU and nitazoxanide in combination were tested in MKN28 GC cells, and the results obtained showed that nitazoxanide alone was the most promising drug for GC therapy. This work demonstrated that the repurposing of drugs as single agents has the ability to decrease GC cell viability in a concentration-dependent manner.

Evaluation of Tazemetostat as a Therapeutically Relevant Substance in Biliary Tract Cancer

Biliary tract cancer (BTC) is a gastrointestinal malignancy associated with a poor survival rate. Current therapies encompass palliative and chemotherapeutic treatment as well as radiation therapy, which results in a median survival of only one year due to standard therapeutic ineffectiveness or resistance. Tazemetostat is an FDA-approved inhibitor of enhancer of Zeste homolog 2 (EZH2), a methyltransferase involved in BTC tumorigenesis via trimethylation of histone 3 at lysine 27 (H3K27me3), an epigenetic mark associated with silencing of tumor suppressor genes. Up to now, there are no data available regarding tazemetostat as a possible treatment option against BTC. Therefore, the aim of our study is a first-time investigation of tazemetostat as a potential anti-BTC substance in vitro. In this study, we demonstrate that tazemetostat affects cell viability and the clonogenic growth of BTC cells in a cell line-dependent manner. Furthermore, we found a strong epigenetic effect at low concentrations of tazemetostat, which was independent of the cytotoxic effect. We also observed in one BTC cell line that tazemetostat increases the mRNA levels and protein expression of the tumor suppressor gene Fructose-1,6-bisphosphatase 1 (FBP1). Interestingly, the observed cytotoxic and epigenetic effects were independent of the mutation status of EZH2. To conclude, our study shows that tazemetostat is a potential anti-tumorigenic substance in BTC with a strong epigenetic effect.

Six-well plate-based colony-forming efficacy assay and Co-Culture application to assess toxicity of metal oxide nanoparticles

The development of a universal, label-free, and reliable in vitro toxicity testing method for nanoparticles is urgent because most nanoparticles can interfere with toxicity assays. In this regard, the colony-forming efficacy (CFE) assay has been suggested as a suitable in vitro toxicity assay for testing nanoparticles without such interference. Recently, the Organisation for Economic Co-operation and Development (OECD) developed a 60 × 15 mm Petri dish-based CFE assay for testing nanoparticles in MDCK-1 cells. However, further investigations are needed, including testing with other cell types, at a smaller scale for greater efficiency, and the application of the co-culture technique. In this study, we selected TiO₂, CuO, CeO₂, and SiO₂ as test nanoparticles and successfully developed a 6-well plate-based CFE assay using HepG2 and A549 cells and a co-culture assay for combinations of HepG2 cells and THP-1 macrophages or A549 cells and THP-1 monocytes. The results suggest that the 6-wellplate-based CFE assay for HepG2 and A549 cells can be applied to nanoparticles, but the co-culture CFE assay has limitations in that it is not different from the single culture study, and it inhibits colony-formation by A549 cells in the presence of macrophages; this warrant further study.

Advanced High-Content-Screening Applications of Clonogenicity in Cancer

Since its first report in 1956 by Puck and Marcus, the clonogenic assay has not been completely adapted into high-content-screening (HCS) workflows despite the numerous automated systems available. Initially, clonogenic assays were used to observe the effects of radiation on cell survival, particularly with cancer cells. The clonogenic assay has since been well characterized as a measure of cancer stem cell (CSC) stemness, demonstrating that a single CSC can generate clonogenic colonies. CSCs are highly tumorigenic with an unlimited proliferation potential and capacity to generate malignant tumors. Furthermore, CSCs are also known to resist conventional chemotherapy as well as more contemporary targeted therapies alike. Therefore, given the complexity of CSCs and their clinical relevance, new methods must follow to more effectively study and characterize CSC mechanisms that allow them to proliferate and persist, and to develop drugs and other therapies that can more effectively target these populations. Herein, we present a HCS method to quantify the number and size of colonies in 2D and 3D culture models and to distinguish colonies based on fluorescent markers using an Opera Phenix high-content-screening system. In addition, we present a method to scan at low magnification and rescan at a higher magnification to capture in greater detail colonies or even single cells of interest. These methods can be adapted to numerous applications or other imaging systems to study CSC biology using high-content analysis and for high-throughput drug discovery.

Cisplatin-resistant A549 non-small cell lung cancer cells can be identified by increased mitochondrial mass and are sensitive to pemetrexed treatment

Background

Cisplatin plus pemetrexed combination therapy is considered the standard treatment for patients with advanced, non-squamous, non-small-cell lung cancer (NSCLC). However, advanced NSCLC has a 5-year survival rate of below 10%, which is mainly due to therapy resistance. We previously showed that the NSCLC cell line A549 harbors different subpopulations including a mesenchymal-like subpopulation characterized by increased chemo- and radiotherapy resistance. Recently, therapy resistance in hematological and solid tumors has been associated with increased mitochondrial activity. Thus, the aim of this study was to investigate the role of the mitochondrial activity in NSCLC chemotherapy resistance.

Methods

Based on MitoTracker staining, subpopulations characterized by the highest 10% (Mito-High) or lowest 10% (Mito-Low) mitochondrial mass content were sorted by FACS (Fluorescence-Activated Cell Sorting) from paraclonal cultures of the NSCLC A549 cell line . Mitochondrial DNA copy numbers were quantified by real-time PCR whereas basal cellular respiration was measured by high-resolution respirometry. Cisplatin and pemetrexed response were quantified by proliferation and colony formation assay.

Results

Pemetrexed treatment of parental A549 cells increased mitochondrial mass over time. FACS-sorted paraclonal Mito-High cells featured increased mitochondrial mass and mitochondrial DNA copy number compared to the Mito-Low cells. Paraclonal Mito-High cells featured an increased proliferation rate and were significantly more resistant to cisplatin treatment than Mito-Low cells. Interestingly, cisplatin-resistant, paraclonal Mito-High cells were significantly more sensitive to pemetrexed treatment than Mito-Low cells. We provide a working model explaining the molecular mechanism underlying the increased cisplatin- and decreased pemetrexed resistance of a distinct subpopulation characterized by high mitochondrial mass.

Conclusions

This study revealed that cisplatin resistant A549 lung cancer cells can be identified by their increased levels of mitochondrial mass. However, Mito-High cells feature an increased sensitivity to pemetrexed treatment. Thus, pemetrexed and cisplatin target reciprocal lung cancer subpopulations, which could explain the increased efficacy of the combination therapy in the clinical setting.

The Cancer Stem Cell Inhibitor Napabucasin (BBI608) Shows General Cytotoxicity in Biliary Tract Cancer Cells and Reduces Cancer Stem Cell Characteristics

Biliary tract cancer is a devastating disease with limited therapeutic options. The involvement of cancer stem cells in biliary tract cancer is likely. Napabucasin is a previously described cancer stem cell inhibitor that is currently being used in clinical trials. However, data regarding napabucasin and biliary tract cancer are not available yet. We tested the general cytotoxic effect of napabucasin on a comprehensive biliary tract cancer in vitro model, using resazurin assay and Annexin V/7-AAD staining. The effect of napabucasin on functional cancer stem cell characteristics was analyzed via soft agar assay, aldehyde-dehydrogenase-1 assay, measurement of surface CD326 expression, and measurement of clonogenic growth. The evaluation of the effect of napabucasin on cancer stem cell protein and gene expression was performed using Western blot and reverse transcription-PCR-based human cancer stem cell array. Napabucasin showed a concentration- and cell line-dependent cytotoxic effect, and increased the apoptotic and necrotic cell fractions. Treatment with napabucasin significantly reduced the formation of tumor spheres and clonogenic growth, as well as CD326 surface expression. Expression of cancer stem cell markers were reduced following napabucasin treatment on the protein and mRNA levels. Our study provides first data regarding napabucasin as a promising substance for the treatment of biliary tract cancer.