Pharmacological Isolation of Experimental Models of Drug-resistant Hepatocellular Carcinoma Cell Line

Drug resistance is one of the major challenges facing the success of chemotherapy against human hepatocarcinoma (HCC) as well as other types of cancer. Studies with cell lines can serve as initial screening for agents that could modulate drug resistance. Development of a good experimental model of drug-resistant cells is a prerequisite for the success of such cellular studies; but could be laborious and generally time-consuming. Additionally, the high mortality rate associated with advanced HCC calls for a probe into the mechanism of resistance by developing experimental model that mimics clinical method of its treatment. Consequently, we have reported a simplified method of selection of drug-resistant hepatocarcinoma cells from human hepatocellular carcinoma (HEPG2) cell line using pharmacologic agents, cisplatin (CDDP) and 5-fluorouracil (5-FU). HEPG2 cell line was incubated for 24 hours with different concentrations of CDDP (0 - 20 μM) or 5-FU (0 - 100 μM). Cell viability was assayed by CCK-8 (Cell Counting Kit) analysis, and the inhibitory concentrations (IC50) for CDDP and 5-FU were established by dose-dependent cytotoxicity curves. The IC50(s) were confirmed by flow cytometric analysis of cell death due to CDDP or 5-FU. Clinical method of treatment was imitated by treating the parental HEPG2 cell line in pulse, at the optimal concentration of either CDDP or 5-FU for 4 to 6 hours. Induction was repeated 6 times, whilst allowing the cells to attain at least 70% confluence between intervals of induction. The resultant drug-resistant sublines, (HEPG2CR) and (HEPG2FR) were found to be stable after over 3 months of drug withdrawal and maintenance in drug-free medium. This was done with the views of establishing a simple, efficient and direct protocol for the development of good cellular models for the study of drug resistance in liver cancer, with possible application in other cancer types

Biological functionalities of Transglutaminase 2 and the possibility of its compensation by other members of the transglutaminase family

Transglutaminase 2 (TG2) is the most widely distributed and most abundantly expressed member of the transglutaminase family of enzymes, a group of intracellular and extracellular proteins that catalyze the Ca2+-dependent post-translational modification of proteins. It is a unique member of the transglutaminase family owing to its specialized biochemical, structural and functional elements, ubiquitous tissue distribution and sub-cellular localization, and substrate specificity. The broad substrate-specificity of TG2 and its flexible interaction with numerous other gene products may account for its multiple biological functions. In addition to the classic Ca2+-dependent transamidation of proteins, which is a hallmark of transglutaminase enzymes, additional Ca2+-independent enzymatic and non-enzymatic activities of TG2 have been identified. Many such activities have been directly or indirectly implicated in diverse cellular physiological events, including cell growth and differentiation, cell adhesion and morphology, extracellular matrix stabilization, wound healing, cellular development, receptor-mediated endocytosis, apoptosis, and disease pathology. Given the wide range of activities of the transglutaminase gene family it has been suggested that, in the absence of active versions of TG2, its function could be compensated for by other members of the transglutaminase family. It is in the light of this assertion that we review herein, TG2 activities and the possibilities and premises for compensation for its absence

Agouti signalling protein is an inverse agonist to the wildtype and agonist to the melanic variant of the melanocortin-1 receptor in the grey squirrel (Sciurus carolinensis)

The melanocortin-1 receptor (MC1R) is a key regulator of mammalian pigmentation. Melanism in the grey squirrel is associated with an eight amino acid deletion in the mutant melanocortin-1 receptor with 24 base pair deletion (MC1RΔ24) variant. We demonstrate that the MC1RΔ24 exhibits a higher basal activity than the wildtype MC1R (MC1R-wt). We demonstrate that agouti signalling protein (ASIP) is an inverse agonist to the MC1R-wt but is an agonist to the MC1RΔ24. We conclude that the deletion in the MC1RΔ24 leads to a receptor with a high basal activity which is further activated by ASIP. This is the first report of ASIP acting as an agonist to MC1R

Inhibition of Transglutaminase 2 activity increases cisplatin cytotoxicity in a model of human hepatocarcinoma chemotherapy

Transglutaminase 2 (TG2) is a ubiquitous multifunctional enzyme whose expression has been found to be altered in numerous studies of apoptosis and cell survival; its activity has been found to be increased in many types of cancer, where it is often over-expressed. Cisplatin has long been used as an effective therapeutic drug to treat numerous cancers. Although its activity is based on cross-linking of DNA, cisplatin may also operate via other mechanisms that involve modification and alteration in the activity of protein and RNA modulators of the cell cycle and apoptotic processes; these mechanisms are less well characterised. In this study, we investigated the effects of cisplatin-induced apoptosis on TG2 expression and activity in the human hepatocarcinoma (HepG2) cell line. Through a combination of Western blotting, enzymatic activity assays, flow cytometry and fluorescence microscopy we provide evidence that TG2 is inhibited during initiation of apoptosis by cisplatin, an observation that was reversed by increasing the expression of TG2, by treating cells with retinoic acid. We also report, for the first time, that cisplatin can directly inhibit transglutaminase activity in vitro. Collectively, these studies increase our understanding of the mechanism(s) of action of cisplatin, as cisplatin–mediated reduction in TG2 activity appears to act as an early activator of apoptosis during chemotherapeutic treatment of hepatocarcinoma cells. This observation suggests an explanation as to how increased levels of TG2 activity in cancer cells could contribute to chemotherapeutic resistance to cisplatin, and so has implications for novel approaches to cisplatin therap

A novel combined resveratrol/berberine phytochemotheraputic using the HePG2 cell line as a model for the treatment of hepatocarcinoma

The results presented herein show that at clinically relevant concentrations (0–30 µM), the well-tolerated phytochemical berberine (BER) induces cell death in cultured human hepatocarcinoma (HepG2) cells as a model for liver cancer, primarily via apoptosis. Similar, relatively low-concentration single treatments using the structurally related phytochemical resveratrol (RSV), had little or no effect on cell viability but inhibited the cell cycle, while simultaneously increasing the strength of cellular adhesion. When used in combination, an RSV/BER cotreatment appeared to retain the ability of a single RSV treatment to increase cellular adhesion, but also induced a massive loss in hepatocarcinoma cellular viability, inducing cell death in more than 90% of cells. This model, therefore, suggests that it may be possible to use RSV to stabilise hepatocarcinomas against metastasis while using cotreatment with BER to simultaneously induce cell death. By measuring the changes in the activity of the pleiotropic enzyme transglutaminase 2 (TGM2), which is known to be overexpressed in hepatocarcinoma and many other tumours, we hypothesise a role for this enzyme in the activities of these two phytochemicals, and propose the potential use of this RSV/BER cotreatment as a chemotherapeutic in TGM2+ hepatocarcinomas

Feasibility Study of Human Corneal Endothelial Cell Transplantation Using an In Vitro Human Corneal Model

Purpose: To test the feasibility of a cell-therapy approach to treat corneal endothelial (CE) disorders using an in vitro model of human corneal decompensation. Materials and Methods: A CE decompensation model was established by removal of the DM/Endothelium complex from human cadaveric corneas in an air-interface organ culture system (Group 2) and compared to normal corneas (Group 1). The posterior stroma of decompensated corneas was seeded with immortalized human corneal endothelial cells (HCEC-12) in Group 3 and passage 0 primary human corneal endothelial cells (hCECs) in Group 4 corneas. Functional effects on stromal thickness were undertaken with histological analysis 3-10 days post-cell therapy treatment. Results: Removal of the DM/Endothelium complex in Group 2 corneas resulted in a stromal thickness of 903 ± 86 μm at 12 hours in comparison to 557 ± 72 μm in Group 1 corneas. The stromal thickness reduced from 1218 ± 153 μm to 458 ± 90 μm (63 ± 6 %, p=0.001) post cell transplantation in Group 3) and from 1100 ± 86 μm to 489 ± 94 μm (55 ± 7 %, p=0.00004 in Group 4 respectively. Post-transplantation histology demonstrated the formation of a monolayer of corneal endothelium attached to the posterior stromal surface. Conclusion: Direct transplantation of cultured hCECs and immortalized HCEC-12 to bare posterior corneal stroma resulted in the formation of an endothelial monolayer and restoration of stromal hydration to physiological thickness, demonstrating the feasibility of cell therapy in the treatment of corneal endothelial decompensation in a human in vitro model