Inhibition of Ion Channels and Heart Beat in Drosophila by Selective COX-2 Inhibitor SC-791

Recent findings suggest that modulation of ion channels might be implicated in some of the clinical effects of coxibs, selective inhibitors of cyclooxygenase-2 (COX-2). Celecoxib and its inactive analog 2,5-dimethyl-celecoxib, but not rofecoxib, can suppress or augment ionic currents and alter functioning of neurons and myocytes. To better understand these unexpected effects, we have recently investigated the mechanism of inhibition of human Kv2.1 channels by a highly selective COX-2 inhibitor SC-791. In this study we have further explored the SC-791 action on ion channels and heartbeat in Drosophila, which lacks cyclooxygenases and thus can serve as a convenient model to study COX-2-independent mechanisms of coxibs. Using intracellular recordings in combination with a pharmacological approach and utilizing available Drosophila mutants, we found that SC-791 inhibited voltage-activated K+ and L-type Ca2+ channels in larval body-wall muscles and reduced heart rate in a concentration-dependent manner. Unlike celecoxib and several other K+ channel blockers, SC-791 did not induce arrhythmia. Instead, application of SC-791 resulted in a dramatic slowing of contractions and, at higher concentrations, in progressively weaker contractions with gradual cessation of heartbeat. Isradipine, a selective blocker of L-type Ca2+ channels, showed a similar pattern of heart arrest, though no prolongation of contractions was observed. Ryanodine was the only channel modulating compound of those tested additionally that was capable of slowing contractions. Like SC-791, ryanodine reduced heart rate without arrhythmia. However, it could not stop heartbeat completely even at 500 µM, the highest concentration used. The magnitude of heart rate reduction, when SC-791 and ryanodine were applied together, was smaller than expected for independent mechanisms, raising the possibility that SC-791 might be interfering with excitation-contraction coupling in Drosophila heart

The effects of various combinations of different classes of anticancer drugs and tyrosine kinase inhibitors on the human MCF-7 breast carcinoma cell line

Magister Scientiae (Medical Bioscience) - MSc(MBS)This study investigated the effects of TKIs on the growth and proliferation of MCF-7 breast carcinoma cells in culture. MCF-7 cells were exposed to different concentrations of TKIs alone and in combination with each other. Inhibition of cell growth by TKIs used individually occurred in a dose- and time-dependent manner. When EGFR Inhibitor I, EGFR Inhibitor II/BIBX1382 and the multi-specific EGFR/ErbB-2/ErB-4 Inhibitor were used in combination with each other at equimolar log dose concentrations, the combined effects on cell growth was significantly different to inhibitors used individually as reflected in a decreased EC50 (IC50) during combination treatments. Generally, for the combinations with DOX, CPL and the TKIs, synergistic as well as antagonistic effects were observed at isoeffective concentrations with resultant decreases in dose reduction indices (DRIs) implying greater efficacies with the respective combinations. In this study, conventional PCR was used to detect and illustrate the presence of the EGFR gene in the samples, while RT-qPCR was used to determine the mRNA expression levels of this gene in MCF-7 breast carcinoma cell

Neurotoxicity of polybrominated diphenyl ethers (PBDEs)

Polybrominated diphenylethers (PBDEs), a class of brominated compounds used as flame retardants, are widespread and persistent contaminants, which accumulate in the environment, in animals, in the food chain, and in humans. Several studies have highlighted that the toxicity of this substances impacts the nervous system during development, as perinatal exposure to PBDEs has been shown to affect behavior, in particular motor and cognitive activities. The present research project investigated the neurotoxicity of PBDEs through an in vitro approach. The potential interactions between different PBDEs congeners, and between PBDEs and PCBs, another class of persistent contaminants, to which humans are also exposed, was assessed utilizing the Loewe additive model and the Bliss independence criterion. Additionally, a potential mechanism of PBDEs neurotoxicity was investigated, by studying the involvement of glutamate, the main neurotransmitter of central nervous system. The major findings presented in my thesis confirm the validity of in vitro models as alternatives to in vivo approaches to assess the toxicity of neurotoxicants. Results show that PBDEs cause neuronal toxicity by a mechanism involving in part the over-activation of ionotropic glutamate receptors, followed by oxidative stress leading to cell toxiucity and cell death. Moreover, co-exposure to two PBDEs congeners or a PBDe and a PCB has been shown to modify the toxicity of single compounds, suggesting that the study of interactions, supported by mathematical models, is an important issue that should be considered in risk assessment