| Multidrug resistance (MDR) is the cross-resistance of certain cancer cells to a series of chemically unrelated drugs. It is a main cause of failure of chemotherapy. However, its mechanism is still unknown even after 20 years of investigation, partly due to lack of sophisticated detection techniques. On the other hand, microanalytical techniques for monitoring chemicals are becoming more and more important in basic biological research and clinical diagnostics. One goal of this dissertation is to develop and test novel microchemical techniques for cancer MDR studies, especially aiming at the single cell level. We characterized a novel device, the diffusional microburet (DMB), to deliver drugs and chemicals into a single cancer cell, and a carbon fiber microdisk electrode to directly monitor cancer drug efflux from the same single cancer cell by microvoltammetry. The combination of these two methods would make it possible to study, simultaneously influx, efflux and intracellular drug accumulation characteristics of MDR resistant, as well as sensitive, cells as functions of time in a single cancer cell. With our technique, the results from a sensitive (AUXB1) and a drug resistant (CHRC5) version of Chinese hamster ovarian cancer cells show that resistant cells exhibit a much higher initial efflux rate and shorter efflux time constant when both cell lines are preloaded to the same intracellular drug concentration. Compared with existing methodologies, the technique described here can provide information on the micro-heterogeneity of cancer-cell populations in terms of drug efflux at high temporal resolution.; Another goal of this dissertation work was to develop and utilize microchemical techniques to study respiratory system by monitoring neurotransmitter release from neuron cells. PC-12 cells were used as a model. Micro carbon fiber electrodes were used to study catecholamine release when the PC-12 cell population is under hypoxia condition, and proved that hypoxia can stimulate catecholamine, especially dopamine and norepinephrine release. In addition, studies were carried out to find out carbon fiber microdisk electrode characteristics in microscopic domains, which can eventually help us to analyze experimental data and to facilitate detection of catecholamine release from a single cell. |
