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SASCA tackles single drug-resistant cancer cells It began with a peculiar observation: in precious few cells are at hand. To cirsame cell, but this time, the efflux is 2004, Paul Li and colleagues at Simon cumvent the sample size issue, a singlemeasured in the presence of an inhibiFraser University (Canada) had designed cell microfluidic analysis technique, tor. “We see the results clearly,” says a microfluidic device with 3D flow con- called different-single-cell analysis Paul Li, who notes that much of the trol that could capture and manipulate (DISCA), has been developed to work work was done by his graduate student, single cells (Anal. Chem. 2004, 76, with a limited number of cells. Xiujun Li. “If the cell has low multi5282–5292). While doing drug resistance, then we see the experiments, the investia little bit of a reversal with gators noticed that the single the inhibitor. In the case of yeast cells seemed to spit out high multidrug resistance of the fluorescent marker they a cell, we see a much better were dosed with, causing the and greater reversal effect” fluorescence to decrease. with the inhibitor. The observation prompted Once they were conthe investigators to think vinced that SASCA worked about how they could turn well, the investigators tested the spitting-out phenomtwo compounds from traenon, known as efflux, into ditional Chinese herbal something practical that medicine for the ability met a clinical need. In their to inhibit drug efflux. latest AC paper (2008, 80, Isoliquiritigenin is derived 4095–4102), Paul Li, Xiujun from Chinese licorice; by Li, and Victor Ling describe A captured, live, single cell stained with fluorescein diacetate sits in the SASCA method, it how they use the microfluthe observation chamber of a microfluidic device. Scale bar: 50 μm. didn’t demonstrate any idic device to measure drug inhibition of drug efflux. efflux and the inhibition of efflux in Paul Li and colleagues attempted to Sodium artesunate is an antimalarial multi-drug-resistant leukemia cells. “We use DISCA but ran into problems. In drug suspected of having anticancer envision this will [eventually] help the this method, one cell acts as a control properties. Paul Li had come across the administration of chemotherapy, by and another cell is for the experiment. compound while on a sabbatical leave knowing what kind of efflux process is “We had a hard time observing what in Germany, “so I thought we’d try it. occurring in a patient’s cancer cells and we expected to see,” says Paul Li. “The We found that it indeed showed a drug which inhibitor will reverse the procells came from the same batch of reversal effect. We were so excited about cess,” says Paul Li. cultured cells, but they had different it! There was some preliminary work Multidrug resistance occurs when properties.” done on the drug, but it wasn’t conclucancer cells barricade themselves against Because individual cells differ in sive. But with our SASCA method, we a variety of drugs; it is the bane of their levels of Pgp expression—and thus see very clearly that this drug shows the chemotherapy. One way cells resist is in their extent of drug resistance—the reversal effect.” by pumping out drugs. The membraneinvestigators struggled to compare the Besides further engineering the bound, energy-dependent P-glycoprobehavior of control and experimental microfluidic device to handle multiple tein (Pgp) is a protein that does the cells. To overcome the comparison cells at once, Paul Li wants to use cells pumping and tends to be overexpressed problem, Paul Li and colleagues decided from individual cancer patients. “I hope in cancer cells. Inhibitors can stop Pgp to use the same cell for both the control this method will eventually be used to from functioning, but clinicians need and the experiment. They bestowed provide prognosis information,” he says. to fiddle around with them to come up the name SASCA, for same-single-cell The idea is to let clinicians determine with the magic combination of drug analysis, on their approach. the appropriate combinations of drugs and inhibitor for effective therapy. The first step in the SASCA process and inhibitors by the SASCA method Methods exist to measure multidrug is the control experiment—accumulato figure out the best course of action. resistance, but they have drawbacks. tion of a drug in a cell followed by the Paul Li says, “We’re providing a tool to Flow cytometry requires thousands measurement of its efflux without an do a functional assay that better impleof cells for the analysis, a requirement inhibitor. For the experimental step, ments chemotherapy.” a that’s sometimes hard to meet when drug accumulation is repeated in the —Rajendrani Mukhopadhyay J u n e 1 , 2 0 0 8 / A n a ly t i c a l C h e m i s t r y
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