Quantum dots boost anticancer drug

Quantum dots (QDs) have received significant attention in biological and biomedical fields. Now, UV-Vis spectroscopy and other techniques have been used to investigate their utility in enhancing the activity of the anticancer agent daunorubicin (DNR) in treating leukaemia cells.

Yanyan Zhou, Qingning Li, Hui Jiang, Gang Lv, Juan Zhao, Chunhui Wu, and Xuemei Wang of the State Key Lab of Bioelectronics (Chien-Shiung Wu Laboratory), at Southeast University, in Nanjing, China, and Lixin Shi and Matthias Selke of the Department of Chemistry and Biochemistry, at California State University, Los Angeles, USA, are showing cadmium telluride quantum dots can be used in imaging and inhibition of multi-drug resistant cancer cells.

Photoluminescent semiconductor quantum dots (QDs) have been the focus of research in several fields of biology and biomedical science in recent years. They have some potentially very useful properties above and beyond conventional fluorescent reagents. For instance, they are much brighter (an estimated 20 times) than conventional dyes and also much more stable (some 100 times) and so are neither swamped by other signals nor photobleached. Quantum dots also have the added advantage of having broad absorption and narrow emission spectra. "QD ?uorescence is particularly appealing for the visualization of cellular processes, since this method can facilitate multicolour labelling of living cells. Thus, QDs have been widely used in cellular labelling and in vivo long-term ?uorescence imaging," the team adds.

Zhou and colleagues have explored water-soluble nanocrystalline CdTe QDs that were capped with negatively charged 3-mercapitalpropionic acid (MPA). The capping molecule assists with the uptake of a drug molecule, the anticancer drug daunorubicin, on the QD. These conjugates were developed in previous work. They have now determined efficacy of drug delivery and imaging using a cytotoxicity evaluation on leukaemia sensitive cell K562 and adriamycin-resistant cell K562/A02. They also applied total internal reflection fluorescence microscopy, electrochemistry and UV-Vis absorption spectroscopy to assess the behaviour and characteristics of these particles.

"Our results illustrate that the MPA-CdTe QDs could effectively facilitate the interaction of anticancer agent daunorubicin with leukaemia cells and the efficiency of biolabelling in cancer cells," the team says, "The present study affords a new potential method for simultaneous cellular inhibition and imaging of cancer cells."

The UV-Vis absorption spectroscopy measurements alongside electrochemical experiments carried out at room temperature allowed the team to compare the cellular behaviour under different conditions. Specifically UV-Vis spectroscopy of the daunorubicin residue after treating with leukaemia K562 and K562/A02 cells in the absence and presence of the modified QDs provided additional evidence of the utility of the QDs.

Obvious differences in the absorbance of the daunorubicin residue outside K562 cancer cells depending on whether QDs were used or not reveals just how effective uptake is in the presence of the MPA-CdTe. "It was apparent that the target cells absorbed few daunorubicin molecules in the absence of MPA-CdTe QDs," the team adds.

"We suggest that these nano-crystals interact with the anticancer drug in targeted cancer cells and significantly enhance cytotoxicity on both drug-sensitive and drug-resistant leukaemia cell lines," the researchers conclude. "Our work provides a new strategy for simultaneous cellular imaging and inhibition of multidrug resistance in cancer chemotherapy."