BMC Cancer 2002, 2 http://www.biomedcentral.com/1471-2407/2/20 The data in Figure 4 show that ultrasound does not in- crease the amount of Lysosensor Green uptake by the HL- 60 cells. Neither did it increase the uptake in HeLa cells. This data indicates that ultrasound enhances the uptake of the probe into the cells but does not enhance the amount of the probe present in a pH sensitive compartment. This suggests that the ultrasound enhances drug uptake, but not by stimulating an increase in the extent of endocyto- sis. In summary, entrance of drug into the cells under normal conditions appears to involve endocytosis and acidic ves- icles as well as perhaps some transport through the cell membrane into the cytoplasm. Application of ultrasound increases the rate of uptake by this latter route, but does not appear to increase the uptake of drug into acidic vesi- cles, which still occurs at the normal rate. Although ultra- sound releases drug from the Pluronic micelles, the enhanced uptake appears to be due to more than in- creased passive diffusion due only to increased external concentration of free drug. Apparently this intensity of ul- trasound perturbs the cell membrane, making it more per- meable to drug transport, at least by released drug, and perhaps by whole micelles passing through perturbations in the membrane. This is a very important observation for this drug delivery system, because it indicates that healthy cells that are not exposed to ultrasound when the drug is introduced from Pluronic micelles will not be affected as adversely by the micelle contents compared to tissues exposed to ultra- sound. These data imply that P105 micelles effectively se- quester other hydrophobic molecules in addition to anthracycline drugs. Competing interests None declared Authors' contributions Ghaleb Husseini was responsible for growing the cells, preparing the encapsulated micelles solution, measuring the partition coefficient, incubating and sonicating the cells and preparing the manuscript. Chris Runyan was responsible for operating the flow cy- tometer and helping in the analysis of the data. William Pitt helped in the design of the experiments, and in writing the manuscript. Acknowledgments The authors would like to acknowledge funding from the National Institute of Health (CA 76562) and (HL 59923). References 1. Husseini GA, El-Fayoumi RI, O'Neill KL, Rapoport NY, Pitt WG: DNA Damage Induced by Micellar-Delivered Doxorubicin and Ultrasound: Comet Assay Study. Cancer Lett 2000, 154:211- 216 2. Husseini GA, Myrup GD, Pitt WG, Christensen DA, Rapoport NY: Factors Affecting Acoustically-Triggered Release of Drugs from Polymeric Micelles. Journal of Controlled Release 2000, 69:43- 52 3. 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Journal of Controlled Release 2000, 71:239-249 Pre-publication history The pre-publication history for this paper can be accessed here: http://www.biomedcentral.com/1471-2407/2/20/prepub Page 6 of 6 (page number not for citation purposes)