OBJECTIVE To evaluate the potential efficacy of low-intensity ultrasound （US） in combination with anticancer drugs to reverse multidrug resistance （MDR）in nude mice. METHODS A total of 40 male and female athymic nude mice were inoculated subcutaneously with 5×10^6 HepG2/ADM and HepG2 cells. Ultrasound with pulsed irradiation at an average intensity of 0.5 W/cm^2 was given to the tumor area 10 rain after administration of adriamycin （ADM）. The tumor 3 dimensional diameters were measured by calipers before and after treatment, and the tumor growth indexes （TGI） calculated. RT-PCR was used to detect the gene levels of the HepG2/ADM cells. Immunohistochemical analyses for MDR proteins were conducted on the tumor tissues. RESULTS The ultrasonic treatment resulted in an average reduction in the tumor volume of 62% one month later. The relative mRNA levels of MDR1 and MRP were significantly different among the following 4 groups： untreated group as control, ADM treated; US treated; and ADM plus US treated. The mRNA levels of mdrl and mrp were down-regulated in the US groups compared to those of the non-ultrasound groups by multiple comparisons. The relative mRNA levels of Irp expression were not significantly changed. The results of immunohistochemistry indicated that tumor tissue from animals treated with US had remarkably low mdrl and mrp expression. CONCLUSION The results showed that low-intensity US can effectively reduce the size of adriamycin-resistant human hepotacarcinoma in a nude mouse model, and support the efficacy of US to overcome multiple mechanisms of drug resistance.
OBJECTIVE The aim of the study was to examine the reversal effects of ultrasound （US） on the MDR in HepG2/ADM, a HepG2 cell line resistant to Adriamycin （ADM）, and to study the mechanism of US action.METHODS Using the MTT assay, the effects of US on MDR in HepG2/ADR cells were studied. Before and after the treatment with 0.5 W/cm^2 low intensity ultrasound （LIUS）, the expression of the MDR-related genes, mdrl, mrp and lrp was assayed with the reverse transcriptase polymerase chain reaction （RT-PCR） and the levels of their respective protein expression determined by flow cytometry. By using confocal laser scanning microscopy （CLSM）, we examined the intracellular daunorubicin （DNR） distribution, and the effects on the cells of treatment with US or DNR.RESULTS LIUS significantly reversed MDR in HepG2/ADR cells. After treatment with LIUS at 0.5 W/cm^2, chemosensitivity to ADM and DNR increased 3.35-fold and 2.81-fold, respectively. The reversal activity by LIUS plus verapamil （VER） was stronger than with either US or VER alone. After treatment with 0.5 W/cm^2, the expression of both the MDR1 and the MRP mRNA genes began to decline （P 〈 0.01 and P 〈 0.05, respectively）; the expression of LRP showed no significant changes. Changes in the expression of the P-glycoprotein （P-gp） and MRP were similar to those of their mRNA expressions. Results of the CLSM showed that administration of US （0. 5 W/cm^2） or VER （15.7 uM） with DNR to HepGa/ADM cells showed a significant change in the distribution of DNR in the cells.CONCLUSION Our results show that LIUS can reverse MDR. The reversal effects are stronger than those of either US or VER alone, when combined with VER administration. As LIUS is noninvasive causing no toxicity, it might have potential for clinical application. The reversal mechanism needs further study.
