Objective  To study the effects of ultrasound irradiation microbubbles with verpamil (VER) on reversing tumor multidrug resistance. Methods  VER - PLGA microbubbles were prepared with double emulsion and freeze drying techniques. The neuroblastoma cell line SK - N - SH/VCR with multidrug resistance (MDR) phenotype was established by inducing with small - doses of VCR. Then the cells were divided into 6 groups according to different trea

tments

that is

group A: SK - N - SH/VCR

group B: SK - N - SH/VCR+VER (50 μ g/ml)

group C: SK - N - SH/VCR+VER (250 μ g/ml)

group D: SK - N - SH/VCR+ultrasound

group E: SK - N - SH/VCR+PLGA+ultrasound

group F: SK - N - SH/VCR+VER - PLGA (50 μ g/ml)+ultrasound. RT - PCR and immunocytochemical staining were used to detect the expression levels of MDR1 gene and P - gp respectively. And the effects of VER on reversing multidrug resistance of tumor in different groups were evaluated. Results The VER - PLGA microbubbles were prepared successfully

and the encapsulated rate was 32%. SK - N - SH/VCR cells with MDR phenotype were established and the resistance index (RI) was 2.3 to 5 . 4 times to different chemotherapy drugs when compared with the wild cells. Compared with others

the level of MDR1 gene was the most lowest in group F (

P

0 . 05). The expression levels of P - gp and MDR1 gene were the lowest in group F among the all 6 groups (

P

0 . 05). Conclusion Ultrasound irradiation microbubbles enhance the effects of verapamil to reverse the multidrug resistance of tumor. 15 Refs. In Chinese.