OBJECTIVE: The purpose of the study was to synthesize and characterize folate-targeted microbubbles (MB(F)) as an ultrasound contrast agent and to evaluate their affinity to the folate receptor (FR) in vitro. METHODS: Folate-targeted microbubbles were prepared by incorporating 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000]-folate into the lipid membrane of microbubbles. The diameter and concentration of the MB(F) were determined by a cell counter and sizer. The MB(F), control microbubbles (MB(C)), and MB(F) with a free folic acid block-ade were tested for binding specificity to human ovarian carcinoma SKOV3 cells, which overexpress the FR, by microscopy and confocal imaging, respectively. RESULTS: The basic physical characteristics of MB(F) were similar to those of MB(C). In the cell binding test, the adherence efficiency of MB(F) to the SKOV3 cells (mean +/- SD, 16 +/- 5 microbubbles per cell; P < .01) was significantly higher than that of MB(C) (0.7 +/- 0.4 microbubbles per cell) or MB(F) with the free folic acid blockade (0.7 +/- 0.6 microbubbles per cell). CONCLUSIONS: Folate-targeted microbubbles showed high affinity to SKOV3 cells with FR overexpression. They are potentially useful for ultrasonic molecular imaging and treatment of FR-positive tumors and warrant further investigation.
OBJECTIVE: The purpose of the study was to synthesize and characterize folate-targeted microbubbles (MB(F)) as an ultrasound contrast agent and to evaluate their affinity to the folate receptor (FR) in vitro. METHODS:Folate-targeted microbubbles were prepared by incorporating 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol)-2000]-folate into the lipid membrane of microbubbles. The diameter and concentration of the MB(F) were determined by a cell counter and sizer. The MB(F), control microbubbles (MB(C)), and MB(F) with a free folic acid block-ade were tested for binding specificity to humanovarian carcinoma SKOV3 cells, which overexpress the FR, by microscopy and confocal imaging, respectively. RESULTS: The basic physical characteristics of MB(F) were similar to those of MB(C). In the cell binding test, the adherence efficiency of MB(F) to the SKOV3 cells (mean +/- SD, 16 +/- 5 microbubbles per cell; P < .01) was significantly higher than that of MB(C) (0.7 +/- 0.4 microbubbles per cell) or MB(F) with the free folic acid blockade (0.7 +/- 0.6 microbubbles per cell). CONCLUSIONS:Folate-targeted microbubbles showed high affinity to SKOV3 cells with FR overexpression. They are potentially useful for ultrasonic molecular imaging and treatment of FR-positive tumors and warrant further investigation.