Ultrasound-triggered drug targeting of tumors in vitro and in vivo

The new modality of drug targeting of tumors that we are currently developing is based on drug encapsulation in polymeric micelles, followed by the localized release at the tumor site triggered by focused ultrasound. The rationale behind this approach is that drug encapsulation in micelles decreases systemic concentration of drug, diminishes intracellular drug uptake by normal cells, and provides passive drug targeting of tumors, thus reducing unwanted drug interactions with healthy tissues. Ultrasound irradiation is used to release drug from micelles at the tumor site and to enhance the intracellular drug uptake by tumor cells. An important advantage of ultrasound is that it is noninvasive, can penetrate deep into the interior of the body, can be focused and carefully controlled. Here we describe factors involved in the ultrasound interaction with viable cells in the absence and presence of drug carriers and anti-cancer drugs. We present in vivo effects of 1 MHz ultrasound on drug biodistribution, intratumoral distribution, and survival rates of immuno-compromised athymic nu/nu mice bearing ovarian carcinoma tumors.

Factors affecting acoustically triggered release of drugs from polymeric micelles

A custom ultrasonic exposure chamber with real-time fluorescence detection was used to measure acoustically-triggered drug release from Pluronic P-105 micelles under continuous wave (CW) or pulsed ultrasound in the frequency range of 20 to 90 kHz. The measurements were based on the decrease in fluorescence intensity when drug was transferred from the micelle core to the aqueous environment. Two fluorescent drugs were used: doxorubicin (DOX) and its paramagnetic analogue, ruboxyl (Rb). Pluronic P-105 at various concentrations in aqueous solutions was used as a micelle-forming polymer. Drug release was most efficient at 20-kHz ultrasound and dropped with increasing ultrasonic frequency despite much higher power densities. These data suggest an important role of transient cavitation in drug release. The release of DOX was higher than that of Rb due to stronger interaction and deeper insertion of Rb into the core of the micelles. Drug release was higher at lower Pluronic concentrations, which presumably resulted from higher local drug concentrations in the core of Pluronic micelles when the number of micelles was low. At constant frequency, drug release increased with increasing power density. At constant power density and for pulse duration longer than 0.1 s, peak release under pulsed ultrasound was the same as stationary release under CW ultrasound. Released drug was quickly re-encapsulated between the pulses of ultrasound, which suggests that upon leaving the sonicated volume, the non-extravasated and non-internalized drug would circulate in the encapsulated form, thus preventing unwanted drug interactions with normal tissues.

DNA damage induced by micellar-delivered doxorubicin and ultrasound: comet assay study

To minimize adverse side effects of chemotherapy, we have developed a micellar drug carrier that retains hydrophobic drugs, and then releases the drug by ultrasonic stimulation. This study investigated the DNA damage induced by doxorubicin (DOX) delivered to human leukemia (HL-60) cells from pluronic P-105 micelles with and without the application of ultrasound. The comet assay was used to quantify the amount of DNA damage. No significant DNA damage was observed when the cells were treated with 0.1, 1 and 10 wt% P-105 with or without ultrasound (70 kHz, 1.3 W/cm(2)) for 1 h or for up to 3 h in 10 wt% P-105. However, when cells were incubated with 10 microg/ml free DOX for up to 9 h, DNA damage increased with incubation time (P=0.0011). Exposure of cells to the same concentration of DOX in the presence of 10-wt% P-105 showed no significant DNA damage for up to 9 h of incubation. However, when ultrasound was applied, a rapid and significant increase in DNA damage was observed (P=0.0001). The application of ultrasound causes the release of DOX from micelles or causes the HL-60 cells to take up the micelle encapsulated DOX. Our experiments indicated that the combination of DOX, ultrasound and pluronic P105 causes the largest DNA damage to HL-60 cells. We believe that this technique can be used for controlled drug delivery.

Micellar delivery of doxorubicin and its paramagnetic analog, ruboxyl, to HL-60 cells: effect of micelle structure and ultrasound on the intracellular drug uptake

The effect of Pluronic P-105 micelle structure and ultrasound on the uptake of two anthracycline drugs, doxorubicin and its paramagnetic analogue, ruboxyl, by HL-60 cells was investigated. Pluronic micellization was studied over the temperature range of 25-42 degrees C using the EPR and fluorescence spectroscopy. In the presence of Pluronic P-105 at concentrations corresponding to unimers (or loose aggregates), drug uptake by HL-60 cells was enhanced, apparently due to the effect of the polymeric surfactant on cell membrane permeability. At Pluronic concentrations corresponding to the formation of dense micelles with hydrophobic cores, drug uptake was substantially decreased. However, insonation with 70 kHz ultrasound enhanced the intracellular uptake of drugs encapsulated in dense Pluronic micelles. These findings may provide for developing a new technique of drug targeting by encapsulating the drug in micelles to prevent unwanted interactions with healthy cells and focusing ultrasound on a tumor to enhance drug uptake at the tumor site.