Pulsed High-Intensity Focused Ultrasound Enhances Delivery of Doxorubicin in a Preclinical Model of Pancreatic Cancer

Pancreatic cancer is characterized by extensive stromal desmoplasia, which decreases blood perfusion and impedes chemotherapy delivery. Breaking the stromal barrier could both increase perfusion and permeabilize the tumor, enhancing chemotherapy penetration. Mechanical disruption of the stroma can be achieved using ultrasound-induced bubble activity-cavitation. Cavitation is also known to result in microstreaming and could have the added benefit of actively enhancing diffusion into the tumors. Here, we report the ability to enhance chemotherapeutic drug doxorubicin penetration using ultrasound-induced cavitation in a genetically engineered mouse model (KPC mouse) of pancreatic ductal adenocarcinoma. To induce localized inertial cavitation in pancreatic tumors, pulsed high-intensity focused ultrasound (pHIFU) was used either during or before doxorubicin administration to elucidate the mechanisms of enhanced drug delivery (active vs. passive drug diffusion). For both types, the pHIFU exposures that were associated with high cavitation activity resulted in disruption of the highly fibrotic stromal matrix and enhanced the normalized doxorubicin concentration by up to 4.5-fold compared with controls. Furthermore, normalized doxorubicin concentration was associated with the cavitation metrics (P < 0.01), indicating that high and sustained cavitation results in increased chemotherapy penetration. No significant difference between the outcomes of the two types, that is, doxorubicin infusion during or after pHIFU treatment, was observed, suggesting that passive diffusion into previously permeabilized tissue is the major mechanism for the increase in drug concentration. Together, the data indicate that pHIFU treatment of pancreatic tumors when resulting in high and sustained cavitation can efficiently enhance chemotherapy delivery to pancreatic tumors. .

Dermal and Transdermal Drug Delivery Systems: Current and Future Prospects

The protective function of human skin imposes physicochemical limitations to the type of permeant that can traverse the barrier. For a drug to be delivered passively via the skin it needs to have adequate lipophilicity and also a molecular weight <500 Da. These requirements have limited the number of commercially available products based on transdermal or dermal delivery. Various strategies have emerged over recent years to optimize delivery and these can be categorized into passive and active methods. The passive approach entails the optimization of formulation or drug carrying vehicle to increase skin permeability. Passive methods, however do not greatly improve the permeation of drugs with molecular weights >500 Da. In contrast active methods that normally involve physical or mechanical methods of enhancing delivery have been shown to be generally superior. Improved delivery has been shown for drugs of differing lipophilicity and molecular weight including proteins, peptides, and oligonucletides using electrical methods (iontophoresis, electroporation), mechanical (abrasion, ablation, perforation), and other energy-related techniques such as ultrasound and needless injection. However, for these novel delivery methods to succeed and compete with those already on the market, the prime issues that require consideration include device design and safety, efficacy, ease of handling, and cost-effectiveness. This article provides a detailed review of the next generation of active delivery technologies.

Rectangular cymbal arrays for improved ultrasonic transdermal insulin delivery

Circular cymbal ultrasound arrays have been shown to be effective in delivering therapeutic levels of insulin in rats, rabbits, and pigs. To improve delivery efficiency, a rectangular cymbal design was desired in order to achieve a broader spatial intensity field without increasing the size of the device or the spatial-peak temporal-peak intensity (I(SPTP)). With a similar intensity (50 mWcm(2)), the goal was to determine if the 3x1 rectangular cymbal array could perform significantly better than the 3x3 circular array for glucose reduction in hyperglycemic rabbits. Rabbit experiments were performed using three groups: nonsonicated control (n=3), ultrasound exposure using a circular cymbal array (n=3), and ultrasound exposure using a rectangular cymbal array (n=3). Rabbits were anesthetized and a water tight reservoir that held the insulin was fastened on the rabbit's thigh. At the beginning of the experiment and every 15 min for 90 min, the blood glucose level was determined. For comparison between individual rabbits, the absolute level is normalized by subtracting out the baseline in order to arrive at the change in glucose level. For the control group, the normalized glucose level increased (more hyperglycemic) to +80.0+/-28.8 mgdl (mean+/-SEM). Using the circular array, the glucose level decreased to -146.7+/-17.8 mgdl at 90 min. However, using the rectangular cymbal array, the glucose decreased faster and to a level of -200.8+/-5.9 mgdl after 90 min. These results indicated the feasibility of the rectangular cymbal array as an improved device for drug delivery.

Ultrasound mediated transdermal insulin delivery in pigs using a lightweight transducer

PURPOSE

In previous studies, ultrasound mediated transdermal drug delivery has shown a promising potential as a method for noninvasive drug administration. For prospective future human application, this study was designed to determine the feasibility of lightweight cymbal transducer array as a practical device for noninvasive transdermal insulin delivery in large pigs.

MATERIALS AND METHODS

Six Yorkshire pigs (100-140 lbs) were divided into two groups. As the control (n = 3), the first group did not receive any ultrasound exposure with the insulin. The second group (n = 3) was treated with ultrasound and insulin at 20 kHz with an I(sptp) = 100 mW/cm(2) at a 20% duty cycle for 60 min. With the pigs in lateral recumbency after anesthesia, the ultrasound transducer with insulin was placed on the axillary area of the pig. At the beginning and every 15 min up to 90 min, the blood glucose level was determined using a glucose monitoring system. To compare the results of individual animals, the change of blood glucose level was normalized to each animal's initial glucose value at the start of the experiment.

RESULTS

Although each animal had a different initial glucose level, the mean and standard error for the six animals was 146 +/- 13 mg/dl. For the control group, the blood glucose level increased to 31 +/- 21 mg/dl compared to the initial baseline over the 90 min experiment. However for the ultrasound with insulin treated group, the glucose level decreased to -72 +/- 5 mg/dl at 60 min (p < 0.05) and continued to decrease to -91 +/- 23 mg/dl in 90 min (p < 0.05).

CONCLUSION

The results indicate the feasibility of ultrasound mediated transdermal insulin delivery using the cymbal transducer array in animal with a similar size and weight to a human. Based on these result, the cymbal array has potential as a practical ultrasound system for noninvasive transdermal insulin delivery for diabetes management.

Therapeutic applications of ultrasound

Therapeutic applications of ultrasound predate its use in imaging. A range of biological effects can be induced by ultrasound, depending on the exposure levels used. At low levels, beneficial, reversible cellular effects may be produced, whereas at high intensities instantaneous cell death is sought. Therapy ultrasound can therefore be broadly divided into "low power" and "high power" applications. The "low power" group includes physiotherapy, fracture repair, sonophoresis, sonoporation and gene therapy, whereas the most common use of "high power" ultrasound in medicine is probably now high intensity focused ultrasound. Therapeutic effect through the intensity spectrum is obtained by both thermal and non-thermal interaction mechanisms. At low intensities, acoustic streaming is likely to be significant, but at higher levels, heating and acoustic cavitation will predominate. While useful therapeutic effects are now being demonstrated clinically, the mechanisms by which they occur are often not well understood.

Low-frequency sonophoresis: a review

Application of ultrasound enhances skin permeability to a variety of molecules (sonophoresis). The enhancement induced by ultrasound is particularly significant at low-frequencies (f<100 kHz, low-frequency sonophoresis). This review summarizes mechanisms and applications of low-frequency sonophoresis. In vitro, in vivo, as well as clinical studies demonstrating the effect of low-frequency ultrasound on transdermal drug delivery and glucose extraction are summarized. Mechanistic insights gained through a number of investigations are also reviewed. Finally, reports on the synergistic effect of low-frequency ultrasound with other enhancers including chemicals and iontophoresis are summarized.

Ultrasound-mediated transdermal in vivo transport of insulin with low-profile cymbal arrays

The purpose of this study was to demonstrate the feasibility of ultrasound (US)-mediated transdermal delivery of insulin in vivo using rats with a novel, low profile two-by-two US array based on the "cymbal" (due to its unique shape) transducer. As a practical device, the cymbal array (f = 20 kHz) was 37 x 37 x 7 mm in size, and weighed less than 22 g. A total of 20 Sprague-Dawley rats (350 to 450 g) were divided into four groups, two controls and two US exposure, with five rats in each group. The rats were anesthetized and shaved; a water-tight standoff reservoir, which held the insulin or saline, was sealed against the rat's abdomen and the US array. At the beginning of the experiment and every 30 min for 90 min, 0.3 mL of blood was collected from the jugular vein to determine the blood glucose level (mg/dL). For comparison between the rats, the change in the glucose level for each rat was normalized to a baseline (i.e., 0 mg/dL). The first control group used insulin in the reservoir with no US and the second control group had saline in the reservoir with US operating at I(SPTP) = 100 mW/cm(2) for 60 min. For the experiments, the third group employed insulin with US exposure for 60 min (I(SPTP) = 100 mW/cm(2)), whereas the last group used insulin with US operating with a 20-min exposure (I(SPTP) = 100 mW/cm(2)) to examine the effects of time on delivery. For the 60-min US exposure group, the glucose level was found to decrease from the baseline to -267.5 +/- 61.9 mg/dL in 1 h. Moreover, to study the effects of US exposure time on insulin delivery, the 20-min group had essentially the same result as the 60-min exposure at a similar intensity, which indicates that the expose time does not need to be as long for delivery.

Phonophoresis: efficiency, mechanisms and skin tolerance

Phonophoresis or sonophoresis is the use of ultrasound to increase percutaneous absorption of a drug. The technique has been widely used in sports medicine since the sixties. Controlled studies in humans in vivo have demonstrated absence or mild effects of the technique with the parameters currently used (frequency 1-3 MHz, intensity 1-2 W/cm(2), duration 5-10 mins, continuous or pulse mode). However, it was demonstrated in 1995 that administration of macromolecules with conserved biological activity was feasible in animals in vivo using low frequency ultrasound. This led to new research into this method of transdermal administration. The aim of this review is to present the main findings published with low frequency and high frequency ultrasound over the last ten years, and to discuss the respective roles of thermal, cavitational and non-cavitational effects on the reduction of the skin barrier. Particular attention is paid to the biological effects on living skin which might be of importance for tolerance and practical use in humans.

Dependence of low-frequency sonophoresis on ultrasound parameters; distance of the horn and intensity

Sonophoresis at a frequency of 20 kHz has been shown to enhance transdermal drug delivery, a phenomenon referred to as low-frequency sonophoresis. This study provides an investigation of the dependence of low-frequency sonophoresis on various ultrasound parameters, including the distance of the horn from the skin, intensity, and frequency. We performed in vitro experiments with full thickness pig skin to measure enhancements of skin conductivity and drug permeability. Ultrasound was applied to pretreat the skin using a sonicator operating at a frequency of either 20 or 40 kHz. We also measured pitting of aluminum foil to measure cavitation, which is the principal mechanism of low-frequency sonophoresis. The skin conductivity enhancement was found to be inversely proportional to the distance of the horn from the skin. As the intensity increased, skin conductivity enhancement also increased up to a certain threshold, and then dropped off. The intensities (I(max)) at which maximum enhancement occur are about 14 W/cm2 for 20 kHz and 17 W/cm2 for 40 kHz. These findings may be useful in optimizing low-frequency sonophoresis. Overall, the dependence of transport on ultrasound parameters is similar to that of aluminum foil pitting. These results support the role of cavitation in low-frequency sonophoresis.

Novel mechanisms and devices to enable successful transdermal drug delivery

Optimisation of drug delivery through human skin is important in modern therapy. This review considers drug-vehicle interactions (drug or prodrug selection, chemical potential control, ion pairs, coacervates and eutectic systems) and the role of vesicles and particles (liposomes, transfersomes, ethosomes, niosomes). We can modify the stratum corneum by hydration and chemical enhancers, or bypass or remove this tissue via microneedles, ablation and follicular delivery. Electrically assisted methods (ultrasound, iontophoresis, electroporation, magnetophoresis, photomechanical waves) show considerable promise. Of particular interest is the synergy between chemical enhancers, ultrasound, iontophoresis and electroporation.

Transdermal drug delivery using iontophoresis and phonophoresis

Introducing medicines into the human body by way of the skin is an ancient practice, and transdermal delivery has long been a standard for administering medications such as nitroglycerin and scopalamine. Phoresis, another method of transdermal drug delivery, is now being ordered for an increasing number of orthopaedic patients who suffer from inflammation, strains, or sprains. In phoretic drug delivery, enhancers such as electricity or ultrasound are used to stimulate drug absorption in the treatment area. To guide their patients to explore a variety of treatment options, orthopaedic nurses need a greater understanding of these phoretic modalities.

Defects generated in human stratum corneum specimens by ultrasound

Over the last two decades, ultrasound (US) has been applied to enhance transdermal drug delivery. This method is called sonophoresis. The physical mechanism of the enhancement is far from being fully understood. It has been shown in our study that 168-kHz continuous US of spatially averaged pressure amplitude of 1.9 x 10(5) Pa induced a new structural state and generated defects (entrapped air pockets) in human stratum corneum specimens. The dimensions of the defects were found to be about 20 microns, large enough to allow the transdermal passage of high-molecular-weight drug molecules that normally elude the unenhanced transdermal drug delivery.

[Rationale of noninvasive method of drug administration at the prelymphatic level]

The paper deals with the mode of local drug administration into the biological tissue at the prelympathic level without damaging the skin, which is based on enhancement of skin permeability by exposing to physical factors, including the use of contrast temperatures in the cyclic process of heating-cooling, followed by exposure to contact low-frequency ultrasound. Experimental and clinical studies of the mode versus routine drug administration have shown it to be promising in physiotherapeutic use.

Effect of indomethacin phonophoresis on the relief of temporomandibular joint pain

The pain-relieving effect of indomethacin phonophoresis on temporomandibular (TMJ) joint pain was evaluated in a double-blind, placebo-controlled clinical trial. Twenty subjects, who have TMJ pain, were included for this study and randomly assigned to either the experimental group (n = 10) or the control group (n = 10). Each treatment consisted of the application of ultrasound massage (1.0 MHz, 0.8 to 1.5 W/cm2 continuous output) for 15 minutes to the painful temporomandibular joint. As a conducting medium, 1% indomethacin cream was used for the experimental group and placebo cream for the control group respectively. Pre- and post-treatment pain levels and pain sensitivity were assessed with visual analogue scales (VAS) and pressure pain threshold (PPT). Mean data indicated that post-treatment VAS was significantly decreased and post-treatment PPT was significantly increased in the experimental group, not in the control group. The results of this study suggest that indomethacin phonophoresis provides significant pain relieving effect over the TMJ pain.

Physical enhancement of dermatologic drug delivery: iontophoresis and phonophoresis

Iontophoresis and phonophoresis are emerging technologies capable of enhancing drug penetration through the stratum corneum, the principal barrier to percutaneous absorption. With utilization of applied electric current or ultrasonic waves, respectively, iontophoresis and phonophoresis have shown efficacy in an increasing number of clinical applications. This article reviews the underlying principles, current status, and potential of iontophoresis and phonophoresis in dermatologic therapy.

[The use of ultraphonophoresis in the rehabilitation of myocardial infarct patients]

The action of ultrasound on microcirculation, bioelectrical activity of the myocardium, exercise tolerance and oxyproline metabolism was studied in patients with subacute myocardial infarction. To achieve a better effect of rehabilitation. it is advisable to use ultraphonophoresis of vasoactive ointments venoruton and nitro-ointment in patients having capillary-trophic insufficiency, slow repair of the necrotic zone, postinfarction inflammation in muscular and connective tissue structures of the upper shoulder girdle.

[The use of the phonophoresis of Venoruton ointment and millimeter-range electromagnetic waves for the correction of trophic capillary failure in myocardial infarct patients]

Status of microcirculation, bioelectrical activity of myocardium and tolerability to physical loads were studied in 120 patients with myocardial infarction with capillary and tropic insufficiency, divided into four groups, over time, before and after course exposure to physical factors such as the "Venoruton" ointment phonophoresis and electromagnetic radiation of millimeter range, as well as complex medicamentous therapy, used alone or in combination. The most striking therapeutic effect was achieved with the above physiotherapeutic measures being combined.

Relative transmission of ultrasound by media customarily used for phonophoresis

The purpose of this study was to determine the relative transmission of ultrasound by the media commonly used by physical therapists to apply phonophoresis. The relative transmission of ultrasound energy through various phonophoresis media was compared with that of degassed water, which is the ideal standard. Transmission was assessed by placing a thin layer of the test medium on the transducer of a therapeutic ultrasound unit and measuring delivery of ultrasound with an ultrasound power meter. The media evaluated produced two significantly different groups of transmission results: (1) transmission greater than 80% of that of water and (2) transmission less than 40% of that of water. Media that optimize the therapeutic efficacy of phonophoresis in both clinical and experimental settings are discussed.

[Antibiotic therapy of suppurative-inflammatory lesions of the bronchi with endobronchial use of low-frequency ultrasonic energy]

Gentamycin pharmacokinetics and its concentrations in bronchial secretion were studied in routine endobronchial introduction versus endobronchial aerosol spraying with application of low-frequency ultrasound. The latter technique warranted gentamycin concentrations in bronchial secretion 24 hours after the procedure many times that minimal for inhibition of the pathogen isolated. Secretion levels of gentamycin remained high for 4 days. No side effects were reported. The findings provide evidence in favor of endobronchial aerosol spraying of the drugs for treatment of purulent endobronchitis in bronchiectasis and chronic bronchitis.

[Papain phonophoresis in the treatment of suppurative wounds and inflammatory processes]

The authors studied the effect of papain and dimethyl sulfoxide (DMSO) phonophoresis on the course of purulent wounds and inflammatory processes in patients. It is shown that the use of 1% papain solution together with DMSO by means of phonophoresis is a very effective and promising method for the treatment of purulent wounds and inflammatory infiltrates. The terms of restoration of the structure of the injured tissues are reduced by 1.8 times on the average.

[The use of the vacuum phonophoresis of peloidin on patients with the neurological syndromes of lumbar osteochondrosis]

Isotope capillary permeability and electroneuromyography were employed to study potency of peloidin vacuum-phonophoresis and its combination with pelobalneotherapy for lumbar osteochondrosis (LO). Altogether 108 patients with LO neurological syndromes were treated. Peloidin vacuum-phonophoresis proved a pathogenetic treatment of the condition valuable at all stages of LO patients rehabilitation.