Therapeutic Cardiac Ultrasound

Graham Gardner, M.D.

Division of Cardiology

Beth Israel Deaconess Medical Center

Harvard Medical School

February 2nd, 2005

Introduction

• Novel Mechanisms for Drug Delivery

• Drug Delivery using Ultrasound

• Advantages and Disadvantages of Cardiac Ultrasound

• Specific Applications – Drug Delivery

– Gene Delivery

• Future Directions

Novel Mechanisms for Drug Delivery

Challenges

• Systemic toxicities

• Degradation (proteins)

• Invasive delivery systems

• Metabolism / time to onset

Solutions

• Local / targeted delivery

• Controlled release / stability

• Non-invasive

• Immediate onset

Novel Mechanisms for Drug Delivery

Innovations

– Nanotechnology

– Controlled-release devices and preparations

– Marriage of pharmaceutical compounds with medical devices

– Ultrasound-enabling

Cardiac Ultrasound Principles

• Creation of microspheres

• Incorporation of drugs (and possibly ligands) within the microspheres

• Distribution of drug-containing microspheres through the vascular system

• Delivery of the drugs to target organs via ultrasound

Microsphere Constituents

• Gas– Air: dissolution in blood is < 1 sec– Perflurocarbons

• Low propensity to diffuse remains in the bubble• Low concentration of saturation in blood prolonged

survival

• Shell– Albumin: flexible and binds to injured endothelium– Acrylates: inflexible and require ultrasound destruction– Polymers: custom-designed

Microsphere Formulation

Microsphere Constituents

• Gas– Room air– Perfluorocarbons

• Shell / surface– Fatty acids– Phospholipids– Albumin– Antibodies– Polymers

Microphere Properties

• Cross-sectional area• Persistence / fragility• Resonance• Attenuation• Adhesion

Microsphere Formulation

Drug and Ligand Formulation

• Microspheres can be formulated with multiple different drugs and act as carrier molecules

• Specific ligands can also be attached to help direct the microspheres to a specific organ or disease process

www.hd.org

Injection of Microspheres

www.ocularvision.comwww.ergonext.com

The microspheres can be introduced into the vascular system through regular intravenous access

Application of Ultrasound

• Ultrasound applied over the skin surface can be used to burst the microbubbles over the target area for drug delivery

• Microspheres themselves act as nuclei for cavitation

EKG-Gating for Coronary Delivery

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Destruction of the Microspheres

• Gradual diffusion of gas at low acoustical power

• Formation of shell defect diffusion of gas

• Immediate explosion of the microsphere shell at high acoustical power

• Dispersion of the microspheres into small bubbles

Tsutsui JM, etal. Cardiovascular Ultrasound, 2004.

Additional Effects of Ultrasound

• Creation of extravasation points in skeletal muscle capillaries (micro-fractures)– Microvessels with diameter < 7 um

– Dependent upon ultrasound pulse interval (optimal approx 5 sec)

• Formation of pores in cellular membranes– Best with lower Hz / higher wavelength

• Physical disruption of clot

Tsutsui JM, etal. Cardiovascular Ultrasound, 2004.

Advantages of Ultrasound

• Local or targeted delivery

• Minimize systemic circulation and drug levels

• Delivery of “difficult” compounds– Proteins

– Systemically toxic compounds

• Non-invasive

• Ultrasound facilitation of drug delivery– Microvessel fractures

– Clot dissolution

– Disruption of lipid cellular membranes

Disadvantages of Ultrasound

• “Packaging” requirements– Limitation of total amount

• Cost

• Safety considerations– PVCs

– Disruption of the microvasculature

– Allergy to microsphere preparations or constituents

Specific Applications

• Drug Delivery– Thrombolysis

– Myocarditis

– Angiogenesis

– Restenosis

• Gene Delivery– Cellular transfection

Specific Applications

• Drug Delivery– Thrombolysis

– Myocarditis

– Angiogenesis

– Restenosis

• Gene Delivery– Cellular transfection

Thrombolysis Study: Siegel et al.

• Methods– Bilateral Thrombi in the femoral

and coronary arteries of rabbits induced via electrical current

– Thrombosis confirmed via angiography

– Randomization to 2 of several arms• Ultrasound alone (20-37 kHz)• Thrombolytic alone• Microbubbles alone• Thrombolytic and ultrasound• Microbubbles and ultrasound

Siegel RJ, et al. Echocardiography, 2001.

Thrombolysis Study: Siegel et al.

Siegel RJ, et al. Echocardiography, 2001.

Thrombolysis Study: Siegel et al.

• Significantly improved recanalization of femoral arteries with the application of ultrasound to streptokinase or microbubbles compared with streptokinase or microbubbles alone

Siegel RJ, et al. Echocardiography, 2001.

Thrombolysis Study: Siegel et al.

• Results (coronary)– Significantly improved

patency rates at 30 and 90 minutes when TPA combined with ultrasound

– TIMI 2-3 flow seen in 25% of tPA alone vs 92% of ultrasound-tPA combination

– No assessment of LV function

Siegel RJ, et al. Echocardiography, 2001.

Thrombolysis Study: Siegel et al.

Siegel RJ, et al. Echocardiography, 2001.

Specific Applications

• Drug Delivery– Thrombolysis

– Myocarditis

– Angiogenesis

– Restenosis

• Gene Delivery– Cellular transfection

Restenosis

• Synthetic antisense oligonucleotides (c-myc protooncogene) can bind to mRNA and inhibit the synthesis of the protooncogene

• By inhibiting the c-myc protooncogene, these antisense oligonucleotides could inhibit restenosis after vascular injury

Restenosis Study: Porter et al

• Methods– 21 pigs– Injury to the R carotid artery via oversized balloon inflation– Vessel patency confirmed via angiography– Randomized to three arms

• Synthetic oligodeoxynucleaotide to c-myc• Synthetic oligodeoxynucleaotide to c-myc bound with albumin-coated

microbubbles• Control

– Injected at Time 0 and again at 3 days– Ultrasound applied at 20 kHz– Harvesting performed at 30 days

Porter TR, et al. Ultrasound in Med & Biol, 2001.

Restenosis Study: Porter et al

• Results– Lumen area was significantly

larger at the injury site in pigs that received ODN-myc combined with microbubbles (reduction of 8 +/- 2% vs 19% and 28% in the control and antisense alone groups)

Porter TR, et al. Ultrasound in Med & Biol, 2001.

Specific Applications

• Drug Delivery– Thrombolysis

– Myocarditis

– Angiogenesis

– Restenosis

• Gene Delivery– Cellular transfection

Transfection Study: Bekeredjian et al.

• Methods– Albumin microbubbles with a plasmid encoding luciferase

– Injected into internal jugular vein

– Sonos 5500 with S3 transducer applied to chest wall (1.3 MHz)

– Variable transfection and harvesting timepoints

– Hearts dissected

Transfection Study: Bekeredjian et al.

• Results– Highest transfection rate

seen after 4 days but still detectable at 28 days

– Transfection almost exclusively confined to the heart

– Little transfection seen when ultrasound and microbubble injections separated temporally

Transfection Study: Shohet et al.

• Methods– Perfluoropropane-filled albumin microbubbles

– Attached to adenovirus containing cDNA for E coli β-galactosidase gene

– Rats divided into 6 groups• Echocardiographic destruction of microbubbles without gene

• Echocardiographic destruction of microbubbles with gene

• Microbubbles with gene only

• Gene alone

• Echocardiography with gene alone

• Echocardiographic destriction of microbubbles without gene followed by the infusion of gene alone

Transfection Study: Shohet et al.

• Results– Livers of any animal

receiving some adenovirus showed some activity

– All hearts receiving microbubbles, gene, and ultrasound showed uptake

– No skeletal muscles in this experimental group showed uptake

– No uptake was seen in the hearts of any other animals

Transfection Study: Shohet et al.

• Results– β-galactosidase activity was

10-fold higher in the experimental group that received gene-encoated microbubbles and ultrasound simultaneously

– β-galactosidase activity was 2-fold higher in the group that received microbubble and ultrasound destruction first, followed by gene infusion.

Future Directions

• Application to other disease processes– Oncology

• Delivery of chemotherapy

• Delivery of anti-angiogenesis factors

– Musculoskeletal (arthritis)

– GI

– Endocrine (insulin delivery for diabetes)

– Transdermal drug delivery

Future Directions

• Cardiology Applications– Angiogenesis

• Delivery of VEGF

– Enhanced imaging• Ischemic myocardium

– Arrhythmia management• Combination of monitoring and therapy

? Management of Acute Myocardial Infarctions

www.mayoclinic.org