Author: admin

After more than 20 years working on viral and nonviral delivery modalities, Kenneth Greenberg, PhD, thought he had seen it all in genetic medicine delivery—until he met Steve Feinstein, MD, and Michael Davidson, MD, in 2021. Feinstein, a clinical cardiologist, had been working with ultrasound and contrast ultrasound for decades.

“Steve was scratching his head in the 90s trying to better diagnose heart disease patients, wondering why there’s a contrast agent for every other imaging modality except ultrasound,” Greenberg told Inside Precision Medicine.

Feinstein’s solution was microbubbles. These tiny gas-filled spheres (1-10 μm) with lipid, protein, or polymer shells can safely circulate through capillaries and resonate in response to ultrasound waves when injected intravenously, improving blood flow and tissue perfusion visualization before being cleared by the lungs and liver.

It was Feinstein that got the FDA to approve the first two ultrasound contrast imaging agents. Beyond diagnostics, he found new uses for microbubbles. Certain acoustic conditions could allow them to deliver therapeutic payloads directly into tissues.

Together with Davidson, a lipidologist and preventive cardiology specialist, Feinstein formed a long-term research partnership in Chicago’s academic medical community that resulted in the founding of SonoGene in 2000 to translate and commercialize ultrasound-mediated gene delivery.

Though SonoGene never made a splash, Feinstein and Davidson were able to generate preclinical data, which Greenberg found “mindblowing.”

“It showed me that you could use ultrasound and nonviral DNA payloads to achieve delivery and gene expression,” said Greenberg. “This is in rodents, but it was enough to persuade me that if it worked in humans anywhere near as well as it does in rodents, it could completely change the landscape of gene delivery. I thought it was just such an elegant idea. These components have been available for years, and we can repurpose them in a creative way to accomplish things that you could never do with existing modalities.”

In 2022, Greenberg, Feinstein, and Davidson joined forces to launch SonoThera, backed by a $60.75 million Series A financing with the goal of developing a nonviral, ultrasound-mediated gene delivery platform capable of producing safe, targeted, redosable, and cost-effective genetic medicines.

Four years later, investors are reaffirming that vision. SonoThera closed an oversubscribed $125 million Series B financing to advance its lead programs to the clinic and develop its ultrasound-enabled delivery platform. The funding comes at a crucial time for genetic medicine, where delivery challenges continue to temper therapeutic innovation.

RIPPLE effect

The genetic medicine revolution has produced transformative therapies across rare diseases, oncology, and metabolic disorders. Yet despite the success of viral vectors such as adeno-associated virus (AAV) and nonviral systems such as lipid nanoparticles (LNPs), researchers continue to grapple with payload-size constraints, limited tissue targeting, inability to redose, manufacturing complexity, and immune-related toxicities.

For Kenneth Greenberg, PhD, those challenges create an opening for a fundamentally different delivery strategy. “The field and investors recognize that this is a big problem, and no one has yet been able to solve it,” he said. “Coming up from a very different angle, I think it is getting people excited that this could ever come.”

Rather than engineering new viral capsids or nanoparticle chemistries, SonoThera has built its platform around two technologies already widely used in medicine: ultrasound systems and microbubble contrast agents. The company’s innovation lies in combining them with naked DNA payloads and proprietary ultrasound waveforms, called RIPPLE, to drive gene transfer into tissues.

“Our strategy has been to use the existing infrastructure as much as possible and not to develop bespoke hardware or novel microbubbles,” Greenberg said. “We want this to be widely utilized and have great patient access and clinicians to be familiar with the systems and the components.”

Unlike AAVs or LNPs, SonoThera does not package DNA inside a carrier. Instead, naked DNA and microbubbles circulate independently in the bloodstream until ultrasound is applied to a target organ. “There are some common misconceptions about the mechanism,” Greenberg said. “The mechanism basically involves taking the genetic payload, which is naked DNA. It’s not encapsulated in anything.”

The ultrasound activates circulating microbubbles in a multi-step process. First, acoustic energy creates temporary gaps in the endothelial lining of blood vessels, allowing DNA to access target tissues. The microbubbles are then collapsed, creating transient pores in cell membranes that permit intracellular entry of the payload. Finally, ultrasound-driven modulation of the nuclear pore complex facilitates transport of DNA into the nucleus for transcription and protein production. “The ultrasound can basically do everything in one single profile,” Greenberg said. “We can modulate the waveform in ways to drive this mechanism of delivery. We don’t need receptors, endosomes, or anything like that, which gives the platform a huge advantage in versatility to target different organs.”

That receptor-independent mechanism may offer one of the platform’s biggest advantages. Existing delivery systems typically depend on receptor-mediated cellular uptake, which can activate innate immune pathways and restrict tissue tropism. According to Greenberg, microbubbles largely avoid those limitations. “It’s also key to how we avoid the immune system, the innate immune system’s response that typically gets triggered by viruses and LNPs,” Greenberg said.

Because microbubbles are micron-sized rather than nanosized, they never enter the cell and are destroyed extracellularly after ultrasound activation. The DNA itself enters cells independently. While naked DNA degrades relatively quickly in circulation, Greenberg said its half-life of roughly 30 to 60 minutes is sufficient because infusion and ultrasound delivery occur simultaneously.

In contrast, LNPs enter cells through endocytosis, carrying lipids and genetic cargo that can activate innate immune sensors such as cGAS-STING and TLR9. AAVs similarly rely on receptor-mediated uptake pathways that can provoke immune responses and limit redosing.

From sonoporation to clinical translation

The platform’s flexibility has become increasingly apparent as SonoThera expanded beyond its initial liver studies. The company subsequently evaluated delivery to kidney, skeletal muscle, heart, brain, and adipose tissue. “What we’ve found is that the delivery technology works in all organs in the body, as far as we can tell,” Greenberg said. The notable exception is the lung, where air attenuates ultrasound energy.

Perhaps most striking is the company’s work in the brain. The SonoThera platform can temporarily open the blood-brain barrier and deliver payloads using the same mechanism as other tissues. “A common misconception is that the bone can attenuate the ultrasound energy. But that’s not the case,” Greenberg said. “The frequencies are such that they can penetrate easily through the skull and get into the brain.”

If that capability translates clinically, it could represent a significant advantage over delivery technologies that remain largely confined to the liver or a limited set of tissues.

SonoThera’s initial pipeline targets diseases where current delivery systems struggle. In Duchenne muscular dystrophy (DMD), the full-length dystrophin gene is too large for AAV vectors. The company’s ADPKD program has a larger payload.

“The overarching strategy when we’ve approached indications is that it’s challenging to get access to large payloads that are prohibitively large for AAVs,” Greenberg said. “With our ADPKD program, the payloads are even larger. That’s about a 22 KB payload, while the DMD payload is about 13 kb.”

Redosing is also important. Many genetic diseases require long-term treatment, especially in children whose tissues grow. AAV therapies are rarely administered again due to immune responses, making therapeutic expression difficult. “There are indications where the disease really requires redosing over time,” Greenberg said. “DMD is a good example because we’re treating really young boys as their bodies grow.”

SonoThera delivers mutation-agnostic full-length dystrophin with redoseability. The company also targets skeletal muscle, heart, and diaphragm simultaneously to address cardiopulmonary complications that kill many DMD patients.

The platform uses episomal DNA rather than genome editing. Greenberg believes the DNA behaves like AAV-delivered episomes, becoming chromatinized in the nucleus and maintaining expression. “We’ve got durability data out to a year so far with a single treatment,” he said.

Target tissue will determine redosing frequency: rapidly dividing cells may dilute episomal DNA, but quiescent tissues may maintain expression longer. Despite its focus on gene replacement, SonoThera has shown compatibility with gene editing and targeted integration methods. “For us, it’s really about using the right tool for the right job,” Greenberg said. “We don’t want to do gene editing just because it’s sexy.”

The scientific foundation for SonoThera’s platform is rooted in sonoporation, a concept that has been explored academically for decades but has never successfully reached the clinic. Greenberg believes the field historically struggled with two major hurdles: achieving sufficient transfection efficiency and broad biodistribution. “In the first two years of the company, we basically focused on solving those problems and really innovating to achieve extremely high delivery efficiency and broad organ biodistribution,” he said.

Those advances have now positioned the company to enter clinical development. SonoThera is conducting IND-enabling studies, manufacturing activities, and GLP toxicology work while refining clinical trial designs with physician and disease-area experts. The initial studies will focus primarily on safety while also evaluating biomarkers and early signs of efficacy. In DMD, the company has already generated preclinical biopsies showing expression of full-length dystrophin protein in muscle tissue.

Although SonoThera’s internal pipeline currently focuses on rare diseases, Greenberg sees broader opportunities ahead. Pharmaceutical companies have increasingly shifted attention toward common diseases with larger commercial potential, and many are searching for delivery platforms that can overcome the limitations of AAV-based therapies.

Investor confidence—but can it scale?

Greenberg says industry interest in nonviral, redosable systems may be better for common diseases, especially when manufacturing costs and reimbursement issues make one-time treatments unsustainable. SonoThera will advance its pipeline and partner with larger companies seeking platform access to capitalize on those opportunities. “Our strategy as a small biotech company has been to have our internal pipeline but, in parallel, be able to have licensing deals and partnerships that allow us to expand the reach of the technology and the much larger patient populations.”

The oversubscribed $125 million Series B financing suggests investors increasingly view delivery as the next major frontier in genetic medicine. As SonoThera approaches the clinic, it faces many of the same questions every new gene-delivery platform has faced for creating a paradigm-shifting delivery modality: safety, durability, and scale.

Because SonoThera’s platform relies on ultrasound-driven physical mechanisms rather than biological targeting, factors such as organ size, anatomy, blood flow, and patient variability could provide challenges to translatability.

Delivering DNA to a mouse liver or muscle is very different from delivering therapeutic amounts of genetic cargo throughout the muscles, heart, and diaphragm of a growing child with Duchenne muscular dystrophy. While microbubbles have a decades-long track record as imaging agents, repeated therapeutic delivery tools are a different proposition.

While the company argues that naked DNA and ultrasound avoid many of AAV’s payload limitations, questions remain about the doses required for large organs and whether manufacturing and administration can scale efficiently. Relatedly, SonoThera has reported preclinical expression lasting up to a year after a single treatment, but long-term persistence remains unknown. If repeat dosing is required, the company will need to demonstrate that repeated ultrasound exposure and cycles of vascular permeabilization can be performed safely over time.

SonoThera’s appeal reflects a broader reality: despite decades of innovation, delivery remains genetic medicine’s biggest unsolved problem. The company’s platform is scientifically elegant and potentially transformative, but only clinical data will determine whether ultrasound-mediated gene transfer represents a true breakthrough—or simply the latest attempt to solve one of biotechnology’s most stubborn challenges.

The post Have Microbubbles Burst Through the Barriers of Genetic Medicine Delivery? appeared first on Inside Precision Medicine.