Sumit Paliwal

Low-frequency sonophoresis: current status and future prospects.

Application of ultrasound enhances skin permeability to drugs, a phenomenon referred to as sonophoresis. Significant strides have been made in sonophoresis research in recent years, especially under low-frequency conditions (20 kHz<f<100 kHz). This article reviews the mechanistic principles and current status of sonophoresis under low-frequency conditions. Several therapeutic macromolecules including insulin, low-molecular weight heparin, and vaccines have been delivered using low-frequency sonophoresis in vivo. Clinical trials have been performed with several drugs including lidocaine and cyclosporin. Novel theoretical and experimental approaches have provided insights into the mechanisms of low-frequency sonophoresis. Current understanding of these mechanisms is presented.

Ultrasound-induced cavitation: applications in drug and gene delivery

Ultrasound, which has been conventionally used for diagnostics until recently, is now being extensively used for drug and gene delivery. This transformation has come about primarily due to ultrasound-mediated acoustic cavitation – particularly transient cavitation. Acoustic cavitation has been used to facilitate the delivery of small molecules, as well as macromolecules, including proteins and DNA. Controlled generation of cavitation has also been used for targeting drugs to diseased tissues, including skin, brain, eyes and endothelium. Ultrasound has also been employed for the treatment of several diseases, including thromboembolism, arteriosclerosis and cancer. This review provides a detailed account of mechanisms, current status and future prospects of ultrasonic cavitation in drug and gene delivery applications.

Therapeutic opportunities in biological responses of ultrasound

The therapeutic benefits of several existing ultrasound-based therapies such as facilitated drug delivery, tumor ablation and thrombolysis derive largely from physical or mechanical effects. In contrast, ultrasound can also trigger various time-dependent biochemical responses in the exposed biological milieu. Several biological responses to ultrasound exposure have been previously described in the literature but only a handful of these provide therapeutic opportunities. These include the use of ultrasound for healing of soft tissues and bones, the use of ultrasound for inducing non-necrotic tumor atrophy as well as for potentiation of chemotherapeutic drugs, activation of the immune system, angiogenesis and suppression of phagocytosis. A review of these therapeutic opportunities is presented with particular emphasis on their mechanisms. Overall, this review presents the increasing importance of ultrasounds role as a biological sensitizer enabling novel therapeutic strategies.

One-step acquisition of functional biomolecules from tissues

Direct determination of functional biomolecular chemistry of clinically relevant tissues in vivo is a challenging task. Current approaches, based on tissue retrieval by biopsy and subsequent solubilization, are limited in terms of accurate representation of tissue constituents, reproducibility, and retention of functionality of solubilized tissue biomolecules. Using a pool of known surfactants, we designed and screened a large combinatorial library of surfactant formulations, which led to the discovery of rare synergistic formulations that greatly enhance tissue solubilization as well as preserve bioactivity of solubilized molecules, in particular proteins. By combining these formulations with a short ultrasound application, we developed a tissue sampling method—STAMP (Surfactant-based Tissue Acquisition for Molecular Profiling)—for rapid one-step determination of functional tissue chemistry in vivo. We specifically demonstrate STAMP-assisted profiling of a multitude of proteins, lipids, and genomic DNA in skin and mucosal tissues. Applications of this sampling methodology to rapid molecular diagnostics of cutaneous allergies and infectious diseases are also presented.

Sampling of disease biomarkers from skin for theranostic applications

Dermatological diseases including psoriasis, eczema, infections, and cancer collectively constitute a large category of human conditions. The large area and ease of access of skin open excellent opportunities for theranostic applications, that is, diagnosis as well as therapy of the disease. Such applications can be based on evaluation of skin’s molecular composition in terms of proteins, nucleic acids, and small molecules. Currently, however, such molecular information is not used in clinical practice. To bring this molecular information to routine clinical dermatology, it is essential to develop convenient and minimally invasive methods for rapid sampling molecules from skin. Here, we demonstrate an ultrasonic sampling technique that can recover a wide variety of biomolecules from skin in a minimally invasive manner. We show that ultrasound can retrieve nearly all major tissue constituents, including structural and functional proteins (cytokines, keratins, etc.), lipids (polar and non-polar lipids), and nucleic acids (DNA and RNA). Comparative analyses of skin’s molecular constituents obtained by ultrasonic sampling and skin homogenate showed high resemblance between the two biomolecular profiles, enabling us to build a unique molecular signature of skin. Using different mouse models of dermatological conditions, the ultrasonic analysis for changes in the molecular composition of skin confirmed specific regulation of several established biomarkers.

Ultrasound‐assisted skin diagnostics

The biomolecular composition of human skin, represented by a multitude of lipids, proteins, nucleic acids, and other miscellaneous molecules, is a sensitive indicator of skin’s local health, as well as the body’s systemic health. However, this information is not easily accessible, and consequently not used in the current diagnostic methods. To address the lack of quantitative methods for non‐invasive skin diagnostics, herein, we describe the use of ultrasound to rapidly extract biological markers from skin. Specifically, we extracted several types of proteins (keratins, beta‐actin, cytokines, and others), lipids (cholesterol, ceramides, fatty acids, and others), nucleic acids, small molecules (natural moisturizing factors and exogenous molecules), and microbes enabling us to create skin’s unique biomolecular signature. The extracted biomolecules showed quantitative correlations with their composition in the epidermal skin. Extraction of these entities from skin using our method is convenient and reproduci...

Developing novel therapeutic strategies through biological effects of ultrasound

Ultrasound‐mediated cavitation has been shown to facilitate delivery of drugs across biological barriers in cells and tissues. However, these nonthermal mechanisms can also trigger various biochemical pathways in the biological milieu, opening up doors to interesting ultrasonic therapeutic applications. For example, a brief application of ultrasound followed by treatment with quercetin (a poorly potent chemotherapeutic drug) becomes selectively cytotoxic towards prostate and skin cancer cells. As opposed to the increased delivery of drugs to cancer cells, this treatment methodology is hypothesized to be mediated through inhibition of heat shock protein‐hsp72, a vital stress‐protein essential for the survival of cancer cells. Additional examples demonstrating the use of ultrasound’s biological effects for therapeutic applications will be discussed. For example, ultrasound is demonstrated to work as a vaccination adjuvant by activating the Langerhans cells (immune cells present in skin) and leading to a robust immune response against tetanus toxoid. Overall, this presentation will demonstrate the increasing importance of ultrasound’s role as a biological sensitizer enabling novel therapeutic strategies, a role which is beyond its conventional use as a drug delivery tool.