Acoustic mechanogenetics

Sonogenetics for Monitoring and Modulating Biomolecular Function by Ultrasound

Ultrasound technology, synergistically harnessed with genetic engineering and chemistry concepts, has started to open the gateway to the remarkable realm of sonogenetics-a pioneering paradigm for remotely orchestrating cellular functions at the molecular level. This fusion not only enables precisely targeted imaging and therapeutic interventions, but also advances our comprehension of mechanobiology to unparalleled depths. Sonogenetic tools harness mechanical force within small tissue volumes while preserving the integrity of the surrounding physiological environment, reaching depths of up to tens of centimeters with high spatiotemporal precision. These capabilities circumvent the inherent physical limitations of alternative in vivo control methods such as optogenetics and magnetogenetics. In this review, we first discuss mechanosensitive ion channels, the most commonly utilized sonogenetic mediators, in both mammalian and non-mammalian systems. Subsequently, we provide a comprehensive overview of state-of-the-art sonogenetic approaches that leverage thermal or mechanical features of ultrasonic waves. Additionally, we explore strategies centered around the design of mechanochemically reactive macromolecular systems. Furthermore, we delve into the realm of ultrasound imaging of biomolecular function, encompassing the utilization of gas vesicles and acoustic reporter genes. Finally, we shed light on limitations and challenges of sonogenetics and present a perspective on the future of this promising technology.

Sonomechanobiology: Vibrational stimulation of cells and its therapeutic implications

All cells possess an innate ability to respond to a range of mechanical stimuli through their complex internal machinery. This comprises various mechanosensory elements that detect these mechanical cues and diverse cytoskeletal structures that transmit the force to different parts of the cell, where they are transcribed into complex transcriptomic and signaling events that determine their response and fate. In contrast to static (or steady) mechanostimuli primarily involving constant-force loading such as compression, tension, and shear (or forces applied at very low oscillatory frequencies (≤ 1 Hz) that essentially render their effects quasi-static), dynamic mechanostimuli comprising more complex vibrational forms (e.g., time-dependent, i.e., periodic, forcing) at higher frequencies are less well understood in comparison. We review the mechanotransductive processes associated with such acoustic forcing, typically at ultrasonic frequencies (> 20 kHz), and discuss the various applications that arise from the cellular responses that are generated, particularly for regenerative therapeutics, such as exosome biogenesis, stem cell differentiation, and endothelial barrier modulation. Finally, we offer perspectives on the possible existence of a universal mechanism that is common across all forms of acoustically driven mechanostimuli that underscores the central role of the cell membrane as the key effector, and calcium as the dominant second messenger, in the mechanotransduction process.

Mechano-modulation of T cells for cancer immunotherapy

Immunotherapy, despite its promise for future anti-cancer approach, faces significant challenges, such as off-tumor side effects, innate or acquired resistance, and limited infiltration of immune cells into stiffened extracellular matrix (ECM). Recent studies have highlighted the importance of mechano-modulation/-activation of immune cells (mainly T cells) for effective caner immunotherapy. Immune cells are highly sensitive to the applied physical forces and matrix mechanics, and reciprocally shape the tumor microenvironment. Engineering T cells with tuned properties of materials (e.g., chemistry, topography, and stiffness) can improve their expansion and activation ex vivo, and their ability to mechano-sensing the tumor specific ECM in vivo where they perform cytotoxic effects. T cells can also be exploited to secrete enzymes that soften ECM, thus increasing tumor infiltration and cellular therapies. Furthermore, T cells, such as chimeric antigen receptor (CAR)-T cells, genomic engineered to be spatiotemporally controllable by physical stimuli (e.g., ultrasound, heat, or light), can mitigate adverse off-tumor effects. In this review, we communicate these recent cutting-edge endeavors devoted to mechano-modulating/-activating T cells for effective cancer immunotherapy, and discuss future prospects and challenges in this field.

High-frequency noncontact low-intensity pulsed ultrasound modulates Ca2+-dependent transcription factors contributing to cell migration

Chronic wounds have negative physical and psychological effects on patients and increase the health care burden. Consequently, chronic wound in the elderly population is an important issue. Ultrasound can be a great modality for treating chronic wounds because of its noninvasive and safety characteristics; it can accelerate in vitro and in vivo wound healing. In this study, we developed a novel noncontact ultrasound for wound treatment. We stimulated human epidermal keratinocyte migration using low-intensity pulsed ultrasound (LIPUS) with a noncontact transducer to avoid direct contact with the wound. We also compared the effects of 15-min contact and noncontact transducer stimulation, where a 1-MHz contact transducer (intensity = 40 or 200 mW/cm²) and a 0.45-MHz noncontact transducer (intensity = 30 mW/cm²) were used. Both contact and noncontact LIPUS considerably increased cell migration and activated the calcium (Ca²⁺)-dependent transcription factors cAMP-responsive element-binding protein (CREB) and nuclear factor of activated T cells (NFAT). Furthermore, noncontact transducer stimulation did not cause cell death or affect cell proliferation but significantly increased the Ca²⁺ influx-mediated intracellular Ca²⁺ levels. Ca²⁺-free medium and Ca²⁺ channel blockers effectively inhibited LIPUS-induced Ca²⁺-dependent transcription factor activation and cell migration.

Gamma Frequency Inhibits the Secretion and Aggregation of Amyloid-β and Decreases the Phosphorylation of mTOR and Tau Proteins in vitro

Background: Alzheimer’s disease (AD) was the main cause of dementia in an aging society; unfortunately, there is no effective treatment for AD now. Meditation has been reported to thicken the cerebral cortex, and gamma wave at a frequency of 40 hertz (Hz) was recorded during the meditation process from the brain. Previous study showed that non-invasive scintillation gamma frequency oscillation increased the space in recognition and memory of auditory cortex hippocampal gyrus in AD mice model. However, the AD-related molecular change by exposure of 40 Hz gamma frequency in brain cells was still unclear. Objective: We investigated the AD-related molecular change by exposure of 40 Hz gamma frequency in SH-SY5Y cells. Methods: We designed the light and sound generators at 40 Hz gamma frequency for this study. SH-SY5Y cells were exposed to sound or light of 40 Hz gamma frequency, respectively. The concentrations of amyloid-β40 (Aβ40) and amyloid-β42 (Aβ42) were quantified by enzyme-linked immunosorbent assay. The protein levels were examined by western blotting. The aggregation of Aβ42 was examined by thioflavin T assay. Results: Our results showed that the secretion of Aβ, phosphorylation of AKT, mTOR, and tau, and aggregation of Aβ42 were significantly inhibited by 40 Hz gamma frequency in SH-SY5Y cells. The phosphorylation of 4E-BP1, downstream of mTOR, was induced by 40 Hz gamma frequency in SH-SY5Y cells. Conclusion: Our study showed 40 Hz gamma frequency involved in the inhibition of secretion and aggregation of Aβ and inhibition of p-Tau protein expression through the mTOR/4E-BP1/Tau signaling pathway.

Ultrasound Therapy, Chemotherapy and Their Combination for Prostate Cancer

Prostate cancer is the second leading cause of cancer death in men. Its current treatment includes various physical and chemical approaches for the localized and advanced prostate cancer [e.g. metastatic castrate resistant prostate cancer (mCRPC)]. Although many new drugs are now available for prostate cancer, none is suitable for local treatment that can reduce adverse effects often associated with the current physical treatment. Of the drugs approved by FDA for mCRPC, the best mean improvement in overall survival is only about 4.8 months. Therefore, there is a need for improved treatment approaches for prostate cancer, especially drug-resistant cancer.

Ultrasound therapy represents a useful new physical approach for the drug-resistant cancer treatment by facilitating the entry of the related chemotherapy drug into the target cancer cells. There are two versions of ultrasound: High Intensity Focused Ultrasound (HIFU) and Low Intensity Pulsed Ultrasound (LIPUS). HIFU has been a promising treatment option for prostate cancer due to its noninvasiveness and various biological effects on cancer tissue. It has been approved for the treatment of cancer and in recent years there have been numerous findings suggesting HIFU can reduce cancer cell viability and possibly reverse the spread of cancerous tumors. LIPUS is currently being studied as an alternative treatment option for prostate cancer. Preliminary studies have found LIPUS to reduce cancer cell viability without the side effects seen in HIFU. Reversible cell membrane damage caused by LIPUS could allow increased uptake of anticancer drugs, enhancing cytotoxicity and death of cancer cells. In this way, a low dose of anticancer drug is more effective toward cancer cells while there is less damage to normal cells. The combination of LIPUS with certain chemotherapeutic agents can be an exciting physical-chemical combination therapy for prostate cancer. This review will focus on this topic as well as the clinical use of HIFU to provide an understanding of their current use and future potential role for prostate cancer therapy.

Measurements of acoustic radiation force of ultrahigh frequency ultrasonic transducers using model-based approach

Even though ultrahigh frequency ultrasonic transducers over 60 MHz have been used for single-cell-level manipulation such as intracellular delivery, acoustic tweezers, and stimulation to investigate cell phenotype and cell mechanics, no techniques have been available to measure the actual acoustic radiation force (ARF) applied to target cells. Therefore, we have developed an approach to measure the ARF of ultrahigh frequency ultrasonic transducers using a theoretical model of the dynamics of a solid sphere in a gelatin phantom. To estimate ARF at the focus of a 130 MHz transducer, we matched measured maximum displacements of a solid sphere with theoretical calculations. We selected appropriate ranges of input voltages and pulse durations for single-cell applications, and the estimated ARF was in the range of tens of μN. To gauge the influence of pulse duration, an impulse of different pulse durations was estimated. Fluorescence resonance energy transfer live cell imaging was demonstrated to visualize calcium transport between cells after a target single cell was stimulated by the developed ultrasonic transducer.

Mechanogenetics for cellular engineering and cancer immunotherapy

Recent synthetic biology advancements have shown that cells can be engineered to respond to external stimuli such as chemical compounds and light, which significantly improves the specificity and controllability of CAR T therapy. However, the lack of both spatiotemporal and depth control is still the main issue in the clinic of CAR T treatment. At the same time, mechanogenetics, capable of penetrating deep tissues with high spatiotemporal precision, is rapidly evolving and advancing to reveal its potential for cancer immunotherapy. In the past few years, researchers have demonstrated the precise and remote control of engineered cells with mechanical perturbation originated from ultrasound, which may become a new solution to circumvent the limitations of CAR T therapy in the future. This review will discuss mechanobiology and the state-of art designs of controllable CAR T cells. A specific focus of this review will be on the mechanical control of CAR T therapy.

Synthetic immunity by remote control

Cell-based immunotherapies, such as T cells engineered with chimeric antigen receptors (CARs), have the potential to cure patients of disease otherwise refractory to conventional treatments. Early-on-treatment and long-term durability of patient responses depend critically on the ability to control the potency of adoptively transferred T cells, as overactivation can lead to complications like cytokine release syndrome, and immunosuppression can result in ineffective responses to therapy. Drugs or biologics (e.g., cytokines) that modulate immune activity are limited by mass transport barriers that reduce the local effective drug concentration, and lack site or target cell specificity that results in toxicity. Emerging technologies that enable site-targeted, remote control of key T cell functions - including proliferation, antigen-sensing, and target-cell killing - have the potential to increase treatment precision and safety profile. These technologies are broadly applicable to other immune cells to expand immune cell therapies across many cancers and diseases. In this review, we highlight the opportunities, challenges and the current state-of-the-art for remote control of synthetic immunity.

Radiation Force as a Physical Mechanism for Ultrasonic Neurostimulation of the Ex Vivo Retina

Focused ultrasound has been shown to be effective at stimulating neurons in many animal models, both in vivo and ex vivo Ultrasonic neuromodulation is the only noninvasive method of stimulation that could reach deep in the brain with high spatial-temporal resolution, and thus has potential for use in clinical applications and basic studies of the nervous system. Understanding the physical mechanism by which energy in a high acoustic frequency wave is delivered to stimulate neurons will be important to optimize this technology. We imaged the isolated salamander retina of either sex during ultrasonic stimuli that drive ganglion cell activity and observed micron scale displacements, consistent with radiation force, the nonlinear delivery of momentum by a propagating wave. We recorded ganglion cell spiking activity and changed the acoustic carrier frequency across a broad range (0.5-43 MHz), finding that increased stimulation occurs at higher acoustic frequencies, ruling out cavitation as an alternative possible mechanism. A quantitative radiation force model can explain retinal responses and could potentially explain previous in vivo results in the mouse, suggesting a new hypothesis to be tested in vivo Finally, we found that neural activity was strongly modulated by the distance between the transducer and the electrode array showing the influence of standing waves on the response. We conclude that radiation force is the dominant physical mechanism underlying ultrasonic neurostimulation in the ex vivo retina and propose that the control of standing waves is a new potential method to modulate these effects.SIGNIFICANCE STATEMENT Ultrasonic neurostimulation is a promising noninvasive technology that has potential for both basic research and clinical applications. The mechanisms of ultrasonic neurostimulation are unknown, making it difficult to optimize in any given application. We studied the physical mechanism by which ultrasound is converted into an effective energy form to cause neurostimulation in the retina and find that ultrasound acts via radiation force leading to a mechanical displacement of tissue. We further show that standing waves have a strong modulatory effect on activity. Our quantitative model by which ultrasound generates radiation force and leads to neural activity will be important in optimizing ultrasonic neurostimulation across a wide range of applications.