Erratum: Focused ultrasound activates voltage-gated calcium channels through depolarizing TRPC1 sodium currents in kidney and skeletal muscle.

[This corrects the article DOI: 10.7150/thno.33876.].

Pulsed-Focused Ultrasound Slows B16 Melanoma and 4T1 Breast Tumor Growth through Differential Tumor Microenvironmental Changes.

Focused ultrasound (FUS) has shown promise as a non-invasive treatment modality for solid malignancies. FUS targeting to tumors has been shown to initiate pro-inflammatory immune responses within the tumor microenvironment. Pulsed FUS (pFUS) can alter the expression of cytokines, chemokines, trophic factors, cell adhesion molecules, and immune cell phenotypes within tissues. Here, we investigated the molecular and immune cell effects of pFUS on murine B16 melanoma and 4T1 breast cancer flank tumors. Temporal changes following sonication were evaluated by proteomics, RNA-seq, flow-cytometry, and histological analyses. Proteomic profiling revealed molecular changes occurring over 24 h post-pFUS that were consistent with a shift toward inflamed tumor microenvironment. Over 5 days post-pFUS, tumor growth rates were significantly decreased while flow cytometric analysis revealed differences in the temporal migration of immune cells. Transcriptomic analyses following sonication identified differences in gene expression patterns between the two tumor types. Histological analyses further demonstrated reduction of proliferation marker, Ki-67 in 4T1, but not in B16 tumors, and activated cleaved-caspase 3 for apoptosis remained elevated up to 3 days post-pFUS in both tumor types. This study revealed diverse biological mechanisms following pFUS treatment and supports its use as a possible adjuvant to ablative tumor treatment to elicit enhanced anti-tumor responses and slow tumor growth.

Acoustic Radiation or Cavitation Forces From Therapeutic Ultrasound Generate Prostaglandins and Increase Mesenchymal Stromal Cell Homing to Murine Muscle.

Non-ablative ultrasound (US)-based techniques to improve targeted tropism of systemically infused cell therapies, particularly mesenchymal stromal cell (MSC), have gained attention in recent years. Mechanotransduction following targeted US sonications have been shown to modulate tissue microenvironments by upregulating cytokines, chemokines, and trophic factors in addition to vascular cell adhesion molecules (CAM) that are necessary to promote tropism of MSC. While numerous US treatment parameters have demonstrated increased MSC homing, it remains unclear how the different mechanical US forces [i.e., acoustic radiation forces (ARF) or cavitation forces] influence tissue microenvironments. This study sonicated murine muscle tissue with pulsed focused ultrasound (pFUS) at 0.5 or 1.15 MHz each over a range of US intensities. Following sonication, tissue was assayed for the prostaglandins (PG) PGH2 and PGE2 as indicators of microenvironmental changes that would support MSC tropism. PGH2 and PGE2 levels were correlated to physical pFUS parameters and acoustic emissions measured by hydrophone. While ARF (pFUS with absence of cavitation signatures) was sufficient to increase PGH2 and PGE2, non-linear curve fitting revealed a frequency-independent relationship between prostaglandin production and mechanical index (MI), which accounts for increased cavitation probabilities of lower frequencies. The prostaglandin data suggested molecular changes in muscle would be particularly sensitive to cavitation. Therefore, low-intensity pulsed ultrasound (LIPUS) at 1 MHz was administered with low ARF (MI = 0.2) in combination with intravenous (IV) infusions of microbubble (MB) contrast agents. This combination upregulated prostaglandins and CAM without ultrasound-mediated microbubble destruction and ultimately promoted tropism of IV-infused MSC. This study revealed that accentuating non-destructive MB cavitation by US using parameters similar to diagnostic US contrast imaging increased MSC homing. Such approaches are particularly attractive to overcome clinical translation barriers of many still-experimental US parameters used in previous stem cell tropism studies.

The Impact of Focused Ultrasound in Two Tumor Models: Temporal Alterations in the Natural History on Tumor Microenvironment and Immune Cell Response.

Image-guided focused ultrasound (FUS) has been successfully employed as an ablative treatment for solid malignancies by exposing immune cells to tumor debris/antigens, consequently inducing an immune response within the tumor microenvironment (TME). To date, immunomodulation effects of non-ablative pulsed-FUS (pFUS) on the TME are poorly understood. In this study, the temporal differences of cytokines, chemokines, and trophic factors (CCTFs) and immune cell populations induced by pFUS were interrogated in murine B16 melanoma or 4T1 breast cancer cells subcutaneously inoculated into C57BL/6 or BALB/c mice. Natural history growth characteristics during the course of 11 days showed a progressive increase in size for both tumors, and proteomic analysis revealed a shift toward an immunosuppressive TME. With respect to tumor natural growth, pFUS applied to tumors on days 1, 5, or 9 demonstrated a decrease in the growth rate 24 h post-sonication. Flow cytometry analysis of tumors, LNs, and Sp, as well as CCTF profiles, relative DNA damage, and adaptive T-cell localization within tumors, demonstrated dynamic innate and adaptive immune-modulation following pFUS in early time points of B16 tumors and in advanced 4T1 tumors. These results provide insight into the temporal dynamics in the treatment-associated TME, which could be used to evaluate an immunomodulatory approach in different tumor types.

Focused ultrasound activates voltage-gated calcium channels through depolarizing TRPC1 sodium currents in kidney and skeletal muscle.

Pulsed focused ultrasound (pFUS) technology is being developed for clinical neuro/immune modulation and regenerative medicine. Biological signal transduction of pFUS forces can require mechanosensitive or voltage-gated plasma membrane ion channels. Previous studies suggested pFUS is capable of activating either channel type, but their mechanistic relationship remains ambiguous. We demonstrated pFUS bioeffects increased mesenchymal stem cell tropism (MSC) by altering molecular microenvironments through cyclooxygenase-2 (COX2)-dependent pathways. This study explored specific relationships between mechanosensitive and voltage-gated Ca2+ channels (VGCC) to initiate pFUS bioeffects that increase stem cell tropism. Methods: Murine kidneys and hamstring were given pFUS (1.15 or 1.125 MHz; 4MPa peak rarefactional pressure) under ultrasound or magnetic resonance imaging guidance. Cavitation and tissue displacement were measure by hydrophone and ultrasound radiofrequency data, respectively. Elastic modeling was performed from displacement measurements. COX2 expression and MSC tropism were evaluated in the presence of pharmacological ion channel inhibitors or in transient-receptor-potential-channel-1 (TRPC1)-deficient mice. Immunohistochemistry and co-immunoprecipitation examined physical channel relationships. Fluorescent ionophore imaging of cultured C2C12 muscle cells or TCMK1 kidney cells probed physiological interactions. Results: pFUS induced tissue deformations resulting in kPa-scale forces suggesting mechanical activation of pFUS-induced bioeffects. Inhibiting VGCC or TRPC1 in vivo blocked pFUS-induced COX2 upregulation and MSC tropism to kidneys and muscle. A TRPC1/VGCC complex was observed in plasma membranes. VGCC or TRPC1 suppression blocked pFUS-induced Ca2+ transients in TCMK1 and C2C12 cells. Additionally, Ca2+ transients were blocked by reducing transmembrane Na+ potentials and observed Na+ transients were diminished by genetic TRPC1 suppression. Conclusion: This study suggests that pFUS acoustic radiation forces mechanically activate a Na+-containing TRPC1 current upstream of VGCC rather than directly opening VGCC. The electrogenic function of TRPC1 provides potential mechanistic insight into other pFUS techniques for physiological modulation and optimization strategies for clinical implementation.