A review of ultrasound-mediated microbubbles technology for cancer therapy: a vehicle for chemotherapeutic drug delivery

A Promising Therapeutic Strategy of Combining Acoustically Stimulated Nanobubbles and Existing Cancer Treatments

In recent years, ultrasound-stimulated microbubbles (USMBs) have gained great attention because of their wide theranostic applications. However, due to their micro-size, reaching the targeted site remains a challenge. At present, ultrasound-stimulated nanobubbles (USNBs) have attracted particular interest, and their small size allows them to extravasate easily in the blood vessels penetrating deeper into the tumor vasculature. Incorporating USNBs with existing cancer therapies such as chemotherapy, immunotherapy, and/or radiation therapy in several preclinical models has been demonstrated to have a profound effect on solid tumors. In this review, we provide an understanding of the composition and formation of nanobubbles (NBs), followed by the recent progress of the therapeutic combinatory effect of USNBs and other cancer therapies in cancer treatment.

Efficient ultrasound-mediated drug delivery to orthotopic liver tumors - Direct comparison of doxorubicin-loaded nanobubbles and microbubbles

Liver metastasis is a major obstacle in treating aggressive cancers, and current therapeutic options often prove insufficient. To overcome these challenges, there has been growing interest in ultrasound-mediated drug delivery using lipid-shelled microbubbles (MBs) and nanobubbles (NBs) as promising strategies for enhancing drug delivery to tumors. Our previous work demonstrated the potential of Doxorubicin-loaded C3F8 NBs (hDox-NB, 280 ± 123 nm) in improving cancer treatment in vitro using low-frequency unfocused therapeutic ultrasound (TUS). In this study, we investigated the pharmacokinetics and biodistribution of sonicated hDox-NBs in orthotopic rat liver tumors. We compared their delivery and therapeutic efficiency with size-isolated MBs (hDox-MB, 1104 ± 373 nm) made from identical shell material and core gas. Results showed a similar accumulation of hDox in tumors treated with hDox-MBs and unfocused therapeutic ultrasound (hDox-MB + TUS) and hDox-NB + TUS. However, significantly increased apoptotic cell death in the tumor and fewer off-target apoptotic cells in the normal liver were found upon the treatment with hDox-NB + TUS. The tumor-to-liver apoptotic ratio was elevated 9.4-fold following treatment with hDox-NB + TUS compared to hDox-MB + TUS, suggesting that the therapeutic efficacy and specificity are significantly increased when using hDox-NB + TUS. These findings highlight the potential of this approach as a viable treatment modality for liver tumors. By elucidating the behavior of drug-loaded bubbles in vivo, we aim to contribute to developing more effective liver cancer treatments that could ultimately improve patient outcomes and decrease off-target side effects.

Efficient ultrasound-mediated drug delivery to orthotopic liver tumors - Direct comparison of doxorubicin-loaded nanobubbles and microbubbles

Liver metastasis is a major obstacle in treating aggressive cancers, and current therapeutic options often prove insufficient. To overcome these challenges, there has been growing interest in ultrasound-mediated drug delivery using lipid-shelled microbubbles (MBs) and nanobubbles (NBs) as promising strategies for enhancing drug delivery to tumors. Our previous work demonstrated the potential of Doxorubicin-loaded C3F8 NBs (hDox-NB, 280 ± 123 nm) in improving cancer treatment in vitro using low-frequency ultrasound. In this study, we investigated the pharmacokinetics and biodistribution of sonicated hDox-NBs in orthotopic rat liver tumors. We compared their delivery and therapeutic efficiency with size-isolated MBs (hDox-MB, 1104 ± 373 nm). Results showed a similar accumulation of hDox in tumors treated with hDox-MBs and unfocused therapeutic ultrasound (hDox-MB+TUS) and hDox-NB+TUS. However, significantly increased apoptotic cell death in the tumor and fewer off-target apoptotic cells in the normal liver were found upon the treatment with hDox-NB+TUS. The tumor-to-liver apoptotic ratio was elevated 9.4-fold following treatment with hDox-NB+TUS compared to hDox-MB+TUS, suggesting that the therapeutic efficacy and specificity are significantly increased when using hDox-NB+TUS. These findings highlight the potential of this approach as a viable treatment modality for liver tumors. By elucidating the behavior of drug-loaded bubbles in vivo, we aim to contribute to developing more effective liver cancer treatments that could ultimately improve patient outcomes and decrease off-target side effects.

Ultrasound-Stimulated Microbubbles Enhance Radiation-Induced Cell Killing

Recent in vivo studies using ultrasound-stimulated microbubbles as a localized radiosensitizer have had impressive results. While in vitro studies have also obtained similar results using human umbilical vein endothelial cells (HUVEC), studies using other cell lines have had varying results. This study was aimed at investigating any increases in radiation-induced cell killing in vitro using two carcinoma lines not previously investigated before (metastatic follicular thyroid carcinoma cells [FTC-238] and non-small cell lung carcinoma cells [NCI-H727]), in addition to HUVEC. Cells were treated using a combination of 1.6% (v/v) microbubbles, ∼90 s of 2-MHz ultrasound (mechanical index = 0.8) and 0-6 Gy of kilovolt or MV X-rays. Cell viability assays obtained 72 h post-treatment were normalized to untreated controls, and analysis of variance was used to determine statistical significance. All cells treated with combined ultrasound-stimulated microbubbles and radiation exhibited decreased normalized survival, with statistically significant effects observed for the NCI-H727 cells. No statistically significant differences in effects were observed using kV compared with MV radiation. Further studies using increased microbubble concentrations may be required to achieve statistically significant results for the FTC-238 and HUVEC lines.

Recent Advances in Stimuli-Responsive Doxorubicin Delivery Systems for Liver Cancer Therapy

Doxorubicin (DOX) is one of the most commonly used drugs in liver cancer. Unfortunately, the traditional chemotherapy with DOX presents many limitations, such as a systematic release of DOX, affecting both tumor tissue and healthy tissue, leading to the apparition of many side effects, multidrug resistance (MDR), and poor water solubility. Furthermore, drug delivery systems' responsiveness has been intensively studied according to the influence of different internal and external stimuli on the efficiency of therapeutic drugs. In this review, we discuss both internal stimuli-responsive drug-delivery systems, such as redox, pH and temperature variation, and external stimuli-responsive drug-delivery systems, such as the application of magnetic, photo-thermal, and electrical stimuli, for the controlled release of Doxorubicin in liver cancer therapy, along with the future perspectives of these smart delivery systems in liver cancer therapy.

Drug Delivery by Ultrasound-Responsive Nanocarriers for Cancer Treatment

Conventional cancer chemotherapies often exhibit insufficient therapeutic outcomes and dose-limiting toxicity. Therefore, there is a need for novel therapeutics and formulations with higher efficacy, improved safety, and more favorable toxicological profiles. This has promoted the development of nanomedicines, including systems for drug delivery, but also for imaging and diagnostics. Nanoparticles loaded with drugs can be designed to overcome several biological barriers to improving efficiency and reducing toxicity. In addition, stimuli-responsive nanocarriers are able to release their payload on demand at the tumor tissue site, preventing premature drug loss. This review focuses on ultrasound-triggered drug delivery by nanocarriers as a versatile, cost-efficient, non-invasive technique for improving tissue specificity and tissue penetration, and for achieving high drug concentrations at their intended site of action. It highlights aspects relevant for ultrasound-mediated drug delivery, including ultrasound parameters and resulting biological effects. Then, concepts in ultrasound-mediated drug delivery are introduced and a comprehensive overview of several types of nanoparticles used for this purpose is given. This includes an in-depth compilation of the literature on the various in vivo ultrasound-responsive drug delivery systems. Finally, toxicological and safety considerations regarding ultrasound-mediated drug delivery with nanocarriers are discussed.

Synthesis and physicochemical evaluation of fluorinated lipopeptide precursors of ligands for microbubble targeting

Ligand-targeted microbubbles are focusing interest for molecular imaging and delivery of chemotherapeutics. Lipid-peptide conjugates (lipopeptides) that feature alternating serine-glycine (SG) n segments rather than classical poly(oxyethylene) linkers between the lipid polar head and a targeting ligand were proposed for the liposome-mediated, selective delivery of anticancer drugs. Here, we report the synthesis of perfluoroalkylated lipopeptides (F-lipopeptides) bearing two hydrophobic chains (C n F2 n +1, n = 6, 7, 8, 1-3) grafted through a lysine moiety on a hydrophilic chain composed of a lysine-serine-serine (KSS) sequence followed by 5 SG sequences. These F-lipopeptides are precursors of targeting lipopeptide conjugates. A hydrocarbon counterpart with a C10H21 chain (4) was synthesized for comparison. The capacity for the F-lipopeptides to spontaneously adsorb at the air/water interface and form monolayers when combined with dipalmitoylphosphatidylcholine (DPPC) was investigated. The F-lipopeptides 1-3 demonstrated a markedly enhanced tendency to form monolayers at the air/water interface, with equilibrium surface pressures reaching ≈7-10 mN m-1 versus less than 1 mN m-1 only for their hydrocarbon analog 4. The F-lipopeptides penetrate in the DPPC monolayers in both liquid expanded (LE) and liquid condensed (LC) phases without interfacial film destabilization. By contrast, 4 provokes delipidation of the interfacial film. The incorporation of the F-lipopeptides 1-3 in microbubbles with a shell of DPPC and dipalmitoylphosphatidylethanolamine-PEG2000 decreased their mean diameter and increased their stability, the best results being obtained for the C8F17-bearing lipopeptide 3. By contrast, the hydrocarbon lipopeptide led to microbubbles with a larger mean diameter and a significantly lower stability.