Optimal treatment occasion for ultrasound stimulated microbubbles in promoting gemcitabine delivery to VX2 tumors

Focused ultrasound-induced cell apoptosis for the treatment of tumours

Cancer is a serious public health problem worldwide. Traditional treatments, such as surgery, radiotherapy, chemotherapy, and immunotherapy, do not always yield satisfactory results; therefore, an efficient treatment for tumours is urgently needed. As a convenient and minimally invasive modality, focused ultrasound (FUS) has been used not only as a diagnostic tool but also as a therapeutic tool in an increasing number of studies. FUS can help treat malignant tumours by inducing apoptosis. This review describes the three apoptotic pathways, apoptotic cell clearance, and how FUS affects these three apoptotic pathways. This review also discusses the role of thermal and cavitation effects on apoptosis, including caspase activity, mitochondrial dysfunction, and Ca2+ elease. Finally, this article reviews various aspects of FUS combination therapy, including sensitization by radiotherapy and chemotherapy, gene expression upregulation, and the introduction of therapeutic gases, to provide new ideas for clinical tumour therapy.

Progression in low-intensity ultrasound-induced tumor radiosensitization

BACKGROUND

Radiotherapy (RT) is a widely utilized tumor treatment approach, while a significant obstacle in this treatment modality is the radioresistance exhibited by tumor cells. To enhance the effectiveness of RT, scientists have explored radiosensitization approaches, including the use of radiosensitizers and physical stimuli. Nevertheless, several approaches have exhibited disappointing results including adverse effects and limited efficacy. A safer and more effective method of radiosensitization involves low-intensity ultrasound (LIUS), which selectively targets tumor tissue and enhances the efficacy of radiation therapy.

METHODS

This review summarized the tumor radioresistance reasons and explored LIUS potential radiosensitization mechanisms. Moreover, it covered diverse LIUS application strategies in radiosensitization, including the use of LIUS alone, ultrasound-targeted intravascular microbubble destruction, ultrasound-mediated targeted radiosensitizers delivery, and sonodynamic therapy. Lastly, the review presented the limitations and prospects of employing LIUS-RT combined therapy in clinical settings, emphasizing the need to connect research findings with practical applications.

RESULTS AND CONCLUSION

LIUS employs cost-effective equipment to foster tumor radiosensitization, curtail radiation exposure, and elevate the quality of life for patients. This efficacy is attributed to LIUS's ability to utilize thermal, cavitation, and mechanical effects to overcome tumor cell resistance to RT. Multiple experimental analyses have underscored the effectiveness of LIUS in inducing tumor radiosensitization using diverse strategies. While initial studies have shown promising results, conducting more comprehensive clinical trials is crucial to confirm its safety and effectiveness in real-world situations.

Augmentation of tumour perfusion by ultrasound and microbubbles: A preclinical study

BACKGROUND

Hypoperfusion and the resulting hypoxia in solid tumours are critical causes of treatment resistance. Ultrasound-stimulated microbubbles (USMB) enhance tumour perfusion in a mechanism named the "sononeoperfusion" effect, which may relieve tumour hypoperfusion and hypoxia. The aim of this study was to determine the optimal mechanical index (MI) and therapeutic ultrasound exposure time for the sononeoperfusion effect and preliminarily explore the mechanism of sononeoperfusion and its effect on tumours.

METHODS

A total of 155 mice bearing MC38 tumours were included in this study. A modified diagnostic ultrasound and microbubbles (Zhifuxian) was used for USMB treatment. Tumour perfusion was evaluated by contrast-enhanced ultrasound (CEUS) and Hoechst 33342. The therapeutic pulse was operated with MIs of 0.1 to 0.5. The ultrasound exposure time was set from 150 s to 600 s. Endothelial nitric oxide synthase (eNOS) inhibition and NO, ATP, and phospho-eNOS (p-eNOS) detection were performed to explore the mechanisms of sononeoperfusion. Hypoxia-inducible factor-1α (HIF-1α) and tumour oxygen partial pressure (pO2) represent hypoxic tumour conditions.

RESULTS

Tumour perfusion was increased after USMB treatment at MIs of 0.1-0.4 and ultrasound exposure times of 150 s to 600 s, with optimal augmentation achieved at an MI of 0.3 and ultrasound exposure time of 450 s. The mean fluorescence intensity of Hoechst 33342 after USMB treatment was stronger than that of the control group. Biochemical assays showed a significant increase in ATP, p-eNOS and NO after USMB treatment. PO2 in tumour tissue increased significantly after USMB treatment and was maintained for more than 20 min.

CONCLUSIONS

The best sononeoperfusion effect was obtained with an MI of 0.3 and an ultrasound exposure time of 450 s. The effect is most likely related to NO and ATP increases. The sononeoperfusion effect might be a novel way to ameliorate tumour hypoperfusion and hypoxia.

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.

Clinical sonochemotherapy of inoperable pancreatic cancer using diagnostic ultrasound and microbubbles: a multicentre, open-label, randomised, controlled trial

OBJECTIVES

Sonochemotherapy, which uses microbubble (MB)-assisted ultrasound (US) to deliver chemotherapeutic agents, has the potential to enhance tumour chemotherapy. The combination of US and MB has been demonstrated to prolong the survival of patients with pancreatic cancer. This phase 2 clinical trial aimed to determine the clinical efficacy and safety of sonochemotherapy for inoperable pancreatic ductal adenocarcinoma by using US and MB.

METHODS

Eighty-two patients with stage III or IV pancreatic cancer were recruited from July 2018 to March 2021 and followed up until September 2022. US treatment was performed with a modified diagnostic US scanner for 30 min after chemotherapeutic infusion. The primary endpoint was overall survival (OS), and the secondary endpoints were Eastern Cooperative Oncology Group (ECOG) status < 2, progression-free survival (PFS), disease control rate (DCR), and adverse events.

RESULTS

Seventy-eight patients were randomly allocated (40 to chemotherapy and 38 to sonochemotherapy). The median OS was longer with sonochemotherapy than with chemotherapy (9.10 vs. 6.10 months; p = 0.037). The median PFS with sonochemotherapy was 5.50 months, compared with 3.50 months (p = 0.080) for chemotherapy. The time of ECOG status < 2 was longer with sonochemotherapy (7.20 months) than with chemotherapy (5.00 months; p = 0.029). The DCR was 73.68% for sonochemotherapy compared with 42.50% for the control (p = 0.005). The incidence of overall adverse events was balanced between the two groups.

CONCLUSIONS

The use of sonochemotherapy can extend the survival and well-being time of stage III or IV pancreatic cancer patients without any increase in serious adverse events.

TRIAL REGISTRATION

ChineseClinicalTrials.gov ChiCTR2100044721 CLINICAL RELEVANCE STATEMENT: This multicentre, randomised, controlled trial has proven that sonochemotherapy, namely, the combination of diagnostic ultrasound, microbubbles, and chemotherapy, could extend the overall survival of patients with end-stage pancreatic ductal adenocarcinoma from 6.10 to 9.10 months without increasing any serious adverse events.

KEY POINTS

• This is the first multicentre, randomised, controlled trial of sonochemotherapy for clinical pancreatic cancer treatment using ultrasound and a commercial ultrasound contrast agent. • Sonochemotherapy extended the median overall survival from 6.10 (chemotherapy alone) to 9.10 months. • The disease control rate increased from 42.50% with chemotherapy to 73.68% with sonochemotherapy.

Sononeoperfusion effect by ultrasound and microbubble promotes nitric oxide release to alleviate hypoxia in a mouse MC38 tumor model

Tumor hypoperfusion not only impedes therapeutic drug delivery and accumulation, but also leads to a hypoxic and acidic tumor microenvironment, resulting in tumor proliferation, invasion, and therapeutic resistance. Sononeoperfusion effect refers to tumor perfusion enhancement using ultrasound and microbubbles. This study aimed to further investigate hypoxia alleviation by sononeoperfusion effect and explore the characteristics and mechanism of sononeoperfusion effect. To stimulate the sononeoperfusion effect, mice bearing MC38 colon cancers were included in this study and diagnostic ultrasound for therapy was set at a mechanical index (MI) of 0.1, 0.3, and 0.5, frequency of 3 MHz, pulse length of 5 cycles, and pulse repetition frequency of 2000 Hz. The results demonstrated that a single ultrasound and microbubble (USMB) treatment resulted in tumor perfusion enhancement at MI = 0.3, and nitric oxide (NO) concentration increased at MI = 0.3/0.5 (P < 0.05). However, there were no significant difference in the hypoxia-inducible factor-1α (HIF-1α) or D-lactate (D-LA) (P > 0.05) levels. Multiple sononeoperfusion effects were observed at MI = 0.3/0.5 (P < 0.05). For each treatment, USMB slightly but steadily improved the tumor tissue oxygen partial pressure (pO2) during and post treatment. It alleviated tumor hypoxia by decreasing HIF-1α, D-LA level and the hypoxic immunofluorescence intensity at MI = 0.3/0.5 (P < 0.05). The sononeoperfusion effect was not stimulated after eNOS inhibition. In conclusion, USMB with appropriate MI could lead to a sononeoperfusion effect via NO release, resulting in hypoxia amelioration. The tumors were not resistant to multiple sononeoperfusion effects. Repeated sononeoperfusion is a promising approach for relieving tumor hypoxia and resistance to therapy.

A new sonoablation using acoustic droplet vaporization and focused ultrasound: A feasibility study

BACKGROUND

Histotripsy and boiling histotripsy are two methods of mechanical ablation that use high-pressure focused ultrasound (FUS).

PURPOSE

Here, a new bubble sonoablation technique was investigated using low-pressure FUS in combination with local injection of perfluoropentane (PFP) in rabbit liver.

METHODS

Fifteen healthy New Zealand white rabbits were treated with FUS alone, FUS + PFP or PFP alone. FUS was performed using a single-element focused transducer (frequency 596 kHz, 0.27 ms pulses, 0.54% duty cycle, and peak negative pressure 2.0 MPa). Ten minutes before FUS treatment, the PFP droplet was locally injected into the rabbit liver, where the ultrasound was focused. Contrast-enhanced ultrasound (CEUS) of the liver was performed, and the temperature at the liver surface in the targeted liver region was recorded during treatment. The livers were collected for pathological examination. Statistical significance was set at p < 0.05. Paired t-tests were used to compare the pre- and post-treatment values. One-way analysis of variance was performed to compare multiple groups, and the least significant difference method was used for further comparisons between the two groups.

RESULTS

Analysis of CEUS data showed that the values of area under the curve (AUC) were significantly different in the PFP + FUS group pre- (10453.644 ± 1182.93) and post-treatment (4058.098 ± 2720.41), and the AUC values of PFP + FUS post-treatment (4058.098 ± 2720.41) were also significantly lower than those of the FUS (9946.694 ± 1071.54) and the PFP (10364.794 ± 2181.53) groups. The peak intensity values also showed the same results, the value of peak intensity of PFP+FUS post-treatment was 82.958 ± 13.99, whereas there was no difference between FUS (106.61 ± 7.61) and PFP (104.136 ± 10.55). Hematoxylin and eosin (H&E) staining revealed that the pathological damage ratings of the PFP + FUS, PFP, and FUS groups were grade 3, grade 1, and grade 0, respectively. Specifically, the area of liver necrosis in the PFP + FUS group (0.99 ± 0.29 cm2 ) was 198 times higher than that in the PFP group (0.005 ± 0.008 cm2 ), whereas no necrosis was observed in the livers treated with FUS alone. Simultaneously, the number of vacuoles in the liver of the PFP + FUS group (35.50 ± 23.31) was approximately five times that of the PFP group (7.00 ± 12.88), whereas no vacuoles were found in the liver treated with FUS alone.

CONCLUSION

PFP droplets combined with FUS can destroy liver tissue and cause tissue necrosis in the droplet injection area, without affecting the structure of surrounding tissue.