Pulsed high-intensity focused ultrasound enhances apoptosis of pancreatic cancer xenograft with gemcitabine

Integrating intratumoral and peritumoral radiomics with clinical risk factors for prognostic prediction in pancreatic ductal adenocarcinoma patients undergoing combined chemotherapy and HIFU ablation

OBJECTIVE

A radiomics nomogram will be created utilizing MRI data from intratumoral and peritumoral areas to forecast survival outcomes in patients who have had treatment for pancreatic ductal adenocarcinoma (PDAC).

METHODS

A total of 87 individuals diagnosed with PDAC were included in the study, with 60 patients in the training cohort and 27 patients in the validation cohort. A grand total of 2395 radiomics characteristics were extracted from the tumor region and the peritumoral region. The least absolute shrinkage and selection operator (LASSO) method was used to select features and create a radiomics score, also known as the Rad-score. A multivariate regression analysis was then conducted to build the radiomics nomogram. The evaluation of the nomogram included discrimination, calibration, and clinical utility assessments.

RESULTS

Based on the conclusions derived from the multivariate Cox model, Rad-Score, jaundice, and tumor size were identified as independent risk factors for overall survival (OS). The inclusion of the Rad-score in the radiomics nomogram led to improved accuracy in predicting survival compared to the clinical model. Patients were categorized into high-risk and low-risk groups based on their Rad-Score. Kaplan-Meier analysis revealed a statistically significant difference between the two groups (p < 0.05). Furthermore, the radiomics nomogram demonstrated excellent ability to differentiate, calibrate, and provide clinical utility in both the training and validation groups.

CONCLUSIONS

The MRI-based intratumoral and peritumoral radiomics nomogram, integrating the Rad-score and clinical data, provided better prognostic prediction for PDAC patients after HIFU treatment, which may hold great potential for guiding personalized care for these patients.

Dynamic mode decomposition based Doppler monitoring of de novo cavitation induced by pulsed HIFU: an in vivo feasibility study

Pulsed high-intensity focused ultrasound (pHIFU) has the capability to induce de novo cavitation bubbles, offering potential applications for enhancing drug delivery and modulating tissue microenvironments. However, imaging and monitoring these cavitation bubbles during the treatment presents a challenge due to their transient nature immediately following pHIFU pulses. A planewave bubble Doppler technique demonstrated its potential, yet this Doppler technique used conventional clutter filter that was originally designed for blood flow imaging. Our recent study introduced a new approach employing dynamic mode decomposition (DMD) to address this in an ex vivo setting. This study demonstrates the feasibility of the application of DMD for in vivo Doppler monitoring of the cavitation bubbles in porcine liver and identifies the candidate monitoring metrics for pHIFU treatment. We propose a fully automated bubble mode identification method using k-means clustering and an image contrast-based algorithm, leading to the generation of DMD-filtered bubble images and corresponding Doppler power maps after each HIFU pulse. These power Doppler maps are then correlated with the extent of tissue damage determined by histological analysis. The results indicate that DMD-enhanced power Doppler map can effectively visualize the bubble distribution with high contrast, and the Doppler power level correlates with the severity of tissue damage by cavitation. Further, the temporal characteristics of the bubble modes, specifically the decay rates derived from DMD, provide information of the bubble dissolution rate, which are correlated with tissue damage level-slower rates imply more severe tissue damage.

Dynamic Mode Decomposition for Transient Cavitation Bubbles Imaging in Pulsed High-Intensity Focused Ultrasound Therapy

Pulsed high-intensity focused ultrasound (pHIFU) can induce sparse de novo inertial cavitation without the introduction of exogenous contrast agents, promoting mild mechanical disruption in targeted tissue. Because the bubbles are small and rapidly dissolve after each HIFU pulse, mapping transient bubbles and obtaining real-time quantitative metrics correlated with tissue damage are challenging. Prior work introduced Bubble Doppler, an ultrafast power Doppler imaging method as a sensitive means to map cavitation bubbles. The main limitation of that method was its reliance on conventional wall filters used in Doppler imaging and its optimization for imaging blood flow rather than transient scatterers. This study explores Bubble Doppler enhancement using dynamic mode decomposition (DMD) of a matrix created from a Doppler ensemble for mapping and extracting the characteristics of transient cavitation bubbles. DMD was first tested in silico with a numerical dataset mimicking the spatiotemporal characteristics of backscattered signal from tissue and bubbles. The performance of DMD filter was compared to other widely used Doppler wall filter-singular value decomposition (SVD) and infinite impulse response (IIR) high-pass filter. DMD was then applied to an ex vivo tissue dataset where each HIFU pulse was immediately followed by a plane wave Doppler ensemble. In silico DMD outperformed SVD and IIR high-pass filter and ex vivo provided physically interpretable images of the modes associated with bubbles and their corresponding temporal decay rates. These DMD modes can be trackable over the duration of pHIFU treatment using k-means clustering method, resulting in quantitative indicators of treatment progression.

Tumor suppression effect of ultrasound-sensitive nanoparticles with focused ultrasound in a pancreas cancer xenograft model

BACKGROUND

We investigated the tumor suppression effect of an ultrasound-sensitive doxorubicin-loaded liposome-based nanoparticle, IMP301, to enhance the synergistic effect with focused ultrasound (FUS) in an animal model of pancreatic cancer.

METHODS

Thirty nude mice with xenografts of PANC-1 human pancreatic cancer cells were randomly and prospectively allocated to 6 different groups (5 per group) each for Study-1 (dose-response test) and Study-2 (synergistic effect test). Study-1 consisted of control, gemcitabine, Doxil with FUS, and three different doses of IMP301 (2, 4, 6 mg/kg) with FUS groups. Study-2 consisted of control, FUS only, gemcitabine, Doxil with FUS, and IMP301 (4 mg/kg) with or without FUS groups. Differences in tumor volume and growth rate were evaluated by one-way ANOVA and Student-Newman-Keuls test.

RESULTS

In Study-1, 4 mg/kg or greater IMP301 with FUS groups showed lower tumor growth rates of 14 ± 4 mm3/day (mean ± standard deviation) or less, compared to the control, gemcitabine, and Doxil with FUS groups with rates exceeding 28 ± 5 (p < 0.050). The addition of FUS in Study-2 decreased the tumor growth rate in the IMP301-treated groups from 36 ± 17 to 9 ± 6, which was lower than the control, FUS only, gemcitabine, and Doxil with FUS groups (p < 0.050).

CONCLUSIONS

IMP301 combined with FUS exhibited higher tumor growth suppression compared to the use of a conventional drug alone or the combination with FUS. The present study showed the potential of IMP301 to enhance the synergistic effect with FUS for the treatment of pancreatic cancer.

RELEVANCE STATEMENT

This article aims to evaluate the synergistic effect of FUS and ultrasound-responsive liposomal drug in tumor growth suppression by using xenograft mouse model of pancreatic ductal adenocarcinoma. FUS-induced ultrasound-sensitive drug release may be a potential noninvasive repeatable treatment option for patients with locally advanced or unresectable pancreatic cancer.

KEY POINTS

• Modification of conventional drugs combined with FUS would maximize tumor suppression. • IMP301 with FUS had higher tumor suppression effect compared to conventional chemotherapy. • This image-guided drug delivery would enhance therapeutic effects of systemic chemotherapy.

Dynamic Mode Decomposition for Transient Cavitation Bubbles Imaging in Pulsed High Intensity Focused Ultrasound Therapy

Pulsed high-intensity focused ultrasound (pHIFU) can induce sparse de novo inertial cavitation without the introduction of exogenous contrast agents, promoting mild mechanical disruption in targeted tissue. Because the bubbles are small and rapidly dissolve after each HIFU pulse, mapping transient bubbles and obtaining real-time quantitative metrics correlated to tissue damage are challenging. Prior work introduced Bubble Doppler, an ultrafast power Doppler imaging method as a sensitive means to map cavitation bubbles. The main limitation of that method was its reliance on conventional wall filters used in Doppler imaging and optimized for imaging blood flow rather than transient scatterers. This study explores Bubble Doppler enhancement using dynamic mode decomposition (DMD) of a matrix created from a Doppler ensemble for mapping and extracting the characteristics of transient cavitation bubbles. DMD was first tested in silico with a numerical dataset mimicking the spatiotemporal characteristics of backscattered signal from tissue and bubbles. The performance of DMD filter was compared to other widely used Doppler wall filters - singular value decomposition (SVD) and infinite impulse response (IIR) highpass filter. DMD was then applied to an ex vivo tissue dataset where each HIFU pulse was immediately followed by a plane wave Doppler ensemble. In silico DMD outperformed SVD and IIR high pass filter and ex vivo provided physically interpretable images of the modes associated with bubbles and their corresponding temporal decay rates. These DMD modes can be trackable over the duration of pHIFU treatment using k-means clustering method, resulting in quantitative indicators of treatment progression.

Combination of chemotherapy and focused ultrasound for the treatment of unresectable pancreatic cancer: a proof-of-concept study

OBJECTIVES

To investigate the safety and preliminary efficacy of the combined treatment of focused ultrasound (FUS) and chemotherapy (nab-paclitaxel plus gemcitabine, nPac/Gem) for patients with unresectable pancreatic cancer.

METHODS

Patients pathologically diagnosed with unresectable pancreatic cancer were included. Low (Isppa = 1.5 kW/cm²), intermediate (2.0 kW/cm²), and high (2.5 kW/cm²) FUS intensity treatment groups were predefined. A 1% duty cycle and the 3+3 scheme were used. Six combined treatments were performed, and adverse events were assessed. Changes in tumor size and tumor response, CA 19-9 level, and patient-reported outcomes at the immediate follow-up (F/U) and/or at the 3-month F/U and survival were evaluated.

RESULTS

Three participants were enrolled in each intensity group. No adverse device effect or dose-limiting toxicity occurred in any of the participants. Seven of the nine participants experienced a >15% tumor size decrease at the immediate F/U CT and at the 3-month F/U CT. The CA 19-9 level decreased in all of the participants at the immediate F/U. All participants in the intermediate-intensity treatment group showed a > 30% tumor size decrease, partial response, and a significant decrease in the CA 19-9 level at 3-month F/U and longer survival (p < 0.05).

CONCLUSION

FUS with an intensity of 1.5 to 2.5 kW/cm² was safe in the combined treatment of FUS and nPac/Gem. Considering the results of the change in tumor size, the change in CA 19-9 level, tumor response, and survival, these FUS parameters can be used for subsequent clinical trials.

KEY POINTS

• No adverse device effect or dose-limiting toxicity occurred in any of the participants when focused ultrasound with an intensity of 1.5-2.5 kW/cm² and a low duty cycle of 1% was combined with chemotherapy. • The intermediate-intensity group showed a >30% tumor size decrease, partial response, and a significant decrease in CA 19-9 in all of the participants at the 3-month follow-up and the longest survival. • Any focused ultrasound setting used in this study could be safe and optimal for subsequent clinical trials.

Low-Intensity Focused Ultrasound Produces Immune Response in Pancreatic Cancer

Pancreatic adenocarcinoma is an aggressive malignancy with limited therapeutic treatments available and a 5-y survival less than 10%. Pancreatic cancers have been found to be immunogenically "cold" with a largely immunosuppressive tumor microenvironment. There is emerging evidence that focused ultrasound can induce changes in the tumor microenvironment and have a constructive impact on the effect of immunotherapy. However, the immune cells and timing involved in these effects remain unclear, which is essential to determining how to combine immunotherapy with ultrasound for treatment of pancreatic adenocarcinoma. We used low-intensity focused ultrasound and microbubbles (LoFU + MBs), which can mechanically disrupt cellular membranes and vascular endothelia, to treat subcutaneous pancreatic tumors in C57BL/6 mice. To evaluate the immune cell landscape and expression and/or localization of damage-associated molecular patterns (DAMPs) as a response to ultrasound, we performed flow cytometry and histology on tumors and draining lymph nodes 2 and 15 d post-treatment. We repeated this study on larger tumors and with multiple treatments to determine whether similar or greater effects could be achieved. Two days after treatment, draining lymph nodes exhibited a significant increase in activated antigen presenting cells, such as macrophages, as well as expansion of CD8+ T cells and CD4+ T cells. LoFU + MB treatment caused localized damage and facilitated the translocation of DAMP signals, as reflected by an increase in the cytoplasmic index for high-mobility-group box 1 (HMGB1) at 2 d. Tumors treated with LoFU + MBs exhibited a significant decrease in growth 15 d after treatment, indicating a tumor response that has the potential for additive effects. Our studies indicate that focused ultrasound treatments can cause tumoral damage and changes in macrophages and T cells 2 d post-treatment. The majority of these effects subsided after 15 d with only a single treatment, illustrating the need for additional treatment types and/or combination with immunotherapy. However, when larger tumors were treated, the effects seen at 2 d were diminished, even with an additional treatment. These results provide a working platform for further rational design of focused ultrasound and immunotherapy combinations in poorly immunogenic cancers.

Interstitial fluid streaming in deep tissue induced by ultrasound momentum transfer for accelerating nanoagent transport and controlling its distribution

Objective. This study aims to theoretically investigate the dynamics of ultrasound-induced interstitial fluid streaming and tissue recovery after ultrasound exposure for potentially accelerating nanoagent transport and controlling its distribution in tissue. Approach. Starting from fundamental equations, the dynamics of ultrasound-induced interstitial fluid streaming and tissue relaxation after an ultrasound exposure were modeled, derived and simulated. Also, both ultrasound-induced mechanical and thermal effects were considered in the models. Main results. The proposed new mechanism was named squeezing interstitial fluid via transfer of ultrasound momentum (SIF-TUM). It means that an ultrasound beam can squeeze the tissue in a small focal volume from all the directions, and generate a macroscopic streaming of interstitial fluid and a compression of tissue solid matrix. After the ultrasound is turned off, the solid matrix will recover and can generate a backflow. Rather than the ultrasound pressure itself or intensity, the streaming velocity is determined by the dot product of the ultrasound pressure gradient and its conjugate. Tissue and nanoagent properties also affect the streaming and recovery velocities. Significance. The mobility of therapeutic or diagnostic agents, such as drugs, drug carriers, or imaging contrast agents, in the interstitial space of many diseased tissues, such as tumors, is usually extremely low because of the inefficiency of the natural transport mechanisms. Therefore, the interstitial space is one of the major barriers hindering agent deliveries. The ability to externally accelerate agent transport and control its distribution is highly desirable. Potentially, SIF-TUM can be a powerful technology to accelerate agent transport in deep tissue and control the distribution if appropriate parameters are selected.

High-intensity focused ultrasound therapy for pancreatic cancer

Pancreatic cancer (PC) has one of the poorest prognoses among solid cancers, and its incidence has increased recently. Satisfactory outcomes are not achieved with current therapies; thus, novel treatments are urgently needed. High-intensity focused ultrasound (HIFU) is a novel therapy for ablating tissue from the outside of the body by focusing ultrasonic waves from multiple sources on the tumor. In this therapy, only the focal area is heated to 80-100 ºC, which causes coagulative necrosis of the tissue, with hardly any impact on the tissue outside the focal area. Although HIFU is a minimally invasive treatment and is expected to be useful, it is not yet generally known. Here, we discuss the usefulness of HIFU treatment for un-resectable advanced PC using the results of previous research, meta-analyses, and systematic reviews on its efficacy and safety. HIFU therapy for un-resectable PC is useful for its anti-tumor effect and pain relief, and is expected to prolong survival time and improve quality of life. Although HIFU for PC has several limitations and further study is needed, this technique can be safely performed on un-resectable advanced PC. In future, HIFU could be utilized as a minimally invasive treatment strategy for PC patients with a poor prognosis.

Contrast-enhanced ultrasound for evaluating response to pulsed-wave high-intensity focused ultrasound therapy in advanced pancreatic cancer

OBJECTIVE

To examine whether contrast-enhanced ultrasound (CEUS) parameters in patients with advanced pancreatic cancer could be used to assess response to treatment with pulsed-wave high intensity focused ultrasound (PW-HIFU).

METHODS

We prospectively recorded the pretreatment and posttreatment CEUS related parameters, CA19-9, pain scores of 30 patients with advanced pancreatic cancer treated with PW-HIFU treatment. Correlation of clinical parameters, tumor characteristics, and PW-HIFU treatment energy with CEUS parameters were analyzed.

RESULTS

Pain score decreased after treatment (from 4.80±2.14 to 3.28±1.93, p = 0.001). CA19-9 dropped in RT decreased group, 4 weeks after one session PW-HIFU, compared with prolonged group (p = 0.013). According to the display of blood vessels in the mass by CEUS, tumors were classified by vessel grade (VG), VG1: no vessel can be seen; VG 2: vessels diameter < 5 mm; VG 3: vessels diameter > 5 mm. VGs were different between increased and decreased relative rise intensity (rRI) groups (p = 0.008). VG1 group shown a decreased rRI after treatment, while VG3 group showed the opposite trend (p = 0.006).

CONCLUSIONS

CEUS can evaluating response to PW-HIFU in advanced pancreatic cancer. Quantitative analysis may help to assess the short-term efficacy of patients and help for individualized treatment.

Novel Therapeutic Method for Unresectable Pancreatic Cancer-The Impact of the Long-Term Research in Therapeutic Effect of High-Intensity Focused Ultrasound (HIFU) Therapy

High-intensity focused ultrasound (HIFU) is a novel advanced therapy for unresectable pancreatic cancer (PC). HIFU therapy with chemotherapy is being promoted as a novel method to control local advancement by tumor ablation. We evaluated the therapeutic effects of HIFU therapy in locally advanced and metastatic PC. PC patients were treated with HIFU as an optional local therapy and systemic chemotherapy. The FEP-BY02 (Yuande Bio-Medical Engineering) HIFU device was used under ultrasound guidance. Of 176 PC patients, 89 cases were Stage III and 87 were Stage IV. The rate of complete tumor ablation was 90.3%, while that of symptom relief was 66.7%. The effectiveness on the primary lesions were as follows: complete response (CR): n = 0, partial response (PR): n = 21, stable disease (SD): n = 106, and progressive disease (PD): n = 49; the primary disease control rate was 72.2%. Eight patients underwent surgery. The median survival time (MST) after diagnosis for HIFU with chemotherapy compared to chemotherapy alone (100 patients in our hospital) was 648 vs. 288 days (p < 0.001). Compared with chemotherapy alone, the combination of HIFU therapy and chemotherapy demonstrated significant prolongation of prognosis. This study suggests that HIFU therapy has the potential to be a novel combination therapy for unresectable PC.

Synergistic Effects of Pulsed Focused Ultrasound and a Doxorubicin-Loaded Microparticle-Microbubble Complex in a Pancreatic Cancer Xenograft Mouse Model

The synergistic effects of a doxorubicin (Dox)-loaded microparticle-microbubble complex (DMMC) and focused ultrasound (FUS) with a short duty cycle (5%) were evaluated in a pancreatic cancer xenograft model established by inoculating immunodeficient mice with CFPAC-1 cells. The efficacy of the DMMC with FUS (study 1), the effect of conjugating the particles as opposed to mixing them (study 2) and the levels of tumor apoptosis and intracellular Dox (study 3) were evaluated. The DMMC with FUS exhibited the lowest tumor growth rate (30.8 mm³/wk) and the highest intracellular Dox uptake (8.8%) and tumor cell apoptosis rate (58.7%) among all treatments. DMMC had a significantly lower growth rate than the mixture of Dox-loaded microparticles and microbubbles (44.2 mm³/wk, p < 0.01) when they were combined with FUS. In conclusion, DMMC with short-duty-cycle FUS holds promise for tumor growth suppression, which may be attributed to high intracellular Dox uptake.

HIFU is safe, effective, and feasible in pancreatic cancer patients: a monocentric retrospective study among 523 patients

Purpose

This study aimed to evaluate the clinical value of high-intensity focused ultrasound (HIFU) combined with gemcitabine (GEM) in treating unresectable pancreatic ductal adenocarcinoma (PDAC).

Patients and methods

A total of 523 unresectable PDAC patients were recruited from December 30, 2007 to January 30, 2015 at Fudan University Shanghai Cancer Center. Among them, 347 received HIFU combined with GEM (with regional intra-arterial chemotherapy [RIAC] or with systemic chemotherapy) and the remaining patients received GEM only. Postoperative complications were observed, and overall survival was recorded.

Results

The median overall survival of patients who received HIFU combined with GEM vs GEM alone was 7.4 vs 6.0 months (P=0.002); the 6-month, 10-month, 1-year, and 2-year survival rates for patients in these two groups were 66.3% vs 47.5% (P<0.0001), 31.12% vs 15.9% (P<0.0001), 21.32% vs 13.64% (P=0.033), and 2.89% vs 2.27% (P=0.78), respectively. In the combined therapy group, the most obvious survival benefits were obtained among patients who received HIFU plus RIAC and systemic chemotherapy (used in the intervals between RIAC treatments). There were no severe complications in patients undergoing HIFU treatment.

Conclusion

We demonstrated the survival benefit of HIFU among PDAC patients treated with GEM. The benefit was most obvious in PDAC patients treated with HIFU plus RIAC and systemic chemotherapy.

Thermal ablation of pancreatic cancer: A systematic literature review of clinical practice and pre-clinical studies

PURPOSE

Pancreatic cancer is a challenging malignancy with low treatment option and poor life expectancy. Thermal ablation techniques were proposed as alternative treatment options, especially in advanced stages and for unfit-for-surgery patients. This systematic review describes the thermal ablative techniques -i.e., Laser (LA), Radiofrequency (RFA), Microwave (MWA) Ablation, High-Intensity Focused Ultrasound (HIFU) and cryoablation- available for pancreatic cancer treatment. Additionally, an analysis of the efficacy, complication rate and overall survival for each technique is conducted.

MATERIAL AND METHODS

This review collects the ex vivo, preclinical and clinical studies presenting the use of thermal techniques in the pancreatic cancer treatment, searched up to March 2018 in PubMed and Medline. Abstracts, letters-to-the-editor, expert opinions, reviews and non-English language manuscripts were excluded.

RESULTS

Sixty-five papers were included. For the ex vivo and preclinical studies, there are: 12 records for LA, 8 for RFA, 0 for MWA, 6 for HIFU, 1 for cryoablation and 3 for hybrid techniques. For clinical studies, 1 paper for LA, 14 for RFA, 1 for MWA, 17 for HIFU, 1 for cryoablation and 1 for hybrid techniques.

CONCLUSIONS

Important technological advances are presented in ex vivo and preclinical studies, as the real-time thermometry, nanotechnology and hybrid techniques to enhance the thermal outcome. Conversely, a lack of standardization in the clinical employment of the procedures emerged, leading to contrasting results on the safety and feasibility of some analyzed techniques. Uniform conclusions on the safety and feasibility of these techniques for pancreatic cancer will require further structured investigation.

Analysis of the cytotoxic effects of combined ultrasound, microbubble and nucleoside analog combinations on pancreatic cells in vitro

Ultrasonically-stimulated microbubbles enhance the therapeutic effects of various chemotherapy drugs. However, the application of ultrasound and microbubbles (USMB) for enhancing the therapeutic effect of nucleoside analogs, which are used as front-line treatments in a range of cancers, and its underlying mechanism is not well understood. This study investigated the effect of gemcitabine, a nucleoside analog drug, in combination with USMB in increasing cell cytotoxicity relative to either treatment alone in BxPC3 pancreatic cancer cells. Cells were sonicated using low frequency (0.5 MHz) ultrasound in combination with Definity® microbubbles (1.7% v/v) in the presence of 1 µM of gemcitabine for a total of 2 h. USMB in combination with gemcitabine decreased cell viability (48 h) to 44.7 ± 5.2%, 27.7 ± 4.3%, and 12.5 ± 3.4% with increasing ultrasound peak negative pressures (220, 360, 530 kPa) from 84.7 ± 3.6%, 54.2 ± 3.8%, and 26.8 ± 3.0%, respectively, when USMB was applied in the absence of drug. We further confirmed that USMB did not enhance the internalization of 1 µM of a radiolabeled nucleoside analog (2-chloroadenosine) at each of the three chosen ultrasound PNPs, determined by radiolabeled scintillation counting. These data suggest that USMB in combination with nucleoside analog drugs leads to an additive effect on cell toxicity and that USMB does not impair transporter-mediated uptake of nucleoside analogs.

Focused ultrasound for immuno-adjuvant treatment of pancreatic cancer: An emerging clinical paradigm in the era of personalized oncotherapy

Current clinical treatment regimens, including many emergent immune strategies (e.g., checkpoint inhibitors) have done little to affect the devastating course of pancreatic ductal adenocarcinoma (PDA). Clinical trials for PDA often employ multi-modal treatment, and have started to incorporate stromal-targeted therapies, which have shown promising results in early reports. Focused ultrasound (FUS) is one such therapy that is uniquely equipped to address local and systemic limitations of conventional cancer therapies as well as emergent immune therapies for PDA. FUS methods can non-invasively generate mechanical and/or thermal effects that capitalize on the unique oncogenomic/proteomic signature of a tumor. Potential benefits of FUS therapy for PDA include: (1) emulsification of targeted tumor into undenatured antigens in situ, increasing dendritic cell maturation, and increasing intra-tumoral CD8+/ T regulatory cell ratio and CD8+ T cell activity; (2) reduction in intra-tumoral hypoxic stress; (3) modulation of tumor cell membrane protein localization to enhance immunogenicity; (4) modulation of the local cytokine milieu toward a Th1-type inflammatory profile; (5) up-regulation of local chemoattractants; (6) remodeling the tumor stroma; (7) localized delivery of exogenously packaged immune-stimulating antigens, genes and therapeutic drugs. While not all of these results have been studied in experimental PDA models to date, the principles garnered from other solid tumor and disease models have direct relevance to the design of optimal FUS protocols for PDA. In this review, we address the pertinent limitations in current and emergent immune therapies that can be improved with FUS therapy for PDA.

Therapeutic Effects of Microbubbles Added to Combined High-Intensity Focused Ultrasound and Chemotherapy in a Pancreatic Cancer Xenograft Model

Objective

To investigate whether high-intensity focused ultrasound (HIFU) combined with microbubbles enhances the therapeutic effects of chemotherapy.

Materials and Methods

A pancreatic cancer xenograft model was established using BALB/c nude mice and luciferase-expressing human pancreatic cancer cells. Mice were randomly assigned to five groups according to treatment: control (n = 10), gemcitabine alone (GEM; n = 12), HIFU with microbubbles (HIFU + MB, n = 11), combined HIFU and gemcitabine (HIGEM; n = 12), and HIGEM + MB (n = 13). After three weekly treatments, apoptosis rates were evaluated using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay in two mice per group. Tumor volume and bioluminescence were monitored using high-resolution 3D ultrasound imaging and in vivo bioluminescence imaging for eight weeks in the remaining mice.

Results

The HIGEM + MB group showed significantly higher apoptosis rates than the other groups (p < 0.05) and exhibited the slowest tumor growth. From week 5, the tumor-volume-ratio relative to the baseline tumor volume was significantly lower in the HIGEM + MB group than in the control, GEM, and HIFU + MB groups (p < 0.05). Despite visible distinction, the HIGEM and HIGEM + MB groups showed no significant differences.

Conclusion

High-intensity focused ultrasound combined with microbubbles enhances the therapeutic effects of gemcitabine chemotherapy in a pancreatic cancer xenograft model.

Gel phantom study with high-intensity focused ultrasound: influence of metallic stent containing either air or fluid

We aimed to investigate whether a cylindrical structure containing either air or fluid and with or without a metallic stent affects the volume and density of cavitation produced by high-intensity focused ultrasound via a gel phantom study. Sixteen tissue-mimicking phantoms based on a polyacrylamide gel mixed with bovine serum albumin with a cylindrical hole 1 cm in diameter and 7.5 cm in length were divided into four groups of four phantoms with air in the holes (group 1), four phantoms with fluid in the holes (group 2), four phantoms with air-containing metallic stents (group 3) and four phantoms with fluid-containing metallic stents (group 4). A pulsed high-intensity focused ultrasound beam (50% duty cycle, 40-Hz pulse repetition frequency) at 75 W of acoustic power was directed perpendicularly to the longitudinal axis of the hole, with its focus at the posterior wall of the hole. The size of the cavitation on the x-, y-, and z-axes was measured, and the volumes of cavitation and coagulation were calculated using the formula for the volume of an elliptical cone. The density of cavitation was measured in the tissue phantom anterior to the hole with a 1 × 1-cm square region of interest. For statistical analysis, the Kruskal-Wallis test and Mann-Whitney U-test were used. The phantoms with air-containing holes (groups 1 and 3) developed larger and denser cavitations anterior to the focus, without unnecessary coagulation posterior to the focus, compared with the phantoms with fluid-containing holes (groups 2 and 4), regardless of the presence of stents. All of the axes and volumes of the anterior cavitations were significantly larger than those of the posterior cavitations in groups 1 and 3 (all p-values <0.05). The results of this study might be applied to maximize cavitation to enhance drug delivery into tumors.

Dynamic contrast-enhanced ultrasonographic (DCE-US) assessment of the early response after combined gemcitabine and HIFU with low-power treatment for the mouse xenograft model of human pancreatic cancer

PURPOSE

To assess therapeutic efficacy of gemcitabine and HIFU for a mouse model of pancreatic cancer, and the role of DCE-US for predicting early treatment response compared with pathology.

MATERIALS AND METHODS

In 48 PANC-1- nude mice (G1, HIFU_higher power [n = 14]; G2, gemcitabine [n = 12]; G3, combined gemcitabine and HIFU_low power [n = 12]; and G4, control [n = 10]), pulsed HIFU or gemcitabine therapy was used. DCE-US was performed 1 day before and after first treatment. Seven DCE-US perfusion parameters were obtained. Therapeutic efficacy was estimated using necrotic fraction and apoptosis. Correlation between tumour size and US perfusion parameters was analysed.

RESULTS

Pathology results showed that combined gemcitabine and HIFU using low-power treatment had a more effective response than other treatments, including in the control group, i.e. necrotic fraction: 40.5 ± 4.9 vs. 16.9 ± 8.0, p = 0.000 and apoptosis: 44.3 ± 29.4 vs. 7.9 ± 4.9, p = 0.002. In this group, US perfusion parameters, including peak intensity (22.6 ± 22.6 vs. 9.6 ± 6.3, p = 0.002), AUC (961.8 ± 96.9 vs. 884.4 ± 91.4, p = 0.000), and AUCout (799.9 ± 75.6 vs. 747.1 ± 77.9, p = 0.000), had significantly decreased 1 day following first treatment (p < 0.05). In addition, peak intensity, AUC, and AUCout showed a tendency to decrease in treated groups. Alternatively, peak intensity, AUC, and AUCout showed a tendency to increase in control group.

CONCLUSION

Gemcitabine and HIFU were more effective and safer than other treatments. US perfusion parameters were useful for predicting early therapeutic response 1 day following treatment.

KEY POINTS

Recently, treatment of pancreatic cancer has changed based on a multidisciplinary approach. Combined gemcitabine_HIFU demonstrated more effective therapeutic response than other treatments. DCE-US is useful for predicting early therapeutic response 1 day after treatment. In the combined group, PI, AUC, and AUC (out) decreased 1 day after treatment.