Ultrasound cavitation therapy: inducing tumor drug delivery and blood flow changes with clinical ultrasound tools.

The tumor microenvironment (TME) often hinders effective cancer treatment, where elevated interstitial fluid pressure (IFP) acts as a key barrier to drug penetration. This study investigates the distribution of IFP in VX2 tumors and the effect of ultrasound-mediated microbubble (USMB) therapy on reducing IFP to improve drug delivery. Following approval from the Animal Ethics Committee of the South China University of Technology and adhering to NIH animal care guidelines, forty-one healthy female New Zealand White rabbits with VX2 tumors underwent USMB therapy at varying ultrasound pressures (1MPa, 2MPa, 3MPa, and 5MPa). IFP measurements across different tumor regions were performed pre- and post-treatment using the wick-in-needle (WIN) method to assess IFP variability and distribution. Contrast-enhanced ultrasound (CEUS) was used to evaluate changes in tumor perfusion associated with USMB treatment. Significant regional differences in tumor IFP were observed, with the central region (23.79 ± 8.07mmHg) markedly higher than the peripheral 1/2 (15.58 ± 5.22mmHg) and peripheral 1/4 regions (8.29 ± 3.47mmHg). After treatment, 3MPa and 5MPa ultrasound pressures significantly reduced IFP in the central region to 18.05 ± 8.1mmHg and 14.69 ± 4.72mmHg, respectively. Histological analysis showed that higher pressures caused greater tumor cell and vascular damage, with extensive necrosis and vascular disruption in the central tumor area at 3MPa and 5MPa, demonstrating the impact of USMB therapy on the tumor microenvironment. USMB therapy reduces IFP in solid tumors. At 2MPa, IFP reduction occurs with minimal perfusion change, potentially favoring drug delivery. In contrast, higher pressures (3-5MPa) also lower IFP but markedly decrease perfusion through vascular disruption, which may hinder drug transport. These findings highlight the need to adjust ultrasound parameters based on regional IFP distribution and to balance IFP reduction with perfusion preservation to optimize treatment outcomes.

Interstitial fluid pressure (IFP) is elevated in most malignant tumors, mainly as a result of the abnormal tumor vasculature that develops from unregulated angiogenesis. Theoretical models predict that IFP should correlate with capillary flow resistance in tumors, and therefore also with perfusion and oxygenation. However, a prospective clinical study in patients with cervical cancer at Princess Margaret Hospital failed to demonstrate a relationship between IFP and oxygenation. Despite this, high IFP was strongly associated with inferior survival after radiotherapy independent of clinical prognostic factors and tumor oxygen status. This suggests that IFP and direct needle oxygen measurements may provide information about different aspects of tumor oxygenation, such as chronic versus intermittent hypoxia. Alternatively, IFP may reflect an aspect of tumor biology that is largely unrelated to perfusion and oxygenation. One possibility is that tumors with high pretreatment angiogenesis levels, as indicated by high IFP, may be more radioresistant because the vascular endothelium is more likely to survive during and after treatment. The mechanistic link between elevated IFP and the abnormal tumor vasculature and the strong prognostic effect of IFP in our cervix study together suggest that drugs targeted at angiogenesis, when combined with radiotherapy, may lead to improved tumor control and patient survival.

The relationship between elevated interstitial fluid pressure and blood flow in tumors: a bioengineering analysis

High interstitial fluid pressure (IFP) represents a barrier for drug uptake in human GBM, the most common malignant primary brain tumor in adults. Increased IFP is due to leakiness of blood vessels and reduced drainage of fluid. This accumulation of fluid and high cell density compresses tumor tissue and promotes swelling of tumor cells. Although studies have clarified the role of tumor vasculature, it is still unclear if elevated IFP and swelling of cancer cells regulates tumor growth and drug uptake. Inhibition of NKCC1 (Na-K-Cl cotransporter) activity with bumetanide renders glioma cells unable to restore cell volume following osmotic challenges, blocks invasion in GBM xenografts, and augments temozolomide-mediated apoptosis in vitro. However, concerns about side-effects following bumetanide treatment warrants development of new approaches. Our preliminary data show that induction of antisecretory factor (AF), a regulator of fluid secretion, inhibited phosphorylation of NKCC1 in intracranial xenografts of human primary GBMs. Since AF therapy is safe in patients and lowers IFP in experimental models of solid tumors, we hypothesize that AF induction lowers IFP levels and increases drug uptake in xenografted GBMs. We have established novel methodology to study IFP in GBMs intracranially grafted into mice and the effects of compression in 3D-cultures. Our preliminary data show that elevated IFP and compression promotes tumor growth of GBMs. Our data suggest that AF induction lowers IFP levels by blocking restoration of cell volume and increases uptake of chemotherapy. Surprisingly, we found that AF induction alone reduced tumor growth and extended the survival of transplanted mice. Our work establish a role for IFP and cell swelling as potential therapeutic targets in GBMs and other solid cancers. As a novel pressure-reducing therapy, AF-induction represents an attractive strategy to reduce tumor growth, increase drug uptake, and improve survival in brain tumor patients.

To investigate the effects of high infusion pressure in conjunction with pars plana vitrectomy (PPV) on retinal morphology and function in rabbits. Pars plana vitrectomy was performed under urethane (0.8 mg/kg) anaesthesia in the right eye of albino rabbits following phacoemulsification and aspiration (PEA). The left eyes were not touched. After PEA, the animals were divided into two groups. In six eyes, intraocular pressure (IOP) was increased to 80 mmHg for 30 mins (high-pressure group) and in five eyes IOP was maintained at 40 mmHg for 30 mins (low-pressure group). The IOPs were regulated by the height of the bottle of balanced salt solution (BSS) and monitored with a pressure transducer. After the pressure elevation, vitreous fluid was collected to measure the glutamate concentration. Then, PPV was performed for 15 mins in both groups under an infusion pressure of 40 mmHg. In five additional rabbits, PEA alone was performed in the right eye, and vitreous fluid was collected (PEA group). Functional alterations were assessed by recording visual evoked potentials (VEPs) and electroretinograms (ERGs). Ten days after the IOP changes, the animals were killed with intravenous pentobarbital sodium and the eyes were prepared for histological analysis. Damage to retinal ganglion cells (RGCs) was quantified by counting the number of cells in the ganglion cell layer (GCL). The contralateral eyes in the high-pressure group served as controls (n = 6). The mean implicit time (IT) of the VEPs in the high-pressure group was significantly longer than that before the IOP elevation, by 114-124% (p < 0.05, paired t-test), and also than that of control eyes (p < 0.05, anova followed by t-test). No significant changes in the VEPs were detected in either the low-pressure group or the PEA group. There were significantly fewer cells in the GCL in the high-pressure group (24.7/mm) than in the control animals (41.4/mm; p < 0.05, Dunnett's test). The number of cells in the GCL in the low-pressure and PEA groups did not significantly differ to that in the controls. The amplitudes of the ERG a- and b-waves were not significantly changed (p > 0.05, paired t-test). These results suggest that high infusion pressure in conjunction with PPV leads to morphological and functional changes in the retina. The absence of ERG changes and presence of VEP changes suggest that these changes were due to damage to RGCs, which supports the morphological observations.

In order to elucidate further the mechanisms of central necrosis formation and drug delivery into tumor tissue, the interstitial fluid pressure in the normal subcutis and in rat ascites hepatoma AH109A and AH272 tumors was measured by means of a modified diffusion chamber technique. Using our apparatus for determining tissue pressures, we can obtain an exact zero reference-point and thus analyze daily changes in tumor interstitial fluid pressure. Tumor interstitial fluid pressure was found to be always positive and significantly higher than that in the normal subcutis, which was negative (P less than 0.001). The pressure increased with tumor growth. Highly significant correlations between the tumor size and the tumor interstitial fluid pressure were observed in both AH109A (r = 0.87; P less than 0.001) and AH272 (r = 0.86; P less than 0.001). The rate of increase in this pressure differed between AH109A and AH272 (P less than 0.001). It is concluded that the elevated interstitial fluid pressure in tumors could induce central necrosis and attenuate drug delivery to tumor tissue.

Compression of Pancreatic Tumor Blood Vessels by Hyaluronan Is Caused by Solid Stress and Not Interstitial Fluid Pressure

Animal experiments showed that elevated interstitial fluid pressure (IFP) is associated with poor blood supply and inadequate supply of drugs to solid tumours. IFP is approximately 0 mmHg in most normal tissues. Up to now there have been only few studies showing elevated interstitial pressure in human tumours in situ: Mammary carcinomas, cervical carcinomas and colorectal cancers have an elevated IFP. We measured IFP in squamous cell carcinomas of the head and neck region in humans using the "wick-in-needle" technique. In all lesions (n = 25), the IFP was elevated (4-39 mmHg). The IFP increased with tumour size. The highest IFP was 39 mmHg in a 26 ml tumour. These results show that squamous cell carcinomas of the head and neck region in humans have an elevated interstitial fluid pressure. The elevation of IFP associated with inadequate delivery of drugs to the interstitium of malign tumours may reduce the response to therapy.

Background and Objectives:To reduce the subacute stent thrombosis, the use of high pressure final balloon dilatations and confirmation of adequate stent expansion by intravascular ultrasound has been recommended. The purpose of this study is to compare incidence of stent thrombosis and major cardiac events (MACE between high and moderate pressure balloon technique without using intravascular ultrasound (IVUS guidance. Materials and Methods:We prospectively studied 147 patients (110 males & 37 females, mean; 56.9±9.9 years, 154 lesions who were deployed intracoronary stents with the use of conventional technique except IVUS guidance. According to inflation pressure, patients were divided into two groups;G1 (moderate pressure group, maximum inflation balloon pressure <14ATM, 77 lesion & G2 (high pressure group, maximum inflation balloon pressure ≥14ATM, 77 lesions. We investigated the incidence of stent thrombosis and MACE between two groups during the 10 month follow up examination. Results:1 The mean inflation presure is different between two groups by definition (G1:G2 10.2±1.8;15.2±1.3 ATM p<0.001. 2 The stenotic lesion lengths of the group of patients treated with the moderate pressure techique were longer than those treated under the high pressure technique (G1:G2 19.8±7.1 mm;16.3±4.1 mm p=0.002. 3 There were no significant differences between the moderate pressure group and the high pressure group during the 10 month follow-up examination in terms of MACE(early event (0-14D -subacute thrombosis G1:G2 0:0 death G1;G2 1:1/late events (15D-10M -repeat revascularization:G1;G2 8;7, CABG G1;G2 1;0, Q.M.I G1;G2 1;0). Conclusion:On selected patients, it is possible to consider moderate pressure technique as an other option for coronary stenting. (Korean Circulation J 1998;28(8 :1272-1279

Although a number of new systemic therapeutic options in patients with advanced solid cancers have emerged due to the improved knowledge of molecular dysregulation in cancers, the durable, long-term, objective responses infrequently occur. This editorial article highlights the major limitation of current systemic therapy due to an inefficient drug delivery. While several mechanisms contributing to cancer drug resistance have been described, the common key barrier among solid cancers is the unique tumor microenvironment that causes the high interstitial fluid pressure (IFP). We discussed the mechanism causing an elevated IFP and how it interferes with drug delivery. To target the high IFP, we demonstrated the novel approach using gold nanoparticle carrying recombinant human tumor necrosis factor (TNF), a vascular disrupting agent, that preferentially and specifically targets tumors while the systemic toxicity is markedly reduced. The addition of cytotoxic agent by either directly conjugating to the gold nanoparticle or by systemic administration following gold nanoparticle carrying TNF resulted in significantly reduced tumor burden and increased survival in multiple mouse models with primary and metastatic endocrine cancer and pancreatic ductal carcinoma. A clinical trial in patients with advanced solid cancers is warranted based on the promising results in preclinical studies.

A solid tumor is composed of a population of cells that is expanding as a result of cell division. With dense cell packing, the solid matrix of the interstitial tissue is subject to residual stress. In addition, elevated interstitial fluid pressure (IFP) has been reported by researchers for a number of solid tumors. These features were incorporated into a mathematical model that predicts the mechanical response of a solid tumor within its host environment. A theoretical framework accounting for volumetric expansion, transvascular exchange and extravascular transport of fluids was developed using poroelastic theory, and applied to a spherical, vascularized, alymphatic tumor undergoing small growth increments. Simulations of tumor IFP were similar to those predicted by Jain and Baxter, showing elevated IFP that is driven by microvascular fluid pressure. Tumor growth, tissue stiffness, and IFP contribute to the compressive stresses predicted in the solid tumor interior. Tensile and compressive stresses were predicted in adjacent host tissues corresponding to radial and circumferential directions, respectively. An application of this model includes a solid stress-based framework for predicting regions of vascular collapse within the tumor interior.

BACKGROUND: High interstitial fluid pressure (IFP) represents a barrier for drug uptake in human GBM, the most common primary brain tumor. Fluid accumulation and high cell density compress tumors and promote osmotic swelling of tumor cells. Although studies have clarified the role of tumor vasculature, it remains unclear whether osmotic swelling of cancer cells regulates tumor growth and drug uptake. METHODS: To address this, we used human GBM tumorspheres and xenografts. We developed methodology to measure IFP in GBM xenografts and mechanical compression in 3D-cultures. Fluorescent-based sensors were used to measure cell volume and chloride levels. To reduce IFP and osmotic swelling in GBM cells, we established exogenous or endogenous induction of antisecretory factor (AF), known to be safe in patients, reduces elevated intracranial pressure in rodents, and lowers IFP in subcutaneous solid tumors. RESULTS: Intriguingly, our data demonstrate that elevated pressure drives proliferation of GBM tumorspheres. Transcriptional profiling showed that increased compression regulates genes involved in translation and ion transport. AF peptide completely blocked compression-induced proliferation and transcriptional changes. We found that AF targeted the sodium-potassium-chloride channel (NKCC1), more potently than the NKCC1 inhibitor bumetanide, and prevented restoration of cell volume and chloride permeability under hyperosmotic conditions. AF therapy effectively reduced tumor growth, increased drug uptake, and extended survival in GBM xenografts, effects that were mediated through lowering of IFP, reduced cell volume, and inhibition of NKCC1 activity. CONCLUSIONS: We find that elevated IFP in human GBMs maintains osmotic swelling in tumor cells as a second barrier for drug uptake. Our results further show that elevated pressure is a driver of proliferation, survival, and translational control. AF therapy represents a novel approach to inhibit NKCC1 activity and osmotic swelling in human GBMs, leading to reduced tumor growth and increased drug uptake, ultimately improving the outcome for this disease.

The unique microenvironment of solid tumors, including desmoplasia within the extracellular matrix, enhanced vascular permeability, and poor lymphatic drainage, leads to an elevated interstitial fluid pressure which is a major barrier to drug delivery. Reducing tumor interstitial fluid pressure is one proposed method of increasing drug delivery to the tumor. The goal of this topical review is to describe recent work using focused ultrasound with or without microbubbles to modulate tumor interstitial fluid pressure, through either thermal or mechanical effects on the extracellular matrix and the vasculature. Furthermore, we provide a review on techniques in which ultrasound imaging may be used to diagnose elevated interstitial fluid pressure within solid tumors. Ultrasound-based techniques show high promise in diagnosing and treating elevated interstitial pressure to enhance drug delivery.

Introduction: Many studies have shown that tumor vascular network and the assortment of tumorous cells inside and on the periphery of solid tumors are spatially heterogeneous. Variation in cell packing density (VCPD), hypoxia, acidosis, and elevated interstitial fluid pressure (IFP) are main characteristic features of solid tumors. Elevated IFP and VCPD in solid tumors can be generally relevant to the pathological structures at the cellular level that is fundamental to understanding the chance of response to treatment and recurrence. Therefore, non-invasive quantification of tumor heterogeneity for the same types of tumors can play an important role in diagnosis and treatment planning. Hypothesis: In this pilot study, using Nested Model (NM) selection technique, Model Evolution (ME) concept is framed and introduced to quantify the evolutions of 3 different physiologically NM that are derived from standard Tofts model, throughout the course of Dynamic Contrast Enhanced (DCE) Magnetic Resonance Imaging (MRI) experiment. Using ME technique for pharmacokinetic (PK) modeling and DCE-MRI data analysis, a heterogeneity measure is formulated and introduced based on the evolutionary profile of the estimated extra-cellular extra-vascular (ve) volume. We hypothesized that the ME profiles in the course of DCE-MRI experiment, highly depend on the inward diffusion and outward convection of contrast agent concentration and contain abundant information for describing the compartmentalization and heterogeneity levels of solid tumors. Material and Methods: 24 athymic Nude rats with U251n rat tumor model of cerebral tumor were studied. Look-Locker T1 mapping and DCE-MRI experiments (Dual Gradient Echo, 150 image sets at 4.0 sec intervals over 10 min: matrix = 128×64, five 2.0 mm slices, NE = 2, NA = 1, TE/TE/TR = 2.0/4.0/40ms with bolus intravenous injection of the Magnevist at 0.25 mmol/kg) acquired at 7T field strengths. In each animal, in-vivo measurement of tumor IFP was done right after the DCE-MRI experiment using a wick-in-needle technique. The ME technique was applied on DCE-MR data of 24 U251n rat tumors to characterize the heterogeneity of each tumor and then the results were compared to their known in vivo measure of IFPs. Results and Conclusions: Results of this pilot study clearly attest that the evolutionary profile of ve can be used to characterize the heterogeneity level of solid tumors. The ME results imply that as the slop of the evolutionary profile increases, the IFP of tumor increases. Also, the latency of the profile during the course of MR experiment can reliably explain the tumor compartmentalization and their elevated IFP. This pilot study confirms that the ME concept can make a paradigm shift in non-invasive quantification of tumor heterogeneity from DCE-MRI studies Citation Format: Hassan Bagher-Ebadian, Azimeh NV Dehkordi, Rasha Alamgharibi, David Nathanson, Hamid Soltanian-Zadeh, Arbab S. Ali, Stephen Brown, Meser M. Ali, Tom Mikkelsen, James R. Ewing. Model evolution technique as a novel concept for characterization of tumor heterogeneity in dynamic contrast enhanced MRI studies. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2710.

Lack of General Correlation between Interstitial Fluid Pressure and Oxygen Partial Pressure in Solid Tumors