Computational Modeling of Combination of Magnetic Hyperthermia and Temperature-Sensitive Liposome for Controlled Drug Release in Solid Tumor

Combination therapy, a treatment modality that combines two or more therapeutic methods, provides a novel pathway for cancer treatment, as it targets the region of interest (ROI) in a characteristically synergistic or additive manner. To date, liposomes are the only nano-drug delivery platforms that have been used in clinical trials. Here, we speculated that it could be promising to improve treatment efficacy and reduce side effects by intravenous administration of thermo-sensitive liposomes loaded with doxorubicin (TSL-Dox) during magnetic hyperthermia (MHT). A multi-scale computational model using the finite element method was developed to simulate both MHT and temperature-sensitive liposome (TSL) delivery to a solid tumor to obtain spatial drug concentration maps and temperature profiles. The results showed that the killing rate of MHT alone was about 15%, which increased to 50% using the suggested combination therapy. The results also revealed that this combination treatment increased the fraction of killed cells (FKCs) inside the tumor compared to conventional chemotherapy by 15% in addition to reducing side effects. Furthermore, the impacts of vessel wall pore size, the time interval between TSL delivery and MHT, and the initial dose of TSLs were also investigated. A considerable reduction in drug accumulation was observed in the tumor by decreasing the vessel wall pore size of the tumor. The results also revealed that the treatment procedure plays an essential role in the therapeutic potential of anti-cancer drugs. The results suggest that the administration of MHT can be beneficial in the TSL delivery system and that it can be employed as a guideline for upcoming preclinical studies.

Fluid and Electrolyte Transport across the Peritoneal Membrane during CAPD According to the Three-pore Model

In the present review, we summarize the principles governing the transport of fluid and electrolytes across the peritoneum during continuous ambulatory peritoneal dialysis (CAPD) in “average” patients and during ultrafiltration failure (UFF), according to the three-pore model of peritoneal transport. The UF volume curves as a function of dwell time [V( t)] are determined in their early phase by the glucose osmotic conductance [product of the UF coefficient (LpS) and the glucose reflection coefficient (σg)] of the peritoneum; in their middle portion by intraperitoneal volume and glucose diffusivity; and in their late portion by the LpS, Starling forces, and lymph flow. The most common cause of UFF is increased transport of small solutes (glucose) across the peritoneum, whereas the LpS is only moderately affected. Concerning peritoneal ion transport, ions that are already more or less fully equilibrated across the membrane at the start of the dwell, such as Na+(Cl–), Ca2+, and Mg2+, have a convection-dominated transport. The removal of these ions is proportional to UF volume (approximately 10 mmol/L Na+and 0.12 mmol/L Ca2+removed per deciliter UF in 4 hours).

The present article examines the impact on fluid and solute transport of varying concentrations of Ca2+and Na+in peritoneal dialysis solutions. Particularly, the effect of “ultralow” sodium solutions on transport and UF is simulated and discussed. Ions with high initial concentration gradients across the peritoneum, such as K+, phosphate, and bicarbonate, display a diffusion-dominated transport. The transport of these ions can be adequately described by non-electrolyte equations. However, for ions that are in (or near) their diffusion equilibrium over the peritoneum (Na+, Ca2+, Mg2+), more complex ion transport equations need to be used. Due to the complexity of these equations, however, non-electrolyte transport formalism is commonly employed, which leads to a marked underestimation of mass transfer area coefficients (PS). This can be avoided by determining the PS when transperitoneal ion concentration gradients are steep.

Biocompatibility of Peritoneal Dialysis Fluids: Long-term Exposure of Nonuremic Rats

Objectives

Long-term peritoneal dialysis (PD) leads to structural and functional changes in the peritoneum. The aim of the present study was to investigate the long-term effects of PD fluid components, glucose and glucose degradation products (GDP), and lactate-buffered solution on morphology and transport characteristics in a nonuremic rat model.

Methods

Rats were subjected to two daily intraperitoneal injections (20 mL/day) during 12 weeks of one of the following: commercial PD fluid (Gambrosol, 4%; Gambro AB, Lund, Sweden), commercial PD fluid with low GDP levels (Gambrosol trio, 4%; Gambro AB), sterile-filtered PD fluid (4%) without GDP, or a glucose-free lactate-buffered PD fluid. Punctured and untreated controls were used. Following exposure, the rats underwent a single 4-hour PD dwell (30 mL, 4% glucose) to determine peritoneal function. Additionally, submesothelial tissue thickness, percentage of high mesothelial cells (perpendicular diameter > 2 μm), vascular density, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) β1mRNA expression were determined. Submesothelial collagen concentration was estimated by van Gieson staining.

Results

Submesothelial tissue thickness and vascular density, mediated by VEGF and TGFβ production, in the diaphragmatic peritoneum increased significantly in rats exposed to any PD fluid. Gambrosol induced a marked increased fibrosis of the hepatic peritoneum. A significant increase in high mesothelial cells was observed in the Gambrosol group only. Net ultrafiltration was reduced in the Gambrosol and in the glucose-free groups compared to untreated controls. Small solute transport was unchanged, but all groups exposed to fluids showed significantly increased lymph flow.

Conclusions

Our results show that long-term exposure to different components of PD fluids leads to mesothelial cell damage, submesothelial fibrosis, and neoangiogenesis. Mesothelial cell damage could be connected to the presence of GDP; the other changes were similar for all fluids. Peritoneal transport characteristics did not change in any consistent way and the neoangiogenesis observed was not paralleled by increased solute transport.

Magnetically assisted intraperitoneal drug delivery for cancer chemotherapy

Intraperitoneal (IP) chemotherapy has revived hopes during the past few years for the management of peritoneal disseminations of digestive and gynecological cancers. Nevertheless, a poor drug penetration is one key drawback of IP chemotherapy since peritoneal neoplasms are notoriously resistant to drug penetration. Recent preclinical studies have focused on targeting the aberrant tumor microenvironment to improve intratumoral drug transport. However, tumor stroma targeting therapies have limited therapeutic windows and show variable outcomes across different cohort of patients. Therefore, the development of new strategies for improving the efficacy of IP chemotherapy is a certain need. In this work, we propose a new magnetically assisted strategy to elevate drug penetration into peritoneal tumor nodules and improve IP chemotherapy. A computational model was developed to assess the feasibility and predictability of the proposed active drug delivery method. The key tumor pathophysiology, including a spatially heterogeneous construct of leaky vasculature, nonfunctional lymphatics, and dense extracellular matrix (ECM), was reconstructed in silico. The transport of intraperitoneally injected magnetic nanoparticles (MNPs) inside tumors was simulated and compared with the transport of free cytotoxic agents. Our results on magnetically assisted delivery showed an order of magnitude increase in the final intratumoral concentration of drug-coated MNPs with respect to free cytotoxic agents. The intermediate MNPs with the radius range of 200-300 nm yield optimal magnetic drug targeting (MDT) performance in 5-10 mm tumors while the MDT performance remains essentially the same over a large particle radius range of 100-500 nm for a 1 mm radius small tumor. The success of MDT in larger tumors (5-10 mm in radius) was found to be markedly dependent on the choice of magnet strength and tumor-magnet distance while these two parameters were less of a concern in small tumors. We also validated in silico results against experimental results related to tumor interstitial hypertension, conventional IP chemoperfusion, and magnetically actuated movement of MNPs in excised tissue.

Quantification of osmotic water transport in vivo using fluorescent albumin

Osmotic water transport across the peritoneal membrane is applied during peritoneal dialysis to remove the excess water accumulated in patients with end-stage renal disease. The discovery of aquaporin water channels and the generation of transgenic animals have stressed the need for novel and accurate methods to unravel molecular mechanisms of water permeability in vivo. Here, we describe the use of fluorescently labeled albumin as a reliable indicator of osmotic water transport across the peritoneal membrane in a well-established mouse model of peritoneal dialysis. After detailed evaluation of intraperitoneal tracer mass kinetics, the technique was validated against direct volumetry, considered as the gold standard. The pH-insensitive dye Alexa Fluor 555-albumin was applied to quantify osmotic water transport across the mouse peritoneal membrane resulting from modulating dialysate osmolality and genetic silencing of the water channel aquaporin-1 (AQP1). Quantification of osmotic water transport using Alexa Fluor 555-albumin closely correlated with direct volumetry and with estimations based on radioiodinated ((125)I) serum albumin (RISA). The low intraperitoneal pressure probably accounts for the negligible disappearance of the tracer from the peritoneal cavity in this model. Taken together, these data demonstrate the appropriateness of pH-insensitive Alexa Fluor 555-albumin as a practical and reliable intraperitoneal volume tracer to quantify osmotic water transport in vivo.

Multiscale tumor spatiokinetic model for intraperitoneal therapy

This study established a multiscale computational model for intraperitoneal (IP) chemotherapy, to depict the time-dependent and spatial-dependent drug concentrations in peritoneal tumors as functions of drug properties (size, binding, diffusivity, permeability), transport mechanisms (diffusion, convection), spatial-dependent tumor heterogeneities (vessel density, cell density, pressure gradient), and physiological properties (peritoneal pressure, peritoneal fluid volume). Equations linked drug transport and clearance on three scales (tumor, IP cavity, whole organism). Paclitaxel was the test compound. The required model parameters (tumor diffusivity, tumor hydraulic conductivity, vessel permeability and surface area, microvascular hydrostatic pressure, drug association with cells) were obtained from literature reports, calculation, and/or experimental measurements. Drug concentration-time profiles in peritoneal fluid and plasma were the boundary conditions for tumor domain and blood vessels, respectively. The finite element method was used to numerically solve the nonlinear partial differential equations for fluid and solute transport. The resulting multiscale model accounted for intratumoral spatial heterogeneity, depicted diffusive and convective drug transport in tumor interstitium and across blood vessels, and provided drug flux and concentration as a function of time and spatial position in the tumor. Comparison of model-predicted tumor spatiokinetics with experimental results (autoradiographic data of 3H-paclitaxel in IP ovarian tumors in mice, 6 h posttreatment) showed good agreement (1% deviation for area under curve and 23% deviations for individual data points, which were several-fold lower compared to the experimental intertumor variations). The computational multiscale model provides a tool to quantify the effects of drug-, tumor-, and host-dependent variables on the concentrations and residence time of IP therapeutics in tumors.

Isolation of interstitial fluid and demonstration of local proinflammatory cytokine production and increased absorptive gradient in chronic peritoneal dialysis

In peritoneal dialysis (PD) patients, the frequent exposure to "unphysiological" dialysis fluids elicits a chronic state of a low-grade peritoneal inflammation leading to interstitial matrix remodeling and angiogenesis. Proinflammatory cytokines are important regulators involved in this inflammatory process that ultimately leads to dysfunction of the peritoneum as a dialysis membrane. We aimed to measure the local concentrations of proinflammatory cytokines in the peritoneal interstitial fluid (IF). Furthermore, we wanted to assess how the driving forces for fluid and solute exchanges are affected in a remodeled interstitial matrix and thus measured the colloid osmotic pressure (COP) gradient in rats that were exposed to chronic PD. After 8 wk of peritoneal dialysis, IF from peritoneum was isolated using a centrifugation method, and was analyzed for cytokine content and COP along with plasma. For several of the proinflammatory cytokines there were gradients from IF to plasma, showing local production. For some cytokines, the concentration in IF was increased severalfold, whereas IL-18 was increased systemically due to PD. Furthermore, the presence of the catheter per se seemed to increase cytokine levels. COP in IF was significantly decreased in the PD group, while collagen and hyaluronan content was increased. Collectively, our data suggest that the increased levels of proinflammatory cytokines after PD may be an integral component of the development of fibrosis and angiogenesis commonly seen in PD patients, and the decreased COP in IF after chronic PD may shift the Starling equilibrium across peritoneal capillaries to an absorptive state.

Transdiaphragmatic transport of tracer albumin from peritoneal to pleural liquid measured in rats

In conscious Wistar-Kyoto rats, we studied the uptake of radioactive tracer (125)I-albumin into the pleural space and circulation after intraperitoneal (IP) injections with 1 or 5 ml of Ringer solution (3 g/dl albumin). Postmortem, we sampled pleural liquid, peritoneal liquid, and blood plasma 2-48 h after IP injection and measured their radioactivity and protein concentration. Tracer concentration was greater in pleural liquid than in plasma approximately 3 h after injection with both IP injection volumes. This behavior indicated transport of tracer through the diaphragm into the pleural space. A dynamic analysis of the tracer uptake with 5-ml IP injections showed that at least 50% of the total pleural flow was via the diaphragm. A similar estimate was derived from an analysis of total protein concentrations. Both estimates were based on restricted pleural capillary filtration and unrestricted transdiaphragmatic transport. The 5-ml IP injections did not change plasma protein concentration but increased pleural and peritoneal protein concentrations from control values by 22 and 30%, respectively. These changes were consistent with a small (approximately 8%) increase in capillary filtration and a small (approximately 20%) reduction in transdiaphragmatic flow from control values, consistent with the small (3%) decrease in hydration measured in diaphragm muscle. Thus the pleural uptake of tracer via the diaphragm with the IP injections occurred by the near-normal transport of liquid and protein.

Measurement of Translymphatic Fluid Absorption Using Technetium-99mHuman Serum Albumin Diethylenetriamine Pentaacetic Acid in Continuous Ambulatory Peritoneal Dialysis Patients

We have established a new method of measuring translymphatic fluid absorption (TLA) using technetium-99m ((99m)Tc) human serum albumin diethylenetriamine pentaacetic acid ((99m)Tc-HSAD) that can be used commonly in clinical practice. This new method was applied in 13 continuous ambulatory peritoneal dialysis patients (11 males and two females) who had various peritoneal permeability and capacities for peritoneal transport of water. (99m)Tc-HSAD 740MBq was injected in 2 L of peritoneal dialysis fluid with 2.5% glucose, mixed well, and administered intraperitoneally. The fluid was drained extraperitoneally after 4 h and TLA was determined by the in vivo loss of (99m)Tc-HSAD. TLA was 1.41 +/- 1.11 mL/min (mean +/- SD; range, 0.27-3.69 mL/min). The estimated reduction rate by TLA in trans-peritoneally removed fluid ranged from 14.2 to 84.4%, indicating that TLA could have an extremely significant negative effect in some cases on total drainage volume. The present study, using new tracer (99m)Tc-HSAD, could confirm a large individual difference in TLA, indicating TLA as an important contributing factor for fluid-removal failure in continuous ambulatory peritoneal dialysis patients.

Recombinant adenovirus administration in rat peritoneum: endothelial expression and safety concerns

BACKGROUND

Initial studies of adenovirus-mediated gene transfer to the peritoneum have shown transgene expression in the mesothelium from the parietal peritoneum. Using a replication-deficient adenovirus encoding beta-galactosidase (Ad beta Gal), we investigated the expression efficiency and the distribution of the transgene to different areas of both visceral and parietal peritoneum and to extra-peritoneal tissues.

METHODS

Male Wistar rats received an intraperitoneal injection of 15 ml of 0.9% NaCl alone or containing 1 x 10(9) or 3 x 10(9) p.f.u. of Ad beta Gal. Evaluations of the histology of the peritoneum, the transgene expression and the safety of adenovirus-mediated gene transfer, using measurement of both beta Gal activity and staining, were performed 1, 3 and 5 days post-injection.

RESULTS

At 1 day post-injection of 3 x 10(9) p.f.u. of Ad beta Gal, significant beta Gal activity and staining were detected in the omentum and mesenteric peritoneum. beta Gal staining was observed in endothelial cells, mesothelial cells and adipocytes. Focal mononuclear infiltrates restricted to the submesothelial area of the visceral peritoneum were also observed. No expression was detected in the mesocolon and parietal peritoneum, where the mesothelium was damaged. Significant beta Gal activity and staining were observed in lymph nodes, lungs, liver, heart and kidneys, in the absence of inflammatory changes.

CONCLUSIONS

Intraperitoneal delivery of adenoviral vectors allows highly efficient transgene expression in mesothelial cells, but also in endothelial cells and adipocytes of the visceral peritoneum. Adverse focal mononuclear infiltrates, as well as spreading of the adenoviral vector from the abdominal cavity to the systemic circulation, were observed in parallel. Transgene expression in endothelial cells is potentially important since the latter play a key role in the alterations of the peritoneal membrane associated with long-term peritoneal dialysis. However, these data emphasize the need for less immunogenic adenoviral vectors, ideally containing an endothelial cell-specific promoter, to overcome immune response-related problems and spreading to extra-peritoneal tissues.

Comparison of plasma and peritoneal concentrations of various categories of MRI blood pool agents in a murine experimental pharmacokinetic model

The aim of this study was to validate an experimental model designed to distinguish four categories of contrast agents, non specific agents (NDA, Gd-DOTA) characterized by rapid and total extravasation; low diffusion agents (LDA, P760) characterized by delayed extravasation; and rapid (P792) and slow clearance (P717) blood pool agents (BPA) characterized by limited extravasation. Plasma and peritoneal gadolinium concentrations were simultaneously measured after intravenous injection of various contrast agents in mice. Products of each category were compared in this model.The plasma pharmacokinetic profiles were similar for Gd-DOTA and P760 (t1/2=13.3 and 13.8 min, respectively), whereas the half-lives were 22 and 1212 min for P792 and P717, respectively. The plasma clearance was inversely related to the size of the contrast agent. The intraperitoneal diffusion patterns of the various products were related to the molecular volume: C(max) per dose decreased progressively (78.7, 51.2, 44.2, 33.5 1/l) and t(max) increased (7, 15, 40, and 120 min) for Gd-DOTA, P760, P792 and P717, respectively. Nevertheless, the same quantities of Gd-DOTA and P760 (AUC ratio of 78.4 and 76.8, respectively) diffused into the peritoneum, whereas only 44.5% of P792 and 21.5% of P717 extravasated.The data obtained in this peritoneal permeability model with the various categories of contrast agents provide an estimation of the quantities of contrast agents diffusing into a permeable interstitium and may be used to predict the corresponding signal intensity, which can be measured locally.

Effects of peritoneal hyaluronidase treatment on transperitoneal solute and fluid transport in the rat

The importance of the interstitium and its major ground substance component, hyaluronan (HA), for solute and fluid transport across the peritoneal membrane has been debated during the last few years. We therefore partly removed HA from the peritoneal membrane using enzymatic digestion with hyaluronidase for 2 h, after which the transport properties of the peritoneal membrane were studied in peritoneal dialysis dwells. A dialysis fluid containing 3.86% glucose was used. As a marker of macromolecular transport, the total peritoneal clearance of radiolabelled albumin out of the peritoneal cavity and its clearance to plasma were measured, as well as the albumin clearance from plasma to dialysate. Transport of small solutes between plasma and dialysate was measured by assessing the mass transfer area coefficient of 51Cr-EDTA and glucose. Hyaluronidase preincubation yielded a 78% reduction of HA in the superficial layer of the peritoneal membrane, without alterations in the transport of either small or large solutes compared with the situation in preincubated controls. The only changes observed were between rats incubated with either hyaluronidase or vehicle alone compared to non-incubated controls. In conclusion, despite a large reduction of the HA content of the tissues surrounding the peritoneal cavity, hyaluronidase incubation did not produce any significant changes in solute and fluid transport across the peritoneal membrane. Our data indicate that peritoneal membrane HA in physiological concentrations plays a rather subordinate role in the overall transport of small solutes and water across the capillary-interstitial peritoneal barrier.