The electrical properties of resting and secreting pancreas

Establishing an immunocompromised porcine model of human cancer for novel therapy development with pancreatic adenocarcinoma and irreversible electroporation

New therapies to treat pancreatic cancer are direly needed. However, efficacious interventions lack a strong preclinical model that can recapitulate patients’ anatomy and physiology. Likewise, the availability of human primary malignant tissue for ex vivo studies is limited. These are significant limitations in the biomedical device field. We have developed RAG2/IL2RG deficient pigs using CRISPR/Cas9 as a large animal model with the novel application of cancer xenograft studies of human pancreatic adenocarcinoma. In this proof-of-concept study, these pigs were successfully generated using on-demand genetic modifications in embryos, circumventing the need for breeding and husbandry. Human Panc01 cells injected subcutaneously into the ears of RAG2/IL2RG deficient pigs demonstrated 100% engraftment with growth rates similar to those typically observed in mouse models. Histopathology revealed no immune cell infiltration and tumor morphology was highly consistent with the mouse models. The electrical properties and response to irreversible electroporation of the tumor tissue were found to be similar to excised human pancreatic cancer tumors. The ample tumor tissue produced enabled improved accuracy and modeling of the electrical properties of tumor tissue. Together, this suggests that this model will be useful and capable of bridging the gap of translating therapies from the bench to clinical application.

Identification of low-dose multidrug combinations for sunitinib-naive and pre-treated renal cell carcinoma

Background

Combinations of drugs can improve the efficacy of cancer treatment, enable the reduction of side effects and the occurrence of acquired drug resistance.

Methods

We approached this challenge mathematically by using the validated technology called the Therapeutically Guided Multidrug Optimization (TGMO) method. In a set of genetically distinct human renal cell carcinoma (RCC) cell lines, either treated chronically with sunitinib (−ST) or sunitinib-naive, we identified cell line-specific low-dose-optimised drug combinations (ODC).

Results

Six cell-type-specific low-dose drug combinations for three sunitinib-naive as well as three sunitinib pre-treated cells were established. These ODCs effectively inhibited the RCC cell metabolic activity while being ineffective in non-cancerous cells. Based on a single screening test and three searches, starting with ten drugs, we identified highly efficacious drug mixtures containing four drugs. All ODCs contained AZD4547 (FGFR signalling pathway inhibitor) and pictilisib (pan-phosphatidylinositol 3-kinase inhibitor), but varied in the third and fourth drug. ODC treatment significantly decreased cell metabolic activity (up to 70%) and induced apoptosis, independent of the pretreatment with sunitinib. The ODCs outperformed sunitinib, the standard care for RCC. Moreover, short-term starvation potentiated the ODC activity. The translation of the 2D-based results to 3D heterotypic co-culture models revealed significant inhibition of the spheroid growth (up to 95%).

Conclusion

We demonstrate a promising low-dose drug combination development to obtain drug combinations effective in naive as well as resistant tumours. Nevertheless, we emphasise the need for further mechanistic investigation and preclinical development.

In-vitro bipolar nano- and microsecond electro-pulse bursts for irreversible electroporation therapies

Under the influence of external electric fields, cells experience a rapid potential buildup across the cell membrane. Above a critical threshold of electric field strength, permanent cell damage can occur, resulting in cell death. Typical investigations of electroporation effects focus on two distinct regimes. The first uses sub-microsecond duration, high field strength pulses while the second uses longer (50 μs+) duration, but lower field strength pulses. Here we investigate the effects of pulses between these two extremes. The charging behavior of the cell membrane and nuclear envelope is evaluated numerically in response to bipolar pulses between 250 ns and 50 μs. Typical irreversible electroporation protocols expose cells to 90 monopolar pulses, each 100 μs in duration with a 1 second inter-pulse delay. Here, we replace each monopolar waveform with a burst of alternating polarity pulses, while keeping the total energized time (100 μs), burst number (80), and inter-burst delay (1s) the same. We show that these bursts result in instantaneous and delayed cell death mechanisms and that there exists an inverse relationship between pulse-width and toxicity despite the delivery of equal quantities of energy. At 1500 V/cm only treatments with bursts containing 50 μs pulses (2×) resulted in viability below 10%. At 4000 V/cm, bursts with 1 μs (100×), 2 μs (50×), 5 μs (20×), 10 μs (10×), and 50 μs (2×) duration pulses reduced viability below 10% while bursts with 500 ns (200×) and 250 ns (400×) pulses resulted in viabilities of 31% and 92%, respectively.

Comparison of simulation-based treatment planning with imaging and pathology outcomes for percutaneous CT-guided irreversible electroporation of the porcine pancreas: a pilot study

PURPOSE

To investigate the reliability of simulations for planning pancreatic irreversible electroporation (IRE) ablations compared with computed tomography (CT) and pathology outcomes in an animal model.

MATERIALS AND METHODS

Simulations were performed varying treatment parameters, including field strength (1.5-2.5 kV/cm), pulse number (70-90 pulses), and pulse length (70-100 µs). Pancreatic IRE was performed in six pigs under CT guidance. Two animals each were sacrificed for histology after 1 day, 14 days, and 28 days. Follow-up CT scans were performed on day 0, day 1, day 14, and day 28. Biochemical markers were collected before the procedure, 1 day after the procedure, and 14 days after the procedure.

RESULTS

All ablation zones could be visualized on CT scan immediately after the procedure and on day 1 follow-up CT scan, and all animals survived until the designated endpoints. Histopathology revealed necrosis and edema on day 1 and fibrosis and glandular atrophy after 28 days. Blood vessels close to the ablation zone appeared normal. Laboratory analysis indicated mild to moderate amylasemia and lipasemia with normalization after 14 days. The ablation size on CT scan measured a mean (± SD) 146% ± 18 (day 0, P < .126) and 168% ± 18 (day 1, P < .026) of the simulation and on pathology measured 119% ± 10 (day 1, not significant) of the simulation.

CONCLUSIONS

Results from simulations for planning IRE ablations, CT, and pathology may differ from each other. Ablation zones on CT and pathology appear larger than simulated, suggesting that clinically used treatment planning may underestimate the ablation size in the pancreas.

The influence of the splanchnic nerves on the external secretion, blood flow and electrical conductance of the cat pancreas

1. Electrical stimulation of the cut peripheral end of the splanchnic nerves results in a biphasic change in electrical conductance measured across the tail of the pancreas. A phase of decreased conductance is followed by a more prolonged phase of increased conductance.2. Simultaneous measurements of pancreatic blood flow indicate that the phase of decreased conductance occurs as a result of vasoconstriction, whilst the phase of increased conductance is due to vasodilatation.3. The initial phase of decreased conductance and vasoconstriction is abolished by alpha-receptor blocking agents such as phenoxybenzamine and the phase of increased conductance blocked by beta-receptor blocking agents such as pronethalol.4. Short periods of electrical stimulation applied to the splanchnic nerves result in a secretion of amylase and a reduction in the volume rate of secretion.5. When the vasoconstrictor response was abolished by phenoxybenzamine, nerve stimulation still reduced the rate of secretion, suggesting that the inhibitory effect is in part due to a direct action of the secretory cells.6. After bretylium tosylate, splanchnic nerve stimulation no longer produced vasomotor changes in the pancreas and the inhibitory effect on the volume response was converted to one of augmentation, but the secretion of enzymes was unaffected.7. The secretion of amylase on splanchnic stimulation was abolished by intravenous injection of atropine, suggesting that a cholinergic mechanism is involved.8. Noradrenaline did not mobilize pancreatic enzymes.

X-ray microanalysis of resting and stimulated rat pancreas

The elemental distribution in acinar cells of rat pancreas was investigated by X-ray microanalysis of thin, freeze-dried cryosections. In the resting cell, the highest calcium concentrations were found in the basal part of the cell (including the endoplasmic reticulum) and in the zymogen granules. Mitochondrial calcium concentrations were low. Zymogen granules were rich in sulphur, but low in phosphorus, sodium and potassium. Stimulation of the pancreas by perfusion in vivo with the cholinergic agonist carbachol caused a significant decrease of the calcium concentration in the basal part of the cell and an increase in the calcium concentration in the apical part of the cell. The mitochondrial calcium concentration was not significantly altered. In addition, increased sodium and decreased potassium concentrations, giving rise to a significant increase in Na/K ratio were observed in all cell compartments measured, except in the zymogen granules.

The response of the pancreas of the anaesthetized cat to secretin before, during and after reversible vagal blockade

Cooling the cervical vagi of the anaesthetized splanchnectomized cat to 2 degrees C caused a 54.4 +/- 8.8% inhibition of pancreatic electrolyte secretion stimulated submaximally with pure secretin. On rewarming the vagi there was a prolonged increase in secretion rate over and above the control rate which existed before cooling. The increase lasted about 90 min. There were no changes in acid/base status due to interference of the lung inflation reflex which could account for the inhibition of secretion and the subsequent rebound. Cold block of the cervical vagi increased the transpancreatic electrical conductance, indicating that vasodilation had occurred and therefore eliminated a vasomotor cause for the inhibition. Electrolyte secretion was also inhibited by bilateral vagal section. Atropine only partially prevented the inhibitory response to vagal cooling. A cholinergic mechanism, therefore, accounted for some but not all of the response to vagal cooling. It is concluded that even in the fasted, anaesthetized animal vagal impulses facilitate the action of secretin on the pancreas. This facilitation is only partially cholinergic; the major part of the response is due to some non-cholinergic transmitter substance. Such a mechanism may be necessary to potentiate the action of the very small amounts of secretin which appear to be released during a meal.

Formation of a [99mTc]polypeptide hormone: characterization and chemical quality control by ampholyte displacement radiochromatography

99mTc-complexes with the polypeptide hormone secretin in very low concentration were formed by the concentrated hydrochloric acid/vacuum evaporation/gentisic acid method. The 99mTc-secretin was characterized by a modified ampholyte radiochromatographic procedure, in addition to thin layer chromatography, gel chromatography and paper electrophoresis. High radiochemical purity and specific radioactivity were obtained. In vivo distribution studies were performed, and the conditions necessary for application of [99mTc]polypeptides as scintigraphic agents are discussed.

Disappearance half-time of endogenous and exogenous secretin in dogs

We have used a sensitive and specific radioimmunoassay to measurespectively. the disappearance half-times of exogenous porcine secretin and endogenous canine secretin in the dog and found them to be 2-45 and 2-85 minutes, respectively.

The effects of cholecystokinin-pancreozymin, acetylcholine and secretin on the membrane potentials of mouse pancreatic cells in vitro

Cell membrane potentials in an in vitro preparation of mouse pancreas have been measured and the effects of cholecystokinin-pancreozymin, acetylcholine and secretin studied. The membrane potential-frequency histogram has four distinct peaks and was split into the sum of four Gaussian distributions with means of minus 14, minus 23, minus 32 and minus 41mV. The minus 32 mV peak is attributed to acinar cells which respond to cholecystokinin-pancreozymin or acetylcholine by depolarising to minus 15 to minus 20 mV, the response lasting up to 10 min. The minus 23 and minus 41 mV peaks are due to duct cells. A duct cell has a resting membrane potential of minus 23 mV and hyperpolarises to minus 41 mV in response to secretin stimulation, the response lasting for longer than 15 min. Duct cells regardless of their position in the duct system function electrophysiologically in identical fashion. The secretory sites for enzyme and electrolyte are distinct, the duct cells secrete only electrolyte while the acinar cells secrete only enzymes.

The kinetics of pancreatic amylase secretion and its relationship to volume flow and electrical conductance in the anaesthetized cat

1. Enzyme secretion in response to short duration vagal stimulation or to rapid I.V. injections of cholecystokinin-pancreozymin (CCK-PZ) or gastrin or to intra-arterial injections of acetylcholine is a function of the volume of juice secreted and not primarily a function of time.2. The output of amylase in response to each stimulus occurred in a constant volume of approximately 15 drops (0.5 ml.) regardless of the rate of background secretin stimulated flow of water and electrolyte.3. It is argued that because amylase secretion occurs in this constant volume, it is due to the rapid secretion of enzyme into the duct system from the acini, and subsequently the secretin stimulated secretion of water and bicarbonate washes the enzyme from the duct system.4. When enzyme secretion is stimulated an increase in the electrical conductance (measured at 1.592 kHz) occurs across the tail of the pancreas. This increased conductance has two components. An early peak associated with the extrusion of enzyme from the acinar cell and a later peak which is probably due to vasodilatation.5. Atropine was without effect on both enzyme secretion and the conductance record when the stimulant was CCK-PZ. Atropine blocked enzyme secretion and both peaks of the conductance record in response to stimulation by acetylcholine. Atropine blocked enzyme secretion and abolished the early phase of the conductance record, on vagal stimulation. It was without effect on the later peak which probably indicates an atropine resistant vasodilation of the pancreatic vessels.6. When the vagus is stimulated on a background of submaximal electrolyte secretion caused by the intravenous infusion of secretin, the volume rate of secretion and the rate of amylase secretion follow a similar time course. The maximal volume response occurred between 7 Hz and 15 Hz and the maximal amylase output per impulse was at 5 Hz.

Prostaglandin action on pancreatic blood flow and on electrolyte and enzyme secretion by exocrine pancreas in vivo and in vitro

1. Intra-arterial injection or infusion of prostaglandins E(1) and E(2) into anaesthetized cats caused a fall in arterial blood pressure, a reduction in pancreatic blood flow and an inhibition of secretin-stimulated pancreatic electrolyte secretion. In some experiments these effects were preceded by a transient increase in blood flow and secretion.2. The fall in blood pressure and reduction in blood flow, but not the inhibition of secretion, were much less marked following administration of the alpha-adrenergic blocking agent phenoxybenzamine.3. Prostaglandins F(1alpha) and F(2alpha) caused only a slight reduction in blood pressure and had very little effect on pancreatic blood flow or electrolyte secretion.4. Addition of prostaglandins to the perfusate of the saline-perfused cat pancreas stimulated electrolyte secretion, with E(1) = E(2) >> F(1alpha) = F(2alpha). This stimulatory action was markedly potentiated by theophylline.5. Enzyme secretion was not stimulated by any of the prostaglandins, even in the presence of theophylline.6. It is concluded that prostaglandins can stimulate electrolyte transport by exocrine pancreas, perhaps through a mechanism involving adenylate cyclase, but that in vivo this action is masked by a secondary inhibition resulting either from vasoconstriction, or from the libration of an antisecretory agent, or both.

Cyclic adenosine 3',5'-monophosphate concentration in the pancreas following stimulation by secretin, cholecystokinin-pancreozymin and acetylcholine

1. Following an I.V. injection of secretin into anaesthetized cats, the pancreatic cyclic AMP concentration rose within 30 sec and reached near-maximal values within 1 min. Pancreatic secretion began only after 45 sec. As secretion declined, the cyclic AMP concentration also fell. However, after 40 min, when secretion had ceased, the concentration again rose, reaching a maximum after about 80 min and returned to basal values within 140 min.2. During secretin infusion the pattern of cyclic AMP changes was the same, except that the initial rise was maintained as long as secretin was infused.3. Following either pancreozymin or acetylcholine, alone or super-imposed on secretin stimulation, similar changes in cyclic AMP concentration were observed. However, the initial rise lasted only 30 sec, basal concentrations being approached within 1 min, and was accompanied by enzyme secretion. The concentration of cyclic AMP subsequently rose and fell again, in the absence of enzyme secretion, exactly as after secretin stimulation.4. Similar observations were made using an isolated, saline-perfused preparation of the cat's pancreas.5. By using very low doses of pancreozymin it was possible to observe the first rise in cyclic AMP concentration in the absence of enzyme secretion. Similarly atropine, while blocking enzyme secretion, did not affect the rise in cyclic AMP concentration after acetylcholine. The second increase in concentration was never associated with secretion (it may have been connected with the synthesis of exportable enzymes by the gland).6. While these observations suggest that cyclic AMP may be involved in the response of the pancreas to secretin, pancreozymin and acetylcholine, no simple relation exists between cyclic AMP concentration and secretion.

The effect of adrenaline and noradrenaline on the blood flow, electrical conductance and external secretion of the pancreas

1. Adrenaline and noradrenaline cause a biphasic change in the transverse electrical conductance across the cat pancreas. After a latent period of from 5 to 30 sec a phase of decreased conductance lasting about 30 sec occurs which gives way to a phase of increased conductance lasting from 5 to 8 min.2. Coincidentally with the phase of decreased conductance, vasoconstriction and a reduction in blood flow occurs and an increased blood flow with the phase of increased conductance. The blood flow and conductance records run a parallel time course.3. Weight for weight adrenaline produces changes of greater magnitude than noradrenaline.4. The phase of decreased conductance and blood flow was abolished by an alpha-receptor blocking agent and the phase of increased conductance and blood flow by a combination of alpha- and beta-receptor blocking agents.5. Inhibition of the volume rate of secretion coincident with the phase of decreased conductance followed rapid intravenous injection of adrenaline or noradrenaline. During the phase of increased conductance secretion either returned to control values or was transiently augmented.6. Inhibition of secretion occurred after alpha-receptor blockade in the absence of vasoconstriction, suggesting that the catecholamines have a direct action on the cell.7. beta-receptor blockade increased the effectiveness of adrenaline to inhibit pancreatic secretion. When the effects of the catecholamines on secretion were tested, secretion was always induced by secretin.