A Phase 1b/2 trial of mapatumumab in patients with relapsed/refractory non-Hodgkin's lymphoma.

BACKGROUND: we conducted a multicentre Phase 1b/2 trial to evaluate the safety and efficacy of mapatumumab, a fully human agonistic monoclonal antibody to the tumour necrosis factor-related apoptosis-inducing ligand receptor 1 (TRAIL-R1) in patients with relapsed non-Hodgkin's lymphoma (NHL). METHODS: forty patients with relapsed or refractory NHL were treated with either 3 or 10 mg kg(-1) mapatumumab every 21 days. In the absence of disease progression or prohibitive toxicity, patients received a maximum of six doses. RESULTS: mapatumumab was well tolerated, with no patients experiencing drug-related hepatic or other dose-limiting toxicity. Three patients with follicular lymphoma (FL) experienced clinical responses, including two with a complete response and one with a partial response. Immunohistochemistry staining of the TRAIL-R1 suggested that strong staining in tumour specimens did not appear to be a requirement for mapatumumab activity in FL. CONCLUSIONS: mapatumumab is safe and has promising clinical activity in patients with FL.

Piroxicam--dietary interactions in a long-term tolerance study in mice.

Piroxicam is a commonly prescribed nonsteroidal anti-inflammatory drug. In this study, piroxicam was fed at 60 ppm to mice in a semipurified AIN-76A (low-fat) control diet and in a Western-style diet (i.e., a modified AIN-76A diet with increased fat and reduced calcium and vitamin D, developed as a mimic of the human "Western" diet in the United States). Piroxicam in the AIN-76A diet produced only small adverse effects. However, 21-28 weeks of feeding piroxicam in the Western-style diet was lethal to mice. This suggest potent magnification of piroxicam toxicity in a high-fat-containing Western-style diet. This surprising finding suggests careful consideration of diet composition when potent agents such as nonsteroidal anti-inflammatory drugs are tested in animal studies and in clinical trials by humans who ingest the high-fat diets of Western countries.

Cromakalim and pinacidil dilate small mesenteric arteries but not small cerebral arteries.

Small elevations in external K+ hyperpolarize and dilate small cerebral arteries. The hyperpolarization and dilation to K+ are blocked by barium (less than 0.1 mM). Since membrane hyperpolarization appears to be an important mechanism for dilation of these small cerebral arteries, we investigated the effects of the hyperpolarizing vasodilators, cromakalim and pinacidil, on isolated pressurized rat cerebral arteries (diameter of 158 +/- 5 microns at 50% of the systolic blood pressure). Cromakalim and pinacidil, which are potent relaxants of a variety of muscle types, were without effect on posterior cerebral arteries at concentrations that completely dilate similarly sized rat mesenteric arteries (diameter 134 +/- 6 microns at 50% of the systolic blood pressure). The mesenteric artery dilation to cromakalim and pinacidil was reversed by glibenclamide. However, unlike the cerebral arteries, mesenteric arteries did not exhibit a barium-sensitive dilation to external K+. Thus it appears that there may be differences in the types of K+ channels that are activated by dilating mechanisms in small cerebral and mesenteric arteries.

In vitro methodology for resistance arteries.

Two commonly used methods for examining the physiological and pharmacological properties of isolated resistance arteries are the ring-mounted preparation and the cannulated, pressurized vessel. Each technique is discussed and consideration given to limitations and advantages. Also presented are examples of comparative differences between them, and practical experimental schemes for calibrating cannulae and for perfusing resistance arteries. Although both methods are valuable, the cannulated approach may better reflect the in vivo properties of the arteries.

Impaired potassium-induced dilation in hypertensive rat cerebral arteries does not reflect altered Na+,K(+)-ATPase dilation.

We have recently demonstrated that K(+)-induced dilation of cerebral resistance-sized vessels has two independent components, only one of which seemed sodium pump dependent. In our current investigation, potassium-induced dilation of spontaneous tone was compared in cerebral arteries from normotensive Wistar-Kyoto rats and age-matched stroke-prone spontaneously hypertensive rats. Branches of the posterior cerebral artery were cannulated and pressurized, and these vessels developed spontaneous tone. After a 5-minute period in K(+)-free physiological saline solution, K+ was increased in 1-mM increments to a final concentration of 15 mM. In the normotensive arteries, K+ concentrations between 0 and 5 mM K+ resulted in dilations that had a transient (sodium pump-dependent) component, and K+ concentrations in excess of 7 mM produced dilations that lacked a transient (sodium pump-independent) component. Similar branches from the hypertensive rat also responded with transient dilations to K+ (less than 5 mM), and these were significantly greater at 3 mM K+. However, the maintained dilations to K+ (greater than 7 mM), noted in preparations from Wistar-Kyoto rats, were absent in seven of eight preparations. Thus, the impaired dilations, in the hypertensive vessels, to K+ described here is a consequence of altered function of some sodium pump-independent component rather than altered Na+,K(+)-ATPase activity.

Potassium dilates rat cerebral arteries by two independent mechanisms.

Cerebral blood flow is regulated by brain metabolism, and there is evidence to suggest that changes in extracellular potassium concentration are important in linking brain metabolic activity with blood supply. In this study, the effect of low concentrations of potassium on the spontaneous tone of resistance-sized isolated posterior cerebral arteries from Wistar-Kyoto rats was examined. At a transmural pressure of approximately 58 mmHg, the vessels developed spontaneous tone that was 69 +/- 2% of their fully relaxed diameter of 184 +/- 2 microns (n = 50). Introduction of potassium (less than 5 mM) after a 5-min period in potassium-free physiological saline solution resulted in transient dilations, which were not attenuated by barium or cesium but abolished by ouabain. However, potassium concentrations between 7 and 15 mM produced dilations that lacked a transient component and were sensitive to barium, cesium, and ouabain. Maintained dilations to 10 mM K+ persisted in tetrodotoxin, tetraethylammonium, and glibenclamide and after endothelium removal. These results suggest that potassium dilation of cerebral arteries has two independent components, the first of which may be caused by stimulation of the electrogenic sodium pump (0-5 mM K+), whereas the second (greater than 7 mM K+) results from activation of a ouabain-, barium-, and cesium-sensitive process. The latter process describes a means by which potassium may effect prolonged changes in cerebral blood flow.

Pre-existing level of tone is an important determinant of cerebral artery autoregulatory responsiveness.

The objective of this study was to test the hypothesis that cerebral artery autoregulatory responses to increasing transmural pressure depend on the pre-existing level of vascular tone. Pial arteries were obtained from adult normotensive Wistar-Kyoto (WKY) rats, and were cannulated and studied under pressurized conditions using a video-assisted perfusion system. Myogenic tone developed spontaneously during equilibration, reducing the lumen diameter by 31% (n = 6). Each artery was then subjected to a series of step increases in transmural pressure of between 50 and 100 mmHg, a manoeuvre that produces autoregulatory constriction. Afterwards, serotonin was added to the perfusate to decrease lumen diameter by another 27% and the transmural pressure changes were repeated once more. The autoregulatory effectiveness in response to a change of 50----100 mmHg in transmural pressure was expressed as both the percentage change in diameter and the myogenic 'gain'. During the increased activation induced by serotonin, the autoregulatory responses to a change in transmural pressure were completely abolished; lumen diameter, which had previously decreased by 4.9 +/- 1.5%, increased by 10.5 +/- 4.5% (P less than 0.05). The nature of this change is further reflected in the myogenic gain, which was 0.39 +/- 0.14 in vessels with myogenic tone alone, and -1.14 +/- 0.56 for the same arteries at the higher level of activation (P less than 0.05). In additional experiments (n = 6), a comparable degree of constriction was induced with 0.5% ethanol, which increases calcium influx through receptor-independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential contractile responses of pressurized porcine coronary resistance-sized and conductance coronary arteries to acetylcholine, histamine and prostaglandin F2 alpha.

The reactivities of porcine resistance-sized arteries (270 microns o.d.) and conductance coronary arteries (4.2 mm o.d.) were compared in the presence of a functional and morphologically intact endothelium using a pressurized in vitro preparation. In resistance vessels, acetylcholine (ACh) produced maximal diameter reductions of 42% and the EC50 was 0.19 microM. Constrictions to histamine and prostaglandin F2 alpha (PGF2 alpha), however, were either absent or minimal. In contrast, maximum diameter constrictions of conductance vessels were 19, 33 and 22% in response to ACh, histamine and PGF2 alpha, respectively. Corresponding EC50 values were 0.58, 2.8 and 2.9 microM. The significant differences in reactivity between resistance and conductance arteries underscore the potential importance of regional specialization in the coronary blood flow regulation.

Asymmetry of responses to norepinephrine in perfused resistance arteries.

Diameter constrictor responses were significantly greater when norepinephrine (NE) was delivered intraluminaly compared to extraluminal application in isolated perfused mesenteric resistance arteries of the rat. The difference in response via the two routes was abolished by cocaine, a neuronal uptake blocker. Endothelium removal enhanced NE-induced constrictions but responses remained significantly greater when delivered intraluminally. This study provides evidence of asymmetry of vascular smooth muscle in resistance arteries due to a greater neuronal uptake of NE on the adventitial surface.

Endothelium-dependent and endothelium-independent vasodilation in resistance arteries from hypertensive rats.

The endothelium-dependent and presumed endothelium-independent vasodilators acetylcholine and sodium nitroprusside, respectively, were used to characterize relaxation responses of mesenteric resistance arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto rats (WKY). Vessels were preconstricted using concentrations of norepinephrine or 5-hydroxytryptamine, which reduced their diameters by 50 to 60%. Relaxation responses to acetylcholine (10(-8) - 10(-7) M) were significantly smaller (p less than 0.05) in vessel segments from SHRSP, but the maximal relaxations at higher concentrations were the same in both strains. However, SHRSP vessels relaxed to a greater extent than did those of the WKY at all concentrations of sodium nitroprusside. Endothelium removal significantly enhanced sodium nitroprusside-induced dilations in both rat strains, and the dilations were significantly greater in segments from SHRSP in the concentration range of 3 X 10(-8) to 10(-6) M. The decreased relaxation to acetylcholine in resistance arteries from adult hypertensive rats compared with those from the normotensive strain suggests that functional alterations in the endothelium may play a role in hypertensive disease.

Reactivity of isolated porcine coronary resistance arteries to cholinergic and adrenergic drugs and transmural pressure changes.

The reactivity of porcine intramyocardial resistance arteries (223 +/- 7 micron i.d., n = 30) was investigated with a pressurized in vitro preparation. Diameter changes in response to acetylcholine and to adrenergic drugs and dynamic changes in transmural pressure changes were investigated. Acetylcholine produced concentration-dependent constrictions, causing maximal reductions of 71 +/- 3% in lumen diameter, with EC50 values averaging 1.9 X 10(-7) M (n = 7). These responses were inhibited by atropine (10(-7) M) and therefore were mediated by muscarinic receptors. In addition, acetylcholine did not elicit relaxation in nine out of 10 vessels precontracted with U46619 (10(-7) M). Norepinephrine and epinephrine never produced constrictions (n = 6) even in the presence of propranolol (10(-6) M). Both norepinephrine and isoproterenol caused dose-dependent relaxations in acetylcholine-precontracted vessels, with IC50 values of 8.2 X 10(-7) M (n = 5) and 6.6 X 10(-8) M (n = 6), respectively. These relaxations were suppressed by propranolol. Between transmural pressures of 10 and 90 mm Hg, there was no intrinsic myogenic tone (n = 7). In addition, the vessels responded only passively to sudden pressure changes of 40 mm Hg. In all vessels, the functional integrity of the endothelium was verified by relaxations to substance P (10(-8) M) and/or bradykinin (10(-8) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous vasomotion in pressurized cerebral arteries from genetically hypertensive rats.

Resistance-sized branches of posterior cerebral arteries from Wistar-Kyoto (WKY), spontaneously hypertensive (SHR), spontaneously hypertensive stroke-prone (SHRSP), and antihypertensive-treated SHRSP (SHRSP-TRT) rats were studied in vitro. After the rats were killed, arterial segments were excised, mounted on microcannulas, and pressurized. After equilibration, intravascular pressure was increased in a stepwise fashion from 30 to 150-200 mmHg. All vessels developed a myogenic tone, which resulted in diameter reductions of 31-37% at 100 mmHg when compared with fully relaxed diameters [approximately 200 micron in 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid]. Differences in the extent of tone were not significant between animal groups (P greater than 0.05). Rhythmic vasomotion was present in 94% SHRSP and 100% SHRSP-TRT, 83% SHR, and only 6% of the WKY arteries. At higher pressures, the amplitude of the diameter oscillations decreased and frequency increased. Vasomotion was unaltered by tetrodotoxin or indomethacin, but could be abolished by cooling to 34 degrees C, ouabain (a depolarizing solution containing 125 mM K+), potassium-free physiological saline solution, or by calcium entry blockade with diltiazem or MnCl2. In normally quiescent WKY arteries, vasomotion, which was qualitatively similar to that observed in the hypertensive strains, could be induced by the addition of 5 mM tetraethylammonium chloride. Thus intrinsic oscillations in membrane calcium and potassium conductance may underlie the rhythmic contractile activity of rat cerebral arteries. This property appears to have a major genetic component, the expression of which is relatively independent of blood pressure history and is not related to the myogenic properties of the preparation.

Modulation of adrenergic responses in pressurized resistance arteries by flow.

The effects of perfusion on the reactivity of isolated rat resistance mesenteric arteries (200 micron ID) to electrical stimulation and exogenous norepinephrine (NE) were investigated. Diameter constrictions of these arteries that have an intact endothelium in response to the stimuli were significantly greater (P less than 0.05) in the presence than in the absence of flow. Inhibition of NE uptake and metabolism with cocaine, normetanephrine, and pargyline increased constrictor responses to electrical stimulation and NE in the presence and absence of flow, but responses remained larger in the presence of flow. Endothelial cell removal augmented the NE-induced diameter constrictions, which were not different whether or not flow was present. Perfusion at similar flows but a higher shear stress using a dextran solution led to smaller constrictions than obtained at lower shear stress in response to NE. However, NE-induced constrictions at high and low shear stresses were the same after endothelium removal. These observations suggest that NE and elevated levels of shear stress induce the release of relaxing factors from the endothelium, which attenuates direct NE smooth muscle cell constrictor responses.

Effect of antihypertensive treatment on myogenic properties of brain arteries from the stroke-prone rat.

Using an in vitro pressurized technique, we measured the myogenic pressure range and degree of myogenic activity in posterior cerebral arteries from stroke-prone spontaneously hypertensive rats (SHRSP) and rats of the same strain maintained by antihypertensive therapy. Treatment lowered the upper myogenic pressure limit and increased the strength of the myogenic response to levels comparable with those previously found in normotensive (Wistar-Kyoto, WKY) rats, suggesting that blood pressure history is the primary determinant of myogenic properties in the cerebral circulation.

Synthetic atrial natriuretic factor does not dilate resistance-sized arteries.

The effects of synthetic atrial natriuretic factor and atriopeptin III on induced tone in resistance-sized arteries from the rat were examined in vitro. Cylindrical segments of small mesenteric or cerebral arteries were mounted on a microcannula and pressurized to a transmural pressure of 75 mm Hg. After equilibration, the level of tone in cerebral arteries was on the order of - 35 change in diameter; addition of atrial natriuretic factor or atriopeptin III in cumulative doses from 10(-10) to 10(-7) M did not produce any transient or sustained changes in diameter. Similarly, atrial natriuretic factor or atriopeptin III did not alter the contractile responses of cerebral vessels to serotonin or prostaglandin F2 alpha. Mesenteric arteries, which do not possess an intrinsic myogenic tone, were precontracted with potassium (30 mM), norepinephrine (10(-6) M), or prostaglandin F2 alpha (1.1 X 10(-5) M) and exposed to the synthetic natriuretic peptides, also without effect. Transmural electrical stimulation (0.3-msec pulses; 180 mA; 4/second) relaxed cerebral and contracted mesenteric arteries; preincubation in 10(-7) M atrial natriuretic factor or atriopeptin III did not alter subsequent responses. These observations suggest that the hypotensive action of atrial natriuretic factor cannot be attributed to direct vasodilation of splanchnic or cerebral resistance-sized arteries.

Resistance vessels in hypertension.

Hypertension differentially affects the functional behavior of the mesenteric resistance arteries compared with similar sized arteries from the cerebral vascular autoregulatory bed. Antihypertensive drug treatment may, or may not, reverse the vascular wall structural composition and smooth muscle cell receptor sensitivity and contractile properties. These effects depend on the agent used, the length of treatment, and the vascular bed. Rat brain resistance arteries are myogenic at transmural pressures that are similar to those measured in autoregulatory, in vivo flow studies, as is the elevation of this range as a consequence of hypertension. The methods we have developed afford the investigator quantitative control over the variables that might affect the function of resistance vessels when tested in vitro. These techniques maintain the vessel close to physiological, in vivo conditions, and are useful tools for unraveling the complex mechanisms that define both, the normal vessel properties, and those of the vessel which has undergone modifications as a result of hypertension. Whether the vascular changes that we find in the SHR rat model parallel those which occur in human essential hypertension must yet be ascertained.

Myogenic properties of cerebral blood vessels from normotensive and hypertensive rats.

Myogenic properties of posterior cerebral arteries from normotensive and hypertensive rats were analyzed in vitro and quantified in terms of both pressure range limits and degree of myogenic activity. Spontaneously hypertensive rat (SHR) vessels were significantly narrower in a fully relaxed state, and both wall thickness and wall-to-radius ratios were increased. After equilibration in 1.6 mM calcium physiological saline solution a substantial tone developed which resulted in average diameter decreases of 34 and 37% in Wistar-Kyoto (WKY) and SHR, respectively; average lumen diameters were approximately 125 micron. Rapid changes in transmural pressure (delta P 10-25 mmHg/s) were applied and diameter responses measured continuously. Myogenic responses began 1-3 s after a change in transmural pressure, and arteries regained their initial diameters after a pressure step in about 2 min; a final, steady-state diameter was achieved in 4-5 min. Myogenic pressure ranges were 49-145 mmHg in WKY and 64-181 in SHR; when responses were segregated according to positive and negative pressure steps, more myogenic responses were observed at lower pressures for pressure step decreases when compared with pressure step increases. Thus myogenic ranges for increasing pressure steps were 71-151 (WKY) and 72-188 mmHg (SHR) and for decreasing steps 45-117 (WKY) and 57-148 mmHg (SHR). Myogenic responses in SHR were weaker than in WKY rats: the former maintained essentially a constant diameter over a wide range of pressures, whereas arteries from the latter decreased diameter with increasing pressures.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of transmural pressure of myogenic responses of isolated cerebral arteries of the rat.

We examined the diameter responses of isolated and pressurized posterior cerebral artery branches to various static and dynamic pressure alterations. These vessels, dissected from an anatomically identifiable location in the rat brain, developed tone when placed in a normal calcium physiological salt solution (1.6 mM Ca-PSS). Following a series of transmural pressure steps (delta p) of 25 or 50 mm Hg completed in 1-2 s and made every 5 min, they attained additional tone resulting in a mean luminal diameter of 139 micron at 100 mm Hg which was 35% less than their relaxed size measured in 1 mM EGTA-PSS. Continuous measurements of wall thickness and lumen diameter were obtained using a video electronic system in 1-2 mm long arterial segments, and autoregulatory gain factors calculated. Myogenic responses were obtained from each of 6 vessels taken from 6 WKY rats. Diameters following the step pressure changes were usually stable within 2-4 min. The data defined a myogenic regulatory pressure range from 49-145 mm Hg. Gain values averaged about 17% of that necessary for these arteries to maintain perfect flow autoregulation. Our results for myogenicity are comparable with the pressure range for blood flow autoregulation reported by others for the rat. We conclude that myogenic mechanisms, at least in this size artery, are partly responsible for flow autoregulation, and that they are supplemented by metabolic mechanisms operative in the intact rat brain.