Biomedical subjects

R L Dedrick

Publications and source records attributed to R L Dedrick.

At least 73 records · Page 4Linked to original sources

PubMed1987

Purified RNA polymerase II recognizes specific termination sites during transcription in vitro.

We have studied the ability of certain well-defined prokaryotic DNA sequences to act as specific termination signals for highly purified calf thymus RNA polymerase II. We used duplex DNA fragments modified to direct efficient and specific transcription of defined DNA templates to follow transcription with RNA polymerase alone in the absence of additional protein factors. Elongation of RNA chains by RNA polymerase II is processive through most DNA sequences. However, certain DNA sequences serve as effective "intrinsic" terminators for RNA polymerase II; in this they resemble the "rho-independent" terminators for the bacterial RNA polymerase. Several rho-independent bacterial terminators are also able to act as termination signals for RNA polymerase II. However, there is no apparent correlation between the efficiency of termination for the bacterial enzyme and that found for the calf thymus enzyme. One very efficient bacterial terminator (phage T7 early terminator) gives no termination with RNA polymerase II, and we have identified at least two sites that cause the eukaryotic enzyme to terminate but have no effect on transcription by the bacterial enzyme. Hence, the signals recognized as intrinsic termination sites for the two enzymes are substantially different. All of the sites that act as intrinsic terminators for RNA polymerase II contain a series of consecutive thymidine residues in the nontranscribed DNA strand (T-run), and the 3' end of the completed RNA normally lies within this sequence. It is plausible that the T-run is part of the signal for an RNA polymerase II termination site; however, there is no apparent correlation between the number of T residues and the efficiency of the terminator, suggesting that other sequence elements are required for, or modulate, termination. Several lines of evidence suggest that the formation of RNA secondary structures in the nascent transcript is not an essential element of the intrinsic RNA polymerase II termination signal.

Animals↗

PubMed1987

Reduced systemic drug exposure by combining intraarterial cis-diamminedichloroplatinum(II) with hemodialysis of regional venous drainage.

During cancer chemotherapy toxicity to normal tissues often limits the tolerable dose. To increase drug delivery to tumor while maintaining tolerable systemic exposure, regional treatments, such as intraarterial drug delivery, have been used. Despite intraarterial delivery, systemic toxicity often remains the dose-limiting sensitivity. If systemic drug exposure could be reduced after intraarterial infusion, the intraarterial dose could be increased, which should increase the therapeutic response. We compared the pharmacokinetic advantage after cisplatin infusion into the internal carotid artery to that obtained after infusing cisplatin into the internal carotid artery during extracorporeal removal of cisplatin from the jugular blood by hemodialysis. Four patients with malignant gliomas received intracarotid cisplatin, 100 mg/m2 over 60 min, every 4 weeks. During one treatment, while cisplatin was infused into the internal carotid artery, the jugular blood was dialyzed extracorporeally at 300 ml/min and returned to the inferior vena cava. Seventy to 96% of the free platinum that entered the dialyzer was removed. By aspirating blood from the jugular vein at 300 ml/min, 30-79% of the ipsilateral carotid blood was collected for extracorporeal circulation. Hemodialysis of the cerebral venous drainage during intracarotid infusion reduced the systemic exposure to cisplatin by 51-61% when compared to the exposure from internal carotid artery infusion without hemodialysis. The pharmacokinetic advantage (brain/body exposure ratio) was increased from 3 to 5/1 during internal carotid artery infusion alone to as much as 15/1 during treatment combining intracarotid infusion with hemodialysis of the jugular blood. Systemic toxicity now limits the dose of cisplatin that can be administered safely. Increased tumor exposure without increased systemic toxicity may be possible with the technique described and greater doses of cisplatin. Assuming no associated local toxicities, the results of the current study indicate that the dose of intracarotid cisplatin can be increased while maintaining tolerable systemic exposure.

Brain Neoplasms↗

PubMed1987

Implications of pharmacokinetic modeling in risk assessment analysis.

Physiologic pharmacokinetic models are a useful interface between exposure models and risk assessment models by providing a means to estimate tissue concentrations of reactive chemical species at the site of action. The models utilize numerous parameters that can be characterized as anatomical, such as body size or tissue volume; physiological, such as tissue blood perfusion rates, clearances, and metabolism; thermodynamic, such as partition coefficients; and transport, such as membrane permeabilities. The models provide a format to investigate how these parameters can influence the disposition of chemicals throughout the body, which is an important consideration in interpreting toxicity studies. Physiologic models can take into account nonlinear effects related to clearance, metabolism, or transport. They allow for extrapolation of tissue concentration from high dose to low dose experiments and from species to species and can account for temporal variations in dose.

Animals↗

PubMed1987

Carotid artery mixing with diastole-phased pulsed drug infusion.

Focal injury to the brain or retina is a frequent complication of drug delivery to the internal carotid artery (ICA) and may be due to poor mixing of the drug with blood at the infusion site. Rhesus monkeys were studied to determine whether phased drug delivery during diastole from a modified pulsatile angiographic injector would improve drug mixing in vivo. A radiolabeled flow tracer, carbon-14-iodoantipyrine (14C-IAP), was injected into the ICA of three monkeys in 80-msec pulses, each ending at least 50 msec before the end of local diastole. Local isotope concentration in the brain was determined by quantitative autoradiography. The ratio of highest to lowest concentration was 1.86 +/- 0.26 (mean +/- standard deviation) in the frontoparietal cortex, 1.65 +/- 0.42 in the frontoparietal white matter, 1.89 +/- 0.28 in the temporal cortex, and 1.39 +/- 0.17 in the basal ganglia. These results were similar to recordings in three control animals that received intravenous 14C-IAP to demonstrate complete drug mixing (1.37 +/- 0.12, 1.41 +/- 0.11, 1.70 +/- 0.08, 1.22 +/- 0.24, respectively), and contrasted to findings in five animals which received continuous intracarotid infusions to demonstrate standard ICA drug delivery (4.54 +/- 2.07, 2.94 +/- 1.45, 5.43 +/- 3.57, 3.60 +/- 2.90, respectively). Pulsed intra-arterial infusion during diastole provides a technically simple method for improving intravascular drug mixing, and results in drug delivery to tissue capillaries that is proportional to blood flow.

Animals↗

PubMed1986

Transport of cisplatin in rat brain following microinfusion: an analysis.

The post-microinfusion transport of cis-diamminedichloroplatinum(II) (cisplatin) in rat brain has been modeled as a linear diffusion-reaction-permeation process. The model has been used to analyze the experimental data of Kroin and Penn to obtain the macromolecular binding constant of cisplatin in the brain, k = 0.0050 +/- 0.0023 min-1, and the capillary permeability, p = (9.0 +/- 4.4) X 10(-7) cm/s. Inclusion of saturation effects led to the same p value and a higher k value of 0.007 min-1. The corresponding diffusion length is 0.8 mm. The reaction constant is similar to those reported for plasma (0.008 min-1) and muscle (0.004 min-1), and the permeability value is within the range predicted by correlation with the permeability-octanol/water partition coefficient. Fits to data were accomplished with mathematical expressions giving the average total platinum concentration in saggital cerebellar sections which were not subdivided. Both time-dependent and steady-state solutions were obtained for the transport model, the former predicting a half-time to steady state of 3 h. Boundary effects were also investigated. Concentration profiles, calculated for a point source and for a 23-gauge cannula, were shown to differ by 7%. Similar comparisons between two profiles, one computed for an infinite diffusion range and another computed for drug diffusion into a flowing cerebrospinal fluid (CSF) at a finite range of 3 mm, showed differences of less than 3%. Free and bound drug forms, protein turnover, and CSF uptake have been accounted for as well as the percent infusate recoveries at 100 and 160 h reported by Kroin and Penn.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Interspecies scaling of regional drug delivery.

Calculation of the pharmacokinetic advantage of regional drug administration requires knowledge of the relevant intercompartment transport parameter. In a lumped model this is the blood (or plasma) flow rate for intra-arterial drug infusion or the permeability-area product for intraperitoneal or intrathecal administration. It is suggested that the perfusion of many tissues and the intrinsic permeability of the peritoneal surface or the brain-cerebrospinal fluid interface are similar among mammals. This provides a clear allometric basis for interspecies scaling based on organ size or surface areas. Intra-arterial or intrathecal treatment of the brain or meninges is a particularly interesting problem because of the relatively large brain of humans and because increased folding results in a cortical surface area that is almost proportional to brain size. Major unresolved issues remain concerning the distributed character of the processes such as streaming of drug infused into an artery and nonuniform mixing of cerebrospinal fluid.

Animals↗

PubMed1986

Physiological pharmacokinetic modeling of cis-dichlorodiammineplatinum(II) (DDP) in several species.

A physiological pharmacokinetic analysis of cis-dichlorodiammineplatinum(II) (DDP) is presented for the rabbit, dog, and human. The results are compared to a previous analysis for the rat. DDP binds irreversibly to low-molecular weight nucleophiles and macromolecules to form mobile and fixed metabolites at rates which are tissue-specific. The rate constant for the formation of fixed metabolite in plasma, determined by in vitro incubation, ranges from 0.004 to 0.008 min-1 in all species. Urinary excretion is the major route of platinum elimination in all species, with a kidney clearance of DDP approximating GFR in all species. Biliary clearance accounts for the elimination of 1-5% of dose and was neglected. The tissue-specific DDP-to-protein binding rates are in the order: kidney/skin/liver/gut/muscle for the beagle dog and rat. The rate constants for the rabbit and mongrel dog are similar, except that the skin and liver are reversed. The binding rate constants for various tissues are similar for all species. The rate constants for release of Pt from macromolecules are similar to protein turnover rate constants and decrease with increasing body weight. Human pharmacokinetic behavior was predicted by estimating human parameters by extrapolation of the animal data. The simulations in humans are compared to experimental plasma concentration and urine excretion profiles for several doses and durations of infusion.

Animals↗

PubMed1986

Glioblastoma: catheter techniques for isolated chemotherapy perfusion.

Techniques have been developed for isolated perfusion of chemotherapeutic agents in patients with glioblastoma. Three catheters that facilitate crossing the carotid siphon have been developed; two are based on an everting or toposcopic principle, and one uses microjets for deflectability and improved mixing. Blood from the ipsilateral jugular vein is aspirated at high volumes (300 ml/min) for extracorporeal circulation through an adsorption column (for recovery of carmustine) or dialysers (for recovery of cisplatin). Preliminary experience in 10 patients suggests that high doses of chemotherapeutic agent can be administered using these catheters, with reduced retinal and systemic toxicity.

Brain Neoplasms↗

PubMed1986

Mixing studies during intracarotid artery infusions in an in vitro model.

Sporadic instances of retinal damage and of focal brain toxicity have been observed following intracarotid artery infusions of chemotherapeutic agents (such as BCNU and cis-platinum) for the treatment of glioblastomas. The episodic nature of these toxicities is consistent with the possibility that the drug solutions were streaming from the catheter tip and, therefore, were not well mixed or not uniformly distributed in all branches distal to the catheter tip location. To test this hypothesis, an in vitro system was fabricated which included a transparent model of the human carotid artery and its major branches. These were furnished with pulsatile flow of a blood simulant. Dye solutions infused at several infusion rates through various types of catheters in both supraophthalmic and infraophthalmic positions were monitored and recorded on videotape and photographic film. The effluent streams from distal branches of the model were collected, and the relative concentrations of dye in each branch were determined spectrophotometrically. The results indicate that infusate streaming occurs at low infusion rates. In some cases, the concentration in a given branch can be at least five times the expected concentration. Similar occurrences of streaming in vivo could cause focal toxicity. Methods to improve mixing should be used during intra-arterial administration of drugs; these include increasing the infusion rates and improving catheter tip design.

Antineoplastic Agents↗

PubMed1986

Drug streaming during intra-arterial chemotherapy.

Treatment of brain tumors by intra-arterial (IA) chemotherapy is occasionally complicated by sites of focal toxicity in the brain and retina. A possible cause of focal toxicity is non-uniform drug delivery due to intravascular drug streaming. To investigate this phenomenon in vivo, the authors examined the distribution of drug delivery after internal carotid artery (ICA) infusion in rhesus monkeys. Carbon-14 (14C)-labeled iodoantipyrine was delivered into the ICA of eight monkeys at slow infusion rates (1% to 2% of ICA flow) or at fast infusion rates (20% of ICA flow) combined with additional techniques to promote mixing with ICA blood. Two monkeys received intravenous (IV) 14C-antipyrine. Uniformity of delivery was assessed by comparing high-to-low ratios of isotope concentration in four brain regions evaluated by quantitative autoradiography. There was striking non-uniformity of drug delivery in the slow IA infusion group, with as much as 13-fold differences in drug concentration in anatomically contiguous areas. The values of high-to-low concentration ratios (mean +/- standard deviation) in individual autoradiographic planes were: 1) frontoparietal cortex: slow IA infusion 4.54 +/- 2.07, fast IA infusion 1.71 +/- 0.31, IV infusion 1.30 +/- 0.174; 2) frontoparietal white matter: slow IA infusion 2.94 +/- 1.45, fast IA infusion 1.59 +/- 0.41, IV infusion 1.34 +/- 0.21; 3) temporal cortex: slow IA infusion 5.43 +/- 3.57, fast IA infusion 1.69 +/- 0.24, IV infusion 1.67 +/- 0.25; 4) basal ganglia: slow IA infusion 3.6 +/- 2.9, fast IA infusion 1.18 +/- 0.10, IV infusion 1.09 +/- 0.04. Differences between concentration ratios after slow IA and fast IA infusion are significant (p less than 0.01); those between fast IA and IV infusion are not significant. Intra-arterial drug administration at infusion rates analogous to those currently used clinically results in drug streaming with markedly heterogeneous drug deposition in the perfused hemisphere. This may cause suboptimal drug levels in the tumor, and toxic levels at sites within the perfused hemisphere. This effect can be abrogated by techniques that eliminate drug streaming.

Animals↗

PubMed1986

Potential roles for preclinical pharmacology in phase I clinical trials.

Concepts elucidated from preclinical pharmacology studies have made a substantial impact on the clinical use of anticancer drugs. However, the majority of animal pharmacology results have not been available until after drugs have entered clinical trials. Since clinical pharmacokinetic measurements are already part of many phase I trials, human data could be directly compared with mouse data if mouse pharmacology studies were completed before clinical trials were initiated. Once the starting dose in a phase I clinical trial has been evaluated, subsequent doses are escalated until the maximum tolerated dose is reached. The rate of escalation is empirically defined by a modified Fibonacci series. This universal escalation scheme is applied to all drugs, with no modifications based upon pharmacology or other factors. If the starting dose is far removed from the maximum tolerated dose, a large number of dose escalations are required. Consequently, most patients receive subtherapeutic doses, and the amount of resources allocated to each drug increases. We are exploring potential strategies for controlling the rate of dose escalation based upon pharmacokinetic determinations in mouse and man. Retrospective analyses indicate that 20%-50% savings in the total number of dose escalations are possible.

Aminoacridines↗

PubMed1985

Studies on transcription of 3'-extended templates by mammalian RNA polymerase II. Parameters that affect the initiation and elongation reactions.

Addition of short sequences of dCMP residues to the 3'-OH end of duplex linear DNAs allows rapid and efficient transcription to be initiated at these sites by purified mammalian RNA polymerase II [Kadesch, T. R., & Chamberlin, M. J. (1982) J. Biol. Chem. 257, 5286-5295]. The use of such tailed DNA templates should allow biochemical studies on transcription elongation and termination with almost any desired DNA sequence. However, in vitro transcription with RNA polymerase II is aberrant in that the DNA template is not re-formed after transcription; rather, the DNA strands are separated, and most of the RNA product is found as a DNA-RNA hybrid. To better understand the factors that affect the process of transcription with these tailed DNA templates, we have varied a number of parameters that might be expected to play a role in the reaction. RNA polymerase II preparations from calf thymus, HeLa cells, and Drosophila all fail to displace the product RNA. However, RNA polymerase II from wheat germ gives only free RNA as a product, as does the Escherichia coli RNA polymerase. Hence, the displacement of the nascent RNA from a transcription complex seems to depend on some intrinsic property of the polymerase itself and not simply on the nature of the template. Variation of reaction conditions, or of the divalent metal ion, does not restore the renaturability of the DNA template. However, variation of the duplex 3'-terminal sequence of the template led to significant alterations. In general, GC-rich sites enhanced the displacement of the nascent RNA, while AT-rich sites enhanced formation of the DNA-RNA hybrid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Physiological model for the pharmacokinetics of cis-dichlorodiammineplatinum (II) (DDP) in the tumored rat.

A physiological model has been developed to describe the disposition of cis-dichlorodiammine-platinum(II) (DDP) following i.v. dosing in the female rat bearing the Walker 256 carcinoma. The model simulates concentrations of DDP and its mobile and fixed metabolites in plasma, liver, gut, skin, muscle, tumor, carcass, and kidney, and DDP and mobile metabolite excretion following a 4 mg/kg dose. In the kinetic model, DDP binds irreversibly to low MW nucleophiles and macromolecules (largely proteins) within the plasma and tissue compartments to form mobile and fixed metabolites, respectively. Reaction rates for the formation of each metabolite are tissue/organ specific. The rate constant for the biotransformation of DDP to fixed metabolite in plasma (k2P = 0.0082 min-1) was determined from in vitro incubation studies. This rate was used as the basis for estimating the biotransformation rate constants for DDP to fixed and mobile metabolites in other compartments. Both DDP and mobile metabolite are assumed to follow flow-limited transport, to freely traverse compartmental barriers, and to partition equally in all compartments. Both are excreted in the urine, the major route of Pt elimination. Urinary excretion is modeled as a linear process involving filtration only; an assumption based on a calculated renal clearance of 1.1 ml/min, a value very similar to the estimated GFR. Biliary excretion is a minor route of mobile metabolite elimination and is modeled as a linear process occurring in the liver. Four hours after dosing, approximately 60% of the administered Pt remains in the tissues and plasma. Of this, over 75% of the plasma Pt and 90% of the metal ion in every other compartment is fixed (protein bound). Fixed Pt can be eliminated from a compartment only after its biotransformation to mobile metabolite. In most compartments this rate of elimination corresponds closely to the average rate of protein turnover in that compartment.

Animals↗

PubMed1985

Exchange of macromolecules between peritoneal cavity and plasma.

The exchange of fluorescein isothiocyanate-labeled dextrans ranging in weight-averaged molecular weight from 19,400 to 160,000 and 125I-bovine serum albumin (BSA) between dialysis fluid (5% BSA in Krebs-Ringer solution) in the peritoneal cavity and the plasma was studied in anesthetized female Sprague-Dawley rats. Plasma and peritoneal samples were collected for 3-4 h after either 1) an intraperitoneal injection of dialysis fluid with tracer or 2) an intravenous injection of tracer material simultaneously with an intraperitoneal injection of dialysis solution without tracer. Analysis of the data by means of a mathematical model of the transport process suggests a functional asymmetry in transport of large molecules across the blood capillary wall. Substances injected intravenously have a net transport from the blood capillaries to the peritoneal cavity. Substances of molecular weight greater than or equal to 39,000 transport from the cavity to the plasma via peritoneal lymphatics; 19,400 molecular-weight dextran transports from the cavity to the plasma primarily via lymphatics with some blood capillary uptake. Tissue diffusivities and capillary mass transport coefficients are derived for the substances tested.

Animals↗

PubMed1985

Peritoneal absorption of macromolecules studied by quantitative autoradiography.

Transport experiments of 125I-human serum albumin from the peritoneal cavity to the plasma were conducted in 200-g female rats. Blood and peritoneal samples were collected at intervals over 2-3 h. After death and rapid freezing of the animal, transverse sections were cut in a cryomicrotome from several tissues surrounding the peritoneal cavity, and the distribution of the labeled albumin was measured by computerized quantitative macroautoradiography. Tissue concentrations (counts/min per wet tissue wt) in parietal tissues (anterior abdominal wall and the diaphragm) were relatively constant versus distance from the peritoneum and represented a large fraction (0.5-1.0) of the concentration in the peritoneal cavity. Fractional concentrations in visceral tissues (liver, stomach, intestine) decreased from 0.20-0.35 at the peritoneal surface to 0.03-0.06 at a distance of 900 micron from the peritoneum. Uterine tissue concentrations lay between those of the parietal tissues and those of the viscera. The data are related to mechanisms of interstitial and lymphatic transport in these tissues.

Abdominal Muscles↗

PubMed1985

A distributed model of peritoneal-plasma transport: analysis of experimental data in the rat.

Transport of uncharged, water-soluble substances (ranging in molecular weight from 180 to 5,000) between the fluid in the peritoneal cavity and plasma was studied in anesthetized female Sprague-Dawley rats. In certain experiments the effect of fluid shifts on the transport was observed by manipulating the effective osmotic pressure or the hydrostatic pressure of the dialysis fluid. Parameters for the distributed model outlined in previous work were obtained from the experimental data for the substances tested. Capillary membrane transport was modeled by pore theory. A single pore radius of 40 A and a pore density of 600 cm-2 were satisfactory. Tissue diffusivities for these substances were found to correspond closely to those in the literature. Additional simulations were performed with a three-compartment model and the results were compared with those of the distributed model.

Animals↗

PubMed1985

A distributed model of peritoneal-plasma transport: tissue concentration gradients.

Peritoneal dialysis transport studies were carried out in anesthetized rats. Injections of [14C]EDTA were made by intravenous bolus or intraperitoneal dialysis solution, and blood and peritoneal fluid samples were collected for 1 h. After death and rapid freezing of the animal, transverse sections through the abdominal cavity were cut for quantitative macroautoradiography. The plasma-to-peritoneal transport experiments with a clinical dialysis solution resulted in essentially horizontal concentration profiles versus distance in all tissues except large intestine. Estimates of the extracellular tissue fraction were: small intestine, 0.34; large intestine, 0.28; stomach, 0.30; uterus, 0.66; liver 0.35; diaphragm, 0.16; and anterior abdominal wall, 0.15. Similar experiments with an isotonic salt solution resulted in larger (13-300%) extracellular fractions in all tissues. In contrast, peritoneal-to-plasma transport studies demonstrated decreasing concentration profiles in all visceral tissues, with the first 90% of the gradient contained in the initial 400 micron of tissue from the peritoneum. Parietal tissue gradients were less steep and had higher concentration levels deep within the tissue than visceral tissues. Computer simulations using a distributed model approach compared favorably with the experimental measurements and established the validity of this approach.

Animals↗

PubMed1985

Aspiration of blood from the jugular vein during intracarotid drug infusion in monkeys. Implications for extracorporeal drug removal.

Circulation of blood in the ipsilateral jugular vein through an extracorporeal circuit for drug removal during intracarotid chemotherapy has recently been reported to decrease the systemic drug exposure. The reduced systemic exposure achieved by the use of this technique should permit a several-fold increase of the intracarotid dose of chemotherapy without increasing systemic toxicity. To determine the influence of the rate of blood removal from the jugular vein on the fraction of the blood flowing through the ipsilateral internal carotid artery (ICA) collected for extracorporeal drug removal, the authors aspirated blood from the jugular bulb into an extracorporeal circuit at varying rates during a constant infusion of the indicator dye, indocyanine green (ICG), into the ICA of rhesus monkeys. The fraction of the ipsilateral carotid blood channeled into the extracorporeal circuit increased linearly with the rate of aspiration of jugular blood. This suggests that the absence of valves in the intracranial venous system should permit increasing fractions of drug removal during intracarotid infusion by increasing the rate of collection of venous blood from the ipsilateral jugular bulb. The measurement of ICG concentrations in a similar manner in patients undergoing isolated perfusion may prove to be a clinically useful method for estimating the maximum safe dose in high-dose intra-arterial chemotherapy.

Animals↗