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Biomedical subjects

C J Springer

Publications and source records attributed to C J Springer.

At least 55 records · Page 3Linked to original sources
PubMed1994

Antibody directed enzyme prodrug therapy (ADEPT). A review of some theoretical, experimental and clinical aspects.

The concept of generating cytotoxic agents from non-toxic prodrugs at tumour sites by antibody vectored enzyme introduces a wide range of opportunities. Various prodrug-enzyme combinations have been described and encouraging results reported in xenograft models. Whilst the mouse model is a valuable tool in this approach translation to the human patient may expose more complex issues. The objective of restricting drug action to tumour sites and thus allowing greatly increased cytotoxic action requires more precise restriction of enzyme activity to tumour sites than has been achieved with an antibody vector and natural clearance alone. Assisted clearance mechanisms have been found effective. Alternatively, or additionally, the difference between prodrug and active drug creates the opportunity to degrade active drug selectively in blood and thus protect normal tissues. In order to give more than one cycle of treatment it will be necessary for the antibody-enzyme conjugate to be nonimmunogenic or for the concurrent administration of immunosuppressive agents. A pilot scale clinical trial with a prototype prodrug indicated the feasibility of antibody directed enzyme prodrug therapy (ADEPT).

Animals↗
PubMed1992

The cytotoxicity, DNA crosslinking ability and DNA sequence selectivity of the aniline mustards melphalan, chlorambucil and 4-[bis(2-chloroethyl)amino] benzoic acid.

Three aniline derivatives melphalan (L-PAM), chlorambucil (CHL) and 4-[bis(2-chloroethyl)amino] benzoic acid (BAM) have been compared on the basis of their in vitro cytotoxicities, DNA interstrand crosslinking ability and DNA sequence selectivity. Cytotoxicity was assessed in the human colonic adenocarcinoma LS174T and leukaemic K562 cell lines using the sulpho-rhodamine B and tetrazolium dye reduction assays. The order of cytotoxicities was L-PAM greater than CHL greater than BAM in both cell lines with K562 being less sensitive than LS174T. This was different from the order CHL greater than L-PAM greater than BAM which would be predicted from simple chemical reactivity or rate of hydrolysis, parameters which have been used previously as indicators of biological potency for aromatic nitrogen mustards. DNA interstrand crosslinking in cells as determined by alkaline elution showed a correlation with IC50 values. The ranking order of activity was further predicted by the ability of the agents to produce interstrand crosslinks in isolated DNA. The extent of guanine N-7 alkylation, assessed using a modified DNA sequencing technique, mirrored cytotoxicity and crosslinking ability, but at equivalent levels of alkylation there was no significant difference in DNA sequence selectivity. These data demonstrates that simple chemical reactivity or hydrolysis rate is not a good indicator of DNA reactivity or cytotoxicity for a number of aniline mustards, whereas DNA interstrand crosslinking ability either measured directly in cells or in isolated DNA, gives a good indication of biological activity.

4-Aminobenzoic Acid↗
PubMed1991

Accelerated in vitro degradation of CCK-58 in blood and plasma of patients with acute pancreatitis.

Proteases released into the circulation during acute pancreatitis may hydrolyse circulating peptide hormones leading to altered regulatory functions. Cholecystokinin is a major regulator of postprandial gut function; stimulating pancreatic enzyme secretion, gallbladder contraction and diminishing food intake. Cholecystokinin-58 is the largest and most abundant form of this hormone in acid extracts of human intestine, and major amounts are released into the circulation after feeding. In order to test whether cholecystokinin-58 is degraded more rapidly due to the increased circulating of enzymes, this peptide was added to blood and plasma of patients with acute pancreatitis and incubated for various time intervals. The in vitro half life of cholecystokinin-58 was 10 +/- 1 minutes (mean +/- SE) in plasma and 11 +/- 1 min in blood from patients with acute pancreatitis, about four fold lower than the half life in plasma of healthy volunteers; 45 +/- 5 min. Degradation of cholecystokinin-58 produced immunoreactive forms of cholecystokinin that eluted in the positions of cholecystokinin-8 and cholecystokinin-33/39. We conclude that acute pancreatitis increases the degradation of CCK molecules.

Acute Disease↗
PubMed1991

Ablation of human choriocarcinoma xenografts in nude mice by antibody-directed enzyme prodrug therapy (ADEPT) with three novel compounds.

Three novel prodrugs have been designed for use as anticancer agents. Each is a bifunctional alkylating agent which has been protected to form a relatively inactive prodrug. They are designed to be activated to their corresponding alkylating agents at a tumour site by prior administration of an antitumour antibody conjugated to the bacterial enzyme carboxypeptidase G2 (CPG2) in a two-phase system called antibody-directed enzyme prodrug therapy (ADEPT). The Km and Vmax values for three different antibody-CPG2 conjugates were determined in relation to each prodrug. The Km values ranged from 4.5-12 mumol/l and the Vmax from 0.5-1.6 mumol/U/min. Athymic Nu/Nu mice with palpable transplanted human choriocarcinoma xenografts, which are resistant to conventional chemotherapy, were treated with anti-human chorionic gonadotropin antibodies conjugated to CPG2. This was followed by each of the three novel prodrugs. Significant increase in survival was obtained in three of the regimens tested using only one course of treatment. This demonstrates the potential of a tumour-localised bacterial enzyme to activate protected alkylating agents in order to eradicate an established human xenograft.

Alkylating Agents↗
PubMed1991

Comparison of half-lives and cytotoxicity of N-chloroethyl-4-amino and N-mesyloxyethyl-benzoyl compounds, products of prodrugs in antibody-directed enzyme prodrug therapy (ADEPT).

The synthesis of two novel drugs, 4-[bis[2-(mesyloxy)ethyl]amino]benzoic acid (7) and 4-[(2-chloroethyl)[2-(mesyloxy)ethyl]amino]benzoic acid (8) is described here. They are the active drugs of two prodrugs (9 and 10) designed for use as anti-cancer agents. The prodrugs (9, 10 and 11) were made as a series of compounds which are bifunctional alkylating agents in which the activating effect of the ionized carboxyl function is masked through an amide bond to a glutamic acid residue. These relatively inactive prodrugs were designed to be activated to their corresponding alkylating agent active drugs (7, 8 and 12 respectively) at a tumour site by prior administration of a monoclonal antibody conjugated to a bacterial enzyme. This system is called antibody-directed enzyme prodrug therapy (ADEPT). The chemical half-lives of the prodrugs and their active drugs were measured in order to determine their relative reactivities. The half-lives ranged from 21 to 324 min for the active drugs and from 42 to 1158 min for the prodrugs. The viability of two different tumour cell lines was monitored with each active drug and prodrug. The IC50 values varied from 65 to 625 microM for the active drugs: no IC50 values could be obtained for the prodrugs, using a rapid incubation procedure. Each in vitro technique demonstrated the ability of the glutamic acid moiety to deactivate the drugs, forming effective prodrugs.

Antibodies, Monoclonal↗
PubMed1990

Do normal plasma neurotensin concentrations increase ileal output?

Infusions of neurotensin increase ileal secretion in experimental animals, and the volume of ileal effluent in patients with ileostomies. The aim of the present study was to determine whether normal postprandial plasma concentrations of neurotensin increase the volume of fluid leaving the ileum. Basal and peak postprandial plasma neurotensin concentrations were 23 (17-36) and 39 (25-43) pmol/l (median and range) respectively in five subjects with ileostomies and 15 (3-27) and 32 (15-82) pmol/l respectively in nine normal subjects. Infusion of neurotensin for 30 min at a rate of 6.3 pmol/kg/min into six patients with ileostomies increased ileostomy output about 10-fold, and produced a significant decrease in the concentration of solid material, but plasma neurotensin concentrations rose to 237 (82-422) pmol/l during infusion at this rate. Infusion of neurotensin at 2.3 pmol/kg/min, producing plasma levels of 60 (16-108), had no significant effect the amount or nature of ileostomy effluent. We conclude that normal postprandial plasma concentrations of neurotensin are unlikely to influence the volume of fluid leaving the ileum.

Adult↗
PubMed1990

Novel prodrugs which are activated to cytotoxic alkylating agents by carboxypeptidase G2.

The synthesis of three novel prodrugs, 4-[bis[2-(mesyloxy)ethyl]amino]benzoyl-L-glutamic acid (7), 4-[(2-chloroethyl)[2-(mesyloxy)ethyl]amino]benzoyl-L-glutamic acid (8), and 4-[bis(2-chloroethyl)amino]benzoyl-L-glutamic acid (9), for use as anticancer agents, is described here. Each is a bifunctional alkylating agent in which the activating effect of the ionized carboxyl function is masked through an amide bond to the glutamic acid residue. These relatively inactive prodrugs are designed to be activated to their corresponding nitrogen alkylating agents (10, 11, and 12, respectively) at a tumor site by prior administration of a monoclonal antibody conjugated to the bacterial enzyme carboxypeptidase G2 (CPG2). The viability of two different tumor cell lines was monitored with each prodrug in the presence of CPG2. All three compounds showed substantial prodrug activity--with conversion to the corresponding active drug leading to greatly increased cytotoxicity.

Alkylating Agents↗
PubMed1990

Disposition of the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid and its active parent drug in mice.

A novel therapy for improving selectivity in cancer chemotherapy aims to modify distribution of a cytotoxic drug by generating it selectively at tumour sites. In this approach an antibody-enzyme conjugate is allowed to localise at the tumour sites before injecting a prodrug which is converted to an active drug specifically by the targeted enzyme in the conjugate. We present here pharmacokinetic studies on the prodrug 4-(bis (2-chloroethyl) amino) benzoyl-L-glutamic acid and its activated derivative, benzoic acid mustard. The glutamic acid is cleaved from the prodrug to form the active drug by carboxypeptidase G2 (CPG2), an enzyme from Pseudomonas sp., which is not found in mammalian cells. The prodrug and its parent active drug were rapidly distributed in plasma and tissues after administration of prodrug or active drug (41 mumol kg-1 intraperitoneally) to mice bearing human choriocarcinoma xenografts. Prodrug and active drug both followed a two-compartment kinetic model. Prodrug was eliminated more rapidly (t1/2 alpha = 0.12 h, t1/2 beta = 0.70 h) than active drug (t1/2 alpha = 0.37 h, t1/2 beta = 1.61 h). Conversion of the prodrug to the activated parent drug was detected within 5 min of administration to mice which had previously received a F(ab')2-anti-human chorionic gonadotrophin antibody (W14A) conjugated to the enzyme, CPG2 (1,000 U kg-1). Tumour was the only tissue that activated all the prodrug reaching the site. It contained the highest concentration of targeted enzyme conjugate capable of catalysing the reaction of prodrug to drug. Plasma and other tissues were also capable of activating the prodrug but active drug production was limited by the amount of enzyme present. The active drug measured in plasma and tissues other than tumour was attributable to residual antibody-enzyme conjugate at non-tumour sites. Low levels of conjugate in tissues and plasma militate against the advantage of tumour localised enzyme therefore necessitating removal of non-localised enzyme.

Animals↗
PubMed1990

Gastric enterochromaffin-like (ECL) cells in hypergastrinaemic duodenal ulcer disease.

Patients with hypergastrinaemic duodenal ulcer disease were studied to determine whether chronic moderate hypergastrinaemia produces hyperplasia of gastric enterochromaffin-like cells in man. Eight patients had peak postprandial plasma gastrin concentrations greater than 200 pmol/l, which is the 92nd percentile for patients with duodenal ulcer disease in this laboratory. The control group was eight patients with duodenal ulcers whose peak postprandial gastrin concentrations were less than 200 pmol/l. Basal and peak postprandial plasma gastrin concentrations were 107 (37) and 306 (66) pmol/l (mean (SEM] respectively in the hypergastrinaemic patients compared with 26 (4) and 137 (14) pmol/l respectively in the controls. There was no significant difference in the density of gastrin enterochromaffin-like cells between the two groups. The number of enterochromaffin-like cells per high power field was 53 (8) in the hypergastrinaemic patients compared with 50 (8) in the controls. We conclude that chronic moderate hypergastrinaemia does not produce hyperplasia of enterochromaffin-like cells in man. Our hypergastrinaemic group had plasma gastrin concentrations similar to, or greater than those reported during treatment with drugs such as omeprazole and histamine H2 receptor blockers.

Adult↗
PubMed1989

Postprandial gastrin concentrations are higher in female patients with duodenal ulcers.

We compared plasma gastrin concentrations in male and female patients with duodenal ulcers because a group in Denmark reported a difference, but two groups in the Far East did not. Median basal gastrin was 23 pmol/l in males compared with 43 pmol/l in females. Median peak postprandial gastrin was 71 pmol/l in males, compared with 142 pmol/l in females (p less than 0.03). Elevated gastrin may reflect diminished sensitivity of parietal cells to gastrin in females.

Adolescent↗
PubMed1988

Cholecystokinin cleavage to cholecystokinin-octapeptide in vivo and in vitro: accelerated cleavage in acute pancreatitis.

We have examined the possibility that the 33- and 39-amino acid forms of cholecystokinin (CCK) are cleaved to produce CCK-octapeptide (CCK-8) during circulation in humans. When a mixture of the 33- and 39-amino acid forms of porcine CCK was infused at 0.1-2.5 pmol/kg.min into normal subjects, material indistinguishable from CCK-8 by gel filtration and in region-specific radioimmunoassays appeared in plasma, together with an intermediate form that eluted between the 33- and 8-amino acid peptides. During infusions, plasma concentrations of CCK-33/39, CCK-8, and the intermediate CCK rose to 63 +/- 26 (mean +/- SE), 57 +/- 12, and 18 +/- 10 pmol/L, respectively. Cholecystokinin-octapeptide appeared rapidly and constituted approximately 40% of total CCK-like immunoreactivity after 5 min of infusion. Octapeptide-like material also appeared, but at a slower rate, when CCK-33 was incubated at 37 degrees C with human plasma. Thus after 5 min, and throughout the incubation, CCK-8 comprised approximately 20% and CCK-33 approximately 75% of total immunoreactivity. Cholecystokinin-33 disappeared more rapidly and small forms appeared in higher concentrations in plasma from patients with acute pancreatitis. Thus, after incubation for 120 min, CCK-33 and CCK-8 comprised 45% +/- 7% and 13% +/- 3% of initial immunoreactivity in normal plasma, but 18% +/- 6% and 33% +/- 9%, respectively, in plasma from patients with pancreatitis. Ethylenediaminetetraacetic acid, but not aprotinin, inhibited the cleavage of CCK-33 to produce CCK-8, and the degradation of CCK-8 in normal plasma in vitro.

Acute Disease↗
PubMed1988

A cytotoxic agent can be generated selectively at cancer sites.

Attempts to improve the selectivity of anti-cancer agents by conjugating them to antibodies directed at tumour associated antigens have demonstrated tumour localisation but only limited therapeutic success. We report here the advantage of a 2-stage approach in which the first component combines the selective delivery of antibody with a capability to generate a cytotoxic agent from a second subsequently administered component. A bacterial enzyme, carboxypeptidase G2 (CPG2) was conjugated with F(ab')2 fragment of a monoclonal antibody directed at beta subunit of human chorionic gonadotrophin (beta-hCG) and injected into nude mice bearing hCG producing CC3 xenografts of human choriocarcinoma. Time was allowed for the conjugate to localise at tumour sites and clear from blood before injecting para-N-bis (2-chloroethyl) aminobenzoylglutamic acid. Cleavage of the glutamic acid moiety from this molecule by CPG2 released a benzoic acid mustard. Growth of the tumour which is resistant to conventional chemotherapy was markedly depressed by a single course of treatment. This demonstrates for the first time the potential of an antibody directed enzyme to activate an alkylating agent and to eradicate an established human cancer xenograft.

4-Aminobenzoic Acid↗
PubMed1988

Effects of vasoactive intestinal polypeptide infusions on renal function in patients with liver disease.

1. The effect of intravenous vasoactive intestinal peptide (VIP, 6 pmol/kg per min) on renal function in six patients with cirrhosis of the liver was examined. 2. VIP caused generalized vasodilation and increased plasma renin activity, but diminished the glomerular filtration rate by about one third. 3. The excretion of water, sodium, potassium and calcium also fell significantly. 4. These results differ from our findings in normal man in whom VIP diminished water and electrolyte secretion largely by increasing tubular reabsorption. 5. It is concluded that the elevated VIP levels present in patients with severe liver disease may affect renal function, but that the presence of liver disease may affect renal responses to VIP.

Blood Cell Count↗
PubMed1987

Raw soya-bean flour increases cholecystokinin release in man.

1. The aim of the present study was to determine whether oral ingestion of raw soya-bean flour, which contains trypsin inhibitors, alters the release of cholecystokinin (CCK) in man. 2. Eleven healthy volunteers ate two mixed meals: one with raw soya-bean flour and the other with soya-bean flour that had been heat-treated. The two flours inhibited 34 and 3 mg trypsin/g flour respectively. 3. CCK was measured in plasma using a bioassay based on the release of amylase (EC 3.2.1.1) from dispersed rat pancreatic acini. 4. The peak CCK response was 16.8 (SE 8.1) pmol/l with raw soya-bean flour but 4.9 (SE 2.8) pmol/l with heat-treated flour (P less than 0.05). 5. We conclude that ingestion of raw soya-bean flour increases CCK release in man and that heat treatment which reduces the trypsin inhibitor content of the flour also diminishes its CCK-releasing effect.

Adult↗
PubMed1986

Graphemic and semantic similarity effects in the picture-word interference task.

Two experiments were performed using the picture-word interference task in which a word is superimposed on a line drawing of a picture which subjects must name. Incongruent words result in interference in naming the picture and the present studies examined the effect of graphemic and semantic similarity between the printed word and the picture label on naming times. Consistent with prior research a category effect was obtained such that a printed word from the same category as the object resulted in more interference than did a printed word not from the category of the object. However, it was also found that graphemic similarity between the printed word and the picture label reduced the size of the category effect. The time course of these effects was examined by varying the stimulus onset asynchrony between the print and the picture. The results are discussed within the logogen and pictogen framework.

Adult↗
PubMed1985

On the immunology of nerve growth factor.

We report some experiments on the immunological properties of nerve growth factor from the venom of Heloderma horridum and from bull seminal vesicles. On the basis of these results, taken together with results already in the literature, we propose an operational definition of the term nerve growth factor.

Animals↗
PubMed1982

Depression and failure to resume social activities after stroke.

In 91 stroke patients, the incidence of depression was 26% (24 patients) 6 months after stroke. Depression was significantly correlated with failure to resume premorbid social activities; depressed patients lost a mean of 67% previous activities while nondepressed patients lost a mean of 43% (p less than 0.01). Depression status was not significantly related to age, sex, marital or cognitive status, or side of brain involvement. Independence in ADL and ambulation or change in residence after stroke also were not significantly related to depression status. Since depression is common after stroke, is associated with failure to return to previous activities, and cannot be predicted by commonly used patient characteristics, the health care team must carefully identify, monitor, and manage depression in the patient recovering from stroke.

Activities of Daily Living↗