PubMed Health⌕ Search

Biomedical subjects

D J Kerr

Publications and source records attributed to D J Kerr.

At least 37 records · Page 2Linked to original sources
PubMed1996

Vascular endothelial growth factor stimulates protein kinase C-dependent phospholipase D activity in endothelial cells.

Many tumors produce vascular endothelial growth factor (VEGF), a paracrine factor acting selectively on endothelial cells. VEGF has many effects on cultured endothelial cells and mediates angiogenesis and enhanced vascular permeability in vivo. The endothelial signal transduction pathways of VEGF represent novel targets for cancer therapy because they are readily accessible to systemically administered drugs. We have examined VEGF-stimulated signals generated in HUVEC to identify potential targets for therapeutic intervention. The transphosphatidylation reaction has been used to monitor phospholipase D (PLD) activity; total inositol phosphates have been measured after prelabeling of cells with [3H]myoinositol; and intracellular free calcium has been measured using Fura-2 fluorescence. After HUVEC-stimulation with VEGF, there is an early influx of calcium (maximal by 100 seconds) followed by activation of PLD (half maximal by 100 seconds, EC50 70 pm). The PLD activity was inhibited by reducing extracellular calcium (150 nM, 50% inhibition), exposure to 12-O-tetradecanoylphorbol 13 acetate (200 nM, 24 hours, 100% inhibition), Roche 31,8220 (10 microM, 15 minutes, 72% inhibition), or genestein (100 microM, 30 minutes, 56% inhibition), which suggests a dependence on both protein kinase C and tyrosine phosphorylation. Activation of phospholipase C-catalyzed hydrolysis of phosphatidylinositol-4,5-bisphosphate was inferred from the production of inositol phosphates, although this response was slower (half maximal by 3 minutes). The phospholipase C activity was also dependent on influx of calcium and was partially inhibited by low (150 nM) extracellular calcium. PLD may be involved in mediating a number of endothelial responses to tumor-secreted VEGF, notably cytoskeleton-dependent effects such as the cell migration involved in angiogenesis. This signal transduction pathway could represent an accessible and vulnerable target for cancer therapeutic intervention and has the novelty of being located within normal cells rather than tumor cells.

Calcium↗
PubMed1995

Melanoma cell lines express VEGF receptor KDR and respond to exogenously added VEGF.

Tumour-secreted vascular endothelial growth factor (VEGF) exerts a number of effects which are important in tumour pathology, including stimulation of angiogenesis and permeabilisation of tumour-associated vasculature. In this study we have examined the possibility that VEGF may also play an autocrine role in tumour growth. Using reverse-transcriptase polymerase chain reaction (RT-PCR), the expression of VEGF was found in 15/15 human tumour cell lines examined, while the VEGF receptor KDR was detected only in three melanoma cell lines (MeWo and A375, both wild type and metastatic variant). Exogenously added VEGF (10ng/ml) was able to stimulate up to 40% increased proliferation of A375 M melanoma cells following a 48-h period of quiescence, suggesting that VEGF may indeed play a role in autocrine, as well as paracrine, stimulation of melanoma growth.

Base Sequence↗
PubMed1995

Wortmannin and its structural analogue demethoxyviridin inhibit stimulated phospholipase A2 activity in Swiss 3T3 cells. Wortmannin is not a specific inhibitor of phosphatidylinositol 3-kinase.

Wortmannin and its structural analogue demethoxyviridin (DMV) have been reported to be specific inhibitors of phosphatidylinositol 3-kinase activity. Here we report that these compounds are not as selective as assumed and demonstrate inhibition of bombesin-stimulated phospholipase A2 activity by both wortmannin and DMV with an IC50 (2 nM) which is slightly more potent than the inhibition of insulin-stimulated phosphatidylinositol 3,4,5-trisphosphate generation in these cells (approximately 10nM). While it has not been possible to fully block in vitro phospholipase A2 activity with wortmannin, inhibition cannot be a consequence of inhibition of PI 3-kinase activity since bombesin fails to generate 3-phosphorylated lipids in the intact cell. Therefore, while wortmannin is indeed a PI 3-kinase inhibitor, it is not as specific as previously reported, and experimental conclusions based solely on its use should be treated with caution.

3T3 Cells↗
PubMed1995

The control of apoptosis and drug resistance in ovarian cancer: influence of p53 and Bcl-2.

Modulation of apoptosis may influence resistance to chemotherapy and therefore affect the outcome of cancer treatment. Ovarian cancer, one of the most fatal malignancies in women, is often associated with drug resistance but the cellular pathways contributing to this effect remain obscure. We have found that Bcl-2 and p53, two proteins implicated in the control of apoptosis, are frequently expressed in fresh biopsies of primary ovarian carcinoma. Examination of Bcl-2 and p53 protein levels in pairs of cis-platin sensitive and resistant ovarian cell lines demonstrated that the resistant variants over-express Bcl-2 and/or p53, apparently due to progressive expansion of Bcl-2 and/or p53 positive subpopulations during the in vitro development of resistance. Exogenous expression of Bcl-2 or a temperature sensitive mutant p53 (ts p53) in the ovarian cell line A2780 resulted in protection from drug-induced apoptosis and a delay in drug-mediated S-phase arrest. Interestingly, p53 accumulation in response to DNA damage induced by different agents was significantly delayed and reduced in the Bcl-2 transfectants compared to the control A2780 line, suggesting that Bcl-2 may act upstream of the p53 pathway. Similarly, the induction of Bax mRNA and protein was also found to be delayed in the presence of Bcl-2. Overall, our data provide further evidence for cross-talk between Bcl-2, p53 and Bax and suggest that these genes are important determinants of drug-induced apoptosis thereby modulating resistance to chemotherapy.

Apoptosis↗
PubMed1995

Induction of the c-myc but not the cH-ras promoter by platinum compounds.

The recombinant plasmids p324, p330 and p323 carrying the aminoglycoside phosphotransferase (aph) gene and 5' flanking c-myc sequences linked to the reporter gene chloramphenicol acetyl-transferase (cat) were introduced into the mouse erythroleukaemic cell line F412B2TK- and stable transfectants resistant to geneticin G418 were obtained. The effects of cis-platin and two novel platinum compounds, D19466 (lobaplatin) and D17872, on c-myc promoter regions were studied using a large range of drug concentrations and correlated with cytotoxicity data. It was found that cis-platin and D19466 show a similar pattern of cytotoxicity and activation of c-myc promoter-driven cat gene expression with maximum effect (increased expression of 7.4- and 8.1-fold, respectively) at a concentration of 5 x 10(-5) M, while the less cytotoxic D17872 only slightly activates cat expression at the same concentration. However, when the F412B2TK- cell line was transfected with a plasmid carrying 5' flanking sequences of the c-Hras1 gene with promoter/enhancer function, linked to the cat reporter, no similar inductive effect was observed with any of the platinum drugs used. These data suggest that platinum compounds and possibly other DNA-damaging agents may specifically influence the expression of certain genes.

Animals↗
PubMed1995

Allosteric regulation of [3H]vinblastine binding to P-glycoprotein of MCF-7 ADR cells by dexniguldipine.

Plasma membranes were prepared from the P-glycoprotein expressing human breast cancer cell line MCF-7 ADR. [3H]Vinblastine bound to these membranes saturably with a Bmax of 24 pmol/mg of protein and KD of 23 nM. In contrast, membranes from the parent cells MCF-7 WT, which do not express P-glycoprotein, did not bind [3H]vinblastine with high affinity. Cytotoxics known to be transported by P-glycoprotein inhibited the binding of [3H]vinblastine, as did multidrug reversing agents including the 1,4-dihydropyridine, dexniguldipine-HCl (Ki, 15 nM). In dissociation kinetic experiments, dexniguldipine-HCl accelerated the dissociation of [3H]vinblastine from P-glycoprotein, indicating a negative heterotropic allosteric mechanism of action through a drug binding site distinct from that of vinblastine. Other 1,4-dihydropyridines tested also accelerated [3H]vinblastine dissociation from P-glycoprotein, however, multidrug reversing drugs of different chemical classes, including quinidine, verapamil and cyclosporin A did not. These results suggest that P-glycoprotein of MCF-7 ADR cell membranes possesses at least two drug acceptor sites which are allosterically coupled: receptor site-1 which binds vinca alkaloids, and receptor site-2 which binds 1,4-dihydropyridines such as dexniguldipine-HCl, which had the highest affinity of the tested derivatives.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Determination of quercetin in human plasma using reversed-phase high-performance liquid chromatography.

A method is reported for the measurement of quercetin in human plasma using reversed-phase high-performance liquid chromatography (HPLC). Quercetin and kaempferol (as internal standard) were spiked into plasma samples and extracted using C18 Sep-Pak Light cartridges (efficiency > 85%). Flavonoids were eluted with aqueous acetone (50% v/v, pH 3.5), dried down and redissolved in aqueous acetone (45% v/v, pH 3.5). The increased osmolarity promoted a phase separation and the water-saturated acetone layer, containing the flavonoids, was analysed by HPLC with aqueous acetone mobile phase (45% v/v acetone in 250 mM sodium dihydrogen sulphate. The mixture was adjusted to pH 3.5 with phosphoric acid and used at a flow-rate of 1.0 ml/min) and mu Bondapak C18 column (150 x 3.9 mm I.D., 10 microns particle size). The detection limit (A375 nm) for quercetin in plasma was 0.1 microgram/ml (300 nM). The method also detects metabolites of quercetin, although these are not yet identified.

Chromatography, High Pressure Liquid↗
PubMed1995

Etoposide protein binding in cancer patients.

The protein binding of etoposide was studied in vivo in 36 cancer patients receiving etoposide therapy. Free etoposide was separated from plasma using an ultrafiltration method and the etoposide concentrations (free and total) were measured by high-performance liquid chromatography (HPLC). Considerable interpatient variation in the protein binding of etoposide was observed. The protein binding of etoposide varied from 80% to 97% (mean, 93%). Univariate analysis showed a significant inverse correlation between the free fraction of etoposide and serum albumin (r = 0.74), daily dose (r = 0.37) and age (r = -0.34). Multivariate analysis demonstrated that serum albumin and age were independent predictors of the etoposide free fraction. Serum bilirubin showed no correlation with etoposide protein binding. There is wide variation in etoposide protein binding in cancer patients, which is mostly dependent on serum albumin concentration.

Administration, Oral↗
PubMed1995

Phase II trials of rhizoxin in advanced ovarian, colorectal and renal cancer.

Rhizoxin is a tubulin-binding anti-neoplastic agent which is active in a range of murine tumour models. The recommended schedule, of intravenous (i.v.) bolus administration at a dose of 2 mg m-2 every 3 weeks, has been assessed in three phase II trials of ovarian, renal and colorectal cancer. In general terms the drug was fairly well tolerated, but the response rate was disappointing: 0/18, colorectal cancer; 0/18, renal cancer; 1 partial response (PR)/17, ovarian cancer.

Adult↗
PubMed1995

Phase I clinical and pharmacokinetic study of leucovorin and infusional hepatic arterial fluorouracil.

PURPOSE: A phase I and pharmacokinetic trial was performed between October 1993 and June 1994 to determine the maximum-tolerated dose of hepatic arterial infusion (HAI) of fluorouracil (5-FU) and intravenous (IV) leucovorin (folinic acid; FA) in patients with hepatic metastases from colorectal cancer. PATIENTS AND METHODS: Forty-three patients received 310 courses of HAI chemotherapy administered over 48 hours every 2 weeks. The regimen consisted of FA 200 mg/m2 by IV infusion over 2 hours, followed by a loading dose of 5-FU 400 mg/m2 by HAI over 15 minutes, followed by a 22-hour infusion of 5-FU at doses ranging from 0.8 to 1.84 g/m2, with identical chemotherapy on day 2. Pharmacokinetic studies were performed to determine peak and steady-state plasma concentrations (Css) of 5-FU. RESULTS: Severe diarrhea and cardiac and neurologic toxicity were dose-limiting at 1.84 g/m2. The recommended dose for the 22-hour component of the schedule was 1.6 g/m2 and was associated with tolerable toxicity. A Css of 2.2 +/- 0.8 mumol/L for 5-FU was achieved on the recommended schedule, which compares favorably with conventional IV 5-FU regimens. Among 30 patients assessable for response, there were four complete responses and seven partial responses, and 12 patients with stable disease and seven with progressive disease, reported after 3 months (ie, six cycles) of therapy. CONCLUSION: A regimen that combines 5-FU and FA has been identified for regional chemotherapy in patients with hepatic metastases from colorectal cancer. The systemic levels of 5-FU achieved are similar to the conventional IV de Gramont regimen using an identical schedule of 5-FU and FA, which implies that this chemotherapy has the best of both worlds, ie, a regional advantage in delivering high drug concentrations to the target organ with adequate systemic cover for extrahepatic micrometastases.

Adult↗
PubMed1995

Hemangioblastoma of the optic nerve: case report.

An optic nerve hemangioblastoma arising in the optic nerve of a patient with von Hippel-Lindau syndrome is reported. This represents the 10th published example of a hemangioblastoma arising at this site, the second description of the magnetic resonance imaging features of a hemangioblastoma at this location, and the second patient from whom an optic nerve hemangioblastoma has been removed with the goal of preserving the optic nerve as well as vision. A majority of these optic nerve hemangioblastomas have arisen in patients with von Hippel-Lindau syndrome. All patients experienced progressive loss of vision either to blindness or surgical intervention, although a vast majority of the lesions were sharply demarcated from the adjacent nerve and, thus, potentially resectable. Optic nerve hemangioblastomas are a rare cause of blindness but potentially preventable when treated with a conservative surgical approach aided by neuroimaging guidance. The recognition of discordance between the degree of vision loss and the extent or progression of a retinal hemangioblastoma may be an important clue to diagnosis in the patient with von Hippel-Lindau syndrome.

Adult↗
PubMed1994

Dexniguldipine-HCl is a potent allosteric inhibitor of [3H]vinblastine binding to P-glycoprotein of CCRF ADR 5000 cells.

Cell membranes were prepared from the multidrug resistant, P-glycoprotein expressing human lymphoblastoid cell line CCRF-ADR 5000. The P-glycoprotein of these membranes possessed high affinity binding sites for [3H]vinblastine, with a Kd of 8 +/- 2 nM and Bmax of 17 +/- 8 pmol/mg of protein. The binding of [3H]vinblastine to P-glycoprotein was not ATP-dependent, and was inhibited by cytotoxic drugs with the following potency order; vincristine > doxorubicin > etoposide. The 1,4-dihydropyridine and multidrug resistance reversing agent, dexniguldipine-HCl, inhibited binding with a Ki value of 37 nM. The multidrug resistance reversing agent cyclosporin A, and the cytotoxics doxorubicin and etoposide did not alter the kinetics of [3H]vinblastine dissociation from P-glycoprotein; however, the 1,4-dihydropyridines dexniguldipine-HCl and nicardipine accelerated dissociation of [3H]vinblastine. These data suggest that P-glycoprotein possesses at least two allosterically coupled drug acceptor sites; receptor site 1 which binds vinblastine, doxorubucin, etoposide and cyclosporin A, and receptor site 2 which binds dexniguldipine-HCl and other 1,4-dihydropyridines.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

A phase I-II study of N-(phosphonacetyl)-L-aspartic acid (PALA) added to 5-fluorouracil and folinic acid in advanced colorectal cancer.

N-(phosphonacetyl)-L-aspartic acid (PALA) inhibits the enzyme L-aspartic acid transcarbamoylase (ATCase) which is important in de novo pyrimidine synthesis. Low dosages of PALA modulate the in vitro activity of 5-fluorouracil (5-FU) and PALA (250 mg/m2) inhibits pyrimidine synthesis in patients. PALA (250 mg/m2 day 1) was combined with an established 5-FU/folinic acid (FA) regimen [FA (200 mg/m2 over 2 h days 2 + 3) and bolus and 22 h infusional 5-FU (300-500 mg/m2 days 2 + 3)] without the need for dose reduction of 5-FU or FA. 35 patients were entered. Treatment was well tolerated; 4/27 patients experienced > or = ECOG grade 3 toxicity at full 5-FU dosage (500 mg/m2 bolus/infusion). However, the response rate in 33 evaluable patients was only 6.1% [95% confidence intervals (C.I.) 0.2-21.8%]. Median response duration was short (4 months, 95% C.I. 3-6 months) and overall median survival was 10 months (95% C.I. 7-16 months). Although PALA (250 mg/m2) can be combined with full dosage 5-FU/FA, the combination has poor activity in colorectal cancer.

Adolescent↗
PubMed1994

A phase II study of regional 5-fluorouracil infusion with intravenous folinic acid for colorectal liver metastases.

Regional chemotherapy, delivered via the hepatic artery, may significantly increase tumour response rates in patients with colorectal liver metastases. However, survival is limited by extrahepatic disease progression. We have developed a novel therapeutic approach for patients with metastases confined to the liver. In order to achieve high local response rates and also inhibit extrahepatic progression, 5-fluorouracil (5-FU) was infused intra-arterially at a dose previously calculated to achieve both high-dose regional therapy and adequate systemic levels. To enhance efficacy further, 5-FU was combined with high-dose systemic folinic acid (FA). Thirty-one patients were evaluated in a phase II study. 5-FU (1.5 g m2) was infused via a surgically implanted hepatic artery catheter over a 24 h period; FA (total 400 mg m-2) was infused intravenously during the initial and final 2 h. Treatments were given weekly for cycles of 6 weeks' duration. To date, median duration of treatment is 6 months and the median follow-up period is 17 months. The overall response rate was 48% with two complete and 13 partial responses. Predicted median time to progression is 8 months. The site of first progression was hepatic in 10 (42%) and extrahepatic in 14 (58%) patients. Seven patients developed local complications; one required emergency surgery. Side-effects were limited to grade 3 toxicity (four patients) or less. Predicted median survival is 19 months. This approach, which is associated with a high response rate and low systemic toxicity, warrants further evaluation. A phase III study is planned.

Adult↗
PubMed1994

Pharmacokinetic study of 5-fluorouracil in a novel dialysate solution: a long-term intraperitoneal treatment approach for advanced colorectal carcinoma.

Five patients with advanced colorectal and gastric carcinoma with peritoneal deposits were treated by continuous weekdays intraperitoneal (i.p.) instillation of 5-fluorouracil (5-FU) 200 mg m-2 day-1 in a novel dialysate solution that ensures maximal exposure of peritoneal areas liable to bear tumours for 24 h. A solution of icodextrin, a glucose polymer, in a 21 twin-bag delivery system allowed a single daily exchange and demonstrated the feasibility of long-term continuous ambulatory treatment with up to 17.4 g of 5-FU, delivered intraperitoneally, in this initial study. During the entire study, there were 235 fluid exchanges or 470 connections and disconnections and no bacterial peritonitis or exit site infection were observed. There was no treatment-associated toxicity worse than WHO grade 2. Drug concentrations in both peritoneal and plasma compartments followed a first-order model with similar half-life value of 1.3 h. 5-FU pharmacokinetic parameters (half-life values, total body clearance, peritoneal clearance and pharmacological advantage of the i.p. route) with this novel icodextrin carrier solution were similar to those obtained in other referenced pharmacokinetic studies with other carrier solutions (dextrose dialysate and lactated Ringer's solutions). This confirms that icodextrin solution is physiologically neutral, drug compatible and allows adequate dwell times with constant fluid balance for long-term continuous intraperitoneal chemotherapy. The pharmacokinetic parameters from this study will be used to design a loading dose infusion schedule in an attempt to maintain steady-state i.p. 5-FU levels in a new multicentre phase I trial.

Colorectal Neoplasms↗
PubMed1994

Hepatic arterial chemotherapy for metastatic colorectal carcinoma.

In this review, the rationale of regional chemotherapy for treatment of hepatic metastases in advanced colorectal carcinoma is discussed. Pharmacokinetic principles and early clinical experience of hepatic arterial drug administration are summarised. The regional advantage of fluoropyrimidine compounds in this setting is well established, and recent evidence suggests that 5-fluorouracil (5-FU) is more efficacious than the analogue 5-fluoro-2'-deoxyuridine (FUDR). However, while significantly higher clinical response rates can be achieved with hepatic arterial infusion (HAI) chemotherapy compared with conventional intravenous drug administration, patient survival benefit is not significantly different. Several novel approaches to overcome the limitations of HAI therapy are currently being explored. These include concomitant use of biodegradable microspheres, which both slow tumour blood flow and enhance tumour drug uptake, and use of vasoactive agents to redistribute arterial blood flow towards tumours. In addition, novel chemotherapeutic agents which exploit unique biological characteristics of hepatic tumours are entering clinical trial.

Colorectal Neoplasms↗