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Biomedical subjects

T C Hamilton

Publications and source records attributed to T C Hamilton.

At least 109 records · Page 6Linked to original sources
PubMed1990

Synthesis and antihypertensive activity of 4-(substituted-carbonylamino)-2H-1-benzopyrans.

The synthesis and antihypertensive activity of a series of novel 4-(substituted-carbonylamino)-2H-1-benzopyran-3-ols, administered orally to conscious spontaneously hypertensive rats, are described. Optimum activity was observed for compounds with alkyl, amino, or aryl groups flanking the carbonyl group. Of the alkyl and amino series the most potent compounds contained the methyl and methylamino groups, respectively. Several analogues have been compared with cromakalim (1) for their effects on potassium ion efflux in the rabbit mesenteric artery using rubidium-86 as a marker. The ability of each compound to enhance rubidium-86 efflux is approximately parallelled by its blood pressure lowering activity, and thus these analogues, like compound (1), belong to the series of drugs which have been classified as potassium-channel activators.

Animals↗
PubMed1990

Multidrug resistance to alkylating agents and platinum compounds: state of our knowledge.

Resistance to platinum-containing drugs and alkylating agents is multifactorial. Relapsed patients and those who have an incomplete response to induction chemotherapy are unlikely to achieve a complete response to other treatments. This pattern of resistance to therapy is very broad in that patients not only fail to respond to drugs from the same pharmacologic classes as used in primary treatment, but also do not respond to other available drugs or irradiation. Using ovarian cancer as a prototype tumor, researchers have initiated laboratory studies to determine the mechanisms responsible for this drug-resistance phenotype. Insights into this action may promote development of therapeutic strategies to prevent the onset of resistance or reverse resistance when it occurs.

Alkylating Agents↗
PubMed1989

Effect of glutathione on DNA repair in cisplatin-resistant human ovarian cancer cell lines.

We have studied the effect of glutathione reduction by buthionine sulfoximine (BSO), a specific inhibitor of gamma -glutamyl cysteine synthetase, on DNA repair after cisplatin damage in an ovarian cancer cell line with in vitro induced resistance to cisplatin. In addition, we have examined the effect of aphidicolin, a specific inhibitor of DNA polymerase alpha, in combination with BSO on cisplatin-associated DNA repair. BSO treatment was found to partially inhibit DNA repair, and the addition of aphidicolin caused nearly a 100% inhibition in DNA repair activity. Treatment of cells with glutathione ester after BSO resulted in complete recovery of DNA repair activity or partial recovery if aphidicolin was present. The significance of these results to the chemosensitizing effects of BSO medicated glutathione reduction is discussed.

Aphidicolin↗
PubMed1989

Estrogen and anti-estrogen effects on the growth of human epithelial ovarian cancer in vitro.

An epithelial ovarian cancer cell line, PE04, has been shown to contain high levels of cytosolic estrogen receptor-like binding. Analysis of PE04 cytosol on low-salt sucrose density gradients demonstrated 7-9S binding of [3H]17 beta-estradiol, with specificity consistent with that of an estrogen receptor. When compared with the proliferation of cells grown in monolayer without steroids, a 50% increase in growth rate of the cell line was observed by treatment with 17 beta-estradiol (E2). Growth stimulation was dose-dependent and maximal at 10(-10) M. The E2 effect on substrate-independent growth was more striking; 3 x 10(-9) M produced a 30-fold increase in cloning efficiency. Treatment with 4-hydroxytamoxifen resulted in a dose-dependent inhibition (maximal at 3 x 10(-9) M) of cell growth, which was reversible by E2. Although treatment with estrogen in systems containing functional estrogen receptor commonly results in progesterone receptor synthesis, E2 induction of progesterone receptor could not be demonstrated in this cell line. The endocrine characteristics of PE04 contrast with those of another ovarian cancer cell line, NIH:OVCAR-3, in which E2 induces progesterone receptor but does not stimulate cell proliferation. This is the first report of an ovarian cancer cell line in which the clinically important end-effect of estrogen, cell growth, has been observed. Furthermore, retention of a mitogenic response to estrogen in the apparent absence of progesterone receptor induction has not been described previously in model systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenocarcinoma, Mucinous↗
PubMed1989

Inhibition by glibenclamide of the vasorelaxant action of cromakalim in the rat.

1. In rat isolated thoracic aortic rings pre-contracted with noradrenaline (10(-6) M), cromakalim (3 x 10(-7)-3 x 10(-5) M) produced concentration-related relaxation. This effect was progressively inhibited by increasing concentrations of the anti-diabetic sulphonylurea drug, glibenclamide (10(-6)-10(-5) M). 2. In rat isolated portal veins, cromakalim (3 x 10(-8)-10(-6) M) produced concentration-related inhibition of the spontaneous contractive activity and glibenclamide (3 x 10(-7)-3 x 10(-6) M) prevented this inhibitory action in a concentration-dependent manner. 3. In both rat aortic rings and portal veins, cromakalim (10(-5) M) stimulated 86Rb efflux. Prior exposure to glibenclamide (10(-7)-10(-6) M) produced a concentration-related inhibition of this response. 4. In conscious rats, cromakalim, 0.075 mg kg-1 i.v., produced a rapid and sustained fall in arterial blood pressure which was not influenced by pretreatment (2 h) with a large oral dose of glibenclamide (100 mg kg-1). 5. In conscious rats, the hypotensive action of cromakalim, 0.075 mg kg-1 i.v., was abolished by pretreatment (30 min) with glibenclamide, 20 mg kg-1, given by the intravenous route. 6. The results suggest that the vasorelaxant and hypotensive actions of cromakalim involve a K+ channel which can be inhibited by glibenclamide, but which may be distinct from the ATP-sensitive K+ channel of the pancreatic beta-cell.

Animals↗
PubMed1988

Genes amplified and overexpressed in human multidrug-resistant cell lines.

Multidrug resistance (MDR) is associated with overproduction of Mr 170,000 membrane proteins (P-glycoproteins) caused by either gene amplification, transcriptional activation, or both. In rodents the amplified domain comprises genes that encode P-glycoproteins and at least five unrelated genes, one of which encodes the calcium-binding protein sorcin. The amplification and increased expression of these genes always includes one P-glycoprotein-encoding gene (pgp1 in hamsters, homologous to mdr1 in humans). In human MDR cells only elevated mdr1 expression has been shown thusfar, although another P-glycoprotein encoding gene (mdr3, homologous to hamster pgp3) is closely linked. Here we show that the human homolog of the hamster sorcin gene resides on chromosome 7 like the P-glycoprotein-encoding genes. Furthermore, gene classes designated 4, 5, and 6 are coamplified with mdr1 and mdr3 in the human ovarian carcinoma cell line 2780AD, which strongly suggests that the overall structure of the human MDR domain is the same as in rodents. Class 6 was moderately and mdr1 was highly overexpressed in this cell line. Four other human MDR cell lines also have much higher mdr1 overexpression than expected from the relatively low levels (2- to 30-fold) of gene amplification. This contrasts with the results of previous work with rodent MDR cells, in which the increase in P-glycoprotein mRNA levels usually parallels the increase in gene copy number. Although four of the five human MDR cell lines have coamplified mdr3, its expression was undetectable. Our results confirm the central role of the mdr1 (pgp1) gene in MDR and suggest that different cross-resistance patterns are not due to differential expression of different P-glycoprotein genes.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1988

Increased DNA repair as a mechanism of acquired resistance to cis-diamminedichloroplatinum (II) in human ovarian cancer cell lines.

A human ovarian cancer cell line, A2780, derived from an untreated ovarian cancer patient and relatively sensitive to cisplatin was treated by stepwise incubation with cisplatin to produce a cisplatin-resistant variant, 2780CP. The relative abilities of these cell lines to repair cisplatin-induced damage to cellular DNA then was examined by measure of [3H]thymidine incorporation into normal density DNA separated from bromodeoxyuridine-substituted DNA on alkaline cesium chloride gradients. These studies revealed that primary cisplatin resistance present in 2780CP was associated with a near twofold-increased ability to repair damage induced by the drug under conditions where 2780CP was approximately 5-fold resistant to cisplatin. Aphidicolin, a specific inhibitor of DNA polymerase alpha, showed a dose-dependent capacity to inhibit DNA repair in this system with maximum inhibition of 63% at 4 micrograms/ml. It was also found that inhibition of DNA repair during and shortly after cisplatin exposure resulted in an approximately threefold increase in the cytotoxicity of cisplatin as monitored by clonogenic cell survival in the resistant but not the sensitive parental cell line.

Aphidicolin↗
PubMed1988

Comparative effects of K+ channel blockade on the vasorelaxant activity of cromakalim, pinacidil and nicorandil.

Three agents with K+ channel blocking activity, procaine, 4-aminopyridine (4-AP) and tetraethylammonium (TEA), were tested for inhibition of vasorelaxation and 86Rb+ efflux induced by cromakalim (BRL 34915), pinacidil and nicorandil in rabbit isolated mesenteric artery. The potency order for inhibition of vasorelaxation was procaine greater than 4-AP greater than TEA and for inhibition of efflux was procaine = 4-AP greater than TEA. The K+ channel blockers did not discriminate between cromakalim, pinacidil or nicorandil on efflux but demonstrated preferential inhibition of vasorelaxation to cromakalim greater than pinacidil greater than nicorandil. In addition, the maximum response to cromakalim was depressed but that to pinacidil and nicorandil was not. The results confirm the role of K+ channel activation in vasorelaxation to cromakalim, pinacidil and nicorandil, but suggest that additional mechanisms may be involved for pinacidil and, in particular, for nicorandil.

4-Aminopyridine↗
PubMed1988

Modulation of induced resistance to adriamycin in two human breast cancer cell lines with tamoxifen or perhexiline maleate.

The clinical utility of adriamycin in the treatment of patients with metastatic breast cancer is often-limited by the development of drug resistance. It has been recognized that in addition to the development of primary resistance against adriamycin, malignant cells can simultaneously develop cross-resistance to other agents. An adriamycin-resistant human breast cancer cell line (MCF 7Ad) was developed by exposing the parent line (MCF 7) to gradually increasing concentrations of adriamycin while the cells were being grown in monolayer. Using these lines in a clonogenic assay, the relative drug sensitivities to adriamycin, vinblastine, melphalan, 5-fluorouracil and methotrexate were studied. MCF 7Ad was 12.5-fold more resistant to adriamycin than MCF 7 and 500-fold cross-resistant to vinblastine. There was no cross-resistance to melphalan, 5-fluorouracil or methotrexate. The resistance of MCF 7Ad was decreased by simultaneous exposure to tamoxifen (by a factor of 3.33) or perhexiline maleate (by a factor of 7.50). This decreased resistance was evidenced by a shift to the left of the sensitivity curves. However, there was no consistent change in the sensitivity curves of MCF 7. At the selected concentration of tamoxifen and perhexiline maleate, the cloning efficiency of MCF 7 and MCF 7Ad was 80%-90% of control values in medium without tamoxifen, perhexiline maleate or cytotoxic drugs. The resistance of MCF 7Ad to adriamycin was associated with a lower accumulation of [14C]adriamycin than exhibited by the sensitive MCF 7 line. There was no consistent change in [14C]adriamycin accumulation in MCF 7 or MCF 7Ad when tamoxifen was added, but when perhexiline maleate was added the [14C] accumulation increased. These results suggest that the tamoxifen-induced change in MCF 7Ad adriamycin resistance was not due to an increase in the amount of cell-associated adriamycin, but rather to some other mechanism that increased the cytotoxicity of the adriamycin.

Breast Neoplasms↗
PubMed1988

Cromakalim, a potassium channel activator: a comparison of its cardiovascular haemodynamic profile and tissue specificity with those of pinacidil and nicorandil.

Studies have been performed to compare the cardiovascular haemodynamic profiles of the potassium channel activator, cromakalim (BRL 34915), with those of pinacidil and nicorandil. In conscious renal hypertensive cats, cromakalim was 10 times more potent than pinacidil as an antihypertensive agent while nicorandil was 10 times less potent than pinacidil. Cromakalim and pinacidil had a similar duration of action while nicorandil was short acting. In anaesthetised cats, hypotension evoked by intravenous infusions of cromakalim, pinacidil, or nicorandil was associated with a decrease in mesenteric vascular resistance but only cromakalim produced a marked reduction in renal vascular resistance. Cromakalim, pinacidil, and nicorandil were highly specific as inhibitors of tension in vascular (rabbit portal vein) (IC50 = 2.1 x 10(-8), 4.6 x 10(-8), and 1.3 x 10(-6)M, respectively,) rather than cardiac (rabbit papillary muscle), tissue. In view of its antihypertensive efficacy, specificity for vascular tissue, and beneficial effect upon renal haemodynamics, the potassium channel activator, cromakalim, has advantages in its profile of activity compared to pinacidil and nicorandil.

Animals↗
PubMed1988

Antihypertensive and angiotensin converting enzyme inhibitory activities of a novel dihydrobenzofuran analogue.

1. The biochemical and pharmacological profiles of the novel, orally active angiotensin converting enzyme (ACE) inhibitor, N-[N-[[4-(2, 3-dihydro-2-benzofuranyl)-1-(ethoxycarbonyl)]butyl]-(s)-alanyl]- (s)-proline (BRL 36378), have been compared with those of enalapril and captopril. 2. In the conscious sodium deficient spontaneously hypertensive rat, BRL 36378 and enalapril (0.3-10 mg/kg orally) produced comparable falls in blood pressure; at 3 mg/kg orally, captopril was less active than BRL 36378 and enalapril. 3. In the anaesthetised spontaneously hypertensive rat, enalapril was slightly more potent than BRL 36378 as an inhibitor of angiotensin I (AI) pressor responses whilst BRL 36378 was about twice as potent as captopril in this test (i.v. route used). BRL 36378 and enalapril were equipotent as potentiators of bradykinin depressor responses. 4. In the anaesthetised Wistar rat, the maximum inhibition of AI pressor responses by 0.1 microgram/kg i.v. BRL 36378 and captopril was achieved sooner than after the same dose of enalapril. The inhibitory effect of captopril subsided completely by 40-50 min but the maximum effects of BRL 36378 and enalapril persisted for at least 60 min. 5. In the conscious renal hypertensive cat, captopril was slightly more potent than BRL 36378 or enalapril as a blood pressure lowering agent, over 1-10 mg/kg orally. BRL 36378 was more potent than enalapril as an inhibitor of AI induced pressor responses in this model. Captopril possessed similar inhibitory activity to BRL 36378 although minor differences in time course were apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1988

Mechanisms of cross-resistance between radiation and antineoplastic drugs.

The mechanisms responsible for the cross-resistance between radiation and certain antineoplastic agents have been examined in human ovarian cancer cell lines. Cell lines established from patients at a time when they were resistant to combination chemotherapy regimens, which included cisplatin and an alkylating agent as well as cell lines with resistance induced in vitro to melphalan and cisplatin, all have increased cellular levels of glutathione (GSH) compared with drug-sensitive cell lines from untreated patients. In addition, cell lines with acquired resistance to melphalan and cisplatin, but not to doxorubicin, were cross-resistant to radiation. L-Buthionine sulfoximine (BSO), an irreversible inhibitor of gamma-glutamylcysteine synthetase, lowered GSH levels in all the resistant cell lines studied. Lowering of GSH levels to less than 10% of control values potentiated the in vitro cytotoxicity of melphalan and cisplatin. Furthermore, BSO was also shown to potentiate the cytotoxicity of melphalan in a nude mouse model system of ovarian cancer in which mice die of disseminated intra-abdominal carcinomatosis. The BSO administered in the drinking water decreased GSH levels by 96%. A single melphalan treatment of 5 mg/kg following GSH depletion produced a 72% increase in median survival time compared with treatment with melphalan alone. In addition, depletion of GSH levels in cell lines with acquired resistance to melphalan led to a marked sensitization of these cells to irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

Antineoplastic Agents↗
PubMed1987

Biologic therapy for the treatment of malignant common epithelial tumors of the ovary.

There are a number of strategies to the treatment of gynecologic tumors that involve the use of biologic agents. Biologic agents may be immunologic in nature and act directly on the tumor or to boost an immune response to the tumor, or they may be nonimmune in nature and directly affect the tumor or a physiologic process on which the tumor depends. Although the potential for these agents in the treatment of all gynecologic tumors is great, most of the data to date have been generated in ovarian cancer. Clinical trials of alpha interferon administered intraperitoneally in patients with small volume ovarian cancer have revealed high response rates with acceptable toxicity. The mechanism of the antitumor effect (i.e., direct tumor killing vs. indirect boosting host immune response) has not yet been determined. Clinical trials of intraperitoneal lymphokine-activated killer (LAK) cells plus recombinant interleukin-2 have also been started based upon significant antitumor effects noted in xenogeneic systems. The finding that the peritoneal fluid of interferon-treated patients is rich with monocytes and macrophages has led to the development of a clinical trial using intraperitoneal human monocytes activated with recombinant gamma interferon along with gamma interferon. Monoclonal antibodies have already made a significant impact on the diagnosis of ovarian cancer, and are being brought to clinical trial as therapeutic agents. The OC-125 antigen is shed by ovarian tumor cells and its elevation in the serum of patients with undiagnosed pelvic masses is highly predictive for ovarian neoplasia. Furthermore, its persistence in the serum of patients with ovarian cancer during chemotherapy is nearly always associated with persistent disease. A number of monoclonal antibodies specific for ovarian cancer have been developed. Radiolabeled antibodies administered intralymphatically and intraperitoneally may be able to demonstrate the presence of tumor reliably enough to save some patients from second-look laparotomy. In addition, clinical trials are underway using immunotoxins, antitumor antibodies conjugated to potent plant or bacterial toxins that are effective at killing cells with amazing efficiency. Antibodies conjugated to alpha-emitting radioisotopes like astatine-211 or to radioisotopes emitting gamma or beta waves or Auger electrons are candidates for clinical trial. There is also some interest in attempting to improve the therapeutic index by using antibodies conjugated to cytotoxic chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)

Antibodies, Monoclonal↗