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M P Murphy

Publications and source records attributed to M P Murphy.

At least 109 records · Page 6Linked to original sources
PubMed1989

Characterization of cisplatin-resistant COLO 316 human ovarian carcinoma cells.

The biochemical changes responsible for acquired resistance to cisplatin (DDP) are not fully understood. We have developed DDP-resistant sublines of COLO 316 human ovarian carcinoma cells in vitro and characterized a number of biochemical features of these cells. Following selection with either continuous 50 nM DDP (COLO/DDP50 cells) or intermittent 1 microM DDP (COLO/B, COLO/C, or COLO/D cells) the onset of resistance was rapid. The resistance of the COLO/B cells gradually fell from 14-fold to 5-fold over 6 months in drug-free media. Both selection procedures produced cells exhibiting broad cross-resistance to other platinum analogs, natural products and alkylating agents. There was no significant change in the growth rate (doubling time = 36 h, cloning efficiency (28%), protein content (0.55 mg/10(6) cells), or morphology of these cells. Cell cycle distributions of log-phase cells were similar (60% G0/G1, 35% S, 5% G2/M) as determined by flow cytometry. Glutathione (GSH) levels, while not elevated in COLO-B cells at low levels of resistance (2-3-fold), were 30% elevated at higher levels of resistance (9-fold). However, GSH levels in COLO/DDP50 cells with 13-fold resistance were 2.3-fold elevated. The resistance of both cell types could be partially reversed by extended depletion of GSH with D,L-buthionine-S,R-sulfoximine. COLO/D cells had a 48% decrease in DDP accumulation at 1 h while COLO/DDP50 cells had no change in DDP accumulation. The cross-resistance profiles, GSH biochemistry and DDP accumulation data indicate that acquired DDP-resistance is a complex, multifactorial response in these cells. The specific combination of mechanisms expressed in these cells appears to depend upon the selection procedure.

Cell Line↗
PubMed1988

Membrane-potential-dependent changes in the stoichiometry of charge translocation by the mitochondrial electron transport chain.

The charge/oxygen (q+/O) stoichiometry of mitochondria respiring on succinate was measured under conditions of high membrane potential (delta psi). The technique used was a variation of the steady-state method of Al-Shawi and Brand [(1981) Biochem. J. 200, 539-546]. We show that q+/O was about 2.7 at high values of delta psi (170 mV). As delta psi was lowered from 170 mV to 85 mV with the respiratory inhibitor malonate the q+/O stoichiometry increased to 6.0. A number of artefacts which could have led to an underestimation of the q+/O stoichiometry were eliminated. These included effects of any rapid change in mitochondrial volume, internal pH, activity of the endogenous K+/H+ exchanger or in H+ conductance due to changes in delta psi after the addition of inhibitor. The experiments presented here are the first direct demonstration that the stoichiometry of proton pumping by the mitochondrial respiratory chain changes as delta psi is varied.

Animals↗
PubMed1988

The stoichiometry of charge translocation by cytochrome oxidase and the cytochrome bc1 complex of mitochondria at high membrane potential.

The q+/2e stoichiometries (number of charges translocated per electron pair transferred) of cytochrome oxidase and the cytochrome bc1 complex in rat liver mitochondria were determined at a range of membrane potentials up to 180 mV. The method used was similar to the one used in the preceding paper by us in this journal to determine the q+/O stoichiometry of the mitochondrial electron transport chain from succinate to oxygen. The measured q+/2e stoichiometry of cytochrome oxidase was 3.5 positive charges per O atom reduced at low membrane potential (120 mV) and it decreased to about 1.5 at high membrane potential (180 mV). The measured q+/2e stoichiometry of the cytochrome bc1 complex was between 1 and 1.25 positive charges ejected per electron pair and did not change significantly as delta psi was varied from 85 mV to 157 mV. The sum of the q+/2e stoichiometries of cytochrome oxidase and the cytochrome bc1 complex determined separately was similar to their value determined together for electron transport from succinate to oxygen over the range of membrane potentials studied. The most probable interpretation of these results is that the stoichiometry of the cytochrome bc1 complex is invariant over a range of membrane potentials and that the q+/2e stoichiometry of cytochrome oxidase decreases from 4 at low membrane potential to 2 at high membrane potential.

Animals↗
PubMed1988

Enhanced potentiation of cisplatin cytotoxicity in human ovarian carcinoma cells by prolonged glutathione depletion.

We have determined the effect of extended glutathione (GSH) depletion on cis-diamminedichloroplatinum(II) (DDP) cytotoxicity in parent and DDP-resistant human ovarian carcinoma cells. Cells were exposed to 50 microM buthionine sulfoximine (BSO) for 48 h and exposed to DDP for the last 24 h of this time. This treatment protocol sensitized 2008 cells to DDP. The dose modification factor (DMF) defined as IC50 control cells/IC50 GSH depleted cells was 1.6 +/- 0.5 (N = 9). DDP-resistant cells selected by acute, high dose DDP exposure were also sensitized by this treatment; the DMF in the 3-6-fold resistant 2008/DDP cells was 2.4 +/- 1.2 (N = 9). The sensitization was not significantly greater in the resistant cells than in the parent cells (P greater than 0.05). When the rebound of GSH following BSO exposure was reexamined, the GSH levels were found to rise rapidly following trypsinizing and plating. BSO treatment following DDP exposure had no effect on DDP cytotoxicity in 2008 and 2008/DDP cells. These results indicate that simply depleting GSH prior to DDP exposure is not sufficient for sensitizing these cells to DDP. In contrast to the potentiation of nitrogen mustard cytotoxicity, exposure to GSH depletion must be maintained during DDP treatment for enhancement of DDP cytotoxicity to occur.

Buthionine Sulfoximine↗
PubMed1987

The control of electron flux through cytochrome oxidase.

1. The electron flux through cytochrome oxidase is a linear function of the net thermodynamic force across the complex over a limited range of conditions. 2. Over a wide range of conditions the electron flux is a complicated function of the percentage reduction of the cytochrome c pool and of delta psi (at low values of delta pH). 3. We have estimated the elasticities of electron flux through cytochrome oxidase to delta Eh of the redox reaction catalysed by cytochrome oxidase (or to cyt c2+/cyt c3+) and to delta psi. The elasticities varied depending on the values of delta psi and of the percentage reduction of the cytochrome c pool. 4. At intermediate rates (which may correspond to those in vivo) the electron flux through cytochrome oxidase is controlled to about the same extent by delta psi and by delta Eh.

Animals↗
PubMed1987

Metallothionein-mediated cisplatin resistance in human ovarian carcinoma cells.

We have determined the ability of two human ovarian carcinoma cells to over-express metallothioneins (MTs) and the subsequent effect this elevation has on DDP cytotoxicity. Cells of 2008 and COLO 316 human ovarian carcinomas that were resistant to CdCl2 were obtained by stepwise selection and chronic culture in CdCl2 and ZnCl2. The 2008/MT cells were 3.2-fold resistant to CdCl2 and 4.1-fold resistant to DDP; they had 23-fold elevated MTs. The COLO/MT cells were 1.2-fold resistant to CdCl2 and 3.3-fold resistant to DDP, and they had 9-fold elevated MTs. Glutathione (GSH) was also elevated in the Cd-resistant sublines. However, four times more intracellular thiols were contributed by the MTs than by the GSH. 2008 and 2008/MT cells were examined in more detail to elucidate the mechanism of DDP resistance. Depletion of GSH with D,L-buthionine-S,R-sulfoximine (BSO) had no effect on the sensitivity of these cells to either CdCl2 or DDP. Uptake of [195m Pt]DDP in 2008 and 2008/MT cells was identical. Fractionation of the cytosol from [195mPt]DDP-exposed cells on Sephadex G-75 revealed that 17% of the total cellular Pt in 2008/MT cells was associated with the MT fraction, as against 4% in the parent 2008 cells. This increase corresponded to a concomitant loss of Pt from the particulate fraction. Fractionation of 2008 cells selected with DDP (2008/DDP cells) indicated that elevated MTs did not contribute to the DDP resistance of these cells. Only 2% of the total cellular Pt was in the MT fraction in 2008/DDP cells. These results showed that elevation of MTs may be one mechanism of DDP resistance in ovarian carcinoma; however, in vitro selection with DDP does not trigger this mechanism.

Cadmium↗
PubMed1987

Glutathione depletion reverses cisplatin resistance in murine L1210 leukemia cells.

Little is understood about the mechanism of acquired resistance to the widely used antineoplastic drug, cisplatin. The cisplatin-resistant murine leukemia L1210 cell line L1210/PAM has an elevated cellular glutathione content, as compared to its sensitive parent cell line, L1210/*. Exposure to D,L-buthionine-S,R-sulfoximine reduced L1210/PAM cells' glutathione content to nearly that of L1210/* cells and abrogated the resistance to cisplatin.

Animals↗
PubMed1987

Gene therapy for thioguanine-resistant human leukemia.

The feasibility of using retroviral gene therapy to overcome drug resistance was assessed by determining the efficiency by which a retrovirus containing the human HGPRT gene could sensitize hypoxanthine-guanine phosphoribosyltransferase (HGPRT) negative human promyelocytic leukemia cells to 6-thioguanine. A single three-hour exposure at a virus to cell ratio of 6 X 2:1 restored sensitivity to 70(+/- 18)% of the clonogenic cells. The efficacy varied as a function of virus concentration and duration of viral exposure; the time allowed for integration and expression between one and five days post-infection had little effect. Cells successfully sensitized contained a proviral insert and expressed HGPRT activity that ranged from 1 to 92% of that in the wild-type cells. The mutation rate of the inserted gene varied from the same as that of the endogenous HGPRT gene to 200-fold greater in different clones. Failure of sensitization following viral exposure was associated with absence of an integrated provirus, and clonogenic cells failing to be sensitized by one virus exposure were sensitized with approximately the same efficiency by a second viral exposure. These results demonstrate the feasibility of transferring a drug sensitivity gene to a human leukemia cell line.

Cell Line↗
PubMed1986

Differential sensitization of human ovarian carcinoma and mouse L1210 cells to cisplatin and melphalan by glutathione depletion.

We have investigated the role of glutathione in determining the macromolecular binding and cytotoxicity of cisplatin (DDP) and melphalan (LPAM) in human ovarian carcinoma cells and DDP-resistant L1210 mouse leukemia cells. Glutathione reacted avidly with DDP in normal saline with a bimolecular rate constant of 16.2 M-1 hr-1. Glutathione had no effect on the rate of hydrolysis of LPAM, consistent with the SN1-like reaction mechanism of LPAM. Glutathione protected calf thymus DNA and bovine serum albumin from DDP platination and LPAM alkylation. Glutathione also protected nuclei isolated from human ovarian carcinoma cells from DDP platination. The importance of intracellular glutathione in determining the cytotoxicity of DDP and LPAM was assessed by depletion of glutathione with buthionine sulfoximine in three cell types. Exposure to 0.5 mM buthionine sulfoximine for 20-28 hr depleted glutathione to levels that were 10-20% of control levels. COLO 316 and 2008 human ovarian carcinoma cells, and ZCR9 mouse leukemia cells were all sensitized to LPAM cytotoxicity by this level of glutathione depletion. The dose modification factors, defined as the IC50 control cells/IC50 depleted cells, were: 2.6 +/- 0.5 for COLO 316 cells, 1.6 +/- 0.1 for 2008 cells, and 2.1 +/- 1.1 for ZCR9 cells. In contrast, glutathione depletion had a minimal effect on DDP cytotoxicity in these cells with dose modification factors of: 1.2 +/- 0.2 for COLO 316 cells, 0.8 +/- 0.3 for 2008 cells, and 1.1 +/- 0.1 for ZCR9 cells. The differential potentiation of DDP and LPAM cytotoxicity by glutathione depletion in these cells, despite the similar protection that glutathione affords macromolecules from drug binding, suggests that there are fundamental differences in the intracellular interaction of these electrophilic drugs with glutathione.

Animals↗
PubMed1985

Mitochondrial enzyme retention by irreversibly damaged rectangular isolated adult rat heart myocytes.

A one hour hypoxic incubation causes the release of a small but significant amount of cytosolic lactic dehydrogenase from glucose-deprived isolated adult rat heart myocytes. However, enzymes associated with the mitochondria are not liberated, and there is no increase in the number of hypercontracted cells. These observations led Piper et al. (Life Sciences 35, 127-134 [1984]) to conclude that reversibly injured myocytes can release cytosolic proteins. This conclusion was based on the supposition that irreversibly hypoxic injury must cause mitochondrial enzyme efflux and hypercontracture. The present study establishes that this supposition is invalid.

Adenosine Triphosphate↗
PubMed1985

Effects of ionic strength and sulfhydryl reagents on the binding of creatine phosphokinase to heart mitochondrial inner membranes.

The concept that creatine phosphokinase is bound to the outer surface of the heart mitochondrial inner membrane originated from observations that the enzyme is retained by water-swollen heart mitochondria and by digitonin-treated heart mitochondria suspended in isotonic sucrose. The present study establishes that digitonin-treated mitochondria release creatine phosphokinase in isotonic KCl, and other investigators have reported an identical response for the water-swollen organelles. These observations suggest that mitochondrial creatine phosphokinase is not bound to the outer surface of the inner membrane at a site adjacent to the adenine nucleotide translocase under physiologic conditions.

Adenylate Kinase↗
PubMed1985

High-dose cisplatin with sodium thiosulfate protection.

Nephrotoxicity frequently limits the dose of cisplatin to less than 120 mg/m2 per injection. Sodium thiosulfate is a neutralizing agent for cisplatin that protects against renal damage. To determine whether injection of thiosulfate would permit larger doses of cisplatin to be administered, a fixed 9.9-g/m2 dose of thiosulfate was given intravenously over three hours concurrently with escalating doses of cisplatin. Cisplatin was administered over the last two hours of the thiosulfate infusion. Using this technique, it was possible to escalate the cisplatin dose to 225 mg/m2 before dose-limiting toxicities were encountered. Comparison of cisplatin pharmacokinetics in patients treated with 202.5 mg/m2 plus thiosulfate to those in patients treated with 100 mg/m2 without thiosulfate indicated that there were no changes in the elimination rate constant, volume of distribution, or total body clearance of cisplatin. The total drug exposure for the plasma was approximately twofold at the higher cisplatin dose. This study demonstrates that concurrent administration of thiosulfate permits at least a twofold increase in dose and total exposure to cisplatin.

Adolescent↗
PubMed1985

Pharmacokinetics of 5-fluorouracil during hyperthermic pelvic isolation-perfusion.

The pharmacokinetics of 5-fluorouracil (5-FU) injected into a surgically isolated pelvic circuit during hyperthermic perfusion was studied in five patients with local recurrence of anorectal cancer. 5-FU doses ranged from 11 to 23 mg/kg. The geometric mean ratio of peak plasma 5-FU in the isolated to systemic circuits was 10, the ratio at the end of the 45-minute perfusion was 12.5. The mean half-life of 5-FU in the isolated circuit was 18.5 minutes. Total drug exposure for the isolated circuit was 7.8-fold greater than for the systemic compartment. These results demonstrate a large pharmacologic advantage for the use of the isolation-perfusion technique.

Adenocarcinoma↗
PubMed1985

Differential potentiation of alkylating and platinating agent cytotoxicity in human ovarian carcinoma cells by glutathione depletion.

We have determined the effect of glutathione (GSH) depletion on the cytotoxicity of three nitrogen mustards, six platinum complexes, and mitomycin C in a human ovarian carcinoma cell line. GSH levels in COLO 316 cells were depleted by exposure of cell monolayers to 0.5 mM D,L-buthionine-S,R-sulfoximine. GSH depletion significantly potentiated the cytotoxicity of L-phenylalanine mustard, chlorambucil, and mechlorethamine as determined by clonogenic assay on plastic plates. The dose modification factors were 2.6, 2.6, and 1.9, respectively. The same level of GSH depletion had a minimal effect on the cytotoxicity of cis-diamminedichloroplatinum(II) (cis-DDP), carboplatin, dichloro(ethylenediamine)platinum(II), 1,2-diaminocyclohexylplatinum(II) malonate, and iproplatin. The dose modification factors of GSH depletion for these drugs were 1.4 or less. trans-Diamminedichloroplatinum(II) was, however, markedly potentiated by GSH depletion with a dose modification factor of 2.7. Mitomycin C was minimally potentiated by GSH depletion. We have also generated cis-DDP-resistant cells from COLO 316 and 2008 human ovarian carcinoma cells by in vitro selection with cis-DDP. These cis-DDP-resistant cells had identical levels of GSH as the parental cells. GSH depletion sensitized these cells only to the same degree as the parental cells and did not reverse the resistant phenotype. Our results indicate that intracellular GSH levels are not an important determinant of the cytotoxicity of cis-platinum(II) or cis-platinum(IV) complexes in COLO 316 and 2008 cells. In addition, altered GSH metabolism does not appear to be a component of the cis-DDP-resistant phenotype in these cells.

Alkylating Agents↗