Biomedical subjects

E Mayhew

Publications and source records attributed to E Mayhew.

At least 73 records · Page 4Linked to original sources

PubMed1986

Immune rejection of metastases arising from intraocular tumors in mice.

The role of the immune response in the elimination of spontaneous metastases arising from intraocular tumors was examined in a syngeneic intraocular murine tumor model. P91 mastocytoma (DBA/2 origin) expresses strong tumor-specific transplantation antigens and grows transiently in the eyes of syngeneic hosts before undergoing spontaneous rejection. An organ culture technique was used to detect spontaneous metastases in the lungs, spleens, brains, and thymuses of intraocular tumor-bearing mice. Metastatic tumor cells were detected in all organs of immunodeficient mice (i.e., athymic, nude, or x-irradiated DBA/2 mice) within 14 days of intraocular transplantation, and grew progressively thereafter. By contrast, metastatic tumors were rejected in 100% of the immunocompetent DBA/2 mice examined on day 15. Timed enucleation experiments demonstrated that the immune rejection of disseminated tumor cells occurred within 24-48 hr of their arrival at the various organs. The immune rejection of spontaneous metastases could be adoptively transferred to immunodeficient tumor-bearing mice using spleen cells, but not immune serum, from intraocular tumor-bearing immunocompetent donors. Selective cell depletion experiments revealed that the immune spleen cell effecting immunity was an Lyt 1+, 2+ T cell. The results indicate that the immune rejection of the spontaneous metastases arising from primary intraocular tumors is a T cell-dependent, radiosensitive process that rapidly eliminates metastases within the lungs, brain, thymus, and the spleen of the immunocompetent host.

Animals↗

PubMed1986

Approaches to overcome in vivo anti-cancer drug resistance.

Therapeutic efficacy of anticancer drugs against malignant diseases is limited because of the selection and regrowth of drug resistant cells. This problem is compounded by the development of cross-resistance to other useful chemotherapeutic agents which severely limits treatment alternatives. Development of approaches to overcome and/or circumvent drug resistance will depend on the precise understanding of the mechanism(s) of resistance not only at the target tumor cell level (in vitro) but also in vivo. The data on L1210 sensitive to araC transplanted s.c. demonstrated that although target cells are highly sensitive to araC, the lack of in vivo response of solid L1210 cells (s.c.) is primarily due to limited drug delivery to the target. Approaches that would modify these processes should improve on the therapeutic selectivity of this agent. In contrast, in cells where the mechanism of resistance is deletion of a key anabolic enzyme (e.g. CdR kinase), these cells are collaterally sensitive in vitro and in vivo to DAUR. This type of resistance, however, could not be overcome by liposome encapsulation of araC or araCTP. With respect to AM resistance, the concentration of VRP for in vitro reversal of resistance of P-388/AM was difficult to achieve in vivo without significant host toxicity. Continuous infusion of VRP, however, demonstrated that at the maximally tolerated doses of VRP it was not possible to achieve any significant therapeutic effects against P-388/AM. The use of liposomes or modulation by VRP does not appear to be a fruitful approach in overcoming AM resistance, especially in cells which possess a high degree of resistance. Metabolic modulation of FU by dLCF appears to be a promising area of investigation and deserves further investigation concerning quantitation of the intracellular pools of folate and ways to modulate them.

3-Deazauridine↗

PubMed1986

Drug delivery to tumors. A problem requiring microscopic resolution.

One factor in the effectiveness of chemotherapy for both primary tumors and their metastases is the delivery of the drug to the cancer cells within the tumor. The uptake of Adriamycin, assayed in 8 cu mm samples from primary tumors, lung metastases and "normal" lung tissue (unaffected by the metastases) in mice, showed wide variations between different tumors, between primary tumors and their metastases and between different metastases. The heterogeneity of uptake was greater in tumors than in normal lung tissues, whose uptake was in the range of the metastases, i.e., higher than in the tumor itself. Studies of Adriamycin uptake within individual tumors showed a wide range of values; this variability was statistically significantly increased as compared with the variation in normal lung tissues. Since the lower levels found in some tumor areas were below the cytotoxic level, those areas may represent "drug-resistant" cells from which tumor recurrence could ensue. In a three-dimensional reconstruction, the areas of lowest uptake were found at both peripheral and internal regions, a finding not in accord with the concentric zonal concentration expected on the basis of considerations of tumor vascularity. It is suggested that the problem of drug delivery to tumors needs further study at the microscopic level and that automated microscopic image analysis and three-dimensional reconstructions of serial sections could greatly extend the macroscopic findings of this study.

Animals↗

PubMed1985

An approach to the therapy of metastases from cancer of the upper rectum: a working hypothesis.

Previously reported analyses of autopsy data gathered from patients dying from the sequelae of adenocarcinomas of the upper rectum revealed a step-wise sequence in the development of distant metastases. First, dissemination via the portal vein led to secondary hepatic metastases. Cancer cells from these liver metastases (not the primary cancer) disseminated via the inferior vena cava to generate tertiary pulmonary metastases. Cancer cells from the lung metastases (not the primary or secondary cancers) then disseminated via the arterial route to give rise to metastases in other organs. We propose a protocol for the treatment of patients with upper rectal carcinomas, based on the expectation that, at different times after diagnosis, some patients will have no distant metastases, metastases in the liver only, or in the liver and lungs only. The protocol for therapy is based on currently available liposome technology, by means of which high doses of drugs can be targeted to the liver and lungs containing the metastases, yet distinct from the metastases. It is argued that selective local delivery of this type would increase the dose of cytotoxic agent delivered, thereby increasing the chances of overcoming the relative drug-resistance of the metastatic cancer cells and, at the same time, reduce the risk of nonspecific toxicity. Liver and lung-selective liposomes could, when necessary, be delivered at the same time, in the same systemic venous infusion.

Adenocarcinoma↗

PubMed1985

The use of liposomes as carriers of therapeutic agents.

Adriamycin (Doxorubicin) is an important chemotherapeutic agent, but is limited in its clinical usefulness by dose-related cardiomyopathy. Attempts are being made to reduce this toxicity while retaining anti-tumor activity. These include development of chemically modified anthracycline derivatives and coupling of adriamycin to or into macromolecular carriers. We and several other laboratories have shown that entrapment of adriamycin in liposomes (phospholipid vesicles) can reduce toxicity while retaining or, in some cases, enhancing anti-tumor activity. Here we report further results of experiments in mice on toxicity reduction and anti-tumor activity. Approximate maximum tolerated doses (MTD) of adriamycin were determined from normal mouse survival at 240 days after initial treatment. I.V. bolus injection of liposomal-adriamycin was superior to i.v. bolus or i.v. infusion of free drug after a single injection, 5 daily injections or 5 biweekly (every 2 weeks) injections. Using L1210 tumor as a model for systemic leukemia, liposomal adriamycin was as effective as free adriamycin at equal doses, however liposomal-adriamycin was more effective at MTD. M5076 tumor was used as a limited model for comparisons of the effects of liposomal-adriamycin on "primary" and "metastatic" disease. The results showed that whereas free and liposomal adriamycin were without significant effect on "primary", subcutaneous tumor, that liposomal adriamycin, but not free adriamycin had very strong effects on liver "metastases". The results suggest that liposomally administered drugs, including adriamycin, may have utility for treatment of certain types of cancer and for metastases in organs where liposomes accumulate. Where improved anti-tumor activity is coupled with toxicity reduction and simplicity of administration, liposomal administration could be a useful method of drug delivery.

Animals↗

PubMed1984

Characterization of liposomes prepared using a microemulsifier.

A new type of device can prepare liposomes continuously, in large quantities and with excellent aqueous space capture efficiency. At initial lipid concentration of 300 mumol/ml these liposomes capture approx. 75% of cytosine arabinoside used as an aqueous space marker. Liposome size can be reduced by increasing the number of times the preparations are recycled through the microemulsifier. Liposomes less than 0.1 micron in diameter, as shown by electron microscopy, can be made easily. Liposomes prepared at 300 mumol/ml, composed of phosphatidylglycerol/phosphatidylcholine/cholesterol in a 0.1:0.4:0.5 molar ratio leaked less than 1% of entrapped cytosine arabinoside (Ara-C) at 4 degrees C, and less than 10% Ara-C at 37 degrees C plus serum, over a 48 h period. These liposomes could be useful for a number of applications including diagnostics, therapeutics and model membrane studies.

Biochemistry↗

PubMed1984

Quantitation of tumorigenic disseminating and arrested cancer cells.

The numbers of potentially tumorigenic cancer cells released into the circulation and secondarily arrested in the lungs of mice bearing B16F10 melanomas or Lewis lung carcinomas were systematically quantified throughout i.m. tumour growth using a bioassay procedure capable of detecting as few as 10 to 100 tumorigenic cells in the circulation or lungs. Viable disseminating cancer cells were detectable within 4 days of i.m. tumour growth and reached 10(6) per 0.5 ml of blood in carcinoma-bearers and 2 X 10(4) per 0.5 ml in melanoma-bearers; 98% of mice with circulating cancer cells had potentially tumorigenic cells in their lungs, even in the absence of overt metastases. The numbers of cancer cells present in the circulation and lungs were related to the growth rate of the i.m. lesion, more cells being released from faster-growing tumours. The numbers of tumorigenic carcinoma cells were compared with the total numbers of cells released into the circulation as quantitated by direct counting procedures, and it was found that the vast majority of these circulating cells were potentially tumorigenic. These studies provide quantitative information about cancer cell input into the metastatic process. Also, the bioassay procedure provides a useful experimental model for the development of regimens for therapy of metastases since it is a sensitive method of monitoring not only the size of disseminated populations of cancer cells but also their clinically relevant property namely, their tumorigenic potential.

Animals↗

PubMed1984

Selective therapy of metastasis. I. Quantitation of tumorigenic circulating and covert cancer cells disseminated from metastatic and nonmetastatic tumors.

To determine the potential efficacy of therapeutic agents and different drug delivery systems against metastases, it is necessary to develop methodologies that can assay the effects of treatment at each step of the metastatic process. This report presents quantitative studies on the total numbers and potential tumorigenicity of cancer cells in the circulation and also secondarily arrested in the lungs of mice following their spontaneous dissemination from methylcholanthrene-induced fibrosarcomas. MC1 fibrosarcomas rarely metastasize but MC2 fibrosarcomas frequently generate pulmonary metastases and it was found, using a combination of direct cancer cell isolation techniques and quantitative bioassays, that MC2 tumors released cancer cells into the bloodstream earlier and with greater frequency than MC1 fibrosarcomas. Also, although similar doses of radiolabeled MC1 and MC2 cells injected intravenously were cleared equally effectively following their arrest in the lung microvasculature, those MC2 cells that survived clearance processes had 10-fold greater lung colonization potential than MC1 cells. Therefore, these experimental systems can be used critically to evaluate the effects of therapeutic agents at individual stages of metastasis as an alternative to measuring their effects solely on solid tumors or the final incidence of metastases, which represents the net result of a number of sequential, complex interactions between cancer cells and the host.

Animals↗

PubMed1983

Alteration of liposome disposition in vivo by bilayer situated carbohydrates.

The inclusion of either lactosylcerebroside or dimannosyldiglyceride at a 9% molar ratio in small unilamellar vesicles increased by two-three fold the fraction of the I.V. dose that appeared in mouse liver. For lactosylcerebroside containing liposomes, the half-time for clearance from plasma was 1.2 hours compared to 5.5 hours for liposomes of similar size, charge, and composition but lacking the glycolipid. Uptake of the lactosylcerebroside containing liposomes by the liver could be significantly reduced but not eliminated by the simultaneous injection of asialoorosomucid.

Animals↗

PubMed1983

Inhibition of liver metastases of M 5076 tumor by liposome-entrapped adriamycin.

The toxicity and therapeutic efficacy of free adriamycin (AM) and AM entrapped in standardized liposomes (AM-MLV) were evaluated in normal mice and in mice bearing M 5076 murine tumor, which metastasizes to the liver after i.v. and s.c. transplants of tumor cell suspensions. Acute and chronic toxicity to AM could be reduced by drug encapsulation in liposomes. The data indicated that at approximately equitoxic doses of free AM (10 mg/kg) and AM-MLV (greater than 20 mg/kg), the increase in survival times of mice transplanted i.v. with tumor cells were 25% and 100%, respectively. Furthermore, only in the AM-MLV-treated mice were long-term survivors observed. In contrast AM-MLV were equally effective as free AM in mice transplanted s.c. with tumor cell suspensions. AM-MLV, however, were more effective than free AM against liver metastases in mice bearing s.c. tumor, indicating differential antitumor activities against the same tumor type growing at different locations in the same animals.

Animals↗

PubMed1983

Enhanced natural killer cell activity in experimental murine encephalitozoonosis.

Spleen cells from mice infected with the protozoan parasite Encephalitozoon cuniculi demonstrated enhanced in vitro cytolysis of YAC-1 lymphoma cells. Selective cell depletion experiments showed that the dominant cell population mediating cytolysis of YAC-1 tumor cells expressed the characteristic phenotype of murine natural killer (NK) cells because (i) pretreatment of spleen cells with anti-asialo GM 1 antiserum plus complement abolished the cytotoxic activity; (ii) augmented cytolysis was found in athymic nude mice; (iii) pretreatment of spleen cells with anti-Thy 1.2 plus complement did not affect the level of cytolysis; and (iv) nylon wool removal of adherent cells did not reduce the augmented cytolysis. The augmented cytolysis peaked 7 days after infection, gradually diminished, and finally returned to control levels by 21 days postinfection. The parasite-induced augmentation of NK cell activity was dose-dependent: inoculation of 10(7) parasites gave maximum enhancement, whereas 10(5) or 10(4) parasites had an insignificant effect on spontaneous NK cell cytolysis. The augmented NK cell cytotoxicity was dependent upon viable parasites; inoculation of killed parasites failed to stimulate a significant increase in spontaneous cytolysis. An active infectious process was an important component of this process. The peak of NK activity in euthymic mice was closely correlated with the active stage of infection, and reduction of NK cell activity coincided with recovery from infection. By contrast, athymic nude mice were unable to control E. cuniculi infections yet maintained persistently elevated NK responses. The present data, along with previous reports, indicate that infection with E. cuniculi evokes transient modulation of host immune functions.

Animals↗

PubMed1982

Reversible depression of the reticuloendothelial system by liposomes.

The effect of various doses of different types (reverse phase evaporation vesicles and small unilamellar vesicles) of intravenously injected liposomes on reticuloendothelial activity, as measured by the blood clearance rate of intravenously injected carbon, was investigated. Also the effect of pretreatment with reverse phase evaporation vesicles on blood clearance and tissue distribution of a second dose of similar vesicles was determined. For all concentrations used reverse phase evaporation vesicles caused a reduction in reticuloendothelial activity at least up to 4 h after injection. 24 h after administration the rate of carbon clearance returned to the control level. On the contrary small unilamellar vesicles did not block reticuloendothelial activity. Pretreatment with reverse phase evaporation vesicles (250 mumol/kg) caused an increased blood level and a decreased hepatic uptake of a second dose of the vesicles, injected 1 h after the first dose. This seems to be due to a depression of reticuloendothelial activity and not to a depletion of opsonins. Pretreatment with small unilamellar vesicles (250 mumol/kg) had no significant influence on the tissue distribution of a second dose of vesicles. Our results clearly indicate that reverse phase evaporation vesicles cause a reversible depression of reticuloendothelial activity and this depression seems to be induced by a saturation of reticuloendothelial cells with liposomes.

Animals↗

PubMed1982

Characterization, toxicity and therapeutic efficacy of adriamycin encapsulated in liposomes.

The inherent toxicities of drug-free liposomes were compared. Positively charged liposomes were more toxic in vitro (chick heart cells) and in vivo (5-fold reduction in LD50 in mice) than neutral or negatively charged liposomes. Based on these findings, adriamycin was encapsulated in negatively charged liposomes (PG: PC: Chol--1:4:5), sequentially extruded through polycarbonate membranes (to 0.2 micrometer pore size) and purified by exhaustive dialysis. This preparation had a mean vesicle diameter of 0.24 micrometer and was stable in serum (24 hr drug retention of 85%). As compared with free drug, liposome-encapsulated adriamycin was less toxic in vitro to chick heart cells. In mice, adriamycin displayed short- (4-14 day) and long- (45-70 day) term toxicity. Encapsulating adriamycin increased both short- (20-50 mg/kg) and long- (10-15 mg/kg to 25-30 mg/kg) term LD50 levels. As compared with free drug, administering encapsulated adriamycin in vivo reduced the incidence of cardiac histopathologic lesions at 20 and 40 mg/kg. Compared in vivo, plasma levels of liposome-encapsulated adriamycin were 2/3-fold higher than free drug up to 24 hr post drug administration. Cardiac uptake of adriamycin was reduced 2-fold (conc x time value for 48 h) following encapsulated drug administration. Encapsulating adriamycin in liposomes did not alter its therapeutic effect against L1210 leukemic cells in vivo.

Animals↗

PubMed1982

Metastatic inefficiency in mice bearing B16 melanomas.

When injected i.v. into mice, the F10 subline of B16 melanoma cells produced significantly more lung tumours over a 3-week period than cells of the F101.r-6 subline. However, in animals bearing intramuscular tumours produced by these sublines, the high pulmonary-colonization potential of the F10 cells was not realized, and no significant differences in natural pulmonary metastasis formation were observed in animals with untreated primary cancers, even when they progressed to the moribund state. Massage of i.m. tumours derived from the two sublines produced no change in metastasis and no changes in the numbers of cancer cells in the blood detectable by bioassay. In contrast, massage increased metastasis from tumours derived from an invasive BL6 subline and B16 wild-type cells and, in the case of the wild-type, the numbers of circulating cancer cells. In vitro experiments show that blood cells from non-tumour-bearing animals are toxic to both sublines; but less to F10 than to F101.r-6. In addition, after i.v. injection of radiolabelled cells, more of the F10 subline were retained in the lungs of recipients than the F101.r-6. In spite of these apparent metastatic advantages of the F10 subline following intravasation, the incidence of natural metastases from i.m. F10 and F101.r-6 tumours was similar, suggesting that substantially fewer F10 than F101.r-6 cells gained access to the circulation. Thus, the higher colonization potential of the F10 cells was not matched by its intravasation potential, since metastatic efficiency is determined by the least efficient step in the metastatic process.

Animals↗

PubMed1982

Effects of partially thiolated polycytidylic acid and liposomes on in vitro colony-forming cells of leukemic mice.

Partially thiolated polycytidylic acid (MPC), an antileukemic agent, when administered to leukemic RF/UN mice inhibited the clonogenicity of bone marrow progenitor cells in a time- and dose-dependent manner. The effect of a single dose of MPC disappeared within 40 hr due to the rapid degradation of this compound in mice. When MPC was encapsulated in liposomes before injection, its activity at 19 hr after inoculation was similar to that of free MPC. The inhibitory effect of this liposome-MPC complex, however, persisted for at least 40 hr, indicating that the MPC was protected from hydrolysis by the nucleases present in blood. Drug-free liposomes increased the number of clonogenic progenitor cells, whereas a mixture of plain liposomes and MPC decreased the number of clonogenic cells to a greater extent than did MPC alone or MPC within liposomes. A possible explantation for these observations is that the liposomes per se altered the clearance function of the reticuloendothelial system and completed with MPC for uptake by the reticuloendothelial system cells, thereby resulting in increased plasma levels of MPC which in turn resulted in greater killing of the target cells.

Animals↗

PubMed1982

Distribution and metabolism of lipsome-encapsulated and free 1-beta-D-arabinofuranosylcytosine (Ara-C) in dog and mouse tissues.

The effect of liposome encapsulation of the metabolic activation (phosphorylation) and degradation (deamination) of arabinofuranosylcytosine (Ara-C) in liver and spleen of dogs and mice was investigated. Ara-C in free or liposome-encapsulated form was administered i.v. to dogs and DBA2/CR mice bearing leukemia L1210. At various times after injection the concentration of Ara-C and Ara-C metabolites in the blood, liver and spleen was measured. It was shown that liposome encapsulation results in an increased Ara-C/arabinofuranosyluracil ratio in the liver and spleen of dogs and leukemic mice and that encapsulated Ara-C generates a sustained level of Ara-C triphosphate in the liver and spleen of leukemic mice. These results clearly indicate that 1) encapsulated Ara-C is protected against deamination in the liver, 2) encapsulated Ara-C is slowly released from liposomes in liver and spleen and 3) that liposomes may act as a local depot for Ara-C in these tissues.

Animals↗

PubMed1981

Interactions of La2+ with phosphatidylserine vesicles: binding, phase transition, leakage, 31P-NMR and fusion.

The interaction of La2+ with phosphatidylserine vesicles is studied by differential scanning calorimetry, 140La binding, 31P-NMR chemical shifts and relaxation rates, carboxyfluorescein and [14C]sucrose release, X-ray diffraction and freeze-fracture electron microscopy. In the presence of La3+ concentrations above 1 mM and an incubation temperature of 38 degrees C, i.e., at the phase transition temperature of the complex La/phosphatidylserine, the binding ratio of La/lipid exceeds a 1/3 ratio, reaching saturation at a 1/2 ratio. Analysis, employing a modified Gouy-Chapman equation, indicates a significant increase in the intrinsic binding constant of La/phosphatidylserine when the La3+ concentrations exceeds the threshold concentration for leakage. The analysis illustrates that at the molecular level the binding of La3+ can be comparable to or even weaker than that of Ca2+, but that even when present at smaller concentrations La3+ competes with and partially displaces Ca2+ from membranes or other negatively charged surfaces. The results suggest that the sequence La3+ greater than Ca2+ greater than Mg2+ reflects both the binding strength of these cations to phosphatidylserine as well as their ability to induce leakage, enhancement of 31P spin-lattice relaxation rates, fusion and other structural changes. The leakage, fusion, and other structural changes are more pronounced at the phase transition temperature of the La/lipid complex.

Electron Spin Resonance Spectroscopy↗

PubMed1981

Cytochalasin B binding to Ehrlich ascites tumor cells and its relationship to glucose carrier.

Cultured Ehrlich ascites tumor cells equilibrate D-glucose via a carrier mechanism with a Km and V of 14 mM and 3 mu mol/s per ml cells, respectively. Cytochalasin B competitively inhibits this carrier-mediated glycose transport with an inhibition constant (Ki) of approx. 5.10(-7) M. Cytochalasin E does not inhibit this carrier function. With cytochalasin B concentrations up to 1.10(-5) M, the range where the inhibition develops to practical completion, three discrete cytochalasin B binding sites, namely L, M and H, are distinguished. The cytochalasin B binding at L site shows a dissociation constant (Kd) of approx. 1.10(-6) M, represents about 30% of the total cytochalasin B binding of the cell (8.10(6) molecules/cell), is sensitively displaced by cytochalasin E but not by D-glucose, and is located in cytosol. The cytochalasin B binding to M site shows a Kd of 4--6.10(-7) M, represents approx. 60% of the total saturable binding (14.10(6) molecules/cell), is specifically displaced by D-glucose with a displacement constant of 15 mM, but not by L-glucose, and is insensitive to cytochalasin E. The sites are membrane-bound and extractable with Triton X-100 but not by EDTA in alkaline pH. The cytochalasin B binding at H site shows a Kd of 2--6.10(-8) M, represents less than 10% of the total sites (2.10(6) molecules/cell), is not affected by either glucose or cytochalasin E and is of non-cytosol origin. It is concluded that the cytochalasin B binding at M site is responsible for the glucose carrier inhibition by cytochalasin B and the Ehrlich ascites cell is unique among other animal cells in its high content of this site. Approx. 16-fold purification of this site has been achieved.

Animals↗