Showing papers by "Garth Powis published in 1986"

Development of Experimental Models for Meningeal Neoplasia Using Intrathecal Injection of 9L Gliosarcoma and Walker 256 Carcinosarcoma in the Rat

Abstract: Two models for meningeal neoplasia have been developed in rats using intrathecal injection of 9L gliosarcoma and Walker 256 carcinosarcoma cells. Tumor cells were injected in unanesthetized animals through an indwelling catheter inserted at the cisterna magna to the level of the lumbar enlargement of the spinal cord. Survival of rats was dependent on the number of tumor cells injected. Spread of tumor was quantified by histology using a grading scale, and functional and behavioral changes were measured. Rats injected with 10 6 9L gliosarcoma cells showed progressive weight loss, flaccid paralysis, and neurogenic bladder dysfunction and had a median survival of 11 days. The tumor frequently grew as a mass compressing the spinal cord. The 9L gliosarcoma tumor cells markedly invaded the Virchow-Robin spaces but exhibited only minimal invasion of the central nervous system parenchyma. The tumor reached the brain by day 10. Rats injected with 2 × 10 5 Walker 256 carcinosarcoma cells showed progressive weight loss and weakness and had a median survival of 6 days. The tumor grew within the leptomeninges in a discontinuous multifocal fashion and reached the brain by day 4. There was extensive invasion of the central nervous system parenchyma by Walker 256 tumor cells along the Virchow-Robin spaces resulting in hemorrhage and necrosis of grey and white matter. Hot plate and tail flick response times were significantly delayed only in the days immediately preceding death of animals with either 9L or Walker 256 tumor and were not good indicators of tumor progression. Loss of motor coordination and failure of the stepping and placing reflex on the other hand showed good correlation with spread of tumor measured histologically. Control animals injected with 0.9% NaCl or with lethally irradiated tumor cells showed no significant weight loss or functional or behavioral changes. The intrathecal 9L gliosarcoma and Walker 256 carcinosarcoma models show different characteristics of human meningeal carcinomatosis and will be used for studies of experimental chemotherapy with intrathecally administered antitumor drugs.

Anthracycline-induced inhibition of a calcium action potential in differentiated murine neuroblastoma cells

Abstract: The effects of some anthracyclines on a Ca 2+ -dependent action potential have been studied in differentiated murine neuroblastoma cells (N1E-115 clone). The differentiated neuroblastoma cell possesses characteristics of an electrically excitable cell and can generate propagated potential spikes in which Ca 2+ is the inward charge carrier. This was shown by the fact that action potentials recorded from differentiated neuroblastoma cells in the presence of 10 -7 g of tetrodotoxin per ml, which inhibits active Na + channels, had a spike amplitude that depended upon the extracellular Ca 2+ concentration in a manner close to that predicted by the Nernst equation. The peak potential changed 28.9 mV/decade change in extracellular Ca 2+ . Local application to a cell of 10 -8 m doxorubicin produced inhibition of this Ca 2+ -dependent action potential within 5 s of drug application and a maximum inhibition of 13% 60 s after drug application. There was almost complete recovery to the initial spike amplitude value within 10 min after removing drug. The same concentration of doxorubicin also produced complete inhibition, without recovery, of a Ca 2+ -dependent after-discharge which followed the initial action potential in about half the cells studied. Increasing concentrations of doxorubicin produced dose-dependent inhibition of the initial Ca 2+ -dependent action potential. Cells exposed to 10 -5 m doxorubicin showed 88% inhibition of the Ca 2+ -dependent action potential with no recovery even 10 min after removing the drug. Daunomycin, 10 -6 m, produced 90% inhibition of the Ca 2+ -dependent action potential. Daunomycin aglycone (10 -6 m), which lacks antitumor activity, had no significant effect on the Ca 2+ -dependent action potential. The rapid onset of the drug-induced response together with the low concentrations of anthracyclines needed to inhibit voltage-dependent Ca 2+ channels in the neuroblastoma cells suggest a direct effect of anthracyclines on the cell surface membrane. The findings are discussed in light of the possible role of Ca 2+ in cancer cells.

Disposition of tricyclic nucleoside-5'-monophosphate in blood and plasma of patients during phase I and II clinical trials.

Abstract: Tricyclic nucleoside-5'-monophosphate (TCN-P) and its dephosphorylated metabolite tricyclic nucleoside (TCN) have been measured in the blood and plasma of patients receiving TCN-P by rapid iv infusion in a phase I trial at daily doses of 24-55 mg/m2 for 5 days and in patients receiving TCN-P in a phase II trial at a single dose of 250 mg/m2. TCN-P was rapidly accumulated by rbcs and had an initial half-life in blood of 6.1 hours and a terminal half-life of 89.2 hours. Total-body blood clearance of TCN-P was 2.6 ml/minute/m2. The concentration of TCN-P in blood was not related to the dose of TCN-P and did not increase over 5 days' administration in the phase I patients. Plasma contained little detectable TCN-P even 5 minutes after administration. Plasma contained low concentrations of TCN, up to 0.4 microgram/ml, which were maintained over several days. TCN did not accumulate in the plasma with repeated administration of TCN-P in the phase I patients. No other metabolites of TCN-P, apart from TCN, were detected in blood or plasma. No relationship was detected between pharmacokinetics and toxic response of TCN-P in the phase II patients.

Effects of advanced leukemia on hepatic drug-metabolizing activity in the mouse.

Abstract: Mice that had received 106 P388 leukemia cells IV 8 days previously exhibited a decrease in the components of the hepatic microsomal mixed function oxidase, with a 58% decrease in cytochrome P-450, and up to a 60% decrease in hepatic microsomal metabolism of biphenyl. Liver weight was increased by 49% due to infiltration of the liver with leukemic cells. Changes in liver drug-metabolizing activity and liver weight were not seen 6 days after administration of P388 leukemia. There was a small increase in serum liver enzyme but no increase in total serum bilirubin in tumor-bearing mice. In vivo total-body plasma clearance of cyclophosphamide, a drug metabolized by hepatic cytochrome P-450, was decreased to 53 ml/min/kg in mice that had received P388 cells 8 days earlier, as against 97.2 ml/min/kg in control mice. Cytochrome P-450-independent metabolism of [14C]5-fluorouracil, measured by means of [14C]CO2in the breath over 3 h, was decreased to 21% of the dose administered by 8 days after tumor cell administration, compared with 31% of the dose in control mice. P388 leukemia cells growing in the ascitic form in the intraperitoneal cavity of mice did not release an inhibitor of 5-fluorouracil metabolism into the ascitic fluid. Total-body plasma clearance of indocyanine green was decreased to 11 ml/min/kg by 8 days after P388 cell administration, compared with 36 ml/min/kg in control mice. The decrease in indocyanine green clearance might reflect a decrease in hepatic blood flow in the tumor-bearing mice. A possible explanation for the decrease in hepatic drug metabolism caused by P388 leukemia is that the hepatocytes are deprived of oxygen and nutrients by the tumor in the liver, coupled with or caused by a physical obstruction of hepatic blood flow.

Metabolic stability of experimental chemotherapeutic agents in hepatocyte: tumor cell co-cultures

Abstract: A U.S. National Cancer Institute screening program for new anticancer drugs, based on the growth of primary human tumor cells in an in vitro soft agar colony formation assay, has resulted in the identification of a number of compounds that have cytotoxic activity against primary human tumor cells in vitro but are inactive in the conventional in vivo murine P388 leukemia animal model pre-screen. To investigate whether metabolic inactivation ov the compounds might be a factor in the lack of in vivo cytotoxicity we have co-cultured rat hepatocytes with A204 rhabdomyosarcoma and murine P388 leukemia cell lines in the soft agarose colony formation assay for 24 h during exposure to the compounds. Twenty compounds with a range of in vitro activities were studied. Thirteen compounds exhibited cytotoxicity against A204 cells in culture; nine of them were less active when co-cultured with hepatocytes, two were activated by hepatocyte co-culture, and two showed no effect of hepatocyte co-culture. P388 cells were more sensitive to the antiproliferative effects of the compounds than A204 cells. Two compounds that were not active against A204 cells exhibited cytotoxicity against P388 cells. One compound was inactivated by hepatocyte co-culture and one showed no effect. Five compounds showed no cytotoxicity toward either A204 cells or P388 cells. Two of the compounds showing hepatocyte inactivation in vitro possess activity in one or more in vivo tumor models. Thus, evidence for metabolic inactivation in hepatocyte co-culture is not always an indication for lack of in vivo antitumor activity. Hepatocyte co-culture methodology provides a simple and objective means, amenable to large-scale screening, of distringuishing metabolic activation or inactivation of a given compound from other pharmacokinetic and pharmacodynamic factors with a minimum of material.

Increased toxicity of the antitumor drug cyclophosphamide in mice in the presence of the volatile anesthetic agent halothane

Abstract: Exposure of mice to 0.5% halothane in air, which is close to a maintenance concentration in man, after an IP dose of cyclophosphamide produced an increase in the lethality of cyclophosphamide. The LD50 (30 day) for cyclophosphamide without halothane was 251 mg/kg; with 2 h subsequent exposure to halothane it was 152 mg/kg; and with 20 h subsequent exposure to halothane it was 158 mg/kg. The median survival time of mice receiving cyclophosphamide at doses between 137 and 240 mg/kg was more than 30 days in the absence of halothane, 12 days with 2 h halothane, and 10.5 days with 20 h halothane exposure. Survival of mice was decreased irrespective of whether 2 h halothane exposure preceded or followed cyclophosphamide administration. Separation of cyclophosphamide administration and preexposure to halothane by breathing air for 1 h abolished the decrease in survival. Halothane exposure for 2 h after cyclophosphamide had no effect on the antitumor activity of cyclophosphamide. Total-body clearance of cyclophosphamide in mice exposed to halothane was 60 ml/min/kg, as against 188 ml/min/kg in nonexposed mice. No change was produced by halothane in the area under the plasma concentration-time curve over 2 h for 4-hydroxycyclophosphamide following cyclophosphamide administration. The reason for the increased lethality of cyclophosphamide in the presence of halothane could not be determined. There was no increase in leukopenia caused by cyclophosphamide and no increase in bladder toxicity, in liver toxicity, in renal toxicity, or in the penetration of cyclophosphamide into the brain. The study, together with reports of increased toxicity in patients receiving cancer chemotherapy in close proximity to general anesthesia, should alert physicians and others to the possibility of an interaction between volatile anesthetic agents and chemotherapeutic drugs.

Disposition and metabolism of the antitumor glycoside phyllanthoside in mouse and beagle dog

Abstract: Phyllanthoside is a naturally occurring glycoside with activity against IP transplantable murine tumors. Phyllanthoside administered IV, to mice at a nontoxic dose of 16 mg/kg could not be detected in blood or plasma even 30 s after administration. There was rapid formation of a less polar metabolite, which disappeared with a half-life of about 10 min. When phyllanthoside was administered as an IV bolus to beagle dogs at doses of 0.1, 0.5, and 3.0 mg/kg the mean half-life of phyllanthoside elimination from plasma was 1.3 min and total body clearance 85.8 ml min-1 kg-1. A second phase of elimination was seen but could not be accurately defined. Only trace amounts of the less polar metabolite were detected in dog plasma. Infusion of phyllanthoside to beagle dogs at doses of 0.5 and 3.0 mg/kg over 70 min gave values for an initial half-life of 0.3 and 0.6 min, a terminal half-life of 99.4 and 16.5 min, and a total body clearance of 11.2 and 49.2 ml min-1 kg-1, respectively. The highest nontoxi dose of phyllanthoside in dog was 0.1 mg/kg, while doses of 0.5 mg/kg and 3.0 mg/kg resulted in ataxia and death of the dog. There was no difference in toxicity to dog according to whether phyllanthoside was given by IV bolus or continuous infusion. Isolated hepatocytes from rat metabolized phyllanthoside at a rate of 4.4 μg/min per 106 cells to form the less polar metabolite. Coculture with isolated hepatocytes decreased the cytotoxicity of phyllanthoside to A204 human rhabdomyosarcoma cell line growing in soft agarose. It is suggested that rapid metabolism of phyllanthoside in mouse as against dog might account for the lower toxicity of phyllanthoside in mouse, and might also account for the reported poor antitumor activity of IV-administered phyllanthoside in the mouse.