Inhibition of ferrous-induced lipid peroxidation by dipyridamole, RA-642 and mopidamol in human lung tissue.

1. The in vitro production of ferrous-induced lipid peroxidation was 5.71 times higher in rat lung tissue than in human lung membranes. 2. The pyrimido-pyrimidine derivative RA-642 shows a more potent inhibition of ferrous-induced lipid peroxidation than dipyridamole; mopidamol had no effect. All the compounds showed higher anti-peroxidative effect in rat than in human lung tissue.

The pyrimido-pyrimidine derivatives, dipyridamole, mopidamol and RA-642, prevent from retinal vascular defects in experimental diabetes mellitus.

We compared the effects of dipyridamole, RA-642, and mopidamol on platelet activity and thromboxane/prostacyclin balance in relation to the degree of retinal vascularization in a model of experimental streptozotocin-induced diabetes in rats. After 3 months, collagen-induced platelet aggregation in whole blood was 25% higher in diabetic animals than in nondiabetics. Dipyridamole inhibited 43% platelet aggregation, mopidamol 39%, and RA-642 36%. Platelet production of thromboxane B2 was 87% higher in untreated diabetic rats. Mopidamol and RA-642 produced a 46% and 41% inhibition of thromboxane B2. Dipyridamole did not inhibited thromboxane B2 synthesis. Aortic production of 6-keto-PGF1 alpha was 43% lower in untreated diabetic animals and showed no change after treatment with either mopidamol or RA-642. In contrast, dipyridamole caused a 90% increase in aortic production of prostacyclin. Computerized analysis of retinal vascularization showed that untreated diabetic rats had a 81% decrease in the area occupied by peroxidase-labelled vessels as compared with nondiabetics. Treatment with dipyridamole, mopidamol, and RA-642 caused 2.5-fold, 2.8-fold and four-fold increases, respectively, in the percentage of retinal surface occupied by peroxidase-labelled vessels. Differences in retinal vascularization between diabetic animals given RA-642 and nondiabetic controls were negligible.

Hemorrheologic effects of pyrimido-pyrimidine derivatives.

A series of pyrimido-pyrimidine derivatives were tested for their effect on membrane fluidity-deformability of human red blood cells and on human platelet aggregation. These agents were also tested for their intracellular cAMP increasing activity and proliferation inhibitory activity in neoplastic cells. The order of activity was established and clinical implications discussed. Several derivatives are under study as antineoplastic agents.

The pyrimido-pyrimidine derivatives, dipyridamole and RA-642, reduce opacification of crystalline lens in diabetic rats.

We assessed the effect of dipyridamole, RA-642 and mopidamol, on lenticular opacities in a model of experimental diabetic cataracts in rats. All three pyrimido-pyrimidine derivatives caused a statistically significant reduction of opacification in crystalline lens as compared with untreated diabetic animals. The production of superoxide anions (phenazine methosulphate [PMS]-induced nitroblue tetrazolium [NBT] reduction) showed a decrease of 81.6%, 78.9% and 1.8% in lens tissue homogenates from rats treated with dipyridamole, RA-642 and mopidamol, respectively. Dipyridamole and RA-642 produced a statistically significant inhibition (50% and 64.8%, respectively) of lipid peroxidation (ferrous sulphate and ascorbic acid [FeAs]-induced malondialdehyde [MDA] production) as compared with the group of untreated diabetic rats. Mopidamol did not exert any inhibitory effect on lipid peroxidation. There was a statistically significant correlation between opacification of lens and PMS-induced NBT reduction and FeAs-induced MDA production. We conclude that the protective effect of dipyridamole and RA-642 from free radical damage to crystalline lens in the model of experimental diabetes used in this study, is the result of the antioxidant action of these compounds. The effect exerted by mopidamol, however, suggest a possible complementary effect of the pyrimido-pyrimidine derivatives through interaction with other mechanisms (e.g., the sorbitol pathway) implicated in the development of cataracts.

Differential effects of the pyrimido-pyrimidine derivatives, dipyridamole and mopidamol, on platelet and vascular cyclooxygenase activity.

The chronic administration of 10 mg/kg/day of dipyridamole to rats produced 33.7% inhibition of platelet aggregation induced with ADP and a 93% increase in 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) in vascular samples, versus saline-treated rats. Mopidamol, 8.3 mg/kg/day, caused 50.6% inhibition of ADP-induced platelet aggregation, 37.6% inhibition of aggregation induced with arachidonic acid, a 47.6% decrease in serum levels of thromboxane B2 and a 23.7% increase in the vascular production of 6-keto-PGF1 alpha, versus saline-treated rats. Dipyridamole showed a higher in vitro anti-aggregating effect in whole blood (IC50 6.6 microM) than in platelet-rich plasma (PRP) (IC50 210 microM), when ADP was used as inducer, and had no effect in the presence of arachidonic acid. Mopidamol exerted a similar effect in whole blood (IC50 3.7-20 microM, depending on the inducer) and PRP (IC50 11-17.3 microM), and showed a dose-dependent inhibition of platelet aggregation and thromboxane B2 synthesis induced with arachidonic acid (IC50 16.8-22.3 microM). Mopidamol also inhibited enzymatically induced lipid peroxidation) (IC50 89 +/- 5.9 mumol/L) and had no effect on free radical-induced lipid peroxidation. The dose-dependent increase in 6-keto-PGF1 alpha in vascular samples after incubation with dipyridamole showed a negative linear correlation with inhibition of lipid peroxidation (r2 = 0.77). It is concluded that the phosphodiesterase inhibitors, dipyridamole and mopidamol, interfere in a different manner with platelet function. It seems that mopidamol may also exert a selective effect on platelet thromboxane synthesis.

Prevention of human pancreatic cancer cell-induced hepatic metastasis in nude mice by dipyridamole and its analog RA-233.

BACKGROUND: Several studies have provided evidence suggesting that platelets play a key role in tumor metastasis. A number of antiplatelet agents have been used to prevent tumor metastasis in animal models and humans. Antiplatelet agents, dipyridamole (adenosine transport inhibitor), and RA-233 (inhibitor of cAMP PDE) were used to prevent tumor-cell-platelet interactions both in in vitro and in vivo systems; however, the data were not very conclusive. METHODS: Our studies used dipyridamole and RA-233 alone and in combination to investigate their effects on human pancreatic tumor cells (RWP-2)-induced platelet aggregation in human blood and on hepatic metastasis in nude mice. To examine effects of dipyridamole and RA-233 on liver metastasis, the tumor cells (RWP-2) were injected intrasplenically in nude mice grouped into control, dipyridamole (8 mg/kg), RA-233 (8 mg/kg), and dipyridamole plus RA-233 (8 mg/kg each). The agents were administered intraperitoneally 1 hour before and 24 hours after the tumor cell injection. RESULTS: When dipyridamole and RA-233 were used alone, only weak to moderate effects were seen on RWP-2 tumor cell-induced platelet aggregation. However, these agents, when combined, strongly inhibited the tumor cell-induced aggregation in human platelet-rich plasma. In tumor metastasis experiments, reductions of approximately 70% in hepatic nodules and 90% in surface area occupied by the tumor were seen with the combination treatment (dipyridamole plus RA-233) as compared with the control group of mice. CONCLUSIONS: This study suggests that the combination of dipyridamole and RA-233 provides an effective intervention for the antithrombotic approach to the treatment of cancer metastases.

The pyrimido-pyrimidine derivative RA-642 protects from brain injury in a combined model of permanent focal ischemia and global ischemia reperfusion.

The effects of pyrimido-pyrimidine derivatives (dipyridamole, RA-642 and mopydamole) on lipid peroxidation (inhibition of the production of malondialdehyde, MDA) in different regions of the rat brain were studied. Ferrous sulfate and ascorbic acid (FeAs) were used to induce lipid peroxidation via the formation of hydroxyl anions. The antiperoxidative effect of RA-642 (in the microM range) was 10 times more potent than that of dipyridamole. Mopydamole did not exert any inhibitory effect on MDA production. In a model of ischemia reperfusion with bilateral occlusion of the common carotid arteries for 1 h and restoration of circulation for a period of 2 h, dipyridamole inhibited FeAs-induced MDA production but did not protect from postischemic brain tissue damage (measured by mitochondrial reduction of tetraphenyl tetrazolium). RA-642 inhibited FeAs-induced MDA production and showed 50-67% protection from tissue damage as compared with untreated animals, while mopydamole did not inhibit MDA production and showed 30-48% protection. No correlation was found between inhibition of lipid peroxidation and protection from brain tissue damage.

Inhibition of ferrous-induced lipid peroxidation by pyrimido-pyrimidine derivatives in human liver membranes.

The effects of pyrimido-pyrimidine derivatives (dipyridamole, RA-642, and RA-233) on lipid peroxidation, using d-alpha-tocopherol as standard, were studied in enriched membrane fractions from human and rat hepatocytes. Equimolar concentrations of ferrous sulfate and ascorbic acid were used to induce lipid peroxidation. The amount of peroxidized lipids observed in membrane fractions from human liver was smaller than in those from rat liver. In both species, however, pyrimido-pyrimidine derivatives, except for RA-233 in rat liver, inhibited lipid peroxidation dose-dependently in the following sequence: RA-642 greater than dipyridamole greater than d-alpha-tocopherol RA-233.

The pyrimido-pyrimidine derivative RA-642: a potent inhibitor of ferrous-induced lipid peroxidation in cell membranes.

The effects of three pyrimido-pyrimidine derivatives (RA-642, dipyridamole and mopidamol) on hydroxyl anion-induced lipid peroxidation in cell membranes from liver, brain, kidney, lung and heart rat tissue were studied using d-alpha-tocopherol as standard for lipid peroxidation. Ferrous sulfate and ascorbic acid (FeAs) were used to induce lipid peroxidation via the formation of hydroxyl anions. The products resulting from the reaction with thiobarbituric acid were taken to be indicators of lipid peroxidation. Thiobarbituric acid reactive substances (TBARS) were produced by different rat tissues in the following sequence: brain greater than liver greater than kidney greater than heart greater than lung. Dose-response and time-response curves were plotted for all compounds. Inhibiting concentrations, 50% (IC50), ranged from 0.3-1.4 microM for RA-642, and 2.5 and 4.6 microM for dipyridamole. In liver mitochondrial membranes, IC50s of these compounds were 0.4 +/- 0.2 and 5.8 +/- 1.2 microM, respectively. At 15 min after beginning TBARS production, dipyridamole and RA-642 did not exert any inhibitory effect.

Adenylate cyclase system is essential for long-term facilitation at the crayfish neuromuscular junction.

Long-term facilitation (LTF), a form of synaptic plasticity demonstrated at the crayfish neuromuscular junction, is induced by tetanic stimulation and persists for hours. LTF can be divided into 2 phases: a tetanic phase, which occurs during stimulation, and a long-lasting phase, which persists after stimulation. Activators and potentiators of cAMP (forskolin and 3-isobutyl-methyl-xanthine) produce facilitation of excitatory postsynaptic potentials, which attain approximately the amplitude of the long-lasting phase of LTF but last for a shorter time. Localized presynaptic injection of a protein inhibitor ("Walsh inhibitor") specific for the cAMP-dependent protein kinase blocks the long-lasting phase of LTF at synapses near the injection site with no apparent effect on the tetanic phase. Normal LTF develops and persists at synapses of the same axon distant from the injection site. Localization of the injected inhibitor was confirmed by fluorescent tagging. Localized injection of SQ22,536, an adenylate cyclase inhibitor, also blocks the second phase of LTF near the injection site, but not at distant synapses. These experiments establish a role for adenylate cyclase activation in the long-lasting phase of LTF. The phosphatidylinositol second-messenger system is not important in LTF as inhibition of phospholipase C by injection of RA233, which blocks facilitatory effects of serotonin, does not affect any aspect of LTF.

Drug treatments for metastasis of the Lewis lung carcinoma: lack of correlation between inhibition of lung metastasis and survival.

The abilities of the Eli Lilly compounds LY150310, LY189332, and LY135305 to inhibit spontaneous metastasis and to increase animal survival were evaluated. These compounds represent widely varied structures and were evaluated because they have been found to inhibit thromboxane synthetase, cyclooxygenase, and thrombin activation, respectively. These biochemical processes have been proposed in the literature as targets for antimetastatic drugs. The purpose of this investigation was twofold: (a) to compare the antimetastatic activities of the Eli Lilly compounds to those of the reference antimetastatic compounds nafazatrom and RA233, and (b) to examine the correlation between inhibition of spontaneous lung metastasis and survival. Spontaneous metastasis of the Lewis lung carcinoma was used to evaluate the antimetastatic activity of the compounds. In this model 5 x 10(5) tumor cells were implanted into the gastrocnemius muscle, the primary tumor was resected on Day 14, and metastatic lung lesions were counted on Day 25. Compounds were administered every 12 h on Days 5 through 19. Nafazatrom, LY150310, LY189332, and LY135305 were found to inhibit spontaneous lung metastasis in a dose-dependent manner. The ED50 values for the respective inhibitions with these compounds were 50, 0.5, 2, and 0.35 mg/kg/day; the respective therapeutic indexes (LD50/ED50) were 7, 180, 255, and 511. To evaluate the effect of nafazatrom, LY150310, LY189332, and LY135305 on animal survival, the compounds were given at maximally antimetastatic doses of 200, 60, 20, and 6 mg/kg/day, respectively. Two dosing schedules were used: (a) on Days 5 through 19 and (b) on Day 5 until death. Neither the median survival times nor the numbers of long-term survivors were significantly changed with any of the compounds at any dosing schedule. RA233, given to a maximally tolerated dose of 200 mg/kg/day on Day 5 until death, did not inhibit lung metastasis and did not increase median survival time. Postmortem examination of animals dosed with nafazatrom, LY150310, LY189332, and LY135305 showed complete inhibition in lung lesions and the appearance of lesions in the liver, kidney, spleen, and brain. The results of this investigation show that the effect a compound has on the number of metastatic lesions in a target organ may not be predictive of its effect on survival. To successfully translate laboratory data into the clinic, survival should be considered as a predictor of a compound's potential clinical utility.

Phosphatidylinositol system's role in serotonin-induced facilitation at the crayfish neuromuscular junction.

1. In a crustacean neuromuscular preparation, the walking leg opener muscle of the freshwater crayfish Procambarus clarkii, application of serotonin (1 microM) produces presynaptic depolarization and long-lasting facilitation of excitatory postsynaptic potentials (EPSPs). The frequency of spontaneously released transmitter quanta also increases. Facilitation of evoked EPSPs declines after serotonin application in two phases. 2. Serotonin-induced facilitation was examined using simultaneous pre- and postsynaptic intracellular microelectrode recording. A presynaptic microelectrode recorded action potentials and membrane potential of a presynaptic axonal branch, and one or more postsynaptic microelectrodes recorded EPSPs in muscle fibers innervated by the excitatory motor axon. Components of the phosphatidylinositol second messenger system and pharmacologic agents affecting this system were injected through the presynaptic electrode, and changes in synaptic transmission were measured. 3. Presynaptic injection of inositol 1,4,5-triphosphate (IP3) causes presynaptic depolarization, increases the frequency of spontaneously released transmitter quanta, and promotes a relatively short-lasting facilitation of evoked EPSPs. These actions are consistent with elevation of intracellular Ca2+ and resemble the early phase of serotonin-induced facilitation. 4. Application of a phorbol ester, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), that activates protein kinase C (C-kinase), produces a long-lasting, low-level facilitation of evoked EPSPs. Application of another phorbol ester, phorbol-12-monoacetate (PTMA), which does not activate C-kinase has no effect. 5. Presynaptic injection of RA 233, a phospholipase C (PLP-C) inhibitor, blocks all aspects of serotonin-induced facilitation. This compound was found to have no general deleterious effects on synaptic transmission and does not block other forms of synaptic facilitation in this preparation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of RA 233 treatment on the adhesive, invasive and metastatic properties of 13762NF rat mammary tumor cells.

The pyrimido-pyrimidine analogue RA 233 has pleiotropic and differential effects on cultured tumor cell clones isolated from the 13762NF rat mammary adenocarcinoma. A nonresponsive clone of low metastatic potential (MTC) was not modified in its cell fragility or invasive, adhesive or lung-colonizing properties by RA 233 treatment. In contrast, a drug-responsive clone of high metastatic potential (MTLn3) was rendered less invasive and its cell fragility was decreased with RA 233 treatment, although its adhesiveness to lung microvascular endothelial cells and subendothelial matrix was unaffected by RA 233. Lung colonization of intravenously injected MTLn3 cells in syngeneic rats was significantly increased by RA 233 treatment, whereas spontaneous metastasis from the mammary fat pad to lung sites was decreased, although this decrease was not statistically significant.

A sensitive in vivo platelet function test in rats based on intravenously injected collagenase.

The transient decrease of the platelet concentration in the flowing blood after intravenous injection of collagenase was used as a measure for the effectiveness of the platelet-vessel wall interactions in rats. The decrease of the concentration in circulating platelets was regarded as an expression of the in vivo platelet function. The influence of acetylsalicylic acid, imidazole, indomethacin, ketanserin, RA 233, and dipyridamole on this test was investigated in anaesthetized rats. All tested drugs showed an effect on the extent of the platelet concentration decrease after the collagenase injection compared to the control values, but no drug was significantly effective. This test could prove to be a valuable tool for testing the efficiency of antithrombotic drugs in vivo.

Pyrimido-pyrimidine modulation of EGF growth-promoting activity and p21ras expression in rat mammary adenocarcinoma cells.

RA 233, a pyrimido-pyrimidine analogue developed originally as an antiplatelet agent, has reduced the incidence of tumor metastases in clinical trials. However, in animal tumor models antimetastatic therapy using RA 233 has been inconsistent. We therefore tested RA 233 for additional effects, such as its direct action on tumor cells. Using the rat 13726NF mammary adenocarcinoma tumor system, low, nontoxic concentrations of RA 233 had pleiotropic and differential effects on two 13762NF tumor cell clones. The growth of MTC cells (low spontaneous metastatic potential) was not affected by low concentrations of RA 233 (50 microM) or epidermal growth factor (EGF) (up to 10 ng/ml) for 3 days in 0.5-10% fetal bovine serum. In contrast, MTLn3 (high spontaneous metastatic potential) cell cultures maintained for 3 days in low (0.5-1%) serum in the presence of 1.25-10 ng/ml EGF doubled in cell numbers compared with control cultures, and addition of 50 microM RA 233 abrogated the growth-stimulatory effect of EGF. The inhibitory effect of RA 233 on MTLn3 cells was dose dependent and not due to cell toxicity as determined by cell viability, cell growth, and colony formation properties after drug removal. In addition, incubation of MTLn3 cells with 50 microM RA 233 resulted in an increase of p21ras protein expression, whereas there was no effect on the level of p21ras in identically treated MTC cells or when either clone was treated with 10 ng/ml EGF. The results suggest that among the heterogeneous effects of RA 233 on tumor cells, modulation of growth factor responses and regulatory molecules may be important.

Cytotoxic effect of RA233 on hypoxic B16 melanoma cells in vitro.

The pyrimido-pyrimidine derivative RA233 was found to selectively kill cultured mouse B16 melanoma cells after prolonged hypoxia. At the optimum cytotoxic concentration (100 microM), RA233 reduced cell clonogenicity by about 80% when administered during long-term hypoxia of 4 days. Comparable cytotoxicity was also evident when RA233 was present only during re-oxygenation following 4 days of hypoxia. RA233 treatment during both hypoxia and re-oxygenation resulted in the greatest cytotoxicity, with only about 1% of cells surviving such treatment. By contrast, the hypoxic cell sensitizer misonidazole was cytotoxic only when administered during hypoxia. RA233 appears to be a unique hypoxic cell sensitizer that kills long-term hypoxic tumor cells principally during re-oxygenation.

Effect of mopidamol on survival in carcinoma of the lung and colon: final report of Veterans Administration Cooperative Study No. 188.

Mopidamol (RA-233), a derivative of dipyridamole, is a phosphodiesterase inhibitor that has been shown previously to limit progression of malignancy in certain experimental animal models and in a pilot study in humans. RA-233 plus chemotherapy was compared with chemotherapy alone in a 5-year double-blind trial involving 719 patients with advanced carcinomas of the lung and of the colon. RA-233 treatment was associated with a statistically significant prolongation of survival in patients with non-small cell lung cancer (N-SCLC) limited to one hemithorax and with reduction in mean plasma fibrogen concentration. RA-233 was not toxic. The favorable effects on survival could not be explained by any factor other than the RA-233 treatment. In other tumor categories tested, no differences in survival were observed. These results suggest that RA-233 is useful in the treatment of N-SCLC of limited extent. They also suggest that therapeutic intervention aimed at modified intracellular pathways might constitute a novel investigative approach to the treatment of cancer.

Effect of RA-233 on erythrocytes from patients with eczema.

Erythrocytes (RBCs) from patients with eczema are less flexible than erythrocytes obtained from normal healthy individuals. The addition of RA-233 (a membrane-active agent which is a phosphodiestrase inhibitor) improved the deformability of these rigid RBCs, and this improvement was found to be statistically significant at p less than 0.0001. The increase in deformability that was observed after the addition of the drug is assumed to be related to the increases in intracellular Ca2+,K+ and blood ATP levels which are brought about by the action of this drug.