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.

Pretreatment fibrinogen levels are associated with response to chemotherapy in patients with small cell carcinoma of the lung: Department of Veterans Affairs Cooperative Study 188.

Small cell carcinoma of the lung (SCCL) responds commonly to combination chemotherapy but resistance to therapy follows. Prior reports have suggested that a relationship may exist between plasma fibrinogen levels and response to therapy in SCCL. This study was designed to determine the possible predictive value of the fibrinogen level for tumor response (chemoresistance) in SCCL. Pretreatment fibrinogen levels were correlated with outcome and response to therapy in a cohort of 119 previously untreated patients with SCCL who were admitted to VA Cooperative Study 188. Higher pretreatment fibrinogen levels at diagnosis correlated significantly with more advanced stage of disease at entry (P < 0.001) and with reduced overall survival (P = 0.030). In addition, higher pretreatment fibrinogen levels were correlated significantly with a reduced likelihood of achieving subsequent disease regression with combination chemotherapy (P = 0.005). Because several clinical trials have shown that anticoagulant therapy improves tumor response rates and survival of SCCL, we postulate that tumor cell thrombin generation not only promotes SCCL growth but may also be primarily responsible for both increased fibrinogen levels and for resistance to chemotherapy. These findings provide incentive for studies of thrombin effects on the development of multidrug resistance, and for new clinical trials of more potent and specific inhibitors of thrombin that may further improve tumor response and survival in SCCL.

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.

The stable prostacyclin analogue Cicaprost inhibits metastasis to lungs and lymph nodes in the 13762NF MTLn3 rat mammary carcinoma.

Prostacyclin and its stable analogues have been shown to interfere specifically with certain steps of the metastatic cascade. The antimetastatic activity of the stable prostacyclin analogue Cicaprost (Schering AG) on haematogenous metastasis in a series of tumours in rats and mice has been well established. In order to test the effect of Cicaprost on lymphogenous metastasis we chose the metastatic cell clone MTLn3 derived from the 13762NF rat mammary carcinoma. The effect of Cicaprost on prevention of lung metastasis, lymph node metastasis and primary tumour growth was investigated. Cicaprost given in daily doses of 0.01, 0.03 and 0.1 mg/kg orally, reduced the number of lung metastases in a dose-dependent manner. Whereas the median number of lung metastases in the controls was greater than 1000, Cicaprost at a dose of 0.1 mg/kg reduced the number of lung metastases to between 11 and 100. The weight of the ipsilateral axillary lymph nodes was diminished by Cicaprost to 30-50% of controls. Moreover, metastasis to the contralateral axillary lymph node was completely inhibited by Cicaprost at all three doses tested. Cicaprost did not influence the growth rate of the MTLn3 cell clone implanted into the mammary fat pad or the weight of the primary tumour at the end of treatment. In conclusion, in addition to its dose-dependent effect on haematogenous metastasis, Cicaprost strongly inhibits lymph node metastasis.

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.

Placebo-controlled study on the efficacy of the pyrimido-pyrimidine derivative RA 233 in ovarian cancer.

This prospective double-blind, multicenter study was aimed at evaluating the clinical efficacy of RA 233 (a derivative of dipyridamole) in ovarian cancer. Following primary surgery, 497 patients with ovarian cancer were treated with combination cytotoxic chemotherapy; those in clinical stage II were also treated with pelvic irradiation. The patients were randomly allocated to receive RA 233 (N = 251) or placebo (N = 246) for 2 years. The groups did not significantly differ from each other in any of the clinical, therapeutic, or histopathological variables evaluated. There were no significant differences between RA 233-treated patients and placebo-treated patients with respect to appearance of new metastases, progressive growth of malignancy, or survival of all patients, in any of the clinical stages of the disease, in radically operated patients or in nonradically operated patients, in different histopathological groups, or in different age groups. Hence, supplementation of carcinoma therapy with long-term administration of the antiplatelet drug RA 233 has no clinical benefit in this malignancy. Using Cox's multifactorial stepwise analysis, this study revealed that the clinical stage of the disease, the extent of surgery, and the histopathology of the tumor, but not the age of the patient or the use of RA 233, were significant and independent predictors of survival. With respect to the histopathology, the poor prognosis of serous and mesonephric carcinomas appeared to be independent of the other prognosis indicators.

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)

Chemotherapy plus RA233 in the treatment of oat cell lung cancer.

One hundred and one patients with oat (small) cell lung cancer have been treated with CAVE [Cytoxan, Adriamycin, Vincristine, and etoposide (VP-16)] chemotherapy +/- RA233 (a platelet-inhibiting agent). There was no difference in disease-free interval, pattern of relapse, or survival between groups.

[Adjuvant therapy of non-small cell bronchial cancer with mopidamol]. / Adjuvante Therapie des nicht-kleinzelligen Bronchialkarzinoms mit Mopidamol.

Between January 1982 and April 1986 a double-blind randomized placebo controlled study of mopidamol, employed as adjunct therapy to surgery in patients with non-small cell bronchial carcinoma, was performed at 7 hospitals. The main criteria were occurrence of metastases and survival. Mopidamol was given perioperatively at a dose of 2 x mg i.v. daily, and postoperatively orally at a dose of 3 x 500 mg daily. The treatment period was scheduled to at least 2 years and in some of the patients was prolonged to 3 years. The standard therapy of each individual center was given as basic therapy. A total of 270 patients were included in the study, 147 in the placebo and 123 in the mopidamol group. By the end of the study 52 deaths from metastases had occurred in the placebo group (35%) compared with only 32 (26%) in the mopidamol group. This difference is statistically significant at p less than 0.05 with the one-sided test. A comparison of life-tables according to Kaplan-Meier shows a statistically significant difference in favour of the group treated with mopidamol (savage p less than 0.05). Cox's multivariate analysis confirmed the statistically significant difference in favour of the group treated with mopidamol, the inclusion of the risk factors tumour stage and histology in the evaluation results in a p-value of 0.02. With respect to the incidence of metastases there were no appreciable differences between the treatment groups. The incidence of side effects or undesired events was equal in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The pyrimido-pyrimidine derivatives RA233 and RX-RA85 affect cell cycle distribution of two murine tumour cell lines.

The pyrimido-pyrimidine derivatives RA233 and RX-RA85, which are potent inhibitors of platelet and tumour phosphodiesterases, were developed as antitumour agents. Clinical as well as animal studies suggest a tumour type specific, although moderate, antitumour activity for RA233. In our search for more potent congeners of RA233, we found that RX-RA85 was cytotoxic for cultured B16 melanoma and Lewis lung carcinoma cells at drug concentrations above 4 micrograms/ml whereas RA233 concentrations up to 400 micrograms/ml were tolerated. When tested for their effects on cell cycle distribution, RX-RA85 was 100-fold more potent than RA233 in producing an increase in the proportion of cells in S and G2 + M phase in 3LL cells. Progression of 3LL cells through the cell cycle was delayed for 5 h by RA233 treatment, whereas RX-RA85 was ineffective. In contrast, B16 cells responded poorly to either drug. The effects of both compounds were not only tumour cell specific but also dependent on the stage of tumour cell growth (drugs added to synchronously vs. asynchronously growing cultures). In the case of RX-RA85, the potency to affect tumour cell cycle distribution was highly dependent on tumour cell number, making the potential of this drug as an antitumour agent somewhat limited.