On the trough-to-peak ratio of drug effect in antihypertensive trials.

Blood pressure in hypertensives (treated or untreated) varies over the course of the day, and, although animal models and human intervention studies have demonstrated that the ill effects of hypertension are mediated by the pressure itself, and not by some confounder, it remains unknown what time-related function of pressure (simple mean, root-mean-square, duration of pressure above some threshold, and so on) might be the best predictor of hypertension-related morbidity There is no accepted means of describing the time course of blood pressure, let alone a difference between two such descriptions, which might then be a description of the time course of a drug effect. In a document dated 1988, the US Food and Drug Administration (FDA) defined the trough-to-peak drug-effect ratio and indicated that drug approval would be granted only when values of this statistic were satisfactory. The FDA's belief in the importance of the time-course of drug effect has grown stronger over time, but the idea that only drugs with certain trough-to-peak ratios could be approved was discarded by the FDA within months of its appearance. In recent years, more promising means of assessing the time-course of drug effect have begun to take shape.

Comparative antithrombotic activities of the phosphodiesterase inhibitors pelrinone (AY-26,768), AY-31,390 and milrinone.

The phosphodiesterase (PDE) inhibitors AY-31,390, milrinone and pelrinone (AY-28,768) were analyzed in human platelet aggregatory systems and in a rabbit arteriovenous shunt model to delineate their activity. AY-31,390 showed a remarkably potent capacity to inhibit human antithrombotic platelet aggregation. AY-31,390 inhibited arachidonic acid, U46619, collagen, epinephrine (second phase) and adenosine diphosphate (second phase) induced platelet aggregation (PA) with IC50 values of 0.18, 0.21, 0.54, 0.43 and 0.20 microM, respectively. Milrinone, although less potent than AY-31,390, inhibited PA with IC50 values of 2.1, 2.0, 5.4, 3.7 and 4.1 microM and pelrinone's IC50 values were 2.8, 6.6, 13.3, 18.6 and 11.8 microM, respectively. Platelets which were incubated with AY-31,390, milrinone or pelrinone, washed with Hanks' balanced salt solution and then resuspended in platelet poor plasma, lost their inhibitory activity in collagen and arachidonic acid PA systems. These results suggested that AY-31,390, milrinone and pelrinone did not bind tightly to cAMP PDE. If human platelet-rich plasma was pretreated with adenosine deaminase, an enzyme that degrades adenosine, the inhibitory effect of milrinone and to a lesser extent pelrinone was reversed. AY-31,390 did not produce a loss of activity with adenosine deaminase in the arachidonic acid system and only a small loss in the collagen system. Adenosine did not appear to be a meaningful factor in AY-31,390's inhibitory activity. Pelrinone, milrinone to a greater extent, and AY-31,390 to the greatest extent were effective inhibitors of white thrombus formation in the in vivo rabbit arteriovenous shunt model. These PDE III inhibitors were potent deterrants of platelet aggregation and white thrombus formation; these agents would be expected to be efficacious therapeutic antithrombotics.

Analysis of the potassium channel openers celikalim, pinacidil and cromakalim in platelet models of thrombosis.

The antihypertensive agents pinacidil, cromakalim and celikalim lower blood pressure by opening potassium channels in vascular smooth muscle. The role of these compounds in inhibiting human platelet aggregation and preventing white thrombus formation in a rabbit arteriovenous shunt model was examined. None of these agents (100 microM), substantially inhibited platelet aggregation induced by epinephrine or arachidonic acid. Only celikalim (100 microM) inhibited collagen (45%), ADP (56%), or serotonin (61%) induced platelet aggregation and ADP- (41%) or epinephrine-potentiated (61%) serotonin-induced platelet aggregation. Celikalim inhibited white thrombus formation at i.v. doses of 0.25 mg/kg (46% inhibition) but not 0.1 mg/kg; (14.6%); equihypotensive doses of pinacidil (0.5 mg/kg; 21.7%) and cromakalim (0.2 mg/kg, 7.5%; 0.4 mg/kg, 33%) were less effective. Glyburide (i.v. dose of 0.5 mg/kg) inhibited the antithrombotic activity of celikalim and to a lesser extent cromakalim. The greater antithrombotic activity of celikalim in vivo may be related to beneficial effects on blood rheology and reduced red blood cell deformability.

Clearance of a novel recombinant tissue plasminogen activator in rabbits.

The pharmacokinetic properties of hPA(B), characterized by the insertion of a urokinase kringle coding region before the double kringle of tPA plus the complete tPA coding region, were investigated and compared to those of melanoma tPA (mtPA). Mean peak plasma concentrations at the end of infusion were 4.7 micrograms/ml for hPA(B) and 4.6 micrograms/ml for mtPA. The pharmacokinetics of both hPA(B) and mtPA showed a biexponential disappearance from plasma which is consistent with a two-compartment model of t 1/2 (lambda 1) = 2 minutes, t 1/2 (lambda 2) = 58 minutes for hPA(B), and t 1/2 (lambda 1) = 2.2 minutes, t 1/2 (lambda 2) = 61 minutes for mtPA. However, this very fast decaying lambda 1 phase of mtPA lasted five times longer than that of hPA(B) which resulted in very low concentrations of mtPA. Thus, hPA(B) exhibited larger AUC, slower clearance rate, and smaller volume of distribution (P less than 0.01) than those of mtPA. The fibrinolytic activity of hPA(B) in rabbit plasma as determined by zymography lasted up to 120 minutes after the end of infusion as compared to that of 2 minutes for mtPA. This indicates that mtPA, despite its t 1/2 (lambda 2) being similar to that of hPA(B), is no longer at physiologically meaningful concentrations at the start of the lambda 2 phase.

Structural variants of verapamil and W-7 with combined Ca2+ entry blockade/myosin phosphorylation inhibitory mechanisms.

Arylalkylsulfonamides, identified as Wy-46,622 and Wy-47,324, combine pharmacological properties of the Ca2+ entry blocker verapamil and the calmodulin antagonist W-7. These agents directly inhibit arterial actin-myosin interactions via inhibition of myosin light chain (MLC) phosphorylation in actomyosin. Potencies of both Wy-46,622 (IC50 = 26 microM) and Wy-47,324 (IC50 = 18 microM) are greater than W-7 (IC50 = 35 microM); verapamil is inactive at 100 microM. Both Wy-46,622 and Wy-47,324 are less potent than verapamil, but more potent than W-7, at inhibiting K+-depolarized force development in paced rabbit atria. At higher concentrations (30 microM) which inhibit MLC phosphorylation, Wy-46,622 and Wy-47,324 are either equal to or more efficacious than verapamil in inhibiting receptor-mediated contractions in intact porcine coronary (histamine, serotonin, prostaglandin F2 alpha, carbocyclic thromboxane A2) or guinea pig aortic (leukotriene C4) smooth muscle. Both Wy-47,324 (IC50 = 16 microM) and Wy-46,622 (IC50 = 23 microM) are inhibitors of the second phase of epinephrine-induced human platelet aggregation; Wy-47,324 is more potent than verapamil or W-7 (IC50 for each = 29 microM). These results suggest that these agents possess combined Ca2+ entry blocker/MLC phosphorylation inhibitory mechanisms. Furthermore, they are more vascular specific than verapamil, and are effective inhibitors of intracellular Ca2+-mediated events in vascular smooth muscle and platelets.

Anti-tumour and anti-metastatic activity of 3-(P-Chlorophenyl)-2,3-Dihydro-3-Hydroxythiazolo (3,2-A)-Benzimidazole-2-acetic acid (WY-13,876).

Extensive investigation of 3-(p-chlorophenyl)-2,3-dihydro-3-hydroxythiazolo(3,2-alpha)-benzimidazole-2-acetic acid (Wy-13,876) in BDF1 mice implanted with Lewis lung tumour has shown that it is an effective anti-tumour and anti-metastatic agent. In vitro examination using HEp-2 human epidermal tumour cells has indicated that Wy-13,876 is not cytotoxic. When mice implanted with Lewis lung tumour and treated with Wy-13,876 are also injected with anti-thymocyte serum, an increase in lung metastases is observed suggesting that thymocyte activity is involved in the drug's mechanism of action. An increase in peripheral T lymphocytes observed in rats 18 h after a single oral dose of Wy-13,876 further supports this possibility. When Wy-13,876 is given to tumour -bearing mice in combination with low, ineffective doses of 5-fluorouracil or cyclophosphamide, further reduction of primary tumour growth is observed.

Immunomodulating and antimetastatic activity of 3-(p-chlorophenyl) thiazolo[3,2-a]benzimidazole-2-acetic acid (Wy-18,251, NSC 310633).

The antimetastatic activity of a thiazolobenzimidazole, Wy-18,251 was investigated using various dosage regimens in mice with implanted Lewis lung tumors. The low doses, 1 and 5 mg/kg (i.p.) given 24 hours after implantation with two subsequent doses at 1 week intervals were most effective in reducing lung metastases. Delayed hypersensitivity reactions in guinea pigs were significantly increased by oral doses of 50 and 150 mg/kg. In normal rats, peripheral blood lymphocytes determined by rosette assay, were significantly increased by oral doses of 50 to 150 mg/kg of Wy-18,251 and in a more sensitive assay using anti-theta serum the lymphocyte levels were increased by doses of 7.5 and 10 mg/kg. When cultured T lymphocytes from CBA/J mouse spleens were incubated with a suboptimal concentration of Concanavalin A, [3H]thymidine uptake was significantly increased in the presence of 0.05 to 1.0 microgram per culture. These results suggest that Wy-18,251 may have potential therapeutic value as an antimetastatic agent through its stimulation of the cellular immune system.

Immunomodulating activity of 3-(p-chlorophenyl)thiazolo-[3,2-a] benzimidazole-2-acetic acid (Wy-18,251, NSC 310633) in mice implanted with Lewis lung tumor. Effect of Wy-18,251 on lymphocyte proliferation and phagocytosis.

Proliferation of B lymphocytes is depressed in Lewis lung tumor bearing mice. Treatment of these mice with Wy-18,251 (5 mg/kg) significantly increased the responsiveness of their splenic T cells to concanavalin A in cell culture. Levamisole (5 mg/kg) acted more weakly than Wy-18,251. Neither Wy-18,251 nor levamisole elevated the depressed B cell mitogenesis. Wy-18,251 significantly increased macrophage phagocytosis against 51chromium labeled opsonized chicken red blood cells. Levamisole behaved differently: it either had no effect on phagocytosis, or depressed it.