Biochemical differences among four inosinate dehydrogenase inhibitors, mycophenolic acid, ribavirin, tiazofurin, and selenazofurin, studied in mouse lymphoma cell culture

The mechanism of the cellular toxicity of four inosinate dehydrogenase (IMP-DH) inhibitors with different antitumor and antiviral pharmacological profiles was investigated in mouse lymphoma (S-49) cell culture. Drug effects on cell growth, nucleotide pools, and DNA and RNA synthesis were measured in the presence and absence of guanine salvage supplies. Both guanine and guanosine were capable of bypassing the IMP-DH block, while they also demonstrated some growth-inhibitory effects when added alone in high concentrations. All four drugs reduced cellular guanosine triphosphate levels and caused secondary changes of the uridine, cytidine, and adenosine triphosphate pools that were similar among the four drugs. However, several drug effects in addition to IMP-DH inhibition were observed except with mycophenolic acid which may represent a pure IMP-DH inhibitor. Both tiazofurin and selenazofurin interfered with the uptake and/or metabolism of uridine and thymidine tracers; however, this effect appeared not to contribute to their cellular toxicity in vitro. Moreover, selenazofurin and tiazofurin impaired the utilization of exogenous guanine salvage supplies for DNA and RNA synthesis, and guanine was particularly ineffective in reversing the toxic effects of tiazofurin on cell growth. This finding is important in view of the available guanine salvage supplies in vivo. Since tiazofurin, selenazofurin, and their known metabolites failed to inhibit hypoxanthine-guanine-phosphoribosyl transferase, guanosine monophosphate kinase, and guanosine diphosphate kinase in cell extracts or permeabilized cells, these drugs may interfere with salvage transport across cellular membranes. The toxic effects of mycophenolic acid and ribavirin were similarly reversed by salvage supplies of up to 200 microM guanine, which suggests that ribavirin primarily acts as an IMP-DH inhibitor under these conditions. This result could explain the rather low antitumor efficacy of both mycophenolic acid and ribavirin in vivo. However, increasing the guanine salvage supply in the medium above 200 microM further reversed the toxic effects of mycophenolic acid to maximum rescue, while it increased the toxicity of ribavirin (300 microM). This finding suggests the presence of a toxic mechanism of ribavirin at higher concentrations that is dependent upon the presence of guanine supplies sufficient to fully overcome the IMP-DH inhibition. This study documents that each antimetabolite displays a unique spectrum of activities with multiple toxic targets.

Synthesis of a new anti-inflammatory steroidal acid ester: methyl 11 beta-hydroxy-3,20-dioxo-1,4-pregnadien-21-oate

The synthesis and anti-inflammatory activity of a new steroidal acid ester, methyl 11 beta-hydroxy-3,20-1,4-pregnadien-21-oate (5), are described. This compound has been prepared via three different synthetic routes. The first involves oxidation of the benzoate 3 to the aldehyde 4 followed by a Mattox-type rearrangement of the side chain in conjunction with elimination of the benzoyloxy group. The second method, prolonged reaction of 1-dehydrocorticosterone (8) with methanolic cupric acetate, affords methyl ester 5 in low yield. The third approach consists of selective oxidation at C-20 of the methyl 11 beta, 20 alpha and 20 beta-dihydroxy-3-oxo-1,4-pregnadien-21-oates (7a and 7b) with sulfur trioxide-pyridine complex. The local anti-inflammatory activities of the new ester 5 and intermediates 3, 4, 7a and 7b were determined by the cotton-pellet granuloma assay in rats. The anti-inflammatory activity of the title compound is equal to that of the parent steroid, prednisolone. However, unlike the latter compound, the ester does not cause reduction of adrenal and thymus weights or a lowering of plasma corticosterone levels.

Anti-inflammatory activity of the epimers of N-propyl 20 xi-dihydroprednisolonamide

The epimers of a steroid carboxamide, N-propyl 20 alpha- and 20 beta -dihydroprednisolonamide, were evaluated for their local and systemic effects on granuloma formation, pituitary-adrenal function and liver glycogen content in rats. When the carboxamides were administered locally, the 20 beta-epimer exhibited greater activity than the 20 alpha-epimer in suppressing cotton pellet granuloma formation. Neither epimer had suppressive effects on thymus weight and plasma corticosterone levels at the dose level used. When the carboxamides were administered systemically, they were pharmacologically inactive. Furthermore, in acute pharmacological studies, the carboxamides neither increased tyrosine aminotransferase activity and glycogen deposition in the liver nor decreased plasma corticosterone levels and relative thymus weight.

Temporal consistency of individual differences in cardiac response to a video game

Three experiments are reported which examined the temporal stability of cardiac reactions to a video game of the 'space invaders' genre. Experiment 1 also addressed the matter of inter-task consistency; in addition to the video game, subjects were presented with an unsignalled reaction time task and led to believe that relatively quick reactions attracted financial reward, while slower ones brought either a burst of loud noise or withdrawal of money previously earned. Forty-two male subjects were tested on both tasks on two occasions, a week apart. Of the two tasks, the video game elicited the greater reactivity. In addition, individual variations in reactivity showed striking temporal stability for both tasks. However, inter-task consistency was much less marked; in fact, a significant inter-task correlation was obtained only on the first occasion of testing. It is probable that limited consistency here was in some measure due to the ineffectiveness of our reaction time task in eliciting substantial reactivity. Finally, reactivity was independent of baseline heart rate level. In experiment 2, three extreme high and three extreme low cardiac reactors were selected from an initial sample of 23 male subjects, on the basis of reactivity during an initial session with the video game, and subsequently studied during four further sessions. Once more, impressive stability of heart rate reactivity was apparent over sessions. In experiment 3, we examined the reliability of individual variations in cardiac reactivity in women and the issue of whether temporal stability is constrained by menstrual cycle effects. Twenty-four females were tested on the video game both preovulatory and postovulatory, with half being tested first during the preovulatory phase and half being tested first during the postovulatory phase. Again, the most striking finding was the marked stability of individual variations in cardiac reactivity over both time and menstrual cycle phase.

Monitoring protein conformational changes by quenching of intrinsic fluorescence

The quenching of intrinsic fluorescence of human serum albumin and pigeon liver malic enzyme by acrylamide was studied after the proteins were denatured to different stages. The progress of protein denaturation induced by guanidine hydrochloride was accompanied by increasing of effective dynamic quenching constant which provides a convenient parameter for monitoring protein conformational change.

Systemic effects of chronically administered methyl prednisolonate and methyl 17-deoxyprednisolonate

The systemic activities of methyl prednisolonate and methyl 17-deoxyprednisolonate (1) were studied in rats. Methyl 17-deoxyprednisolonate produced significant changes in the amount of sodium ion (decreased) and potassium ion (increased) in urine; however, methyl prednisolonate had no effect on electrolyte balance. Both methyl prednisolonate and methyl 17-deoxyprednisolonate had no effect on liver glycogen content, plasma corticosterone level and relative adrenal weight. In contrast, the parent compound prednisolone caused a significant decrease in liver glycogen content, plasma corticosterone level and relative adrenal weight.

Role of chloride ion as an allosteric activator of angiotensin-converting enzyme

The nature of chloride ion as an activator of angiotensin-converting enzyme was studied by a series of kinetic experiments with hog plasma enzyme preparation. The enzyme required the presence of chloride ion for its full catalytic activity, but its requirement of monovalent anion was not absolute. The KA value for the enzyme-chloride binding was estimated to be about 150 mM in all cases regardless of the peptide substrates employed. In the presence of chloride ion, the activity of the enzyme was increased, but its optimum pH was shifted gradually to the alkaline region up to pH 8.2 depending on the concentration of chloride ion. In addition, in the presence of chloride ion, the apparent Km values were reduced markedly while the Vmax values were not much altered; for example, for the hydrolysis of angiotensin I decapeptide, the Km value decreased by a factor of 50 while only an 18% increase in Vmax was observed when the enzyme was saturated with chloride ion. The result suggests that chloride ion acts as a conformational modifier inducing the affinity of synergistic binding of substrate.

Systemic activities of a new anti-inflammatory steroid: methyl 20-dihydroprednisolonate

The systemic activities of methyl 20-dihydroprednisolonate (1), a new local anti-inflammatory steroid synthesized by modifying the 17 beta-ketol side-chain of prednisolone, on pituitary-adrenal function and liver glycogen content were investigated in rats. The parent compound, prednisolone, administered intramuscularly, caused a significant dose-related decrease in plasma levels of corticosterone, adrenocorticotropic hormone (ACTH), and liver glycogen content in rats. In contrast, methyl 20-dihydroprednisolonate caused mild PA suppression and liver glycogen depletion only at high doses. The steroid acid ester did not exert glycogenic activity, unlike prednisolone, in the adrenalectomized rats.

Anti-inflammatory steroids without pituitary-adrenal suppression

When two new steroids, methyl prednisolonate and methyl 20-dihydroprednisolonate, were applied locally their anti-inflammatory activities were nearly equivalent to those of the parent compound prednisolone in the cotton pellet granuloma bioassay. However, when these two derivatives were administered systemically, their anti-inflammatory activities were weaker than those of the parent compound. Furthermore, unlike the parent compound, these new anti-inflammatory steroids did not suppress pituitary-adrenal function or cause liver glycogen depletion in rats.

Stabilization of rat liver lysosomes by new anti-inflammatory steroids in vitro

Steroid acid esters, synthesized by modifying the 17-ketol side chain of prednisolone, were tested for their in vitro ability to stabilize heavy mitochondrial lysosomes prepared from rat liver. Membrane stabilization was determined by assessing capability of steroids to decrease extrusion of the marker enzymes (acid phosphatase, beta-glucuronidase and aryl sulfatase) from lysosomes incubated in hypo-osmotic sucrose-Tris acetate buffer. Results indicated that prednisolone (1) significantly inhibited the lysosomal release of acid phosphatase as did the new anti-inflammatory steroid, methyl 20-dihydroprednisolonate. Methyl prednisolonate exhibited weak membrane stabilization capacities and 20-dihydroprednisolonic acid, a metabolic product of methyl 20-dihydroprednisolonate, showed virtually no membrane stabilization.

Local antiinflammatory activity of acid ester derivatives of prednisolone

The antiinflammatory activity of two steroid acid esters, methyl prednisolonate and methyl 20-dihydroprednisolonate, synthesized by modifying the 17 beta ketol side chain of prednisolone has been investigated in the cotton pellet granuloma bioassay in rats. The inhibitory effect of the ester derivatives on granuloma formation was equivalent to that of the parent compound. At dose of 5 mg/cotton pellet, methyl prednisolonate exhibited a highly significant thymolytic effect comparable to that of prednisolone, while methyl 20-dihydroprednisolonate had a weaker thymolytic effect. However, the local antiinflammatory activity of the two esters was not accompanied by a decrease in adrenal weight observed with the parent compound.

Antiinflammatory activity of two novel derivatives of prednisolone

The antiinflammatory activity of two new steroids synthesized by modifying the 17 beta-ketol side chain of prednisolone to the glycolate and glyoxylate methyl esters has been investigated in the carrageenin pedal edema test in rats. The two ester derivatives retained anti-inflammatory potency, nearly equivalent to that of the parent compound, when administered subcutaneously at the site of inflammation. However, the glyoxylate ester, when administered by systemic route, showed a weaker suppression of inflammation. The glycolate ester showed a reverse trend in that it was more effective when it was administered by systemic route than when it was applied topically.

Stereoselective effects of cis- and trans-cyclopropylbis (dioxopiperazines) related to ICRF-159 on metastases of hamster lung adenocarcinoma

The synthesis for cis-4,4' (1,2-cyclopropanediyl)bis(2,6-piperazinedione) (cis-3) is discussed. Stereoselective effects on metastases of cis-3 and the previously reported trans-2 isomer were compared to conformationally mobile ICRF-159 using a Syrian hamster lung adenocarcinoma (LG1002). Whereas ICRF-159 and cis-3 significantly inhibited lung metastases the trans-2 isomer significantly increased the number of metastatic nodules in the lung. Thus, these studies have revealed that, at least in one tumor model, antimetastatic activity can be separated from metastatic potentiating activity by controlling drug geometry.

Ventricular aneurysmectomy for the treatment of intractable angina pectoris

Resection of a large postinfarctional ventricular aneurysm led to termination of intractable angina pectoris in one patient. The patient has been followed for 5 years and remains angina-free, even though aorto-coronary bypass surgery was not performed in this patient. The patient presented no evidence of congestive heart failure, arterial emboli, or cardiac arrhythmia before or after the surgery. Intractable angina alone in the absence of congestive heart failure, systemic embolism, and refractory ventricular tachyarrhythmia may constitute another indication for ventricular aneurysmectomy with or without concomitant aorto-coronary bypass surgery.

Oxidation of corticosteroids to steroidal carboxylic acids by an enzyme preparation from hamster liver

Enzyme activity which catalyzes the oxidation of 11-deoxycorticosterone to 21-oic acids accompanies the "detritiating" enzyme (isomerase) of hamster liver recently isolated by Martin, K. O., et al. ((1977) Biochemistry 16 (preceding paper in this issue)). The metabolites isolated were 20alpha- and 20beta-hydroxy-3-oxo-pregn-4-en-21-oic acid and 3,20-dioxo-pregn-4-en-21-oic acid. When 21-hydroxy[4-14C, 21-3H]pregn-4-en-3,20-dione was the substrate, about half of the tritium was retained in position 20 of the hydroxy acids. The system which catalyzes the conversion of the ketol side chain of corticosteroids to acid metabolites appears to be a cluster of closely related enzymes. As a result of these studies, we believe that the hamster liver enzyme preparation provides a useful model system for studies on the biosynthesis of acid metabolites of the corticosteroids in man.

Study of trans-cyclopropylbis (diketopiperazine) and chelating agents related to ICRF 159. Cytotoxicity, mutagenicity, and effects on scheduled and unscheduled DNA synthesis

The cytotoxicity, mutagenicity, and DNA damaging potential of trans-cyclopropylbis (diketopiperazine) (3) and chelating agents related to ICRF 159 (1) were examined as a function of concentration and duration of exposure in the Chinese hamster cell line V79A. At a concentration of 10(-3) M, 1 and the trans-cyclopropanediamine tetraacid 8 and ester 7 proved to be cytotoxic and mutagenic. The trans-cyclopropyl analogue 3 of ICRF 159 and acyclic tetraacid 6 were less cytotoxic at all concentrations; analogue 3 exhibited no mutagenic activity at any of the concentrations tested. Compounds 1, 7, and 8, at lethal concentrations, exhibited significantly different mutation frequencies with 7 being sixfold more mutagenic than 8 at the same molar concentration. At 10(-3) M compounds 8 was several times more effective blocking DNA replication than other analogues but did not induce unscheduled DNA synthesis as did 1,3, and 6. With the exception of 8, there was an excellent correlation between mutagenesis and the induction of unscheduled DNA synthesis.