Brigitte Blöchl-Daum

Measurement of extracellular fluid carboplatin kinetics in melanoma metastases with microdialysis

Clinical anti-tumour efficacy of anti-cancer drugs is a function of dose intensity, i.e. the concentration--time profile in tumour tissue. Hence, information on drug concentration profiles in tumours is of critical importance but appropriate methods for measurement are lacking. The aim of the present study was to obtain, by microdialysis sampling, concentration--time profiles in a solid tumour (melanoma) of a model anti-cancer drug, carboplatin, and thereby to assess the scope of microdialysis for tumour pharmacokinetic studies in man. Six patients with cutaneous melanoma metastases at the extremities or body trunk, scheduled to receive carboplatin (400 mg m-2 i.v.) were studied. Carboplatin concentrations were monitored in serum, intratumoral and subcutaneous tissue. Calibration of the microdialysis probes was carried out in vitro and in vivo with use of the retrodialysis method. Complete carboplatin concentration vs time profiles in tumour and subcutaneous tissue were obtained. Major pharmacokinetic parameters (maximum concentration, time to maximum concentration, area under the curve, elimination half-life) were calculated for tissues and tumour/serum concentration ratios for carboplatin were derived. Mean free concentrations of carboplatin in cutaneous melanoma metastases reached only about 50-60% of total serum levels; maximal intratumoral concentrations were 7.6 (+/-2.0; s.e.m.) microgram/ml, mean concentrations in subcutaneous tissue were similar to those in tumour. The present study demonstrates that microdialysis is a novel tool for measuring drug concentrations in solid tumours in humans in vivo and appears to be a valuable addition for pharmacokinetic/pharmacodynamic studies in oncology.

Primary defect in α‐adrenergic responsiveness in patients with varicose veins

Responsiveness of superficial hand veins to local infusions of noradrenaline was compared in patients with primary varicose veins and in healthy volunteers by use of the dorsal hand vein technique. Patients with varicose veins required significantly higher doses of noradrenaline for half‐maximal venoconstriction than the dose required by control subjects (geometric mean, 11.6 ng/min in patients compared with 4.8 ng/min in control subjects; p = 0.006). Noradrenaline responsiveness in varicose veins was not significantly different from hand vein responsiveness in the same patients. Our findings indicate a constitutional decrease in venous a‐adrenergic receptor responsiveness in patients with varicosities. Dilation of varicose veins does not further affect noradrenaline‐induced venoconstriction.

Escalating dose regimen of intraperitoneal mitoxantrone: phase I study ― clinical and pharmacokinetic evaluation

Mitoxantrone, a recent anthracenedione derivative, is a potentially useful drug for direct intraperitoneal (i.p.) application because of its high tissue binding and therapeutic index. We have carried out studies to establish maximum tolerated doses as well as pharmacokinetic studies with i.p. mitoxantrone in 21 patients (5 male, 16 female) with gastrointestinal (9), ovarian (6), unknown (2) and other (4) primary cancers and peritoneal carcinomatosis. Increasing doses (10-40 mg/m2) were given i.p. every 4 weeks. Five partial remissions (2-8+ months) and 7 stable disease courses (2-6+ months) were achieved. A reduction or disappearance of ascites was seen in an additional 3 patients. Severe toxicity (leucopenia) was observed in 4 patients only after 35 and 40 mg/m2 i.p. Pharmacokinetic analysis using high performance liquid chromatography yielded the following data: The mean ratio of area under curve peritoneal fluid to plasma was 1109. The peritoneal clearance rate was 680 ml/min and the mean disappearance half life was 13.1 h. Mean urinary excretion within 24 h was 0.42% of the i.p. dose. These data indicate that mitoxantrone is sequestered in the intraperitoneal tissue compartment and only slowly released. Based on the outcome of this phase I study we recommend phase II studies at a dose of 30 mg/m2 i.p., repeated every 3-4 weeks.

In vivo studies on alpha-adrenergic receptor subtypes in human veins

SummaryWe studied in vivo responsiveness of venous α1 and α2-adrenoceptors, measuring the diameter changes in superficial veins in response to α-adrenergic agonists and antagonists in healthy human volunteers. The dorsal hand vein technique was used because it permits complete dose-response studies of venous constriction without confounding reflex alterations.Local infusions of all agonists studied induced dose-dependent contraction of the hand vein; the maximal effects (Emax) were: norepinephrine (88% ± 10%), methox amine (97% ± 5%), phenylephrine (95% ± 6%), clonidine (54% ± 12%), and azepexole (68% ± 26%). Clonidine reduced the norepinephrine-induced venoconstriction by 11% ± 10%. Oral doses of 1 mg prazosin antagonized the venoconstriction induced by norepinephrine, methoxamine, and clonidine, but not by azepexole. Yohimbineantagonism was observed against all agonists studied. Inhibition by yohimbine of clonidine-induced venoconstriction was irreversible over 60–180 min.Results show that the in vivo effects on veins of α-adrenergic agonists are in good agreement with results from in vitro experiments. Agonists with α1- and α2-adrenoceptor subtype selectivity cause venoconstriction in vivo, but α2-receptor mediated constriction is intrinsically weaker. Clonidine acts as a partial antagonist against norepinephrine, presumably on postsynaptic α2-receptors. At high doses, α2-adrenoceptor subtype selectivity of clonidine and yohimbine appear to be partially lost in vivo.

Cilazapril and enalapril inhibit local angiotensin I conversion in human veins but lack direct venodilating properties.

We studied the angiotensin-converting enzyme (ACE)-dependent and ACE-independent (direct) effects of two ACE inhibitors, cilazaprilat and enalaprilat, in 12 healthy human subjects. The dorsal hand vein compliance technique was used because venous constriction and relaxation, independent of reflex responses and systemic ACE inhibition, can be measured by local infusions of very small amounts of drugs. Angiotensin I (dose range 6–1,550 ng/min) was infused alone or coinfused with cilazaprilat or enalaprilat (dose range 7.8–3,900 ng/min). In separate experiments, cilazaprilat or enalaprilat (dose range 3.9–31 μg/min), or prostaglandin I2 (PGI2, dose range 0.13–32 ng/min) was infused into veins that had been submaximally preconstricted with phenylephrine. Angiotensin I caused a marked venoconstriction limited by rapid tachyphylaxis. At doses >78 ng/min, cilazaprilat and enalaprilat completely inhibited angiotensin I-induced venoconstriction. This inhibition was reversible after 14–31 min, suggesting an inhibition of ACE associated with the vein wall. Infusions of cilazaprilat or enalaprilat had no effect on the diameter of the vein at rest or after submaximal preconstriction with phenylephrine. In contrast, exogenous PGI2 was a potent venodilator in our system. We conclude that cilazaprilat and enalaprilat are inhibitors of ACE associated with the vein wall, but there is no evidence for either drug of direct, ACE-independent, prostaglandin-mediated vasodilation.

Effects of cisplatin on urinary thromboxane B2 excretion

Thromboxane A2 (TxA2) is implicated in the pathogenesis of various forms of drug‐induced renal damage. Based on previous functional studies, we postulated that cis‐dichlorodiammineplatinum (cisplatin) induces intrarenal TxA2 synthesis. To test this hypothesis, we measured urinary excretion of thromboxane B2 (TxB2), the stable inactive metabolite of TxA2, during and after cisplatin administration.

Effect of ritanserin, a 5‐hydroxytryptamine2– receptor antagonist, on platelet function and thrombin generation at the site of plug formation in vivo

To investigate the role of serotonin in platelet plug formation we studied, in eight healthy volunteers, the effect of ritanserin (a 5‐hydroxytryptamine2–receptor antagonist) on the platelet release reaction (represented by β‐thromboglobulin release) platelet prostaglandin metabolism (represented by thromboxane B2 formation), and thrombin generation (represented by fibrinopeptide A formation) in the microvasculature. After administration of ritanserin lower amounts of thromboxane B2 were generated in the initial stages of plug formation, suggesting an inhibitory effect on the platelet prostaglandin metabolism. Similar amounts of β‐thromboglobulin were released after the administration of ritanserin compared with placebo, indicating a minor effect of ritanserin on the release reaction. Reduction of thrombin formation by ritanserin in the later stages of hemostasis suggested an inhibitory effect of this substance on the procoagulatory activity of platelets or endothelial cells. This could be attributable to interference with the formation or function of coagulation factor complexes on cell surfaces, or it could be the consequence of a reduction of the platelet activity.

Phase-I Study of Intraperitoneal Mitoxantrone – Clinical and Pharmacokinetic Evaluation

Mitoxantrone, a recent anthracenedione derivative is a potentially useful drug for direct intraperitoneal (i.p.) application because of its high tissue-binding and therapeutic index. We have carried out studies to establish maximum tolerated doses as well as pharmacokinetic studies with i.p. mitoxantrone in 21 patients (5 male, 16 female) with gastrointestinal (9), ovarian (6), unknown (2) and other (4) primary cancers and peritoneal carcinomatosis. Increasing doses (10-40 mg/m2) were given i.p. every 4 weeks. Five partial remissions (2-8+ months) and 7 stable disease courses (2-6+ months) were achieved. A reduction or disappearance of ascites was seen in an additional 3 patients. Severe toxicity (leukopenia) was observed in 4 patients only after 35 mg/m2 and 40 mg/m2 i.p. Pharmacokinetic analysis using high-performance liquid chromatography yielded the following data: The mean ratio of area under curve peritoneal fluid to serum was 1,108. The peritoneal clearance ranged from 2 ml/min to 9,617 ml/min and the disappearance half-life from 0.6-28.9 h. Mean urinary excretion within 24 h was 0.42% of the i.p. dose. These data indicate that mitoxantrone is sequestered in the intraperitoneal tissue compartment and only slowly released. Based on the outcome of this phase-I study we recommend phase-II studies at a dose of 30 mg/m2 i.p., repeated every 3-4 weeks.

Poly(I) · Poly(C), a potential drug carrier for the antitumor agent mitoxantrone: in vitro drug binding study

SummaryCoupling of mitoxantrone, a new antitumor agent, to a macromolecular carrier system may improve the drugs selectivity of action and pharmacokinetic properties. We have studied in vitro binding of mitoxantrone to poly(I)·poly(C), a macromolecular, double-stranded homoribopolymer, by equilibrium dialysis and high-performance liquid chromatography (HPLC).Results showed high binding affinity for mitoxantrone to poly(I)·poly(C) (Kd=1.05·10-6M), the calculated number of mitoxantrone-binding sites is 60 per molecule poly(I)·poly(C). In view of the good tolerance in clinical studies, poly(I)·poly(C) may thus be a useful drug carrier for mitoxantrone. A mitoxantrone:poly(I)·poly(C) ratio of 1:30 (w/w) is recommended for therapeutic studies.

Normal responsiveness of superficial hand veins to alpha- and beta-adrenergic stimuli in allergic asthma: Effects of terbutaline and prednisolone on beta-adrenergic responsiveness

Impaired function of the adrenergic-receptor system has been postulated to contribute to the pathogenesis of bronchial asthma. Using the dorsal hand-vein compliance technique, we compared the changes in diameter of superficial hand veins in response to phenylephrine, an alpha-adrenoceptor agonist, and to isoproterenol, a beta-adrenoceptor agonist, in 14 untreated patients with allergic asthma and in 16 nonatopic control subjects. There were no significant differences in the median effective dose of phenylephrine that produced 50% of maximal venoconstriction (ED50) or in the maximal response (Emax) between the two groups. Bronchial hyperreactivity (assessed by methacholine-challenge tests) in the patients with asthma was uncorrelated with the ED50 or Emax of isoproterenol. These results demonstrate no evidence for a generalized change in alpha- or beta-adrenergic responsiveness on smooth muscle cells in asthma. Hand-vein responsiveness to isoproterenol was unchanged after treatment for 7 days with oral terbutaline (5 mg three times per day). Thus, unlike leukocytes, smooth muscle appears not readily susceptible to beta-adrenoceptor desensitization in vivo. Local infusions of prednisolone or dexamethasone during 2 hours and systemic administration of dexamethasone (24 hours) caused a significant fall in the Emax for isoproterenol. The mechanism of attenuation of beta-adrenoceptor responsiveness by corticosteroids remains to be determined.