Pharmacokinetics of phenoxodiol, a novel isoflavone, following intravenous administration to patients with advanced cancer.

BACKGROUND: Phenoxodiol is a novel isoflavone currently being studied in clinical trials for the treatment of cancer. This study reports the pharmacokinetics of phenoxodiol in patients with cancer. METHODS: The pharmacokinetics of phenoxodiol was studied following a single intravenous (iv) bolus dose and during a continuous intravenous infusion. Three men with prostate cancer and 3 women with breast cancer received IV bolus phenoxodiol (5 mg/kg) and plasma was sampled for free and total phenoxodiol levels. On a separate occasion 5 of the same patients received a continuous intravenous infusion of phenoxodiol (2 mg/kg/h) and plasma was again sampled for free and total phenoxodiol levels. Phenoxodiol was measured using gradient HPLC with ultraviolet detection. RESULTS: Following bolus injection, free and total phenoxodiol appeared to follow first order pharmacokinetics. The elimination half-lives for free and total phenoxodiol were 0.67 ± 0.53 h and 3.19 ± 1.93 h, respectively, while the total plasma clearance rates were 2.48 ± 2.33 L/h and 0.15 ± 0.08 L/h, respectively. The respective apparent volumes of distribution were 1.55 ± 0.69 L/kg and 0.64 ± 0.51 L/kg. During continuous intravenous infusion, free phenoxodiol accumulated rapidly to reach a mean concentration at steady state of 0.79 ± 0.14 µg/ml after 0.87 ± 0.18 h. The apparent accumulation half-life of free phenoxodiol was 0.17 ± 0.04 h while the plasma clearance during continuous infusion was 1.29 ± 0.23 L/h. CONCLUSIONS: Phenoxodiol has a short plasma half-life, particularly in the free form, leading to a rapid attainment of steady state levels during continuous intravenous infusion. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry (ANZCTR): ACTRN12610000334000.

Arterial stiffness and haemodynamic response to vasoactive medication in subjects with insulin-resistance syndrome.

INSR (insulin-resistance syndrome) affects 25% of the Australian population and is associated with increased cardiovascular risk. In the present study, we postulated that early cardiovascular changes in these individuals may be associated with an activated RAS (renin-angiotensin system). We studied 26 subjects: 13 with INSR [waist circumference, 99+/-6 cm; HOMA (homoeostasis model assessment) score, 2.5+/-0.3] and 13 NCs (normals controls; waist circumference, 77+/-2 cm; HOMA score, 1.4+/-0.2). All received intravenous GTN (glyceryl trinitrate; 10, 20 and 40 microg/min), L-NMMA (N(G)-monomethyl-L-arginine; 3 mg/kg of body weight), AngII (angiotensin II; 8 and 16 ng/min), the selective AT(2)R (AngII type 2 receptor) inhibitor PD123319 (10 and 20 microg/min) and AngII (16 ng/min)+PD123319 (20 microg/min). At the end of each infusion, arterial stiffness indices [SI (stiffness index) and RI (reflection index)] and haemodynamic parameters were measured. There was a significantly higher RI response to AngII (P=0.0004 for both 8 and 16 ng/min doses) and to PD123319 (P=0.004 and P=0.03 for 10 and 20 microg/min doses respectively) in subjects with INSR compared with NCs. Co-infusion of AngII and PD123319 did not lead to additive changes in RI. RI responses to L-NMMA and GTN were not significantly different in both groups. No significant differences in SI and haemodynamic responses were detected. In conclusion, AT(1)R (AngII type 1 receptor) and AT(2)R activity produce arterial stiffness changes in subjects with INSR. Evidence of increased AT(1)R- and AT(2)R-mediated responses in small-to-medium-sized arteries in INSR was found, and may play an early role in the pathogenesis of vascular changes in INSR before haemodynamic changes become apparent.

Phase Ib single- and multiple-dose pharmacokinetic study of oral NV-52 in healthy volunteers.

BACKGROUND AND OBJECTIVE: NV-52 is a novel synthetic flavonoid thromboxane synthase (TXS) inhibitor that may be useful for the maintenance of remission in inflammatory bowel disease (IBD). This study was conducted to determine the single- and multiple-dose pharmacokinetics of NV-52 in nine healthy volunteers (five men, four women; mean [+/- SD] age 23 +/- 2 years). METHODS: NV-52 400 mg was administered once daily for 10 days (excluding day 2) in an open-label study. Plasma was sampled and urine was collected for 48 hours after the first and last doses. Plasma and urine unconjugated and total (unconjugated plus glucuronide and sulphate conjugated) NV-52 concentrations were measured using liquid chromatography-mass spectrometry. RESULTS: No adverse events were observed. Unconjugated and total NV-52 appeared and rose rapidly in plasma following the first dose. Time to maximum concentration values were 1.92 +/- 1.17 and 2.72 +/- 1.52 hours for unconjugated and total NV-52, respectively. Unconjugated and total NV-52 were eliminated with plasma half-lives of 13.12 +/- 17.31 and 18.03 +/- 19.06 hours, respectively, following the first dose. Pre-dose levels following multiple-dose administration were 135.17 +/- 120.03 and 751.9 +/- 679.74 ng/mL for unconjugated and total NV-52, respectively. Multiple-dose administration did not significantly alter the pharmacokinetics of NV-52. Renal elimination accounted for about 20-35% of the total (largely conjugated) drug but only 1% of unconjugated NV-52. CONCLUSIONS: Plasma concentrations of unconjugated NV-52 following single- and multiple-dose administration were well above the range found to be associated with suppression of colitis in a murine model of IBD.

Phase I and pharmacokinetic study of weekly NV06 (Phenoxodiol), a novel isoflav-3-ene, in patients with advanced cancer.

BACKGROUND: We wished to define the maximum tolerated dose (MTD), toxicity, and pharmacokinetics of the novel isoflav-3-ene, NV06 (Phenoxodioltrade mark), a compound with a diphenolic structure related chemically and biologically to genistein and flavopiridol. PATIENTS AND METHODS: Twenty-one patients with advanced cancers were treated with weekly intravenous administration of NV06 at escalating dose levels with 1-4 patients at each dose cohort. Plasma sampling was undertaken to characterize the pharmacokinetic (PK) profile of the compound. RESULTS: Toxicity was minimal, with asymptomatic Grade 3 lymphocytopenia occurring in nine patients. Nine patients developed Grade 1 nausea, six patients developed Grade 1 increases in alkaline phosphatase, and six patients developed Grade 1 increases in transaminases. Two patients experienced hypersensitivity reactions. The MTD was not reached. Most patients had progressive disease on treatment but eight completed 12 weeks and two completed 24 weeks of treatment. The best response was stable disease of 6 months duration. The plasma half-life (T1/2), clearance (Cl), and volume of distribution (VD) were 304 (+/-91) min, 82 (+/-19) ml/min and 32,663 (+/-7,199) ml, respectively, for total NV06. CONCLUSIONS: NV06 is well tolerated and can be given safely as an intravenous infusion over 1-2 h at a dose of at least 30 mg/kg.

Isoflavone therapy for menopausal flushes: a systematic review and meta-analysis.

OBJECTIVE: To perform a systematic review and meta-analysis of all randomized, controlled trials of isoflavone supplementation to determine the efficacy of isoflavone therapy in reducing the number of daily menopausal flushes. METHODS: A comprehensive search of published studies of isoflavone treatment and menopausal flushing was undertaken. Studies were selected if they were randomized, were placebo controlled, provided the number of baseline flushes, the variance in flushes and the reduction in flushes. Effects for isoflavone treatment compared to control were calculated and a meta-analysis was performed. Regression analysis, weighted for the size of the study was performed to investigate the relationship between the dose of isoflavone, or number of baseline flushes and the reduction in flushes achieved compared to control. RESULTS: Isoflavone supplementation was found to be associated with a significant reduction in flushes (effect size -0.28, 95% confidence intervals -0.39 to -0.18, P < 0.0001). Marked heterogeneity was found between the studies, but the effect remained significant when analyzed using a random effects model (delta = -0.49, 95% confidence intervals -0.81 to -0.17, P = 0.001). The percentage reduction in flushes was significantly related to the number of baseline flushes per day and the dose of isoflavone studied (beta = -0.49 and -0.26, respectively, both P < 0.0001). CONCLUSIONS: These results suggest that isoflavone supplementation may produce a slight to modest reduction the number of daily flushes in menopausal women and that the benefit may be more apparent in women experiencing a high number of flushes per day.

Effects of intravenous PD 123319 on haemodynamic and arterial stiffness indices in healthy volunteers.

Relatively little is known about the functional expression of cardiovascular angiotensin type 2 (AT2)-receptors in healthy young adult humans. We performed a randomised, placebo-controlled crossover study of the effects of intravenous administration of the selective AT2-receptor antagonist PD 123319 on haemodynamics and arterial stiffness in normal volunteers. Sixteen normal subjects aged 29.9+/-13.8 years (range 18-30 years) received an intravenous infusion of PD 123319 (10 mcg/minute for 5 minutes) and placebo, separated by one week. Haemodynamics (cardiac index, stroke index and systemic vascular resistance) were measured non-invasively using a BioZ.com thoracic impedance detection system. Blood pressure was measured from an arm cuff using oscillometry. Stiffness index, a measure of arterial stiffness, was measured using a Pulse Trace recorder. No significant changes in blood pressure (p=0.92), cardiac index (p=0.52), stroke index (p=0.61), systemic vascular resistance index (p=0.32) or stiffness index (p=0.57) was demonstrated following PD 123319 infusion, compared with placebo. The results of this study do not support the functional presence of cardiovascular AT2-receptors that mediate acute haemodynamic effects in healthy young adults. It remains possible that higher doses of PD 123319 may be required to demonstrate functional cardiovascular AT2-receptors in this population, if they are present.

Can angiotensin receptor antagonists be used safely in patients with previous ACE inhibitor-induced angioedema?

Angioedema is an uncommon but potentially life-threatening adverse event associated with ACE inhibitor therapy which is believed to be due to potentiation of the vascular effects of bradykinin. Angiotensin receptor antagonists were not expected to produce angioedema, as they do not inhibit the catabolism of bradykinin. However, it is now apparent that angioedema is occasionally associated with angiotensin receptor antagonist therapy and may be more likely to occur in patients who have previously experienced angioedema while receiving ACE inhibitors. Angiotensin receptor antagonists cannot be considered to be a safe alternative therapy in patients who have previously experienced ACE inhibitor-associated angioedema.

Selective cyclo-oxygenase-2 inhibitors and myocardial infarction: how strong is the link?

There are concerns that selective cyclo-oxygenase (COX)-2 inhibitors may be prothrombotic and increase the risk of myocardial infarction. This has largely arisen because of an unexpected finding of a higher rate of myocardial infarction in patients receiving rofecoxib compared with patients receiving naproxen in a study of gastrointestinal toxicity. The results of this study, a similar study of celecoxib versus ibuprofen or diclofenac, and data obtained from a meta-analysis of aspirin (acetylsalicylic acid) primary prevention trials suggest that differences in the rates of myocardial infarction between rofecoxib and naproxen may have been due to an unexpectedly low rate of myocardial infarction in patients receiving naproxen. However, population surveillance data also suggest that rofecoxib may be associated with a greater risk of myocardial infarction than celecoxib and certain nonselective nonsteroidal anti-inflammatory drugs. The magnitude of this increase in risk, if real, is uncertain but it is likely to be relatively small in patients for whom cardiovascular prophylaxis with aspirin is not indicated. Patients who require nonsteroidal anti-inflammatory therapy for arthritis and who are at high risk of cardiovascular disease should receive aspirin, probably in conjunction with selective COX-2 inhibitor therapy, as the risk of gastrointestinal ulceration may be lower than for aspirin plus a nonselective nonsteroidal anti-inflammatory drug. In patients who do not require aspirin for the prevention of cardiovascular events, the lower risk of gastrointestinal ulceration associated with COX-2 inhibitor compared with non-selective nonsteroidal anti-inflammatory drugs would be expected to outweigh any increase in the risk of myocardial infarction, if one exists.

Long-term pharmacokinetics of an extract of isoflavones from red clover (Trifolium pratense).

OBJECTIVES: To study the pharmacokinetics of isoflavones from red clover (Trifolium pratense) after long-term administration as a once-daily dietary supplementary. DESIGN: Fourteen (14) subjects who had been consuming a low-isoflavone diet for 2 weeks were given an oral dose of two isoflavone tablets (approximately 80 mg of total isoflavones) daily for 2 weeks and appeared for a study day at 9:00 AM after an overnight fast on the day that they were to receive the last dose. Plasma samples were collected for a 48-hour period after the last dose. Plasma isoflavones were assayed by high-performance liquid chromatography (HPLC). RESULTS: Trough plasma levels were significantly higher for daidzein and genistein after long-term dosing than levels taken prior to the commencement of the study and plasma levels of isoflavones after long-term dosing were in the range previously reported in populations that consume an isoflavone-rich diet. The plasma half-lives observed after long-term administration were, in most cases, consistent with once-daily administration. CONCLUSIONS: Isoflavones have pharmacokinetic characteristics that suggest that once-daily administration is adequate when they are administered long-term as dietary supplements.

Clinical pharmacology of isoflavones and its relevance for potential prevention of prostate cancer.

Isoflavones are phytoestrogens that have pleiotropic effects in a wide variety of cancer cell lines. Many of these biological effects involve key components of signal transduction pathways within cancer cells, including prostate cancer cells. Epidemiological studies have raised the hypothesis that isoflavones may play an important role in the prevention and modulation of prostate cancer growth. Since randomized phase III trials of isoflavones in prostate cancer prevention are currently lacking, the best evidence for this concept is presently provided by case control studies. However, in vitro data are much more convincing in regard to the activity of a number of isoflavones, and have led to the development of genistein and phenoxodiol in the clinic as potential treatments for cancer. In addition, the potential activity of isoflavones in combination with cytotoxics or radiotherapy warrants further investigation. This review focuses on the clinical pharmacology of isoflavones and its relevance to their development for use in the prevention of prostate cancer, and it evaluates some of the conflicting data in the literature.

Arterial stiffness in insulin resistance: the role of nitric oxide and angiotensin II receptors.

The insulin resistance syndrome (INSR) is associated with increased cardiovascular risk, and affects up to 25% of the Australian population aged >20 years. Increased arterial stiffness has been proposed as a common pathway by which INSR leads to increased cardiovascular risk. We have reviewed the role of nitric oxide (NO) and angiotensin II receptors in the modulation of arterial stiffness in the setting of insulin resistance. There is emerging evidence that early stages of INSR may be characterized by increased basal nitric oxide activity and increased activity of non-NO vasodilators such as endothelial derived hyperpolarization factor (EDHF) which is manifest by reduced arterial stiffness. Depletion of NO or ineffectiveness of NO mediated vasodilator mechanisms associated with the progression of INSR to type 2 diabetes may result in increased arterial stiffness, which predicts the development of cardiovascular disease. Thus in the early stages of INSR, increased NO and EDHF activity may represent compensatory mechanisms to early vascular damage. The renin-angiotensin system is activated in diseased vascular beds, with up regulation of the two known angiotensin II receptors: the angiotensin II type 1 receptor (AT1R) and the angiotensin II type 2 receptor (AT2R). Increased AT1R mediated activity in the vasculature is central to the development of increased arterial stiffness and is enhanced in INSR states. AT2R activity is increased in early in INSR and may contribute to the apparent increase in basal NO activity. AT1R blockade may therefore be valuable treatment for early INSR as antagonism of AT1 receptors would allow angiotensin II to act unopposed at AT2 receptors.

Arterial stiffness indices in healthy volunteers using non-invasive digital photoplethysmography.

BACKGROUND: Increased arterial stiffness is a marker of cardiovascular damage, even in the absence of clinically apparent disease. It is likely to become an important clinical tool in cardiovascular risk assessment. AIMS AND METHODS: We studied a group of healthy subjects and measured their arterial stiffness by digital photoplethysmography. We aimed to obtain a range of arterial stiffness values, and investigated the influence of age, gender, race, body mass index, fasting lipids and haemodynamic factors. RESULTS: One hundred and fifty-two healthy subjects, aged between 18 and 67 years, on no medications and with no significant medical illnesses were recruited. The population was predominantly Caucasian (n = 112). Two measures of arterial stiffness were obtained: stiffness index (SI), a measure of large arterial stiffness, and reflection index (RI), a measure of small to medium-sized arterial stiffness. SI and RI were significantly correlated with age, total cholesterol, low-density lipoprotein-cholesterol, heart rate (HR), systolic blood pressure (SBP) and diastolic blood pressure (DBP). Race was a significant independent predictor of SI. CONCLUSION: Digital photoplethysmography is a portable, operator-independent, reproducible and simple method of measuring arterial stiffness. Ranges of normality of arterial stiffness will depend on the individual's age, race, lipid levels, HR and blood pressure.

The withdrawal of torcetrapib from drug development: implications for the future of drugs that alter HDL metabolism.

In December 2006, Pfizer withdrew torcetrapib, a cholesterol ester transferase protein (CETP) that elevates plasma HDL levels, from further development following an excess in mortality in the active treatment arm of the study. Although torcetrapib successfully elevated HDL levels, significant increases in blood pressure were observed in three surrogate outcome studies that were conducted over the approximate same time period. Two of these studies examined carotid intima-medial thickness and one examined coronary artery atheroma load and none of the studies found a significant benefit in favour of torcetrapib therapy. It is likely that the torcetrapib-induced increase in blood pressure contributed to the apparent adverse effect of the drug on mortality and further studies are needed to determine why this occurred and whether it is a class effect of CETP inhibitors. In addition, further research is needed to determine whether the manner which CETP alters vascular biology and, in particular, the effect that it has on vascular inflammation associated with denuded endothelium. Despite disappointing results so far, CETP inhibitors should not be abandoned as much remains to be learnt from them and they may yet prove to be a valuable class of lipid-modifying drug.