Investigation of bioavailability and pharmacokinetics of treosulfan capsules in patients with relapsed ovarian cancer

Purpose: Treosulfan (l-threitol-1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. In a pharmacologic study of the bioavailability of treosulfan in a capsule formulation, patients with relapsed ovarian carcinoma were treated with alternating doses of oral and intravenous (i.v.) treosulfan of 1.5 or 2.0 g daily for 5 to 8 days. Methods: A sensitive method for the determination of treosulfan in plasma and urine by reversed-phase high-performance liquid chromatography had previously been developed. Pharmacokinetic analyses of treosulfan were carried on plasma and urine samples from 20 i.v. courses and 20 courses of oral administration. Results: The bioavailability ratio (f) of oral to i.v. administration was calculated as 0.97 ± 0.18 (mean ± SD) using the values AUC_oral=82.1 ± 39.4 μg/ml h and AUC_i.v.=85.4 ± 30.3 μg/ml h. The peak plasma concentration c_max (29 ± 14 μg/ml vs 65 ± 23 μg/ml) was significantly (P < 0.01) higher after i.v. administration and the t_max after oral administration was 1.5 ± 0.34 h. The terminal half-life of treosulfan was about 1.8 h. The mean urinary excretion of the parent compound was about 15% of the administered total dose over 24 h (range 6–26%). Conclusions: The high and relatively constant bioavailability of treosulfan indicates that capsules provide a satisfactory noninvasive treatment alternative. A feasible and reliable oral treosulfan formulation could provide the basis for the development of long-term low-dose outpatient treatment of patients with malignant diseases. Received: 28 July 1999 / Accepted: 16 December 1999     

Phase I and pharmacokinetic study of d-limonene in patients with advanced cancer

Purpose: d -Limonene is a natural monoterpene with pronounced chemotherapeutic activity and minimal toxicity in preclinical studies. A phase I clinical trial to assess toxicity, the maximum tolerated dose (MTD) and pharmacokinetics in patients with advanced cancer was followed by a limited phase II evaluation in breast cancer. Methods: A group of 32 patients with refractory solid tumors completed 99 courses of d-limonene 0.5 to 12 g/m² per day administered orally in 21-day cycles. Pharmacokinetics were analyzed by liquid chromatography-mass spectrometry. Ten additional breast cancer patients received 15 cycles of d-limonene at 8 g/m² per day. Intratumoral monoterpene levels were measured in two patients. Results: The MTD was 8 g/m² per day; nausea, vomiting and diarrhea were dose limiting. One partial response in a breast cancer patient on 8 g/m² per day was maintained for 11 months; three patients with colorectal carcinoma had prolonged stable disease. There were no responses in the phase II study. Peak plasma concentration (C_max) for d-limonene ranged from 10.8 ± 6.7 to 20.5 ± 11.2 μM. Predominant circulating metabolites were perillic acid (C_max 20.7 ± 13.2 to 71 ± 29.3 μM ), dihydroperillic acid (C_max 16.6 ± 7.9 to 28.1 ± 3.1 μM ), limonene-1,2-diol (C_max 10.1 ± 8 to 20.7 ± 8.6 μM ), uroterpenol (C_max 14.3 ± 1.5 to 45.1 ± 1.8 μM ), and an isomer of perillic acid. Both isomers of perillic acid, and cis and trans isomers of dihydroperillic acid were in urine hydrolysates. Intratumoral levels of d-limonene and uroterpenol exceeded the corresponding plasma levels. Other metabolites were trace constituents in tissue. Conclusions: d-Limonene is well tolerated in cancer patients at doses which may have clinical activity. The favorable toxicity profile supports further clinical evaluation. Received: 25 June 1997 / Accepted: 6 November 1997     

Clinical pharmacokinetics of intravenous treosulfan in patients with advanced solid tumors

Treosulfan (l-threitol-1,4-bis-methanesulfonate, Ovastat) is a prodrug of a bifunctional alkylating agent with activity in ovarian carcinoma and other solid tumors. For a clinical and pharmacology study, patients with advanced, refractory, or resistant solid tumors were treated with a single-dose intravenous 30-min infusion of 8 or 10 g/m² treosulfan. A sensitive method for the determination of treosulfan in plasma and urine by reverse-phase high-performance liquid chromatography was developed. A total of 14 plasma and urine treosulfan pharmacokinetics determinations were analyzed in the 8-g/m² group and 7 were analyzed in the 10-g/m² group, the maximum tolerated dose for this group of pretreated patients. The terminal half-life of treosulfan was in the range of 1.8 h. AUC and C_max values were significantly (P < 0.01) higher in the 10-g/m² group (AUC 708 ± 168 versus 977 ± 182 μg ml⁻¹ h, C_max 465 ± 98 versus 597 ± 94 μg/ml). The mean urinary excretion of the parent compound was about 25% of the total dose delivered over 48 h (range 5–49%), and about 20% was excreted during the first 6 h after administration. Currently, a clinical phase I pharmacokinetics and dose-escalation trial with autologous blood stem-cell support has been started at 20 g/m² treosulfan using a 2-h infusion protocol. Received: 25 August 1997 / Accepted: 15 December 1997     

Bioavailability and phase II study of oral UFT plus leucovorin in patients with relapsed or refractory colorectal cancer

Purpose: This study was undertaken to address the influence of concurrent administration on the pharmacokinetics of UFT (uracil plus tegafur) and leucovorin (LV), and to measure the antitumor activity of a 28-consecutive-day oral regimen of UFT plus LV in patients with relapsed or refractory colorectal cancer. Methods: Patients with advanced measurable colorectal cancer who had failed previous therapy with intravenous bolus 5-fluorouracil (5-FU) were eligible. Patients were treated with UFT 300 mg/m² per day plus LV 90 mg per day in three divided doses every 8 h for 28 days, repeated at 35-day intervals. In addition, a three-treatment by three-period crossover bioavailability comparison of oral LV 30 mg plus UFT 200 mg versus either LV or UFT alone was scheduled for the 8 days preceding the first cycle of therapy. Results: Of 19 patients enrolled, 18 were assessable for pharmacokinetics and response. When LV was coadministered with UFT, there were no statistically significant effects on tegafur, uracil, or 5-FU C_max, AUC, or T_max, with the exception of a delayed T_max for tegafur (P = 0.03). No statistically significant differences were found in LV and 5-methyltetrahydrofolate plasma levels when LV was administered alone or with UFT. However, wide interpatient variability was observed for all parameters. There were no antitumor responses seen. Conclusions: Although the T_max for tegafur is delayed with the concurrent administration of LV, there were no differences (P > 0.05) in any pharmacologic parameters that are of likely clinical significance. However, the great interpatient variability observed in UFT and LV pharmacology may have obscured true bioavailability effects in this small patient population. Daily oral UFT plus LV is inactive as second-line therapy in patients who have failed bolus 5-FU. Received: 13 March 1998 / Accepted: 1 June 1998     

The effects of food and divided dosing on the bioavailability of oral vinorelbine

 The effects of food and divided dosing on the bioavailability of a liquid-filled gelatin capsule formulation of vinorelbine (Navelbine), a semisynthetic vinca alkaloid with broad clinical activity, was evaluated in patients with advanced solid tumors. A group of 13 patients were randomized to treatment with the oral formulation at the recommended phase II dose of 80 mg/m² per week either in the fasting state or after ingestion of a standard meal. Patients were treated 1 week later in the alternate state relative to their first dose. The effects of divided dosing were assessed during the 3rd week, at which time vinorelbine was administered in two divided doses. After the completion of pharmacokinetic and bioavailability studies, patients received the oral formulation at a dose of 80 mg/m² per week in two divided doses to evaluate the feasibility of chronic oral drug administration. Both manipulations resulted in small, albeit statistically significant, reductions in the relative bioavailability of this oral formulation. The relative bioavailability decreased by 22±28% when treatment followed the ingestion of a standard meal, possibly due to a delay in gastrointestinal transit time. The mean time of maximum plasma concentration (T_max) increased from 1.3±1.6 h in the fasting state to 2.5±1.6 h in the fed state, although this difference was not statistically significant. Similarly, the relative bioavailability declined by 16±51% when vinorelbine was administered in two divided doses. An analysis of dose proportionality revealed disproportionate increases in dose-normalized C_max and AUC values with single oral doses above 120 mg, which may account for this phenomenon. The high clearance of vinorelbine, which approaches hepatic blood flow, and the lack of dose proportionality after oral administration, indicate that there is a large first-pass effect which may be saturable, or nonlinear, above single doses of 120 mg. In addition, the toxicological and pharmacological characteristics of oral vinorelbine indicate that treatment after a standard meal or on a divided dosing schedule is safe. Chronic oral administration of the agent in two divided doses was also well tolerated. However, the small reduction in the relative bioavailability following the ingestion of a standard meal and with divided dosing suggest the need for further pharmacodynamic studies to determine if reductions in drug exposure of this magnitude may portend diminished antitumor activity. Received: 4 October 1994/Accepted: 15 December 1995     

Effect of gastric pH on the relative oral bioavailability and pharmacokinetics of temozolomide

Purpose: Temozolomide is an imidazotetrazine alkylating agent which undergoes chemical conversion at physiological pH to the active species 5-(3-methyltriazene-1-yl)imidazole-4-carboxamide (MTIC) but is stable at acid pH. This study evaluated the effect of an increase in gastric pH, through the use of ranitidine, on the oral bioavailability and plasma pharmacokinetics of temozolomide and MTIC. Methods: Fifteen patients with advanced cancer were enrolled of which 12 were evaluable, all of whom had pharmacokinetic blood sampling. Each patient received temozolomide 150 mg m⁻² day⁻¹ for 5 days in cycle 1 and also received ranitidine 150 mg every 12 h either on days 1 and 2 or days 4 and 5. Gastric pH was monitored by the use of the Heidelberg capsule system. Results: Following the administration of ranitidine there was a rise in gastric pH by 1–2 pH units over the duration of the study period (pH range 2.2–5.2 without ranitidine and 3.5–6.0 with ranitidine). There was no difference in the pharmacokinetic parameters of temozolomide or MTIC with or without the concomitant administration of ranitidine. There was however, a lower C_max for temozolomide and MTIC for patients receiving ranitidine on day 1 and 2 versus day 4 and 5. Temozolomide was rapidly absorbed [time to maximum plasma concentration (t _max) 1.8 h] and eliminated [elimination half-life (t _1/2) 1.8 h] and MTIC followed a similar pattern with a t _max of 1.9 h and a t _1/2 of 1.9 h. Overall, the AUC of the MTIC represented about 2–4% of the AUC for temozolomide. Received: 15 December 1998 / Accepted: 16 March 1999     

Interpatient variability in bioavailability of the intravenous formulation of topotecan given orally to children with recurrent solid tumors

Purpose: Evaluation of inter- and intrapatient variability of topotecan oral bioavailability and disposition was performed in children with malignant solid tumors. Patients and methods: Topotecan i.v. formulation was given orally on schedules of daily for 21 consecutive days (d × 21) or daily for 5 days per week for 3 weeks [(d × 5)3], in both cases repeated every 28 days. Topotecan doses of 0.8 and 1.1 mg/m² per day were evaluated on both schedules. Serial plasma samples were obtained after oral and i.v. administration of topotecan at the beginning and end of the first course of therapy. Topotecan lactone and total concentrations were measured by a high-performance liquid chromatography (HPLC) assay, and a one-or two-compartment model was fit to the plasma concentration-time data after oral or i.v. administration, respectively. Topotecan oral bioavailability (F) was calculated as the ratio of the AUC determined after oral treatment (AUC_po) divided by the AUC calculated after i.v. administration. Results: Pharmacokinetics studies were performed on 15 and 11 patients receiving 0.8 and 1.1 mg/m² per day, respectively. After oral administration the topotecan lactone AUC_po and F determined for 0.8 and 1.1 mg/m² per day were 13.6 ± 5.8 and 25.1 ± 12.9 ng ml⁻¹ h and 0.34 ± 0.14 and 0.34 ± 0.16, respectively. The within-patient variance for AUC_po and F was much smaller than the between-patient variance. The ratio of topotecan lactone to total concentration was consistently higher after oral as compared with i.v. administration. Conclusions: Large interpatient variability was noted in topotecan pharmacokinetics, whereas intrapatient variability was relatively small. Further studies of oral topotecan are warranted to evaluate the tolerance of shorter courses and to define further the interpatient variability. Received: 14 August 1998 / Accepted: 9 November 1998     

Pharmacokinetics of intraperitoneal hyperthermic perfusion with mitoxantrone in ovarian cancer

Purpose: Theoretical data and experimental assumptions indicate that intraperitoneal hyperthermic chemotherapy may play a role in the treatment of peritoneal carcinomatosis. The feasibility, tolerability and pharmacokinetics of intraperitoneal hyperthermic perfusion with mitoxantrone were studied in patients with pretreated ovarian cancer. Methods: After cytoreductive surgery, 11 patients underwent intraperitoneal hyperthermic perfusion with mitoxantrone. A heated (42–43 °C) solution of the drug (28 mg/m²) was recycled through a perfusion apparatus into the abdominal cavity for 90 min. Treatment was repeated every month for two to four cycles. In six patients blood and peritoneal perfusate samples were collected at 0.5, 1, 1.5, 2, 4, 8, 16 and 24 h after drug administration and mitoxantrone was assayed by an HPLC method. Results: Although treatment was generally well tolerated, all patients developed transient intestinal subocclusion. Maximal mitoxantrone plasma concentrations (C_max), times to C_max (T_peak) and area under the curves (AUC) were highly variable between subjects (C_max 14–337 ng/ml; T_peak 0.5–8 h; AUC 222–4130 ng · ml⁻¹ · h). The plasma to peritoneal fluid AUC ratio was significantly higher during the second (0.177) than during the first cycle (0.066), suggesting a cycle-dependent increase in systemic bioavailability. Furthermore, when comparing present data with those reported previously, hyperthermic perfusion may have lowered the mitoxantrone levels in the peritoneal fluid without greatly influencing plasma levels. Conclusions: Intraperitoneal mitoxantrone administered under hyperthermia to advanced ovarian cancer patients is feasible and well tolerated. Mitoxantrone pharmacokinetics may be altered by repeated intraperitoneal administration (increased bioavailability) and by hyperthermic perfusion (possibly, increased peritoneal tissue uptake). Received: 6 September 1999 / Accepted: 11 January 2000     

Pharmacokinetics of paclitaxel administered in combination with cisplatin, etoposide and bleomycin in patients with advanced solid tumours

 Purpose: To evaluate the pharmacokinetics of paclitaxel and cisplatin administered in combination with bleomycin and etoposide and Granulocyte Colony-Stimulating Factor (G-CSF) in patients with advanced solid tumours. Methods: Patients were recruited to a phase I trial where escalating doses of paclitaxel (125 to 200 mg/m²) were administered in combination with etoposide 100 or 120 mg/m², and fixed dose of cisplatin 20 mg/m² and bleomycin 30 mg, with the concomitant use of G-CSF. Paclitaxel (3-h infusion) was followed by 1-h etoposide, 4-h cisplatin and 30-min bleomycin infusions, respectively. Pharmacokinetics sampling for paclitaxel analysis was performed in ten patients from dose levels II–V. Results: The mean paclitaxel area under the plasma concentration-versus-time curves (AUC) for the 125-mg/m² dose level (II) was 7.0 ± 3.6 h μmol⁻¹ l⁻¹, for the 175-mg/m² dose level (III) 10.6 ± 2.8 h μmol⁻¹ l⁻¹, for the 200-mg/m² dose level (IV) it was 16.0 ± 5.0 h μmol⁻¹ l⁻¹, and for the 175-mg/m² dose level (V) it was 12.5 ± 6.1 h μmol⁻¹ l⁻¹. The mean peak plasma concentration (C_max) values for dose levels II–V were 1.9 ± 1.1 μmol/l, 3.4 ± 1.2 μmol/l, 4.3 ± 1.0 μmol/l and 3.8 ± 1.2 h μmol/l, respectively. Conclusion: In this study, relevant pharmacokinetic parameters of paclitaxel like AUC, C_max and the paclitaxel plasma concentration above the pharmacologically relevant 0.1-μmol/l threshold concentration (t > 0.1 μM) when administered in combination with cisplatin, etoposide and bleomycin (PEB) were not statistically different from paclitaxel data of historical controls. However, given the trial design, pharmacokinetic interactions between the agents cannot be excluded. Received: 29 June 1998 / Accepted: 29 January 1999     

Erucylphosphocholine: pharmacokinetics, biodistribution and CNS-accumulation in the rat after intravenous administration

The clinical use of alkylphosphocholines (APC) in cancer patients is restricted because of the high gastrointestinal toxicity and the need for oral administration. Therefore we evaluated the clinical pharmacology of erucylphosphocholine (ErPC), the first derivative of the APC family suitable for intravenous administration with strong antineoplastic activity, in vitro and in vivo in rats. The pharmacokinetic parameters after a single intravenous dose of 40 mg/kg were calculated using a two-compartment model: C_max= 1.6 ± 0.3 μmol/ml, T_1/2α= 0.18 ± 0.09 h, T_1/2β= 3.3 ± 0.88 h, clearance = 9.7 ± 1.2 ml/h, AUC = 2.5 ± 0.3 μmol/ml per h and Vss = 40.4 ± 7.9 ml. Biodistribution studies were performed after repeated ErPC administration at different doses. Intravenous injections of 20 mg/kg given at intervals of 48 h for up to 4 weeks were well tolerated. Neither clinical evaluation nor laboratory parameters (haematology and clinical chemistry) revealed toxic side effects. In contrast, higher doses of ErPC (40 mg/kg per 48 h) led to weight loss. After 2 and 4 weeks of therapy with 20 mg/kg per 48 h a high ErPC accumulation was found in the adrenal glands, small intestine and brain. The brain to serum concentration ratios averaged 2.1 after 2 weeks and 4.5 after 4 weeks. Significant leucocytosis and thrombocytosis were observed after 4 weeks of ErPC treatment. The findings suggest that ErPC is a suitable candidate for clinical trials. In particular, owing to the high accumulation in brain tissue, ErPC is a potential agent for chemotherapy against malignant brain tumours. Received: 4 January 1999 / Accepted: 6 May 1999     

Pharmacokinetics of 2-chloro-2′-deoxyadenosine administered subcutaneously or by continuous intravenous infusion

Purpose: Cladribine (2-chlorodeoxyadenosine, 2-CDA) is effective in the treatment of various lymphoproliferative disorders. In the standard protocol the compound is administered by continuous intravenous (i.v.) infusion. In order to allow outpatient therapy alternative modes of administration such as subcutaneous (s.c.) injection would be desirable. The aim of the present study was to compare the pharmacokinetics of 2-CDA after i.v. and s.c. administration. Patients and methods: Nine patients received 0.1 mg/kg 2-CDA per 24 h on one occasion by continuous i.v. infusion and on another occasion as a bolus subcutaneously. The concentrations of 2-CDA in the plasma and urine were determined by HPLC. Results: During i.v. infusion the concentration of 2-CDA in the plasma reached a plateau after 4–8 h, whereas with s.c. administration almost ten times higher peak concentrations were reached within 20 to 60 min. A two-compartment model was fitted to the data points whereby the goodness-of-fit statistics showed R ² values of >0.98. The calculated rate of elimination, k_elim, averaged 0.336 h⁻¹ with s.c. and 0.397 h⁻¹ with i.v. administration. The estimated volumes of distribution were 1.67 and 1.58 l/kg. The areas under the concentration time curves (608 ± 65 pmol · h/ml after s.c. administration vs 571 ± 50 pmol · h/ml during i.v. infusion) and the urinary excretion of 2-CDA in 24 h (4.75 ± 0.95 vs 3.55 ± 0.53 μmol/24 h) were similar in both groups, indicating identical bioavailability. Conclusions: Although the pharmacokinetic profile of 2-CDA administered s.c. differs substantially from the profile of a continuous i.v. infusion the areas under the plasma concentration time curves, the urinary excretion of unchanged drug and the estimated pharmacokinetic variables were similar with both modes of administration, indicating that the different time-courses of the plasma concentration did not influence the fraction metabolized or eliminated. Received: 3 November 1999 / Accepted: 3 March 2000     

Plasma and cerebrospinal fluid pharmacokinetics of valproic acid after oral administration in non-human primates

Purpose Valproic acid (VPA), a widely used antiepileptic, also inhibits histone deacetylase (HDAC), and is undergoing evaluation as an anti-cancer agent. We studied the pharmacokinetics of VPA in the plasma and cerebrospinal fluid (CSF) in a non-human primate model that is highly predictive of human CSF penetration to determine if levels of VPA required to inhibit HDAC in in vivo models can be attained. Methods Oral VPA, 75 mg/kg, was administered to four non-human primates. Serial samples of blood (n = 4) and CSF (n = 3) were obtained for pharmacokinetic studies of total and free VPA. Plasma and CSF VPA concentrations were measured using the commercially available Abbott AxSYM VPA assay reagent system (Abbott Laboratories, Abbott Park, IL, USA). The resultant plasma and CSF data were evaluated using pharmacokinetic modeling methods. Results At a dose of 75 mg/kg, the maximum plasma concentration of VPA was 130.1 ± 70.6 μg/ml (mean ± standard deviation) for total drug and 53.3 ± 44.4 μg/ml for free drug. The mean plasma area under the curve (AUC) for total drug was 680 ± 233 μg/ml h and for free drug 146 ± 89 μg/ml hr. The maximum CSF concentration occurred 2–3 h after administration and was 28.2 ± 18.6 μg/ml. The CSF AUC for VPA was 108 ± 52 μg/ml h. The CSF penetration of VPA was 12.9 ± 5.1% for total drug and 57.0 ± 8.7% for free drug. Disappearance from the plasma followed non-linear kinetics with a V _max of 321.2 ± 65.6 μg/kg/min and a K _m of 17.2 ± 13.7 mg/l. Conclusion Valproic acid deserves further study for the treatment of CNS tumors given its high CSF penetration after oral dosing coupled with the anti-tumor activity observed in preclinical studies.     

N,N-diethyl-2-[4-(phenylmethyl)phenoxy] ethanamine (DPPE), a chemopotentiating and cytoprotective agent in clinical trials: interaction with histamine at cytochrome P450 3A4 and other isozymes that metabolize antineoplastic drugs

Purpose: N,N-diethyl-2-[4-(phenylmethyl)phe- noxy]ethanamine · HCl (DPPE), an intracellular histamine (HA) antagonist with chemopotentiating and cytoprotective properties, is currently in phase 2 and 3 clinical trials in breast and prostate cancer. DPPE modulates growth at in vitro concentrations that antagonize HA binding to cytochromes P450 in rat liver microsomes. HA inhibits P450 metabolism of some drugs. Recent in vitro studies in human colon cancer cells have linked DPPE enhancement of paclitaxel, doxorubicin and vinblastine cytotoxicity to inhibition of the P-glycoprotein (P-gp) pump. Many substrates of P-gp are also substrates of CYP3A4, a P450 isozyme that metabolizes a variety of antineoplastic agents and is highly expressed in some malignant tissues. Therefore, we assessed whether (a) DPPE and HA interact at CYP3A4 and other P450 human isozymes, and (b) DPPE inhibits the catalytic activity of CYP3A4. Methods: Using spectral analysis, we measured DPPE and HA binding to insect microsomes that express human P450 isozymes 1A1, 2B6, 2D6 or 3A4. Employing thin-layer chromatography, we assessed the metabolism of DPPE by each isozyme and DPPE inhibition of testosterone metabolism by CYP3A4 and by rat liver microsomes. Results: (1) DPPE evoked “type I” (substrate site binding) absorbance-difference spectra with CYP2D6 (K_s=4.1 ± 0.4 μM), CYP3A4 (K_s= 31 ±15 μM) and CYP1A1 (K_s=40 ± 9 μM), but not with CYP2B6. (2) In correspondence with the binding studies, DPPE was metabolized by CYP2D6, CYP3A4 and CYP1A1; no metabolism occurred with CYP2B6. (3) HA evoked “type II” (heme iron binding) absorbance-difference spectra with all four isozymes, with K_s values in the range 80–600 μM. DPPE inhibited HA (600 μM) binding to CYP2D6 (IC₅₀=4 μM, 95% CI=1.8–8.9 μM) and CYP1A1 (IC₅₀=135 μM: 95% CI=100–177 μM), but stimulated HA (500 and 1000 μM) binding to CYP3A4 (EC₅₀=155 μM, 95% CI=104–231 μM). DPPE did not affect HA binding to CYP2B6. (4) DPPE inhibited the metabolism of testosterone by CYP3A4. The concentration/effect curve was biphasic: DPPE inhibited metabolism by 30% at the first site (IC₅₀=3 μM, 95% CI=0.5–25.5 μM), and an additional 70% inhibition occurred at the second site (IC₅₀=350 μM, 95% CI=215–570 μM). A similar result was observed with rat liver microsomes. Conclusion: DPPE is a substrate for CYP3A4, CYP2D6 and CYP1A1, but not CYP2B6. DPPE inhibits testosterone metabolism by interacting at two sites on CYP3A4, the first correlating with its K_s value to bind the substrate site and the second, with its EC₅₀ value to enhance HA binding to the heme iron. We postulate that (1) the inhibitory effect of DPPE on CYP3A4 activity is mediated directly at the substrate site and indirectly by its enhancement of the binding of HA to the heme moiety; (2) in tumor cells that express high constitutive levels of CYP3A4, potentiation of chemotherapy cytotoxicity by DPPE results, in part, from inhibition of CYP3A4-mediated metabolism and P-gp-mediated efflux of antineoplastic drugs; (3) in normal cells that express low constitutive levels of the isozyme, cytoprotection by DPPE results, in part, from induction of CYP3A4 and P-gp, resulting in an increase both in metabolism and efflux of antineoplastic drugs. Received: 26 April 1999 / Accepted: 3 September 1999     

A pharmacokinetic and phase II study of gallium nitrate in patients with non-small cell lung cancer

This study investigated the pharmacokinetics and activity of gallium nitrate in non-small cell lung cancer when 700 mg/m² was given as a 30-min infusion with prehydration every 2 weeks. Gallium was measured in plasma and urine using flameless atomic absorption spectrophotometry, and pharmacokinetics of total and ultrafilterable gallium were calculated. Twenty-five patients with non-small cell lung cancer received 1–12 (median 2) courses of gallium nitrate every 2 weeks. Of 21 patients evaluable for response, 1 partial response was recorded, 4 patients had stable disease, and 16 had progressed. The most serious toxicities were renal impairment and optic neuritis. Hypocalcaemia was recorded in 3 patients. The mean C_max was 15.2 ± 3.1 μg/ml (range 9.5–21.2). Most gallium remained ultrafilterable for the first 10 h, after which plasma protein binding increased, and at 48 h only 11% was present as ultrafilterable gallium. The elimination profiles of both total and ultrafilterable gallium were biphasic, and the distribution phase consisted of ultrafilterable gallium, with a distribution half-life of 1.4 h. Total gallium plateaued at 1.9 μg/ml at between 8 and 12 h, and the estimated elimination half-life was 63 h. The elimination half-life of ultrafilterable gallium was 16.5 h. Inter- and intra-patient variability in pharmacokinetics was minimal. A mean of 50 ± 14% of the gallium dose was excreted in the urine within 48 h. A short infusion of gallium nitrate achieving high peak plasma concentrations results in little efficacy in non-small cell lung cancer. Received: 5 March 1999 / Accepted: 24 May 1999     

Effect of 5-(phenylselenenyl)acyclouridine, an inhibitor of uridine phosphorylase, on plasma concentration of uridine released from 2′,3′,5′-tri-O-acetyluridine, a prodrug of uridine: relevance to uridine rescue in chemotherapy

Purpose: The purpose of this investigation was to study the effects of combining oral 5-(phenylselenenyl)acyclouridine (PSAU) with 2′,3′,5′-tri-O-acetyluridine (TAU) on the levels of plasma uridine in mice. PSAU is a new lipophilic and potent inhibitor of uridine phosphorylase (UrdPase, EC 2.4.2.3), the enzyme responsible for uridine catabolism. PSAU has 100% oral bioavailability and is a powerful enhancer of the bioavailability of oral uridine. TAU is a prodrug of uridine and a far superior source of uridine than uridine itself. Methods: Oral TAU was administered to mice alone or with PSAU. The plasma levels of uridine and its catabolites as well as PSAU were measured using HPLC and pharmacokinetic analysis was performed. Results: Oral administration of 2000 mg/kg TAU increased plasma uridine by over 250-fold with an area under the curve (AUC) of 754 μmol · h/l. Coadministration of PSAU at 30 and 120 mg/kg with TAU further improved the bioavailability of plasma uridine resulting from the administration of TAU alone by 1.7- and 3.9-fold, respectively, and reduced the C_max and AUC of plasma uracil. Conclusion: The exceptional effectiveness of PSAU plus TAU in elevating and sustaining a high plasma uridine concentration could be useful in the management of medical disorders that are remedied by administration of uridine, as well as the rescue or protection from host toxicities of various chemotherapeutic pyrimidine analogues. Received: 10 November 1999 / Accepted: 14 March 2000     

Disposition of irinotecan and SN-38 following oral and intravenous irinotecan dosing in mice

The present study was conducted to quantitate the disposition of irinotecan lactone and its active metabolite SN-38 lactone in mice following oral and intravenous administration, and to evaluate the systemic exposure of irinotecan lactone and SN-38 lactone associated with antitumor doses of irinotecan lactone in mice bearing human tumor xenografts. Nontumor-bearing mice were given a single oral or intravenous irinotecan dose (5, 10, 40, or 75 mg/kg), and serial plasma samples were subsequently obtained. Irinotecan and SN-38 lactone plasma concentrations were measured using an isocratic HPLC assay with fluorescence detection. The disposition of intravenous irinotecan lactone was modeled using a two-compartment pharmacokinetic model, and the disposition of oral irinotecan and SN-38 lactone was modeled with noncompartmental methods. Irinotecan lactone showed biphasic plasma disposition following intravenous dosing with a terminal half-life ranging between 1.1 to 3 h. Irinotecan lactone disposition was linear at lower doses (5 and 10 mg/kg), but at 40 mg/kg irinotecan lactone clearance decreased and a nonlinear increase in irinotecan lactone AUC was observed. The steady-state volume of distribution ranged from 19.1 to 48.1 l/m². After oral dosing, peak irinotecan and SN-38 lactone concentrations occurred within 1 h, and the irinotecan lactone bioavailability was 0.12 at 10 mg/kg and 0.21 at 40 mg/kg. The percent unbound SN-38 lactone in murine plasma at 1000 ng/ml was 3.4 ± 0.67%, whereas at 100 ng/ml the percent unbound was 1.18 ± 0.14%. Irinotecan and SN-38 lactone AUCs in micebearing human neuroblastoma xenografts were greater than in nontumor-bearing animals. Systemic exposure to unbound SN-38 lactone in nontumor-bearing animals after a single oral irinotecan dose of 40, 10, and 5 mg/kg was 28.3, 8.6, and 2.9 ng h/ml, respectively. Data from the present study provide important information for the design of phase I studies of oral irinotecan. Received: 30 August 1996 / Accepted: 27 November 1996     

Potentiation of BCNU antitumor efficacy by 9-substituted O 6-benzylguanines. Effect of metabolism

Purpose: O ⁶-Benzylguanine (BG), an O ⁶-methylguanine-DNA methyltransferase (MGMT) inactivator, potentiates the efficacy of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and of other DNA chloroethylating and methylating anticancer drugs and is currently undergoing clinical trials. O ⁶-Benzyl-2′-deoxyguanosine (dBG), a less effective MGMT inactivator than BG in vitro, is at least as effective as BG in combination with BCNU against tumor xenografts in athymic mice. In order to identify the mechanism of dBG activation in in vivo systems we tested the metabolism, ability to inactivate MGMT, and efficacy to potentiate BCNU in vivo of two additional 9-substituted derivatives of BG, namely O ⁶-benzyl-9-cyanomethylguanine (CMBG) and O ⁶-benzylguanosine (BGS). Methods: Metabolism and disposition of these drugs was examined in athymic mice and Sprague-Dawley rats. MGMT suppression was determined in human medulloblastoma (Daoy) tumor xenografts in athymic mice following treatment with BGS, dBG, and CMBG and was compared with the loss of resistance to BCNU as determined by tumor growth delays. Results: Growth delays at 25 mg/m² BCNU and 133 mg/m² BG or equimolar doses of CMBG, BGS or dBG were 23.0, 2.5, 21.3 days, and 30.4 days, respectively. The above differences did not correlate with the ED₅₀s of 0.2, 13, 11 μM, and 2 μM determined for the above compounds, respectively, in cell free extracts. Differences in the efficacies of the 9-substituted compounds did correlate, however, with the extent of their metabolic conversion to BG. The maximum concentrations of BG in blood achieved after the administration of equimolar (250 μmol/kg) doses of CMBG, BGS and dBG were 10, 30 μM, and 55 μM, respectively. Although such levels were lower than those achieved in circulation by administration of an equimolar amount of BG, BG levels persisted longer following treatments with BGS or dBG than after treatment with BG itself. Formation of BG was required for continuous and prolonged (>16 h) suppression of MGMT activity to non-detectable levels (<5 fmol/mg protein). Conclusion: Metabolism of BGS and dBG to BG explains the unexpected high efficacy of these compounds in potentiating the antitumor activity of BCNU in the athymic mouse model. The faster and more effective suppression of tumor MGMT by dBG and its greater efficacy, as compared with BGS, also correlates with a more rapid accumulation of BG in blood after dBG than after BGS administration, which results in faster and complete suppression of MGMT in Daoy xenografts. Thus, metabolism of dBG and BGS to BG appears to be the determining factor for continuous and prolonged suppression of MGMT activity, and that near complete suppression of such activity during and following BCNU administration is required for the higher efficacy of treatments. Similarly, the failure of CMBG to suppress tumor MGMT to the same extent as BGS, in spite of their similar ED₅₀ values, could be attributed to the metabolism of this compound mainly by pathways other than conversion to BG. Received 9 February 1999 / Accepted 21 June 1999     

Pharmacokinetics and pharmacodynamics of MX2 hydrochloride in patients with advanced malignant disease

The purpose of the present study was to investigate the pharmacokinetics and pharmacodynamics of the new morpholino anthracycline drug MX2. A total of 27 patients with advanced cancer participated in a dose-escalation study in the first cycle of treatment with drug given i.v. at doses of 10–50 mg/m² (total dose 16.8–107.5 mg). The mean total systemic plasma clearance (CL) of MX2 was 2.98 ± 1.68 l/min, the mean volume of distribution at steady state was 1460 ± 749 l and mean elimination half-life was 10.8 ± 5.1 h. The area under the plasma concentration-time curve (AUC) of MX2 was linearly related to the dose per kilogram and the dose per body surface area (r ² = 0.43, P < 0.01 and r ² = 0.44, P < 0.01, respectively). CL did not correlate with total body weight, lean body mass or body surface area. The mean elimination half-lives of the metabolites M1, M2, M3 and M4 were 11.8 ± 5.0, 21.9 ± 11.8, 19.0 ± 11.3 and 12.3 ± 6.3 h, respectively. The fractional E _max model produced a much better fit to the relative nadir neutrophil count versus dose data (r ² = 0.42) than to the relative nadir neutrophil count versus AUC or peak concentration (C _max) data (r ² = 0.15 and 0.09, respectively). There seemed to be a threshold dose of about 65 mg of MX2 at or above which a large proportion of patients had a nadir neutrophil count of less than 0.5 × 10⁹/l. This study shows that the pharmacokinetics of MX2 are similar to those of other anthracyclines. With other anthracyclines the degree of myelosuppression seems to depend more on the AUC and C _max than on the delivered dose; however, with MX2 the degree of myelosuppression depends more on the dose given than on drug exposure expressed as the AUC or C _max. Received: 18 February 1996 / Accepted: 20 December 1996     

Plasma and CSF pharmacokinetics of ganciclovir in nonhuman primates

Purpose: The antiviral nucleoside analogue ganciclovir is a potent inhibitor of replication in herpes viruses and is effective against cytomegalovirus infections in immunocompromised patients. Ganciclovir is also used in cancer gene therapy studies that utilize the herpes simplex virus thymidine kinase gene (HSV-TK). The pharmacokinetics of ganciclovir in adults and children have been described previously but there are no detailed studies of the CNS pharmacology of ganciclovir. We studied the pharmacokinetics of ganciclovir in plasma and CSF in a nonhuman primate model that is highly predictive of the CSF penetration of drugs in humans. Methods: Ganciclovir, 10 mg/kg i.v., was administered over 30 min to three animals. Ganciclovir concentrations in plasma and CSF were measured using reverse-phase HPLC. Results: Peak plasma ganciclovir concentrations ranged from 18.3 to 20.0 μg/ml and the mean plasma AUC was 1075 ± 202 μg/ml · min. Disappearance of ganciclovir from the plasma was biexponential with a distribution half-life (t_1/2α) of 18 ± 7 min and an elimination half-life (t_1/2β) of 109 ± 7 min. Total body clearance (Cl_TB) was 9.4 ± 1.6 ml/min/kg. The mean CSF ganciclovir AUC was 168 ± 83 μg/ml · min and the mean peak CSF concentration was 0.7 ± 0.3 μg/ml. The ratio of the AUCs in CSF and plasma was 15.5 ± 7.1%. Conclusions: Ganciclovir penetrates into the CSF following i.v. administration. This finding will be useful in the design of gene therapy trials involving the HSV-TK gene followed by treatment with ganciclovir in CNS or leptomeningeal tumors. Received: 8 May 1998 / Accepted: 25 September 1998     

Pharmacokinetics of oxaliplatin in patients with normal versus impaired renal function

Purpose: The pharmacokinetics (PK) of platinum was investigated and compared in patients with normal (NRF) and impaired renal function (IRF), after they had received oxaliplatin at the recommended dose and delivery modality. Methods: Oxaliplatin was administered at 130 mg/m² as a 2-h infusion without hydration. Patients were recruited and classified according to their creatinine clearance (CrCl > or < 60 ml/min), calculated using the Cockcroft and Gault formula. Blood was taken for PK analysis during and after the infusion. Twenty-three patients were included in the PK analysis (13 NRF and 10 IRF). At inclusion, the median CrCls were 70.5 ml/min (range 63–136) for the NRF group and 42 ml/min (range 27–57) for the IRF group. Three patients underwent a second course of treatment and additional blood sampling for analysis. Platinum levels in the plasma, ultrafiltrate and red blood cells (RBCs) were measured using flameless atomic absorption spectrophotometry (FAAS). Results: Following the administration of oxaliplatin, platinum binding to plasma proteins and RBCs was rapid and extensive; at the end of the 2-h infusion, 27% of the platinum in the plasma remained free (40% bound to RBCs, 33% bound to plasma proteins). Neither the mean maximal concentration (C_max) of total platinum in the plasma, the mean C_max of ultrafilterable platinum in the plasma, nor the maximal platinum content in the RBCs differed significantly between the two groups (2.59 vs 2.58 μg/ml, 1.09 vs 1.28 μg/ml and 2.06 vs 2.17 μg/ml, respectively, for patients with NRF vs IRF). After the end of the infusion, levels of total and free (ultrafilterable) platinum in the plasma declined biexponentially. The plasma clearance of both total and free platinum as well as the area under the curve (AUC) of the free platinum fraction correlate with the calculated CrCl (P=9 × 10⁻³, P=3.1 × 10⁻⁵ and P=9 × 10⁻⁶, respectively). After a single course of oxaliplatin, toxicities reported in the two groups of patients were similar. Conclusions: Our results are in agreement with the in vitro data concerning the extensive binding of oxaliplatin to plasma proteins and RBCs. They also reveal a strong negative correlation between free drug plasma availability and renal function, with a corresponding positive correlation between clearance of the plasmatic platinum and renal function. Thus, renal impairment entails a greater overall exposure to platinum in the plasma. However, this study failed to elicit any relationship between moderate renal impairment and the acute toxicity associated with oxaliplatin. Received: 8 April 1999 / Accepted: 30 July 1999