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     

A Bayesian dosing method for carboplatin given by continuous infusion for 120 h

Carboplatin (CBDCA), an analogue of cisplatin, exhibits reduced toxicity but wide interpatient variability of its pharmacokinetic parameters. Individualization of the CBDCA dose is therefore necessary. Although various formulas have been developed for this purpose, major side effects have been reported on CBDCA administration by short-term infusion (0.5 or 1h). We therefore propose a new schedule of CBDCA administration. Instead of a dosing method based on the estimation of renal function when a classic administration schedule is used, we propose a pharmacokinetic dosing method (Bayesian method), whereby CBDCA is given by continuous infusion for 120 h. First, CBDCA was given to 21 patients to determine the population pharmacokinetic parameters of carboplatin. Then, on the basis of total platinum plasma concentration measurements and Bayesian estimation of pharmacokinetic parameters, it was possible to individualize the CBDCA dose within the first 24 h of the infusion. This new protocol for CBDCA administration was evaluated in 36 new patients (60 courses). Three theoretical end points at the end of the infusion were considered. For a given theoretical end point, 20 courses were taken into account. The theoretical end points (i.e., 1, 1.5, and 1.8 mg/l) were compared with the concentrations measured at the end of the infusion, which were 0.99 ± 0.10, 1.41 ± 0.13, and 1.72 ± 0.20 mg/l, respectively. This Bayesian dosing method can easily be used in clinical practice, and the determination of predictive performances has shown that the method is precise and unbiased. With no more toxicity or practical difficulties than those produced by other methods, and with acceptable tolerance, it was possible to reach a median dose that was 20% higher than the usual dose (484 ± 190 mg/m² as compared with 400 mg/m²). In conclusion, this new schedule of CBDCA administration appears to be interesting in terms of tolerance. However, new studies are required to confirm that this new scheme leads to equal or better efficacy than the classic protocol. Received: 10 December 1995 / Accepted: 15 December 1996     

Pharmacokinetics of dolasetron with coadministration of cimetidine or rifampin in healthy subjects

Purpose: Dolasetron is a selective 5-HT₃ receptor antagonist. The purpose of this study was to determine the effect of cimetidine and rifampin on the steady-state pharmacokinetics of orally administered dolasetron and its active reduced metabolite, hydrodolasetron. Methods: A group of 18 healthy men (22 to 44 years old) were randomized to receive each of the following three treatments in a three-period crossover design: 200 mg dolasetron daily (treatment A); 200 mg dolasetron daily plus 300 mg cimetidine four times daily (treatment B); or 200 mg dolasetron daily plus 600 mg rifampin daily (treatment C). Each study period was separated by a 14-day washout period. Serial blood samples were collected before the first dose (baseline) on day 1 and at frequent intervals up to 48 h after the morning dose on day 7 for quantification of dolasetron and its metabolites, hydrodolasetron (both isomers), 5′OH hydrodolasetron, and 6′OH hydrodolasetron. Serial urine samples were also collected at baseline and during the periods 0–24 and 24–48 h following the morning dose on day 7, and analyzed for dolasetron and its metabolites. Results: Plasma and urine dolasetron concentrations were below quantifiable concentrations for all three treatments. Mean steady-state area under the plasma concentration-time curve (AUC_ss(0–24)) of hydrodolasetron increased by 24%, mean apparent clearance (CL_app,po) decreased by 19%, and maximum plasma hydrodolasetron concentration (C_max,ss) increased by 15% when dolasetron was coadministered with cimetidine. When dolasetron was given with rifampin, mean hydrodolasetron AUC_ss(0–24) decreased by 28%, CL_app,po increased by 39%, and hydrodolasetron C_max,ss decreased by 17%. Small differences were found in mean t_max (0.7 to 0.8 h), CL_r (2.0 to 2.6 ml/min per kg), and t_1/2 (7.4 to 8.8 h) for hydrodolasetron between treatment periods. Approximately 20% and 2% of the dolasetron dose were excreted in urine as the R(+) isomer and S(−) isomer of hydrodolasetron, respectively, across all three treatments. Dolasetron mesylate was well tolerated in this study during all three treatment periods, with the highest incidence of adverse events reported during the control period when dolasetron mesylate was given alone. Conclusion: Based on the small changes in the pharmacokinetic parameters of dolasetron and its active metabolites, as well as the favorable safety results, no dosage adjustments for dolasetron mesylate are recommended with concomitant administration of cimetidine or rifampin. Received: 10 February 1998 / Accepted: 1 June 1998     

A phase I study of recombinant human soluble interleukin-1 receptor (rhu IL-1R) in patients with relapsed and refractory acute myeloid leukemia

Purpose: The recombinant human interleukin-1 receptor (rhu IL-1R) is a soluble truncated form of the type 1 full-length membrane-bound receptor that binds IL-1 with identical affinity to that of the membrane form. As such, it may have clinical potential by sequestering IL-1, thereby preventing it from binding to its membrane-bound receptor and eliciting a biological effect. As IL-1 has been shown to regulate leukemic cell proliferation in an autocrine fashion, a phase I trial of rhu IL-1R was conducted in patients with relapsed and refractory acute myeloid leukemia (AML). Methods: The study group comprised 11 patients who were sequentially treated on one of three dose levels, receiving a single intravenous (i.v.) bolus dose on day 1 followed by 13 days of daily subcutaneous (s.c.) injections with the option of an additional 14 days of treatment if a response of stable disease or better was achieved. Dose level 1 i.v. bolus 500 g/m², s.c. dose 250 g/m² per day (five patients); dose level 2 i.v. bolus 1000 g/m², s.c. dose 500 g/m² per day (three patients); dose level 3 i.v. bolus 2000 g/m², s.c. dose 1000 g/m² per day (three patients). Owing to limited drug availability, the study was designed to only examine these three dose levels. Results: rhu IL-1R was well tolerated. There was no grade 3 or 4 non-hematological toxicity related to the study drug and the maximum tolerated dose was not reached. No IL-1R-blocking antibodies developed during the course of the study. Serum levels of IL-1, IL-6 and TNF were undetectable before, during and after rhu IL-1R administration. The terminal half-life after i.v. dosing was at least 7–12 h, and after s.c. dosing 2–4 days. Serum levels of rhu IL-1R up to 360- and 25-fold those of pretreatment levels were achieved after i.v. and s.c. dosing respectively. No patient had a complete, partial or minor response to treatment; four had stable disease and seven had progressive disease. Conclusions: rhu IL-1R therapy was safe but did not have any apparent antileukemic effect at the doses administered. Received: 6 October 1997 / Accepted: 1 April 1998     

Phase II study of CI-958 in colorectal cancer

Purpose: We completed a phase II trial of CI-958 (NSC #635371) in patients with advanced colorectal cancer given at a dose of 700 mg/m² every 21 days. Methods: All 15 patients had metastatic disease and had been previously treated with one 5-fluorouracil-based regimen in an adjuvant (six) or metastatic (nine) setting. Results: None of the patients treated with CI-958 had an objective response to treatment. Median survival was 4.8 months after the start of treatment. Leukopenia was the major toxicity, but no patient experienced febrile neutropenia. An acute febrile reaction was seen after infusion in four of the first nine patients treated. This was abrogated by pretreatment with dexamethasone in the remaining patients. Conclusions: CI-958 was not effective at this dose and schedule in patients with previously treated advanced colorectal cancer. Received: 31 March 1998 / Accepted: 1 June 1998     

Dose intensity of uracil and tegafur in postoperative chemotherapy for patients with poorly differentiated gastric cancer

A retrospective analysis of postoperative chemotherapy had shown the continuous administration of UFT, an oral preparation of 1-(2-tetrahydrofuryl)-5-fluorouracil (tegafur) and uracil at a molar ratio of 1:4, to be effective for poorly differentiated gastric cancer. We therefore sought to determine prospectively the effective dose of postoperative chemotherapy with UFT for patients with poorly differentiated gastric cancer following a curative resection. We determined the effect of the combined intravenous administration of mitomycin C (MMC) and oral treatment with protein-bound polysaccharide Kreha (PSK), extracted from the basidiomycete Coriolus versicolor, and UFT at a dose of either 8 mg/kg or 12 mg/kg daily for 1 year. A total of 224 patients with poorly differentiated stage II–IV gastric cancer were entered into this study after undergoing a curative resection. No differences were observed between the two treatment groups in terms of prognostic factors, the toxicity rate or the doses of the drugs prescribed, other than UFT. The higher dose of UFT in maintenance therapy led to a decrease in the recurrence rate (P < 0.05), and increases in disease-free survival and cause-specific survival (P < 0.05). UFT at 12 mg/␣kg in postoperative chemotherapy was thus found- to improve the postoperative results with no increase in toxicity for poorly differentiated gastric cancer, and is also cost-effective for outpatients. Received: 8 February 1996 / Accepted: 27 November 1996     

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     

Metabolism of 6-mercaptopurine in the erythrocytes, liver, and kidney of rats during multiple-dose regimens

Purpose: To describe the metabolism of 6-mercaptopurine (6-MP) in erythrocytes and tissues of rats after repeated administration of 6-MP at two dose levels and to provide evidence that in vivo modulation of 6-MP anabolism can be obtained by simultaneous treatment with ribavirin or hydroxyurea, two inhibitors of enzymes involved in the bioactivation of 6-MP to the active 6-thioguanine nucleotides (6-TGN). Methods: Rats were treated i.p. with 6-MP at 12.5 and 25 mg/kg daily for 12 days and erythrocyte, liver, and kidney levels of 6-mercaptopurine nucleotides (6-MPN) and 6-TGN were investigated during the accumulation phase and for 50 days after the end of treatment. In combination studies, ribavirin at 75 and 100 mg/kg per day (for 6-MP, 25 and 12.5 mg/kg per day) or hydroxyurea at 200 mg/kg per day were given i.p. for 12 days. The measurements of thionucleotide levels in rat samples were performed by high-pressure liquid chromatography (HPLC). Results: The maximal concentration (C_max) and the area under the concentration versus time curve (AUC) of 6-MPN and 6-TGN in erythrocytes and tissues increased significantly after the administration of 6-MP at 25 mg/kg per day as compared with 12.5 mg/kg per day. In particular, the C_max and AUC of 6-TGN in erythrocytes of rats treated with 6-MP at 25 mg/kg per day were approximately 5-fold higher than the 6-TGN values observed following treatment at 12.5 mg/kg per day. Moreover, 6-TGN levels in erythrocytes were significantly higher than those of 6-MPN (910.9 ± 53.1 and 286.8 ± 23.4 pmol/8 × 10⁸ cells for 6-TGN and 6-MPN, respectively, P < 0.05) after treatment with 6-MP at 25 mg/kg per day. The administration of ribavirin, an inhibitor of inosine monophosphate dehydrogenase, in association with 6-MP increased the amount of 6-MPN detected in erythrocytes and tissues while reducing 6-TGN levels in samples. The production and accumulation of 6-MPN and 6-TGN were increased in erythrocytes and tissues by hydroxyurea, an inhibitor of ribonucleotide reductase. Finally, a significant correlation between thionucleotide concentrations and erythrocyte counts was observed. Conclusion: The overall results demonstrate that 6-MP is actively metabolized in rats and that its biotransformation can be modulated by agents acting on enzymes of the purine metabolism, resulting in significant changes in erythrocyte and tissue levels of 6-MPN and 6-TGN. These findings provide evidence that the rat is a suitable model for investigation of the metabolism of 6-MP and its possible pharmacologic modulation. Received: 17 December 1997 / Accepted: 29 June 1998     

The venotonic drug hydroxyethylrutosiden does not prevent or reduce docetaxel-induced fluid retention: results of a comparative study

Purpose: Fluid retention, which includes peripheral edema, ascites, pleural or pericardial effusion, or a combination of these that is sometimes associated with significant weight gain, is one of the most troublesome cumulative side effects of docetaxel. A suggestive observation from the data base available at the manufacturer (Rhone-Poulenc Rorer) was that patients who received venotonic drugs appeared to tolerate more courses of docetaxel. This prompted a comparative study to investigate whether the venotonic drug hydroxyethylrutosiden could reduce or delay docetaxel-related fluid retention. Methods: A total of 85 patients with metastatic breast cancer who were treated with docetaxel at a dose of 100 mg/m² with corticoid comedication were allocated to receive either 300 mg hydroxyethylrutosiden given orally four times daily (group A) or no hydroxyethylrutosiden (group B). The end point for analysis was the development of fluid retention of ≥grade 2. Results: Fluid retention of ≥grade 2 was reported in 14 of 42 patients (33%) in group A and in 15 of 43 patients (35%) in group B and occurred after a median of 4 cycles of docetaxel in both groups. Weight gain was similar in groups A and B. Conclusion: We conclude that hydroxyethylrutosiden does not reduce or delay the incidence and severity of docetaxel-related fluid retention. Received: 19 March 1998 / Accepted: 6 July 1998     

Effect of single and multiple administration of an O 6-benzylguanine/temozolomide combination: an evaluation in a human melanoma xenograft model

The purpose of the present study was to examine the effect of O ⁶-benzylguanine (O ⁶-BG) on the antitumour activity and toxicity of 8-carbamoyl-3-methylimidazo [5, 1-d ] -1,2,3,5-tetrazine-4(3H)-one (temo-zolomide) in a human malignant melanoma xenograft model following single and multiple administration of the combination. O ⁶-BG irreversibly inactivates the DNA-repair protein O ⁶-alkylguanine-DNA alkyltransferase (AGT), which confers resistance to temozolomide. Preadministration of O ⁶-BG (35 mg/kg, i.p.) 1 h prior to temozolomide (i.p.) was examined using single and daily × 5 dosing regimens in athymic mice bearing subcutaneous A375P xenografts. The AGT activity of A375P tumors was 95 ± 8 fmol/mg protein (mean ± SE, n = 4). O ⁶-BG alone completely suppressed xenograft AGT activity within 1 h of administration but had no effect upon tumor growth. O ⁶-BG did not significantly increase the tumor growth delay induced by a single 200-mg/kg dose of temozolomide (P>0.05, two-tailed Mann-Whitney test) but did increase the associated mean body weight loss (P<0.025). In contrast, when the same dose of temozolomide was divided into five equal fractions (40 mg/kg) and given with O ⁶-BG on 5 consecutive days, a comparable increase in toxicity was accompanied by a very significant increase in tumor growth delay (P<0.0025), equivalent to that produced by a 3-fold greater dose of temozolomide alone. O ⁶-BG with temozolomide also produced a greater antitumour effect than an equitoxic dose of temozolomide alone on this schedule (P<0.005). These data indicate that the enhancement of temozolomide antitumour activity by O ⁶-BG preadministration is dependent upon the schedule of drug administration, with multiple dosing of O ⁶-BG + temozolomide producing the greatest effect. The results also suggest that prolonged administration of the combination can lead to an increase in the therapeutic index of temozolomide. Received: 8 September 1996 / Accepted: 8 February 1997     

Depletion of p185erbB2, Raf-1 and mutant p53 proteins by geldanamycin derivatives correlates with antiproliferative activity

Purpose: Recently, it has been shown that geldanamycin (GA), a benzoquinone ansamycin, is able to deplete mutant p53, p185^erbB2 and Raf-1 proteins in cancer cells. However, the relationship between these activities of GA and its antiproliferative activity is not clear. Here we investigated the effects of 28 GA derivatives in SKBr3, a human breast cancer cell line. Methods: We performed Western blot analysis of Raf-1, p185^erbB2 and mutant p53 proteins following drug treatment and correlated these findings with the cytotoxicity of the various GA derivatives. Results: We found that downregulation of Raf-1, p185^erbB2 and mutant p53 proteins was correlated. Thus, a drug that was active against one oncoprotein was equally active against the two others. Inactive derivatives were identified by their inability to downregulate these oncoproteins, even at a high dose (2 μM). These inactive drugs also had no or minimal antiproliferative activity (IC₅₀ > 3 μM). All other analogs (at a concentration of 2 μM) downregulated p53, p185^erbB2, and Raf-1, and also displayed cytotoxicity (IC₅₀ in the range 6–600␣nM). This category of drugs was further divided into more- and less-active agents by testing at lower doses (40 nM). The drugs that remained active against their molecular targets had an IC₅₀ for antiproliferative activity of less than 40 nM. Maximal effects on mutant p53, p185^erbB2 and Raf-1 were observed at doses that were 4–5 times greater than the cytotoxic IC₅₀. Conclusions: These findings suggest that GA and its derivatives are cytostatic/cytotoxic at concentrations that also downregulate Raf-1, p185^erbB2 and mutant p53, and raise the possibility that depletion of these proteins and the antiproliferative activities of GA have a common mechanism. Received: 6 June 1996 / Accepted: 28 September 1996     

Pharmacokinetics of intrapericardial administration of 5-fluorouracil

A 30-year-old patient with metastatic breast adenocarcinoma was diagnosed as having a malignant pericardial effusion. Methods: The patient was treated with two courses of 200 mg 5-fluorouracil (5-FU) followed by 20 mg cisplatin 5 h later directly infused into the pericardial space through a catheter. The drug levels of the 5-FU were monitored during the second treatment. The half-life of 5-FU in the pericardial space was 168.6 min with a concentration of 0.113 mg/ml still detected at 5 h. The area under the curve (AUC) was estimated to be 4.739 mg h/ml. The plasma concentrations of 5-FU ranged from 0.022 to 0.04 mg/ml throughout the infusion. Results: There was no significant change in the patient's blood counts or chemistry profile. She did not experience any side effects during the treatment. A pericardial window was performed 2 days later when balloon pericardiectomy was unsuccessful. The patient eventually succumbed to her disease 4 months later, but without evidence of pericardial effusion. Conclusions: We conclude that pericardial infusion of 5-FU allowed a high concentration of 5-FU to be achieved within the pericardial sac with a greatly increased half-life over that of systemic 5-FU treatment (168 min vs 6–20 min), and with little systemic toxicity. Received: 12 September 1996 / Accepted: 12 December 1996     

Antibody-directed enzyme prodrug therapy: pharmacokinetics and plasma levels of prodrug and drug in a phase I clinical trial

Antibody-directed enzyme prodrug therapy (ADEPT) was administered to ten patients in a phase I clinical trial. The aim was to measure plasma levels of the prodrug 4-[(2-chloroethyl)(2-mesyloxyethyl) amino] benzoyl-l-glutamic acid (CMDA) and the bifunctional alkylating drug (CJS11) released from it by the action of tumour-localised carboxypeptidase G2 (CPG2) enzyme. New techniques were developed to extract the prodrug and drug from plasma by solid-phase adsorbtion and elution and to measure CPG2 activity in plasma and tissue. All extracts were analysed by high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). CPG2 activity was found in metastatic tumour biopsies but not in normal tissue, indicating that localisation had been successful. The clearing agent SB43-gal, given at 46.5 mg/m², achieved the aim of clearing non-tumour-localised enzyme in the circulation, indicating that conversion of prodrug to drug could take place only at the site of localised conjugate. Plasma prodrug did not always remain above its required threshold of 3 μM for the “therapeutic window” of 120 min after dosing, but the presence of residual prodrug after the first administration of each day indicated that this could be achieved during the remaining four doses over the following 8 h. Despite considerable inter-patient prodrug plasma concentration variability, the elimination half-life of the prodrug was remarkably reproducible at 18 ± 8 min. Rapid appearance of the drug in plasma indicated that successful conversion from the prodrug had taken place, but also undesirable leakback from the site of localisation into the bloodstream. However, drug plasma levels fell rapidly by at least 50% at between 10 and 60 min with a half-life of 36 ± 14 min. Analysis of the plasma extracts by LC/MS indicated that this technique might be used to confirm qualitatively the presence of prodrug, drug and their metabolites. Received: 21 July 1996 / Accepted: 20 January 1997     

Protection against doxorubicin-induced cardiotoxicity in weanling rats by dexrazoxane

Purpose: Dexrazoxane (DZR) protects against anthracycline-induced cardiotoxicity in several laboratory animal species and in patients with breast cancer. Encouraging results have also been obtained in a limited number of pediatric oncology patients. We conducted studies to determine the safety and cardioprotective activity of DZR in the doxorubicin (DOX)-treated weanling rat simulating the rapidly growing immature child. Methods: Male weanling rats and young adult rats, 20␣days old and 7 weeks old, respectively, were given 1 mg/kg DOX i.v., either alone or with 20 mg/kg DZR, once weekly for 7 weeks. Rats were sacrificed at weeks 8, 12 or 26 following blood collection for hematology and serum chemistry. Hearts were weighed and examined histologically. Results: DOX, either alone or with DZR, inhibited growth, and body weight remained below that of controls throughout the 26 weeks of study. There were no biologically significant hematologic changes in either the DOX- or DZR + DOX-treated young rats. DOX caused a slight increase in liver and kidney weights relative to body weight and a slight increase in serum cholesterol and triglycerides in the young rats. These effects were ameliorated or delayed by DZR. DOX, either alone or with DZR, caused a marked atrophy of the testes in the young rats which had recovered by week 26. In the mature rats, DOX caused a significant decrease in the WBC 1 week after the last treatment, and the WBC was significantly lower in the rats given DZR + DOX compared to those given DOX alone. There were marked increases in liver and kidney weight, serum cholesterol and triglycerides in the mature rats given DOX alone but not in those given DZR + DOX. There was also a marked testicular atrophy in the mature rats given either DOX or DZR + DOX but, unlike that observed in the young rats, this had not returned to normal by week 26. DOX-induced cardiotoxicity was less severe in the younger rats than in the mature rats but in both age groups, the lesion progressed rapidly until week 12, 5 weeks after the last dose, and remained relatively stable or progressed slightly thereafter. DZR provided significant cardioprotection in both age groups at all time points examined. Moreover, in both age groups, the severity of the cardiomyopathy in the DZR-treated rats was somewhat less at week 26 than it was at week 12. Conclusions: The results indicate that the pharmacologic effects of DZR, including its ability to protect against cardiotoxicity, are similar in immature and adult male animals treated with DOX. Received: 3 March 1998 / Accepted: 13 May 1998     

Bladder tissue pharmacokinetics of intravesical taxol

Our previous studies have suggested that the ineffectiveness of intravesical mitomycin C or doxorubicin therapy against muscle-invading bladder cancer is in part because of the inability of these drugs to penetrate the urothelium (the urothelial drug concentration is <5% of the concentration in urine). The goal of the present study was to identify agents that are efficiently absorbed across the urothelium. To evaluate the potential use of taxol in intravesical therapy for bladder cancer, we examined the bladder tissue and systemic plasma pharmacokinetics of intravesical taxol in dogs. Animals (∼8 kg body weight) were given an instillation of taxol at 500 μg in 20 ml water. At 120 min postinstillation, the bladder was emptied and excised, and about 85% of the dose was recovered in the urine. The taxol concentration in the urothelium was about 50% of the concentration in the urine, the concentrations then declined logarithmically in the underlying capillary-perfused tissues. The average tissue concentration (∼2 μg/g) was two to three times the reported plasma concentration of 0.75 μg/ml in patients following intravenous infusion of the >100-fold higher dose of 250 mg/m². The steady-state plasma concentration was <0.02% of the average tissue concentration, and was <0.05% of the maximally tolerated plasma concentration in patients. The octanol:water partitioning coefficients of taxol, doxorubicin, and mitomycin were >99, 0.52, and 0.41, which parallels the rank order of the partitioning across urothelium, i.e. taxol (∼50%) >> doxorubicin ≈ mitomycin C (∼3%). In summary, the partitioning of taxol across the urothelium was more favorable than the partitioning of mitomycin C and doxorubicin, and the systemic concentration of taxol resulting from intravesical treatment was insignificant in spite of the extensive absorption into the bladder. We conclude that intravesical delivery of taxol provides a significant bladder tissue targeting advantage, and that taxol represents a viable candidate drug for intravesical bladder cancer therapy. Received: 20 September 1996 / Accepted: 2 December 1996     

Disposition of conjugate-bound and free doxorubicin in tumor-bearing mice following administration of a BR96-doxorubicin immunoconjugate (BMS 182248)

Purpose: The chimeric BR96–doxorubicin (DOX) immunoconjugate, BMS 182248, has induced remissions and cures of human lung adenocarcinoma (L2987) implanted in athymic mice. The purpose of this study was to evaluate the biodistribution of DOX after BMS 182248 administration to tumor-bearing mice and to evaluate the ability of BMS 182248 to target DOX to tumors. Methods: For this evaluation, L2987-implanted mice were given BMS 182248 (5 mg DOX/kg; three doses 4 days apart) and the levels of both conjugate-bound and free DOX in plasma, tumor, liver and heart were determined. Results: Conjugate-bound DOX comprised the majority of plasma DOX, with relatively low levels of free DOX present. From plasma, conjugate-bound DOX distributed to the tissues examined with the order of concentration (per gram of tissue) being tumor > liver > heart. Free DOX was also detected in liver and heart, but at concentrations lower than those present after an equivalent DOX dose (5 mg/kg; three doses 4 days apart). The total exposure of heart to free DOX after BMS 182248 administration was about one- quarter of that found after the administration of DOX alone. The elimination kinetics of both conjugate-bound and free DOX from heart and liver after BMS 182248 administration paralleled those observed from plasma, indicating that equilibrium had been attained between these nontumor tissues and plasma. The elimination kinetics of both entities from tumors, however, were different from those from plasma, liver and heart. BMS 182248 produced sustained levels of both conjugate-bound and free DOX which were present throughout the experiment. This suggested that, in contrast to normal tissues, tumor tissue retention of BMS 182248 by antigen-promoted binding had occurred and that the kinetics of free DOX in the tumors were controlled by the rate of release of DOX from tumor-associated BMS 182248. As a result of this retention, the tumor concentrations of free DOX after BMS 182248 administration exceeded those produced by i.v. administration of DOX at the same dose, a finding consistent with the greater antitumor activity of BMS 182248 relative to DOX. BMS 182248 also liberated DOX upon incubation with rat liver lysosomes and was accumulated by L2987 cells in culture, with the subsequent intracellular release of DOX. Conclusions: BMS 182248 effectively delivered DOX to L2987 xenografts implanted in athymic mice and produced higher and more prolonged tumor concentrations of free DOX than the administration of DOX alone. Following BMS 182248 administration, normal tissues (liver and heart) were exposed to lower overall concentrations of free DOX than were produced by administration of an equivalent DOX dose. Received: 18 June 1996 / Accepted: 27 November 1996     

Measurement of nitrobenzylthioinosine in plasma and erythrocytes: a pharmacokinetic study in mice

Purpose: Nitrobenzylthioinosine (NBMPR), a potent inhibitor of nucleoside transport in many cell types, modulates the in vivo disposition of several cytotoxic nucleoside analogs. In this study, a radioligand binding assay was developed for measurement of the NBMPR content of plasma and erythrocytes. Methods: The assay was based on the competition between NBMPR and [³H]NBMPR for high-affinity sites on human erythrocyte membranes. With this assay, we followed in mice changes in the NBMPR content of blood plasma and erythrocytes, following the intraperitoneal injection of the disodium salt of NBMPR 5′-monophosphate (NBMPR-P), a prodrug form of NBMPR. Results: The radioligand binding assay was able to measure precisely as little as 2.5 pmol of NBMPR, allowing the direct determination of NBMPR concentrations in plasma as low as 16 nM. As few as 8 × 10³ molecules of NBMPR per cell could be determined in erythrocytes. The NBMPR content of plasma from mice injected with NBMPR-P was maximal at about 20 min after injection and declined to <0.2% of the peak value by 10 h. Erythrocyte-associated NBMPR was also maximal at 20 min, and declined to 11% of the peak value by 10 h after injection. Time courses for the disappearance of NBMPR from plasma and erythrocytes were monoexponential and yielded half-life values of 0.39 h and 0.68 h, respectively, an apparent volume of distribution of 0.61 l/kg, and a clearance of 1.1 l/h per kg. Conclusions: The radioligand binding assay is a sensitive and facile method for monitoring NBMPR concentrations in mammalian plasma and tissue extracts. Received: 20 August 1995 / Accepted: 17 December 1996     

Pharmacokinetics and clinical impact of all-trans retinoic acid in metastatic breast cancer: a phase II trial

Purpose: The purpose of this trial was to evaluate tumor cytoreduction by all-trans retinoic acid (ATRA) in patients with metastatic breast cancer and to characterize the initial pharmacokinetics of this agent. Methods: The study was a single institution, phase II study. The treatment regimen consisted of ATRA administered orally at a dose of 50 mg/m² three times a day for 14 consecutive days of a 21-day cycle. Cycles were repeated until disease progression, unacceptable toxicity or patient withdrawal. Plasma samples were obtained following the first dose of ATRA for pharmacokinetic analysis. Results: A total of 17 patients with metastatic breast cancer were enrolled in the study, and 14 completed at least one cycle of therapy and were evaluable for response. One patient achieved a partial response in soft tissue of 4 months duration. Three patients had stable disease for 4, 2, and 2 months duration. The remainder had progressive disease. ATRA was reasonably well tolerated. Pharmacokinetic analysis revealed a high degree of interpatient variability in systemic exposure following the initial dose of ATRA. Conclusions: We conclude, that in the dose and schedule tested, ATRA does not have significant activity in patients with hormone-refractory, metastatic breast cancer. Future studies should focus on more intensive investigation of those individuals with very high or low ATRA initial systemic exposure in the hope of expanding our understanding of ATRA's clinical pharmacology, ultimately leading to improved efficacy. Received: 25 September 1996 / Accepted: 9 December 1996     

Phase I and pharmacologic study of 7- and 21-day continuous etoposide infusion in patients with advanced cancer

 Purpose. This phase I study was undertaken to evaluate the safety and tolerability of prolonged infusional etoposide, and to evaluate its pharmacokinetic/pharmacodynamic profile in patients with advanced cancer. Methods. A group of 17 patients received a 7-day infusion of etoposide (schedule A) every 21 days at doses from 30 to 75 mg/m² per day, and a second group of 37 patients a 21-day infusion (schedule B) every 28 days at doses from 18 to 40 mg/m² per day. Patients had a median Karnofsky performance status (PS) of 80%, and 34 patients had no prior chemotherapy. Etoposide concentrations at steady state (Css) and other pharmacokinetic parameters (plasma clearance, CLp; area under the curve, AUC) were determined during the first treatment cycle. Correlation coefficients were calculated to measure the relationship between variables. Results. Myelosuppression was the major toxicity, and was associated with three deaths. The maximum tolerated dose due to neutropenia was 75 mg/m² per day for schedule A and 40 mg/m² per day for schedule B. There was significant interpatient pharmacokinetic variability in both infusional schedules. Even though etoposide dose levels did not significantly correlate with plasma levels, the Css was ≥1 μg/ml in the majority of the patients. A significant correlation between AUC and neutrophil absolute decrease was noted only in schedule B (r=0.56,  P=0.003). There were several marginal relationships in schedule B: PS versus Css (r=0.31,  P=0.058), PS versus AUC (r=−0.38; P= 0.058) and age versus CLp (r=−0.31, P=0.057). Conclusion. Overall, significant correlations were found for several hematologic variables and etoposide dose levels, but not with the Css values. One major problem with the application of pharmacodynamic models to predict hematologic toxicity in clinical practice is the presence of significant interpatient variability. Received: 3 April 1995/Accepted: 6 December 1995     

A phase I study of carboplatin and etoposide administered in conjunction with dipyridamole, prochlorperazine and cyclosporine A

Purpose: In recognition of the variety of available chemotherapeutic modulating agents and their potential to enhance the efficacy of platinum-based therapy, we embarked upon a phase I study to investigate the feasibility of combining fixed doses of carboplatinum (CBDCA) and etoposide (VP-16) with 24-h concurrent infusions of dipyridamole (DP), prochlorperazine (PCZ) and cyclosporine A (CSA) administered in escalating doses. Methods: Patients received intravenous VP-16 (200 mg/m²) and CBDCA (300 mg/m²), each over 30 min, starting at hour 6 of the modulator infusions. Resistance modulators were escalated sequentially to determine their respective maximally tolerated doses (MTDs). The pharmacokinetics (PK) of VP-16, CBDCA, and the three drug resistance (DR) modifiers were studied in eight patients. Results: A total of 59 patients were entered on study. The MTD was established at DP 5 mg/kg per day, PCZ 24 mg/h, and CSA 9.5 mg/kg per day. Dose-limiting toxicities included hypotension and severe sedation, presumably related to PCZ. No objective responses were seen. PK studies were performed when PCZ and DP doses were 24 mg/h and 3.3 mg/kg, and the CSA dose was either 8.5 mg/kg (five patients) or 9.5 mg/kg (three patients). The median clearance of VP-16 was 0.96 l/h per m² (range 0.8–1.5 l/h per m²), which is lower than for VP-16 alone and similar to previously reported effects of CSA on VP-16 elimination. The median measured CBDCA AUC was 3.0 mg/ml · min (range 2.4–4.8 mg/ml · min). CBDCA AUC predicted by the Calvert formula using measured creatinine clearance underestimated the actual AUC in seven of the eight patients, in one case by as much as twofold. The median end of infusion PCZ and total DP plasma concentrations were 1.2 μM (range 0.5–2.2 μM) and 4.4 μM (range 1.3–5.9 μM), respectively, consistent with in vitro resistance modulatory levels. However, free DP was only 0.02 μM (range 0.004–0.04 μM). The median CSA level at 24 h of 1450 μg/l (range 1075–1640 μg/l) is in agreement with concentrations required for partial DR reversal in vitro, although it is much lower than levels achieved in our previous phase I study of CBDCA + CSA alone using similar doses of CSA. The CSA dose on the current trial was escalated beyond the MTD for the previous phase I study, suggesting that there may be an interaction between CSA and one of the other modulators. Conclusion: These results demonstrate that in vitro DR- reversing levels of two of the three agents used in this study can be achieved in vivo, and that this combination of DR modulators has significant effects on the pharmacokinetics of VP-16. Received: 2 September 1999 / Accepted: 25 April 2000