Cardioprotection by dexrazoxane in rats treated with doxorubicin and paclitaxel

Purpose: Results of several clinical studies suggest that the combination of doxorubicin (DOX) and paclitaxel (PTX) is highly active against solid tumors. Both drugs are known to cause adverse cardiac effects, cardiomyopathy in the case of DOX and acute changes in cardiac rhythm in the case of PTX. It has been suggested that the addition of dexrazoxane (DZR) to this regimen may reduce the risk of cardiotoxicity. A model of chronic cardiomyopathy in the rat was used to determine whether DZR was tolerated and cardioprotective in a DOX+PTX combination. Methods: Male rats were treated once weekly for 7 weeks with one of the following vehicle and/or drug sequences: Group A, M/6 sodium lactate/saline/Cremophor EL (CEL); Group B, lactate/DOX/CEL; Group C, DZR/DOX/CEL; Group D, lactate/DOX/PTX; and Group E, DZR/DOX/PTX. DZR and DOX or their respective vehicles were given i.v. whilst PTX or CEL were given i.p. DZR, DOX and PTX were administered at 16 mg/kg, 0.8 mg/kg and 2.4 mg/kg, respectively, doses which caused minimal noncardiac toxicities. The hearts were examined histologically 5 weeks following the last treatment. Results: There were no deaths and no signs of overt toxicity during the 12 weeks of study. There was a significant decrease (P < 0.01) in white blood cell count in rats treated with DZR+DOX, DOX+PTX or DZR+ DOX+PTX but not in those given DOX alone. Liver and kidney weights were increased in rats given DOX (P < 0.05) but not in those given DZR+DOX. PTX had no effect on the DOX-induced liver and kidney changes and did not interfere with the protective effect of DZR on the kidney. The severity and extent of cardiomyopathy expressed as the mean total score (MTS) for each treatment group, was similar for DOX and DOX+PTX (4.6 and 4.2, respectively). DZR provided significant cardioprotection (P < 0.01) when added to either DOX (MTS 2.0) or to DOX+PTX (MTS 2.1). Conclusions: The results suggest that PTX does not exacerbate the chronic cardiomyopathy caused by DOX and when added to the DOX+PTX combination, DZR retains its protective activity against DOX-induced cardiotoxicity without increasing noncardiac toxicity. Received: 7 October 1998 / Accepted: 3 December 1998     

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     

Methotrexate increases red blood cell concentrations of 6-methylmercaptopurine ribonucleotide in rats in vivo

Purpose: To elucidate the effect of methotrexate (MTX) on 6-mercaptopurine (6-MP) metabolism in rats. Methods: Fourteen rats were given 6-MP 20 mg/kg daily for 7 days. Seven of the rats were also given MTX 20 mg/kg on days 5 and 7. Blood samples were obtained from all rats on days 0, 5 and 8, and red blood cell (RBC) lysates were analysed for thiopurine methyltransferase (TPMT) activity and the concentration of methylated 6-MP metabolites [methyl mercaptopurine ribonucleotides (MMPRP)] and 6-thioguanine nucleotides (6-TGN). Results: The concentration of MMPRP increased 2.4 times from day 5 to day 8 in RBCs from rats given MTX in addition to 6-MP, as against 1.2 times in rats given 6-MP alone (P = 0.003). 6-TGN levels increased and TPMT activity decreased from day 5 to day 8, with no difference between the 6-MP and the 6-MP plus MTX groups. Conclusions: Single bolus doses of MTX increase the concentration of MMPRP in rats given daily s.c. doses of 6-MP, with no effect on 6-TGN concentration or TPMT activity. Received: 20 October 1996 / Accepted: 15 February 1997     

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     

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     

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     

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     

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     

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     

A pilot phase I trial of continuous hyperthermic peritoneal perfusion with high-dose carboplatin as primary treatment of patients with small-volume residual ovarian cancer

Purpose: Because intraperitoneal (i.p.) therapy may provide a therapeutic advantage and because hyperthermia enhances carboplatin (CBDCA) cytotoxicity, we evaluated the feasibility, toxicity, and pharmacokinetics of CBDCA given via continuous hyperthermic peritoneal perfusion (CHPP) in patients with small-volume residual ovarian cancer. Patients and Methods: Six patients underwent optimal cytoreductive procedures (residual disease ≤5 mm) as initial treatment of stages II and III epithelial ovarian adenocarcinoma. All patients received a 90-min CHPP at a CBDCA dose of 800–1200 mg/m², with the perfusate being recirculated rapidly from a reservoir through a heat exchanger, resulting in i.p. temperatures of 41–43 °C. Plasma, perfusate, and urine samples were collected and platinum was quantified by flameless atomic absorption spectrophotometry. Results: At no time did any patient's core temperature exceed 40 °C. Peak perfusate platinum concentrations were 8- to 15-fold higher than peak ultrafilterable plasma concentrations. The permeability-area product was extremely high and variable (14–90 ml/min), resulting in a regional advantage of 1.9–5.3. The percentage of the dose absorbed ranged widely from 27% to 77%. Dose-limiting hematologic toxicity was observed at a dose of 1200 mg/m² and this was associated with a CBDCA AUC in plasma of 11 mg min ml⁻¹. Conclusions: CHPP with CBDCA was safely given to three patients at a dose of 800 mg/m², and dose-limiting hematologic toxicities observed at 1200 mg/m², correlated with the plasma CBDCA exposure established when lower doses of CBDCA are given systemically. The pharmacokinetic data are consistent with the expected effect of vigorous mixing on the exposed peritoneal surface area. Variable drug absorption and clearance make the prediction of systemic exposure highly uncertain. These findings may have important implications for novel therapies given i.p. Received: 9 March 1998 / Accepted: 11 June 1998     

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     

Antiestrogenic activities of alternate-substituted polychlorinated dibenzofurans in MCF-7 human breast cancer cells

Purpose: 1,3,6,8-Substituted alkyl polychlorinated dibenzofurans (PCDFs), typified by 6-methyl-1,3,8-triCDF (MCDF), inhibit 17β-estradiol (E2)-induced responses in the rodent uterus and human breast cancer cells. The major purpose of the experiments reported here was to determine the structure-dependent antiestrogenic activities of several alternate-substituted (1,3,6,8- and 2,4,6,8-) PCDFs. Methods: The antiestrogenic activities were determined in MCF-7 human breast cancer cells using two assays, that is E2-induced cell proliferation and induction of chloramphenicol acetyl transferase (CAT) activity in cells transiently transfected with the E2-responsive Vit-CAT plasmid. Results: MCDF (10⁻⁵ M ), 6-isopropyl-1,3,8-triCDF, 6-ethyl-1,3,8-triCDF, 3-isopropyl-6-methyl-1,8-diCDF, and 6-methyl-2,4,8-triCDF, inhibited both E2-induced cell proliferation and CAT activity in MCF-7 cells. All of the remaining ten congeners inhibited either E2-induced cell proliferation or CAT activity, but not both responses. Conclusions: The antiestrogenic activity of the alternate-substituted PCDFs involves interactions between the aryl hydrocarbon and estrogen receptor signaling pathways. Although these compounds exhibited antiestrogenic activity in MCF-7 cells, the effects of individual congeners were response-specific, and there were no apparent structure-activity relationships. Received: 26 July 1996 / Accepted: 16 November 1996     

Human tumor models in the severe combined immune deficient (scid) mouse

Purpose: To test a number of established human tumor cell lines and early passage breast cancer (UACC2150) and melanoma cells (UACC1273) for growth in the scid mouse and the tumors' response to conventional chemotherapeutic drugs. Methods: Established melanoma (A375, C81-61), colon (SW480), lung (A549), lymphomoblastoid leukemia (LCL-B), promyelocytic leukemia (HL60), prostate (PC-3, DU145), and breast (MCF7) cell lines were injected at subcutaneous (s.c.), intraperitoneal (i.p.), or mammary fat pad (MFP) sites. Tumor volume growth curves and survival curves were established for the various tumor cell lines. Carmustine (BCNU), cisplatin (CDDP), cyclophosphamide (CPA), doxorubicin, dacarbazine (DTIC), tamoxifen and vincristine were injected s.c. or i.p.. The chemotherapeutic drug effects on tumor volumes and survival were determined. Results: Tumor growth occurred with each cell type. After i.p. injection, 90% mortality occurred within 26 to 60 days except for the early passage melanoma cell line UACC1273 with which mortality occurred within approximately 90 days. In the MCF7 breast model, treatment with tamoxifen (P < 0.001) and CPA (P < 0.0001) resulted in significant tumor growth delay compared with control groups. BCNU and CDDP resulted in significant tumor growth delays relative to control in SW480 colon cancer (P < 0.0014) and A375 melanoma (P < 0.0001) models, respectively. CPA and doxorubicin improved survival in the HL60 leukemia model (P = 0.0018). Conclusions: These scid mouse human tumor models appear to reflect the clinical situation in that clinically active chemotherapeutic drugs are similarly active in the scid mouse models. Therefore, the scid mouse models may be useful for testing new chemotherapeutic agents against various human cancer types. Received: 6 March 1996 / Accepted: 3 October 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     

Protective role of metallothionein in renal toxicity of cisplatinum

To elucidate the protective role of metallothionein (MT) in the prevention of cisplatinum (cis-DDP) toxicity, we investigated the lethal and renal toxicities caused by cis-DDP in MT-null transgenic mice in comparison with wild-type control mice, and examined the effect of pretreatment with bismuth nitrate or zinc sulfate on the cis-DDP nephrotoxicity. The MT-null mice were of mixed 129 Ola and C57BL/6 genetic background. Since no differences in cis-DDP nephrotoxicity were observed between these strains, C57BL/6J mice were used as the wild-type control. The basal MT levels in the kidneys were negligible in the MT-null mice and 2.93 ± 0.77 μg/g tissue in the C57BL/6J mice. In terms of both the lethal and renal toxicities of cis-DDP, MT-null mice were far more sensitive than C57BL/6J mice. Preinduction of renal MT synthesis by administration of bismuth nitrate or zinc sulfate protected C57BL/6J mice from cis-DDP nephrotoxicity. In the case of MT-null mice, however, renal MT could not be induced by pretreatment with these metal compounds, and renal toxicity of cis-DDP was not prevented by this pretreatment. These results suggest that MT is an important factor with the potential to suppress the development of cis-DDP toxicity. Received: 17 June 1996 / Accepted: 27 November 1996     

In vitro antitumor activity of 3′-desamino-3′(2-methoxy-4-morpholinyl) doxorubicin on human melanoma cells sensitive or resistant to triazene compounds

A new methoxymorpholinyl derivative of Adriamycin (ADR), FCE 23762 (MRD), has recently been selected for phase I clinical trials for its reduced cardiotoxicity and for its cytotoxic activity against a broad spectrum of solid tumors and leukemias that are sensitive or resistant to ADR. The purpose of the present study was to compare the in vitro antitumor activity of MRD and ADR on human melanoma lines with different chemosensitivity to triazene compounds, among which dacarbazine remains a reference drug in the treatment of melanoma. Both MRD and ADR were tested in vitro on three melanoma lines, MI13443-MEL, SK-MEL-28, and M14, previously screened for their chemosensitivity to the triazene compound p-(3-methyl-1-triazeno) benzoic acid, potassium salt (MTBA). The three lines were also analyzed for P-170 expression, total glutathione (GSH) content, and GSH-related enzyme activity. All melanomas, whether sensitive or resistant to MTBA, were susceptible to anthracycline treatment. The cytotoxic activity of MRD was comparable with that of ADR, and no substantial difference was found in cell growth inhibition between the two drugs. When the relative chemosensitivity of the three lines was considered, SK-MEL-28 was found to be slightly less sensitive to MRD treatment than the other tumors. This finding seems to correlate with the higher GSH-peroxidase activity of this melanoma relative to that of the MI13443 and M14 lines. These results show a homogeneous response of melanoma lines to MRD treatment in vitro, suggesting that phase I clinical trials concerning this drug, which in vivo appears to be activated to a more cytotoxic metabolite, could be extended to metastatic melanomas, including those completely resistant to triazene compounds. Received: 11 August 1996 / Accepted: 20 January 1997     

Lack of correlation between mitotic arrest or apoptosis and antitumor effect of docetaxel

Purpose: To determine, as we did for paclitaxel, whether mitotic arrest and apoptosis induced in murine tumors in vivo by docetaxel correlate with the drug's antitumor effect and whether the antitumor efficacy of docetaxel depends on p53 mutational status of tumors. Methods: C3Hf/Kam mice were implanted with one of the following 15 syngeneic tumors: seven adenocarcinomas (MCa-4, MCa-29, MCa-35, MCa-K, OCa-I, ACa-SG, and HCa-I), two squamous cell carcinomas (SCC-IV and SCC-VII), five sarcomas (FSa, FSa-II, Sa-NH, NFSa, and Sa-4020) and one lymphoma (Ly-TH). When the tumors had grown to 8 mm in diameter, the mice were treated with 31.3 mg/kg docetaxel i.v. Tumor growth delay was the endpoint of docetaxel's antitumor effect. In separate groups of mice, mitotic arrest and apoptosis were determined micromorphometrically 1 to 72 h after docetaxel treatment. Tumors were assayed for their p53 status by sequence analysis of RNA prepared from freshly excised tumors. Results: Docetaxel caused statistically significant growth delay in six of seven adenocarcinomas, three of five sarcomas, and the lymphoma, but not in either of the squamous cell carcinomas. The drug induced mitotic arrest in all tumor types, but to various degrees ranging from 6.4 +/− 0.4% to 25.1 +/− 0.1%. In contrast, docetaxel induced appreciable apoptosis in only 5 of 15 tumors, with 10.3 +/− 1.6% being the highest apoptotic value. Neither mitotic arrest nor apoptosis were significantly correlated with tumor growth delay. However, tumors that responded to docetaxel by significant tumor growth delay histologically displayed massive cell destruction by cell lysis, and four of these tumors also showed marked infiltration with mononuclear lymphoid cells. Of the 15 tumors only 3 had mutant p53. Conclusions: Docetaxel exhibited a strong antitumor effect in two-thirds of murine tumors, and on a milligram per kilogram basis was more effective than paclitaxel against the same tumors. The drug was a potent inducer of mitotic arrest but a weak inducer of apoptosis, neither of which correlated with its antitumor effect. Tumor cell lysis appeared to be a major mode of tumor cell destruction and can be regarded as the main mechanism underlying antitumor efficacy of docetaxel. In contrast, paclitaxel's antitumor efficacy is related to its ability to induce apoptosis. At the molecular level, there was no dependency of antitumor efficacy of docetaxel on p53 mutational status of tumors. Received: 3 March 1998 / Accepted: 14 May 1998     

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     

Inter- and intraindividual variation in dihydropyrimidine dehydrogenase activity in peripheral blood mononuclear cells

Purpose: The activity of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in fluorouracil catabolism, has been reported to vary according to time of day. We wished to determine whether peak and trough DPD activities occurred at uniform times in six subjects, whether individual patterns fit a discernible profile, and whether such patterns were consistent and reproducible over time. Methods: Mononuclear cells were isolated from peripheral blood at 3-h intervals over a 24-h period on three different dates over a 6-month period. DPD activity was determined by incubating cellular lysates with [³H]FUra and measuring [³H]dihydrofluorouracil formation over time. Results: When the data were averaged by study date for each subject, the median value for the average DPD activity (11.0 pmol/min per 10⁶ cells) was significantly different from both the median peak (21.1 pmol/min per 10⁶ cells, P = 0.004) and median trough activities (4.0 pmol/min per 10⁶ cells, P = 0.002). Within the six␣subjects, the average DPD activity for the three study dates differed by a median of 2.4-fold (range 1.2- to 4.8-fold). The time at which peak and trough DPD activities occurred varied between subjects: 8 of the 17 peaks (47%) occurred between 10:00 p.m. and 6:00 a.m., 6 (35%) occurred between 8:00 a.m. and 3:00 p.m., and 3 (18%) occurred between 5:00 p.m. and 8:15 p.m. Thus, the time of day when the peak occurred was essentially randomly distributed over the 24-h period of observation (P = 0.68). Ten (59%) of the trough DPD activities occurred between 7:00 a.m. and 3:00 p.m. The median interval between the peak and trough was 6.5 h. The data were also expressed as percent of the mean for each individual's 24-h sampling period, and reordered as time from peak rather than as the actual time of day. When the combined data for all cycles was considered, the trough occurred 6–9 h after the peak, and the DPD levels subsequent to the peak did not display merely random variation (P = 0.0055). Conclusions: DPD activity levels and the times at which peak and trough DPD activities occurred varied both between and within subjects. If fluctuations in DPD activity influence the tolerability of fixed-rate infusions of FUra, these data suggest that a single variable-rate infusion regimen may not be suitable for all patients nor for a given individual treated over several months. Received: 1 April 1996 / Accepted: 7 October 1996