Pharmacokinetics of pyrazoloacridine in the rhesus monkey.

Pyrazoloacridine is a rationally synthesized acridine derivative with in vitro activity against solid tumor cell lines, noncycling and hypoxic cells, and tumor cell lines that exhibit the multidrug resistance phenotype. The pharmacokinetic behavior of pyrazoloacridine after a 1- or 24-h i.v. infusion was studied in 5 rhesus monkeys that received a total of 10 courses of pyrazoloacridine at 300 or 600 mg/m2. Pyrazoloacridine levels in plasma and cerebrospinal fluid were measured by high-pressure liquid chromatography. For 1-h infusions, the plasma disappearance was biexponential with a t 1/2 alpha of 31 min and t 1/2 beta of 11 h. The mean volume of distribution at steady state was 1380 liters/m2. The clearance was 1660 ml/min/m2. For the 300 mg/m2 dose, the mean area under the concentration-time curve was 759 microM.min, and the mean peak concentration was 1.3 microM. For the 600 mg/m2 dose, the area under the concentration-time curve was 1330 microM.min, and the peak concentration was 2.5 microM. The steady-state plasma concentrations during the 24-h continuous infusions were 0.27 microM for the 300 mg/m2 dose and 0.45 microM for the 600 mg/m2 dose. The mean clearance calculated from these steady-state concentrations was 2420 ml/min/m2. Cerebrospinal fluid levels were less than 0.1 microM for all doses and schedules. There was no evidence of toxicity at any dose or schedule. These results contrast strikingly with those obtained in mice and dogs in which, despite a more rapid clearance of pyrazoloacridine, significant toxicities were observed at doses that were nontoxic in the monkey. These interspecies differences in the pharmacokinetic and pharmacodynamic behavior of pyrazoloacridine have important implications for the design of Phase I trials in humans.

Plasma and cerebrospinal fluid pharmacokinetics of O6-benzylguanine and time course of peripheral blood mononuclear cell O6-methylguanine-DNA methyltransferase inhibition in the nonhuman primate.

O6-Benzylguanine (O6BG) enhances the cytotoxicity of the nitrosoureas by irreversibly binding and inhibiting the DNA repair enzyme O6-methyl-guanine-DNA methyltransferase (MGMT). The plasma and cerebrospinal fluid (CSF) pharmacokinetics of O6BG and its active metabolite, O6-benzyl-8-oxoguanine, were studied in a nonhuman primate model after 200 mg/m2 had been injected i.v. The parent drug and the metabolite were measured with a reverse-phase HPLC assay. A pharmacokinetic model incorporating separate compartments for O6BG and the O6-benzyl-8-oxoguanine metabolite, first-order conversion of O6BG to the metabolite, and additional first-order elimination rate constants for each compound, was simultaneously fitted to the parent drug and metabolite plasma concentration time data. Elimination of O6BG from plasma was rapid; it had a half-life of 1.6 h and a clearance of 68 ml/min/m2. On the basis of the pharmacokinetic model, essentially all of the O6BG was converted to O6-benzyl-8-oxoguanine. The plasma pharmacokinetic profile of the metabolite differed considerably from that the parent drug. The half-life (14 h) was 10-fold longer and the area under the curve (2420 microM/h) was 11-fold higher than that of O6BG (212 microM/h). The clearance rate of O6-benzyl-8-oxoguanine was 6.4 ml/min/m2. The CSF:plasma ratio was 4.3% for O6BG and 36% for O6-benzyl-8-oxoguanine, and the metabolite area under the curve was 90-fold higher than that of O6BG in CSF. The excellent CSF penetration of the active metabolite provides a rationale for the use of O6BG as a chemosensitizing agent for brain tumors. We also studied the duration of MGMT inhibition in peripheral blood mononuclear cells. By 2 h after a 200 mg/m2 dose of O6BG, > 98% of MGMT activity was suppressed, and > 95% suppression of enzyme activity persisted at 18 and 48 h after the dose. By 2 weeks after the treatment, MGMT levels had returned to baseline. Persistent high concentrations of the active metabolite appear to provide a pharmacological explanation for the prolonged suppression of MGMT activity.

Pharmacokinetics of piroxantrone in a phase I trial of piroxantrone and granulocyte-colony stimulating factor.

Piroxantrone is an anthrapyrazole derivative with broad antitumor activity in vitro. In previous phase I trials, the dose-limiting toxicity of this agent was myelosuppression. Therefore, a phase I and pharmacokinetic study of a 1-h infusion of piroxantrone in combination with granulocyte-colony stimulating factor was conducted. In this article, we report the results of the pharmacokinetic analysis. Thirty-seven patients were studied over a dosage range of 150 to 555 mg/m2. The plasma elimination of piroxantrone was biexponential with a mean (+/- SD) t1/2 alpha of 3.2 +/- 2.7 min and a mean (+/- SD) t1/2 beta of 82 +/- 92 min. Clearance was 840 +/- 230 ml/min/m2. A limited sampling strategy was developed to allow the estimation of total drug exposure (area under the plasma concentration-time curve) from the plasma piroxantrone concentrations at 30, 60, and 120 min after the start of the infusion. The pharmacokinetic behavior of a presumed piroxantrone metabolite not previously described in plasma was also characterized. Based on in vitro cytotoxicity studies with partially purified extract of this compound, we do not believe that it contributes to the antitumor effects of piroxantrone at the concentrations observed in plasma. Finally, piroxantrone elimination was linear over the nearly 4-fold dose range studied, indicating that when dose adjustments are made, systemic drug exposure will remain predictable.

A phase I trial of amifostine (WR-2721) and melphalan in children with refractory cancer.

Melphalan has a steep dose-response curve, but the use of high doses results in unacceptable myelosuppression. Strategies to circumvent this dose-limiting myelosuppression would allow for the administration of higher, more effective doses of melphalan. Amifostine (WR-2721) has been shown in preclinical studies to protect the bone marrow from the myelotoxicity of melphalan, and in clinical trials, to protect from the myelotoxicity of other alkylating agents. A Phase I trial of the combination of amifostine and melphalan was performed in children with refractory cancers to: (a) define the acute toxicities of amifostine and its maximum tolerated dose (MTD); and (b) to determine whether the dose of melphalan could be safely escalated when administered in combination with amifostine. Amifostine was administered i.v. as a 15-min infusion 30 min before melphalan. The starting dose of amifostine was 750 mg/m2, with planned dose escalations in 30% increments. Melphalan was administered as a 5-min infusion using the previously defined MTD in heavily pretreated patients, 35 mg/m2, as the starting dose. The dose of melphalan was escalated by 30% increments. Nineteen patients, ranging in age from 3 to 24 years (median, 15 years), were entered on trial. The dose of amifostine was escalated to 2700 mg/m2, which is approximately 3-fold higher than the adult recommended dose, without reaching a MTD. Fifteen patients experienced nondose-limiting (< 25%), transient decreases in blood pressure after the amifostine infusion. Other nondose-limiting toxicities of amifostine included mild nausea and vomiting, flushing, anxiety, diarrhea, and urinary retention. Six patients, three each at the 2100 and 2700 mg/m2 amifostine dose levels were treated with an escalated dose of melphalan (45 mg/m2). All of these patients experienced grade 4 neutropenia (< 500/mm3), and five of six patients had grade 4 thrombocytopenia. The duration of this dose-limiting myelosuppression exceeded 7 days in four of six patients. Although no dose-limiting (grade 3 or 4) toxicity was attributed to amifostine, significant anxiety and reversible urinary retention occurred at the two highest amifostine dose levels. A dose of 1650 mg/m2 for pediatric Phase II trials is recommended. High doses of amifostine, however, do not appear to allow for escalation of melphalan beyond its single agent MTD of 35 mg/m2.

Paclitaxel in doxorubicin-refractory or mitoxantrone-refractory breast cancer: a phase I/II trial of 96-hour infusion.

PURPOSE: A phase I study of paclitaxel infused over 96-hours was performed to determine toxicity, maximum-tolerated dose (MTD), and pharmacokinetics in patients with incurable lymphomas and solid tumors. A phase II study was performed at the MTD of paclitaxel in patients with doxorubicin/mitoxantrone-refractory metastatic breast cancer. PATIENTS AND METHODS: In the phase I study, paclitaxel dose levels ranged from 120 to 160 mg/m2, administered on a 21-day cycle. Patients with metastatic breast cancer who had either no response or a partial response (PR) to doxorubicin or mitoxantrone and had measurable disease were eligible for the phase I and II studies. Expression of the multidrug resistance (mdr-1) gene was determined in tumor biopsies by mRNA quantitative polymerase chain reaction. RESULTS: Twelve patients received a total of 73 cycles of paclitaxel on the phase I study. Dose-limiting mucositis and/or grade IV granulocytopenia was reached at 160 mg/m2, and 140 mg/m2 was selected as the phase II dose. Thirty-six consecutive patients with metastatic breast cancer were treated, of whom three were not assessable. The median age was 49 years, with disease in the liver and/or lung in 76%. Patients received a median of two prior regimens for metastatic disease, and 73% had no response to prior doxorubicin or mitoxantrone. Of 33 patients treated with paclitaxel, 16 patients (48%) achieved a PR and five (15%) achieved a minor response (MR). With a median potential follow-up duration of 60 weeks, the median progression-free and overall survival durations were 27 and 43 weeks, respectively. No correlation was found between extent of prior treatment or prior response to doxorubicin/mitoxantrone, and response to paclitaxel. Paclitaxel pharmacokinetics showed a correlation between both granulocyte and mucosal toxicity, and serum steady-state concentrations (Css) more than 0.07 mumol/L. Patients with liver metastases had significantly decreased paclitaxel clearance and higher paclitaxel Css. Levels of mdr-1 were uniformly low in all tumor biopsies studied. CONCLUSION: The recommended phase II dose of paclitaxel is 140 mg/m2 in patients without liver metastases and 105 mg/m2 in patients with liver metastases. Ninety-six-hour infusions of paclitaxel were effective and well tolerated in patients with doxorubicin/mitoxantrone-refractory breast cancer. Prolonged infusion schedules may be more effective than shorter schedules and deserve further study.

Phase I trial of intrathecal liposomal cytarabine in children with neoplastic meningitis.

PURPOSE: We performed a phase I trial of intrathecal (IT) liposomal cytarabine (DepoCyt; Enzon Pharmaceuticals, Piscataway, NJ and SkyePharma Inc, San Diego, CA) to determine the maximum-tolerated dose, the dose-limiting toxicities, and the plasma and CSF pharmacokinetics of IT lipsomal cytarabine in children >/= 3 years of age with advanced meningeal malignancies. PATIENTS AND METHODS: Eighteen assessable patients received IT liposomal cytarabine through either an indwelling ventricular access device or via lumbar puncture. Liposomal cytarabine was given once every 2 weeks during induction, once every 4 weeks during consolidation, and once every 8 weeks during the maintenance phase of treatment. The initial dose was 25 mg, with subsequent escalations to 35 and 50 mg. CSF pharmacokinetic samples were obtained in a subset of patients. RESULTS: Arachnoiditis, characterized by fever, headache, nausea, vomiting, and back pain was noted in the first two patients at the 25 mg dose level. Therefore, subsequent patients were treated with dexamethasone, beginning the day of liposomal cytarabine administration and continuing for 5 days. Headache (grade 3) was dose limiting in two of eight patients enrolled at the 50 mg dose level. Eight of the 14 patients assessable for response demonstrated evidence of benefit manifest as prolonged disease stabilization or response. CONCLUSION: The maximum-tolerated dose and recommended phase II dose of liposomal cytarabine in patients between the ages of 3 and 21 years is 35 mg, administered with dexamethasone (0.15 mg/kg/dose, twice a day for 5 days). A phase II trial of IT liposomal cytarabine in children with CNS leukemia in second or higher relapse is in development.

Effect of R-verapamil on the pharmacokinetics of paclitaxel in women with breast cancer.

PURPOSE: To study the effect of the multidrug-resistance reversal agent R-verapamil on the pharmacokinetic behavior of paclitaxel. METHODS: Six women with breast cancer who received paclitaxel as a 3-hour infusion with and without R-verapamil were monitored with frequent plasma sampling up to 24 hours postinfusion. Paclitaxel concentrations were measured using a reverse-phase high-pressure liquid chromatography assay. RESULTS: Concomitant administration of R-verapamil resulted in a decrease in mean (+/- SD) paclitaxel clearance from 179 +/- 67 mL/min/m2 to 90 +/- 34 mL/min/m2 (P < .03) and in a twofold increase in paclitaxel exposure (area under the curve [AUC]). The mean end-infusion paclitaxel concentration was also twofold higher: 5.1 +/- 1.8 mumol/L versus 11.3 +/- 4.1 mumol/L (P < .03). CONCLUSION: The alteration in paclitaxel pharmacokinetics when paclitaxel and R-verapamil are coadministered complicates the interpretation of response and toxicity data from clinical trials of this drug combination.

Phase I/II trial and pharmacokinetics of intrathecal diaziquone in refractory meningeal malignancies.

PURPOSE: Because there is a compelling need to develop new agents for intrathecal use, we investigated the safety, efficacy, and CSF pharmacokinetics of diaziquone (AZQ) following intrathecal administration in patients with refractory meningeal malignancies. PATIENTS AND METHODS: Thirty-nine patients received 45 courses of intrathecal AZQ. Two schedules were studied; twice-weekly administration of a 1- or 2-mg dose and "concentration times time" (C x T) administration of 0.5 mg every 6 hours for three doses, administered once weekly. RESULTS: Dose-limiting toxicity consisting of headache, nausea, or vomiting occurred in only three patients and only at the 2-mg, twice weekly dose. The schedules of 1 mg twice-weekly and 0.5 mg every 6 hours for three doses were well tolerated. Thirty-seven courses were assessable for response. The overall response rate was 62%. Complete responses (CRs) occurred in 14 of 37 courses (38%) and partial responses (PRs) occurred in nine of 37 courses (24%). Among patients with meningeal leukemia, CRs were observed in 11 of 26 courses (42%) and PRs in nine of 26 courses (35%). There was no difference in response rate related to dose or schedule. The pharmacokinetic behavior of intrathecally administered AZQ was characterized by biexponential disappearance from ventricular CSF, with mean half-lives of 18.2 and 78.6 minutes. The mean clearance rate was 0.37 mL/min. CONCLUSION: Intrathecal AZQ is safe, well tolerated, and highly active against refractory meningeal malignancies.

Phase I trial and pharmacokinetic study of all-trans-retinoic acid administered on an intermittent schedule in combination with interferon-alpha2a in pediatric patients with refractory cancer.

PURPOSE: To determine the maximum-tolerated dose (MTD) of all-trans-retinoic acid (ATRA) administered on an intermittent oral schedule with interferon-alpha2a (IFN-alpha2a) in children with refractory cancer, and whether the marked reduction in plasma ATRA concentrations observed with chronic daily oral dosing could be circumvented with an intermittent dosing schedule. PATIENTS AND METHODS: Thirty-three children with refractory cancer (stratified by age, < or = 12 and > 12 years) were treated with ATRA 3 consecutive days per week and IFN-alpha2a 3 x 10(6) U/m2 5 consecutive days per week, both repeated weekly. The starting dose of ATRA was 60 mg/m2/d divided into three doses, with planned escalations to 90 and 120 mg/m2/d. Because severe headaches have been noted to occur on the initial day of ATRA administration, only two of three doses of ATRA were administered on day 1 of each week. RESULTS: Pseudotumor cerebri or dose-limiting headache was observed in two of five patients older than 12 years treated at the 120-mg/m2/d dose level and in one of six < or = 12 years at the 90-mg/m2/d level. Other non-dose-limiting toxicities of ATRA included reversible elevations in hepatic transaminases and triglycerides, dry skin, cheilitis, and nausea/vomiting. One child with recurrent neuroblastoma had an objective response of 6 months' duration, and one with recurrent Wilms' tumor had histologic maturation of multiple tumors. This intermittent schedule allowed for exposure to relatively high plasma concentrations of ATRA on a repetitive basis. Following 30-mg/m2 doses, the ATRA area under the concentration-time curve (AUC) decreased from 96 +/- 14 micromol/L/min on day 1 to 26 +/- 24 micromol/L/min by day 3 of drug administration, but on day 1 of the fourth consecutive week of therapy, the AUC averaged 110 +/- 16 micromol/L/min. The recommended pediatric phase II dose of ATRA administered on this schedule is 90 mg/m2/d. CONCLUSION: An intermittent schedule of ATRA administration appears to circumvent the low plasma drug exposure that is a result of the sustained upregulation of metabolism when this drug is administered on a chronic daily schedule. Based on the results of this trial, a phase II trial of ATRA/IFN-alpha2a in neuroblastoma and Wilms' tumor using this schedule is in progress.

Phase I trial and pharmacokinetic study of pyrazoloacridine in children and young adults with refractory cancers.

PURPOSE: To define the maximum-tolerated dose (MTD), quantitative and qualitative toxicities, recommended phase II dose, and pharmacokinetics of pyrazoloacridine (PZA) administered as a 1- or 24-hour infusion in children and young adults with refractory cancers. PATIENTS AND METHODS: Twenty-two patients received PZA as a 1-hour infusion at doses of 380 mg/m2 (n = 3), 495 mg/m2 (n = 6), 640 mg/m2 (n = 6), and 835 mg/m2 (n = 7). An additional four patients received PZA as a 24-hour infusion at the MTD (640 mg/m2) for the 1-hour infusion schedule. Plasma samples were obtained for pharmacokinetic analysis in 17 patients. PZA concentration in plasma was measured by reverse-phase high-performance liquid chromatography (HPLC). A two-compartment pharmacokinetic model was fit to the PZA plasma concentration data. RESULTS: On the 1-hour infusion schedule, dose-limiting myelosuppression (neutropenia more than thrombocytopenia) was observed in two of seven patients at the 835-mg/m2 dose level. Myelosuppression did not appear to be ameliorated by prolonging the infusion to 24 hours. Nonhematologic toxicities were minor. Significant neurotoxicity, which was dose-limiting in adults treated with a 1-hour infusion of PZA, was observed in one patient treated at 640 mg/m2, but was not dose-limiting. There was marked interpatient variability in plasma PZA concentrations at all dose levels. The pharmacokinetic profile of PZA was characterized by an initial rapid decline (alpha half-life [t(1/2)alpha], 0.5 hours) followed by a prolonged elimination phase (t(1/2)beta, 30 hours). The volume of distribution at steady-state (Vd(ss)) was 700 L/m2 and the clearance was 300 mL/min/m2. There was no evidence of dose-dependent clearance. The area under the PZA concentration-time curve (AUC) correlated poorly with dose and was more predictive of the degree of myelosuppression than was PZA dose. CONCLUSION: PZA administered as 1- or 24-hour infusion is well tolerated by children and young adults. The dose-limiting toxicity (DLT) is myelosuppression. Neurotoxicity is not prominent in this age group. There was marked interpatient variation in plasma concentrations of PZA. The recommended dose for phase II studies is 640 mg/m2.

Phase I study of high-dose piroxantrone with granulocyte colony-stimulating factor.

PURPOSE: We performed a phase I trial of piroxantrone with and without granulocyte colony-stimulating factor (G-CSF) to determine whether the use of this cytokine would enable us to increase the dose-intensity of piroxantrone. PATIENTS AND METHODS: Thirty-eight patients received 121 courses of piroxantrone administered once every 21 days. Initial patient cohorts received piroxantrone alone starting at 150 mg/m2 and the dose was escalated in subsequent patients until dose-limiting toxicity (DLT) was reached. Patient cohorts then received escalating doses of piroxantrone starting at 185 mg/m2 administered with G-CSF beginning day 2. RESULTS: Dose-limiting neutropenia occurred in three of six patients treated with 185 mg/m2 piroxantrone; the maximum-tolerated dose (MTD) of piroxantrone alone was 150 mg/m2. Three of six patients treated with piroxantrone and G-CSF exhibited dose-limiting thrombocytopenia at 445 mg/m2; the MTD of piroxantrone with G-CSF was thus 355 mg/m2. Seven patients developed symptomatic congestive heart failure (CHF) at cumulative piroxantrone doses ranging from 855 to 2,475 mg/m2 and two have died of cardiotoxicity. Of these patients, six of seven had previously received doxorubicin. Other nonhematologic toxicity was mild. CONCLUSION: The use of G-CSF results in a more than twofold increase in the MTD of piroxantrone. However, symptomatic cardiotoxicity is prominent, especially in patients who have received prior treatment with anthracyclines.

Phase I trial of docetaxel administered as a 1-hour infusion in children with refractory solid tumors: a collaborative pediatric branch, National Cancer Institute and Children's Cancer Group trial.

PURPOSE: A phase I trial of docetaxel was performed to determine the maximum-tolerated dose (MTD), the dose-limiting toxicities, and the incidence and severity of other toxicities in children with refractory solid tumors. PATIENTS AND METHODS: Forty-four children received 103 courses of docetaxel administered as a 1-hour intravenous infusion every 21 days. Doses ranged from 55 to 150 mg/m2, MTD was defined in heavily pretreated and less heavily pretreated (< or = 2 prior chemotherapy regimens, no prior bone marrow transplantation [BMT], and no radiation to the spine, skull, ribs, or pelvic bones) patients. RESULTS: Dose-related neutropenia was the primary dose-limiting toxicity. The MTD in the heavily pretreated patient group was 65 mg/m2, but the less heavily pretreated patients tolerated a significantly higher dose of docetaxel (maximum-tolerated dose, 125 mg/m2). Neutropenia and constitutional symptoms consisting of malaise, myalgias, and anorexia were the dose-limiting toxicities at 150 mg/m2 in the less heavily pretreated patients. Thrombocytopenia was not prominent, even in patients who experienced dose-limiting neutropenia. Common nonhematologic toxicities of docetaxel included skin rashes, mucositis, and mild elevations of serum transaminases. Neuropathy was uncommon. Peripheral edema and weight gain were observed in two of five patients who received more than three cycles of docetaxel. A complete response (CR) was observed in one patient with rhabdomyosarcoma, a partial response (PR) in one patient with peripheral primitive neuroectodermal tumor (PPNET), and a minimal response (MR) in two patients with PPNET. Three of the four responding patients were treated at doses > or = 100 mg/m2. CONCLUSION: The recommended phase II dose of docetaxel administered as a 1-hour intravenous infusion in children with solid tumors in 125 mg/m2. Because neutropenia was the dose-limiting toxicity and thrombocytopenia was mild, further escalation of the dose should be attempted with granulocyte colony-stimulating factor (G-CSF) support.

Randomized trial of the cardioprotective agent ICRF-187 in pediatric sarcoma patients treated with doxorubicin.

PURPOSE: We conducted an open-label, randomized trial to determine whether ICRF-187 would reduce doxorubicin-induced cardiotoxicity in pediatric sarcoma patients. METHODS: Thirty-eight patients were randomized to receive doxorubicin-containing chemotherapy (given as an intravenous bolus) with or without ICRF-187. Resting left ventricular ejection fraction (LVEF) was monitored serially with multigated radionuclide angiography (MUGA) scan. The two groups were compared for incidence and degree of cardiotoxicity, response rates to four cycles of chemotherapy, event-free and overall survival, and incidence and severity of noncardiac toxicities. RESULTS: Eighteen ICRF-187-treated and 15 control patients were assessable for cardiac toxicity. ICRF-187-treated patients were less likely to develop subclinical cardiotoxicity (22% v 67%, P < .01), had a smaller decline in LVEF per 100 mg/m2 of doxorubicin (1.0 v 2.7 percentage points, P = .02), and received a higher median cumulative dose of doxorubicin (410 v 310 mg/m2, P < .05) than did control patients. Objective response rates were identical in the two groups, with no significant differences seen in event-free or overall survival. ICRF-187-treated patients had a significantly higher incidence of transient grade 1 serum transaminase elevations and a trend toward increased hematologic toxicity. CONCLUSION: ICRF-187 reduces the risk of developing short-term subclinical cardiotoxicity in pediatric sarcoma patients who receive up to 410 mg/m2 of doxorubicin. Response rates to chemotherapy, event-free and overall survival, and noncardiac toxicities appear to be unaffected by the use of ICRF-187. Additional clinical trials with larger numbers of patients are needed to determine if the short-term cardioprotection afforded by ICRF-187 will reduce the incidence of late cardiac complications in long-term survivors of childhood cancer.

Phase I crossover study of paclitaxel with r-verapamil in patients with metastatic breast cancer.

PURPOSE: We conducted a phase I crossover study of escalating doses of both paclitaxel (Taxol; Bristol-Myers, Squibb, Princeton, NJ) and r-verapamil, the less cardiotoxic stereoisomer, in heavily pretreated patients with metastatic breast cancer. PATIENTS AND METHODS: Twenty-nine patients refractory to paclitaxel by 3-hour infusion were treated orally with r-verapamil every 4 hours starting 24 hours before the same-dose 3-hour paclitaxel infusion and continuing for a total of 12 doses. Once the maximum-tolerated dose (MTD) of the combination was determined, seven additional patients who had not been treated with either drug were evaluated to determine whether the addition of r-verapamil altered the pharmacokinetics of paclitaxel. Consenting patients had tumor biopsies for P-glycoprotein (Pgp) expression before receiving paclitaxel and after becoming refractory to paclitaxel therapy. RESULTS: The MTD of the combination was 225 mg/m2 of r-verapamil every 4 hours with paclitaxel 200 mg/m2 by 3-hour infusion. Dose-limiting hypotension and bradycardia were observed in three of five patients treated at 250 mg/m2 r-verapamil. Fourteen patients received 32 cycles of r-verapamil at the MTD as outpatient therapy without developing cardiac toxicity. The median peak and trough serum verapamil concentrations at the MTD were 5.1 micromol/L (range, 1.9 to 6.3), respectively, which are within the range necessary for in vitro modulation of Pgp-mediated multidrug resistance (MDR). Increased serum verapamil concentrations and cardiac toxicity were observed more frequently in patients with elevated hepatic transaminases and bilirubin levels. Hematologic toxicity from combined paclitaxel and r-verapamil was significantly worse compared with the previous cycle of paclitxel without r-verapamil. In the pharmacokinetic analysis, r-verapamil delayed mean paclitaxel clearance and increased mean peak paclitaxel concentrations. CONCLUSION: r-Verapamil at 225 mg/m2 orally every 4 hours can be given safely with paclitaxel 200 mg/m2 by 3-hour infusion as outpatient therapy and is associated with serum levels considered active for Pgp inhibition. The addition of r-verapamil significantly alters the toxicity and pharmacokinetics of paclitaxel.

Pharmacokinetics of O6-benzylguanine and its active metabolite 8-oxo-O6-benzylguanine in plasma and cerebrospinal fluid after intrathecal administration of O6-benzylguanine in the nonhuman primate.

O6-Benzylguanine (O6BG) irreversibly inactivates the single-turnover DNA repair protein alkylguanine-alkyltransferase. Thus, O6BG increases tumor-cell sensitivity to alkylating agents such as carmustine, lomustine, procarbazine, and temozolomide. We investigated the pharmacokinetic behavior of O6BG and O6-benzyl-8-oxoguanine (8-oxo-O6BG) in cerebrospinal fluid (CSF) and plasma after intraventricular administration of O6BG in a nonhuman primate model. In our study, three animals received a single 1-mg dose of O6BG into the lateral ventricle. CSF from the 4th ventricle and plasma samples were collected after administration, and O6BG and 8-oxo-O6BG concentrations were measured by high-performance liquid chromatography. Four additional animals received 1 mg of O6BG via the intralumbar route weekly for 6 weeks to assess the feasibility and toxicity of this route of administration. The peak O6BG CSF concentration was 412+/-86 microM, the t1/2 was 0.52+/-0.02 h, the clearance was 0.22+/-0.01 ml/min, and the area under the concentration-time curve was 319+/-15 microM x h in 4th ventricular CSF. The peak CSF concentration of 8-oxo-O6BG in CSF was 1.9+/-0.4 microM, the t1/2 was 0.76+/-0.03 h, and the area under the concentration-time curve was 5.0+/-1.1 microM x h. Both O6BG and 8-oxo-O6BG were detected in the plasma 0.5-3 h after intraventricular O6BG administration. The plasma peak concentration of O6BG was 0.4 microM at 30 min, and the concentration was <0.1 microM by 3 h. The plasma concentration of 8-oxo-O6BG was 0.2 microM at 30 min and 0.6 microM at 3 h. The animals tolerated the single intraventricular dose and 6 weekly intralumbar doses of O6BG without toxicity. We concluded that intrathecal administration of O6BG is well tolerated in the nonhuman primate and seems to have a substantial pharmacokinetic advantage over systemic administration for meningeal tumors.

A phase I study of irinotecan in pediatric patients: a pediatric oncology group study.

A Phase I trial of irinotecan was performed to determine the maximum tolerated dose (MTD), the dose-limiting toxicities (DLTs), and the incidence and severity of other toxicities in children with refractory solid tumors. Thirty-five children received 146 courses of irinotecan administered as a 60-min i.v. infusion, daily for 5 days, every 21 days, after premedication with dexamethasone and ondansetron. Doses ranged from 30 mg/m2 to 65 mg/m2. An MTD was defined in heavily pretreated and less-heavily pretreated (i.e., two prior chemotherapy regimens, no prior bone marrow transplantation, and no radiation to the spine, skull, ribs, or pelvic bones) patients. Myelosuppression was the primary DLT in heavily pretreated patients, and diarrhea was the DLT in less-heavily pretreated patients. The MTD in the heavily pretreated patient group was 39 mg/m2, and the MTD in the less-heavily pretreated patients was 50 mg/m2. Non-dose-limiting diarrhea that was well controlled and of brief duration was observed in approximately 75% of patients. A partial response was observed in one patient with neuroblastoma, and in one patient with hepatocellular carcinoma. Stable disease (4-20 cycles) was observed in seven patients with a variety of malignancies including neuroblastoma, pineoblastoma, glioblastoma, brainstem glioma, osteosarcoma, hepatoblastoma, and a central nervous system rhabdoid tumor. In conclusion, the recommended Phase II dose of irinotecan administered as a 60-min i.v. infusion daily for 5 days, every 21 days, is 39 mg/m2 in heavily treated and 50 mg/m2 in less-heavily treated children with solid tumors.

Plasma and cerebrospinal fluid pharmacokinetics of O6-benzylguanine and analogues in nonhuman primates.

O6-Benzylguanine (BG) is a potent, specific inactivator of the DNA repair protein, O6-alkylguanine-DNA alkyltransferase, that enhances the sensitivity of tumor cell lines and tumor xenografts to chloroethylnitrosoureas. To search for BG analogues with greater penetration into the cerebrospinal fluid (CSF), we evaluated plasma and CSF pharmacokinetics of BG, 8-aza-O6-benzylguanine (8-azaBG), O6-benzyl-8-bromoguanine (8-BrBG), O6-benzyl-8-oxoguanine (8-oxoBG), O6-benzyl-8-trifluoromethylguanine (8-tfmBG), and O6-benzyl-2'-deoxyguanosine (B2dG) after i.v. administration of 200 mg/m2 of drug through an indwelling Ommaya reservoir in a nonhuman primate model. BG and its analogues were quantified in plasma and CSF using reverse-phase high-performance liquid chromatography assays. The plasma clearances of the four 8-substituted BG analogues were similar (0.04-0.06 l/h/kg), but half-lives ranged from <2 to >24 h. BG was converted to 8-oxoBG, an equally potent O6-alkylguanine-DNA alkyltransferase inactivator, and the elimination of 8-oxoBG was much slower than that of BG. As a result, the plasma area under the curve of 8-oxoBG was 3.5-fold greater than that of BG. B2dG was metabolized to BG and 8-oxoBG, but this pathway accounted for only 20% of B2dG elimination. The CSF penetration percentages (based on the ratio of AUC(CSF): AUCplasma) for BG, 8-azaBG, 8-oxoBG, 8-tfmBG, 8-BrBG, and B2dG were 3.2, 0.18, 4.1, 1.4, <0.3, and 2.0%, respectively. The CSF penetration of BG and its active metabolite 8-oxoBG is greater than the penetration of 8-azaBG, 8-BrBG, 8-tfmBG, and B2dG.

Pharmacokinetics and cerebrospinal fluid penetration of CI-994 (N-acetyldinaline) in the nonhuman primate.

CI-994 is a substituted benzamide derivative that has demonstrated significant antitumor activity in vitro and in vivo against a broad spectrum of murine and human tumor models. Its mechanism of action is still unknown but seems to be novel compared with existing anticancer drugs. We studied the plasma and cerebrospinal fluid (CSF) pharmacokinetics of CI-994 in nonhuman primates. Three animals (total 4 doses) received an 80 mg/m2 dose of CI-994 administered over 20 min, and one animal received a dose of 100 mg/m2. Serial plasma and fourth ventricular CSF samples were obtained from 0 to 4320 min after administration of the 80-mg/m2 dose, and only plasma samples were obtained after the 100-mg/m2 dose. CI-994 was measured using a previously validated reverse-phase high-performance liquid chromatography assay. Elimination of CI-994 from plasma was triexponential (4 of 5 cases) or biexponential (1 of 5 cases), with a terminal half life (t1/2) of 7.4 +/- 2.5 h, volume of distribution of 15.5 +/- 1.8 L/m2, and clearance of 40 +/- 6 ml/min/m2. The area under the concentration-time curve (AUC) for the 80-mg/m2 dose was 125 +/- 17 microM x hr. CI-994 was first detected in CSF at the completion of the i.v. infusion. Peak concentrations of CI-994 in CSF were 3.4 +/- 0.3 microM. Elimination from CSF was monoexponential (2 of 4 cases) or biexponential (2 of 4 cases) with a terminal t1/2 in CSF of 12.9 +/- 2.5 h and AUC of 55 +/- 18 microM x hr. The AUC(CSF):AUCplasma ratio was 43 +/- 10%. This study demonstrates that there is excellent CSF penetration of CI-994 after i.v. administration. Additional studies are needed to evaluate the potential role of CI-994 in the treatment of central nervous system neoplasms.

Phase II trial of topotecan administered as 72-hour continuous infusion in children with refractory solid tumors: a collaborative Pediatric Branch, National Cancer Institute, and Children's Cancer Group Study.

The antitumor activity of topotecan administered as a 72-h continuous i.v. infusion was evaluated in children with refractory neuroblastoma and sarcomas of soft tissue and bone. We also attempted to increase the dose intensity of topotecan by including an intrapatient dose escalation in the trial design. Ninety-three children (85 eligible and evaluable for response) with recurrent or refractory neuroblastoma, osteosarcoma, Ewing's sarcoma/peripheral neuroectodermal tumor, rhabdomyosarcoma, or other soft-tissue sarcomas received topotecan administered as a 72-h i.v. infusion every 21 days. The initial dose was 1.0 mg/m2/day, with subsequent intrapatient dose escalation to 1.3 mg/m2/day for those patients who did not experience dose-limiting toxicity after their first cycle of topotecan. There was one complete response in a patient with neuroblastoma (n = 26) and one partial response in a patient with Ewing's sarcoma/peripheral neuroectodermal tumor (n = 25). No complete or partial responses were observed in 17 patients with osteosarcoma, 15 patients with rhabdomyosarcoma, or 2 patients with other soft-tissue sarcomas; however, 8 patients had prolonged (15-48 weeks) stable disease while receiving topotecan. Topotecan was well tolerated. The most commonly observed toxicities were myelosuppression (dose-limiting) and nausea and vomiting. Intrapatient dose escalations were performed in 68% of the patients who received more than one cycle of topotecan, and 1.3 mg/m2/day was tolerated by 79% of the patients who received the higher dose and were evaluable for hematological toxicity. In conclusion, topotecan administered as a 72-h continuous infusion every 21 days is inactive (objective response rate, < 20%) in children with refractory or recurrent neuroblastoma and sarcomas of soft tissue or bone.

Cytotoxicity and DNA damage associated with pyrazoloacridine in MCF-7 breast cancer cells.

We examined the effects of pyrazoloacridine (PZA), an investigational anticancer agent in clinical trials, on cytotoxicity, DNA synthesis, and DNA damage in MCF-7 human breast carcinoma cells. With PZA concentrations ranging from 0.5 to 50 microM for durations of 3-72 hr, cytotoxicity increased in proportion to the total PZA exposure (concentration x time). Inhibition of DNA and RNA syntheses increased with increasing PZA concentration x time (microM.hr). A 24-hr exposure to 1 and 10 microM PZA reduced DNA synthesis to 62 and 5% of control, respectively, decreased the proportion of cells in S phase with accumulation of cells in G2 + M phase, and inhibited cell growth at 72 hr by 68 and 100%. Newly synthesized DNA was more susceptible to damage during PZA exposure, with subsequent induction of parental DNA damage. Significant damage to newly synthesized DNA as monitored by alkaline elution was evident after a 3-hr exposure to > or = 5 microM PZA. Longer PZA exposures (> or = 10 microM for 16 hr) were required to elicit damage to parental DNA. Induction of single-strand breaks in parental DNA correlated closely with induction of double-strand breaks and detachment of cells from the monolayer. PZA-mediated DNA fragmentation was not accompanied by the generation of oligonucleosomal laddering in MCF-7 cells, but induction of very high molecular weight DNA fragmentation (0.5 to 1 Mb) was detected by pulsed-field gel electrophoresis. In vitro binding of PZA to linear duplex DNA (1 kb DNA ladder) and closed, circular plasmid DNA was demonstrated by a shift in migration during agarose electrophoresis. PZA interfered with topoisomerase I- and II-mediated relaxation of plasmid DNA in a cell-free system, but the cytotoxic effects of PZA did not appear to involve a direct interaction with topoisomerase I or II (stabilization of the topoisomerase I- or II-DNA cleavable complex). PZA-mediated cytotoxicity correlated strongly with inhibition of DNA and RNA syntheses, and damage to both nascent and parental DNA. Neither the cytotoxicity of PZA nor induction of double-stranded DNA fragmentation was prevented by aphidicolin, indicating that PZA-mediated lethality occurred in the absence of DNA replication. Since free radical formation was not detected, induction of nascent and parental DNA damage appeared to be a consequence of the avid binding of PZA to DNA, presumably by interfering with the access of replication, repair, and transcription enzyme complexes.