Cytotoxicity of adriamycin combined with methotrexate against L1210 leukemia in mice.

The combination of adriamycin and methotrexate was found in mice to be synergistic in cytotoxicity to L1210 leukemia cells for a range of time intervals between the two agents. Cytotoxicity for normal hematopoietic stem cells was less than additive. Spleen colony assays were used to quantitate both cell populations. Increase in life-span assays yielded similar results. Also, the extent of synergy was dependent on the dose of adriamycin only.

Cellular quantitation of in vivo effects of 1-beta-D-arabinofuranosylcytosine on leukemia L1210.

We derived a cellular model for the use of the cytidine analogue 1-beta-D-arabinofuranosylcytosine (ara-C) against L1210 leukemia in vivo from dose- and time-survival studies. We employed a quantitative assay for leukemia colony-forming cells to construct dose- and time-survival curves for single, divided, and infused doses of ara-C. Time-survival curves for a large dose range of ara-C indicated not only cell killing but also progression delay effects in vivo. Divided dose studies showed the extent of cell killing (optimum effect) to be dependent upon both the dose and the interval of time between administration of the drugs. When the drug was given as an infusion, the extent of cell killing was as great as that produced by the best fractionation schedule, an effect which was verified in terms of therapeutic efficacy in leukemic mice.

Chemotherapy of L1210 leukemia with 5-azacytidine in combination with vincristine, adriamycin, or beta-cytosine arabinoside.

The cytotoxicity of vincristine (VCR), beta-cytosine arabinoside (Ara-C), or adriamycin (ADRIA) in combination with 5-azacytidine (Aza-CR) to L1210 leukemia in vivo was measured to determine if schedule-dependent synergistic or antagonistic drug interaction occurred. Two dose levels of Aza-CR were studied (0.1 and 0.5 mg/mouse), and cytotoxicity was measured by the spleen colony assay. For the combination of Aza-CR plus VCR, cytotoxicity was essentially additive or antagonistic when VCR preceded Aza-CR and additive or synergistic when VCR followed Aza-CR. When Aza-CR was combined simultaneously with either Ara-C or ADRIA, cytotoxicity was markedly antagonistic but was additive if drugs were given sequentially. When Ara-C was given as a 24-hour infusion before Aza-CR, the resultant cell kill was antagonistic (although slightly greater than that obtained for Ara-C alone). However, antagonism was even more marked when Aza-CR was given before the 24-hour infusion of Ara-C; cell kill was less than that observed with Ara-CR alone. Synergistic cytotoxicity was observed only with VCR administered after a low dose of of Aza-CR. Therefore, scheduling of drugs in combination with Aza-CR may be critical in the determination of the antileukemic cytotoxic effects.

Contrasting cytotoxicity kinetics of 5-azacytidine and dihydro-5-azacytidine hydrochloride in L1210 leukemia in mice.

For a comparison of the kinetics of the cytotoxicity of dihydro-5-azacytidine hydrochloride (DHAzaCR) and 5-azacytidine (AzaCR) in L1210 leukemia, the spleen colony assay was used to determine the surviving fraction of normal hematopoietic colony-forming units (NCFU) and leukemia colony-forming units (LCFU). Increasing doses of DHAzaCR above 1 mg per mouse enhanced cytotoxicity to LCFU but not to NCFU. The NCFU dose-survival curve showed a plateau with DHAzaCR, such that increasing the dose from 1 to 80 mg per mouse produced no further decrease in NCFU survival. In contrast, AzaCR produced a biphasic dose-NCFU survival curve without a plateau. Although DHAzaCR produced less cytotoxicity on a milligram basis than did AzaCR, both DHAzaCR and AzaCR elicited a biphasic dose-survival curve for LCFU. An infusion of DHAzaCR was less cytotoxic than was a similar dose of DHAzaCR administered as an iv bolus. Although high doses of AzaCR administered as an iv bolus. Although high doses of AzaCR delayed LCFU repopulation, both low and high doses of DHAzaCR were associated with prompt LCFU repopulation. Confirming this prompt repopulation of LCFU, there was a good correlation between the increase in life-span of mice with leukemia predicted by LCFU data following DHAzaCR treatment, compared to the discrepancy between predicted survival and observed survival following AzaCR. Therefore, the kinetics of cytotoxicity of DHAzaCR differ from those of AzaCR.

The enhanced cytotoxicity of combinations of 1-beta-D-arabinofuranosylcytosine and methotrexate.

Although both 1-beta-D-arabinofuranosylcytosine (ara-C) and methotrexate are presumed to be toxic as a result of their interference with DNA synthesis, results obtained with L1210 cells in vivo suggest that the combination of ara-C and methotrexate is capable of killing cells by a mechanism not related simply to DNA synthesis inhibition. Simultaneous administration of ara-C and methotrexate, or administration of these two agents within a 10-hr interval, independent of order, produces a synergistic cell kill of L1210 cells but a less than additive effect on normal hematopoietic stem cells. The extent of synergy seems dependent upon the dose of ara-C.

Effect of dose fractionation of daunorubicin on survival of leukemic cells.

Mice bearing transplanted AKR leukemia received daunorubicin either as a single dose or as four equally divided doses (0.2 mg/mouse; four times) with the time interval between the divided doses varying from 12 to 36 hr; survival of leukemia colony-forming cells was then assayed. When daunorubicin was administered in any of the fractionated schedules, the dose-survival curve was exponential with a shoulder region demonstrable. As expected, there was significantly less cell killing for the fractionated schedule than for a comparable accumulated single dose; however, with administration of the fourth dose for any interval studied, the increment in cell killing was so large that it was quite similar to that resulting from a single 0.8-mg/mouse dose. We examined the time course of cell killing for the 24-hr fractionation schedule and found greater killing than expected after each subsequent dose with the most pronounced increase occurring after the fourth dose. Possible mechanisms for this effect are discussed.

Biological characterization of a prolonged antileukemic effect of 5-azacytidine.

A prolonged cytotoxic effect of 5-azacytidine (aza-CR) on leukemic colony-forming units (LCFU) was observed in mice with transplanted L1210 leukemia. LCFU showed rapid reaccumulation in the marrow 12 hr after injection of 0.1 mg of aza-CR per mouse. However, after 0.5 mg of aza-CR, repopulation was delayed for at least 6 days. Experiments were performed to determine the mechanism of this prolonged antileukemic effect. Suspensions of leukemic marrow prepared from mice treated 4 days previously with 0.5 mg of aza-CR were exposed to [3H]thymidine in vitro in order to kill cells in S phase. Suspensions exhibited a 40% reduction in LCFU, indicating the prolonged effect was not due to cell cycle progression delay. Mice given whole-body irradiation prior to receiving L1210 demonstrated the same delayed repopulation following the high dose of aza-CR as nonirradiated mice, suggesting that the effect was likely not due to an immune reaction. aza-CR, when given to normal mice as long as 2 days prior to leukemic transplantation, was able to prolong the survival of leukemic mice, but not when given at longer intervals. Administration of aza-CR to mice 1 day or 1 hr prior to leukemic transplantation resulted in decreased LCFU survival as well as delayed repopulation of LCFU; the rate of repopulation was not changed. This indicated a prolonged residual activity of the drug, but not sufficient to explain the total in vivo suppression. In contrast, administration of aza-CR to leukemic mice suppressed repopulation of a subsequent leukemic transplant for 4 days, even when the cells were given 2 days after the aza-CR. Cytidine was partially able to reverse the delayed repopulation of LCFU when given 1 day after aza-CR, but it was unable to reverse the phenomenon 2 days after aza-CR. Therefore, a high dose of aza-CR produces a prolonged antileukemic effect which is probably mediated by continued availability of an aza-CR metabolite. Since this effect is more pronounced in leukemic mice than in nonleukemic mice, the pharmacokinetics of high doses of aza-CR probably differ in normal and leukemic mice.

Kinetics of both leukemic and normal cell population reduction following 5-azacytidine.

The cytotoxic effect of 5-azacytidine (AzaCR) on normal hematopoietic colony-forming units (NCFU) and L1210 leukemic colony-forming units (LCFU) in the femoral marrow of BALB/c x DBA/2 F1 mice was studied using the spleen colony assay. Dose-survival curves for LCFU and NCFU were biphasic. Repopulation of LCFU was rapid at a low dose of AzaCR (0.1 mg/mouse) but was delayed for greater than 6 days at higher doses (0.25 mg/mouse and above). Of the agents tested in this system, only AzaCR exhibited these properties. Survival of mice with L1210 leukemia following AzaCR administration was prolonged beyond that predicted by the degree of LCFU reduction alone, and reflected the delay in LCFU repopulation. In contrast, repopulation of NCFU in normal mice was not delayed at a high dose of AzaCR (0.5 mg/mouse). AzaCR produced a nine-fold greater reduction of NCFU in leukemic mice than in normal mice, measured 5 days after AzaCR injection. While divided doses of AzaCR produced LCFU cytotoxicity equivalent to a single dose, 24-hr infusions of high doses were inferior to single infections.

Synergistic antileukemic effect of 6-aminonicotinamide and 1,3-bis(2-chloroethyl)-1-nitrosourea on L1210 cells in vitro and in vivo.

A series of nicotinamide analogs were evaluated for their ability to inhibit L1210 cell poly(adenosine diphosphoribose) polymerase, and also for their ability to potentiate the cytocidal effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), nitrogen mustard, and gamma-irradiation. In L1210 cells growing in culture and in vivo. In vitro, nicotinamide, 5-methylnicotinamide, 6-aminonicotinamide, and benzamide effectively inhibited L1210 cell poly(adenosine diphosphoribose) polymerase; 1-methylnicotinamide, nicotinic acid, and benzoic acid did not. In culture, 6-aminonicotinamide potentiated the cytocidal effect of BCNU; however, it did not significantly potentiate the effects of nitrogen mustard or gamma-irradiation in vivo, both 6-aminonicotinamide and nicotinamide potentiated the cytocidal effect of BCNU; however, the concentrations of nicotinamide required for this effect were 10- to 20-fold higher than those of 6-aminonicotinamide. None of the analogs significantly potentiated the in vivo effect of nitrogen mustard or gamma-irradiation. Treatment of L1210-bearing mice with varying combinations of BCNU and 6-aminonicotinamide produced a synergistic increase in life span; in some cases, the combination led to the production of long term disease-free survivors.

Phase I and clinical pharmacological study of mercaptopurine administered as a prolonged intravenous infusion.

The bioavailability of oral mercaptopurine (MP) is poor, and plasma levels following p.o. dosing are highly variable. In an attempt to circumvent these problems, we conducted a Phase I trial and clinical pharmacological study of MP administered as a prolonged i.v. infusion. An infusion rate of 50 mg/sq m/h, which was designed to achieve therapeutic drug levels in plasma, was used in all patients. The infusion duration was escalated in 12-h increments. Thirty-eight patients were evaluated. The dose-limiting toxicity was mucositis. Other reversible toxicities were myelosuppression and hepatotoxicity. An infusion duration of 48 h was found to be safe, unassociated with dose-limiting toxicity. Objective responses were seen in five patients. The mean plasma steady-state MP concentration achieved was 6.9 microM with little interpatient variability seen. Allopurinol coadministration had no effect on the plasma pharmacokinetics of i.v. MP. However, allopurinol did alter the urinary metabolite pattern, decreasing thiouric acid and increasing MP and thioxanthine levels. The steady-state cerebrospinal fluid:plasma ratio for MP was 0.27, suggesting that this approach may be of value in the treatment of central nervous system cancer. MP can be safely administered as a 48-h i.v. infusion at a dose rate which reliably achieves MP levels associated with optimal antileukemic activity in vitro.

Up-front window trial of topotecan in previously untreated children and adolescents with metastatic rhabdomyosarcoma: an intergroup rhabdomyosarcoma study.

PURPOSE: To investigate the antitumor activity and toxicity of topotecan, used alone and in combination with conventional therapy, in patients with metastatic rhabdomyosarcoma (RMS). PATIENTS AND METHODS: Forty-eight patients younger than 21 years of age with newly diagnosed metastatic RMS received 2.0 to 2.4 mg/m(2) of topotecan intravenously daily for 5 days every 21 days before standard therapy. Two courses were given in the absence of progressive disease or excessive toxicity and response was assessed. Patients with at least a partial response (PR) to topotecan proceeded to therapy with alternating courses of vincristine 1.5 mg/m(2), dactinomycin 1.5 mg/m(2), and cyclophosphamide 2.2 g/m(2) (VAC) and vincristine 1.5 mg/m(2), topotecan 0.75 mg/m(2) daily x 5, and cyclophosphamide 250 mg/m(2) daily x 5. Patients who did not respond to topotecan received continuation therapy with VAC alone. RESULTS: The overall response rate to topotecan was 46% (complete response, 4%; partial response 42%). Unexpectedly, patients with alveolar RMS had a higher rate of response (65%) than those with embryonal RMS (28%; P: = .08). The most common grade 3 or 4 toxicities were neutropenia (67%), anemia (33%), thrombocytopenia (25%), and infection (21%). Two-year failure-free survival and survival estimates were 24% and 46%, respectively. Response to window therapy did not correlate with survival. CONCLUSION: The high response rate and acceptable toxicity profile of topotecan in children with advanced RMS support further evaluation of this agent in phase III trials. The superior responses in alveolar RMS are of interest.

Multimodal therapy for the management of primary, nonmetastatic Ewing's sarcoma of bone: a long-term follow-up of the First Intergroup study.

A total of 342 previously untreated eligible children were entered into the first Intergroup Ewing's Sarcoma Study (IESS) between May 1973 and November 1978. In group I institutions, patients were randomized between treatment 1 (radiotherapy to primary lesion plus cyclophosphamide, vincristine, dactinomycin, and Adriamycin [doxorubicin; Adria Laboratories, Columbus, OH] [VAC plus ADR]) or treatment 2 (same as treatment 1 without ADR), and group II institutions randomized patients between treatment 2 or treatment 3 (same as treatment 2 plus bilateral pulmonary radiotherapy [VAC plus BPR]). The percentages of patients relapse-free and surviving (RFS) at 5 years for treatments 1, 2, and 3 were 60%, 24%, and 44%, respectively. There was strong statistical evidence of a significant advantage in RFS for treatment 1 (VAC plus ADR) versus 2 (VAC alone) (P less than .001) and 3 (P less than .05) and also of treatment 3 versus 2 (P less than .001). Similar significant results were observed with respect to overall survival. Patients with disease at pelvic sites have significantly poorer survival at 5 years than those with disease at nonpelvic sites (34% v 57%; P less than .001). Among pelvic cases, there was no evidence of differing survival by treatment (P = .81), but among nonpelvic cases, there was strong evidence of differing survival by treatment (P less than .001). The overall percentage of patients developing metastatic disease was 44%; the percentages by treatments 1, 2, and 3 were 30%, 72%, and 42%, respectively. The overall incidence of local recurrence was 15%, and there was no evidence that local recurrence rate differed by treatment. Patient characteristics related to prognosis, both with respect to RFS and overall survival experience, were primary site (nonpelvic patients were most favorable) and patient age (younger patients were more favorable).

A comparison of induction and maintenance therapy for acute nonlymphocytic leukemia in childhood: results of a Pediatric Oncology Group study.

Two hundred fifty-six children with previously untreated acute nonlymphocytic leukemia (ANLL) were evaluated on a Pediatric Oncology Group (POG) phase III randomized trial of both induction and continuation chemotherapies. Induction therapy compared vincristine, cytarabine, and dexamethasone (VADx) with daunorubicin, cytarabine, and thioguanine (DAT). The complete remission (CR) rate using DAT was superior (82% v 61%, P = .02). Postremission therapy consisted of either "standard" two-cycle therapy or a more intensive four-cycle regimen given for 2 years. Overall, there was no difference in outcome for patients randomized to either continuation regimen. The overall complete continuous remission rate (CCR) for the "best" induction/continuation therapy combination at 2 years was .50 (SE = .06), at 3 years was .35 (.04), and at 4 years was .34 (.05). Analysis of selected clinical and laboratory parameters demonstrated differences in induction responses favoring DAT induction but did not impact eventual disease-free survival. There were two subgroups of patients who responded better to four-cycle continuation therapy. These were patients with French-American-British (FAB) M1/M2 (2-year CCR was .20 v .44, P = .01) and patients older than 10 years at diagnosis (.32 v .62, P = .004).

Ewing's sarcoma in bones of the hands and feet: a clinicopathologic study and review of the literature.

Review of current data from the Intergroup Ewing's Sarcoma Study (IESS) shows that Ewing's sarcoma (ES) is rare in bones of the hands and feet. Only 12 of 377 evaluable patients in the first two IESS studies had a primary tumor in these small, distal bones. The age distribution was typical for that seen in patients with ES at other sites. Males were affected twice as often as females, and tumors in the bones of the feet were much more common than those in the hands. All signs and symptoms were local in distribution. As in other sites, the dominant histologic pattern was categorized as diffuse. With the exception of those patients with lesions in the calcaneus, the prognosis for disease-free survival was excellent. A literature review of cases of ES reported in bones of the hands and feet showed generally comparable results.

Phase I trial of paclitaxel in children with refractory solid tumors: a Pediatric Oncology Group Study.

PURPOSE: A phase I study was performed to describe the principal toxicities and identify the maximum-tolerated dose (MTD) of Taxol (paclitaxel; Bristol-Myers Squibb Co, Wallingford, CT) in children with therapy-resistant solid tumors. Additionally, the pharmacokinetic disposition of Taxol in children was studied, and preliminary evidence of the activity of Taxol against pediatric solid tumors was assessed. PATIENTS AND METHODS: Twenty-four-hour continuous infusions of Taxol were administered every 21 days to children (median age, 12 years; range, 2 to 22) with refractory solid tumors. Doses ranged from 200 to 420 mg/m2, there was no intrapatient dose escalation. RESULTS: A total of 62 courses of Taxol were administered to 31 patients. Two patients developed acute anaphylaxis during their second infusion of taxol at doses of 200 mg/m2 and 350 mg/m2, respectively. No other allergic reactions were documented. Myelosuppression occurred at all dose levels, but was of short duration (< or = 7 days) and did not appear to increase with consecutive courses or at higher dosage levels. A stocking-and-glove peripheral neuropathy became evident at doses > or = 290 mg/m2. Dose-limiting neurotoxicity occurred at 420 mg/m2 and comprised a significant fine-motor and peripheral neuropathy in one patient, and a tonic-clonic seizure in another. End-of-infusion plasma concentrations ranged from 0.40 to 6.4 mumol/L, and were not found to be dose-dependent over the range of doses studied. A complete response was documented in one patient, partial response in two, and minimal response in one for an overall response rate of 13%. CONCLUSION: Neurotoxicity was dose-limiting when Taxol was administered by 24-hour continuous infusion to pediatric patients with relapsed solid tumors. In this population, the recommended dose for phase II trials is 350 mg/m2/d.

Combined etoposide and 5-azacitidine in children and adolescents with refractory or relapsed acute nonlymphocytic leukemia: a Pediatric Oncology Group Study.

An intensive regimen of combined etoposide (VP-16) and 5-azacitidine (5-Az) was used to treat 96 children and adolescents with refractory or relapsed acute nonlymphocytic leukemia (ANLL). Patients were given two sequential five-day courses of VP-16, 250 mg/m2 for three days, followed by 5-Az, 300 mg/m2 for two days. An additional five-day course was administered if marrow aplasia was not evident by day 13. A complete remission rate of 45% was achieved with a median of two courses of VP-16 and 5-Az. The outcome of induction therapy was not influenced by prior treatment, blast cell morphology, or disease status on study entry (refractory or relapsed). Twenty-seven patients have relapsed after remission periods of 35 to 920 days (median, 110 days); seven others are free of leukemia for up to 519 days. The effectiveness of VP-16/5-Az combination therapy in patients refractory to anthracyclines and cytarabine indicates a potential role for these compounds in first-line treatment of patients with ANLL.

Multimodal therapy for the management of nonpelvic, localized Ewing's sarcoma of bone: intergroup study IESS-II.

Two hundred fourteen eligible patients with previously untreated, localized Ewing's sarcoma of bone were randomized on IESS-II to receive Adriamycin (ADR; doxorubicin; Adria Laboratories, Columbus, OH), cyclophosphamide, vincristine, and dactinomycin by either a high-dose intermittent method (treatment [trt] 1) or a moderate-dose continuous method (trt 2) similar to the four-drug arm of IESS-I. Patient characteristics (sex, primary site, type of surgery) were stratified at the time of registration; these and other patient characteristics (age, time from symptoms to diagnosis, race) were distributed similarly between treatments. Surgical resection was encouraged, but not mandatory. Local radiation therapy was the same as for IESS-I. The median follow-up time is 5.6 years. The overall outcome was significantly better on trt 1 than on trt 2. At 5 years, the estimated percentages of patients who were disease-free, relapse-free, and surviving were 68%, 73%, and 77% for trt 1 and 48%, 56%, and 63% for trt 2 (P = .02, .03, and .05, respectively). The major reason for treatment failure for both treatment groups was the development of metastatic disease. The lung was the most common site of metastases followed by bone sites. The combined incidence of severe or worse toxicity (67%) was comparable between the treatments; however, severe or worse cardiovascular toxicity was significantly greater on trt 1. Tne only treatment-associated deaths (N = 3) were on trt 1 and were cardiac-related.

Multimodal therapy for the management of localized Ewing's sarcoma of pelvic and sacral bones: a report from the second intergroup study.

A total of 59 eligible patients with localized Ewing's sarcoma of the pelvic and sacral bones were entered into a multimodal Intergroup Ewing's Sarcoma Study (IESS-II) (1978 to 1982) and compared with a historical control series of 68 patients entered into an earlier multimodal Intergroup Ewing's Sarcoma Study (IESS-I) (1973 to 1978). High-dose intermittent multiagent chemotherapy (vincristine, cyclophosphamide, Adriamycin [doxorubicin; Adria Laboratories, Columbus, OH], and dactinomycin) was given to all patients for 6 weeks before and for 70 weeks following local therapy. All patients who had a tumor biopsy or incomplete resection performed received a dose of 55 Gy to the tumor bed. With a median follow-up time of 5.5 years, two of 59 patients (3%) had a local recurrence, five patients (8%) had a local recurrence and metastases, and 17 patients (29%) developed metastases only. There was significant statistical evidence of an advantage in relapse-free survival (RFS) and survival (S) for patients on IESS-II versus IESS-I, P = .006 and P = .002, respectively. At 5 years, the comparison between IESS-II versus IESS-I was 55% versus 23% for RFS and 63% versus 35% for S.

Preservation of the bladder in patients with rhabdomyosarcoma.

PURPOSE: To review the pathologic findings from children with gross residual rhabdomyosarcoma (RMS) of the bladder and compare the treatment outcome of those who underwent cystectomy with those who did not. PATIENTS AND METHODS: Primary and follow-up records and pathology specimens for 28 patients with gross residual disease entered onto the intergroup Rhabdomyosarcoma Study (IRS) III were reviewed. These patients were assigned to receive 20 weeks of multiagent induction chemotherapy and 4 weeks of radiotherapy. Future therapy decisions were based on clinical and histologic evaluation at 20 weeks. RESULTS: All patients had a clinical and histologic response. Thirteen patients underwent cystectomy at intervals that ranged from 1.5 to 38 months after the start of therapy. All but one patient are alive and well without recurrence. Reasons for cystectomy included presumed evidence of tumor growth from imaging studies, findings at cystoscopy, or histologic interpretation of biopsies. In 12 of 14 specimens from 15 patients who retained their bladder, no tumor cells were seen at first or second evaluation. In cystectomy specimens, tumor cellularity was markedly reduced and all tumor cells were in varying degrees of cellular maturation. Review of primary tumor specimens showed a greater degree of cellular maturation in patients with retained bladders than in those who underwent cystectomy. CONCLUSION: Bladder RMS is responsive to chemotherapy and radiotherapy. Twelve of 26 patients showed complete loss of tumor cells after induction therapy. Cystectomy specimens showed diminished tumor cells with varying degrees of cellular maturation. It is hypothesized that these tumors may have shown further maturation and ultimate loss of matured cells with continuing therapy.

Phase I trial of 9-aminocamptothecin in children with refractory solid tumors: a Pediatric Oncology Group study.

PURPOSE: A phase I trial of 9-aminocamptothecin (9-AC) was performed in children with solid tumors to establish the dose-limiting toxicity (DLT), maximum-tolerated dose (MTD), and the pharmacokinetic profile in children and to document any evidence of activity. PATIENTS AND METHODS: A 72-hour infusion of 9-AC dimethylacetamide formulation was administered every 21 days to 23 patients younger than 21 years of age with malignant tumors refractory to conventional therapy. Doses ranged from 36 to 62 microg/m2 per hour. Pharmacokinetics were to be performed in at least three patients per dose level. The first course was used to determine the DLT and MTD. RESULTS: Nineteen patients on four dose levels were assessable for toxicities. At 62 microg/m2 per hour, three patients experienced dose-limiting neutropenia and one patient experienced dose-limiting thrombocytopenia. Pharmacokinetics were performed on 15 patients (nine patients had complete sets of plasma sampling performed). The pharmacokinetics of both lactone and total 9-AC were highly variable. The percentage of 9-AC lactone at steady-state was 10.8% +/- 3.6%. Total 9-AC and its lactone form had a terminal half-life of 8.1 +/- 3.8 and 7.1 +/- 3.9 hours, respectively, and a volume of distribution at steady-state (Vdss) of 21.2 +/- 13.3 L/m2 and 135.3 +/- 52.5 L/m2, respectively. Hepatic metabolism and biliary transport had an important role in 9-AC disposition. CONCLUSION: The recommended phase II dose of 9-AC administered as a 72-hour infusion every 21 days to children with solid tumors is 52 microg/m2 per hour. Neutropenia and thrombocytopenia were dose limiting.