Pharmacokinetics and pharmacodynamics of oral methotrexate and mercaptopurine in children with lower risk acute lymphoblastic leukemia: a joint children's cancer group and pediatric oncology branch study.

We prospectively assessed the pharmacokinetics of methotrexate, mercaptopurine, and erythrocyte thioguanine nucleotide levels in a homogenous population of children with lower risk acute lymphoblastic leukemia and correlated pharmacokinetic parameters with disease outcome. The maintenance therapy regimen included daily oral mercaptopurine (75 mg/m2) and weekly oral methotrexate (20 mg/m2). One hundred ninety-one methotrexate doses and 190 mercaptopurine doses were monitored in 89 patients. Plasma drug concentrations of both agents were highly variable. The area under the plasma concentration-time curve (AUC) of methotrexate ranged from 0.63 to 12 micromol*h/L, and the AUC of mercaptopurine ranged from 0.11 to 8 micromol*h/L. Drug dose, patient age, and duration of therapy did not account for the variability. Methotrexate AUC was significantly higher in girls than boys (P =.007). There was considerable intrapatient variability for both agents. Erythrocyte thioguanine nucleotide levels were also highly variable (range, 0 to 10 pmol/g Hgb) and did not correlate with mercaptopurine dose or AUC. A Cox regression analysis showed that mercaptopurine AUC was a marginally significant (P =.043) predictor of outcome, but a direct comparison of mercaptopurine AUC in the remission and relapsed patient groups failed to show a significant difference. Methotrexate and mercaptopurine plasma concentrations and erythrocyte thioguanine nucleotide levels were highly variable, but measurement of these pharmacokinetic parameters at the start of maintenance will not distinguish patients who are more likely to relapse.

A phase II trial of continuous-infusion 6-mercaptopurine for childhood leukemia.

A phase II pediatric trial of a continuous intravenous infusion of 6-mercaptopurine (6MP) in patients with refractory leukemia was performed. The dosing schedule, 50 mg m-2 h-1 for 48 h, was based on the results of a previous phase I trial of this approach. Among the 40 children treated for acute lymphoblastic leukemia (ALL), all of whom had received prior therapy with oral 6MP, 1 complete and 1 partial response were achieved. No response was observed in 17 patients with refractory acute nonlymphocytic leukemia (ANLL). Reversible hepatotoxicity, the primary dose-limiting toxicity, was observed in approximately 50% of cases. Mucositis was encountered infrequently and was usually not severe. 6MP given on the present continuous intravenous infusion schedule overcomes the limited and variable bioavailability of oral 6MP but shows limited activity as induction agent in children with recurrent ALL.

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.

A phase II trial of continuous-infusion 6-mercaptopurine for childhood solid tumors.

A phase II pediatric trial of a continuous intravenous infusion of 6-mercaptopurine (6-MP) in patients with refractory solid tumors or lymphoma was performed. The dosing schedule of 50 mg/m2 per hour for 48 h was chosen to produce optimal cytotoxic concentrations of 6-MP. There were no complete or partial responses in the 40 patients entered in the trial. Accrual was sufficient for the conclusion to be drawn that there was greater than 95% probability that the true response rate was no greater than 22% and 26% in osteosarcoma and Ewing's sarcoma, respectively. Dose-limiting toxicity was observed in one-third of the patients and included reversible hepatotoxicity, myelosuppression, and mucositis. The excellent penetration of drug into the cerebrospinal fluid (CSF) suggests that future trials of this intravenous dosing schedule should be conducted on tumors of the CNS.

A phase II trial of intraperitoneal cisplatin and etoposide for primary treatment of ovarian epithelial cancer.

We conducted a phase II trial of intraperitoneal (IP) cisplatin (DDP) and etoposide (VP-16) in stage III and IV newly diagnosed ovarian carcinoma patients with residual disease of any size. Twenty-three patients were entered, 19 had stage III and four stage IV disease. DDP 200 mg/m2 and VP-16 350 mg/m2 were given in 2 L saline IP via a Port-A-Cath (Pharmacia-Deltec, St Paul, MN). Sodium thiosulfate 4 g/m2 was given intravenously (IV) just before the start of IP instillation, and continued as a constant IV infusion of 2 g/m2/hr IV for a total of 6 hours. Treatment was given once every 4 weeks; six cycles of therapy were planned. Thirteen patients (56%) were in complete clinical remission at the end of treatment (normal physical exam, computed tomographic [CT] scan, CA-125, and peritoneal cytology). Seven of these 13 underwent a second-look laparotomy: three (13%) were in pathologic complete remission and four (17%) had microscopic disease only. Projected survival is 68% at 27 months, with 10 patients being alive and continuously free of disease. There was a very rapid fall in mean CA-125 to within normal limits at the end of the second course of treatment. The major toxicity was myelosuppression with median nadir WBC, granulocyte, and platelet counts of 2,600, 896, and 205,000/microL, respectively. There was no cumulative renal damage, anemia, hypomagnesemia, or chemical peritonitis. Neurotoxicity was similar to that observed with IV dosing. We conclude that therapy with the IP DDP/VP-16/IV thiosulfate regimen, in which all cytotoxic drugs are given only by the IP route, produces less anemia and renal damage than standard IV DDP-containing regimens, and that survival with this regimen appears to be at least as good as that produced by IV programs.

Extremely prolonged continuous intraperitoneal infusion of cytosine arabinoside.

Intraperitoneal administration of ara-C produces a peritoneal/plasma concentration ratio of 330-1,000: In principle, optimal tumor-cell kill should be obtained when high ara-C concentrations ar maintained in the environment of the tumor for very long periods of time. A phase 1 study was undertaken to determine the maximum tolerated dose of ara-C that could be given as a continuous i.p. infusion for 3 weeks. A total of 14 patients with refractory malignancies were given 28 courses in the outpatient setting. Ara-C infusions were given using a portable programmable pump (Pancreatec Provider Model 2000). No significant side effects were observed in patients receiving 30 mg/m2 per day (five courses) or 40 mg/m2 per day x 21 days (seven courses). However, at a dose of 60 mg/m2 per day, although 10/16 courses were tolerated for at least 1 week, only 3/16 attempted courses could be continued for the full 3 weeks. The dose-limiting toxicity was chemical peritonitis, which occurred during 7/16 courses at this dose level and required termination of therapy in 4 courses. Myelosuppression was also observed at this dose. There was a large variation in the ara-C and ara-U peritoneal concentrations both within and between patients. The mean peritoneal ara-C concentration increased nonlinearly with ara-C dose whereas the mean ara-U concentration decreased. This study establishes the feasibility and safety of giving a cell-cycle-specific drug intraperitoneally over an extremely prolonged period. For subsequent studies a dose of 40 mg/m2 per day for 21 days is recommended.

Selective intraperitoneal biochemical modulation of methotrexate by dipyridamole.

Dipyridamole increases the toxicity of methotrexate in a concentration-dependent manner. We hypothesized that concurrent intraperitoneal administration of both drugs would result in high peritoneal concentrations with much lower plasma concentrations, permitting a selective increase in the activity of methotrexate against intraperitoneal tumors without enhancing systemic toxicity. Initially, 2.16 mg/m2/d methotrexate and 12 mg/m2/d dipyridamole were delivered together as a constant intraperitoneal infusion for 48 hours. With escalation of chemotherapy, eventually 4.32 mg/m2/d methotrexate was administered for 168 hours. Forty-seven courses were administered to 18 patients. The mean peritoneal to plasma concentration ratios of methotrexate and non-protein bound dipyridamole were 71.6 +/- 34.8 and over 2,300, respectively. Chemical peritonitis was the dose-limiting toxicity. Three patients had some evidence of a response (two with decreasing tumor markers, and the third with a reduction in ascites). We conclude that the drug concentrations are in an appropriate range for selective intraperitoneal biochemical modulation of methotrexate, and that it is feasible to expose tumors confined to the peritoneal cavity to these drugs for long periods of time.

Phase I/pharmacokinetic study of thioguanine administered as a 48-hour continuous intraperitoneal infusion.

Thioguanine (TG) is an antimetabolite with established antileukemic activity. The most pharmacologically rational manner of TG administration is continuous infusion. Intraperitoneal (IP) delivery of TG provides the opportunity to definitively test the concept of high-dose, long-term antimetabolite administration. The high systemic clearance and in vitro activity of TG against ovarian carcinoma suggested that it would be an excellent candidate for IP administration as a prolonged infusion. TG was administered as a 48-hour continuous IP infusion in this phase I/pharmacokinetic study. TG infusions were administered using a portable, programmable pump (Pancretec Provider Model 2000; Pancretec, Inc, San Diego). Twenty-five patients were treated. At a dose of 900 mg/m2/48 h, TG produced unacceptably severe myelosuppression. The dose-limiting toxicity was granulo-cytopenia. Other toxicities were mild: emesis, alopecia, skin rashes, and photosensitivity reactions. IP TG did not produce chemical peritonitis, hepatotoxicity, or mucositis. The pharmacokinetics of IP TG were determined in 16 patients. TG levels were measured by reverse-phase high-performance liquid chromatography (HPLC). At steady state, the mean peritoneal to plasma TG ratio was 1,800 at the maximum tolerated dose (MTD). Steady-state TG levels in the peritoneal cavity and plasma were 2 mmol/L and 1.1 mumol/L, respectively, at a dose of 744 mg/m2. The elimination half-life of TG from the peritoneal cavity was one hour. TG exhibited linear pharmacokinetics over the dosage range investigated. Encouraging clinical activity was seen with IP TG. There was one partial response (PR) and four minor responses (MR). TG can be safely administered by the IP route. The recommended dose for phase II testing is 744 mg/m2/48 h. IP TG has a favorable pharmacokinetic advantage and has demonstrated encouraging clinical activity. Further studies of IP TG infusions are warranted.

Pharmacokinetics of intraperitoneally administered dipyridamole in cancer patients.

The pharmacokinetics of i.p. administered dipyridamole was studied in six patients to explore the feasibility of using this drug as a modulator of antimetabolite activity in extravascular spaces. Infusions of dipyridamole (50 mg/m2 in 2 liters of normal saline) into the peritoneal cavity resulted in peak drug concentrations 5 to 20 times higher in that cavity than in the plasma. The peritoneal decay data for dipyridamole fitted very well to a single compartment open pharmacokinetic model with one exponential term, while the plasma data are adequately described by a single compartment model with two exponentials (a short absorption phase). The mean peritoneal half-life for total extractable dipyridamole was 3.3 +/- 1.9 (SD) h, and the mean peritoneal clearance was 0.4 +/- 0.3 liters/h/m2. The mean plasma half-life of total dipyridamole in our patients was 2.2 +/- 1.2 h, and the mean clearance value was 5.7 +/- 4.7 liters/h/m2. The area under the concentration versus time curve was calculated to be 626 +/- 312 microM-h for the peritoneal cavity and 45 +/- 20 microM-h for the plasma. Using membrane ultrafiltration, we have measured the concentration of free (non-protein bound) dipyridamole in each patient. While the peritoneal clearance values of free and total drug are comparable, the plasma clearance of free dipyridamole was 47 +/- 39 liters/h/m2. This increased plasma clearance resulted in a plasma area under the concentration versus time curve of 8.3 +/- 5.1 microM-h, which suggests minimal systemic exposure. Our data show that instillation of dipyridamole into the peritoneal cavity resulted in much higher local drug exposure than systemic exposure, confirming the feasibility of using this drug to augment antimetabolite activity within the peritoneal cavity. Since dipyridamole is highly protein bound in the plasma but less so in the peritoneal cavity, these data imply that peritoneal exposure to active (free) dipyridamole is far greater than systemic exposure in our patients.

Long-term survival of advanced refractory ovarian carcinoma patients with small-volume disease treated with intraperitoneal chemotherapy.

Ninety ovarian carcinoma patients failing primary intravenous (IV) combination chemotherapy were treated with cisplatin-based combination intraperitoneal therapy. Sixty-five patients had residual disease greater than 2 cm at the start of intraperitoneal therapy. Their median survival was 8 months. Twenty-five patients had disease less than 2 cm; their median survival was greater than 49 months, and the survival curve has an apparent plateau at 69%, with no relapses having occurred after 32 months. The median survival for all 90 patients was 15 months. The median duration of follow-up for all patients was 37 months. These results confirm the critical role of tumor bulk in determining the effectiveness of intraperitoneal therapy, and suggest a role for intraperitoneal salvage treatment in patients with small-volume disease.

Pediatric phase I trial and pharmacokinetic study of trimetrexate.

Trimetrexate, a new nonclassical antifolate, was evaluated in a phase I trial in children with refractory cancer including nine with acute leukemia and 21 with solid tumors. The drug was administered as an i.v. bolus injection weekly for three doses, and courses were repeated every 28 days. The dose ranged from 35 to 145 mg/m2. Thirty patients who received a total of 33 courses were evaluable for toxicity, including 19 who were evaluable for hematological toxicity. The maximally tolerated dose for patients with a solid tumor and leukemia was 110 mg/m2. The dose-limiting toxicities were myelosuppression, mucositis and a pruritic, diffuse maculopapular rash. Other side effects observed included transient, mild elevations of serum transaminases, mild nausea and vomiting, and a local phlebitis at the site of injection at higher dose levels. A single patient with delayed drug clearance had evidence of renal toxicity with a transient increase in serum creatinine. The pharmacokinetics of trimetrexate were studied in 25 patients over the entire dose range. There was considerable interpatient variability in total drug clearance (range 9.2 to 215 ml/min/m2) and half-life (2.1 to 20 h). There was a suggestion of a correlation between plasma concentration at 24 h and the development of hematological toxicity at the highest dose level. Trimetrexate was cleared primarily by biotransformation with renal clearance accounting for only 10% of total clearance. Two metabolites of trimetrexate which inhibit the enzyme dihydrofolate reductase were identified in the urine. One of these appears to be a glucuronide conjugate.

The effect of methotrexate on the bioavailability of oral 6-mercaptopurine.

Fourteen children (aged 3 to 14 years) with average-risk acute lymphoblastic leukemia were studied after an oral dose of 6-mercaptopurine (6-MP) (75 mg/m2) administered alone and, on the next day, concurrently with oral methotrexate (20 mg/m2). When 6-MP was administered alone, both the peak plasma concentration (15 to 150 ng X ml-1) and the AUC (36 to 340 ng X ml-1 X hr) were highly variable. Concurrent methotrexate resulted in a 31% increase in the AUC (P less than 0.01) and a 26% increase in peak plasma levels (P less than 0.05) of 6-MP. The AUC of methotrexate correlated with the degree of increase in 6-MP plasma concentrations. These findings are consistent with previous in vitro studies demonstrating that methotrexate is an inhibitor of xanthine oxidase, the enzyme that catabolizes 6-MP to the inactive metabolite thiouric acid. Although the increases in 6-MP AUC and peak plasma concentrations resulting from concurrent methotrexate administration were statistically significant, this interaction is probably not clinically significant at standard low oral doses of methotrexate in light of the wide interpatient variability in these pharmacokinetic parameters of 6-MP.

Phase I/pharmacokinetic study of intraperitoneal cisplatin and etoposide.

We administered cisplatin and etoposide by peritoneal dialysis to 39 patients with i.p. malignancies in order to investigate the toxicity, pharmacokinetics, and clinical activity of this 2-drug combination. All patients received i.v. sodium thiosulfate concurrently with the i.p. chemotherapy. Myelosuppression, nausea, vomiting, and malaise were the primary toxicities encountered. The maximum tolerated dose of etoposide was 350 mg/m2, when administered with a fixed dose of cisplatin, 200 mg/m2. Although the total (free and protein-bound) etoposide exposure for the peritoneal cavity was only 1.5-fold greater than that for the plasma, the free (non-protein bound) etoposide peritoneal exposure was 65-fold greater than the plasma. Tumor regressions were noted in patients with ovarian and pancreatic carcinomas. This study is the first demonstration of the large pharmacokinetic advantage that exists for the i.p. administration of highly protein-bound drugs, and it also documents the clinical activity of i.p. cisplatin and etoposide.

A clinically useful ion-pairing high-performance liquid chromatographic assay for the monophosphate metabolites of thioguanine and mercaptopurine in human neoplastic cells.

A sensitive and rapid assay for the quantitation of thioinosine monophosphate and thioguanosine monophosphate, the major intracellular active metabolites of mercaptopurine and thioguanine, respectively, has been developed. Neoplastic cells are extracted with trichloracetic acid, and the neutralized acid extracts are analyzed by ion-pairing high-performance liquid chromatography with dual-channel uv-wavelength detection. This technique provides a lower limit of sensitivity of 30 pmol of thioinosine monophosphate and 10 pmol of thioguanosine monophosphate. The number of cells assayed per sample was 2 X 10(7). This assay makes it possible to detect and quantitate low levels of thioinosine monophosphate and thioguanosine monophosphate present in neoplastic cells obtained directly from patients receiving mercaptopurine or thioguanine chemotherapy.

Modulation of thiopurine cytotoxicity in the HL-60 cell line by physiological concentrations of hypoxanthine.

Thioguanine and mercaptopurine are clinically important agents in widespread use for the treatment of acute leukemia. In this study the effect of low, physiological concentrations of hypoxanthine on thiopurine cytotoxicity was examined in the HL-60 human acute promyelocytic leukemia cell line. Initially the effect of cell concentration on medium hypoxanthine levels was investigated. When 10(5) to 10(6) cells/ml were used, medium hypoxanthine concentrations fell to undetectable (less than 0.1 microM) levels by 24 h, due to cell utilization. However, when the cell density was reduced to 10(3) cells/ml, it was possible to maintain a medium hypoxanthine level as low as 0.5 microM for 24 h without significant hypoxanthine depletion. This allowed for the investigation of the extent to which physiological concentrations of hypoxanthine (1.0 to 10 microM) could modulate thiopurine cytotoxicity. HL-60 cells were incubated in medium containing from 1.0 to 100 microM hypoxanthine concentrations and varying levels of thioguanine or mercaptopurine for 24 h. Cells were then washed and cloned in soft agar. Physiological concentrations of hypoxanthine (1.0 to 10 microM) provided significant protection to HL-60 cells from the cytotoxic effects of both thioguanine and mercaptopurine. An increase in medium hypoxanthine level from 1.0 to 3.0 microM resulted in a 3-fold increase in the thiopurine concentration required to kill 50% of cells. There was a linear relationship between the thiopurine concentration required to reduce clonogenic survival by 50% and medium hypoxanthine level over the hypoxanthine concentrations studied. Although thioguanine was 200-fold more potent than mercaptopurine, and an analogue of guanine rather than hypoxanthine, there was a similar degree of modulation of the cytotoxicity of both agents by hypoxanthine. These results indicate that low, physiological hypoxanthine concentrations can significantly modulate thiopurine cytotoxicity and suggest that endogenous hypoxanthine pools may have an important effect on the clinical activity of thioguanine and mercaptopurine.

The pharmacology of orally administered chemotherapy. A reappraisal.

Rational treatment of pediatric malignancies requires a detailed knowledge of the clinical pharmacology of those antineoplastic agents used therapeutically. A number of different agents are administered by the oral route. Recently, the clinical pharmacology of 6-mercaptopurine (6-MP) and methotrexate (MTX), the two agents that are the mainstay of maintenance chemotherapy in acute lymphoblastic leukemia (ALL), were investigated. Studies of oral 6-MP indicate that, contrary to previous information, the bioavailability of this drug is relatively poor after oral administration, and that plasma 6-MP concentrations achieved after uniform oral dosing are highly variable. Similarly, study of the pharmacology of orally administered MTX indicates that there is little correlation between MTX dose and the peak serum level achieved. These findings suggest that some patients may not be exposed to adequate systemic concentrations of 6-MP and/or MTX after oral administration, and raise the possibility that the development of relapse in some patients with ALL may be the result of a pharmacologic failure of oral maintenance therapy. A comprehensive prospective study of the clinical pharmacology of MTX and 6-MP in patients with ALL undergoing maintenance chemotherapy is currently in progress.

Biochemical parameters of mercaptopurine activity in patients with acute lymphoblastic leukemia.

Mercaptopurine (MP) is a purine antimetabolite widely used for remission maintenance in the therapy of acute lymphoblastic leukemia. In order to study the biochemical parameters affecting MP activity, leukemic cells were obtained from ten patients with acute lymphoblastic leukemia at the time of diagnosis and from the same patients at the time of their initial marrow relapse. Hypoxanthine phosphoribosyltransferase (HPRT), the enzyme that converts MP to its active, nucleotide metabolite, thioinosine monophosphate; alkaline phosphatase, the primary catabolic enzyme of thioinosine monophosphate; and 5-phosphoribosyl-1-pyrophosphate (PRPP), the cellular ribose-phosphate donor essential for MP activation, were all measured within the patients' leukemic cells. There was marked interpatient variability in the three biochemical parameters studied with a greater than 10-fold range in alkaline phosphatase activity and an approximately 100-fold range in HPRT activity and PRPP levels. Four patients developed changes in biochemical parameters that influence MP activity at the time of relapse. In three of the four patients, alterations in more than one of these three biochemical parameters were noted. Three of four patients had a greater than 50% decrease in intracellular HPRT activity, four of four had a greater than 50% decrease in intracellular PRPP, and two of four had a greater than 9-fold increase in intracellular alkaline phosphatase activity at relapse. Two of four patients demonstrated changes in all three parameters at relapse in the directions that could have resulted in decreased MP sensitivity (i.e., decreased HPRT, decreased PRPP, and increased alkaline phosphatase). There was no correlation between pretreatment values of HPRT, PRPP, and alkaline phosphatase and remission duration. These results indicate that: (a) there is marked variation in HPRT, PRPP, and alkaline phosphatase in patients with acute lymphoblastic leukemia and b) following MP-containing maintenance chemotherapy, some patients develop biochemical changes that may result in decreased sensitivity to MP.

The effect of amitriptyline on the central nervous system penetration of methotrexate.

The reported ability of amitriptyline to enhance the penetration of diffusion limited substances across the blood brain barrier was investigated. The CSF:plasma ratio of methotrexate in primates was not significantly altered by amitriptyline pretreatment. Nor was methotrexate plasma clearance altered.