Population Pharmacokinetics of Selumetinib and Its Metabolite N-desmethyl-selumetinib in Adult Patients With Advanced Solid Tumors and Children With Low-Grade Gliomas

Selumetinib (AZD6244, ARRY‐142886), a mitogen activated protein kinases (MEK1 and 2) inhibitor, has been granted orphan drug designation for differentiated thyroid cancer. The primary aim of this analysis was to characterize the population pharmacokinetics of selumetinib and its active metabolite N‐desmethyl‐selumetinib in patients with cancer. Concentration–time data from adult and pediatric clinical trials were pooled to develop a population pharmacokinetic model using a sequential approach where selumetinib and N‐desmethyl‐selumetinib data were modeled separately. A sequential zero‐ and first‐order absorption with lag time with a two‐compartment model for selumetinib and a two‐compartment model for N‐desmethyl‐selumetinib best described the concentration–time data. Intrapatient variability in absorption was higher than interpatient variability. The apparent drug clearance (CL/F) from the central compartment was 13.5 L/hr (RSE 4.9%). Significant covariates for CL/F were age, alanine aminotransferase, and body surface area. This study confirms that flat dosing is appropriate in adults, whereas body‐surface area based dosing should be used in pediatric patients.

Translational Pharmacokinetic-Pharmacodynamic Modeling and Simulation: Optimizing 5-Fluorouracil Dosing in Children With Pediatric Ependymoma

We previously investigated novel therapies for pediatric ependymoma and found 5‐fluorouracil (5‐FU) i.v. bolus increased survival in a representative mouse model. However, without a quantitative framework to derive clinical dosing recommendations, we devised a translational pharmacokinetic‐pharmacodynamic (PK‐PD) modeling and simulation approach. Results from our preclinical PK‐PD model suggested tumor concentrations exceeded the 1‐hour target exposure (in vitro IC₉₀), leading to tumor growth delay and increased survival. Using an adult population PK model, we scaled our preclinical PK‐PD model to children. To select a 5‐FU dosage for our clinical trial in children with ependymoma, we simulated various 5‐FU dosages for tumor exposures and tumor growth inhibition, as well as considering tolerability to bolus 5‐FU administration. We developed a pediatric population PK model of bolus 5‐FU and simulated tumor exposures for our patients. Simulations for tumor concentrations indicated that all patients would be above the 1‐hour target exposure for antitumor effect.

Assessing vascular effects of adding bevacizumab to neoadjuvant chemotherapy in osteosarcoma using DCE-MRI

BACKGROUND

The purpose of this study was to assess the impact of bevacizumab alone and in combination with cytotoxic therapy on tumour vasculature in osteosarcoma (OS) using DCE-MRI.

METHODS

Six DCE-MRI and three (18)F-FDG PET examinations were scheduled in 42 subjects with newly diagnosed OS to monitor the response to antiangiogenic therapy alone and in combination with cytotoxic therapy before definitive surgery (week 10). Serial DCE-MRI parameters (K(trans), v(p), and v(e)) were examined for correlation with FDG-PET (SUV(max)) and association with drug exposure, and evaluated with clinical outcome.

RESULTS

K(trans) (P=0.041) and v(p) (P=0.001) significantly dropped from baseline at 24 h after the first dose of bevacizumab alone, but returned to baseline by 72 h. Greater exposure to bevacizumab was correlated with larger decreases in v(p) at day 5 (P=0.04) and week 10 (P=0.02). A lower K(trans) at week 10 was associated with greater percent necrosis (P=0.024) and longer event-free survival (P=0.034).

CONCLUSIONS

This is the first study to demonstrate significant changes of the plasma volume fraction and vascular leakage in OS with bevacizumab alone. The combination of demonstrated associations between drug exposure and imaging metrics, and imaging metrics and patient survival during neoadjuvant therapy, provides a compelling rationale for larger studies using DCE-MRI to assess vascular effects of therapy in OS.

Deriving therapies for children with primary CNS tumors using pharmacokinetic modeling and simulation of cerebral microdialysis data

The treatment of children with primary central nervous system (CNS) tumors continues to be a challenge despite recent advances in technology and diagnostics. In this overview, we describe our approach for identifying and evaluating active anticancer drugs through a process that enables rational translation from the lab to the clinic. The preclinical approach we discuss uses tumor subgroup-specific models of pediatric CNS tumors, cerebral microdialysis sampling of tumor extracellular fluid (tECF), and pharmacokinetic modeling and simulation to overcome challenges that currently hinder researchers in this field. This approach involves performing extensive systemic (plasma) and target site (CNS tumor) pharmacokinetic studies. Pharmacokinetic modeling and simulation of the data derived from these studies are then used to inform future decisions regarding drug administration, including dosage and schedule. Here, we also present how our approach was used to examine two FDA approved drugs, simvastatin and pemetrexed, as candidates for new therapies for pediatric CNS tumors. We determined that due to unfavorable pharmacokinetic characteristics and insufficient concentrations in tumor tissue in a mouse model of ependymoma, simvastatin would not be efficacious in further preclinical trials. In contrast to simvastatin, pemetrexed was advanced to preclinical efficacy studies after our studies determined that plasma exposures were similar to those in humans treated at similar tolerable dosages and adequate unbound concentrations were found in tumor tissue of medulloblastoma-bearing mice. Generally speaking, the high clinical failure rates for CNS drug candidates can be partially explained by the fact that therapies are often moved into clinical trials without extensive and rational preclinical studies to optimize the transition. Our approach addresses this limitation by using pharmacokinetic and pharmacodynamic modeling of data generated from appropriate in vivo models to support the rational testing and usage of innovative therapies in children with CNS tumors.

A phase I/II study of CY and topotecan in patients with high-risk malignancies undergoing autologous hematopoietic cell transplantation: the St Jude long-term follow-up

Fifty-eight consecutive children with high-risk malignancies were treated with CY, and targeted topotecan followed by autologous hematopoietic cell transplantation (AHCT) in a phase I/II Institutional Review Board-approved study. Twelve participants enrolled in phase I; 5 received dose level 1 of topotecan 3 mg/m(2) per day, with subsequent doses targeted to total systemic exposure of 100±20 ng h/mL and CY 750 mg/m(2) per day. Seven participants received dose level 2. CY dose escalation to 1 g/m(2) per day was considered excessively toxic; one died from irreversible veno-occlusive disease and two experienced reversible hepatotoxicity. These adverse events halted further dose escalation. A total of 46 participants were enrolled in phase II; results are on the 51 participants who received therapy at dose level 1, the maximum tolerated dose. Diagnoses included neuroblastoma (26), sarcoma (9), lymphoma (8), brain tumors (5), Wilms (2) and retinoblastoma (1). Twenty participants (39.3%) were in CR1 at enrollment; median age was 5.1 years. Most common non-hematological grade III-IV toxicity was gastrointestinal (n=37). Neutrophil and platelet engraftment occurred at a median of 15 and 24 days, respectively. Twenty-six (51%) participants remain alive at a median of 6.4 years after AHCT. CY 3.75 g/m(2), and targeted topotecan followed by AHCT are feasible and produce acceptable toxicity in children with high-risk malignancies.

A phase I pharmacokinetic trial of sonic hedgehog (SHH) antagonist GDC-0449 in pediatric patients with recurrent or refractory medulloblastoma: A Pediatric Brain Tumor Consortium study (PBTC 25)

CRA9501

Background:Aberrant signaling in SHH pathway is implicated in causing medulloblastoma in approximately 20% of children with this disease. GDC-0449 is an orally active agent that binds to the SMO receptor and prevents downstream signaling through GLI. Preclinical murine models predict efficacy of an SMO antagonist to treat tumors dependent on the SHH pathway. Adult studies have documented the efficacy of this compound against recurrent medulloblastoma and basal cell carcinoma. A phase I pharmacokinetic trial of GDC 0449 was conducted in children with recurrent or refractory medulloblastoma to select, based on safety and pharmacokinetics, one of two dosages to recommend for a pediatric phase II trial. We also used immunonistochemistry (IHC) and in situ hybridization (ISH) on paraffin-embedded tissue to determine which tumors belonged to the SHH subtype.

Methods: GDC 0449 was administered once daily for 28 days dose levels of (1) 85 mg/m2/dose and (2) 170 mg/m2/dose. A course was defined as 28 days in duration. PK analysis was performed during the first course and steady-state concentrations were obtained prior to each subsequent course (day 21). MRI scans of the knees were obtained at baseline and 3 mos to assess abnormalities in bone development.

Results: To date 11 eligible patients have been enrolled on the trial (10 males, median age 11.6 years (range 4.4–20.9). All patients were fully evaluable for toxicity. 1 DLT, grade 3 gamma-Glutamyl transpeptidase, occurred in a patient enrolled at 170 mg/m2/dose. There were no grade 4 toxicities. The median (range) steady-state day 21 concentration at 85 mg/m2 (n=5) is 10.15 μ M (9.10–18.99 μ M) and at 170 mg/m2 (n=2) is 14.50 μ M (14.43–14.57 μ M). The steady-state GDC-0449 clearance (n=7) is 0.86 (0.44 – 1.17 L/h/m2). At steady state (day 21), the ratio of GDC-0449 CSF to plasma is 1.3%, which is an estimate of the CSF penetration of GDC-0449.

Conclusions: GDC 0449 is well-tolerated in children with recurrent or refractory medulloblastoma. The phase I study estimating the recommended phase II dose of GDC 0449 is ongoing; final results including medulloblastoma subgroup data will be presented.

[Table: see text]

Irinotecan plus temozolomide in children with recurrent or refractory neuroblastoma: A phase II Children's Oncology Group study

10011

Background: Treatment of children with relapsed or refractory neuroblastoma (NB) remains a challenge. Responses to irinotecan (IRN) + temozolomide (TEM) were seen in NB xenograft-bearing mice, and objective responses were observed in patients with NB treated on a phase I study of this combination. Methods: A phase II study of IRN (10 mg/m2/dose IV daily × 5 days times; 2 weeks) + TEM (100 mg/m2/dose PO daily × 5 days) for children with relapsed or refractory NB was conducted. A one-stage design (endpoint: best overall response) required 5 or more responders out of the first 25 evaluable patients on each of two strata: 1) patients with disease measurable by CT or MRI; and 2) patients with disease detected only by bone marrow aspirate/biopsy and/or MIBG scan. Patients with stable disease or better after 3 cycles could receive an additional 3 cycles of study therapy. International Neuroblastoma Response Criteria were used for response assessment. Radiographic responses were centrally reviewed. Results: Fifty-five eligible and evaluable patients were enrolled, 28 on stratum 1 and 27 on stratum 2. Four responses were observed in the first 25 evaluable stratum 1 patients, and five responses were observed in the first 25 evaluable stratum 2 patients. Three patients had complete responses, but the overall objective response rate (CR+PR) was 16% (9/55). Eleven (stratum 1) and 13 (stratum 2) patients had stable disease. Less than 5% of patients experienced Grade 3 or 4 diarrhea. Although 18% of patients on stratum 1 and 35% of patients on stratum 2 experienced Grade 3 or 4 neutropenia during the first 3 cycles of therapy, <10% of all patients developed evidence of infection while neutropenic. Thrombocytopenia (Grade 3 or 4) was observed in only 7% of patients on stratum 1 and 12% on stratum 2. Conclusions: The combination of IRN+TEM was well tolerated in patients with recurrent or refractory NB. There were 9 objective responses, including 3 complete responses. The minimum desired response rate was attained within stratum 2, but not stratum 1. IRN+TEM may be an appropriate backbone for further study in the relapse setting in combination with novel, targeted agents.

No significant financial relationships to disclose.

A phase I trial of vorinostat in children with refractory solid tumors: A Children's Oncology Group Study

9569

Background: Vorinostat, an orally administered histone deacetylase inhibitor, has potent antitumor activity against human cell lines in vitro (IC50 0.5 to 5 μM) and in xenograft models. A phase I trial of vorinostat was conducted in children with recurrent or refractory solid tumors to determine the maximum tolerated dose (MTD), dose limiting toxicity (DLT), pharmacokinetics (PK) of vorinostat, and to assess accumulation of histone acetylation in peripheral blood mononuclear cells (PBMCs). Methods: Vorinostat was administered once daily at dose levels of 180, 230, and 300 mg/m2/d. Courses were 28 days in duration, without interruption. PK analysis was performed during the 1st course. Vorinostat's ability to induce acetyl-histone (H3) accumulation in vivo was studied by western blot analysis. Results: 30 patients, 17 males, median age 15 years (range 4–21), were enrolled; 24 patients were fully evaluable for toxicity. At 180 mg/m2/d, 1/6 pts developed DLT (deep vein thrombosis) and at 230 mg/m2/d 1/6 pts developed DLT (hypokalemia). At 300 mg/m2/d, DLTs consisted of reversible hypokalemia (n=1), neutropenia (n=1) and thrombocytopenia (n=2), defining the MTD as 230 mg/m2/d. Other non-dose limiting grade 3 or 4 toxicities included elevated ALT/AST, hyperbilirubinemia, leucopenia, and lymphopenia. Western blot analysis of PBMC protein isolates found clear evidence of dose- dependent accumulation of acetylated H3 histones. 1 patient with a spindle cell sarcoma received 8 courses and 1 patient with a low-grade astrocytoma had an unconfirmed minor response. Conclusions: Vorinostat is well tolerated in children with recurrent or refractory solid tumors and inhibits histone deacetylase activity in PBMC. The recommended phase II dose for children with solid tumors is 230 mg/m2/d.

No significant financial relationships to disclose.

Phase I trial of VNP40101M in children with recurrent brain tumors—A Pediatric Brain Tumor Consortium (PBTC) study

2059

Background: VNP40101M, a novel DNA alkylating agent and a potent inhibitor of alkylguanine alkyl transferase (AGT) in pre- clinical studies, was evaluated in a phase I study in children with recurrent brain tumors. Methods: VNP40101M was given intravenously (i.v) daily for 5 days q 6 weeks up to 8 cycles. Using the continual reassessment method, dose escalation was performed independently in pts stratified based on intensity of prior therapy (stratum I-less-heavily pre-treated; stratum II- heavily pre-treated). Dose limiting toxicities (DLTs) and responses were assessed at the end of the first and 2nd cycles of treatment, respectively. Correlative studies included pharmacokinetics and measurement of AGT activity in peripheral blood mononuclear cells (PBMC) before and after treatment. Results: 41 eligible pts (stratum I- 19, stratum II- 22; median age 9.3 yrs, range 0.9 to 21.5) were enrolled on this study. Dose levels (in mg/m2/day) evaluated in Stratum I were 45, 60, and 78 mg; In Stratum II 20, 30, 45, and 60 mg. DLT in evaluable pts was myelosuppression (grade IV neutropenia for > 7 days or any grade IV thrombocytopenia) and occurred in 4/16 pts in stratum I [45 mg (n=1/12), 60 mg (n=1/2), 78 mg (n= 2/2)] and 3/19 pts in stratum II [45 mg (n= 3/4), 60 mg (n=0/1), 30 mg (n= 0/12), and 20 mg (n= 0/2)] respectively. Other significant toxicities post first course included renal failure (n=2), pulmonary (n=2), and fatal infection (n=1). PK studies showed median (range) terminal half-life of 62 mins (7.3 to 522 min). The MTDs in stratum I and II were 45 mg/m2/day and 30 mg/m2/day daily for 5 days q 6 weeks, respectively. Objective responses were observed in one pt each with brain stem glioma and medulloblastoma respectively. PBMC AGT levels did not decrease following VNP40101M treatment. Conclusions: The recommended pediatric phase II dose of VNP40101M given i.v daily for 5 days q 6 weeks is 45 mg/m2/day in less-heavily treated and 30 mg/m2/day in heavily treated pts.

[Table: see text]

A phase I study of oxaliplatin (OXA) and irinotecan (IRN) in pediatric patients with refractory solid tumors: A Children's Oncology Group study

9546

Background: Platinum analogues in combination with topoisomerase 1 inhibitors have been shown in in vitro studies to have synergistic anti-tumor activity. This study estimated the maximum tolerated dose (MTD) of OXA in combination with a protracted schedule of IRN in children with refractory solid tumors. Methods: OXA was administered over 2 hrs on days 1 and 8 in combination with IRN iv over 1 hr on days 1–5 and 8–12 of a 21-day cycle. An oral cephalosporin was administered daily to ameliorate IRN-associated diarrhea. Pharmacokinetic studies of OXA and UGT1A1 genotyping were performed during course 1 in consenting patients. Results: 13 patients (median age 16 yrs, 4 M) were enrolled. Dose-limiting diarrhea (n=3), serum lipase elevation (n=3), serum amylase elevation (n=2), colitis (n=1), abdominal pain (n=1) and headache (n=1) occurred at the 1st dose level (60 mg/m2/dose OXA; 20 mg/m2/dose of IRN) in the first 3 patients. Only 1/7 patients treated with reduced doses of both agents (40 mg/m2/dose OXA; 15 mg/m2/dose IRN) experienced DLT, diarrhea. When the OXA dose (60 mg/m2) was increased with the reduced IRN dose (15 mg/m2) 2/3 patients had DLT (1 diarrhea, 1 hypokalemia). Myelosuppression was minimal at all dose levels. One patient with alveolar rhabdomyosarcoma previously treated with irinotecan (dose level 2: 40 mg/m2/dose OXA; 15 mg/m2/dose IRN) had an unconfirmed complete response of her breast metastases and one patient with refractory neuroblastoma had disease stabilization through 6 courses of therapy. The frequency of 6/6, 6/7, and 7/7 UGT1A1 promoter genotypes were 5/10, 4/10, and 1/10, respectively. Conclusions: The MTD using this schedule with oral cephalosporin support was oxaliplatin 40 mg/m2/dose with irinotecan 15 mg/m2/dose. There was some evidence of benefit but significant toxicity, both expected (diarrhea) and unexpected (elevation in pancreatic enzymes), was also observed.

[Table: see text]

Phase I study of oral irinotecan, temozolomide, and vincristine for children with refractory solid tumors: A Children's Oncology Group study

9563

Background: Both temozolomide (TEM) and vincristine (VCR) can increase the preclinical activity of low-dose protracted irinotecan (IRN) against pediatric solid tumors. Because these drugs have different dose-limiting toxicities (DLTs) and mechanisms of action, we combined these three agents and sought to determine the maximum tolerated dose (MTD) of orally administered IRN when given with fixed- dose TEM and VCR in children with relapsed or refractory solid tumors, using the antibiotic cefixime to reduce IRN-associated diarrhea. Methods: We studied two dose levels of oral IRN (35 or 50 mg/m2) administered on days 1–5 and 8–12, combined with oral TEM 100 mg/m2 on days 1–5 and intravenous VCR 1.5 mg/m2 on days 1 and 8. Courses were repeated every 21 days. Oral cefixime was started 5 days before chemotherapy and continued daily. Results: Of 21 patients enrolled, 17 (ages 3–21, median 14 yrs) were evaluable for toxicity and have to date received 46 courses (range 1–8, median 2). At the IRN dose of 50 mg/m2/d, 4 of 12 patients had DLT, including elevated ALT/AST (1), abdominal pain (1), hypokalemia (1), anorexia (1), thrombocytopenia (1), and fatal liver failure in a patient with metastatic disease in the liver and porta hepatis (1). In contrast, none of 5 patients treated at the dose of 35 mg/m2/d experienced first-course DLT, defining this dose as the MTD. UGT1A1 genotype did not correlate with DLT in this small trial. The median SN-38 lactone area under the curve (0–6h) at the IRN dose of 50 mg/m2/day was 13.5 ng/ml*h (range 3.8 to 30.9); pharmacokinetic analysis of patients treated at 35 mg/m2/day is ongoing. Six patients with the following tumors received more than 2 courses: neuroblastoma, ependymoma, hepatoblastoma, fibrillary astrocytoma, osteosarcoma, and Ewing sarcoma. Central review of response data is underway. Three patients continue on therapy at the MTD. Conclusions: Oral administration of IRN together with TEM and VCR was feasible and well tolerated at the MTD of 35 mg/m2 given dx5x2. Further study using a shorter 5-day course of oral IRN is planned.

No significant financial relationships to disclose.

Phase I study of erlotinib administered concurrently with and after irradiation (RT) in the treatment of children, adolescents, and young adults with newly diagnosed intracerebral high-grade glioma

9553

Background: High-grade gliomas are uncommon neoplasms in childhood that portend a poor prognosis. Because of the promising activity of erlotinib in adults with high-grade glioma, we conducted this Phase I study to determine the maximum tolerated dose and dose limiting toxicity (DLT) of erlotinib administered concurrently with and after RT. Methods: Patients between 3 and 25 years of age with newly diagnosed high-grade glioma received erlotinib continuously once daily during and after RT for a maximum of 52 weeks. Pharmacokinetic studies of erlotinib and its metabolite OSI-420, and genotyping were performed during course 1 in consenting patients. Use of enzyme-inducing anticonvulsants was an exclusion criterion. Dose escalation followed a typical Phase I design (dosage levels of 70, 90, and 120 mg/m2 per day). The DLT-evaluation period comprised the first 8 weeks of erlotinib. Results: Seventeen patients (median age 10.4 yrs; 10 males) were enrolled. Diagnoses consisted of glioblastoma (n=9), anaplastic astrocytoma (n=4), and other high-grade gliomas (n=4). Two of seven patients experienced reversible grade 3 hypokalemia / hypophosphatemia at the 70 mg/m2 level. Once electrolyte abnormalities were excluded as DLT, only one of seven patients at the 120 mg/m2 level has experienced grade 3 diarrhea so far. Pharmacokinetic studies were obtained in 14/17 patients. At the 70 mg/m2 dosage level, the median (range) erlotinib and OSI-420 Cmax and Tmax were 1,405 ng/ml (937–2,180) and 4.1 hr (2.2–8.2) and 158.5 ng/ml (45–203) and 4.1 hr (2.2–7.9), respectively. Three patients have received erlotinib for more than 1 year with disease stabilization. Six patients have already experienced disease progression. Conclusions: Erlotinib administered concurrently with RT on this schedule has been well tolerated. Preliminary pharmacokinetic results are comparable to those observed in adults. Rather than continue to escalate erlotinib dosages, we plan to complete this study and open a phase II study of erlotinib and RT for this same patient population.

No significant financial relationships to disclose.

Phase I study of oral irinotecan and temozolomide in children with relapsed high-risk neuroblastoma: A New Approach to Neuroblastoma Therapy (NANT) Consortium study

9567

Background: Irinotecan (IRN) and temozolomide (TEM) have single-agent activity and schedule-dependent synergy against neuroblastoma. Because intravenous IRN is costly and inconvenient, especially with protracted scheduling common in pediatric trials, we sought to determine the maximum tolerated dose (MTD) of oral IRN combined with TEM in children with recurrent/resistant high-risk neuroblastoma, using the antibiotic cefixime to reduce IRN-associated diarrhea. Methods: Patients received oral TEM on days 1–5 and oral IRN on days 1–5 and 8–12, with courses repeated every 21 days. Oral cefixime 8 mg/kg (max 400 mg/day) was started on day -5 and continued daily. Results: Fifteen patients (median age 7 years, range 2–22) with a median of 3.5 previous treatment regimens were evaluable for toxicity and have to date received 71 courses (median 2, range 1–19+). Neutropenia and thrombocytopenia were dose-limiting in the first 6 patients, and TEM was reduced from 100 to 75 mg/m2/day for all subsequent patients. IRN was then escalated from 30 to 60 mg/m2/day. First-course grade 3 diarrhea was dose-limiting in 1 of 6 patients treated at the IRN MTD of 60 mg/m2/day. Other toxicities were mild and reversible. No grade 4 therapy-related toxicity occurred in 27 courses administered at the MTD. The median SN-38 lactone AUC at this dose was 72 ng*hr/ml, similar to that reported with protracted intravenous IRN at the single-agent MTD. Of 14 patients evaluable for response, one with measurable nodal disease had a very good partial response through 6 courses. Six additional patients had stable disease for a median of 7.5 courses (range 6–19+). Two patients remain on study after 10 and 19 courses. Conclusions: This combination was well tolerated in heavily-pretreated children with resistant neuroblastoma, and 7 (50%) of 14 evaluable patients had response/stable disease for 6 or more courses in this Phase I trial. This all-oral regimen was feasible and resulted in favorable SN-38-lactone exposures. The dose recommended for further study in this patient population is TEM 75 mg/m2/day plus IRN 60 mg/m2/day when given with cefixime.

No significant financial relationships to disclose.

UGT1A1 promoter genotype correlates with pharmacokinetics but not toxicity in patients receiving protracted irinotecan (IRN)

3078

Background: Recent USFDA recommendations include a dosage adjustment for patients who are homozygous for the UGT1A1*28 allele (i.e., 7 TA repeats in the promoter) due to an increase in neutropenia when those patients receive IRN. However, this recommendation was based upon data from adults treated with high IRN dosage (e.g., 350 mg/m2). This study evaluates the relationship between UGT1A1 promoter genotype and phenotype (i.e., SN-38 glucuronidation and IRN toxicity) in patients treated with low-dose, protracted IRN. Methods: 31 children treated on 2 institutional protocols received low dosage (20 to 60 mg/m2) i.v. IRN daily for 5 days of 2 consecutive weeks. PK sampling and UGT1A1 genotyping were performed during cycle 1. Patients were designated as 6/6, 6/7, or 7/7 depending on the number of TA repeats in the UGT1A1 promoter region. All patients were evaluable for gastrointestinal and hematological toxicity, primarily grades 3 and 4 neutropenia and diarrhea. Results: The frequencies of 6/6, 6/7, and 7/7 genotypes were 9/31 (29%), 15/31 (48%), and 7/31 (23%), respectively. Patients with 7/7 genotype had a statistically greater baseline bilirubin than patients with 6/6 or 6/7 genotype (p<0.03), but the difference was not considered clinically significant. In females, the SN-38:IRN AUC ratio was greater in patients with 7/7 vs. 6/6 or 6/7 genotype (0.15 vs. 0.05 vs. 0.09;p<0.005). Similarly the SN-38G:SN-38 ratio was less in females with 7/7 vs. 6/6 or 6/7 genotype (1.5 vs. 4.1 vs. 3.5;p<0.03). Patients with 7/7 genotype did not have a greater incidence of diarrhea (0/7) or neutropenia (0/7) than patients with 6/6 (3/9 with diarrhea, 2/9 with neutropenia) or 6/7 (3/15 with diarrhea, 1/15 with neutropenia) genotype. Conclusions: Although female patients with a 7/7 genotype did have altered SN-38 disposition, toxicity was not increased in patients with the 7/7 genotype treated with a low dose protracted schedule of irinotecan. Therefore, no dosage adjustment for genotype is indicated with this IRN dosing schedule.

No significant financial relationships to disclose.

A topotecan-containing induction regimen for treatment of high risk neuroblastoma

9013

Background: We assessed the toxicity and feasibility of adding dose-intensive topotecan and cyclophosphamide to a multi-agent chemotherapy induction regimen for treatment of newly diagnosed high-risk neuroblastoma. Methods: Patients received 2 cycles of topotecan (starting dose 1.2 mg/m2/day for 5 days) and cyclophosphamide (400 mg/m2/day for 5 days) (T/C) followed by an additional 4 cycles of chemotherapy; cisplatin, etoposide alternating with vincristine, doxorubicin, cyclophosphamide. Pharmacokinetically guided topotecan dosing (target systemic exposure of AUC 50 - 70 ng/ml*hr determined by single day topotecan lactone levels) was performed. Chemotherapy cycles were scheduled every 21 days, PBSC harvest occurred after T/C cycles and surgical resection of residual primary tumor after cycle 5. Results: Thirty-one patients, 3 with INSS Stage 3 and 28 with Stage 4, were enrolled between April 2004 and November 2005. Median age at diagnosis was 2.5 years (range 0.9 - 9.35 years). Ten of 25 patients had tumor cell MYCN amplification and 21 of 22 tumors were classified as unfavorable Shimada histology by central review. Targeted topotecan systemic exposure was achieved in 87% (27/31) of patients during T/C cycle 1 and in 85% (23/27) of patients during T/C cycle 2. PBSC collections occurred as intended in 95% of patients (21/22 patients), median harvest 30.8 × 106 CD34+cells cell/kg (range 2.24 - 542). No dose limiting toxicities occurred. All patients experienced Grade 3 or 4 hematopoietic toxicity. Febrile neutropenia occurred in 79% (19/24) of patients during T/C cycles and 78% (18/23) of patients during subsequent cycles of induction therapy. Documented infection occurred in 12.5% (3/24) patients during T/C cycles and 26% (6/23) during subsequent induction cycles. Dose intensity of all chemotherapy agents was maintained in 95.8% (23/24) of patients. Conclusions: This pilot induction regimen was well tolerated with expected and reversible toxicities. Dose intensity of standard induction chemotherapy agents was not limited by the addition of dose-intensive topotecan. These data support investigation of efficacy in a Phase III clinical trial for newly diagnosed high-risk neuroblastoma.

[Table: see text]

Topoisomerase I interactive agents

Elucidation of the exact crystal structure of topoisomerase I will be essential to the rationale development of topoisomerase I interactive agents. Although the initial topoisomerase I interactive agents were camptothecin derivatives, future drugs may be designed to take advantage of the knowledge of the mechanism of interaction to increase the therapeutic index. However, preclinical studies designed to determine the precise mechanism by which the topoisomerase I interactive agents lead to cell death will be essential. Future clinical trials must rationally utilize the results of preclinical studies in the design of combination regimens, both with other cytotoxics and with the newer cytostatics. Moreover, the optimum schedule of administration for irinotecan and topotecan are not known, although results of preclinical studies clearly point to protracted dosing of these S-phase-specific agents. Future clinical trials should evaluate these schedules in an effort to optimize the currently available agents, prior to introducing new analogs, which may not provide any therapeutic benefit over the current agents properly dosed. Finally, numerous groups are trying to better understand the mechanism(s) of the dose-limiting toxicities observed with the currently available topoisomerase I interactive agents (e.g., glucuronidation for irinotecan diarrhea). The results of these studies may also enable the maximal dosing of the currently available agents. Even though the first priority must be to determine the therapeutic potential of the currently available agents, it is reassuring to know that many topoisomerase I interactive agents are currently under development. However, it is essential that these agents have the proper preclinical studies performed and that they be developed rationally.

Topotecan-filgrastim combination is an effective regimen for mobilizing peripheral blood stem cells

We compared the efficacy, toxicity, and cost of topotecan-filgrastim and filgrastim alone for mobilizing peripheral blood stem cells (PBSCs) in 24 consecutive pediatric patients with newly diagnosed medulloblastoma. PBSCs were mobilized with an upfront window of topotecan-filgrastim for 11 high-risk patients (residual tumor > or =1.5 cm2 after resection; metastases limited to neuraxis) and with filgrastim alone for 13 average-risk patients. All patients subsequently underwent craniospinal irradiation and four courses of high-dose chemotherapy with stem cell rescue. Target yields of CD34+ cells (> or =8 x 10(6)/kg) were obtained with only one apheresis procedure for each of the 11 patients treated with topotecan-filgrastim, but with a mean of 2.3 apheresis procedures for only six (46%) of the 13 patients treated with filgrastim alone (P = 0.0059). The median peak and median total yield of CD34+ cells were six-fold higher for the topotecan-filgrastim group (328/microl and 21.5 x 10(6)/kg, respectively) than for the filgrastim group (54/microl and 3.7 x 10(6)/kg, respectively). Mean times to neutrophil and platelet engraftment were similar. Myelosuppression was the only grade 4 toxicity associated with topotecan-filgrastim mobilization and lasted a median of 5 days. Compared with filgrastim mobilization, topotecan-filgrastim mobilization resulted in a mean cost saving of $3966 per patient. Topotecan-filgrastim is an efficacious, minimally toxic, and cost-saving combination for PBSC mobilization.

Pharmacodynamic model of topotecan-induced time course of neutropenia

Pharmacodynamic measures of neutropenia, such as absolute neutrophil count at nadir and neutrophil survival fraction, may not reflect the overall time course of neutropenia. We developed a pharmacokinetic-pharmacodynamic model to describe and quantify the time course of neutropenia after administration of topotecan to children and to compare this with nonhuman primates (NHPs) as a potential preclinical model of neutropenia. Topotecan was administered as a 30-min infusion daily for 5 days, repeated every 21 days. As part of a Phase I Pediatric Oncology Group study, topotecan was administered at 1.4 and 1.7 mg/m(2)/day without filgrastim (POG), and at 1.7, 2, and 2.4 mg/m(2)/day with filgrastim (POG+G). In NHPs, topotecan was administered at 5, 10, and 20 mg/m(2)/day without filgrastim. A pharmacokinetic-pharmacodynamic model was fit to profiles of topotecan lactone plasma concentrations and neutrophil survival fraction from cycle 1 and used to calculate topotecan lactone area under the plasma concentration-versus-time curve from 0 to 120 h (AUC(LAC)) and the area between the baseline and treatment-related neutrophil survival fraction (ABC) from 0 to 700 h. The mean +/- SD neutrophil survival fraction at nadir for the POG, POG+G, and NHP groups was 0.12 +/- 0.09, 0.11 +/- 0.17, and 0.09 +/- 0.08, respectively (P > 0.05). The mean +/- SD for the ratio of ABC to AUC(LAC) for the POG and NHP groups was 1.02 +/- 0.38 and 0.16 +/- 0.09, respectively (P < 0.05). The model estimate of ABC and the ratio of ABC to AUC(LAC) in children and NHPs may better reflect sensitivity to chemotherapy-induced neutropenia.

Effect of hemodialysis on topotecan disposition in a patient with severe renal dysfunction

The pharmacokinetics of topotecan have been extensively studied in patients with normal renal function and there is one study of patients with mild to moderate renal insufficiency. However, the effect of hemodialysis on topotecan disposition has not been reported. The objective of this study was to characterize the disposition of topotecan in a patient with severe renal insufficiency receiving hemodialysis. Topotecan lactone disposition was characterized in a patient on and off hemodialysis. The topotecan lactone clearance determined after administration of topotecan alone and with hemodialysis was 5.3 l/h per m(2) vs 20.1 l/h per m2 respectively. At 30 min after the completion of hemodialysis, the topotecan plasma concentration obtained was greater than that measured at the end of hemodialysis (i.e. 8.0 ng/ml vs 4.9 ng/ml), suggesting a rebound effect. The topotecan terminal half-life off dialysis was 13.6 h, compared with an apparent half-life determined during hemodialysis of 3.0 h. These results demonstrate that topotecan plasma clearance while on hemodialysis increased approximately fourfold. Hemodialysis may be an effective systemic clearance process for topotecan and should be considered in selected clinical situations (e.g. inadvertent overdose, severe renal dysfunction).

Relation between 9-aminocamptothecin systemic exposure and tumor response in human solid tumor xenografts

9-Aminocamptothecin (9-AC) is a topoisomerase I inhibitor with activity against xenografts from childhood solid tumors; however, clinical trials with this compound have been disappointing, resulting in discontinuation of further development. The objectives of this study were to evaluate the antitumor activity of 9-AC in a panel of pediatric solid tumor xenografts and to relate the 9-AC lactone systemic exposure, defined as area under the concentration time curve (AUC), to the antitumor dose associated with tumor regression in the xenograft model. We evaluated protracted administration of i.v. and oral therapies (daily times 5) for 1, 2, or 3 weeks and for 1 or 3 cycles. The minimum effective dose of 9-AC causing objective regression of advanced tumors was determined for each schedule. 9-AC lactone plasma concentration-time profiles associated with the lowest dose achieving complete and partial responses for each xenograft were then determined for each regimen. Tumors were highly sensitive to 9-AC therapy, but the systemic exposure required for antitumor effect is in excess of that achievable in patients.

Antitumor activity of temozolomide combined with irinotecan is partly independent of O6-methylguanine-DNA methyltransferase and mismatch repair phenotypes in xenograft models

The activity of temozolomide combined with irinotecan (CPT-11) was evaluated against eight independent xenografts (four neuroblastomas, three rhabdomyosarcomas, and one glioblastoma). In all studies, temozolomide was administered p.o. daily for 5 consecutive days/cycle, found in preliminary studies to be the optimal schedule for administration. Irinotecan was administered i.v. for 5 days for 2 consecutive weeks/cycle. Treatment cycles were repeated every 21 days for a total of three cycles over 8 weeks. In combination, temozolomide and CPT-11 induced complete responses in four neuroblastomas, two rhabdomyosarcomas, and the glioblastoma line. The activity of the combination was significantly greater than the activity of either agent administered alone in four tumor lines. Of interest, the interaction appeared independent of tumor MGMT or mismatch repair phenotype, suggesting that the mechanism of synergy may be independent of O6-methylation by temozolomide. Pharmacokinetic studies indicated no detectable interaction between these two agents. Further, coadministration of CPT-11 appeared to reduce the toxicity of temozolomide in tumor-bearing mice.

Clinical use of topoisomerase I inhibitors in anticancer treatment

The camptothecin analogs topotecan and irinotecan have shown to be among the most effective anticancer agents and, as S-phase specific agents, their antitumor effect is maximized when they are administered in protracted schedules. The documented activity as single agents in many adult and pediatric malignancies has been followed by their use in combination with other anticancer agents. These studies have shown promising results, and have placed topotecan and irinotecan in the first line treatment for some malignancies. However, studies to better determine the optimal schedules and sequence of combinations are needed.

Activation of CPT-11 in mice: identification and analysis of a highly effective plasma esterase

The camptothecin prodrug CPT-11 (irinotecan, 7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin) is converted by esterases to yield the potent topoisomerase I poison SN-38 (7-ethyl-10-hydroxycamptothecin). Recently, a mouse strain (Es1(e)) has been identified that demonstrates reduced plasma esterase activity, and we have monitored the ability of plasma from these mice to metabolize CPT-11. Total plasma esterase activity was reduced 3-fold in Esl(e)mice in comparison to control mice, and this resulted in a 200-fold reduction in SN-38 production after incubation with CPT-11 in vitro. In addition, pharmacokinetic studies of CPT-11 and SN-38 in these animals demonstrated approximately 5-fold less conversion to SN-38. However, extracts derived from tissues from Es1(e) animals revealed total esterase activities similar to those of control mice, and these extracts metabolized CPT-11 with equal efficiency. Northern analysis of RNA isolated from organs indicated that the liver was the primary source of Es-1 gene expression and that very low levels of Es-1 RNA were present in Es1(e) mice. These results suggest that the reduced levels of Es-1 esterase present in Es1(e) mice are due to down-regulation of gene transcription, and that this plasma esterase is responsible for the majority of CPT-11 metabolism in mice.

Biochemical correlates of temozolomide sensitivity in pediatric solid tumor xenograft models

The antitumor activity of the methylating agent temozolomide has been evaluated against a panel of 17 xenografts derived from pediatric solid tumors. Temozolomide was administered p.o. daily for five consecutive days at a dose level of 66 mg/kg. Courses of treatment were repeated every 21 days for three cycles. Tumor lines were classified as having high, intermediate, or low sensitivity, determined by complete responses, partial responses, or stable disease, respectively. Overall, temozolomide induced complete responses in five lines and partial responses in three additional tumor lines, giving objective regressions in 47% of xenograft lines. Analysis of temozolomide plasma systemic exposure indicated that this dose level was relevant to exposure achieved in patients. Tumors were analyzed by immunoblotting for levels of O6-methylguanine-DNA methyltransferase (MGMT) and two mismatch repair proteins, MLH-1 and MSH-2. Tumors classified as having high or intermediate sensitivity had low or undetectable MGMT and expressed detectable MLH-1 and MSH-2 proteins. Tumors classified as having low sensitivity had either (a) high MGMT or (b) low or undetectable MGMT but were deficient in MLH-1. The relationship between p53 and response to temozolomide was also examined. In vitro temozolomide did not induce p21cip1 in p53-competent NB-1643 neuroblastoma cells. Suppression of p53 function in NB1643 clones through stable expression of a trans dominant negative p53 (NB1643p53TDN) did not confer temozolomide resistance. Similarly, tumor sensitivity to temozolomide did not segregate with p53 genotype or p53 functional status. These results indicate that MGMT is the primary mechanism for temozolomide resistance, but in the absence of MGMT, proficient mismatch repair determines sensitivity to this agent.

Pharmacokinetics of irinotecan and its metabolites SN-38 and APC in children with recurrent solid tumors after protracted low-dose irinotecan

Irinotecan (IRN), a topoisomerase I interactive agent, has significant antitumor activity in early Phase I studies in children with recurrent solid tumors. However, the disposition of IRN and its metabolites, SN-38 and APC, in children has not been reported. Children with solid tumors refractory to conventional therapy received IRN by a 1-h i.v. infusion at either 20, 24, or 29 mg/m2 daily for 5 consecutive days for 2 weeks. Serial blood samples were collected after doses 1 and 10 of the first course. IRN, SN-38, and APC lactone concentrations were determined by an isocratic high-performance liquid chromatography assay. A linear four-compartment model was fit simultaneously to the IRN, SN-38, and APC plasma concentration versus time data. Systemic clearance rate for IRN was 58.7 +/- 18.8 liters/h/m2 (mean +/- SD). The mean +/- SD ng/ml x h single-day lactone SN-38 area under the concentration-time curve (AUC(0-->6) was 90.9 +/- 96.4, 103.7 +/- 62.4, and 95.3 +/- 63.9 at IRN doses of 20, 24, and 29 mg/m2, respectively. The relative extent of IRN conversion to SN-38 and metabolism to APC measured after dose 1 were 0.49 +/- 0.33 and 0.29 +/- 0.17 (mean +/- SD). No statistically significant intrapatient difference was noted for SN-38 area under the concentration-time curve. Large interpatient variability in IRN and metabolite disposition was observed. The relative extent of conversion and the SN-38 systemic exposure achieved with this protracted schedule of administration were much greater than reported in adults or children receiving larger intermittent doses.

Synergy of topotecan in combination with vincristine for treatment of pediatric solid tumor xenografts

Topotecan and vincristine were evaluated alone or in combination against 13 independent xenografts and 1 vincristine-resistant derivative, representing childhood neuroblastoma (n = 6), rhabdomyosarcoma (n = 5), or brain tumors (n = 3). Topotecan was given by i.v. bolus on a schedule found previously to be optimal. Drug was administered daily for 5 days on 2 consecutive weeks with cycles repeated every 21 days over a period of 8 weeks. Doses of topotecan ranged from 0.16 to 1.5 mg/kg to simulate clinically achievable topotecan lactone plasma systemic exposures. Vincristine was administered i.v. every 7 days at a fixed dose of 1 mg/kg. Given as a single agent, vincristine induced complete responses (CRs) in all mice bearing two rhabdomyosarcomas (Rh28 and Rh30) and some CRs in Rh12-bearing mice (57%) but relatively few CRs (<29%) in other tumors. As a single agent, topotecan induced CR in a low proportion of tumor lines. A dose-response model with a logit link function was used to investigate whether the combination of topotecan and vincristine resulted in greater than expected responses compared with the activity of the agents when administered alone. Only CR was used to evaluate tumor responses. The combination resulted in significantly greater than expected CRs than individual agents in nine tumor lines (four neuroblastoma, three brain tumors, and two rhabdomyosarcomas). Similar event-free (failure) distributions were shown in SJ-GBM2 glioblastoma xenografts, whether vincristine was administered on day 1 or day 5 of each topotecan course. To determine whether the increased antitumor activity with the combination was attributable to a change in drug disposition, extensive pharmacokinetic studies were performed. However, little or no interaction between these two agents was determined. Toxicity of the combination was marked by prolonged thrombocytopenia and decreased hemoglobin. However, approximately 75 and 80% of the maximum tolerated dose of each single agent, topotecan (1.5 mg/kg) or vincristine (1 mg/kg), could be given in combination, resulting in a combination toxicity index of approximately 1.5. These results show that the therapeutic effect of combining topotecan with vincristine was greater than additive in most tumor models of childhood solid tumors, and toxicity data suggest that this can be administered to mice with only moderate reduction in the dose levels for each agent.

Direct translation of a protracted irinotecan schedule from a xenograft model to a phase I trial in children

PURPOSE

In a preclinical model of neuroblastoma, administration of irinotecan daily 5 days per week for 2 consecutive weeks ([qd x 5] x 2) resulted in greater antitumor activity than did a single 5-day course with the same total dose. We evaluated this protracted schedule in children.

PATIENTS AND METHODS

Twenty-three children with refractory solid tumors were enrolled onto a phase I study. Cohorts received irinotecan by 1-hour intravenous infusion at 20, 24, or 29 mg/m(2) (qd x 5) x 2 every 21 days.

RESULTS

The 23 children (median age, 14.1 years; median prior regimens, two) received 84 courses. Predominant diagnoses were neuroblastoma (n = 5), osteosarcoma (n = 5), and rhabdomyosarcoma (n = 4). The dose-limiting toxicity was grade 3/4 diarrhea and/or abdominal cramps in six of 12 patients treated at 24 mg/m(2), despite aggressive use of loperamide. The maximum-tolerated dose (MTD) on this schedule was 20 mg/m(2)/d. Five patients had partial responses and 16 had disease stabilization. On day 1, the median systemic exposure to SN-38 (the active metabolite of irinotecan) at the MTD was 106 ng-h/mL (range, 41 to 421 ng-h/mL).

CONCLUSION

This protracted schedule is well tolerated in children. The absence of significant myelosuppression and encouraging clinical responses suggest compellingly that irinotecan be further evaluated in children using the (qd x 5) x 2 schedule, beginning at a dose of 20 mg/m(2). These results imply that data obtained from xenograft models can be effectively integrated into the design of clinical trials.

Interpatient variability in bioavailability of the intravenous formulation of topotecan given orally to children with recurrent solid tumors

PURPOSE

Evaluation of inter- and intrapatient variability of topotecan oral bioavailability and disposition was performed in children with malignant solid tumors.

PATIENTS AND METHODS

Topotecan i.v. formulation was given orally on schedules of daily for 21 consecutive days (d x 21) or daily for 5 days per week for 3 weeks [(d x 5)3], in both cases repeated every 28 days. Topotecan doses of 0.8 and 1.1 mg/m2 per day were evaluated on both schedules. Serial plasma samples were obtained after oral and i.v. administration of topotecan at the beginning and end of the first course of therapy. Topotecan lactone and total concentrations were measured by a high-performance liquid chromatography (HPLC) assay, and a one-or two-compartment model was fit to the plasma concentration-time data after oral or i.v. administration, respectively. Topotecan oral bioavailability (F) was calculated as the ratio of the AUC determined after oral treatment (AUCpo) divided by the AUC calculated after i.v. administration.

RESULTS

Pharmacokinetics studies were performed on 15 and 11 patients receiving 0.8 and 1.1 mg/m2 per day, respectively. After oral administration the topotecan lactone AUCpo and F determined for 0.8 and 1.1 mg/m2 per day were 13.6 +/- 5.8 and 25.1 +/- 12.9 ng ml(-1) h and 0.34 +/- 0.14 and 0.34 +/- 0.16, respectively. The within-patient variance for AUCpo and F was much smaller than the between-patient variance. The ratio of topotecan lactone to total concentration was consistently higher after oral as compared with i.v. administration.

CONCLUSIONS

Large interpatient variability was noted in topotecan pharmacokinetics, whereas intrapatient variability was relatively small. Further studies of oral topotecan are warranted to evaluate the tolerance of shorter courses and to define further the interpatient variability.

Topotecan for the treatment of recurrent or progressive central nervous system tumors - a pediatric oncology group phase II study

Topotecan was studied as a 72 h infusion given every 3 weeks. Treatment began at a dose of 1.0 mg/m2/day and was increased to 1.25 mg/m2/day after the first 6 patients tolerated this higher dose without excessive toxicities. Eighty-eight evaluable children were accrued in 6 strata. There were no complete nor partial responses. Twenty subjects had stable disease (astrocytoma 5/11, malignant glioma 5/13, medulloblastoma 0/12, brain stem tumor 4/19, ependymoma 5/17, and miscellaneous histologies 1/16). Two patients (astrocytoma, ependymoma) completed the maximum 18 topotecan courses. The remaining 68 children developed progressive disease within 2 months. Myelosuppression was the main toxicity. Grade 4 leukopenia, neutropenia, anemia, and thrombocytopenia were observed in 18, 32, 5, and 23 participants, respectively. It was concluded that topotecan as given according to this schedule showed insufficient activity to promote it to frontline protocol usage.