Biomedical subjects

Clinton F Stewart

Publications and source records attributed to Clinton F Stewart.

At least 19 recordsLinked to original sources

PubMed2007

Phase I study of gefitinib, irinotecan, 5-fluorouracil and leucovorin in patients with metastatic colorectal cancer.

PURPOSE: To determine the maximum tolerated doses (MTD), toxicities, efficacy, and pharmacokinetics (PK) of gefitinib combined with irinotecan, 5-fluorouracil (5-FU) and leucovorin (IFL) in patients with previously untreated advanced colorectal cancer. EXPERIMENTAL DESIGN: Starting doses were gefitinib 250 mg/day orally without interruption, irinotecan 100 mg/m(2) as a 90 min intravenous (i.v.) infusion, 5-FU 400 mg/m(2) bolus i.v. and leucovorin 20 mg/m(2) i.v. on days 1 and 8 of a 21-day cycle. Dose escalations involved increasing gefitinib to 500 mg then increasing irinotecan to 125 mg/m(2) and 5-FU to 500 mg/m(2). RESULTS: Twenty-four patients received therapy. The starting doses proved to be the MTD, as attempts to increase the dose of either gefitinib or the chemotherapeutic agents resulted in dose-limiting toxicities. Gastrointestinal effects and bone marrow suppression were the principal toxicities; however, only 1/17 (6%) patients treated with the MTD had severe (grades 3-4) diarrhea and severe neutropenia occurred in only two (12%) patients. Partial responses occurred in 10/17 patients receiving the MTD and another five had stable disease. Median progression-free and overall survivals were 12.2 and 26.6 months, respectively. In ten patients treated with the MTD, the steady-state PK of gefitinib was not affected by IFL nor did gefitinib appear to influence the PK of either irinotecan or 5-FU. CONCLUSIONS: Gefitinib can be safely combined with an intermittent weekly schedule of IFL. Evidence of promising activity should encourage further clinical evaluation of epidermal growth factor receptor tyrosine kinase inhibitors, such as gefitinib, combined with multiagent chemotherapy for metastatic colorectal cancer.

Adult↗

PubMed2007

Interferon beta-mediated vessel stabilization improves delivery and efficacy of systemically administered topotecan in a murine neuroblastoma model.

BACKGROUND: We have recently demonstrated that continuous delivery of interferon beta (IFN-beta) stabilizes solid tumor vasculature and improves tumor perfusion. In this study, we have further investigated the functional consequences of this effect by assessing delivery and efficacy of conventional chemotherapy against neuroblastoma xenografts when used in combination with IFN-beta. METHODS: Mice with established retroperitoneal tumors received adeno-associated virus vector encoding IFN-beta (AAV IFN-beta) or control vector. One week later, at 1 hour before sacrifice, a 1 mg/kg i.v. bolus of topotecan (TPT) was given. Intratumoral levels of TPT were measured by high-performance liquid chromatography and then standardized to plasma levels to determine tumor TPT penetration. Subsequent experiments evaluated the antitumor efficacy of topotecan alone or in combination with AAV IFN-beta. RESULTS: As observed in prior experiments, AAV IFN-beta resulted in a marked increase in tumor vessel association with stabilizing perivascular smooth muscle cells. These more "matured" vessels facilitated improved tumor TPT penetration (51.2% +/- 4.2%) compared with controls (30.8% +/- 4.7%, P = .004). In additional cohorts of mice, this resulted in an improved antitumor effect. Mice with established tumors (301.8 +/- 18.1 mm3) were treated with TPT (1 mg/kg daily for 5 days for 2 consecutive weeks) either alone or in combination with AAV IFN-beta (5 x 10(10) vector particles per mouse). Topotecan monotherapy resulted in a reduction in mean tumor volume of 12% (264.2 +/- 65.8 mm3, P = .66). However, when the same regimen was administered to mice receiving continuous IFN-beta therapy, a 61% (118.9 +/- 42.3 mm3, P = .004) reduction in mean tumor volume was achieved. CONCLUSION: Interferon beta-mediated vessel stabilization resulted in improved intratumoral delivery of systemically administered TPT, enhancing its antitumor efficacy. This approach of altering the tumor vasculature provides a strategy to help overcome solid tumor resistance to traditional cytotoxic agents.

Adenoviridae↗

PubMed2006

Topotecan central nervous system penetration is altered by a tyrosine kinase inhibitor.

A potential strategy to increase the efficacy of topotecan to treat central nervous system (CNS) malignancies is modulation of the activity of ATP-binding cassette (ABC) transporters at the blood-brain and blood-cerebrospinal fluid barriers to enhance topotecan CNS penetration. This study focused on topotecan penetration into the brain extracellular fluid (ECF) and ventricular cerebrospinal fluid (CSF) in a mouse model and the effect of modulation of ABC transporters at the blood-brain and blood-cerebrospinal fluid barriers by a tyrosine kinase inhibitor (gefitinib). After 4 and 8 mg/kg topotecan i.v., the brain ECF to plasma AUC ratio of unbound topotecan lactone was 0.21 +/- 0.04 and 0.61 +/- 0.16, respectively; the ventricular CSF to plasma AUC ratio was 1.18 +/- 0.10 and 1.30 +/- 0.13, respectively. To study the effect of gefitinib on topotecan CNS penetration, 200 mg/kg gefitinib was administered orally 1 hour before 4 mg/kg topotecan i.v. The brain ECF to plasma AUC ratio of unbound topotecan lactone increased by 1.6-fold to 0.35 +/- 0.04, which was significantly different from the ratio without gefitinib (P < 0.05). The ventricular CSF to plasma AUC ratio significantly decreased to 0.98 +/- 0.05 (P < 0.05). Breast cancer resistance protein 1 (Bcrp1), an efficient topotecan transporter, was detected at the apical aspect of the choroid plexus in FVB mice. In conclusion, topotecan brain ECF penetration was lower compared with ventricular CSF penetration. Gefitinib increased topotecan brain ECF penetration but decreased the ventricular CSF penetration. These results are consistent with the possibility that expression of Bcrp1 and P-glycoprotein at the apical side of the choroid plexus facilitates an influx transport mechanism across the blood-cerebrospinal fluid barrier, resulting in high topotecan CSF penetration.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Pharmacokinetics and pharmacodynamics of intravenous epoetin alfa in children with cancer.

BACKGROUND: Epoetin alfa (EPO, PROCRIT) pharmacokinetics and pharmacodynamics were evaluated in children with malignant solid tumors receiving chemotherapy. PROCEDURE: Children initially received IV EPO 600 IU/kg (max dose 40,000 IU) or placebo once weekly for 16 weeks. Dose was increased to 900 IU/kg (max dose 60,000 IU) for patients not achieving a 1 g/dl increase in hemoglobin by study week 3 or 4. Serial PK samples were collected for 24 hr after the first study dose, and after the 10th or 11th dose. Serum EPO concentrations were analyzed using an ELISA assay, and pharmacokinetics were evaluated using compartmental methods. RESULTS: Twelve children participated; six (median age 15.2 years; range 9.3-18.6 years) were randomized to receive EPO. All children required dosage increases to 900 IU/kg due to no response. The median (range) apparent EPO AUC0-24 and clearance (CL) were 67.1 IU/ml.hr (13.8-102.6) and 0.26 L/hr/m2 (0.19-1.08), respectively. After the 10th or 11th EPO dose in four of these six EPO patients, the median (range) apparent AUC0-24 and CL of EPO was 126.5 IU/ml.hr (107.3-161.1) and 0.21 L/hr/m2 (0.15-0.25), respectively. No significant correlations were observed between pharmacokinetic parameters and pharmacodynamic effects. CONCLUSIONS: EPO disposition in our patients was similar to other pediatric patient populations or adults receiving IV EPO. Interesting but insignificant trends were noted in pharmacodynamic effects.

Adolescent↗

PubMed2006

Phase I study of depsipeptide in pediatric patients with refractory solid tumors: a Children's Oncology Group report.

PURPOSE: To determine the maximum-tolerated dose (MTD), dose-limiting toxicities (DLT), pharmacokinetic profile, and pharmacodynamics of the histone deacetylase inhibitor, depsipeptide, in children with refractory or recurrent solid tumors. PATIENTS AND METHODS: Depsipeptide was administered as a 4-hour infusion weekly for 3 consecutive weeks every 28 days at dose levels of 10 mg/m2, 13 mg/m2, 17 mg/m2, and 22 mg/m2. Pharmacokinetics and histone acetylation studies were performed in the first course. The levels of H3 histone and acetyl-H3 histone were evaluated in peripheral blood mononuclear cells (PBMC) using immunofluorescence techniques. RESULTS: There were 24 patients, and 18 who were assessable were enrolled. DLTs included reversible, asymptomatic T-wave inversions, without any associated changes in troponin levels or evidence of ventricular dysfunction, in the inferior leads in two patients at 22 mg/m2 and in the lateral leads in one patient at 13 mg/m2 (n = 1), and transient asymptomatic sick sinus syndrome and hypocalcemia in one patient at 17 mg/m2. At the MTD (17 mg/m2), the median depsipeptide clearance was 6.8 L/h/m(2) with an area under the plasma depsipeptide concentration-time curve from 0 to infinity of 2,414 ng/mL/h, similar to adults. Accumulation of acetylated H3 histones was seen in all patients in a dose independent manner, with maximal accumulation at a median of 4 hours, (range, 0 hours to 20 hours) after the end of the infusion. No objective tumor responses were observed. CONCLUSION: Depsipeptide is well tolerated in children with recurrent or refractory solid tumors when administered weekly for 3 consecutive weeks every 28 days and inhibits histone deacetylase activity in PBMC in a dose-independent manner. The recommended phase II dose in children with solid tumors is 17 mg/m2.

Acetylation↗

PubMed2006

Gefitinib modulates the function of multiple ATP-binding cassette transporters in vivo.

The 4-anilinoquinazoline (4-AQ) derivative gefitinib (Iressa) is an oral epidermal growth factor receptor tyrosine kinase inhibitor. Oral administration of 4-AQ molecules, such as gefitinib, inhibits ATP-binding cassette (ABC) transporter-mediated drug efflux and strongly increases the apparent bioavailability of coadministered drug molecules that are transporter substrates. Based on in vitro studies investigating 4-AQ interactions with several transporters, these effects have primarily been attributed to the inhibition of breast cancer resistance protein (BCRP; ABCG2). Although 4-AQ shows in vitro inhibition of P-glycoprotein [multidrug resistance protein (MDR1); ABCB1], the in vivo effect on this and other transporters is not known. In our studies, pretreatment of Abcg2(-/-) and Mdr1(a/b)(-/-) mice with gefitinib increased oral absorption and decreased systemic clearance of topotecan, a model substrate, indicating that additional transporters were inhibited. These results were extended to human orthologues using engineered cell lines to show that gefitinib inhibited the efflux of BCRP and MDR1 substrates and restored vincristine sensitivity in MDR1-expressing cells. Although gefitinib inhibited BCRP more potently than MDR1 (10-fold), the inhibition of both transporters occurred at clinically relevant concentrations (e.g., 1-5 micromol/L). These studies illustrate the broad implications for the therapeutic combination of gefitinib or other 4-AQ molecules with agents that are BCRP and MDR1 substrates. 4-AQ molecules may offer a means to increase the low and variable oral drug absorption of transporter substrates while decreasing interpatient variability and reversing tumor drug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Using plasma topotecan pharmacokinetics to estimate topotecan exposure in cerebrospinal fluid of children with medulloblastoma.

The purpose of this study was to estimate ventricular cerebrospinal fluid (vCSF) topotecan lactone (TPT) exposures in pediatric medulloblastoma patients from plasma concentration-time data by using a pharmacokinetic (PK) model. We studied children with high-risk medulloblastoma who received pharmacokinetically guided TPT (target plasma area under the concentration-time curve [AUC], 120-160 ng/ml-h) and obtained serial vCSF samples to assess TPT exposure. Population pharmacokinetic parameters were determined by using linear mixed-effects modeling via the two-stage approach. We simulated TPT vCSF exposure duration at plasma TPT AUC values of 120 to 200 ng/ml-h and determined percentages of studies meeting or exceeding the vCSF exposure duration threshold (EDT) of 1 ng/ml for 8 h. We then used bootstrap methods to estimate variability in vCSF EDT. Eighteen PK studies were conducted in six patients (median age, 4.8 years). In these patients, seven of nine studies attaining target plasma TPT AUC achieved the vCSF EDT. Given a plasma TPT AUC of 120 ng/ml-h, the median percentage of results meeting or exceeding EDT was 78% (95% CI, 61%-100%). One patient (four studies) with tumor blockage of CSF flow, which can alter CSF pharmacokinetics, was removed, and the bootstrap analysis was repeated. In this subset, a median 93% (95% CI, 79%-100%) of studies achieved vCSF EDT. Increasing plasma TPT AUC values resulted in increased ability to achieve vCSF EDT. We demonstrated that a plasma PK model could estimate vCSF TPT concentrations. Further, our results indicate that the TPT vCSF EDT can be achieved in more than 80% of studies targeted to a plasma TPT AUC of 120 ng/ml-h.

Adolescent↗

PubMed2006

Cefixime allows greater dose escalation of oral irinotecan: a phase I study in pediatric patients with refractory solid tumors.

PURPOSE: Irinotecan is active against a variety of malignancies; however, severe diarrhea limits its usefulness. In our phase I study, the intravenous formulation of irinotecan was administered orally daily for 5 days for 2 consecutive weeks (repeated every 21 days) to children with refractory solid tumors. Our objectives were to determine the maximum-tolerated dose (MTD), dose-limiting toxicity, and pharmacokinetics of oral irinotecan and to evaluate whether coadministration of cefixime (8 mg/kg/d beginning 5 days before irinotecan and continuing throughout the course) ameliorates irinotecan-induced diarrhea. PATIENTS AND METHODS: In separate cohorts, irinotecan doses were escalated from 15 to 45 mg/m2/d without cefixime and then from 45 to 60 and 75 mg/m2/d with cefixime. RESULTS: Without cefixime, diarrhea was dose limiting at irinotecan 45 mg/m2/d. Myelotoxicity was not significant at any dose. The MTD was 40 mg/m2/d without cefixime but 60 mg/m2/d with cefixime. Systemic exposure to SN-38 at the MTD was significantly higher with cefixime than without cefixime (mean SN-38 area under the curve: 19.5 ng x h/mL; standard deviation [SD], 6.8 ng x h/mL v 10.4 ng x h/mL; SD, 4.3 ng x h/mL, respectively; P = .030). CONCLUSION: Cefixime administered with oral irinotecan is well tolerated in children and allows greater dose escalation of irinotecan. Because diarrhea is a major adverse effect of both intravenous and oral irinotecan, further evaluation of the use of cefixime to ameliorate this adverse effect is warranted.

Administration, Oral↗

PubMed2006

Evaluation of the antitumor efficacy, pharmacokinetics, and pharmacodynamics of the histone deacetylase inhibitor depsipeptide in childhood cancer models in vivo.

PURPOSE: Histone acetyltransferases and histone deacetylases (HDAC) control the acetylation state of histones and other proteins regulating transcription and protein function. Several structurally diverse HDAC inhibitors have been developed as cancer therapeutic agents and in vitro have been shown to cause differentiation, cell cycle arrest, or apoptosis. Here, we have evaluated depsipeptide, a natural tetrapeptide HDAC inhibitor, against a panel of pediatric solid tumor models in vivo and evaluated pharmacokinetic and pharmacodynamic variables with tumor sensitivity. EXPERIMENTAL DESIGN: Depsipeptide was administered at the maximum tolerated dose (4.4 mg/kg administered every 7 days x 3 i.v. repeated q21d for a total of two cycles) to scid mice bearing 39 independently derived childhood tumors (9 brain tumors, 11 kidney cancers, 9 rhabdomyosarcomas, 3 neuroblastomas, and 7 osteosarcomas). Pharmacokinetic variables were determined, as were changes in histone and p53 acetylation, induction of p53 and p53 genotype, and alterations in Akt phosphorylation. RESULTS: Of 39 tumors evaluated, three showed objective tumor regressions [two brain tumors (primitive neuroectodermal tumor and atypical teratoid malignant rhabdoid tumor) and one Wilms' tumor]. Depsipeptide inhibited growth of many tumor lines but achieved stable disease (<25% increase in volume during treatment cycle 1) in only two tumor models (anaplastic astrocytoma, two rhabdomyosarcomas, and a Wilms' tumor). Pharmacokinetic analysis showed that the population estimated AUC(0-24) was 1,123 ng h/mL, similar to the exposure following 13 mg/m2 in ongoing phase I trials. Pharmacodynamic changes in histone acetylation (H2A, H2B, H3, and H4) in three depsipeptide-sensitive and three intrinsically resistant tumors followed a similar pattern; maximal increases in histone acetylation occurred at 8 hours and were elevated for up to 96 hours. In two sensitive tumor lines, IRS56 and BT27 (both wild-type p53) p53 increased in treated tumors being maximal at 8 hours and associated with induction of p21(cip1), whereas p53 was stable in tumors with mutant p53. Sensitivity to depsipeptide did not correlate with p53 genotype, p53 acetylation, cleaved poly(ADP-ribose) polymerase, or phosphorylation of Akt (Ser473). CONCLUSIONS: Our results show that depsipeptide inhibits its target in vivo causing increased histone acetylation; however, this does not correlate with drug sensitivity. The relatively low objective response rate [3 of 39 (8%) tumor lines showing greater than or equal to partial response and 4 (10%) stable disease] administered at dose levels that give clinically relevant drug exposures suggests that as a single agent depsipeptide may have limited clinical utility against pediatric solid tumors in a first-line setting.

Acetylation↗

PubMed2006

Cyclophosphamide disposition in an anephric child.

Although limited data are available about cyclophosphamide disposition in patients with renal insufficiency, nothing has been reported in anephric patients. We characterized cyclophosphamide pharmacokinetics in an anephric child with bilateral Wilms tumor, both on (day 1) and off (day 2) hemodialysis. The median cyclophosphamide clearance on and off hemodialysis was 5.34 and 3.82 L/hr*m(2), respectively, demonstrating elimination of cyclophosphamide in this anephric child. The off hemodialysis clearance was similar to that in children with normal renal function. Hydroxycyclophosphamide (HCY) AUC was 20.6 and 8.77 microM*hr on and off hemodialysis. Carboxyethylphosphoramide mustard (CEPM) AUC obtained on hemodialysis (i.e., 194 microM*hr) was similar to that in children with normal renal function, although an elevated CEPM AUC was observed when hemodialysis was not received (i.e., 383 microM*hr). With the recent findings that clinical outcomes are related to CEPM AUC, further data are needed regarding the pharmacokinetics of cyclophosphamide and relevant metabolites in anephric children.

Antineoplastic Agents, Alkylating↗

PubMed2006

Temozolomide after radiotherapy for newly diagnosed high-grade glioma and unfavorable low-grade glioma in children.

Chemotherapy is commonly used in the treatment of children with high-grade glioma, although its usefulness is uncertain. We conducted a multi-institutional study to evaluate the efficacy of temozolomide given after radiotherapy in children with newly diagnosed high-grade glioma and unfavorable low-grade glioma (gliomatosis cerebri or bithalamic involvement). Optional window therapy of intravenous irinotecan (10 doses of 20 mg/m2 per cycle x 2) was given over 6 weeks. The 5-day schedule of temozolomide (200 mg/m2 per day) started 4 weeks after the completion of radiotherapy and continued for a total of 6 cycles. Thirty-one eligible patients (median age: 12.3 years) participated. Tumors most commonly involved cerebral hemispheres (n = 13, 42%) and thalamus (n = 14, 45%). Whereas six patients underwent radical resection, the remainder had limited surgery, including biopsy (n = 14, 45%). The predominant histologic diagnoses were glioblastoma multiforme (n = 15, 48%) and anaplastic astrocytoma (n = 10, 32%). Two patients had bithalamic grade II astrocytoma. Twenty-seven patients received radiotherapy (median dose: 59.4 Gy), including craniospinal irradiation in 3 because of leptomeningeal spread. Four patients did not receive radiotherapy in this study because of consent withdrawn (n = 2), toxicity during window therapy (n = 1), or at the physician's discretion (n = 1). Twenty-three patients received 112 cycles of temozolomide therapy. The 2-year progression-free and overall survival estimates were 11 +/- 5% and 21 +/- 7%, respectively. Although the heterogeneity of prognostic factors in our patients made assessment of treatment outcome more difficult, the addition of 6 cycles of temozolomide after radiotherapy did not seem to alter the poor outcome of these patients.

Adolescent↗

PubMed2006

A phase II window trial of procarbazine and topotecan in children with high-grade glioma: a report from the children's oncology group.

The role of chemotherapy in the treatment of high-grade gliomas in children is unclear. Early reports were suggestive of improved outcome in children with high-grade glioma with the addition of chemotherapy after surgery and radiation therapy. Subsequent studies did not show similar favorable contribution of chemotherapy to the outcome of these children. Further efforts to identify active chemotherapy agents in children include use of agents that have shown efficacy in adult patients with high-grade glioma and agents that have shown promise in mice bearing human xenografts of brain tumors. A Pediatric Oncology Group (POG 9431) trial tested the activity of two such agents, procarbazine and topotecan in newly diagnosed patients with high-grade glioma who had measurable disease after diagnostic surgery. Neither agent showed efficacy within the confines of the statistical design of the study. This study showed that children with high-grade glioma have an innate resistance to alkylating agents based on mismatch repair deficiency and high levels of alkyguanine transferase (AGT). Future trials should consider strategies to overcome the resistance mechanisms in children with high-grade glioma.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Risk-adapted craniospinal radiotherapy followed by high-dose chemotherapy and stem-cell rescue in children with newly diagnosed medulloblastoma (St Jude Medulloblastoma-96): long-term results from a prospective, multicentre trial.

BACKGROUND: Current treatment for medulloblastoma, which includes postoperative radiotherapy and 1 year of chemotherapy, does not cure many children with high-risk disease. We aimed to investigate the effectiveness of risk-adapted radiotherapy followed by a shortened period of dose-intense chemotherapy in children with medulloblastoma. METHODS: After resection, patients were classified as having average-risk medulloblastoma (< or = 1.5 cm2 residual tumour and no metastatic disease) or high-risk medulloblastoma (> 1.5 cm2 residual disease or metastatic disease localised to neuraxis) medulloblastoma. All patients received risk-adapted craniospinal radiotherapy (23.4 Gy for average-risk disease and 36.0-39.6 Gy for high-risk disease) followed by four cycles of cyclophosphamide-based, dose-intensive chemotherapy. Patients were assessed regularly for disease status and treatment side-effects. The primary endpoint was 5-year event-free survival; we also measured overall survival. This study is registered with ClinicalTrials.gov, number NCT00003211. FINDINGS: Of 134 children with medulloblastoma who underwent treatment (86 average-risk, 48 high-risk), 119 (89%) completed the planned protocol. No treatment-related deaths occurred. 5-year overall survival was 85% (95% CI 75-94) in patients in the average-risk group and 70% (54-84) in those in the high-risk group (p=0.04); 5-year event-free survival was 83% (73-93) and 70% (55-85), respectively (p=0.046). For the 116 patients whose histology was reviewed centrally, histological subtype correlated with 5-year event-free survival (p=0.04): 84% (74-95) for classic histology, 77% (49-100) for desmoplastic tumours, and 57% (33-80) for large-cell anaplastic tumours. INTERPRETATION: Risk-adapted radiotherapy followed by a shortened schedule of dose-intensive chemotherapy can be used to improve the outcome of patients with high-risk medulloblastoma.

Adolescent↗

PubMed2006

Immunohistochemical detection of multidrug-resistant protein expression in retinoblastoma treated by primary enucleation.

PURPOSE: To compare the expression of multidrug-resistant proteins in retinoblastoma tumors among eyes treated with primary enucleation. METHODS: A group of 18 patients with unilateral retinoblastoma with advanced intraocular disease was selected for the study. All patients had undergone primary enucleation. A histologic specimen from each patient was retrieved from the pathology archives and a tissue gene microarray was constructed (0.6 x 3-4 mm). Standard immunohistochemical techniques were used to study the tissue microarrays for the expression of the ATP-binding cassette (ABC) transporters: breast cancer resistance protein (BCRP; ABCG2), multidrug-resistant protein 1/P-glycoprotein (MDR1/Pgp; ABCB1), multidrug-resistant-associated protein 1 (MRP1; ABCC1), MRP2 (ABCC2), and MRP4 (ABCC4). RESULTS: Of the 18 specimens retrieved, 16 had adequate tissue for study. MRP1 was expressed in 8 (50%) of 16 tumors, and MRP2 was expressed in 5 (31%) of 16 tumors. MDR1/Pgp was found in 2 (12%) of 16 retinoblastomas. MRP4 and BCRP were not detected in any of the tumors studied. CONCLUSIONS: The results show that multiple ABC transporters were present in a cohort of sporadic patients with unilateral retinoblastoma who underwent primary enucleation. Studies are planned of the expression of ABC transporters in eyes treated by chemotherapy and/or radiation as a comparison with this group.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2006

Pharmacokinetic considerations in the treatment of CNS tumours.

Despite aggressive therapy, the majority of primary and metastatic brain tumour patients have a poor prognosis with brief survival periods. This is because of the different pharmacokinetic parameters of systemically administered chemotherapeutic agents between the brain and the rest of the body. Specifically, before systemically administered drugs can distribute into the CNS, they must cross two membrane barriers, the blood-brain barrier (BBB) and blood-cerebrospinal fluid (CSF) barrier (BCB). To some extent, these structures function to exclude xenobiotics, such as anticancer drugs, from the brain. An understanding of these unique barriers is essential to predict when and how systemically administered drugs will be transported to the brain. Specifically, factors such as physiological variables (e.g. blood flow), physicochemical properties of the drug (e.g. molecular weight), as well as influx and efflux transporter expression at the BBB and BCB (e.g. adenosine triphosphate-binding cassette transporters) determine what compounds reach the CNS. A large body of preclinical and clinical research exists regarding brain penetration of anticancer agents. In most cases, a surrogate endpoint (i.e. CSF to plasma area under the concentration-time curve [AUC] ratio) is used to describe how effectively agents can be transported into the CNS. Some agents, such as the topoisomerase I inhibitor, topotecan, have high CSF to plasma AUC ratios, making them valid therapeutic options for primary and metastatic brain tumours. In contrast, other agents like the oral tyrosine kinase inhibitor, imatinib, have a low CSF to plasma AUC ratio. Knowledge of these data can have important clinical implications. For example, it is now known that chronic myelogenous leukaemia patients treated with imatinib might need additional CNS prophylaxis. Since most anticancer agents have limited brain penetration, new pharmacological approaches are needed to enhance delivery into the brain. BBB disruption, regional administration of chemotherapy and transporter modulation are all currently being evaluated in an effort to improve therapeutic outcomes. Additionally, since many chemotherapeutic agents are metabolised by the cytochrome P450 3A enzyme system, minimising drug interactions by avoiding concomitant drug therapies that are also metabolised through this system may potentially enhance outcomes. Specifically, the use of non-enzyme-inducing antiepileptic drugs and curtailing nonessential corticosteroid use may have an impact.

Animals↗

PubMed2005

Determination of lapatinib (GW572016) in human plasma by liquid chromatography electrospray tandem mass spectrometry (LC-ESI-MS/MS).

A sensitive method for the determination of lapatinib (GW572016) in human plasma was developed using high-performance liquid chromatographic separation with tandem mass spectrometric detection. Plasma samples (100 microL) were prepared using solid phase extraction (SPE) columns, and 6.0 microL of the reconstituted eluate was injected onto a Phenomenex CuroSil-PFP 3 mu analytical column (50 mm x 2.0mm) with an isocratic mobile phase. Analytes were detected with a PE SCIEX API-365 LC-MS/MS system at unit (Q1) and low (Q3) resolution in positive multiple reaction monitoring mode (m/z 581 (precursor ion) to m/z 364 (product ion) for lapatinib). The mean recovery for lapatinib was 75% with a lower limit of quantification of 15 ng/mL (S/N=11.3, CV< or =14%). This method was validated over a linear range of 100-10,000 ng/mL, and results from a 5-day validation study demonstrated good within-day and between-day precision and accuracy. This method has been used to measure plasma lapatinib concentrations in a Phase I study in children with cancer.

Child↗

PubMed2005

Phase I study of the combination of topotecan and irinotecan in children with refractory solid tumors.

PURPOSE: We have shown in xenograft studies that the antitumor activities of topotecan and irinotecan are highly schedule- and dose-dependent, with a high frequency of response at low, protracted dose schedules. Preclinical and clinical data suggest that topotecan and irinotecan have different antitumor activities and mechanisms of resistance, and non-overlapping toxicities, providing a rationale for their combination. Combining both agents may increase the amount of camptothecin delivered to the tumor, without additive toxicity. METHODS: We conducted a phase I study in children with refractory solid tumors to determine the maximum tolerated dose (MTD) of irinotecan when administered with a targeted systemic exposure (TSE) of topotecan and to define the dose-limiting toxicity (DLT) of this combination. Irinotecan was administered IV over 60 min followed by topotecan over 30 min daily for 5 days for two consecutive weeks. We initially fixed the topotecan-TSE to 80+/-10 ng*h/ml and investigated the ability to escalate irinotecan (starting dose 16 mg/m2/d). Topotecan and irinotecan pharmacokinetics were determined. RESULTS: Eleven patients (median age 10 years) were enrolled. Owing to DLT, irinotecan was de-escalated to 12 (level -1; n = 3) and 9 (level -2; n = 3) mg/m2/day, and topotecan-TSE was reduced to 60+/-10 ng*h/ml (level -3; n = 2). DLTs were neutropenia (n = 8), typhlitis (n = 5), and skin rash (n = 1). MTD could not be reached. Median (range) irinotecan and topotecan lactone systemic clearances were 50.3 (16.6-76.2) l/h/m2 and 27.6 (14.7-55.9) l/h/m2, respectively. The pharmacokinetics profile of each agent was similar to that seen in previous single agent studies. One patient with neuroblastoma and one with rhabdomyosarcoma had a partial and a complete response, respectively. CONCLUSION: Despite promising antitumor activity, the combination of topotecan and irinotecan given on a protracted schedule does not warrant further development in children due to unacceptable toxicity.

Adolescent↗

PubMed2005

Phase I and pharmacokinetic study of gefitinib in children with refractory solid tumors: a Children's Oncology Group Study.

PURPOSE: Epidermal growth factor receptor is expressed in pediatric malignant solid tumors. We conducted a phase I trial of gefitinib, an epidermal growth factor receptor tyrosine kinase inhibitor, in children with refractory solid tumors. PATIENTS AND METHODS: Gefitinib (150, 300, 400, or 500 mg/m2) was administered orally to cohorts of three to six patients once daily continuously until disease progression or significant toxicity. Pharmacokinetic studies were performed during course one (day 1 through 28). RESULTS: Of the 25 enrolled patients, 19 (median age, 15 years) were fully evaluable for toxicity and received 54 courses. Dose-limiting toxicity was rash in two patients treated with 500 mg/m2 and elevated ALT and AST in one patient treated with 400 mg/m2. The maximum-tolerated dose was 400 mg/m2/d. The most frequent non-dose-limiting toxicities were grade 1 or 2 dry skin, anemia, diarrhea, nausea, and vomiting. One patient with Ewing's sarcoma had a partial response. Disease stabilized for 8 to > or = 60 weeks in two patients with Wilms' tumor and two with brainstem glioma (one exophytic). At 400 mg/m2, the median peak gefitinib plasma concentration was 2.2 microg/mL (range, 1.2 to 3.6 microg/mL) and occurred at a median of 2.3 hours (range, 2.0 to 8.3 hours) after drug administration. The median apparent clearance and median half-life were 14.8 L/h/m2 (range, 3.8 to 24.8 L/h/m2) and 11.7 hours (range, 5.6 to 22.8 hours), respectively. Gefitinib systemic exposures were comparable with those associated with antitumor activity in adults. CONCLUSION: Oral gefitinib is well tolerated in children. Development of the drug in combination with cytotoxic chemotherapy will be pursued.

Administration, Oral↗