Biomedical subjects

Mark N Kirstein

Publications and source records attributed to Mark N Kirstein.

11 recordsLinked to original sources

PubMed2006

High-performance liquid chromatographic method for the determination of gemcitabine and 2',2'-difluorodeoxyuridine in plasma and tissue culture media.

Gemcitabine, a pyrimidine antimetabolite undergoes metabolism by plasma and liver cytidine deaminase to form the inactive compound, 2',2'-difluorodeoxyuridine (dFdU). The parent molecule is activated by intracellular phosphorylation. To evaluate the population pharmacokinetics in patients receiving gemcitabine, and to test the relation between gemcitabine infusion rate and antitumor activity in an in vitro bioreactor cell culture system, we developed and validated a sensitive and specific HPLC-UV method for gemcitabine and dFdU. Deproteinized plasma is vortexed, centrifuged, and 25 microL of the acidified extract sample is injected onto a Waters Spherisorb 4.6 mm x 250 mm, 5 microm C18 column at 40 degrees C. The mobile phase (flow rate, 1.0 mL/min) consists of 10:90 (v/v) acetonitrile-aqueous buffer (50 mM sodium phosphate and 3.0 mM octyl sulfonic acid, pH 2.9). Gemcitabine, dFdU, and the internal standard, 2'-deoxycytidine (2'dC) were detected with UV wavelength set at 267 nm. The standard curves for gemcitabine in both matrices ranged from 2 to 200 microM, and for dFdU in plasma, from 2 to 100 microM. Within-run and between-run component precision (CV%) was <or=6.1 and 5.7%, respectively for both human plasma and tissue culture media, and for dFdU, 2.3 and 2.7%. Total accuracy ranged from 98.7 to 106.2% for human plasma and from 96.9 to 99.2% for tissue culture media, respectively, and for dFdU, from 96.5 to 99.6%. Tetrahydrouridine (THU), an inhibitor of cytidine deaminase is used to prevent breakdown in human plasma. With one method we can measure gemcitabine in both plasma and tissue culture media. Utility is demonstrated by evaluation of the disposition of gemcitabine in an in vitro bioreactor cell culture system.

Bioreactors↗

PubMed2006

Characterization of an in vitro cell culture bioreactor system to evaluate anti-neoplastic drug regimens.

A dynamic 3-dimensional tissue culture system has been developed that will allow for control of gemcitabine exposure to mimic concentration-time profiles measured from biologic samples. Gemcitabine was infused into a central reservoir. Media is mixed and delivered through hollow fiber capillaries, where it diffuses into the extracapillary space containing anchorage-dependent MDA-231 cells. To test for control of gemcitabine concentration-time profiles, drug was first infused through bioreactors without cells, and gemcitabine concentrations were measured with HPLC. Concentrations could be controlled to simulate 30-min and 2.5 h infusions, and were similar in both the lumen and extracapillary space. MDA-231 cells were then seeded into control (n = 4) and gemcitabine treatment (n = 4) groups, and maintained in culture for 2 weeks. Gemcitabine (5.3 mg) was infused over 30 min to the treatment group, and blank media to the control group. Accuracy of measured gemcitabine maximum concentration (Cmax) was 83.4%, and area under the curve (AUC), 106.2%, relative to pre-experimental theoretical values. With cells present, gemcitabine AUC in the extracapillary space was 32% of the value in the lumen. For the control group, 21.2 million cells (94.3% viable) were recovered, and for the gemcitabine-treated group, 16.8 million cells (87.1 % viable). Flow cytometry showed that 13.3 % of cells in the control group were in S-phase and 34.3 % in the gemcitabine-treated group were in S-phase (p = 0.003). In conclusion, gemcitabine concentration-time profiles could be accurately controlled through dosage, infusion rate, and pump flow rate, and cells could be recovered afterward to evaluate drug treatment.

Antimetabolites, Antineoplastic↗

PubMed2005

Development of a pharmacokinetic limited sampling model for temozolomide and its active metabolite MTIC.

PURPOSE: To develop a pharmacokinetic limited sampling model (LSM) for temozolomide and its metabolite MTIC in infants and children. METHODS: LSMs consisting of either two or four samples were determined using a modification of the D-optimality algorithm. This accounted for prior distribution of temozolomide and MTIC pharmacokinetic parameters based on full pharmacokinetic sampling from 38 patients with 120 pharmacokinetic studies (dosage range 145-200 mg/m(2) per day orally). Accuracy and bias of each LSM were determined relative to the full sampling method. We also assessed the predictive performance of the LSMs using Monte-Carlo simulations. RESULTS: The four strategies generated from the D-optimality algorithm were as follows: LSM 1=0.25, 1.25, and 3 h; LSM 2=0.25, 1.25, and 6 h; LSM 3=0.25, 0.5, 1.25, and 3 h; LSM 4=0.25, 0.5, 1.25, and 6 h. LSM 2 demonstrated the best combination of low bias [0.1% (-8.9%, 11%) and 11% (4.3%, 15%)] and high accuracy [-1.0% (-12%, 24%) and 14% (7.9%, 37%)] for temozolomide clearance and MTIC AUC, respectively. Furthermore, adding a fourth sample (e.g., LSM 4) did not substantially decrease the bias or increase the accuracy for temozolomide clearance or MTIC AUC. Results from Monte-Carlo simulations also revealed that LSM 2 had the best combination of lowest bias (0.1+/-6.1% and -0.8+/-6.5%), and the highest accuracy (4.5+/-4.1% and 5.0+/-4.3%) for temozolomide clearance and MTIC apparent clearance, respectively. CONCLUSIONS: Using data derived from our population analysis, the sampling times for a limited sample pharmacokinetic model for temozolomide and MTIC in children are prior to the temozolomide dose, and 15 min, 1.25 h and 6 h after the dose.

Antineoplastic Agents, Alkylating↗

PubMed2005

A phase I trial defining the maximum tolerated systemic exposure of topotecan in combination with Carboplatin and Etoposide in extensive stage small cell lung cancer.

PURPOSE: Topotecan is active in relapsed small cell lung cancer; thus, its addition to the standard carboplatin-etoposide regimen may improve outcomes in extensive-stage small cell lung cancer (ES-SCLC) patients. Significant interpatient variability in the topotecan systemic exposure results when it is dosed based on body surface area (mg/m2). The purpose of this Phase I trial was to determine the maximally tolerated systemic exposure (MTSE) of topotecan in combination with carboplatin and etoposide. METHODS: Thirty-four chemotherapy-naïve ES-SCLC patients received topotecan in combination with carboplatin AUC 5 mg/mL*min and oral etoposide 100 mg/m2/day. Topotecan was administered as a 30-minute infusion either on Days 1-5 or Days 1-3 and the dosage was individualized to attain a topotecan lactone AUC range (ng/mL*hr) in successive patient cohorts from 7 to 23; 24 to 36; 37 to 53; 54 to 66. RESULTS: The majority (67 percent) of the measured topotecan AUCs were within target range. Overall, 8 of 34 patients experienced Cycle 1 dose-limiting toxicity (DLT), either neutropenia or thrombocytopenia. Carboplatin administration prior to topotecan resulted in 2 of 6 patients having Cycle 1 DLT. When the administration sequence was changed (topotecan, carboplatin, etoposide), Cycle 1 hematologic toxicity decreased; however, the maximum topotecan lactone AUC of 24-36 ng/mL*hr (median dose 0.82 mg/m2) had significant cumulative hematologic toxicity. The number of topotecan doses were reduced from 5 to 3, which resulted in a maximum topotecan lactone AUC of 37 to 53 ng/mL*hr with only 1 of 6 patients having Cycle 1 DLT. Overall response rate was 71 percent with median survival of 10.8 months. CONCLUSION: It is feasible to target topotecan lactone AUC in adult ES-SCLC patients. However, this triplet regimen resulted in considerable hematologic toxicity and has a median survival comparable to carboplatin-etoposide. Alternative, less toxic regimens should be investigated for improving survival in ES-SCLC.

Adult↗

PubMed2003

Population pharmacokinetics of temozolomide and metabolites in infants and children with primary central nervous system tumors.

PURPOSE: To construct a population pharmacokinetic model for temozolomide (TMZ), a novel imidazo-tetrazine methylating agent and its metabolites MTIC and AIC in infants and children with primary central nervous system tumors. METHODS: We evaluated the pharmacokinetics of TMZ and MTIC in 39 children (20 boys and 19 girls) with 132 pharmacokinetic studies (109 in the training set and 23 in the validation set). The median age was 7.1 years (range 0.7 to 21.9 years). Children received oral TMZ dosages ranging from 145 to 200 mg/m(2) per day for 5 days in each course of therapy. Serial plasma samples were collected after the first and fifth doses of the first and third courses. Approximately eight plasma samples were collected up to 8 h after each dose, and assayed for TMZ, MTIC, and AIC by HPLC with UV detection. A one-compartment model was fitted to the TMZ and metabolite plasma concentrations using maximum likelihood estimation. Covariates, including demographics and biochemical data were tested for their effects on TMZ clearance (CL/F) and MTIC AUC utilizing a two-stage approach via linear mixed-effects modeling. RESULTS: The population mean (inter- and intrapatient variability expressed as %CV) for the pharmacokinetic parameters (based on the training set) were as follows: TMZ CL/F 5.4 l/h (53.4, 17.5), Vc/F 14.0 l (48.5, 39.2), C(max) 9.1 mg/l (20.8, 29.1), and MTIC AUC 1.0 microg/ml.h (13.9, 30.0). Covariate analysis showed that increasing age and body surface area (BSA) were associated with a significant increases in TMZ CL, Vc, and C(max) ( P<0.05), and that increasing age was associated with significant decreases in TMZ and MTIC AUC. Indicators of liver and renal function were not significantly associated with TMZ pharmacokinetics or MTIC AUC. The final model with the significant covariates was validated using the remaining 23 pharmacokinetic studies. CONCLUSIONS: This study extends previous work done in adults, and identified BSA and age as covariates that account for variability in TMZ disposition in infants and children with primary CNS malignancies.

Adolescent↗

PubMed2003

Determination of plasma topotecan and its metabolite N-desmethyl topotecan as both lactone and total form by reversed-phase liquid chromatography with fluorescence detection.

Topotecan (TPT) undergoes hepatic N-demethylation forming N-desmethyl topotecan (NDS). To evaluate the effect of drug-drug interactions on NDS disposition in children receiving TPT we developed and validated a sensitive and specific HPLC-fluorescence detection method for lactone and total (lactone plus carboxylate) TPT and NDS. Deproteinized plasma is vortexed, centrifuged, and the methanolic extract diluted with water for the lactone form of NDS and TPT or diluted with 1.5% phosphoric acid for NDS and TPT total. A 100 microL sample is injected onto a Varian ChromGuard RP column attached to an Agilent SB-C(18) reversed-phase analytical column held at 50 degrees C. The mobile phase (flow-rate, 0.8 mL/min) consists of methanol-aqueous buffer (27:73, v/v) (75 mM potassium phosphate and 0.2% triethylamine, pH 6.5). TPT and NDS were detected with excitation and emission wavelengths set at 376 and 530 nm, respectively. The standard curves for both forms of TPT ranged from 0.25 to 80 ng/mL, and for NDS ranged from 0.10 to 8.0 ng/mL. Within-day and between-day precision (% RSD) was </=4% for TPT and </=6.2% for NDS, respectively. Within-day and between-day percentage error ranged from 1.4 to 6.3% and from 1.4 to 2.4% for TPT, and from 1.6 to 3.1% and from 0.0 to 3.7% for NDS, respectively. No significant on-column conversion from TPT or NDS lactone to carboxylate was observed. With one method we can measure lactone and total TPT and NDS with adequate sensitivity to allow for evaluation of the disposition of these compounds in children receiving TPT.

Antineoplastic Agents↗

PubMed2003

A mechanistic mathematical model of temozolomide myelosuppression in children with high-grade gliomas.

Temozolomide (TMZ) is currently being evaluated for the treatment of high-grade gliomas in children. Myelosuppression (the suppression of bone marrow activity) is the dose-limiting toxicity for TMZ in adults and children. Empirical methods (i.e. relations between the percent change in absolute neutrophil count (ANC) and the area under the plasma concentration curve (AUC) of TMZ or its active metabolite MTIC) showed poor results when attempting to describe myelosuppression from serial data derived during TMZ therapy in a Phase II study of children with high-grade glioma. Therefore, to improve our understanding of the myelosuppressive effects of TMZ and MTIC in children we developed a mechanistic mathematical model. The model describes the progression of neutrophils from their production in the bone marrow to their release in the plasma. Included in the model are the feedback effects of granulocyte colony stimulating factor (G-CSF), which stimulates neutrophil production when there is a decrease in circulating neutrophils. The model is fit to serial ANC measurements obtained after TMZ dosing and it is able to explain, among other things, the lag in ANC reduction following a dose of TMZ, the ANC nadir, and the 'rebound effect' observed where the ANC recovers to levels greater than that observed pre-TMZ dose. This model will be useful for the prospective design of clinical trials of TMZ in children with cancer.

Adolescent↗

PubMed2003

Molecular targets in the inhibition of angiogenesis.

Angiogenesis, the process of blood vessel formation, is crucial for malignant tumour growth and metastases; therefore, it has become an attractive target for anticancer therapy. Theoretically applicable to most solid tumours, this therapy may be advantageous over existing cytotoxic therapy, since it is directed at genetically stable endothelium growing within tumours rather than at malignant cells, which acquire resistance to treatment. Many promising angiogenesis inhibitors have been developed, although their activity has yet to be demonstrated in human clinical trials. To improve therapeutic benefit, this may require further insight into tumour angiogenesis, development of appropriate surrogate markers of activity, treatment of early stage neoplastic disease and probably a combination of different classes of antiangiogenesis agents to overcome redundant mechanisms of angiogenesis control.

Angiogenesis Inhibitors↗

PubMed2003

A pilot study of protracted topotecan dosing using a pharmacokinetically guided dosing approach in children with solid tumors.

PURPOSE: To assess the use of a pharmacokinetically guided topotecan strategy and evaluate the toxicity of protracted i.v. topotecan in children with recurrent solid tumors. EXPERIMENTAL DESIGN: Fifteen children with measurable relapsed or refractory solid tumors received topotecan i.v. over 30 min 5 days a week for two consecutive weeks. Doses were individualized based on the patient's topotecan systemic clearance to attain a single day topotecan lactone area under the plasma concentration time curve (AUC) of 120-180 ng/ml x h (cohort 1) or 80-120 ng/ml x h (cohort 2). Clinical responses and toxicity were assessed by standard criteria. RESULTS: Twenty-nine courses of topotecan were administered, 11 in cohort 1 and 18 in cohort 2. The median topotecan dosages required to achieve the target AUCs for cohorts 1 and 2 were 4 mg/m(2) (range, 2.6-6) and 3 mg/m(2) (range, 2.6-4.2), respectively. The intersubject variance for topotecan clearance exceeded the intrasubject variance by 2-fold. With the pharmacokinetic targeting approach, we observed that 78% (46 of 59) of the measured AUC values were within the target range. The median number of days to an absolute neutrophil count >/=500/mm(3) was similar between the two cohorts; however, febrile neutropenia and serious infections limited our ability to deliver drug dosages needed to secure the higher systemic exposure (cohort 1). Five partial responses were observed. CONCLUSION: Protracted topotecan dosing using a pharmacokinetic strategy was possible in this heavily pretreated group of children.

Adolescent↗

PubMed2002

New liquid chromatographic assay with electrochemical detection for the measurement of amifostine and WR1065.

A high-performance liquid chromatographic method (HPLC) was developed for the analysis of the radio- and chemo-protectant, amifostine and its active metabolite-WR1065 in deproteinized human whole blood and plasma. The two compounds were quantified by measuring WR1065 after two different sample pretreatment procedures. During these procedures, amifostine was quantitatively converted into WR1065, by incubating the sample at 37 degrees C for 4 h at pH<1.0. The resulting amounts of WR1065 were determined by HPLC with coulometric detection (analytical cell: E(1)=200 mV and E(2)=600 mV; guard cell: E(G)=650 mV). The WR1065 standard curve ranged from 0.37 to 50.37 microM. The lower limit of quantitation of WR1065 was 0.25 microM. The within- and between-day precisions were < or = 4.3% and < or = 6.0% for amifostine, < or = 4.4% and < or = 3.8% for WR1065, respectively. The within- and between-day accuracy ranged from 95.4 to 97.7% and 95.4 to 97.8% for amifostine, and from 97.1 to 101.7% and 97.2 to 99.7% for WR1065, respectively. This method minimizes WR1065 loss during sample preparation, and allows for rapid analysis of both compounds on one system. Furthermore, the application of a coulometric electrode is more efficient and requires less maintenance than previously published methods for the two compounds.

Amifostine↗

PubMed2002

Topoisomerase I interactive agents.

Elucidation of the crystal structure of topoisomerase I will enhance the rational development of topoisomerase I interactive agents. Although the first topoisomerase I interactive agents were camptothecin derivatives, future drugs may be designed to take advantage of the knowledge of the mechanism of interaction with topoisomerase I to increase the therapeutic index. 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, many investigators 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 rationally developed.

Animals↗