112 research outputs found
Inhibition of OATP1B1 by tyrosine kinase inhibitors: In vitro-in vivo correlations
Background:Several tyrosine kinase inhibitors (TKIs) can decrease docetaxel clearance in patients by an unknown mechanism. We hypothesised that these interactions are mediated by the hepatic uptake transporter OATP1B1.Methods:The influence of 16 approved TKIs on transport was studied in vitro using HEK293 cells expressing OATP1B1 or its mouse equivalent Oatp1b2. Pharmacokinetic studies were performed with Oatp1b2-knockout and OATP1B1-transgenic mice.Results:All docetaxel-interacting TKIs, including sorafenib, were identified as potent inhibitors of OATP1B1 in vitro. Although Oatp1b2 deficiency in vivo was associated with increased docetaxel exposure, single- or multiple-dose sorafenib did not influence docetaxel pharmacokinetics.Conclusion: These findings highlight the importance of identifying proper preclinical models for verifying and predicting TKI-chemotherapy interactions involving transporters
Topotecan lacks third space sequestration
The objective of this study was to determine the influence of pleural and
ascitic fluid on the pharmacokinetics of the antitumor camptothecin
derivative topotecan. Four patients with histological proof of malignant
solid tumor received topotecan (0.45 or 1.5 mg/m2) p.o. on several
occasions in both the presence and absence of third space volumes. Serial
plasma and pleural or ascitic fluid samples were collected during each
dosing and analyzed by high-performance liquid chromatography for both the
intact lactone form of topotecan and its ring-opened carboxylate form. The
apparent topotecan clearance demonstrated substantial interpatient
variability but remained unchanged within the same patient in the presence
[110 +/- 55.6 liters/ h/m2 (mean +/- SD of eight courses)] or absence of
pleural and ascitic fluid [118 +/- 31.1 liters/h/m2 (mean +/- SD of seven
courses)]. Similarly, terminal half-lives and area under the
concentration-time curve ratios of lactone:total drug in plasma were
similar between courses within each patient. Topotecan penetration into
pleural and ascitic fluid demonstrated a mean lag time of 1.61 h (range,
1.37-1.86 h), and ratios with plasma concentration increased with time
after dosing in all patients. The mean ratio of third space topotecan
total drug area under the concentration-time curve to that in plasma was
0.55 (range, 0.26-0.87). These data indicate that topotecan can be safely
administered to patients with pleural effusions or ascites and that there
is substantial penetration of topotecan into these third spaces, which may
prove beneficial for local antitumor effects
Effects of St. John's wort on irinotecan metabolism
St. John's wort (SJW), a widely used herbal product, has been implicated
in drug interactions resulting from the induced expression of the
cytochrome P450 CYP3A4 isoform. In this study, we determined the effect of
SJW on the metabolism of irinotecan, a pro-drug of SN-38 and a known
substrate for CYP3A4. Five cancer patients were treated with irinotecan
(350 mg/m(2), intravenously) in the presence and absence of SJW (900 mg
daily, orally for 18 days) in an unblinded, randomized crossover study
design. The plasma levels of the active metabolite SN-38 decreased by 42%
(95% confidence interval [CI] = 14% to 70%) following SJW cotreatment with
1.0 micro M x h (95% CI = 0.34 micro M x h to 1.7 micro M x h) versus 1.7
micro M x h (95% CI = 0.83 micro M x h to 2.6 micro M x h) (P =.033,
two-sided paired Student's t test). Consequently, the degree of
myelosuppression was substantially worse in the absence of SJW. These
findings indicate that patients on irinotecan treatment should refrain
from taking SJW because plasma levels of SN-38 were dramatically reduced,
which may have a deleterious impact on treatment outcome
Inter- and intrapatient variability in oral topotecan pharmacokinetics: implications for body-surface area dosage regimens
Anticancer drugs still are dosed based on the body-surface area (BSA) of
the individual patient, although the BSA is not the main predictor of the
clearance for the majority of drugs. The relevance of BSA-based dosing has
not been evaluated for topotecan yet. A retrospective pharmacological
analysis was performed of kinetic data from four clinical Phase I studies
in which topotecan was administered p.o. as a single agent combined with
data from a combination study of topotecan and cisplatin. A strong
correlation (r = 0.91) was found between the area under the plasma
concentration time curve of the lactone and carboxylate forms of topotecan
by plotting 326 data sets obtained from 112 patients receiving oral
topotecan at dose levels ranging from 0.15-2.70 mg/m2. The intrapatient
variability, studied in 47 patients sampled for 3 or more days, for the
apparent lactone clearance, ranged from 7.4-69% (mean, 24 +/- 13%; median,
20%). The interpatient variabilities in the lactone clearance, calculated
with the data of all studied patients, expressed in liter/h/m2 and in
liter/h were 38% and 42%, respectively. In view of the relatively high
inter- and intrapatient variabilities in topotecan clearance, in contrast
to a variability of only 12% in the BSA of the studied patients, no
advantage of BSA-based dosing was found over fixed dose regimens
Determination of the lactone and lactone plus carboxylate forms of 9-aminocamptothecin in human plasma by sensitive high-performance liquid chromatography with fluorescence detection
Two sensitive reversed-phase high-performance liquid chromatographic fluorescence methods, with simple sample handling at the site of the patient, are described for the determination of the lactone and lactone plus carboxylate forms of g-aminocamptothecin (9AC). For 9AC lactone, the sample preparation was a liquid-liquid extraction with acetonitrile-n-butyl chloride (1:4, v/v), whereas the sample preparation for 9AC total (lactone plus carboxylate) was a simple deproteinization with 5% perchloric acid-methanol (1:1, v/v), which results in the conversion of the carboxylate into the lactone form. The lower limits of quantitation were 50 pg/ml and 100 pg/ml for 9AC lactone and 9AC total, respectively. The within-run precisions at four tested concentrations were ≤6.3% for 9AC lactone and ≤5.3% for 9AC total. The between-run precisions were ≤8.9% and ≤5.6%, respectively. The assays were developed to enable pharmacological analysis of 9AC in a bioavailability and oral phase I study in patients with solid tumors
Dose banding as an alternative to body surface area-based dosing of chemotherapeutic agents
Background: Dose banding is a recently suggested dosing method that uses predefined ranges (bands) of body surface area (BSA) to calculate each patients dose by using a single BSA-value per band. Thus, drugs with sufficient long-term stability can be prepared in advance. The main advantages of dose banding are to reduce patient waiting time and improve pharmacy capacity planning; additional benefits include reduced medication errors, reduced drug wastage, and prospective quality control. This study compares dose banding with individual BSA dosing and fixed dose according to pharmacokinetic criteria.Methods:Three BSA bands were defined: BSA1.7 m2, 1.7 m2 BSA1.9 m 2, BSA1.9 m2 and each patient dose was calculated based on a unique BSA-value per band (1.55, 1.80, and 2.05 m 2, respectively). By using individual clearance values of six drugs (cisplatin, docetaxel, paclitaxel, doxorubicin, irinotecan, and topotecan) from 1012 adult cancer patients in total, the AUCs corresponding to three dosing methods (BSA dosing, dose banding, and fixed dose) were compared with a target AUC for each drug.Results:For all six drugs, the per cent variation in individual dose obtained with dose banding compared with BSA dosing ranged between 14% and 22%, and distribution of AUC values was very similar with both dosing methods. In terms of reaching the target AUC, there was no significant difference in precision between dose banding and BSA dosing, except for paclitaxel (32.0% vs 30.7%, respectively; P=0.05). However, precision was significantly better for BSA dosing compared with fixed dose for four out of six drugs.Conclusion:For the studied drugs, implementation of dose banding should be considered as it entails no significant increase in interindividual plasma exposure
Determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection
Sensitive high-performance liquid chromatographic assays have been developed to determine the levels of the lactone and lactone plus carboxylate (total) forms of the antitumor agent irinotecan (CPT-11) and its active metabolite SN-38, in human plasma. The related compound camptothecin was used as the internal standard. The selective sample pretreatment for the lactone forms involved a single solvent extraction with acetonitrile-n-butyl chloride (1:4, v/v), whereas the sample clean-up for the total forms was a simple protein precipitation with aqueous perchloric acid-methanol (1:1, v/v), which results in the conversion of the carboxylate to the lactone forms. Chromatography was carried out on a Hypersil ODS column, with detection performed fluorimetrically. The methods have been validated, and stability tests under various conditions have been performed. The lower limits of quantitation are 0.5 and 2.0 ng/ml for the lactone and total forms, respectively. The assays have been used in a single pharmacokinetic experiment in a patient to investigate the applicability of the method in vivo
Effect of food on the pharmacokinetics of oral MMI270B (CGS 27023A), a novel matrix metalloproteinase inhibitor
MMI270B is a matrix metalloproteinase inhibitor (MMPI) with in vitro and
in vivo activity. To exert optimal target inhibition, MMPI must be given
chronically, and therefore, oral bioavailability is important. We analyzed
the effect of food intake on AUC0-8 h, Cmax, and Tmax. Seventeen patients
were entered into the study. Doses of MMI270B were 150, 400, and 600 mg.
The first day, patients ingested the drug in a fasted state and were not
allowed to eat for 2 h. The second day, patients ingested the drug 30 min
after a light breakfast. Mean AUC0-8 h was not significantly influenced by
food intake. Plasma concentrations were well above the IC50 of several
MMPs at all doses tested. Mean Cmax was significantly decreased after food
intake. Mean Tmax was significantly delayed after food intake. Food intake
did not result in a significant change in exposure to MMI270B (AUC0-8 h)
but did result in a significant, although not clinically relevant,
decrease in peak plasma levels and time to reach peak plasma levels. No
specific guidelines concerning the ingestion of MMI270B in either a fed or
a fasted state are recommended
Factors involved in prolongation of the terminal disposition phase of SN-38: clinical and experimental studies
The active metabolite of irinotecan (CPT-11),
7-ethyl-10-hydroxycamptothecin (SN-38), is either formed through enzymatic
cleavage of CPT-11 by carboxyl esterases (CEs) or through cytochrome P-450
3A-mediated oxidation to 7-ethyl-10-[4-(1-piperidino)-1-amino]
carbonyloxycamptothecin (NPC) and a subsequent conversion by CE. In the
liver, SN-38 is glucuronidated (SN-38G) by UGT1A1, which also conjugates
bilirubin. Fourteen patients were treated with 350 mg/m2 CPT-11, and we
performed pharmacokinetic analysis during a 500-h collection period. The
half-life and area under the plasma concentration-time curve of SN-38 were
47+/-7.9 h and 2.0+/-0.79 microM x h, respectively, both representing a
2-fold increase as compared with earlier reported estimates (A. Sparreboom
et al, Clin. Cancer Res., 4: 2747-2754, 1998). As an explanation for this
phenomenon, we noted substantial formation of SN-38 from CPT-11 and NPC by
plasma CE, consistent with the low circulating levels of NPC observed. In
addition, transport studies in Caco-2 monolayers indicated that
nonglucuronidated SN-38 could cross the membrane from apical to
basolateral, indicating the potential for recirculation processes that can
prolong circulation times. Interestingly, individual levels of fecal
beta-glucuronidase, which is known to mediate SN-38G hydrolysis, were not
related to any of the SN-38 kinetic parameters (r = 0.09; P = 0.26),
suggesting that interindividual variation in this enzyme is unimportant in
explaining SN-38 pharmacokinetic variability. We have also found, in
contrast to earlier data, that SN-38G/SN-38 plasma concentration ratios
decrease over time from approximately 7 (up to 50 h) to approximately 1
(at 500 h). This decrease could be explained by the fact that
glucuronidation of SN-38 and bilirubin is increasingly competitive at
lower drug levels. In addition, no evidence was found for SN-38G transport
through the Caco-2 cells. Our findings indicate that until now the
circulation time of SN-38 has been underestimated. This is of crucial
importance to our understanding of the clinical action of CPT-11 and for
future pharmacokinetic/pharmacodynamic relationships
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