Inhibition of OATP1B1 by tyrosine kinase inhibitors: in vitro-in vivo correlations.

This corrects the article DOI: 10.1038/bjc.2013.811.

Role of genetic variation in docetaxel-induced neutropenia and pharmacokinetics.

Docetaxel is used for treatment of several solid malignancies. In this study, we aimed for predicting docetaxel clearance and docetaxel-induced neutropenia by developing several genetic models. Therefore, pharmacokinetic data and absolute neutrophil counts (ANCs) of 213 docetaxel-treated cancer patients were collected. Next, patients were genotyped for 1936 single nucleotide polymorphisms (SNPs) in 225 genes using the drug-metabolizing enzymes and transporters platform and thereafter split into two cohorts. The combination of SNPs that best predicted severe neutropenia or low clearance was selected in one cohort and validated in the other. Patients with severe neutropenia had lower docetaxel clearance than patients with ANCs in the normal range (P=0.01). Severe neutropenia was predicted with 70% sensitivity. True low clearance (1 s.d.

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.

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 patient's 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: BSA<1.7 m(2), 1.7 m(2)≤ BSA<1.9 m(2), BSA ≥ 1.9 m(2) 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.

Modulation of erlotinib pharmacokinetics in mice by a novel cytochrome P450 3A4 inhibitor, BAS 100.

Administration of BAS 100, a novel mechanism-based CYP3A4 inhibitor isolated from grapefruit juice, resulted in a 2.1-fold increase in erlotinib exposure following oral administration to wild-type and humanized CYP3A4 transgenic mice. This study illustrates the potential of BAS 100 to increase the low and variable oral bioavailability of erlotinib in cancer patients.

Irinotecan-induced diarrhea: functional significance of the polymorphic ABCC2 transporter protein.

Interindividual pharmacokinetic variability of the anticancer agent irinotecan is high. Life-threatening diarrhea is observed in up to 25% of patients receiving irinotecan and has been related with irinotecan pharmacokinetics and UGT1A1 genotype status. Here, we explore the association of ABCC2 (MRP2) polymorphisms and haplotypes with irinotecan disposition and diarrhea. A cohort of 167 Caucasian cancer patients who were previously assessed for irinotecan pharmacokinetics (90-min infusion given every 21 days), toxicity, and UGT1A1*28 genotype were genotyped for polymorphisms in ABCC2 using Pyrosequencing. Fifteen ABCC2 haplotypes were identified in the studied patients. The haplotype ABCC2*2 was associated with lower irinotecan clearance (28.3 versus 31.6 l/h; P=0.020). In patients who did not carry a UGT1A1*28 allele, a significant reduction of severe diarrhea was noted in patients with the ABCC2*2 haplotype (10 versus 44%; odds ratio, 0.15; 95% confidence interval, 0.04-0.61; P=0.005). This effect was not observed in patients with at least one UGT1A1*28 allele (32 versus 20%; odds ratio, 1.87; 95% confidence interval, 0.49-7.05; P=0.354). This study suggests that the presence of the ABCC2*2 haplotype is associated with less irinotecan-related diarrhea, maybe as a consequence of reduced hepatobiliary secretion of irinotecan. As the association was seen in patients not genetically predisposed at risk for diarrhea due to UGT1A1*28, confirmatory studies of the relationships of ABCC2 genotypes and irinotecan disposition and toxicity are warranted.

Variants in the SLCO1B3 gene: interethnic distribution and association with paclitaxel pharmacokinetics.

To explore retrospectively the relationships between paclitaxel pharmacokinetics and three known, non-synonymous single-nucleotide polymorphisms (SNPs) in SLCO1B3, the gene encoding organic anion transporting polypeptide (OATP)1B3. Accumulation of [(3)H]paclitaxel was studied in Xenopus laevis oocytes injected with cRNA of Oatp1b2, OATP1A2, OATP1B1, OATP1B3, OAT1, OAT3, OCT1, and NTCP. The 334T>G (Ser112Ala), 699G>A (Met233Ile), and 1564G>T (Gly522Cys) loci of SLCO1B3 were screened in 475 individuals from five ethnic groups and 90 European Caucasian cancer patients treated with paclitaxel. Only OATP1B3 was capable of transporting paclitaxel to a significant extent (P=0.003). The 334T>G and 699G>A SNPs were less common in the African-American and Ghanaian populations (P<0.000001). Paclitaxel pharmacokinetics were not associated with the studied SNPs or haplotypes (P>0.3). The studied SNPs in SLCO1B3 appear to play a limited role in the disposition of paclitaxel, although their clinical significance in other ethnic populations remains to be investigated.

Dexamethasone as a probe for CYP3A4 metabolism: evidence of gender effect.

BACKGROUND: A study was conducted to evaluate prospectively the correlation between docetaxel clearance and pharmacokinetics of dexamethasone previously obtained in 21 patients. PATIENTS AND METHODS: Dexamethasone pharmacokinetics were performed in 17 patients 24 h before docetaxel treatment as monochemotherapy. Dexamethasone and docetaxel plasma concentrations were determined by HPLC methods. Determination of docetaxel unbound fraction in plasma was performed using microequilibrium dialysis. RESULTS: Significant correlation was observed between observed plasma docetaxel clearances (CL(docetaxel)) and values predicted from dexamethasone plasma clearance (CL(dexa)), unbound plasma docetaxel fraction estimated from serum alpha1-acid glycoprotein level (fu(alpha1-AAG)), and hepatic metastasis status. However, after splitting of the prospective data set according to gender, no correlation was observed for males (R(2) = 0.08, NS, n = 10), then strong correlation was observed for females (R(2) = 0.78, P < 0.01, n = 7). Multivariate analysis was performed from data obtained in the women included in the first study and those of this prospective study (n = 18). Docetaxel CL was significantly correlated with CL(dexa) (P = 0.001) and fu(alpha1-AAG) (P = 0.01) according to the relationship (with +/-95% confidence intervals): CL(docetaxel) (l/h) = 1.92 (+/-0.94) x CL(dexa) (l/h) + 2.68 (+/-1.95) x fu(alpha1-AAG) (%) (R(2) = 0.68). CONCLUSION: Dexamethasone may be used to predict docetaxel clearances in females, but not in males.

Predicting transporter-mediated drug interactions: Commentary on: "Pharmacokinetic evaluation of a drug transporter cocktail consisting of digoxin, furosemide, metformin and rosuvastatin" and "Validation of a microdose probe drug cocktail for clinical drug interaction assessments for drug transporters and CYP3A".

Transporters, expressed in various tissues, govern the absorption, distribution, metabolism, and excretion of drugs, and consequently their inherent safety and efficacy profiles. Drugs may interact with a transporter as a substrate and/or an inhibitor. Understanding transporter-mediated drug-drug interactions (DDIs), in addition to enzyme-mediated DDIs, is an integral part of risk assessment in drug development and regulatory review because the concomitant use of more than one medication in patients is common.

Influence of OATP1B1 Function on the Disposition of Sorafenib-ß-D-Glucuronide.

The oral multikinase inhibitor sorafenib undergoes extensive UGT1A9-mediated formation of sorafenib-ß-D-glucuronide (SG). Using transporter-deficient mouse models, it was previously established that SG can be extruded into bile by ABCC2 or follow a liver-to-blood shuttling loop via ABCC3-mediated efflux into the systemic circulation, and subsequent uptake in neighboring hepatocytes by OATP1B-type transporters. Here we evaluated the possibility that this unusual process, called hepatocyte hopping, is also operational in humans and can be modulated through pharmacological inhibition. We found that SG transport by OATP1B1 or murine Oatp1b2 was effectively inhibited by rifampin, and that this agent can significantly increase plasma levels of SG in wildtype mice, but not in Oatp1b2-deficient animals. In human subjects receiving sorafenib, rifampin acutely increased the systemic exposure to SG. Our study emphasizes the need to consider hepatic handling of xenobiotic glucuronides in the design of drug-drug interaction studies of agents that undergo extensive phase II conjugation.

Identification of OAT1/OAT3 as Contributors to Cisplatin Toxicity.

Cisplatin is among the most widely used anticancer drugs and known to cause a dose-limiting nephrotoxicity, which is partially dependent on the renal uptake carrier OCT2. We here report a previously unrecognized, OCT2-independent pathway of cisplatin-induced renal injury that is mediated by the organic anion transporters OAT1 and OAT3. Using transporter-deficient mouse models, we found that this mechanism regulates renal uptake of a mercapturic acid metabolite of cisplatin that acts as a precursor of a potent nephrotoxin. The function of these two transport systems can be simultaneously inhibited by the tyrosine kinase inhibitor nilotinib through noncompetitive mechanisms, without compromising the anticancer properties of cisplatin. Collectively, our findings reveal a novel pathway that explains the fundamental basis of cisplatin-induced nephrotoxicity, with potential implications for its therapeutic management.

Nonlinear pharmacokinetics of paclitaxel in mice results from the pharmaceutical vehicle Cremophor EL.

Studies in humans and mice have demonstrated a nonlinear pharmacokinetic behavior of paclitaxel. Because of its poor water solubility, the drug is formulated in a mixture of Cremophor EL and ethanol (1:1, v/v; Taxol). We hypothesized that the substantial amounts of concurrently administered Cremophor EL on the disposition of paclitaxel, female FVB mice received paclitazel by i.v. injection at does levels of 2, 10, and 20 mg/kg by appropriate (standard) dilution of the commercially available formulation of paclitaxel (Taxol) with saline. The drug was also given at 2 mg/kg with supplemental Cremophor EL-ethanol to achieve the same amount of vehicle as by standard administration of 10 mg/kg. Furthermore, paclitaxel formulations in Tween 80-ethanol (1:1, v/v) and dimethylacetamide were tested. Plasma samples were collected between 5 min and 48 h, and tissue specimens were sampled at 1, 4, and 8 h after drug administration. Paclitaxel and metabolites were quantified by high-performance liquid chromatography. Cremophor EL levels were determined by a novel high-performance liquid chromatography procedure. For comparative reasons, Cremophor EL was also assayed in plasma samples from three patients receiving a 3-h i.v. infusion of 175 mg/m2 of paclitaxel. A marked nonlinear pharmacokinetic behavior of paclitaxel was observed when the drug was formulated in Cremophor EL-ethanol. The clearance of 2.37 L/h/kg at 2 mg/kg was reduced to 0.33 and 0.15 L/h/kg at 10 and 20 mg/kg, respectively. When 2 mg/kg were given with an amount of Cremophor EL-ethanol matching that of the 10-mg/kg dose level, the clearance was 0.56 L/h/kg. If administered at 10 mg/kg in Tween 80-ethanol or at 2 and 10 mg/kg in dimethylacetamide, the clearances were 2.66, 2.57, and 2.62 L/h/kg, respectively. Despite the fact that much higher plasma levels of paclitaxel are reached when given in the Cremophor EL-ethanol formulation, the tissue levels were essentially similar with all tested drug preparations. The Cremophor EL levels in patients were in the same order of magnitude as those observed in mice after administration of 2 and 10 mg/kg. These data demonstrate that Cremophor EL has a profound effect on the pharmacokinetics of paclitaxel im mice. Because Cremophor EL also contributes substantially to the nonlinear pharmacokinetic behavior of paclitaxel observed in humans.

Cremophor EL-mediated alteration of paclitaxel distribution in human blood: clinical pharmacokinetic implications.

We have determined the in vitro and in vivo cellular distribution of the antineoplastic agent paclitaxel (Taxol) in human blood and the influence of Cremophor EL (CrEL), the vehicle used for i.v. drug administration. In the absence of CrEL, the blood:plasma concentration ratio was 1.07+/-0.004 (mean+/-SD). The addition of CrEL at concentrations corresponding to peak plasma levels achieved after the administration of paclitaxel (175 mg/m2 i.v. over a 3-h period; ie., 0.50%) resulted in a significant decrease in the concentration ratio (0.690+/-0.005; P < 0.05). Kinetic experiments revealed that this effect was caused by reduced erythrocyte uptake of paclitaxel by polyoxyethyleneglycerol triricinoleate, the major compound present in CrEL. Using equilibrium dialysis, it was shown that the affinity of paclitaxel for tested matrices was (in decreasing order) CrEL > plasma > human serum albumin, with CrEL present at or above the critical micellar concentration (approximately 0.01%). Our findings in the present study demonstrate a profound alteration of paclitaxel accumulation in erythrocytes caused by a trapping of the compound in CrEL micelles, thereby reducing the free drug fraction available for cellular partitioning. It is proposed that the nonlinearity of paclitaxel plasma disposition in patients reported previously should be reevaluated prospectively by measuring the free drug fractions and whole blood:plasma concentration ratios.

Drug Transporters: Advances and Opportunities.

Drug transporter research conducted over the last several decades has led to a greatly advanced understanding of the mechanisms underlying the principles of drug absorption and disposition. Although many transporters remain poorly characterized, there is ample evidence that the drug transporter field will ultimately provide vital support to routine patient management, and will play a key role in the discovery, development, and evaluation of innovative, cutting-edge therapies.

ABCC4 Is a Determinant of Cytarabine-Induced Cytotoxicity and Myelosuppression.

Resistance to cytarabine remains a major challenge in the treatment of acute myeloid leukemia (AML). Based on previous studies implicating ABCC4/MRP4 in the transport of nucleosides, we hypothesized that cytarabine is sensitive to ABCC4-mediated efflux, thereby decreasing its cytotoxic response against AML blasts. The uptake of cytarabine and its monophosphate metabolite was found to be facilitated in ABCC4-expressing vesicles and intracellular retention was significantly impaired by overexpression of human ABCC4 or mouse Abcc4 (P < 0.05). ABCC4 was expressed highly in AML primary blasts and cell lines, and cytotoxicity of cytarabine in cells was increased in the presence of the ABCC4 inhibitors MK571 or sorafenib, as well as after ABCC4 siRNA. In Abcc4-null mice, cytarabine-induced hematological toxicity was enhanced and ex vivo colony-forming assays showed that Abcc4-deficiency sensitized myeloid progenitors to cytarabine. Collectively, these studies demonstrate that ABCC4 plays a protective role against cytarabine-mediated insults in leukemic and host myeloid cells.

Inherited variation in OATP1B1 is associated with treatment outcome in acute myeloid leukemia.

Using broad interrogation of clinically relevant drug absorption, distribution, metabolism, and excretion (ADME) genes on the DMET platform, we identified a genetic variant in SLCO1B1 (rs2291075; c.597C>T), encoding the transporter OATP1B1, associated with event-free (P = 0.006, hazard ratio = 1.74) and overall survival (P = 0.012, hazard ratio = 1.85) in children with de novo acute myeloid leukemia (AML). Lack of SLCO1B1 expression in leukemic blasts suggested the association might be due to an inherited rather than a somatic effect. rs2291075 was in strong linkage with known functional variants rs2306283 (c.388A>G) and rs4149056 (c.521T>C). Functional studies in vitro determined that four AML-directed chemotherapeutics (cytarabine, daunorubicin, etoposide, and mitoxantrone) are substrates for OATP1B1 and the mouse ortholog Oatp1b2. In vivo pharmacokinetic studies using Oatp1b2-deficient mice further confirmed our results. Collectively, these findings demonstrate an important role for OATP1B1 in the systemic pharmacokinetics of multiple drugs used in the treatment of AML and suggest that inherited variability in host transporter function influences the effectiveness of therapy.

Mechanism-based pharmacokinetic model for paclitaxel.

PURPOSE: To create a model based on known mechanisms of paclitaxel distribution that could describe the pharmacokinetics (PK) of total and unbound plasma concentrations, as well as blood concentrations. In addition, to investigate the relationship between exposure, based on unbound and total concentrations, and neutropenia. PATIENTS AND METHODS: Paclitaxel and Cremophor EL (CrEL) concentrations were obtained from 23 female and three male patients (50 courses in total) with different cancer types that received paclitaxel (Taxol; Bristol-Myers Squibb Co, Princeton, NJ) (135 to 225 mg/m(2)) as 3- or 24-hour intravenous infusions. Seven of the patients received combination therapy with doxorubicin or cisplatin. The population PK model was built to fit three types of data simultaneously: unbound, total plasma, and blood concentrations. The area under the curve, threshold, and general models were used to relate neutrophil survival fraction from 19 patients (29 courses in total) to exposure based on unbound and total plasma concentration, respectively. RESULTS: The PK model included a linear three-compartment model for unbound concentration, binding directly proportional to CrEL, linear and nonlinear binding to plasma proteins, and linear and nonlinear binding to blood cells. The threshold model best described the PK/pharmacodynamic (PD) relationship for total concentration. No distinction could be made between the models for unbound drug. CONCLUSION: Earlier PK models for paclitaxel have been empirical. This study shows that a mechanistic model can be used to describe the nonlinear PK of paclitaxel. There is an indication that the PK/PD relationship is not the same for unbound and total plasma concentrations.

Phase I study of 3-week schedule of irinotecan combined with cisplatin in patients with advanced solid tumors.

PURPOSE: To assess the feasibility, pharmacokinetic interaction, and possible sequence-dependent effects of the irinotecan/cisplatin combination given every 3 weeks, and to assess the influence of additional granulocyte colony-stimulating factor (G-CSF) on the hematologic toxicity. PATIENTS AND METHODS: Patients who had received no more than one prior combination chemotherapy regimen or two single-agent regimens were entered. Treatment consisted of a 90-minute irinotecan infusion followed by a 3-hour cisplatin infusion on day 1, with cycles repeated once every 3 weeks. After the maximum-tolerated dose was determined, the sequence of administration was reversed. In a separate cohort of six patients, we assessed the effect of G-CSF on the experienced hematologic toxicity and dose-intensity. Irinotecan doses ranged from 175 to 300 mg/m(2) and cisplatin doses ranged from 60 to 80 mg/m(2). RESULTS: Fifty-two patients entered the study; one was not eligible, and two were not assessable for response. Twenty-five patients were pretreated, and 26 were not. Fifty-one patients received a total of 223 courses. The dose-limiting toxicity was a combination of neutropenic fever, diarrhea, and fatigue at a dose level combining irinotecan 300 mg/m(2) with cisplatin 80 mg/m(2). Neutropenia was common (grades 3 to 4, 68%). Irinotecan pharmacokinetics were linear over the dose range studied. No sequence-dependent side effects were observed. Tumor responses included three complete responses and eight partial responses. CONCLUSION: For phase II studies, we recommend irinotecan 260 mg/m(2) combined with cisplatin 80 mg/m(2) once every 3 weeks for chemotherapy-naive patients in good physical condition, and irinotecan 200 mg/m(2) combined with cisplatin 80 mg/m(2) for other patients.

Body-surface area-based dosing does not increase accuracy of predicting cisplatin exposure.

PURPOSE: Most anticancer drugs are dosed based on body-surface area (BSA) to reduce interindividual variability of drug effects. We evaluated the relevance of this concept for cisplatin by analyzing cisplatin pharmacokinetics obtained in prospective studies in a large patient population. PATIENTS AND METHODS: Data were obtained from 268 adult patients (163 males/105 females; median age, 54 years [range, 21 to 74 years]) with advanced solid tumors treated in phase I/II trials with cisplatin monotherapy or combination chemotherapy with etoposide, irinotecan, topotecan, or docetaxel. Cisplatin was administered either weekly (n = 93) or once every 3 weeks (n = 175) at dose levels of 50 to 100 mg/m(2) (3-hour infusion). Analysis of 485 complete courses was based on measurement of total and non-protein-bound cisplatin in plasma by atomic absorption spectrometry. RESULTS: No pharmacokinetic interaction was found between cisplatin and the anticancer drugs used in combination therapies. A linear correlation was observed between area under the curves of unbound and total cisplatin (r = 0.63). The mean plasma clearance of unbound cisplatin (CL(free)) was 57.1 +/- 14.7 L/h (range, 31.0 to 116 L/h), with an interpatient variability of 25.6%. BSA varied between 1.43 and 2.40 m(2) (mean, 1.86 +/- 0.19 m(2)), with an interpatient variability of 10.4%. When CL(free) was corrected for BSA, interindividual variability remained in the same order (23.6 v 25.6%). Only a weak correlation was found between CL(free) and BSA (r = 0.42). Intrapatient variability in CL(free), calculated from 90 patients was 12.1% +/- 7.8% (range, 0.30% to 32.7%). CONCLUSION: In view of the high interpatient variability in CL(free) relative to variation in observed BSA, no rationale for continuing BSA-based dosing was found. We recommend fixed-dosing regimens for cisplatin.

Phase I pharmacologic study of oral topotecan and intravenous cisplatin: sequence-dependent hematologic side effects.

PURPOSE: In in vitro studies, synergism and sequence-dependent effects were reported for the combination of topotecan and cisplatin. Recently, an oral formulation of topotecan became available. This phase I study was performed to assess the feasibility of the combination of oral topotecan and cisplatin, the pharmacokinetic interaction, and sequence-dependent effects. PATIENTS AND METHODS: Topotecan was administered orally (PO) daily for 5 days in escalating doses and cisplatin was given intravenously (IV) at a fixed dose of 75 mg/m(2) either before topotecan administration on day 1 (sequence CT) or after topotecan administration on day 5 (sequence TC) once every 3 weeks. Patients were treated in a randomized cross-over design. RESULTS: Forty-nine patients were entered onto the study; one patient was not eligible. Sequence CT induced significantly more severe myelosuppression than did sequence TC, and the maximum-tolerated dosage of topotecan in sequence CT was 1.25 mg/m(2)/d x 5. In sequence TC, the maximum-tolerated dosage of topotecan was 2.0 mg/m(2)/d x 5. Dose-limiting toxicity consisted of myelosuppression and diarrhea. Pharmacokinetics of topotecan and cisplatin were linear over the dose range studied; no sequence-dependent effects were observed. In addition, topotecan did not influence the protein binding of cisplatin or the platinum-DNA adduct formation in peripheral leukocytes in either sequence. CONCLUSION: The recommended dosages for phase II studies involving patients like the patients in our study are topotecan 1.25 mg/m(2)/d PO x 5 preceded by cisplatin 75 mg/m(2) IV day 1 once every 3 weeks, and topotecan 2.0 mg/m(2)/d PO followed by cisplatin 75 mg/m(2) IV day 5. No pharmacokinetic interaction could be discerned in our study. The antitumor efficacy of both schedules should be evaluated in a randomized phase II study.