P. de Bruijn

Conjunctive Therapy of Cisplatin With the OCT2 Inhibitor Cimetidine: Influence on Antitumor Efficacy and Systemic Clearance

The organic cation transporter 2 (OCT2) regulates uptake of cisplatin in proximal tubules, and inhibition of OCT2 protects against severe cisplatin‐induced nephrotoxicity. However, it remains uncertain whether potent OCT2 inhibitors, such as cimetidine, can influence the antitumor properties and/or disposition of cisplatin. Using an array of preclinical assays, we found that cimetidine had no effect on the uptake and cytotoxicity of cisplatin in ovarian cancer cells with high OCT2 mRNA levels (IGROV‐1 cells). Moreover, the antitumor efficacy of cisplatin in mice bearing luciferase‐tagged IGROV‐1 xenografts was unaffected by cimetidine (P = 0.39). Data obtained in 18 patients receiving cisplatin (100 mg/m2) in a randomized crossover fashion with or without cimetidine (800 mg × 2) revealed that cimetidine did not alter exposure to unbound cisplatin, a marker of antitumor efficacy (4.37 vs. 4.38 µg·h/ml; P = 0.86). These results support the future clinical exploration of OCT2 inhibitors as specific modifiers of cisplatin‐induced nephrotoxicity.

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.

Differential modulation of cisplatin accumulation in leukocytes and tumor cell lines by the paclitaxel vehicle Cremophor EL

BACKGROUND Several clinical studies have shown that polychemotherapy with the taxanes paclitaxel or docetaxel preceded or followed by cisplatin is associated with important schedule-dependent differences in toxicities, such as leukocytopenia. In general, the pharmacokinetics of both drugs during the combined treatment are unaltered, suggesting that a pharmacodynamic interaction might have occurred. MATERIALS AND METHODS In order to gain insight into this pharmacologic interaction, we performed in vitro drug accumulation studies using peripheral blood leukocytes and a panel of tumor and non-malignant cell lines with paclitaxel and docetaxel, as well as with their respective formulation vehicles Cremophor EL and Tween 80. RESULTS Our results show a significant reduction in the intracellular cisplatin concentration in leukocytes of up to 42% in the presence of Cremophor EL and Tween 80 as compared to the control. This pharmacodynamic interaction of these surfactants with cisplatin seems to be specific for haematopoietic cells, and does not occur in solid tumor cells. CONCLUSION The present data suggest that the pharmaceutical vehicles Cremophor EL and Tween 80 might contribute to the reduced cisplatin-associated myelotoxicity observed in the clinical combination chemotherapy studies with paclitaxel and docetaxel.

Irinotecan pharmacokinetics-pharmacodynamics: the clinical relevance of prolonged exposure to SN-38

We have shown previously that the terminal disposition half-life of SN-38, the active metabolite of irinotecan, is much longer than earlier thought. Currently, it is not known whether this prolonged exposure has any relevance toward SN-38-induced toxicity. Here, we found that SN-38 concentrations present in human plasma for up to 3 weeks after a single irinotecan infusion induce significant cytotoxicity in vitro. Using pharmacokinetic data from 26 patients, with sampling up to 500 h, relationships were evaluated between systemic exposure (AUC) to SN-38 and the per cent decrease in absolute neutrophil count (ANC) at nadir, or by taking the entire time course of ANC into account (AOC). The time course of SN-38 concentrations (AUC500 h) was significantly related to this AOC (P<0.001). Based on these findings, a new limited-sampling model was developed for SN-38 AUC500 h using only two timed samples: AUC500 h=(6.588×C2.5 h)+(146.4×C49.5 h)+15.53, where C2.5 h and C49.5 h are plasma concentrations at 2.5 and 49.5 h after start of infusion, respectively. The use of this limited-sampling model may open up historic databases to retrospectively obtain information about SN-38-induced toxicity in patients treated with irinotecan.

Phase I and pharmacokinetic study of irinotecan in combination with R115777, a farnesyl protein transferase inhibitor.

The aims of this study were to determine the maximum-tolerated dose (MTD), toxicity profile, and pharmacokinetics of irinotecan given with oral R115777 (tipifarnib), a farnesyl protein transferase inhibitor. Patients were treated with escalating doses of irinotecan with interval-modulated dosing of R115777 (continuously or on days 1–14, and repeated every 21 days). In total, 35 patients were entered onto the trial for a median duration of treatment of 43 days (range, 5–224 days). Neutropenia and thrombocytopenia were the dose-limiting toxicities; other side effects were mostly mild. The MTD was established at R115777 300 mg b.i.d. for 14 consecutive days with irinotecan 350 mg m−2 given every 3 weeks starting on day 1. Three patients had a partial response and 14 had stable disease. In the continuous schedule, the area under the curves of irinotecan and its active metabolite SN-38 were 20.0% (P=0.004) and 38.0% (P<0.001) increased by R115777, respectively. Intermittent dosing of R115777 at a dose of 300 mg b.i.d. for 14 days every 3 weeks is the recommended dose of R115777 in combination with the recommended single-agent irinotecan dose of 350 mg m−2.

Pazopanib exposure decreases as a result of an ifosfamide-dependent drug–drug interaction: results of a phase I study

Background:The vascular endothelial growth factor receptor (VEGFR) pathway plays a pivotal role in solid malignancies and is probably involved in chemotherapy resistance. Pazopanib, inhibitor of, among other receptors, VEGFR1–3, has activity as single agent and is attractive to enhance anti-tumour activity of chemotherapy. We conducted a dose-finding and pharmacokinetic (PK)/pharmacodynamics study of pazopanib combined with two different schedules of ifosfamide.Methods:In a 3+3+3 design, patients with advanced solid tumours received escalating doses of oral pazopanib combined with ifosfamide either given 3 days continuously or given 3-h bolus infusion daily for 3 days (9 g m−2 per cycle, every 3 weeks). Pharmacokinetic data of ifosfamide and pazopanib were obtained. Plasma levels of placental-derived growth factor (PlGF), vascular endothelial growth factor-A (VEGF-A), soluble VEGFR2 (sVEGFR2) and circulating endothelial cells were monitored as biomarkers.Results:Sixty-one patients were included. Pazopanib with continuous ifosfamide infusion appeared to be safe up to 1000 mg per day, while combination with bolus infusion ifosfamide turned out to be too toxic based on a variety of adverse events. Ifosfamide-dependent decline in pazopanib exposure was observed. Increases in PlGF and VEGF-A with concurrent decline in sVEGFR2 levels, consistent with pazopanib-mediated VEGFR2 inhibition, were observed after addition of ifosfamide.Conclusion:Continuous as opposed to bolus infusion ifosfamide can safely be combined with pazopanib. Ifosfamide co-administration results in lower exposure to pazopanib, not hindering biological effects of pazopanib. Recommended dose of pazopanib for further studies combined with 3 days continuous ifosfamide (9 g m−2 per cycle, every 3 weeks) is 800 mg daily.

Influence of OATP1B1 Function on the Disposition of Sorafenib‐β‐D‐Glucuronide

The oral multikinase inhibitor sorafenib undergoes extensive UGT1A9‐mediated formation of sorafenib‐β‐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.

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.<mean clearance) was identified in 80% of cases. These models however did not reach statistical significance. To improve the predictive value of these models, the addition of non-genetic influencing factors is needed.

Abstract 4627: Fasting reduces the systemic exposure to irinotecan and its active metabolite SN-38

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Limitations to the use of chemotherapeutic agents are the often severe adverse side-effects which may lead to early discontinuation of treatment. Most anticancer agents have a narrow therapeutic index. In previous work we have shown that 72 hours of fasting prior to treatment with a high dose of irinotecan prevents the occurrence of adverse side effects in C26 colon carcinoma bearing mice, while the antitumor activity is not abrogated. To elucidate the mechanism of fasting induced resistance against adverse side effects, we have examined the pharmacokinetics of irinotecan in 72 hours fasted mice in plasma and liver. Male BALB/c mice were divided into four groups (n=18/group). Two groups were fasted for 72 hours and two groups were fed ad libitum. After the fasting period, mice were fed ad libitum again. One group of ad libitum and fasted animals was treated with 50 mg/kg and the other with 100 mg/kg irinotecan intraperitoneally. Plasma and liver were collected at 1,4,8,12,24 and 48 hours after irinotecan injection. Tissues were homogenized in lithium heparinized plasma and concentrations of irinotecan (CPT-11) and the active metabolite SN-38 were determined using a validated reversed-phase high-performance liquid chromatography (HPLC) system with fluorescence detection. Pharmacokinetic parameters, including peak concentration, area under the plasma concentration-time curve (AUC), clearance (CL), and the half-life of the terminal disposition phase were calculated. In the fasted group, plasma levels of SN-38 in the 50 mg/kg and 100 mg/kg group showed a 57% and 53% reduction, respectively, compared with ad libitum fed controls (AUC0-inf 5,149 vs. 2,242 ng*h/mL and 7,507 vs. 3,562 ng*h/mL). For CPT-11 the effects of fasting were smaller. An increase of 26% in the 50 mg/kg group and a reduction of 15% in the 100 mg/kg group were observed (AUC0-inf 9,715 vs. 12,235 and 37,360 vs. 31,924 ng*h/mL). In the liver, SN-38 levels in the 50 mg/kg and 100 mg/kg group showed a reduction of 51% and 30%, respectively, in the fasted animals (AUC0-inf 85.4 vs. 41.5 µg*h/g and 126 vs. 87.6 µg*h/g), while CPT-11 levels were reduced with 19% in the 50 mg/kg group and 28% in the 100 mg/kg group (AUC0-inf 218 vs. 177 µg*h/g and 712 vs. 512 µg*h/mg). Our data demonstrate that 72 hours of fasting prior to irinotecan administration induces an important change in its metabolism. Plasma and liver levels of the pro-drug CPT-11 were only slightly reduced in fasted animals. Levels of the active metabolite SN-38 were considerably lower in fasted animals compared to ad libitum fed animals. These data suggest that the reduction of side effects by fasting is due to the lower systemic exposure to SN-38, and may have important clinical implications if also found in humans. Citation Format: Sander A. Huisman, P de Bruijn, I.M. Ghobadi Moghaddam-Helmantel, J.N.M. IJzermans, E Wiemer, A.H.J. Mathijssen, R.W.F. de Bruin. Fasting reduces the systemic exposure to irinotecan and its active metabolite SN-38. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4627. doi:10.1158/1538-7445.AM2014-4627

1595PTHE PROTECTIVE EFFECTS OF FASTING ON IRINOTECAN INDUCED SIDE EFFECTS; A PHARMACOKINETIC STUDY

Aim: Limitations to the use of chemotherapeutic agents are the often severe side-effects which may lead to early discontinuation of treatment. In previous work we have shown that 3 days of fasting prior to treatment with a high dose of irinotecan prevents the occurrence of side-effects in C26 colon carcinoma bearing mice, while the antitumor activity is not abrogated. To elucidate the mechanism of fasting induced resistance against adverse side effects, we have examined the pharmacokinetics of irinotecan in both fasted and ad libitum fed mice in plasma, liver and tumor. Methods: Tumor bearing BALB/c mice were divided into three groups (n=18/group). Two groups were fasted for 3 days and one group was fed ad libitum. The ad libitum fed group and one group of fasted animals were treated with 100 mg/kg irinotecan. The other fasted group received a flat dose (i.e., the same dose as ad libitum fed mice). Plasma, liver-, and tumor tissue were collected at 1,4,8,12 and 24 hours after injection. Tissues were homogenized and concentrations of irinotecan and its active metabolite SN-38 were determined using a validated reversed-phase high-performance liquid chromatography (HPLC) system.