Nielka P. van Erp

Clinical pharmacokinetics of tyrosine kinase inhibitors.

In the recent years, eight tyrosine kinase inhibitors (TKIs) have been approved for cancer treatment and numerous are under investigation. These drugs are rationally designed to target specific tyrosine kinases that are mutated and/or over-expressed in cancer tissues. Post marketing study commitments have been made upon (accelerated) approval such as additional pharmacokinetic studies in patients with renal- or hepatic impairment, in children, additional interactions studies and studies on the relative or absolute bioavailability. Therefore, much information will emerge on the pharmacokinetic behavior of these drugs after their approval. In the present manuscript, the pharmacokinetic characteristics; absorption, distribution, metabolism and excretion (ADME), of the available TKIs are reviewed. Results from additional studies on the effect of drug transporters and drug-drug interactions have been incorporated. Overall, the TKIs reach their maximum plasma levels relatively fast; have an unknown absolute bioavailability, are extensively distributed and highly protein bound. The drugs are primarily metabolized by cytochrome P450 (CYP) 3A4 with other CYP-enzymes playing a secondary role. They are predominantly excreted with the feces and only a minor fraction is eliminated with the urine. All TKIs appear to be transported by the efflux ATP binding-cassette transports B1 and G2. Additionally these drugs can inhibit some of their own metabolizing enzymes and transporters making steady-state metabolism and drug-drug interactions both complex and unpredictable. By understanding the pharmacokinetic profile of these drugs and their similarities, factors that influence drug exposure will be better recognized and this knowledge may be used to limit sub- or supra-therapeutic drug exposure.

Pharmacogenetic Pathway Analysis for Determination of Sunitinib-Induced Toxicity

PURPOSE To identify genetic markers in the pharmacokinetic and pharmacodynamic pathways of sunitinib that predispose for development of toxicities: thrombocytopenia, leukopenia, mucosal inflammation, hand-foot syndrome, and any toxicity according to National Cancer Institute Common Toxicity Criteria higher than grade 2. PATIENTS AND METHODS A multicenter pharmacogenetic association study was performed in 219 patients treated with single-agent sunitinib. A total of 31 single nucleotide polymorphisms in 12 candidate genes, together with several nongenetic variants, were analyzed for a possible association with toxicity. In addition, genetic haplotypes were developed and related to toxicity. RESULTS The risk for leukopenia was increased when the G allele in CYP1A1 2455A/G (odds ratio [OR], 6.24; P = .029) or the T allele in FLT3 738T/C (OR, 2.8; P = .008) were present or CAG in the NR1I3 (5719C/T, 7738A/C, 7837T/G) haplotype (OR, 1.74; P = .041) was absent. Any toxicity higher than grade 2 prevalence was increased when the T allele of vascular endothelial growth factor receptor 2 1191C/T (OR, 2.39; P = .046) or a copy of TT in the ABCG2 (-15622C/T, 1143C/T) haplotype (OR, 2.63; P = .016) were present. The risk for mucosal inflammation was increased in the presence of the G allele in CYP1A1 2455A/G (OR, 4.03; P = .021) and the prevalence of hand-foot syndrome was increased when a copy of TTT in the ABCB1 (3435C/T, 1236C/T, 2677G/T) haplotype (OR, 2.56; P = .035) was present. CONCLUSION This exploratory study suggests that polymorphisms in specific genes encoding for metabolizing enzymes, efflux transporters, and drug targets are associated with sunitinib-related toxicities. A better understanding of genetic and nongenetic determinants of sunitinib toxicity should help to optimize drug treatment in individual patients.

Sunitinib in Refractory Adrenocortical Carcinoma: A Phase II, Single-Arm, Open-Label Trial

CONTEXT Treatment of refractory adrenocortical carcinoma (ACC) is not established. Animal experiments pointed toward adrenal toxicity of sunitinib. OBJECTIVE The objective of the study was to determine the antitumor effects of sunitinib in refractory ACC. DESIGN This was a phase II, open-label trial using a two-stage accrual design. SETTING The study was conducted at two tertiary referral centers. PATIENTS Thirty-eight patients with refractory ACC progressing after mitotane and one to three cytotoxic chemotherapies participated in the study. INTERVENTION The intervention included sunitinib at a standard dose (50 mg/d, 4 wk on, 2 wk off). MAIN OUTCOME MEASURE Response was defined as progression-free survival (PFS) of 12 wk or longer (first tumor evaluation). RESULTS Thirty-five patients could be evaluated for response. Five patients experienced stable disease, 24 had progressive disease, and six patients died from ACC before the first evaluation (naïve estimate five of 35=14.3%, median unbiased response rate 15.4%, 95% confidence interval 5.0-33.4%). The median PFS was 2.8 months. In responders, PFS ranged between 5.6 and 11.2 months and overall survival between 14.0 and 35.5 months. Of 36 serious adverse events, only nine were possibly related to sunitinib. Concomitant mitotane appeared to negatively impact on outcome. Furthermore, a negative correlation between the serum concentrations of sunitinib plus its active metabolite N-desethylsunitinib (SU12662) and mitotane (r=-0.650; P=0.114) was observed in seven evaluable patients suggestive of a relevant drug interaction. CONCLUSION Sunitinib has modest activity in advanced refractory ACC, which compares favorably with other targeted treatments in these patients. Sunitinib serum levels might have been profoundly reduced by mitotane induced cytochrome P450-3A4 activity attenuating its antitumor activity and adverse effects. Together these findings suggest that sunitinib deserves further investigation in mitotane-naïve ACC patients.

Mitotane has a strong and a durable inducing effect on CYP3A4 activity.

OBJECTIVE The effects of mitotane on the pharmacokinetics (PK) of co-administered drugs are mostly unknown. The aim of the present study was to describe the effects of mitotane on the PK of the phenotypic probe midazolam and of the tyrosine kinase inhibitor sunitinib. DESIGN A serendipitous observation was made in two of nine patients who volunteered in a sunitinib pharmacokinetic study. Both patients were diagnosed with adrenocortical carcinoma (ACC) and were exposed to mitotane. The sunitinib PK study was designed to determine the relationship between CYP3A4 activity and sunitinib exposure using 7.5 mg midazolam orally as a phenotypic probe. Patient and methods Serial blood samples for PK analysis of midazolam, 1-hydroxy-midazolam, and sunitinib were collected at steady-state sunitinib PK (between days 14 and 20). To confirm this observation in the mitotane-exposed patients, midazolam PK was evaluated in two additional patients with ACC and mitotane treatment. RESULTS The four mitotane-treated patients showed highly induced CYP3A4 activity, even after interrupting mitotane therapy months before study entry, reflected by decreased midazolam exposure compared with the other seven patients (mean AUC(0)(-)(12 h) (95% CI): 7.6 (5.5-9.7) vs 139.0 (95.1-182.9) μg×h/l respectively P=0.001) and increased 1-hydroxy-midazolam exposure (mean AUC(0)(-)(12 h) (95% CI): 409.6 (290.5-528.7) vs 35.0 (26.4-43.6) μg×h/l, P=0.008). Sunitinib exposure was decreased in the two patients who were co-treated with mitotane (267 and 268 μg×h/l versus 1344 (1079-1609) (mean (95% CI)) μg×h/l). CONCLUSION Mitotane has a strong and long-lasting inducing effect on CYP3A4 activity, which will result in clinically relevant interactions with multiple drugs since many drugs are metabolized by this enzyme.

Mammalian target of rapamycin inhibitor-associated stomatitis

With the recent introduction of inhibitors of mammalian target of rapamycin (mTOR) in oncology, distinct cutaneous and oral adverse events have been identified. In fact, stomatitis and rash are documented as the most frequent and potentially dose-limiting side effects. Clinically, mTOR inhibitor-associated stomatitis (mIAS) more closely resembles aphthous stomatitis than oral mucositis due to conventional anticancer therapies. While most cases of mIAS are mild to moderate and self-limiting, more severe and persistent mIAS can become a dose-limiting toxicity. Small ulcerations may cause significant pain and mucosal sensitivity may occur in the absence of clinical changes. Use of clinical assessment tools that are primarily driven by ulceration size may underestimate mIAS, and assessment should include patient-reported outcomes. This article provides an up-to-date review of the clinical presentation, terminology, pathogenesis, assessment and management of mIAS and other mTOR inhibitor-associated oral adverse events. In addition, areas of future research are considered.

Individualized dosing of tyrosine kinase inhibitors: are we there yet?

Tyrosine kinase inhibitors (TKIs) are registered at a fixed oral dose, despite their large variability in pharmacokinetics (PK). Given that the evidence for a relation between drug exposure and treatment outcome is growing, this one-dose-fits-all approach can unintentionally lead to under- and overexposure. Dose individualization could lower this variability and thereby beneficially effect treatment outcome. In this article, we explore whether TKIs used for solid tumors meet the criteria for dose individualization. Despite limitations such as retrospective analysis, current data suggest that the following Ctrough levels could be used: imatinib 1100ng/ml, sunitinib when continuously dosed 37.5ng/ml, intermittent 50ng/ml and pazopanib 20μg/ml. A comprehensive review of the literature also shows that prospective trials investigating the influence of dose individualization on treatment outcome are warranted.

A validated assay for the simultaneous quantification of six tyrosine kinase inhibitors and two active metabolites in human serum using liquid chromatography coupled with tandem mass spectrometry

A sensitive, sophisticated and practical bioanalytical assay for the simultaneous determination of six tyrosine kinase inhibitors (imatinib, sunitinib, nilotinib, dasatinib, pazopanib, regorafenib) and two active metabolites (N-desmethyl imatinib and N-desethyl sunitinib) was developed and validated. For the quantitative assay, a mixture of three stable isotopes as internal standards was added to human serum, standards and controls. Thereafter, samples were pre-treated using protein precipitation with methanol. The supernatant was diluted with water and injected into an ultra pressure liquid chromatographic system with an Acquity TQ tandem mass spectrometry detector. The compounds were separated on an Acquity BEH C18 analytical column (100mm×2.1mm ID, 1.7μm particle size) and eluted with a linear gradient system. The ions were detected in the multiple reaction monitoring mode. The lower limit of quantification and the linearity of all compounds generously met with the concentrations that are to be expected in clinical practice. The developed bioanalytical assay can be used for guiding TKI therapy in daily clinical practice as well as for investigator-initiated research.

mTOR inhibitor-induced interstitial lung disease in cancer patients: Comprehensive review and a practical management algorithm

Mammalian target of rapamycin inhibitors (mTORi) have clinically significant activity against various malignancies, such as renal cell carcinoma and breast cancer, but their use can be complicated by several toxicities. Interstitial lung disease (ILD) is an adverse event of particular importance. Mostly, mTORi‐induced ILD remains asymptomatic or mildly symptomatic, but it can also lead to severe morbidity and even mortality. Therefore, careful diagnosis and management of ILD is warranted. The reported incidence of mTORi‐induced ILD varies widely because of a lack of uniform diagnostic criteria and active surveillance. Because of the nonspecific clinical features, a broad differential diagnosis that includes (opportunistic) infections should be considered in case of suspicion of mTORi‐induced ILD. The exact mechanism or interplay of mechanisms leading to the development of ILD remains to be defined. Suggested mechanisms are either a direct toxic effect or immune‐mediated mechanisms, considering mTOR inhibitors have several effects on the immune system. The clinical course of ILD varies widely and is difficult to predict. Consequently, the discrimination between when mTOR inhibitors can be continued safely and when discontinuation is indicated is challenging. In this review, we give a comprehensive review of the incidence, clinical presentation and pathophysiology of mTORi‐induced ILD in cancer patients. We present newly developed diagnostic criteria for ILD, which include clinical symptoms as well as basic pulmonary function tests and radiological abnormalities. In conjunction with these diagnostic criteria, we provide a detailed and easily applicable clinical management algorithm.

Therapeutic drug monitoring to individualize the dosing of pazopanib: a pharmacokinetic feasibility study

Background: Patients treated with the standard dose of pazopanib show a large interpatient variability in drug exposure defined as the area under the plasma concentration–time curve (AUC0–24h). The primary objective of this study was to evaluate the feasibility of pharmacokinetics (PK)-guided individualized dosing to reduce the interpatient variability in pazopanib exposure. Methods: Thirteen patients were treated with pazopanib for 3 consecutive periods of 2 weeks. During the first period, all patients received 800 mg of pazopanib once daily to reach steady-state exposure. During the second period, the patients either received a PK-guided individualized pazopanib dose or the registered fixed 800-mg dose. During the third period, these 2 dosing regimens were switched. Results: The interpatient variability in pazopanib AUC0–24h during fixed dosing (27.3 coefficient of variation) was not significantly different when compared with the variability in AUC0–24h during PK-guided dosing (24.8 coefficient of variation). The percentage of patients within the target window during PK-guided dosing (53.9%) was not significantly different from the percentage during fixed dosing (46.2%). Both Ctrough and C24 were significantly (P < 0.001) correlated to pazopanib AUC0–24h (R2 = 0.596 and R2 = 0.940, respectively). Pazopanib AUC0–24h decreased 17% over time. Conclusions: PK-guided dosing did not reduce the interpatient variability in pazopanib exposure. In this study, the intrapatient variability in pazopanib exposure was relatively large compared with interpatient variability. This makes it challenging to achieve a target exposure within a predefined window. The causes of intrapatient variability must first be better understood and controlled, before PK-guided dosing can reduce the interpatient variability.

Effect of Cigarette Smoking on Imatinib in Patients in the Soft Tissue and Bone Sarcoma Group of the EORTC

Purpose: Smoking is a potent inducer of cytochrome P450 (CYP) 1A2 and may affect the pharmacokinetics of CYP1A2 metabolized drugs. The effect of smoking on the pharmacokinetics of imatinib, which is metabolized by CYP3A4 and partly by CYP1A2, is unknown. We studied the effect of smoking on imatinib pharmacokinetics, safety, and efficacy. Experimental Design: Imatinib pharmacokinetics, safety, and efficacy was analyzed in 45 patients with gastrointestinal stromal tumors (GIST) or soft-tissue sarcoma included in two European Organisation for Research and Treatment of Cancer Soft Tissue and Bone Sarcoma Group trials, including 15 smokers and 30 nonsmokers. Apparent oral clearance, distribution volume, elimination half-life, and dose-standardized area under the concentration curve (AUC) were assessed in 34 patients using nonlinear mixed-effect modeling. Results: Mean ± SD pharmacokinetic variables in smokers (n = 9) versus nonsmokers (n = 25) groups were 9.6 ± 5.5 versus 9.2 ± 4.6 L/h (apparent oral clearance), 216.5 ± 114.3 versus 207.0 ± 116.9 L (distribution volume), 16.1 ± 6.0 versus 16.5 ± 6.0 h (elimination half-life), and 133.6 ± 71.0 versus 142.3 ± 84.0 ng h/mL mg area under the concentration curve; P > 0.05. Smokers experienced more grade 2/3 anemia (P = 0.010) and fatigue (P = 0.011) and those with GIST had a significantly shorter overall survival (P = 0.037) and time to progression (P = 0.052). Conclusions: This retrospective study suggests that the pharmacokinetics of imatinib is not affected by smoking. However, smokers have an increased risk of anemia and fatigue. Smokers with GIST have a shorter overall survival and time to progression.