Marginal increase of sunitinib exposure by grapefruit juice

Tyrosine kinase inhibitors in cancers: Treatment optimization - Part II

Real-life populations are more heterogeneous than those included in prospective clinical studies. In cancer patients, comorbidities and co-medications favor the appearance of severe adverse effects which can significantly impact quality of life and treatment effectiveness. Most of tyrosine kinase inhibitors (TKI) have been developed with flat oral dosing exposing patients to the risk of poor adherence due to side effects. Additionally, genetic or physiological factors, differences in diet, and drug-drug interactions can lead to inter-individual variability affecting treatment outcomes and increasing the risk of adverse events. Knowledge of the different factors of variability allows individualized patient management. This review examines the effects of adherence, food intake, and pharmaceutical form on the pharmacokinetics of oral TKI, as well as evaluating pharmacokinetics considerations improving TKI management. Concentration-effectiveness and concentration-toxicity data are presented for the selected TKI, and a simple therapeutic drug monitoring schema is outlined to help individualize dosing of oral TKI.

Interactions between natural products and cancer treatments: underlying mechanisms and clinical importance

Natural products, also referred to as dietary supplements, complementary and alternative medicines, and health or food supplements are widely used by people living with cancer. These products are predominantly self-selected and taken concurrently with cancer treatments with the intention of improving quality of life, immune function and reducing cancer symptoms and treatment side effects. Concerns have been raised that concurrent use may lead to interactions resulting in adverse effects and unintended treatment outcomes. This review provides an overview of the mechanisms by which these interactions can occur and the current evidence about specific clinically important natural product-drug interactions. Clinical studies investigating pharmacokinetic interactions provide evidence that negative treatment outcomes may occur when Hypericum perforatum, Grapefruit, Schisandra sphenanthera, Curcuma longa or Hydrastis canadensis are taken concurrently with common cancer treatments. Conversely, pharmacodynamic interactions between Hangeshashinto (TJ-14) and some cancer treatments have been shown to reduce the side effects of diarrhoea and oral mucositis. In summary, research in this area is limited and requires further investigation.

Dose Individualization of Oral Multi-Kinase Inhibitors for the Implementation of Therapeutic Drug Monitoring

Oral multi-kinase inhibitors have transformed the treatment landscape for various cancer types and provided significant improvements in clinical outcomes. These agents are mainly approved at fixed doses, but the large inter-individual variability in pharmacokinetics and pharmacodynamics (efficacy and safety) has been an unsolved clinical issue. For example, certain patients treated with oral multi-kinase inhibitors at standard doses have severe adverse effects and require dose reduction and discontinuation, yet other patients have a suboptimal response to these drugs. Consequently, optimizing the dosing of oral multi-kinase inhibitors is important to prevent over-dosing or under-dosing. To date, multiple studies on the exposure-efficacy/toxicity relationship of molecular targeted therapy have been attempted for the implementation of therapeutic drug monitoring (TDM) strategies. In this milieu, we recently conducted research on several multi-kinase inhibitors, such as sunitinib, pazopanib, sorafenib, and lenvatinib, with the aim to optimize their treatment efficacy using a pharmacokinetic/pharmacodynamic approach. Among them, sunitinib use is an example of successful TDM implementation. Sunitinib demonstrated a significant correlation between drug exposure and treatment efficacy or toxicities. As a result, TDM services for sunitinib has been covered by the National Health Insurance program in Japan since April 2018. Additionally, other multi-kinase targeted anticancer drugs have promising data regarding the exposure-efficacy/toxicity relationship, suggesting the possibility of personalization of drug dosage. In this review, we provide a comprehensive summary of the clinical evidence for dose individualization of multi-kinase inhibitors and discuss the utility of TDM of multi-kinase inhibitors, especially sunitinib, pazopanib, sorafenib, and lenvatinib.

A Review of CYP3A Drug-Drug Interaction Studies: Practical Guidelines for Patients Using Targeted Oral Anticancer Drugs

Many oral anticancer drugs are metabolized by CYP3A. Clinical drug-drug interaction (DDI) studies often only examine the effect of strong CYP3A inhibitors and inducers. The effect of moderate or weak inhibitors or inducers can be examined using physiologically based pharmacokinetic simulations, but data from these simulations are not always available early after approval of a drug. In this review we provide recommendations for clinical practice on how to deal with DDIs of oral anticancer drugs if only data from strong CYP3A inhibitors or inducers is available. These recommendations were based on reviewed data of oral anticancer drugs primarily metabolized by CYP3A and approved for the treatment of solid tumors from January 1st, 2013 to December 31st, 2015. In addition, three drugs that were registered before the new EMA guideline was issued (i.e., everolimus, imatinib, and sunitinib), were reviewed. DDIs are often complex, but if no data is available from moderate CYP3A inhibitors/inducers, a change in exposure of 50% compared with strong inhibitors/inducers can be assumed. No a priori dose adaptations are indicated for weak inhibitors/inducers, because their interacting effect is small. In case pharmacologically active metabolites are involved, the metabolic pathway, the ratio of the parent to the metabolites, and the potency of the metabolites should be taken into account.

Potential Cytochrome P450-mediated pharmacokinetic interactions between herbs, food, and dietary supplements and cancer treatments

Herbs, food and dietary supplements (HFDS), can interact significantly with anticancer drug treatments via cytochrome p450 isoforms (CYP) CYP3A4, CYP2D6, CYP1A2, and CYP2C8. The objective of this review was to assess the influence of HFDS compounds on these cytochromes. Interactions with CYP activities were searched for 189 herbs and food products, 72 dietary supplements in Web of Knowledge® databases. Analyses were made from 140 of 3,125 clinical trials and 236 of 3,374 in vitro, animal model studies or case reports. 18 trials were found to report direct interactions between 9 HFDS with 8 anticancer drugs. 21 HFDS were found to interact with CYP3A4, a major metabolic pathway for many anticancer drugs. All 261 HFDS were classified for their interaction with the main cytochromes P450 involved in the metabolism of anticancer drugs. We provided an easy-to-use colour-coded table to easily match potential interactions between 261 HFDS and 117 anticancer drugs.

Clinical implications of food-drug interactions with small-molecule kinase inhibitors

During the past two decades, small-molecule kinase inhibitors have proven to be valuable in the treatment of solid and haematological tumours. However, because of their oral administration, the intrapatient and interpatient exposure to small-molecule kinase inhibitors (SMKIs) is highly variable and is affected by many factors, such as concomitant use of food and herbs. Food-drug interactions are capable of altering the systemic bioavailability and pharmacokinetics of these drugs. The most important mechanisms underlying food-drug interactions are gastrointestinal drug absorption and hepatic metabolism through cytochrome P450 isoenzymes. As food-drug interactions can lead to therapy failure or severe toxicity, knowledge of these interactions is essential. This Review provides a comprehensive overview of published studies involving food-drug interactions and herb-drug interactions for all registered SMKIs up to Oct 1, 2019. We critically discuss US Food and Drug Administration (FDA) and European Medicines Agency (EMA) guidelines concerning food-drug interactions and offer clear recommendations for their management in clinical practice.

Imatinib, sunitinib and pazopanib: From flat-fixed dosing towards a pharmacokinetically guided personalized dose

Tyrosine kinase inhibitors (TKIs) are anti‐cancer drugs that target tyrosine kinases, enzymes that are involved in multiple cellular processes. Currently, multiple oral TKIs have been introduced in the treatment of solid tumours, all administered in a fixed dose, although large interpatient pharmacokinetic (PK) variability is described. For imatinib, sunitinib and pazopanib exposure‐treatment outcome (efficacy and toxicity) relationships have been established and therapeutic windows have been defined, therefore dose optimization based on the measured blood concentration, called therapeutic drug monitoring (TDM), can be valuable in increasing efficacy and reducing the toxicity of these drugs.

In this review, an overview of the current knowledge on TDM guided individualized dosing of imatinib, sunitinib and pazopanib for the treatment of solid tumours is presented. We summarize preclinical and clinical data that have defined thresholds for efficacy and toxicity. Furthermore, PK models and factors that influence the PK of these drugs which partly explain the interpatient PK variability are summarized. Finally, pharmacological interventions that have been performed to optimize plasma concentrations are described. Based on current literature, we advise which methods should be used to optimize exposure to imatinib, sunitinib and pazopanib.

Pharmacogenetic-Based Interactions between Nutraceuticals and Angiogenesis Inhibitors

Background: Angiogenesis inhibitors (AIs) have become established as an effective cancer treatment. Whereas their interactions with antineoplastic drugs have extensively been investigated, little is known of the effect of their co-administration with nutraceuticals/dietary supplements (N/DSs), which are often self-prescribed. N/DSs comprise a wide range of products such as herbs, nutrients, vitamins, minerals, and probiotics. Assessment of their interactions with cancer drugs, particularly AIs, is hampered by the difficulty of gauging the amount of active substances patients actually take. Moreover, there is no agreement on which approach should be used to determine which N/DSs are most likely to influence AI treatment efficacy. We present a comprehensive review of the metabolic routes of the major AIs and their possible interactions with N/DSs. Methods: The PubMed and Cochrane databases were searched for papers describing the metabolic routes of the main AIs and N/DSs. Results: Data from the 133 studies thus identified were used to compile a diagnostic table reporting known and expected AI-N/DS interactions based on their metabolization pathways. AIs and N/DSs sharing the cytochrome P450 pathway are at risk of negative interactions. Conclusions: Recent advances in pharmacogenetics offer exceptional opportunities to identify prognostic and predictive markers to enhance the efficacy of individualized AI treatments. The table provides a guide to genotyping patients who are due to receive AIs and is a promising tool to prevent occult AI-N/DS interactions in poor metabolizers. N/DS use by cancer patients receiving AIs is a topical problem requiring urgent attention from the scientific community.

Clinically relevant drug interactions with multikinase inhibitors: a review

Multikinase inhibitors (MKIs), including the tyrosine kinase inhibitors (TKIs), have rapidly become an established factor in daily (hemato)-oncology practice. Although the oral route of administration offers improved flexibility and convenience for the patient, challenges arise in the use of MKIs. As MKIs are prescribed extensively, patients are at increased risk for (severe) drug–drug interactions (DDIs). As a result of these DDIs, plasma pharmacokinetics of MKIs may vary significantly, thereby leading to high interpatient variability and subsequent risk for increased toxicity or a diminished therapeutic outcome. Most clinically relevant DDIs with MKIs concern altered absorption and metabolism. The absorption of MKIs may be decreased by concomitant use of gastric acid-suppressive agents (e.g. proton pump inhibitors) as many kinase inhibitors show pH-dependent solubility. In addition, DDIs concerning drug (uptake and efflux) transporters may be of significant clinical relevance during MKI therapy. Furthermore, since many MKIs are substrates for cytochrome P450 isoenzymes (CYPs), induction or inhibition with strong CYP inhibitors or inducers may lead to significant alterations in MKI exposure. In conclusion, DDIs are of major concern during MKI therapy and need to be monitored closely in clinical practice. Based on the current knowledge and available literature, practical recommendations for management of these DDIs in clinical practice are presented in this review.

Pharmacological Utilization of Bergamottin, Derived from Grapefruits, in Cancer Prevention and Therapy

Cancer still remains one of the leading causes of death worldwide. In spite of significant advances in treatment options and the advent of novel targeted therapies, there still remains an unmet need for the identification of novel pharmacological agents for cancer therapy. This has led to several studies evaluating the possible application of natural agents found in vegetables, fruits, or plant-derived products that may be useful for cancer treatment. Bergamottin is a furanocoumarin derived from grapefruits and is also a well-known cytochrome P450 inhibitor. Recent studies have demonstrated potent anti-oxidative, anti-inflammatory, and anti-cancer properties of grapefruit furanocoumarin both in vitro and in vivo. The present review focuses on the potential anti-neoplastic effects of bergamottin in different tumor models and briefly describes the molecular targets affected by this agent.

Pharmacodynamic and Pharmacokinetic Markers For Anti-angiogenic Cancer Therapy: Implications for Dosing and Selection of Patients

Angiogenesis is integral to tumour growth and invasion, and is a key target for cancer therapeutics. However, for many of the licensed indications, only a modest clinical benefit has been observed for both monoclonal antibody and small-molecule tyrosine kinase inhibitor anti-angiogenic therapy. Pre-clinical and clinical studies have attempted to evaluate circulating, imaging, genomic, pharmacokinetic, and pharmacodynamic markers that may aid both the selection of patients for treatment and define dosing. Correct dosing is likely to be critical in the context of vascular normalization to allow better delivery of concomitant anti-cancer therapy and novel imaging techniques hold much promise in the early evaluation of pharmacodynamic response to improve efficacy.

Oral antineoplastic agent interactions with medicinal plants and food: an issue to take into account

OBJECTIVE

To review interactions between oral antineoplastic agents (OAAs) for the treatment of solid and hematological tumors and common food and medicinal plants.

MATERIALS AND METHODS

All potential interactions between OAAs, medicinal plants and food were reviewed. OAAs were considered to be drugs for oral administration that have direct antitumor activity and were approved by the European Medicines Agency in April 2015. We performed the literature search in Pubmed(®) considering only medicinal plants and food. In addition, available data were analyzed from each OAA in secondary data sources taken from Thomson Micromedex(®) and Lexi-comp(®), as well as in the summary of product characteristics.

RESULTS

Fifty-eight OAAs were analyzed. We found interactions in 60.3 % of OAAs. Those with most interactions described were: imatinib and procarbazine (4 interactions) and erlotinib, vemurafenib, pomalidomide, medroxyprogesterone and methotrexate (3 interactions).

MEDICINAL PLANTS

We found 39 interactions (74.4 % important). St. John's wort was the medicinal plant with most interactions (92.6 % were considered important). The rest were: important (ginseng-imatinib, methotrexate-cola and tobacco-erlotinib and tobacco-pomalidomide) and moderate (caffeine-vemurafenib/medroxyprogesterone, medroxyprogesterone-ruxolitinib/St. John's wort, garlic-anagrelide and ginseng-procarbazine).

FOODS

Twenty-six interactions (61.5 % important). Grapefruit had most interactions (82.4 % were considered important). The rest were: important (alcohol-procarbazine) and moderate (dairy-estramustine, methotrexate-ethanol, procarbazine-tyramine, vitamin A-tretinoin/bexarotene and grapefruit-bexarotene/etoposide/sunitinib).

CONCLUSION

A review of interactions of medicinal plants and food should be taken into account in the management of OAAs, since more than half have interactions with MPs and food, of which 70.3 % are considered important. The most relevant are HSJ, grapefruit, ginseng and tobacco. This review is intended to serve as a support to all healthcare professionals at the time of prescribing or dispensing OAAs.

Effect of Low-Furanocoumarin Hybrid Grapefruit Juice Consumption on Midazolam Pharmacokinetics

The objectives of this study were to investigate the effect of grapefruit juice low in furanocoumarins on CYP3A activity and to summarize previous findings of enzyme inhibition measured by the metabolism of midazolam after intake of grapefruit juice. Twelve healthy volunteers participated in a prospective, randomized, double-blinded, 3-way crossover clinical study to determine the effect of regular grapefruit juice (RGJ) and a novel, low-furanocoumarin hybrid grapefruit juice (HGJ) on the metabolism of oral midazolam, used as a probe for in vivo CYP3A activity, compared with water as a control. The RGJ was 100% hand-squeezed "Hudson" grapefruit juice, and the HGJ contained low amounts of furanocoumarin constituents. The point estimates (90% confidence intervals) for the RGJ/water midazolam AUC geometric mean ratio was 122% (107-140). The point estimate for the HGJ/water midazolam AUC ratio was within the 80% to 125% bioequivalence range, indicating an absence of interaction. This finding also prompted a systematic review of available evidence on the pharmacokinetic alteration of midazolam by grapefruit juice. Although most studies demonstrated alteration in midazolam pharmacokinetics supporting inhibition of CYP3A activity as a likely mechanism, the cohorts included in these studies and the extent of the pharmacokinetic interaction varied widely. The current study indicated grapefruit juice-drug interaction varies substantially based on patient characteristics and/or grapefruit juice product-related factors, including the amount of furanocoumarin constituents present in the juice.

Ultra High Performance Liquid Chromatography Method for the Determination of Two Recently FDA Approved TKIs in Human Plasma Using Diode Array Detection

Generally, tyrosine kinase inhibitors have narrow therapeutic window and large interpatient variability compared to intrapatient variability. In order to support its therapeutic drug monitoring, two fast and accurate methods were developed for the determination of recently FDA approved anticancer tyrosine kinase inhibitors, afatinib and ibrutinib, in human plasma using ultra high performance liquid chromatography coupled to PDA detection. Diclofenac sodium was used as internal standard. The chromatographic separation was achieved on an Acquity UPLC BEH C18 analytical column using a mobile phase combining ammonium formate buffer and acetonitrile at a constant flow rate of 0.4 mL/min using gradient elution mode. A µSPE (solid phase extraction) procedure, using Oasis MCX µElution plates, was processed and it gave satisfying and reproducible results in terms of extraction yields. Additionally, the methods were successfully validated using the accuracy profiles approach (β = 95% and acceptance limits = ±15%) over the ranges 5-250 ng/mL for afatinib and from 5 to 400 ng/mL for ibrutinib in human plasma.

Management of dose variability and side effects for individualized cancer pharmacotherapy with tyrosine kinase inhibitors

Molecular-targeted therapies with tyrosine kinase inhibitors (TKIs) have provided a major breakthrough in cancer treatment. These agents are given orally and demonstrated to be substrates for drug transporters. In clinical settings, TKIs are mainly used at a fixed dose, but wide interpatient variability has been observed in their pharmacokinetics and/or pharmacodynamics. Genetic polymorphisms of ABC transporters, drug-drug interaction and adherence are among the factors causing such variation. To overcome these problems, therapeutic drug monitoring has been applied in clinical practice for patient care. Skin disorders are frequently observed as adverse drug reactions when using TKIs, and are commonly managed by symptomatic therapy based on clinical experience. Recent studies have provided some insights into the molecular mechanisms underlying skin disorders induced by TKIs. This review article summarizes the accumulated clinical and basic pharmacological evidence of TKIs, focusing on erlotinib, sorafenib and sunitinib.

Variability in bioavailability of small molecular tyrosine kinase inhibitors

Small molecular tyrosine kinase inhibitors (smTKIs) are in the centre of the very quickly expanding area of personalized chemotherapy and oral applicability thereof. The number of drugs in this class is rapidly growing, with twenty current approvals by both the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The drugs are, however, generally characterized by a poor oral, and thus variable, bioavailability. This results in significant variation in plasma levels and exposure. The cause is a complex interplay of factors, including poor aqueous solubility, issued permeability, membrane transport and enzymatic metabolism. Additionally, food and drug-drug interactions can play a significant role. The issues related with an impaired bioavailability generally receive little attention. To the best of our knowledge, this article is the first to provide an overview of the factors that determine the bioavailability of the smTKIs.

Clinical trial simulation to evaluate population pharmacokinetics and food effect: capturing abiraterone and nilotinib exposures

The objectives of this study were to determine (1) the accuracy with which individual patient level exposure can be determined and (2) whether a known food effect can be identified in a trial simulation of a typical population pharmacokinetic trial. Clinical trial simulations were undertaken using NONMEM VII to assess a typical oncology pharmacokinetic trial design. Nine virtual trials for each compound were performed for combinations of different levels of between-occasion variability, number of patients in the trial, and magnitude of a food covariate on oral clearance. Less than 5% and 20% bias and precision were obtained in individual clearance estimated for both abiraterone and nilotinib using this design. This design resulted in biased and imprecise population clearance estimates for abiraterone. The between-occasion variability in most trials was captured with less than 30% of percent bias and precision. The food effect was detectable as a statistically significant covariate on oral clearance for abiraterone and nilotinib with percent bias and precision of the food covariate less than 20%. These results demonstrate that clinical trial simulation can be used to explore the ability of specific trial designs to evaluate the power to identify individual and population level exposures, covariate, and variability effects.

The pharmacokinetic interaction between levofloxacin and sunitinib

BACKGROUND

The aim of this study was to evaluate the impact of sunitinib on pharmacokinetics of levofloxacin. The previous study proved that levofloxacin co-administered with sunitib changes the following pharmacokinetic parameters i.e. Cmax and AUC for both sunitinib and SU012662 (sunitinib metabolite). We will also investigate if the limited sample strategy can be applied for levofloxacin.

METHODS

Rabbits were divided into two groups. In both groups there were six animals. In the control group levofloxacin was administered and in investigated group levofloxacin and sunitinib were co-administered. The dose of levofloxacin was 20mg/kg and the dose of sunitinib was 25mg. The concentration in plasma was determined by HPLC-FLD. The pharmacokinetic parameters were evaluated by WinNonLin software. The results were evaluated by the following statistical tests: Shapiro-Wilk, t-Student and Mann-Whitney test.

RESULTS

Pharmacokinetics of levofloxacin obeys the two-compartment model. Sunitinib influences the following pharmacokinetic parameters of levofloxacin: half-life, elimination constant and volume of distribution. Statistical analysis proved that there is a correlation between AUC and the following five time-points: 0.25 h, 4h, 6h, 10h and 12h.

CONCLUSIONS

The study proved that there is a potential pharmacokinetic interaction between sunitinib and levofloxacin. The statistical analysis proved that the limited sample strategy can be applied for levofloxacin.

Drug-drug interactions with tyrosine-kinase inhibitors: a clinical perspective

In the past decade, many tyrosine-kinase inhibitors have been introduced in oncology and haemato-oncology. Because this new class of drugs is extensively used, serious drug-drug interactions are an increasing risk. In this Review, we give a comprehensive overview of known or suspected drug-drug interactions between tyrosine-kinase inhibitors and other drugs. We discuss all haemato-oncological and oncological tyrosine-kinase inhibitors that had been approved by Aug 1, 2013, by the US Food and Drug Administration or the European Medicines Agency. Various clinically relevant drug interactions with tyrosine-kinase inhibitors have been identified. Most interactions concern altered bioavailability due to altered stomach pH, metabolism by cytochrome P450 isoenzymes, and prolongation of the QTc interval. To guarantee the safe use of tyrosine-kinase inhibitors, a drugs review for each patient is needed. This Review provides specific recommendations to guide haemato-oncologists, oncologists, and clinical pharmacists, through the process of managing drug-drug interactions during treatment with tyrosine-kinase inhibitors in daily clinical practice.

Drug interactions with sunitinib

PURPOSE

Sunitinib is a tyrosine kinase inhibitor indicated for the treatment of gastrointestinal stromal tumor, advanced renal cell carcinoma, and pancreatic neuroendocrine tumors. The aim of this article is to describe the pharmacological interactions between sunitinib and commonly prescribed drugs.

METHOD

We reviewed available information on pharmacological interactions between sunitinib and concomitantly prescribed drugs. Drugs were grouped into different therapeutic groups according to the Anatomical Therapeutic Chemical (ATC) classification.

RESULTS

Sunitinib interacts with CYP3A4 inducers or inhibitors and with P-glycoprotein and ABCG2 substrates. Pharmacodynamic interactions with drugs have also been found.

CONCLUSION

Current information on drug interactions between sunitinib and other drugs is scarce and most of the times it is difficult to apply to clinical practice. Even so, this difficulty in managing drug interactions should not be a reason to ignore them as they can help to explain intolerances and treatment failures.

Drug interactions with solid tumour-targeted therapies

Drug interactions are an on-going concern in the treatment of cancer, especially when targeted therapies, such as tyrosine kinase inhibitors (TKI) or mammalian target of rapamycin (mTOR) inhibitors, are being used. The emergence of elderly patients and/or patients with both cancer and other chronic co-morbidities leads to polypharmacy. Therefore, the risk of drug-drug interactions (DDI) becomes a clinically relevant issue, all the more so as TKIs and mTOR inhibitors are essentially metabolised by cytochrome P450 enzymes. These DDIs can result in variability in anticancer drug exposure, thus favouring the selection of resistant cellular clones or the occurrence of toxicity. This review provides a comprehensive overview of DDIs that involve targeted therapies approved by the FDA for the treatment of solid tumours for more than 3 years (sorafenib, sunitinib, erlotinib, gefitinib, imatinib, lapatinib, everolimus, temsirolimus) and medicinal herb or drugs. This review also provides some guidelines to help oncologists and pharmacists in their clinical practice.

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.

Everolimus therapy for progressive adrenocortical cancer

Patients with advanced adrenocortical carcinoma (ACC) have limited treatment options after failure of chemotherapy. Tumor IGF2 expression has been shown to be amplified in the majority of cases of ACC and autocrine/paracrine activation of the IGF receptor (IGF-R) is thought to play a major role in the pathogenesis of ACC. It has been shown in vitro that inhibition of the IGF-R inhibits ACC cell proliferation. mTOR is a downstream effector of the IGFR signaling pathway; therefore, the rapamycin analog everolimus could prove to be useful for treatment of patients with ACC. Four women with ACC (ages 25-60 years) developed stage IV disease after surgery. All had progressive disease (PD) despite treatment with mitotane and other treatment modalities (etoposide, doxorubicin, cis-platinum in 3/4 patients, further streptozotocin + 5-FU in 1/4 patients, further thalidomide therapy in 2/4 patients; 1 patient progressed on an IGF-R antagonist). The patients were started on everolimus 10 mg/day orally and 2/4 patients also continued mitotane. Disease progression was monitored monthly by CT in 3/4 and after 3 months in 1/4. In all patients everolimus was well tolerated. In the three patients monitored monthly, PD was evident after 1, 3, and 4 months; in the patient evaluated after 3 months PD was also evident. In this small exploratory study, no clinically meaningful response was observed with everolimus in four patients with advanced ACC. The failure of efficacy could be related to an interaction with mitotane, multiple signaling pathways, and/or other downstream IGF-R effectors operative in the pathogenesis of ACC.

Effect of P-glycoprotein and breast cancer resistance protein inhibition on the pharmacokinetics of sunitinib in rats

The aim of this study was to elucidate the roles of P-glycoprotein (P-gp/ABCB1) and breast cancer resistance protein (BCRP/ABCG2) in the plasma concentration, biliary excretion, and distribution to the liver, kidney, and brain of sunitinib. The pharmacokinetics of sunitinib was examined in rats treated with PSC833 (valspodar) and pantoprazole, potent inhibitors of P-gp and BCRP, respectively. The sunitinib concentrations in plasma, bile, liver, kidney, and brain were determined by liquid chromatography-tandem mass spectrometry. It was found that the area under the concentration-time curve for 4 hours (AUC0-4) and maximum concentration (Cmax) of sunitinib administered intraintestinally were significantly increased by pretreatment with PSC833 or pantoprazole. Each inhibitor markedly reduced the biliary excretion of sunitinib for 60 minutes after an intravenous administration and significantly increased the distribution of sunitinib to the liver as well as kidney. In addition, the brain distribution of sunitinib was significantly increased by PSC833 but not pantoprazole, and coadministration of both inhibitors further enhanced the accumulation of sunitinib in the brain. These results demonstrate that plasma concentrations of sunitinib and the biliary excretion and distribution to the kidney, liver, and brain of sunitinib are influenced by pharmacologic inhibition of P-gp and/or BCRP.

A physiologically based pharmacokinetic (PBPK) approach to evaluate pharmacokinetics in patients with cancer

Potential differences in pharmacokinetics (PK) between healthy subjects and patients with cancer were investigated using a physiologically based pharmacokinetic approach integrating demographic and physiological data from patients with cancer. Demographic data such as age, sex and body weight, and clinical laboratory measurements such as albumin, alpha-1 acid glycoprotein (AAG) and hematocrit were collected in ~2500 patients with cancer. A custom oncology population profile was built using the observed relationships among demographic variables and laboratory measurements in Simcyp® software, a population based ADME simulator. Patients with cancer were older compared with the age distribution in a built-in healthy volunteer profile in Simcyp. Hematocrit and albumin levels were lower and AAG levels were higher in patients with cancer. The custom population profile was used to investigate the disease effect on the pharmacokinetics of two probe substrates, saquinavir and midazolam. Higher saquinavir exposure was predicted in patients relative to healthy subjects, which was explained by the altered drug binding due to elevated AAG levels in patients with cancer. Consistent with historical clinical data, similar midazolam exposure was predicted in patients and healthy subjects, supporting the hypothesis that the CYP3A activity is not altered in patients with cancer. These results suggest that the custom oncology population profile is a promising tool for the prediction of PK in patients with cancer. Further evaluation and extension of this population profile with more compounds and more data will be needed.

Drug interactions with mitotane by induction of CYP3A4 metabolism in the clinical management of adrenocortical carcinoma

Mitotane [1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane, (o,p'-DDD)] is the only drug approved for the treatment for adrenocortical carcinoma (ACC) and has also been used for various forms of glucocorticoid excess. Through still largely unknown mechanisms, mitotane inhibits adrenal steroid synthesis and adrenocortical cell proliferation. Mitotane increases hepatic metabolism of cortisol, and an increased replacement dose of glucocorticoids is standard of care during mitotane treatment. Recently, sunitinib, a multityrosine kinase inhibitor (TKI), has been found to be rapidly metabolized by CYP3A4 during mitotane treatment, indicating clinically relevant drug interactions with mitotane. We here summarize the current evidence concerning mitotane-induced changes in hepatic monooxygenase expression, list drugs potentially affected by mitotane-related CYP3A4 induction and suggest alternatives. For example, using standard doses of macrolide antibiotics is unlikely to reach sufficient plasma levels, making fluoroquinolones in many cases a superior choice. Similarly, statins such as simvastatin are metabolized by CYP3A4, whereas others like pravastatin are not. Importantly, in the past, several clinical trials using cytotoxic drugs but also targeted therapies in ACC yielded disappointing results. This lack of antineoplastic activity may be explained in part by insufficient drug exposure owing to enhanced drug metabolism induced by mitotane. Thus, induction of CYP3A4 by mitotane needs to be considered in the design of future clinical trials in ACC.

The metabolic and toxicological considerations for mTOR inhibitors in the treatment of hepatocarcinoma

INTRODUCTION

Hepatocellular carcinoma (HCC) is a major health problem worldwide. Several molecular pathways involved in HCC growth and progression have recently been identified. Rapamycin analogs are able to inhibit one of the most active oncogenic molecular pathways in HCC cells: the mammalian target of rapamycin (mTOR) pathway.

AREAS COVERED

In this review, the authors analyze the principal molecular features of the mTOR pathway and the use of rapamycin analogs in the treatment of hepatocarcinoma. The article also looks at the reoccurrence of HCC following liver transplantation as well as after the treatment of de novo neoplasms. Finally, the authors discuss the advantage of using a combined HCC pharmacological therapy to obtain a synergistic effect on tumor mass.

EXPERT OPINION

Among the available options for the treatment of advanced-stage HCC, mTOR pathway inhibitors show great promise. Once these agents have their safety and efficacy confirmed, in the treatment of liver disease, their use should be considered in patients affected by HCC. This should especially be the case for those who have had liver transplants or suffered with de novo tumors. Moreover, the authors believe that mTOR inhibitors could be used in a combined pharmacological approach to improve HCC molecular-targeted therapy by producing a multiple-level block of tumor intracellular signaling.

Influence of dietary substances on intestinal drug metabolism and transport

Successful delivery of promising new chemical entities via the oral route is rife with challenges, some of which cannot be explained or foreseen during drug development. Further complicating an already multifaceted problem is the obvious, yet often overlooked, effect of dietary substances on drug disposition and response. Some dietary substances, particularly fruit juices, have been shown to inhibit biochemical processes in the intestine, leading to altered pharmacokinetic (PK), and potentially pharmacodynamic (PD), outcomes. Inhibition of intestinal CYP3Amediated metabolism is the major mechanism by which fruit juices, including grapefruit juice, enhances systemic exposure to new and already marketed drugs. Inhibition of intestinal non-CYP3A enzymes and apically-located transport proteins represent recently identified mechanisms that can alter PK and PD. Several fruit juices have been shown to inhibit these processes in vitro, but some interactions have not translated to the clinic. The lack of in vitroin vivo concordance is due largely to a lack of rigorous methods to elucidate causative ingredients prior to clinical testing. Identification of specific components and underlying mechanisms is challenging, as dietary substances frequently contain multiple, often unknown, bioactive ingredients that vary in composition and bioactivity. A translational research approach, combining expertise from clinical pharmacologists and natural products chemists, is needed to develop robust models describing PK/PD relationships between a given dietary substance and drug of interest. Validation of these models through well-designed clinical trials would facilitate development of common practice guidelines for managing drug-dietary substance interactions appropriately.

The effect of grapefruit juice on drug disposition

INTRODUCTION

Since their initial discovery in 1989, grapefruit juice (GFJ)-drug interactions have received extensive interest from the scientific, medical, regulatory and lay communities. Although knowledge regarding the effects of GFJ on drug disposition continues to expand, the list of drugs studied in the clinical setting remains relatively limited.

AREAS COVERED

This article reviews the in vitro effects of GFJ and its constituents on the activity of CYP enzymes, organic anion-transporting polypeptides (OATPs), P-glycoprotein, esterases and sulfotransferases. The translational applicability of the in vitro findings to the clinical setting is discussed for each drug metabolizing enzyme and transporter. Reported AUC ratios for available GFJ-drug interaction studies are also provided. Relevant investigations were identified by searching the PubMed electronic database from 1989 to 2010.

EXPERT OPINION

GFJ increases the bioavailability of some orally administered drugs that are metabolized by CYP3A and normally undergo extensive presystemic extraction. In addition, GFJ can decrease the oral absorption of a few drugs that rely on OATPs in the gastrointestinal tract for their uptake. The number of drugs shown to interact with GFJ in vitro is far greater than the number of clinically relevant GFJ-drug interactions. For the majority of patients, complete avoidance of GFJ is unwarranted.