The clinical pharmacology of alkylating agents in high-dose chemotherapy

CRISPR screens reveal convergent targeting strategies against evolutionarily distinct chemoresistance in cancer

Resistance to chemotherapy has been a major hurdle that limits therapeutic benefits for many types of cancer. Here we systematically identify genetic drivers underlying chemoresistance by performing 30 genome-scale CRISPR knockout screens for seven chemotherapeutic agents in multiple cancer cells. Chemoresistance genes vary between conditions primarily due to distinct genetic background and mechanism of action of drugs, manifesting heterogeneous and multiplexed routes towards chemoresistance. By focusing on oxaliplatin and irinotecan resistance in colorectal cancer, we unravel that evolutionarily distinct chemoresistance can share consensus vulnerabilities identified by 26 second-round CRISPR screens with druggable gene library. We further pinpoint PLK4 as a therapeutic target to overcome oxaliplatin resistance in various models via genetic ablation or pharmacological inhibition, highlighting a single-agent strategy to antagonize evolutionarily distinct chemoresistance. Our study not only provides resources and insights into the molecular basis of chemoresistance, but also proposes potential biomarkers and therapeutic strategies against such resistance.

Chemotherapeutic drugs for soft tissue sarcomas: a review

Despite the low incidence of soft tissue sarcomas (STSs), hundreds of thousands of new STS cases are diagnosed annually worldwide, and approximately half of them eventually progress to advanced stages. Currently, chemotherapy is the first-line treatment for advanced STSs. There are difficulties in selecting appropriate drugs for multiline chemotherapy, or for combination treatment of different STS histological subtypes. In this study, we first comprehensively reviewed the efficacy of various chemotherapeutic drugs in the treatment of STSs, and then described the current status of sensitive drugs for different STS subtypes. anthracyclines are the most important systemic treatment for advanced STSs. Ifosfamide, trabectedin, gemcitabine, taxanes, dacarbazine, and eribulin exhibit certain activities in STSs. Vinca alkaloid agents (vindesine, vinblastine, vinorelbine, vincristine) have important therapeutic effects in specific STS subtypes, such as rhabdomyosarcoma and Ewing sarcoma family tumors, whereas their activity in other subtypes is weak. Other chemotherapeutic drugs (methotrexate, cisplatin, etoposide, pemetrexed) have weak efficacy in STSs and are rarely used. It is necessary to select specific second- or above-line chemotherapeutic drugs depending on the histological subtype. This review aims to provide a reference for the selection of chemotherapeutic drugs for multi-line therapy for patients with advanced STSs who have an increasingly long survival.

PROTAC'ing oncoproteins: targeted protein degradation for cancer therapy

Molecularly targeted cancer therapies substantially improve patient outcomes, although the durability of their effectiveness can be limited. Resistance to these therapies is often related to adaptive changes in the target oncoprotein which reduce binding affinity. The arsenal of targeted cancer therapies, moreover, lacks coverage of several notorious oncoproteins with challenging features for inhibitor development. Degraders are a relatively new therapeutic modality which deplete the target protein by hijacking the cellular protein destruction machinery. Degraders offer several advantages for cancer therapy including resiliency to acquired mutations in the target protein, enhanced selectivity, lower dosing requirements, and the potential to abrogate oncogenic transcription factors and scaffolding proteins. Herein, we review the development of proteolysis targeting chimeras (PROTACs) for selected cancer therapy targets and their reported biological activities. The medicinal chemistry of PROTAC design has been a challenging area of active research, but the recent advances in the field will usher in an era of rational degrader design.

Analysis of the Fragmentation Pathways for the Collision-Induced Dissociation of Protonated Cyclophosphamide: A Mass Spectrometry and Quantum Mechanical Study

Cyclophosphamide is a well-known anticancer agent acting by means of DNA alkylation. Associated with its tumor selectivity, it also possesses a wide spectrum of toxicities. As the requirement of metabolic activation before cyclophosphamide exerts either its therapeutic or toxic effects is well recognized, research aiming at elucidating the pathways that lead to the activation of this drug is of key importance. This has created the necessity for developing an effective analytical method for detecting cyclophosphamide and its breakdown products. In this paper, an Acquity TQ tandem quadrupole mass spectrometer equipped with electrospray ionization in positive-ion mode was employed for detecting cyclophosphamide in its protonated form. The full-scan mass spectrum of cyclophosphamide shows two ion clusters displaying the characteristic isotopic pattern of two chlorine atoms and assigned as sodiated cyclophosphamide, [CP + Na]⁺, and protonated cyclophosphamide, [CP + H]⁺ or PCP. With the aid of quantum mechanical DFT calculation, free energy differences in the gas phase among PCP protomers were computed with respect to the most stable protomer being protonated on the 2-oxide oxygen of the 1,3,2-oxazaphosphorine-2-oxide ring. In addition, the interconversion mechanisms among the different protomers were also proposed by intercepting the corresponding transition states in the gas phase. Collision-induced dissociation (CID) of PCP generated six characteristic product ions. Fragmentation mechanisms were proposed and supported by computation. The calculated energy barriers for all of the located transition states were found to be accessible under the reported experimental conditions.

Antineoplastics Encapsulated in Nanostructured Lipid Carriers

Ideally, antineoplastic treatment aims to selectively eradicate cancer cells without causing systemic toxicity. A great number of antineoplastic agents (AAs) are available nowadays, with well-defined therapeutic protocols. The poor bioavailability, non-selective action, high systemic toxicity, and lack of effectiveness of most AAs have stimulated the search for novel chemotherapy protocols, including technological approaches that provide drug delivery systems (DDS) for gold standard medicines. Nanostructured lipid carriers (NLC) are DDS that contain a core of solid and lipid liquids stabilised by surfactants. NLC have high upload capacity for lipophilic drugs, such as the majority of AAs. These nanoparticles can be prepared with a diversity of biocompatible (synthetic or natural) lipid blends, administered by different routes and functionalised for targeting purposes. This review focused on the research carried out from 2000 to now, regarding NLC formulations for AAs (antimetabolites, antimitotics, alkylating agents, and antibiotics) encapsulation, with special emphasis on studies carried out in vivo. NLC systems for codelivery of AAs were also considered, as well as those for non-classical drugs and therapies (natural products and photosensitisers). NLC have emerged as powerful DDS to improve the bioavailability, targeting and efficacy of antineoplastics, while decreasing their toxic effect in the treatment of different types of cancer.

Relevant pharmacological interactions between alkylating agents and antiepileptic drugs: Preclinical and clinical data

Seizures are relatively common in cancer patients, and co-administration of chemotherapeutic and antiepileptic drugs (AEDs) is highly probable and necessary in many cases. Nonetheless, clinically relevant interactions between chemotherapeutic drugs and AEDs are rarely summarized and pharmacologically described. These interactions can cause insufficient tumor and seizure control or lead to unforeseen toxicity. This review focused on pharmacokinetic and pharmacodynamic interactions between alkylating agents and AEDs, helping readers to make a rational choice of treatment optimization, and thus improving patients' quality of life. As an example, phenobarbital, phenytoin, and carbamazepine, by increasing the hepatic metabolism of cyclophosphamide, ifosfamide and busulfan, yield smaller peak concentrations and a reduced area under the plasma concentration-time curve (AUC) of the prodrugs; alongside, the maximum concentration and AUC of their active products were increased with the possible onset of severe adverse drug reactions. On the other side, valproic acid, acting as histone deacetylase inhibitor, showed synergistic effects with temozolomide when tested in glioblastoma. The present review is aimed at providing evidence that may offer useful suggestions for rational pharmacological strategies in patients with seizures symptoms undertaking alkylating agents. Firstly, clinicians should avoid the use of enzyme-inducing AEDs in combination with alkylating agents and prefer the use of AEDs, such as levetiracetam, that have a low or no impact on hepatic metabolism. Secondly, a careful therapeutic drug monitoring of both alkylating agents and AEDs (and their active metabolites) is necessary to maintain therapeutic ranges and to avoid serious adverse reactions.

Nitrogen Mustards as Anticancer Chemotherapies: Historic Perspective, Current Developments and Future Trends

Nitrogen mustards, a family of DNA alkylating agents, marked the start of cancer pharmacotherapy. While traditionally characterized by their dose-limiting toxic effects, nitrogen mustards have been the subject of intense research efforts, which have led to safer and more effective agents. Even though the alkylating prodrug mustards were first developed decades ago, active research on ways to improve their selectivity and cytotoxic efficacy is a currently active topic of research. This review addresses the historical development of the nitrogen mustards, outlining their mechanism of action, and discussing the improvements on their therapeutic profile made through rational structure modifications. A special emphasis is made on discussing the nitrogen mustard prodrug category, with Cyclophosphamide (CPA) serving as the main highlight. Selected insights on the latest developments on nitrogen mustards are then provided, limiting such information to agents that preserve the original nitrogen mustard mechanism as their primary mode of action. Additionally, future trends that might follow in the quest to optimize these invaluable chemotherapeutic medications are succinctly suggested.

High-dose thiotepa-related neurotoxicity and the role of tramadol in children

Background

Serious neurological adverse events (NAE) have occurred during treatment with high-dose thiotepa regimens of children with high-risk solid tumours. The objective was to assess the incidence of NAE related to high-dose thiotepa and to identify potential contributing factors that could exacerbate the occurrence of this neurotoxicity.

Methods

From May 1987 to March 2011, children with solid tumours treated with high-dose thiotepa were retrospectively identified. Each NAE detected led to an independent case analysis. Potential contributing factors were pre-specified and univariate/multivariable analyses were performed.

Results

Three hundred seven courses of thiotepa (251 patients) were identified. The total dose per treatment ranged from 600 to 900 mg/m². 81 NAE (26%) were identified. 46 NAE were related to high-dose thiotepa during the first course (18.3%) and 11 during the second course (19.6%). The symptoms appeared in a median time of 2 days after the introduction of thiotepa. Central and peripheral symptoms were headaches, tremors, confusion, seizures, cerebellar syndrome, and coma. High-dose thiotepa was reintroduced in 18 cases and symptoms reappeared in 5 children. For 3 patients who had seizures during the first course, premedication with clonazepam for the second course has prevented recurrence of NAE. As contributing factors, brain tumour and tramadol treatment increased the risk of thiotepa-related neurotoxicity by 2 to 6 times respectively.

Conclusions

The incidence of neurotoxicity was 18.3%. Brain tumours and tramadol treatment are risk factors to consider when using high-dose thiotepa. The outcome of patients was favourable without sequelae in all cases and rechallenge with thiotepa was possible.

Dioscorea bulbifera polysaccharide and cyclophosphamide combination enhances anti-cervical cancer effect and attenuates immunosuppression and oxidative stress in mice

Cyclophosphamide (CTX) is commonly used in cancer chemotherapy, which causes immunosuppression and tissue oxidative stress at high doses. As potential protective agents, some polysaccharides were shown to have anti-tumor, anti-inflammatory and/or anti-oxidant properties. This study explored potential effects of oral treatment of Dioscorea bulbifera polysaccharides (DBLP at 100 or 150 mg/kg) in U14 cervical tumor-bearing mice treated with CTX (25 mg/kg). While CTX suppressed tumor growth (65.4% inhibition) and DBLP alone also inhibited tumor (25.6% at 100 mg/kg or 37.6% at 150 mg/kg), CTX+DBLP combination produced tumor inhibition rates of 5.6 (for 100 mg/kg DBLP) or 9% (for 150 mg/kg) higher than CTX alone. While tumor itself and CTX treatment reduced thymus and/or spleen/body weight indices, DBLP alone or CTX + DBLP combination attenuated this reduction. DBLP lowered peripheral blood T-cell subpopulation CD⁴⁺/CD⁸⁺ ratio, and DBLP+CTX combination attenuated CTX effect in lifting CD⁴⁺/CD⁸⁺ ratio. Tumor itself and CTX treatment heightened oxidative stress (with decreased superoxide dismutase but increased lactate dehydrogenase and malondialdehyde levels in serum and tissues), which was attenuated by DBLP treatment, and DBLP+CTX combination suppressed CTX-induced oxidative stress. Combination use of DBLP with CTX can potentially enhance CTX anti-tumor effect and can attenuate CTX-induced immunosuppression and oxidative stress in U14 cervical tumor-bearing mice.

A novel approach for testing the teratogenic potential of chemicals on the platform of metabolomics: studies employing HR-MAS nuclear magnetic resonance spectroscopy

The objective is to develop a quick, reliable method for testing the teratogenic potential of a new chemical entity (NCE) on the platform of metabonomics, as an alternative to conventional procedures.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

Chemotherapy agents: a primer for the interventional radiologist

In this article, the authors review the basic principles of cancer chemotherapy and provide an overview of each of the general classes of chemotherapeutic agents with a target audience of interventional radiologists in mind. Special attention is paid to agents used in regional chemotherapy as well as agents commonly included in systemic chemotherapeutic regimens for patients who also require regional chemotherapy.

Alkylating chemotherapeutic agents cyclophosphamide and melphalan cause functional injury to human bone marrow-derived mesenchymal stem cells

The adverse effects of melphalan and cyclophosphamide on hematopoietic stem cells are well-known; however, the effects on the mesenchymal stem cells (MSCs) residing in the bone marrow are less well characterised. Examining the effects of chemotherapeutic agents on patient MSCs in vivo is difficult due to variability in patients and differences in the drug combinations used, both of which could have implications on MSC function. As drugs are not commonly used as single agents during high-dose chemotherapy (HDC) regimens, there is a lack of data comparing the short- or long-term effects these drugs have on patients post treatment. To help address these problems, the effects of the alkylating chemotherapeutic agents cyclophosphamide and melphalan on human bone marrow MSCs were evaluated in vitro. Within this study, the exposure of MSCs to the chemotherapeutic agents cyclophosphamide or melphalan had strong negative effects on MSC expansion and CD44 expression. In addition, changes were seen in the ability of MSCs to support hematopoietic cell migration and repopulation. These observations therefore highlight potential disadvantages in the use of autologous MSCs in chemotherapeutically pre-treated patients for future therapeutic strategies. Furthermore, this study suggests that if the damage caused by chemotherapeutic agents to marrow MSCs is substantial, it would be logical to use cultured allogeneic MSCs therapeutically to assist or repair the marrow microenvironment after HDC.

Cyclophosphamide-metabolizing enzyme polymorphisms and survival outcomes after adjuvant chemotherapy for node-positive breast cancer: a retrospective cohort study

INTRODUCTION

Cyclophosphamide-based adjuvant chemotherapy is a mainstay of treatment for women with node-positive breast cancer, but is not universally effective in preventing recurrence. Pharmacogenetic variability in drug metabolism is one possible mechanism of treatment failure. We hypothesize that functional single nucleotide polymorphisms (SNPs) in drug metabolizing enzymes (DMEs) that activate (CYPs) or metabolize (GSTs) cyclophosphamide account for some of the observed variability in disease outcomes.

METHODS

We performed a retrospective cohort study of 350 women enrolled in a multicenter, randomized, adjuvant breast cancer chemotherapy trial (ECOG-2190/INT-0121). Subjects in this trial received standard-dose cyclophosphamide, doxorubicin and fluorouracil (CAF), followed by either observation or high-dose cyclophosphamide and thiotepa with stem cell rescue. We used bone marrow stem cell-derived genomic DNA from archival specimens to genotype CYP2B6, CYP2C9, CYP2D6, CYP3A4, CYP3A5, GSTM1, GSTT1, and GSTP1. Cox regression models were computed to determine associations between genotypes (individually or in combination) and disease-free survival (DFS) or overall survival (OS), adjusting for confounding clinical variables.

RESULTS

In the full multivariable analysis, women with at least one CYP3A4 *1B variant allele had significantly worse DFS than those who were wild-type *1A/*1A (multivariate hazard ratio 2.79; 95% CI 1.52, 5.14). CYP2D6 genotype did not impact this association among patients with estrogen receptor (ER) -positive tumors scheduled to receive tamoxifen.

CONCLUSIONS

These data support the hypothesis that genetic variability in cyclophosphamide metabolism independently impacts outcome from adjuvant chemotherapy for breast cancer.

Polymorphisms of drug-metabolizing enzymes (GST, CYP2B6 and CYP3A) affect the pharmacokinetics of thiotepa and tepa

AIMS

Thiotepa is widely used in high-dose chemotherapy. Previous studies have shown relations between exposure and severe organ toxicity. Thiotepa is metabolized by cytochrome P450 and glutathione S-transferase enzymes. Polymorphisms of these enzymes may affect elimination of thiotepa and tepa, its main metabolite. The purpose of this study was to evaluate effects of known allelic variants in CYP2B6, CYP3A4, CYP3A5, GSTA1 and GSTP1 genes on pharmacokinetics of thiotepa and tepa.

METHODS

White patients (n = 124) received a high-dose regimen consisting of cyclophosphamide, thiotepa and carboplatin as intravenous infusions. Genomic DNA was analysed using polymerase chain reaction and sequencing. Plasma concentrations of thiotepa and tepa were determined using validated GC and LC-MS/MS methods. Relations between allelic variants and elimination pharmacokinetic parameters were evaluated using nonlinear mixed effects modelling (nonmem).

RESULTS

The polymorphisms CYP2B6 C1459T, CYP3A4*1B, CYP3A5*3, GSTA1 (C-69T, G-52A) and GSTP1 C341T had a significant effect on clearance of thiotepa or tepa. Although significant, most effects were generally not large. Clearance of thiotepa and tepa was predominantly affected by GSTP1 C341T polymorphism, which had a frequency of 9.3%. This polymorphism increased non-inducible thiotepa clearance by 52% [95% confidence interval (CI) 41, 64, P < 0.001] and decreased tepa clearance by 32% (95% CI 29, 35, P < 0.001) in heterozygous patients, which resulted in an increase in combined exposure to thiotepa and tepa of 45% in homozygous patients.

CONCLUSIONS

This study indicates that the presently evaluated variant alleles explain only a small part of the substantial interindividual variability in thiotepa and tepa pharmacokinetics. Patients homozygous for the GSTP1 C341T allele may have enhanced exposure to thiotepa and tepa.

Carbamazepine induces bioactivation of cyclophosphamide and thiotepa

PURPOSE

We report a patient with metastatic breast cancer who received three cycles of high-dose chemotherapy with cyclophosphamide [1,000 mg/(m(2) day)], thiotepa (80 mg/(m(2) day) and carboplatin (dose calculated based on modified Calvert formula with 3.25 mg min/ml as daily target AUC) over 4 days, followed by peripheral blood progenitor cell support. During the first two cycles the patient concomitantly used carbamazepine for the treatment of epilepsy. Due to severe nausea and vomiting the patient was unable to ingest carbamazepine; therefore, this was discontinued after the second cycle.

METHODS

Blood samples were drawn on 2 days (day 1 and 2, 3 or 4) of each cycle and plasma levels of cyclophosphamide, its active metabolite 4-hydroxycyclophosphamide, thiotepa, its main, active metabolite tepa and carboplatin were determined.

RESULTS

Exposure to 4-hydroxycyclophosphamide and tepa on day 1 was increased in the presence of carbamazepine (58 and 75%, respectively), while exposure to cyclophosphamide and thiotepa was reduced (40 and 43%, respectively).

CONCLUSION

Since increased exposure to the active metabolites is associated with an increased risk of toxicity, it is important to be aware of this drug-drug interaction.

A systematic review of limited sampling strategies for platinum agents used in cancer chemotherapy

Despite evidence in the literature suggesting that a strong correlation exists between the pharmacokinetic parameters and pharmacodynamic effect of anticancer agents, many of these agents are still dosed by body surface area. Therapeutic drug monitoring with the aim of pharmacokinetic-guided dosing would not only maintain target concentrations associated with efficacy but may potentially minimise the likelihood of dose-related systemic toxicities. The pharmacokinetic parameter that displays the best correlation with the pharmacodynamics of anticancer drugs is the area under the plasma concentration-time curve (AUC). However, accurate determination of the AUC requires numerous blood samples over an extended interval, which is not feasible in clinical practice. Therefore, limited sampling strategies (LSSs) have been proposed as a means to accurately and precisely estimate pharmacokinetic parameters with a minimal number of blood samples. LSSs have been developed for many drugs, particularly ciclosporin and other immunosuppressants, as well as for certain anticancer drugs. This systematic review evaluates LSSs developed for the platinum compounds and categorises 18 pertinent citations according to criteria adapted from the US Preventive Services Task Force. Thirteen citations (four level I, six level II-1, three level II-2) pertained to LSSs for carboplatin, four citations (one level II-1, one level II-2, two level III) to cisplatin LSSs, and one citation (level II-2) to nedaplatin. Based on the current evidence, it appears that LSSs may be useful for pharmacokinetic-guided dosage adjustments of carboplatin in both adults and children with cancer. Although some validation studies suggest that LSSs can be extended to different cancer populations or different chemotherapy regimens, other studies dispute this finding. Although the use of LSSs to predict the pharmacokinetic parameters of cisplatin and nedaplatin appear promising, the quality of evidence from published studies does not support routine implementation at this time.LSSs represent one approach in which clinicians can make specific dosage adjustments for individual patients to optimise outcomes. However, the limitations of these strategies must also be taken into consideration. There is also a need for prospective studies to demonstrate that application of LSSs for platinum agents ultimately improves patient response and decreases systemic toxicities.

Necrotic pathway in human osteosarcoma Saos-2 cell death induced by chloroacetaldehyde

Chloroacetaldehyde, a metabolite of the anticancer drug ifosfamide, may be responsible for serious adverse effects like encephalopathy in ifosfamide chemotherapy. In this study, we demonstrate that chloroacetaldehyde, but not ifosfamide, induces cell death in human osteosarcoma Saos-2 cells and we investigated the mechanism by which this occurs. Chloroacetaldehyde above 30 micromol/l induced significant cell death in a time-dependent manner. Thiol compounds such as N-acetyl cysteine, glutathione and dithiothreitol protected the cells against chloroacetaldehyde-induced cell death, although other nonthiol compounds and the antioxidative enzymes superoxide dismutase and catalase did not, suggesting that reactive oxygen species might not mediate cell death. In cells exposed to chloroacetaldehyde, levels of both total thiols and glutathione were significantly reduced. Chloroacetaldehyde also collapsed the mitochondrial membrane potential of these cells, induced the release of cytochrome c from mitochondria to the cytosol and significantly reduced cellular ATP levels during the course of death. The mitochondrial potential collapse was also prevented by thiol compounds. Flow cytometric analyses by means of annexin-V and propidium iodide double staining and immunofluorescence staining of active caspase-3 revealed that cells subjected to a lethal dose of chloroacetaldehyde displayed features characteristic of necrosis and that caspase-3 was not activated in response to chloroacetaldehyde. Taken together, these findings suggest that Saos-2 cells exposed to chloroacetaldehyde die by necrosis resulting from a decrease in intracellular thiols, disruption of the mitochondrial membrane potential and the depletion of cellular ATP.

Peripheral white blood cell toxicity induced by broad spectrum cyclin-dependent kinase inhibitors

Cyclin-dependent kinases (CDKs) have been pursued for more than a decade for the treatment of cancer. CDK inhibitors are expected to slow the rate of cell division and potentially increase the apoptotic fraction of rapidly dividing cells. Although CDK activity is often increased in tumors, normal dividing tissues are also susceptible to the cytostatic and cytotoxic effects of CDK inhibitor action. Therefore the typical toxicity profile associated with cytotoxic anti-cancer therapy, bone marrow suppression and gastrointestinal toxicity, is expected with CDK inhibitors. Bone marrow toxicity and the ensuing delayed peripheral leukocyte suppression often limit the therapeutic application of cytotoxic anticancer drugs. Here we characterize an unusual bone marrow-independent acute toxicity toward leukocytes from broad spectrum CDK inhibitors in monkeys and rodents. The potential combination of both acute and delayed immunosuppression would likely further restrict the application of these particular compounds. Since the cells targeted were non-proliferating, it was assumed that the toxicity was not driven by the intended pharmacological mechanism thereby facilitating the development of a testing strategy to identify compounds with a reduced potential for acute leukocyte toxicity. This testing strategy resulted in a CDK inhibitor void of bone marrow-independent leukocyte toxicity that is currently undergoing clinical testing.

Population pharmacokinetics of cyclophosphamide and its metabolites 4-hydroxycyclophosphamide, 2-dechloroethylcyclophosphamide, and phosphoramide mustard in a high-dose combination with Thiotepa and Carboplatin

The anticancer prodrug cyclophosphamide (CP) is activated by the formation of 4-hydroxycyclophosphamide (4OHCP), which decomposes into phosphoramide mustard (PM). This activation pathway is inhibited by thiotepa. CP is inactivated by formation of 2-dechloroethylcyclophosphamide (2DCECP). The aim of this study was to develop a population pharmacokinetic model describing the complex pharmacokinetics of CP, 4OHCP, 2DCECP, and PM when CP is administered in a high-dose combination with thiotepa and carboplatin. Patients received a combination of CP (1000-1500 mg/m/d), carboplatin (265-400 mg/m/d), and thiotepa (80-120 mg/m/d) administered in short infusions over 4 days. Twenty blood samples were collected per patient per course. Concentrations of CP, 4OHCP, 2DCECP, PM, thiotepa, and tepa were determined in plasma. Using NONMEM, an integrated population pharmacokinetic model was used to describe the pharmacokinetics of CP, 4OHCP, 2DCECP, and PM, including the already described processes of autoinduction of CP and the interaction with thiotepa. Data were available on 35 patients (70 courses). The pharmacokinetics of CP were described with a 2-compartment model, and those of 4OHCP, 2DCECP, and PM with 1-compartment models. Before onset of autoinduction, it was assumed that CP is eliminated through a noninducible pathway accounting for 20% of total CP clearance, whereas 2 inducible pathways resulted in formation of 4OHCP (75%) and 2DCECP (5%). It was assumed that 4OHCP was fully converted to PM. Induction of CP metabolism was mediated by 2 hypothetical amounts of enzyme whose quantities increased in time in the presence of CP (kenz=0.0223 and 0.0198 hours). Induction resulted in an increased formation of 4OHCP (approximately 50%), PM (approximately 50%), and 2DCECP (approximately 35%) during the 4-day course, and concomitant decreased exposure to CP (approximately 50%). The formation of 2DCECP was not inhibited by thiotepa. Apparent volumes of distribution of CP, PM, and 2DCECP could be estimated being 43.7, 55.5, and 18.5 L, respectively. Exposure to metabolites varied up to 9-fold. The complex population pharmacokinetics of CP, 4OHCP, 2DCECP, and PM in combination with thiotepa and carboplatin has been established and may form the basis for further treatment optimization with this combination.

Effects of amifostine on liver oxidative stress caused by cyclophosphamide administration to rats

Cyclophosphamide is an inactive cytostatic, which is metabolised into active metabolites mainly in the liver. During bioactivation, reactive oxygen species (ROS) are also formed, which can modify the components of both healthy and neoplastic cells leading to decreased antioxidative capacity. Amifostine is a drug that can inactivate ROS. The aim of the present study was to evaluate the influence of amifostine on the antioxidative system of the liver of rats exposed to cyclophosphamide. Intraperitoneal administration of cyclophosphamide was found to decrease the activity of liver antioxidative enzymes, i.e. superoxide dismutase, glutathione peroxidase and glutathione reductase, and to increase catalase activity. Amifostine slightly influenced antioxidative enzyme activity, causing a significant increase only in superoxide dismutase activity. Co-administration of cyclophosphamide and amifostine nearly prevented changes in activities of superoxide dismutase, glutathione reductase and catalase, as well as to a high degree of glutathione peroxidase. Cyclophosphamide also evoked a decrease in the level of non-enzymatic antioxidants, such as reduced glutathione and vitamins C, E and A, as well as total antioxidant status. Administration of amifostine alone caused a significant increase in non-enzymatic antioxidant level that resulted in an increase in total antioxidant status. Administration of amifostine together with cyclophosphamide to a large extent prevented changes in the evaluated non-enzymatic antioxidative parameters, decreasing values of their concentration to the values of control group. Changes of liver antioxidative abilities during detoxification of cyclophosphamide were accompanied by intensified lipid peroxidation, manifested by an increase in concentration of products such as malondialdehyde and 4-hydroxynonenal. Amifostine caused the inhibition of lipid peroxidation in the liver of both control and cyclophosphamide-treated rats. In conclusion, our results suggest that amifostine significantly protects liver antioxidant properties from changes caused by cyclophosphamide treatment and in consequence prevents oxidative stress and phospholipid peroxidative damage.

Pharmacokinetic-pharmacodynamic guided trial design in oncology

The application of pharmacokinetic (PK) and pharmacodynamic (PD) modeling in drug development has emerged during the past decades and it is has been suggested that the investigation of PK-PD relationships during drug development may facilitate and optimize the design of subsequent clinical development. Especially in oncology, well designed PK-PD modeling could be extremely useful as anticancer agents usually have a very narrow therapeutic index. This paper describes the application of the current insights in the use of PK-PD modeling to the design of clinical trials in oncology. The application of PK-PD modeling in each separate stage of (pre)clinical drug development of anticancer agents is discussed. The implementation of this approach is illustrated with the clinical development of docetaxel.

Relationship between exposure and toxicity in high-dose chemotherapy with cyclophosphamide, thiotepa and carboplatin

BACKGROUND

High-dose chemotherapy in combination with peripheral blood progenitor cell transplantation is widely used in the treatment of several malignancies. The use of high-dose chemotherapy can be complicated by the occurrence of severe and sometimes life threatening toxicity. A wide interpatient variability in toxicity is encountered, which may be caused by variability in the pharmacokinetics of the agents. The aim of this study was to establish the pharmacokinetics of cyclophosphamide, thiotepa, carboplatin and all relevant metabolites in a widely used high-dose combination and to study possible relationships between the pharmacokinetics and toxicity.

PATIENTS AND METHODS

Blood samples were collected from patients treated with modifications of the CTCb regimen consisting of cyclophosphamide (1000-1500 mg/m2/day), carboplatin (265-400 mg/m2/day) and thiotepa (80-120 mg/m2/day) as short infusions for four consecutive days. Thiotepa and its main metabolite tepa, ultrafilterable carboplatin, cyclophosphamide and its activated metabolites 4-hydroxycyclophosphamide and phosphoramide mustard were determined. Pharmacokinetics were assessed with the use of population pharmacokinetic analyses. Relationship between the area under the concentration-time curves (AUCs) of these compounds and toxicity were tested.

RESULTS

A total of 46 patients (83 courses of chemotherapy) was included. Relationships were identified between elevation of transaminases and the thiotepa and tepa AUC, mucositis and the tepa AUC and ototoxicity and the carboplatin AUC. A strong trend between the 4-hydroxycyclophosphamide AUC and veno-occlusive disease was found.

CONCLUSIONS

The complex pharmacokinetics of the different agents and their metabolites have been established and several relationships between the pharmacokinetics and toxicity were identified. These findings may form the basis for further treatment optimisation and dose-individualisation in this high-dose chemotherapy combination.

Validation of a therapeutic drug monitoring strategy for thiotepa in a high-dose chemotherapy regimen

Thiotepa is an alkylating agent widely used in high-dose chemotherapy. The pharmacokinetics of thiotepa and its main metabolite tepa show a wide interpatient variability, which may be responsible for the interpatient variability in toxicity. The aim of this study was to develop and validate a pharmacokinetically guided dosing strategy with the sum of the thiotepa and tepa area under the concentration-time curve (AUC) as the target parameter. A total of 46 patients received 77 courses of chemotherapy with thiotepa (80-120 mg/m(2) per day) divided into two daily 30-minute infusions in combination with cyclophosphamide and carboplatin. Patients received up to three courses of chemotherapy. The interpatient, course-to-course, day-to-day, and residual variability in the pharmacokinetics of thiotepa and tepa were estimated with a population analysis with the software program NONMEM. The planned strategy consisted of the collection of blood samples on day 1 and either day 3 or day 4 of each 4-day course. The thiotepa dose was planned to be adjusted on day 3 of each course and before the start of a new course on the basis of Bayesian predictions of the pharmacokinetics with data of day 1 and/or the possible previous course. The prediction procedure was validated by dividing the dataset into an index and validation set. The Bayesian predictions of the validation set were compared with true AUC values generated with individual fits of each course. The performance of the complete strategy was tested with a simulation procedure in 1,000 patients. Interpatient variability and course-to-course variability were in the same order (+/-20%); day-to-day variability was less (+/-15%). The sampling strategy resulted in predictions of the AUC without bias with acceptable precision (+/-20%). The simulation showed that variability in exposure was effectively decreased by the dosing strategy. This strategy resulted in a reduction in the variability of the exposure to thiotepa and tepa and can be implemented in a clinical study.

Sensitive gas chromatographic determination of the cyclophosphamide metabolite 2-dechloroethylcyclophosphamide in human plasma

Cyclophosphamide (CP) is one of the most frequently used anticancer agents. It is a prodrug requiring activation before exerting cytotoxicity. CP is deactivated to 2-dechloroethylcyclophosphamide (2-DCECP) with formation of an equimolar amount of chloroacetaldehyde. The aim of this study was to develop and validate a sensitive and simple assay for 2-DCECP in plasma of patients treated with CP. Sample pre-treatment consisted of solid-phase extraction of 500 microl of plasma over OASIS HLB (1 ml) cartridges with trofosfamide as internal standard. Separation and detection of underivatized 2-DCECP was performed with capillary gas chromatography with nitrogen/phosphorous selective detection. Extraction recovery of 2-DCECP exceeded 87%. No interference from endogenous compounds, other metabolites of CP and frequently coadministered drugs was detected. The assay was linear in the range of 5-5000 ng/ml in plasma. Accuracy, within-day and between-day precision were less than 11% for the complete concentration range. In plasma, 2-DCECP was stable for at least 1 month when kept at -70 degrees C. Analysis of samples from patients treated with CP demonstrated the applicability of the assay. In conclusion, a sensitive and simple assay for 2-DCECP in plasma, which meets the current requirements for bioanalytical assays, was developed.