Pharmacometrics for treatment optimization and drug development in oncology

This thesis describes the application of pharmacometrics to optimize treatment with existing therapies and to support development of novel drugs in the area of oncology. In the field of pharmacometrics, data on pharmacokinetic (PK) and pharmacodynamic (PD) properties of drugs are characterized using a combination of mathematical and statistical models. These properties give insight in the fate of a drug in the body (PK) and in its desired and undesired (toxic) effects (PD). Quantification of PK-PD relationships in mathematical and statistical models allows for understanding the characteristics of a drug. Additionally, these models can help answer questions to improve clinical application of drugs and supports decision making in drug development. This thesis describes various examples of applying modeling and simulation methods to improve current treatments and support development of new drugs in oncology. Chapter 1 focuses on the pharmacology of tamoxifen and strategies to individualize dosing of tamoxifen by applying dose adjustments based on endoxifen concentrations. In chapter 2 a pharmacometric approach is used to determine a first-in-human dose for a novel monoclonal antibody and to evaluate its pharmacokinetic properties. In chapter 3 PK-PD modeling is performed to describe pharmacodynamic properties (i.e. toxicity) of different anti-cancer drugs, such as anthracyclines, trastuzumab and docetaxel.This thesis demonstrates that pharmacometrics provides powerful techniques to answer (clinical) pharmacological questions that are often impossible to answer using conventional statistical methods. The examples in this thesis, are applied to the therapeutic area of oncology, though can in part also be applied to answer pharmacological questions in other therapeutic fields and contribute to improved and safer drug treatment in patients

Pharmacometrics for treatment optimization and drug development in oncology

This thesis describes the application of pharmacometrics to optimize treatment with existing therapies and to support development of novel drugs in the area of oncology. In the field of pharmacometrics, data on pharmacokinetic (PK) and pharmacodynamic (PD) properties of drugs are characterized using a combination of mathematical and statistical models. These properties give insight in the fate of a drug in the body (PK) and in its desired and undesired (toxic) effects (PD). Quantification of PK-PD relationships in mathematical and statistical models allows for understanding the characteristics of a drug. Additionally, these models can help answer questions to improve clinical application of drugs and supports decision making in drug development. This thesis describes various examples of applying modeling and simulation methods to improve current treatments and support development of new drugs in oncology. Chapter 1 focuses on the pharmacology of tamoxifen and strategies to individualize dosing of tamoxifen by applying dose adjustments based on endoxifen concentrations. In chapter 2 a pharmacometric approach is used to determine a first-in-human dose for a novel monoclonal antibody and to evaluate its pharmacokinetic properties. In chapter 3 PK-PD modeling is performed to describe pharmacodynamic properties (i.e. toxicity) of different anti-cancer drugs, such as anthracyclines, trastuzumab and docetaxel.This thesis demonstrates that pharmacometrics provides powerful techniques to answer (clinical) pharmacological questions that are often impossible to answer using conventional statistical methods. The examples in this thesis, are applied to the therapeutic area of oncology, though can in part also be applied to answer pharmacological questions in other therapeutic fields and contribute to improved and safer drug treatment in patients

Effects of Pharmacogenetics on the Pharmacokinetics and Pharmacodynamics of Tamoxifen

The antiestrogenic drug tamoxifen is widely used in the treatment of estrogen receptor-α-positive breast cancer and substantially decreases recurrence and mortality rates. However, high interindividual variability in response is observed, calling for a personalized approach to tamoxifen treatment. Tamoxifen is bioactivated by cytochrome P450 (CYP) enzymes such as CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4/5, resulting in the formation of active metabolites, including 4-hydroxy-tamoxifen and endoxifen. Therefore, polymorphisms in the genes encoding these enzymes are proposed to influence tamoxifen and active tamoxifen metabolites in the serum and consequently affect patient response rates. To tailor tamoxifen treatment, multiple studies have been performed to clarify the influence of polymorphisms on its pharmacokinetics and pharmacodynamics. Nevertheless, personalized treatment of tamoxifen based on genotyping has not yet met consensus. This article critically reviews the published data on the effect of various genetic polymorphisms on the pharmacokinetics and pharmacodynamics of tamoxifen, and reviews the clinical implications of its findings. For each CYP enzyme, the influence of polymorphisms on pharmacokinetic and pharmacodynamic outcome measures is described throughout this review. No clear effects on pharmacokinetics and pharmacodynamics were seen for various polymorphisms in the CYP encoding genes CYP2B6, CYP2C9, CYP2C19 and CYP3A4/5. For CYP2D6, there was a clear gene-exposure effect that was able to partially explain the interindividual variability in plasma concentrations of the pharmacologically most active metabolite endoxifen; however, a clear exposure-response effect remained controversial. These controversial findings and the partial contribution of genotype in explaining interindividual variability in plasma concentrations of, in particular, endoxifen, imply that tailored tamoxifen treatment may not be fully realized through pharmacogenetics of metabolizing enzymes alone

Effects of Pharmacogenetics on the Pharmacokinetics and Pharmacodynamics of Tamoxifen

The antiestrogenic drug tamoxifen is widely used in the treatment of estrogen receptor-alpha-positive breast cancer and substantially decreases recurrence and mortality rates. However, high interindividual variability in response is observed, calling for a personalized approach to tamoxifen treatment. Tamoxifen is bioactivated by cytochrome P450 (CYP) enzymes such as CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4/5, resulting in the formation of active metabolites, including 4-hydroxy-tamoxifen and endoxifen. Therefore, polymorphisms in the genes encoding these enzymes are proposed to influence tamoxifen and active tamoxifen metabolites in the serum and consequently affect patient response rates. To tailor tamoxifen treatment, multiple studies have been performed to clarify the influence of polymorphisms on its pharmacokinetics and pharmacodynamics. Nevertheless, personalized treatment of tamoxifen based on genotyping has not yet met consensus. This article critically reviews the published data on the effect of various genetic polymorphisms on the pharmacokinetics and pharmacodynamics of tamoxifen, and reviews the clinical implications of its findings. For each CYP enzyme, the influence of polymorphisms on pharmacokinetic and pharmacodynamic outcome measures is described throughout this review. No clear effects on pharmacokinetics and pharmacodynamics were seen for various polymorphisms in the CYP encoding genes CYP2B6, CYP2C9, CYP2C19 and CYP3A4/5. For CYP2D6, there was a clear gene-exposure effect that was able to partially explain the interindividual variability in plasma concentrations of the pharmacologically most active metabolite endoxifen; however, a clear exposure-response effect remained controversial. These controversial findings and the partial contribution of genotype in explaining interindividual variability in plasma concentrations of, in particular, endoxifen, imply that tailored tamoxifen treatment may not be fully realized through pharmacogenetics of metabolizing enzymes alone

Incidence of hematologic toxicity in older adults treated with gemcitabine or a gemcitabine-containing regimen in routine clinical practice : a multicenter retrospective cohort study

PURPOSE: Older adults receiving cytotoxic agents may be more susceptible to hematologic toxicities because of progressive reduction in organ functions and multiple co-morbidities. Because older adults are under-represented in clinical trials, this retrospective study aims to evaluate hematologic toxicity of gemcitabine-based regimens in older patients compared with their younger counterparts in clinical practice. PATIENTS AND METHODS: A total of 494 patients routinely treated with gemcitabine, either alone or in combination with platinum-based drugs, in the Slotervaart Hospital or The Netherlands Cancer Institute between January 2003 and January 2013 were enrolled. Patient characteristics, underlying malignancy, treatment regimen, administered doses of gemcitabine, and laboratory values were retrospectively collected from electronic patient records. The relative dose intensity achieved in older patients and their younger counterparts was evaluated using the Wilcoxon rank sum test. Incidence of hematologic toxicity in older adults (age ≥70 years) and their younger counterparts (age <70 years) was compared using the Fisher's exact test. Predictors of experiencing Grade 3 or 4 hematologic toxicity were evaluated using logistic regression. RESULTS: Patient characteristics and baseline laboratory values were equally distributed among the two age groups, except for the estimated glomerular filtration rate being significantly lower in the older patients. Reduction of the first administered dose of gemcitabine was significantly more frequently applied in the older patients (p = 0.03). However, no significant difference in the gemcitabine relative dose intensity over the median number of four treatment cycles was observed (65 % in the older patients group vs. 67 % in the younger control group). Incidence of severe hematologic toxicity (Grade ≥3) was not significantly higher in the older patients. A subset analysis of nadir blood counts showed a trend towards an increased incidence of Grade ≥3 hematologic toxicity for the older patients in the gemcitabine-cisplatin treatment group. Moreover, the relative risk for developing Grade 3 or 4 leukocytopenia in the older patients was increased fivefold (p = 0.007) for combination therapy with gemcitabine and cisplatin. Blood transfusions were administered nearly twofold more frequently in the older patients, but this difference did not reach statistical significance. CONCLUSION: Treatment with gemcitabine or a gemcitabine-containing regimen appeared to be feasible and well tolerated in the older patients who were selected to receive chemotherapy. Overall, patients ≥70 years of age did not incur a higher incidence of severe or life-threatening hematologic toxicity nor did they undergo more frequent or larger dose adjustments. These data support additional treatment-specific prospective studies and clinical trials in older cancer patients to optimize treatment benefit and risk in this heterogeneous older patient population

Incidence of hematologic toxicity in older adults treated with gemcitabine or a gemcitabine-containing regimen in routine clinical practice: a multicenter retrospective cohort study

PURPOSE: Older adults receiving cytotoxic agents may be more susceptible to hematologic toxicities because of progressive reduction in organ functions and multiple co-morbidities. Because older adults are under-represented in clinical trials, this retrospective study aims to evaluate hematologic toxicity of gemcitabine-based regimens in older patients compared with their younger counterparts in clinical practice. PATIENTS AND METHODS: A total of 494 patients routinely treated with gemcitabine, either alone or in combination with platinum-based drugs, in the Slotervaart Hospital or The Netherlands Cancer Institute between January 2003 and January 2013 were enrolled. Patient characteristics, underlying malignancy, treatment regimen, administered doses of gemcitabine, and laboratory values were retrospectively collected from electronic patient records. The relative dose intensity achieved in older patients and their younger counterparts was evaluated using the Wilcoxon rank sum test. Incidence of hematologic toxicity in older adults (age ≥70 years) and their younger counterparts (age <70 years) was compared using the Fisher's exact test. Predictors of experiencing Grade 3 or 4 hematologic toxicity were evaluated using logistic regression. RESULTS: Patient characteristics and baseline laboratory values were equally distributed among the two age groups, except for the estimated glomerular filtration rate being significantly lower in the older patients. Reduction of the first administered dose of gemcitabine was significantly more frequently applied in the older patients (p = 0.03). However, no significant difference in the gemcitabine relative dose intensity over the median number of four treatment cycles was observed (65 % in the older patients group vs. 67 % in the younger control group). Incidence of severe hematologic toxicity (Grade ≥3) was not significantly higher in the older patients. A subset analysis of nadir blood counts showed a trend towards an increased incidence of Grade ≥3 hematologic toxicity for the older patients in the gemcitabine-cisplatin treatment group. Moreover, the relative risk for developing Grade 3 or 4 leukocytopenia in the older patients was increased fivefold (p = 0.007) for combination therapy with gemcitabine and cisplatin. Blood transfusions were administered nearly twofold more frequently in the older patients, but this difference did not reach statistical significance. CONCLUSION: Treatment with gemcitabine or a gemcitabine-containing regimen appeared to be feasible and well tolerated in the older patients who were selected to receive chemotherapy. Overall, patients ≥70 years of age did not incur a higher incidence of severe or life-threatening hematologic toxicity nor did they undergo more frequent or larger dose adjustments. These data support additional treatment-specific prospective studies and clinical trials in older cancer patients to optimize treatment benefit and risk in this heterogeneous older patient population

Pharmacokinetics and excretion of 14C–Plitidepsin in patients with advanced cancer

Summary: Plitidepsin (Aplidin®) is a marine-derived anticancer compound currently investigated in phase III clinical trials. This article describes the distribution, metabolism and excretion of this novel agent and it mainly aims to identify the major routes of elimination. Six subjects were enrolled in a mass balance study during which radiolabelled plitidepsin was administered as a 3-h intravenous infusion. Blood samples were taken and urine and faeces were collected. Total radioactivity (TRA) analysis using Liquid Scintillation Counting (LSC) was done to determine the amount of radioactivity excreted from the body and plitidepsin concentrations in whole blood, plasma and urine were determined by validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays. In total, a mean of 77.4% of the administered radioactivity was excreted over a time period of 20 days, of which 71.3% was recovered in faeces and 6.1% was found in urine. The majority excreted in urine was accounted for by unchanged plitidepsin, with only 1.5% of the total administered dose explained by metabolites in urine. Faeces, on the other hand contained low levels of parent compound, which means that most of the TRA excreted in faeces was accounted for by metabolites. TRA levels were 3.7 times higher in whole blood compared to plasma. Plitidepsin was widely distributed and plasma clearance was low. This study shows that red blood cells are a major distribution compartment and that the biliary route is the main route of total radioactivity excretion