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

Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) methods for the therapeutic drug monitoring of cytotoxic anticancer drugs: An update

In the era of precision medicine, there is increasing evidence that conventional cytotoxic agents may be suitable candidates for therapeutic drug monitoring (TDM)- guided drug dosage adjustments and patient's tailored personalization of non-selective chemotherapies. To that end, many liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) assays have been developed for the quantification of conventional cytotoxic anticancer chemotherapies, that have been comprehensively and critically reviewed. The use of stable isotopically labelled internal standards (IS) of cytotoxic drugs was strikingly uncommon, accounting for only 48 % of the methods found, although their use could possible to suitably circumvent patients' samples matrix effects variability. Furthermore, this approach would increase the reliability of cytotoxic drug quantification in highly multi-mediated cancer patients with complex fluctuating pathophysiological and clinical conditions. LC-MS/MS assays can accommodate multiplexed analyses of cytotoxic drugs with optimal selectivity and specificity as well as short analytical times and, when using stable-isotopically labelled IS for quantification, provide concentrations measurements with a high degree of certainty. However, there are still organisational, pharmacological, and medical constraints to tackle before TDM of cytotoxic drugs can be more largely adopted in the clinics for contributing to our ever-lasting quest to improve cancer treatment outcomes.

Therapeutic drug monitoring

PURPOSE OF REVIEW

Traditionally, therapeutic drug monitoring has been used for the management of epilepsy, cardiac arrhythmias, asthma and depression. This review provides an update, particularly for the newer clinical applications, and how therapeutic drug monitoring (including use of analytical and interpretation tools) can improve clinical outcomes.

RECENT FINDINGS

Improved drug assay methodologies and a greater understanding of pharmacokinetic and pharmacodynamic mechanisms has allowed the use of therapeutic drug monitoring for immunosuppressant drugs in organ transplant recipients, antiretroviral agents for HIV/AIDS and antimetabolite drugs for leukaemia. In addition, new computer software to analyse drug concentrations in complex populations is being developed and introduced into routine clinical applications to allow increasingly patient-specific assay interpretation.

SUMMARY

Therapeutic drug monitoring assists in improving clinical success rates and minimizing toxicity. The use of therapeutic drug monitoring is therefore likely to become more widespread as new modalities are adopted.

Real-time dose adjustment of cyclophosphamide in a preparative regimen for hematopoietic cell transplant: a Bayesian pharmacokinetic approach

PURPOSE

Dose-related toxicity of cyclophosphamide may be reduced and therapeutic efficacy may be improved by pharmacokinetic sampling and dose adjustment to achieve a target area under the curve (AUC) for two of its metabolites, hydroxycyclophosphamide (HCY) and carboxyethylphosphoramide mustard (CEPM). To facilitate real-time dose adjustment, we developed open-source code within the statistical software R that incorporates individual data into a population pharmacokinetic model.

EXPERIMENTAL DESIGN

Dosage prediction performance was compared to that obtained with nonlinear mixed-effects modeling using NONMEM in 20 cancer patients receiving cyclophosphamide. Bayesian estimation of individual pharmacokinetic parameters was accomplished from limited (i.e., five samples over 0-16 hours) sampling of plasma HCY and CEPM after the initial cyclophosphamide dose. Conditional on individual pharmacokinetics, simulations of the AUC of both HCY and CEPM were provided for a range of second doses (i.e., 0-100 mg/kg cyclophosphamide).

RESULTS

The results compared favorably with NONMEM and returned accurate predictions for AUCs of HCY and CEPM with comparable mean absolute prediction error and root mean square prediction error. With our method, the mean absolute prediction error and root mean square prediction error of AUC CEPM were 11.0% and 12.8% and AUC HCY were 31.7% and 44.8%, respectively.

CONCLUSIONS

We developed dose adjustment software that potentially can be used to adjust cyclophosphamide dosing in a clinical setting, thus expanding the opportunity for pharmacokinetic individualization of cyclophosphamide. The software is simple to use (requiring no programming experience), reads individual patient data directly from an Excel spreadsheet, and runs in less than 5 minutes on a desktop PC.

Role of Cytochrome P450 Activity in the Fate of Anticancer Agents and in Drug Resistance

Although activity of cytochrome P450 isoenzymes (CYPs) plays a major role in the fate of anticancer agents in patients, there are relatively few clinical studies that evaluate drug metabolism with therapeutic outcome. Nevertheless, many clinical reports in various non-oncology fields have shown the dramatic importance of CYP activity in therapeutic efficacy, safety and interindividual variability of drug pharmacokinetics. Moreover, variability of drug metabolism in the liver as well as in cancer cells must also be considered as a potential factor mediating cancer resistance. This review underlines the role of drug metabolism mediated by CYPs in pharmacokinetic variability, drug resistance and safety. As examples, biotransformation pathways of tamoxifen, paclitaxel and imatinib are reviewed. This review emphasises the key role of therapeutic drug monitoring as a complementary tool of investigation to in vitro data. For instance, pharmacokinetic data of anticancer agents have not often been published within subpopulations of patients who show ultra-rapid, extensive or poor metabolism (e.g. due to CYP2D6 and CYP2C19 genotypes). Besides kinetic variability in the systemic circulation, induction of CYP activity may participate in creating drug resistance by speeding up the cancer agent degradation specifically in the target cells. For one cancer agent, various mechanisms of resistance are usually identified within different cell clones. This review also tries to emphasise that drug resistance mediated by CYP activity in cancer cells should be taken into consideration to a greater degree. The unequivocal identification of the metabolising enzymes involved in clinical conditions will eventually allow improvement and individualisation of anticancer agent therapy, i.e. drug dosage and selection. In addition, a more complete understanding of the metabolism of anticancer agents will assist in the prediction of drug-drug interactions, as anticancer agent combinations are becoming more prevalent.

Pharmacokinetics of high-dose chemotherapy

There is considerable variation in the severity of preparative regimen-related toxicity (RRT) in hematopoietic stem-cell transplantation (HSCT). This variation has been recognized to be due, in part, to the wide variation in the pharmacokinetics (PK) of high-dose chemotherapy (HDC). Consequently, therapeutic drug modeling and pharmacokinetic-directed therapy (PKDT) represents an attractive strategy in this setting. Advances in our understanding of drug metabolism, the nature of the active metabolites, and the ability to measure drug concentrations have led to the point where for some agents it is now possible to treat to a given PK end point with a great deal of reliability. In-depth knowledge of the PK and pharmacodynamics (PD) associations of the agents employed in the high-dose setting will make possible more efficient research into preparative regimen dosing intensity and comparisons of different preparative regimens as well as safer HSCT overall. In this review, we discuss PK and PD studies of high-dose cyclosphamide, melphalan, thiotepa, carmustine, cisplatin, carboplatin, paclitaxel, docetaxel, and busulfan.

Toxicity of the high-dose chemotherapy CTC regimen (cyclophosphamide, thiotepa, carboplatin): the Netherlands Cancer Institute experience

High-dose chemotherapy (HD-CT) has a role in the potentially curative treatment of several tumours. The relative efficacies of the different regimens have not been studied in comparative trials, but it is clear that toxicities differ significantly between them. We analysed the immediate and long-term toxicity in the first 100 consecutive patients treated with the CTC regimen (cyclophosphamide 6000 mg m(-2), carboplatin 1600 mg m(-2) (or 20 mg ml(-1) min under the curve (AUC)) both as daily 1 h infusion, thiotepa 480 mg m(-2) as twice daily 30 min infusion, all divided over 4 consecutive days) followed by peripheral blood progenitor cell reinfusion (PBPC-Tx). Most patients had high-risk (n=86) or metastatic (n=4) breast cancer, or a germ cell tumour (n=8). Two patients (with a medulloblastoma and an aesthesioneuroblastoma, respectively) received CTC as off-protocol salvage regimen. The main toxicity was bone marrow suppression. Most patients had PBPC-Tx with granulocyte colony-stimulating factor (G-CSF), and the median time to neutrophil count 500 x 10(6) l(-1) and platelet count >20 x 10(9) l(-1) without transfusion independence was 10 (range 8-25) and 13 (8-60) days, respectively. The toxic death rate was 1%. Other frequent toxicities were neutropenic fever requiring antibiotics (n=65), central catheter-related infection (n=12) or a bleeding episode (n=48), mostly epistaxis (n=26). Reversible cardiac toxicity was seen in six patients and pulmonary events occurred in seven patients (infection (n=6), embolism (n=1)). Grade 3-4 gastrointestinal toxicity was frequent: nausea and vomiting 55%, diarrhoea 28% and mild liver toxicity (transaminase elevations) 9%. One patient pretreated with cisplatin had a kidney transplantation 8 years after HD-CT. Late complications included reversible radiation pneumonitis (n=12) and chronic heart failure (n=2). We found five second solid malignancies and two myelodysplasias. In conclusion, the CTC regimen is associated with a moderate, mainly reversible, toxicity. Future studies need to compare the efficacy and toxicity of the different HD-CT regimens.

Evaluation of the nutritional and inflammatory status in cancer patients for the risk assessment of severe haematological toxicity following chemotherapy

BACKGROUND

The toxicity outcome of cancer patients receiving chemotherapy is difficult to predict. In this study the influence of malnutrition and inflammation on acute haematological toxicity was investigated.

PATIENTS AND METHODS

Between January 1999 and January 2000, 48 consecutive cancer patients experienced severe haematological toxicity (SHT), either neutropenic fever or severe thrombocytopenia, following various chemotherapy regimens. Their baseline characteristics were compared with those of 59 control patients. Previous chemotherapy regimens, type of chemotherapy, performance status (PS), calculated creatinine clearance, bilirubin, C-reactive protein (1), alpha-1 acid glycoprotein (2), albumin (3), pre-albumin (4) and the nutritional and inflammatory status (NIS) ratio [NIS = (1 x 2)/(3 x 4)] were studied. Statistical analysis was carried out using either a t-test or a chi-square test. A receiver operating characteristic (ROC) curve determined the cut-off value for NIS.

RESULTS

Patients experiencing SHT had a higher PS (P <0.001), inflammatory serum protein levels (P <0.001) and NIS ratio (P <0.0001), but lower haemoglobin (P <0.05) and serum-albumin levels (P <0.0001). Using a cut-off of 0 or 1 for PS and 1 for NIS, sensitivity was 98%, 43% and 89%; specificity was 38%, 90% and 66%, respectively. In 37 patients treated with topotecan as single agent, the determinants for SHT were PS (P <0.0001) and NIS (P <0.0001).

CONCLUSIONS

Altered nutritional and inflammatory status correlates with increased risk of severe haematological toxicity following anticancer chemotherapy.