High-dose ifosfamide for soft tissue sarcomas: set the scene, or senescence?

Systematic therapy for unresectable or metastatic soft-tissue sarcomas: past, present, and future

Unresectable or metastatic disease occurs in 40% to 60% of soft-tissue sarcoma (STS) patients and portends a poor prognosis. For decades, doxorubicin has formed the backbone of systemic treatment, with response rates of approximately 26%. Patients progressing following first-line therapy were left with few proven options. No other cytotoxic chemotherapy agent or combination has demonstrated superiority to doxorubicin. Advances in targeted therapy of STS have been hindered by STS heterogeneity and poorly understood disease biology. Despite challenges, progress has been made in specific STS subtypes. Here, we highlight the challenges, progress, and lessons learned from STS trials published in the last 20 to 25 years.

The use of chemotherapy in soft-tissue sarcomas

The treatment of advanced soft-tissue sarcomas is often palliative, although a subset of patients may be cured or have a long disease-free interval. This paper reviews the historical data over 30 years of treatment that has led to the use of ifosfamide and doxorubicin as the mainstay in the treatment of metastatic disease. These treatments have a high toxicity, relative to other chemotherapeutic regimens, with median response durations on the order of months. Agents developed in the last few years, whose role in the treatment of sarcomas is still evolving, are discussed as well. Finally, we discuss the role of chemotherapy in combination with surgery and radiation in the adjuvant and neoadjuvant settings.

Dose-finding and pharmacological study of ifosfamide in combination with paclitaxel and carboplatin in resistant small-cell lung cancer

BACKGROUND

To find the maximum tolerated dose for ifosfamide in combination with paclitaxel and carboplatin in small-cell lung cancer patients (SCLC), who are resistant to cyclophosphamide, doxorubicin and etoposide (CDE).

PATIENTS AND METHODS

Different dose schedules of ifosfamide were combined with fixed doses of paclitaxel 175 mg/m2 and carboplatin AUC 6 mg/ml min. Included were 30 patients, with a median age of 60 years, and median time off prior cytotoxic treatment of 8 weeks. All patients were previously treated with CDE and 11 had received re-induction CDE.

RESULTS

Dose limiting toxicity of our schedule was persistent thrombocytopenia. None of the patients developed neutropenic fever. Non-haematological toxicity was mild, although two treatment-related deaths occurred. Fifty-four percent of patients had a partial response and median survival time was twenty-five weeks.

CONCLUSIONS

The maximum tolerated dose of this combination for patients with resistant SCLC is ifosfamide 2000 mg/m2 in combination with paclitaxel 175 mg/m2 and carboplatin AUC 6 mg/ml min administered on the first day of a 21-day cycle.

Clinical pharmacokinetics and pharmacodynamics of ifosfamide and its metabolites

This review discusses several issues in the clinical pharmacology of the antitumour agent ifosfamide and its metabolites. Ifosfamide is effective in a large number of malignant diseases. Its use, however, can be accompanied by haematological toxicity, neurotoxicity and nephrotoxicity. Since its development in the middle of the 1960s, most of the extensive metabolism of ifosfamide has been elucidated. Identification of specific isoenzymes responsible for ifosfamide metabolism may lead to an improved efficacy/toxicity ratio by modulation of the metabolic pathways. Whether ifosfamide is specifically transported by erythrocytes and which activated ifosfamide metabolites play a key role in this transport is currently being debated. In most clinical pharmacokinetic studies, the phenomenon of autoinduction has been observed, but the mechanism is not completely understood. Assessment of the pharmacokinetics of ifosfamide and metabolites has long been impaired by the lack of reliable bioanalytical assays. The recent development of improved bioanalytical assays has changed this dramatically, allowing extensive pharmacokinetic assessment, identifying key issues such as population differences in pharmacokinetic parameters, differences in elimination dependent upon route and schedule of administration, implications of the chirality of the drug and interpatient pharmacokinetic variability. The mechanisms of action of cytotoxicity, neurotoxicity, urotoxicity and nephrotoxicity have been pivotal issues in the assessment of the pharmacodynamics of ifosfamide. Correlations between the new insights into ifosfamide metabolism, pharmacokinetics and pharmacodynamics will rationalise the further development of therapeutic drug monitoring and dose individualisation of ifosfamide treatment.

Evaluation of the autoinduction of ifosfamide metabolism by a population pharmacokinetic approach using NONMEM

AIMS

This study investigated the population pharmacokinetics of ifosfamide in 15 patients treated for soft tissue sarcoma with 9 or 12 g m-2 ifosfamide by means of a 72 h continuous i.v. infusion.

METHODS

A model was developed using nonlinear mixed effects modelling (NONMEM) to describe the nonlinear pharmacokinetics of ifosfamide by linking the ifosfamide plasma concentrations to the extent of the autoinduction.

RESULTS

The proposed model revealed the effect of autoinduction on the disposition of ifosfamide. The initial clearance, volume of distribution, rate constant for enzyme degradation, induction half-life of the enzyme and the ifosfamide concentration at 50% of the maximum inhibition of enzyme degradation were estimated at 2.94 +/- 0.27 l h-1, 43.5 +/- 2.9 l, 0.0546 +/- 0. 0078 h-1, 12.7 h and 30.7 +/- 4.8 microM, respectively. Interindividual variabilities of initial clearance, volume of distribution, rate constant for enzyme degradation were 24.5, 23.4 and 22.7%, respectively. Proportional and additive variability not explained by the model were 13.6% and 0.0763 microM, respectively.

CONCLUSIONS

The absence of a lag time for the autoinduction of ifosfamide metabolism could be the result of an immediate inhibition of the enzymatic degradation of CYP3A4 by ifosfamide. By application of the autoinduction model individual pharmacokinetic profiles of patients were described with adequate precision. This model may therefore be used in the future development of a model to individualize dose selection in patients.