A. Sparreboom

Irinotecan-induced diarrhea: Functional significance of the polymorphic ABCC2 transporter protein

Interindividual pharmacokinetic variability of the anticancer agent irinotecan is high. Life‐threatening diarrhea is observed in up to 25% of patients receiving irinotecan and has been related with irinotecan pharmacokinetics and UGT1A1 genotype status. Here, we explore the association of ABCC2 (MRP2) polymorphisms and haplotypes with irinotecan disposition and diarrhea. A cohort of 167 Caucasian cancer patients who were previously assessed for irinotecan pharmacokinetics (90‐min infusion given every 21 days), toxicity, and UGT1A1*28 genotype were genotyped for polymorphisms in ABCC2 using Pyrosequencing. Fifteen ABCC2 haplotypes were identified in the studied patients. The haplotype ABCC2*2 was associated with lower irinotecan clearance (28.3 versus 31.6u2009l/h; P=0.020). In patients who did not carry a UGT1A1*28 allele, a significant reduction of severe diarrhea was noted in patients with the ABCC2*2 haplotype (10 versus 44% odds ratio, 0.15; 95% confidence interval, 0.04–0.61; P=0.005). This effect was not observed in patients with at least one UGT1A1*28 allele (32 versus 20% odds ratio, 1.87; 95% confidence interval, 0.49–7.05; P=0.354). This study suggests that the presence of the ABCC2*2 haplotype is associated with less irinotecan‐related diarrhea, maybe as a consequence of reduced hepatobiliary secretion of irinotecan. As the association was seen in patients not genetically predisposed at risk for diarrhea due to UGT1A1*28, confirmatory studies of the relationships of ABCC2 genotypes and irinotecan disposition and toxicity are warranted.

Mechanism-based models for topotecan-induced neutropenia

A semiphysiologic pharmacokinetic‐pharmacodynamic model was applied to describe topotecan‐induced neutropenia, to quantify interindividual and intraindividual pharmacodynamic variability, and to study the effect of covariates on the model.

The use of oral cytotoxic and cytostatic drugs in cancer treatment

Although with a few exceptions, most new anticancer agents are initially developed for intravenous use, oral treatment with anticancer agents is, if feasible, to be preferred, as this route of administration is convenient to patients, reduces administration costs and facilitates the use of more chronic treatment regimens. Recent studies have identified various physiological barriers limiting the oral absorption of anticancer drugs. Presently, several strategies are explored to alter the low and variable oral bioavailability of several important anticancer agents by taking advantage of an intentional interaction between anticancer agents and drugs that modulate active intestinal drug transporters or (intestinal) enzymes.

Factors affecting pharmacokinetic variability of oral topotecan: A population analysis

The aim of this study was to characterise the pharmacokinetics of the anticancer agent topotecan, and explore the influence of patient covariates and interoccasion variability on drug disposition. Data were obtained from 190 patients who received the drug as a 30-min infusion (N=72) or orally (N=118). The population model was built with the use of NONMEM to identify candidate covariates, and obtain models for clearance (CL) and volume of distribution. The final models were based on first-order absorption with lag-time (oral data), and a two-compartment model with linear elimination from the central compartment. The Cockcroft–Gault creatinine clearance (CrCl) and WHO performance status (PS) were the only significant covariates: CL=(12.8+2.1 × CrCl) × (1−0.12 × PS). For the volume of distribution, a correlation was found between body weight and the central volume (V1)=0.58 × body weight. Based on the structural models, a limited-sampling strategy was developed with minor bias and good precision that can be applied a posteriori using timed samples obtained at 1.5, and 6u2009h after the administration of topotecan. In conclusion, a population pharmacokinetic model for topotecan has been developed that incorporates measures of renal function and PS to predict CL. In combination with drug monitoring, the limited sampling strategy allows individualised treatment for patients receiving oral topotecan.

Dose-dense cisplatin/paclitaxel: a well-tolerated and highly effective chemotherapeutic regimen in patients with advanced ovarian cancer

A randomised phase I/II trial with weekly cisplatin 70 mg/m(2) (days 1, 8, 15, 29, 36, 43) in combination with escalating doses of paclitaxel either 4-weekly or weekly was conducted in 49 patients with ovarian cancer; patients were chemotherapy-nai;ve or had a first relapse after platinum-based chemotherapy. Paclitaxel could be safely escalated to 225 mg/m(2) 4-weekly or 100 mg/m(2) weekly, with fatigue as the major adverse event. Myelosuppression, renal toxicity and neurotoxicity were mild to moderate. Pharmacokinetic analysis showed an approximately 2-fold reduction of DNA-adduct formation in leucocytes compared with cisplatin without paclitaxel. No pharmacokinetic interaction was found between paclitaxel and cisplatin. After (re-)induction, additional chemotherapy consisted of conventional paclitaxel/cisplatin, paclitaxel/carboplatin, paclitaxel single agent or carboplatin/cyclophosphamide. The overall response rate was 94% in 17 evaluable chemotherapy-nai;ve patients and 84% in 25 patients with recurrent disease. Median progression-free survival (PFS) was 17 months (chemotherapy-nai;ve: 23 months, recurrent: 11 months) and median overall survival was 41 months (chemotherapy-nai;ve: 48 months, recurrent: 24 months). In conclusion, both cisplatin/paclitaxel regimens showed excellent activity with manageable toxicity in patients with advanced ovarian cancer.

The development of combination therapy involving camptothecins: a review of preclinical and early clinical studies

Camptothecin analogues are a family of anticancer agents with a unique mechanism of action, which is the reversible inhibition of DNA topoisomerase I (1, 2). DNA topoisomerases are essential nuclear enzymes involved in multiple functions such as chromosomal recombination, DNA repair, transcription and chromatin assembly. Topoisomerase I inhibitors exert their cytotoxic action through the stabilization of the topoisomerase I-DNA complex, the so-called cleavable complex. This results in collision of the DNA replication fork, finally leading to irreversible DNA double-strand breaks and cell death (3,4). Topoisomerase I inhibitors are of great clinical interest because of their unique mode of action, their important antitumour activity as single agents in a broad spectrum of tumour types (5-30 and the high expression of the enzyme in various human tumour types (31-34). In addition, topoisomerase I inhibitors may also interfere with the processes involved in DNA repair (35-37). The latter renders them attractive for further investigations of combination therapies, especially involving those with DNA-damaging agents. Preclinical studies have revealed synergism between topoisomerase I inhibitors and drugs such as cisplatin, topoisomerase II inhibitors and paclitaxel in a number of different human cancer cell lines and xenografts. This paper reviews the development of combination therapy with topoisomerase I inhibitors with a focus on the two topoisomerase I inhibitors [irinotecan and

Differential modulation of cisplatin accumulation in leukocytes and tumor cell lines by the paclitaxel vehicle Cremophor EL

BACKGROUNDnSeveral clinical studies have shown that polychemotherapy with the taxanes paclitaxel or docetaxel preceded or followed by cisplatin is associated with important schedule-dependent differences in toxicities, such as leukocytopenia. In general, the pharmacokinetics of both drugs during the combined treatment are unaltered, suggesting that a pharmacodynamic interaction might have occurred.nnnMATERIALS AND METHODSnIn order to gain insight into this pharmacologic interaction, we performed in vitro drug accumulation studies using peripheral blood leukocytes and a panel of tumor and non-malignant cell lines with paclitaxel and docetaxel, as well as with their respective formulation vehicles Cremophor EL and Tween 80.nnnRESULTSnOur results show a significant reduction in the intracellular cisplatin concentration in leukocytes of up to 42% in the presence of Cremophor EL and Tween 80 as compared to the control. This pharmacodynamic interaction of these surfactants with cisplatin seems to be specific for haematopoietic cells, and does not occur in solid tumor cells.nnnCONCLUSIONnThe present data suggest that the pharmaceutical vehicles Cremophor EL and Tween 80 might contribute to the reduced cisplatin-associated myelotoxicity observed in the clinical combination chemotherapy studies with paclitaxel and docetaxel.

Irinotecan pharmacokinetics-pharmacodynamics: the clinical relevance of prolonged exposure to SN-38

We have shown previously that the terminal disposition half-life of SN-38, the active metabolite of irinotecan, is much longer than earlier thought. Currently, it is not known whether this prolonged exposure has any relevance toward SN-38-induced toxicity. Here, we found that SN-38 concentrations present in human plasma for up to 3 weeks after a single irinotecan infusion induce significant cytotoxicity in vitro. Using pharmacokinetic data from 26 patients, with sampling up to 500u2009h, relationships were evaluated between systemic exposure (AUC) to SN-38 and the per cent decrease in absolute neutrophil count (ANC) at nadir, or by taking the entire time course of ANC into account (AOC). The time course of SN-38 concentrations (AUC500u2009h) was significantly related to this AOC (P<0.001). Based on these findings, a new limited-sampling model was developed for SN-38 AUC500u2009h using only two timed samples: AUC500u2009h=(6.588×C2.5u2009h)+(146.4×C49.5u2009h)+15.53, where C2.5u2009h and C49.5u2009h are plasma concentrations at 2.5 and 49.5u2009h after start of infusion, respectively. The use of this limited-sampling model may open up historic databases to retrospectively obtain information about SN-38-induced toxicity in patients treated with irinotecan.

Dose and schedule-finding study of oral topotecan and weekly cisplatin in patients with recurrent ovarian cancer

Both weekly cisplatin chemotherapy and single agent topotecan have proven to be effective in recurrent ovarian cancer. Preclinical data show synergism between cisplatin and topotecan. Side effects for this combination are drug sequence dependent and predominantly haematologic. Since preclinical data suggest that Cremophor EL (CrEL), the formulation vehicle of paclitaxel, has a protective effect on haematological toxicity of cisplatin, CrEL was added to the combination cisplatin and topotecan. In this phase I study, escalating doses of oral topotecan administered on day 1, 2, 8, 9, 15, 16, 29, 30, 36, 37, 43, 44 were combined with weekly cisplatin 70 mg m–2d–1on day 1, 8, 15, 29, 36, 43 (scheme A) or with the presumably less myelotoxic sequence weekly cisplatin day 2, 9, 16, 30, 37, 44 (scheme B). In scheme C, CrEL 12 ml was administered prior to cisplatin in the sequence of Scheme A. 18 patients have received a total of 85 courses. In scheme A 4/10 patients, all treated with topotecan 0.45 mg m–2d–1, experienced DLT: 1 patient had vomiting grade 4, 1 patient had grade 4 neutropenia >5 days, 1 patient had >2 weeks delay due to thrombocytopenia and 1 patient due to neutropenia. Both patients in scheme B (topotecan 0.45 mg m–2d–1) had DLT due to a delay > 2 weeks because of prolonged haematological toxicity. No DLT was observed in the first 3 patients in scheme C (topotecan 0.45 mg m–2d–1). However, 2 out of 3 patients treated at dose level topotecan 0.60 mg m–2d–1in scheme C experienced DLT due to >2 weeks delay because of persistent thrombocytopenia or neutropenia. We conclude that there is a modest clinical effect of CrEL on haematological toxicity for this cisplatin-based combination regimen, which seems to reduce these side effects but does not really enable an increase of the oral topotecan dose.

Modulation of cisplatin pharmacodynamics by Cremophor EL: experimental and clinical studies

The paclitaxel vehicle Cremophor EL (CrEL) has been shown to selectively inhibit the accumulation of cisplatin in peripheral blood leucocytes, but not in tumour cells in vitro, and we hypothesised that this phenomenon is responsible for the improvement of the therapeutic index of cisplatin observed in combination studies with paclitaxel. Here, we report on studies assessing the interaction between CrEL and cisplatin in a murine model, and involving the potential clinical applicability of CrEL as a protector for cisplatin-associated haematological side-effects. In mice, CrEL (0.17 ml/kg, intravenous (i.v.)) given in combination with cisplatin (10 mg/kg, intraperitoneal (i.p.)) did not change the pharmacokinetics of cisplatin. Cisplatin-induced haematological toxicity, expressed as white blood cells (WBC) at nadir, was significantly reduced by CrEL from 5.05+/-0.95 to 6.50+/-1.31 x 10(9)/l (P=0.0009). Data obtained from cancer patients treated with cisplatin (70 mg/m(2), 3-h i.v.) and topotecan (0.45 or 0.60 mg/m(2)/day x 2) preceded by CrEL (12 ml, 3-h i.v.) (n=6) or without CrEL (n=10) similarly indicated significant differences in the percent decrease in WBC between the groups (46.5+/-18.7 versus 67.2+/-15.0%; P=0.029). Likewise, the percent decrease in platelet count was significantly greater in the absence of CrEL (23.9+/-5.38 versus 73.3+/-15.5%; P=0.0003). Pharmacokinetic parameters of unbound and total cisplatin and of topotecan lactone and total drug were not significantly different from historic control values (P>or=0.245). Overall, this study provides further evidence on the important role of CrEL in the pharmacological and toxicological profile of cisplatin, and implies that reformulation of cisplatin with CrEL for systemic treatment might achieve an improvement of its therapeutic index, particularly in the setting of a weekly dose-dense concept.