Determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma by reversed-phase high-performance liquid chromatography with fluorescence detection

Fecal SN-38 Content as a Surrogate Predictor of Intestinal SN-38 Exposure and Associated Irinotecan-induced Severe Delayed-Onset Diarrhea by a Novel Use of the Spectrofluorimetric Method

BACKGROUND

Irinotecan administration can lead to severe delayed-onset diarrhea (SDOD) in clinical practice. Currently, there is no reliable surrogate predictor of intestinal exposure to SN-38 and subsequent diarrhea incidence.

METHODS

The relationship between fecal 7-ethyl-10-hydroxycamptothecin (SN-38) content and SDOD was investigated in Fisher 344 rats using a novel spectrofluorimetric method. Additionally, a pharmacokinetic study of irinotecan was performed to evaluate the biodistribution of SN-38 to establish the relationship between tissue and fecal SN-38 exposure.

RESULTS

The spectrofluorimetric method was successfully employed to measure fecal SN-38 and CPT-11 content from Day 3 to Day 6 post-irinotecan administration. Only fecal SN-38 content on Day 3 exhibited a significantly positive correlation with SDOD incidence on Days 4 and 5. A cutoff value of SN-38 ≥ 0.066 mg/g in feces was identified, predicting severe diarrhea incidence with 81% accuracy and 80% specificity. The positive correlation between fecal SN-38 content and SN-38 exposure in the ileum on Day 3 was also reflected in the changes of indicators during intestinal injury, such as prostaglandin E2 level and antioxidant activity.

CONCLUSION

Fecal SN-38 content proves to be representative of intestinal exposure to SN-38, indicative of intestinal injury, and predictive of SDOD incidence in rats, while the spectrofluorimetric method demonstrates the translational potential.

Targeting efficacy and anticancer activity of polymeric nanoparticles of SN-38 on colon cancer cell lines

Background

Colorectal cancer is the third most prevailing cancer in the whole world. Chemotherapeutic agents which are used for treatment have severe side effects and also have unwanted exposure to healthy cells. In the present study, polymeric nanoparticles of SN-38 were prepared (using cationic and anionic polymers). They were optimized by Box Behnken design and characterized for its physicochemical properties and in vitro drug release. Optimized formulation (CsENP) was evaluated for its targeting efficacy by Gamma Scintigraphy studies on Swiss Albino mice and in vitro Cytotoxic assay against colon cancer cell line, viz. HT-29.

Results

The images of Whole body gamma scintigraphy imaging of Swiss Albino mice show that CsENP remained intact till 2 h and after that at 4 h imaging it started dispersing and releasing drug which continued till 20 h. In Organ distribution studies, no radioactivity was traced in heart from the formulation. Even in liver, spleen, kidney and lung trace radioactivity was seen after 6 h. In case of CsENP radioactivity was seen in small intestine after 2 h and maximum (87.8% radioactivity) is seen in colon and rectum area after 4 h. At equivalent concentrations, the in vitro cell viability of HT-29 cells after 72 h incubation time showed that CsENP have enhanced cytotoxicity.

Conclusions

The results obtained of Whole body gamma scintigraphy imaging and organ distribution of Swiss Albino mice show that CsENP is Colon targeting and was found to be effective against colon cancer cell lines.

The Current Treatment Paradigm for Pancreatic Ductal Adenocarcinoma and Barriers to Therapeutic Efficacy

Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis, with a median survival time of 10-12 months. Clinically, these poor outcomes are attributed to several factors, including late stage at the time of diagnosis impeding resectability, as well as multi-drug resistance. Despite the high prevalence of drug-resistant phenotypes, nearly all patients are offered chemotherapy leading to modest improvements in postoperative survival. However, chemotherapy is all too often associated with toxicity, and many patients elect for palliative care. In cases of inoperable disease, cytotoxic therapies are less efficacious but still carry the same risk of serious adverse effects, and clinical outcomes remain particularly poor. Here we discuss the current state of pancreatic cancer therapy, both surgical and medical, and emerging factors limiting the efficacy of both. Combined, this review highlights an unmet clinical need to improve our understanding of the mechanisms underlying the poor therapeutic responses seen in patients with PDAC, in hopes of increasing drug efficacy, extending patient survival, and improving quality of life.

Effects of Protein and Calorie Restriction on the Metabolism and Toxicity Profile of Irinotecan in Cancer Patients

Preclinical data suggests that protein and calorie restriction (PCR) might improve treatment tolerability without impairing antitumor efficacy. Therefore, we have studied the influence of PCR on irinotecan pharmacokinetics and toxicity. In this crossover trial, patients with liver metastases of solid tumors were included and randomized to treatment with irinotecan preceded by 5 days of PCR (~ 30% caloric and ~ 70% protein restriction) during the first cycle and a second cycle preceded by a normal diet or vice versa. Pharmacokinetic blood sampling and biopsies of both healthy liver and liver metastases were performed. The primary end point was the relative difference in geometric means for the active metabolite SN-38 concentration in healthy liver analyzed by a linear mixed model. No significant differences were seen in irinotecan (+ 16.8%, P = 0.22) and SN-38 (+ 9.8%, P = 0.48) concentrations between PCR and normal diet in healthy liver, as well as in liver metastases (irinotecan: -38.8%, P = 0.05 and SN-38: -13.8%, P = 0.50). PCR increased irinotecan plasma area under the curve from zero to 24 hours (AUC_0-24h ) with 7.1% (P = 0.04) compared with normal diet, whereas the SN-38 plasma AUC_0-24h increased with 50.3% (P < 0.001). Grade ≥ 3 toxicity was not increased during PCR vs. normal diet (P = 0.69). No difference was seen in neutropenia grade ≥ 3 (47% vs. 32% P = 0.38), diarrhea grade ≥ 3 (5% vs. 21% P = 0.25), and febrile neutropenia (5% vs. 16% P = 0.50) during PCR vs. normal diet. In conclusion, plasma SN-38 exposure increased dramatically after PCR, whereas toxicity did not change. PCR did not alter the irinotecan and SN-38 exposure in healthy liver and liver metastases. PCR might therefore potentially improve the therapeutic window in patients treated with irinotecan.

Fluorescent Imprinted Nanoparticles for the Effective Monitoring of Irinotecan in Human Plasma

Fluorescent, imprinted nanosized polymers for the detection of irinotecan have been synthesised using a napthalimide polymerisable derivative (2-allyl-6-[2-(aminoethyl)-amino] napthalimide) as functional monomer. The imprinted polymers contain ethylene glycol dimethacrylate (EGDMA) as a cross-linker and were prepared by high dilution radical polymerisation in dimethylsulphoxide (DMSO). The material was able to rebind irinotecan up to 18 nmol/mg with good specificity. Fluorescence emission at 525 nm (excitation at 448 nm) was quenched by increasing concentrations of irinotecan via a static mechanism and also in analytically useful environments as mixtures of human plasma and organic solvents. This allowed the direct detection of irinotecan (in the 10 nM-30 µM range) in human plasma treated with acetonitrile; the limit of detection (LOD) was 9.4 nM, with within-run variability of 10% and day-to-day variability of 13%.

Nanoliter-Scale Droplet-Droplet Microfluidic Microextraction Coupled with MALDI-TOF Mass Spectrometry for Metabolite Analysis of Cell Droplets

The further miniaturization of liquid-phase microextraction (LPME) systems has important significance and major challenges for microscale sample analysis. Herein, we developed a rapid and flexible droplet-droplet microfluidic microextraction approach to perform nanoliter-scale miniaturized sample pretreatment, by combining droplet-based microfluidics, robotic liquid handling, and LPME techniques. Differing from the previous microextraction methods, both the extractant and sample volumes were decreased from the microliter scale or even milliliter scale to the nanoliter scale. We utilized the ability of a liquid-handling robot to manipulate nanoliter-scale droplets and micrometer-scale positioning to overcome the scaling effect difficulties in performing liquid-liquid extraction of nanoliter-volume samples in microsystems. Two microextraction modes, droplet-in-droplet microfluidic microextraction and droplet-on-droplet microfluidic microextraction, were developed according to the different solubility properties of the extractants. Various factors affecting the microextraction process were investigated, including the extraction time, recovery method of the extractant droplet, static and dynamic extraction mode, and cross-contamination. To demonstrate the validity and adaptability of the pretreatment and analysis of droplet samples with complex matrices, the present microextraction system coupled with MALDI-TOF mass spectrometry (MS) detection was applied to the quantitative determination of 7-ethyl-10-hydroxylcamptothecin (SN-38), an active metabolite of the anticancer drug irinotecan, in 800-nL droplets containing HepG2 cells. A linear relationship (y = 0.0305x + 0.376, R² = 0.984) was obtained in the range of 4-100 ng/mL, with the limits of detection and quantitation being 2.2 and 4.5 ng/mL for SN-38, respectively.

Fasting protects against the side effects of irinotecan treatment but does not affect anti-tumour activity in mice

BACKGROUND

The main limitation to the use of irinotecan in the treatment of colorectal cancer is the severity of side effects, including neutropaenia and diarrhoea. Here, we explored the effects of 3 days of fasting on irinotecan-induced toxicities, on plasma, liver and tumour pharmacokinetics and on anti-tumour activity in mice.

EXPERIMENTAL APPROACH

Male BALB/c mice received C26 colon carcinoma cells subcutaneously. They were randomized 1:1 into equally sized ad libitum fed and fasted groups after which they were treated with irinotecan. Weight and adverse side effects were recorded daily. At the end of the experiment, tumours were resected and weighed, and concentrations of irinotecan and its active metabolite SN-38 were determined in plasma and tumour.

KEY RESULTS

Fasting prevented the diarrhoea and visible signs of discomfort induced by irinotecan. Ad libitum fed animals developed leucopenia compared with untreated controls, whereas fasted mice did not. Irinotecan suppressed tumour growth equally in both treated groups, compared with untreated controls. Levels of the active irinotecan metabolite SN-38 9 (calculated as AUC values) were significantly lower in fasted mice in both plasma and liver, but not in tumour tissue.

CONCLUSIONS AND IMPLICATIONS

Fasting protected against irinotecan-induced side effects without interfering with its anti-tumour efficacy. Fasting induced a lower systemic exposure to SN-38, which may explain the absence of adverse side effects, while tumour levels of SN-38 remained unchanged. These data offer important new approaches to improve treatment with irinotecan in patients.

Clinical validity of new genetic biomarkers of irinotecan neutropenia: an independent replication study

The overall goal of this study was to provide evidence for the clinical validity of nine genetic variants in five genes previously associated with irinotecan neutropenia and pharmacokinetics. Variants associated with absolute neutrophil count (ANC) nadir and/or irinotecan pharmacokinetics in a discovery cohort of cancer patients were genotyped in an independent replication cohort of 108 cancer patients. Patients received single-agent irinotecan every 3 weeks. For ANC nadir, we replicated UGT1A1*28, UGT1A1*93 and SLCO1B1*1b in univariate analyses. For irinotecan area under the concentration-time curve (AUC0-24), we replicated ABCC2 -24C>T; however, ABCC2 -24C>T only predicted a small fraction of the variance. For SN-38 AUC0-24 and the glucuronidation ratio, we replicated UGT1A1*28 and UGT1A1*93. In addition to UGT1A1*28, this study independently validated UGT1A1*93 and SLCO1B1*1b as new predictors of irinotecan neutropenia. Further demonstration of their clinical utility will optimize irinotecan therapy in cancer patients.

Quantitative determination of irinotecan and the metabolite SN-38 by nanoflow liquid chromatography-tandem mass spectrometry in different regions of multicellular tumor spheroids

A new and simple method was developed to evaluate the distribution of therapeutics in three-dimensional multicellular tumor spheroids (MCTS) by combining serial trypsinization and nanoflow liquid chromatography-tandem mass spectrometry (nLC-MS/MS). This methodology was validated with quantitative measurements of irinotecan and its bioactive metabolite, SN-38, in distinct spatial regions of HCT 116 MCTS. Irinotecan showed a time-dependent permeability into MCTS with most of the drug accumulating in the core after 24 h of treatment. The amount of SN-38 detected was 30 times lower than that of the parent drug, and was more abundant in the outer rim and intermediate regions of MCTS where proliferating cells were present. This method can be used to investigate novel and established drugs. It enables investigation of drug penetration properties and identification of metabolites with spatial specificity in MCTS. The new approach has great value in facilitating the drug evaluation process.

Interaction of human organic anion transporter 2 (OAT2) and sodium taurocholate cotransporting polypeptide (NTCP) with antineoplastic drugs

The ability of an antineoplastic drug to exert its cytostatic effect depends largely on the balance between its uptake into and extrusion from the cancer cells. ATP driven efflux transporter proteins drive the export of antineoplastic drugs and play a pivotal role in the development of chemoresistance. As regards uptake transporters, comparably less is known on their impact in drug action. In the current study, we characterized the interactions of two uptake transporter proteins, expressed mainly in the liver; the organic anion transporter 2 (OAT2, encoded by the SLC22A7 gene) and the sodium taurocholate cotransporting polypeptide (NTCP, encoded by the SLC10A1 gene), stably transfected in human embryonic kidney cells, with some antineoplastic agents that are routinely being used in cancer chemotherapy. Whereas NTCP did not show any strong interactions with the cytostatics tested, we observed a very strong inhibition of OAT2 mediated [(3)H] cGMP uptake in the presence of bendamustine, irinotecan and paclitaxel. The Ki values of OAT2 for bendamustine, irinotecan and paclitaxel were determined to be 43.3±4.33μM, 26.4±2.34μM and 10.4±0.45μM, respectively. Incubation of bendamustine with OAT2 expressing cells increased the caspase-3 activity, and this increase was inhibited by simultaneous incubation with bendamustine and probenecid, a well-known inhibitor of OATs, suggesting that bendamustine is a substrate of OAT2. A higher accumulation of irinotecan was observed in OAT2 expressing cells compared to control pcDNA cells by HPLC analysis of cell lysates. The accumulation was diminished in the presence of cGMP, the substrate we used to functionally characterize OAT2, suggesting specificity of this uptake and the fact that OAT2 mediates uptake of irinotecan.

Quantification of irinotecan, SN38, and SN38G in human and porcine plasma by ultra high-performance liquid chromatography-tandem mass spectrometry and its application to hepatic chemoembolization

An analytical method was developed and validated for the quantitative determination of irinotecan, its active metabolite SN38, and glucuronidated SN38 (SN38-G) in both porcine and human plasma. Calibration curves were linear within the concentration range of 0.5-100 ng/mL for SN38 and SN38-G, and 5-1000 ng/mL for irinotecan. Sample pretreatment involved solid-phase extraction of 0.1 mL aliquots of plasma. Irinotecan, SN38, SN38-G, and the internal standards, irinotecan-d10, tolbutamide, and camptothecin, respectively, were separated on a Waters ACQUITY UPLC BEH RP18 column (2. 1mm × 50 mm, 1.7 μm), using a mobile phase composed of methanol and 0.1% formic acid. Accuracy of quality control samples in human plasma ranged from 98.5 to 110.3%, 99.5 to 101.7% and 96.2 to 98.9% for irinotecan, SN38, and SN38-G, respectively. Precision of the three analytes in the same order ranged from 0.8 to 2.8%, 2.4 to 5.7%, and 2.4 to 2.8%. All three analytes proved stable in plasma through four freeze/thaw cycles, as well as through 6h in whole blood at room temperature. The method was likewise validated in porcine plasma with comparable accuracies and precisions also within the generally acceptable range. The validated method was applied to both preclinical and clinical trials involving hepatic chemoembolization of irinotecan drug-eluting beads to study the pharmacokinetics of the three analytes.

Factors affecting the stability of drugs and drug metabolites in biological matrices

Evaluation of the stability of drugs and drug metabolites in a biological matrix is a critical element to bioanalytical method validation. It is critical to understand the most common factors that affect the stability of such analytes in order to properly develop methods for their detection and measurement. The degradation of drugs and drug metabolites in samples can occur through either reversible or irreversible processes. Common factors that affect this stability include temperature, light, pH, oxidation and enzymatic degradation. Special considerations are also required when dealing with chiral molecules, deuterated internal standards and large biomolecules. Relevant examples of these degradation effects and approaches for dealing with them are presented is this review as taken from the fields of pharmaceutical testing, clinical research and forensic analysis. It is demonstrated through these examples how an understanding of the chemical and physical factors that affect sample stability can be used to avoid stability problems and to create robust and accurate methods for the analysis of drugs and related compounds.

Development and characterization of a novel lipid nanocapsule formulation of Sn38 for oral administration

The purpose of this work was to encapsulate 7-Ethyl-10-hydroxy-camptothecin (Sn38) in lipid nanocapsules (LNCs) using phase inversion-based method in order to deliver Sn38 by oral route. LNCs were prepared by a low-energy emulsification method and were characterized for size, polydispersity index (PDI), surface charge, drug payload, in vitro drug release, and storage stability. Moreover, in view of an oral administration, in vitro stability in gastrointestinal fluid and permeability across Caco-2 cells were tested. Sn38-loaded LNCs with a mean particle size of 38±2 nm were obtained. The particles displayed a narrow size distribution and a drug payload of 0.40±0.07 mg/g of LNC dispersion. In vitro stability in simulated gastric and intestinal media was also observed. Finally, Sn38-loaded LNCs improved permeability of Sn38 across Caco-2 cells (5.69±0.87×10(6) cm s(-1) at 6h vs 0.31±0.02×10(6) cm s(-1)) and intracellular concentration compared with free Sn38. In conclusion, Sn38 nanocarriers have been developed and display a strong potential for oral administration.

Effect of omeprazole on the pharmacokinetics and toxicities of irinotecan in cancer patients: a prospective cross-over drug-drug interaction study

BACKGROUND

Omeprazole is one of the most prescribed medications worldwide and within the class of proton pump inhibitors, it is most frequently associated with drug interactions. In vitro studies have shown that omeprazole can alter the function of metabolic enzymes and transporters that are involved in the metabolism of irinotecan, such as uridine diphosphate glucuronosyltransferase subfamily 1A1 (UGT1A1), cytochrome P-450 enzymes subfamily 3A (CYP3A) and ATP-binding cassette drug-transporter G2 (ABCG2). In this open-label cross-over study we investigated the effects of omeprazole on the pharmacokinetics and toxicities of irinotecan.

METHODS

Fourteen patients were treated with single agent irinotecan (600mg i.v., 90min) followed 3weeks later by a second cycle with concurrent use of omeprazole 40mg once daily, which was started 2weeks prior to the second cycle. Plasma samples were obtained up to 55h after infusion and analysed for irinotecan and its metabolites 7-ethyl-10-hydroxycampothecin (SN-38), SN-38-glucuronide (SN-38G), 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC) and 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC) by high-performance liquid chromatography (HPLC). Non-compartmental modelling was performed. Toxicities were monitored during both cycles. Paired statistical tests were performed with SPSS.

RESULTS

The exposure to irinotecan and its metabolites was not significantly different between both cycles. Neither were there significant differences in the absolute nadir and percentage decrease of WBC and ANC, nor on the incidence and severity of neutropenia, febrile neutropenia, diarrhoea, nausea and vomiting when irinotecan was combined with omeprazole.

CONCLUSION

Omeprazole 40mg did not alter the pharmacokinetics and toxicities of irinotecan. This widely used drug can, therefore, be safely administered during a 3-weekly single agent irinotecan schedule.

Irinotecan and its active metabolite, SN-38: review of bioanalytical methods and recent update from clinical pharmacology perspectives

The introduction of irinotecan has revolutionized the applicability of camptothecins as predominant topoisomerase I inhibitor for anti-cancer therapy. The potent anti-tumor activity of irinotecan is due to rapid formation of an in vivo active metabolite, SN-38. Therefore, irinotecan is considered as a pro-drug to generate SN-38. Over the past decade, side-by-side with the clinical advancement of the use of irinotecan in the oncology field, a plethora of bioanalytical methods have been published to quantify irinotecan, SN-38 and other metabolites. Because of the availability of HPLC, LC-MS and LC-MS/MS methods, the pharmacokinetic profiling of irinotecan and its metabolites has been accomplished in multiple species, including cancer patients. The developed assays continue to find use in the optimization of newly designed delivery systems with regard to pharmacokinetics to promote safe and effective use of either irinotecan or SN-38. This review intends to: firstly, provide an exhaustive compilation of the published assays for irinotecan, SN-38 and other metabolite(s) of irinotecan, as applicable; secondly, to enumerate the validation parameters and applicable conclusions; and thirdly, provide some recent perspectives in the clinical pharmacology arena pertaining to efflux transporters, pediatric profiling, role of kidney function in defining toxicity, drug-drug interaction potential of irinotecan, etc.

Simple liquid chromatography method for the quantification of irinotecan and SN38 in sheep plasma: application to in vivo pharmacokinetics after pulmonary artery chemoembolization using drug eluting beads

A rapid and simple liquid chromatography-fluorescence detection (LC-FD) method was developed and validated for the simultaneous quantification of irinotecan (CPT11) and SN38 in sheep plasma. Camptothecin (CPT) was used as the internal standard. A single step protein precipitation with acetonitrile was used for sample preparation. The separation was achieved using a 5 microm C18 column (250 mm x 4.5 mm, 5 microm) with a mobile phase composed of 36 mM sodium dihydrogen phosphate dehydrate and 4 mM sodium 1 heptane sulfonate-acetonitrile (72:28), the pH of the mobile phase was adjusted to 3. The flow rate was 1.45 mL/min and the fluorescence detection was operated at 355/515 nm (excitation/emission wavelengths). The run time was 13 min. The method was validated with respect to selectivity, extraction recovery, linearity, intra- and inter-day precision and accuracy, limit of quantification and stability. The method has a limit of quantification of 5 ng/mL for both CPT11 and SN38. The assay was linear over concentrations ranging from 5 to 5000 ng/mL and to 240 ng/mL for CPT11 and SN38, respectively. This method was used successfully to perform plasma pharmacokinetic studies of CPT11 after pulmonary artery embolization (PACE) in a sheep model. It was also validated for CPT11 and SN38 analysis in sheep lymph and human plasma.

Phase I clinical and pharmacokinetic study of oxaliplatin, irinotecan and capecitabine

PURPOSE

To determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT) of the combination of weekly oxaliplatin x 4, weekly irinotecan x 4 and capecitabine Monday through Friday for 4 weeks of every 6 week cycle in patients with solid tumors; to determine the pharmacokinetic profile of these agents in this combination; to observe patients for clinical anti-tumor response.

METHODS

Twenty-two patients with metastatic solid tumors received oxaliplatin 60 mg/m(2) weekly x 4, irinotecan beginning at a dose of 40 mg/m(2) weekly x 4, and capecitabine Monday through Friday for 4 weeks of every 6 week cycle, initially at 1,000 mg twice daily (bid).

RESULTS

The MTD was oxaliplatin 60 mg/m(2) weekly x 4, irinotecan 50 mg/m(2) weekly x 4 and capecitabine 450 mg bid Monday through Friday for 4 weeks of every 6 week cycle. One of six patients at this dose level developed DLT of nausea, vomiting, and diarrhea. Among patients treated with a constant capecitabine dose of 450 mg bid, there was a higher mean AUC of 5-FU in women than in men (mean +/- SD: 892 +/- 287 nM h vs. 537 +/- 182 nM h; Mann-Whitney two-tailed, P = 0.02). There was one complete response in a patient with gastric cancer.

CONCLUSION

The novel schedule of weekly oxaliplatin, weekly irinotecan, and capecitabine Monday through Friday, all administered for 4 weeks of every 6 week cycle, evaluated in this phase I trial is well-tolerated and demonstrated activity in a patient with gastric cancer.

Renal function as a predictor of irinotecan-induced neutropenia

Although approximately half of the administered dose of irinotecan is recovered in urine, scarce data are available on the association of renal function with irinotecan pharmacokinetics and toxicity. Here, these relationships are investigated in 187 patients treated with irinotecan in a three-weekly schedule. No significant effects on irinotecan pharmacokinetics were found in these patients. However, in 131 patients treated with the registered dose, categorized renal function was related to hematological toxicity. The incidence of grade 3-4 neutropenia decreased as function of creatinine clearance, particularly in nonsmoking patients (P < 0.01). Patients with slower creatinine clearance (35-66 ml/min) had a four-times higher risk of grade 3-4 neutropenia (58% vs. 14%; P < 0.001). This study suggests that pretreatment renal function values are associated with irinotecan-induced neutropenia. A confirmatory analysis is warranted to determine whether measures of renal function should be incorporated in future attempts toward individualized treatment with irinotecan.

Associations of ABCB1, ABCC2, and ABCG2 polymorphisms with irinotecan-pharmacokinetics and clinical outcome in patients with advanced non-small cell lung cancer

BACKGROUND

The authors investigated whether ABCB1, ABCC2, and ABCG2 genetic polymorphisms affect pharmacokinetics (PK) of irinotecan and treatment outcome of patients with advanced nonsmall cell lung cancer (NSCLC).

METHODS

Blood samples from 107 NSCLC patients treated with irinotecan and cisplatin chemotherapy were used for genotyping ABCB1 (1236C > T, 2677G > T/A, 3435C > T), ABCC2 (-24C > T, 1249G > A, 3972C > T), and ABCG2 (34G > A, 421C > A) polymorphisms. Genotypes were correlated with irinotecan-PK, toxicity, tumor response, and survival.

RESULTS

Among 8 polymorphisms, 3435TT and 2677TT were associated with AUC(SN-38G) and CL(SN-38G). When haplotypes are assigned, 2677TT/3435TT carriers showed significantly lower AUC(SN-38G) (P = .006), whereas 2677GG/3435CC carriers showed significantly higher AUC(SN-38) (P = .039). These findings suggest that 2677TT and 3435TT variants are associated with higher efflux activity. In toxicity, the 2677G/T or A was associated with grade 4 neutropenia. The 2677GG carriers showed significantly lower absolute neutrophil count during the 1(st) cycle (P = .012) as well as entire course of chemotherapy (P = .042). The 3435TT was associated with higher frequency of grade 3 diarrhea (P = .047). In tumor response, ABCC2 -24TT and 3972TT genotypes were associated with higher response rates (P = .031 and P = .048, [corrected] respectively) and longer progression-free survival (P = .010 and P = .019, [corrected] respectively), which was sustained in haplotype analysis.

CONCLUSIONS

Specific polymorphisms of ABCB1 and ABCC2 can influence disposition and tumor response to irinotecan by regulating transporter activity. These findings may help to individualize irinotecan-based chemotherapy in patients with advanced NSCLC.

Cigarette smoking and irinotecan treatment: pharmacokinetic interaction and effects on neutropenia

PURPOSE

Several constituents of cigarette smoke are known to interact with drug metabolizing enzymes and potentially affect treatment outcome with substrate drugs. The purpose of this study was to determine the effects of cigarette smoking on the pharmacokinetics and adverse effects of irinotecan.

PATIENTS AND METHODS

A total of 190 patients (49 smokers, 141 nonsmokers) treated with irinotecan (90-minute intravenous administration on a 3-week schedule) were evaluated for pharmacokinetics. Complete toxicity data were available in a subset of 134 patients receiving 350 mg/m2 or 600 mg flat-fixed dose irinotecan.

RESULTS

In smokers, the dose-normalized area under the plasma concentration-time curve of irinotecan was significantly lower (median, 28.7 v 33.9 ng x h/mL/mg; P = .001) compared with nonsmokers. In addition, smokers showed an almost 40% lower exposure to SN-38 (median, 0.54 v 0.87 ng x h/mL/mg; P < .001) and a higher relative extent of glucuronidation of SN-38 into SN-38G (median, 6.6 v 4.5; P = .006). Smokers experienced considerably less hematologic toxicity. In particular, the incidence of grade 3 to 4 neutropenia was 6% in smokers versus 38% in nonsmokers (odds ratio [OR], 0.10; 95% CI, 0.02 to 0.43; P < .001). There was no significant difference in incidence of delayed-onset diarrhea (6% v 15%; OR, 0.34; 95% CI, 0.07 to 1.57; P = .149).

CONCLUSION

This study indicates that smoking significantly lowers both the exposure to irinotecan and treatment-induced neutropenia, indicating a potential risk of treatment failure. Although the underlying mechanism is not entirely clear, modulation of CYP3A and uridine diphosphate glucuronosyltransferase isoform 1A1 may be part of the explanation. The data suggest that additional investigation is warranted to determine whether smokers are at increased risk for treatment failure.

Medicinal Cannabis Does Not Influence the Clinical Pharmacokinetics of Irinotecan and Docetaxel

OBJECTIVE

To date, data regarding the potential of cannabinoids to modulate cytochrome P450 isozyme 3A (CYP3A) activity are contradictory. Recently, a standardized medicinal cannabis product was introduced in The Netherlands. We anticipated an increased use of medicinal cannabis concurrent with anticancer drugs, and undertook a drug-interaction study to evaluate the effect of concomitant medicinal cannabis on the pharmacokinetics of irinotecan and docetaxel, both subject to CYP3A-mediated biotransformation.

PATIENTS AND METHODS

Twenty-four cancer patients were treated with i.v. irinotecan (600 mg, n = 12) or docetaxel (180 mg, n = 12), followed 3 weeks later by the same drugs concomitant with medicinal cannabis (200 ml herbal tea, 1 g/l) for 15 consecutive days, starting 12 days before the second treatment. Blood samples were obtained up to 55 hours after dosing and analyzed for irinotecan and its metabolites (SN-38, SN-38G), respectively, or docetaxel. Pharmacokinetic analyses were performed during both treatments. Results are reported as the mean ratio (95% confidence interval [CI]) of the observed pharmacokinetic parameters with and without concomitant medicinal cannabis.

RESULTS

Medicinal cannabis administration did not significantly influence exposure to and clearance of irinotecan (1.04; CI, 0.96-1.11 and 0.97; CI, 0.90-1.05, respectively) or docetaxel (1.11; CI, 0.94-1.28 and 0.95; CI, 0.82-1.08, respectively).

CONCLUSION

Coadministration of medicinal cannabis, as herbal tea, in cancer patients treated with irinotecan or docetaxel does not significantly influence the plasma pharmacokinetics of these drugs. The evaluated variety of medicinal cannabis can be administered concomitantly with both anticancer agents without dose adjustments.

Prophylaxis of irinotecan-induced diarrhea with neomycin and potential role for UGT1A1*28 genotype screening: a double-blind, randomized, placebo-controlled study

OBJECTIVE

Delayed-type diarrhea is a common side effect of irinotecan and is associated with a bacterial-mediated formation of the active irinotecan metabolite SN-38 from its glucuronide conjugate in the intestine. Based on a pilot study, we hypothesized that concomitant administration of the antibiotic neomycin would diminish exposure of the gut to SN-38 and ameliorate the incidence and severity of diarrhea.

PATIENTS AND METHODS

Patients were treated with irinotecan in a multicenter, double-blind, randomized, placebo-controlled trial. Eligible patients received irinotecan (350 mg/m(2) once every 3 weeks) combined with neomycin (660 mg three times daily for three consecutive days, starting 2 days before chemotherapy) or combined with placebo. Blood samples were obtained for additional pharmacokinetic and pharmacogenetic analyses.

RESULTS

Sixty-two patients were evaluable for the toxicity analysis. Baseline patient characteristics, systemic SN-38 exposure, and UGT1A1*28 genotype status (i.e., an additional TA repeat in the promoter region of uridine diphosphate-glucuronosyltransferase isoform 1A1) were similar in both arms. Although distribution, severity, and duration of delayed-type diarrhea did not differ significantly between arms, grade 3 diarrhea tended to be less frequent in the neomycin arm. The presence of at least one UGT1A1*28 allele was strongly related to the incidence of grade 2-3 diarrhea. In the neomycin arm, grade 2 nausea was significantly more common.

CONCLUSION

Our results do not suggest a major role for neomycin as prophylaxis for irinotecan-induced delayed-type diarrhea. It is suggested that the UGT1A1*28 genotype status could be used as a screening tool for a priori prevention of irinotecan-induced delayed-type diarrhea.

Randomized Phase II study of two opposite administration sequences of irinotecan and cisplatin in patients with advanced nonsmall cell lung carcinoma

BACKGROUND

Combined chemotherapy with irinotecan and cisplatin (IP) is active in patients with nonsmall cell lung carcinoma (NSCLC). However, the optimal administration schedule needs to be defined to maximize its synergic effect. The authors evaluated the efficacy, toxicity, and pharmacokinetics (PK) of IP chemotherapy given on two administration sequences in chemotherapy-naive patients with NSCLC.

METHODS

Eighty eligible patients were assigned randomly to receive 1 of 2 irinotecan and cisplatin administration sequences on Day 1: irinotecan followed by cisplatin (I-P) (n = 39 patients) or cisplatin followed by irinotecan (P-I) (n = 41 patients). Treatment was comprised of irinotecan at a dose of 80 mg/m(2) intravenously on Days 1 and 8 and cisplatin at a dose of 60 mg/m(2) intravenously on Day 1 of a 21-day cycle for a maximum of 6 cycles. For PK analysis, serial plasma samples were obtained on Day 1 of the first cycle.

RESULTS

In total, 77 patients were assessable for efficacy. The overall response rate was 47%, and there was a trend in favor of P-I (54%) compared with I-P (39%). In multivariate logistic regression analysis, the P-I sequence and female gender were found to be significant predictors of a better response (P = 0.047 and P = 0.011, respectively). Overall toxicity profiles and PK parameters were similar in both arms.

CONCLUSIONS

IP chemotherapy showed promising activity with a favorable 1-year survival rate. For future clinical use, the authors recommend administering cisplatin first and then irinotecan, because that sequence was associated with a higher response rate.

A phase I clinical trial of the sequential combination of irinotecan followed by flavopiridol

PURPOSE

Flavopiridol potently enhances the effect of irinotecan with cures in colorectal cancer xenografts, and is associated with modulation of several molecular targets, including p21, Differentiation-related gene 1 (Drg1), and p53. We initiated a phase I trial of the sequential combination of irinotecan followed by flavopiridol to determine the maximal tolerated dose of this combination therapy.

PATIENTS AND METHODS

Forty-five patients with advanced solid tumors were enrolled. Irinotecan was administered first (100 or 125 mg/m(2)) followed 7 hours later by escalating flavopiridol (10-70 mg/m(2)) given weekly over 1 hour for 4 of 6 weeks. At the maximal tolerated dose, the pharmacokinetic analysis was expanded and pre- and posttreatment tumor biopsies were done.

RESULTS

At irinotecan 100 mg/m(2), dose-limiting diarrhea and myelosuppression were observed with flavopiridol 70 mg/m(2). At irinotecan 125 mg/m(2), we observed dose-limiting hyperbilirubinemia, fatigue, and myelosuppression at flavopiridol 60 mg/m(2). Peak flavopiridol concentrations of >/=2 mumol/L were achieved above flavopiridol 50 mg/m(2). No significant pharmacokinetic interactions with irinotecan were noted. Baseline serum bilirubin significantly predicted cycle 1 dose-limiting toxicity and neutropenia. We observed partial responses in three patients and prolonged stable disease (i.e., >6 months) in 36% of patients including adrenocortical cancer and hepatocellular cancer. Patients with wild-type p53 and either no change or low posttreatment biopsy p21 and a decrease in Drg1 expression showed stable or responsive disease to the combination therapy.

CONCLUSIONS

The recommended phase II dose with irinotecan 100 mg/m(2) is flavopiridol 60 mg/m(2) and with irinotecan 125 mg/m(2) is flavopiridol 50 mg/m(2). Toxicity can be predicted by baseline bilirubin. Clinical activity is encouraging and may correlate to changes in p21 and Drg1 levels in patients with wild type p53 tumors following therapy.

Liquid chromatographic–tandem mass spectrometric assay for the simultaneous quantification of Camptosar® and its metabolite SN-38 in mouse plasma and tissues

A simple, rapid and sensitive LC-MS/MS bioanalytical method has been developed to simultaneously quantify Camptosar (CPT-11) and its active metabolite, SN-38, in mouse plasma and tissues. A single step protein precipitation with acetonitrile in 96-well plates was used for sample preparation. Camptothecin (CPT) was used as the internal standard. Fast separation of SN-38, CPT-11 and CPT was carried out isocratically on a C18, 2 mm x 50 mm, 5 microm HPLC column with a mobile phase containing acetonitrile and 20 mM ammonium acetate (pH 3.5) and a 2.5 min chromatographic run time. The API 4000 MS/MS system was operated in positive ionization multiple reaction monitoring mode, and the transitions for SN-38, CPT-11 and CPT were 393.4 --> 349.3, 587.6 --> 167.2 and 349.3 --> 305.3, respectively. The SN-38 and CPT-11 concentrations in samples were calculated from a standard curve of peak area ratios of the analyte to that of the internal standard using a 1/chi2 weighted linear regression. The quantitation limit of 0.5 ng/mL was achieved by using a low sample volume (100 microL) of plasma or tissue homogenates. The assay was linear over the concentration range of 0.5-500 ng/mL with acceptable precision and accuracy. The method was used for the quantification of CPT-11 and SN-38 in plasma and tissues to support a preclinical pharmacokinetics and tissue distribution study of CPT-11 in mice.

A simple and sensitive LC/MS/MS assay for 7-ethyl-10-hydroxycamptothecin (SN-38) in mouse plasma and tissues: application to pharmacokinetic study of liposome entrapped SN-38 (LE-SN38)

An LC/MS/MS method to quantify SN-38 in mouse plasma and tissue homogenates containing liposome entrapped SN-38 (LE-SN38) was developed. Camptothecin (CPT) was used as the internal standard (IS). Sample preparation consisted of simple protein precipitation by acetonitrile containing 0.5% acetic acid. SN-38 and IS were separated by a C18 HPLC column and detected using a mass spectrometer operating in the multiple reaction monitoring (MRM) mode. The peak area of the m/z 393.3-->349.1 transition of SN-38 and that of the m/z 349.1-->305.2 transition of the IS were measured and a standard curve was generated from their ratios. The method had a LLOQ of 0.5 ng/mL in mouse plasma, which corresponds to 2.5 pg for the 5 microL injection volume. The linear range was 0.5-1000 ng/mL of SN-38 in plasma sample spiked with LE-SN38. The LLOQ in tissue homogenates (5%, w/v) quantitation was 1 ng/mL (20 ng/g tissue) of SN-38 in kidney, liver, lung, and spleen homogenates, and 2 ng/mL (40 ng/g tissue) in heart homogenate containing LE-SN38. The assay was linear up to 400 ng/mL of SN-38 in tissue homogenates, and may be extended to 120 microg/mL by proper dilution of samples over the upper limit of quantitation. Acceptable precision and accuracy were obtained for concentrations over the entire standard curve range, both between-run and within-run for plasma and tissue homogenates. The method was successfully used to quantify SN-38 in plasma and tissues samples for pharmacokinetic and tissue distribution studies of LE-SN38 in mice.

Prediction of irinotecan pharmacokinetics by use of cytochrome P450 3A4 phenotyping probes

BACKGROUND

Irinotecan is a topoisomerase I inhibitor that has been approved for use as a first- and second-line treatment for colorectal cancer. The response to irinotecan is variable, possibly because of interindividual variation in the expression of the enzymes that metabolize irinotecan, including cytochrome P450 3A4 (CYP3A4) and uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1). We prospectively explored the relationships between CYP3A phenotype, as assessed by erythromycin metabolism and midazolam clearance, and the metabolism of irinotecan and its active metabolite SN-38.

METHODS

Of the 30 white cancer patients, 27 received at least two treatments with irinotecan administered as one 90-minute infusion (dose, 600 mg) with 3 weeks between treatments, and three received only one treatment. Before the first and second treatments, patients underwent an erythromycin breath test and a midazolam clearance test as phenotyping probes for CYP3A4. Erythromycin metabolism was assessed as the area under the curve for the flux of radioactivity in exhaled CO2 within 40 minutes after administration of [N-methyl-14C]erythromycin. Midazolam and irinotecan were measured by high-performance liquid chromatography. Genomic DNA was isolated from blood and screened for genetic variants in CYP3A4 and UGT1A1. All statistical tests were two-sided.

RESULTS

CYP3A4 activity varied sevenfold (range = 0.223%-1.53% of dose) among patients, whereas midazolam clearance varied fourfold (range = 262-1012 mL/min), although intraindividual variation was small. Erythromycin metabolism was not statistically significantly associated with irinotecan clearance (P = .090), whereas midazolam clearance was highly correlated with irinotecan clearance (r = .745, P<.001). In addition, the presence of a UGT1A1 variant with a (TA)7 repeat in the promoter (UGT1A1*28) was associated with increased exposure to SN-38 (435 ng x h/mL, 95% confidence interval [CI] = 339 to 531 ng x h/mL in patients who are homozygous for wild-type UGT1A1; 631 ng x h/mL, 95% CI = 499 to 762 ng . h/mL in heterozygous patients; and 1343 ng x h/mL, 95% CI = 0 to 4181 ng x h/mL in patients who are homozygous for UGT1A1*28) (P = .006).

CONCLUSION

CYP3A4 phenotype, as assessed by midazolam clearance, is statistically significantly associated with irinotecan pharmacokinetics. Evaluation of midazolam clearance combined with UGT1A1*28 genotyping may assist with optimization of irinotecan chemotherapy.

Determination of irinotecan (CPT-11) and SN-38 in human whole blood and red blood cells by liquid chromatography with fluorescence detection

An analytical method was developed for the anticancer agent irinotecan (CPT-11) and its main metabolite SN-38 in human whole blood and in red blood cells (RBCs). Sample pretreatment involved deproteinization of whole blood or plasma-diluted RBCs isolated by MESED instruments, with a mixture of aqueous perchloric acid and methanol (1:1, v/v). Separation was carried out using isocratic elution on a Hypersil ODS stationary phase, with detection at excitation and emission wavelengths of 355 and 515 nm, respectively. The lower limit of quantitation (LLQ) in blood was established at 5.00 ng/ml for both compounds, with values for within-run precision (WRP) and between-run precision (BRP) of less than 10%. The method is currently being applied to investigate the blood distribution of CPT-11 and SN-38 in cancer patients.

Sensitive HPLC-fluorescence method for irinotecan and four major metabolites in human plasma and saliva: application to pharmacokinetic studies

BACKGROUND

We developed gradient HPLC methods for quantification of the antimitotic drug irinotecan (CPT-11) and its four metabolites, SN-38, SN-38 G, 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC), and 7-ethyl-10-[4amino-1-piperidino]-carbonyloxycamptothecin (NPC), as the sum of the lactone and carboxylate forms, in human plasma and saliva. Camptothecin was used as internal standard.

METHODS

The sample pretreatment involved protein precipitation with methanol-acetonitrile (50:50 by volume) followed by acidification with hydrochloric acid to convert the lactone ring-opened form into its lactone form, quantitatively. HPLC separation was performed on a Xterra RP18 column. The excitation wavelength was 370 nm, and the emission wavelength was set at 470 nm for the first 24 min and then at 534 nm for the next 4 min. The stabilities of irinotecan and its four metabolites in plasma, saliva, and acidic extracts were also investigated under various conditions.

RESULTS

Assays were linear in the tested range of 0.5-1000 micro g/L. For the five analytes, limits of quantification were 0.5 micro g/L in both matrices. The interassay imprecision (as relative standard deviation) was 3.2-14% in plasma and 2.6-5.6% in saliva. Assay recoveries ranged from 92.8% to 111.2% for plasma and 100.1% to 104.1% for saliva. Mean extraction recovery from plasma or saliva was 90%.

CONCLUSION

The developed assay can be used to determine pharmacokinetic parameters for CPT-11, SN-38, SN-38 G, APC, and NPC in plasma and saliva from patients with metastatic colorectal cancer.

Liquid chromatography determination of 10-hydroxycamptothecin in human serum by a column-switching system containing a pre-column with restricted access media and its application to a clinical pharmacokinetic study

A simple, rapid, sensitive column-switching HPLC method is described for the analysis of the 10-hydroxycamptothecin (HCPT) in human serum. A pre-column containing restricted access media (RAM) is used for the sample clean-up and trace enrichment and is combined with a C18 column for the final separation. The analytical time is 8 min. The HCPT is monitored with fluorescence detector, excitation and emission wavelengths being 385 and 539 nm, respectively. There is a linear response range of 1-1000 ng/ml with correlation coefficient of 0.998 while the limit of quantification is 0.1 ng/ml. The intra-day and inter-day variations are less than 5%. This analytic procedure has been applied to a pharmacokinetic study of HCPT in clinical patients and the pharmacokinetic parameters of one-compartment model are calculated.

Determination by liquid chromatography with fluorescence detection of total 7-ethyl-10-hydroxy-camptothecin (SN-38) in beagle dog plasma after intravenous administration of liposome-based SN-38 (LE-SN38)

An HPLC- fluorescence method to quantitate total 7-ethyl-10-hydroxy-camptothecin (SN-38) in beagle dog plasma spiked with liposome based formulation of SN-38 (LE-SN38) and using camptothecin (CPT) as the internal standard (I.S.) was developed and validated to support pharmacokinetics/toxicokinetics studies. Sample preparation was done by protein precipitation using acetonitrile with 0.5% acetic acid. The supernatant was evaporated, and reconstituted in acetonitrile-20 mM ammonium acetate, pH 3.5 (20:80, v/v). When injected onto a Zorbax SB-C(18) HPLC column SN-38 as well as I.S. were detected by fluorescence using an excitation at 368 nm and emission at 515 nm. The SN-38 concentrations in samples were calculated from a standard curve of peak area ratios of SN-38 to the I.S. using weighted linear regression. The sensitivity limit for SN-38 was 1.00 ng/ml in beagle dog plasma with a precision (expressed as relative standard deviation) of 12.4% and an accuracy (expressed as analytical recovery) of 104%. The assay was linear within the standard curve range of 1-750 ng/ml. Acceptable precision and accuracy were also obtained for concentrations over the balance of the standard curve range from between-run and within-run calculations.

High-performance liquid chromatographic analysis of the anticancer drug irinotecan (CPT-11) and its active metabolite SN-38 in human plasma

A rapid, sensitive, and specific high-performance liquid chromatography (HPLC) method for the simultaneous determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma is described. The analytes are quantified as the totals of their carboxylate and lactone form. The sample pretreatment consisted of a simple protein precipitation with acetonitrile-methanol (1:1, v/v), after which CPT-11 and SN-38 were quantitatively converted to their carboxylate form by adding 0.01 mol/L sodium tetraborate (pH, 9). Chromatography was carried out on a Zorbax SB-C18 column with fluorescence detection. The method has been validated, and stability tests under various clinically relevant conditions have been performed. The lower limit of quantification (LLOQ) was 5.0 ng/mL for CPT-11 and 0.5 ng/mL for SN-38. Standard concentration ranges were linear between 5 and 1,500 ng/mL for CPT-11 and between 0.5 and 100 ng/mL for SN-38. This assay is simple, rapid, and very useful for therapeutic monitoring of CPT-11 and SN-38.

A sensitive and rapid liquid chromatography tandem mass spectrometry method for quantitative determination of 7-ethyl-10-hydroxycamptothecin (SN-38) in human plasma containing liposome-based SN-38 (LE-SN38)

7-Ethyl-10-hydroxycamptothecin (SN-38) is an active metabolite of Irinotecan (CPT-11), an anticancer pro-drug. To support clinical pharmacokinetic studies for liposome based formulation of SN-38 (LE-SN38) in cancer patients, a rapid, simple and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the quantification of total SN-38 in human plasma. Sample preparation was carried out by one-step protein precipitation using cold acetonitrile with 0.5% acetic acid (v/v). Camptothecin was used as an internal standard (IS). Chromatographic separation of SN-38 and IS was achieved using a Synergi Hydro-RP column (C(18), 50 x 2 mm, 4 micro m), with a gradient elution of acetonitrile and 0.1% acetic acid. After ionization in electrospray source (positive ions), the acquisition was performed in the multiple reactions monitoring mode. Quantitation was accomplished using the precursor-->product ion combinations of m/z 393.1-->349.2 for SN-38 and 349.1-->305.1 for IS. The quantification limit of 0.05 ng/mL was achieved by using much lower volume (0.2 mL) of plasma and in the presence of LE-SN38. The method was validated over the concentration range of 0.05-400 ng/mL. Accuracy was within +/-12% of nominal at all concentration levels. Inter-day and intra-day precisions expressed as percentage coefficient of variation (%CVs) for quality control (QC) samples were less than 14 and 5%, respectively.

Clinical pharmacokinetics of irinotecan and its metabolites: a population analysis

PURPOSE

To build population pharmacokinetic (PK) models for irinotecan (CPT-11) and its currently identified metabolites.

PATIENTS AND METHODS

Seventy cancer patients (24 women and 46 men) received 90-minute intravenous infusions of CPT-11 in the dose range of 175 to 300 mg/m(2). The PK models were developed to describe plasma concentration profiles of the lactone and carboxylate forms of CPT-11 and 7-ethyl-10-hydroxycamptothecin (SN-38) and the total forms of SN-38 glucuronide (SN-38G), 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC), and 7-ethyl-10-[4-amino-1-piperidino]-carbonyloxycamptothecin (NPC) by using NONMEM.

RESULTS

The interconversion between the lactone and carboxylate forms of CPT-11 was relatively rapid, with an equilibration half-life of 14 minutes in the central compartment and hydrolysis occurring at a rate five times faster than lactonization. The same interconversion also occurred in peripheral compartments. CPT-11 lactone had extensive tissue distribution (steady-state volume of distribution [Vss], 445 L) compared with the carboxylate form (Vss, 78 L, excluding peripherally formed CPT-11 carboxylate). Clearance (CL) was higher for the lactone form (74.3 L/h) compared with the carboxylate form (12.3 L/h). During metabolite data modeling, goodness of fit indicated a preference of SN-38 and NPC to be formed out of the lactone form of CPT-11, whereas APC could be modeled best by presuming formation from CPT-11 carboxylate. The interconversion between SN-38 lactone and carboxylate was slower than that of CPT-11, with the lactone form dominating at equilibrium. The CLs for SN-38 lactone and carboxylate were similar, but the lactone form had more extensive tissue distribution.

CONCLUSION

Plasma data of CPT-11 and metabolites could be adequately described by this compartmental model, which may be useful in predicting the time courses, including interindividual variability, of all characterized substances after intravenous administrations of CPT-11.

Modulation of irinotecan metabolism by ketoconazole

PURPOSE

Irinotecan (CPT-11) is a prodrug of SN-38 and has been registered for the treatment of advanced colorectal cancer. It is converted by the cytochrome P450 3A4 isozyme (CYP3A4) into several inactive metabolites, including 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC). To investigate the role of CYP3A4 in irinotecan pharmacology, we evaluated the consequences of simultaneous treatment of irinotecan with a potent enzyme inhibitor, ketoconazole, in a group of cancer patients.

PATIENTS AND METHODS

A total of seven assessable patients was treated in a randomized, cross-over design with irinotecan (350 mg/m(2) intravenously for 90 minutes) given alone and followed 3 weeks later by irinotecan (100 mg/m(2)) in combination with ketoconazole (200 mg orally for 2 days) or vice versa. Serial plasma, urine, and feces samples were obtained up to 500 hours after dosing and analyzed for irinotecan, metabolites (7-ethyl-10-hydroxycamptothecin [SN-38], SN-38 glucuronide [SN-38G], and APC), and ketoconazole by high-performance liquid chromatography.

RESULTS

With ketoconazole coadministration, the relative formation of APC was reduced by 87% (P =.002), whereas the relative exposure to the carboxylesterase-mediated SN-38 as expected on the basis of dose (area under the plasma concentration-time curve normalized to dose) was increased by 109% (P =.004). These metabolic alterations occurred without substantial changes in irinotecan clearance (P =.90) and formation of SN-38G (P =.93).

CONCLUSION

Inhibition of CYP3A4 in cancer patients treated with irinotecan leads to significantly increased formation of SN-38. Simultaneous administration of various commonly prescribed inhibitors of CYP3A4 can potentially result in fatal outcomes, and up to four-fold reductions in irinotecan dose are indicated.

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 500 h, 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 (AUC(500 h)) was significantly related to this AOC (P<0.001). Based on these findings, a new limited-sampling model was developed for SN-38 AUC(500 h) using only two timed samples: AUC(500 h)=(6.588 x C(2.5 h))+(146.4 x C(49.5 h))+15.53, where C(2.5 h) and C(49.5 h) are plasma concentrations at 2.5 and 49.5 h 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.

Simultaneous determination of the carboxylate and lactone forms of 10-hydroxycamptothecin in human serum by restricted-access media high-performance liquid chromatography

A simple restricted-access media (RAM) HPLC method for simultaneous determination of the lactone and carboxylate forms of 10-hydroxycamptothecin (HCPT) in human serum was established. Using a RAM Hisep analytical column, serum samples were directly injected into the HPLC system. The eluted peaks of two forms of HCPT were monitored with a fluorescence detector. The separation was completed in 17 min. The linear range was 20-1000 ng/ml, intra-day and inter-day variations being less than 5%. The kinetic equation was introduced according to the analytical results. The equation shows that the course of the HCPT lactone form converting to carboxylate form in human serum at 4 degrees C is a first-order kinetic course. The concentration of each form at the moment of sampling was calculated by extrapolation.

Impact of body-size measures on irinotecan clearance: alternative dosing recommendations

PURPOSE

To evaluate relationships between various body-size measures and irinotecan (CPT-11) clearance and metabolism in cancer patients, and to provide future dosing recommendations for this agent.

PATIENTS AND METHODS

Pharmacokinetic data were obtained from 82 adult patients (50 men, 32 women; median age, 54 years) receiving CPT-11 as a 90-minute intravenous infusion (dose range, 175 to 350 mg/m(2)). In each patient, plasma samples were collected at timed intervals in the first administration of a 3-week schedule, and CPT-11 and its metabolite, SN-38, were measured by a liquid chromatographic assay.

RESULTS

The mean (+/- SD) CPT-11 clearance was 33.6 +/- 10.8 L/h, with an interindividual variability (IIV) of 32.1%. When clearance was adjusted for body-surface area (BSA), the IIV was similar (34.0%). In addition, in a multiple linear regression analysis, none of the studied measures (BSA, lean body mass, [adjusted] ideal body weight, and body mass index) was a significant covariate (P >.13; r(2) <.014) in our population. Similarly, BSA did not significantly contribute to variability in the relative extent of conversion to SN-38 (P =.26).

CONCLUSION

BSA is not a predictor of CPT-11 clearance or SN-38 pharmacokinetics and does not contribute to reducing kinetic variability. These findings provide a rationale for the conduct of a comparative phase III study between BSA-based dosing and flat or fixed dosing of CPT-11.

Separation methods for camptothecin and related compounds

This paper reviews working procedures for the analytical determination of camptothecin and analogues. We give an overview of aspects such as the chemistry, structure-activity relationships, stability and mechanism of action of these antitumor compounds. The main body of the review describes separation techniques. Sample treatment and factors influencing high-performance liquid chromatography development are delineated. Published high-performance liquid chromatographic methods are summarized to demonstrate the variability and versatility of separation techniques and a critical evaluation of separation efficiency, detection sensitivity and specificity of these methods is reported.

Antitumor drugs possessing topoisomerase I inhibition: applicable separation methods

Separation methods for antitumor drugs capable of topoisomerase I inhibition were reviewed in this study. Camptothecin (CPT) its related analogues seemed to be promising anticancer drugs that exhibit topoisomerase I inhibition. This group of compounds contain a closed alpha-hydroxy-delta-lactone ring (lactone form) that can undergo reversible hydrolysis to form the open-ring form (carboxylate form). In vitro pharmacological study showed that the antitumor activity of the lactone form was higher than that of the carboxylate form. Thus a quantitative method to separate these two forms is important to evaluate the pharmacokinetics and pharmacodynamics of these compounds. Nevertheless, current separation methods are complicated by the pH-dependent instability of the lactone moiety. High-performance liquid chromatography (HPLC) coupled with fluorometric detection has been widely used for the quantitation of the drug as the intact lactone form or as the total lactone carboxylate forms in biological matrices. In this report we reviewed current applicable chromatographic techniques for further bioanalytical studies of CPT derivatives including sample preparations, HPLC columns, mobile phases and additives.

Quantitation of camptothecin and related compounds

Camptothecin and congeners represent a clinically very useful class of anticancer agents. Proper identification and quantitation of the original compounds and their metabolites in biological fluids is fundamental to assess drug metabolism and distribution in animals and in man. In this paper we will review the recent literature available on the methods used for separation and quantitative determination of the camptothecin family of drugs. Complications arise from the fact that they are chemically labile, and the pharmacologically active lactone structure can undergo ring opening at physiological conditions. In addition, a number of metabolic changes usually occur, producing a variety of active or inactive metabolites. Hence, the conditions of extraction, pre-treatment and quantitative analysis are to be carefully calibrated in order to provide meaningful results.