Camptothecin analog (CPT-11)-sensitive human pancreatic tumor cell line QGP-1N shows resistance to SN-38, an active metabolite of CPT-11

Review : Topoisomerase I inhibitors: 2. Irinotecan

Purpose. The primary objective of this article is to discuss the pharmacology, pharmacokinetics, clinical use, and adverse effects of the approved topoisomer ase I inhibitors. This is the second in a series of two articles and will focus on irinotecan.

Data Sources. We reviewed the literature through a MEDLINE search of English language arti cles from 1985 through 1998. Relevant articles cited in the titles obtained from the MEDLINE search were also used. The following terms were used for purpose of conducting the MEDLINE search: topoisomerase inhibitors, irinotecan, topoisomerase I, camptosar, and CPT-11.

Data Extraction. We have reviewed the current literature to discuss the pharmacology, pharmacokinet ics, clinical use, toxicity, drug interactions, indications, formulation, dosage and administration, and pharmaceu tical issues surrounding the use of irinotecan.

Data Synthesis. The topoisomerase I inhibitors are new antineoplastic agents with a unique mechanism of action. Promising areas of application include colo rectal cancer, non-small-cell lung cancer, small-cell lung cancer, cervical cancer, and lymphomas. Clinical trials detailing the activity of topoisomerase I inhibitors in these areas are presented.

Metastatic pancreatic cancer: old drugs, new paradigms

PURPOSE OF REVIEW

Metastatic pancreatic ductal adenocarcinoma has a grim prognosis and gemcitabine has been the reference treatment for 15 years. In this article, we will review current first-line treatments for metastatic pancreatic adenocarcinoma focusing on randomized studies.

RECENT FINDINGS

Among the numerous randomized phase III studies comparing gemcitabine as single agent to gemcitabine combined to a new agent, only the gemcitabine-erlotinib combination has shown a small, but statistical improvement in survival. A trend to better survival was also observed with a gemcitabine-capecitabine regimen. The use of low-weight heparin may be of value to reduce venous thromboembolic events. In selected patients with good performance status ECOG 0-1, the Folfirinox regimen, when compared with gemcitabine, was associated with more toxicities and significantly increased median survival from 6.8 to 11.1 months.

SUMMARY

Gemcitabine (with or without erlotinib or capecitabine) is still the reference treatment in patients with ECOG performance status 2. Folfirinox is a new more toxic and more efficient regimen that may be considered in patients with good performance status.

Irinotecan plus oxaliplatin and leucovorin-modulated fluorouracil in advanced pancreatic cancer--a Groupe Tumeurs Digestives of the Federation Nationale des Centres de Lutte Contre le Cancer study

PURPOSE

To evaluate response rate and toxicity of irinotecan and oxaliplatin plus fluorouracil (FU) and leucovorin (Folfirinox) in advanced pancreatic adenocarcinoma (APA).

PATIENTS AND METHODS

Chemotherapy-naive patients with histologically proven APA and bidimensionally measurable disease were treated with Folfirinox therapy every 2 weeks, which comprised oxaliplatin 85 mg/m(2) and irinotecan 180 mg/m(2) plus leucovorin 400 mg/m(2) followed by bolus FU 400 mg/m(2) on day 1, then FU 2,400 mg/m(2) as a 46-hour continuous infusion. Quality of life (QOL) was assessed using European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30).

RESULTS

Forty-seven patients were entered, and 46 received treatment. Thirty-five patients (76%) had metastatic disease. A total of 356 cycles were delivered, with a median of eight cycles per patient (range, one to 24 cycles). All patients were assessable for safety. No toxic death occurred. Grade 3 to 4 neutropenia occurred in 52% of patients, including two patients with febrile neutropenia. Other relevant toxicities included grade 3 to 4 nausea (20%), vomiting (17%), and diarrhea (17%) and grade 3 neuropathy (15%; Levi's scale). The confirmed response rate was 26% (95% CI, 13% to 39%), including 4% complete responses. Median time to progression was 8.2 months (95% CI, 5.3 to 11.6 months), and median overall survival was 10.2 months (95% CI, 8.1 to 14.4 months). Between baseline and end of treatment, patients had improvement in all functional scales of the EORTC QLQ-C30, except cognitive functioning. Responders had major improvement in global QOL.

CONCLUSION

With a good safety profile, a promising response rate, and an improvement in QOL, Folfirinox will be further assessed in a phase III trial.

A phase II irinotecan-cisplatin combination in advanced pancreatic cancer

We report a cisplatin and irinotecan combination in patients with biopsy-proven advanced pancreatic adenocarcinoma. Patients were selected from a specialist centre and required good performance status (KPS>70%), measurable disease on CT scan, and biochemical and haematological parameters within normal limits. Based on a two-stage phase II design, we aimed to treat 22 patients initially. The study was stopped because of the death of the 19th patient during the first treatment cycle, with neutropenic sepsis and multiorgan failure. A total of 89 treatments were administered to 17 patients. Serious grade 3/4 toxicities were haematological (neutropenia) 6%, diarrhoea 6%, nausea 7% and vomiting 6%. Using the clinical benefit response (CBR) criteria, no patients had an overall CBR. For responses confirmed by CT examination, there was one partial response (5%), three stable diseases lasting greater than 6 weeks (16%), with an overall 22% with disease control (PR+SD). The median progression-free and overall survival was 3.1 months (95% CI: 1.3-3.7) and 5.0 (95% CI: 3.9-10.1) months, respectively. Although this synergistic combination has improved the response rates and survival of other solid tumours, we recommend caution when using this combination in the palliation of advanced pancreatic cancer, because of unexpected toxicity.

Clinical pharmacokinetics of irinotecan

This article reviews the clinical pharmacokinetics of a water-soluble analogue of camptothecin, irinotecan [CPT-11 or 7-ethyl-10-[4-(1-piperidino)-1-piperidino]-carbonyloxy-camptoth eci n]. Irinotecan, and its more potent metabolite SN-38 (7- ethyl-10-hydroxy-camptothecin), interfere with mammalian DNA topoisomerase I and cancer cell death appears to result from DNA strand breaks caused by the formation of cleavable complexes. The main clinical adverse effects of irinotecan therapy are neutropenia and diarrhoea. Irinotecan has shown activity in leukaemia, lymphoma and the following cancer sites: colorectum, lung, ovary, cervix, pancreas, stomach and breast. Following the intravenous administration of irinotecan at 100 to 350 mg/m2, mean maximum irinotecan plasma concentrations are within the 1 to 10 mg/L range. Plasma concentrations can be described using a 2- or 3-compartment model with a mean terminal half-life ranging from 5 to 27 hours. The volume of distribution at steady-state (Vss) ranges from 136 to 255 L/m2, and the total body clearance is 8 to 21 L/h/m2. Irinotecan is 65% bound to plasma proteins. The areas under the plasma concentration-time curve (AUC) of both irinotecan and SN-38 increase proportionally to the administered dose, although interpatient variability is important. SN-38 levels achieved in humans are about 100-fold lower than corresponding irinotecan concentrations, but these concentrations are potentially important as SN-38 is 100- to 1000-fold more cytotoxic than the parent compound. SN-38 is 95% bound to plasma proteins. Maximum concentrations of SN-38 are reached about 1 hour after the beginning of a short intravenous infusion. SN-38 plasma decay follows closely that of the parent compound with an apparent terminal half-life ranging from 6 to 30 hours. In human plasma at equilibrium, the irinotecan lactone form accounts for 25 to 30% of the total and SN-38 lactone for 50 to 64%. Irinotecan is extensively metabolised in the liver. The bipiperidinocarbonylxy group of irinotecan is first removed by hydrolysis to yield the corresponding carboxylic acid and SN-38 by carboxyesterase. SN-38 can be converted into SN-38 glucuronide by hepatic UDP-glucuronyltransferase. Another recently identified metabolite is 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxy-camptothecin (APC). This metabolite is a weak inhibitor of KB cell growth and a poor inducer of topoisomerase I DNA-cleavable complexes (100-fold less potent than SN-38). Numerous other unidentified metabolites have been detected in bile and urine. The mean 24-hour irinotecan urinary excretion represents 17 to 25% of the administered dose. Recovery of SN-38 and its glucuronide in urine is low and represents 1 to 3% of the irinotecan dose. Cumulative biliary excretion is 25% for irinotecan, 2% for SN-38 glucuronide and about 1% for SN-38. The pharmacokinetics of irinotecan and SN-38 are not influenced by prior exposure to the parent drug. The AUC of irinotecan and SN-38 correlate significantly with leuco-neutropenia and sometimes with the intensity of diarrhoea. Certain hepatic function parameters have been correlated negatively with irinotecan total body clearance. It was noted that most tumour responses were observed at the highest doses administered in phase I trials, which indicates a dose-response relationship with this drug. In the future, these pharmacokinetic-pharmacodynamic relationships will undoubtedly prove useful in minimising the toxicity and maximise the likelihood of tumour response in patients.

SN-38, a metabolite of the camptothecin derivative CPT-11, potentiates the cytotoxic effect of radiation in human colon adenocarcinoma cells grown as spheroids

BACKGROUND AND PURPOSE

CPT-11 (7-ethyl-10-[4-(1-piperidino)-1-piperidino] carbonyloxycamptothecin) is anew semisynthesized derivative of camptothecin. SN-38 (7-ethyl-10-hydroxycamptothecin), a metabolite of CPT-11, plays a key role in the action of CPT-11.

MATERIALS AND METHODS

To determine whether SN-38 potentiates the cytotoxic effect of radiation, we investigated the interaction of SN-38 and radiation in vitro in monolayer cultures and multicellular spheroids of HT-29 human colon adenocarcinoma cells.

RESULTS

HT-29 spheroids were more resistant to both SN-38 and irradiation than monolayer cells. SN-38 at a concentration of 2.5 microg/ml, which by itself was not cytotoxic, greatly increased the lethal effects of radiation in spheroids, but not in monolayer cultures. Exposure to SN-38 following irradiation inhibited the potentially lethal damage repair (PLDR) in spheroids. It is suggested that the mechanism of the radiosensitization by SN-38 is due to the PLDR inhibition.

CONCLUSIONS

These results indicate that CPT-11 may play a role as radiosensitizer and that a combination of CPT-11 and irradiation could prove to be a particularly effective strategy with which to treat human colon adenocarcinoma.

Limited sampling models for simultaneous estimation of the pharmacokinetics of irinotecan and its active metabolite SN-38

Irinotecan (CPT-11) is a novel topoisomerase I inhibitor with clinical activity in human malignancies. The objective of this study was to develop efficient limited sampling models (LSMs) to estimate simulataneously the area under the plasma concentration versus time curves (AUC) for both CPT-11 and its active metabolite SN-38. A total of 64 pharmacokinetic sets (> or = 24-h sampling) were obtained in phase I studies at doses ranging from 50 to 750 mg/m2 (0.5-h i.v. infusion). The patients were randomly assigned to a training data set (n = 32) and a test set (n = 32). Multiple linear regression analyses were used to determine the optimal LSMs based on the correlation coefficient (r), bias (MPE%, percentage of mean prediction error), and precision (RMSE%, percentage of root mean squared prediction error). Of these LSMs, the ones including maximal concentrations of CPT-11 (0.5 h, the end of the i.v. infusion) and metabolite SN-38 (approximately 1 h) were favored along with predictive precision and clinical constraints. Several bivariate models including a 6-h time point as the last sampling time (or 7 h) were found to be highly predictive of either the CPT-11 AUC or the SN-38 AUC. The chosen sampling time points were the ones that allowed the best compromise between the accurate determination of either compound alone with the same sampling times. The simultaneously best prediction of both CPT-11 and SN-38 AUCs was obtained with sampling time points harvested at 0.5, 1, and 6 h (or 7 h). With these sampling time points a trivariate model was selected for the determination of CPT-11 AUC namely, CPT-11 AUC (ng h ml-1) = 0.820 x C0.5h + 0.402 x C1h + 15.47 x C6h + 928, and a corresponding model was selected for the determination of metabolite AUC, i.e., SN-38 AUC (ng h ml-1) = 4.05 x C0.5h -0.81 x C1h + 23.01 x C6h - 69.78, where C(t) is the concentration in nanograms per milliliter of either compound at a given time t. These models performed well with the test data sets for CPT-11 AUC (r = 0.98, MPE% = -1.4, RMSE% = 13.9) and for SN-38 AUC (r = 0.95, MPE% = -6.5, RMSE% = 37.7). In addition to the determination of AUCs (and hence clearance), these models also allow the determination of the maximal concentrations of both compounds, which might be needed for pharmacodynamics studies.(ABSTRACT TRUNCATED AT 400 WORDS)