A novel risk score to identify the need for triple antithrombotic therapy in patients with atrial fibrillation undergoing percutaneous coronary intervention: a post hoc analysis of the RE-DUAL PCI trial

BACKGROUND

Current guidelines recommend treating atrial fibrillation (AF) patients who undergo percutaneous coronary intervention (PCI) with triple antithrombotic therapy (TAT) for up to one month in patients at high thrombotic risk. It is unclear how to select these high-risk patients.

AIMS

The aim of this study was to identify patients at high thrombotic risk who might benefit from TAT over double antithrombotic therapy (DAT).

METHODS

This study was a post hoc subanalysis of the RE-DUAL PCI trial. A Cox proportional hazards model was built by stepwise selection of plausible predictor variables for a composite ischaemic endpoint, defined as cardiovascular death, myocardial infarction (MI), stent thrombosis (ST) or ischaemic stroke. The effect of TAT versus DAT was calculated for those patients with the highest proportion of predicted thrombotic risk. A simplified risk score was constructed based on beta-coefficients.

RESULTS

For 209 patients (7.7%) the composite ischaemic endpoint occurred during the first year. The simplified risk score contained six variables. In patients with a score ≥5 (n=154, 5.7%), a significant reduction in the composite of MI and ST was observed with TAT versus DAT (6.3% vs 21.0%, p=0.041), without a penalty in terms of bleeding. In patients at low thrombotic risk, a significant increase in bleeding was observed without a reduction of ischaemic events.

CONCLUSIONS

Our findings support the use of DAT in the majority of patients. A small subgroup of patients might benefit from TAT and we propose a novel clinical risk score to select these patients.

Safety of Selective Intracoronary Hypothermia During Primary Percutaneous Coronary Intervention in Patients With Anterior STEMI

OBJECTIVES

The aim of this study was to determine the safety of selective intracoronary hypothermia during primary percutaneous coronary intervention (PPCI) in patients with anterior ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

Selective intracoronary hypothermia is a novel treatment designed to reduce myocardial reperfusion injury and is currently being investigated in the ongoing randomized controlled EURO-ICE (European Intracoronary Cooling Evaluation in Patients With ST-Elevation Myocardial Infarction) trial (NCT03447834). Data on the safety of such a procedure during PPCI are still limited.

METHODS

The first 50 patients with anterior STEMI treated with selective intracoronary hypothermia during PPCI were included in this analysis and compared for safety with the first 50 patients randomized to the control group undergoing standard PPCI. In-hospital mortality, occurrence of rhythm or conduction disturbances, stent thrombosis, onset of heart failure during the procedure, and subsequent hospital admission were assessed.

RESULTS

In-hospital mortality was 0%. One patient in both groups developed cardiogenic shock. Atrial fibrillation occurred in 0 and 3 patients (P = 0.24), and ventricular fibrillation occurred in 5 and 3 patients (P = 0.72) in the intracoronary hypothermia group and control group, respectively. Stent thrombosis occurred in 2 patients in the intracoronary hypothermia group; 1 instance was intraprocedural, and the other occurred following interruption of dual-antiplatelet therapy consequent to an intracranial hemorrhage 6 days after enrollment. No stent thrombosis was observed in the control group (P = 0.50).

CONCLUSIONS

Selective intracoronary hypothermia during PPCI in patients with anterior STEMI can be implemented within the routine of PPCI and seems to be safe. The final safety results will be reported at the end of the trial.

Large fluctuations in locational marginal prices

This paper investigates large fluctuations of locational marginal prices (LMPs) in wholesale energy markets caused by volatile renewable generation profiles. Specifically, we study events of the form [Formula: see text] where LMP is the vector of LMPs at the n power grid nodes, and α^-, [Formula: see text] are vectors of price thresholds specifying undesirable price occurrences. By exploiting the structure of the supply-demand matching mechanism in power grids, we look at LMPs as deterministic piecewise affine, possibly discontinuous functions of the stochastic input process, modelling uncontrollable renewable generation. We use techniques from large deviations theory to identify the most likely ways for extreme price spikes to happen, and to rank the nodes of the power grid in terms of their likelihood of experiencing a price spike. Our results are derived in the case of Gaussian fluctuations, and are validated numerically on the IEEE 14-bus test case. This article is part of the theme issue 'The mathematics of energy systems'.

2020 ESC Guidelines on acute coronary syndrome without ST-segment elevation : Recommendations and critical appraisal from the Dutch ACS and Interventional Cardiology working groups

Recently, the European Society of Cardiology (ESC) has updated its guidelines for the management of patients with acute coronary syndrome (ACS) without ST-segment elevation. The current consensus document of the Dutch ACS working group and the Working Group of Interventional Cardiology of the Netherlands Society of Cardiology aims to put the 2020 ESC Guidelines into the Dutch perspective and to provide practical recommendations for Dutch cardiologists, focusing on antiplatelet therapy, risk assessment and criteria for invasive strategy.

Identifying high thrombotic risk in atrial fibrillation patients undergoing percutaneous coronary intervention: is there a benefit of triple therapy?

Introduction

Patients requiring concomittant use of oral anticoagulants for atrial fibrillation and dual antiplatelet therapy after percutaneous coronary intervention (PCI) are at increased risk of bleeding and mortality. Omittance of aspirin (dual antithrombotic therapy, DAT) reduces bleeding as compared to triple antithrombotic therapy (TAT), but might not ascertain antithrombotic efficacy, especially in high-risk patients.

Purpose

To identify a subgroup of patients at high thrombotic risk that might benefit most from TAT over DAT.

Methods

The study was performed in a combined cohort of two randomised controlled trials (WOEST, RE-DUAL PCI) comparing TAT versus DAT after PCI. A Cox proportional hazards model predictive for the composite thrombotic endpoint of cardiovascular death, myocardial infarction (MI), stent thrombosis, and ischaemic stroke was built by stepwise selection of plausible predictor variables. Area under the receiver operating curve (AUC) was obtained, and clinical outcomes (thrombotic endpoint, bleeding [BARC 2,3+5], and all-cause mortality) were compared between the highest quintile of predicted thrombotic risk (high risk) and the remainder of patients (low-intermediate risk). Within the different risk groups, effect of TAT versus DAT was compared.

Results

A total of 3288 patients in the combined WOEST and RE-DUAL cohorts were included in this analysis. Approximately half underwent PCI for acute coronary syndrome. In 250 patients (7.6%) the composite thrombotic endpoint occurred during the first year. The final Cox proportional hazards model predicting thrombotic events contained: left ventricular ejection fraction, 3-vessel disease, MI at index PCI, peripheral artery disease, prior stroke, left circumflex coronary artery stenting, a history of MI, PCI to a bypass graft, and platelet count. The discriminatory capacity of the ischaemic model was fair (AUC 0.68, 95% confidence interval 0.64–0.71). Incidence of thrombotic events and mortality was higher in the high-risk as compared to low-intermediate risk patients (15.8% vs 5.6%, and 8.4% vs 3.2%, respectively, both p<0.001), whereas bleeding was comparable (20.5% vs 19.6%, p=0.60). No statistically significant effect of TAT over DAT was seen with regards to the thrombotic endpoint in both high and low-intermediate risk patients (13.9% vs 17.0%, p=0.36, and 6.5% vs 5.0%, p=0.11, respectively). Bleeding was significantly reduced with DAT versus TAT in both high and low-intermediate risk patients (minus 12.8% and 8.1%, both p<0.02). For low-intermediate risk patients a statistically significant increase in mortality was found with TAT versus DAT (4.2% vs 2.5%, p=0.02), whereas this was not found in high-risk patients (7.2% vs 9.1%, p=0.47).

Conclusions

No significant antithrombotic advantage of TAT over DAT was found in high-risk patients. However, TAT increased bleeding risk in all patients, and increased mortality in low-intermediate risk patients.

Funding Acknowledgement

Type of funding source: None

Use of glycoprotein IIb/IIIa antagonists to prevent stent thrombosis in morphine-treated patients with ST-elevation myocardial infarction

Morphine can delay absorption of P2Y₁₂-inhibitors in ST-elevation myocardial infarction (STEMI) patients, which has the potential to expose these patients to increased stent thrombosis risk after primary percutaneous coronary intervention (PPCI). Limited evidence exists for pharmacotherapeutic strategies aiming to mitigate this risk. We evaluated the impact of guideline-driven 'routine' glycoprotein IIb/IIIa antagonist (GPI) use in morphine-treated patients undergoing PPCI. A total of 3224 consecutive STEMI patients undergoing PPCI at a large tertiary cardiac center between 2012 and 2017 were evaluated. GPI use and outcomes before and after introduction of a local guideline were compared, and rates of definite stent thrombosis were identified at 24 h and 30 days. GPI use increased from 42.4% to 69.9% after the introduction of the new guideline. Stent thrombosis occurred in 1.3% (26/1947) pre-guideline and 0.6% (7/1244) post-guideline (P = .037). Of the 33 stent thrombosis cases, 90% (27/30) had received morphine, of whom 85.2% (23/27) had not received adjunctive GPI. Complete records for assessing 30-day bleeding rates were only available in 374 patients and, in this subset, there was no significant difference in rates of GUSTO moderate or severe bleeding before vs. after introduction of the local guideline (1.7% vs 2.8%; P = .47) although, in both cohorts combined, any GUSTO bleeding was observed more frequently in GPI-treated patients (21.8%) compared to those not receiving a GPI (10.0%; P = .002). In conclusion, routine GPI use in morphine-treated STEMI patients undergoing PPCI appears to protect against stent thrombosis. Large-scale studies are needed to establish the overall risk-benefit of GPI therapy in morphine-treated PPCI patients and to assess alternative strategies for preventing acute stent thrombosis in these patients.

High risk of stent thrombosis in the first 6 months after coronary stenting: Do not discontinue clopidogrel early after ACS

OBJECTIVES

To estimate the incidence of stent thrombosis (ST) after early discontinuation of clopidogrel.

BACKGROUND

Premature discontinuation of clopidogrel is the strongest risk factor for ST. In contrast, recent studies suggest that shorter dual antiplatelet therapy (DAPT) can be discontinued as soon as 3 months after stenting. However, these studies included very few ACS patients and were not powered for ST. Hence, little is known about the occurrence of ST in high-risk populations when DAPT is discontinued early.

METHODS

This is a subanalysis of The Dutch ST Registry 437 ST cases (mainly first-generation DES and BMS). Acute coronary syndrome was the indication for index-PCI in 74% of the patients. Clopidogrel discontinuation rates in ST patients and matched controls were used to calculate the absolute incidence of ST after early clopidogrel discontinuation.

RESULTS

The overall rate of ST after cessation of clopidogrel was 4.6% (95%CI: 3.9-5.4%), as compared to 1.7% (95%CI: 1.5-1.9%) in patients who did not discontinue clopidogrel. The incidence of ST was 35.4% when clopidogrel was discontinued in the first 30 days after index-PCI declining to 11.7% when clopidogrel was discontinued in the first 180 days.

CONCLUSIONS

This dedicated ST registry shows that ST rates were very high when clopidogrel was discontinued before 6 months after index-PCI and therefore suggests that clopidogrel discontinuation in the first 6 months after ACS should be avoided.

Short-term career perspectives of young cardiologists in the Netherlands

Background

Since it was anticipated that the need for doctors would increase due to demographic changes, the number of positions for medical specialty training programs has increased from the year 2000 onwards. However, the number of permanent positions for young cardiologists did not follow that trend leading to concerns about future employment. Therefore, the aim of the current study was to assess short-term career perspectives of young cardiologists in the Netherlands.

Methods

All cardiologists who ended their training between 1 January 2011 and 31 December 2014 were invited to fill in a questionnaire about their first employment status and were followed yearly until the participant had a permanent position. The timespan between the end of training and the moment of permanent employment was assessed. Furthermore, the association between professional profile and short-term career perspectives was investigated.

Results

The observed unemployment was 1.6% and lasted less than a year in all cases. Of the participants, 77% started their career with a temporary contract; within four years this was 7%. Of young cardiologists, 46% started their career as a fellow and 24% as an attending physician. A total of 29% of male cardiologists started their career with a permanent contract as compared with 12% of females (p = 0.01). Within two years this difference was no longer observed.

Conclusions

Unemployment is low among young cardiologists. Most cardiologists start their career with a temporary contract. The time to a permanent contract is slightly longer for female cardiologists as compared with males.

Effect of Tailored Antiplatelet Therapy to Reduce Recurrent Stent Thrombosis and Cardiac Death After a First Episode of Stent Thrombosis

The recurrence rate of coronary stent thrombosis (ST) is high. Patients with ST often demonstrate high on-treatment platelet reactivity (HPR). It is suggested that patients at high risk of atherothrombotic events, that is patients with ST, could benefit from tailored antiplatelet therapy (APT). This study evaluated whether tailored APT, based on platelet function testing, reduced the rate of cardiac death and/or recurrent ST at 1 year after ST, compared with a historical cohort of patients with ST without tailored APT. Patients with definite ST visited our ST outpatient clinic for platelet function testing and tailored APT. These patients were evenly matched to a historical cohort of patients with ST treated with aspirin and clopidogrel, which was the standard of care at that time. The primary end point was a composite of cardiac death and/or recurrent definite ST after 1 year. In total, 113 patients who visited the outpatient clinic were included. HPR was observed in 46%, 6.7%, and 0% of the patients on clopidogrel, prasugrel, and ticagrelor, respectively. After tailored APT, 93% of the patients with HPR demonstrated normal platelet reactivity. The primary end point was observed in 4 patients who had visited the outpatient clinic and in 23 patients of the historical cohort. The odds ratio of tailored APT on the primary end point was 0.26 (95% confidence interval 0.11 to 0.64, p = 0.003), independent from the possible confounders prior myocardial infarction and stent type. In conclusion, the outpatient ST clinic was associated with lower HPR rates in patients with ST after tailored APT. Patients who visited the ST outpatient clinic had a lower risk for cardiac death and/or recurrent ST compared with a historical cohort of patients with ST without tailored APT. Regarding the high HPR rate in patients with ST on clopidogrel, these patients might benefit in particular from the strategy of tailored APT.

Gaussian expansions and bounds for the Poisson distribution applied to the Erlang B formula

This paper presents new Gaussian approximations for the cumulative distribution function P(Aλ ≤ s) of a Poisson random variable Aλ with mean λ. Using an integral transformation, we first bring the Poisson distribution into quasi-Gaussian form, which permits evaluation in terms of the normal distribution function Φ. The quasi-Gaussian form contains an implicitly defined function y, which is closely related to the Lambert W-function. A detailed analysis of y leads to a powerful asymptotic expansion and sharp bounds on P(Aλ ≤ s). The results for P(Aλ ≤ s) differ from most classical results related to the central limit theorem in that the leading term Φ(β), with is replaced by Φ(α), where α is a simple function of s that converges to β as s tends to ∞. Changing β into α turns out to increase precision for small and moderately large values of s. The results for P(Aλ ≤ s) lead to similar results related to the Erlang B formula. The asymptotic expansion for Erlang's B is shown to give rise to accurate approximations; the obtained bounds seem to be the sharpest in the literature thus far.

Triggering mechanisms of stent thrombosis

AIMS

The aim of this study was to determine the role of potential triggers of stent thrombosis.

METHODS AND RESULTS

Patients (n = 437) with "definite" ST were recruited consecutively in the setting of a large multicentre observational cohort study. Patients were interviewed with validated questionnaires to identify one of the following triggers: i) timing of onset of ST, ii) performance of vigorous ( ≥ 6 MET) physical activity in the two hours preceding ST, iii) presence of emotional stress (experiencing a serious life event in the 14 days preceding the ST or feelings of anger in the 12 hours of ST) and iv) presence of a documented active infection at the time of ST. A total of 363 patients (83.1%) were able to supply adequate information. A significant trigger was identified in 83 patients (22.9%). Analysis of the different categories according to timing of ST revealed a higher prevalence of triggers with an increasing time-interval between index PCI and ST. Analysis of circadian variation showed a steep peak incidence from 7 am-12 pm.

CONCLUSIONS

Triggering mechanisms such as time of the day, physical exertion, emotional stress and infection may play an important role in a considerable number of patients presenting with ST, in particular in patients with (very) late ST.

Acute and subacute stent thrombosis after primary percutaneous coronary intervention for ST-segment elevation myocardial infarction: incidence, predictors and clinical outcome

BACKGROUND

Early coronary stent thrombosis occurs most frequent after primary percutaneous coronary intervention (PCI) for ST-segment elevation myocardial infarction (STEMI).

OBJECTIVES

To identify the specific predictors of, respectively, acute and subacute stent thrombosis in patients after primary PCI for STEMI.

PATIENTS/METHODS

Consecutive STEMI patients with angiographically confirmed early stent thrombosis were enrolled and compared in a 2 : 1 ratio with a matched control group. Clinical outcome was collected up to 1 year.

RESULTS

Of 5842 STEMI patients treated with primary PCI, 201 (3.5%) presented with a definite early stent thrombosis. Of these, 97 (1.7%) had acute stent thromboses and 104 (1.8%) had subacute stent thromboses. Postprocedurally discovered dissection, undersizing and smaller stent diameter were the strongest predictors for acute stent thrombosis. No glycoprotein IIb/IIIa therapy and the use of drug-eluting stents were also associated with acute stent thrombosis. Lack of clopidogrel therapy in the first 30 days after the index PCI was the strongest predictor for subacute stent thrombosis. Mortality rates at 1-year follow-up were lower for acute stent thrombosis than for subacute stent thrombosis (8.3% vs. 13.2%, P = 0.294). The incidence of definite recurrent stent thrombosis at 1-year follow up was significantly lower after a first definite acute stent thrombosis than after a first definite subacute stent thrombosis (6.4% vs. 19.3%, P = 0.007 at 1 year).

CONCLUSIONS

The specific risk factors for, respectively, acute and subacute stent thrombosis after primary PCI vary greatly. Mortality rates are high for both categories of stent thrombosis. However, recurrent stent thrombosis occurs more frequently after subacute stent thrombosis.

CYP2C19*2 and CYP2C9*3 alleles are associated with stent thrombosis: a case-control study

AIMS

despite treatment with clopidogrel on top of aspirin, stent thrombosis (ST) still occurs being the most serious complication after percutaneous coronary interventions (PCIs). In this study, we aimed to determine the effect of variations in genes involved in the absorption (ABCB1 C1236T, G2677T/A, C3435T), metabolism (CYP2C19*2 and *3, CYP2C9*2 and *3, CYP3A4*1B and CYP3A5*3), and pharmacodynamics (P2Y1 A1622G) of clopidogrel on the occurrence of ST.

METHODS AND RESULTS

the selected genetic variants were assessed in 176 subjects who developed ST while on dual antiplatelet therapy with aspirin and clopidogrel and in 420 control subjects who did not develop adverse cardiovascular events, including ST, within 1 year after stenting. The timing of the definite ST was acute in 66, subacute in 87, and late in 23 cases. The presence of the CYP2C19*2 and CYP2C9*3 variant alleles was significantly associated with ST (OR(adj): 1.7, 95% CI: 1.0-2.6, P = 0.018 and OR(adj): 2.4, 95% CI: 1.0-5.5, P = 0.043, respectively). The influence of CYP2C19*2 (OR(adj): 2.5, 95% CI: 1.1-5.5, P = 0.026) and CYP2C9*3 (OR(adj): 3.3, 95% CI: 1.1-9.9, P = 0.031) was most strongly associated with subacute ST. No significant associations of the other genetic variations and the occurrence of ST were found.

CONCLUSION

carriage of the loss-of-function alleles CYP2C19*2 and CYP2C9*3 increases the risk on ST after PCI.

Time does not heal every wound: coronary stent thrombosis of a bare-metal stent more than one decade after its implantation

In the present report, we describe a unique case of very late stent thrombosis with a bare-metal stent that occurred more than a decade after stent implantation. Potential explanations for the late stent thrombosis are non-compliance to aspirin, late acquired malapposition of the stent, progression of atherosclerosis or in-stent restenosis. In our patient, none of these explanations seems to have played a role. Although the occurrence of (very) late stent thrombosis is not uncommon with drug-eluting stent (DES), it is rather unusual with bare-metal stent (BMS). Nevertheless, cardiologists should be aware of the potential complication of late stent thrombosis, even with bare-metal stents.

Long-Term Clinical Outcome After a First Angiographically Confirmed Coronary Stent Thrombosis

Background— There are limited data on the long-term clinical outcome after an angiographically confirmed (definite) stent thrombosis (ST).

Methods and Results— Four hundred thirty-one consecutive patients with a definite ST were enrolled in this multicenter registry. The primary end point was the composite of cardiac death and definite recurrent ST. Secondary end points were all-cause death, cardiac death, definite recurrent ST, definite and probable recurrent ST, any myocardial infarction, and any target-vessel revascularization. The primary end point occurred in 111 patients after a median follow-up of 27.1 months. The estimated cumulative event rates at 30 days and 1, 2, and 3 years were 18.0%, 23.6%, 25.2%, and 27.9%, respectively. The cumulative incidence rates of definite recurrent ST, definite or probable recurrent ST, any myocardial infarction, and any target-vessel revascularization were 18.8%, 20.1%, 21.3%, and 32.0%, respectively, at the longest available follow-up. Independent predictors for the primary end point were diabetes mellitus, total stent length, severe calcification, American College of Cardiology/American Heart Association B2-C lesions, TIMI (Thrombolysis In Myocardial Infarction) flow grade <3 after percutaneous coronary intervention, and left ventricular ejection fraction <45%. The implantation of an additional coronary stent during the first ST was also associated with unfavorable outcome. Clinical outcome was not affected by the type of previously implanted stent (drug-eluting or bare-metal stent) or the category of ST (early versus late).

Conclusions— The long-term clinical outcome after a first definite ST is unfavorable, with a high mortality and recurrence rate. Diabetes mellitus, left ventricular ejection fraction <45%, long total stent length, complex coronary lesions, TIMI flow grade <3 after percutaneous coronary intervention, and implantation of an additional coronary stent during the emergent percutaneous coronary intervention for the ST were associated with this unfavorable outcome.

Chromatin-independent binding of serum amyloid P component to apoptotic cells

Human serum amyloid P component (SAP) is a glycoprotein structurally belonging to the pentraxin family of proteins, which has a characteristic pentameric organization. Mice with a targeted deletion of the SAP gene develop antinuclear Abs, which was interpreted as evidence for a role of SAP in controlling the degradation of chromatin. However, in vitro SAP also can bind to phosphatidylethanolamine, a phospholipid which in normal cells is located mainly in the inner leaflet of the cell membrane, to be translocated to the outer leaflet of the cell membrane during a membrane flip-flop. We hypothesized that SAP, because of its specificity for phosphatidylethanolamine, may bind to apoptotic cells independent of its nuclear binding. Calcium-dependent binding of SAP to early, nonpermeable apoptotic Jurkat, SKW, and Raji cells was indeed observed. Experiments with flip-flopped erythrocytes confirmed that SAP bound to early apoptotic cells via exposed phosphatidylethanolamine. Binding of SAP was stronger to late, permeable apoptotic cells. Experiments with enucleated neutrophils, with DNase/RNase treatment of late apoptotic Jurkat cells, and competition experiments with histones suggested that binding of SAP to late apoptotic cells was largely independent of chromatin. Confocal laser microscopic studies indeed suggested that SAP bound to these apoptotic cells mainly via the blebs. Thus, this study shows that SAP binds to apoptotic cells already at an early stage, which raises the possibility that SAP is involved in dealing with apoptotic cells in vivo.

[Eleven-Cities skating marathon and the windchill factor]

The weather conditions during the 15th Eleven Cities ice skating marathon (200 kilometers) in Friesland (the Netherlands) on 4 January, 1997, were better than predicted. For measurement of the windchill factor the Steadman scale is preferred to the Siple and Passel scale. For ice skaters the windchill factor is lower than for the spectators, due to the drag effect.

CPT-11 in human colon-cancer cell lines and xenografts: characterization of cellular sensitivity determinants

CPT-11, a new semisynthetic derivative of camptothecin, is active in a number of tumor types in the clinic, including colon cancer. CPT-11 is a drug that is converted into the active metabolite SN-38 by a carboxylesterase. Experiments were performed to obtain more insight in the cellular characteristics in 5 unselected human colon-cancer cell lines that account for the differential sensitivity to CPT-11 and SN-38. In vitro, the sensitivity to CPT-11 and SN-38 was highest in LS174T and COLO 320 cells, intermediate in SW1398 cells and lowest in COLO 205 and WiDr cells. SN-38 was 130 to 570 times more active than CPT-11. CPT-11 induced complete remissions in 6 out of 12 COLO 320 tumors grown as subcutaneous xenografts, but was not effective in WiDr tumors. The cellular carboxylesterase activity did not relate to the sensitivity to CPT-11. The enzyme activity was higher in normal mouse tissues, i.e., serum and liver, than in COLO 320 or WiDr xenografts, indicating that tumor carboxylesterase is of minor importance for CPT-11 efficacy. The topoisomerase-1 mRNA expression in tumor cells was not predictive of the antiproliferative effects of CPT-11 or SN-38. We observed a positive relationship between the DNA topoisomerase-1 activity and the cellular sensitivity to carboxylesterase-activated CPT-11 (r = 0.75, p < 0.1) as well as to SN-38 (r = 0.89, p < 0.05). The higher topoisomerase-1 activity in COLO 320 cells and tumors when compared with that in WiDr cells and tumors reflected the differences in sensitivity to the drug(s). In conclusion, the DNA topoisomerase-1 activity was the best determinant for CPT-11/SN-38 sensitivity in this panel of unselected human colon-cancer cell lines.