Abstract
BackgroundStudies in taxane and/or anthracycline refractory metastatic breast cancer (mBC) patients have shown approximately 30 % response rates to irinotecan. Hence, a significant number of patients will experience irinotecan-induced side effects without obtaining any benefit. The aim of this study was to lay the groundwork for development of predictive biomarkers for irinotecan treatment in BC.MethodsWe established BC cell lines with acquired or de novo resistance to SN-38, by exposing the human BC cell lines MCF-7 and MDA-MB-231 to either stepwise increasing concentrations over 6 months or an initial high dose of SN-38 (the active metabolite of irinotecan), respectively. The resistant cell lines were analyzed for cross-resistance to other anti-cancer drugs, global gene expression, growth rates, TOP1 and TOP2A gene copy numbers and protein expression, and inhibition of the breast cancer resistance protein (ABCG2/BCRP) drug efflux pump.ResultsWe found that the resistant cell lines showed 7–100 fold increased resistance to SN-38 but remained sensitive to docetaxel and the non-camptothecin Top1 inhibitor LMP400. The resistant cell lines were characterized by Top1 down-regulation, changed isoelectric points of Top1 and reduced growth rates. The gene and protein expression of ABCG2/BCRP was up-regulated in the resistant sub-lines and functional assays revealed BCRP as a key mediator of SN-38 resistance.ConclusionsBased on our preclinical results, we suggest analyzing the predictive value of the BCRP in breast cancer patients scheduled for irinotecan treatment. Moreover, LMP400 should be tested in a clinical setting in breast cancer patients with resistance to irinotecan.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2071-1) contains supplementary material, which is available to authorized users.
Highlights
Studies in taxane and/or anthracycline refractory metastatic breast cancer patients have shown approximately 30 % response rates to irinotecan
Irinotecan, etirinotecan and topotecan have been tested in clinical trials in metastatic breast cancer (mBC) [6], and irinotecan and etirinotecan regimens were shown to benefit a considerable proportion of mBC patients who had relapsed on prior treatment with anthracyclines and taxanes [7, 8]
There was a trend towards association between topoisomerase I gene (TOP1) and centromere 20 (CEN-20) copy numbers as reflected in a TOP1/CEN-20 ratio close to 1 for the majority of the cell lines (Additional file 1: Figure S1a)
Summary
Studies in taxane and/or anthracycline refractory metastatic breast cancer (mBC) patients have shown approximately 30 % response rates to irinotecan. This study is based on data from a report that evaluated etirinotecan in 70 taxane-resistant mBC patients and an objective response rate of 29 % was observed when this drug was given as second- or third-line treatment [8]. These data was reproduced in the BEACON study, which demonstrated that etirinotecan was at least as efficient as the physichian’s choice of treatment [9]
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