Molecular characterization of irinotecan (SN-38) resistant human breast cancer cell lines

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.

A novel chemotherapeutic protocol for peritoneal metastasis and inhibition of relapse in drug resistant ovarian cancer

“…However, the expression level was in low intensity meaning that ABCG2 existed in low copy numbers on the cell surfaces (Figure S1). Since OVASC‐1 cells express MDR1 in high copy numbers but ABCG2 in low copy numbers, our data related to the sensitivity of OVASC‐1 to SN‐38 at nanomolar (nmol/L) concentrations appears to rule out MDR1 as a prominent mediator of SN‐38 resistance, and agree with the more recent studies reported in 2016 22, 23. This interesting observation highlights the importance of personalized therapy, in which an IP sample could be taken from each patient and analyzed for ABCG2 expression.…”

“…The sensitivity of the OVASC‐1 cells to SN‐38 was also interesting. Some older studies have indicated that SN‐38 is a substrate for both the MDR1 and the ABCG2 drug efflux pumps,21 whereas recent evidence suggests that the ABCG2 pump is a key mediator of SN‐38 resistance 22, 23. To shed more light on this ambiguity, we measured the expression levels of the ABCG2 transporter in OVASC‐1 cells.…”

Combining ABCG2 Inhibitors with IMMU-132, an Anti–Trop-2 Antibody Conjugate of SN-38, Overcomes Resistance to SN-38 in Breast and Gastric Cancers

“…When cultured in vitro, SN-38-resistant sublines of MCF-7 or MDA-MB-231 had longer doubling times than their parental cells (43). Thus, it is not surprising that NCI-N87-S120 xenografts grew significantly slower in the mice than NCI-N87, which is consistent with the notion that drug-resistant tumor sublines selected in vitro frequently manifest less aggressive properties than their drugsensitive parental cell lines (49).…”

“…Cross-resistance of these sublines to doxorubicin varied somewhat, with the resistance ratio (IC 50 in resistant subline divided by IC 50 in the parental cell) being less than 1.3 for the sublines of PC-6 (17), 2.5 for the sublines of HeLa (45), and about 7.0 for the subline of H23 (44). Whereas cross-resistance to doxorubicin was not determined for the SN-38-resistant sublines derived from MCF-7 (42,43) or MDA-MB-231 (43), these sublines remained sensitive to vincristine (42), cisplatin (42,43), and docetaxel (43). Although we and others have established ABCG2 as a key player in reducing SN-38 sensitivity of various SN-38-resistant cancer sublines, the potential involvement of DNA topoisomerase I (Top1), to which SN-38 specifically binds and acts as an inhibitor, in the SN-38 resistance mechanism of such cancer cells, is less defined and remains a focus of continuous research, with the current knowledge pointing to Top1 mutation (46,47) and degradation (48) as the two main roles of Top1 underlying the molecular mechanism of resistance to camptothecin in general and SN-38 in particular.…”

“…Together, these in vivo results suggest that suitable inhibitors that are tolerated well by the host animals can overcome ABC resistance and that the resistant tumor lines can become appreciably responsive to IMMU-132 and to a lesser extent to irinotecan. We are pursuing further work to address the feasibility of preclinical testing for such drug resistance as a predictive bioassay (43,44) to select patients who should receive ABC-blocking therapy with IMMU-132. Meanwhile, we are examining the suitability of clinically tested tyrosine kinase inhibitors, some of which interfere with the functions of ABC transporters at nontoxic levels (50), to enhance the potency of IMMU-132 in cancer cells that are intrinsically or made resistant to SN-38.…”