Cellular uptake mechanism and comparative evaluation of antineoplastic effects of paclitaxel–cholesterol lipid emulsion on triple-negative and non-triple-negative breast cancer cell lines

Abstract

There is no effective clinical therapy for triple-negative breast cancers (TNBCs), which have high low-density lipoprotein (LDL) requirements and express relatively high levels of LDL receptors (LDLRs) on their membranes. In our previous study, a novel lipid emulsion based on a paclitaxel–cholesterol complex (PTX-CH Emul) was developed, which exhibited improved safety and efficacy for the treatment of TNBC. To date, however, the cellular uptake mechanism and intracellular trafficking of PTX-CH Emul have not been investigated. In order to offer powerful proof for the therapeutic effects of PTX-CH Emul, we systematically studied the cellular uptake mechanism and intracellular trafficking of PTX-CH Emul and made a comparative evaluation of antineoplastic effects on TNBC (MDA-MB-231) and non-TNBC (MCF7) cell lines through in vitro and in vivo experiments. The in vitro antineoplastic effects and in vivo tumor-targeting efficiency of PTX-CH Emul were significantly more enhanced in MDA-MB-231-based models than those in MCF7-based models, which was associated with the more abundant expression profile of LDLR in MDA-MB-231 cells. The results of the cellular uptake mechanism indicated that PTX-CH Emul was internalized into breast cancer cells through the LDLR-mediated internalization pathway via clathrin-coated pits, localized in lysosomes, and then released into the cytoplasm, which was consistent with the internalization pathway and intracellular trafficking of native LDL. The findings of this paper further confirm the therapeutic potential of PTX-CH Emul in clinical applications involving TNBC therapy.

Keywords:

• paclitaxel
• lipid emulsion
• triple-negative breast cancers
• low-density lipoprotein
• tumor targeting

Supplementary materials

Figure S1 HPLC analysis of MCF7 cells incubated with PTX-CH Emul diluted in culture medium with 10% FBS, 10% LPDS, or 10% LPDS plus LDL.

Notes: **P<0.01. Each value represents the mean ± SD (n=3).

Abbreviations: HPLC, high-performance liquid chromatography; PTX-CH Emul, paclitaxel–cholesterol emulsion; FBS, fetal bovine serum; LPDS, lipoprotein-deficient serum; LDL, low-density lipoprotein; SD, standard deviation.

Figure S2 In vitro cytotoxicity studies of PTX-CH Emul on MCF7 and MDA-MB-231 cells at 72 hours. Each value represents the mean ± SD (n=3).

Abbreviations: PTX, paclitaxel; PTX-CH Emul, paclitaxel–cholesterol emulsion; SD, standard deviation.

Figure S3 Confocal microscopy observation of the binding of FL-PTX-CH Emul to MDA-MB-231 and MCF7 cells.

Notes: MDA-MB-231 cells were incubated with FL-DMSO, FL-PTX Emul, and FL-PTX-CH Emul, and MCF7 cells were incubated with FL-PTX-CH Emul for 2 hours at 4°C. Scale bar 10 µm.

Abbreviations: CH, cholesterol; DMSO, dimethyl sulfoxide; Emul, emulsion; FL, fluorescein-labeled; PTX, paclitaxel.

Acknowledgments

This work was financially supported by the National Mega-project for Innovative Drugs (2012ZX09301002-001) and Beijing Municipal Science and Technology Commission Preclinical Research Projects (500101009). The authors thank Liang-Nian Song for his assistance in language polishing.

Disclosure

The authors report no conflicts of interest in this work.