Reversal of BCRP-mediated multidrug resistance by stable expression of small interfering RNAs

Pyrotinib Sensitizes 5-Fluorouracil-Resistant HER2+ Breast Cancer Cells to 5-Fluorouracil

5-Fluorouracil (5-FU) is a widely used chemotherapeutic agent for breast cancer. However, acquired chemoresistance leads to a loss of its efficacy; methods to reverse are urgently needed. Some studies have shown that pyrotinib, an ErbB receptor tyrosine kinase inhibitor, is effective against HER2⁺ breast cancer. However, whether pyrotinib sensitizes 5-FU-resistant breast cancer cells to 5-FU is unknown. We hypothesized that the combination of pyrotinib and 5-FU would show synergistic antitumor activity, and pyrotinib could reverse 5-FU resistance in HER2⁺ breast cancer cells in vitro and in vivo. Our data showed that pyrotinib inhibited the growth of 5-FU-resistant SKBR-3/FU and MDA-MB-453/FU cell lines and the parental cell lines. 5-FU remarkably suppressed the growth of SKBR-3 and MAD-MB-453 cells. However, SKBR-3/FU and MAD-MB-453/FU cells showed resistance to 5-FU. A combination of pyrotinib and 5-FU resulted in the synergistic inhibition of the growth of the 5-FU-resistant SKBR-3/FU and MDA-MB-453/FU cell lines and the parental cell lines. Pyrotinib decreased significantly the IC₅₀ values of 5-FU and the thymidylate synthase (TS) mRNA expression levels in the 5-FU-resistant SKBR-3/FU and MDA-MB-453/FU cell lines and the parental cell lines and increased significantly the intracellular concentration of 5-FU in SKBR-3/FU and MDA-MB-453/FU cells. In addition, pyrotinib reduced the ABCG2 mRNA and protein expression levels in SKBR-3/FU and MDA-MB-453/FU cells and downregulated the protein expression levels of pAKT, pHER2, and pHER4 in all four cell lines. After TS or ABCG2 in 5-FU-resistant breast cancer cells was knocked down, the sensitivity of SKBR-3/FU and MDA-MB-453/FU cells to 5-FU was restored. Moreover, in vivo experiments demonstrated that pyrotinib in combination with 5-FU more effectively inhibited SKBR-3/FU tumor growth than either pyrotinib or 5-FU alone. In conclusion, our findings suggest that pyrotinib could restore sensitivity of 5-FU-resistant HER2⁺ breast cancer cells to 5-FU through downregulating the expression levels of TS and ABCG2.

Importance of ABCC1 for cancer therapy and prognosis

Multidrug resistance presents one of the most important causes of cancer treatment failure. Numerous in vitro and in vivo data have made it clear that multidrug resistance is frequently caused by enhanced expression of ATP-binding cassette (ABC) transporters. ABC transporters are membrane-bound proteins involved in cellular defense mechanisms, namely, in outward transport of xenobiotics and physiological substrates. Their function thus prevents toxicity as carcinogenesis on one hand but may contribute to the resistance of tumor cells to a number of drugs including chemotherapeutics on the other. Within 48 members of the human ABC superfamily there are several multidrug resistance-associated transporters. Due to the well documented susceptibility of numerous drugs to efflux via ABC transporters it is highly desirable to assess the status of ABC transporters for individualization of treatment by their substrates. The multidrug resistance associated protein 1 (MRP1) encoded by ABCC1 gene is one of the most studied ABC transporters. Despite the fact that its structure and functions have already been explored in detail, there are significant gaps in knowledge which preclude clinical applications. Tissue-specific patterns of expression and broad genetic variability make ABCC1/MRP1 an optimal candidate for use as a marker or member of multi-marker panel for prediction of chemotherapy resistance. The purpose of this review was to summarize investigations about associations of gene and protein expression and genetic variability with prognosis and therapy outcome of major cancers. Major advances in the knowledge have been identified and future research directions are highlighted.

Recent insights into hepatic cancer stem cells

It has been suggested that the development of hepatocellular carcinoma (HCC) is related to the existence of cancer stem cells (CSCs) or tumor-initiating cells. Although CSCs populations may be recognized by use of stem cell markers and/or their functional capacities, their profiles might be diverse, because of the heterogeneity of HCC among individuals. Recent studies indicate that activation of CSCs is related to dysregulation of crucial molecular signaling pathways able to alter the intrinsic properties of normal stem cells. This short review describes the latest evidence of the presence of CSCs, alteration of several developmental and oncogenic pathways, CSC-related microRNAs, and drug resistance in HCC. This information may aid the development of potential novel therapy targeting CSCs in HCC.

Cancer stem cell targeting: the next generation of cancer therapy and molecular imaging

Cancer stem cells (CSCs) have the capacity to generate the heterogeneous lineages of all cancer cells comprising a tumor and these populations of cells are likely to be more relevant in determining prognosis. However, these cells do not operate in isolation, but instead rely upon signals co-opted from their microenvironment, making the targeting and imaging of CSCs within a cancer mass a daunting task. A better understanding of the molecular cell biology underlying CSC pathology will facilitate the development of new therapeutic targets and novel strategies for the successful eradication of cancer. In addition, the continued investigation of sensitive molecular-imaging modalities will enable more accurate staging, treatment planning and the ability to monitor the effectiveness of CSC-targeted therapies in vivo. In this review, we explore the possibilities and limitations of CSC-directed therapies and molecular imaging modalities.

Up-regulation of breast cancer resistance protein plays a role in HER2-mediated chemoresistance through PI3K/Akt and nuclear factor-kappa B signaling pathways in MCF7 breast cancer cells

Human epidermal growth factor receptor 2 (HER2/neu, also known as ErbB2) overexpression is correlated with the poor prognosis and chemoresistance in cancer. Breast cancer resistance protein (BCRP and ABCG2) is a drug efflux pump responsible for multidrug resistance (MDR) in a variety of cancer cells. HER2 and BCRP are associated with poor treatment response in breast cancer patients, although the relationship between HER2 and BCRP expression is not clear. Here, we showed that transfection of HER2 into MCF7 breast cancer cells (MCF7/HER2) resulted in an up-regulation of BCRP via the phosphatidylinositol 3-kinase (PI3K)/Akt and nuclear factor-kappa B (NF-κB) signaling. Treatment of MCF/HER2 cells with the PI3K inhibitor LY294002, the IκB phosphorylation inhibitor Bay11-7082, and the dominant negative mutant of IκBα inhibited HER2-induced BCRP promoter activity. Furthermore, we found that HER2 overexpression led to an increased resistance of MCF7 cells to multiple antitumor drugs such as paclitaxel (Taxol), cisplatin (DDP), etoposide (VP-16), adriamycin (ADM), mitoxantrone (MX), and 5-fluorouracil (5-FU). Moreover, silencing the expression of BCRP or selectively inhibiting the activity of Akt or NF-κB sensitized the MCF7/HER2 cells to these chemotherapy agents at least in part. Taken together, up-regulation of BCRP through PI3K/AKT/NF-κB signaling pathway played an important role in HER2-mediated chemoresistance of MCF7 cells, and AKT, NF-κB, and BCRP pathways might serve as potential targets for therapeutic intervention.

Downregulation of CD44 reduces doxorubicin resistance of CD44CD24 breast cancer cells

BACKGROUND

Cells within breast cancer stem cell populations have been confirmed to have a CD44(+)CD24(-) phenotype. Strong expression of CD44 plays a critical role in numerous types of human cancers. CD44 is involved in cell differentiation, adhesion, and metastasis of cancer cells.

METHODS

In this study, we reduced CD44 expression in CD44(+)CD24(-) breast cancer stem cells and investigated their sensitivity to an antitumor drug. The CD44(+)CD24(-) breast cancer stem cells were isolated from breast tumors; CD44 expression was downregulated with siRNAs followed by treatment with different concentrations of the antitumor drug.

RESULTS

The proliferation of CD44 downregulated CD44(+)CD24(-) breast cancer stem cells was decreased after drug treatment. We noticed treated cells were more sensitive to doxorubicin, even at low doses, compared with the control groups.

CONCLUSIONS

It would appear that expression of CD44 is integral among the CD44(+)CD24(-) cell population. Reducing the expression level of CD44, combined with doxorubicin treatment, yields promising results for eradicating breast cancer stem cells in vitro. This study opens a new direction in treating breast cancer through gene therapy in conjunction with chemotherapy.

Nanomedicinal strategies to treat multidrug-resistant tumors: current progress

Multidrug resistance (MDR) is a major impediment to the success of cancer chemotherapy. P-glycoprotein is an important and the best-known membrane transporter involved in MDR. Several strategies have been used to address MDR, especially P-glycoprotein-mediated drug resistance in tumors. However, clinical success has been limited, largely due to issues regarding lack of efficacy and/or safety. Nanoparticles have shown the ability to target tumors based on their unique physical and biological properties. To date, nanoparticles have been investigated primarily to address P-glycoprotein and the observed improved anticancer efficacy suggests that nanomedicinal strategies provide a new opportunity to overcome MDR. This article focuses on nanotechnology-based formulations and current nanomedicine approaches to address MDR in tumors and discusses the proposed mechanisms of action.

Therapeutic potential of RNA interference in drug-resistant cancers

Resistance including multidrug resistance to chemotherapy is a common clinical problem in patients suffering from cancer. Multidrug resistance is often mediated by overexpression of transmembrane xenobiotic transport molecules belonging to the superfamily of ATP-binding cassette (ABC)-transporters. Inhibition of ABC-transporters by low-molecular weight compounds in cancer patients has been extensively investigated in clinical trials, but the results have been disappointing. Thus, alternative experimental therapeutic strategies for overcoming multidrug resistance are under investigation. These include the application of RNA interference (RNAi) technology. Various RNAi strategies were applied to reverse multidrug resistance in different tumor models in vitro and in vivo. Results and conclusions of these RNAi studies as well as their potential impact for the development of potential RNAi therapeutics will be discussed.

Silencing the breast cancer resistance protein expression and function in caco-2 cells using lentiviral vector-based short hairpin RNA

A series of stable breast cancer resistance protein (BCRP, ABCG2) knockdown cell lines were produced by transduction of Caco-2 cells with lentiviral vector-based short hairpin RNA (shRNA). Caco-2 cell is a human intestinal-derived cell line widely used to study intestinal drug absorption. Caco-2 expresses three apical drug efflux transporters: BCRP, P-glycoprotein (P-gp; ABCB1), and multidrug resistance protein 2 (MRP2, ABCC2). BCRP and P-gp in particular play a significant role in pharmacokinetics because of their expression at several key interfaces. Overexpression of BCRP in cancer cells may also be a mechanism of tumor resistance to chemotherapeutic drugs. The goal of this study was to engineer and characterize Caco-2 cell clones with stable knockdown of BCRP expression. The shRNA/BCRP lentiviral particles were used to infect a stable clone of Caco-2 cells. Expression of BCRP was monitored using quantitative polymerase chain reaction (qPCR), Western blotting, immunofluorescence microscopy, and bidirectional transport of probe substrates, estrone-3-sulfate (E3S), and pheophorbide A (PhA). Based on qPCR, expression of BCRP mRNA was knocked down in five clones with a maximum of 97% silencing in clone D. Silencing of BCRP gene expression was maintained for at least 25 passages. Expression of BCRP protein was also reduced significantly. Functionally, BCRP knockdown was reflected in significant reduction of the efflux ratio of E3S and PhA. Clone D in particular should be a useful model for identifying and characterizing P-gp substrates and inhibitors without interference from BCRP and/or MRP2. In addition, it can be used in conjunction with wild-type or vector control Caco-2 cells to identify BCRP substrates.

Role of BCRP as a biomarker for predicting resistance to 5-fluorouracil in breast cancer

PURPOSE

Chemotherapy is not only important but also necessary for the patient of breast cancer. Breast cancer resistance protein (BCRP), an atypical drug efflux pump, mediates multidrug resistance in breast cancer. The aim of this study is to search new substrate of BCRP. The result will guide the drug selection of chemotherapy in BCRP-positive breast cancer.

METHODS

PA317/Tet-on/TRE-BCRP cell induced with doxycycline was used to screen the possible substrates of BCRP by MTT assay. The suspicious substrate [5-fluorouracil (5-Fu)] was further confirmed in PA317 and breast cancer cell MCF-7 by HLCP, apoptosis assay (staining and FACS) and RNAi technique.

RESULTS

Mitoxantrone, 5-Fu, adriamycin, Methotrexate, Pirarubicin, and Etoposide were identified as substrates of BCRP. However, Paclitaxel, Vincristine, Vindesine, Mitomycin C, and cisplatin were not mediated by BCRP. 5-Fu was identified as substrate of BCRP for the first time. The further study showed that the intracellular retention dose of 5-Fu and the 5-Fu induced cellular apoptosis all decreased when BCRP highly expressed. Furthermore, 5-Fu accumulation and 5-Fu induced DNA damage increased when BCRP was silenced by RNAi in breast cancer cells.

CONCLUSIONS

5-Fluorouracil may be a specific substrate which can be bound by BCRP. BCRP can predict the sensitivity of breast cancer to 5-Fu. And BCRP-targeted therapy will reverse the resistance of breast cancer to 5-Fu.