Breast Cancer Resistance Protein Expression and 5-Fluorouracil Resistance

Objective To filtrate breast cancer resistance protein （BCRP）-mediated resistant agents and to investigate clinical relationship between BCRP expression and drug resistance. Methods MTT assay was performed to filtrate BCRP-mediated resistant agents with BCRP expression cell model and to detect chemosensitivity of breast cancer tissue specimens to these agents. A high performance liquid chromatography （HPLC） assay was established, and was used to measure the relative dose of intracellular retention resistant agents. RT-PCR and immunohistochemistry （IHC） were employed to investigate the BCRP expression in breast cancer tissue specimens. Results MTT assay showed that the expression of BCRP increased with the increasing resistance of 5-fluorouracil （5-Fu） （P〈0.05, n=3） in the cell model, while HPLC assay indicated that the intracellular retention dose of 5-Fu was significantly correlated with the expression of BCRP （t=-0.897, P〈0.05, n=3）. A total of 140 breast cancer tissue specimens were collected. BCRP-positive expression was detected in forty-seven specimens by both RT-PCR and IHC. As shown by MTT assay subsequently, the resistance index （RI） of 47 BCRP-positive breast cancer tissue specimens to 5-Fu was 7-12 times as high as that of adjacent normal tissue samples. BCRP expression was related to 5-Fu resistance （R2=0.8124, P〈0.01）. Conclusion Resistance to 5-Fu can be mediated by BCRR Clinical chemotherapy for breast cancer patients can be optimized based on BCRP-positive expression.

Breast cancer resistance protein （Bcrp） and the testis--an unexpected turn of events

Breast cancer resistance protein （Bcrp） is an ATP-dependent efflux drug transporter. It has a diverse spectrum of hydrophilic and hydrophobic substrates ranging from anticancer, antiviral and antihypertensive drugs, to organic anions, antibiotics, phytoestrogens （e.g., genistein, daidzein, coumestrol）, xenoestrogens and steroids （e.g., dehydroepiandrosterone sulfate）. Bcrp is an integral membrane protein in cancer and normal cells within multiple organs （e.g., brain, placenta, intestine and testis） that maintains cellular homeostasis by extruding drugs and harmful substances from the inside of cells. In the brain, Bcrp is a major component of the blood- brain barrier located on endothelial cells near tight junctions （TJs）. However, Bcrp is absent at the Sertoli cell blood-testis barrier （BTB）; instead, it is localized almost exclusively to the endothelial TJ in microvessels in the interstitium and the peritubular myoid cells in the tunica propria. Recent studies have shown that Bcrp is also expressed stage specifically and spatiotemporally by Sertoli and germ cells in the seminiferous epithelium of rat testes, limited only to a testis-specific cell adhesion ultrastructure known as the apical ectoplasmic specialisation （ES） in stage VI-early VIII tubules. These findings suggest that Bcrp is equipped by late spermatids and Sertoli cells to protect late-stage spermatids completing spermiogenesis. Furthermore, Bcrp was found to be associated with F （filamentous）-actin and several actin regulatory proteins at the apical ES and might be involved in the organisation of actin filaments at the apical ES in stage VII-VIII tubules. These findings will be carefully evaluated in this brief review.

Modulation of breast cancer resistance protein mediated atypical multidrug resistance using RNA interference delivered by adenovirus

Clinical multidrug resistance ( MDR ) of malignancies to many antineoplasticagents is the major obstacle in the successful treatment of cancer. The emergence of breast cancerresistance protein ( BCRP), a member of the adenosine triphosphate ( ATP ) binding cassette ( ABC )transporter family, has necessitated the development of antagonists. To overcome the BCRP-mediatedatypical MDR, RNA interference (RNAi) delivered by adenovirus targeting BCRP mRNA was used toinhibit the atypical MDR expression by infecting MCF-7/MX100 cell lines with constructed RNAiadenovirus.

Pharmacological role of efflux transporters: Clinical implications for medication use during breastfeeding

The World Health Organisation recommends exclusive breastfeeding for the first six months of an infant’s life and in combination with solid food thereafter. This recommendation was introduced based on research showing numerous health benefits of breastfeeding for both the mother and the infant. However, there is always concern regarding the transfer of medications from mother to their breastfed baby via milk. Pharma-cokinetic properties of a drug are usually used to pre-dict its transferability into breast milk. Although most drugs are compatible with breastfeeding, cases of toxic drug exposure have been reported. This is thought to be due to active transport mechanisms whereby effux transporter proteins expressed in the epithelial cells of the mammary gland actively secrete drugs into milk. An example of such effux transporters including the breast cancer resistance protein which is strongly induced during lactation and this could result in contamination of milk with the substrates of this transporter which may place the suckling infant at risk of toxicity. Furthermore, there is little known about the substrate specifcity of most effux transporters as we have highlighted in this review. There also exists some degree of contradiction between in vivo and in vitro studies which makes it difficult to conclusively predict outcomes and drug-drug interactions.

Mobilization of hematopoietic progenitor cells in patients with liver cirrhosis

AIM:To test the hypothesis that liver cirrhosis is associated with mobilization of hematopoietic progenitor cells. METHODS:Peripheral blood samples from 72 patients with liver cirrhosis of varying etiology were analyzed by flow cytometry.Identified progenitor cell subsets were immunoselected and used for functional assays in vitro. Plasma levels of stromal cell-derived factor-1(SDF-1) were measured using an enzyme linked immunosorbent assay.RESULTS:Progenitor cells with a CD133 + /CD45 + CD14 + phenotype were observed in 61%of th patients.Between 1%and 26%of the peripheral bloo mononuclear cells(MNCs)displayed this phenotype Furthermore,a distinct population of c-kit + progenito cells(between 1%and 38%of the MNCs)could b detected in 91%of the patients.Additionally,18% of the patients showed a population of progenito cells(between 1%and 68%of the MNCs)that wa characterized by expression of breast cancer resistanc protein-1.Further phenotypic analysis disclosed tha the circulating precursors expressed CXC chemokin receptor 4,the receptor for SDF-1.In line with thi finding,elevated plasma levels of SDF-1 were presen in all patients and were found to correlate with th number of mobilized CD133 + progenitor cells.

How to overcome ATP-binding cassette drug efflux transporter-mediated drug resistance?

P-glycoprotein(ABCB1),multidrug resistance protein-1(ABCC1)and breast cancer resistance protein(ABCG2)belong to the ATP-binding cassette(ABC)superfamily of proteins that play an important physiological role in protection of the body from toxic xenobiotics and endogenous metabolites.Beyond this,these transporters determine the toxicity profile of many drugs,and confer multidrug resistance(MDR)in cancer cells associated with a poor treatment outcome of cancer patients.It has long been hypothesized that inhibition of ABC drug efflux transporters will increase drug accumulation and thereby overcome MDR,but until now no approved inhibitor of these transporters is available in the clinic.In this review we present molecular strategies to overcome this type of drug resistance and discuss for each of these strategies their promising value or indicate underlying reasons for their limited success.

Recent advances in the search of BCRP- and dual P-gp/BCRP-based multidrug resistance modulators

The development of multidrug resistance (MDR) is one of the major challenges to the success of chemotherapy treatment of cancer. This phenomenon is often associated with the overexpression of the ATP-binding cassette (ABC) transporters P-gp (P-glycoprotein, ABCB1), multidrug resistance-associated protein 1, ABCC1 and breast cancer resistance protein, ABCG2 (BCRP). These transporters are constitutively expressed in many tissues playing relevant protective roles by the regulation of the permeability of biological membranes, but they are also overexpressed in malignant tissues. P-gp is the first efflux transporter discovered to be involved in cancer drug resistance, and over the years, inhibitors of this pump have been disclosed to administer them in combination with chemotherapeutic agents. Three generations of inhibitors of P-gp have been examined in preclinical and clinical studies;however, these trials have largely failed to demonstrate that coadministration of pump inhibitors elicits an improvement in therapeutic efficacy of antitumor agents, although some of the latest compounds show better results. Therefore, new and innovative strategies, such as the fallback to natural products and the discover of dual activity ligands emerged as new perspectives. BCRP is the most recently ABC protein identified to be involved in multidrug resistance. It is overexpressed in several haematological and solid tumours together with P-gp, threatening the therapeutic effectiveness of different chemotherapeutic drugs. The chemistry of recently described BCRP inhibitors and dual P-gp/BCRP inhibitors, as well as their preliminary pharmacological evaluation are discussed, and the most recent advances concerning these kinds of MDR modulators are reviewed.