Optimization of Western blotting analysis for the isolation and detection of membrane xenobiotic transporter ABCG2.

All organisms are exposed to numerous stress factors, which include harmful xenobiotics. The diversity of these compounds is enormous, thus in the course of evolution diverse biological defense mechanisms at various levels of organization have developed. One of them engages an evolutionarily conserved family of transporters from the ABC superfamily, found in most species - from bacteria to humans. An important example of such a transporter is the breast cancer resistance protein (BCRP/ABCG2), a typical integral membrane protein. It plays a key role in the absorption, distribution and elimination of a wide variety of xenobiotics, including drugs used in chemotherapy, and is involved in multidrug resistance. It also protects against phototoxic chlorophyll derivatives of dietary origin. BCRP is a hemitransporter which consists of one transmembrane domain, made of six alpha-helices forming a characteristic pore structure, and one ATP-binding domain, which provides the energy from ATP hydrolysis, required for active transport of the substrates. The isolation of BCRP is still not an easy task, because its insolubility in water and the presence of membrane rafts pose serious methodological and technical challenges during the purification. The aim of this study was to optimize the methods for detection and isolation of BCRP-enriched fractions obtained from animal tissue samples. In this report we describe an optimization of isolation of a BCRP-enriched membrane fraction, which is suitable for further protein quantitative and qualitative analysis using the molecular biology tools.

Enhancing the anti-multiple myeloma efficiency in a cancer stem cell xenograft model by conjugating the ABCG2 antibody with microbubbles for a targeted delivery of ultrasound mediated epirubicin.

BACKGROUND: Although multiple myeloma (MM) treatment has improved in the last decade, it remains largely incurable. One of main reasons is that there are cancer stem cells (CSCs) in MM, which are responsible for MM's drug resistance and relapse. In this study, we used the targeting microbubbles (MBs) conjugated with anti-ABCG2 monoclonal antibody (mAb) for ultrasound mediated epirubicin (EPI) delivery to evaluate the therapeutic effectiveness of the novel agent in MM CSC xenograft model. METHODS: MM CSCs, marked by CD138-CD34- cell phenotypes were isolated from human MM RPMI8226 cell line using immune magnetic activated cell sorting system, and inoculated into nonobese diabetic/severe combined immunodeficient mice by subcutaneous or intravenous injection. After the mice developed MM, they were intravenous injection treated with EPI, EPI-MBs+mAb, and EPI-MBs+mAb with ultrasound exposure, respectively. RESULTS: All treated mice showed inhibited tumor sizes or bone lesions, decreased renal damages and anemia, and increased MM bearing mice' survival. In particular, the EPI-MBs+mAb plus ultrasound exhibited significantly enhanced therapeutic MM effectiveness by inducing apoptosis compared with other biologic agents. CONCLUSION: The data provide evidence that EPI-MBs+mAb with ultrasound exposure might be available for treatment MM patients in clinic.

Antibody validation and scoring guidelines for ABCG2 immunohistochemical staining in formalin-fixed paraffin-embedded colon cancer tissue.

Overexpression of the ATP-dependent drug efflux pump ABCG2 is a major molecular mechanism of multidrug resistance in cancer and might be a predictive biomarker for drug response. Contradictory results have been reported for immunohistochemical studies of ABCG2 protein expression in colorectal cancer (CRC), probably because of the use of different antibodies and scoring approaches. In this study, we systematically studied six commercially available anti-ABCG2 antibodies, using cell lines with up-regulation of ABCG2, and selected one antibody for validation in CRC tissue. Furthermore, we established scoring guidelines for ABCG2 expression based on the clinically used guidelines for HER2 immunohistochemistry assessment in gastric cancer. The guidelines provide a semi-quantitative measure of the basolateral membrane staining of ABCG2 and disregard the apical membrane staining and the cytoplasmic signal. Intra-tumor heterogeneity in ABCG2 immunoreactivity was observed; however, statistical analyses of tissue microarrays (TMAs) and the corresponding whole sections from primary tumors of 57 metastatic CRC patients revealed a strong positive correlation between maximum TMA scores and whole sections, especially when more than one core was used. In conclusion, here, we provide validated results to guide future studies on the associations between ABCG2 immunoreactivity in tumor cells and the benefits of chemotherapeutic treatment in patients with CRC.

Expression levels of ABCG2 on cord red blood cells and study of fetal anemia associated with anti-Jr(a).

BACKGROUND: The Jr(a) antigen of JR blood group systems is located on ABCG2 and Jr(a-) subjects whose red blood cells (RBCs) lack ABCG2 have been identified mostly among the Japanese. Although anti-Jr(a) can cause fetal anemia, little is known regarding its mechanism. STUDY DESIGN AND METHODS: We reviewed clinical courses of all reported cases with fetal anemia due to anti-Jr(a) . We analyzed the ABCG2 expressions of cord RBCs at various gestational ages. We examined the effects of sera containing anti-Jr(a) from three pregnancies with fetal anemia or monoclonal anti-Jr(a) on erythropoiesis and phagocytosis. We also examined epitopes of anti-Jr(a) . RESULTS: Case series suggested that the majority of fetal anemia with anti-Jr(a) may not be progressive in the later gestational ages. ABCG2 expression levels of cord RBCs were significantly higher than those of adults and neonates with high individual variation and gradually decreased with advancing gestational ages. Anti-Jr(a) did not significantly impact erythroid colony formation, although we detected a tendency toward the suppression of erythroid burst-forming unit formation by anti-Jr(a) using feline marrow cells. Anti-Jr(a) did not induce phagocytosis of sensitized RBCs by monocytes. While many anti-Jr(a) recognized the same regions as a monoclonal anti-ABCG2, 5D3, epitopes of anti-Jr(a) did not correlate with the incidence of fetal anemia. CONCLUSION: ABCG2 expression levels in cord RBCs are higher than those of adults, and the change of ABCG2 expression in erythroid lineage cells may influence the clinical course of fetal anemia with anti-Jr(a) , although we could not detect significant effects of anti-Jr(a) on erythroid colony formation or phagocytosis.