Abstract
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.
Highlights
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
The present study focused on validation of anti-ABCG2 antibodies for the detection of ABCG2 protein expression in formalin-fixed paraffin-embedded (FFPE) colorectal cancer (CRC) tissue samples
The specificity of six commercially available anti-ABCG2 antibodies was evaluated by western blotting (WB) and immunocytochemistry (ICC) assays using the LoVo, MDA-MB-231, and MCF7 cell lines, each with an ABCG2 up-regulated variant (Table 1)
Summary
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. 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. ABCG2, known as breast cancer resistant protein (BCRP), is encoded by the ABCG2 gene and belongs to the G subfamily of ABC transporters[1] It was first discovered in the multidrug resistant breast cancer cell line MCF7/AdrVp2 and has since been found in both tumor tissue and normal tissue[3,4]. Previous immunohistochemical studies of the association between ABCG2 protein expression and clinical outcome have used different antibodies and different scoring guidelines[10,11,12,13]. These guidelines were used to investigate the correlation between ABCG2 basolateral membrane staining in TMA and whole sections of CRC tissue
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