Neither P-gp SNP variants, P-gp expression nor functional P-gp activity predicts MDR in a preliminary study of plasma cell myeloma

Introduction: Multidrug resistance (MDR) mediated by P-glycoprotein (P-gp) can compromise the successful treatment of many malignancies including plasma cell myeloma (PCM). However, methods do not yet exist that can accurately determine P-gp activity in PCM patient samples. Methods: In this study, we have utilized new advances in flow cytometric methods to determine the activity of P-gp in PCM tumor cells. Furthermore, we have used several PCR-based approaches to perform a pilot study determining the functional impact of ABCB1 SNPs in patients with PCM. Results: No associations were seen between P-gp activity or expression and subgroups of PCM. Similarly, no association was seen between P-gp expression and SNPs within ABCB1 although a nonsignificant reduction in activity was demonstrated for rs1045642 (P = 0.121). Conclusions: We have described a new method for the determination of P-gp and MRP activity suitable for use in clinical studies and have optimized this method to include a gating strategy, allowing routine use on PCM bone marrow aspirate samples. This is the first patient study to consider the full impact of SNPs within ABCB1 all the way from the genome to the proteome in PCM. The methods described here could also be utilized for future studies of stem cell like side populations in PCM that are considered to be drug resistant. Furthermore, minor amendments to these methods will facilitate studies of P-gp, MRP, and BCRP activity in other haematological malignancies. (c) 2012 International Clinical Cytometry Society