A novel assay to test multidrug-resistance of mucosa-infiltrating and peripheral blood lymphocytes in patients with inflammatory bowel disease (IBD)

Background: Many of current drugs to treat IBD are substrates of ABC-MDR transporters. Until now, no methods were available to screen patients for individual transporter status, although expression of these proteins can be induced by drug therapy and it may change during ongoing treatment.

Methods: We have modified a commercial functional assay for detection of MDR-transporters (SOLVO MDQ test). Biopsies from inflamed gut mucosa were dissociated to a single cell suspension. Afterwards, lymphocytes were stained by allophycocyanin (APC) labeled CD45 antibodies. It is necessary, that the emission spectrum of the fluorescent label of the antibody used for the immunological detection can be distinguished electronically from calcein and the viability dye. Therefore, in contrast to the previously described calcein method (Br J Cancer 73(7): 849–55, 1996) green fluorescence was detected in FL2 and viability is assessed by 7AAD in FL3 that enables electronic compensation, as well as exclusion of dead cells in one single FL2-FL3 dot-plot. MDR1 and MRP1 function is assessed as described in the original kit (http://www.solvobiotech.com).

Results: Lymphocytes can be gained with excellent viability from the gut mucosa w/o ATP depletion or loss of antigenic surface markers. The functional calcein assay could be reproducibly performed. Among the patients tested in a pilot series, there is a tendency for an association of MDR-transporter expression and therapy response.

Conclusion: Prospective clinical studies have to investigate the association of MDR-transporter expression with drug-resistant phenotype in IBD.