A NEW IMMUNOHISTOCHEMICAL METHODOLOGY FOR THE SPECIFIC DETECTION OF MDR1-P-GLYCOPROTEIN IN HUMAN TISSUES BASED ON PHAGE-DISPLAYED PEPTIDES MIMICKING THE MM4.17 EPITOPE

It is not rare that controversial indications about the presence or th e expression level of multidrug-resistant (MDR) proteins come out from different laboratories upon examination of identical tumor specimens. Distinct aspects, including the use of weakly discriminating monoclon al antibodies (MAbs) and/or unsuitable techniques and procedures, cont ribute in generating differences in the MDR phenotype evaluation of ca ncer cells. In this regard we describe here an innovative immunohistoc hemical approach for the determination of P-glycoprotein expression in cells and tissues. The method is based on the ability of phage-displa yed peptides to mimic antibody epitopes. For this purpose we utilized the phage clone #55, which was affinity-purified from a phage-displaye d random-peptide library using the MAb MM4.17 (specific for MDR1-P-gly coprotein) as previously described, This clone has been chosen since i t clearly and undoubtedly reacts with its cognate MAb, as was determin ed by ELISA and dot blot tests, Inhibition of the MAb MM4.17 binding t o MDR1-P-glycoprotein-expressing cells could be performed by adding a calibrated concentration of phage clone #55 particles, which mimic MDR 1-P-glycoprotein antigen, This methodology can eliminate misleading in terpretations concerning the presence and expression level of MDR1-P-g lycoprotein and might well contribute in routine clinical determinatio ns of MDR in tumor specimens, thus contributing to our understanding o f the basis of the mechanisms of tumor cell resistance to drugs.