IDENTIFICATION OF NOVEL DRUG RESISTANCE-ASSOCIATED PROTEINS BY A PANEL OF RAT MONOCLONAL-ANTIBODIES

Since some multidrug-resistant (MDR) tumor cell lines show drug accumu lation defects but do not over-express Pgp or MDR protein (MRP), a sea rch was made for novel MDR-related transporter proteins by immunizing rats with nonsmall cell lung cancer SW-1573/2R120 cells to produce mon oclonal antibodies (MAbs). Five rat MAbs (LMR-4, -12, -42, -44 and -94 ) were generated, showing strong membranous staining of non-Pgp MDR SW -1573/2R120 tumor cells and minimal reactivity to the corresponding pa rental and revertant cell lines. In addition, a 6th MAb (LMR-5) was is olated, recognizing the MDR-related lung resistance protein (LRP), pre viously identified as the major vault protein. The first 5 LMR MAbs sh ow predominantly membranous staining of several non-Pgp MDR tumor cell lines of different histogenetic origins, except for LMR-4, which reco gnizes only MDR sublines of the SW-1573 cell line. Flow-cytometric ana lysis revealed that all MAbs, except LMR-4 and -5, detect outside epit opes. Functional studies showed that these MAbs did not restore the da unorubicin accumulation defect. All but one of the MAbs (LMR-42) showe d staining of distinct normal human tissues, notably epithelial cells lining the airways and digestive tract. In addition, staining of vascu lar endothelial cells was found with all MAbs except LMR-4, Three MAbs (LMR-I2, -44 and -94) showed remarkable immunoreactivity with vincris tine-selected SW-1573 sublines. By immunoblotting and precipitation, t he LMR antigens were found to be in the 42-69 kDa range. (C) 1997 Wile y-Liss, Inc.