Overcoming multi-drug resistance using an intracellular anti-MDR1 sFv

We made an intracellular single-chain variable fragment (sFv) from the C219 monoclonal antibody that recognized the intracellular domain of the multid rug resistance (MDR) gene product, P-glycoprotein (P-gp), Immuno-cytochemis try using the FITC conjugated anti-C-myc tag antibody showed that the sFv p rotein was expressed in the cytoplasm of the cells. Although transfection o f the sFv did not result in the down-regulation of P-gp expression in P-gp positive MDR cells as determined by flow cytometry analysis, Adriamycin (AD M) uptake and Rhodamine123 (Rh123) retention were increased by the C219 int ra-cellular sFv transfection. The transfected cells exhibited a higher sens itivity to ADM using a 10-day colony formation assay. The conventional 3-da y MTT assay showed the drug resistant tendency in C219 sFv transfected cell we tested. The growth rate of C219 sFv transfected cells was delayed in al l non-MDR and MDR cells that might be the reason why C219 transfected cells exhibited the drug resistant tendency in the MTT assay. Despite this unexp ected effect of C219 sFv on growth rate, our data suggest that the intra-ce llular sFv technique could knockout MDR functionally and may offer a means of increasing the effectiveness of tumor chemotherapy. (C) 2001 Wiley-Liss, Inc.