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 multidrug resistance (MDR) gene product, P-glycoprotein (P-gp). Immuno-cytochemistry using the FITC conjugated anti-C-myc tag antibody showed that the sFv protein was expressed in the cytoplasm of the cells. Although transfection of 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 (ADM) uptake and Rhodamine123 (Rh123) retention were increased by the C219 intra-cellular sFv transfection. The transfected cells exhibited a higher sensitivity to ADM using a 10-day colony formation assay. The conventional 3-day 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 all 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 unexpected effect of C219 sFv on growth rate, our data suggest that the intra-cellular sFv technique could knockout MDR functionally and may offer a means of increasing the effectiveness of tumor chemotherapy. Copyright 2001 Wiley-Liss, Inc.