Cell uptake assay pLuc705 cells were seeded 20 h prior to treatment in 12-well plates at 100 000 cells/well. Cells were treated with 2 mM fluorescein-tagged CPPÀPMO conjugates for 24 h. After treatment, cells were washed with 500 ml of 7 RXRXRXRXRXRXRXB 7 (RX) 5 RXRXRXRXRXB 5 (RX) 3 RXRXRXB 3 (RXR) 4 RXRRXRRXRRXRXB 5 (rXR) 4 rXRrXRrXRrXRXB 5 (rXr) 4 rXrrXrrXrrXrXB 5 (RB) 8 RBRBRBRBRBRBRBRBB 0 (rB) 8 rBrBrBrBrBrBrBrBB 0 (RB) 7 RBRBRBRBRBRBRBB 0 (RB) 5 RBRBRBRBRBB 0 (RB) 3 RBRBRBB 0 Ã The sequences of peptides are written from N to C terminus. R = arginine, r = D-arginine, X = 6-aminohexanoic acid, B = b-alanine. Each peptide had an acetyl group at the N-terminus and a carboxyl group at the C-terminus. Cell viability assay and microscopy pLuc705 cells were seeded 20 h before the treatment in 96-well plates at 9000 cell/well and then treated with the conjugates. The microscopic phase images of treated cells were visualized by a Nikon Diaphot inverted microscope (Melville, NY), captured by an Olympus digital camera and processed by the Magnafire software (Optronics, Goleta, CA). After imaging the cells, the cell viability was determined by the methylthiazoletetrazolium assay (MTT, Sigma, St. Louis, MO) assay. MTT solution (5 mg/ml) was added to the treatment medium to a final concentration of 0.5 mg/ml and incubated for 4 h at 378C. 85% of the media of each well was then replaced with DMSO containing 0.01M HCl and further incubated for 10 min at 378C and the absorbance measured at 540 nm. Percent cell viability was determined by normalizing the absorbance of each treated sample to the mean of untreated samples.