A: Evaluation of cell association mediated by liposomes bearing FAP peptide-lipopolymer at various membrane loading densities (0.1, 0.5, 1, 2, 4 mol%). MB49 cells were treated with Cy5.5-labeled liposomes bearing different concentrations of RWFV-PEG2000-DSPE and incubated for 1 h at 37 °C. The media was then aspirated and the cells washed with PBS, trypsinized, and analyzed by flow cytometry for the number of cells displaying Cy5.5 fluorescence. Liposome diameters: 55–65 nm. Liposome composition: 64.5-x:35:x:0.5 DPPC:Chol:RWFV-PEG2000-DSPE:Cy5.5-DSPE. Control: no liposome treatment. Error bars indicate the standard deviation of the mean with n=3. B: Comparison of cell association events between 2 mol% targeted (RWFV-PEG2000-DSPE) and non-targeted (mPEG2000-DSPE) liposomes in MB49 cells. The liposomes were incubated with cells for 1 h at 37 °C, followed by media aspiration, washing with PBS, trypsinization, and flow cytometry analysis for Cy5.5 fluorescence. Liposome diameters: 58 nm. Liposome composition (targeted): 62.5:35:2:0.5 DPPC:Chol:RWFV-PEG2000-DSPE:Cy5.5-DSPE. Liposome composition (non-targeted): 62.5:35:2:0.5 DPPC:Chol:mPEG2000-DSPE:Cy5.5-DSPE. Control: no liposome treatment. Error bars indicate the standard deviation of the mean with n=3 (ANOVA: *p < 0.05, **p < 0.01, ***p < 0.005, ****p < 0.001).