As the last element of proof for receptor mediated activity of ADC, we used soluble fluorescein and observed that this measure precludes activity of ADC, as would be expected for a competitive saturation of the antibody by the soluble ligand (Figure?4D). Open in a separate window Figure 4 A) Schematic illustration of the antibody\drug conjugate that contains a cathepsin\sensitive scissile bond (valine\citruline), a self\immolative linker, and a conjugated drug, monomethyl auristatin E (MMAE); B,C) dose dependent toxicity of ADC in MOLT4 cells equipped with artificial synthetic receptors (R1,2,4) as a function of KIAA1516 ADC concentrations ((B): receptors feed concentration 10??10?6?m) or as a function of receptor feed concentration ((C): ADC concentration 100??10?9?m) D) toxicity of fluorescein\targeted ADC negated by an addition of soluble fluorescein; E) fluorescence microscopy images illustrating toxicity in HAP1 cell spheroids mediated by artificial synthetic receptors and the corresponding ADC. of designed cells as tools of biotechnology and biomedicine. = 11 or 45), TEA (2 equiv.), Ti(OiPr)4 (1.32 equiv.), CH2Cl2:MeOH (1:1), r.t., then NaBH4 (1.2 equiv.), ?78 C; Boc\deprotection for R2 and R3: TFA (200 equiv.), MeOH, 0 C to r.t.; iii) FITC (1.2 equiv.), TEA (2.5 equiv.), C) artificial receptor based on a 1,2\distearoyl\sn\glycero\3\phosphorylethanolamine (DSPE) lipid; D) fluorescence microscopy images of MOLT cells made up of artificial receptor R1 and R4, scale bars: 10?m; E) flow\cytometry\based quantification of cells fluorescence upon integration of artificial receptors R1C4; receptor feed concentration 4??10?6?m; F) quantified cells fluorescence upon integration of receptors R1C4 from solutions with varied receptor feed concentration. For installation into cells (MOLT4 cells, monocytic T cell derived cell line), receptors were administered as dimethylsulfoxide solutions onto cells with gentle vortexing. For each receptor molecule, this simple procedure resulted in efficient anchoring of amphiphilic molecules into the lipid bilayer of the cell, as visualized by fluorescence microscopy (Physique?1D). Cells fluorescence was quantified via flow cytometry, which indicated a narrow distribution of cells by the receptor content (Physique?1E). Fluorescence intensity expectedly increased with L-Lysine hydrochloride increased concentration of receptor molecules in the feed solution (Physique?1F). Interestingly, at matched concentrations, the four fluorescein\made up of molecules afforded different absolute levels of cell fluorescence, with receptor R2 being most fluorescent. This may indicate that this four molecules differ in their propensity to anchor into mammalian cells and/or result from a change in the fluorophore quantum yield of fluorescence due to microenvironment. Association of cholesterol and DSPE with cell membranes is usually non\specific and non\covalent and in a mixed populace of vesicles, cholesterol readily partitions between donor and acceptor lipid bilayers.[ 24 ] Receptor sharing can decrease the ability to target designed cells in circulation and therefore be unwanted, or have a beneficial effect and through receptor sharing, distribute artificial receptor molecules to the surrounding tissue. We quantified this phenomenon in cell culture using mixed populations of designed (R+) and receptor\na?ve (R?) cells, at a 1% content of R+ cells. Over time in cell culture, the two cell populations (originally R+ and R?) converged by mean cell fluorescence value, a result which illustrates the expected receptor sharing (Physique? 2 ). Nevertheless, two cell populations could be reliably distinguished by intensity of fluorescence for at L-Lysine hydrochloride least 48 h in cell co\culture, and for receptor R4 for at least 72 h. Open in a separate window Physique 2 Flow\cytometry\based analysis of MOLT4 cells cultured as a 1:99 mixture of designed (receptor\equipped) to na?ve (receptor\negative) cells, over 72 h. For targeting artificial receptors, we rely on anti\fluorescein antibodies. Antibody binding to fluorescein is usually accompanied by a decrease of fluorescein fluorescence, and this phenomenon lends itself to quantify binding between the antibody and the antigen via facile fluorescence readout (Physique? 3A). In answer, dose dependent fluorescence quenching curves were rather comparable for fluorescein and the receptor molecules derived thereof and reveal high affinity that characterizes the artificial antibody\ligand pair used in this work. Fluorescence quenching was also observed upon antibody binding to the receptors integrated into lipid bilayers (Physique?3B), which can be used to quantify relative amounts of receptor molecules at cell surface (amenable to quenching by antibody) and within the cell interior (not subject to quenching by added antibody). Flow cytometry revealed that this four receptor molecules differed significantly in this readout. R3 molecules were largely confined to the cell interior, which was observed already at the earliest quantification time\point (20?min). In turn, R2 molecules were gradually re\distributed over time toward predominant intracellular localization (from 20?min to 4 h). Finally, R1 and R4 receptors were consistently found at L-Lysine hydrochloride cell surface in 75% quantity, and were amenable to antibody targeting. These data illustrate that a small variation in receptor design can lead to a pronounced change in the receptor properties, specifically in terms of cell membrane\to\interior distribution. This conclusion qualitatively agrees with prior publications.