*2.1. Materials*

All chemicals and reagents were of analytical grade. Unmodified polymers used here were as follows: 10 kDa branched PEI (Polysciences, Eppelheim, Germany), 5 kDa branched PEI (a kind gift from BASF, Ludwigshafen, Germany), 5 kDa and 10 kDa linear PEIs (Sigma-Aldrich, Taufkirchen, Germany) and PPI dendrimer generation 4 (SyMO-Chem, Eindhoven, The Netherlands). *N*-Boc-tyrosine-OH, *N*-hydroxysuccinimide, EDC·HCl and benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate (PyBOP) were from Carbolution Chemicals (Saarbrücken, Germany). Dry *N*,*N*-Dimethylformamide (DMF) and dimethylsulfoxide (DMSO) was from VWR (Darmstadt, Germany), Trifluoroacetic acid (TFA) and diisopropyalamine (DIPEA) were from Carl Roth (Karlsruhe, Germany). Dialysis tubes (MWCO 1 kDa and 3.5 kDa) were Spectra/Por, from Serva (Heidelberg, Germany).

Cell culture plastics and consumables were purchased from Sarstedt (Nümbrecht, Germany). Cell culture media were from Sigma-Aldrich (Taufkirchen, Germany) and fetal calf serum was from Biochrom (Berlin, Germany). The cell lines HT29 (colorectal carcinoma), PC3 (prostate carcinoma), MV4-11 (biphenotypic B-myelomonocytic leukemia) were obtained from ATCC/LGC Promochem (Wesel, Germany). The cells were routinely tested for Mycoplasma using the Venor(R) GeM Classic kit (Minerva Biolabs, Berlin, Germany) and determined to be free of any contamination. All cell lines were cultivated in a humid atmosphere at 37 ◦C and 5% CO2. HT29 and PC3 cells were grown in Iscove's Modified Dulbecco Medium (IMDM), and MV-4-11 cells were cultured in RPMI 1640 medium. All media were supplemented with 10% FCS and 2 mM alanyl-glutamine. Cell culture and all transfection experiments were conducted in the absence of antibiotics. Stably dual expressing EGFP/Luciferase-expressing reporter cell lines were prepared by lentiviral transduction as previously described [52].

SiRNA sequences and RT-qPCR primer sequences are given in Table S1.
