a) Cyclic peptides reduce HeLa cells viability, as measured by MTT assay. Ub4ix inhibits the cell viability of HeLa cells with an IC50 of 1.6 μM after 48 hr incubation. Viability was measured after 72 hr for Ub2i, Ub2ii, Ub4i and linear-Ub4ix. Error bars represent SD of technical replicates (n=16). b) Ub4ix induces apoptosis in HeLa cells. Cells were exposed to the Ub4ix cyclic or linear peptide, MG132 (all at 10 μM) for 24 and 48 hr, FACS was used to follow apoptosis and cumulative cell death, bars represent mean values.