Herceptin Conjugate Induces Tumor Cell Necrosis cell viability was observed in the two independent Her2-under- expressing cell lines, MDA-MB-468 [17] and Col (Figures 2a and b). In agreement with this observation, the inhibition of tumor cell survival by the EDC conjugate was dose dependent. We noticed that Her2-positive cell lines responded differently to treatment with the EDC-Herceptin conjugate. OS187 and CCH.OS.D cell lines, which were more sensitive, and we found that a low dose (20 mg/mL) treatment could reduce cell survival (Figure 2a). However, SKBR3 cells were less sensitive, and a high concentra- tion (80 mg/mL) treatment had significant effect (Figure 2a). Figure 2. Treatment of Her2-positive or Her2-negative tumor cells by EDC-Herceptin conjugate. (a) Comparison of cell survival rates between wild-type Herceptin and EDC-Herceptin conjugate treatments in Her2-positive (OS187, CCH.OS.D, and SKBR3) and Her2-negative (Col and MDA-MB-468) cell lines. MTT assay was used after cells were treated with the described antibody at low concentration (20 mg/mL) or high concentration (80 mg/mL) for 72 h. (b) Her2 expression analysis in tested cell lines using flow cytometry as described in Figure 1. *, P,0.05; **, P,0.01; ***, P,0.001. doi:10.1371/journal.pone.0023270.g002 PLoS ONE | www.plosone.org 3 August 2011 | Volume 6 | Issue 8 | e23270