Figure 1. siRNA screening reveals PLK1 as a selective therapeutic target in preneoplastic and HNSCC cells.

(A) Plot of the effect on cell viability of the 319 lethal siRNA SMARTpools and controls screened in VU-preSCC-M3. Black open dots represent the median values of the 319 pools tested in triplicate, and grey squares all siCONs (negative controls). The dotted line indicates 50% survival, and 98 siRNA pools were below this value. (B) In addition to VU-preSCC-M3, four other preneoplastic cell lines also demonstrated ≥50% decrease of cell viability after transfection with the PLK1 SMARTpool. (C) Primary cell cultures of non-tumor tissue samples were less sensitive to knockdown of PLK1. VU-preSCC-M3 and VU-SCC-120 were included as reference. The differences between fibroblasts and keratinocytes versus VU-preSCC-M3 and VU-SCC-120 cells were highly significant. ^* P<0.003; Mann–Whitney-U-test. (D) Deconvolution of the SMARTpool in the four separate siRNAs showed an almost identical phenotype for three out of four separate siRNAs for all cell cultures tested. (E) The SMARTpool and the four individual siRNAs directed against PLK1 resulted in at least 70% knockdown of PLK1 mRNA levels. Bars represent the mean values of three independent experiments typically executed in triplicate in B, C and D. The error bars represent the SEM. Bars in figure E represent mean values of two independent measurements, with error bars representing the SD.