The main goal of this work was to assess in vitro the potential of Polo-like kinase gene (PLK-1) as a molecular
target within the tumor microenvironment, namely in both cancer cells of tumors of different histological origin and endothelial
cells from angiogenic blood vessels, upon silencing with anti-PLK-1 siRNA. In addition, the effect of Plk-1 downregulation
on the cancer cells chemosensitization to paclitaxel was further assessed.
Downregulation of Plk-1 reduced cancer cells viability from 40 to 85% and up to 59% in endothelial cells. Regarding the
latter, it compromised their ability to form new tube-like structures, decreasing the formation of network projections up to
46%. This suggested for the first time, PLK-1 as a valuable angiogenic molecular target. In combination with paclitaxel,
anti-PLK-1 siRNA chemosensitized non-small cell lung cancer (NSCLC) and prostate carcinoma cell lines, leading up to
a 2-fold increase in the drug cytotoxic effect. Moreover, the sequential incubation of anti-PLK-1 siRNA and paclitaxel led
to a decrease in the IC50 of the latter up to 2.7- and 4.1-fold, in A-549 and PC-3 cells, respectively. The combination of
anti-PLK-1 siRNA with paclitaxel led to cell cycle arrest, increasing the number of cells at the G2/M and S phases to 1.5
and 1.3-fold in PC-3 cells, and to 1.6 and 1.4-fold in A-549 cells, respectively. Overall, it has been demonstrated that
PLK-1 silencing with siRNA can impact multiple cellular players of tumor aggressiveness, thus enabling the opportunity
to interfere with different hallmarks of cancer, in tumors with diverse histological origin.